The Messinian Salinity Crisis Revisited - Corte, July 2004

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1) -MESSINIAN EVENTS IN THE WESTERN MEDITERRANEAN: THE RECORD IN THE NEOGENE ALMERÍA BASINS AND ALBORÁN SEA

Julio AGUIRRE1, Juan C. BRAGA1, Jaume DINARÈS-TURELL2, José M. MARTÍN1, Robert RIDING3 and Isabel M. SÁNCHEZ-ALMAZO1

1: Departamento de Estratigrafía y Paleontología, Universidad de Granada, Campus Fuentenueva, 18002, Granada, Spain.
2: Istituto Nazionale di Geofisica e Vulcanología, Via di Vigna Murata, 605, 00143 Roma, Italy.
3: School of Earth, Ocean and Planetary Sciences, Cardiff University, Cardiff CF10 3YE, U.K
.

The sedimentary record in the Neogene Vera, Sorbas, Almería-Nijar and Carboneras- Agua Amarga basins in Almería, SE Spain, and in deep-sea cores from the Alborán Sea suggests a sequence of major events in the palaeoenvironmental evolution of the western Mediterranean during the Messinian. Non-reefal carbonates formed at the basin margins during the latest Tortonian-earliest Messinian. Subsequent carbonate deposition during the early Messinian was dominated by coral reef and Halimeda accumulations. The regional extent of these deposits together with oxygen stable isotope signals indicates that surface-water temperatures were the main factor controlling the carbonate lithofacies. Shallow-water carbonates change basinwards into cyclic fine-grained basin deposits enclosing re-deposited material from the platforms. A major erosion surface cut into both the platform carbonates and the basin deposits records subaerial exposure of the basins, and was probably coeval with the desiccation of the Mediterranean Sea that led to evaporite deposition in the centre of the deep Mediterranean basin. Although geochemical data suggest a certain degree of isolation from the Atlantic Ocean, probably related to the closure of the Betic corridors, the palaeontological record in shallow and deep water deposits indicates that normal marine conditions prevailed in the western Mediterranean until desiccation. When the Mediterranean Sea recovered its normal level during the late Messinian, marginal basins were reflooded. Deposition of evaporites took place in those basins semiisolated from the main Mediterranean body. Gypsum beds and pelitic interbeds onlap the major erosion surface and are gradually followed by marine sediments in the marginal basins. The occurrence of coral reefs on the platforms, and the widespread record of planktonic foraminifers and nannoplankton in deeper-water deposits, indicate re-establishment of normal marine conditions in the western Mediterranean before the end of the Messinian. Continued uplift of the Betic Cordillera promoted the emersion of the inner basins (most distant from the present-day coast line), such as the Sorbas Basin, during the latest Messinian. Red fluviatile and lacustrine deposits locally formed in these basins, whilst marine sedimentation continued to Pliocene times in the outer basins and in the Alborán Sea.


2) -EVIDENCE FOR AFRICAN-IBERIAN MAMMAL EXCHANGES IN THE LATE MIOCENE-EARLY PLIOCENE CONTINENTAL BEDS OF THE GUADIX FORMATION (GUADIX-BAZA BASIN, SE SPAIN)

Jordi AGUSTÍ1, Raef MINWER-BARAKAT2 and Oriol OMS3

1 : Institut de Paleontologia M. Crusafont (D. Barcelona-Unidad Asociada CSIC). 08201, Sabadell, Spain.
2 : Dep. de Estratigrafía y Paleontología. Facultad de Ciencias. Campus de Fuentenueva. Universidad de Granada, Granada, Spain.
3 : Departament de Geología. Universitat Autònoma de Barcelona. 08193, Bellaterra, Spain.

In this paper, we present data from fossil mammal localities in the late Miocene-early Pliocene continental deposits of the Guadix Formation from the Guadix-Baza Basin. Since these deposits should be coeval with the Messinian Salinity Crisis of the Mediterranean (5.96-5.33 Myr), it can be investigated if this dramatic event in the marine realm had any impact on the terrestrial ecosystems. The various African immigrant species invading Iberia during the Messinian can now be studied in a high-resolution time frame, which may significantly help to understand the geodynamic and paleogeographic evolution of the marine and continental gateways in the western Mediterranean region. One of the main events that have been related to the Messinian Salinity Crisis is the dispersal of gerbil rodents into Southern Spain. The gerbils are subdesertic rodents that today inhabit the dry landscapes of northern Africa and southwestern Asia. They appear as rare elements in a number of early Ruscinian localities from Southern Spain (Caravaca, Gorafe 1; Bruijn, 1974) and have been usually interpreted as African elements having entered Spain during the Messinian, at the same time that Paraethomys or Paracamelus. This hypothesis gained further support after the discovery in Spain of fissure infillings in which other north African rodents such as the Myocricetodontine hamsters appeared associated with gerbils. This is the case of Salobreña (Aguilar et al., 1983) and Almenara M (= Casablanca M, Agustí & Galobart, 1986). However, because of their karstic character the exact chronology of these localities remained uncertain for years. Therefore, the locality of Negratín has delivered a small mammalian fauna including Parasorex ibericus, Soricidae indet., Apodemus gudrunae, Paraethomys meini, Stephanomys dubari, Occitanomys alcalai, Apocricetus alberti, Ruscinomys sp., Debruijnimys sp., Myocricetodon sp., Eliomys sp., Atlantoxerus sp. Negratín 1 is the first fluvio-lacustrine locality in which African rodents other than the gerbils Debruijnimys or Protatera have been recovered. The recent advances in the chronostratigraphy of Guadix-Baza and other Betic basins enables one to shed light on the dating of the gerbil dispersal into Spain. The detailed mammal record allows us furthermore to study the zoogeographical changes that took place in southeastern Spain during the time interval from 7.6 to 4.8 Ma.


3) -THE MESSINIAN OF TUSCANY: TECTONO-SEDIMENTARY EVOLUTION ALONG A TRANSECT FROM THE PERI-THYRRENIAN RIDGE TO THE CHIANTI MOUNTS

Mauro ALDINUCCI1, Alessandro BOSSIO2, Luca FORESI1, Roberto MAZZEI1, G. SALVATORINI1 and Fabio SANDRELLI1

1 : Department of Earth Sciences, University of Siena, Italy.
2 : Department of Earth Sciences, University of Pisa, Italy

Neogene Tuscan basins provide a valuable record of Messinian time in a variety of depositional systems whose evolution resulted from the complex interplay between regional tectonics, climate and sea-level changes related to the salinity crisis of Mediterranean Sea. Such basins resulted from the Late Miocene block-faulting which gave rise to NNE-SSW oriented tectonic depressions limited by emerging topographic highs. In this work a review of the Messinian deposits exposed along a transect from the Thyrrenian Sea to the Chianti Mounts is proposed. The main morphological features along this transect are, from west to east: the Pery-Thyrrenian Ridge, the Fine Basin, the Castellina Ridge, the Volterra-Radicondoli Basin, the Middle Tuscan Ridge, the Valdelsa Basin and the Chianti Mounts. The Middle Tuscan Ridge played a major role in governing the depositional evolution of these basins, separating the western ones, in which short-lived marine conditions developed, from the eastern ones, characterized by continental sedimentation.
WEST OF THE MIDDLE TUSCAN RIDGE - In the marginal highs of Fine Basin, Early Messinian deposits rest onto the allochthonous Ligurian Units (ophiolites, pelagic and flysch deposits) and are represented by the Rosignano Limestone. It records two main sedimentary cycles, each one consisting of basal conglomerates overlying by platform carbonate deposits (barrier reef and lagoonal carbonates in the lower one, patch reef carbonates in the upper one) which pass basinward to marine fines (e.g. laminated marine clayey marls and diatomitic marls). In the Volterra-Radicondoli Basin, early Messinian deposits comprise brackish marls with a first horizon of laminated gypsum (“Balatino” Auct.) and laminated marls with serpulids. They rest unconformably onto the pre-neogene substratum or conformably onto upper Tortonian lacustrine fines (“Serie Lignitifera” Auct.). In the marginal part of the basin, the brackish lithofacies are separated from patch reef lithofacies (correlable with the upper part of the Rosignano Limestone exposed in the Fine Basin) by an angular unconformity marked by conglomerates. Such an unconformity passes basinward to a correlative conformity and the marginal carbonate lithofacies are replaced by marine fines (marine clays with Neopycnodonte navicularis). Evaporitic Messinian deposition begins in the Fine Basin and in the Volterra Radicondoli Basin with gypsum horizons; a following erosional phase gave rise to an unconformity surface separating the marine deposits from the overlying, brackish to continental-lacustrine clays, marls, gypsum, sands and conglomerates, typically referred to the Lac-Mer succession.
EAST OF THE MIDDLE TUSCAN RIDGE - In the Valdelsa Basin, early Messinian deposits are represented by a few metres of brackish clays overlying the uppermost siliciclastic fines of the “Serie Lignitifera” succession. An intense erosional phase gave rise to an unconformity separating the brackish clays from the late Messinian fluviolacustrine sediments, which can be referred to the Lac Mer depositional phase recorded in the western basins, although devoid of gypsum lithofacies. The Early Pliocene marine transgression overstepped the Middle Tuscan Ridge up to the Chianti Ridge, leading to the dominantly sedimentation of outer platform clayey sediments with subordinate sands and conglomerates. In the basin depocentres, these deposits typically overlies the Lac-Mer successions without intervening unconformities. This suggests that the transition from the Lac Mer continental-lacustrine sedimentation to the Early Pliocene sea took probably place within a submerged setting.


4) -SEQUENTIAL SCHEME OF THE MESSINIAN SINIS PENINSULA SUCCESSION (SARDINIA)

France Jean-Pierre ANDRE1, Frédéric GARCIA2, Jean-Jacques CORNEE3, Pierre MOISSETTE3, Jean-Paul SAINT MARTIN4 and Michelle FERRANDINI5

1 : Laboratoire de Géologie, UPRES EA 2644, Université d'Angers, Bd Lavoisier, 49045 Angers cedex, France.
2 : Centre de Sédimentologie-Paléontologie, UMR 6019, Université de Provence, 3 place Victor-Hugo, 13331 Marseille cedex 03, France
3 : UFR Sciences de la Terre, UMR 5125 PEPS, Université de Lyon I, 27 Bd du 11 Novembre, 69622 Villeurbanne cedex, France
4 : MNHN, Département Histoire de la Terre, UMR 5143 Paléobiodiversité, 8 Rue Buffon 75231 Paris Cedex 05, France
5 : Laboratoire de Géologie, Université de Corse, BP 52, 20250 Corte

The unusual Messinian succession in the Sinis Peninsula raises several correlational questions (André et al., 2004). On the basis of biostratigraphical and sedimentological data a new sequence stratigraphic interpretation is proposed. Four lithostratigraphical units are distinguished: the Basal Marls, the Capo San Marco Formation, the Sinis Limestones and the Torre del Sevo Formation. The three lower formations developed during one and a half progradation-retrogradation cycle, the latter is composed of minor order stacked prograding sequences. The Basal Marls and the Capo San Marco Formation display a marly facies at the base, followed by silty and sandy marls, and capped by organic buildups with vermetid gastropods and diverse shallow-water bivalves at the top. Fauna and microfauna indicate deep-waters at the bottom changing upward into shallower associations. The succession is an overall upward-shallowing sequence typical of a prograding prism comprising deposits from a Southwest gently dipping mixed carbonate-siliciclastic ramp. The upper part of the Capo San Marco Formation and the whole Sinis Limestones compose a second prograding unit. This second unit rests upon a transgression surface merged with a maximum flooding surface at the top of the uppermost microbialbryozoan- serpulid buildups. Facies and sedimentary structures are indicative carbonate platform of great extent, most of it being considered as a prograding prism terminated by bioclastic and oolitic facies. The top of the Sinis Limestones is capped by an aerial surface. The Torre del Sevo Limestones Formation is made of stacked progradational subunits, each constituted of marine shallow water carbonate deposits (ooids, vermetids, stromatolites and subaerial exposures at the top). The Torre del Sevo Limestones was deposited in a regional shallow-water carbonate platform. Compared with other Messinian Mediterranean carbonate platforms, the Sinis Peninsula exhibits several unusual features such as the notable absence of scleractinian coral reefs and the widespread occurrence of microbial-bryozoan-serpulid carbonate buildups. These features are regarded as related to upwelling currents.


