49) - EROSIONAL PROCESSES AND PALEO-ENVIRONMENTAL CHANGES IN THE GULF OF LION (SW FRANCE) DURING THE MESSINIAN SALINITY CRISIS (5.96-5.32 MY)
Johanna LOFI1, Serge BERNE2, Georges CLAUZON3, Christian GORINI4, William B.F. RYAN5 and Mike STECKLER5
1: ISMAR- CNR- Via Gobetti, 101, 40 129 Bologna, Italy. (johanna.lofi@bo.ismar.cnr.it)
2: IFREMER, DRO/GM Technopôle Brest-Iroise, B.P. 70, 29 280 Plouzané, France.
3: CEREGE, Europôle de l’Arbois, 13 545 Aix-en-Provence Cedex 04, France.
4: Université de Lille 1, SN5 F, 59 655 Villeneuve d'Ascq Cedex, France.
5: Lamont-Doherty Earth Observatory, Palisades, NY 10964, USA
The interpretation of the Messinian Salinity Crisis (MSC) currently involves the partial desiccation of the Mediterranean sea coupled with the deposition of thick evaporites in the deep basins. In the Gulf of Lions, new sets of seismic data (TotalFinaElf, IFREMER) confirm the basinward extent of the Messinian erosion and allow the mapping of distinctive Messinian seismic markers indicating the erosional surface, basin-margin detrital deposits and evaporite sequence. The geometrical relationship among these three elements and their relation to the paleogeography of the margin during the MSC provide information concerning the past evolution of this area The Messinian erosional surface (MES), correlated with the “desiccation” phase (and deposition of deep evaporites), is commonly interpreted as a subaerial feature. In the Gulf of Lions, the MES is a complex diachronic polygenic erosional surface, whose morphology reflects a buried drainage pattern, supporting the interpretation of fluvial erosion driven by a substantial sea level drop. However, our results also suggest that large submarine gravity flows occurred prior to significant accumulation of salt and upper evaporites in the basin. As a result, interbedded clastic deposits may account for the conformable reflectors of the so-called deep "lower evaporites". Since erosion by rivers persisted all along the MSC, salt and upper evaporites may also contain a large part of detrital sediments. Thanks to the improved quality of seismic data, fan-shaped Messinian accumulation are becoming evident in the downstream part of the main Messinian valleys (Nile, Var, Spanish rivers…). The depositional reconstructions generally involve a substantial sealevel fall coupled with deltaic/pro-deltaic accumulations. Over the study area, a chaotic seismic unit filling Messinian lows and extending beneath the salt is interpreted as a Messinian clastic unit. We propose a polyphased scenario of detrital fan edification, involving ante-, syn- and post-salt deposition in subaqueous/subaerial environments. In the Gulf of Lions, an upper Miocene tectonic phase may have played an important role in the Messinian fluvial network organisation and in the maximum erosion and detrital fan depocenter location. To progress in our understanding of the Messinian event, we need to compare the evolution of other margins presenting contrasting tectonic, morphologic and geologic settings. This should be initiated during the Eclipse II French program. This work has been supported by the GDR "marges" and Eclipse I French programs.
Presentation (PDF - 2,6 Mb)
50) - THE MIOCENE/PLIOCENE TRANSITION IN THE GULF OF LION FROM EXPLORATORY BOREHOLE DATA AND SEISMIC PROFILE ANALYSIS
Johanna LOFI1, Christian GORINI2, Serge BERNE3 and Alain MAUFFRET4
1: ISMAR- CNR- Via Gobetti, 101, 40 129 Bologna, Italy (johanna.lofi@bo.ismar.cnr.it)
2: Université de Lille 1, SN5 F, 59 655 Villeneuve d'Ascq Cedex, France.
3: IFREMER, DRO/GM Technopôle Brest-Iroise, B.P. 70, 29 280 Plouzané, France.
4: Laboratoire de Tectonique, Université Pierre et Marie Curie, 75252 Paris Cedex 05, France.
Scant information exists about how rapid the sea-level rise was at the end of the Messinian Salinity Crisis (MSC). At the present day, studies of the Messinian peripheral successions led to varied interpretations regarding the duration of refilling (a few thousand years (Clauzon et al., 1996) vs. &Mac197; 200 000 years (Krijgsman et al., 1999)). In the Gulf of Lion, seismic profiles (TotalFinaElf and Ifremer) and data from nine exploratory boreholes allowed the investigation of the offshore Miocene/Pliocene transition. The architecture of the western margin consists in a thick faulted Miocene sequence eroded at the top by a major discontinuity corresponding to the Messinian Erosional Surface (MES). This surface extends downslope beneath the upper evaporites and salt accumulated above the abyssal plain during the "desiccation" phase. The post- Messinian deposits consist in a thick Plio-Quaternary sequence, which deposited since the Early Pliocene and led to the progradation of the margin as much as 120 km seaward (Lofi et al., 2003). The MES was tied to boreholes. Lithologic descriptions after drilling reports and biostratigraphic analysis carried out by Cravatte et al. (1974) on four of the wells confirm the presence of a major discordance at the base of the Plio-Quaternary sequence. Beneath the shelf, the Pliocene/Miocene transition mostly consists in a sharp contact between Lower Pliocene clays (occurrence of Globorotalia margaritae and/or Sphaeridinellopsis subdehiscens) and some deposits of varied ages and lithologies (ex. Jurassic dolomites in the Cicindèle borehole, Lower Langhian clays in Agde Maritime…). Downslope, the Lower Pliocene sediments drilled in GLP2 (MPL1 biozone, acme of Sphaeroidinellopsis subd.) overly a 300 m thick sequence composed of alternating salt, anhydrite and marls, corresponding to the upper Messinian evaporites. Over the shelf and slope, dip seismic profiles clearly evidence that the Lower Pliocene clinoforms downlap on the MES, showing that the new margin prograded directly over the eroded margin. Despite the seismic resolution scale (30-50 m), the absence on of any transgressive system tracts at the base of the Plio-Quaternary sequence is in agreement with the abundance of planctonic microfauna recovered in the deposits just above the MES. Transgressive sediments may nevertheless have deposited in the axis of the Messinian valleys as the river mouths retreated during the re-filling of the basin. In the Gulf of Lion, as in the rest of the Mediterranean, the Miocene/Pliocene boundary corresponds to the reestablishment of open marine circulation after the MSC. At least in the offshore domain, seismic and borehole data support the idea of a rapid marine Lower Pliocene transgression at the achievement of the crisis. This work has been supported by the GDR "marges" and Eclipse I French programs.
51) - NUMERICAL MODELING OF THE MESSINIAN SEA-LEVEL FALL: SOME IMPLICATIONS ON EROSION DYNAMICS
Nicolas LOGET*, Jean VAN DEN DRIESSCHE, Julien BABAULT and Philippe DAVY
Géosciences Rennes, UMR 6118, Université de Rennes 1, Campus de Beaulieu, Avenue du Général Leclerc, 35042 Rennes cedex, France
By using a surface process model (EROS) we investigate the consequences of the dramatic sea-level fall on erosion dynamics during the Messinian. The erosion law include in the model belongs to the classical power-law framework, where the erosion flux depends on local slope and water flow. The transfer model is completed by a transfer or deposition terms, allowing to simulate many kind of rivers. We first model the morphological evolution of the Rhone valley, which is one of the best documented Messinian canyons, in order to calibrate the parameters of the erosion law used in EROS. Starting from realistic pre- Messinian topography, we then simulate erosion dynamics at the scale of the Western Mediterranean, with particular attention to the Strait of Gibraltar and the Ebro River. Until now, mechanisms proposed for both the initiation and the end of the Messinian Salinity Crisis (MSC) are related to external forcing, i.e. tectonics (Weijermars, 1988; Krijgsman et al., 1999; Duggen et al., 2003) combined in a more or less complex way with global eustasy (Kastens, 1992; Hodell et al., 1994; Clauzon et al., 1996; Krijgsman et al., 1999). Although a major effect of the Mediterranean sea-level drop was the dramatic increase of continental erosion, this “internal forcing” as a plausible cause for the end of the MSC has been poorly considered. Recently Blanc (2002) has argued by examining the morphological evolution of the Strait of Gibraltar that its opening was achieved through retrogressive erosion by an eastwards-flowing Messinian stream. Hsü et al. (1973) first suggested a similar interpretation but involving a westwards-flowing stream that might be turned into a tidal inlet. According to Blanc (2002), the retrogressive erosion might be able to attack in the rear the Atlantic continental slope but the difference in base-level on each side of the Gibraltar isthmus during the MSC (i.e. much lower base level on the Mediterranean side) rather suggests a piracy phenomenon by an eastwards-flowing stream. The present modeling shows that using pertinent parameters, the “internal hypothesis” of a re-flooding of the Mediterranean by the capture of the Atlantic waters due to erosion of the Gibraltar threshold is viable. The Ebro Basin in NE Spain corresponds to the southern foreland basin of the Pyrenees with a Tertiary sedimentary fill. Until the end of the Eocene, the basin was open towards the Atlantic Ocean. Further tectonic shortening along the Pyrenees and the Iberian Range closed this western marine connection, resulting in endorheic drainage and lacustrine sedimentation during the Oligocene and the Miocene (e.g. Coney et al. 1996). At present the Ebro basin is drained through the Ebro River toward the Mediterranean Sea. When does the piracy of the endoreic Ebro basin exactly occur is still the subject of debate. For some authors the capture started during the Late Miocene (around 10 Ma) (Garcia-Castellanos et al., 2003), but for others it was induced by the Messinian Salinity Crisis (MSC) (e.g.Nelson and Maldonado, 1990). The present drainage area of the Ebro basin (A=0.9.105 Km2) is similar to that of the Rhone (A=1.105 Km2). We first show that the main pre-Messinian drainage areas were of the same order as the present ones. If the Ebro basin had been connected to the Mediterranean before or during the MSC, then deep canyons would have entered the Ebro Basin, but none has been identified at present. We conclude that the Ebro basin as a whole was not connected to the Mediterranean before the Pliocene.
52) - SYNTHETIC MESSINIAN DINOFLAGELLATE CYST RECORD FROM SICILY
Laurent LONDEIX
Département de Géologie et Océanographie, UMR CNRS 5805, Université Bordeaux 1, avenue des facultés, 33405 Talence cedex, France (l.londeix@epoc.u-bordeaux1.fr)
Surficial hydrological conditions prevailing before, during and after the Messinian salinity crisis in Sicily have been approached using dinoflagellate cyst records. The synthetic sequence considered is based on 5 outcrops from the Caltanissetta Basin. Following interpretations are supported by the use of newly enlarged modern dinocysts data base (e.g. Henry et al., 2003; Londeix, 2004). All along the Sicilian Messinian sequence, dinocyst taxa encountered are thermophylous and no important climatic change is expressed. During the Tripoli deposition (Capodarso section), sea surface conditions are marine (neritic), with some slight discrepancies to normal salinities at the base of the sequence (abundance of Homotryblium spp.) in a context of cyclic sea level changes, as expressed by relays between neritic and oceanic taxa dominances. Thin clayey layers interbeded in the salts of the Lower Evaporitic Complex (Realmonte and Racalmuto mines) provided numerous palynomorphs, but with several antagonist signals [concomitant variations of neritic and oceanic taxa percentages; concomitant variations of Messinian and reworked dinocyst concentrations; and concomitant abundance of confined environment taxa (Homotryblium spp.) and very high dinocyst diversity]. That evidences strong mixings of autochtonous, allochtonous and reworked dinocyst populations. Abundance of Prasynophyceae algae in such levels indicates a fluviatile influence. It is of note that taxa present in modern slightly sub-saline water (e.g. Pyxidinopsis spp.) show an increase of their percentages in these levels. The river inputs appear weaker during the deposition of the clays of the Upper Evaporites Complex (Eraclea Minoa section), and dinocyst assemblages give evidence of a shallow marine context. In the Lago Mare clays of Eraclea Minoa, the dinocyst assemblages are dominated by taxa, which tolerate confined environment with salinities aside from normal marine ones until more than 10‰ (e.g. Homotryblium spp., Lingulodinium machaerophorum). River inputs are still present. These fluviatile inputs went on during the deposition of the Arenazzolo silts, and the very high concentration of cretaceous reworked dinocysts could give evidence of intensified terrestrial erosion. The dominance of confined environment dinocysts indicates brackish to marine water, but the more peculiar feature is the presence, at the base of this formation, of Galeacysta etrusca, a species though to become from Paratethys surficial sea waters. The transition to the Pliocene calcareous marls of Trubi is extremely sharp and marked, as early as the lowest base of the formation, by the strong dominance of oceanic species (e.g. Impagidinium patulum, Nematosphaeropsis labyrinthus).
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53) - RADIATION OF LACUSTRINE COCKLES (LYMNOCARDIINAE; BIVALVIA) IN THE PARATETHYS AND ITS IMPLICATIONS FOR THE ”LAGO MARE”
Imre MAGYAR
T035168 MOL Rt., H-1039 Budapest, Batthyany u. 45, Hungary
The lacustrine (non-marine) cardiid bivalves (subfamily Lymnocardiinae) are perhaps the most characteristic members of the modern and ancient "caspi-brackish" faunas of southern and southeastern Europe. These faunas flourished primarily in the Paratethyan basins during intervals of restricted or closed marine connections, and also appeared in the Mediterranean "Lago Mare". There were four major radiations of Lymnocardiinae since the Oligocene. In all four cases, marine Cerastoderma is proved or suspected to be the ancestral form; Cerastoderma itself is assigned to Lymnocardiinae. The first two events can be classified as "simple" radiations. They took place in the Early Oligocene and Early Miocene, respectively, and led to the appearance of a few endemic genera. These were relatively short-term events, affecting the entire Paratethys. With re-establishment of normal marine conditions, the endemic cardiid genera went extinct. The next two events, however, were more complex and longlasting. Complexity was caused by apparently chance events; some representatives of a given endemic fauna survived the environmental change that exterminated the rest of the fauna, and continued to radiate under the new environmental conditions. Survival could be either in situ or associated with migration. The complex radiations generally involved individual basins rather than the entire Paratethys, and produced dozens of endemic genera. The first complex radiation commenced in the Middle Miocene and lasted until the Early Pleistocene. Temporally and geographically it consisted of three parts: started in the Middle Miocene in the entire Paratethys (Sarmatian "Sea"), continued in the Late Miocene in the Pannonian basin (Lake Pannon), and ended in the Late Miocene to Early Pleistocene in the Eastern Paratethys (Ponto-Caspian region). The second complex – twofold – radiation started in the Caspian basin in the Late Pliocene, and continued in the Pleistocene to present in the Caspian Lake and Black Sea. Within the time frame of the Messinian, Lymnocardiinae inhabited two Paratethyan waterbodies: Lake Pannon and the Pontian ?lake of the Eastern Paratethys, the Aegean basin, and they also appeared in the Mediterranean ”Lago Mare”. Stratigraphic correlation between these basins is still far from being satisfactory, although now a consensus seems to emerge concerning the correlation of the Pontian Stage with the Upper Messinian. The base of the Pontian Stage of the Eastern Paratethys is characterized by a sudden appearance of a Lymnocardiinae association. The Russian school, which gave the best experts of non-marine cardiids ever, traditionally holds that the majority of these forms, namely Euxinicardium, Pontalmyra, Pseudocatillus, Prosodacnomya, Eupatorina, and Paradacna originated in the northern, freshened part of the Messinian Mediterranean Sea (?Aegean basin) from where they migrated into the Black Sea basin at the beginning of the Pontian. Stratigraphic and evolutionary study of Lake Pannon Lymncoardiinae, however, shows that with the exception of Eupatorina, these genera appeared in the Pannonian basin during the Tortonian. The stratigraphic data thus seem to support the following migration routes for Lymnocardiinae: Lake Pannon (Tortonian) - Euxinian basin (Early Pontian) - Aegean basin (Late Messinian) -Mediterranean (latest Messinian, ”Lago Mare”). Study supported by OTKA
54) - EVIDENCES FOR EROSIONAL EPISODES AND “LAGO-MARE” TYPE ENVIRONMENT IN THE MESSINIAN UNITS OF THE VALENCIA TROUGH
Agnès MAILLARD1, Christian GORINI2 and the SESAME3 group
1: LMTG, UMR 5563; 14, avenue Edouard Belin, 31400 Toulouse, France.
