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Geological history of Catalonia
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Geological history of Catalonia
The inorganic world, the geosphere, is the physical support of the world of life on Earth, the biosphere. The geosphere
contributes the substratum and the necessary resources (water, rocks and minerals) for the development of the life that
takes place on our planet. The Earth also offers to man, a rational being, the capacity to know his position in nature, the
immediate pleasure of perceiving its features and of being able to learn about the planet’s past and the origins of life.
Introduction
Exactly as presented to our sight (figure 1), the Earth is the result of the extraordinary diversity of the internal and
external geodynamic processes that the planet has undergone since its inception, which go back to some 4 500 million
years (Ma). The Earth was formed from a dust and gas interstellar cloud together with the Sun and the other planets of
the Solar System. On the Earth there are no traces of rocks from an earlier history; the Solar System, mainly the other
planets of the group known as inner or terrestrial planets (Mercury, Venus, and Mars), the Moon and the meteorites, give
information about this stage. The oldest mineral dated up to now is a zircon crystal found in Australia, which has a
radiometric age of 4 300 Ma. The oldest rocks, from the region of the Great Slave Lake in Canada, have been dated at 3
960 Ma. In Catalonia, we have more than 550 Ma of geological history recorded in the outcroping rocks.
Figure 1: Present day image of the Earth.
Observing a world map in certain detail, it could be said that the shapes of the coasts of some of the emerged land are
like the “negative” of the coastal shapes of the land situated in front; it seems that they could fit together, as if they were
pieces of a puzzle. The continents form part of the tectonic plates and, in fact, some of the plates fit perfectly. It is know
that some plates move with respect to others. Sometimes they separate, and sometimes they move closer and
sometimes collide or slip and rub against each other. The result is the distribution of the seas and the emerged land
changes with time, but the volume of the Earth remains constant. The space that remains between the plates that
separate is occupied by volcanic materials coming from the interior of the Earth, which constitute the oceanic crust;
these areas are occupied by the oceans in which marine sediments are deposited. The collision between plates
produces deformations of their edges, like gigantic wrinkles, creators of reliefs. These are the great mountain ranges.
Their formation process lasts some tens of millions of years, and involves a great amount of energy.
The Iberian Plate
The Iberian Peninsula is the emerged part of an ancient tectonic plate, the Iberian Plate. Of modest proportions, the
Iberian Plate is situated to the north of the African Plate and is, at the present time, welded to the European Plate. Its
geological configuration is the result of the interactions of these two larger plates since some 200 Ma ago, that is to say,
during the Alpine cycle (see geological events).
The Pyrenees, which join the peninsula with the European continent, are the result of the collision between the Iberian
and European continental plates and retain the sedimentary and tectonic historical record of the edges of both. The
Catalan Coastal Range and the Iberian Range reflect an approximation between the African and the Iberian Plates. The
Ebro Basin is the depression which extends between the Pyrenean Range, the Coastal Range and the Iberian Range
and stored, in the sediments that fill it, the record of the main events that took place during the formation of the mountain
ranges that determine its boundaries. To the east, the Mediterranean System (the group of mountain ranges and coastal
depressions) has registered the opening of the Valencia Trough Margin and of the Gulf of Lion. This particular
geodynamic context determined in the past, and continues in the present, the extraordinary geological diversity that
characterizes the Iberian Peninsula, its actual geographical situation and the one it will have in the geological future.
The oldest traces
The geological features of the Iberian Peninsula are a result of the superimposition of three great orogenic cycles: the
Cadomian, which was developed from 750 Ma until 480 Ma ago, the Hercynian cycle (or Variscan), which was started
480 Ma and finished around 250 Ma ago, and finally, the Alpine cycle which started around 250 Ma ago and continues at
the present time. These cycles are related to the formation and the subsequent fragmentation of the two large
supercontinents: Gondwana and Pangea. To form them it was necessary for continental fragments, that had been
initially separated, to converge, collide and weld, forming mountain ranges with important reliefs, and also the
subsequent fragmentation and the continental drift. So, we are talking about cyclic processes of the Earth’s evolution.
The information on the geological history of the portion of the Iberian Plate, which at the present time occupies
Catalonia, goes back at least 550 Ma. Practically no traces are left of the Cadomian cycle; it is known that between 650
Ma and 600 Ma ago a supercontinent called Gondwana was formed (figure 2).
