Download Geological Features and Evolution

Geología
Geology
árido
odf tehleentorno
Arid
Zone
of
f
almeriense
Almería
South East Spain
An educational field guide
Geology
of the Arid Zone of
f
Almería
South East Spain
An educational field guide
This guide has been produced and financed with the support of the hydrological management project between the
Carboneras Desalinisation Plant and Almanzora-Western Almería Council. In the Natural Park of Cabo de Gata and its
area of influence, a grant given by the Southern State Water Company (ACUSUR) and the Regional Ministry of
Environment (la Consejería de la Junta de Andalucía), is gratefully acknowledged
Editor, Technical Director and Co-ordinator: Miguel Villalobos Megía
Scientific Supervisor: Juan C. Braga Alarcón
Authors: Juan C. Braga Alarcón
José Baena Pérez
José Mª. Calaforra Chordi
José V. Coves Martínez
Cristino Dabrio González
Carlos Feixas Rodríguez
Juan M. Fernández Soler
José A. Gómez Navarro
José L. Goy Goy
Adrian M. Harvey
José M. Martín Martín
Antonio Martín Penela
Anne E. Mather
Martin Stokes
Miguel Villalobos Megía
Caridad Zazo Cardeña
Word Processing: Juan González Lastra
Infographics: Félix Reyes Morales
Design: Teresa del Arco Rodríguez, Juan Sánchez Rodríguez, Juan González Cué
Photography: The photographs are the property of the authors whose names are inserted in the section headings,
except for where specified at the foot of the photograph (in brackets)
Translation: Jason Wood
© of the edition: State Water Company for the Southern Basin SA (ACUSUR), 2003
© of the edition: Regional Ministry of Environment, 2003
© of the 2nd edition: Fundación Gypaetus, 2007
© of the data, text, photos and illustrations: Authors, 2003
Technical Assistance: Tecnología de la Naturaleza, SL (TECNA)
Printing: Bouncopy
ISBN: 978-84-935194-7-6
Legal Deposit: xxxxxx
D
uring recent decades, the Province of Almería has developed as one of the more
economically dynamic regions of Andalucía and Spain. Its exceptional environmental
conditions due to a favourable geographical situation, and the enterprising character of
its people, have made the blossoming prosperity and rapid consolidation of one of the
most vigorous and technologically advanced horticultural zones in Europe possible. However,
through time, this shining development has come to have a negative bearing on a historical problem
in Almería: the scarcity of hydrological resources. In reality the hydrological demands for agricultural
use considerably exceed the natural resources that are available, so that as a consequence, it has
motivated a growing social sensitivity and demands for solutions to this problem.
This situation has required, on the basis of their competency, the intervention of the Medio Ambiente
(Environmental Agency), which through the public company Aguas de la Cuenca Sur S.A. (ACUSUR),
has put an ambitious plan of action into practise: the Global Plan of Priority Hydrological Action in
Almería Province, known as Almería Plan, whose work, is declared to be of general state interest. This
plan has meeting the demands for water of the agricultural organisations in the Almerían coastal
zone as the main objective.
Part of this work, on the other hand, has been the need to achieve protection of a region with
exceptional ecological and environmental value, at times not fully recognised amongst its own
population. Indeed, through strict application of the criteria developed by the European Union in its
Strategy for the Preservation of Biodiversity, the Province of Almería, and especially its semi-arid
zones, are declared to be one of the regions of greatest environmental and ecological importance in
Europe. The presence of unique habitats, the biological diversity that provides a wealth of species,
turns the east coast of Almería into a veritable “Natural Wonder” in the context of continental Europe.
To all this can be added the exceptional geological value placed on these arid landscapes. All of these
conditions mean that Protected Natural Spaces have already been declared and proposed as places
of community interest, and these occupy a considerable area of Almería. By European law, the Spanish
government must guarantee their conservation.
In order for the partly unavoidable work of the Almería Plan to go through in these precious spaces,
both the Junta de Andalucía (provincial government) and the Medio Ambiente (environmental
agency), given their respective environmental concerns, decided to maximise the methods of
environmental protection. All joint work has been subjected to rigorous controls and has employed
a significant use of correctional means, whose aim is to reduce the extent of the possible
environmental impact that work generates in the construction phase.
In a complementary fashion, several administrations had agreed to fulfill the European Habitat
Directive, putting into place a broad program of compensatory measures. In this case the ultimate
aim is contributing to an improvement in the global quality of the natural environment of these
regions that were affected by the management of new hydrological resources, but also with the
purpose of spreading an awareness amongst the inhabitants of these regions that everyone must
keep a vigil and act in a responsible manner in order to conserve the environment.
The volume that is presented is framed in this context. A publication that we hope will contribute to
drawing the Almerían population closer to the exceptional qualities of the natural environment which
surrounds them. A recognition essential for establishing the basis of respectful relationship, that will
make both the conservation and sustainable use of this noble region a possibility.
Teófilo García Buendía
Manging Director of ACUSUR
Fuensanta Coves Botella
Director of the Medio Ambiente
Index
PROLOGUE
Prologue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
How to use this guide
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
INTRODUCTION
The Geological Timescale and some basic geological principles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Largescale Geological Units in Andalucia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Largescale Geological Units in the arid region of SE Almeria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Geological History and Geographical Evolution of SE Almeria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13
16
17
20
NEOGENE BASINS OR DEPRESSIONS OF ALMERIA
The Almeria-Nijar Basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
· Geological Features and Evolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
· Volcanic Periods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
- Origin of magmatic processes and volcanic features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25
- The Cabo de Gata volcanic complex . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
- Hydrothermal Alteration and mineralisation in the volcanic complex . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
- The gold of Rodalquilar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
· Sedimentary periods in the volcanic archipelago . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
- Sedimetary episodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
- Deposits of the earliest marine basins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
- Re-initiation of sedimentation since the last volcanic period . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
- Messinian reefs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
- Evaporites and carbonates since reflooding of the Mediterranean . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
· The last period: recent evolution and continentalisation of the Bay of Almería . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
· DIDACTIC ITINERARY: THE ALMERIA-NIJAR BASIN
..................................................................................
1. Alluvial dynamics of the ramblas: Las Amoladeras . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2. Fossil beaches of the Rambla de las Amoladeras . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3. The dune system at the outlet mouth of Rambla Morales . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
47
49
52
55
Index
4. The lagoon of Rambla Morales . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5. The Salinas (Saltpans) of Cabo de Gata . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6. Volcanic Domes of Punta Baja, El Faro and Vela Blanca . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7. The volcanoes of Mónsul . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8. The Barronal dunefield . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9. The Los Frailes volcano . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10. The fossil dunefield of los Escullos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11. Infilling Alluvial Fans of la Isleta-Los Esculllos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12. Volcanic calderas of Rodalquilar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13. Mining and mineralogical processes in Rodalquilar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.Post-volcanic sediments at la Molata de Las Negras . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15. The bentonites of Cabo de Gata . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16. Marine sediments of Cañada Méndez . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17. The quay at Agua Amarga . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18. The Mesa Roldán reef . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19. El Hoyazo de Níjar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
56
58
61
64
65
66
68
70
73
76
79
82
86
89
92
95
The Sorbas Basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
· Main Geological Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
· The Sorbas Karst . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
- Origin of the Sorbas gypsum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
- Karst : slow dissolution of rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
- Genesis and evolution of the gypsum karst of Sorbas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
- Surficial karst landscape of Sorbas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
- Subterranean scenery: dissolution features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
- Subterranean scenery: crystallisation features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
97
99
102
102
105
106
107
108
110
· DIDACTIC ITINERARY: THE SORBAS BASIN
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
1. The southern margin of the Sorbas Basin and panorama at Peñas Negras . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
2. Turbidites of the peñas negras fan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
Index
3. Infilling of the basin through until deposition of the gypsum: the Los Molinos del Río Aguas series . . . . . . . . . . . . . . . . . . . . . . . . 117
4. The karst plain, the cornice (escarpment) and block falls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
5. The resurgence (springs) of Los Molinos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
6. Infilling of the basin after gypsum deposition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
7.Fluvial-karst barrancos: the Barranco del Infierno . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
8.Fossil Beaches of Sorbas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
9. Dolinas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
10. Lapiés . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
11. Túmulus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
12. The Cariatiz Reef . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
The Tabernas Basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
· Rasgos geológicos y evolución . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
· Erosional Landscape . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
· Evolution of the drainage networ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
· The ramblas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
· Mechanisms of erosion in the desert: currents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
· Mechanisms of erosion in the desert: evolution of slopes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
135
137
140
141
143
144
146
· DIDACTIC ITINERARY: THE TABERNAS BASIN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
149
151
154
157
159
161
1. The turbidite succession of the Tabernas submarine fan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2. The Las Salinas travertines of the Tabernas Desert . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.Escarpment landforms in the vicinity of Cerro Alfaro . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4. Tunnel erosion (piping) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5. Quaternary alluvial fan-lake system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
PROLOGUE
T
he arid landscapes of Almería are
well known amongst professors of
geology, and other taught subjects
related to the teaching of earth
sciences, of an astonishingly high number
of European universities, who appreciate it and
use it as a huge natural laboratory to carry out
practical field investigation. This has been due
to two special features, an extraordinary
geological record within its sedimentary basins
and the high quality of outcrop exposure.
The geology of this region has, in fact, inspired
an enormous scientific literature produced at
the highest level. However, up until now
publications of a more informative tone that
seek to focus their efforts on the general
educational potential of this exceptional
geological landscape, have not existed.
This has been the objective of this work, to deal
with this singularly important geological region
with a broad vision in a manner that is more
widely informative. Within this volume, three
itineraries are put forward, each one of which
connects a series of field stops where it is
10
possible to observe or interpret several of the
most outstanding geological features in Almería
Province. These features are of great importance
for understanding the origin and evolution of
the geological landscape in Almería; a history
peppered with events so extraordinary as the
formation of the volcanic archipelago of Cabo
de Gata, the desiccation of the Mediterranean
Sea or the colonisation of the coastline by
tropical coral reefs.
The guide aims to be a product that is simple to
use. On one hand it is intended for
self-interpretation, or interpretation without the
assistance of a guide or teaching professional, at
the higher end of secondary education, the
university level, for different disciplines related
to the teaching of earth and environmental
sciences. On the other hand, it is a didactic
guide to support the teaching professional, that
clearly “translates” information, so that it can be
adapted to the most suitable pedagogical level
each time.
It has been structured into four large chapters,
an initial one of introductory character, and
three more corresponding to each of the three
sedimentary basins that might be visited.
These three chapters each consist of a general
part, in which basic concepts required in order
to understand the phenomena that are
interpreted in the field locations of the itinerary
area explained, folowed by a detailed
description of the proposed itinerary.
The itineraries are can be completed within the
three most emblematic Natural Protected
Spaces in eastern Almería and the immediate
surrounding area: the Cabo de Gata-Níjar
Natural Park, the Gypsum Karst Natural Park of
Sorbas and the Tabernas Desert Natural Park.
These are places where the didactic use of the
guide for environmental purposes will arise, as
well as it being the first, basic line of evidence in
management material used by the public. It is
hoped that in this sense the guide can be easily
used and will increase the environmental
understanding of the population visiting these
emblematic Natural Spaces.
Miguel Villalobos Megía
Guide Co-ordinator
How to use this guide
THE COLOURS IN THE GUIDE
SYMBOLS AND COLOURS OF LOCATION MAPS FOR POINT OF INTEREST
This guide is structured in various sections that can be identified
by a colour code in the lower and upper right corners of each
page.
Location maps for points of interest are found in the didactic itinerary
sections. These are located in a box in the upper right corner of the page.
The full page maps that appear at the beginning of each chapter have an
additional explicative legend.
The colours correspond as follows:
The symbols and colours correspond as follows:
Introduction
The Almería-Níjar Basin
Didactic Itinerary of the Almería-Níjar Basin
The Sorbas Basin
Didactic Itinerary of the Sorbas Basin
The Tabernas Basin
Didactic Itinerary of the Tabernas Basin
11
INTRODUCTION. The Geological Timescale and some basic geological principles
Juan C. Braga - José M. Martín
There is a series of basic principles that one
needs to understand prior to setting out on any
explanation about the geology of a region:
◗ The geography and landscape of a region are
always changing. The mountains and valleys
that surround us or the position of the
coastline today have not always been as we
know them now, now, neither have these
features always been there. The land that we
walk on, in the majority of cases, has risen up
from the depths of an ancient sea, and the
distribution of land and sea will change
through time.
◗ These changes result from complex geological
processes: sediments that are transformed into
new rocks and erosion of rocks that already
exist into sediments; uplift or emergence of
land areas, with the consequent retreat of the
sea, and flooding of other areas, that are
invaded by seas and oceans, where
accumulation of sediment starts again that will
later be transformed into other rocks, followed
by renewed emergence and further
destruction, etc.
◗ By studying the internal structure and
composition of rocks, their age (that should be
measured in millions of years) and the way
that they are distributed in a region, geologists
can reconstruct the way in which the
landscape and geography of the region has
changed, where the coastline was situated at
different times, where there was a volcano,
when the mountains were uplifted that are
emerged now, etc. This reconstruction is not
simple and requires the accumulation of much
knowledge from very distinctive specialist
fields within geology. However, once
recognised, even with provisional status, such
that our understanding will improve with time,
it is converted into a story that can be
entertained.
◗ All of these geological processes, without
exception, are extraordinarily slow from a
human perspective.The duration, the pace,
of geological processes is counted in millions of
years.The pre-history and history of humans
has been instantaneous in comparison with the
long history of our planet that began at least
4,600 million years ago.
13
◗ That the Palaeozoic era, in which distinct forms of life
THE GEOLOGICAL YEAR
If we compressed all of the known geological time of our
◗ That the Tertiary era, with the development of the
developed and diversified, reached up to the 13th of
majority of mammals, reached up to the 30th of
December.
December. The first primates did not appear until the
29th of December.
planet, some 4,600 million years, into a natural year of only
◗ That the Mesozoic era, that of the large reptiles, lived
365 days, we would observe:
through to the 26th of December, the time at which, for
◗ That through the Precambrian, about which we know
◗ That the Quaternary era, with the appearance of our
more immediate relatives, occupied only part of the
example, the great dinosaurs became extinct.
virtually nothing, save that it gave shelter to practically
31st of December. In fact, only towards the last minute
no life, only extremely primitive forms lived through
of the year did Homo sapiens sapiens, ourselves,
until the 16th of November, almost a complete year.
appear.
JANUARY
MAY
SEPTEMBER
Precambrian
FEBRUARY
MARCH
JUNE
OCTOBER
JULY
NOVEMBER
Palaeozoic era
APRIL
AUGUST
20 : 19 : 00.00
Sudden extinction of large reptiles (65 m.a.)
19 : 99 : 33.91
Appearance of the first primates (40 m.a.)
18 : 17 : 19.19
Appearance of Homo erectus (3 m.a.)
21 : 08 : 58.52
Appearance of Homo habilis (1.5 m.a.)
23 : 52 : 00.11
Appearance of Homo sapiens neanderthalensis (70,000 a.)
23 : 58 : 00.09
Appearance of Homo sapiens sapiens (35,000 a.)
23 : 59 : 48.28
Start of the Christian era (2,000 a.)
23 : 59 : 49.02
Fall of the Roman Empire (1,600 a.)
23 : 59 : 58.57
Discovery of America (500 a.)
23 : 59 : 58.89
French Revolution (200 a.)
29 : 59 : 59.30
Start of the industrial revolution (100 a.)
00 : 00 : 00.48
Average duration of human life (70 a.)
DECEMBER
Mesozoic era
Tertiary era
Quaternary era
Holocene
Pleistocene
QUATERNARY
0.01
1.8
Upper
272
Lower
Miocene
Oligocene
34
Eocene
Upper
Upper
325
Lower
53
PALAEOZOIC
Upper
385
Lower
410
SILURIAN
96
Lower
375
Middle
Upper
MILLIONS OF YEARS
360
Palaeocene
65
CRETACEOUS
CARBONIFEROUS
300
DEVONIAN
NEOGENE
5.3
23.5
PALAEOGENE
CENOZOIC/TERTIARY
Pliocene
425
Lower
435
ORDOVICIAN
154
JURASSIC
Middle
DOGGER
180
Lower
LÍAS
Upper
Middle
Lower
455
470
500
Upper
CAMBRIAN
MESOZOIC
135
Upper
MALM
205
TRIASSIC
TABLE OF
GEOLOGICAL TIME
PERMIAN
250
Upper
230
Middle
Middle
Lower
245
Lower
540
250
PRECAMBRIAN
Proterozoic
Archean
2.500
4.600
15
Largescale Geological Units in Andalucia
Juan C. Braga - José M. Martín
In Andalucía three largescale geological units may be differentiated:
1. The Iberian Massif or Hercynian Massif
of the Meseta outcrops to the north of
Guadalquivir and forms the mountainous
lineament of Sierra Morena. It consists
mainly of strongly folded and deformed,
metamorphic (schists, quartzites and
limestone marbles) and igneous (granites
and similar) rocks, of very ancient age
formed between more than 550 and 250
million years ago (Precambrian and
Palaeozoic). They form part of the old Iberian
continent whose coasts were covered by
the sea that occupied the greater part of the
modern Andalucían territory.
2. The Betic Cordillera constitutes the second
largescale unit, and the first formed from
extension. This much younger, large alpine
mountain chain, had already started uplifting
approximately 25 million years ago (in the
Lower Miocene) and continues uplifting
today. It runs from Cádiz in the west to
Almería in the east, extending to Murcia,
Valencia and the Balearics. At the latitude of
the Rock of Gibraltar it is inflexed producing
a more or less symmetrical structure along
the north of Africa. Internally, a complex
structure is present as a consequence of the
16
piling up of rocks through thrusting during
the slow collision of the Alboran Plate up and
onto the Iberian Plate, and later uplifting.
The primary internal structure is divided into
a younger External Zone, nearer to the
Iberian Massif, and an older Internal Zone,
closer to the modern littoral zone. Within
the latter, several stacked tectonic units can
be recognised, in turn, essentially from
the bottom towards the top they include the
Nevado Filábride Complex, Alpujárride
Complex and Maláguide Complex.
3. The Neogene Basins or depressions overall
comprise the third largescale unit in
Andalucía. During the emergence of the Betic
Cordillera there were times in which the sea
extensively covered depressed regions that
are emerged today, such as the Guadalquivir
Basin and other intermontane basins like
Guadix-Baza, Tabernas, Sorbas or AlmeríaNíjar. They are young sediments, less than 25
million years old, characterised by having a
very limited degree of deformation, such that
they hold a great value for studying the
recent geological history in this western
sector of the Mediterranean.
GEOLOGICAL UNITS
Hercynian Massif of the Meseta
Neogene Depressions
BETIC CORDILLERA
Campo de Gibraltar Complex
External Zone
Internal Zone
Largescale Geological Units in the arid region of SE Almeria
Juan C. Braga - José M. Martín
Almería is located, from a geological point of
view, at the southeastern extreme of the Betic
Cordillera. The old Betic relieves (Sierra de
Gádor, Filabres, Alhamilla, Cabrera, etc.)
constitute the margin and the basement of a
series of much younger intermontane marine
basins (Tabernas, Sorbas, Almería), that were
filled with sediments simultaneously with the
emergence of the Betic Cordillera structure.
Meanwhile, in the vicinity of Cabo de Gata,
numerous similarly recent volcanoe rumbled in
full activity. These three geological terrains are
clearly distinguishable today in the surrounding
Almerían desert landscape.
Characteristic flaggy appearance (schistosity) of dark
micaschists in the core of the Nevado- Filábride Complex.
Quartzite crests in the Nevado- Filábride core of the Sierra
Alhamilla (photo M. Villalobos).
THE BETIC SIERRAS
The core of the mountains in this region
consists of very old rocks, some even around
550 million years old. They are grouped under
the generic name of the Nevado-Filábride
Complex (alluding to the fact that they make
up a good part of the Sierra Nevada, and its
eastern extension, the Sierra de los Filabres).
They are mainly graphitic micaschists: display
dark, yellowish and orange colours with a slaty
appearance and a flaggy characteristic, that is
to say, they are divided into well-defined,
more or less irregular laminations. Quartzites
which form rough crests and sharp cliffs, due
to their better resistance to erosion, are also
common.
Quartzites display dark, yellowish and orange
colours, and also have a flaggy appearance,
although poorly defined. Metamorphosed
limestones and marbles are also found but
to a lesser extent, such as those quarried in
the Sierra de Macael. Locally rocks related to
granite appear, known as gneiss. All of these
arose from the transformation
(metamorphism) of existing rocks that
suffered elevated temperatures and pressures
at great depth in the interior of the earth.
Skirting the core of the previously mentioned
mountains another band appears, also
consisting of very old rocks although somewhat
younger than the former, that are grouped
under the name of Alpujárride Complex
(alluding to the fact that it extends from
Alpujarra, where for one part it constitutes the
southern flank of the Sierra Nevada, and for
the other, the coastal chain: sierras de Lújar,
Contraviesa, Gádor, etc.).
17
Largescale Geological Units in the arid region of SE Almeria
This strip mainly comprises two very distinct
types of rock, easily recognisable in the field.
One of these are schists, known in the region as
'Launa', which are slightly transformed clays, of
vivid blue, red and glossy grey colours.
Traditionally they have been used to make
impermeable roof slates in the construction
industry. The other rocks are limestones and
dolomites, composed of calcium and
magnesium carbonates, which produce white,
grey or black escarpment relieves, for example,
the north flank of the Sierra Cabrera, Sierra
Alhamilla, the escarpments of Lucainena or
Turillas, close to Níjar, or the many cliffs of the
Sierra de Gador. All of these limestones and
dolomites were formed at the bottom
of a tropical sea more than 200 million years
ago. Afterwards, in the same manner as the rest
of the material from the Alpujarride complex,
they suffered transformation (metamorphism) at
elevated temperatures and pressures, which
came about at great depth in the earth's
interior.
Material from the old Betic mountains has
suffered an intense deformation expressed as
folds of distinct scales and fractures, in addition
to their slaty characteristics (schistosity). In some
places the rocks are literally destroyed, mashed
18
Typical purple colour of phyllites or 'Launas' in the material of
the Alpujarride Complex (Photo, M. Villalobos).
up by fractures. They are also mineralised, and
have historically been the object of exploitation
to yield iron (Sierra Alhamilla), lead and silver
(Sierra de Gador and Sierra Almagrera), and
other minerals.
Alpujarride limestone relief of the Sierra de Gador (Photo, M.
Villalobos).
THE SIERRA DE CABO DE GATA
The Sierra de Cabo de Gata is an individual
mountain range, different to the others, formed
from volcanic rocks during two stages of
volcanicity, one from approximately 14 to 10
million years ago and the other from 9 to 7.5
million years ago. In reality, they represent only
a small percentage of rocks of this nature,
constituting the bottom of the Alboran
seafloor and extending to Melilla, outcropping
discretely in the Isla de Alboran.
Major Geological Units of arid SW Almeria
DEPRESSIONS OR LOW-LYING AREAS
Detail of stratification in Alpujarride limestone rocks (Photo,
M.Villalobos).
Volcanic rocks from this area formed a
landscape of volcanoes, submarine or emergent,
individual or grouped, to form small islands.
These volcanic structures are recognisable in the
terrain of Cabo de Gata, in many cases, where
they are seen to form steep, more or less conical
hills in the area: Los Frailes, Mesa de Roldan,
Cerro de los Lobos, La Tortola, etc. Brecciated
volcanic rocks (formed from fragments
of different composition or aspect) are very
abundant, resulting from diverse volcanic
processes: differential cooling of distinct parts of
lava flows, eruptions, nuee ardentes, avalanches
down the sides of volcanoes, etc.
The rocks that occupy the low-lying areas of
the Almerían landscape, modern depressions
such as the Almanzora Valley, Andarax Valley,
Tabernas, Sorbas Basin, Campo de Níjar plain
or El Poniente or El Poniente, consists of
geologically young material, accumulated in
the last 15 million years, while the Mediterranean
Sea surrounded the mountains and the
volcanoes of Cabo de Gata forming a small
archipelago. The Betic mountains, and in general
all of the Iberian Peninsula, were uplifted from
the depths of the Mediterranean Sea.
In these marine inlets the products of
sedimentary erosion of the emerged land
accumulated: boulders, pebbles, gravel, sand
and mud. Limestone rocks also formed from
the accumulation of the remains of marine
creatures. In a changing global climate, the
region passed through cold and much warmer
periods.
In the warm periods, the seawater temperature
(in the western Mediterranean) was similar to
those of the tropics today, in the order of 20º C,
and coral reefs developed along the margins of
islands and emerged lands. Theses coral reefs,
like those of Purchena, Cariatiz, Nijar, Mesa
Roldan, etc., are amongst the best fossil
examples that exist in the world.
In colder periods, the western Mediterranean
had a temperature similar to today, and
limestones were formed from the remains of red
algae, bryozoans, molluscs etc., like those
occurring on the actual seafloor of the platform
that encircles Cabo de Gata. These conditions, or
yet colder ones, prevailed in the region from
5 million years ago.
19
Geological history and geographical evolution of SE Almeria
Juan C. Braga - José M. Martín
The Betic mountains (Nevado-Filabride and
Alpujarride complexes) originated from
collision of the African continent with Europe.
The Betic rocks are formed from sediments
deposited at the bottom of the sea hundreds of
millions of years ago. These rocks were buried
at many kilometres of depth (beneath other
rocks), under such pressure and temperature
that they were transformed, changing the
appearance of the minerals that make them up
(this process is known as metamorphism). Later,
they slowly emerged. The structure of the Betic
Cordillera was yet to be uplifted at different
speeds according to the arrangement of blocks
compartmentalised by large regional fractures.
The Sierra Nevada-Sierra de los Filabres block,
for example, was the first to emerge from the
sea, around 15 million years ago, and has
stayed up since this time, as the most elevated
relief in Andalucía and one of the most
elevated in Spain and Europe. The bottom of
the Alborán Sea is subsiding and extending,
thanks to fractures through which volcanic
material of Cabo de Gata was once extruded.
Since emergence of the Sierra Nevada-Sierra
de los Filabres, that still continue to be
uplifted, the Sierra de la Estancias emerged
from the sea around 9 million years ago.
20
Later, around 7 million years ago, the Sierra de
Gádor and Sierra Alhamilla emerged. Although
today they seem like high mountains to us,
they are believed to be quite young in
geological terms, and their rate of uplift on
a human scale is very low, For example, the
average velocity of uplift for the Sierra
Alhamilla since emergence from the sea is less
than 2 cm each year.
