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Earth and Planetary Science Letters 205 (2002) 1^12
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The Mediterranean: Mare Nostrum of Earth sciences
Wout Krijgsman Paleomagnetic Laboratory ‘Fort Hoofddijk’, Budapestlaan 17, 3584 CD Utrecht, The Netherlands
Received 3 June 2002; received in revised form 3 October 2002; accepted 3 October 2002
Abstract
The Mediterranean area is one of the most appealing natural laboratories in the world to study geodynamic and
paleoclimatic processes on different scales. Consequently, the Mediterranean Sea can be considered as the Mare
Nostrum (‘our sea’) of Earth sciences. Its semi-enclosed land-locked configuration in a convergent setting between
Africa in Europe, in combination with its latitudinal position, makes the Mediterranean extremely suitable to study
both fundamental plate tectonic processes and astronomically induced oscillations in climate. For many years to
come, the Mediterranean will certainly remain a fascinating area, where an integrated and multi-disciplinary approach
will increasingly contribute to our understanding of geological, geophysical, geodetical and geochemical processes in
an accurate and high-resolution time-frame.
3 2002 Elsevier Science B.V. All rights reserved.
Keywords: Mediterranean region; geodynamics; paleoclimate; Miocene; gateways
1. Introduction
Ever since the ascent of western civilization
(about 3^4 kyr ago) the Mediterranean has been
a sea of mystery, leaving most societies puzzled
about the origin and evolution of the world on
which they lived. Earth scienti¢c processes had
major impact on Mediterranean history as complete cities and civilizations have been destroyed
by volcanic eruptions, destructive earthquakes
and rapid subsidence (e.g. Atlantis, Pompei, Izmit, Minoans) while entire subcontinents may
have been drowned during the dramatic sea-level
rise of Noah‘s £ood [1]. In the early days, these
* Tel.: +31-30-253-1672; Fax: +31-30-253-1677.
E-mail address: [email protected] (W. Krijgsman).
catastrophies were ascribed to the activity of angry gods, but only since the advent of the theories
of plate tectonics and astronomical forcing of ice
ages (less than 0.05 kyr ago) may we con¢dently
say that we are beginning to understand the
underlying mechanisms and geological processes.
Subsequently, the Mediterranean has always been
one of the best natural laboratories in the world
to study the fundamental geodynamic and paleoclimatic processes of the Earth. According to the
myth of Odysseus, the Greeks’ voyages of adventure were among the ¢rst to explore all corners of
the Mediterranean Sea. The only way out was
through the so-called Pillars of Heracles in the
west. If this narrow strait (of Gibraltar) was to
be passed one would enter the exterior oceans and
chances of returning were thought to be minimal
(Fig. 1). It is exactly this land-locked con¢guration of the Mediterranean which largely controls
0012-821X / 02 / $ ^ see front matter 3 2002 Elsevier Science B.V. All rights reserved.
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W. Krijgsman / Earth and Planetary Science Letters 205 (2002) 1^12
its geologic processes and which also makes it
such a unique recorder of past climate variations.
During the last decade, the Mediterranean area
has been the source of new insights of geodynamic and paleoclimatic processes on Earth. The complexity of the tectonically active land-locked Europe^Africa collision zone (Fig. 1) provides the
opportunity to study and understand fundamental
plate tectonic processes, like arc migration, slab
roll-back and slab detachment, in di¡erent evolutionary stages of subduction zones [2]. In addition, the semi-enclosed con¢guration in combination with its latitudinal position makes the
Mediterranean particularly sensitive to record, in
the geological archive, astronomically induced oscillations in climate [3]. Today, the functioning of
the Mediterranean Sea largely depends on the
water exchange with the open ocean and, as
such, on the geometry of the Strait of Gibraltar
[4]. Consequently, the paleogeographic evolution
of the Atlantic gateway is crucial for understanding the temporal and spatial distribution of sedimentation patterns in the Mediterranean basins
in terms of both the geodynamic and environmental (oceanographic, climatic) evolution. This is especially evident in the ongoing debates on the
processes that have led to the ‘Messinian Salinity
Crisis’, a dramatic event during which the water
exchange with the Atlantic was strongly reduced
and ¢nally cut o¡, leading to kilometers thick
evaporite deposits in a largely desiccated Mediterranean basin [5,6].