2: Université de Lille 1, Laboratoire P.B.D.S. (UMR 8110), SN5 F, 59 655 Villeneuve d'Ascq Cedex, France.
3: Virginie GAULLIER (LEGEM, Univ. de Perpignan), Jacques DEVERCHERE (UBO-IUEM, CNRS-UMR6538, Plouzané, France.
The Valencia Trough is an aborted Tertiary rift whose formation was associated with the opening of the Ligurian-Provençal oceanic basin. Because the Valencia Trough is located between the marginal Messinian basins and the deep Mediterranean oceanic basins, it is a key basin for investigating the Messinian Salinity Crisis. We present new isobath and thickness maps of Messinian sequences in the Valencia Trough. Analysis of the seismic facies and geometries of the Messinian units, their chronologic and stratigraphic relationships at the transition between the shelf and the deep basin allows to better understand the impact of the margin’s morphology on the distribution of Messinian depositional systems tracts. The distribution of Messinian deposits in the Valencia Basin shows that they are sandwiched between two major erosion surfaces: (1) An early basal erosion affected the Pre-Messinian units in the entire Valencia Basin, with valleys incising the Miocene units on the margins. Except for the abyssal plain linking the Valencia basin to the Provencal basin in the NE, the entire area was subjected to aerial erosion resulting from the drastic sealevel drop at the beginning of the salinity crisis. During that first event, the salt was deposited in the Provençal basin and in the deep parts of the Valencia basin. The products of erosion were deposited first along what was then the Messinian nearshore (a distal area at present time), coevally with salt deposition offshore and erosion onshore. The salt and early detritals are thus considered as early low-stand systems tract related to the first rapid sea-level drop. Deposition of the Upper Evaporites on the Basal Erosional Surface and on the first detritals supports their transgressive character. Although some amount of sea-level rise is necessary to explain the deposition of the Upper Evaporites sedimentation, the occurrence of fluctuations in sea level (recorded by alternating episodes of deposition and erosion in the Upper Evaporites Unit) indicates that the global sea level rise could not be important and that global sea level stayed low. As erosion of the margins persisted during all duration of the Crisis, detritals products filled the valleys by retrogression as sea level rise, coevally to deposition of the Upper Evaporites. The Messinian deposits (Upper Evaporites and Detritals) can then be interpreted as late low-stand system tracts. (2) A late Erosional episode is the last event clearly recorded in the Valencia basin and affected both the top of the Upper Evaporites unit and detrital deposits. It is characterised by numerous incisions forming an intricate drainage network of Messinian valleys, later filled by marine Pliocene sequences. One last drop in sea level must therefore have occurred before the Pliocene marine reflooding. This episode correlates with the « Lago Mare » episode (Orszag et al., 2000; Rouchy et al., 2001), which represents a major environmental change at the end of Messinian times. The Lago Mare erosional episode described onshore is coeval with to freshwater dilution, paleosol formation, and karstification at the upper evaporitic sequence. It implies a decrease of oceanic inputs and increase of the run-off at the end of Messinian period, conditions responsible for the creation of small subbasins or shallow and episodically desiccated lakes, below word sealevel. Lacustrine muds have been found in Messinian interval at site DSDP 372 (Hsü et al., 1978) in the Valencia Basin, where a « Lago Mare » type environment with formation of lakes in the depressions or erosion is probable.
55) - DEEP CLASTIC EVAPORITES DEPOSITION IN THE MESSINIAN ADRIATIC FOREDEEP (NORTHERN APENNINES, ITALY)
Vinicio MANZI1, Stefano LUGLI2, Franco Ricci LUCCHI3 and Marco ROVERI1
1: Dipartimento di Scienze della Terra, Università di Parma, Parco Area delle Scienze 157A, 43100, Parma, Italy
2: Dipartimento di Scienze della Terra, Università di Modena, Largo S. Eufemia, 41100, Modena, Italy
3: Dipartimento di Scienze della Terra e Geologico-Ambientali, Università di Bologna, Via Zamboni 67, 40100, Bologna, Italy
The Messinian Salinity Crisis was accompanied by an intense phase of geodynamic reorganisation affecting the Mediterranean area that produced the fragmentation of the Miocene Apennine foredeep basin. During this event the deposition of primary evaporites occurred within growing semi-closed thrust-top basins whereas, in the adjacent deeper and more subsident parts of the foredeep, only organic-rich shales were deposited. The progressive tectonic uplift affecting the evaporitic basins, e.g. the Vena del Gesso basin, caused first the stop of the shallow-water evaporite deposition and then the development of a wide-spread phase of collapse leading to the resedimentation of the evaporites into the evolving deeper parts of the Apennine foredeep, that never underwent desiccation. A detailed facies analysis on the products of the post-evaporitic dismantlement phase has been carried out during the last years in the northern Apennines in order to define: 1) their genetic relationship with the primary evaporites of the Vena del Gesso; 2) the sedimentary processes controlling their deposition; 3) the possible occurrence of a lithological cyclicity comparable to the well-developed one characterising the shallowwater primary evaporites. Due to the burial-induced re-crystallisation affecting the resedimented evaporites of the Apennines, their study is not an easy task. The application of a siliciclastic-approach to field recognition, together with microscope analysis and geochemistry has been utilised to define a more accurate facies interpretation of the large variety of resedimented evaporites and led to the some important implications for the events that characterised the Messinian salinity crisis in this area. A great variety of gravity-driven deposits, ranging from debris flow to low-density turbidites have been recognised within the Gessoso-solfifera Formation of the northern Apennines between the eastern edge of the Vena del Gesso, i.e., the Forlì Line, and the Laga basin. The deposition of such a wide variety of gravity-driven deposit was probably related to the formation of large submarine collapses and glides triggered by tectonic-induced gravitational instability, as witnessed by the diffuse presence of slides, slumps and gravity-driven deposits. Two main depositional units of resedimented evaporites were recognised in the deeper “basinal” succession. Their formation can be related to different tectonic phases or, as here proposed, to the cannibalisation and resedimentation of two distinct primary evaporite members, producing different type of gravity flows. As an inversion of the stratigraphic succession, the upper gypsarenite-rich cycles were first resedimented as low-density gravity flows, then the lower selenite cycles dismantlement produced glides and higher density gravity flows, finally the fine-grained siliciclastic deposits of the S. Donato Formation, derived from the erosion of the pre-evaporitic units. Although evaporites resedimentation occurred within a fragmented foredeep, their wide distribution and depositional character indicates the complete absence of desiccation. This important evidence ought to be taken into consideration even in the study of the other Mediterranean basins, especially in the interpretation of the deepsea evaporitic deposits.
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56) - SUBTERRANEAN TESTIMONIES OF THE MESSINIAN SALINITY CRISIS: THE RHÔNE'S MIDDLE VALLEY ENDOKARSTIC RECORDS
France Ludovic MOCOCHAIN1 and Georges CLAUZON2
1: Ecole des Mines de Paris, CGES de Fontainebleau, 35 rue st-Honoré, 77 305 Fontainebleau, France.
2: CEREGE, Europôle Méditerranéen de l'Arbois - BP 80 - 13545 Aix En Provence cedex 04
On shore, the Messinian salinity crisis resulted in unusual karstic base level fluctuations. First, this base level underwent a collapse down to the abyssal plains. This fall carvedout the margins with the famous sub-aerial Messinian canyons (such as the Rhône canyon in the studied area) by retrogressive erosion. This huge fall was followed by a two step rise in Mediterranean sea level, constituting the delayed Pliocene impacts of the crisis. The first rise is consistent with the Mediterranean flooding at 5,32 Ma: the Messinian canyons are suddenly transformed into Pliocene rias. The second rise, slower than the first one, is due to the sedimentary aggradation of tributary rivers during their infill of the rias by Gilbert type fan deltas. Our study of the karstic units located on the right bank of the middle Rhône valley (Saint-Remèze plateau in Ardèche region, Méjanne-le-Clap plateau in the Gard region) reveals a strange stepped endokarstic drainage pattern. Obviously, this underground arrangement is linked to the Messinian-Pliocene external bench-mark levels: - the pre-evaporitic abandonment surface of Saint-Restitut (5.95 Ma), - the thalweg of the Rhône’s Messinian canyon near Pierrelatte, - the marine/non-marine transition at Trignan , - the Pliocene abandonment surface of Saint-Marcel d'Ardèche (2 Ma). These four reference levels enable us to follow the karstic base level between 5,95 and 2 Ma, both in terms of their chronology and elevation. In totality, it appears that the endokarstic evolution is closely linked to the external Messinian-Pliocene mega-cycle. This per ascensum structuring of the karst can be read in two ways: - the first is geometric, by altitudinal concordance between the marker levels previously outlined and the different phases of the karst drainage pattern. Three relative levels have been identified: (1) the Messinian canyons, (2) the Pliocene high stand (indicated by the marine-continental transition), and finally (3) the high level aggradation (as revealed by the Pliocene abandonment surface). - the second point is dynamic and corresponds to the karst’s response to each of the base-level variations, during and posterior to the crisis. This dynamic is translated in the karst by the formation of vertical drainage channels, whose morphologies are downwards during the base-level fall and upwards during the successive rises. The latter vertical drainage channels (relative to the base-level rises) reveal an exceptional hydrological dynamic, in that the three levels are interconnected. This characteristic suggests that a phase of base-level rise leads to a rising drainage channel. The channel develops at the contact of the new base level, between the submerged level and the level in genesis. Such a system is similar to current processes observed at the Fontaine de Vaucluse, the difference being that here the rising channel emerges in a superior level under formation. Consequently, throughout the Messinian-Pliocene cycle, each drainage phase is marked by the superposition and interconnection of the karst system. Today we observe a polyphased karst, marked by three distinct and interconnected levels. Only the Messinian level is presently active in the Vauclusian system (a karst deep draining the massif, before following one or more ascending channels to emerge), because it is below the current base level.
57) - SPECIES RICHNESS, COMMUNITIES AND CLIMATE: THE CASE OF MAMMALIAN FAUNAS
Sophie MONTUIRE1, Serge LEGENDRE2 and Loïc COSTEUR2
1: UMR CNRS 5561, Biogéosciences & EPHE, Ecole Pratique des Hautes Etudes. Centre des Sciences de la Terre, Université de Bourgogne, 6 Boulevard Gabriel, 21000 Dijon, France. (Sophie.Montuire@u-bourgogne.fr)
2: UMR CNRS 5125—Paléoenvironnements & Paléobiosphère, Université Claude Bernard-Lyon 1, Bât. Geode, Campus de la Doua, 69622 Villeurbanne Cédex, France (Serge.Legendre@univ-lyon1.fr)
The study of mammalian communities provides useful knowledge of palaeoenvironments and palaeoclimate. Palaeoecological reconstructions and quantification of climatic parameters are based on the analysis of species richness, body mass and new methods for quantifying climatic parameters (temperatures and precipitations). Geographical distribution and species richness in mammals seem to be highly dependant on climate. Correlations between climatic parameters, as mean annual temperatures, and number of species in some rodent sub-families are high. Such relationships yielded to the construction of quantification models based on linear regression technique to estimate past temperatures. Different models using arvicolines, murines, and sigmodontines (taken as analogues for Old World cricetines) have been proposed in order to quantify past climates and to analyse changes through time. Based on rodents, temperatures are estimated here for Late Miocene-Early Pliocene (MN 9 to MN 15) European faunas at regional scale. Two kinds of continental patterns in temperatures are observed with homogenous temperatures for MN 9 up to MN 11 or contrasted temperatures at the end of the Miocene. The onset of a latitudinal effect is also supposed during MN 15. Cenogram analysis (Calatayud-Daroca-Teruel Basin, Castillon-Valencia Basin, Languedoc-Roussillon Basin) has been made for the Messinian to understand the impact of the crisis on the continental mammalian faunas. No change has been observed between the Late Miocene and the Pliocene. The palaeoenvironments are similar inside the two regions before or after the Messinian event.
58) - BIOCHRONOLOGY OF THE TORTONIAN-MESSINIAN PISSOURI SECTION (CYPRUS)
Caterina MORIGI1, Simona GIUNTA1, Tanja KOUWENHOVEN2, Alessandra NEGRI1, Wout KRIJGSMAN3, Marie-Madeleine BLANC-VALLERON4, Fabienne ORSZAGSPERBER5 and Jean-Marie ROUCHY4
1: Dipartimento di Scienze del Mare, Università Politecnica delle Marche, Ancona, Italia;
2: Faculty of Geosciences, Dept. of Earth Sciences, Utrecht University, The Netherlands.
3: Paleomagnetic Laboratory Fort Hoofddijk, Utrecht.
4: CNRS-UMR 5143, Dept. Histoire de la Terre, Muséum national Histoire naturelle, Paris, France.