The last relief to emerge, which is for certain
the youngest mountain range of the peninsula,
is Sierra Cabrera that came out of the sea
5.5 million years ago.
During the past 2 million years, Almería, like
the rest of the planet, has suffered from strong
Quaternary climatic variations. In the glacial
stages, the sea fell more than 100 metres from
its present level and the climate was much
colder. In the interglacial stages, as now, the
sea was in a position similar to that of today,
and the climatic conditions would also have
been similar in character.
The process of marine retreat from these
basins can also be seen in relation to the
present-day geography, in that the interior
depressions, those most removed from the
modern Mediterranean, were the first to
emerge, whilst those closest to the coast have
been abandoned by the sea only recently from
a geological point of view. For example, the
high valley of Almanzora, above Albox, was
vacated by the sea around 7 million years ago,
however, the sea extended over land
surrounding the Bay of Almería until just
100,000 years ago.
With the final retreat of the sea to its current
position, for the moment, the impressive
geological record for this area, accumulated
over a period of 15 million years, is exhibited in
Almería under exceptional conditions of
preservation. It is an area of maximum
educational and scientific value for studying
and understanding the evolution of the
Mediterranean and the formation of the Betic
Cordillera over the past 15 million years.
The Almeria-Nijar Basin
Geological Features
Geological Features and Evolution
Juan C. Braga - José M. Martín
The Almería-Níjar Basin has been a small
marine sedimentary trough since 15 million
years ago, the time at which emergence of
the relieves occurred, that today constitute the
Sierra Nevada and the Sierra de los Filabres
massifs, whose foothills were located at the
coastline.
GEOLOGICAL LOCATION OF THE ALMERIA-NIJAR BASIN
SIERRAS
Sorbas Basin
2
Tabernas Basin
Vera
Vera Basin
In this period, however, the Almería Basin was
not individualised from the Sorbas and
Tabernas basins. In this marine basin,
sediments started to arrive from the
dismantling of the emergent relieves through
the fluvial network. Extensive submarine fans
were generated on top of the marine platform,
while the fully active volcanoes of Cabo de
Gata were rumbling, probably fashioning
a tropical volcanic archipelago.
It was much later, about 7 million years ago,
when uplift of the Sierra de Gádor and Sierra
Alhamilla caused the individualisation of the
Almería-Níjar Basin, to the south of these same
hills and between the emerged volcanic relieves
of Cabo de Gata.
Sierra Cabrera emerged 5 million years ago, and
it definitively separated the Sorbas and Vera
basins.
Sorbas
1
Tabernas
5
1. Sierra Nevada
2. Filabres
3. Sierra de Gádor
4. Alhamilla
5. Cabrera
6. Sierra de Cabo de Gata
4
Carboneras
Níjar
Almería
3
El Ejido
6
Almería-Níjar Basin
Campo de Dalias Basin
Neogene-Quaternary sediments
The Almería-Níjar Basin therefore included all
of the current, low-lying land present between
Sierra de Gádor, Sierra Alhamilla, Sierra Cabrera
and the coastline, including the volcanic
relieves of the Sierra de Cabo de Gata.
Neogene volcanic rocks
Betic substratum
A region that had constituted a marine seafloor
during the last 15 million years in which
a sedimentary record has remained, with
unsurpassed observable characteristics,
exceptional for the understanding of evolution in
the Mediterranean Basin at this time, and its
geography, climate and ecology.
23
Geological Features and Evolution
SIMPLIFIED GEOLOGICAL MAP OF THE ALMERIA BASIN
According to Zazo and J. L. Goy
Sierra de Alhamilla
Níjar
Ga
ta
Sierra de Gádor
Sª Alhamilla
Sie
rra
d
Cabo
de Gata
Roquetas de mar
eC
ab
o
de
Almería
Alquián
Sea level
Sª Alhamilla
Pozo de Los Frailes
Níjar
Sea level
Old Quaternary terrain
(Pleistocene: 1.8 Ma to 10,000 yrs)
Miocene volcanic
formations (15.7 to 7.9 Ma)
Pliocene terrain (5.2 to 1.8 Ma)
Ancient basement
Miocene terrain (23.7 to 5.2 Ma)
24
Recent Quaternary (Holocene) formations, from 10,000 years ago
to present
Fluvial deposits
Albuferas
(saltpans)
Alluvial fans
Travertines
Littoral barries and/or fringes
Deltas
Dunefields
VOLCANIC EPISODES
Origin of magmatic processes and volcanic features
Juan M. Fernández
MAGMAS AND MAGMATIC ROCKS
MELTING OF PRIMARY
MAGMAS
Main cone
Magmas are formed through the partial melting
and emplacement of rocks at high temperature
in the interior of the Earth. They consist of a
mixture of liquid, dissolved gases (water vapour
and carbon dioxide) and minerals.
Magmas that come directly from the partial
melting of rocks at depth are called primary
magmas. Sometimes they reach the surface
straight away, however, it is more common that
they remain static at different levels within
the mantle and the continental crust, forming
magmatic chambers. In such a situation the
magmas may partly crystallize, assimilate
the country rock and suffer other modifications,
the final result of which is a series of derived
magmas of different compositions. This process
is known as magmatic differentiation.
Magmas are generally less dense than the
material within which they are forming, and,
therefore, they tend to climb up through the
mantle and continental crust, until they cool and
crystallize, giving place to intrusive rocks.
Magmas that solidify slowly underneath the
terrestrial surface form bodies of intrusive
rocks. Cooling happens very slowly, so that the
Parasitic cone
Lava flow
Plutonic rocks
Magma
chamber
Dykes
Derived
magma
Partial melting
of the crust
CRUST
MANTLE
minerals may crystallise in an ideal manner,
creating rocks with large-sized crystals such as
granites.
matrix a proportion of small minerals of larger
size (phenocrysts) may be present, which had
crystallised previously in the magma chamber.
When the magma reaches the surface, it gives
way to volcanic or eruptive activity. The results
are volcanic rocks and so-called volcanic
features. Cooling is very rapid, so that the rocks
do not crystallise well, forming a vitreous
matrix or a very fine crystal size. Within this
At times, during its ascent, the magma is
injected into fissures, forming dykes. These are
also known as hypabyssal rocks.
25
Origin of magmatic processes and volcanic features
MAGMAS AND PLATE TECTONICS
Although there are a great variety of types
and compositions of magmas, the three most
important generic types are the basaltic group
(or basic, 50% of silica), the siliceous group
(or acid, 65 to 70% of silica), and the andesitic
group (or intermediate) such as those of Cabo
de Gata.
The origin of magma is related to the dynamics
of the lithospheric plate margins:The majority of
basaltic magmas originate through partial
melting of the mantle in divergent plate
boundaries (mid-oceanic ridges). Andesitic and
siliceous magmas are generated in subduction
zones by partial melting of both the oceanic plate
and the continental crust.
OCEANIC CRUST
Island arc
Trench
Mid-oceanic ridge
The origin of Cabo de Gata volcanism is
complex, and under discussion at present.
In whatever case, it is related with the orogenic
process of crustal thickening in this area,
the Alborán domain, due to the collision of the
African and European plates; and afterwards
their thinning through phenomena of
extensional or transtensional character.
CONTINENTAL CRUST
Trench
Rift valley
Plateau
basalts
Oceanic
crust
26
Continental
crust
Upper mantle
(asthenosphere)
Lithospheric
mantle
Origin of magmatic processes and volcanic features
ACTIVITY AND VOLCANIC FEATURES
The type of eruption and the products resulting
from volcanic activity depend, above all, on two
important aspects: the viscosity of the lava,
which determines fluidity, and the gas content
of the lava.
Basaltic magmas, poor in silica, are fluid. At the
surface they flow rapidly, forming lava flows
that at times travel great distances (this type of
volcanism is known as effusive). If the basaltic
lava is rich in gas, it is released with ease by
means of intermittent explosions, creating
pyroclastic types of cone (also known as cinder
cones). The alternation of lava flows and
pyroclastic episodes fashions another type of
volcanic edifice known as the Stratocone
volcano.
Acidic magmas, on the other hand, rich in
silica, are much more viscous. Upon exiting
onto the surface, they cannot flow easily, and
form accumulations around the eruptive
mouth (domes), or flow very slowly forming
lava flows over short distances (this type of
volcanism is called extrusive).
BASALTIC MAGMAS
PYROCLASTIC CONE OR CINDER CONE
STRATOCONE
Lava flows
Pyroclastic
levels
ACIDIC MAGMAS
DOMES OF SILICEOUS MAGMA
Pelean Dome
Cumulate Dome
Crypto-dome
SOME TYPES OF DOME
27
Origin of magmatic processes and volcanic structures
EXPLOSIVE VOLCANISM
PYROCLASTIC FLOWS
The high viscosity of lavas from acidic magmas
means that on occasions gases cannot be
easily liberated, accumulating as bubbles, and
increasing their internal pressure until they are
unleashed in enormous explosive phenomena
that violently erupt huge volumes of
semi-molten rock into the atmosphere.
The so-called pyroclastic flows are generated
by this means, their solidification then
produces rocks known as pyroclastics.
They can be of different types:
28
IGNIMBRITES
Ash
cloud
Eruptive Column
Volcanic
ash fall
Nuee Ardente
Pyroclastic flow
BRECCIAS AND AGGLOMERATES
FORMATION OF A VOLCANIC CALDERA
Ignimbrites
A mixture of very hot gas, ash and rock
fragments is launched from the volcano in an
eruptive column. The density of the mixture,
greater than that of air, means that it falls
rapidly, smothering the underlying hillside in
the form of a covering flow comprising a
glowing cloud of gas. They create rocks rich
in ash and pumice.
CALDERAS
Lithic Breccias or Agglomerates
The flow forms from the rupture, explosive or
otherwise, of the summit of the volcano.
Rock fragments that made up the actual dome
dominate in this case.
The largest and most explosive volcanic eruptions
throw out tens and hundreds of cubic kilometres
of magma onto the earth's surface.When too
high a volume of magma is extruded from a
magmatic chamber, the earth subsides or
Pyroclastic flow
collapses into the vacated space, forming an
enormous depression called a caldera. Some
calderas can be more than 25 kilometres in
diameter and several kilometres deep.When, after
the formation of a caldera, the magmatic chamber
receives new supplies from deeper zones, the
interior of the caldera can return to a state of
uplift, a phenomenon known as resurgence.
The calderas are one of the most dynamically
active volcanic features and are frequently
associated with earthquakes, thermal activity,
geysers, hydrothermal waters etc.
Nuee
Ardente
Dome
1
2
3
The Cabo de Gata Volcanic Complex
Juan M. Fernández
GEOLOGICAL CONTEXT AND AGE
The Cabo de Gata volcanic complex is the
largest-sized element of all the volcanic
manifestations in SE Spain. It continues to
expand beneath the Alboran Sea, and has been
brought into its present position by the
operation of the Carboneras-Serrata Fault. The
greater part of volcanism in the Alboran basin is
actually submerged. The volcanic structures of
Cabo de Gata also indicate signs of having been
generated, by and large, beneath the sea. Some
of the oldest volcanic structures could have
grown out of the sea sufficiently enough to
reach the surface, forming islands of volcanic
origin fringed by marine sedimentary platforms.
in various cycles.The better-known and
conserved volcanic features are the most recent,
produced between 9 and 7.5 million years ago.
The age of the Cabo de Gata volcanic complex is
known through the study of fossils present in
sedimentary rocks associated with the volcanic
elements and from dating with isotopes (mostly
Potassium/Argon) in the volcanic rocks. Volcanic
activity developed in a broad period that extends
from around 14-15 to around 7.5 million years
ago (that is to say, Middle and Upper Miocene).
During this interval the volcanic activity occurred
The base of the volcanic complex outcrops at
various points (Serrata de Níjar and Carboneras)
and is formed of Betic basement rocks
(carbonate rocks and phyllites of the Malaguide
and Alpujarride complexes) and some marines
sediments (marls) from the Lower-Middle
Miocene. Towards the top, the volcanic activity is
fossilised by marine sedimentary deposits of the
terminal Miocene (Messinian reefs).
THE CABO DE GATA VOLCANIC COMPLEX WITHIN THE CONTEXT OF THE ALBORAN SEA
SUBMARINE VOLCANISM
Calderas
Sª de Los Filabres
Sorbas
Basin
Sª Nevada
Sª Alhamilla
Almería
Basin
Sª de Gádor
Sorbas
Mediterranean
Sea
(Alboran Sea)
Sedimentary
levels
Volcaniclastic
deposits
Sea level
Níjar r
íja
eN
d
ta
Las Negras
rra
Se
Polarca
Ridge
Almería
Adra
Alboran Basin
Betic Basement
Chella
Bank
Neogene Basins
Volcanic Rocks
ult
Fa
s
a
er
on
on
rb
a
ny
C
Ca
a
í
Pollux
er
m
Bank
Al
Cabo de
Gata
S. Jose Islet
Platform
Genoveses
Ridge
Sabinal Bank
Hydrothermal
Systems
Magmatic Chambers
Emerged
Submerged
29
The Cabo de Gata Volcanic Complex
RELIEF FEATURES OF THE CABO DE GATA VOLCANIC COMPLEX
A
Nijar-Almeria
Basin
Serrata de
Nijar
Sierra de
Cabo de Gata
PlioQuaternary
Carboneras
Miocene
Volcanic Complex
Basement
Carboneras Fault
rb
Ca
La Serrata de Nijar is a zone of volcanic origin, associated with the Carboneras
Fault. The rocks, concealed beneath the sedimentary filling of the Campo de
Níjar, have been uplifted and project outwards at the surface of La Serrata
because they are caught up between different fractures in the fault zone.
on
s
era
u
Fa
Mesa Roldán
lt
C
Agua Amarga
A
Se
ta
rra
N
de
í
jar
Las Negras
D
B
Rodalquilar
Del Garbanzal Dome-Flow
Miocene sediments
Ancient massive rocks
E
White ignimbrites
El Cerro de Garbanzal is a unique volcanic structure, almost circular in plan,
formed by the extrusion of a massive dome-flow. The geometry of this type of
structure is known in some places as fortified domes or 'tortas'. Quite eroded,
it is preserved as a ceiling above marine sedimentary remains.
San José
Barronal
Cabo de Gata
30
Los lobos
LA ISLETA
B
Los Frailes
Caldera
Rodalquilar
Caldera
The Cabo de Gata Volcanic Complex
C
D
Conglomerates
(reworked breccias)
Messinian
Carbonates
Caldera
Dome Breccias
Sediments (Messinian and Pliocene)
Rodalquilar Complex
Volcanic Ashes
Massive Nucleus
MAGMATIC CHAMBER
Mesa Roldan (and Los Lobos) are excellent examples of volcanic structures
fossilised by marine sedimentary rocks and crowned by terminal Miocene
coral reefs. It may be characterised by an andesitic lava dome, enclosed by
fragmented rocks (dome breccias), produced by submarine eruptions with
little or no explosiveness. Linked with the Los Frailes volcano, they are the
most recent volcanic emissions in Cabo de Gata.
RECENT SEDIMENTS
Post-Volcanic
Sediments
Pre-Caldera
Rocks
The Rodalquilar Caldera, one of the most notable volcanic features, was generated
because of the collapse of the caldera floor into the underlying magma chamber in
a series of highly explosive volcanic processes, producing the deposition of various
pyroclastic rock units (ignimbrites). The later hydrothermal alteration of these rocks
gave place to the characteristic mineral deposits of this area, especially gold.
E
Los Frailes Caldera
MESSINIAN CARBONATES
Pyroxene Andesites
MIOCENE SEDIMENTS
Frailes
Rodalquilar
Complex
LA SERRATA SEQUENCES
Volcanic
Sequences
PYROXENE ANDESITES
LAS NEGRAS AND CARBONERAS SEQUENCE
ESTRADA DOME, PANIZA DOME, ETC.
GARBANZAL DOME
RODALQUILAR DOME
SEDIMENTS AND ALLUVIUM
ANDESITES
WHITE RHYOLITES
Substratum
Lighthouse
BETIC BASEMENT
White Rhyolites
Amphibole Andesites
The Los Frailes Volcano formed around 8 million years ago above older rocks (more than 10-12 ma)
that extended towards the southern limit of the Sierra de Cabo de Gata. In this case, the volcanic
activity did not give place to typical central volcanoes, but to an extensive landscape of more or less
dispersed volcanic domes. Levels of fossiliferous marine sediments were deposited between the phases
of eruption of the different domes that serve as guide levels. Additionally, they produced some highly
explosive eruptive processes (ignimbrites), related to the collapse of calderas.
31
Hydrothermal Alteration and Mineralization of the Volcanic Complex
Juan M. Fernández
The hydrothermal systems associated with the
volcanic complex of Cabo de Gata has
generated important mineralization of
economic interest whose profits have left a
marked impression in the history and upon
the countryside of this district. Without doubt,
the most acclaimed deposits are gold from
Rodalquilar, exploited until very recent times.
Exploitation of other lesser metals has existed,
however, such as lead and zinc, copper and
manganese.
Other non-metallic mineralization of
commercial interest has also been generated in
association with this system. Bentonites are
actually the most important. Long ago the area
had benefited from alunite, a mineral
(aluminium sulphate and sodium or potassium)
that was concentrated in yellow-coloured virgin
seams cutting the white-coloured and
pulverised looking, altered volcanic rock. It has
numerous industrial applications, amongst
others it is used as a source for the production
of alum, for the tanning of leather, etc.
Hydrothermal processes are a frequent
phenomenon in volcanic areas. They are
produced when a magmatic body cannot reach
32
A. GEOLOGICAL SKETCH
B. HYDROTHERMAL SYSTEM
Rodalquilar Caldera
Fumeroles
Cinto
Los Tolles
Meteoric
Waters
Magmatic
Vapours
(SO2, HCl, etc.)
Magma
the surface, cooling slowly at hundreds of
metres or a few kilometres of depth. In these
conditions, the sub-volcanic body supplies heat
to the surrounding area, that can reach
temperatures of around 400-500 C, and emits
gases and acid-rich fluids, such as hydrochloric
or sulphurous (between 200 and 350 C).
These hydrothermal fluids rise up through the
intruded rocks, transforming them
(hydrothermal alteration) and cleaning many
chemical components out of them (lixiviation),
such as gold and many other metals that were
originally very dispersed in the rocks. Upon
arriving in more surficial zones the fluids cool
and mix with water of subterranean or marine
origin, which provokes the metals and other
Simplified from Arribas et al., 1995
HYDROTHERMAL SYSTEMS
Degassing from Magma
disassociated components to precipitate in
fissures and fractures, forming hydrothermal
deposits, such as the famous Rodalquilar gold.
In Cabo de Gata, the main hydrothermal gold
deposits are located in the Rodalquilar complex
of calderas, associated with an intense zone of
hydrothermal alteration. This alteration zone is
produced by intrusion and cooling, beneath the
calderas, of a magmatic body. The hydrothermal
fluids carried by this body wash out the gold at
depth and utilised the various fractures existing
in the caldera to circulate and deposit the gold
in more superficial zones. The formation age of
the deposits is estimated at around 10.4 million
years.
Hydrothermal Alteration and Mineralization of the Volcanic Complex
MINERALIZATION
LOCATION OF MINERALIZATION THROUGHOUT
CABO DE GATA
La Islica
El Llano de D. Antonio
Carboneras
Agua Amarga
Fernán Pérez
Las Hortichuelas
Rodalquilar
Las Negras
Smelting works of Los Alemanes Nuevos, to
the west of San José, for the recovery of lead
and zinc (photo J. M. Alonso).
Bluish and greenish colouration
corresponding to superficial alteration
minerals of copper and lead sulphides.
El Barranquete
El Cabo
de Gata
El Pozo de
los Frailes
Los Escullos
San José
Overview of typical scenery
in bentonite clays: whitecoloured powdered masses,
greasy to the touch and very
plastic.
INDUSTRIAL MINERALS
Bentonites
Alunite
Exploitation of Manganese
from Cerro del Garbanzal.
Mineralization corresponds to
the dark zone.
METALLIC MINERALS
Gold
Galena and Blende
Copper
Manganese
Exploitation of alunite from
galleries in the proximity of
Rodalquilar.The
mineralization corresponds
to yellow-coloured veins
(lodes).
Hydrothermal breccia of white
chalcedony with native gold
(Photo Arribas).
33
The Rodalquilar Gold
Carlos Feixas
THE DISCOVERY
(End of the 19th century - 1939)
delayed the mine consolidation throughout the
whole of the 20th century.
The existence of gold in the Almerian district of
Rodalquilar was casually discovered at the end
of the 19th century. Gold was detected in lead
smelting works of Cartegena and Mazarron, that
utilised quartz coming from the lead mines
of Cabo de Gata as a flux. The Mazarron smelters
sought out the gold-bearing quartz, and with its
scarce gold content they financed the cost of
transport.
This first stage of discovery of gold from
Rodalquilar, and the development of the first
mines, coincided with the great Almerian
economic crisis. This involved emigration
of workers to Algeria, and subsequently to
America, a decline in lead mining and later in
iron mining, and a crisis in the grape market.
The English company Minas de Rodalquilar
handled a total of 107,000 tons of mineralized
rocks until 1939, obtaining 1,125.5 kg of gold.
Of these only 39 tons corresponded to the
period 1936-1939.
In an authentic state of gold fever many
concessions were registered in this era
that gave way to a multitude of litigation that
Ruins from the first treatment plant installed around 1915 in
the Ma Josefa mine, in El Madronal (Rodalquilar) (Photo, Col.
Evaristo Gil Picon).
34
Old lodes economic for lead at the end of the 19th century in
quartz dykes, from some of which the existence of gold was
detected in Rodalquilar (Photo, Col. Evaristo Gil Picón).
Extraction workers in the Los Ingleses Mine (around 1930)
(Photo, Col. Evaristo Gil Picón).
The Rodalquilar Gold
THE DREAM (1940-1966)
In 1940, the state decreed the seizure of the
mines, entrusting the task of investigation to
the Spanish Institute for Geology and Mining
(IGME), that looked at the old lodes that had
been exploited without favourable results. Until
1942, the date at which this seizure ended, a
total of 37 kg of gold was recovered.
Cerro del Cinto area, where mineralisation
appeared in a disseminated form in the acidic
volcanic rock body, determining a 4000 ton
mass of mineralised rock with 4.5 grams of gold
per ton.
Until 1966 Rodalquilar lived its golden dream.
Its population came to reach 1400 inhabitants.
It was furnished with infrequent services for this
time in rural populations, cinema, social club,
administration buildings, school, etc.
Drilling workers in the open cast mines opened during the
ENADIMSA period of exploitation (Photo, Col. Evaristo Gil
Picon).
May 1956.The head of state at that time attends the production
of one of the gold ingots, with all of the propaganda exhibited
by the regime (Photo, Col. Evaristo Gil Picón).
At the end of 1942 the National Institute of
Industry (INI), through the Adaro National
Enterprise for Mineral Investigation (ENADIMSA),
amplified and intensified investigations,
abandoning the lodes and concentrating in the
'El Ruso’, first transport lorry for the Rodalquilar mines
(around 1940) (Photo, Col. Evaristo Gil Picon).
The Rodalquilar Gold
In the first years of activity from this period
in the order of 700 manual labourers worked in
Rodalquilar, the greater part of them dedicated
to the construction of infrastructure and
workings. At the end of this, between 200 and
300 workers were permanently involved in the
exploitation. ENADIMSA continued, in principle,
with the subterranean system of extraction
that had been emplaced by the English.
In1961, however, the first open cast workings
were undertaken in the Cerro del Cinto.
REALITY (1967-1990)
The closure of the mines in 1966 put an end to
the period of splendour. A little afterwards the
population declined very abruptly to 75
inhabitants, in summary nearly identical to that
of today.
After exploitation was carried out by ENADIMSA
in the previous period, the concessions and
licences returned to their owners. Even though
investigation had been forgotten in this period,
During this period the bulk of gold production
in Spain shifted to Rodalquilar, with more than
90% of the total production. However this
dream only lasted a while. Investment exerted
pressure to make new workings, and salary
rises in the 70's decade considerably increased
the production costs in a deposit already so
difficult because of the irregular distribution of
economic reserves. All of this forced the
closure of the workings in 1966.
Mining town of Rodalquilar (photo Evaristo Gil Picón).
36
so often realised by national mineral concerns,
including, to a greater degree, foreign ones.
This period is characterised by intensive
investigation of the Rodalquilar mining district,
but having emphasis on genetic models of gold
mineralisation.
In spite of all this reality prevailed, although it is
estimated that that around 3 tons of gold
reserves are awaiting recovery, their exploitation
is not possible because of the complexity of the
deposit.
SEDIMENTARY BASINS IN THE VOLCANIC ARCHIPELAGO
Sedimentary Episodes
Juan C. Braga - José M. Martín
From the first volcanic episodes and
subsequent to the last, the sea invaded the
volcanic relieves generating an extensive
archipelago. In the marine basins between
volcanic relieves marine sedimentary
deposits were produced. Five sedimentary
episodes can be recognised:
TERTIARY BASINS IN THE SOUTHEASTERN PENINSULA
1. In an early episode sediments were
deposited upon the first volcanic rocks.
Their age is Lower Tortonian (between
9 and 8.7 million years). They are mainly
bioclastic carbonates.
Sierra de Gádor
Almería
2. In a second phase sediments formed above
rocks of the last volcanic event. Their age is
Upper Tortonian to Messinian (between
5.5 and 6.5 million years ago). They are also
bioclastic carbonates, and marls, that
accumulated in deeper zones.
3. Above the previous episode, a series of
related units characterised by the presence
of reef bodies were deposited. Their age is
Messinian (around 6 million years old).
a de
Sierr
res
Filab
GEOLOGICAL MAP OF THE CABO DE GATA AREA
Vera
Sorbas Cabrera
Alhamilla
Carboneras
Níjar
Carboneras
Fernán Pérez
Cabo de Gata
Almería Basin
ta
rra
Se
Neogene Sediments
Neogene Volcanic Rocks
Las Negras
Betic Substratum
Rodalquilar
Cabo de Gata
San José
Key in the following page >>
37
Sedimentary Episodes
SEDIMENTARY EPISODES
Undifferentiated Recent detritus
5º
Conglomerates
Bioclastic Sands
4. After the deposition of the reefs a
phenomenon known as the Mediterranean
Messinian Salinity Crisis took place.The
Mediterranean dried out 5.5 million years ago
as a consequence of its disconnection with the
Atlantic. During this period material around
the borders underwent partial erosion and in
the central area of the large Mediterranean
Basin, and in its marginal basins, important
thicknesses of gypsum and other salts were
deposited. Above these, or above the eroded
surface, carbonate sediments typical of warm
seas were deposited: oolites and stromatolites.