Figure 2: Image of the Earth some 600 Ma ago.
In fact, the oldest rocks dated up to now in the Pyrenees are volcanic and plutonic rocks from the last stages of this
cycle (580 and 560 Ma). Even so, very probably earlier sedimentary rocks exist, the ages of which are unknown.
Formation of a world supercontinent and of a global ocean. The Paleozoic
In that which will be the future Iberian Plate, the sedimentary record of the Cambrian and the Ordovician is mainly formed
of siliciclastic and carbonate deposits from the marine platform or deeper, in which the first trilobites lived and where
archeocyatids colonies are formed. One of the characteristics of the Cambrian is the appearance of numerous forms of
life; many of them with skeletal components, and which is called the great life explosion of the Cambrian. At the end of
the Ordovician an emersion period took place, during which the detrital deposits settled and an intensive volcanic activity
was registered. At the end of this period the first great extinction took place, in which 85% of the species disappeared.
The Gondwana supercontinent started its fragmentation some 480 Ma ago, during the Paleozoic, marking the beginning
of the Hercynian cycle. With time, three large continental plates called Siberia, Laurentia and Baltica, were separated
(figure 3) and other smaller continental fragments, such as Avalonia, separated from the rest of the supercontinent by the
Reic Ocean.
Figure 3: Situation of Gondwana, Laurencia, Siberia and Baltica with Avalonia some 440 Ma ago.
With this fragmentation the marine conditions returned, mainly in platform environments. During the Silurian (figure 3) the
environmental conditions were very peculiar with deposits of black clays, very rich in organic matter, an indication of
euxinic (anaerobic and reducing) conditions. Graptolites and some cephalopods are the typical organisms of this period.
During the Devonian and part of the Carboniferous shallow marine platform carbonates were deposited. These deposits
were very rich in fauna (cephalopods, trilobites, corals, fish and other organisms). Some deep marine sediments were
also deposited, such as the red limestone with goniatites (griotte limestone) and cumulative levels of radiolarians. At the
same time, the first plants and amphibians started to colonize the emerged land. Towards the end of the Devonian, the
second great extinction took place.
During the Carboniferous period, the fragmented plates at the beginning of the Hercynian cycle re-converged and collided
with the remains of Gondwana, giving place to an important deformation event, the Hercynian orogeny. This belt is
characterized by fold structures accompanied by metamorphic processes of great importance and by an intense
intrusive magmatic activity. The sediments of this stage are marine detritals (those denominated Culm facies), indicative
of the tectonic activity and of the erosion of the large mountain ranges which were being formed. The remains of the
Hercynian mountain range are, even today, well visible throughout the west of Europe, especially to the west of the
Iberian Peninsula. In Catalonia, smaller fragments crop out in the Pyrenees, in the Coastal Mountain Ranges and in the
basement of the Ebro Basin.
At the end of the Hercynian orogeny, some 305 Ma ago, the continental masses of the planet were joined together
(figures 4 and 5), forming one supercontinent called Pangea, which in Greek means “all the Earth”. Pangea was
surrounded by a global ocean, known as Panthalassa, which means “all the seas”. A large gulf extended on the eastern
side of Pangea which received the name of Tethys.
Figure 4: The configuration of the Earth some 280 Ma ago: a global supercontinent, Pangea, and a global ocean,
Panthalassa.
Figure 5: Restoration of Pangea, with the emerged lands, the continental platforms and the distribution of seas and
oceans. The future limits of the plates and the position of the future Iberian Plate (Ib) are indicated.
Broadly speaking the future Iberian Plate was, at that moment, situated at the extreme west of Tethys and limited to the
north with the future European Plate, to the west with the future North American Plate and to the south with the future
African Plate (figure 5).
At the end of the Carboniferous and the beginning of the Permian, some 300 Ma ago, the reliefs created during the
Hercynian orogeny were subjected to intense erosion. The fault systems generated in an extensive tectonic context
individualized structural summits and intra-mountain basins, which received alluvial sediments and were occupied, to a
great extent, by marshy and lacustrine areas. In the area that at the present time corresponds to the Pyrenees, the
volcanic activity was outstanding. The vegetation, which from the Devonian had started to colonize the continents, was
luxuriant. In some of these marshy areas important quantities of plant remains were accumulated which, on maturing,
were converted to coal: hence, the name of this period. Towards the end of the Permian, some 250 Ma ago, vast areas
of the continent had been reduced by the erosion to extensive plains, those called peneplains. Also, at this moment the
third great extinction took place. All these circumstances determine the boundary between the Paleozoic and the
Mesozoic, some 250 Ma ago.