5) -MESSINIAN PROLAGUS (LAGOMORPHA, MAMMALIA) OF ITALY

Chiara ANGELONE

Dipartimento di Scienze Geologiche, Università Roma Tre, Largo San L. Murialdo, 1 – 00146 Roma, Italy

Since the Middle/Late Miocene boundary and during all Late Miocene, after a severe exctinction phenomenon (López Martínez, 2001), the distribution of the genus Prolagus in continental Europe consists in a succession of single species. During Messinian (corresponding to the second half of the Turolian Mammal Age and to the Late MN12- MN13 Units), Prolagus is quite widespread in continental Europe with a wellcharacterized species, P. michauxi. In Italy, Messinian Prolagus remains have been reported from the following fossiliferous sites: Brisighella (Emilia-Romagna, latest MN13), Prolagus cf. P. sorbinii (Masini, 1989); Monte Castellaro (Marche, MN13), Prolagus sorbinii (Masini, 1989); Ciabòt Cagna (Piedmont, MN13), Prolagus michauxi (Cavallo et al., 1996); Velona Basin (Tuscany, MN13), Prolagus ex gr. P. sorbinii-P. michauxi (Rook & Ghetti, 1997); Capo di Fiume (Abruzzi, earliest MN13), Prolagus cf. P. apricenicus (Mazza et al., 1995). To this list it should be added P. apricenicus and P. imperialis from the Gargano fossil archipelago (Apulia) (Mazza, 1987), related to the Middle Miocene species P. oeningensis. Their age attribution probably ranges between late MN13(?) and early MN14. Being P. sorbinii a species close to P. michauxi, italian Messinian Prolagus findings are ascribed or are closely related to P. michauxi or to P. oeningensis (P. apricenicus, P. imperialis and referable forms). Such systematic considerations give some palaeobiogeographical and temporal hints, confirmed by the faunal assemblages associated to Prolagus: - the above mentioned Italian fossiliferous sites belong to different palaeobioprovinces: a southern, insular domain (Abruzzi-Apulia PB) characterized by insular endemic species, and a northern domain (NI), representing a peripheral continental European appendix and populated by non-endemic faunal elements; - different faunal affinities for the palaeobioprovinces and consequently different “source areas”: a Balkan affinity for the Abruzzi-Apulia PB and a European affinity for the NI; - distinct ages and modalities of colonization. The age of Prolagus colonization of Gargano is uncertain, since P. oeningensis does not survive in central Europe longer than earliest MN9 but no data are available for the Balkan area; moreover the nature of the connection is not clear. On the other hand for NI, a continuous interchange with continental Europe should be invoked, probably with minor geographical filters.
References:
CAVALLO O. ET AL. (1996) – Riv. Piemontese St. Nat., 14: 3-22.
MASINI F. (1989) - Boll. Soc. Pal. It., 28: 295-306.
MAZZA P. (1987) - Boll. Soc. Pal. It., 26: 233-244.
MAZZA P. ET AL. (1995) – Boll. Soc. Pal. It., 34: 55-66.
LÓPEZ MARTÍNEZ N. (2001) - Lynx, n.s., 32: 215-231.
ROOK L. & GHETTI P. (1997) – Boll. Soc. Geol. It., 116: 335-346.


6) -MESSINIAN EVENTS IN A RAPIDLY SUBSIDING AND TECTONICALLY CONTROLLED FORELAND BASIN: THE SOUTHERN LAGA BASIN (CENTRAL APENNINES, ITALY)

Andrea ARTONI

Dipartimento di Scienze della Terra Università degli Studi di Parma, Parco Area delle Scienze 157/A I-43100 Parma, Italy. (andrea.artoni@unipr.it)

The Southern Laga Basin of Northern Abruzzo is considered to have been the largest and most rapidly subsiding turbiditic depocenter of the Apennine foredeep during the Messinian. Taking a physical stratigraphic approach, a new stratigraphic scheme, consisting of four unconformity bounded stratigraphic units (U.B.S.U.), is proposed for the deepest portion of the Laga basin. The depositional events together with the palaeoenvironmental interpretation of the depositional units framed within the 4 U.B.S.U. reveal the vertical transition from deep marine to lacustrine and fluvio-deltaic environments, encouraging reconsideration of the real bathymetry of the Southern Laga Basin in Northern Abruzzo. The four Messinian units document also the transition from a foredeep to a wedge-top basin; a transition controlled by a progressive shortening and uplift of the thrust-related folds present in the Southern Laga Basin. The Messinian sedimentary and tectonic events recorded in the Southern Laga Basin are strikingly similar to those recognised in less subsiding and marginal sectors of the Apennine foreland, which thus preserves a similar tectonic and sedimentary evolution over an area as wide as the whole Adriatic foredeep.

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7) -THE “SALINITY CRISIS” STRATIGRAPHIC AND STRONTIUM ISOTOPES RECORD IN THE MESSINIAN SOUTHERN APENNINES FORELAND BASIN, ITALY

Maurizio BARBIERI1, Silvio DI NOCERA2, Fabio MATANO2 and Mario TORRE2

1 : Dipartimento di Scienze della Terra, Università degli Studi “La Sapienza”, Piazzale A. Moro 5, 00185 Roma, Italy
2 : Dipartimento di Scienze della Terra, Università degli Studi "Federico II", Largo S. Marcellino 10, 80138 Napoli, Italy

The Mediterranean region was involved during the Messinian in a pervasive salinity crisis, characterised by two major evaporitic sedimentary cycles, as the lower evaporites and upper evaporites in Sicily and Tyrrhenian Sea bottom. In Northern Apennines the upper evaporites are not present and are substituted by clastic post-evaporitic deposits, formed by two mainly terrigenous unconformity-bounded units. Two Messinian evaporite-bearing units crop out in Irpinia-Daunia Mountains (southern Apennines, Italy). The Daunia and Vallone del Toro units record the tectonic and palaeogeographic evolution of the Messinian southern Apennine foreland basin system during the salinity crisis, and have never been studied with an integrated stratigraphic and Sr geochemical regional approach. Detailed mapping, stratigraphic studies, facies analyses of gypsum lithologies, strontium content and 87Sr/86Sr isotopes ratio analytical determinations have been carried out in order to: (i) evaluate depositional conditions of the evaporites, (ii) discriminate between lower and upper type evaporite, (iii) discuss the palaeogeographic and tectonic controls on the evaporite sedimentation. The Daunia unit comprises the Monte Castello Evaporites, formed by euxinic diatomitic marls, evaporitic limestones and shallow-water gypsum, characterised by a 87Sr/86Sr average value of 0.70898 ± 0.00005, very close to the Sr isotopic value of the coeval seawater. These marginal evaporites are capped by an erosional unconformity and continental clastic deposits. The Vallone del Toro unit is made up of thin-bedded marls, claystones, calcilutites and diatomite layers with small gypsum crystals, laminated gypsum and gypsarenite layers without desiccation traces, suggesting deposition in relatively deep-water settings. The Vallone del Toro unit gypsum presents variable Sr isotopic data, with the average value of 0.70899 ± 0.00005 for the "Argilliti policrome del Torrente Calaggio" formation and the average value of 0.70863 ± 0.00014 for the "Argilliti di Mezzana di Forte" formation, reflecting major riverine freshwater input. The strontium content and 87Sr/86Sr isotopes ratios of primary gypsum lithofacies allowed us to discriminate between "lower" and "upper" type evaporites in the southern Apennines foreland basin. The different patterns of lithofacies and isotopic composition of gypsum characterizing the evaporites of the marginal and basinal deposits reflect the tectonic control and the palaeogeographic setting with respect to the Apennine thrust front and the Mediterranean Basin. The southern Apennine foreland basin evaporites data confirms the presence of basins in the central and eastern Mediterranean Sea, which never desiccated during the entire salinity crisis and evolved to widespread Lago-Mare conditions in the latest Messinian.


8) -MESSINIAN SEDIMENTARY EVOLUTION OF THE ROSSANO BASIN (CALABRIA, ITALY): PRELIMINARY INVESTIGATIONS

Mirko BARONE1, Rocco DOMINICI1, Stefano LUGLI2, Francesco MUTO1, Cesare RODA3, Salvatore CRITELLI1 and Maurizio SONNINO1

1: Università degli Studi della Calabria, Dipartimento di Scienze della Terra, 87036 Arcavacata di Rende, Cosenza, Italy.
2: Dipartimento di Scienze della Terra, Università degli Studi di Modena e Reggio-Emilia, Largo S. Eufemia 19, 41100 Modena, Italy.
3: Dipartimento di Georisorse e Territorio, Università degli Studi di Udine, Via Cotonificio 114, 33100 Udine, Italy.

Neogene sedimentary basins of eastern Calabria include abundant Messinian primary and resedimented evaporite sedimentation in the Crotone and Rossano basins. These basins are filled by Tortonian to Pleistocene dominantly clastic sedimentation interbedded with Messinian evaporite cycles. New geological, sedimentological and petrographic data are here used to describe the stratigraphic architecture of the Rossano Basin. The Tortonian sequence unconformably covers the Paleozoic plutonic-metamorphic complex of the Sila Massif or the Late Oligocene to early Miocene clastics of the Paludi Formation. The Tortonian sequence, represents a characteristic transgressive system with an alluvial red conglomerate, passing into nearshore sediments and deep-marine turbidite strata probably deposited during a low-stand system tract. The latter strata are followed, throughout an angular unconformity, by marls and diatomaceous shales including sulphate nodules (Tripoli Fm.), carbonates with decimetric intercalation of varicolored marl-clays (Calcare di Base Fm.) and gypsumrudite-gypsumarenite deposits associated with clastic carbonates. This first evaporite deposits pass throughout a second angular unconformity to arenites, marls, halite, gypsarenites and olistostromes of variegated clays. In the eastern sector of the basin the euxinic shales of the Tripoli Fm. are truncated by an important erosional surface and followed by a chaotic complex including large gypsarenite and nodular gypsum blocks and by a succession of gypsum siltstone, gypsumarenite and breccia. The clastic evaporite sedimentation is capped by deep-marine hemipelagic marls and sandstone turbidites (Garicchi Fm.) and sandstones (Palopoli Fm.). The Rossano basin records the Messinian salinity crisis events in a complex basinal setting related to the foreland fold-thrust belt of southern Italy orogen.


9) -STRATIGRAPHY AND DETRITAL MODES OF THE LATE MESSINIAN POST-EVAPORITIC SANDSTONES OF THE SOUTHERN APENNINES FORELAND BASIN SYSTEM, ITALY

Mirko BARONE1, Salvatore CRITELLI1, Silvio DI NOCERA2, Emilia LE PERA3, Fabio MATANO2 and Mario TORRE2

1 : Dipartimento di Scienze della Terra, Università degli Studi della Calabria, Rende (CS), Italy.
2 : Dipartimento di Scienze della Terra, Università degli Studi Federico II, Napoli, Italy.
3 : CNR - Istituto di Ricerca per la Protezione Idrogeologica, Rende (CS), Italy

Post-evaporitic sandstones in the Irpinia-Daunia sector of the southern Apennines foreland basin system records both the effects of the foreland evolution and the Messinian salinity crisis occurred in vaste areas of the Mediterranean region. During the Messinian salinity crisis, the southern Apennines experienced intense accretion and uplift. The Irpinian-Daunia ranges of the southern Apennines preserve remnants of the Messinian thrust-belt. The Messinian stratigraphy includes: (a) preevaporitic thin-bedded euxinic marly clay interbedded with diatomaceous marls. The environmental conditions are referred to a pelagic starved basin; (b) evaporitic limestone, crystalline shallow-water gypsum and reworked gypsum. The evaporitic and post-evaporitic sequences are separated by an erosive unconformity; (c) the postevaporitic deposits are subdivided in three subunits. The Torrente Fiumarella unit, composed of lacustrine and alluvial conglomerate, sandstone, shale and reworked clastic gypsum; the Anzano Molasse, composed of thick bedded conglomerate and turbidite sandstone, passing upward to thin bedded turbidite sandstone and marlyclayey siltstones. Rare freshwater ostracods are present. Volcaniclastic layers are interbedded with turbidites in the upper part of the sequence. The "Lago-Mare" facies deposits are represented by arenite and silty-marly clay with abundant Ostracoda shells (Ilyocypris gibba, Cyprideis torosa and Candona sp.). The Torrente Fiumarella sandstones are quartzolithic and include abundant carbonate lithic fragments. Sandstones of the Anzano Molasse are quartzofeldspathic; aphanitic lithic fragments are dominantly sedimentary, both carbonate and siliciclastic particles. Total rock fragments include variable proportions of plutonic and sedimentary fragments. In particular, two populations are evident, one plutonic-rich, and a mixed plutonic and sedimentary. Anzano Molasse volcaniclastic strata are composed of dominantly vitric particles (shards and pumice). Arenites of the Lago-Mare facies are hybrid arenites, having abundant intrabasinal carbonate particles (ooids, peloids, and bioclast) and subordinate extrabasinal noncarbonate and carbonate particles. The interplay of the accretionary tectonics of the Irpinian sector of the thrust belt and the evaporite sedimentation caused key perturbations in the sedimentary record of the basin fillings. The abrupt change from hemipelagic and turbidite sedimentation and the evaporite and clastic sedimentation is here explained by the interplay of accretionary tectonic and regional and local sea-level changes. Detrital modes testify complex provenance relations from the accreted terranes forming the late Messinian thrust-belt. All sandstones have abundant plutonic and sedimentary detritus. Sedimentary detritus consists of both carbonate and siliciclastic particles. Carbonate detritus includes both pelagic and shelfal microfacies suggesting provenance from deformed basinal and platform sequences assembled within the thrust-belt. The abundance of plutonic and metamorphic detritus may suggest a provenance from both the accreted Calabrian Arc terranes or recycling from older clastics as suggested by the presence of variable percentages of siliciclastic debris.


10) -CLAY MINERALS STUDY OF THE TORTONIAN TO MESSINIAN PLATFORM TRANSECT ACROSS THE LORCA BASIN (SE SPAIN)

Danièle BARTIER1, Emmanuelle VENNIN2, Jean Marie ROUCHY2, Marie-Madeleine BLANC-VALLERON2 and Vincent ROMMEVAUX2

1: UMR 7566 CNRS, G2R, Université Henri Poincaré, Vandoeuvre-les-Nancy, France.
2: UMR 5143 CNRS, Département Histoire de la Terre - Géologie, Muséum National d'Histoire Naturelle, 43 rue Buffon, 75005-Paris, France.