5: CNRS-UMR 8616, Univ. Paris Sud, Orsay, France
The ‘Pissouri motorway’ section on Cyprus covers the interval from ~7.6 Ma (Late Tortonian) to the start of the Messinian salinity crisis (MSC, 5.96 Ma). This section is one of the most suitable sedimentary successions to study the onset of the Messinian Salinity Crisis in the Eastern Mediterranean. In this section previous biostratigraphic studies revealed several planktonic foraminifera events that have been astronomically dated in other Mediterranean sections, and as such provide an excellent first-order age control. In addition magnetostratigraphic results are in good agreement with the biostratigraphic data and show that all magnetic chrons between C4n.1n and C3An.1n are present. The microfaunal and nannofloral assemblages are well preserved and abundant in the lower part of the section that predates the Tortonian - Messinian boundary. In particular the nannoflora shows a twofold distribution: starting from the bottom of the section to 6.6 Ma the superficial assemblage is typical of normal marine conditions whereas, after this point, it shows frequent and extreme fluctuations in abundance showing in some cases oligotypic communities (e.g. consisting of 99% sphenoliths). Also the planktonic foraminifera assemblage is well diversified in the first part of the section until ~6.7 Ma, and mainly consists of Globigerina decoraperta, Globigerinoides spp. and Globorotalia genera. Our results confirm the isochrony and reliability of some calcareous nannofossil events (Amaurolithus primus FO, A. delicatus FO, Reticulofenestra rotaria FO and FCO) thus contributing to a better time constraint of the Tortonian - Messinian Boundary.
59) - LAGO-MARE: WHAT DOES THAT MEAN?
Fabienne ORSZAG-SPERBER
Université de Paris-Sud, Département des Sciences de la Terre, Bâtiment 504, 91405 ORSAY cedex, France.
The Alpine orogeny (Cenozoic time) caused the partition of Tethys into several basins. During Late Neogene, the “Mediterranean” came into its definitive configuration existence, whereas, eastwards, the “Paratethys”, isolated (temporarily?) from the World Ocean, disintegrated progressively into smaller basins. Thus an endemic fauna developed in these basins, mainly composed of low salinity faunas, with congeriids, cardiids, melanopsids and specific ostracods, indicating an environment subjected to changes in the water salinity. In the Mediterranean, at the end of the Neogene, sediments are characterized by similar fauna, leading Gignoux (1936) to carry the notion of “Sea-Lake” created previously by Andrussov, for the Paratethys, and translated into French by “Lac-Mer”, and now largely known as “Lago-Mare” (after Ruggieri in 1967). These last decades, numerous scientific investigations about the history of the Mediterranean during the Messinian were devoted to the understanding of the conditions prevailing after the deposition of evaporites. Brackish fauna are found in several outcrops and boreholes in the Mediterranean, already in the lastest beds of the Upper Evaporites and then, also present in coarse clastic sediments, just before the flooding of the marine Pliocene waters. Fresh water fauna are also found thus showing alternations of saline and fresh-water environments during this period. These fauna, because their similarities with the fauna described in the Paratethys, were named incorrectly “Paratethyan, or caspi-brackish” fauna leading some authors to consider a necessary migration of the fauna from Paratethys to Mediterranean, whereas others refute this hypothesis. Such seems to have been the starting point of a drifting in the meaning of “Lago Mare”, now often wrongly used as an “event”, a transitory period before the Pliocene marine flooding, periods of connections between Paratethys and the Mediterranean, etc… But also, this drift in meaning spurred, thanks to recent data about the Black Sea, the Dacic basin, the Pannonian basin, etc…, and the Mediterranean (Greece, Cyprus, Sicily) , researches of questionable connections between the Mediterranean and the Paratethys during and after the Messinian Salinity Crisis. Included in different models proposed so far by authors to explain the cause/effects relationships leading to the Messinian Salinity Crisis, the notion of “Lago Mare”, is, here also subject to different vicissitudes. After all these comments on the use of ”Lago-Mare”, the goal is now to look for evidences of potential connections Atlantic-Mediterranean-Paratethys during this Miocene-Pliocene boundary period. This requires more accurate controls to correlate the Messinian-Pliocene time with the stratigraphy of the Paratethys, more studies on the environmental specifications of these fauna (indicators of environmental changes or adaptation with regard to water evaporation and salinity ?, colonization ?), the significance of the coarse clastic unit ending the Messinian time, climatic and sea-levels changes with a better knowledge of the Messinian impact out of the Mediterranean.
60) - THE MESSINIAN-ZANCLEAN TRANSITION IN CYPRUS
Fabienne ORSZAG-SPERBER1, Marie-Madeleine BLANC-VALLERON2, Catherine PIERRE3 and Jean-Marie ROUCHY2
1: Université de Paris-Sud, Département des Sciences de la Terre, bat.504, 91405 Orsay Cedex, France.
2: CNRS-UMR 5143, Département des Sciences de la Terre, Géologie, Museum National d’Histoire Naturelle, 43, rue Buffon, 75005, Paris, France.
3: CNRS-URA 1761, LODYC, Université P.et M.Curie, 4 Place Jussieu, 75252 Paris Cedex, France
The study of the late Messinian-Early Pliocene sediments in South Cyprus (Polemi and Pissouri basins) and the comparison with the offshore coeval deposits drilled in the ODP Leg 160 boreholes, illustrate the environmental changes which occurred in the Eastern Mediterranean at the end of the salinity crisis. The latest Messinian interval includes the so-called “Lago-Mare” environment. In the Polemi Basin, at Kathikas, the brackish fauna appears into the marly-chalky beds intercalated between the two last gypsum beds. The uppermost gypsum beds consists of gypsified stromatolites. At Giolou (Yolou), the uppermost bed of gypsum which contains molluscs (Abra alba), is overlain by varved marls containing numerous Melanopsis, Melania, Planorbis, Cyprideis and fragments of Chara.. Pedogenetic carbonate concretions and roots imprints also indicate episodes of subaerial exposures. In the Pissouri Basin, the last “Lago-Mare” sediments developed after an episode of erosion of the Upper Gypsum beds and consist of an alternation of conglomerates with paleosols and chalky marls. These latter contain at their base Ammonia beccarri and Cyprideis, followed by a fresh-water to brackish fauna (Limnocardium, Melanopsis, Melanoides and Congeria) The Pliocene marls (Trubi) belong to the MPL1 zone. At ODP Hole 968 A, sediments contain a faunal association with Cyprideis pannonica and Ammonia tepida and include a gypsum-rich intercalation which indicates that the Lago-Mare environment began before the end of the gypsum deposits. A pulmonate gastropod also indicate an emersion. A very sharp contrast in lithology, sedimentology, faunal assemblages and stable isotope composition of carbonates characterizes the Messinian-Pliocene boundary with an abrupt passage from oligo-mesohaline environments to deep marine conditions. In the land sections, horizons of paleosols intercalated with conglomerates indicate periods of subaerial exposure alternating with several discharges of detrital sediments resulting from the emerging Troodos. This detrital input of conglomerates is related to an important change in the hydrological balance (rainfall), leading to the dilution of basin waters. The processes of dilution started before the end of the Upper gypsum deposits the isotopic composition of which indicate an important contribution of freshwaters.
61) -THE ONSET OF THE MESSINIAN SALINITY CRISIS IN THE EASTERN MEDITERRANEAN. A CASE STUDY: CYPRUS
Fabienne ORSZAG-SPERBER1, Marie-Madeleine BLANC-VALLERON2, Jean GAUDANT3, Didier MERLE3 and Jean Marie ROUCHY2
1: Université de Paris-Sud, Département des Sciences de la Terre, bat.504, 91405 Orsay Cedex, France.
2: CNRS-UMR 5143,Département des Sciences de la Terre, Géologie, Museum National d’Histoire Naturelle, 43, rue Buffon, 75005, Paris, France.
3: CNRS-UMR 5143, Département des Sciences de la Terre, Paléontologie, Museum National d’Histoire Naturelle, 8, rue Buffon, 75005, Paris, France.
South of the Troodos mountain (Cyprus), a fragment of an ancient oceanic crust, three main basins formed during Neogene times, the Polemi, Pissouri and Psematismenos basins. The Messinian sedimentary succession is characterized by pre-evaporite deposits, overlain by a massive Lower Gypsum Unit and an Upper Gypsum Unit comprising six levels of gypsum intercalated with marls and sandy marls. These two units are separated by a breccia. The so called “Lago-Mare” facies appears within the Upper Gypsum Unit and develops above the younger gypsum beds. It is made of conglomerates and marls with brackish fauna including several episodes of emersion (paleosols). These deposits are sharply overlain in the three basins by the Trubi marls of the Early Pliocene. Very suitable sedimentary successions were measured, which allow, thanks to numerous investigations and recent data, to document the evolution of the depositional environments before the onset of evaporites and to evidence tectonic pulses. - It is clearly shown that, during the deposition of the pre-evaporitic sediments, the environment progressively through the Upper Tortonian-Early Messinian, from a depth of about 500 m, up to very shallow conditions just before the onset of evaporitic conditions. Both shallowing and salinity increase are indicated by the decrease of the species diversity of planktonic foraminifera; this is confirmed by the abundance of miliolids and Glabratella, and the low diversity of the calcareous nannoplankton, dominated by Reticulofenestra. Diatoms microflora suggests a depth of 400-500 m. The malacofauna indicates an upper bathyal - deep circalittoral environment, evolving to an upper circalittoral environment just before the onset of the gypsum deposition. The disappearance of mollusks representative species also confirms the restriction of the environment. Also, the increasing number of Syngnathid remains and the disappearance of Myctophids are good indicative of a reduction of depth and an increasing isolation of the basin. In some sections, stromatolites developed below the gypsum. - Several pulsations of tectonic instability are recognized before the evaporitic deposits, and documented by slumps, breccias, and sedimentary features like water escapes and hydroplastic structures. - High resolution integrated studies performed in the Pissouri section show that the onset of the evaporites occurred around 5.96 Ma, in good agreement with the age proposed for other sections in the Mediterranean, thus allowing accurate correlations between different basins.
62) - LATE MESSINIAN VALLEY FILL IN THE ASINARA GULF (NW SARDINIA, ITALY)
Vincenzo PASCUCCI, Mauro TEDDE and Giacomo OGGIANO
Istituto di Scienze Geologico-Mineralogico, Università di Sassari, Corso Angioy 10, 07100 Sassari, Italy. (pascucci@uniss.it)
The Asinara Gulf (North-West Sardinia) represents the offshore prosecution of the inland Porto Torres-Lugodoro basin. It is a half graben with the master fault located on the eastern border, and developed during the post-orogenic, post-collisional phase active in Sardinia from the Burdigalian to the late Tortonian. The sedimentary fill of the Gulf has been recently grouped into three Neogene-Quaternary depositional sequences. Sequence 1 is characterized by continental, to deltaic, to marine deposits unconformably overlying the Aquitanian volcanic strata. Its age is Burdigalian-Langhian. Sequence 2 is characterized by deltaic, to marine deposits onlapping onto sequence 1. Its age is Serravalian-late Tortonian (possibly early Messinian). Sequence 3 is characterized by continental and possibly marine post-rift deposits resting unconformably on the older sequences. Its age ranges from the late Messinan to the Present. The basal deposits of Sequence 3 crop out only in a small area close to Stintino (SW border of the gulf), but can been followed offshore through the seismic lines covering the gulf. In outcrop the sequence is characterized by alternating of clays and conglomerates. Clays are reddish, massive, highly bioturbated and pedogenized. Paleosols are occasionally found in the clays. They have been interpreted to be alluvial plain deposits. Conglomerates are organized in clast- to matrix-supported amalgamated beds (10 m wide and 2-3 m high) showing cut-and-fill structures. Clasts dimension vary from cobble to pebble and reduce in size from west to east. Clasts composition (mainly Paleozoic metamorphic rocks and Permian sandstones) and paleoflow (clasts imbrication and channels orientation) indicate that the headwaters was to the SW; that is, close to the present western coast of North Sardinia (Cala Viola, Torre del Porticciolo areas). Most of the metamorphic clasts are highly weathered and show a reddish color. The conglomerates have been interpreted to be a braided stream deposit. The basal part of Sequence 3 is interpreted to be a valley fill deposit. Inland, the valley was SW-NE oriented, 60 km long and 2 km wide. It can be also followed offshore where it cut through Sequence 2, and ends at the edge of the Sardinia. A deep canyon has developed in correspondence of the fossil valley. Canyons such as that of Castel Sardo are documented on the North Sardinia shelf and have been interpreted to have formed during the transgression associated with the Messinian salinity crisis. No fossils have been found in Sequence 3 strata leaving opened its age. However, on seismic profiles it has been interpreted as a low stand deposit. Moreover, the highly weathered clasts are indicative of tropical to sub-tropical conditions similar to those occurred of the late Messinian time. If these were true, the valley deposits of Sequence 3 can represent the pre early-Pliocene transgressive system tract.
63) - THE BEGINNING AND THE TERMINATION OF THE MIDDLE MIOCENE BADENIAN SALINITY CRISIS IN CENTRAL PARATETHYS
Tadeusz Marek PERYT
Panstwowy Instytut Geologiczny, Rakowiecka 4, 00-975 Warszawa, Poland
The age and correlation of evaporites occurring in different parts of the Badenian Carpathian Foredeep Basin, and hence the reconstruction of basin history during deposition of evaporites, are subject to controversies. Recent study of calcareous nannoplankton indicates that the Badenian sulfates of the Carpathian Foredeep represent the lower part of the NN6 zone. Basin-marginal Badenian evaporites formed in a standing body of water, as well as in desiccated environments subject to floods. The lateral persistence of thin beds over large areas with only minor changes in thickness and facies indicates that they formed on broad, very low relief areas which were affected by rapid transgressions that led to major changes in brine chemistry. Halite and associated deposits in the central part of the Badenian evaporite basin show the same facies successions and marker beds can be traced across and between individual basins. The Badenian evaporite basin was located in a depression in which the brine top level was located below the contemporaneous sea level. Accordingly, during sea-level rises new marine water could enter this depression and bring with it a temporary pulse of marine fauna. Although the correlation of different Badenian evaporite facies is difficult (if possible et all), there are no such problems in the case of particular evaporite facies zones. The correlation between facies zones of the marginal sulfate platform was based on the occurrence of characteristic marker beds, as well as the observations made in areas transitional between the facies zones. The marker beds seem to reflect events that may be related to sudden and widespread changes in water chemistry, which in turn imply major changes in basin hydrology. However, physical stratigraphic relationships between sulfates occurring in the marginal sulfate platform and sulfates from sulfate basin and the relation of the areas of halite and sulfate deposition remain enigmatic The scenario of events leading to the deposition of widespread evaporites, being a synchronous event, in the Badenian is not established in detail. Isotopic studies of Badenian foraminifers occurring below and above evaporites suggest that the interrupted communication of the Paratethys with the ocean was a consequence of eustatic sea-level fall, possibly related to climatic cooling. However, a tectonic closure of connection with the Tethys could also contribute to the origin of salinary crisis. Sedimentological and geochemical data indicate “cannibalisation” of evaporites throughout the most time of evaporite deposition. The cannibalization at the end of gypsum deposition in the marginal sulfate platform was accompanied by the blocktectonics that resulted in the creation of bathymetric difference at least a few ten of meters as indicated by the occurrence of Ratyn Limestone on stratigraphically different parts of the gypsum section. It was accompanied by a change in the hydrology of the Central Paratethys that was tectonically-driven, and possibly related to the block tectonic phase manifested in the marginal part of the Carpathian Foredeep Basin. The change in hydrology implied the dilution of brines by inflowing marine water and this terminated the Badenian salinity crisis.