5. A last marine episode that passes into
continental deposition half way through
(in the Pliocene, between 5 and 2 million
years ago).
Marl, Mud and Sand
STRATIGRAPHY OF THE CABO DE GATA AREA
Calcareous Breccia
Gypsum
Coastal reefs
3º
Bioherms, patch reefs
Reef Blocks, slumps
Sierra Cabrera
Cabo de Gata
QUATERNARY
PLIOCENE
Carbonates with oolites and stromatolites
MESSINIAN
4º
Volcanic rocks of around 8 million years old
1º
Bioclastic carbonates, locally volcaniclastic conglomerates
Volcaniclastic rocks more than 9 million years old or undifferentiated
Betic Substratum: Micaschists, Quartzites, Dolomites, Amphibolites, etc
38
Millions of years
Bioclastic carbonates, locally volcaniclastic conglomerates
TORTONIAN
Marls, at times with intercalated diatomites or calci-turbidites
2º
Deposits of the First Marine Basins
Juan C. Braga - José M. Martín
Since the formation of the earliest volcanic
relieves of Cabo de Gata the sea invaded the
area generating small marine basins, extensions
of the self-same Mediterranean Sea. In these
small marine basins, and above the volcanic
relieves, the first marine sediments known in the
Cabo de Gata area were deposited, some 9 to
8.7 million years ago (Lower Tortonian).
The majority of the rocks are carbonates coming
from sediments formed by skeletons (fossils) of
bryozoans, bivalves, calcareous red algae,
echinoderms (sea urchins), barnacles, and
foraminferans (these types of rock are denoted
as bioclastic carbonates). These fossil remains
(shells, winkles etc.) are quite similar to those
organisms that are actually living in the
Mediterranean waters just off of Cabo de Gata
today. Together with carbonates generated by
living marine beings, sediments also
accumulated through the denudation of the
volcanic relieves emerged there (these are
called volcaniclastic deposits).
The Agua Amarga Basin, towards the west of the
town, is one of the areas where these sediments
are better represented.
The sea, in the Lower Tortonian, surrounded
the volcanic relieves. The coastline had
characteristics similar to those of today.
Details of the present-day sea bottom at La
Polarca. The organisms (bryozoans and red
algae) are similar to those that were living
and producing sediment in this period.
The Agua Amarga Basin, for example, was
a small prolongation of the
Mediterranean during this period that
extended between recently emerged
volcanic relieves in the Cabo de Gata area.
Sedimentary structures indicate that the
bioclastic carbonates from the Lower
Tortonian in the Agua Amarga Basin
formed in littoral and shallow
marine environments.
Furthermore, one can
understand a succession in this
material, in which each phase
had a distinctive geography,
characterised by different
sedimentary processes.
Sediments (bioclastic carbonates) from
the Lower Tortonian comprising the
remains of fossils of bryozoans, red
algae and bivalves.
PALAEOGEOGRAPHY OF THE AGUA AMARGA AREA 9 MILLION YEARS
AGO (LOWER TORTONIAN)
PalaeoCoast
line
Emerged
Land
Sedimentation within
marine basin
Agua
Amarga
Present
Coastline
Taken from Betzler et al. 1997
Cross stratification stemming from the
accumulation of sand-sized carbonate grains
of the skeletons of marine organisms
(bryozoans, bivalves, red algae, etc.) in
submarine dunes at little depth.
39
The Re-initiation of Sedimentation After the Last Volcanic Episode
Juan C. Braga - José M. Martín
The last volcanoes in the Cabo de Gata area
were active between 8.7 and 7.5 million years
ago. In this period the domes of some of the
most characteristic relieves of the Natural Park
were formed, like those of the upper part of
Los Frailles, the Cerise de Lobos and Mesa de
Roldan. The extrusion of volcanic material
broke through the older sedimentary rocks in
some places, enclosing blocks within some of
the lavas.
On top of these new volcanoes, and on
occasions on top of older rocks, towards the
end of the Tortonian geological stage, around
7 million years ago, a shallow marine platform
was initiated that marked a renewed incursion
of the Mediterranean around the archipelago
of small islands generated by the volcanic
activity. In this shallow marine environment
mostly carbonate sediments formed from the
remains of marine fossils that were deposited,
for which reason they are called bioclastic
carbonates.
Volcanic eruptions fragmented the sedimentary rocks from the lower episode (Lower Tortonian), light pink
material in the photo, and enveloped them in lavas, dark material in the photo.
Present-day marine bottom in Cabo de Gata. The
organisms present (bryozoans, bivalves and red algae),
are the carbonate producers, that accumulate on the
bottom generating carbonate sediment.
40
Upper Tortonian bioclastic carbonates comprising the
fossil remains of bryozoans, bivalves and red algae.
The Re-initiation of Sedimentation After the Last Volcanic Episode
Inside these shallow marine basins the organisms
produced from carbonate, that is to say those that
have shells, chambers etc., lived in a preferred style
immediately beneath the zone pounded by the
surf, associated to a great extent by plant meadows
with a marine flora.The carbonate particles
produced in this factory were distributed by storms
towards the coast, where they accumulated
in beaches and bars, and out towards the sea, in
successive sheets.Towards zones of even greater
depth the carbonate particles became finer each
time and, finally, gave way to marls formed from
a mixture of clays, transported into the sea by
suspension, and microskeletons of planktonic
organisms.
SEDIMENTARY MODEL FOR THE UPPER TORTONIAN
Nivel del mar
Beaches
Shoals
Factory
Fan Sheets
Stratification and cross-lamination typical
of beach depsoits.
Trough stratification typical of submarine
dunes in shoals.
Accumulations of the remains of organisms
that produce carbonates.
Sheeted fans in the Rambla de los Viruegas.
41
Messinian Reefs
Juan C. Braga - José M. Martín
CORAL REEFS
Some 6 million years ago, in the Messinian
geological stage, and after deposition of the
temperate carbonates and marls described
previously, an increase in the water
temperature allowed the formation of coral
reefs in the SE Peninsula and, particularly, in
the Cabo de Gata region. At the present day,
coral reefs live in waters of little depth in
intertropical latitudes, where the average
winter water temperature does not fall under
20º C. In these sites huge volumes of rock and
sediment are constructed by means of their
calcareous skeletons. The presence of reefs in
our region indicates that, in the period of their
formation, the water was warmer than in the
modern Mediterranean.
Reefs constructed from coral (light tones in the photo), fringing islands of volcanic origin in modern seas, as
would have happened 6 million years ago in Cabo de Gata.
In Cabo de Gata the coral reefs formed on top
of or around the volcanic relieves.
Some of the most characteristic places within
the Natural Park are found to be the reefs of
Cerro de Los Lobos, la Molata de Las Negras,
La Higueruela and Mesa de Roldan. These
relieves were islands or high sea bottoms that
were colonised by coral reefs and could be
completely covered or surrounded by reefs.
Coral reef
Volcanic Dome
Calcareous corals that presently live in the tropics are
the constructors of reefs.
42
In Mesa Roldán, 6 million years ago, a coral reef fringed
and covered a volcanic dome (dark tone).
Evaporites and Carbonates After the Recovery of the Mediterranean
Juan C. Braga - José M. Martín
In certain sectors of Cabo de Gata such as
La Molata de las Negras, Mesa Roldan and
others, above the last reefal episode an
erosion surface is observed that affects
the reef and removes the greater part of its
deposits. This erosion surface is the
expression of Messinian desiccation in
this part of the Mediterranean, known as the
Salinity Crisis.
Field view of
gypsum banks.
Field view of
stromatolites
features, with
their typical
laminar
structure.
Following deposition of the gypsum, both above this level and on top of the erosion surface
Its age is approximately 5.5 million years
that reached the reefs, a sedimentary deposit formed fundamentally by carbonates with
(Terminal Messinian). In effect, around this
stromatolites and oolites can be identified.
time the Mediterranean dried-up, by closing
the communication between the Atlantic
The oolites are particularly spherical, with an internal structure of concentric calcium carbonate
and the Mediterranean, therefore removing
layers.
the entry of water from the former. During
this period, the reefs around the border
remained exposed to erosion, and in
the central sectors, as much in
the main marine basin, the
SEDIMENTARY INTERPRETATION FOR THE GYPSUM IN A MEDITERRANEAN CONTEXT
Mediterranean, as in the small
marginal basins that
5.9 Ma bp
(5.5 Ma bp)
Coastal reef
communicated with it, like
Erosion
Sill
Marginal Basin
Desiccation
that of Sorbas or Almería,
Normal Salinity
important massive deposits of
Gypsum
Gypsum and
Precipitation
other evaporites
gypsum were formed.
Situation prior to deposition of the evaporites,
with formation of reefs in the margins and
muddy-marly sediments in the basin.
Deposition of evaporites in the centre of the
Mediterranean while it is disconnected from the
Atlantic and dries out.
Deposition of evaporites in the interior of
marginal basins as they are being invaded by
the first pools of water in the process of
Mediterranean reflooding.
43
RECENT EVOLUTION AND EMERGENCE OF THE BAY OF ALMERÍA
J. Baena - C. Zazo - J. L. Goy - C. J. Dabrio
The Bay of Almería and Andarax Valley, Campo
de Níjar and area of Roquetas del Mar
surrounding it, made up a large sedimentary
basin during the Pliocene and Quaternary (since
5.2 million years ago), with material mostly
deposited in a marine environment.
At the start of the Pliocene the sea occupied all
of the present low-lying areas: in the west up
to the slope of the Sierra de Gádor, through
the Andarax Valley reaching up to the location
of Rioja and bordering the Sierra Alhamilla,
penetrating across all of the Campo de Níjar
where only the Sierra de Cabo de Gata and
parts of the Serrata de Níjar were emerged.
The Andarax River, that presently discharges
into the sea close to Almería and in a northsouth direction, was located further to the
northeast, between Rioja and Viator, during
the Pliocene.
The high relieves that bordered the
sedimentary basin were traversed by ramblas
which, as at present, provided detrital material
(blocks, pebbles, sand) to the marine basin.
During the Plio-Quaternary uplift in the region
was initiated, leading to the displacement of the
coastline in a southerly direction.
44
Detail of a cemented sand beach. Remains
of a typical tropical marine fauna
(Strombus bubonius) indicated by the
pencil. Rambla de Amoladeras.
Marine deposits of a pebble beach covered
by continental deposits with a calcareous
crust above it. Retamar.
During the Quaternary, as a consequence of
repeated climatic changes, alternating cold
glacial periods and warm interglacials, the sea
level suffered strong variations that could have
been in the order of 130 metres. These
variations were responsible for continuous
changes in the position of the coastline, and for
the distribution and abundance of the different
marine and continental deposits.
In the Bay of Almería a magnificent record of
these distinctive sedimentary environments can
be observed, ranging from continental (alluvial
fans, dune systems, etc.) to littoral and
transitional (submarine deltas in ramblas,
beaches, lagoons and littoral features, etc.).
Detail of a cemented pebble
beach. Retamar.
Deep marine
deposits in the Bay
of Almería.Yellow
muddy
limestones, locally
called Marls with
Leprosy.
Shallow
marine
carbonate
deposits.
Whitish
calcarenites
with fauna.
RECENT EVOLUTION AND EMERGENCE OF THE BAY OF ALMERÍA
EVOLUTION OF THE COASTLINE IN THE BAY OF ALMERÍA FROM THE PLIOCENE (5 MILLION YEARS AGO) UNTIL THE PRESENT
SIERRA ALHAMILLA
SIERRA DE GÁDOR
Ancient position
of the Rio Andarax
SIERRA DE GÁDOR
Ancient
Coastline
Ancient position of
the Rio Andarax
Modern position
of the Rio Andarax
Modern position
of the Rio Andarax
SIERRA ALHAMILLA
SIERRA ALHAMILLA
SIERRA DE GÁDOR
Ancient
Coastline
Modern position
of the Rio Andarax
Almería
Almería
Almería
Modern
Coastline
Modern
Coastline
Modern
Coastline
5,000,000 YEARS AGO
CONTINENTAL AREAS
Airport
Airport
Airport
Ancient
Coastline
Ancient position of
the Rio Andarax
1,800,000 YEARS AGO
900,000 YEARS AGO
MARINE AREAS
Continental Interior
Shallow Water
Ancient Delta
Littoral Fringe
Deep Water
Modern Delta
Ancient Coastline
Modern Coastline
45
RECENT EVOLUTION AND EMERGENCE OF THE BAY OF ALMERÍA
ILLUSTRATIVE GEOLOGICAL PROFILES OF THE STRUCTURE OF THE SEDIMENTARY FILL IN THE BAY OF ALMERÍA
Sª Alhamilla
Sª Alhamilla
Pozo de los Frailes
Sea Level
Níjar
Alquián
Sea Level
Sierra Alhamilla
de
Ní
ja
r
Níjar
Ca
m
po
Sierra de Gádor
Quaternary Deposits
(from 1.8 million years ago to Present)
El Alquián
at
a
ALMERÍA
Upper Pliocene Deposits
(from 3 to 1.8 million years ago)
Sie
rra
de
G
Aguadulce
Bay of Almería
Lower Pliocene Deposits
(from 5.2 to 3 million years ago)
Roquetas de Mar
Miocene Deposits
(from 23.7 to 5.2 million years ago)
Cabo de Gata
Mediterranean Sea
Punta del Sabinar
Volcanic Terrain
(from 15,7 to 6,5 million years ago)
Pre-Neogene
Substratum
Neogene
Volcanic Rocks
Ancient Basement
Sª de Gádor
Almería
46
El Pozo de
los Frailes
Almería Basin
Extension of
La Serrata
Cabo de Gata Basin
Pollux Bank
Sea Level
Neogene and
Quaternary Basins
The Almeria-Nijar Basin
Didactic Itinerary
CABO DE GATA-NIJAR
NATURAL PARK
1
1. Alluvial Dynamics of Ramblas: Las Amoladeras
A. Martín Penela
THE RAMBLAS
Channels
Bars
The Rambla de las Amoladeras is a superb
example of alluvial systems in arid zones. These
river courses, usually dry, represent channels in
which currents of short duration can flow as a
direct result of precipitation, scarcely receiving
water from other sources.
The dynamics of this alluvial system are
fundamentally controlled by the climate and the
shortage of vegetation. Seasonal rains,
frequently stormy and of short duration, create
an important surface torrent, with great erosive
power, that supplies water and sediment to
theses river beds.
A broad valley floor is exhibited, usually with a low sinuosity.
Its river bed is occupied by numerous interweaved channels
and the bottom covered by sediments organised into bars
and channel deposits.Their sediments are mostly made up of
gravel-sized particles.
The channels are very mobile, and develop as furrows
that interweave amongst themselves, adjacent to the
bars, that appear as small mounds, upon which
vegetation is frequently established. The bars, of
different form and size, change their arrangement
and morphology after each flood.
0
Channels
Bars
10/100 m
The floodplain represents a portion of the river bed
that is only inundated during important floods. In it a
great part of the fine materials that were transported
in suspension can be deposited, giving rise to deposits
that favour the development of fertile soils.
Floodplain occupied by
water only during the
largest flood events
49
1. Alluvial Dynamics of Ramblas: Las Amoladeras
FLOODS
As a result of intense storms, the dry
riverbeds in the ramblas can be
transformed, in a short time, into violent
torrents of water loaded with sludge and
detritus. These very intensive floods, sudden
and powerful, can be unduly catastrophic
and cause great destruction in agricultural
zones and to built structures, in the river
beds of the ramblas or within the same
floodplain. The large floods take place
sporadically, tied to seasonal changes or
times of rain.
Damage caused by a flood .
50
PHASES IN A FLOOD
1. DRY PERIOD
2. PERIOD OF STRONG FLOODS
3. PERIOD OF DIMINISHING FLOW
4. PERIOD OF SCARCE ACTIVITY
1. Alluvial Dynamics of Ramblas: Las Amoladeras
ALLUVIAL TERRACES
STAGES IN THE FORMATION OF A SYSTEM OF TERRACES
Alluvial terraces are deposits positioned
sporadically along the side of a valley that
correspond to non-eroded segments of
earlier alluvial sediments. When a
rejuvenation of the alluvial system is
produced by climatic, tectonic or other
changes, water currents deeply erode the
sediments within their channel, giving
rise to a new river course in a lower
topographic position with respect to the
older channel.
1
Stage of alluvial infilling. The
current deposits most of the
sediments that it transports
and produces a river fill.
Alluvial Terrace in the Rambla de Amoladeras.
A change in base level
means that the rambla
evolves in order to reach
a state of equilibrium.
On top of the previously
formed deposits a new
channel is emplaced
which erodes the preexisting alluvium that
had come to construct
the older terrace level.
2
1st Terrace
Older Terraces
Flood-susceptible river bed
Channel
3
Bars
1st Terrace
2nd Terrace
Substratum
If the conditions repeat
themselves, they will be
succeeded by new phases of
filling and erosion from which
various terrace levels will
originate.
51
2. Fossil Beaches of the Rambla de Las Almoladeras
C. Zazo - J. L. Goy - C. J. Dabrio - J. Baena
The surrounding area of the Rambla de las
Amoladeras are characterised by the presence
of one of the most complete geological records
of fossil Quaternary beaches, and with the best
conditions for observation, in the Spanish
coastal zone. These marine beaches, that
fundamentally developed between the last
200,000 years and the present day, were
partially covered on the surface by a dune
system that started to form around 2500 years
ago. In the talus of the right hand margin of the
river mouth of the rambla, a mixture of deposits
consisting of well-cemented sands and pebbles
with a marine fauna can be seen, that represent
ancient beaches, and consequently, the position
of the coast at that time. Average absolute
dating (Uranium-Thorium), has obtained ages
of 180,000 years, 128-130,000 years and
95-100,000 years for the three differentiated
beach levels. All of the beaches contain fossils of
Strombus bubonius. They dominate Tyrrhenian
beaches, a name that is derived from the
Tyrrhenian Sea, for it was there that beaches
with this characteristic fauna were described for
the first time.
An interpretation of the geometry of the
outcrop allows differentiation of, from left to
right: in the first place some conglomeratic
sediments (A) corresponding to the oldest
52
beach, of unknown age, which contains the
remains of a fossil fauna like that which actually
lives in our coasts.
This beach is separated from those which follow
it by a deposit of cemented sand that
corresponds to a fossil dune field, that formed
when the sea descended, leaving the beach
deposits emerged and dried out, such that it
allowed the wind to accumulate sand.
The following deposits (B, C and D) consist of
cemented conglomerates rich in Strombus
bubonius. The separation between the distinct
beaches consists of erosive surfaces, generated
during falling sea level in the coldest periods.
2. Fossil Beaches of the Rambla de Las Almoladeras
Surge
Channels/Grooves
Beach Level
Fault Plane
or Wall
Fosil dune
ACTUAL SECTION
Fault planes
Modern Beach
Sea Level
Well
Modern Dunes
Rambla Amoladeras
INTERPRETED SECTION
SO
NE
Modern Beach
Sea Level
Dunes
D
95.000 years
A
128.000 years
C
B
180.000 years
>250.000 years
Each position of the coastline has left behind an associated fossil beach level. In the river mouth outcrop of the Rambla de las Almoladeras, four superimposed fossil beach levels can be observed
with ages of more than 250000, 180000, 128000 and 95000 years, respectively.The latter three levels contain the remains of a marine mollusc (Strombus bubonius), that still persists in modern
tropical coasts, so that a warm, almost tropical, climatic character existed in the coast during these stages.
53
2. Fossil Beaches of the Rambla de Las Almoladeras
MODERN AND ANCIENT GEOGRAPHIC
DISTRIBUTION OF STROMBUS BUBONIUS
0
IBERIA
Lake Chad
ge
River Nile
Atlantic Ocean
Tropic of Cancer
Ni
r
54
Mediterranean Sea
Canary
Islands
ÁFRICA
Equator
Strombus bubonius is a marine mollusc
Gastropod, typical of warm seas, originating
from the African equatorial Atlantic, entering
into the Mediterranean through the Straits of
Gibraltar when the atmospheric and surface
water temperature of the sea are a few degrees
higher than they are at present. During the last
glaciation, between 65000 and 10000 years
ago, oceanic waters cooled, so that they
prompted a new migration of this species
towards the African equator, in whose
coastline they are found living today, actually
forming part of the diet of townsfolk in this
littoral zone.
1000km
r
ve
Ri
The fossil beaches of the littoral zone in
Almería contain abundant fossils of marine
species that do not inhabit theses coasts at
Present times, although they had populated
the littoral zone between 180,000 and 70,000
years ago. Strombus bubonius is, amongst
others, a fossil of special importance. This has
become used as an excellent palaeoecological
indicator, in that it reveals variations in salinity
and water temperature of the sea with great
sensitivity. Its presence in these fossil beaches
tells us that the sea which bathed the Almería
coastline was at other times warmer,
possessing subtropical conditions.
Gulf of Guinea
S. bubonius, (modern)
Details of the shape of Strombus bubonius from fossil beach
levels, above which the modern littoral boundary is positioned.
S. bubonius, (fóssil)
Cold Canary Current
Dorsal and Ventral views of an example of Strombus bubonius.
3. The Dune System in the River Mouth of Rambla Morales
C. Dabrio - J. L. Goy - J. Baena - C. Zazo
The dune systems that are observed in the
surroundings of the river mouth of the Rambla
Morales are produced by the action of westerly
winds, that lift up sand from the beaches and
transport it towards the river bed, accumulating
it around small bushes or topographic
irregularities in the surface. In this way dune
construction is initiated.
The variation in sea level occurring in this coast
throughout the Pleistocene-Holocene has given
rise to various phases of dune formation.
The oldest dunes are cemented, the most recent
may be: semi-mobile, covered over by
vegetation, or mobile, which are those that
finally bury the earlier ones, in their advance
towards the land.
FORMATION AND DEGRADATION OF THE DUNE SYSTEMS OF CABO DE GATA
B
A
Strombus bubonius
Sea level
C
Westerly Winds
Active beach
Sea level
1
1
1
1
Strombus bubonius
1
2
Primary dune system
Fossil Pleistocene dunes
Fossil
Pleistocene beaches
A slight fall of sea level leaves the beach, slightly more
extended, under the effects of erosion by westerly winds, that
carry along the finest elements (sand) in the form of a train of
dunes (primary system).
On top of the fossil beaches and dunes, the first active beach
of Holocene (less than 10,000 years old) is deposited (1).
2nd active beach episode
1
1
1
Holocene active beach
A new rise in sea level deposits another beach episode (2)
above the previous erosional surface. Dunes continue
advancing.
E
D
2
2
1
1
1
2
1
Modern active beach
2
Second dune system
Another rapid fall in sea level causes a repetition of the same
phenomenon which forms a new train of dunes (2nd system), that
advances mixing with the previous one.
3
2
Finally the last rapid rise in sea level
emplaces the modern beach (3). The dunes
advance, but they have been disappearing
due to intensive quarrying of sand in order
to cover pastural land with sand.
Exploitation of these dune systems is
actually completely prohibited.
55
4. The Lagoon of Rambla Morales
C. Dabrio - J. L. Goy - J. Baena - C. Zazo
In the river mouth of Rambla Molares a small
lagoon, with an almost permanent character,
has been created. Its origin stems from
interaction between the rambla system itself
with the beach. During two times of the year
(end of spring - start of autumn) the
phenomenon called gota fría is registered in
the Mediterranean coast, that comprises intense
and torrential rains concentrated in periods of
very short time (several days). During these
periods the ramblas transport a great quantity
of water and sediment, that is finally to be
deposited in the sea, eroded from the beaches
that previously closed off the river mouth,
showing a great capacity for cleaning out the
rambla (high energy stage).
River Mouth of
the Rambla de
Morales
Lagoon
Aerial view of the river mouth of Rambla Morales.
These sediments are redistributed along the
length of the coastline, during periods of good
weather (low energy stage), by means of littoral
currents or drift currents, that in the case of the
Rambla Morales circulate in a southeasterly
direction, regenerating beaches and barriers once
more. As these beaches are topographically higher
than the bottom of the rambla, towards the land
they leave a small depression that fills up with
water from scarce rainfall that accumulates during
inter-storm periods.This water, not having the
strength of movement, remains stagnant creating
a lagoon in the river mouth of the rambla.
56
Aspect of the modern beach that forms part of the
littoral fringe which closes off the inlet of the rambla.
Closing barrier of
the river mouth
View of the lagoon from the river mouth of the Rambla
Morales. It can be observed how the present,
topographically higher, littoral barrier causes a closing
of the rambla, such that it impedes its normal drainage
into the sea. This situation persists up until when, in
a state of high energy, the rambla breaks through the
littoral barrier nourishing the sea with sediments.
4. The Lagoon of Rambla Morales
SIMPLIFIED SCHEME OF LAGOON FORMATION PROCESSES IN THE RIVER MOUTH OF THE RAMBLA MORALES
1. HIGH ENERGY STAGE
3. NEW STAGE OF HIGH ENERGY
2. LOW ENERGY STAGE
Littoral Barrier
(Beach-Dunes)
Ancient littoral barrier
New littoral barrier
Lagoon
deposits
Temporary lagoon
Sediments
Sediments
Sediments
Rambla Morales
Bars
Littoral
drift
Rambla
Littoral
drift
Lagoon
Littoral
drift
Rambla
57
5. The Salt Pans (Salinas) of Cabo de Gata
J. L. Goy - C. J. Dabrio - J. Baena - C. Zazo
THE NATURAL ALBUFERA
beaches that wash over the barrier beach and
mud carried by the wind have less importance.
The modern salt pans (salinas) of Cabo de Gata
constitute a magnificent example of an
Evaporation, controlled primarily by direct
'albufera' or backshore lagoon system set up as
sunshine and by the wind, plays a very notable
a Mediterranean salt pan by man. This type of
part in the dynamics of these lagoons,
system is natural, and is generated thanks to a
contributing effectively to their desiccation,
depressed area at the back of the coastline,
which is why they can be a suitable mechanism
where freshwater accumulates. It is
for the manufacture of salt.
permanently separated from the sea by a
beach-barrier, forming mainly from sandy
sediments carried by the ramblas and
IDEALIZED GEOMORPHOLOGICAL SKETCH OF THE SALINAS
displaced along the length of the coastline by
littoral drift.