The Lorca Basin is situated in the Murcia Province (SE Spain), it is one of several interconnected Neogene basins that formed within an extensive northeast trending shear zone of the Betic Cordillera. The Tortonian to Messinian deposits cropping out along the SW margin of the Lorca Basin are composed of five mixed siliciclastic/carbonate units. Each unit is composed of calcarenitic to marly sediments that grade upward into mostly carbonate deposits. Units contain several types of reefs that differ in size, geometry, coral diversity and abundance of coralline algae. The top of each unit is bounded by an erosive surface associated with subaerial exposure. The marls deposited before the first unit start, based on biostratigraphic constrains (planktonic foraminiferal and calcareous nannoplankton), after 10.55 Ma and before 10.02 Ma. The end of the carbonate platform development is uncertain, reef growth probably ceased when the first precursor evaporitic event occurred in the basin centre near the beginning of the Tripoli deposition. This work is the first steep of a more global clay minerals study of the five mixed siliciclastic/carbonate units and their correlations with deposits of the central part of the basin. In this first steep we describe the clay minerals content of about 100 marls samples corresponding to off-reef deposits of each unit and interlayered reef deposits. The clay fraction of the marls deposited before the Unit 1 is composed of about 60% of smectite , 30% of illite and 10% of chlorite. This assemblage differs from the overlying off-reef marls of the Unit 1 which displays smectite (30-60%), illite (30-45%), chlorite (0- 10%) and kaolinite (0-20%). The clay minerals patterns of marls between reef Units 1 and 2 are also different and display smectite (30-60%) illite (15-25) palygorskite (10-15%) chlorite (5-20%) and kaolinite (0-5%). Clay minerals content of marls which crop out between Units 2 and 3 are comparable to clay minerals content of the off-reef marls of the Unit 1 reef. The clay minerals assemblages of the off-reef marls of the Units 4 and 5 are similar and are composed of smectite (40-60%) illite (25-35%) chlorite (0-10%) kaolinite (0-10%) and palygorskite (0-15%). Clay minerals assemblage changes through time and tree assemblages are recognized. The first corresponds to the assemblage of marls deposited before the Unit 1 (smectite, illite and chlorite). Second corresponds to the overlying off-reef marls of the Unit 1 with kaolinite occurrence (smectite, illite, chlorite and kaolinite), the third reflects the clay content of marls deposited after the Unit 1 with the occurence of palygorskite. Clay assemblage is similar for contemporaneous outcrops at different location in the basin. For example, two sections of marls between Unit 1 and 2 (first in NW second in SE) present the same assemblage. Clay minerals assemblages seem to be controlled by two main factors which are the source rocks and local sedimentary setting. The Lorca basin is enclosed within the mountain ranges to the south, to the east, to the north, and to the west. So, different terrigenous assemblage of smectite, illite, chlorite and kaolinite and enrichment can be interpreted as a response of several source rocks through the time. The palygorskite occurrence can be correlated with apparition of restricted local sedimentary setting in the platform (only after the Unit 1) which allow postdepositional processes of detrital aluminosilicates or a another eolian source.


11) - EVOLUTION OF DEPOSITIONAL ENVIRONMENTS AFTER THE END OF MESSINIAN SALINITY CRISIS IN NIJAR BASIN (SE BETIC CORDILLERA)

Maria Angela BASSETTI1-2, Francisco Javier SIERRO1 and Pietro MICULAN3

1: DRO-GM IFREMER, Centre de Brest- France.
2: Departamento de Geologia, Universidad de Salamanca, Spain.
3: Dipartimento di Scienze della Terra e Geoambientali. Univ. Di Bologna, Italy.

The Messinian succession is exceptionally well preserved in the intramontane sedimentary basin of Nijar in the Internal Betic Cordillera (SE Spain). The early Messinian sedimentation in Nijar started with a transgressive sequence of coastal and shallow marine fossil-rich calcarenites (Azagador member) that unconformably overlies Paleozoic Basement. These deposits pass upwards and basinwards into open marine hemipelagic marls (Abad member), indicating rapid deepening of the environments. The sedimentary sequence continues with a large amount of gypsum deposits (Yesares Formation), corresponding to the Messinian Salinity Crisis of the Mediterranean. Gypsum-olistostromes and large slabs of the Azagador member are unconformably overlain by the latest Messinian sediments of the Feos Formation. These latest Messinian deposits are characterized by a marked sedimentary cyclicity and, from the bottom to the top, two units can be distinguished: the lower one that mainly consists of calcarenitic intervals with laminated pelites and limestone beds. The upper unit is made of cyclic alternation of fluvial fan deposits and lacustrine marls, that corresponds to the ‘Lago-mare episode’. The sedimentary succession records very precisely the strongly fluctuating environmental conditions during upper Messinian, as well as the paleomorphological and paleogeographical changes that are likely related to Late Miocene and Pliocene tectonic uplift of the Sierra Cabrera (Betic basement). Detailed sedimentological and paleontological investigations have been carried out on the Feos Formation deposits and the dominant fauna, present throughout the upper unit in the lacustrine white marls of the Feos Formation, is represented by ostracod assemblages that are easily referable to Loxocorniculina diaffarovi FA, a residual assemblage of non-marine, aquatic communities which lived in brackish water bodies (Lago-mare fauna). Grey-reddish continental silty-marls are interbedded with the whitish lacustrine sediments, showing pedogenetic features, roots burrowing and terrestrial gastropods, but a poor fauna in situ. The re-establishment of marine conditions are marked by the presence of shallow-water sand deposits. Unfortunately, little can be said about the precise timing of the marine inundation in this context, although the presence of Globorotalia margaritae and the absence of Globorotalia puncticulata indicates a Lower Pliocene age. If we assume that the return of marine conditions coincide with the Zanclean flooding, we can assert: - the Messinian post-evaporitic deposits record several events of base level oscillations in the Nijar basin likely influenced by both tectonic activity and regional climate variations, as suggested by strongly marked sedimentary cyclicity that would permit stratigraphic correlations at regional scale; - the Lago-mare facies is very well developed in the upper unit of the Feos Formation and the transition to marine deposits does not imply a great change in paleodepth. This suggests that the refill of the Mediterranean was not a catastrophic event and that the base level of the Lago-mare was not much lower than that of the ocean.


12) - PALYNOLOGICAL EVIDENCE AS AN INDICATOR OF PALAEOENVIRONMENTAL CHANGES DURING THE MESSINIAN OF ITALY

Adele BERTINI

Department of Earth Sciences, University of Florence, Italy. (abertini@geo.unifi.it)

The contribution of palynology in the understanding of causes and effects of the Messinian salinity crisis in the Mediterranean area is synthesised in the well known sentence: “climate was dry before, during and after the Messinian salinity crisis” (Suc & Bessais 1990). This idea, used to formulate the two-step model (Clauzon et al. 1996), was supported by later palynological studies, still carried out in southern Italian deposits (Bertini et al. 1998). The stratigraphic record of vegetational and climatic changes from the area of North and Central Italy completed the picture (Bertini 1994, in press). New sites, located on the Tyrrhenian side and central Apennines, have been studied and their record compared to that already well known from key localities such as the Po plain, the Vena del Gesso and Maccarone. The occurrence of a prevalent subtropical to warm temperate climate pointed out major differences (in both temperature and moisture values) with respect to the coeval sections from Southern Italy, confirming the existence of climatic gradients within the Mediterranean area, at least from the Messinian. In addition, palynological data allows the palaeoenvironmental characterization of the two main Messinian post-evaporitic depositional sequences of Northern Apennines: the lower post-evaporitic sequence (also named “di tetto”), and the upper post-evaporitic sequence (also named “Colombacci”). Both are characterized by peculiar pollen and dinocyst assemblages. Specifically the analysis of changes in the composition of dinocyst assemblages, linked to the progressive arrival and/or the dominance of taxa showing affinities with those of the Parathetys (e.g. Impagidinium sp. 1, I. sp. 2 and Galeacysta etrusca), contributes significantly to clarify the supposed connections between the Mediterranean and the Parathetyan realms as well as with the Atlantic ocean. Finally, the biochronological indications yielded from the palynological studies in North and Central Italian sites permit to propose a correlation with other Messinian peri-Mediterranean areas.
References:
Bertini, 1994 - Messinian-Zanclean vegetation and climate in North–Central Italy. Historical Biology, 9: 3-10.
Bertini A., in press - Palynological evidence of upper Neogene environments in Italy. Acta Universitatis Carolinae-Geologica, 46(4): 15-25.
Bertini A., Londeix L., Maniscalco R., di Stefano A., Suc J.P., Clauzon G. & Gautier F., Grasso M., 1998 - Paleobiological evidence of depositional conditions in the Salt Member, Gessoso-Solfifera Formation (Messinian, Upper Miocene) of Sicily according to new paleobiological records. Micropaleontology 44(4): 413-433.
Clauzon G., Suc J.-P., Gautier F., Berger A. & Loutre M.F., 1996 - Alternate interpretation of the Messinian salinity crisis: Controversy resolved. Geology, 4: 363-366.
Suc J.-P & Bessais E., 1990 - Pérennité d'un climat thermo-xérique en Sicile avant, pendant, après la crise de salinité messinienne. Comptes Rendus de l'Académie de Science, Paris, 294(2): 1003-1008.


13) - POLLEN AND MACROFOSSILS OF TERRESTRIAL PLANTS INDICATE PREDOMINANTLY MOIST CLIMATE IN NORTHERN ITALY FROM MESSINIAN TO EARLY PLIOCENE

Adele BERTINI1 and Edoardo MARTINETTO2

1: Dipartimento di Scienze della Terra, Via G.la Pira 4, I-50121 Firenze, Italy. (abertini@geo.unifi.it)
2: Dipartimento di Scienze della Terra, Via Accademia Scienze 5, I-10123 Torino, Italy. (martinetto@dst.unito.it)

The thick and well-exposed Messinian and Zanclean successions of northern Italy provided rich palaeofloral records, thanks to the abundance of both micro- and macroscopic remains of terrestrial plants. Fossil leaves, fruits and seeds, though restricted to a few layers and sites, have been the first source of information on the Messinian to Zanclean palaeoflora and vegetation, and are presently the object of extensive taxonomic revisions, which are aimed to verify the occurrence of problematic taxa, which were often reported in the old literature without a clear indication for reliable and diagnostic characters. In addition, fresh information on plant macrofossils has been recently provided by peculiar methods of preparation (palaeocarpology) and analysis (leaf physiognomy). Nowadays, however, palynology represents one of the most significant tools for the reconstruction of the Messinian-Zanclean flora, vegetation and environment both due to the well-known methodological advantages and because pollen grains can be retrieved in large quantity throughout thick successions of both continental and marine deposits. Thus, the available micro- and macropalaeobotanical information has seen a considerable increase in the last two decades, so that we decided to carry out a comparative analysis of micro- and macropalaeobotanical data from selected sites of the Po Basin and the Apennine foredeep, in order to obtain a more accurate interpretation of the palaeofloristic and vegetational setting. Furthermore, we compared and integrated the climatic reconstructions based either on pollen or macrofossil record. The rich palynoflora provided by Messinian deposits of Piedmont and Emilia-Romagna, characterized by 135 taxa, indicates moist, subtropical to warm-temperate conditions. Cooltemperate taxa are scarcely represented, with the exception of some intervals characterized by the increase in Picea and Cedrus pollen (cooler episodes), especially during the post-evaporitic times. Herbs are rather scanty, indicating the absence of dry conditions. Scattered macrofloral data from the same successions confirm this picture, being characterised by the abundance of laurophyllous, entire-margined leaves, partly identified as Lauraceae. The mid-Messinian climatic reconstructions obtained by analysing the pollen data according the “Climatic Amplitude Method” (Fauquette et al., in press) are in agreement with the ones based on the physiognomic analysis of leaf assemblages (Wiemann M.C. et al., 1998). Minor discrepancies emerge concerning the estimate of precipitations, in fact leaf analysis provides significantly higher values, probably due to a local microclimatic signal. Fruits and seeds of the latest Messinian confirm the presence of taxa which require moist, subtropical to warm-temperate conditions (Visnea, Cyclea, Toddalia, ecc.). The Messinian to Early Pliocene plant communities, as reconstructed by means of this integrated approach, show the highest floristic affinity with the “Mixed Mesophytic” and “Evergreen Broad-Leaved” Forest, developed in warm temperate (MAT 17-14 °C) and moist (GSP> 800 mm) conditions on the relieves of central China.
References:
Fauquette S., Suc J.-P., Bertini A., Popescu S.-M., Warny S., Bachiri Taouiq N., Perez Villa M., Chikhi H., Subally D., Feddi N., Clauzon G., Ferrier J., in press. How much the climate forced the Messinian salinity crisis? Quantified climatic conditions from pollen records in the Mediterranean region. Palaeogeogr., Palaeoclimatol., Palaeoecol.
Wiemann M.C. et al., 1998. Estimation of temperature and precipitation from morphological characters of Dicotyledonous leaves. Amer. Jour. Bot., 85 (12): 1796-1802.