The fragmentation of Pangea. From Triassic to the end of Jurassic
Some fracture areas that were formed during the Carboniferous and the Permian had continued to evolve and Pangea
started to fragment, initiating the Alpine cycle.
During the Triassic, the topographically lowest areas of the future Iberian Plate were occupied by extensive alluvial plains
that were periodically invaded by the sea and they were converted into shallow marine platforms; carbonate mud was
deposited in these and some reefs emerged. Towards the end of the Triassic, 50 million years after the start of the
Pangea fragmentation, those initial fractures had evolved to form some large fault systems that delimited depressions
similar to the present day African Rift valley. One of the “rift” valleys is located in the future Pyrenean area and the other,
more important and which was immediately invaded by the sea, in the area occupied by the actual Betic Mountain
Range, the Alboran Sea and the Gibraltar Strait. Other similar depressions were opened in the interior of the Iberian
Plate. These fault systems favour the ascension of basic volcanic and sub-volcanic rock masses.
At that moment, in the future Iberian Peninsula two emerged massifs stood out: the Iberian Massif (the future Meseta,
Plateau) and the Ebro Massif, today disappeared, which occupied the present eastern areas of the Ebro Basin, of the
southern slope of the Pyrenees and of the Gulf of Lion. Geographically, both massifs were islands surrounded by vast
flooded areas in which salts, gypsums, clays and carbonates were deposited in some very arid climatic conditions.
Between the Iberian Massif and the boundary of the Triassic swamps an extensive dessert-like plain was opened.
With the passing of time, during the Triassic and especially during the Jurassic, the extension along some of the faults
that limit the rift valleys progressed until generating oceanic crust, and in this way new tectonic plates were
individualized. The opening of the central Atlantic had started (figure 6).
Figure 6: The configuration of the Earth 150 Ma ago, at the end of the Jurassic. The outline of the North American Plate
and the western coast of Africa, separated by the central Atlantic and the Iberian Plate can be recognized.
Throughout the Jurassic, during a period of 55 million years, an important part of the future Iberian Plate remained
submerged in a shallow sea (figure 7). In climatic conditions that were warmer than the present ones, mud and
carbonate sands were deposited on the broad continental platforms, which to a greater or lesser degree, were later
shaped by the seas. Those environmental conditions also helped the waters to be colonized by very numerous groups of
cephalopods, mainly ammonites and belemnites, and also by brachiopods and bivalves.
Figure 7: Restoration of the Iberian Plate 145 Ma ago, at the end of the Jurassic.
Towards the end of the Jurassic, some 150 Ma ago, the southern coasts of the Iberian Massif had separated around 500
km from the northern coasts of Africa. Throughout that period, the Tethys Ocean had already connected with the young
Atlantic, which at that time had reached a width of 1 000 km, between the southern coasts of Newfoundland and the
western coasts of the Sahara (figure 7). The rift valley which had started to open in the actual Pyrenean area 50 million
years ago was now a very deep marine trough connected to the broad continental platform which occupied the eastern
half of the present Iberian Peninsula.
The individualization and drift of the Iberian Plate. The Cretaceous
Throughout the early Cretaceous, the opening of the Atlantic Ocean spread towards the north producing the definitive
separation of the North American Plate from the Iberian and the European ones. At the end of the early Cretaceous, 100
Ma ago, the Iberian Plate was completely individualized from the surrounding plates, limited by large strike-slip fault
areas (figure 8). The northern limit was situated in the Pyrenean trough, where the separation of Iberia and Europe had
provoked the opening of the Bay of Biscay and, towards the east, the formation of many narrow, relatively deep basins,
connected with each other, which extended towards the eastern areas of the actual Pyrenean zone.
Figure 8: Restoration of the Iberian Plate 100 Ma ago, at the end of the Late Cretaceous.