64) - RECONSTRUCTION OF THE PALEOENVIRONMENTAL CHANGES AROUND THE MESSINIAN-PLIOCENE BOUNDARY ALONG A W-E TRANSECT ACROSS THE MEDITERRANEAN
Catherine PIERRE1, Marie-Madeleine BLANC-VALLERON2, Antonio CARUSO3, Fabienne ORSZAG-SPERBER4 and Jean Marie ROUCHY2
1: CNRS-UMR 7617, LODYC, Univ. P. & M. Curie, 4 Place Jussieu, 75252 Paris Cedex 05, France.
2: CNRS-UMR 5143, Muséum National d’Histoire Naturelle, 43 rue Buffon, 75005 Paris, France.
3: Geologia e Geodesia, Univ. di Palermo, corso Tukory 131, 90134 Palermo, Italy.
4: CNRS-UMR 8616, Univ. Paris Sud, 91405 ORSAY Cedex, France.
A multidisciplinary study has been carried out with a high sampling resolution of the upper Messinian-Lower Pliocene (biozone MPl 1) sediments along a West-East Mediterranean transect from southern Spain (Vera/Almanzora), Balearic Basin (ODP Site 975b), Sicily (Eraclea Minoa), Zakynthos (Kalamaki), Corfu (Aghios Stefanos), Crete (Aghios Vlasis), including previous data obtained in the Levantin Basin (Cyprus and ODP Sites 968 and 969). All the studied sections have been correlated using planktonic foraminifera assemblages, sedimentological and stable isotope variations, and compared to the lithological cyclicity defined in the Messinian/Pliocene boundary stratotype of Eraclea Minoa, Sicily. The Messinian/Pliocene transition displays strong variations of CaCO3 content, stable isotopes (&Mac182;18O, &Mac182;13C) of carbonates and foraminiferal assemblages that can be correlated between the different studied sections. The uppermost Messinian deposits are barren or characterized by only reworked planktonic foraminifera, except for the sporadic presence of Ammonia beccarii tepida, ostracods and brackish mollusks typical of the “Lago–Mare” conditions. The bulk carbonate oxygen and carbon isotopic compositions usually exhibit large variations with dominant low d values indicating freshwater dilution. The lowermost part of the Pliocene (MPl1 biozone, cycle 1) shows a rapid and progressive increase of the &Mac182;18O values by up to 1 to 3‰ which characterises the restoration of marine conditions after the Lago-Mare event. Normal marine environments were definitely established and stabilized at the base of cycle 2 which corresponds to the base of Sphaeroidinellopsis spp. acme zone, at 5.31 Ma. These data confirm that the inflow of marine waters occurred contemporaneously within the whole Mediterranean at the base of the Pliocene, although the onset of stable marine conditions occurred about 20 ky later.
65) - UPPER MESSINIAN LAGO-MARE DEPOSITS IN THE STRATIGRAPHY OF THE MESSARÀ BASIN (CENTRAL CRETE, GREECE)
Giorgio PIPPONZI, Domenico COSENTINO and Elsa GLIOZZI
Dipartimento Scienze Geologiche, Università Roma TreL.go S. Leonardo Murialdo, 1 I-00146 Roma, Italy
In the Crete Island, late Messinian “Lago-Mare” facies are not well known. At present, the occurrence in Crete of the uppermost Messinian post evaporitic deposits is matter of debate. According to several authors the well-known late Messinian “Lago-Mare” facies did not occur in Crete. There, lower Pliocene open-marine clays of the Finikia Group directly overlie the upper Messinian evaporites of the Hellenikon Group (Dermitzakis et alii, 1979; Frydas, 1998; Fassoulas, 2001). Meulenkamp et alii (1977 and 1979) described continental coarse-grained deposits and lagoonal sediments with Cyprideis pannonica agrigentina Decima (= C. agrigentina) from eastern Crete (Ag. Nicolaos). Moreover, fine-grained deposits with Cyprideis sp. have been, also, detected in a few places of central Crete (Meulenkamp et alii, 1977). The stratigraphic positions of all these Cyprideis-bearing deposits, which occur above upper Messinian gypsum, allow us to consider them as deposited during the late Messinian “Lago-Mare” event. The aim of this paper is to show the preliminary results obtained from the analyses of some stratigraphical sections sampled in the Messarà Plain. Nearby Faneromeni village, the Miocene/Pliocene boundary is well exposed. The uppermost lower Messinian deposits (pre-evaporitic stage) are characterized by brownish laminated tripolaceous marls with intercalations of marl horizons rich in benthic forams, ostracods and molluscs. Moreover, two organic-rich horizons have been found in the uppermost part of the tripolaceous marls. Up section, these marls pass to clays with gypsum, beds of laminate microcrystalline gypsum and gypsiferous breccias. Above these evaporitic deposits, fine-laminated polychrome clays with intercalations of sandstones and conglomerates (bedding attitude N 183°, 17°) have been found resting unconformable below Pliocene grey claysand conglomerates (bedding attitude N 164°, 24°). In this preliminary phase, 12 samples have been collected across the Messinian/Pliocene boundary in the Faneromeni section. In the Kasteli-Ano Akria area, above gypsiferous breccias and laminated microcrystalline gypsum deposits, silty-clays with intercalations of sandstone and conglomerate horizons have been found. In this area, 2 samples from the post evaporitic fine-grained deposits have been collected. More recently, a 20 cm-spaced sampling has been performed in both the sections, for about 100 samples collected. Micropaleontological analyses have been performed on the preliminary sampling of the post evaporitic deposits from both Faneromeni and Kasteli-Ano Akria sections. The results of these analyses point to the presence of an ostracod assemblage containing: Cyprideis sp., Amnicythere spp., Amnicythere cf. A. palimpsesta (Livental), Amnicythere cf. A. propinqua (Livental), Camptocypria sp., and Pseudocythere sp. Reworked planktonic foraminifera and well-preserved charophyte gyrogonites have been also found. The ostracod assemblage found in the Messarà Plain belongs to the Loxoconcha djafarovi Zone (sensu Carbonnel, 1978), which characterizes the uppermost Messinian deposits of the whole Mediterranean Basin. At that time, the well-known “Lago-Mare” biofacies was widespread on the Crete Island also. The presence of Paratethyan ostracods in the post-evaporitic Messinian deposits of both Faneromeni and Kasteli- Ano Akria sections suggests that in the latest Messinian Crete Island was affected by sedimentation processes in brackish water palaeoenvironments.
66) - COEVAL VOLCANISM AND EVAPORITE DEPOSITION IN THE FORTUNA BASIN (NEOGENE, MURCIA, SPAIN): PETROGRAPHIC EVIDENCE OF SYNCHRONISM
Elisabet PLAYÀ and Domingo GIMENO
Departament de Geoquímica, Petrologia i Prospecció Geològica, Universitat de Barcelona. 08028 Barcelona. Spain.
The Neogene basins of the Eastern Betic Moutains, located in a marginal position with respect to the deep Mediterranean basin during the Tortonian and to the Messinian, contain thick gypsum-anhydrite formations resulting from the salinity crisis; the occurrence of halite bodies is known in some basins (e.g., the Lorca basin). The evaporitic sedimentation reached its maximum extension and stratigraphic complexity in the Fortuna basin, which belongs to this geological setting. This work illustrates the presence of peperitic lithofacies in volcanic rocks and discusses their implications in terms of assesment of an age to the coeval evaporite sediments; this information allows us to date the evaporite units of the Fortuna-Lorca basins and to enlighten the controversy around its Tortonian or Messinian age. Five stratigraphic units are distinguished in the Fortuna basin: 1) Lower Gypsum, 2) Chicamo Gypsum, 3) Chicamo Diatomitic-evaporitic cycles, 4) Ribera Gypsum and 5) Rambla Salada Gypsum units. Some of these units occur locally, whereas others can be laterally correlated with those of the Archena-Mula, Guadalentín corridor and Lorca basins. Most of the gypsum units consist of nodular-laminated lithofacies (secondary gypsum); however, primary selenitic, laminated (gypsarenites) and fine-grained (“balatino”) gypsum lithofacies are present. The evaporite units can also be characterized by their geochemical composition: a) highly variable strontium contents, b) isotopic composition of sulphur (&Mac182;34S) ranging from those characteristic of the Tertiary marine water (+20.3 to +25.5‰) to those characteristic of the Triassic sulphates (+8.0 to +16.0‰), and c) strontium isotope ratios (87Sr/86Sr) comprised between 0.70804 to 0.70888. These sulphur-oxygen and strontium isotope compositions indicate precipitation from Tertiary marine brines, or from meteoric waters (recycled Triassic sulphate anion and additional non-marine contributions from country rocks and hydrothermal solutions); intermediate values are attributed to mixed seawater and nonmarine mother brines. The Fortuna basin contains several outcrops of separate lamproitic volcanic to subvolcanic igneous bodies (Cabezos Negros, El Tale, Derramadores); several absolute ages are known. The isotopic age of a volcanic rock provides a good chronostratigraphic marker in the case of lava or pyroclastic flows interbedded in a sedimentary sequence. Also, a sill gives some relative information (it is younger than the intruded rocks). However, the lamproitic rocks present in the Fortuna basin crop out without clear stratigraphic position in the sedimentary sequence: as individual domic volcanos without sedimentary cover (eroded; Cabezos Negros) or as intrusive subvertical dikes (El Tale, Derramadores), a fact that a priori excludes good chronological constraints. Nevertheless, there exists good evidence of several magma-sediment interactions that provided macroglobular peperitic lithofacies. A peperite is produced when two liquids (a hot magma and a fluidized, water-satured sediment) interact and no mixing is possible due to the sharp contrast of viscosity between them. This implies that at the moment of the eruption, the sediment is water-satured (in terms of time, they are nearby coeval).
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67) - THE DINOCYSTS NEW MARKERS OF MEDITERRANEAN - PARATETHYS CONNECTIONS BEFORE AND AFTER THE MESSINIAN SALINITY CRISIS
Speranta-Maria POPESCU
Laboratoire PaléoEnvironnements et PaléobioSphère, Université Cl. Bernard – Lyon 1, 27-43 boulevard du 11 Novembre 69622 Villeurbanne, France. (Speranta.Popescu@univ-lyon1.fr)
Relationships between the Mediterranean Sea and the Paratethys realm are debated from a long time. Normal connections between these seas are generaly considered to have ended in the late Miocene. Two successive Mediterranean nannoplankton influxes belonging to NN11 and NN12 zones have been evidenced in the Dacic and Euxinian basins. Nannoplankton is accompanied by typical marine dinocysts: Spiniferites mirabilis, Spiniferites bentorii, Tectatodinium pellitum, Spiniferites hyperacanthus, identified within the Dacic Basin. More recently, dinocysts such as Galeacysta etrusca, and morphotypes of Spiniferites cruciformis and Pyxidiniopsis psilata (= Impagidinium sp.; Corradini & Biffi, 1988) the usual endemic Paratethyan species have been regularly found in the Mediterranean area (Corradini & Biffi, 1988) and added to the “Lago Mare” biofacies (Bertini et al., 1994, 1995). These data indicate the existence of high sea-level cross exchanges between the Mediterranean Sea and the Eastern Paratethys just before and after the Messinian salinity crisis. Moreover, dinocyst assemblages show a large number of marine species morphotypes in the western part of the Dacic Basin, which probably originate from adaptation to low salinity. Palynological analysis from Site 380 A (Black Sea) shows a very poor assemblage of Paratethyan dinocysts in the late Miocene, a bloom of freshwaters acritarchs (between 5.33 Ma and 5.11 Ma) being followed by an assemblage grouping brackish and marine dinocysts. The presence of typical marine taxa in the western part of the Dacic Basin, the development of marine taxa morphotypes in the eastern part of the basin and the presence of freshwaters acritarchs just after Messinian salinity crisis in the Euxinian Basin suggest that: - the “proto-Bosphore” was closed at this time, - the Dacic Basin should have been directly connected to the Mediterranean Sea, being itself episodically connected to the Black Sea. Dinocysts are highly sensitive to environmental changes, especially to salinity changes. As a consequence, they can adapt to new conditions with some important morphological changes. The Paratethyan endemic species Galeacysta etrusca is a demonstrative example.