14) - IMPACT OF THE MESSINIAN SALINITY CRISIS ON THE EVOLUTION OF THE LEVANT CONTINENTAL MARGIN (EASTERN MEDITERRANEAN): RESULTS FROM 3D SEISMIC ANALYSIS

Claudia BERTONI and Joe CARTWRIGHT

3DLab, School of Earth, Ocean and Planetary Sciences, Cardiff University, Main Building, Park Place, PO Box 914, Cardiff, CF10 3YE, UK. (claudia@earth.cf.ac.uk)

Recently acquired 3D seismic data from the Eastern Mediterranean reveal the complex depositional and structural setting of the Messinian evaporites in the Levant Basin. Since the first discovery in the early 1970s, the origin and evolution of the Messinian Salinity Crisis (MSC) and associated deposits beneath the Mediterranean seafloor has been subject of considerable debate, mainly focused on their depositional environment, age and correlation from the basinal to marginal series. One of the key problems concerns the lack of resolution and 3D geometrical control of this evaporitic system. This research presents the first regional analysis of the Messinian evaporites in the Levant continental margin, based on 3D and 2D seismic data. The dataset covers a total area of 20,000km2, depicting a comprehensive view of the evaporite-bearing basin. Seismic data are tied to key wells located on the continental margin, allowing stratigraphic and lithological correlation. The main aim of this study is to build a framework for the MSC and to highlight its impact on the outbuilding of the Levant continental margin and nearby basin. The high spatial resolution and areal extent of this dataset makes it the ideal tool for analysing the MSC depositional system, through detailed mapping of bounding and internal Messinian horizons and seismic attribute analysis. The preliminary results show that: The seismic character (seismic amplitude, thickness and reflection continuity) of the Messinian series is variable vertically and spatially. There is a lateral transition from an unconformity surface on the basin margin to an extensive evaporite unit 1.5km thick in the basinal area. Remarkably, the presence of a system of pre-Messinian canyons affected the distribution of evaporite facies, even in the deeper part of the basin. The occurrence of the evaporites modified the structural style of the post-Messinian continental margin through evaporite dissolution, flowage, and acted as a detachment layer for gravity gliding-related shortening at the toe of the continental slope. The most relevant collapse and withdrawal features are located at the pinch-out of the evaporites towards the margin. This study documents the importance of 3D seismic analysis in developing a depositional and structural model for the Messinian evaporites. Ultimately, this will allow for an evaluation of the role of local vs. regional factors in controlling their present distribution, linking forward to perspectives for future investigations e.g. ultradeep drilling of the Messinian evaporites.


15) -IS THIS THE MESSINIAN SALINITY CRISIS?

Paul-Louis BLANC

Institut de Radioprotection et de Sûreté Nucléaire, B.P. 17, 92262 Fontenay aux roses Cedex, France. (paul-louis.blanc@irsn.fr)

Ever since the mid-Miocene, the hydrological regime of the Mediterranean Sea has been a contest between the preservation of a normal level and a normal salinity : such objectives are contradictory for a basin with a negative budget. The simple numerical model of the salt & water budgets developed since 1997 now makes it possible to re-assess some conceptual issues on the M.S.C. The conceptual model intimately linked to our quantitative model borrows some features from most of the major concepts of the 70's : • from the model of Van Couvering et al. (1976), we keep the idea that a long phase of rise in salinity took place in the Mediterranean deep basins, and that salt saturation was reached before drawdown could happen. • from the model of Hsü et al. (1973), we keep the idea of the Deep Desiccated Basin, but evaporite deposition did not take place in an already desiccated basin: as also postulated by Rouchy (1982) the drawdown proceeded at the same path as evaporite deposition. • from the model of Busson (1979), we have to keep the idea of a strong density stratification of the waters and brines, in full basins, but the basins do not remain at full level during the crisis, the occurrence of which does not require any significant climatic worsening with reference either to the average Miocene climate, nor to the present Quaternary interglacial climate, which appear to be similar under the latitudes of concern. • from the model of Clauzon et al. (1996) we keep of course the idea that the MSC and drawdown proceeded in two steps - at least in the Western basin. No other lithospheric process is implied in phasing the M.S.C. than the tectonic closure of the Miocene Atlantic straits, nor in its termination. True marginal evaporites can only have been deposited when the Mediterranean level remained high; the marginal basins may not all be contemporaneous with each other, according to physiographic peculiarities. The Mediterranean itself reached salt saturation when the Atlantic water supply only made up for the evaporative loss (the present regime requires a 22-fold higher supply). The double erosion profiles of the valleys of the Western basin tributaries result from a stand of the western basin at an intermediate level, which took place when the restricted Rifian corridor only allowed for the inflow of an intermediate amount of water between the water deficit on the whole Mediterranean Sea and the deficit on the Western basin alone. This basin remained flush to the internal ("Sicily") sill, and only the amount in excess flowed to the Eastern basin : the late Miocene physiography was similar to present. A debate on the Sicilian Messinian deposits being "an emergent deep basin series" against "a marginal series" now appears to be of no avail. The interrupted evaporitic deposition, between the Lower Evaporites and the Upper Evaporites, has the same meaning both in the Western Deep Basin and in the Sicilian Basin. It is caused by the partial de-salination caused by the transfer of a mixture of Atlantic surface waters and Western deep brines towards the Eastern Basin. The main difference between the Deep Western Basin and the Sicilian Basin must be that the true deep series are unlikely to be truncated and reworked at the summit, because they never were emergent. However, it must not be forgotten, that the model essentially describes: - i.- the entry of the chemicals into the basins, - ii.- the possibility of deep-erosion phases. We cannot expect an oceanographic budget model to account for reworking of deposits or detritism.


16) - THE ZANCLIAN CATACLYSM

Paul-Louis BLANC

Institut de Radioprotection et de Sûreté Nucléaire, B.P. 17, 92262 Fontenay aux roses Cedex, France. (paul-louis.blanc@irsn.fr)

Beyond a logical description of the development of the crisis, quantitative modelling also makes it possible to integrate its own end to the salinity crisis. At the end of the M.S.C, the widespread brackish or freshwater Lago-mare facies, coeval with the final deep canyons and detrital discharge, have now found a hydrological significance : they result from a supply limited to the rainfall, runoff and river discharge. Thus, the Plio-Quaternary Gibraltar strait cannot preserve any physiographic common feature with the fully continentalized Miocene portals. A copy of our Mediterranean budget model has been modified to study the re-fill. We adopted a simple exponential law (in cubic meters) for the annual re-increase in Atlantic water influx to the Mediterranean. This increase law is too weak at the beginning, and the level of the basins is not significantly modified for the first 26 years, but the refill of the basins is completed within the 10 to 11 next years. The extreme velocity of the Atlantic flow is reconfirmed both by hydraulic calculations, and by the structural morphology of the present strait itself : • in the Mediterranean domain, it shows a simple corridor, but for a central crest which may originate from a collapsed panel from the northern bank. • in the Atlantic domain, two unequal channels are found, separated by the "Majuan" or "Spartel" bank, which may be an outlier descending from the Trafalgar plateau, north of the northern channel. • the Camarinal sill shows an intricate mosaic of submarine hills and closed basins, and is best explained as outliers slid from the Trafalgar-Tarifa coast towards a deeper channel, the course of the Atlantic stream itself. In fact, the Zanclian deluge was a built-in feature of the M.S.C. : either a strait had to open somewhere, or the whole of the Mediterranean basins had to be filled up with detritals from the surrounding continents and folded belts. The piracy of Atlantic waters by a Mediterranean stream put an end to the M.S.C.


17) - PALEOENVIRONMENTAL CHANGES HERALDING THE MESSINIAN SALINITY CRISIS IN CENTRAL SICILY: THE TRIPOLI FORMATION OF THE FALCONARA-GIBLISCEMI COMPOSITE SECTION

Marie-Madeleine BLANC-VALLERON1, Catherine PIERRE2, Antonio CARUSO3 and Jean-Marie ROUCHY1

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: Dipartimento di Geologia e Geodesia, Università di Palermo, Corso Tukory 131, 90134 Palermo, Italy

The Central Sicilian Basin is a key area to investigate the depositional changes that affected the Mediterranean prior to the beginning of the Messinian salinity crisis. The Tripoli Formation (6.96-5.98 Ma) in the Falconara-Gibliscemi composite section shows a general trend of increasing basin restriction from marine conditions at its base (previous middle Tortonian to early Messinian marls are deep marine sediments) to semi-closed settings in its uppermost part (in the overlying Calcare di Base, the presence of gypsum and halite pseudomorphs indicates incipient evaporitic conditions and a near emersion environment). The Tripoli Formation includes 46 precession-controlled cycles resulting from the periodical increase in biosiliceous productivity (diatomites) that followed the deposition of marls and pinkish laminites. Higher scale environmental changes are superimposed to this precession forced-rhythmicity. From 6.96 Ma until 6.71 Ma, open Atlantic-Mediterranean exchanges maintained relatively stable marine conditions. At 6.71 Ma an important step in the basin restriction occurred with a wider range of salinity fluctuations and increased bottom stagnation; this event may have resulted from shallowing of the Mediterranean gateway under tectonic control. As a result of these reduced oceanic inputs there was an increased climatic constraint of the Mediterranean hydrology. Around 6.29 Ma, stressful conditions for the marine microfauna were induced by an increase of the surface water salinity; this major step in the restriction may be correlated with the intensification of the glaciation recorded in the Atlantic, which could have enhanced the effects of the tectonic closure. Around 6.03 Ma, there was a rapid transition to a semi-closed Mediterranean setting characterized by large variations of salinity from diluted to hypersaline conditions, under a dominant climatic control, and by the near complete disappearance of the marine organisms. Long trend environmental changes recognised within the Tripoli Formation resulted from a complex set of interfering factors controlling the water fluxes exchanged between the Mediterranean and the Atlantic. The environmental changes identified in the Falconara/Gibliscemi sedimentary succession at 6.71 Ma, and 6.03 Ma, occurred simultaneously in western and eastern Mediterranean; they were mainly controlled by the stepwise tectonic closure of the Atlantic connections, although a glacio-eustatic overprint cannot be completely excluded.


18) - EUSTATIC VS TECTONIC CYCLICITY OF MIDDLE MIOCENE (BADENIAN) EVAPORITE FROM FORE- AND INTRACARPATHIAN BASINS (SOUTHERN POLAND AND EAST SLOVAKIAN AREAS)

Krzysztof BUKOVSKI1 and Grzegorz CZAPOWSKI2

1: University of Mining and Metallurgy, Cracow, Poland. (buk@geolog.geol.agh.edu.pl)
2: Polish Geological Institute, Warszawa, Poland. (gcza@pgi.waw.pl)

The Middle Miocene (Badenian) evaporite-bearing formations from the East Slovakian Basin within the Inner Carpathians (Zbudza Fm, Slovakia) and from the Carpathian Foredeep (Wieliczka Fm, Poland) are characterized by a perfect cyclicity expressed by a succession of sulphates (gypsum to anhydrite), and pure up to clayey halite beds, separated by layers of siliciclastics. In both formations were registered 4 (Slovakia) to 5 (Poland) such cycles, hitherto being interpreted as an effect of sea-level fluctuations (possibly eustatic), enabling concentration or dilution/refreshing of salt brines, occupying both basins during the Middle Miocene salinity crisis. Chlorides of both formations represent several varieties: from structureless to laminated pure halites, interpreted as being precipitated from calm bottom brines in deep basin conditions, and pure to clayey halite-rudites and halite-arenites, chaotic or stratified (graded and cross-bedded), deposited by debris flows (subaqueous slumps) and currents. Occurrence of the last ones, registering intensive redeposition and mixture of salts and clastics, in each evaporite unit, as well as coarse material input in non-evaporitic interbeds may indicate episodes of intensive tectonic activity of basin margins. These periods were associated with volcanic phenomena, emitting a lot of pyroclastics, deposited as tuffite laminae and dispersed particles within salts and clastics. Variations in environment dynamics (from calm basinal to dynamic slope settings with slumps), clastic inputs, brine salinity and evidence of volcanic activity suggest that the observed cyclicity could be tectonically determined rather than resulting from eustatic fluctuations. The episodes of intensive tectonic activity of the basin margins remobilize the sediments from marginal salt pans, flats and adjacent uplifts. Periods of “tectonic peace” were dominated by chlorides precipitation from bottom brines and accumulation of clastics in suspension within the density-salinity stratified brines. So the distinguished cycles could be nearly isochronous and correlatable in both studied regions/basins.
These research has been supported by the Polish Committee for Scientific Research (KBN) - projects: 11.11.140.258 (K.B) and 6.20.9065.00.0 (G.Cz.)


19) - PARATETHYAN - MEDITERRANEAN CONNECTIVITY IN THE MARMARA SEA REGION (NW TURKEY) DURING THE MESSINIAN

M. Namik ÇAGATAY1, Naci GÖRÜR1, Mehmet SAKINÇ1, Cemal TÜNOGLU2, Rachel FLECKER3, Robert ELLAM4, Wout KRIJGSMAN5, Stephen VINCENT6 and Aynur DIKBAS1

1: Istanbul Technical University, School of Mines and Eurasian Inst. of Earth Sciences, Istambul, Turkey.
2: Hacettepe University, Geological Engineering Department, Ankara, Turkey.
3: BRIDGE, School of Geographical Sciences, University of Bristol, U.K.
4: Scottish Universities Environmental Research Centre, East Kilbride, U.K.
5: Utrecht University, Netherlands.
6: CASP, Department of Earth Sciences, University of Cambridge, U.K.