The separation between Iberia and Europe throughout this area was greater in the west than in the east, which added an
anticlockwise rotational movement to the displacement of the Iberian Plate. To the south, another fault area connected
that of The Azores-Gibraltar with the Alpine area. The spread along the Central Atlantic Ridge situated Iberia at some
800 km to the west of Newfoundland.
The emerged surface of the Iberian Plate had increased considerably since the late Jurassic and included a great part of
the Iberian Massif. In the areas where the ancient Jurassic carbonate platforms emerged, systems of caverns and
dolines were developed under a tropical climate which favoured the formation of bauxitic and lateritic soils. On the coasts
which opened to Tethys Ocean and to the Bay of Biscay large deltaic fans developed with extensive marshland, which
contained a great diversity of fauna and flora. On the continental platforms, away from the deltaic influence, carbonates
and barrier reefs of rudists and sandbanks were deposited, many of the latter formed by the accumulation of the skeletal
remains of some foraminifera characteristic of that time, the orbitolines. In the deeper marine troughs, situated in the
northern and western zones of the Pyrenean area and of the Bay of Biscay, clastic sediments were deposited and
transported by turbidity currents from the frontal part of deltas. In those oceans the ammonites proliferated.
Towards the middle of the late Cretaceous, around 85 Ma ago, the African Plate started a rotational movement in an
anticlockwise direction in relation to the European Plate and, at the same time, it moved towards the north. This
provoked the progressive closing of a part of the Tethys Ocean (figure 9).
Figure 9: The configuration of the Earth 90 Ma ago, in the Early Cretaceous.
La Placa Ibèrica, situada entre la Placa Africana i la Placa Europea, es veié empesa cap al nord, iniciant-se la
convergència amb la Placa Europea i la conseqüent deformació dels marges contigus d'ambdues plaques. A l'àrea
pirinenca, la deformació es propagà des de les zones orientals cap a les occidentals, en un procés que culminaria, al
cap de 50 milions d'anys, amb l'edificació dels Pirineus i de les cadenes alpines de l'interior de la península.
En aquells temps, l'àrea emergida del Massís Ibèric havia assolit una superfície propera a la de l'actual Península
Ibèrica. A les desembocadures dels grans rius s'edificaven aparells deltaics, i a les àrees de la plataforma continental
que quedaven fora de l'abast de les zones d'influència deltaica es dipositaven carbonats i margues i s'hi desenvolupaven
esculls de rudistes i coralls. La deformació que patia la vora septentrional de la Placa Ibèrica provocava freqüents
situacions d'inestabilitat en els sediments que es dipositaven en la plataforma continental. Una part d'aquells sediments
eren transportats mitjançant corrents de turbidesa i colades de fang submarines fins als fons marins profunds del solc
pirinenc.
The formation of the mountain ranges. Late Mesozoic and Early Paleogene
At the end of the Cretaceous and the beginning of the Paleogene, the general situation had evolved rapidly. The
convergence process between the Iberian Plate and the European Plate had lead to the collision of both plates. The
greater part of the Iberian Plate, including Corsica and Sardinia, which were in the area that at present is occupied by
the Gulf of Valencia and the Gulf of Lion, was emerged and subjected to intensive erosion. The ancient connection
between the Tethys Ocean and the Bay of Biscay throughout the Pyrenean area was interrupted by the emergence of
the eastern area (figure 10).
Figure 10: Restoration of the Iberian Plate 65 Ma ago, late Cretaceous and early Paleogene.
A great part of those recently emerged areas were lowlands and, close the northern Iberian edge, they were covered by
vast alluvial plains through which braided rivers flowed transporting the clastic sediments from the erosion of the interior
of the Iberian Plate. In those lowlands, there were also marshes and shallow lakes where peat and carbonates were
deposited. Some of the latest dinosaurs that populated the Earth roamed through these marshy areas. The collection of
these sediments is called Garumnian facies and there the limit between the Mesozoic and the Cenozoic is located. This
limit is marked by the extinction of 75% of the terrestrial and marine species.