68) - NEW DIATOM AND NANNOFOSSIL RECORDS FROM THE MAEOTIAN–LOWERMOST PONTIAN DEPOSITS OF THE TAMANSKII PENINSULA (BLACK AND AZOV SEA)
Eleonora P. RADIONOVA and Larisa A. GOLOVINA
Geological Institute RAS, Moscow, Pyzhevsky 7, 119017, Russia
Diatoms and nannofossils from the two Maeotian and Lower Pontian reference sections of the Tamanskii Peninsula (Zheleznyi Rog and Taman’) were studied. Both sections are composed of marls, clays, and diatomites and represent more deep-water sediments than their stratotype analogues on the Kerchenskii Peninsula. The deposits were accumulated at different bathymetric levels (the Zheleznyi Rog section is more deep-water than that of Taman’), however, their lithology, cyclicity character and plankton distribution are similar. The Maeotian and lowermost Pontian sediments are represented by three units bearing diatoms. The lower unit corresponds to the interval with the Thalassiosira meotica assemblage and represent the interbedding of carbonate and noncarbonate clays and clayey diatomites that form sedimentary cycles. Its total thickness is 40–80 m. The middle unit bears the Cymatosira savchenkoe assemblage. It is represented by alternation of clayey marls and diatom clays, and is 20–80 m thick. The upper unit with the Actinocyclus ehrenbergii assemblage is composed of laminated diatomite members interbedded with noncarbonate clays and is 20–60 m thick. The diatom assemblages from both sections are characteristic of the Eastern Paratethys (Kozyrenko and Temnishkova-Topalova, 1990; Kozyrenko and Radionova, 2002). They are dominated by marine genera Thalassiosira, Nitzschia, and Actinocyclus (Cestodiscus?) commonly represented by endemic species. The number and abundance of brackish- and fresh-water forms is variable in the sections. The maximum freshening was recorded in the upper part of the unit bearing Thalassiosira meotica and in some horizons of that with Actinocyclus ehrenbergii. In the lower part of the unit with Thalassiosira meotica few nannofossils Reticulofenestra sp. and tropical diatoms Thalassiosira brunii, Nitzschia fossilis, and N. praereinholdii were encountered. According to Barron and Baldauf (1995), the LAD of Thalassiosira brunii is at 8.6 Ma, and the FAD of Nitzschia fossilis, at 8,5 Ma (after scale of Cande and Kent, 1992). The second interval with almost normal salinity is the unit bearing Cymatosira savchenkoe. It contains rare nannofossils Reticulofenestra sp. and Coccolithus pelagicus and the oceanic diatoms Azpeitia komurae, Thalassiosira trifulta, Nitzschia miocenica, N. prolongata and others. The range of Azpeitia komurae is about 7.5–7.1 Ma (Akiba, 1987); of Nitzschia miocenica, 7.4–6.4 Ma (Barron and Baldauf, 1995). The upper unit with Actinocyclus ehrenbergii contains microflora only in the thin-bedded diatomites, where the bedding results from the alternation of carbonate and siliceous layers. The siliceous layers are sharply dominated by Actinocyclus ehrenbergii and the carbonate, by Braarudosphaera bigelowi. In the upper part of this unit the Pontian mollusks Paradacna abi_hi appeared. The peculiar diatom composition (Jousé, 1947) and peculiar rhythmic structure of sediments permitted to refer this unit to the Pontian. The overlying sediments yield the typical Pontian mollusk fauna and lack marine plankton. The correlation of the Maeotian and Pontian with the Mediterranean scale is up to now controversial. According to our records on planktonic groups, the Maeotian sediments are distinctly subdivided into two units: those bearing Thalassiosira meotica and Cymatosira savchenkoe, which age we have refined. The structure of the unit with Actinocyclus ehrenbergii sharply differs from the underlying sediments in the occurrence of laminated diatomites with monospecific plankton assemblages. The conditions of accumulation of these deposits were similar to those of the pre-evaporite Messinian.
69) - THE MESSINIAN SALINITY CRISIS IN THE MEDITERRANEAN: AN INTEGRATED SCENARIO
Jean Marie ROUCHY1 and Antonio CARUSO2
1: CNRS-UMR 5143, Département Histoire de la Terre, Muséum national Histoire naturelle, 43, rue Buffon, 75005 Paris, France.
2: Dipartimento di Geologia e Geodesia, Università di Palermo, Corso Tukory 131, 90134 Palermo, Italy
The knowledge of the Messinian salinity crisis (MSC) improved considerably during the past decade due to the availability of an accurate astronomically calibrated timescale and new studies that renewed both the debate. In this work, the updated reexamination of the most salient features along with consideration of hydrological requirements for evaporite deposition leads to propose an integrated scenario for the MSC. Two major stages of evaporite deposition affected the whole Mediterranean that was configured as an assemblage of deep basins including the Central Sicily, and more marginal basins distributed at shallower depths. This paleogeographical partitioning and the related threshold effects controlled both the diachronic deposition and the fractionation of the evaporite deposits between deep and marginal basins The first stage (lower evaporites) which comprises the thicker halite deposits with K-Mg salt interbeds corresponds to the major phase of drawdown related to higher aridity of the circum-Mediterranean climate. It correlates with the interval marked, in the ocean record, by a strong glacial influence with episodes of global sea-level fall, including the major peaks TG 20 and 22, that lasted around 5.6 Ma. The second stage (upper evaporites) involved a cyclic alternation of reflooding in highly restricted conditions with an intense freshwater contribution, and isolation ending, in some basins, by drying-up episodes. This matches logically the interval of warming recorded in the ocean since 5.6 Ma onwards. Sea water inputs remained the major feedstock for evaporite deposition and, although considerably reduced, never ceased durably through the MSC. However, the freshwater contribution increased drastically during the second stage culminating in the latest Messinian lacustrine conditions (Lago-Mare event), as the result of the worsening of the tectonically induced closure of the marine gateways and wetter climate at least on the peripheral mountains. The restoration of stable open marine conditions took place abruptly at the Messinian-Zanclean boundary. A multistaged erosion (M Horizon), affected the whole Mediterranean margin with a major step coeval of the first evaporitic stage. The erosion was reactivated during the second stage whenever the basin driedup, before a new important stage caused by the latest Messinian dilution, while an earlier event probably pre-dated the MSC. Finally, although the restriction of the Mediterranean was predominantly under a global tectonic control, the hydrological changes that controlled the MSC implied the interplay of glacio-eustatic changes and fluctuations of the circum-Mediterranean climate.
70) - PALEOENVIRONMENTAL CHANGES AT THE MESSINIAN /PLIOCENE BOUNDARY IN THE ALBORAN AREA: THE EXAMPLE OF THE MELILLA BASIN, NE MAROCCO
Jean Marie ROUCHY1, Catherine PIERRE2, Mohamed ET-TOUHAMI3, Karima KERZAZI4, Antonio CARUSO5 and Marie-Madeleine BLANC-VALLERON1
1: CNRS-UMR 5143, Muséum National d’Histoire Naturelle, 43, rue Buffon, 75005 Paris, France.
2: CNRS-URA 1761, LODYC, University P. & M. Curie, 4, place Jussieu, 75252 Paris Cedex 05, France.
3: Université Mohamed Premier, Département Sciences de la Terre, Route Sidi Maâfa, BP 425, 60 000 Oujda, Morocco.
4: Ministère du Commerce, de l’Industrie, de l’Energie et des Mines, Direction de la Géologie, B.P.6208, Rabat/Institut, Morocco.
5: Dipartimento di Geologia e Geodesia, Università di Palermo, Corso Tukory 131, 90134 Palermo, Italy
The Melilla Basin, NE Morocco, located close to the outlet of the southern Mediterranean-Atlantic gateway, is a key area to investigate the depositional changes that affected the Mediterranean at the end of the Messinian Salinity Crisis (MSC). This basin did not experience the Messinian evaporite deposition although the classical succession of the marine preevaporitic deposits i.e., the carbonate platforms and the Tripoli unit, is represented. Three major paleoenvironmental changes are recognized during the late Messinian to Early Pliocene and compared with the events that affected the Mediterranean hydrology at the same time. The first change was the definitive conversion, around 5.8 Ma, of the marine conditions that prevailed in the early Messinian (tripoli deposits and reef carbonate complex) into lacustrine environments. It occurred earlier than in the rest of the Mediterranean where the Lower Evaporites were still forming. Although the absence of typical Paratethyan organisms, these lacustrine settings display great similarities with the classical Lago-Mare event that started in the Mediterranean during the deposition of the Upper Evaporites and climaxed during the latest Messinian. The second change was a long period of subaerial exposure that caused a widespread erosional surface with a deep paleovalley that truncated the whole Messinian deposits in the deeper southwestern part of the basin. This event postdates a lava flow dated at 5.77 Ma and confirms the importance of the latest Messinian erosional event. The third change was the rapid, although progressive, drowning of this topography by the Early Pliocene marine transgression that started there by an intense boring activity, oyster encrusting and deposition of shallow water mollusk-rich deposits. The absence of evaporites in the Melilla Basin may be due to later dissolution, drainage of the brines towards the deeper South Alboran Basin during the MSC or rather low salinity conditions caused by a local excess of continental water inputs. These data confirm that the Rifian gateway was completely closed during the MSC. Such an evolution fits well with the history of depositional environments in the central and southern Alboran area where evaporites are poorly developed and the Messinian mainly represented by an erosional surface.
71) - WHAT CAN BE EXPECTED FROM CORING THE WHOLE MESSINIAN EVAPORITIC SUCCESSION IN THE DEEP BASINS OF THE MEDITERRANEAN?
Jean Marie ROUCHY
CNRS-UMR 5143, Département Histoire de la Terre, Géologie, Muséum National Histoire Naturelle, 43 rue Buffon, 75005 Paris, France
As it is one of the greatest evaporitic episodes of the stratigraphic record, the Messinian Salinity Crisis (MSC) of the Mediterranean has been the subject of active debates and various interpretative models that are still lively discussed. In spite of the unusual volume of high quality data gathered on land-basin and offshore deposits, our knowledge lies on a very small fraction of the evaporitic deposits only. Indeed, the greatest volume of evaporites is located in the huge deep basins where the sedimentary successions reach up to 1.5 km of thickness or much more, including in their lower part a thick massive salt unit whose thickness may exceed locally 1 km. The DSDP-ODP drill cores yielded information on the upper part of the Upper Evaporites only, but never reached the lower massive salt. "The deep sea drilling holes failed to penetrate into the Main Salt Unit. The halite and potash salts encountered in Holes 134, 374 and 376 all belong to the Upper Evaporite” (Hsü et al., 1978). Thus, less than 1% of the salt (halite with associated K-Mg potash deposits) that however represents the greater fraction of the Messinian evaporites has been studied both in land-basins (Sicily, Lorca in SE Spain, Calabria) and in the Sites 134, 374 and 376. Three holes (Sites 372, 375, 654) crossed a complete evaporitic succession, but this succession was similar in thickness and composition to marginal-type evaporites. Thus, most of the evaporite deposits that contain the information crucial for any suitable reconstruction of this event and its consequences still remain inaccessible to direct observation, except for their seismic record. This huge gap in our knowledge should be filled by coring the deep evaporites that could be one of the objectives of an IODP cruise in the Mediterranean (Odysseus project). This would answer most of the crucial questions that are still arising about this unusual event. What is the age of the onset of the MSC in the deeper parts of the basin and the timing of the paleoenvironmental changes that occurred during this period? What do the infrasalt reflectors really represent? What is the magnitude of the evaporative drawdown and its timing? What is the importance of the K-Mg salt deposits trapped in the deeper areas? These deposits are of paramount importance as they record the highest brine concentrations and therefore the maximum evaporative drawdown and hyperarid climate conditions. Was the Mediterranean completely desiccated down to the bottom of the deep basins and if so, how many times did it dry up and how long lasted these episodes of subaerial exposure? Did the post-salt desiccation observed in Sicily affect the deeper basins as well? How deep were the residual brine ponds during salt precipitation? What is the real significance of the cycles in the upper evaporites? To achieve these objectives, the future hole should be drilled in the central part of a deep basin to promote a continuous sedimentary record of the MSC since the pre-crisis paleoenvironmental changes. The area selected should be devoid of significant tectonic influence, as for instance the abyssal plain of the western Mediterranean south of the Gulf of Lion. Due to the mechanical behaviour of the salt, even a moderate deformation would have indeed destroyed the depositional structures. The cores should be submitted to a complete set of integrated studies (sedimentology, geochemistry, micropaleontology, bio-and cyclostratigraphy), with a focus on the salt that is the crucial sedimentary marker of the MSC. This project opens the perspective of a new intellectual adventure that we expect to be as rich and exciting than that which has been initiated by the discovery of this unusual event.
Presentation (PDF - 2,9 Mb)
72) - DIATOM ASSEMBLAGES FROM THE MESSINIAN DIATOMITES OF CASABIANDA (ALERIA FORMATION, EASTER CORSICA)
Simona SAINT MARTIN1, Jean FERRANDINI2, Jean-Paul SAINT MARTIN3 and Michelle FERRANDINI2
1: Université de Bucarest (Roumanie) et MNHN, Département Histoire de la Terre.
2: Laboratoire de Géologie, Université de Corse, BP 52, 20250 Corte, France.
3: MNHN, Dépt. Histoire de la Terre, UMR 5143 Paléobiodiversité, 8 Rue Buffon 75231 Paris Cedex 05, France
The Neogene “Aleria formation”, situated in the northeastern Corsica, consist of siliciclastic deposits from deltaic environment according to Magne et al (1975). In Casabianda section, this formation rests upon erosional surface affecting upper Tortonian sediments and comprises diatomitic lenses and marls with brackish water molluscs (Pilot et al., 1975). Diatomitic deposit of Casabianda section appears white and very homogeneous without stratification and lamination. 15 successive samples were collected. Two of them were steril. Relative abundances (in percentages) of the species in each sample were calculated based on 600 individuals. Diatom microflora of Casabianda is reach and well preserved with 59 species. Pennate indicate a very large diversity with 17 genera and 54 species. Centrics are represented by 4 genera and 5 species. Diatom assemblages show a relative constant composition along the studied interval. The species Aulacoseira granulata is the dominant taxa having about 90% in all samples. All the taxa are represented in Modern diatom assemblages, which allows paleoecological indications for the paleoenvironemental reconstruction. Taxa are of different salinity classes and different mode of life (planktic, tychoplanctic, benthic, epiphytic...) suggesting multiple interactions. The co-occurrence of fresh to marine taxa can be regarded as a result of short term fluctuation in salinity and/or spatial juxtaposition of habitats (Gasse et al., 1987). In the same time, the permanent domination of the planktic freshwater species Aulacoseira granulata should indicate a stable environment. The environmental model suggested by sedimentological and biological data let as to assume a pond-like coastal receptacle common in deltaic system and slowly influenced by marine proximity. Permament freshwater supply is responsible both of nutrient concentration and of the development of a continue freshwater plume (Campeau et al., 1999). These facts can explain the Aulacoseira granulata continuous blooms. A stratified system permits the occurence of the benthic species having a wide salinity range. Among them the constant presence of euryhaline taxa is related to fluctuations in osmotic pressure due to the dispersion of freshwater plume. The geological context suggests an upper Messinian age. References: Campeau S., Pienitz R. & Hequette A. (1999).-Diatoms as quantitative paleodepth ondicators in coastal area of the southern Beaufort Sea, Arctic Ocean. Pal., Pal., Pal., 146: 67-97. Gasse F., Fontes J. c., Plaziat J. C., Carbonel P., Kaczmarska I., De Deckker P., Soulie- Marsche I., Callot Y. & Dupeuble P. A. (1987)-. Biological Remains , Geochemistry and stable isotopes for the reconstruction of the environmental and hydrological changes in the Holocene lakes from north Sahara. Pal., Pal., Pal., 60: 1-46. Magné J., Orszag-Sperber F. & Pilot M.D.(1975)-.La formation d’Aléria : le problème de la limite Miocène-Pliocène en plaine orientale Corse. C.R. Acad. Sci.Paris, t. 280, sér. D : 247-25 Pilot M.D., Brebion ph. & Lauriat-Rage A. (1975)–Les gisements fossilifères du Néogène et du Quaternaire de la région d’Aleria-Vadina. Bull. Soc. Sci. Hist.& Nat. de la Corse, 625, p. 61-75
73) - THE MESSINIAN DETRITAL BODIES: CONFRONTATION OF SEISMIC AND DIVING DATA OFFSHORE MONACO AND CANNES, NW LIGURIAN SEA (NORTHWESTERN MEDITERRANEAN)
Bruno SAVOYE1, Françoise SAGE2, Jean-Pierre REHAULT3, Sébastien ROHAIS4, Cédric BEAUDELOT5 and SESAME team6
1: IFREMER, BP70, 29280 Plouzané, France.