The lagoons receive hydrological supplies from
rainwater, from rivers that discharge into
them and, on occasions, from
Lagoon Border
subterranean aquifers and from
the sea itself.
58
River
Floodplain
Active alluvial fans
Sierra
Bahada
The lagoon tends to fill with
sediments from diverse
sources. The most
important are provided by
the alluvial apparatus
that drain the
surrounding relieves of
the sierras. Sandy
sediments from the
Lagoon
Alluvial
Fan
Evaporation
Bar
Lagoon
R am
bla
rier
Bea
ch
Cabo de Gata
Oleaje
Wind
Bea
Sierra de Gata
Laguna
ch
Waves
Littoral Drift
Aerial view of the active alluvial fan systems that
originate from the Sierra de Cabo de Gata relief. In
many cases they behave as coalescing fans, in that
they are laterally connected and superimposed one
upon another.
5. The Salt Pans (Salinas) of Cabo de Gata
IDEALIZED GEOMORPHOLOGICAL SKETCH OF THE SALINAS
A schematic section of the lagoon
showing the diverse dynamic and
morphological elements.
Atmospheric Dust
Alluvial Fans originating from the
surrounding Relieves
Rain
Evaporation
Currents
A
C
Transfer of Water and Sediment
B
Fine Sediments and
Some Precipitates
Sea
D
E
Infiltration
Groundwater
Depressed Area
Erosion Surface formed
during periods of Low Sea Level
Older Lithified and
Cemented Barrier
Present Barrier
Reworked Littoral Fringe
Fan Cones
Littoral Fringe
Beach
Salt Pans
Albufera
Lagoon
Alluvial Fan
System
Sierra de Cabo de
Gata
The deposits of the lagoon (E) connect
with those of the alluvial fans (A) and
with those of the backshore part of the
beach (B) that obtains sediments
carried during large storms when
swells can spill over the barrier beach.
The model is only active, as at present,
during the periods which high sea level
is maintained that coincide with
interglacials. On the other hand, during
glaciation the sea level had remained
lower, placing the beach towards the
south. In these periods the zone could
remain subjected to the erosive action
of external agents (wind, currents, etc.),
forming an erosive surface (C).
When the lagoon and the littoral fringe
(strandplain) are active, during
interglacial periods, the beach grows
(progrades) towards the sea (D) and
a thick covering of sediments
accumulates in the lagoon (E).
View of the salinas from the south.
59
5. The Salt Pans (Salinas) of Cabo de Gata
WORKINGS OF A MARITIME SALT PAN
The natural lagoon systems like that of Cabo de
Gata have historically been utilised by man in
the extraction of salt: these are the
characteristic maritime Mediterranean salt pans.
Basically this consists of taking water from the
sea in a controlled process of evaporation, by
which means a progressive increase in salinity
is produced, until a stage of saturation and
precipitation of common salts (halite, NaCl) is
reached.
In each a circuit that consists of several
concentration pools (A, B, C) of broad extent and
little depth is established, fed directly by water
from the sea with a salinity of 36 grams per litre.
The seawater is introduced by a channel to
the first concentration pools (A), in which the
marine macrofauna is retained (fish,
gastropods,…) and a settling of (terrigenous)
material from suspension is produced.
Precipitation of calcium-magnesium carbonates
(upon increasing salinity from 36 to 140 grams
per litre) and the elimination of microorganisms (algae, bacteria,…) occurs in the
marine water upon achieving an intermediate
concentration (B). After this initial phase,
the water follows its path through different
concentrations (C), favouring the precipitation
60
SALINISATION PROCESS
Evaporation
Concentrates
Pump
or
basin
C
B
A
350 g/l
140 g/l
80 g/l
(Salinity in grams per litre)
36 g/l
Sea
A
Precipitates
B
C
D
D
325 g/l 370 g/l
Brine
Mg Cl2
Floating salt
(halite) layers
formed in the
absence of
wind.
Aerial view of the salt pans from the east.The letters correspond
to the identification of different areas of the salt pans referred
to in the text.
of calcium sulphate (upon reaching a salinity
of 140 to 325 grams per litre). Once these
undesirable products have been taken out of
solution, the brine goes through crystallisation
(D) where the precipitation of common salt
(at 325-370 grams per litre) occurs, extracted for
storage, purification and finally sale.
6. Volcanic domes of Punta Baja, El Faro and Vela Blanca
Juan M. Fernández
THE VOLCANIC SERIES
The coast in the vicinity of the Cabo de Gata
lighthouse shows an excellent outcrop of massive
volcanic rocks that form the structure of a
volcanic feature known as domes.Their age
of formation is greater than 12 million years.
They are surrounded by a complex sequence of
pyroclastic rocks and lava flows, of varying
composition, that have been affected by
hydrothermal alteration.
Climbing up the vela Blanca hill gives an overview
of the volcanic rock succession that exists in the
southern end of the Sierra de Cabo de Gata.:
◗ The Vela Blanca dome cuts across the tuffs and
might have formed simultaneously with the
previously mentioned lava flows. It is highly
altered and impregnated with manganese
oxides, which give it a very dark coloration
(Punta Negra).
◗ Above the flows, another level of pyroclastic
rocks appears that extends several kilometres
towards the north.
◗ The highest peak (Bujo, 374 m) corresponds to an
andesitic dome that cuts through the previous
sequence. Similar domes are recognised at
different points in the southern massif of Cabo de
Gata.
Bujo (373 m)
◗ Surrounding the Punta Baja-Cabo de Gata
domes, white-coloured rocks known as tuffs
can be recognised. They have a pyroclastic
origin (ignimbrites), that is to say, they are
produced by highly explosive eruptions.
These are the oldest rocks in the area.
◗ Above them, other levels of greyish-coloured
tuffs are developed, also pyroclastic in character.
◗ On top of this andesitic lava flows (rock of
intermediaate character) can be recognised.
They form a well-defined promontory, that is
repeated on the slope through the influence
of various faults. At a distance, columnar
jointing can be recognised.
Dykes
Andesitic pyroclastic levels
Lava flows
Cerro de vela blanca (213 m)
Faults
Grey tuffs
Vela
Blanca Dome
Alluvium
Punta negra
White tuffs
Cala Rajá
Finger reef
Punta Baja Dome
White tuffs (pyroclastic rocks, ignimbites)
Grey tuffs (pyroclastic rocks, ignimbites)
Massive amphibolitic andesites (domes)
Massive amphibolitic andesites (flows, dykes and domes)
Pyroclastic rocks (pyroxene andesites)
Recent alluvial deposits
61
6. Volcanic domes of Punta Baja, El Faro and Vela Blanca
VOLCANIC STRUCTURES
The dome complex of Punta Baja-El Faro-Vela
Blanca comprises several massive lava bodies
aligned in an east-west direction, probably
exploiting a fracture in this orientation as they
are extruded.
Domes are volcanic features that originated
when viscous lava, rich in silica, flowed slowly
onto the surface, and accumulated around,
solidified and plugged its own exit point.
At times the lava does not manage to exit onto
the surface, and forms an accumulation beneath
the intruded rocks, that is called a 'cryptodome'.
The complex in this area contains two principal
domes, one beneath the lighthouse and the
other at Punta Baja, in both of which a
spectacular series of characteristic volcanic
structures may be recognised:
The most pronounced is columnar jointing,
typical of massive rocks. It is produced through
the slow cooling of lava after its emplacement.
Upon cooling the volume of lava diminishes
slightly, and this contraction is accommodated
by the formation of regularly-spaced joints, in a
perpendicular arrangement with respect to the
cooling surface of the lava. The peculiar shape
62
of these hexagonal columns of rock, means that
they have been utilised, in this and many other
place in the Sierra de Cabo de Gata, for
obtaining paving slabs.
generated towards the margins of the domes,
and includes folds that can be formed during
the extrusion. The colour bands indicate slight
differences in the composition of the lava during
extrusion, whilst the flow lamination is produced
by resistance to flow of viscous lava around the
margins of the dome.
Other structures observed in these rocks are
lamination and flow banding. This is mostly
CRYPTODOME AND ASSOCIATED STRUCTURES
Partial emergence
Columnar jointing
Colour bands
Marginal lamination
Country rock (white tuffs)
Nucleus
Breccia (Mónsul type)
6. Volcanic domes of Punta Baja, El Faro and Vela Blanca
White tuff at Cala Rajá, pyroclastic material (ignimbrite) in which the domes of Punta
Baja, El Faro and Vela Blanca are enclosed.
Columnar jointing in the Punta Baja dome.
Fanning of Columnar joints in Punta Baja, traditionally used for the extraction of
decorative paving blocks.
Flow lamination on the margin of the El Faro dome in Cabo de Gata.
63
7. The Mónsul volcanoes
Juan M. Fernández
THE MONSUL SUBMARINE VOLCANOES
The steep volcanic cliffs surrounding the area
of Mónsul consist of volcanic agglomerates
(or breccias).They are a type of rock formed from
angular blocks of (andesitic) volcanic rock, with
a diameter that ranges from millimetres to
metres, enclosed within a fine, sand-sized matrix,
also of volcanic origin.
This material takes its origin from submarine
eruptions produced around 10 to 12 million
years ago, from submerged volcanoes. The
volcanoes were located next to one another, in
a manner in which, once an explosion had
occurred, the erupted material was deposited
in stacked layers on the marine seafloor.
In the panorama in front, the feeder zone of
the volcano can be distinguished. It consists
of darker, andesitic lavas, and exhibits a very
characteristic structure known as columnar
jointing. These structures are produced due to
the contraction of lava upon cooling.
INTERPRETATION OF THE OBSERVED PANORAMA
La Media
Luna inlet
Mónsul inlet
Dunefield Beach
Parking
Agglomerates or volcanic
breccias
Andesitic lavas with
columnar jointing
RECONSTRUCTION OF GENETIC PROCESSES
Sea level during the eruption
Feeding zone of the volcano
64
Beaches and Dunes
Debris
8. The ‘barchan’ dunefield of Barronal or Mónsul
C. Dabrio - J. Baena - J. L. Goy - C. Zazo
Wind carries out two fundamental processes,
erosion and accumulation, which create certain
morphological features; dunes are amongst these.
The term 'dune' is used in a broad sense to
designate the majority of accumulation features, of
sand deposits.
In the dunefields of the Almería littoral zone the
dominant types, according to their morphology in
plan view, are: barchans, or half-moon dunes, with
their corners or points facing in the same
direction as the wind; parabolic dunes, with the
corners (horns) facing in the opposite direction
to the wind; linear (seif) dunes, produced when
a flat zone, with sandy material covering its floor,
exists close to a relief orientated almost
perpendicular to the dominant wind direction.
TYPES OF DUNES IN CABO DE GATA
PARABOLIC DUNES
BARCHAN DUNES
Wind
Crest
Vegetation
Wind
Leeward face
Windward
face
Wind
Depression
Lunite
Corner (horn)
Mónsul barchan dunefield.
1. Accumulation of sand
due to vegetation
2. Migration of the Barchan and
increase in size
Wind
LINEAR (SEIF) DUNES
DUNES ACCUMULATING DUE TO VEGETATION
Wind
Wind
Dune
tum
bstra
nic su
Volca
Movement of sand in favour of the wind
direction in the Mónsul dunefield.
Wind
65
9. The Los Frailes Volcano
Juan M. Fernández
The Los Frailes hill (473 m), is one of the most
distinctive elements of the volcanic Complex.
It consists of two readily distinguishable units
a lower unit of amphibolitic andesites and an
upper unit of dark basaltic andesites, that
correspond to the two main summits (El Fraile
and the more recent El Fraile Chico). Both of the
Los Frailes rest upon andesites, strongly altered
by hydrothermal processes, that make up the
southern volcanic massif of Cabo de Gata.
LOWER UNIT:
AMPHIBOLITIC ANDESITES
The lower unit of Los Frailes constitutes the
collapsed floor of a magma chamber that was
vacated during an individual or several very
intense eruptions. In these eruptions a great
volume of magmatic material left the surface
through rapid and very explosive phenomena,
and the roof of the magma chamber collapsed
giving rise to a chaotic mixture of rock
fragments, associated with dome remains and
lava flows, that constitute the most common
material in this lower unit. The explosive intervals
are marked by intervals of pyroclastic rock (tuffs)
of different types, that are found intercalated
between the units of chaotic breccias. In
numerous places layers of sedimentary rocks are
found in addition, pertaining to beach and
shallow marine environments, rich in fossils;
GEOLOGICAL PANORAMA OF THE LOS FRAILES VOLCANO FROM THE LA ISLETA VIEW POINT
SW
NE
Summit domes
El Fraile Chico
El Fraile (493 m)
BASALTIC ANDESITES
Sedimentary levels
Sacristán
caves
Cerro de
Santa Cruz
Bentonite quarries
Morrón de Mateo
DACITES
AMPHIBOLITIC ANDESITES
San Felipe
castle
Fossil beach of Los Escullos
66
ALLUVIAL FANS
Rambla
SEDIMENTARY UNIT
LA ISLETA DOMES
9. The Los Frailes Volcano
these are intercalated within the volcanic rocks
of the lower unit, and are very abundant
between the lower and upper units. The age of
the lower unit is believed to be between 10.8
and 12.4 million years by some authors, and
around 14.4 million years by others.
UPPER UNIT:
BASALTIC ANDESITES
The summit of Los Frailes is composed of a unit
of basaltic andesites. These rocks are the most
basic (poor in silica) in Cabo de Gata, although
with properties that did not reach the point of
being basalts.
They are relatively well preserved rocks, without
alteration, whose age is estimated at 8.5-8.6
million years. They are also situated above
sediments rich in fossils from the Tortonian,
belonging to shallow marine environments, and
beach sediments. This data indicates that this
upper unit of Los Frailes constituted a volcanic
island during its formation 8 million years ago.
The unit is built from two main emission centres,
that discharged several massive lava flows
(at around 1000º C temperature), whose
characteristic columnar jointing has been utilised
for the quarrying of paving stones (several hills
can be seen in the middle of the slope).
Other eruption phases gave rise to abundant
agglomerates or pyroclastic breccias, in
eruptions somewhat more explosive. The end of
magmatic activity is marked by the extrusion
of the domes that constitute the two
previously-mentioned pinnacles (summit
domes), that sealed the eruption vents. Erosion
has been intense up until now, although the
greater relative resistance of the massive lava
domes has configured a roughly conical erosive
morphology for this unit.
INTERPRETED GEOLOGICAL PANORAMA OF THE LOS FRAILES VOLCANO FROM THE LA ISLETA VIEW POINT
SW
NE
BASALTIC ANDESITES (8 M.A.)
San Cerro de
José Enmedio
RELLLANA de
Rodalquilar
El Fraile
SUMMIT DOMES
IGNIMBRITES OF THE
RODALQUILAR CALDERA
LAVA FLOWS
SEDIMENTARY LEVELS
VOLCANO-SEDIMENTARY UNIT
OLD AGGLOMERATES
(ANDESITES)
AMPHIBOLITIC ANDESITES
(12-10 M.A.)
MASSIVE ANDESITES
67
10. The fossil dunefield of Los Escullos
C. Zazo - J. L. Goy - J. Baena - C. Dabrio
In the Almerían littoral zone there have been
three important phases dune system
development during the Quaternary: greyish
cemented dunes, formed of the fragments of
schists, volcanic rocks, and quartz grains, such as
those that are observed in Rambla Amoladeras,
and which formed at a time known to be
between 250,000 and 180,000 years ago; whitecoloured oolitic dunes, consisting of rounded
grains known as oolites, around 128,000 to
100,000 years old (last interglacial period); and
finally, greyish, uncemented dunes , that illustrate
the same coloration and composition as the first,
although in this case they were not cemented,
formed from around 6,000 years ago to the
Present.
In the Los Escullos cove, beneath the San Felipe
castle, we can observe, without doubt, the best
exposure corresponding to white, oolitic dunes
in the Natural Park. However, other exposures
exist in the Rodalquilar and Los Genoveses
beaches.
These ancient dune systems are excellent
indicators, not only of the position of the
coastline at the time of its formation, but of the
ecological and environmental conditions.
In effect, the oolitic dunes were generated due
to the movement of old oolitic beach sediments
68
by the wind, formed in a warmer environment
than at present. This is knowwn through the
existence of an associated fauna (Strombus
bubonius)that belongs to warm seas, and by the
ooliths themselves. Through the microscope it
can be observed that the ooliths are composed
of a nucleus of quartz grains or rock fragments
or faecal pellets and a coretex that shows
concentric layers of aragonite. Oolites actually
form in the infralittoral zone, at a few metres
depth, on the seafloor of warm waters that are
saturated in carbonate and highly agitated by
waves.
San Felipe castle of los Escullos
Isleta del Moro
Oolitic
dunefield
The San Felipe castle of Los Escullos sits on top of a
spectacular fossil oolitic dunefield.Without doubt the best
record of this type of deposit in the area of the Natural Park.
In the Cabo de Gata Natural Park area, fossil oolitic
dunefields exist in other places: here the exposures of Los
Genoveses may be observed.
10. The fossil dunefield of Los Escullos
OOLITIC DUNES OF LOS ESCULLOS
Los Escullos
Oolitic dunes
Los Frailes
Sea
DETAIL OF THE OUTCROP
A
Ooliths
B
Dirección de paleovientos
INTERNAL STRUCTURE OF THE DUNES
Microscopic view (thin section) of the components of dune
oolites from Los Escullos (Photo A). Upon increasing the
resolution (Photo B) the ooliths can be identified perfectly as
the spherical structures that stand out within the sandy matrix.
69
11. Alluvial fans of the La Isleta-Los Escullos coastal plain
J. L. Goy - C. Zazo - C. Dabrio - J. Baena
The Sierra de Cabo de Gata exhibits an abrupt
relief, with strong slopes, that contrasts with the
gentle morphology of the littoral depressions
(coastal plains).The abrupt change of slope that
is produced in the courses of small barrancos as
they exit from the mountain relieves, and enter
the depression, provokes a fall in their capacity to
transport and the consequent accumulation
(deposition) of the sediments (blocks, pebbles,
silts, etc.) which they moved towards the most
low-lying areas. An open alluvial fan in thus
formed.
SIMPLIFIED GEOLOGICAL SCHEME OF THE QUATERNARY DEPOSITS IN THE LA ISLETA-LOS ESCULLOS AREA
Fluvial deposits
Holocene
Alluvial fan
deposits
Phase 6 (c)
Channel deposits of
terraces and rivers
Present river
Phase 6 (b)
Slope deposits
Gravity deposits
Colluvium and
undifferenciated
slope deposits
Littoral deposits
Marine deposits
Aeolian
deposits
Beach
Littoral barrier
2nd Terrace
Phase 5
Pleistocene
Quaternary
Phase 6 (a)
Phase 4
Phase 3
Phase 2
Phase 1
Miocene
70
1st Terrace
Volcanic rocks
Abandoned
river
Aeolian dunes
11. Alluvial fans of the La Isleta-Los Escullos coastal plain
A fall in sea level, linked to the slow uplift of
the relief, caused incision of the initial
barranco (primary river course) in the
deposits of the older open fan, upon whose
surface soils were already able to develop.
PROCESSES OF DEPOSITION AND INCISION IN ALLUVIAL FANS
OPEN FAN
INCISION
Sierra de Cabo de Gata
Sierra de Cabo de Gata
Paleosuelo
The formation of subsequent fans, during the
initiation of a new rise in sea level, gives way
to incised fans at a lower altitude to the
previous one.
Sea level
In the area of La Isleta-los Escullos, several
incised surfaces (roofs of fans), inclined
gently towards the sea are observed, that
represent distinct phases of fan formation
throughout the Quaternary. Theses are due
to changes in the climatic conditions,
tectonics and eustacy (oscillations of sea
level), and their study provides very
interesting information about such
conditions.:
Sea level
Slow uplift
Fan formation phase 1
Los Escullos
Fan formation phase 2
La Isleta
Aerial view of La Isleta-Los Escullos in which phase 2 alluvial fans may be observed, with a schematic overlay.
71
11. Alluvial fans of the La Isleta-Los Escullos coastal plain
PANORAMA FROM THE LA ISLETA VIEWING POINT AND INTERPRETATION OF THE ALLUVIAL FAN SYSTEM
Alluvial fan
entrenchment
Cerro de Los Filabres
Los Escullos
Phase 3
alluvial fan
Phase 1
alluvial fan
Phase 2
alluvial fan
Beaches
Oolitic dunes
LA ISLETA VIEWING POINT
72
Undifferentiated slope deposits
Beaches
Phase 1 alluvial fans
Volcanic rocks
Fossil oolitic dunes
Phase 2 alluvial fans
Phase 3 alluvial fans
12. Rodalquilar volcanic calderas
Juan M. Fernández
One of the most significant volcanic structures
of the Cabo de Gata Volcanic Complex are the
Rodalquilar calderas, from the centre of which
known gold deposits are located. Rodalquilar
shows the superposition or nesting of two
successive calderas; the larger is the
Rodalquilar caldera, and inside it the La Lomilla
caldera is located (thus named after La Lomilla
de Las Palas). Theses calderas are collapse
structures produced by highly explosive
eruptions, that gave place to tow large units of
pyroclastic rock, known as the Cinto
ignimbrites and the Lázaras Ignimbrites,
respectively. Calderas are collapse features that
are produced when, during an explosion of
great magnitude, the magma chamber is very
rapidly vacated and its roof collapses, leaving
behind a roughly circular depression.
Detail of the Cinto
pumice flows. The dark
stippled area
corresponds to large
quartz crystals.
INTERPRETED GEOLOGICAL SKETCH OF THE RODALQUILAR VOLCANIC CALDERA
Caldera de Rodalquilar
SE
NW
Caldera de la Lomilla
La Rellana
Mines
Lázaras ignimbrite
Cerro del Cinto
La Isleta
Domes of the
caldera margin
Detail of the Cinto collapse breccias. Concentration
of (dark) blocks within a pumice flow (lightcoloured).
Collapse breccias
Pre-caldera
rocks
Altered andesitic
intrusions
Cinto ignimbrite
600
400
200
Sea level
-200
-400
-600
-800 m
Unaltered andesitic intrusions
73
12. Rodalquilar volcanic calderas
GEOLOGICAL HISTORY
The Rodalqular Caldera and the Cinto
Ignimbrite
The Rodalquilar Caldera is the larger, with a 4km
by 8km width and an oval shape. Its origin is
related to the thick pyroclastic unit of the Cinto
Ignimbrite, which formed 11 million years ago,
on top of a mass of older mass of andesitic
flows (A), due to collapse of the magmatic
chamber.
Since the collapse of the Rodalquilar Caldera
and formation of the Cinto Ignimbrite (B), the
magmatic chamber refilled itself, and the
ignimbrites filling the caldera bulged outwards,
making way for the present Cerro del Cinto
(a resurgent dome). This phenomenon is very
common during caldera formation processes,
and is called resurgence (C).
The system of fractures generated during
the collapse were later infilled through the
development of a hydrothermal system and by
mineral deposits.
Thin layers of sedimentary and volcanic rocks
were deposited on top of the planar surface of
the Lázaras Ignimbrite.
FORMATION OF THE MAGMATIC CHAMBER
Pre-caldera volcano
Pre-caldera andesites
Magma chamber
B. FORMATION OF THE RODALQUILAR CALDERA
Rodalquilar Caldera
Cinto Ignimbrite
Filling of the caldera
Collapse
breccias
C. RESURGENCE
La Lomilla Caldera and the Lázaras
Ignimbrite
A new episode of intense eruptive activity gives
way to the formation of the Lázaras Ignimbrite,
simultaneously with the collapse of the La
Lomilla Caldera 9D). this caldera is 2 km in
diameter and is nestled in the Rodalquilar
Caldera.
74
Ring
dome
Resurgent dome
Resurgence
12. Rodalquilar volcanic calderas
D. FORMATION OF THE LA LOMILLA CALDERA
La Lomilla Caldera
Lázaras Ignimbrite
Sediments
RESURGENCE AND FORMATION OF THE HYDROTHERMAL SYSTEM
Hydrothermal system
Andesites
Resurgence and hydrothermal systems
The end of magmatic activity in
Rodalquilar is marked by the emission
of a series of flows and the extrusion of
andesite on the surface, and the formation
of an intrusion just underneath the
Rodalquilar calderas. This new phase
of resurgence of the magmatic system is
accompanied by a doming of the pile of
volcanic material, the opening of fractures
and the development of the hydrothermal
system, which produced alteration of the
rocks and the formation of mineral
deposits. The age is younger than 9 million
years. In this phase a series of very
extensive fractures formed with a northsouth orientation, that were partly infilled
through mineralization.
Finally, all of the associated volcanic
deposits were covered by marine
carbonate sediments at the end of the
Miocene (latest Tortonian and Messinian),
forming the features of La Molata, Romeral,
Molatilla, etc.
Domes formed on the ring-like margin of the caldera.
The Lázaras Ignimbrite corresponds to a tuff formed
from pumice fragments (dark colours) in a matrix of
fine ash (light colours).
Reef complex
Contact
Intrusion
Resurgence
La Molata carbonates on top of the ignimbrites of
the Rodalquilar caldera.
75
13. Mining and metallurgical processes in Rodalquilar
Carlos Feixas
MINING IN RODALQUILAR
Exploitation of gold in Rodalquilar has been
carried out by means of two very different
methods, such that it relates to extraction as
much as to the retrieval of precious metal.
Mining in the 19th century and at the start of
the 20th century, was carried out by internal
exploitation of high-grade quartz veins through
means of shafts and galleries. On the other
hand, mining took a new path from 1956
through the National Company ADARO,
characterised by combined exploitation; interior
workings with high grade material (over 5
g/ton), and cutting or quarries on the outside,
with lower grade material (1 to 1.5 g/ton)> the
mixture of these products allowed intermediate
grades of 3 g/ton to be obtained, optimal for
the type of extraction plant that was working it.
In the last decades of the 19th century and the
start of the 20th century, the recovery of gold
was carried out through means of smelting
furnaces obtaining a lead blende rich in
gold and silver. In the second half of the 20th
century, recovery was carried out through the
operation of electric furnaces, after
concentrating by means of washing with
cyanide solutions.
76
Opening of the track that connected the Cerro del Cinto
mine workings with the grading and concentration plant.
This infrastructure already meant an enormous advance
that opened up the possibility of mechanising the quarrying
system (Photo, Evaristo Gil Picón).