During the Paleocene, the environmental conditions were very similar to those of the late Cretaceous, with a
predominance of continental sedimentation, alluvial or lacustrine. 55 Ma ago, in the early Eocene, the sea started to
invade the lowlands. In the Pyrenean area, the progressive tectonic stacking of material from the basement and from the
old sedimentary basins, which were produced by the effect of the collision between the Iberian and European plates,
placeed an enormous load on its edges. The continuous increase in the load had caused the lithosphere, in the areas
adjacent to the mountain ranges in formation, to flex towards that mountain range. As a consequence of this, some
topographically depressed areas were generated on either side of the mountain range, and parallel to it, called foreland
basins, which were immediately invaded by the sea. A good part of the Pyrenean area, of the Ebro Massif and the actual
Coastal Range became shallow marine platforms where predominantly carbonate sediments were deposited. The typical
foraminifera of this epoch are the alveolines, whose shells accumulated forming coastal sandbanks and bars due to the
action of waves and tides. In the estuaries of the fluvial courses that drained the emerged areas, deltaic systems were
formed which were also, to a lesser or greater degree, reworked by the tides.
As a consequence of the collision process between the Iberian Plate and the European Plate, fold and thrust sheet
systems were formed in the Pyrenean area which inverted and exhumed the old sedimentary basins. These systems
were tectonically displaced towards the south on the Iberian side. The collision process between the Iberian Plate and
the European Plate would have reached its culmination towards the late Eocene and early Oligocene, approximately
between 35 and 30 Ma.
In parallel with the formation of the Pyrenees, during the Eocene and Oligocene, the deformation that took place on the
edge of the Iberian Plate was transmitted to the interior, in such a way that certain areas of intraplate, which had
previously been subjected to extension during the Triassic, the Jurassic and early Cretaceous were deformed in a
compressive context. This gave place to the formation of the Iberian Range and the Catalan Coastal Range. Specifically,
in this latter area, the deformation was translated into the formation of reversed faults, thrusts and fault systems with
horizontal anticlockwise displacement, which were oblique to the direction of maximum contraction of the Pyrenean
area.
The result of all these events was that the area surrounded by the Pyrenees, the Iberian Range and the Catalan Coastal
Range, the old Ebro Massif, disappeared as an emerged area which supplied sediments and became the basement of
the foreland basin generated at the south of the Pyrenean area, the Ebro Basin, receiver of the sediments from the
erosion of the reliefs that were being formed and that had started to emerge, both to the north and on its south east and
south west boundaries.
The Ebro Basin: from an open sea to an alluvial plain. Eocene and Oligocene
In the middle Cretaceous, some 47 Ma ago, the Pyrenees were a series of islands lined up in an west-east direction,
which emerged among the waters that cover the foreland basins of Aquitaine, to the north, and of the Ebro, to the south.
At that time, the Ebro Basin was an extensive bay which opened into the Atlantic through the Bay of Biscay and limited
to the east with the reliefs of the Catalan Coastal Range, in such a way that it was disconnected from the Tethys Ocean.
Flanking the Ebro Basin a detrital marine platform was developed where some reefs grew, at the same time as coastal
and fan deltas were formed in the mouths of the rivers that drained the Catalan Coastal Range, the remains of which are
the mountains of Montserrat and Sant Llorenç del Munt. The climate, the circulation of waters and the rest of the paleoenvironmental conditions, helped those platforms to be colonized by benthic life foraminifers typical of the middle
Eocene, the nummulites.
The Ebro Basin slowly became filled with sediments. Towards the late Eocene, some 37 Ma ago, it has passed from
being connected to the open sea through the Bay of Biscay to a practically endorheic regimen which favoured the
evaporation (figure 11). This determined that in the central areas of the basin, large quantities of salts were deposited,
while in localised marginal areas, small coral reefs were still being formed.
Figure 11: The restoration of the Iberian Plate some 37 Ma ago, towards the late Eocene.
At the same time, the tectonic structures that were formed as a consequence of the collision of Iberia and Europe
continued to extend towards the interior of the Ebro Basin, involving sediments that were increasingly younger. At the
same time, this caused the space occupied by the Ebro Basin to become progressively smaller and also that the
emerged area of the mountain ranges in formation were increasingly more extensive (figure 12). As a consequence, the
volume of available materials to be eroded and transported towards the foreland basin increased.
Figure 12: The configuration of the Earth some 35 Ma ago, in the Oligocene.