2: Géosciences Azur, BP 48, 06235 Villefranche/Mer, France.
3: Univ. de Bretagne Occidentale, Pl. N. Copernic, 29280 Plouzané, France.
4: IFP, 92852 Rueil Malmaison, France.
5: ENSG, 54000 Nancy, France.
6: Virginie GAULLIER (LEGEM, Univ. de Perpignan), Jacques DEVERCHERE, Christian GORINI (Processus et Bilans Sédimentaires, Univ. Lille 1), Agnès MAILLARD (LMTG, Univ. de Toulouse).
The Var submarine fan is located in the Ligurian Sea off France and extends seaward of the Var delta to the base of the northern continental slope of Corsica. It has been deposited throughout the Pliocene and Quaternary in a basin whose shape and architecture were strongly influenced by the Messinian event. High resolution seismic reflection lines have been used to map the Messinian erosion surface and associated basin-margin deposits on the continental margin, off the french Riviera. A palaeovalley extends seaward from the incised Var palaeovalley mapped on land by Clauzon et al. (1995). The lower part of this valley is filled by an acoustically incoherent unit, interpreted as a coarse-grained pro-deltaic deposit that accumulated during Messinian. Along the base of the slope, conglomerates units had been recognized lying between two erosional surfaces below the base of the Pliocene. Several submersible dives (Cyana, Nautile, ROV) investigated strategic outcrops in order to calibrate the interpretation of the seismic profiles. We examined and sampled outcrops of crossbedded sandstones and of a fining-up, predominantly conglomeratic sequence that fills Messinian channels on the continental slope. These conglomerates pass up into Early Pliocene marls and have turbidite sedimentary structures. These are prodeltaic deposits. Based on new seismic facies mapping, sampling and submersible observations, the palaeogeographic scheme is revisited. A basal erosion surface, including the Var palaeovalley, represents extreme dessication of the western Mediterranean and was followed by accumulation of the main Messinian salt. Cross bedded sandstones sampled within the Cirque Marcel are early Messinian in age. Following this, a lake was ponded in the Ligurian Basin, with accumulation of evaporites and shales. Simultaneously, conglomerates started to deposit on the adjacent slopes. They are organised in two successive fans. One profile clearly demonstrates that the upper and most recent one is correlated to upper evaporites showing a gradual transition towards basin. The new data help to understand the relationships between Messinian detrital and evaporite formation in west Mediterranean.
74) - IMPACT OF THE MESSINIAN SALINITY CRISIS OFF THE WEST AFRICAN MARGIN SEDIMENTS / PRELIMINARY SEDIMENTARY AND ISOTOPIC RECORD OF THE ODP SITE 659
Farid SEGUENI1, Giuseppe SIANI1, Christophe COLIN1, Dominique BLAMART2, Jean-Pierre SUC3, Catherine KISSEL2 and Fabienne ORSZAG-SPERBER1
1: FRE 2566 Orsay-Terre, Université Paris- XI, 91405 Orsay Cedex, France.
2: Laboratoire des Sciences du Climat et de l'Environnement, Laboratoire mixte CNRS-CEA, Avenue de la terrasse 91198 Gif sur Yvette Cedex, France.
3: Laboratoire PaléEnvironnements et PalébioSphère, Université Claude Bernard, 27-43, bd du 11 novembre, 69622 Villeubanne cedex, France.
The aim of this study is to investigate global climatic changes during the late Miocene in relation to the Messinian salinity crisis, through a high-resolution oxygen and carbon isotope and sedimentary record from Site 659 (ODP Leg 108, 18°05’N, 21°02’W, water depth 3070 m) located on top of the Cape Verde plateau off northwest Africa. The age model of Site 659 is based on d18O stratigraphy, correlated to the astronomically dated 18O record from western equatorial Atlantic Site 926 (Shackleton and Hall 1997). Site 659 is characterised by a sedimentation rate on the order of 3 to 5 cm/ka induced by surface high carbonate productivity and by eolian dust input of Sahara and Sahel (Tiedemann et al., 1994). A preliminary d18O and d13C record in bulk fine carbonate fraction has been obtained for the Late Miocene (5-6,5 Ma) at 10 cm intervals corresponding to a time resolution of 4 to 10 ky. Long and short-term d18O and d13C fluctuations are observed in the climatic record and discussed in terms of eustatic, deep water temperature and ventilation changes.
References: Shackleton, N.J., Hall, M.A., 1997 - The Late Miocene stable isotope record, Site 926. In: Shackleton, N.J., Curry, W.B., Richter, C., Bralower, T.J. (Eds.), Proc. ODP Sci. Res. 154, 367–373.
Tiedemann R., Sarnthein M., Shackleton N.J., 1994 - Astronomic timescale for the Pliocene Atlantic d18O and dust flux records of Ocean Drilling Program site 659. Marine Geology, vol 180, pp 71-85.
75) - FIRST DATA ON MESSINIAN PORTUGUESE BIVALVE FAUNA FROM ALGARVE
Barbara STUDENCKA1, Grzegorz ZIELINSKI2, Tomasz BOSKI3 and Ana SANTOS3
1: Museum of the Earth, Polish Academy of Sciences, Al. Na Skarpie 20/26, 00-488 Warsaw, Poland. (bstudencka@go2.pl)
2: Institute of the Geological Sciences, PAS, ul. Twarda 51/55, 00-818 Warsaw, Poland
3: University of Algarve, CIMA, Campus de Gambelas, 8000 Faro, Portugal
The Miocene sequence from the Atlantic frontage in Algarve is made up of two superimposed formations. The lower one, cropping out in the western Algarve, namely the Lagos-Portimão Formation consists mainly of carbonate facies while the upper one, exposed in the eastern Algarve is distinguished as the Cacela Formation. The latter formation represented by a fine to very fine grained, unstratified sand and sandstone occurs now as isolated patches due to post-Miocene erosion. The coastal cliff section within the Cacela Fm along the Algarve coast west of the Cacela village represents only portion of the whole upper Miocene sequence. Until 2002, molluscan-dominated Late Miocene fossil assemblages of the eastern Algarve were known to occur only in the famous sequence of the Cacela River. This exposure has attracted attention of geologists since 150 years because of its assemblage of high species diversity and unique shell preservation. The geological age of this fauna is defined as the latest Tortonian (ca 8.6-7.2 Ma) on the basis of nannofossils, planktonic foraminifers and Sr-data as well. The recent fieldwork, financially supported through the EU Marie Curie Fellowship, has resulted in the abundant and diversified bivalve material derived from three localities (Cabanas, Barroquinha and Lacem) which are accessible during the low-tide only. These new findings give new insight into the Late Miocene history of the marine fauna in the western Atlantic region and allow to get more precise image of faunal exchanges before and/or during Messinian via the Betic Corridor connecting Atlantic and Mediterranean Seas. Crucial factor in these considerations is the geological age. On the basis of Sr-isotopic ratios (ranging from 0.708956 to 0.708980) in the newly collected pectinids from Cabanas and Barroquinha, the Messinian age of the bivalve fauna - about 6.8-6.3 (+/-0.4) Ma - has been defined for the first time in Portugal. Apart from pectinids and oysters which are extremely well preserved, the remaining specimens derived in Cabanas needed some preparatory work. Sixty five species are recognized belonging to 20 families of which the family Veneridae is characterized by particularly high taxonomic diversity. Very high proportion of articulated shells, a wide range of modal size values of fossil species and many specimens preserved in their life position indicate minimum post-mortem alteration. Taxonomic composition of the newly collected bivalve material from these localities resembles more closely the latest Tortonian bivalve fauna from the Cacela River section than the Tortonian/Messinian fauna from the Guadalquivir Basin in Spain and than the Messinian fauna from the Sorbas Basin in Spain.
76) - WHY THREE LAGO MARE EVENTS?
Jean-Pierre SUC1 and Georges CLAUZON2
1: PEPS (UMR 5125 CNRS), Université Cl.Bernard – Lyon 1, 27-43 boulevard du 11 Novembre, F-69622 Villeurbanne Cedex, France. (jean-pierre.suc@univ-lyon1.fr)
2: CEREGE, (UMR 6635 CNRS), Europôle de l’Arbois, BP 80, F-13545 Aix-en-Provence Cedex 04, France (clauzon@cerege.fr)
Since the seventies (Hsü et al., 1973, 1977), the Lago Mare has been understood as the infilling of the Mediterranean desiccated basin by Paratethian brackish waters, which corresponded to one event within the latest Messinian. As a consequence, this event had a chronostratigraphic sense. Then, Corradini & Biffi (1988) and Bertini et al. (1995) added an ecostratigraphic significance to Lago Mare, without attenuating its chronologic assumption. More recently, the evidence of Mediterranean marine water influxes in the Dacic Basin has considerably changed the concept of water exchanges between the Mediterranean Sea and Paratethys (Marunteanu & Papaionopol, 1998) that can only be interpreted as connections during high sea-level episodes (Snel et al., in press; Clauzon et al., in press). In this region, Mediterranean nannoplankton influxes have been recorded before and after the Messinian salinity crisis (Snel et al., in press; Clauzon et al., in press), the consequence of which being also specified in the area (Gillet et al., 2003; Clauzon et al., in press). In the frame of the two-step scenario for the Messinian salinity crisis (Clauzon et al., 1996), it is not only obvious that the Lago Mare biofacies corresponds to a high sea-level crossed exchange between the Mediterranean and Paratethys (involving also dinocysts) but also that two similar events occurred just before and just after the Messinian salinity crisis. Some deposits from the deep Mediterranean basins have been related to “Lago Mare” because of the presence of specimens of the Cyprideis pannonica group: they could represent a freshwater inflow into the hypersaline lagoons of the deep desiccated Mediterranean basins at the extreme end of the crisis just before the Zanclean deluge (Iaccarino & Bossio, 1999). In addition, it cannot be excluded that some “Lago Mare” events correspond to local environmental changes (Cyprus?) (Rouchy et al., 2001).
References:
Bertini A., Corradini D., Suc J.-P., 1995. Rom. J. Stratigraphy, 76, suppl. 7: 141-142.
Clauzon G., Suc J.-P., Gautier F., Berger A., Loutre M.-F., 1996. Geology, 24, 4: 363-366.
Clauzon G., Suc J.-P., Popescu S.-M., Marunteanu M., Rubino J.-L., Marinescu F., Jipa D., in press. Bas. Res.
Corradini D., Biffi U., 1988. Bull. Centres Rech. Explor.-Prod. Elf-Aquitaine, 12, 1, 221-236.
Gillet H., Lericolais G., Réhault J.-P., Dinu C., 2003. C. R. Géoscience, 335 : 907-916.
Hsü K.J., Cita M.B., Ryan W.B.F., 1973. Init. Rep. Deep Sea Drill. Proj., 13, 1203-1231.
Hsü K.J., Montadert L., Bernoulli D., Cita M.B., Erickson A., Garrison R.E., Kidd R.B., Mélières F., Müller C., Wright R., 1977. Nature, 267, 399-403.
Iaccarino S., Bossio A., 1999. Proc. Ocean Drill. Progr., Sci. Results, 161: 529-541.
Marunteanu M. & Papaianopol I., 1998. Rom. J. Stratigraphy, 78, 115-121.
Rouchy, J.-M., Orszag-Sperber, F., Blanc-Valleron, M.-M., Pierre C., Rivière M., Combourieu-Nebout N., Panayides I., 2001. Sedim. Geol., 145: 93-117.
Snel E., Marunteanu M., Macalet R., Meulenkamp J.E., Van Vugt N., in press. Palaeogeogr., Palaeoclimatol., Palaeoecol.
77) - CORING THE MESSINIAN EVAPORITES IN THE NORTHWESTERN MEDITERRANEAN REGION: WHAT A CHALLENGE FOR THE UNDERSTANDING OF THE SALINITY CRISIS!
Jean-Pierre SUC1, Georges CLAUZON2 and Jean-Loup RUBINO3
1: PEPS (UMR 5125 CNRS), Université Cl.Bernard – Lyon 1, 27-43 boulevard du 11 Novembre, 69622 Villeurbanne Cedex, France (jean-pierre.suc@univ-lyon1.fr).
2: CEREGE, (UMR 6635 CNRS), Europôle de l’Arbois, BP 80, 13545 Aix-en-Provence Cedex 04, France (clauzon@cerege.fr).
3: Total, TG/ISS, CSTTF, Avenue Laribeau, 64018 Pau Cedex, France (jean-loup.rubino@total.com).
Since the discovery of the Messinian salinity crisis in 1970, several scenarios have been proposed and discussed a lot. The Clauzon et al.’s (1996) scenario derives from that of Hsü et al. (1973) but differs in considering two phases of lowering of sea-level: a moderate phase, of glacio-eustatism origin, which caused the marginal evaporites (including those of Sicily); then, a prominent phase, of tectonic origin (Clauzon et al., 1996; Duggen et al., 2003), which caused the almost complete desiccation of the Mediterranean Sea, and as a consequence, the deposition of the deep basin evaporites and the cutting of aerial canyons by rivers. This scenario is highly consistent with data on shore and benefits from a large support from oceanographic records (Vidal et al., 2002; Lofi et al., 2003; Warny et al., 2003). Another scenario is now in discussion (Krijgsman et al., 1999), which considers only one salinity crisis, i.e. that marginal and central evaporites are coeval. This means that (1) the first scenario considers an age of 5.7 Ma for the beginning of the central evaporites, in correspondence with Oxygen Isotope Stage TG 15 (Shackleton et al., 1995), (2) the second scenario considers an age of 5.96 Ma for the beginning of all the evaporites, whatever marginal or central, i.e. a certain time before glacial Oxygen Isotope Stages TG 22 and TG 20 (Shackleton et al., 1995). Coring the Mediterranean central evaporites will provide, with respect to Oxygen Isotope Stratigraphy of the underlying sediments, the precise age of their beginning. This will solve the present-day discussion. In addition, the Western Mediterranean appears more propitious for such a project because of the lesser complexity in the evaporitic process deposition than the Eastern Mediterranean. The proposed drilling site by C. Gorini in the Gulf of Lion is fully convenient.