This paper reviews the most recent progress
made in our understanding of the geodynamic
and paleoclimatic processes in the Mediterranean
area. For this, the Mediterranean Sea is temporarily regarded as our ‘omphalos’, the center of the
world, like the ancient Greeks did earlier when
placing their omphalos in the city of Delphi.
This is justi¢ed as the Mediterranean is not just
the cradle of modern civilization or a nice holiday
resort for tired earth scientists, but also a highly
dynamic area which contains many answers to
fundamental earth scienti¢c questions locked inside its well-preserved geological records.
2. Mediterranean geodynamic evolution
The geodynamic evolution of the Mediterranean has been largely determined by the convergence of Europe and Africa, resulting from di¡erential spreading along the Atlantic oceanic ridge.
As a consequence, the African plate collided with
Eurasia while its gravitationally unstable oceanic
lithosphere slowly subducted under the European
margin. The total convergence can be estimated at
400^500 km in the west to about 1500 km in the
east, and led to the orogenic Alpine build-up as
well as to the consumption of the former Tethys
Fig. 1. Reconstruction of the Mediterranean area according to the Roman map of Marcus V. Agrippa (A.D. 20) and the plate
boundary evolution map of Wortel and Spakman [2] (A.D. 2000).
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Fig. 2. Present-day tectonic deformation snap-shots of the Mediterranean area compared to physical laboratory experiments.
Contoured geodetic rotation rates of the Aegean region (a) after Duermeijer et al. [12] compared with the honey-box experiments
(b) of Gautier et al. [10]. Tomographic images of the subducting slab underneath the Tyrrhenian basin (c) after Wortel and Spakman [2] compared with the glucose syrup box experiments (d) of Facenna et al. [17].
ocean. In spite of convergence acting as the primary plate tectonic process, the Mediterranean is
also known for its large-scale extensional basins
and its diverse tectonic arcs. They are mainly the
result of the typical land-locked con¢guration of
the Mediterranean region, in which slab roll-back
of the trench systems induced arc migration and
extension in the lithosphere above the subduction
zone [2]. Most of our knowledge on subduction
zones comes from present-day data, such as earth-
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W. Krijgsman / Earth and Planetary Science Letters 205 (2002) 1^12
quakes in Benio¡ zones or tomographic images,
which trace out snapshot images of subducting
slabs (Fig. 2c). Seismic tomography models of
the Mediterranean and surrounding regions have
been fundamental for locating and delineating the
subducted lithosphere [2,7]. They suggest that not
all slabs are connected to the lithosphere at the
surface, which has been interpreted as an indication for slab detachment. Slab detachment can
also migrate laterally since a small tear in the
slab will initiate lateral rupture propagation [2].
2.1. The Hellenic arc and the Aegean basin
In the eastern Mediterranean, the rotation motion of the African plate led to the closure of the
connection between the Tethys and the Indian
Ocean by the collision of the Arabian microplate
with stable Eurasia in the middle Miocene (Fig.
1). Disruption of this seaway had a profound effect on oceanic circulation patterns and caused a
major change in global climate into a much colder
mode (ice house state), while the ocean system
rapidly progressed towards modern conditions
[8]. The Aegean region represents a piece of continental lithosphere undergoing widespread extension in the general frame of Africa^Europe convergence. Most geodynamical models for the
eastern Mediterranean consider the initiation of
extension in the Aegean area as a direct consequence of southward migration of the Hellenic
subduction zone and/or lateral extrusion of Anatolia away from the Arabia^Eurasia collision
front [9]. The minimum age for the onset of extension on the scale of the whole Aegean is estimated at about 20 Ma, based on recent studies
within the Cenozoic metamorphic complexes [10].