In the early Oligocene, approximately 33 Ma ago, the Ebro Basin, isolated from the Bay of Biscay and Tethys, was a
depression subjected to an endorheic continental regime, which received the contributions of the rivers and streams that
drained the areas of the north and the south, topographically elevated by tectonic causes. When arriving at the plain,
those rivers and streams deposited their alluvium, consisting of enormous quantities of gravels, sands and clays, in the
form of systems of alluvial fans and plains through which some rivers with braided beds meandered. In the central areas
of the basin, relatively far from the fronts of the mountain chains, swamps and lacustrine areas developed where marl,
carbonates, gypsum and, sometimes, peat were deposited. It is in these deposits where the remains of small rodents
are found, an indication of the radiation of mammals. In the mouths of the water courses that arrived to those lakes,
small deltas were formed. Probably, the landscape of the central areas of the actual Catalan part of the Ebro Basin
should remind us, in some aspects, of the actual African Savannah: shallow lakes surrounded by vegetation and
temporarily swamped areas.
The opening of the western Mediterranean. The upper Oligocene and the Miocene
Towards the end of the Oligocene and the beginning of the Miocene, some 25 Ma ago, the collision process between the
Iberian and European plates had finished. The Pyrenees, the Catalan Coastal Range and the Iberian Range already had
the same fold structure as they present day. The sediments that formed the alluvial fans, which had been deposited at
the foot of the mountain fronts of the Pyrenees, were now folded forming spectacular progressive unconformities. The
Ebro Basin maintained an endorheic regimen with the eastern area, or Central Catalan Basin, totally filled and occupied
by an extensive alluvial plain which drained towards the west, where the lacustrine conditions are maintained. To the
east, the old Gulf of Tethys had been practically disconnected from the rest of the ocean and an interior sea had been
formed, the Paleomediterranean (figure 13).
Figure 13: The configuration of the Earth 10 Ma ago was already similar to the present one. The vast Gulf of Tethys has
been converted into an interior sea.
The end of the collision process between the Iberian and European plates caused, from the late Oligocene onwards, the
convergence between Africa and Eurasia to manifest itself more to the south, on the limit between the Iberian and
African plates. At the same time a fault system in an extensional geodynamic context was developed. This progressed
though the interior of the European Plate from north to south, forming rift valleys in the actual Rhine and Rhone valleys.
This new situation originated a series of events that should determine the rest of the basic geological features that
configure the actual Catalan area of the Iberian Plate.
The faults that had been formed in the Catalan Coastal Range simultaneously with the formation of the Pyrenees acted
in the new extensional tectonic context as normal faults and they generated deep tectonic grabens which were parallel,
and also oblique, with respect to the coastline. At the eastern end of the Ebro Basin, normal faults were also developed,
in a NW-SE direction. The evolution of the fault systems first provoked the thinning of the continental crust and the
fragmentation of the eastern end of the Iberian Plate, in such a way that the block formed by Corsica, Sardinia and the
Balearics was separated and started to drift towards the east, due to the formation of oceanic crust in the Gulf of Lion
and in the Valencia Trough. In this way, the formation of the actual western Mediterranean started some 20 Ma ago. It
was then when the tectonic grabens recently formed in the Catalan Coastal Range and in the eastern end of the actual
Pyrenees were connected with the newly developed Mediterranean (figure 14). They were immediately occupied by a
shallow sea where clastic and evaporite sediments were deposited and also some coral reefs grew up.
Figura 14: Paleogeographic reconstruction in middle Miocene.
During the late Miocene, in the eastern Pyrenean area, another graben system was generated which severed all fold and
thrust structures that had been formed earlier, and which delimited small intermontane sedimentary basins. In the Seu
d’Urgell and the Cerdanya basins, systems of alluvial fans with marshy and lacustrine areas were formed, in an
endorheic regime, where fine-grained sediments and peat were deposited. In the eastern end of the Ebro Basin, some
10 Ma ago, the start of the basic eruptive episode in favour of the faults oriented NW-SE that delimit the Empordà graben
was registered. The basaltic flows from the volcanic activity still remain.