References:
Clauzon G., Suc J.-P., Gautier F., Berger A., Loutre M.-F., 1996. Geology, 24, 4: 363-366. •
Duggen S., Hoernle K., Van den Bogaard P., Rüpke L., Morgan J.P., 2003. Nature, 422: 602-605. •
Hsü K.J., Cita M.B., Ryan W.B.F., 1973. Init. Rep. Deep Sea Drill. Proj., 13: 1203-1231. •
Krijgsman W., Hilgen F.J., Raffi I., Sierro F.J., Wilson D.S., 1999. Nature, 400: 652-655. •
Lofi J., Rabineau M., Gorini C., Berné S., Clauzon G., De Clarens P., Tadeu Dos Reis A., Mountain G.S., Ryan W.B.F., Steckler M.S., Fouchet C., 2003. Mar. Geol., 198: 289- 317. •
Shackleton N.J., Hall M.A., Pate D., 1995 Proc. Ocean Drill. Progr., Sci. Results, 138, 337-355. •
Vidal L., Bickert T., Wefer G., Röhl U., 2002. Mar. Geol., 180: 71-85. •
Warny S.A., Bart P.J., Suc J.-P., 2003. Palaeogeogr., Palaeoclimatol., Palaeoecol., 202: 59-66.
78) - ORIGIN OF SOLUTES AND EVAPORITE DEPOSITION AT THE END OF THE MESSINIAN SALINITY CRISIS. THE ONSET OF “LAGO MARE” SEDIMENTATION
Conxita TABERNER1, Jean-Marie ROUCHY2, Juan Jose PUEYO3 and Matthew THIRLWALL4
1: Institut de Ciències de la Terra (I.C.T.-C.S.I.C.), Lluis Solé i Sabaris s/n, 08028 Barcelona, Spain.
2: UMR 5143 CNRS, Département Histoire de la Terre, Géologie, Muséum National d'Histoire Naturelle, 43 rue Buffon, 75005-Paris, France.
3: University of Barcelona, Depto Geoquimica, Petrologia i Prospeccio Geologica, Z.U. de Pedralbes, 08071, Barcelona, Spain.
4: Department of Geology, Royal Holloway, University of London, Egham, Surrey TW20 0EX, UK.
There has been an historical debate about the type of environments (marine vs. continental) at the end of the ‘Messinian Salinity Crisis’. The inflow of seawater has been claimed as a major source of solutes at the end of the Messinian evaporite precipitation. However, fresh water inflows have been also proposed as a source of solutes into the Messinian seawaters by some authors. A continuous or sporadic inflow of seawater, during the deposition of the Upper Evaporite is mainly supported by 1) the isotopic composition (d34S, d18O) of sulphate beds (e.g. Pierre, 1982; Ricchiuto and McKenzie, 1978) and 2) the sporadic occurrence of marine organisms in the marls interbedded within the Upper Evaporites or in the marginal carbonate units, stratigraphically equivalent to the evaporites (TCC). Nevertheless, a major inflow of freshwaters during the precipitation of the Upper Gypsiferous Unit may be interpreted from d34S values in some sulphate samples and d18Ocalcite at various levels in the Eraclea Minoa - Sicily section (Longinelli, 1979/1980). d34S and d18O of sulphates are powerful markers for the interpretation of evaporite precipitation from marine brines. However, when previously deposited marine sulphates are recycled, d34S and d18O may not distinguish between sulphates precipitated from SO4 2- dissolved in seawater and sulphates recycled from previous marine evaporite sequences (Taberner et al., 2000). In these cases, the combined use of d34S, d18O and 87Sr/86Sr becomes a powerful tool for the interpretation of the source of sulphates and fluids in continental settings (Carmona et al., 2000; Taberner et al., 2002). This approach has been applied to the Messinian Upper Evaporite Unit outcropping in the Eraclea Minoa section (Sicily) and has provided the basis for new interpretations of its depositional environment. The 87Sr/86Sr ratios and d34S and d18O of sulphate beds from the Upper Gypsiferous Unit can be mostly explained as resulting from recycling, by continental waters, of different proportions of Triassic rocks and older Messinian evaporites (Lower Gypsiferous Unit). The contribution of seawater indicated by geochemical and biological markers will be adressed. Also, the palaeoenvironmental implications for the end of the “Messinian Salinity Crisis” (Hsü et al., 1973, 1978) and starting of the so-called “fresh-water crisis” (Longinelli, 1979) shall be discussed.
79) - THE EFFECTS OF THE MESSINIAN SALINITY CRISIS IN THE LEVANTINE BASIN BETWEEN THE CYPRUS ARC AND THE SYRIAN MARGIN: PRELIMINARY RESULTS FROM THE BLAC CRUISE
Elias TAHCHI1, Virginie GAULLIER1, Jean BENKHELIL1, Agnès MAILLARD2, and the BLAC Scientific Party 3
1: LEGEM, University of Perpignan, 52, avenue Paul Alduy 66860 Perpignan Cedex, France.
2: LMTG, UMR 5563; 14, avenue Edouard Belin, 31400 Toulouse, France.
3: Mazhar BAYERLY (Tishreen university), Stéphane BRANCHOUX (1), Thierry COURP (1), Eliane GONTHIER (University of Bordeaux), Christian HÜBSCHER (University of Hambourg
The recent “BLAC” cruise, onboard the R/V “Suroît”, (October-November 2003) has surveyed the 300 km-long Eastern branch of the Cyprus Arc and recorded swath multibeam bathymetry, backscatter imagery, 3.5 kHz (Chirp) and 6-channels seismic profiling. As one of the scientific objectives, the impact of the Messinian Salinity Crisis detained a special and significant interest in the study area. In the Eastern part of the Mediterranean Sea, the thickness of the sedimentary cover (including the Mesozoic series) is extremely important, up to 16.000 meters (Markis et al., 1983), which includes a fairly thin layer of post-Messinian Plio-Quaternary sediments (200-300 meters thick that can reach 1.000-3.000 meters in limited areas of intense sedimentation in the deep basin (Vidal et al., 2000). In the Western and the middle part of the study area, the “M” reflector (attributed to the top of the Messinian sequence) is identified above the 1.5 km thick Messinian evaporites. Eastward the “M” reflector displays erosional features nearby the Syrian margin and the adjacent Cyprus Arc range with a thinner to nonentity absent Messinian evaporites. The strong “M” reflector identified on our new seismic profiles shows several unconformities related to both salt tectonics and compressional crustal-scale tectonics, especially in the Cyprus front area. On the Hecataeus plateau, in the deformed area, the Messinian sequence is thinner and characterized by a “transparent” seismic facies where no distinguishing can be done between salt and Upper Evaporites. The “M”reflector is flat, onlapping the Miocene sediments to the West and then becomes folded, following deformations of the underlying series, to the East. Wavy structures at the top of the Messinian sequence form and grow as we approach the contractional front. In the Levantine basin near the deformation front, a disturbed and high-energy reflector is identified in the thick Messinian sediments, which seems to mark the limit between the transparent mobile salt and the Upper Evaporites. The seismic analysis, combined with the observation of the bathymetry and subsurface structures, reveals the presence of mud volcanoes in the axis of this regional anticline. In the Northern Larnaca – Lattakia basin, Messinian sequences thicken and salt diapirs are well displayed. The main important features revealed by the “BLAC” Survey are erosional surfaces well observed within and/or on top of the Messinian sequences, which must be interpreted in term of environmental and tectonic changes during Messinian Times. References: J. Markis, Z. Ben-Avraham, A. Behle, A. Ginzburg, P. Giese, L. Steinmetz, R.B. Whitmarsh, and S. Sleftheriou, 1983. Seismic refraction profiles between Cyprus and Israel and their interpretation. Geophys. J. Roy. Astr. Soc., 75(3), p.575-591. N. Vidal, J. Alvarez-Marron and D. Klaeschen, 2000. Internal configuration of the Levantine Basin from seismic reflection data (eastern Mediterranean). Earth and Planetary Sc. Letters, 180. p 77-89.
80) - RECONSTITUTION OF THE MESSINIAN EVENTS ON THE EASTERN CORSICAN MARGIN AND IN THE CORSICA BASIN
Isabelle THINON1, Pol GUENNOC1, Jean-Pierre REHAULT2 and Jean FERRANDINI3
1: BRGM, CDG/MA 3 Claude Guillemin BP6009 45060 Orléans cedex 2, France. (i.thinon@brgm.fr, p.guennoc@brgm.fr)
2: IUEM-U.B.O, UMR 6538 "Domaines Océaniques" Place Nicolas Copernic 29280 Plouzané, France. (rehault@univ-brest.fr)
3: Université de Corse - Sciences de la Terre - BP . 52 – 20250 Corte, France. (jferrand@univ-corse.fr)
The Eastern Corsica margin and the Corsica Basin Messinian formations and structures have been recently resurveyed. From 1997 to 2003, we have gathered, processed and interpreted 7100 km of reflection seismic profiles through collaborations with the University of Corsica, the BRGM and the University of Brest. The compilation of this new seismic set with the previous oil industry and academic seismic profiles lead to a precise Messinian erosion surface on the whole “Corsica Basin” between East of the island and the Elba-Pianosa Ridge. From the seismic surveys of the Corsica Basin, the dense grid gave an accurate cartography of the incision Messinian river system. These incisions groove a layered formation interpreted as a thin endoreic deposit, coeval with the evaporitic series of the Ligurian or Tyrrhenian Seas: i.e. an homogeneous layer between a high amplitude reflector for base and a layered formation at the top looking like the succession carbonatic base, halite, upper evaporites. They affect the top of this unit and cut the whole unit up to the underlying Miocene series. This system is composed by a great N-S valley converging towards a large zone of meanders from the West in the southern central area. More discontinuous and small gullies-type incisions are assigned to the base reflector only, rests of a first sea level lowering. Northward, the main valley running along the foot of the Pianosa Ridge, is now clearly uplifted on his flank. Southward, this valley widens, deepens and bypasses the Pianosa Ridge eastward to run into the deeper Tyrrhenian basin. Nevertheless, this southern ending is "obstructed" by a magmatic intrusion and deformed by the continuous uplift of the Pianosa Ridge and East-Sardinia margin during the Mio- Pliocene epochs. This deep incision and widely eroded area emphasise an extremely short and active connection with the Tyrrhenian domain and illustrate the active tectonic context at the end of the Messinian period. It also suggests that the Corsican Basin was inclined southward in the direction of the Tyrrhenian sea at the Miocene periods. On the eastern margin, the Messinian erosion traces on the shelf are used to reconstruct the Messinian slope along the whole margin. The configuration of this slope evidences the tectonic heritage linked to the deep structural pattern. The seismic data have revealed the presence of a residual Miocene shelf in line with the emerged Aleria Basin. Except for this area, the East-Corsica shelf was built almost everywhere by important progradation and aggradation processes at the Pliocene and Quaternary periods. In the North, at the junction of the Pianosa Ridge and the north-eastern margin, a brittle tectonic has affected the pre-messinian units and the thick Plio-Quaternary sedimentary cover in the basin. On the continental shelf many Messinian residual reliefs are present in the topography. The present platform morphology is herited from the Messsinian times. In the South, the east Bonifacio strait is characterised by the restricted Miocene shelf. The occurrence of some remnants of the base of the Messinian and the exhumation of the Lower Miocene formations, directly covered by the Plio-Quaternary depositions, suggest that the final Messinian erosion was wider in the south Corsica Basin than in the northern area. The Messinian incision river system stopping in the South, as the South larger erosion, the uplift of the Pianosa Ridge and the associated magmatic events outline the active brittle tectonics during the Messinian period whereas the Plio-Quaternary depositioncentre migrates regularly northward.
81) - ORGANIC CARBON COMPOSITION AND NEW ORGANIC LIPID PALEOTEMPERATURE PROXY APPLIED TO THE MESSINIAN TRIPOLI FORMATION, CALTANISETTA BASIN, SICILY
Courtney H. TURICH1, Katherine H. FREEMAN1, Antonio CARUSO2 and Ellen C. HOPMANS3
1: Department of Geosciences, Pennsylvania State University, University Park, PA 16802, USA;
2: Dipartimento di Geologia e Geodesia, Universita di Palermo 90124, Palermo, Italy;
3: Department of Marine Biogeochemistry and Toxicology, Netherlands Institute for Sea Research, 1790 AB Den Burg, The Netherlands
Detailed biostratigraphy and cyclostratigraphy in the Messinian Tripoli Formation exposed in northern (Vaccarizzo) and southern (Serra Pirciata) marginal sub-basins correlate the transition from marine to hypersaline conditions across central Sicily. This allows organic matter properties and a new organic geochemical paleotemperature proxy to be interpreted within a robust stratigraphic framework. The paleotemperature proxy, termed Tetraether Index (TEX86), is based on a correlation between the distribution of membrane ether lipids from picoplankton (specifically Archaea) in coretop sediments and annual mean sea surface temperature in modern oceans. We have evaluated this proxy in extractable organic matter from the Serra Pirciata (Tallarita). Our results reveal fluctuating sea surface temperatures trending to an overall cooling from 33ºC to 19ºC prior to the deposition of the Calcare di Base. This could be a record of local water mass temperature fluctuations, or a more regional temperature decrease. However, high S content and a correlation (r2=0.5) between S and C wt% in organic matter may indicate the presence of organic sulfur compounds. Organic sulfur compounds have been reported in similar Messinian material from the Lorca Basin (Spain) and the Vena del Gesso (N. Italy). Furthermore, isoprenoidal ether lipids similar to those used in the TEX86 proxy have been reported as bithiopenes in other Messinian sediments. In future work, we will determine the distribution of sulfur-linked biomarkers in extractable organic matter and their potential influence on paleotemperature calculations. The northern Vaccarizzo section is composed of cycles of marls, laminated limestones, and diatomitic marls. Organic carbon content varies from 0.88 to > 4.0 wt %. In comparison, the Serra Pirciata section is composed of dolomitic marls and welldeveloped diatomites, with 2.0 to 10.0 wt % organic carbon. The organic carbon content therefore supports lithological evidence of enhanced diatom-driven productivity in the Serra Pirciata relative to the Vaccarizzo. The d13Corg record in the two sections are similar during normal marine deposition (to cycle 48), with relatively constant composition from -23 ‰ to -20‰ PDB, considered a normal range for marine algae using the C3 photosynthetic pathway. In the Serra Pirciata section, the d13Corg increases to ~ -18‰ PDB. Previous work reports isotopically depleted inorganic carbon indicative of mineralization of isotopically depleted organic matter. Just prior to the deposition of evaporites in the Serra Pirciata section (cycle 52), the isotopic enrichment of ~5‰ may signal either increased productivity or increased carbon limitation with the onset of evaporitic conditions.