This implies that the Aegean extension did not
result from the lateral extrusion of Anatolia, because the indentation of Arabia into Eurasia is
thought to have occurred less than 16 Ma. In
addition, numerical modelling of the stress ¢eld
and deformation also indicated that the role of
the lateral push of Anatolia is secondary to that
of slab roll-back in a land-locked basin setting
[11]. Paleomagnetic data from the entire Hellenic
outer-arc indicate clockwise rotations in the western and counter-clockwise rotations in the eastern
Hellenic arc [12]. These block rotations in the Aegean have now been accurately dated and point
towards a very rapid and young (Pleistocene) rotation phase. New space-based geodetic techniques ^ the Global Positioning System (GPS)
and interferometric synthetic aperture radar (INSAR) ^ are now capable of mapping crustal deformation with centimeter precision [13,14]. These
geodetic observations indicate that the rotational
movements in the Aegean area continue even today (Fig. 2a). Physical experiments that simulate
the horizontal spreading of a continental lithosphere toward a free boundary are also in good
agreement with the observed rotations (Fig. 2b;
[10]).
2.2. The Calabrian arc and the Tyrrhenian basin
The opening of the western and central Mediterranean took place mainly in the last 30 Myr by
two rapid episodes of trench migration and backarc opening, which consumed the westernmost extension of the Tethys and created the small oceanic basins we see today (Fig. 1). During the ¢rst
episode, the Algero^Provencal basin opened as a
result of radial back-arc extension caused by rollback of a subducting slab. This phase was accompanied by the counter-clockwise rotation of the
Corsica and Sardinia blocks, possibly including
the Epiligurian units of the northern Apennines
of Italy as well [15]. The rotation ended somewhere in the Langhian ( Q 16 Ma) and was followed by slab detachment along the northern
African margin, according to the model of Carminati et al. [16]. Secondly, an eastward shift of
active extensional deformation resulted in the
opening of the Tyrrhenian basin during the Tortonian to Quaternary. GPS data shows that the
outward migration of the Calabrian arc has
nowadays almost ceased [14], which supports the
conclusion that slab detachment processes under
Calabria have just been completed [2]. Recently
developed laboratory experiments show that the
fast and episodic retreat of the subducting slab is
dynamically consistent with the gravity-driven
subduction of an oceanic lithosphere interacting
with the 670-km discontinuity in the upper mantle
([17] ; Fig. 2d).
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2.3. The Gibraltar arc and the Alboran basin
The geodynamic evolution of the Gibraltar arc
is still subject to controversy. Much of the debate
is focused on the mechanisms required to generate
rapid late-orogenic extension with coeval shortening and on the origin of the Alboran Sea together
with the surrounding Betic^Rif mountain belts in
Morocco and Spain [18,19]. This orocline developed during convergence between Africa and Iberia in late Mesozoic to Tertiary times. Tectonic
models that account for its geometry and evolution include: (a) rapid westward motion of a rigid
Alboran microplate, (b) suduction zone roll-back
and (c) radial extensional collapse caused by rapid
convective removal or delamination of lithosperic
mantle. Recent tomographic images of the Gibraltar area have clearly visualized the remnants of
lithospheric slab structures underneath the Alboran Sea [20]. Paleomagnetic data indicate that
large rotations about vertical axis have also taken
place, with counter-clockwise rotations in the Rif
Mountains and clockwise rotations in the Betic
Cordillera [21]. More detailed tomographic images and the exact timing of these tectonic rotations in the Gibraltar arc are still subjects of
ongoing studies. In addition, controversy also surrounds the timing of closure and paleogeography
of the late Miocene marine passages across the
Gibraltar arc [22]. The intramontane basins of
the Betics and Rif began to form during the late
Miocene, by vertical motions produced by tension
perpendicular to compression. This resulted in the
development of two marine gateways which were
5
progressively closed during the late Miocene by a
complex interplay of both tectonic and glacio-eustatic processes [22,23]. The present-day connection through the Strait of Gibraltar is generally
considered to have opened completely at the beginning of the Pliocene [5].