Following a brief marine transgression from the Mediterranean in the Mid- Late Miocene (late Serravalian-early Tortonian), the Marmara region in NW Turkey became a transitional waterway between the Eastern Paratethys and the Mediterranean during the Neogene and Quaternary. The Pontian (Messinian) sequence in this region is represented by the Alçitepe Formation, which is made up of oolitic and bioclastic limestones with basal clastic rocks. The Alçitepe Formation conformably overlies the fluvio-lacustrine siliciclastic sediments of the Early to Middle Miocene Anafarta and Kirazli formations and is overlain by fluvio-lacustrine sediments of the Kimmerian (5.5-3.2 Ma) Truva and Tevfikiye formations. The bioclastic limestones of the Alçitepe Formation contain a moluscan fauna that is endemic to Paratethys, and indicates deposition in a shallow, brackish water environment. A detailed biolithostratigraphic study of a section of the Alçitepe Formation in Intepe (Çanakkale) confirms that the formation is of Pontian age and that during its deposition, salinity increased from brackish (<10 g/L) at its base to more marine-like salinities (>30 g/L) in its upper part. Paleomagnetic analysis indicates that the Alçitepe Formation has a reverse polarity. Taken together with the biostratigraphic data, this reverse polarity interval probably represents chron C3r (6.04-5.24 Ma). Sr isotope analysis of ostracod valves show low 87Sr/86Sr values relative to Late Miocene ocean water. This indicates that exchange between the Sea of Marmara and the global ocean was restricted throughout this period. The increase in salinity in the upper part of the formation as shown by changes to the ostracod faunal assemblage is accompanied by a drop in 87Sr/86Sr to values low even with respect to the river-dominated signal preserved in Mediterranean Messinian evaporites. This suggests that inflow to the Sea of Marmara was dominated by non-marine sources with low 87Sr/86Sr and that the increase in salinity was generated either by increased evaporation, or by decreasing outflow, trapping salt within the basin, or by influx of saline hydrothermal fluids. Marmara - Paratethyan exchange with the Mediterranean was therefore restricted and possibly severed during the Messinian, and was not re-established until the late Aktchagylian (early Pliocene). This connection was the result of increased activity on the North Anatolian Fault and global sea level rise.


20) - REVISED TIMING AND EVOLUTION OF THE MESSINIAN SALINITY CRISIS IN THE MEDITERRANEAN AREA

Antonio CARUSO1 and Jean Marie ROUCHY2

1: Dipartimento di Geologia e Geodesia, Università di Palermo, corso Tukory 131, 90134 Palermo, Italy.
2: CNRS-UMR 5143, Dept Histoire de la Terre, Géologie, Muséum National Histoire Naturelle, 43 rue Buffon, 75005 Paris, France

A high resolution biostratigraphical and cyclostratigraphical study of various field sections of Sicily and the eastern Mediterranean, covering the entire Messinian Salinity Crisis interval, allows us to propose a revised timing for the major paleoenvironmental changes that affected the Mediterranean during this event. The new ages have been obtained using the astronomically calibrated timescale established by Hilgen and Krijgsman (1999) and with a re-calibration of the sedimentary cyclicities using Laskar 90 (1,1) solution. The study of the pre-evaporitic sedimentary successions of several field sections from Sicily shows that the evaporitic conditions recorded by the gypsum and halite pseudomorph-rich Calcare di Base deposits, associated to precursor gypsum beds, were formed 6.06 Ma in marginal sub-basins. These deposits correlate to an eccentricity minima 100 ky before those described at 5.96 Ma in the deepest part of Caltanissetta basin (Falconara section). However, a significant salinity increase is recognized locally in the Tripoli unit at around 6.25 Ma, coincident with increased glacial influence observed in the ocean record (Hodell et al., 2001; Vidal et al., 2002). The Lower Evaporites (Gypsum and Massive Halite Units) were formed during this long glacial period concomitant to tectonic closure of the Rifian corridor. The end of this cool period (5.57 Ma) corresponds to the last major glacial peak (TG12), correlated with the desiccation of the Caltanissetta basin at the end of the Lower Evaporites deposition. We propose to link the deposition of the potash salt, which requires increased basin restriction and aridity, to the major glacial event recorded by the peaks TG20 and TG22. The Upper Gypsum and Lago-Mare deposits were deposited during the post-glacial period; the abrupt restoration of normal marine conditions occurred synchronously at 5.33 Ma in relation to a geodynamical event in the Gibraltar area. These events were controlled by the complex interplay of regional (initial basin morphology and sedimentary tectonics) and global factors which regulated the influx of ocean water inputs (tectonically-driven closure of the marine gateways and glacio-eustatic variations). The precession-controlled fluctuations of the circum-Mediterranean climate also played an important role, especially during the Upper Evaporites and Lago-Mare deposition.


21) - DISCOVERY OF ANOXIC BRINE-FILLED BASINS IN THE MEDITERRAEAN RIDGE DOCUMENT EXHUMATION AND DISSOLUTION OF THE MESINIAN EVAPORITES IN THE DEEP SEA

Maria Bianca CITA1 and Angelo CAMERLENGHI2

1: Dipartimento di Scienze della Terra "Ardito Desio" , Università di Milano, Italia.
2: Angelo Camerlenghi, Istituto Nazionale di Oceanografia e Geofisica Sperimentale, Trieste, Italia

One of the most striking consequences of the Messinian salinity crisis in the Mediterranean is the formation of deep-seated brines at the bottom of collapse basins due to the exhumation of subcropping Messinian evaporites. The Mediterranean Ridge (MR) is the accretionary prism developed above the Benioff plane of the African slab subducting underneath Eurasia. MR is a very special accretionary wedge both for its unusual width (250 km) and for being flat, with a tapering angle of 1.5° at the deformation front. Both peculiarities are accounted to the presence of evaporites within the accreted terrains, and of their variable thickness across the ridge. Hemipelagic Plio-Pleistocene sediments overlying the Messinian evaporites in the Ionian basin were deposited at a very low rate (less than 2 cm/1000 y) since the MR has always been turbidite-free, and the eastern Mediterranean is known for its low productivity. As a result, the total thickness of the post-Messinian succession may be as low as 100 m. Exhumation of underlying evaporites related to faulting, submarine dissolution and fluid migration or a combination of both resulted in the formation of deep-seated, high density brines. Five such anoxic brine lakes have been discovered from 1983 to 1994 as follows

NAME
YEAR OF DISCOVERY
LOCATION OF BASIN
TYRO
1983
WESTERN STRABO TRENCH
BANNOCK
1984
CLOSE TO THE MR DEFORMATION FRONT FACING THE SIRTE A.P
URANIA
1993
CLOSE TO THE "CLEFT" BIG DEPRESSION WHERE NO MESSINIAN EVAPORITES ARE PRESENT (DSDP SITES 126 AND 377)
ATALANTE
1993
DISCOVERY
1994

Each brine lake has its own chemistry: this finding is accounted to the dissolution of different levels of the evaporitic succession, which is locally unknown, but is interpreted from genetic models and in comparison with the well known sicilian succession. The best known is certainly Bannock Basin, investigated with multipole dedicated cruises in its geology, geomorphology, chemistry, sedimentology (by means of sediment traps), bacteriology (bacterial mats). Atalante Basin brine is strongly enriched in K, whereas brines from Discovery Basin are a concentrated solution of MgCl2 and document that the last evaporative stage (close to total dryness) was reached at the end of the Messinian salinity crisis. It is pointed out that all the brine-filled basins created by exhumation of Messinian evaporites are located in areas of the MR where high precision, deep penetration seismic surveys suggest that the evaporites are thin, or even missing, whereas they are conspicuously absent in areas where large thicknesses of halite are geophysically detected. In conclusion after over thirty years of active research and notwithstanding important advances in stratigraphy, the Messinian is still a (partly) open problem. No ending yet for Messinian research.

22) -THE MESSINIAN – ZANCLEAN CYCLE IN THE NORTHERN AEGEAN SEA

Georges CLAUZON1, Jean-Pierre SUC2, Fabienne ORSZAG-SPERBER3 and Speranta-Maria POPESCU2

1: CEREGE, (UMR 6635 CNRS), Europôle de l’Arbois, BP 80, F-13545 Aix-en-Provence Cedex 04, France. (clauzon@cerege.fr.)
2: 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)
3: Orsay-Terre, Université Paris Sud, F-91405 Orsay, France. (orszag@geol.u-psud.fr)

Several field trips have been realised in the northern Aegean Sea (Serres – Kavala region) in 1991. On these occasions, Gilbert delta fan deposits have been evidenced, for example in the area of Karyani. A recent field trip in 2002 offered the opportunity to observe outstanding Gilbert delta fan deposits along the new coastal highway Thessaloniki – Kavala (E90) in the area of Acto Nea Kerdylion. During this new field trip, it has also been possible to observe a clear erosional surface at the base of the Gilbert delta fan constructions. At Akropotamos, the erosional surface cuts evaporites (gypsum) and is obviously overlain by foreset beds of a Gilbert delta, the bottom set beds of which being nearby exposed southward. An intensive work for dating these deposits has been recently done by Snel et al. (in press). According to their biostratigraphic results, evaporites from Akropotamos belong to the Messinian while deposits overlying the erosional surface belong to the earliest Zanclean. The erosional surface which separates the Messinian deposits from the Zanclean Gilbert delta sediments in this area is an additional argument for the Clauzon et al.’s scenario (1996): evaporites from Akropotamos correspond to the first step of the salinity crisis (first fall in sea-level causing the coastal evaporites), the second step (intense sealevel drawdown and desiccation of the Mediterranean) is locally marked by the erosional surface. The erosional surface could be coeval with the deep basin evaporates well-known off-shore in the nearby Prinos Basin (Proedrou & Sidiropoulos, 1992). Accordingly, the Messinian – Zanclean Mediterranean eustatic cycle is completely represented in the northern Aegean region.
References:
Clauzon G., Suc J.-P., Gautier F., Berger A., Loutre M.-F., 1996. Alternate interpretation of the Messinian salinity crisis: Controversy resolved? Geology, 24, 4: 363-366.
Proedrou P., Sidiropoulos T., 1992. Prinos Field – Greece, Aegean Basin. In “Treatise of Petroleum Geology. Atlas of Oiland and gas Fields”, Foster N.H., Beaumont E.A. eds. Structural Traps VI: 275-291.
Snel E., M„run„eanu M., Meulenkamp J.E., in press. Calcareous nannofossil biostratigraphy and magnetostratigraphy of the Upper Miocene and Lower Pliocene of the Northern Aegean (Orphanic Gulf – Strimon Basin areas), Greece. Palaeogeogr., Palaeoclimatol., Palaeoecol.


23) - LATE MESSINIAN EROSION AND POST-CRISIS REFLOODING IN THE MEDITERRANEAN: CONSTRAINTS FROM MARGINAL BASINS OF NE MOROCCO, SARDINIA AND SICILY

Jean-Jacques CORNEE1, Gilles CONESA2, Georges CLAUZON3, Michelle & Jean FERRANDINI4, Frédéric GARCIA2, Pierre MOISSETTE1, Philippe MÜNCH2, Jean-Paul & Simona SAINT MARTIN5, Anne RIBAUD2, Stephan ROGER2, Jean-Pierre SUC1and Donata VIOLANTI6

1: UMR 5125 Univ. Lyon1, UMR 5125 PEPS, 2 rue Dubois, 69622 Villeurbanne Cedex.
2: FRE6019 Univ.-Aix-Marseille I, 3 pl. Victor Hugo, case 67, 13331 Marseille Cedex 03, France.
3: CEREGE, (UMR 6635 CNRS), Europôle de l’Arbois, BP 80, F-13545 Aix-en-Provence Cedex 04.
4: Univ. Corse, Laboratoire de Géologie, Quartier Grossetti, BP 52, 2050 Corte, France.
5: MNHN, Dépt. Histoire de la Terre, UMR 5143 Paléobiodiversité, 8 Rue Buffon 75231 Paris Cedex 05, France.
6: Earth Science Department, Turin University, via Valpeerga Caluso 35, 10125 Turin, Italy.

The late Messinian erosional surface and the subsequent reflooding deposits were investigated in three marginal basins of the Mediterranean, Melilla-Nador (NE Morocco), Sinis Peninsula (Western Sardinia, Italy) and Eraclea Minoa (SW Sicily, Italy), by using geometrical, sedimentological and biostratigraphical analysis. Results are: The surface was precisely located and characterized in Sardinia and Sicily. Karstic features are widely identified at the top of the underlying Messinian carbonates. In Sicily an erosional surface is identified at the top of the Lago Mare deposits; Gravity-induced erosional features are associated with subaerial erosion. They are recorded in Morocco (km wide landslides) and Sardinia (submarine chaotic deposits); The geometry of the surface is composed of wide-extent erosional plateaus, reaching 20km in length. The margins of the plateaus are indentated by steep cliffs and/or aerial paleovalleys reaching at most 80 metres depth (Morocco); The transgressive system tract of the post-Messinian Salinity Crisis deposits was identified in the three investigated basins; its age is in fact not definitely established and further investigations are necessary for a better precision. It could be late Messinian and/or earlymost Pliocene as only Globorotalia cibaoensis was found, above and under the erosional surface Sicily, above it in Morocco. This indicates that the G. margaritae group foraminifers occured earlier in the Mediterranean than previously accepted, under the Pliocene Trubi deposits. This situation is similar to the Atlantic one where the G. margaritae foraminifer group occured since late Messinian.The transgressive system tract upward passes into undoubtefully early Pliocene deposits (G. puncticulata-G. margaritae). Nevertheless, gaps or condensed deposits might exist during the reflooding. These results allow a better understanding of the late Messinian erosional surface from subsurface data and lead to reinvestigate the Messinian-Zanclean transition for more precise dating and significance.