82) - GEOMETRY AND SEQUENTIAL CORRELATIONS OF TORTONIAN TO MESSINIAN PLATFORM TRANSECT ACROSS THE LORCA BASIN (SE SPAIN)
Emmanuelle VENNIN1, Jean Marie ROUCHY1, Antonio CARUSO2, Conxita TABERNER3, Danièle BARTIER4, Christian CHAIX5, Marie-Madeleine BLANC-VALLERON1, Agata DI STEFANO6, Vincent ROMMEVAUX1 and Jean-Yves REYNAUD1
1: UMR 5143 CNRS, Département Histoire de la Terre, Géologie, Muséum National d'Histoire Naturelle, 43 rue Buffon, 75005, Paris, France.
2: Dipartimento di Geologia e Geodesia, Università di Palermo, Corso Tukory 131, 90134-Palermo, Italy.
3: Institut de Ciències de la Terra (I.C.T.- C.S.I.C.), Lluis Solé i Sabaris s/n, 08028 Barcelona, Spain.
4: UMR 7566 CNRS, G2R, Université Henri Poincaré, Vandoeuvre-les-Nancy, France.
5: UMR 5143 CNRS, Département Histoire de la Terre, Paléontologie, Muséum National d'Histoire Naturelle, 8 rue Buffon, 75005, Paris, France.
6: Dipartimento di Scienze Geologiche, Corso Italia 55, 95129 Catania, Italy
Coral reefs represent one of the main carbonate factories that contributed to the control of the stratigraphic architecture of carbonate platforms. This study presents a high resolution sequence stratigraphic model, that enables: (1) a geometrical reconstruction of the depositional system constrained by timelines, (2) a definition of lateral facies changes within depositional sequences, and (3) an evaluation of the role of coral reefs on the stratigraphic architecture of carbonate platforms. The Tortonian to Messinian deposits crop out in the Lorca Basin, SE Spain, and are composed of five mixed siliciclastic/carbonate units. These excellent outcrop conditions allow surface and bedding planes to be physically traced, guaranteeing a robust stratigraphic correlation scheme. A preliminary biostratigraphical study, based on the planktonic foraminifera and calcareous nannoplankton, allowed us to correlate the basal marls, which record the onset of the sedimentary succession before the first carbonate unit with the MMi 11 biozone of Sprovieri et al. (2002). Consequently, on the basis of these biostratigraphic constraints and correlations with the timescale defined in the Sicilian sections, the deposition of the marls was interpreted to have started after 10.55 Ma and before 10.02 Ma. The age of the end of the carbonate platform development is uncertain as the base of the Tripoli unit that immediately postdates the carbonate deposits is dated around 7.7 Ma (Krijgsman et al., 2000) or 6.7 Ma (Rouchy et al., 1998). Reef development probably ceased when the first precursor evaporitic event occurred in the basin centre near the beginning of the Tripoli deposition. At a platform scale, the carbonates are found intermixed with terrigenous deposits related to two main types of clastic systems: alluvial fans and deltaic to fluvial depositional systems. The amount of clastic input affected reef growth and coral morphologies. Twelve facies are distinguished, from distal to proximal, that correspond to shelf carbonate settings and siliciclastic coastal plain environments. The reef morphologies are variable throughout the mixed siliciclastic/carbonate units at the platform scale. The first unit is dominated by bioclasts, whereas units 2, 3 and 5 are sigmoidal carbonate complexes dominated by Porites sigmoid complexes. Unit 4 is a well-developed biohermal complex mainly composed of Tarbellastraea. Four fourth order sequences (tens of meters thick) can be recognised, each of these composed of higher frequency cycles. The geometry of deposits is described as a large scale sigmoidal wedge, prograding towards the basin, and the sedimentation is disturbed by local syn-sedimentary tectonic. The carbonate production changes, from grainproducing biota in the basal unit to a framework-producing biota in the overlying units, that agrees with an evolution from a distally steepened ramp to a reef-rimmed shelf.
83) - COMPARATIVE ANALYSIS OF ECHINOID AND OYSTER PALAEOECOLOGICAL DISTRIBUTIONS BEFORE, DURING AND AFTER THE MESSINIAN EVAPORITIC EPISODE
Blaise VIDET and Didier NERAUDEAU
Laboratoire de Paléontologie, Géosciences Rennes, Campus de Beaulieu, Avenue du Général Leclerc, 35042 Rennes cedex, France. (blaise.videt@univ-rennes1.fr, didier.neraudeau@univ-rennes1.fr)
A comparative analysis between echinoid and oyster Neogene assemblages of the Sorbas basin (southeast Spain) has been realized to evaluate depth, oxygenation and salinity variations of this basin from the beginning of the Messinian to the Early Pliocene. Both groups have already demonstrate their ability to palaeoenvironmental reconstructions, these reconstructions being facilitated by the survival of most of the Messinian species in the Pliocene and the Present-Day Mediterranean basin. First, the distribution of Messinian echinoids assemblages follows an ecomorphological gradient strongly related to environmental depth, but always under normal conditions of salinity. Most of the taxa, such as Clypeaster marginatus, Schizaster saheliensis, Spatangus purpureus or Schizechinus, characterize normal marine silty and muddy substrates of the infralittoral zone. Other ones, like Echinolampas, Psammechinus and Arbacina mark reefal influences in the photic zone. A few species, such as Brissopis atlantica, both in the Mio-Pliocene and the Recent Mediterranean seas, are known to proliferate in deep poor oxygen substrates (circalittoral to bathial). Finally, other echinoids, like Clypeaster altus, are able to settle very high energy coastal environment, where faint variation in salinity can take place sometimes. In the Recent seas, it was demonstrated that salinity variations lead to monstrous « malformations » in the echinoid development. The Messinian oysters are distributed all along the platform from the intertidal zone to the circalittoral zone. Several species of oysters, with their robust shell, are more able to live in high energy environments than echinoderms. Even if environmental distribution of oysters is broader than the one of echinoids, use of specific ratio of Neopycnodonte cochlear and Ostrea lamellosa allows to characterize bathymetric conditions, whatever be the type of sediment. Another species, Hyotissa hyotis, is more generally pledged to reefal conditions and is therefore associated to Psammechinus and Arbacina echinoids. Finally, a few species, like Crassostrea gryphoides, can settle brackish environments where echinoids are absolutely absent. The combination of these two benthic macro-indices in the palaeoecological analysis of the Neogene series of the Sorbas basin allows to follow acurately the evolution of marine faunas and environments before, during and after the Messinian evaporitic crisis. Multivariate analyses have been realized to test the ways of association and distribution of echinoids and oysters in the different Messinian and Early Pliocene beds.
84) - MESSINIAN FORAMINIFERAL ASSEMBLAGES FROM LAMINITES NEAR NIZZA MONFERRATO (PIEDMONT, NORTHERN ITALY)
Donata VIOLANTI1, Lorenzo Mariano GALLO2 and Agostino RIZZI3
1: Earth Science Department, Turin University, via Valpeerga Caluso 35, 10125 Turin, Italy. (donata.violanti@unito.it)
2: Regional Museum of Natural Sciences, via Giolitti 36, 10123 Turin, Italy. (lorenzom.gallo@regione.piemonte.it)
3: CNR – IDPA (Istituto per la Dinamica dei Processi Ambientali), via Mangiagalli 34, 20133 Milano, Italy. (agostino.rizzi@idpa.cnr.it)
Rich assemblages of planktonic foraminifers have been recovered in laminated clayey marls, exposed by works along the Nizza Torrent, in the surroundings of Nizza Monferrato (Asti, Piedmont, Northern Italy). Messinian fillites outcrop in the nearby hillsides and are inferred to overlay the marls. Geological investigations suggest a tectonic evolution more complex than previously reported. In spite of the laminites small exposure, significant data have been collected, for the first time documenting Messinian pre-evaporitic sediments in this area (Violanti & Gallo, 2002). On the basis of foraminiferal assemblages, the laminated clayey marls have been referred to the Messinian Globorotalia conomiozea biozone. Quantitative foraminiferal analyses have been carried out for this study, and testify a deep marine paleoenvironment. Planktonic specimens are strongly dominant (P/(P+B)=95-100%). Warm water taxa, as Orbulina universa, Globigerinoides seigliei, Globigerinoides sacculifer, are frequent, followed by common Globigerina apertura, Globigerinella obesa, Globorotalia conomiozea, Neogloboquadrina acostaensis (sinistral) and Turborotalita quinqueloba. Benthic taxa are represented by rare specimens of Chilostomella oolina, Globobulimina affinis, frequently reported from disaerobic bottoms and sapropelitic layers. Pyrite and ironoxides aggregates, as pyritized tests of planktonic taxa, are very abundant in some layers. Micropaleontological and sedimentological data provide signals of condensed sedimentation. Moreover, rare specimens of Hastigerinella digitata, reported as fossil only from Messinian assemblages of Piedmont more than 25 years ago (Giannelli et al., 1976; Colalongo et al., 1979), have been collected. This finding allows a better correlation with the historical coeval sections of Piedmont, near Alba (Sturani, 1978) or in the Alto Monferrato (upper Rio Mazzapiedi-Castellania section, Rio et al., 1997) and confirms tropical paleoenvironmental conditions in the Piedmont area during the Messinian.
References:
COLALONGO, M.L., DI GRANDE, A., D’ONOFRIO, S., GIANNELLI, L., IACCARINO, S., MAZZEI, R., ROMEO, M. & SALVATORINI, G., 1979, Stratigraphy of Late Miocene Italian sections straddling the Tortonian/Messinian boundary: Boll. Soc Paleont. Ital., 18 (2): 258-302.
GIANNELLI, L., SALVATORINI, G. & SAMPÒ, M., 1976, Segnalazione di Hastigerinella digitata (Rhumbler) in sedimenti del Miocene superiore del Bacino piemontese: Boll. Soc. Paleont. Ital., 15 (2): 159-166.
RIO D., CITA M.B., IACCARINO S., GELATI R. & GNACCOLINI M., 1997, Langhian, Serravallian, and Tortonian Historical stratotypes. In: Montanari A., Odin G.S. & Coccioni R. (Eds) – Miocene Stratigraphy. An integrated approach, Elsevier: 57-87.
STURANI, C., 1978, Messinian facies in the Piedmont Basin: Mem. Soc. Geol. It., 16 (1976): 11-25.
VIOLANTI D & GALLO L.M., 2002, Nuova segnalazione di Hastigerinella digitata (Rhumbler) nel Messiniano del Piemonte (Nizza Monferrato, Asti, Italia NW): Boll. Soc. Paleont. Ital., 42 (1-2): 197-200.
85) - THE BIOTIC RESPONSE OF CALCAREOUS NANNOPLANKTON AT THE ONSET OF THE MESSINIAN SALINITY CRISIS
Bridget WADE1 and Paul BOWN2
1: School of Earth, Ocean and Planetary Sciences, Cardiff University, Main Building, Park Place, Cardiff, CF10 3YE, UK. (wadeb2@cardiff.ac.uk)
2: Department of Earth Sciences, University College London, Gower Street, London, WC1E 6BT, UK.
The rapidly changing and extreme environmental conditions of the early Messinian Salinity Crisis are reflected in abrupt variations in nannofosssil assemblages within the Messinian units (Kalavasos Formation) from the Polemi Basin, Cyprus. During the Messinian, sedimentary and microfossil data indicate that the Polemi Basin was a semienclosed, neritic to littoral environment, subject to repeated influxes of marine and freshwater. This is supported by the absence of open marine nannoplankton (e.g. Discoaster) and the presence of neritic - littoral and freshwater diatoms (e.g. Thalassionema nitzschioides, Coscinodiscus excentricus). The rapidly changing and extreme environmental conditions of the early Messinian Salinity Crisis are reflected in the abrupt variations in nannofossil assemblages. Nannoplankton diversity (3 to 11 species) is greatly reduced in comparison to the open ocean and the assemblages are highly uneven, with high dominance. One of five species were observed to dominate any of the assemblages, these were Reticulofenestra minuta, Dictyococcites antarcticus, Helicosphaera carteri, Umbilicosphaera jafari and Sphenolithus abies. The associated diatom and sedimentological evidence from the Polemi Basin are used to indicate the palaeoecology of key nannofossil taxa. D. antarcticus predominated in normal salinity, mesotrophic, shallow water environments; H. carteri in shallow, brackish, hyper-eutrophic environments; U. jafari in hypersaline conditions; R. minuta in hypereutrophic conditions with an abnormal salinity from brackish to hypersaline; S. abies in mesotrophic, deeper and normal salinity environments. These species are indicated to be opportunistic, adapted to unstable environments. Fluctuations in nutrient levels and salinity are interpreted as the primary factors controlling the overall nature of the nannoplankton assemblages and the species which dominate at any one level.
86) - AEGEAN BRACKISH MOLLUSKS AND MEDITERRANEAN - EUXINIAN CONNECTIONS DURING THE MESSINIAN
Sergej POPOV and Lidiy A. NEVESSKAYA
Paleontological Institute RAS, Profsojuznaja 123, Moscow 117868, Russia
Brackish Pontian-like mollusks are known in the Mediterranean domain since the 19 century from Barcelona area, North Italy, Sicily, and Aegean area. Many specialists found here species, which were common with the Paratethys, and proposed the Thracian - Aegean Gulf of the Paratethys existed during the Messinian, or in Paratethys scale, during the Pontian, Maeotian, and sometimes - late Sarmatian). Well-preserved Pontian-like mollusks were studied from the Serres basin, Northern Greece. 22 species of brackish and lagoon bivalves and one species of gastropods were determined from Choumnikon formation, from which 6 species and one subgenus of cardiids were described as a new (Popov, Nevesskaya, 2000). 8 species are common with the Eastern Paratethys Pontian, the most characteristic - Lymnocardium (Euxinicardium) nobile, Eupatorina littoralis, Pseudocatillus pseudocatillus, Paradacna abichi. From other side the association include 5-6 species and genera Mactra and Cerastoderma unknown in the Pontian but present in the Upper Messinian complexes of the Spain, North Italy and Sicily. On the base of high specific mollusk fauna, as well as paleomagnetic and astronomical cyclicity data (Snel et al., 2002) the Choumnicon formation is correlatable with the Pontian and the Upper Messinian. Overlying continental Spilia formation contains mammal remains, age of which was defined at the Turolian - Ruscinian transition (Schmidt-Kittler N. (ed), 1995). From paleogeographic point of view the North Aegean basin was not a gulf of the Paratethys. It was more closely connected with the Mediterranean Messinian basin, based on marine polyhaline fauna of underlying Dafni formation (with colonial corals, Pecten benedictus, Arca, Anadara, Chama, Cardita, Venus) and overlying strata (with Neopycnodonte) and faunistic similarity of the Choumnicon mollusks with the Upper Messinian ones. Thick Messinian evaporites are known from this region. It is possible, the North Aegean Basin was the intermediate one, where the Maeotian and Pontian mollusk associations had been formed.