3. Mediterranean paleoclimate records
The theory that (paleo)climate change is dominantly related to perturbations in the Earth’s orbit is at present widely accepted, and astronomical
‘Milankovitch’ cycles are recognized in many sedimentary records of di¡erent depositional environments. The Earth’s orbit around the sun is in£uenced by gravitational interactions with other
planets and with the moon. The resulting orbital
perturbations give rise to variations in eccentricity, obliquity and precession with main periods of
400 and 100 kyr, 41 kyr, and 23 and 19 kyr,
respectively (Fig. 3). These variations in the
Earth’s orbit are climatically important because
they a¡ect the global, seasonal and latitudinal distribution of incoming solar insolation. They are
held responsible for the Pleistocene ice ages but
also a¡ect low-latitude climate, such as the African (and Indian) monsoon system. Orbitally
forced climatic oscillations are recorded in sedimentary archives through changes in physical,
biological and chemical properties. For example,
during relatively dry periods eolian dust of Saharan origin (with high Ti/Al ratios, palygorskite and
kaolinite) is transported to the Mediterranean,
Fig. 3. Overview of the variations of the Earth’s orbit and rotational axis.
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Fig. 4. Location and cyclostratigraphic results of ODP Site 967 from Lourens et al. [3]. The left-hand ¢gure shows the trajectory
of a typical east Mediterranean dust storm which deposits high amounts of Titanium (Ti) in the shaded area during relatively
arid conditions in northern Africa. Sapropels (S62^S69) are indicated by low color-re£ectance values. On the right, the Ti/Al record of Site 967 shows cyclic variability and can consequently be exactly correlated to the summer insolation curve (modi¢ed after
Lourens et al. [3]), providing an unambiguous and high-resolution time-frame. Insolation maxima are labelled (234^276) with
their corresponding insolation-cycle codi¢cation [24].
while during relatively wet periods riverine detrital input (with low Ti/Al ratios, smectite and
chlorite) is dominant (Fig. 4). The Mediterranean
has the unique advantage that its latitudinal position in combination with its semi-enclosed, landlocked con¢guration make its sedimentary record
particularly sensitive to these astronomically induced oscillations in climate.
3.1. Mediterranean astrochronology
The Neogene marine sequences of the Mediterranean provide high-resolution information with
regard to the history of climate change and watermass circulation in semi-enclosed marine basins.
In the last decennium, the sedimentary cyclicity of
these sequences has been used to construct astronomical timescales, which provided a signi¢cant
breakthrough in the dating of the geological record [6,24,25]. The construction of such timescales
involves the calibration of sedimentary cycles or
other cyclic variations in sedimentary sequences
to computed astronomical time series of past variations in the Earth’s orbit or to derived target
curves (Fig. 4). Following the early tuning attempts for the late Pleistocene [26] the astronomical timescale has ¢rmly been established for the
last nine million years and now underlies the standard geological timescale for the Plio^Pleistocene
[27]. In turn, the paleoclimatic records of the
Mediterranean are so exceptionally accurate that
they can be used to test the accuracy of the di¡erent astronomical solutions for the Earth’s orbital
elements [24]. In particular, they shed light upon
the changes in the tidal dissipation and dynamical
ellipticity of the Earth through time, which may
have signi¢cant consequences for mantle viscosity
models [3]. Moreover, it could be derived from
these records that the Plio^Pleistocene ice load
has caused an average acceleration in the Earth’s
rotation over the past three million years [3].
Today, the Mediterranean astronomical timescale has been extended to 13 Ma based on the
marine records which contain the well-known cyclic sapropel sequences [25]. Astronomical tuning
revealed that these dark, organic-rich layers correspond to precession minima and insolation
maxima, and that they are related to enhanced
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£uvial run-o¡ connected to the intensi¢cation of
the African monsoon system [28]. Sapropel formation thus corresponds with relatively wet and
warm climate phases and, as such, the oxygen
isotope record can be used as a guide for correlation purposes. The debate on the exact mechanisms which led to sapropel formation, however,
still remains contentious and unresolved [29,30].
Proposed mechanisms include a change to anoxia
or an increase of primary productivity as the
dominant mechanism, but it may well be that
both processes also in£uence each other. Evidence
for higher productivity comes from chemical analyses of productivity proxies [31], while anoxic
conditions are indicated by the sedimentary facies,
by inorganic geochemical analyses and by isotopic
composition of organic matter [32]. Recently, a
new variant emerged, suggesting that sapropel
formation occurred under oligotrophic conditions
in the sea surface and in association with strati¢ed
conditions in hydrographic fronts [33].