A4-size poster (PDF - 244 kb)


24) - OCEANOGRAPHY AND THE MESSINIAN SALINITY CRISIS

Jacques DEVERCHERE1 and Christian GORINI2

1: UBO-IUEM, CNRS-UMR6538, Plouzané, France.
2: CNRS-UMR8110 Processus et Bilans des Domaines Sédimentaires, Univ. Sciences et technologies Lille 1, 59655 Villeneuve d'Ascq cedex, France

The Messinian Salinity Crisis constitutes an outstanding event with regards to amplitude of sea level changes and to its short duration (about 600 000 years). Since the discovery of the Messinian salt layer in the deep basins of the Mediterranean Sea in the 60's, a large amount of data has been collected on land and at sea, allowing for several scenarii of the Crisis to be proposed and discussed. Nevertheless, the relative chronology of the environmental changes before, during and after the Crisis, and the spatial relationships between both domains are still poorly understood. This can be partly explained by: (1) very different time and space resolutions of data collected onshore and offshore; (2) the tendency of the scientific Community to focus on their respective analyses without crossing independent approaches; and (3) the difficulty to link erosional and depositional processes acting on wide and contrasted domains, especially in a context of sea-level changes controlled both at regional (through climate, tectonics, global isostasy) and local (through evolution of sills and changes in sedimentary inputs) scales. In this opening talk, we aim to illustrate the recent attempts of oceanographers to link these still poorly connected systems of the margins and deep basins, mostly led through an improvement of seismic imagery in vertical and horizontal resolutions. A first important step has been the high-resolution swath bathymetry obtained in several submarine areas, allowing for connecting canyon paths, at least partly inherited from the Crisis, from land to deep sea. After a period when oceanographers were more motivated by identifying deep structures of the basins and margins or by salt mobility and associated tectonics, a growing interest concerns nowadays the transition from the deep seismic facies of the margins to the salt and Upper Evaporites. Especially, the Gulf of Lions (the best documented area), the Liguria, Corsica and West Sardinia margins, and the Valencia trough offered recently new evidences for polygenic and contrasted erosional surfaces which are often covered by highly variable detrital deposits at the foot of margins, interpreted either as alluvial fans (aerial or submarine) or as slope deposits of various extents. Defining the complex geometrical relationships of these surfaces and seismic facies to the deep evaporites (from lower to upper deposits) is one of the main tasks performed since then. Various situations will be shown in the talk, mainly taken from the Gulf of Lions, the Provencal-Ligurian basin, and West Sardinia. The new Project Eclipse 2 (INSU-CNRS, France) aims at improving our understanding of these relationships and at including them in a global scenario of the Crisis evolution. From comparisons between various margins, it is expected to: (1) precise which factors (evolution of drainage systems at sea, lithology of eroded areas, sedimentary inputs in volume and nature, including topographic, climatic and tectonic effects) have controlled the shaping and stratigraphy of the margins; (2) connect the various fossil markers updip and downdip, from the upper margins to the deep basins; and (3) deduce a more detailed evolution, especially at the beginning and end of the Crisis, taking into account the complexity of the Mediterranean paleogeography (particularly the control by morphological sills) in space and time. Deep drillings and high-resolution seismics will definitely help to propose detailed evolutionary models, hopefully in the near future..


25) - MAGNETOBIOSTRATIGRAPHIC AGE CONSTRAINT OF POST-EVAPORITIC DEPOSITS: GAFARES, ALMERÍA-NÍJAR BASIN, SE SPAIN

Jaume DINARÈS-TURELL1, Julio AGUIRRE2 and Isabel M SÁNCHEZ-ALMAZO2

1: Istituto Nazionale di Geofisica e Vulcanología, Via di Vigna Murata, 605, 00143 Rome, Italy (e-mail: dinares@ingv.it).
2. Dpto. Estratigrafía y Paleontología, Facultad de Ciencias, Fuentenueva s/n, Universidad de Granada, 18071 Granada, Spain (jaguirre@ugr.es; sanchez@ugr.es)

Messinian deposits are exceptionally well exposed in the Gafares area, NE Almería- Níjar basin (SE Spain). The uppermost Tortonian-Messinian sedimentary record can be divided into four units. The lower unit, the Azagador Member, lies unconformably both on top of the Betic basement of the Sierra Cabrera and on upper Tortonian marls. These sediments change basinwards and upwards into silts and marls of the Abad Member. Magneto-, cyclo- and bio-stratigraphic data locate the Tortonian/Messinian boundary (7.26 Ma) in silts at the base of the Abad Member, and suggest that the date of the top of the Abad is ~5.9 Ma. The third unit, the evaporitic Yesares Member, unconformably overlies an erosive surface affecting both the Abad basin centre marls and the laterally equivalent basin margin reef deposits. The Yesares is characterised by an alternation of gypsum and siliciclastic beds. It shows gradual upward transition to the post-evaporitic unit , which is up to 150 m thick. This consists of a variety of sediments formed in marine (Sorbas-like) and continental (Zorreras-like) facies. The marine sediments are characterised by foraminifer-bearing silty marls. Storm and turbidite sandstone beds are intercalated into the silty marls. A delta prograded SE towards the centre of the area. Additionally, fan-delta deposits were localised along the basin margins. The continental deposits are represented by fluvial channel conglomerates and alluvial-plain sands and silts where palaeosols developed. Lower Pliocene marine yellowish silts and fine-grained sands unconformably overlie a surface of intense erosion excavated in the top of the post-evaporitic unit. Planktonic foraminifers of the Globorotalia miotumida group are present in the uppermost pelitic intercalation of the Yesares Member and throughout the silty marls of the post-evaporitic deposits up to the Messinian/Pliocene boundary. These foraminifers are abundant, continuously present, and generally well preserved. These assemblages are characterised by stratigraphically and temporally congruent species, indicating that reworking is unlikely. Moreover, size sorting, a typical feature of reworking, is not observed in the studied samples. A magnetostratigraphic study of the post-evaporitic unit has been carried out. Samples at 16 sites were collected up to the Pliocene deposits. Some samples have a weak natural remanent magnetization that provide unreliable demagnetization (both thermal and alternating field) and polarity data. Nonetheless, those reliable samples with a clear magnetic signal show reverse polarity throughout the studied interval. On the basis of their stratigraphic framework and biostratigraphic and paleomagnetic data, the post-evaporitic deposits cropping out in the Gafares area can be assigned to the upper Messinian, within the magnetic chron C3r. One of the implications of this age attribution is that the Miocene/Pliocene boundary is included in the erosional unconformity that overlies the post-evaporitic deposits, and not within the postevaporitic unit, as has been postulated in the Sorbas basin. Another important implication is that marine recovery of the western Mediterranean was Messinian in age, and not Pliocene as traditionally claimed.


26) - STRATIGRAPHY, SEDIMENTOLOGY AND PETROGRAPHY OF THE MESSINIAN CROTONE BASIN SEDIMENTS (CALABRIA, ITALY): PRELIMINARY RESULTS

Rocco DOMINICI1, Nicolò DOGLIONI4, Francesco MUTO1, Stefano LUGLI2, Mirko BARONE1, Cristian CAVOZZI4, Elisabetta COSTA4, Cesare RODA3, Salvatore CRITELLI1 and Maurizio SONNINO1

1 :Università degli Studi della Calabria, Dipartimento di Scienze della Terra, 87036 Arcavacata di Rende, Cosenza.
2 : Dipartimento di Scienze della Terra, Università degli Studi di Modena e Reggio-Emilia, Largo S. Eufemia 19, 41100 Modena, Italy.
3 : Dipartimento di Georisorse e Territorio, Università degli Studi di Udine, Via Cotonificio 114, 33100 Udine, Italy.
4 : Dipartimento di Scienze della Terra Università degli studi di Parma Viale delle Scienze 157/A, 43 100 – Parma.

The Crotone Basin is filled by three main tectono-stratigraphic units bounded by regional unconformities: middle Miocene-middle Messinian unit (Unit a), middle Messinian-lower Pliocene unit (Unit b), and middle Pliocene-Pleistocene unit (Unit c). We investigated the north-western sector of the basin to focus on the relationships between lithostratigraphic units and the characteristics of the halite deposit. Unit a is a trangressive system, consisting of alluvial and near-shore deposits (San Nicola Fm), that pass to a rhytmic alternance of marl and pelite (Ponda Fm.) passing upward to marl with interbedded diatomaceous shale (Tripoli Fm.). The Tripoli Fm. is overlain by a layer of bituminous shale followed by an up to 150 m-thick gypsumarenite body (Lower Evaporites) that underwent dehydration possibly by burial diagenesis. Unit b consists of four formations: 1) mudstones interbedded with arenite strata and halite deposits (Detritico Salina Fm.), 2) marls interbedded with arenite strata having gypsum cement (“Upper Evaporites” corresponding to the Lago Mare facies), 3) conglomerates and sandstones (Carvane Fm.), and 4) mudstone and marl (Cavalieri Fm, Lower Pliocene). The stratigraphic relationships of these formations are complex due to salt tectonics and complex architecture of the basin. From field data and preliminary biostratigraphic analyses, it appears that the “Upper Evaporite sequence” unconformably overlay the “Lower Evaporite sequence”, whereas the rest of the succession represents a continuous stratigraphic record. The halite rocks of the Detritico salina Fm. occur in diapiric structures with sulphate cap rock along a fault system trending N 60°-40°. In the Belvedere di Spinello area, the halite deposit is up to 300 m in thickness. The facies distribution and thickness of the post-Messinian sequences in these areas testify the close controls of the salt tectonics. Four main types of halite rocks have been observed in the two areas: - Banded facies can be interpreted, as the result of flow, disruption and recrystallization of former pairs of pure halite and halite/mudstone/siltstone laminites. - White facies may represent the result of partial recrystallization of primary subacqueous halite to form larger crystals. - Clear facies may be interpreted as a remnant of subacqueos primary crystals (cumulate?) in a rock consisting mostly of crystals grown displacively into the mud together with minor gypsum crystals. - Breccia facies probably represent the result of dissolution collapse of the pairs halite/mudstone/siltstone layers.


27) - E. MEDITERRANEAN SMALLER MAMMALS AT THE L. MIOCENE-E. PLIOCENE TRANSITION

Constantin DOUKAS1, Kees HORDIJK2, Aydin SEN3 and Hans DeBRUIJN2

1: Dept. of Paleontology. University of Athens, Greece. (cdoukas@geol.uoa.gr)
2: Strat/Pal University of Utrecht, The Netherlands
3: University of Sivas, Turkey

The late Turolian coincides with the Messinian Salinity Crisis in the marine sequences in the Mediterranean (de Bruijn, 1973). The changes in composition of land mammals in the E. Mediterranean during this time interval (MN13) are the scope of this study. Four Late Turolian rodent localities from Greece and Turkey are compared: the locality of Tomea Eksi in the Ptolemais basin, Maramena (Greece) and Suleimanli 2, and Kangal 2 (Turkey). Of all the above localities, only Ptolemais basin (localities Komanos 1, 5.25 Ma and Tomea Eksi 5.34 Ma) has been calibrated by combining paleomagnetism, cyclostratigraphy and radiometric dating. Due to this, we have achieved an unprecedented high resolution time control for our rodent assemblages. We assume, based on the observed stage of evolution, that all four localities are coeval. The rodent assemblages from the Late Turolian localities show an unusual patchiness, the presence of exotic fauna elements from different origins (Calomyscus delicatus, Arvicanthis n. sp. Pseudomeriones sp.) and differences in species content (Tbl. 1). The composition of the Late Turolian assemblages does not suggest a dry environment. It is then safe to assume that during the Messinian the terrestrial environments in E. Mediterranean were not dry. The great differences in diversity as well as in content are thought to be of local importance only due to local ecological factors around the localities. Around the Mio/Pliocene boundary there is a change in rodent assemblages. They become more similar than before and lose their “exotic” elements. This is the time when arvicolines enter. The rodent assemblage from Komanos 1, in the Ptolemais basin over the Mio/Pliocene boundary has lost the “exotic” elements: Arvicanthis and Pseudomeriones, but includes the arvicoline Promimomys.


28) - PALEOECOLOGICAL ASPECTS PRECEDING THE MESSINIAN SALINITY CRISIS: A CASE STUDY FROM GAVDOS ISLAND

Hara DRINIA, Asimina ANTONARAKOU, Nikolaos TSAPARAS and George KONTAKIOTIS.