Mine entrance of 'Lode 340' during the period of maximum
activity in the mining district of Rodalquilar. The
photograph is taken roughly in the 50's decade (Photo,
Evaristo Gil Picón).
13. Mining and metallurgical processes in Rodalquilar
QUARRYING METHODS
Spoil rock
Mineralization
The extraction workings in the
interior are achieved by following
the auriferous lodes and exploiting
raised chambers (A); the materials
was removed by shafts and
galleries (B). The outside workings
were carried out on small, terraced,
quarry benches (C). The minerals
obtained in this way were mixed
and piled up ready for transport to
the treatment plant (D).
C
A
B
D
Cerro del Cinto quarry cuttings
completed by ADARO in order to
supply the treatment plant.
The darker structures
correspond to the richest lodes
(Photo, Juan M. Fernández).
77
13. Mining and metallurgical processes in Rodalquilar
METALLURGICAL METHODS
The quarried mineral was mixed in a storage
shed (1), and afterwards subjected to initial
crushing in a grinding machine (2), and secondly
in a mill (3). Later it was classified in vibrating
sieves (4 and 5).This product was submitted to
electromagnetic separation (6), in order to
eliminate metals other than gold. Afterwards it
was milled in ball mills (7).The remains were
classified in pressure washers (8) in order to
separate the fines, without gold, and return the
pieces with gold to the mills for grinding. The
minerals concentrated in this way were mixed in
two heavy tanks (9) with a solution of cyanide
(10) in order to subject it to the following
chemical reaction in a medium with pH 9 to 11:
16) in order to activate gold precipitation in the
following reaction:
2 NaAu(CN)2 + Zn ---> Na2Zn(CN)4 + 2Au.
This process is known as “Merril Crowe”.
The precipitate in the tanks comes from a
process of retrieval through precipitation by
OPERATIONAL RECONSTRUCTION ACCORDING TO THE
METALLURGICAL PROCESSES IN THE ACTUAL
INSTALLATIONS OF RODALQUILAR
1
5
6
2
3
4
Photograph from an era when the mining
installations of Rodalquilar were working. The
photo dates from the 50's decade (Photo, Evaristo
Gil Picón).
8
4 Au + 8 CNNa + O2 + 2 H2O --->
4 Na(CN2 Au) + 4 NaOH.
means of zinc dust, with zinc content of
between 10 and 40%; it is put through an
electric heater for drying, where the last traces
of humidity are removed. The dry product is
precipitated by acid washing and the precipitate
is removed through filtration. The gold is
obtained by fusion in an electric furnace.
7
10
9
9
In 4 cleaning tanks (11) the mixture of mineral
and cyanide is removed and ventilated in order
to obtain the solution rich in gold, that is
reclaimed in the tank (12). The cyanide solution
is rinsed in tanks (13) and afterwards put
through a filter. Immediately following the
ventilation continues under a partial vacuum by
means of pumps in tanks (14) and, straight
afterwards, is added to zinc dust in a tank (15,
78
11
11
11
11
12
13
14
15
16
17
System of cleaning tanks in operation (Photo,
Evaristo Gil Picón).
14. The Post-volcanic sediments of La Molata de las Negras
Juan C. Braga - José M. Martín
In La Molata de Las Negras sedimentary rocks
are present that record the geological history of
the Cabo de Gata region since the volcanic
activity. Above the volcanic basement a series
of sedimentary units may be observed that
correspond to deposits formed in a small basin
(an inlet or bay), connected with the
Mediterranean, and presently emerged, uplifted
above the present sea level. The presence of
coral reefs and oolitic limestones indicates that
during the formation period of units B, C and D
(Messinian), the climate of the western
Mediterranean was warmer than at the present
day and similar to that of tropical latitudes at
present.
La Molata
D
La Joya
Bioherm
C
B
A
UNIT A
Consists of bioclastic limestones; rocks composed
of the remains of bryozoan skeletons, bivalves, red
algae, starfish, sea urchins and foraminiferans.
These organisms lived in the small marine basin of
Las Negras, joined to the Mediterranean in the
Upper Tortonian-Lower Messinian, around 7
million years ago.The organisms whose remains
form these rocks are similar to those that today
live, and produce sediment, in the marine platform
surrounding Cabo de Gata.The climate in the
region during this period would have been similar
to present or slightly warmer. A small proportion of
Volcánics
theses rocks comprises clasts and grains coming
from the erosion of the volcanic relieves.
Field view of
bryozoans and
fossil bivalves
that formed the
limestone
of Unit A.
The remains of calcareous algae and bryozoans
that presently live on the seafloor of the Cabo de
Gata platform produce a sediment similar to that
which formed the limestone of Unit A.
79
14. The Post-volcanic sediments of La Molata de las Negras
UNIT B. CORAL REEFS
TAfter deposition of the bioclastic limestones
there was a stage of uplift and deformation of the
basin seafloor, in such way that before
the following unit (unit B) was deposited, the
bioclastic limestones were inclines and
underwent erosion (observed in the panorama
and view point from the central part of the
hillside).
In Unit B, formed during the Messinian around
6 million years ago, coral reefs stand proud in
the form of isolated pinnacles (bioherms), such
DISTRIBUTION AND STRUCTURE OF BIOHERMS IN THE REEF STRUCTURE
A. Diagram of a reef mound
(bioherm)
Hemispherical colonies
Sticks
10 m
Breccias and calcarenites
Laminar colonies
B.Scattered distribution of
bioherms in the platform
Basin
Slope
as that which stand out in the panorama, easily
appreciable from this perspective. These reefs
are mainly formed through the in situ
accumulation of the calcareous skeletons of
corals belonging to several genera (Porites,
Tarbellastrea and Siderastrea). Between the coral
colonies and around the pinnacles, algae and
invertebrates lived, whose skeletons also
contributed to the formation of carbonate
sediment. Blocks derived from these reefs, such
as that observed to the left of the large pinnacle,
fell down slope and became mixed with the
marls and mud that were being deposited in the
sea offshore, in deeper regions, situated towards
our left. Marls formed through the settling of silt
from suspension in seawater, and through the
accumulation of the skeletons of planktonic
micro-organisms such as foraminifers, unicellular
algae, and at times diatoms.
Platform
100 m
Slumped blocks of bioherms intercalated between fine-grained sediments in the basin
80
Tarbellastrea coral colony, one of the components of the Unit
B bioherms.
14. The Post-volcanic sediments of La Molata de las Negras
UNIT C
Corresponds to a fringing reef that was
advancing from our right towards our left.
Here the corals are almost exclusively Porites
and the coral colonies are surrounded by
foraminifers and encrusting red algae; that in
turn are covered by stromatolites, that is to say,
carbonates that are precipitated (or bound)
by the action of micro-organisms, mainly
cyanobacteria.Towards the sea (towards the
left), the reef gave way to a slope where debris
coming from its destruction accumulated.
The grain size of this debris is segregated
downslope, in a way that it continually
becomes finer. Between the reef debris, other
organisms grew, such as calcareous green
algae (Halimeda) and bivalves.
Unit D is fundamentally formed from stromatolites
and oolitic carbonates. The latter are made up of
microscopic, spherical particles, called ooliths, with
an internal structure of concentric layers of calcium
carbonate. Oolites are presently forming in the
shallow, agitated waters of tropical seas.
Stromatolites are domes or irregular constructions
formed by miilimetre-thick (or less) layers of
carbonate.
DIAGRAM SHOWING ONE PHASE OF REEF GROWTH
N-S
Reef
framework
Distal slope
Proximal slope
UNIT D
Rests on an erosion surface that had an effect on
the reef (Unit C) and removed a large part of its
deposits. This erosion surface is the expression of
the Messinian desiccation of the Mediterranean at
this locality, known as the salinity crisis. Its age is
end Messinian (around 5.5 million years ago).
laguna
Talus
slope
Lagoon
Bioclastic breccias
Reef crest
Coral thicket
Coral pinnacles
Calcirudites
Coral blocks
and breccias
Calcilutites
10 m
0
Calcarenites
10 m
Microscopic view of ooliths that
formed the carbonates of Unit D.
Field view of stromatolites, with their
typical laminated structure.
81
15. Bentonites of cabo de Gata
Carlos Feixas
GENESIS AND NATURE
OF BENTONITES
Bentonite is a rock composed of minerals
from the clay group. Their internal structure
of superimposed layers of different chemical
composition defines their key characteristic:
their capacity to absorb a quantity of water
several times greater than their own volume.
This is produced through storage of fluid
in the spaces that exist between the different
layers.
The Cabo de Gata bentonites are by nature
around 75% to 95% Calcium-SodiumMagnesium types, and the rest of the rock
consists of other types of clays and small
quantities of other minerals originating from
volcanic rocks. They display various colours,
from reds, greens, yellows and blacks, to whites.
The deposits have an irregular and stratified
morphology.
SIMPLIFIED DIAGRAM OF BENTONITE FORMATION
Bentonites originate from the alteration
of volcanic rocks, also through processes of
hydrothermal alteration (rise of hot solutions
through fractures) or also through weathering
alteration (due to the action of meteoric
water).
200 m
Alteration of volcanic
rocks to bentonite
200 m
The special composition of the Cabo de Gata
volcanic complex means that within it the
greatest concentration of bentonite deposits in
Spain formed. In fact, they constitute the only
exploited industrial minerals that exist within
the Natural Park.
Volcanic rock
Bentonite
Descent of cold meteoric water
Increased heat
Increased heat
82
Ascent of hot hydrothermal solutions
15. Bentonites of cabo de Gata
DISTRIBUTION OF QUARRYING. GEOLOGICAL MAP OF THE CABO DE GATA AREA
Undifferentiated Recent detritus
Pliocene sand and conglomerate
Carboneras
Marls, clay, sand and carbonate
Gypsum
Fringing reef, marl and bioclastic carbonate
Bioclastic carbonate
Bentonite quarry exploited in an intermittent fashion in the
Serrata de Níjar. The bentonite masses that display some
colouration hold less commercial interest than those that are
white.
Volcanic rocks
Fernán Pérez
Betic substratum
Se
5 Km
A
ta
rra
B
Las Negras
Rodalquilar
C
Cabo de Gata
Quarrying of white bentonite in the area of Morrón de Mateo.
San José
The main areas of quarrying within Cabo de
Gata are found in:
Cantera de Los Trancos (A)
Cortijo de Archidona (B)
El Morrón de Mateo (C)
83
15. Bentonites of Cabo de Gata
Bentonite mining is carried out through an
open cast quarry method. In a modern quarry
the following activities are undertaken:
◗ Conditioning and preparation
The discovery of productive layers takes place
with the help of excavating machines or
mechanized tractors.
◗ Extraction
Once the surface is cleaned off, quarrying is
carried out by cutting down benches
lengthwise along the face, with a height of
about 10 metres and a length close to 50
metres.
◗ Drying and classification
The material quarried in this way is spread out
across large areas or “heaps”, cleaned of
impurities and classified by qulaity according
to the use for which it is destined.
◗ Storage
The dried and classified material is stored in
large uncovered piles ready for transport to
treatment plants or for direct sale.
84
The mineralized body might be covered by non-mineralized
rocks that need to be removed for quarrying.
Extraction
Los Trancos quarry is the principal bentonite mining concern
in the park. The extent of the quarry benches can be observed,
taking the lorries as a scale.
Conditioning
and preparation
Pile
Drying
Bentonite
Classification
Volcanic rock
15. Bentonites of Cabo de Gata
USES AND APPLICATIONS
Bentonite clays, due to their physical properties,
are utilised in many industrial fields.
◗ In the smelting industry they are used, along
with siliceous sand, to prepare the mould of
manufacture parts, in that they are capable
of fusing together the sand, without altering
the composition of the cast.
cleansing aids and fertilizers, also as
discolourants and clarifiers of wines and oils.
◗ Properly compacted it is an excellent
impermeable material, used to this end for
holding back and securing residues in storage
containers and potentially contaminant
substances.
◗ Addition to cements allows mortars to remain
fluid for a longer period of time, for which its
use is essential in special cements.
◗ As an integral part of drilling mud. Due to its
addition, the viscosity of the drilling mud
increases and is capable of pulling out broken
components more easily. Additionally, it is
capable of covering and keeping the walls of
the borehole intact when drilling of the
borehole finishes.
◗ Its addition to powdered irons minerals means
that they can be recovered in a profitable way
from smelting.
◗ Their capacity for absorbing water and ionic
exchange means that they can serve as
Characteristic field view
of bentonite clays: whitecoloured powdered
masses, greasy to the
touch and very plastic.
85
16. Marine sediments of Cañada Méndez (Agua Amarga)
Juan C. Braga - José M. Martín
In the outcrops of Cañada Méndez,
exceptionally exposed carbonate sediments
generated in temperate and shallow marine
platforms, with temperatures and salinities
identical to the modern Mediterranean, are
exposed. They are located directly on top of
volcanic rocks 9.6 million years in age. At the
very base of the sediment succession, just
above the volcanics and immediately beneath
the carbonates, sand of volcaniclastic character
appear (that is to say, supplied by erosion of the
same volcanic rocks) with a few marine fossils
(essentially the remains of shells).
structures are extremely abundant in the
carbonates, such as lamination, crossstratification, etc., reflecting their transport
through the action of waves and by currents
on the same marine bottom.
Two different carbonate units are represented.
The lower stands out here as the most
important, known informally as the red unit
due to its characteristic colour. It is Lower
Tortonian in age, roughly 9 million years old.
These carbonates are bioclastic in nature.
They consist of the abundant, highly
fragmented remains of calcareous marine
organisms typical of shallow marine
environments (0 to 100 m deep), such as
bryozoans, red algae, bivalves, echinoderms,
brachiopods, benthic foraminiferans,
barnacles, gastropods and solitary corals,
clearly visible in hand specimen and/or by
microscope. Ordered internal sedimentary
86
Fragments of typical carbonate
producing organisms in the
platform environment.
16. Marine sediments of Cañada Méndez (Agua Amarga)
SEDIMENTARY RECORD,
PALAEOGEOGRAPHICAL EVOLUTION
AND SEDIMENTARY MODEL
OF THE AGUA AMARGA BASIN
The sedimentary record in this area allows us to
reconstruct the palaeogeography of the
Agua Amarga Basin during the Lower Tortonian
based on the interpretation of its distinct
environments of deposition. Its
palaeogeography was essentially that of a small
bay, open towards the south, with a small
submarine high (ridge) situated right at its
entrance, especially notorious for determining
episodes in its history. The basin was filled by
different packages of sediments in successive
phases.
PHASE 1: In the initial phase ramblas reached
the bay, extending into the sea in the form of
submarine fans. The underlying volcaniclastic
sands correspond to deposits of the distal part
of these sand fans, coming from the destruction
of volcanic relieves.
Platform carbonates are positioned immediately
above. By means of the dominant sedimentary
structures it is possible to differentiate four units
in the interpreted section:
PHASE 1
PHASE 2
100 m
100 m
Palaeocoastline
Palaeocoastline
600 m
Present coastline
Present coastline
Agua amarga
Agua amarga
PHASE 3
PHASE 4
50 m
Palaeocoastline
100 m
Palaeocoastline
Present coastline
Present coastline
Agua amarga
Agua amarga
Taken from Betzler et al., 1997
87
16. Marine sediments of Cañada Méndez (Agua Amarga)
PHASE 2: A lower unit in which the most
characteristic features are layers of crossstratification (of rectilinear appearance, Photo
A), separated by very low-lying (almost
horizontal), sharp and continuous surfaces.
They are the deposits of storm-generated fans,
deposited on the protected side of a high or
submarine volcanic ridge located to the south.
PHASE 3: An intermediate phase with
abundant trough cross-stratification (in curves,
Photo B). They are interpreted as marine dunes
that migrated parallel to the coast.
PHASE 4: An upper phase in which the most
characteristic sedimentary structures are lowangled parallel lamination (Photo C), this
corresponds to typical beach sediments.
Laterally, and superimposed on the previous
deposits, a last unit composed of fine sands with
high-angled, poorly-developed, and/or
unconsolidated muds without evident
sedimentary structures (Photo D). These are
interpreted as coastal aeolian dunes and
lagoons, respectively.
ACTUAL PANORAMA OF THE INTERPRETED FIELD SECTION
PHOTO A. Field view of layers with tabular
cross-stratification, tied to storm fans.
PHOTO C. Low-angled parallel lamination
corresponding to episodes of beach
progradation.
INTERPRETATION OF THE OBSERVED PANORAMA
PHOTO B. Field view of trough crossstratification produced by the migration of
sub-aquatic dunes.
88
Volcanic
substratum
Storm fans
Beaches
Upper
carbonate unit
Volcaniclasstic
rocks
Sub-aquatic
dunefield
Coastal
Lagoon
Debris
PHOTO D. Mud levels (soft sediments)
formed in coastal lagoons.
17. The Quay at Agua Amarga
José Vicente Coves - José Antonio Gómez
The extensive development of mining
activity during the 19th century and first
decades of the 20th century in Almería
Province furnished the existence of a
mining railway network of which only the
vestiges are preserved at the present day.
One of the routes is that from Lucainena
to Agua Amarga. Across the Natural Park
parts of the railway can still be seen and
are preserved, and the mine workings
quay at Agua Amarga although very
deteriorated. This constitutes, along with
Rodalquilar, one of the 2 most interesting
archaeo-industrial elements of the
Natural Park.
The plans of work were decided, in March 1894
the project wording was finalised and signed off
by D. Cayetano Fuentes, and on the 18th of
February 1895 the concession was granted by
royal order. This was for an economic railroad,
without any government grant and for a period
of 99 years. Nevertheless, in September 1894,
work on the construction of the railway had
already started, and, one month later, the
Biscayan company announced the purchase of
63,000 oak sleepers.
The works were progressing and, GENERAL VIEW OF LUCAINENA - AGUA AMARGA
by the middle of 1895, the
LUCAINENA
quayside-unloading bay had
Pte. Rafaela
NATURAL PARK
been completed. Finally, in
PERALEJOS
Rambla
Pte.
Molinillo
March 1896 the work ended.
Honda
rra lla
Collado de
Sie ami
Bco. del
In May the first shipment of
h
Polopillos
Al
Valenciano
Río Alías
CARBONERAS
minerals accumulated in the
Venta del Pobre CAMARILLAS
d
Agua Amarga storage facilities
a
LA PALMEROSA
ro
ía
er
Línea de
boarded the steamboat ALBIA.
Mesa
lm
NÍJAR
Locomotive LUCAINENA (Nasmyth Wilson 464/95), one of
the machines used on the mineral transport line from
Lucainena to Agua Amarga. The photo dates from the
end of the 19th century (Photo, Col. J.M. Sánchez
Molina).
The cost of installing the
railway was 3,500,000 pts, the
mineral storage area was
credited with a cost of 60,000
pts and the quay 265,000 pts. The total
investment for establishment was around
3,675,000 pts with an average investment cost
of 100,000 pts/km.
-A
ra
Ve
ferrocarril
Roldán
Collado de
Albacete
de
rra
Sie
ta
Ga
AGUA
AMARGA
M
ite
ed
an
ne
rra
a
Se
In 1901 the transport of minerals by railway
was attributed a cost of 0.025 pesetas per ton
per kilometre, and the loading cost was 0.123
pesetas per ton.
89
17. The Quay at Agua Amarga
Although the mining venture company
maintained a good level of activity in the first
decade of the 20th century, in the second the
second the marked started to no longer be
favourable. In the years that followed the First
World War, a grave iron industry crisis which
took place in Europe and Spain, meant a tough
trial for national mining of iron. In 1919 and
1920 the Agua Amarga storage facilities were
completely full of a mineral that no one
bought. These difficulties were compounded
by competition from North-African mines,
salary rises that started to be introduced
around this date, and included the loss of
personnel due to the strong migratory
movement recorded in Almería Province
during this period.
The company endured a marked decline until
in 1931, and faced with the impossibility of
exporting its iron, it was forced to temporarily
suspend operation of the railway. Operation
was sporadically renewed, but in 1930, with the
state of civil war, the situation worsened.
During the three years of struggle the mines
and railway remained in the hands of its own
workforce, although without great activity.
In 1939 transport by rail was restarted until
activity finally ceased in 1942, the date in
which the steamboat Bartolo loaded for the
90
last time in Agua Amarga. A little later the
mining installations and railroad started to be
dismantled. The locomotives, the bridges and
the railway were taken apart and transported
in lorries to Almería.
RECONSTRUCTION OF THE INSTALLATIONS OF THE
MINING QUAY AT AGUA AMARGA
Agua Amarga
17. The Quay at Agua Amarga
Present state of the mining installations in the mineral working quay of Agua Amarga. To the right a general view of the installations can
be observed: in the background the Sierra Alhamilla, place of iron exploitation and origin for the transport network; in the foreground, the
large inclined plane through which the wagons carrying minerals could descend to the silos. On the left, the remains of the said 'silos' used
for mineral storage prior to final loading (Photographs, M. Villalobos).
The boat BARTOLO receiving the last cargo shipped out of Agua Amarga from the
Lucainena mines. With it, a page in the history of mining in Almería closed.
Locomotive LUCAINENA (Nasmyth Wilson 464/95), one of the machines used on the
mineral transport line from Lucainena to Agua Amarga. The photo dates from the end
of the 19th century (Photo, Col. J.M. Sánchez Molina).
91
18. The Mesa Roldán reef
Juan C. Braga - José M. Martín
GEOLOGICAL INTERPRETATION
The Mesa de Roldán relief feature is essentially
a volcanic dome that formed about 8.7 million
years ago. However, the roof of Mesa de
Roldán, the upper platform that gives this hill
the shape of a mesa, owes its structure to the
formation of coral reefs and other sedimentary
deposits above the volcanic dome in more
recent periods. Two sedimentary units may be
distinguished.
PALAEOGEOGRAPHY OF THE CABO DE GATA VOLCANIC
AREA DURING THE DEPOSITION OF THE REEF COMPLEX
Carboneras
INTERPRETATIVE GEOLOGICAL SKETCH OF
THE PANORAMA
Níjar
El Hoyazo
Agua Amarga
Reefs
M
ar
in
e
s
ba
in
Mesa Roldán
Las Negras
W
E
Reefs and oolites
Los Lobos
Reefs
Volcanic rocks
Present
Coastline
Emerged Area
92
5 km
Reefs
20 m
18. The Mesa Roldán reef
LOWER SEDIMENTARY UNIT
THE REEFS
The lower sedimentary unit is constructed
from the remains of coral reefs. As in other
places within the region, during the
Messinian, around 6 million years ago,
corals utilised the raised seafloor that
constituted the volcanic dome to install
themselves and form a reef. The calcareous
skeletons of the corals just as happens in
modern tropical seas (Photo A), finished
constructing a rigid structure of carbonate
rock. In the Mesa de Roldán, the coral
constructors belong to the genera Porites
(Photo B) and, to a lesser extent,
Tarbellastrea and Siderastrea. Other
organisms such as red algae, encrusting
foraminiferans, bivalves, gastropods,
serpulid worms, etc. (Photo C), contributed
with their skeletons to the reef construction
or the accumulation of carbonate sediment.
A
B
Calcareous corals in modern tropical seas construct coral
reefs similar to those that formed in the region 6 million
years ago.
C
The remains of bivalves contribute to the formation of reefal
deposits.
Corals of the genera Porites are the main constructors of
Messinian coral reefs in Almería.
93
18. The Mesa Roldán reef
Above the lower sedimentary unit there is an
erosion surface, and, above it, a new
sedimentary unit is present. The latter, also
Messinian in age, but younger (around 5.5
million years) is again constructed from coral
reefs along with some particulate carbonate
sediments that are called oolites (lower figure).
Here the reefs have only a small dimension,
patches a few metres wide with a height of
1 or 2 metres, formed by corals of the genera
Porites (Photo D) and well-developed micritic
coatings of microbial origin (Photo E). These
reefs grew surrounded by oolitic sediments.
This type of oolitic sediment consist of small
carbonate particles with a spherical shape and
an internal structure of concentric laminations
(Photo F). At present, ooliths, as the particles
are known, are formed in shallow, agitated,
tropical seas.
The oolitic carbonates as much as the coral
reefs testify that in the western part of the
Mediterranean, on the southeast Iberian
peninsula, during the Messinian around 5.5
million years ago, at the end of the Miocene,
a tropical climate prevailed, similar to that now
found in lower latitudes, closer to the equator.
94
Since that period until the Present, the climate
in the region has followed a general trend of
cooling, although this tendency has suffered
strong fluctuations, especially during the last
2 million years.
Ooliths
2m
UPPER SEDIMENTARY UNIT
THE PATCH REEFS
Reef
Ooliths
Breccias
Previous Reef
D
Patch reefs and oolitic limestones appear in the upper unit.
E
F
Coral colonies of the genera Porites (vertical
sticks), surrounded by micritic carbonate
coatings (white hue), that constitute the patch
reefs of the upper unit.
Micritic carbonate
coatings encrusting the
upper part of patch reefs
at the same time as the
coral colonies were
periodically living.
Microscopic image of
oolitic sediments. These
particles, ooliths, constitute
the bulk of sediments in
the upper unit.
19. The Hoyazo de Níjar
Juan C. Braga - José M. Martín
The Hoyazo de Níjar hill is a locality of great
geological interest. This relief feature, with
a circular form, that stands out in the extensive
plain of the Campo de Níjar, in fact constitutes
a small volcano whose crater emerged as an
island in the archipelago of small volcanoes
emplaced in this area around 6 million years
ago.
At the base of the Sierra Alhamilla relief, where
the coastline was located during this period,
and surrounding the volcanic crater of El
Hoyazo, fringing reefs composed of the coral
Porites and typical of warm waters developed.
The reef which capped and surrounded El
Joyazo is magnificently conserved, exhibiting
the complete reef structure.
The Hoyazo de Níjar volcano is also known for
an abundance of garnets, minerals that make
up almost 1% of the volcanic rock. The origin
of the garnets in the volcanic rock is related to
the existence of schists rich in the same semiprecious mineral at depth, which were carried
upwards towards the surface in volcanic
eruptions. The garnets are desirable when they
form well-shaped crystals, like jewels. In the
case of El Hoyazo, people came to benefit as
such in the 19th century.
Later on, through the decades of the 50s and
the 60s in the 20th century, they were quarried
as an abrasive product, due to their great
durability. They were mined in the sediments of
the Rambla de la Granatilla, which formed a
small alluvial fan at the exit of El Hoyazo, in
whose sediments the very resistant garnets had
accumulated, coming from the destruction and
erosive washing of volcanic material. It may be
regarded, as such, as a typical secondary source
or “placer deposit”.