7
show that in several basins regular subsidence was
balanced by a continuous sedimentation without
major hiatuses [34,35]. In addition, it could be
unambiguously demonstrated that the sedimentary cyclicity of these continental successions was
also astronomically controlled, resulting in lakelevel oscillations caused by periodic changes in
climate. For the ¢rst time, long continuous records of continental climate proxies (pollen, mammals, etc.) can now be correlated on a precessional bed-to-bed scale (i.e. 6 10 kyr) with the time
equivalent marine proxy records (oxygen isotopes,
sea-surface temperature, etc.). Recent progress in
palynology revealed that, apart from high-resolution climate variability, changes in paleoaltitude
can also now be semi-quanti¢ed [36]. Clearly,
this will be extremely helpful in the reconstruction
of the paleoclimatic and paleogeographic evolution of the circum-Mediterranean area.
4. Mediterranean^Atlantic connection
3.2. Marine^continental correlations
Until recently, the construction of the astronomical timescale was entirely based on these marine sapropel-bearing sequences. For paleoclimate
and paleoenvironment reconstructions, however,
the inclusion of the continental record would be
very helpful since a comprehensive understanding
of paleoclimate and paleoclimate change is only
achieved by accurate and high-resolution time
stratigraphic correlations between the continental
and marine record. In fact, the terrestrial sedimentary record seems to be the logical place to
look for Milankovitch cycles because, in the absence of oceanographic processes with their intrinsic and complicated non-linear feedback mechanisms, a more direct registration of orbitally
induced changes in climate may be expected. A
potential serious drawback of using continental
successions has been the usual lack of a direct
and su⁄cient time control, also because of the
assumed common occurrence of hiatuses which
may result from intermittent erosion caused by
tectonic activity, base-level changes and autocyclic
processes. High-resolution magnetostratigraphic
studies on Neogene continental sections, however,
The opening and closure of (inter)oceanic gateways is critical in controlling oceanic (paleo)circulation. A prime example is the disruption of the
Tethyan Seaway along the African^Eurasian collision zone: closure of the connection to the Indian Ocean likely triggered the middle Miocene
climate transition [8], while closure of the Atlantic
gateways in the late Miocene resulted in the ‘Messinian Salinity Crisis’ of the Mediterranean [6]. At
present, an anti-estuarine water circulation exists
within the Mediterranean (Fig. 5). This circulation pattern is driven by a number of interactive
factors, but the most important are the climate
and bathymetry of the region [29]. In the
present-day situation of the Mediterranean, the
loss of water by evaporation is more than double
the gain by precipitation and run-o¡. This inequality drives the circulation across much of
the basin and produces an out£ow of saline
warm water at depth across the sill of Gibraltar
and a surface in£ow of less saline Atlantic water
(Fig. 5). Restricting this out£ow would ultimately
result in the precipitation of evaporites, which has
repeatedly taken place in the strongly restricted
circum-Mediterranean basins. Prime examples
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W. Krijgsman / Earth and Planetary Science Letters 205 (2002) 1^12
Fig. 5. Schematic diagram depicting climate and water-mass circulation for the present-day Mediterranean basin during summer.
WMDM = Western Mediterranean Deep Water; EMDM = Eastern Mediterranean Deep water; MIW = Mediterranean Intermediate Water; LIW = Levantine Intermediate Water. Figure is modi¢ed after Cramp and O’Sullivan [29].
are the middle to late Miocene evaporites of the
Red Sea basin, the middle Miocene salt deposits
of the Carpathian foredeep and the Messinian
evaporites of the Mediterranean.
4.1. The Messinian Salinity Crisis
The Messinian Salinity Crisis of the Mediterranean is widely regarded as one of the most dramatic episodes of oceanic change in Neogene
history [5,6]. Earliest explanations were that extremely thick evaporites were deposited in a
deep and desiccated Mediterranean basin that
had been repeatedly isolated from the Atlantic
Ocean, but elucidation of the causes of the isolation ^ whether driven by glacio-eustatic or tectonic processes ^ had been hampered by the absence
of a reliable and accurate time-frame. Recently,
however, an astronomically calibrated chronology
has been developed for the Mediterranean Messinian based on integrated high-resolution stratigraphy and ‘tuning’ of sedimentary cycle patterns
to the astronomical curves [6]. It showed that the
onset of evaporite precipitation, astronomically
dated at 5.96 Ma, was remarkably synchronous
over the entire Mediterranean basin and that the
origin of the Messinian Salinity Crisis was domi-
nantly tectonic, although its exact timing may well
have been controlled by the V400 kyr component
of the Earth’s eccentricity cycle.