The Messinian “crisis”
Seven million years ago, an extraordinary event affected the whole of the Mediterranean basin and the emerged land that
surrounded it: in the Messinian, the Mediterranean dried up. The major part of the area was converted into a gigantic salt
flat situated at hundreds of metres below the level of the Atlantic. It is possible that the landscape was quite similar to a
kind of combination of the Afar triangle with some of the salt flats of the Andean area and of the Dead Sea basin. That
brutal change in the base level provoked the rivers to channel very deeply into the old marine platforms and the erosion
they caused in the areas of the headwaters progressed towards the continent (figure 15).
Figure 15: Reconstrucció paleogeogràfica a finals del MioPaleogeographic reconstruction in late Miocene.
It was probably then when the headwaters of some of the streams that drained the reliefs of the Catalan Coastal
Mountain Range towards the Mediterranean reached the Ebro Basin, capturing fluvial courses from this and constituting
new hydrographic basins: those of the Ter, Llobregat, Francolí and Ebro. From that moment on, the old basin of the
Pyrenean foreland stopped being an endorheic basin and passed to be a tributary of the Mediterranean basin. The
eocene and oligocene sediments deposited in the Ebro Basin during the formation of the mountain ranges that delimit it,
started to be eroded and to be converted into the source area of the majority of the materials that filled the Gulf of
Valencia and the abyssal plain of the Gulf of Lion.
At the beginning of the Pliocene, the connection between the Atlantic and the Mediterranean had been re-established.
By mid Pliocene, some 3 Ma ago, the level of the sea had not only been recovered but it had risen around 100 metres
above the present level, sufficient enough for some of the tectonic graben areas close to the coast to be once again
invaded by a shallow sea (figure 16).
Figur6 16: Paleogeographic reconstruction during the lower Pliocene, 4 Ma ago.
In the mouths of some rivers, some small Gilbert-type deltaic systems were formed. These are typical of the
Mediterranean Pliocene. On the edges of the intermontane depression of La Selva, basaltic volcanic effusions of certain
importance were produced.
From 2 Ma ago to the year 18 000 before common era
It is during the Pleistocene when the Iberian Peninsula acquired the rest of the geographical features that give it the
aspect we know today. From the point of view of geodynamics, from the late Pliocene, some 2 Ma ago, a period of
relative calm started, interrupted now and then by the volcanic eruptions located in the north-east area of Catalonia. But,
climatically, it was an epoch of great variability. After a time of benign climate, which was maintained from the late
Pliocene until the middle Pleistocene, from some 900 000 years ago, five glaciations took place separated by intervals of
warm climate, called interglacials (figure 17).
Figure 17: Climatic curves of the last million years (Pleistocene and Holocene); the even numbers indicate each one of
the glacial epochs and the odd numbers the interglacial warm periods. Detail of the Geological Time Table (ICC, 2006).
During the glacial epochs the snowfall exceeded the summer melting, and year after year, great quantities of ice
accumulated in the polar icecaps and in the areas with the highest reliefs (figure 18). While the glacial conditions were
maintained, the volume of water in the form of ice trapped in the polar ice caps caused the sea level to descend dozens
of metres below the actual level. Consequently, the water courses were strongly incised in the relief and deposited, in
their estuaries, gravels and sands in the form of coastal and delta fans. In the highest areas of the Pyrenees cirques and
valley glaciers were formed, which accumulated and transported boulders and fragments of rock to its moraine at the
same time as they eroded their beds, giving them the typical U-shaped valleys of glacial origin. In the areas with steep
slopes near the glaciers, areas known as periglacials, the repetitive freeze-melt process of the interstitial rock water and
the water retained in cracks and joints provoked mechanical fragmentation and the consequent accumulation of the
boulders and pebbles at the foot of the slopes in the form of typical talus scree.
Figure 18: The configuration of the Earth during the Pleistocene glacial epochs, with extensive polar icecaps.
During the interglacial epochs, a large part of the ice of the polar icecaps was melted, the level of the sea rose and the
water courses deposited the sediments that they transported in the banks of their beds. Far from the glacial areas,
those climatic changes were reflected in the formation of soil and carbonated crusts over the alluvial sediments and in
the periodic accumulation of fine-grained sediments such as loess, which were transported by the wind in the form of
dust clouds.