Exterior view of the small atoll of fringing reefs on top of the volcanic cone. At this point, fluvial erosion by the Rambla de la
Granatilla has dissected the carbonates, facilitating access to the interior of the structure (Photo, M. Villalobos).
95
19. The Hoyazo de Níjar
DIAGRAM OF EL HOYAZO DE NIJAR
C. Dabrio
The Níjar
Volcano
“El Hoyazo”
Sierra Alhamilla
Se
aL
ev
el
Interior view of Hoyazo de Níjar. The interior depression is
carved into the ancient volcanic crater. The upper capping
level corresponds to the reefal carbonates, that are
supported externally upon the volcanic relief in the form of
a small atoll (Photo, M. Villalobos).
Pre-reef substratum
m
0
Reef talus
500
m
96
Basin
50
100 m
Volcanic rocks
Reefs
Detail of the reef carbonates (Photo, M. Villalobos).
The Sorbas Basin
Geological Features
desplegable INGLES OK copia.qxp
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01:43
Página 1
Geological Features and Evolution
STRATIGRAPHY OF THE SORBAS BASIN
Geological Features and Evolution
GEOLOGICAL MAP OF THE SORBAS BASIN
50 m
Uleila
A. UPPER TORTONIAN (around 8 Ma)
QUATERNARY
Graphic Scalebar
Millions of years
1.8
R
SIER
10
9
PLIOCENE
5.3
PALAEOGEOGRAPHICAL EVOLUTION OF THE SORBAS BASIN FROM THE UPPER TORTONIAN (8 Ma) TO THE LOWER PLIOCENE (4 Ma)
GEOLOGICAL CONTEXT OF THE SORBAS BASIN
F
LOS
Conglomerates and sands
AL
Bioclastic sands
ILL
HAM
Emerged land
5 Km
Carboneras
Shallow platform
MESSINIAN
Gypsum
5
Marls
4b
4a
4b Fringing reefs
4a Calcarenites
3
Bioclastic limestones
2b
2c
2a
Open
sea
Lucainena
Submarine high
Cabo de Gata
Present
coastline
Platform
Turrillas
ALHAMILA
Carboneras
FILABRES
Palaeocoastline
Deltas
BÉDAR
Coral reef
Open
Sorbas
sea
Turrillas
Lucainena Shallow sea
ALHAMILA
(reefal lagoon)
Mojácar
Present
coastline
Carboneras
Lucainena
Neogene sediments
Neogene volcanic rocks
Turrillas
Modified from Montenat, 1990
5 Km
Position of geological section
Betic Substratum
D. UPPER MESSINIAN
(evaporitic unit, around 5.5 Ma)
GEOLOGICAL SECTION
E. UPPER MESSINIAN (around 5.4 Ma)
SE
Sierra de los Filabres
Gypsum karst
Sierra Alhamilla
Río Aguas
2b Reefal limestones
2c Marls, sands and conglomerates
Abanicos deltaicos
Uleila
Bédar
FILABRES
Semi-arid basin
Conglomerates and red sands
Open
sea
Barrier
Sorbas
Lucainena ALHAMILA
Uleila
Mojácar
Palaeocoastline
Enclosed
lagoon
CABRERA
Present
coastline
Carboneras
1
Sorbas
Submarine fan
Turrillas Lucainena
Uleila
Mojácar
Tabernas
NW
TORTONIAN
7.1
PRE-MIOCENE
5.9
6.2
6
C. LOWER MESSINIAN (around 6 Ma)
Bédar
FILABRES
Sorbas
Submarine fan
7a Conglomerates, oolites, patch reefs
and stromatolites
7b Sands and muds
Uleila
Uleila
Almería
Conglomerates, sands and muds
7a
7b
B. END TORTONIAN-LOWER MESSINIAN (around 7 Ma)
Vera
Sorbas
RERA
CAB
A
Níjar
SIERRA DE GÁDOR
Sorbas
8
A DE
RES
ILAB
Uleila
Sea Zone
FILABRES
Beach/ Barrier island
CABRERA
Sorbas
Lucainena
ALHAMILA
Turrillas
F. PLIOCENO INFERIOR (around 4 Ma)
FILABRES
Palaeocoastline
Mojácar
Mojácar
Sorbas
Present
coastline
Turrillas
CABRERA
Present
coastline
Lucainena
ALHAMILA
Carboneras
Carboneras
Betic Substratum. Metamorphic rocks:
phyllites, schists, quartzites, marbles, etc...
5 Km
101
desplegable INGLES OK copia.qxp
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01:43
Página 2
Geological Features and Evolution
THE SORBAS KARST. Origin of the Sorbas gypsum
Juan C. Braga - José M. Martín
Juan C. Braga - José M. Martín
200 Km
AEREAL DISTRIBUTION
OF MESSINIAN
SALT DEPOSITS IN
THE MEDITERRANEAN
SEA
Salt
44º
N
Spain
Sorbas
Gibraltar
Taken from Rouchy, 1980
Around 5.5 million years ago (in the Messinian)
the Mediterranean dried up through closure of
its communication with the Atlantic Ocean due
to tectonic uplift, and masses of evaporites
(gypsum and salt) were deposited in its central
and deepest region. The thickness of
accumulated salt (mainly sodium chloride)
exceed 1500 m in some places. In relation to this
phenomenon, important deposits of gypsum
(hydrated calcium sulphate) were also
deposited in the Sorbas Basin, which locally
exceed 130 m in thickness and that outcrop
over an area of nearly 25 square kilometres.
Alborán
Morocco
32º
8º
8º
0º
16º
SEDIMENTARY INTERPRETATION FOR THE SORBAS GYPSUM IN A MEDITERRANEAN CONTEXT
Sorbas Basin
Fringing reef
Mediterranean
Atlantic
A (5.9 Ma bp)
B
Erosion
Desiccation
C (5.5 Ma bp)
Semi-confined Sorbas Basin
Evaporation
Normal salinity
Gypsum
Gypsum and other salts
Situation prior to the deposition of evaporites,
with the formation of reefs along the margins and
marly-muddy sediments in the basin.
102
Evaporite deposits in the centre of the Mediterranean
result from this disconnection with the Atlantic, and drying
out.
Evaporite deposits in the interior of the Sorbas Basin.
The Sorbas Basin constitutes an intermontane
basin of singular geological interest for the
study and understanding of palaeogeographical
and palaeoenvironmental changes occurring on
the Mediterranean coast during the last
8 million years, and its relationship to the
geological evolution of the Betic Cordillera.
Eight million years ago (in the Upper Miocene),
the configuration of land emerged and
submerged beneath the sea along the coastal
zone of Almería was similar to present, but not
identical: the sea spread across the Sorbas Basin,
dry land today, up to the foothills of the Sierra
de los Filabres, in whose margin reefs of fossil
corals from this age remain as testament, closely
marking the position of the ancient coastline.
On the slopes, submarine fans deposited thick
and extensive sediments that the rivers stripped
out from the emergent relief. The later
emergence of Sierra Alhamilla and Sierra
Cabrera configured a long and narrow
intermontane marine basin between these new
relieves, to the south, and Los Filabres, towards
the north, where the deposition of marine
sediments continued: this is today called the
Sorbas Basin.
At the end of the Miocene (around 5,5 million
years ago, during the Messinian) an enhanced
process of desiccation of the Mediterranean Sea
caused the marine Sorbas Basin to become
practically dry, with a very shallow depth
subjected to strong evaporation. In these
circumstances a package of gypsum almost 100
metres in thickness was deposited: the Sorbas
gypsum. Afterwards, the sea reoccupied its
level, continuing the accumulation of marls and
detrital sediments above the gypsum, up until,
around 3.5 million years ago (in the Pliocene),
the coastline progressively retreated until
reaching its present position.
The final retreat of the sea meant that the
marine sediments became exposed to
the action of erosive agents. The removal of the
upper sedimentary layers left the highly soluble
gypsum subjected to the continuous action of
water, which progressively dissolved it.
Therefore, one of the most important gypsum
karst landscapes in the world for its size, worth
and beauty started to form.
DISTRIBUTION OF EMERGED LAND AND SEA 6 MILLION YEARS AGO
Guadalquivir
Basin
Atlantic Ocean
Sorbas
Almería
Mediterranean Sea
Uleila
FILABRES
Mojácar
Sorbas Mediterranean Sea
Turrillas
Lucainena
ALHAMILLA
Present
Coastline
Carboneras
99
Geological Features and Evolution
Juan C. Braga - José M. Martín
The Sorbas Basin constitutes an intermontane
basin of singular geological interest for the
study and understanding of palaeogeographical
and palaeoenvironmental changes occurring on
the Mediterranean coast during the last
8 million years, and its relationship to the
geological evolution of the Betic Cordillera.
Eight million years ago (in the Upper Miocene),
the configuration of land emerged and
submerged beneath the sea along the coastal
zone of Almería was similar to present, but not
identical: the sea spread across the Sorbas Basin,
dry land today, up to the foothills of the Sierra
de los Filabres, in whose margin reefs of fossil
corals from this age remain as testament, closely
marking the position of the ancient coastline.
On the slopes, submarine fans deposited thick
and extensive sediments that the rivers stripped
out from the emergent relief. The later
emergence of Sierra Alhamilla and Sierra
Cabrera configured a long and narrow
intermontane marine basin between these new
relieves, to the south, and Los Filabres, towards
the north, where the deposition of marine
sediments continued: this is today called the
Sorbas Basin.
At the end of the Miocene (around 5,5 million
years ago, during the Messinian) an enhanced
process of desiccation of the Mediterranean Sea
caused the marine Sorbas Basin to become
practically dry, with a very shallow depth
subjected to strong evaporation. In these
circumstances a package of gypsum almost 100
metres in thickness was deposited: the Sorbas
gypsum. Afterwards, the sea reoccupied its
level, continuing the accumulation of marls and
detrital sediments above the gypsum, up until,
around 3.5 million years ago (in the Pliocene),
the coastline progressively retreated until
reaching its present position.
The final retreat of the sea meant that the
marine sediments became exposed to
the action of erosive agents. The removal of the
upper sedimentary layers left the highly soluble
gypsum subjected to the continuous action of
water, which progressively dissolved it.
Therefore, one of the most important gypsum
karst landscapes in the world for its size, worth
and beauty started to form.
DISTRIBUTION OF EMERGED LAND AND SEA 6 MILLION YEARS AGO
Guadalquivir
Basin
Atlantic Ocean
Sorbas
Almería
Mediterranean Sea
Uleila
FILABRES
Mojácar
Sorbas Mediterranean Sea
Turrillas
Lucainena
ALHAMILLA
Present
Coastline
Carboneras
99
STRATIGRAPHY OF THE SORBAS BASIN
10
Conglomerates and sands
9
Bioclastic sands
8
Conglomerates, sands and muds
7a
7b
7a Conglomerates, oolites, patch reefs
and stromatolites
7b Sands and muds
6
Gypsum
5
Marls
4b
4a
4b Fringing reefs
4a Calcarenites
TORTONIAN
3
Bioclastic limestones
2b
2c
2b Reefal limestones
2c Marls, sands and conglomerates
PRE-MIOCENE
Millions of years
QUATERNARY
50 m
2a
Conglomerates and red sands
1
Betic Substratum. Metamorphic rocks:
phyllites, schists, quartzites, marbles, etc...
5.9
6.2
7.1
MESSINIAN
5.3
PLIOCENE
1.8
Geological Features and Evolution
GEOLOGICAL MAP OF THE SORBAS BASIN
GEOLOGICAL CONTEXT OF THE SORBAS BASIN
Uleila
Graphic Scalebar
E
RA D
SIER
BRES
FILA
LOS
AL
ILL
HAM
Sorbas
Sorbas
RERA
CAB
A
Níjar
SIERRA DE GÁDOR
Vera
Carboneras
Almería
Cabo de Gata
Lucainena
Neogene sediments
Neogene volcanic rocks
Turrillas
Modified from Montenat, 1990
5 Km
Position of geological section
Betic Substratum
GEOLOGICAL SECTION
NW
SE
Sierra de los Filabres
Gypsum karst
Sierra Alhamilla
Río Aguas
5 Km
Geological Features and Evolution
PALAEOGEOGRAPHICAL EVOLUTION OF THE SORBAS BASIN FROM THE UPPER TORTONIAN (8 Ma) TO THE LOWER PLIOCENE (4 Ma)
A. UPPER TORTONIAN (around 8 Ma)
B. END TORTONIAN-LOWER MESSINIAN (around 7 Ma)
Emerged land
5 Km
Uleila
Mojácar
FILABRES
Sorbas
Sorbas
Open
sea
Tabernas
Submarine fan
Turrillas Lucainena
Submarine fan
Uleila
Bédar
Uleila
Shallow platform
Lucainena
D. UPPER MESSINIAN
(evaporitic unit, around 5.5 Ma)
Carboneras
E. UPPER MESSINIAN (around 5.4 Ma)
Abanicos deltaicos
Uleila
Bédar
FILABRES
Semi-arid basin
Uleila
Open
sea
Barrier
Sorbas
Lucainena ALHAMILA
Present
coastline
Platform
Turrillas
ALHAMILA
Submarine high
C. LOWER MESSINIAN (around 6 Ma)
Mojácar
Palaeocoastline
Enclosed
lagoon
CABRERA
Present
coastline
Carboneras
Turrillas
Coral reef
Open
Sorbas
sea
Turrillas
Lucainena Shallow sea
ALHAMILA
(reefal lagoon)
Mojácar
Present
coastline
Carboneras
Uleila
Sea Zone
Beach/ Barrier island
CABRERA
Sorbas
ALHAMILA
Deltas
BÉDAR
F. PLIOCENO INFERIOR (around 4 Ma)
FILABRES
Lucainena
FILABRES
Palaeocoastline
FILABRES
Palaeocoastline
Mojácar
Mojácar
Sorbas
Present
coastline
Turrillas
CABRERA
Present
coastline
Lucainena
ALHAMILA
Carboneras
Carboneras
101
THE SORBAS KARST. Origin of the Sorbas gypsum
Juan C. Braga - José M. Martín
200 Km
AEREAL DISTRIBUTION
OF MESSINIAN
SALT DEPOSITS IN
THE MEDITERRANEAN
SEA
Salt
44º
N
Spain
Sorbas
Gibraltar
Taken from Rouchy, 1980
Around 5.5 million years ago (in the Messinian)
the Mediterranean dried up through closure of
its communication with the Atlantic Ocean due
to tectonic uplift, and masses of evaporites
(gypsum and salt) were deposited in its central
and deepest region. The thickness of
accumulated salt (mainly sodium chloride)
exceed 1500 m in some places. In relation to this
phenomenon, important deposits of gypsum
(hydrated calcium sulphate) were also
deposited in the Sorbas Basin, which locally
exceed 130 m in thickness and that outcrop
over an area of nearly 25 square kilometres.
Alborán
Morocco
32º
8º
8º
0º
16º
SEDIMENTARY INTERPRETATION FOR THE SORBAS GYPSUM IN A MEDITERRANEAN CONTEXT
Sorbas Basin
Fringing reef
Mediterranean
Atlantic
A (5.9 Ma bp)
B
Erosion
Desiccation
C (5.5 Ma bp)
Semi-confined Sorbas Basin
Evaporation
Normal salinity
Gypsum
Gypsum and other salts
Situation prior to the deposition of evaporites,
with the formation of reefs along the margins and
marly-muddy sediments in the basin.
102
Evaporite deposits in the centre of the Mediterranean
result from this disconnection with the Atlantic, and drying
out.
Evaporite deposits in the interior of the Sorbas Basin.
Origin of the Sorbas gypsum
PALAEOGEOGRAPHY OF THE SORBAS BASIN DURING GYPSUM DEPOSITION (5.5 Ma bp)
Open sea
Uleila
BÉDAR
Mojácar
FILABRES
PALAEOCOASTLINE SEMI-RESTRICTED LAGOON
BARRIER
CABRERA
Sorbas
Lucainena
ALHAMILLA
Prese
nt co
astlin
e
The gypsum deposits in the Sorbas Basin
were not, however, strictly
contemporaneous with the deposition of
evaporites in the centre of the
Mediterranean, but somewhat later.
This deposition took place during the
reflooding phase of the Mediterranean,
upon refilling with new water, presumably
coming from the Atlantic and invading a
broad semi-restricted depression, that at
the time occupied a large part of what
today constitutes the Sorbas Basin.
Carboneras
The Sorbas gypsum was deposited in an
evaporitic basin, of restricted character,
closed towards the west and separated
from the open sea by a submarine barrier
located at its most easterly end, created
through uplift of the Sierra Cabrera.
Semi-restricted basin
Evaporation
Basement
Gypsum precipitation
Barrier
Open sea
103
Origin of the Sorbas gypsum
In detail, the evaporite sequence of
Sorbas consists of banks of gypsum,
of up to 20 m thickness, separated by
marly-limestone intervals and/or
carbonates. The thickness of the gypsum
banks diminishes towards the top at the
same time as that of the non-evaporitic
intervals increases. The latter, at least in
the higher part, possess a marine
character, in that they incorporate the
remains of the calcareous skeletons
of marine organisms and record the
different episodes of basin inundation.
In the highest banks of gypsum in the
sequence a very spectacular growth
structure of arborescent character
evidently forms, known as supercones
(also called cauliflowers), that are
interpreted as resulting from
competition between the growth
of gypsum and the deposition of
contemporaneous muddy sediments.
STRATIGRAPHICAL COLUMN OF THE SORBAS EVAPORITE
SEQUENCE AND DETAILED STRUCTURE OF THE GYPSUM BANKS
WITHIN THE SUCCESSION
Taken from Dronkert, 1976
Mts.
120
110
Field view of the gypsum banks.
100
Supercones
90
Supercone
80
Palisades
70
60
Detailed field view of the gypsum supercones.
50
Nucleation
Cones
40
30
according to Dronkert, 1977.
Gypsum
20
Marly limestones and/or muds
10
Carbonates
104
Field photograph of the gypsum banks from the upper
part of the evaporite sequence.
Karst: the slow dissolution of the rocks
M. Villalobos
Rainwater and groundwater are capable
of dissolving soluble rocks in a slow
process that takes thousands of years.
The resultant landscape, known as karst
or karstic landscape, is very peculiar.
It is characterised by the presence of
abundant closed depressions at the
surface (dolinas, potholes, etc.) and
a complex subterranean drainage system
(cavities).
FEATURES IN KARST LANDSCAPE
1. Tepuys (Karst en cuarcitas)
2. Pitons, Stacks ,Towers (tropical karst)
3. Lapiés/Karren (high mountain karst)
4. Dissolution Dolina
5. Uvala
6. Polje
7. Ponor
8. Collapse dolinas
9. Rock bridge
10. Joint
11. Sinkhole
12. Pothole
13. Chimney
14. Cascade
15.
16.
17.
18.
19.
20.
21.
22. Column
23. Resurgence
24. Dry valley
25. Trop Plein
26. Cave
27. Canyon
Bedding Plane
Pipe
Sump
Debris cone
Gours
Fossil Gallery
Lake
A
B
Karstification of gypsum is an infrequent
phenomenon in nature.The greater part
of known karst are limestones.The Sorbas
karst is the most important gypsum karst
in Spain, and one of the four best known
examples in Europe. Additionally, it has
a very high scientific and didactic value in
a world context.
C
k
Ta
rom
B
A
Zone of recharge (photo J. M. Calaforra).
f
en
J. L
Zone of transfer (photo J. M. Calaforra).
. Sa
.
ura
C
Flooded Zone (photo J. M. Calaforra).
105
How is the gypsum karst of Sorbas formed?
J. M. Calaforra
1. THE DRAINAGE NETWORK IS ESTABLISHED
1. The gypsum is originally covered by
other sediments, on top of which the
incipient drainage network starts to
install itself.
Sierra de los Filabres
Sierra de los Filabres
Sorbas Basin
Faults
2. THE SURFICIAL DISSOLUTION OF GYPSUM STARTS
2. The drainage network erodes the
upper sediments until exposing
the gypsum in very localised places
where the first dolinas originally start to
be dissolved.
Sierra de los Filabres
Sierra de los Filabres
Sorbas Basin
3. SUBTERRANEAN DRAINAGE IS INITIATED
3. The gypsum is becoming exposed to
a greater extent at the surface through
time. A multitude of dolinas develop that
favour the entrance of water into the
interior.
Sierra de los Filabres
Sierra de losFilabres
Sorbas Basin
4. KARST DEVELOPS
Sierra de los Filabres
Sierra de los Filabres
4. The general entrance of water into
the gypsum mass promotes its slow
dissolution, creating a complex
subterranean network of galleries.
Sorbas Basin
Sediments beneath the gypsum
106
Gypsum
Sediments above the gypsum
Landscape and surface features
M. Villalobos
A multitude of small depressions pepper the surface of the
karst. These are the dolinas. They result from the dissolution or
collapse of the surface layers of the gypsum.
An escarpment cliff delimits the
entire southern margin of the
gypsum outcrop.
The extensive plain, the escarpment cliff and the valley are
the most characteristic elements of the surface landscape.
Above the gypsum rock an extensive karstic
plain is fashioned.
Large gypsum blocks tumble down from
the cliff covering the marl slope. These are
called block falls.
The Río Aguas cuts down towards the south into soft
marly sediments giving rise to a broad valley.
107
Dissolution features: chambers and galleries
J. M. Calaforra - M. Villalobos
3
2
1
Rainwater penetrates into the rock interior, starting to dissolve
the gypsum.
Dissolution progressively enlarges the initial channel.
The water penetrates through to the lower layers. The initial
crystallization features start to form.
(Photo J. Les)
The water infiltrates, slowly dissolving gypsum rock, generating a complex network of subterranean
galleries. Chambers are formed from galleries through the dissolution of the walls, and by the fall of
blocks from the walls and roof.
1
108
2
3
Dissolution features: chambers and galleries
4
Slowly meanders are excavated, on occasions
they are very long.
5
Only the lower section is permanently flooded.
4
5
109
Crystallization features: speleothems
J. M. Calaforra - M. Villalobos
3
2
1
Water circulates through the incipient galleries and chambers,
infiltrating and dissolving the gypsum rock.
Gypsum is saturated in this slow process so that it then
precipitates in the form of small crystals.
The roof, walls and floors of chambers and galleries are
coated with a multitude of gypsum crystals in fanciful designs
and colours.
Water infiltrates dissolving the
gypsum, is saturated and
crystallizes in extremely delicate
forms.These are the speleothems.
It has taken hundreds of
thousands of years, millions at
times, in order for nature to
sculpt them. Respect them, never
touch them, and be careful not to
damage them by accident. They
have an incalculable value, but
only here where they were born,
they have no value elsewhere.
110
Stalagmites.
Columns.
Mamelones.
Rings.
Stalagmite mounds.
Curtains.
Corals.
Balls.
The Sorbas Basin
Didactic Itinerary
1
1. The southern margin of the Sorbas Basin: the area of Peñas Negras
Juan C. Braga - José M. Martín
From the area of Peñas Negras a magnificent
perspective for a good part of the sediments
filling the Sorbas Basin can be seen, and how
they contact with much older material of the
sierras Alhamilla and Cabrera, that constitute
the margin and the substratum or basement
of the basin.
In the southern panorama (towards Sierra
Alhamilla) the contact between the sediments
filling the basin and Betic rocks of the basement
can be observed. The contact appears as a very
notable, rectilinear cutting and corresponds to
an almost vertical fault plane with an east-west
direction. The basement materials are phyllites,
quartzites, limestones and dolomites belonging
to the Alpujárride Complex of the Internal Zone
of the Betic Cordillera, of an age known to be
between approximately 200 and 300 million
years. The filling material of the basin, in lateral
contact with the basement, are muddy
marlstones that intercalate with levels of
sandstone, and locally conglomerates. These
materials correspond to the Unit 2c in the
general stratigraphical scheme. Their age is
Upper Tortonian (around 8 million years).
SOUTHERN PANORAMA
Sierra de Alhamilla
Faulted Margin
Recent debris
SORBAS BASIN
Muddy marlstones with sandstone and
conglomerate intercalations. (Upper Tortonian)
ALPUJARRIDE SUBSTRATUM (BASEMENT)
Motorway
Alpujárride Limestone and Dolomite
Alpujárride phyllites
113
1. The southern margin of the Sorbas Basin: the area of Peñas Negras
In the northern panorama we can make out
the Cerrón de Hueli. In it a good part of the
filling sequence of the Sorbas Basin can be
observed. In the foreground, muddy
marlstones with intercalations of sandstone
and conglomerate (Unit 2c). Above these a
package of deposits (units 3 to 7), in which a
calcareous bench stands out in the mid-height
formed from bioclastic limestones (Unit 3).
Marls are located above (Unit 5) that are a
lateral continuation of the coral/algal reefs
(Unit 4a). On top of the marls the gypsum
forms (Unit 6) and, capping this series, other
carbonates of microbial origin (Unit 7). All of
these units may be seen with greater detail at
different points on the proposed route.
NORTHERN PANORAMA
Microbial carbonates (stromatolites),
sands and conglomerates
(Messinian)
Cerrón de Hueli
Collado de las Cabezas
Gypsum (Messinian)
Marls (Messinian)
Coral reefs (Messinian)
Bioclastic limestones
(Tortonian-Messinian boundary)
Motorway
114
Muddy marlstones with sandstone
and conglomerate intercalations.
(Upper Tortonian)
2. Turbidites of the Peñas Negras fan
Juan C. Braga - José M. Martín
Sedimentary infilling of the Sorbas Basin was
initiated around 8 million years ago (in the
Upper Tortonian). The coastline was located to
the north of the town of Sorbas, at the foot of
the Sierra de los Filabres. The mountainous
Alhamilla-Cabrera lineament was still located at
the bottom of the sea, although Sierra Alhamilla
already formed a submarine high (submarine
ridge) of positive relief. Between the
aforementioned ridge and the Sierra de los
Filabres a deep marine furrow existed, with
several hundreds of metres of depth, in which
large masses of sediments of detrital character
(consisting of isolated particles or clasts,
produced directly from erosion) came to be
deposited, resulting from the destruction
(denudation) of the Sierra de los Filabres relief.
The ramblas through which sediments from the
mountains were cannibalised continued to enter
the sea as submarine canyons. Upon entering the
furrow, the submarine canyons terminated where
the slope rapidly smoothed out, unloading the
majority of sediments that they had transported,
forming a submarine fan.The sediments that we
observe belong to one of these fans, here called
the Peñas Negras fan. It forms Unit 2c of the
general stratigraphical scheme.