National and Kapodistrian University of Athens, Department of Geology, Section of Hist. Geology and Paleontology, Panepistimiopolis, 157 84, Athens, Greece

The Messinian pre-evaporitic sedimentary succession of Gavdos island (Metochia section) is a nearly uninterrupted succession of marine sediments, dominated by finely laminated diatomaceous sediments, which are cyclically alternating with marlstone and white limestone beds. The purpose of this study is to analyze in detail the benthic and planktonic foraminiferal microfauna as well as the ichthyofauna preserved in the sediments of this section. The qualitative and quantitative analysis of the planktonic foraminifera fauna allowed the recognition of six bioevents, which have been astronomically dated for the Mediterranean. The base of the diatomitic succession in Gavdos Island is dated at 6.696 Myr. The section ends at 6.0 Myr. A species proportion matrix from benthic foraminifera was prepared from raw assemblage counts and a Principal Component Factor Analysis was implemented, yielding three principle axes which explain 83,031% of the variability contained in the matrix. The first axis which explains 57,221% of the variance is loaded negatively by Bulimina aculeata group indicating great tolerance for high salinities, oxygen deficiency and nutrient abundance (v.d. Zwaan, 1982; Kouwenhoven et al., 1999). The second axis which explains 13,341% of the variance is loaded negatively by Bolivina plicatela, which is a species highly tolerant to raised salinities and to oxygen deficiency, with probably an epiphytic mode of life (v.d. Zwaan, 1982).). The third axis which explains 12,47% of the total variance has a bipolar character indicating two assemblages. Species loading this axis positively is Asterigerinata planorbis, which is considered to have an epiphytic mode of life, pointing to a tolerance to increased salinities. Species loading the axis negatively Bolivina spathulata group which is known to survive in oxygen deficient environments and is often dominant in the oxygen-minimum zone or in the upwelling zones. The vertical distribution of the revealed scores indicate that throughout the deposition of the diatomaceous sequence of Metochia section extremely stagnant bottom water conditions interrupted by small scale stable marine conditions, prevailed. An assemblage containing Myctophidae and Syngnathidae has been observed throughout the studied section. Such an association of fish having ways of life apparently incompatible can be explained only by the action of marine currents (Gaudant 2002). In particular, Myctophidae attest the existence of deep zones of at least several hundred meters deep, located along the margins of the circalittoral zone.
References:
Gaudant, J., 2002. La crise messinienne et ses effets sur l'ichthyofaune neogene de la Mediterranee : le témoignage des squelettes en connexion de poissons téléostéens. Geodiversitas 24(3) : 691-710.
Kouwenhoven, T.J., Seidenkrantz, M-S. & Van Der Zwaan, G.J., 1999. Deep-water changes: The near-synchronous disappearance of a group of benthic foraminifera from the late Miocene Mediterranean. Paleogeography paleoclimatology paleoecology, 152:259-281.
Van der Zwaan, G.J., 1982. Paleoecology of Late Miocene foraminifera. Utrecht Micropal. Bull., 25. 1-201.


29) - LATEST MESSINIAN “LAGO-MARE” LIMNOCARDIINAE FROM ITALY: STRONG AFFINITY WITH THE PONTIAN FAUNA FROM THE DACIAN BASIN

Daniela ESU

Dipartimento di Scienze della Terra, Università “La Sapienza”, P.le A. Moro 5, 00185, Roma, Italy. (daniela.esu@uniroma1.it)

Sediments of hypo-oligohaline environment laid down during the post-evaporitic phase at the top of the Messinian evaporitic regime (“salinity crisis”) within the Mediterranean basin are rich of mollusc assemblages characterising the “lago-mare” biofacies. Several oligo- mesohaline species of prosobranch gastropods belonging to Neritidae, Thiaridae, Melanopsidae, Hydrobiidae and bivalves of the families Cardiidae (subfamily Limnocardiinae) and Dreissenidae, colonised various districts of the Mediterranean area (Spain, France, Corse, Italian peninsula, Sicily). The occurrence of elements of the subfamily Limnocardiinae Stoliczka in the Mediterranean area is of special palaeobiogeographic interest because of their Paratethyan origin. Limnocardiinae were diffused in shallow water basins with low salinities (5-18‰) displaying repeatead events of adaptive radiation through Neogene in Paratethyan realm (Nevesskaya et al., 2001). New records of significant species belonging to Limnocardium, Euxinicardium, Tauricardium, Paradacna, Phyllocardium, Chartoconcha, Pontalmyra, Pseudocatillus, Eupatorina, Prosodacnomya, Prosodacna, Psilodon from the uppermost Messinian sediments of Tuscany (Borro Strolla, Poggibonsi), Marche (Pietra La Croce, Ancona) and Sicily (NW margin of Hyblean Plateau) and the review of old literature following the new systematics Limnocardiinae arrangement by Nevesskaya et al. (2001) point out close relation of the Italian fauna with that from the lower and upper Pontian sediments of the Dacian basin (Papaianopol, 1989 cum refs.). The ecology of Limnocardiinae is mainly tied to oligohaline water so that spreading of suitable habitats in depositional systems of marginal settings characterized by increasing freshwater influx at the top of the “salinity crisis” (Ricci Lucchi et al., 2002) favoured their dispersal into the Mediterranean area from the Paratethys at the latest Messinian time, since these taxa are not recorded in the lower Messinian lacustrine/brackish episodes of Italy (Esu, 2003). The palaeobiogeographical data referred to Limnocardiinae (Popov & Nevesskaya, 2000) suggest that the Aegean basin could be an intermediate basin from whence the Paratethyan type fauna migrated into the Mediterranean area.
References:
Esu D. (in print). The latest Messinian “lago-mare” mollusc faunas from Italy. Palaeobiogeographic aspects. Rend. Boll. Soc. Paleont. It.
Nevesskaya, L.A., Paramonova, N.P. and Popov, S.V., 2001. History of Lymnocardiinae (Bivalvia, Cardiidae). Paleontological Journal, 35, 3: 147-217.
Papaianopol I., 1989. Considérations sur les mollusques pontiens en Roumanie. Pontien. Chronostratigraphie und Neostratotypen, 8: 582-617.
Popov, A.V. & Nevesskaya, L.A., 2000. Late Miocene brackish-water mollusks and the history of the Aegean basin. Stratigraphy and geological correlation 8, 2: 195-205.
Ricci Lucchi, F., Bassetti, M.A., Manzi, V. & Roveri, M., 2002. Il Messiniano trent'anni dopo: eventi connessi alla crisi di salinità nell'avanfossa appenninica. St. Geol. Camerti, 31: 127-142.


30) - LATE MIOCENE BRACKISH LOXOCONCHIDAE (CRUSTACEA, OSTRACODA) FROM ITALY

Costanza FARANDA, Elsa GLIOZZI and Silvia LIGLIOS

Dip. Scienze Geologiche, Università Roma Tre, Largo S. Leonardo Murialdo, 1 – 00145 Roma, Italy. (gliozzi@uniroma3.it)

The Family Loxoconchidae Sars 1925 includes over 800 fossil and extant species that mainly inhabit littoral and sublittoral marine environments. Only few living species (i.e. Loxoconcha elliptica Brady, Elofsonia baltica (Hirschmann), Hirschmannia viridis (Müller), Sagmatocythere pennata (Schornikov), Loxoconchissa (Loxocaspia) immodulata (Schornikov) can withstand brackish waters. During Late Miocene, in the Paratethyan domain wide brackish basins developed and numerous Loxoconchidae adapted to the decreased salinity. Beside several species pertaining to the genus Loxoconcha, other species have been referred to the genera Loxocorniculina, Loxoconchissa s.s. and Loxoconchissa (Loxocaspia). In the Italian brackish basins developed during Late Miocene it is possible to recognise the presence of all these genera: Loxoconcha and Loxocorniculina are mainly documented in the latest Messinian lago-mare biofacies [i.e. Loxoconcha eichwaldi Livental, Loxoconcha muelleri (Mehés), Loxoconcha rhombovalis Pokorny and Loxocorniculina djafarovi (Sneider in Suzin)]; on the contrary Loxoconchissa s.s. and Loxoconchissa (Loxocaspia) seem to be confined to the Late Tortonian-early Messinian brackish basins of Tuscany (Volterra-Radicondoli, Cinigiano-Baccinello and Velona Basins) and are represented by new species. A re-definition of the genus Loxoconchissa s. l. on the base of the hinge and of the sexual dimorphisms is presented in this paper and its geographic and stratigraphic distribution are discussed.


31) - HOW MUCH DID CLIMATE FORCE THE MESSINIAN SALINITY CRISIS? QUANTIFIED CLIMATIC CONDITIONS FROM POLLEN RECORDS IN THE MEDITERRANEAN REGION

Séverine FAUQUETTE1, Jean-Pierre SUC2, Adèle BERTINI3, Speranta-Maria POPESCU2, Sophie WARNY4, Naïma Bachiri TAOUFIQ5, Maria-Jesus PEREZ VILLA6, Jacqueline FERRIER1, Hafida CHIKHI7, Danica SUBALLY8, Najat FEDDI9 and Georges CLAUZON10

1: Institut des Sciences de l'Evolution (UMR 5554), Université Montpellier 2, 34095 Montpellier Cedex, France.
2: Paléoenvironnements et PaléoBiosphère (UMR 5125), Université Cl. Bernard-Lyon 1, 69622 Villeurbanne Cedex, France.
3: Università degli Studi di Firenze, Dipartimento di Scienze della Terra, 50121 Firenze, Italy.
4: Louisiana State University, Department of Geology and Geophysics, E235, Baton Rouge, LA 70803-4101,USA.
5: Département de Géologie, Faculté des Sciences de Ben M'Sik, Université Hassan II - Mohammedia, BP7955, Casablanca, Morocco.
6: Institut Paleontologic M.Crusafont, 08201 Sabadell, Spain.
7: 44 bis, rue des Papillons 41000 Blois, France.
8: Albert-Ludwigs-Universität Freiburg, Botanischer Garten,79104 Freiburg, Germany.
9: Département des Sciences de la Terre, Faculté des Sciences, Université Caddi Ayyad, BP S15, Marrakech, Morocco.
10: CEREGE (UMR6635), Université d'Aix-Marseille III, BP 80, 13545 Aix-En-Provence Cedex 4, France.

Quantifying the climate of the Mediterranean region during the Messinian salinity crisis will help to better understand climate forcing on this event. The "Climatic Amplitude Method" was used for reconstructing climate from Neogene pollen data, conceived especially for periods devoid of modern vegetation analogue. Twenty Messinian to Lower Zanclean pollen sequences areavailable in the Mediterranean region. Most of them do not cover the whole Messinian interval, particularly those along the Mediterranean shorelines where sedimentation was interrupted during the sea desiccation. In contrast, sedimentation was almost continuous in such areas as Morocco (Atlantic side), the Adriatic coast (Po Valley included), and momentarily the Black Sea. Pollen diagrams reveal a high regional variability and a southward increase in herb frequency. Open and dry environments existed in the southern Mediterranean region prior to, during and after the salinity crisis. Trees developed in areas close to mountains such as in the Po Valley, Cerdanya and the Black Sea region. Most variations are constrained by fluctuations of Pinus pollen amounts, indicating eustatic variations. Climatic quantification from pollen data does not show obvious climatic changes due to the desiccation of the Mediterranean Sea, especially in the dry and warm southwestern Mediterranean area (Sicily, southern Spain and North Africa). At Maccarone, along the Adriatic Sea, a decrease in temperatures of the coldest month and, less importantly, a decrease in mean annual temperatures, correspond to a drastic vegetation change. These temperature variations are assumed to be controlled by regional environmental changes rather than to reflect cooling. Some migrations of plants probably occurred as a response to Mediterranean desiccation. But the climatic contrast that has probably existed at that time between the central Mediterranean and the peripheral areas might be amplified. Climatic reconstruction from pollen data in the western Mediterranean area shows that climate is not the direct cause of the Mediterranean desiccation, as the Mediterranean region had experienced continuously high evaporation long before the crisis.


32) - PALAEOVEGETATION MAPPING WITH INTERPOLATION METHODS OF POLLEN DATA

Eric FAVRE1, Véronique CHARLET1, Rachid CHEDDADI2, Jeanne-Marine DUBOIS2, Séverine FAUQUETTE2, Adèle BERTINI3 and Jean-Pierre SUC1

1: Laboratoire PaléoEnvironnements et PaléobioSphère (UMR5125 CNRS), Université Claude Bernard Lyon1, 27-43 boulevard du 11 Novembre, 69622 Villeurbanne Cedex, France.
2: Institut des Sciences de l’Evolution de Montpellier (UMR5554 CNRS), Paléoenvironnements, Case courrier 061, Université Montpellier 2, Place E. Bataillon, 34095 Montpellier Cedex 05, France.
3: Dipartimento di Scienze della Terra, Università degli Studi di Firenze, via G. La Pira 4, 50121 Firenze, Italy.