Underlying the Messinian evaporites, cyclically
bedded diatomites are generally present in most
Mediterranean sequences, suggesting that the diatomaceous facies is an essential part of the lithological sequence associated with basin restriction
[37]. Despite intensive studies, the origin of these
diatomites remains highly controversial. Partly
opposing scenarios explaining cyclic diatomite
formation include intensi¢cation of Atlantic in£ow, periodic upwellings, surface water warming,
enhanced £uvial run-o¡, global sea-level rise and
pulsating tectonics. Finally, diatomite deposition
may as well be related to the proliferation of diatom species typically adapted to £ourish under the
low-illuminated waters of the thermocline and nutricline, the phytoplankton referred to as the
‘shade £ora’ [33].
4.2. The Mediterranean^Atlantic gateways
Most paleogeographic reconstructions of the
western Mediterranean indicate that the Strait of
Gibraltar originated in early Pliocene times. In
the late Miocene, however, at least two other con-
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W. Krijgsman / Earth and Planetary Science Letters 205 (2002) 1^12
nections between the Mediterranean and Atlantic
existed : the Betic Corridor through southern
Spain and the Ri¢an Corridor through northern
Morocco (Fig. 6b). Based on the sedimentary sequences from the basins in the eastern Betics in
Spain, it was claimed that the Betic Corridor
closed already somewhere in the Tortonian [22,
38]. Hence, the evaporitic sequences of these basins correspond to a ‘Tortonian salinity crisis’ and
are signi¢cantly older than the Messinian evaporites of the Mediterranean [37]. In addition, it
became evident that at least the southern margin
of the Ri¢an Corridor was emergent from 6.0 Ma
onward, while the ¢rst mammal exchange between
Africa and Europe took place at 6.1 Ma, i.e. earlier than the onset of the Messinian Salinity Crisis
[22,23]. At present, the major environmental
changes in the Mediterranean cannot yet be compared to tectonic and climatic events in the gateways, although it seems inevitable that the lithological transitions from open marine marls to
diatomites and evaporites in the Mediterranean
are the result of restriction and/or closure processes in one or both of the gateways. The new Messinian astrochronology can now be used for accurate dating of the sedimentary sequences of the
gateway basins. It is especially relevant to know
and understand the exact timing and mechanism
of closure as well as the paleobathymetric history
of the Mediterranean^Atlantic gateways. Current
quantitative modelling studies of Mediterranean
9
paleoceanography and resulting depositional environments are critically dependent on such data.
5. Forward to the past
The topography and geography of the Mediterranean area, as we know it today, are perfectly
pictured by very accurate satellite images. Even
detailed images of the deep mantle structure of
the Earth can be obtained from tomographic
studies. It is foreseen that ongoing research aiming at an even higher detail of resolution and the
increase of new seismic and GPS stations in the
circum-Mediterranean area will provide a wealth
of new and more accurate data on the ongoing
movements of the di¡erent structural domains,
both in the horizontal and in the vertical plane.
This will provide important observations for numerical modelling studies aiming at our physical
understanding of the underlying mechanisms. The
present-day climate of the Mediterranean area can
also be perfectly measured, since very detailed
oceanic and atmospheric records are continuously
obtained by the numerous weather stations all
around the area. Nowadays, signi¢cant research
e¡ort is directed at the understanding of Holocene
climate change, especially in the context of determining the exact contribution of human activity
to the increasing global warming related to the
greenhouse e¡ect, and the short-term climate
Fig. 6. GIS-based reconstructions by E. van Assen (personal communication, 2002) of the Mediterranean^Atlantic gateway(s)
during (a) the late Tortonian and (b) the present-day, after detailed investigations of various paleogeographic reconstructions (altitudes are only schematic).