FIELD SKETCH OF AN OUTCROP WITH SUBMARINE FAN SEDIMENTS FROM PENAS NEGRAS
Turbidite layer
Thin turbidite layers
Background sediments
(muddy marlstone)
Conglomerate layer
Faults
115
2. Turbidites of the Peñas Negras fan
In the submarine fan the sediments are
structured in an alternation of decimetric
layers of sand (which stick out more
because they are later cemented), formed
by turbidite currents (suspension of sand
and mud), and layers of finer-grained
sediments (muds/silts)that correspond to
background sedimentation in the basin
between each of the turbidity currents.
On a geological timescale the
deposition of a turbidite layer can be
considered practically instantaneous
(in hours to weeks). The frequency of
repetition of this process in the area is
about one turbidite event every few
hundred years. The sediment
intercalated between the turbidite
layers (mud-silt), with an equivalent or
lesser thickness, on the other hand,
were deposited very slowly from
suspension over a time of hundreds
to thousands of years for each layer.
INTERNAL ORGANISATION OF A TURBIDITE SEQUENCE
Mud-silt
Sand
Nevado - Filábride
Submarine canyon
Submarine fan
SUBMARINE MORPHOLOGY OF THE SORBAS-TABERNAS AREA DURING THE UPPER TORTONIAN
SHOWING THE POSITION OF SUBMARINE FANS IN TABERNAS AND PENAS NEGRAS
PALAEOGEOGRAPHY OF THE SOUTHEASTERN PENINSULA DURING THE UPPER TORTONIAN
Palaeocoastline
Sierra de los Filabres
Rambla systems
Almanzora Corridor
Sierra de las
Estancias
Transport direction of
turbiditic sediment
Carbonate
platform
Reefs
Sorbas
Sierra Nevada Filabres
Granada
Tortonian palaeocoastline
Present coastline
Peñas Negras
submarine fan
Palaeocoastline
Tabernas
Almería
Submarine ridge of the proto-Sierra Alhamilla
Tabernas submarine fan
Modified from Haughton, 1994
116
3. The sedimentary fill of the basin up until deposition of the gypsum:
the panorama from Los Molinos
Juan C. Braga - José M. Martín
From this location the succession of sedimentary
deposits that filled the centre of the Sorbas Basin
during the interval between 7.1 and 5.3 million
years ago (Messinian) can be observed.
This sequence of sediments, the stratigraphical
record of the basin, is at the same time a result
of and testament to the geographical and
environmental changes that the Sorbas Basin
and the southeast Iberian Peninsula underwent
throughout their geological history.
The geological study of the sediments allows
the geographical reconstruction of the basin,
and its environmental conditions, for each
episode of fill or sedimentary unit:
Sierra de Filabres
Los Molinos
PALAEOGEOGRAPHY DURING THE DEPOSITION OF BIOCLASTIC LIMESTONES (Unit 3, 7 Ma bp)
The lower unit (unit 3) consists of bioclastic limestones,
known in the region as “Azagador limestones”. They formed
around 7 million years ago in marine platforms of shallow
depth that surrounded the relieves that had already
emerged, the precursors to the modern sierras de los
Filabres and Bédar to the north, and Sierra Alhamilla to the
south. They mainly stem from the accumulation of the
skeletons of fossil algae and marine invertebrates such as
bryozoans, molluscs, etc.
Uleila
Mojácar
Shoals
Seafloor influenced
by storms
Sedimentation of
silt and plankton
from suspension
Lucainena
ALHAMILLA
Platform
Open
sea
Mode
Sorbas
rn co
astlin
e
Palaeocoastline
Beach
In the deeper marine zones, marls were deposited
(Unit 5a), formed from a mixture of silt coming from the
erosion of emerged land and the fossil skeletons of
micro-organisms.
BÉDAR
FILABRES
Carboneras
Substratum
117
3. The sedimentary fill of the basin up until deposition of the gypsum: the panorama from Los Molinos
PALAEOGEOGRAPHY DURING REEF DEPOSITION (Unit 5b, 6 Ma bp)
Uleila
BÉDAR
FILABRES
Mojácar
Coral reef
Lagoon
Coral reef
Sorbas
Open sea
Substratum
Open
sea
DELTA
Reef talus slope
rn co
astlin
e
Palaeocoastline
Mode
The beige coloured marls from
the upper part of Unit 5 (5b)
accumulated at the same time as
coral reefs grew along the
coastline of the emergent
relieves, about 6 million years
ago (unit 4, that does not
outcrop in this section, but does
immediately to the west in the
exposure of Hueli).
Lucainena
Turrillas
Shallow sea
(reef lagoon)
Carboneras
ALHAMILLA
PALAEOGEOGRAPHY DURING GYPSUM DEPOSITION (Unit 6, 5.5 Ma bp)
Unit 6 consists of thick layers of gypsum, between
which thinner layers of silt and fine sand are
intercalated.
Open
sea
Uleila
BÉDAR
Mojácar
FILABRES
CABRERA
Sorbas
Lucainena
ALHAMILLA
e
Semi-restricted basin
rn co
astlin
Palaeocoastline
Ridge
Mode
This gypsum formed around 5.5 million years ago
by chemical precipitation due to the partial
evaporation of seawater. In the Sorbas Basin,
which was already closed to the west and
separated from Tabernas, intense evaporation of
seawater developed as a result of partial isolation
from the main body of the Mediterranean Sea.
Evaporation
The confinement was probably caused by a
marine area of shallow depth (a ridge) that
separated the Sorbas Basin and the rest of the
Mediterranean.
118
Carboneras
Substratum Gypsum precipitation
Semi-restricted basin
Ridge
Open sea
4. The karst plain, the escarpment cliff and block falls
José M. Calaforra
From this position detailed aspects of the
surface karst landscape of Sorbas may be
clearly observed, especially the extensive
karst plain and the escarpment cliff sculpted
on top of the gypsum, and the block falls that
result from the destruction of its own cliff.
The broad overlying plain is a result of
the levelling that was produced by the
introduction of alluvial fans above
the gypsum once the basin had become
terrestrial. After the erosion of this material,
the process of dolina formation was initiated
on the karst plain.
Differential erosion developed between the
hard and resistant gypsum, and the much
softer underlying marls, which progressively
increased the relief of the gypsum cliff.
At the same time, parallel fractures
originated through the gravitational
instability that it started to produce.
These processes caused the carving and fall
of large gypsum blocks onto the slope.
These are known as block falls.
Karst plain.
Longitudinal fracture on the margin
Escarpment and cliff (archive photo, Almería Speleoclub).
Escarpment and cliff (archive photo, Almería Speleoclub).
Longitudinal fractures on the margin of the escarpment that cause
its retreat, detachment and fall of blocks into the barranco.
119
4. The karst plain, the escarpment cliff and block falls
EVOLUTION OF THE SURFACE KARST LANDSCAPE
S
1
N
Fluvial drainage
Karst plain
S
2
N
Gravitational
instability
fractures
Differential erosion
Block falls
Dolinas
Springs
Karstic spring
S
N
Scarp retreat
3
Falls and slides
(block falls)
Gypsum
Marls
Karstic spring
120
Caves
5. Karst: source of water and life
M. Villalobos
Karst functions like a large sponge:
it collects and stores all of the
rainwater, later discharged to the
exterior through resurgence.
These are the karstic springs, source
of water, fertility and life; especially
in a sub-desert environment like
that of Sorbas.
After an episode of rainfall, water filters
through the gypsum and traverses the
network of chambers and galleries until
reaching the lowest point in the cave system,
from where it is discharged into the valley via
a spring.These springs function only in an
intermittent manner, following periods of
rainfall, and may be situated in middle or high
positions on the slopes of the valley.
Another portion of the water, however,
circulates in a much slower fashion, crossing
through the gypsum until reaching the
impermeable marls. The water, which can
therefore no longer continue its journey
towards deeper zones, accumulates at the
base of the gypsum and is displaced
horizontally until it finds a place to exit into
the outside.This point is located at the base
of the Río de Aguas canyon, and gives birth to
the springs of Los Molinos.These springs are
in permanent operation and generate a creek
of great ecological value.
Recharge Zone
Zone of rapid
transmission
Zone of slow
transmission
Accumulation
Zone
Impermeable
Zone
121
6. Basin infilling after deposition of the gypsum
Juan C. Braga - José M. Martín
The lower deposits in this panorama are mostly sands, muds and yellowish-white
coloured marls. During the period of formation of this material, around 5,5 million
years ago (at the end of the Messinian), the Sorbas Basin was a bay closed off to the
west. At the present site of Sorbas town, there was a system of sandy barriers and
beaches that sealed off a lagoon environment to the west. Along the fringe of the
Sierra de los Filabres, discharge of material coming from the erosion of this relief was
concentrated in small deltas (fan deltas) that spread out across a narrow marine
platform where oolitic limestones were forming. The deepest parts of the beaches,
the fan deltas and the platforms were colonised by micro-organisms that formed
microbial carbonates (stromatolites and thrombolites). The Sorbas bay open out
towards the Mediterranean via the Vera Basin, and perhaps via the corridor of the
Rambla de los Feos that separated the sierras Alhamilla and Cabrera.
Uleila
Marine area
Fan deltas
FILABRES
Palaeocoastline
Mojácar
CABRERA
Enclosed
lagoon
Detail of a giant
stromatolite; structures that
are very common in the
Sorbas Basin.
Turrillas
Sorbas
Lucainena
ALHAMILLA
Carboneras
INTERPRETATION OF THE PANORAMA
UNIT 10
UNIT 9
Sorbas
122
Sierra de Filabres
UNIT 7
e
Beach/barrier island
rn co
astlin
The succession of
deposits in this fill records
the last phases in the
history of the Sorbas
Basin as a marine
connection to the
Mediterranean and the
start of its history as
a fluvial basin.
UNIT 7
Mode
From this point, a
panorama of the postevaporitic (after the
formation of the gypsum)
sedimentary filling of the
Sorbas Basin can be
contemplated.
UNIT 8
6. Basin infilling after deposition of the gypsum
UNIT 8
On top of the previous unit, another is present formed from
conglomerates, sands, muds and red silts.They are fluvial sediments
formed during a temporary emergence of the basin. On the floodplain of
the fluvial system, lakes of little permanence were created in which white
limestones were deposited (very apparent in the landscape between red
fluvial material, as may be seen in the photograph opposite).
In the centre of the basin, Unit 8 is essentially formed of red silts of
fluvial origin. However, some intercalated white layers stand out in the
landscape, corresponding to lagoon deposits.
UNIT 9
UNIT 10
After the episode of emersion, the Sorbas Basin underwent its last
invasion by the sea around 5 million years ago, and the yellowish
bioclastic sands of Unit 9 were deposited. The basin is, once again, a bay
closed off to the west with possible connections to the open sea
through the Vera Basin and via the corridor of the Rambla de los Feos,
as is sketched in the figure below.
The last deposits of the sequence are fluvial sediments formed after the final emergence of the basin, less
than 5 million years ago, in the Pliocene and Quaternary. This fluvial material records, through time, the
change in the drainage system of the Sorbas depression, from an initial exit only towards the south (lower
left hand sketch), to a dual drainage system exiting towards the south (Río Alías) and towards the east (Río
Aguas), as occurs today.
Uleila
FILABRES
Carboneras
CABRERA
e
rn co
astlin
CABRERA
Mode
Turrillas Lucainena
ALHAMILLA
Río Aguas
CABRERA
Mojácar
Sorbas
FILABRES
FILABRES
Palaeocoastline
ALHAMILLA
ALHAMILLA
Río Alías
Taken from Mather, 1993
Alluvial fans
Drainage network
Catchment area
123
7. The fluvio-karst Barranco del Infierno and Cueva del Yeso
José Mª Calaforra
The fluvio-karst barrancos, deep and with
sub-vertical walls, are generated by the
combined action of fluvial erosion processes
and karst dissolution.
At an eaarly stage the fluvial network is
established, according to the structural and
lithological conditions of the area (1).
Progressively, the fluvial network incises due to
the local intensification of dissolution processes
and karst erosion (2 and 3). Some fluvial courses
evolved rapidly while others remained as dry
barrancos abandoned by permanent streams.
Groups of galleries appeared at distinct levels,
whose genesis was related to to the progressive
fall in base levels, or, in other cses, the actual
level of the water saturation zone (Phreatic level
or water table) (4).
KARSTIC BARRANCOS
1
Fluvial stream
2
Dolinas
Barrancos
Water table
w.t.
w.t.
3
Simas
4
Incision of
barrancos
Dry caves
Deepening of
barrancos
In the karst barrancos, on occasions, natural arches are
observed that are a relic of the gallery of a cavern which
was located in this position.
Falling water
table
w.t.
w.t.
Caves
124
Ephemeral springs
Evaporite formation: Gypsum (a) with intercalations
of Marl levels (b).
7. The fluvio-karst Barranco del Infierno and Cueva del Yeso
The Barranco del Infierno and Cueva del Yeso
constitute the most notable examples of fluviokarst evolution in the gypsum karst of the Sorbas
Basin.The cavern has developed at the point of
confluence of two karst barrancos (1). At a given
time, a sinkhole was established that allowed the
capture of water which flowed through these
barrancos (2)., In this way, only some stretches of
these fluvial courses continued their deepening
and evolution (3), while part of the barranco
remained at a greater height than base level,
marked by the floor of the main barranco. Actually,
GEOMORPHOLGYC EVOLUTION OF EL BARRANCO DEL INFIERNO (CUEVA DEL YESO)
2
1
Barranco
Phreatic
galleries
Fluvial
capture
Dolinas
Cueva del Yeso
Subterranean course
Water table
w.t.
the Barranco del Infierno represents a surface
course, that drains its water directly from rivers, like
the La Fortuna spring, and a subterranean course
(the Cueva del Yeso) whose genesis and
progressive deepening had followed the same
stages as the barranco that received its water (4).
‘Stratified Chamber’ of
Cueva del Yeso: the
configuration of
galleries at times
relates to collapses of
large layers of gypsum,
destabilised by the
erosion of marl levels
(Photo, El Tesoro
Speleoclub archives).
w.t.
4
3
Hanging valley
Blind valley
Hanging valley
Barranco del
Infierno
Karst barranco
w.t.
Present Cueva del Yeso
La Fortuna springs
Gypsum
Basal marls
Epi-phreatic hanging gallery
Subterranean stream in the Cueva del
Yeso (Photo, Javier Les, G.E.T.).
125
8. Fossil beaches of Sorbas
Juan C. Braga - José M. Martín
The sands and muds visible in this outcrop are
beach sediments deposited around 5.4 million
years ago (at the end of the Messinian) and
correspond to Unit 7a in the general
stratigraphical scheme.This material was
deposited in the interior of a bay, with an
east-west layout, and clearly open towards the
east. A system of barrier islands crossed the
bay from north to south, along a line where today
the town of Sorbas is located, restricting a
shallow lagoon in its most internal part.
The distinctive types of sediments and their
interrelationships allow the interpretation of
a sedimentary model in which the following
environments are differentiated:
◗ Enclosed Lagoon. Muds and fine laminated
silts. In these desiccation cracks and the
footprints of birds and mammals which give
evidence for little depth are frequent.
In this case, the sand is extracted, moved away
from the beach, and carried offshore by
storms. The aeolian dunes constitute the
emerged part of the beach, and the wind is
their principal transport agent. In the beach,
the dominant movement is up and down the
length of its slope, forming a very
characteristic, low-angled, parallel lamination.
In its upper part (transition to the dunes) the
bioturbation structures of crabs and roots are
abundant. Immediately underneath, the
so-called ‘beach rock’ is frequent; produced by
early cementation and breakage in the surf.
PALAEOGEOGRAPHY
Uleila
Fan deltas
FILABRES
Mojácar
Palaeocoastline
Beach/barrier island
Turrillas
Lucainena
ALHAMILLA
126
coa
stli
ne
CABRERA
Sorbas
ern
Enclosed
lagoon
Mod
◗ Barrier Islands. Sandy barriers, partially
emerged, in which three subzones can be
defined: that of the washover fan, that of the
aeolian dunes and that of beaches in the strict
sense.The washover fans correspond to sand
lobes that formed behind the dune barrier and
partially poured into the lagoon.
8. Fossil beaches of Sorbas
◗ Sand Shoals (Bars). Shallow
submarine sand dunes, moved by
waves, that develop trough
cross-stratification as the most evident
internal structure. In the deepest part
(towards the sea) they change to
a planar disposition, covered with
small-scale (centimetre) wave ripples.
◗ Platform. Marine zone dominated by
mud sedimentation at a depth greater
than fair weather wave base (around
10 m). Mounded carbonate structures
(of decimetre to metre width), formed
by micro-organisms and known as
stromatolites, appear at the start of the
platform.
PALAEOGEOGRAPHY
Washover
fans
ENCLOSED
LAGOON
Aeolian
dunes
Beach
Wave ripples
Submarine dunes
BARRIER ISLAND
SAND SHOALS
STROMATOLITES
PLATFORM
The albufera of Cabo de Gata, actually exploited as a salt pan,
constitutes a living example of an enclosed back-barrier
lagoon, very similar to the one that was located close to the
site of Sorbas town during the Miocene.
Aquatic birds that lived in the lagoon left their
footprint traces behind in the mud. These footprints
are found today, converted into trace fossils, therefore
giving evidence of their means of deposition.
Taken from S. M. Stanley (1992)
127
8. Fossil beaches of Sorbas
In this outcrop the observed sediments are
mostly those belonging to the interpreted
lagoon/barrier island system. Much more
modern (Pliocene-Quaternary) red
conglomerates are positioned discordantly
above them, from Unit 10 in the general
stratigraphical scheme.
The lagoon clays (muds/silts) are superposed on
the beach sands and laterally interdigitate with
them towards the east. The beach deposits crop
out in the river bed of the rambla. Each phase of
beach development forms a cemented layer. The
different layers, of metric thickness, dip (are
inclined) gently towards the east. The package
clearly marks the advance (progradation) of the
beach/barrier island system towards the east
and the progressive infilling of the bay.
The sand layers correspond to distinctive
episodes of beach formation. Their internal
structure varies laterally from west to east.
At the western end they appear as massive
sands without structure, formed as dunes in
the emerged part of the beach. These change
rapidly into laminated sands: sands with a
low-angled, parallel lamination (beach in the
strict sense), with cemented fragments (beach
rock) and abundant bioturbation structures.
Finally, towards the most easterly part of the
layers, sand with a trough cross-stratification
appears, linked to the submarine dunefields in
the deepest part of the beach. So then, within
each individual layer, sediments are laterally
distinguished from the aeolian dune zone to
the deepest submerged zone of the beach.
INTERPRETATION OF THE PANORAMA
Beach sediments
128
Lagoon sediments
Washover fans
Plio-Quaternary alluvial sediments
Modern debris
8. Fossil beaches of Sorbas
DETAILS OF THE OBSERVED STRUCTURES
Levels of cemented beach rock.
Bioturbation (trace fossils of biogenic activity) by crabs and
roots in the emerged part of the beach.
Washover fans
Bioturbation
Beach rock
Lagoonal muds and silts
Low-angled parallel lamination
Trough cross-stratification
Layers corresponding to beach levels inclined towards the
southeast.
Wave ripples
Details of trough cross-stratification and ripples in the
submerged part the beach, produced by wave movement.
129
9. Dolinas: windows of the karst
J. M. Calaforra
From the place in which we are located a
multitude of small, circular depressions may be
observed. These depressions terminate in
a well or sinkhole, through which they are
connected with the subterranean caverns of
the Sorbas gypsum karst. They are the dolinas,
the windows of the karst. The sector that we
observe belongs to the Covadura System, and
in its interior a multitude of small depressions
may be counted. The phenomenon may be
better observed from a birds eye view.
The origin of these dolinas is known to be
diverse. The majority are due to dissolution of
the gypsum rock, although they can also
be produced by the cave-in or collapse of the
layers or include erosion of a level of marls.
Birds-eye view of dolinas
(Photo, M.Villalobos).
TYPES OF DOLINAS IN SORBAS
CAVE-IN OF A GYPSUM LEVEL
DISSOLUTION OF A GYPSUM LEVEL
EROSION OF A MARL LEVEL
Marl
Marl
Gypsum
130
Gypsum
Gypsum
10. Lapiés
M. Villalobos
Lapiés are surficial dissolution features of gypsum.
They are characterised by the presence of grooves
Sharp-crested lapiés.
and furrows, separated by sharp crests.They have
different sizes.
Microlapiés (Photo, F. M. Calaforra).
131
11. Túmulos
J. M. Calaforra
LAYERS OF GYPSUM RISE UP
1
2
3
Túmulos Field.
Túmulos (mounds) are features exclusive to
Sorbas.They exhibit a doming of the surface layers
of the gypsum.They are generated through an
132
increase in the volume of water that is absorbed
by the gypsum crystals.They are concentrated in
large expanses forming Túmulos Fields.
Túmulo.
12. The Cariatiz Reef
Juan C. Braga - José M. Martín
One of the most characteristic types of rock in
the landscape of the Sorbas Basin are reef
carbonates, that is to say, carbonates formed
from the skeletons of corals and other
organisms that lived and live in reefs, such as
red algae, molluscs, serpulid worms, etc.
In the Sorbas Basin there are four reef
carbonate episodes (Upper Tortonian to
Messinian). Without doubt, the most spectacular
and well-known, and at the same time, the most
important volumetrically, are the 6 million year
old Lower Messinian reefs.
Presently the coral constructors of reefs live exclusively
in warm tropical seas (Caribbean, Red Sea, Australian Great Barrier Reef, etc.).
Outcrop of the reef framework at Cariatiz.
The framework of coastal (fringing) reefs was formed from colonies of
Porites with a stick and layer form.
Modern reef corals in the Great Barrier Reef, Australia.
Colonies of Acropora, one of the main present-day coral
constructors.
133
12. The Cariatiz Reef
PALAEOGEOGRAPHY OF THE SORBAS BASIN DURING THE
FORMATION OF COASTAL REEFS (LOWER MESSINIAN,
6 MILLION YEARS AGO)
Uleila
BÉDAR
Palaeocoastline
Mojácar
Coral Reef
Sorbas
Open Sea
Deltas
Lucainena
Turrillas
ALHAMILLA
Shallow Sea
(reefal lagoon)
Coas
tline
FILABRES
Prese
nt Da
y
The Cariatiz reef, facing us, constitutes one of
the best examples of fossil reefs within the
Mediterranean Basin. From the point in which
we are situated, and following the length of the
left bank of the Barrnco de los Castaños towards
the north (left), a spectacular section of the
Cariatiz reef platform is visible, formed in
the Lower Messinian around 6 million years ago.
In this platform reef carbonates produced by
the skeletons of corals and other organisms
such as calcareous algae and molluscs
accumulated. Corals (almost exclusively of the
genus Porites) formed fringes (rims) of coastal
reefs surrounding the emerging relieves in this
period. They correspond to Unit 4a in the
general stratigraphical scheme.
Carboneras
Cariatiz reef in the Barranco de los Castaños. The
deposits formed in each phase of reef growth produce a
wedge geometry that is inclined and thins towards
the basin (towards the south), and is easily visible from
the slope on the other side of the barranco. In front of us
various growth phases (wedges) can be observed.
The most spectacular results in the photo.
SCHEMATIC DIAGRAM OF A PHASE OF REEF GROWTH
The reef encloses a reefal lagoon towards the
land where corals and other organisms
produced from calcium carbonate also grew.
Towards the sea, the reef generated a talus slope
in which debris derived from the destruction of
the reef accumulated. The clast size of this debris Lagoon
is separated down slope, in the way that each
time it is finer. Between the reef blocks and
debris, other organisms grew such as calcareous
green algae (Halimeda), bivalves and fish.
Lagoon
Reef Crest
Coral Thicket
Coral Pinnacles
Coral Breccia and Blocks
Framework
Bioclastic Breccias
Upper Talus
Slope
Middle Talus Slope
Calcirudites
Lower Talus Slope
Calcarenites
Calcilutites
134
The Tabernas Basin
Geological Features
GEOLOGICAL FEATURES AND EVOLUTION
J. C. Braga - José M. Martín
SIMPLIFIED GEOLOGICAL MAP AND STRATIGRAPHICAL SUCCESSION FOR THE TABERNAS BASIN
PLIO-PLEISTOCENE
FILABRES
DEPOSITIONAL SETTING
ALLUVIAL FANS. Conglomerates and sands
PLIOCENE
Taken from Weijermars et al, 1985
AGE LITHOLOGY
FAN DELTA and DELTA. Conglomerates and sandstones
Gypsum
RESTRICTED BASIN
Seismite
MARINE BASIN
Marls
NO
Tabernas
MESSINIAN
s
rna
be
a
T
de
bla
m
Ra
Geological Section
Pechina
GÁDOR
Desierto de Tabernas
Rambla de Tabernas
Yesón alto
CN-340
Alhamilla
Cerro
Alfaro
Reefs
SERREVALIAN-TORTONIAN
Baños
Río
An
da
rax
Filabres
Seismite
Alfaro (742 m)
ALHAMILLA
Geological Section
SE
Geological Section
Seismite
(Gordo
Megabed)
SUBMARINE FANS. Marls, sandstones and turbidites
COASTAL PLATFORM. Conglomerates
BETIC BASEMENT
Schists, quartzites, phyllites and marbles
137
GEOLOGICAL FEATURES AND EVOLUTION
About eight million years ago (in the Miocene)
the configuration of emerged and submerged
land around the littoral margin of Almería was
similar to that of today, but not identical: the sea
extended through the territory of the Tabernas
Desert up to the foot of the Sierra de los Filabres
in whose borders fossil coral reefs of this age
formed, reliably marking the position of the
ancient coastline. In the slopes of this ancient
sea, submarine fans deposited a thick and
1
Vélez-Rubio
3
Guadix
Vera
Berja
Almería
Carboneras
Berja
Adra
Adra
Almería
Almería
Adra
Present Day Coastline
Braga, Martín and Quesada
Andarax Corridor
Western Basin
ite
rra
Sorbas
Tabernas Carboneras
Tabernas
a
Vera
Sorbas
Carboneras
Se
Tabernas
Sorbas
an
Huercal
-Overa
Present Day Coastline
Reefs
Vera
Present Day Coastline
ed
Berja
Huercal-Overa
Guadix
ne
Guadix
Alhama
La Tórtola
Motril
Nerja
Almanzora
Corridor
M
Granada
Baza
In this depositional environment, marine at times,
lagoonal for others, the deposition of limestones,
marls, muds and sands, and enclosed gypsum,
continued up until around 2 million years ago (in
the Pliocene, almost at the start of the Quaternary),
when the sea ultimately retreated, leaving the
sediments exposed to the action of erosive agents.