In the zones with extensive outcrops of calcareous rocks, of conglomerates with pebbles and carbonate cement or other
rocks soluble in water or in carbonic acid, karstification processes were developed that gave place to systems of
caverns, chasms and dolines. Some of those dolines evolved to true lacustrine areas. The waters saturated with calcium
carbonate settled at the exits of the karst systems and, in some cases, continue to settle at the present time, some
precipitates and carbonatic incrustations: the travertines. The changes of the base level, together with the combined
action of chemical dissolution and mechanical abrasion, provoked that, on crossing areas composed of carbonates, the
fluvial courses formed narrow and deep gorges.
Thus, during the Pleistocene, the incision of the drainage network continued to generate potential gaps that had a
tendency to fill. The reiteration over time of all the mentioned processes, lead to the formation of stepped terraces and
alluvial fans, to the gorges formation, to the formation of marine abrasive platforms, to the establishment of the fluvial
network almost as we know it nowadays and, finally, to the definition of the basic features of the present sculpture of the
landscape.
The last 18 000 years
Almost 18 000 years ago, very soon after the last glacial maximum, the sea level was a few dozen metres under the
present day level. The glaciers that covered the uppermost areas of the Pyrenees disappeared little by little and, in some
cirques and some hollows of the longitudinal profile of the valleys, small lacustrine basins were formed, sometimes
contained by the old moraines.
The progressive decrease of the extension of the polar ice caps provoked a sea transgression that flooded the coastal
lowlands and the ancient deltaic plains.
11 500 years ago when the Holocene started, the current geological period, the sea level had been stabilizing and was
about 2 metres above the present one. The greater part of the plains of Empordà, the Besòs, the Llobregat Delta and the
Ebre Delta were submerged. They were shallow bays, surrounded by alluvial lowlands, from which some small islands
emerged. Towards the year 1000 BC, the accumulation of sediments contributed by the rivers had considerably
increased the emerged areas and their landscape consisted of bogs and marshy lowlands. In the human settlements,
located in the periphery of these plains and also on some small islands, agriculture and stockbreeding started to
developed; the remains of Iberian villages are a good witness to this fact.
In historical times, the coastal plains of the Empordà, the Baix Llobregat and the Ebre had continued to grow with the
alluvia contributed by the rivers, so that towards the year 50, the coastline was already quite close to the actual one
(figure 19).
Figure 19: Reconstruction of the coastline, in blue, towards the year 50, with the situation of the main Roman cities on
the Catalan coast.
Durant l'Edat Mitjana, a causa de conflictes polítics i militars entre nobles veïns, alguns rius, com el curs baix del Ter,
foren repetidament desviats. A les zones de muntanya, de forts pendents, l'activitat antròpica va deixar la seva
empremta en el paisatge en forma de bancals i terrasses de conreu.
Més tard, al segle XVII, la desforestació de grans àrees de bosc es traduí en un augment considerable de les
aportacions dels rius i, en conseqüència, en un increment de la superfície emergida de les planes deltaiques i costeres.
El delta de I'Ebre assolí la seva extensió màxima cap a finals dels anys 10 del segle XX. Des de llavors, per raó de la
retenció de sediments en els embassaments de la seva conca, el volum de materials del delta roman pràcticament
constant. Els sediments disponibles ara són redistribuïts per l'acció dels corrents de deriva litoral, per les onades i, en
menor mesura, per les marees, de manera que la silueta del delta de l'Ebre tendeix a ser arrodonida, a l'estil de la del
delta del Llobregat. Durant la resta del segle XX el paisatge de Catalunya ha anat evolucionant amb pocs canvis, gairebé
tots deguts a l'acció antròpica fins a assolir l'aspecte que podem percebre actualment.
Global tectonic sketch maps
Evolution of the continents and the oceans from the Neoproterozoic until the present. In the maps, the change in the
position of the continental masses and the formation and the disappearance of the oceans that separate them should be
noted (originals of R. Blakey). The brown colour indicates the distribution of the orogenic belts in the emerged land; the
Hercynian and the Alpine - the two most important ones represented in Catalonia - have been situated. The red lines
represent the zones of subduction, and the yellow lines, with the direction of extension indicated by pairs of arrows, the
position of the mid-ocean ridges; in orange the position of the current Iberian Peninsula is represented. The displacement
of this from southern positions during the Proterozoic and the Paleozoic, the equatorial situation during the PaleozoicMesozoic boundary and the northern position during the entire Mesozoic and Cenozoic should be emphasized.
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