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change on annual to sub-Milankovich timescales.
Oceanic and atmospheric science will bene¢t substantially from these e¡orts in the coming years.
In addition, a combined research e¡ort in applying current global climate models to archives of
past climate (e.g. before the onset of glaciations)
will aid in understanding paleoclimate and paleoceanography and in testing the robustness of
such climate models, which in turn will help us
to better understand the oceanic and atmospheric
systems that determine our present climate.
Taking steps back in time, the situation becomes increasingly complicated. The paleogeographic con¢guration of many areas is still
insu⁄ciently known and, consequently, the paleoceanographic processes are di⁄cult to reconstruct. For instance, the most important sills and
straits that determined the Mediterranean paleocirculation patterns have continuously been subject to tectonic activity, as both the Gibraltar and
Calabrian arc experienced signi¢cant vertical and
horizontal motions. This was caused by fundamental changes in the con¢guration of the western Mediterranean subduction zone, but it is very
di⁄cult to determine exactly in what stage they
were. Moreover, many paleogeographic reconstructions are still subject to controversy, such
as the development of the connection to the Paratethys (the former Black Sea) in both time and
space. Sea surface temperatures and sea-level £uctuations can be reconstructed from detailed stable
isotope curves (N18 O), but changes in humidity
and temperatures on land are still uncertain and
must be derived from detailed palynological and
fossil mammal studies. It is therefore fortunate
that a detailed astrochronological framework is
available for both the marine and continental
realm which allows to correlate and discriminate
between the di¡erent tectonic and climatic events.
Only a multi-disciplinary approach in which all
data are reliably tuned into an accurate timeframe will allow a more detailed comprehension
of the geodynamic and paleoclimatic evolution of
the Mediterranean during its late Neogene evolution. An important step forward will be taken
when a series of deep cores is authorized to be
drilled through the Messinian evaporites in the
various Mediterranean basins, allowing the tuning
of all individual evaporite cycles to the astronomical curve and access to the older archives of the
deepest Mediterranean basins. This will be possible when the new Japanese ship ^ with advanced
drilling techniques ^ of the IODP project will visit
the Mediterranean during one of its forthcoming
campaigns.
If we go further back in time to the middle
Miocene, the situation is even more complex.
During this interval, several important changes
took place, such as the closure of the connection
between the Mediterranean and Indian ocean, the
expansion of the Antarctic ice cap, massive salt
deposits in the former Black Sea area in eastern
Europe, and the onset of near modern oceanographic conditions. At present, however, a reliable
time-frame is still absent, which makes it very
di⁄cult to distinguish between causes and consequences of the various events. Extension of the
Mediterranean astronomical timescale is in progress but it will be di⁄cult to stretch it beyond 15
Ma, due to the lack of suitable successions. There
is still hope, however, since extra-Mediterranean
sequences have enormous potential as well and
are currently under investigation [39,40]. In any
case, the construction of high-resolution timescales for older ages ^ whether or not imported
from extra-Mediterranean sequences ^ will remain
crucial for extending our knowledge and understanding of the major geodynamic and paleoclimatic processes that took place in the geological
past of the ‘Mare Nostrum’ of Earth sciences.
Acknowledgements
I would like to thank Cor Langereis, Charon
Duermeijer, Esther van Assen, Frits Hilgen, Luc
Lourens and Wim Spakman for their input and
stimulating discussions and Judith McKenzie,
Rob van der Voo and an anonymous reviewer
for their constructive comments.[AH]
References
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Wout Krijgsman is a member of the
paleomagnetic
laboratory
‘Fort
Hoofddijk’ of the Utrecht University,
the Netherlands. He has recently acquired an innovation impulse from
the Netherlands Organization of Scienti¢c Research (NWO/ALW) on the
subject ‘Geodynamics and Climate’.
His main research interests are integrated stratigraphic studies of marine
and continental sequences, the construction of (astronomical)
timescales and, in particular, their application to geodynamic
and tectonostratigraphic reconstructions and sedimentary basin analysis.
EPSL 6450 28-11-02 Cyaan Magenta Geel Zwart