DISTRIBUTION OF EMERGED LAND 4 MILLION
YEARS AGO
2
Alcalá la Real
intermontane basin between this new relief, to
the south, and los Filabres, to the north.
Later, some 7 million years ago (in the Upper
Miocene), the Sierra Alhamilla was uplifted,
closing a narrow and elongated, marine
DISTRIBUTION OF EMERGED LAND 7 MILLION
YEARS AGO
DISTRIBUTION OF EMERGED LAND 8 MILLION
YEARS AGO
138
extensive sedimentary package that the rivers
eroded from the emerging relief. This material,
comprising alternations of marl and sand, are
amongst those which have, to a great part,
fashioned the eroded landscape of the Tabernas
Desert.
GEOLOGICAL FEATURES AND EVOLUTION
The Tabernas Basin has been
configured since then as a long
and narrow depression
(approximately 20 km in length
and 10 km in maximum width)
between the Sierra de los
Filabres and the Sierra Alhamilla,
situated to the west of the
Sorbas Basin and in continuation
with it.
Graphic Scalebar
SIER
RA
OS F
DE L
ILAB
RES
VERA
SORBAS
TABERNAS
ALH
AMIL
C AB
RER A
LA
CARBONERAS
NÍJAR
SIERRA DE GÁDOR
ALMERÍA
CABO DE GATA
Neogene Sediment
Neogene Volcanic Rocks
Betic Substratum
139
THE ERODED LANDSCAPE
The soft nature of the sediments that have filled
the Tabernas Basin from 10 to 8 million years
ago, the slow and continual uplift of the sierras
that border it, and the arid yet stormy climate
that has characterised this territory for a good
part of the more recent Quaternary, have
conditioned the model for one of the most
spectacular erosive landscapes in continental
Europe.
A geological landscape reminiscent of Africa
that has captured the attention of geologists,
naturalists, geomorphologists, photographers
and film producers for generations: the Tabernas
Corridor, the most southerly desert in Europe.
This spectacular erosive landscape is not,
therefore, attributable to human action, but to
the concurrence of a series of geological factors
and its own natural evolution, upon which the
peculiarity of being one of the most important
scientific and educational places for the study
and comprehension of the natural phenomena
of erosion and desertification in the
Mediterranean Basin has been conferred.
The temporary and torrential character of
precipitation generates a rambla type of fluvial
system, normally dry, but which discharges
a great amount of sediment and water in an
almost instantaneous manner during strong
140
storms. Within them the riverbeds are very
broad and well-fitting, with steep and vertical
sides, although they generally appear dry.
In the soft and readily eroded foothills, the
stream produces grooves, which grow towards
rills and runnels, and terminate in furrows
separated by sharp crests. This landscape
is given the name ‘Badlands’, alluding to its
difficulty for being worked or put into
agricultural production.
Turbidite sequences in the Tabernas Desert .
Eroded landscape of the
Tabernas Desert.
Evolution of the Drainage Network
Antonio Martín Penela
4 MILLION YEARS AGO
The eroded landscape of the Tabernas desert is
a consequence of the geological evolution of
the region over the length of the last 4 million
years, and more specifically, of its tectonic and
climatic evolution in the past 150,000 years.
Tabernas
Pliocene
Coastline
ALHAMILLA
Mediterranean Sea
GÁDOR
t Day C oa
stli
esen
Pr
n
Almería
e
In the Lower Pliocene, about 4
million years ago, a fall in sea level
took place simultaneously with a
strong uplift of the adjacent relieves,
Sierra Alhamilla, Sierra Gador and
Sierra de los Filabres, already emerged
and with some elevation. As a consequence,
broad surfaces of the region became emergent
and important fan deltas developed that
collected water coming from the Sierra de los
Filabres. One of these is the precursor of the
modern River Andarax, that already occupied
a similar position, although its river mouth
(outlet) is somewhat displaced to the north,
towards the position of La Rioja.
2 MILLION YEARS AGO
FILABRES
During the latter stages of the Pliocene, around
2 million years ago, the elevation of the
mountainous relives and the fall in sea level
continued, since then practically all of the
Province of Almería has become emerged.
In this period, areas subjected to erosion and
areas of sedimentation were differentiated.
The latter were represented by small lakes
installed in the most low-lying zones, and
alluvial fans in those that material coming from
the recently-formed mountainous massifs was
deposited.
FILABRES
Tabernas
ALHAMILLA
The main drainage during this period
were made up of a fluvial system
of close appearance to the
modern River Andarax, which was
forming an important delta in its
outlet to the Mediterranean.
Palaeocoastline
GÁDOR
Present Day Coastline
Almería
141
Evolution of the Drainage Network
THE PRESENT DAY
FILABRES
The establishment of more arid climatic
conditions in the Upper Pliocene, led to the
total desiccation of lacustrine areas and almost
total inactivity in the alluvial fans. It is since this
period when erosive processes clearly became
dominant in the region, initiating the sculpture
of the modern landscape and the
development of the fluvial network, which
deeply excavated the Neogene and Quaternary
sediments in the Tabernas Basin. The Andarax
River continued as the principal river, in which
all the water from the basin is drained, even
if in reality the water and sediment carried by
it to the sea is quite scarce.
Since the late Pleistocene, at a time when the
modern configuration of the fluvial network
was initiated, the factors that have allowed its
strong incision, the development of badlands,
and its general evolution have been: tectonics,
the nature of the material, weak and easilyeroded lithologies, and the climatic conditions.
Tabernas
ALHAMILLA
Distribution of streams in a section of the
Rambla de Tabernas. The high drainage
density (increased number of streams per
unit of surface area) is typical of gullied areas.
GÁDOR
Almería
Characteristic features of the present-day
erosive sculpture in the Tabernas Desert.
142
Ramblas
Antonio Martín Penela
Ramblas constitute the main arteries of
the drainage network in the Tabernas Basin.
Through these the transport, and also the
deposition, of particles coming from the erosion
of the basin and the surrounding sierras is
achieved.
majority of cases, circulating only water from
surface currents originating as a result of
storms. The erosive processes in the ramblas
take place during floods, excavating laterally
along the length of its margins.
They comprise braided fluvial systems,
characterised by the development of numerous
sandy bars between which multiple channels
are initiated during flood periods. The flow of
water in the riverbed is ephemeral, in the
During the last 100,000 years the ramblas have
evolved, deepening and widening their river
beds, starting to form valleys almost 100 metres
deep and river courses whose width exceeds a
hundred metres.This important development of
rambla valleys is a consequence of a combination
1
2
BASE LEVEL
of factors such as progressive uplifting of the
region, the arid and stormy climate, the soft and
erosive nature of the material.
The rivers of the Tabernas Basin are continually
down-cutting, trying to reach their equilibrium
with the base level of the sea. The occasional
torrential precipitation and sparse vegetation
cover allows an intense water-bourne erosion
that unleashes an intense processes of incision,
with a dense drainage network of dendritic
type, and abrupt and unstable hillsides.
3
BASE LEVEL
BASE LEVEL
At the end of the Pleistocene incision of the fluvial network was
initiated.The ramblas adopt a meandering morphological pattern.
In the Holocene the rivers excavated deeply in order to reach their equilibrium with base level.
It produced a generalised incision of the river courses.
143
Mechanisms of erosion in the desert: currents
Antonio Martín Penela
RAINDROP IMPACTS
SHEET EROSION
Raindrops tear away
particles of the ground that
are transported down slope
by saltation. This process
hardens the surface.
Hardened ground
favours the initiation
of sheeted flows,
helped by the slope,
that remove and
entrain the material.
Ground encrusted by the effects of raindrop impacts.
144
Fairy Chimneys : Small mounds of ground protected from sheet erosion by more resistant
fragments of rock.
Mechanisms of erosion in the desert: currents
RILL EROSION
GULLIES AND BARRANCOS
The flow is
channelised forming
furrows or ‘rills’.
Deepening of the rills
increases the capacity for
excavation by concentrated
flows, increasing the process
until rills are created and
barrancos as well.
Erosive rills upon slopes are one of the characteristic features of soft hillsides in semi-arid
regions.
Typical eroded landscape of gullies, known as ‘Badlands’.
145
Mechanisms of erosion in the desert: evolution of slopes
A. Martín Penela
146
LEDGES FROM THE RETREAT OF SLOPES
UNDERMINING BY BASAL UNDERCUTTING
Erosion of the softest material forms unstable cornices in the harder
material above it, which topple down due to gravity.
Lateral erosion of the slope base in meandering areas causes instability
and, afterwards, block falls from above.
Mechanisms of erosion in the desert: evolution of slopes
MASS SLIDES
EROSION IN TUNNELS (PIPING)
Fissures parallel to the slope allow partial slumping and the collapse of
vertical tunnels.
Water penetrates into the ground and generates a network of collectors
through which material is removed. The pipes grow progressively and
the relief ends in collapse giving rise to pseudokarstic morphologies.
Water entry holes
Discharge
holes
Tensional Fissure in the slope
margin
Circ
ulat
ion
pipe
s
Mass slide
147
The Tabernas Basin
Didactic Itinerary
1. The turbidite succession of the Tabernas submarine fan
Juan C. Braga - José M. Martín
TURBIDITES
One of the most significant sedimentary
features of the Tabernas Basin is the
existence of a thick package of detrital
sediment deposited around 8 million
years ago (in the Tortonian) at the
bottom of the sea, at several hundred
metres of depth, in a slope setting, at
the foot of the slope and on the
submarine plain. Two different types of
deposits are distinguished:
8 million years ago (during the Tortonian) the Tabernas Basin
had not been differentiated as such, since the relieves that
delimited it to the south did not exist, like they do at present;
the uplifting of the Sierra Alhamilla was initiated afterwards,
around 7 million years ago.
SIERRA DE LAS
ESTANCIAS
Granada
b) Mass failures on the slope, caused by
seismic movement (earthquakes) of
great magnitude, known as seismites.
Upon this sedimentary unit
characterised by the alternation of
decimetre layers of sandstone and marl,
the characteristic erosive sculpture
(‘Badlands’) of the Tabernas Desert has
been fashioned to a great extent.
Palaeocoastline
SIERRA NEVADA-FILABRES
Modern Coast
a) Those of submarine fans, situated at
the foot of the slope and associated
with turbidity currents, known as
turbidites.
Reefs
Almería
Almanzora
Corridor
PALAEOGEOGRAPHY OF THE TABERNAS BASIN
AROUND 8 MILLION YEARS AGO (TORTONIAN)
Fluvial
apparatus:
ramblas
Main entry
point for
sediments
Nevado-Filabride
Betic Basement
With information taken from Kleverlaan, 1989
The Tabernas Submarine Fan occupied an area
of some 100 km2 extent. In it one can
differentiate the most distinctive elements such
as feeder channels, with a conglomerate fill
(with clasts of up to several cubic metres), and
lobes, that are built as mounded deposits at
located at the exit of channels, consisting of
sand and mud. The source area of all these
sediments is the Sierra de los Filabres, located
on the northern margin.
Platform
Tabernas
Fan
Slope
Basin
Actual location of Tabernas
Main direction
of sediment
distribution
Lobe
Coastline
Slump Scar
Platform Border
151
1. The turbidite succession of the Tabernas submarine fan
The turbidite succession that we observe in the
Barranco del Poblado Mejicano corresponds to
the external zone of the Tabernas Fan and
consists of sand layers linked to turbidity
currents (suspension of sand and mud with
a density of between 1.5 and 2 g/cm3),
intercalated with fine sediments of mud and
clay size. Both types of sediment are present in
decimetre thick layers. Turbidite currents come
from the upper part of the fan, and/or
emergent area, or from the platform situated
well away from here. The sediments that they
transport are essentially deposited in the lobes
and at the margin of the fan. The clay and mud
layers are deposits that are formed at the
bottom of the marine basin between every two
turbidite layers.
In response to differential erosion, the turbidite
layers, which are laterally very continuous,
stand out in the landscape. The succession is
actually found to dip towards the north, as
a consequence of the later uplift of the Sierra
Alhamilla, although the original (very gentle)
inclination of the stratified succession was in
exactly the opposite sense. The turbidite layers,
in detail, consist of sand whose grain size
progressively diminishes upwards, and some
mud in its upper part. Its deposition is
152
INTERNAL STRUCTURE
OF A TURBIDITE LAYER
(Bouma Sequence)
MUD-CLAY
Parallel Lamination
Cross-Lamination
SAND
Parallel Lamination
Normal Grading
Nevado - Filábride
Submarine Canyon
extraordinarily rapid. The most granular (sandy)
intervals were deposited over a period of a few
hours. The finest (muds) take as much as
a few weeks. On the geological timescale
deposition of the turbidite may well be
considered as almost instantaneous.The
frequency of repetition of this process within this
zone was approximately one turbiditic event
every 700 years.The sediment that is intercalated
between the turbidite layers (clay-mud) was,
however, deposited very slowly from
Submarine Fan
suspension, in intervals of time from hundreds
to thousands of years for each layer.
Fan margin
succession.
Alternation
of hard layers of
sandstone
turbidites and
soft layers
consisting of
muddy sediments.
1. The turbidite succession of the Tabernas submarine fan
SEISMITES
Throughout the turbidite succession observed in
the barranco levels of seismites are intercalated
within it. Internally they are composed of two
types of material: (a) a conglomerate, at the base,
with clasts (sometimes up to several cubic
metres) encased in a sand and mud-sized matrix,
and (b) a sand, in the higher part of the layer, of
turbiditic character (up to several metres in
thickness).The origin of these layers is tied to
slumping of material in the marine platform
slope, induced by earthquakes.The poorlyconsolidated sediment that exists there, is easily
mobilised through the shock produced by a
seismic disturbance. If the shock is of sufficient
intensity it slides, towards the frontal slope, at the
same time disrupting and mixing with the fluid,
generating a density flow that is afterwards
going to give rise to a basal conglomerate
deposit.The upper turbidite corresponds to sand
that is lifted into suspension in the roof of the
density flow, that is deposited immediately
afterwards. Seismites correspond to
instantaneous events on the geological
timescale. Many of them have a considerable
extent, and are suitable as correlation levels
(guide levels).Their expanse gives an indirect
estimate to the intensity of the earthquake that
was generated.
At times in these slides only deformation folds
are produced in the layers, without the sediment
affected becoming disrupted, generating
structures known as ‘slumps’. In reality a complete
transition exists between several situations, in
that many slumps, if they continue through the
sliding process, end up by breaking up and
generating a breccia (intraformational breccia),
whose clasts frequently exhibit irregular
geometries, in a recurved form, corresponding to
the remains of folds.
Deformation of layers produced by sliding: Slumps
One of the most characteristic levels in the Tabernas
Basin, interpreted as a seismite, is known as the ‘Gordo
Megabed’, whose thickness reaches up to 40 metres
(Kleverlaan, 1989).
153
2. The Las Salinas Travertines in the Tabernas Desert
A. Mather - M. Stokes
One of the most surprising, and at the same
time poorly known, aspects of recent
geological processes that can be observed in
the Tabernas Desert is the presence of
Quaternary travertine formations from
different areas within it. One of the zones
where the better and most spectacular
development is acquired is located in the place
known as Las Salinas.
The precise age of these formations is uncertain
for the moment. The process is active at present
and most probably it was already in operation
during the Pleistocene.
Gr
an
ad
a
rnas
de Tabe
Mexican
Town
LAS SALINAS
Restaurant
Alfaro
To
Travertines
154
To Tabernas
Los Callejones
Bridge
Al
m
er
ía
Petrol Station
Rambla
Las Salinas
Rambla de
R am
bla
de
Lan
úja
r
R am
To
de
bla
ho
elec
Verd
LOCATION OF THE LAS SALINAS TRAVERTINES IN RELATION TO FAULT LINES
Fault Line
Travertines are a type of natural limestone
rock, formed from the precipitation of
carbonates out of surface and subterranean
water. Modern travertines are developed in
very localised zones associated with active
streams, at springs in fluvial water courses,
and in general, at whatever position a
change in the velocity of flowing water is
produced, so that the degasification and
consequent precipitation of calcium
carbonate is favoured.
2. The Las Salinas Travertines in the Tabernas Desert
At Las Salinas it seems clear that its
present-day operation is due to the
circulation of water, of both pluvial
and subterranean origin, at a certain
depth that ends up appearing at the
surface due to a series of rather
important fractures with an
approximate east-west orientation.
Thanks to this line of tectonic
disturbance, a very slow and
continuous stream of water flows out,
with a large saline concentration
owing, probably, to the washing of
saline material from the area of Yesón
Alto and to progressive concentration
within water from capillary rise.
The carbonate precipitated due to the
slope creates typical travertine
deposits with laminated and
concretionary structures.
IDEALIZED SECTION OF TRAVERTINE GENETIC PROCESSES IN LAS SALINAS, IN RELATION TO THE DISPOSITION OF
GEOLOGICAL FRACTURES AND THE CIRCULATING FLOW OF WATER
Fluvial Recharge
Rising circulation of subterranean flow
Young Quaternary
Travertines
Turbidite Sequence
Fault Zone
Circulation Flow of Water
155
2. The Las Salinas Travertines in the Tabernas Desert
Detail of the internal structure of the travertines (Photo, M.
Villalobos).
Detail of travertine deposits and salt pseudostalagtites in the
accretionary curtain (Photo, M. Villalobos).
Surface crest of the fault zone associated with the formation
of travertine deposits (Photo, M. Villalobos).
General view of the travertine accretionary curtain (Photo, M. Villalobos).
156
3. The Escarpment landforms of the Cerro Alfaro District
M. Villalobos
A very characteristic morphology in the erosive
landscape of the Tabernas Desert are
escarpment landforms, especially visible in the
Cerro Alfaro district. These consist of inclined
layers of hard material, normally sand and/or
conglomerate, that protect the much weaker
underlying material, usually marls, from
erosion.
In the specific case of the Tabernas Desert, the
most visible and spectacular examples have
the peculiarity that the sense of inclination of
the layers (towards the north) is reversed with
respect to the original deposition of the layers
(towards the south), that is to say, that they have
been uplifted from the south and inclined
towards the north. This inversion must be seen
as due to uplifting of the Sierra Alhamilla, just as
reflected in the accompanying figure.
EVOLUTION OF AN ESCARPMENT LANDFORM, WITH A LAYER OF HARD MATERIAL INCLINED ABOVE A PACKAGE OF WEAK MATERIAL THAT IS ERODED LATERALLY
157
3. The Escarpment landforms of the Cerro Alfaro District
INTERPRETATIVE SECTION FOR THE ESCARPMENT LANDFORMS IN THE CERRO ALFARO DISTRICT IN RELATION TO THE EVOLUTIONARY HISTORY OF THE BASIN AND UPLIFT OF THE SIERRA
ALHAMILLA
Almería-Tabernas Basin
Sierra de los Filabres
Sea Level
In the period that existed between15 and 6 million years ago (Serravallian –
Messinian), the sea washed against the foot of the Sierra se los Filabres. Numerous
submarine fans, a continuation of the rivers that drained the sierras, fed sediments
into the marine basin, depositing a thick series of turbidites, alternating layers of
weak, marl sediments and tough sands and conglomerates.
AROUND 8 MILLION YEARS AGO
Sierra de Alhamilla
Sierra de los Filabres
Almería Basin
Tabernas Basin
Sea Level
Approximately 7 million years ago, at the end of the Tortonian, tectonic readjustment
had caused emergence of the Sierra Alhamilla block, separating the Tabernas Basin
towards the north of the Sierra Alhamilla from the Almería Basin towards the south.
They continued to be marine for a significant period of time, up until around 4 million
years ago. Uplift of the sierra elevated and brought up turbiditic material already
deposited, reversing the inclination of the layers.The post-Messinian deposits were
markedly different in these basins.
AROUND 2 MILLION YEARS AGO
Sierra de Alhamilla
Almería Basin
Nivel del mar
Sierra de los Filabres
Cerro de Alfaro, Escarpment landform
Tabernas Basin
Since 4 million years ago (Upper Pliocene and Pleistocene) the environment in
these basins has been virtually continental. Erosive agents have acted upon
exposed material in the basin, especially in Tabernas, forming the erosive landscape
that we can observe. The harder layers of the turbidite series create the typical
landforms of dipping escarpments, also in a reversed sense to that in which they
were deposited.
PRESENT DAY
158
Post-Messinian deposits of the Almería Basin
Serravallian-Messinian deposits of the Almería-Tabernas Basin, hard layers in
dark green, softer layers in light green
Post-Messinian deposits of the Tabernas Basin
Betic Substratum; Nevado-Filábride and Alpujárride complexes
4. Tunnel Erosion (Piping)
Antonio J. Martín Penela
Tunnel erosion (also known as ‘piping’)
constitutes a peculiar erosive mechanism which
may achieve an important development in
semi-arid regions. The resulting landforms, of
great scenic beauty, are known as ‘pseudokarst’
or mechanical karst. In the Tabernas Desert they
are superbly represented.
It originates from the movement of
concentrated flows of water that circulate
through poorly consolidated material,
producing a washout that gives way to the
formation of tubular conduits (tunnels or pipes).
DIFFERENT STAGES OF TUNNEL EROSION
2
1
Collection Pipes
Drainage Pipes
The removal of solid particles through the
drainage orifices produces an increase in the size
of the existing macropores and fissures, creating
more or less complete, continuous channels, that
come from the collection pipes or sinkholes
through to the drainage pipes. These tunnels can
have a diameter between 10 and 40 cm, and a few
metres of length.
Local Base Level
Tunnel erosion is initiated through part of the rainwater permeating
into the ground through fissures and cracks on the surface.
Fissures and
cracks in the
surface.
Collection pipes on a slope, oriented in association
with fractures.
Drainage pipe close to
local base level.
159
4. Tunnel Erosion (Piping)
DIFFERENT STAGES OF TUNNEL EROSION
3
4
The channels grow progressively until they are made
unstable. Partial or total collapse of the walls and roof occur
when they are flooded with intense rainwater, causing an
excess of weight in the overhangs.The phenomenon may
also occur after a significant drought, through the intense
cracking of the material, producing a sudden fall.
Progressive development of the tunnel network,
accompanied by many collapses through part of it. A
system of barrancos is initiated in which numerous failed
channels and blind valleys with U-shaped sections, are
still preserved, that rapidly evolve into V-shaped sections.
Altogether, a net retreat of the slope takes place.
Failed and abandoned drainage pipe, resulting from the
descent of the tunnel network towards local base level.
Large sized collection pipes or sinkholes, originating from the
coalescence of several vertical collection pipes with the
collapse of their walls.
160
Weathered pseudokarstic morphology which evolves
towards a system of gullies.
5. The Quaternary alluvial fan-lake system
A. M. Harvey
One of the most visible and characteristic
features in the recent sculpture of the Tabernas
Desert are alluvial fans.
The development of alluvial fans takes place at a
break of slope produced at the contact between
a more or less mountainous front and a small
sedimentary trough. In this morphological
setting, when the confined river or rambla
courses of the mountainous zone reach the
sedimentary basin, with much lower slope, they
suffer a sharp reduction in their capacity to
transport bedload, generating extensive deposits
in the form of a fan.
The lateral superposition of fans in the same
front generates a system of coalescing fans. In
alluvial fans, the coarsest material is deposited
in the more proximal zones (closer to the
relieves), while the finer, less-heavy sediment,
may be carried to the more distal zones
(furthest from the relieves). In the more distal,
practically planar parts of the fan, marshy or
swampy zones are frequently formed, and
include small lagoonal basins that are filled by
sediments.
Sierra
TYPES OF ALLUVIAL FAN
OPEN FAN
Sierra
ENTRENCHED FANS
Dep
ress
ion
Dep
ress
ion
Sierra
SUPERPOSED FANS
Dep
ress
ion
Sierra
COALESCING FANS
Dep
ress
ion
161
5. The Quaternary alluvial fan-lake system
IDEALIZED SCHEME OF THE ALLUVIAL FAN-LAKE SYSTEM DURING THE
PLEISTOCENE IN THE EASTERN SECTOR OF THE TABERNAS BASIN
Sierra de Alhamilla
Sierra de Filabres
Tabernas Basin
Although alluvial fan morphologies are frequent
and obvious throughout the desert zone, in the
vicinity of the Tabernas District, it is possible to
distinguish an ancient yet still functioning alluvial
fan system, that at present feeds into the main
drainage of this area, the Rambla de Tabernas, an
artery for the removal of sediment and water alike,
that are discharged from the fluvial network in the
eastern sector of the basin.
View of the lacustrine
deposits (photo J. C. Braga).
162
Betic Substratum
Sedimentary Fill of the Basin
Alluvial Fans
Lake-Lacustrine Deposits
Principal drainage direction in the basin
5. The Quaternary alluvial fan-lake system
The fans started to function during the
Pleistocene, after an erosive period that stripped
out the upper part of the sediments in the
basin.
QUATERNARY DEPOSITS OF THE ALLUVIAL FAN-LAKE SYSTEM IN THE TABERNAS AREA
Rambla Honda
During the operation of these alluvial features,
the basin drainage remained interrupted for
some time, generating a lacustrine zone in
which around 20 metres of sediments were
deposited. These deposits are visible in the
vicinity of Tabernas and the Los Callejones
bridge (at the junction of the motorway with
the old Murcia road).
Betic Substratum
Rambla de
los Nudos
Fill material of the
Tabernas depresssion
Lacustrine Sediments
RES
LAB
S FI
O
L
E
RA D
SIER
Alluvial Fans
River Channels
Observation Points
Roads
Rambla de
la Galera
Quarry
Rambla de los Molinos
Rambla de Norias
Sierra del Marchante
In the map several places used for field observations are
located
1. General view of coalescing alluvial fan deposits in Rambla
Honda
2. Coarse river sediments typical of the more proximal part of
the alluvial fan, in relation to the supply front from the Los
Filabres relief
3. Finer sediments characteristic of distal deposits (visible in
the quarry area)
4. Lagoon sediments visible in close vicinity to the Alfaro
petrol station
Rambla de
Tabernas
TABERNAS
Rambla de la Sierra
Bar
Alfaro
SIERRA DE ALHAMILLA
163