Pollen records are an excellent tool for palaeovegetation and climate reconstructions. They have already been used to quantify the Pliocene climate (Fauquette et al., 1998, 1999). In order to better understand continental environments as well as their evolution, palaeovegetation maps have to be established. Each site studied provides a picture of the local and regional vegetation according to the main biases (plant pollen productivity and pollen transport). After a selection of localities, based on their pollen richness, and a taxa grouping based on their climatic meaning (and incidentaly on their behaviour along the last 24 Myrs), we have selected the interpolation method suitable for our study. Among the different kinds of interpolations, it has been decided to use the Thin Plate Spline (TPS) allowing interpolations on shared random data (Charlet, 2002). When data have been described on two or three dimensions, the effects of natural variations and the measurement errors can lead the TPS to produce local artifacts for too high or too low values. We can unbias these situations by applying a TPS which will smooth the surface i.e. we replace the exaggerated values by an average of the closest values. This method presents two advantages: the minimum number of values necessary to interpolate is low ; furthermore, as it uses an exact interpolater, it will take into account the whole dataset by balancing local events. A study carried out with this method (Charlet, 2002) on the early Pliocene of the Northwestern Mediterranean area yielded good results for the various ecosystems with regards to their location on the resulting vegetation map. Similar processes are in progress for the time-window concerning the Messinian salinity crisis. The interpolations processing and visualisation use different programs such as the geographic information system GRASS, the R language and the GMT program (Generic Mapping Tools).
References:
Charlet, V., 2002. Elaboration de paléocartes de végétation du Pliocène en région nordouest méditerranéenne. Mem. DEA. Univ. Lyon 1, 43 p.
Fauquette, S., Quézel, P., Guiot, J., Suc, J.-P. 1998. Signification bioclimatique de taxons-guides du Pliocène méditerranéen. Geobios, 31, 2: 151-169.
Fauquette, S., Suc, J.-P., Guiot, J., Diniz, F., Feddi, N., Zheng, Z., Bessais, E., Drivaliari, A. 1999. Climate and biomes in the West Mediterranean area during the Pliocene. Palaeogeography, Palaeoclimatology, Palaeoecology, 152: 15-36.


33) - THE LATE MESSINIAN LAGO-MARE EPISODE IN THE CENTRAL MEDITERRANEAN BASIN: NEW DATA FROM THE ONSHORE MONDRAGONE 1 WELL (GARIGLIANO PLAIN, CENTRAL ITALY)

Ilaria FEDERICI, Paola CIPOLLARI, Domenico COSENTINO and Elsa GLIOZZI

Dipartimento Scienze Geologiche, Università Roma Tre. L.go S. Leonardo Murialdo, 1 I-00146 Roma, Italy

The Mondragone 1 well, drilled in 1968 by Agip, for hydrocarbon exploration, is located in the plain of the Garigliano River, at about 3 km to the east of Cellole village (lat. 41° 12' 17”, long. 13°48' 52”). The Mondragone 1 well cut across siliciclastic fine-to-coarsegrained upper Miocene-Quaternary deposits, for a total depth of 2002 m. Drilling the Mondragone 1 well, fourteen sediments cores have been recovered from 495 m down to 2000 m; SP and resistivity logs have been also recorded. The Mondragone 1 sediment cores have been recently re-sampled and analysed. This paper deals both with the results of the biostratigraphical analyses performed on the Mondragone 1 re-sampled sediment cores and with the significance of the Mondragone 1 well stratigraphy in the central Mediterranean scenario during the late Messinian Lago- Mare episode. Data from seismic lines have been used to reconstruct the geometry and the structural setting of the Garigliano Basin during the latest Messinian. Moreover, the analysis of the SP log allows us to suggest a possible sequence stratigraphy evolution of the Garigliano Basin during the late Messinian Lago-Mare episode. Since the ostracod assemblages in sediment cores 2-14 contain species belonging to the Loxoconcha djafarovi Zone, as was defined byCarbonnel (1978) (e.g. Loxoconcha (Loxocorniculina) djafarovi, Loxoconcha (L.) eichwaldi; Cyprideis anlavauxensis; Amnicythere palimpsesta; Zalanyiellavenusta), it is reasonable to refer this portion of the Mondragone 1 drilled sediments (from -675 m down to –2002 m) to the late Messinian Lago-Mare biofacies. The uppermost Messinian Lago-Mare deposits drilled by the Mondragone 1 well provided an apparent thickness of 1327 m and a true thickness of about 938 m considering a mean dip value of 45° in the strata measurements. Similar thickness (530 m) of pre-Pliocene sediments has been drilled at ODP Site 652, in the Tyrrhenian bathyal plain. The occurrence in the Unit 4 of the ODP Site 652 of scarce Ammonia beccarii tepida and Cyprideis sp. (Borsetti et al., 1990; Robertson et al., 1990) together with its magnetostratigraphy (Channell et al., 1990) point to time-correlate the ODP Site 652 pre-Pliocene deposits with those drilled at Mondragone 1. Different behaviour between the northern and the southern Tyrrhenian Basin have been shown by differences in the total subsidence rates computed in the late Messinian Lago-Mare rifting areas of the Tyrrhenian Basin. North of the Tiber delta, the uppermost Messinian syn-rift clastic wedges recognized in the northern Latium and in the Tuscany Tyrrhenian margins show similar thickness (250 m and 230 m respectively), lower than that drilled in the Mondragone 1 well and inthe ODP Site 652. Taking into account the duration of the late Messinian Lago-Mare episode (260 ka), a total subsidence rate of about 1 mm/a could be computed for the sedimentary basins north to the Tiber delta, whereas >4mm/a of subsidence rate affected the sedimentary basins developed SE of the R. Selli lineament. This lithosphere feature distinguishes two sectors with different amounts of horizontal stretching (Finetti and DelBen, 1986): 1) a northern Tyrrhenian area, characterized by a thinned continental crust and lower values of late Messinian total subsidence rates; 2) a southern Tyrrhenian area, characterized by an ocean-type crust and higher values of late Messinian total subsidence rates.


34) - WHAT CAUSED THE TRANSITION FROM HYPERSALINE TO BRACKISH WATER CONDITIONS IN THE LATE MIOCENE? TESTING THE DILUTION HYPOTHESES FOR THE LAGO-MARE USING SR-SALINITY MODELLING

Rachel FLECKER1, Stéphanie DE VILLIERS2, Maria Angela BASSETTI3, Robert ELLAM4, Wout KRIJGSMAN5, Namik ÇAGATAY6 and Stephen VINCENT7

1: BRIDGE, School of Geographical Sciences, University Road, Bristol, BS8 1SS UK. (r.flecker@bristol. ac.uk)
2: Department of Chemistry, Stellenbosch University, Stellenbosch 7602, South Africa
3: Departamento de Geologia y Paleontologia, Facultad de Ciencias, Universidad de Salamanca, Spain
4: Scottish Universities Environmental Research Centre, East Kilbride, Glasgow G75 0QF, UK
5: Utrecht University, Netherlands
6: Istanbul Technical University, Maden fakültesi, Turkey
7: CASP, Department of Earth Sciences, Cambridge CB3 0DH, UK

Faunal and lithological data indicate large-scale fluctuations in the salinity of the Mediterranean in the Late Miocene. One of these, the transition from hypersaline conditions that produced widespread evaporite precipitation, to the brackish-water Lago-Mare facies, is attributed to dilution by fresh water. Modelling the hydrologic budget of the Late Miocene Mediterranean indicates that dilution by either river runoff or the fresh water lake system, Paratethys, is not consistent with Sr isotope and salinity constraints. We suggest an alternative hypothesis for this desalination event that depends on changes to outflow from the Mediterranean to the Atlantic Ocean.


35) - MODELLING THE IMPACTS OF THE MESSINIAN SALINITY CRISIS ON CLIMATE AND VEGETATION

Louis FRANÇOIS1-2, Frédéric. FLUTEAU3-4, Eric FAVRE5, Jean-Pierre SUC5 and Séverine FAUQUETTE6

1: Laboratoire de Physique Atmosphérique et Planétaire, Université de Liège, 17 allée du 6 Août, B-4000 Liège, Belgium
2: Centre de Recherches Pétrographiques et Géochimiques, CNRS-UPR 2300, Vandoeuvre-lès-Nancy, France
3: UFR des Sciences Physiques de la Terre, Université Paris 7, Paris, France
4: Laboratoire de Paléomagnétisme, Institut de Physique du Globe de Paris, Paris, France
5: Laboratoire PaléoEnvironnements et PaléobioSphère, Université Claude Bernard, Villeurbanne, France
6: Institut des Sciences de l'Evolution, CNRS-UMR 5554, Université de Montpellier II, Montpellier, France

The major event undergone by the Mediterranean Sea consists in its almost entire desiccation during the Late Miocene known as the Messinian Salinity Crisis (MSC). The Mediterranean Sea was isolated from the Atlantic ocean by sea level change and tectonic activity in the Betico-Rifian area. Because precipitation and continental runoff were not able to compensate evaporation, sea level in the Mediterranean basin dropped abruptly, leading to the deposition of evaporites in perched marginal basin in a first step and then in the abyssal plains and allowing the formation of deep subaerial canyons subsequently filled by Pliocene sediments. If climatic conditions have favoured the desiccation of the Mediterranean basin, what was in turn the influence of the MSC on the climate ? How can we explain that, despite the fact that a large area emerged, regions such as Sicily were not affected by any climate change before, during and after the MSC. What were the consequences for the vegetation in the Mediterranean area, as well as globally ? To address these questions and quantify the impact of the MSC on climate and vegetation, we have performed a set of numerical simulations using the LMDz Atmospheric General Circulation model in combination with the CARAIB vegetation model. In a first experiment, we have forced the LMDz AGCM with pre-Messinian boundary conditions. Paleogeography and sea surface temperature were reconstructed for the Tortonian (Late Miocene). In a second experiment, we reduced the surface of the Mediterranean sea and Black sea keeping solely a few grid cells corresponding to the deeper part of the basin which remained flooded during the MSC. For both experiments, we used pre-industrial values for carbon dioxide and present day orbital parameters. The comparison between the two experiments should highlight the cause as well as the consequences of the MSC. The output climatic fields of both experiments have then been used as inputs to CARAIB, a dynamic global vegetation model. The impacts of the MSC on the vegetation distribution, as calculated by the CARAIB model, will be analysed and compared to information obtained from pollen data.


36) - THE MESSINIAN SUCCESSION OF SINIS PENINSULA (SARDINIA, ITALY): MAIN ASPECTS

Frédéric GARCIA1, Jean-Paul SAINT MARTIN2, Jean-Jacques CORNEE3, Gilles CONESA1, Jean-Pierre ANDRE4 and Pierre MOISSETTE3

1: Centre de Sédimentologie-Paléontologie, UMR 6019, Université de Provence, 3 place Victor- Hugo, 13331 Marseille cedex 03, France
2: MNHN, Département Histoire de la Terre, Paléontologie, 5 Rue Buffon 75005 Paris, France
3: UFR Sciences de la Terre, UMR 5125 PEPS, Université de Lyon I, 27 Bd du 11 Novembre, 69622 Villeurbanne cedex, France
4: Laboratoire de Géologie, UPRES EA 2644, Université d'Angers, Bd Lavoisier, 49045 Angers cedex, France

Different investigations were realized in Sardinia (Sinis Peninsula) in the “Programme Eclipse messinien” : the general sequential scheme is treated by J.P. André et al. and several informations on the last Messinian erosonial surface are treated J.J. Cornée et al. (both this congress). We focalise here on the main aspects of the upper Miocene platform succession. Lithologically, the Sinis Messinian consists of a forty meters mixed carbonate-siliciclastic deposits developed in a global shallowing-upward sequence from offshore Amussium marls to shoreface oolitic and bioclastic limestones. The lower part of the platform is remarquable by the presence of decimetric to plurimetric carbonate buildups widespread in the whole peninsula. They are made of microbial and suspension-feeding invertebrates (mostly bryozoans and serpulids but also bivalves and vermetids) framework. These composite mud-mounds occured in different sedimentary facies (silty marls, sandy and oolitic limestones...) and growed in “normal” shallow marine environments under variable hydrodynamic conditions. Some of the best developed buildups (principaly in the North and South of the Sinis Peninsula) display several development phases and are clearly integrated into eustacy high frequency cycles. The absence of scleractinians, which are usually developed in Mediterranean Messinian littoral environments is related here to cooler seawater inputs. Few meters above the last buildups, an unusual facies made of “azoic” laminated chalky limestones occured. Three to ten meters in thickness, it has a regional extension, and was considered by Cherchi et al. as hyperhaline chemical deposits from lagoonal environment. However, no real evidence of evaporitic features were observed. A marine environment is proposed, based on sedimentological structures and sedimentary continuity with surrounding facies. But the almost total absence (except rare sponge spicules, benthic foraminiferas, pisces? remains and extremely rare centimetric bivalve beds) of fauna is still unexplained. The uppermost part of the Messinian sucession exhibits a wide extent breccia composed by micritic limestones, and parasequences of oolitic and bioclastic limestones with stromatolites. At the base, the breccia shows soft sediment deformations related to major seismic schocks that had affected the whole platform. In its upper part, karstic dissolutions are present and are related to subaerial exposures. This breccia ends with an erosonial surface onto Pliocene deposits had transgressed. Despite the obvious facies dissimilarities with other Messinian marginal platforms, the global biosedimentological evolution, recurrent at this time, allow us to suggest a west Mediterrenean scale correlation.


37) - THE SEDIMENTARY CONSEQUENCES OF THE MESSINIAN SALINITY CRISIS ON THE PROVENÇAL MARGIN, NORTHWESTERN MEDITERRANEAN: PRELIMINARY RESULTS FROM THE “MAURESC” CRUISE

Virginie GAULLIER1, Sandra ADROHER1, Françoise SAGE2 and the MAURESC Scientific Party3

1: LEGEM–E.A. 3678, Université de Perpignan, 52, Avenue Paul Alduy, 66860 Perpignan, France.
2: GEOSCIENCES AZUR–UMR 6526, Observatoire Océanologique de Villefranche-sur-Mer, BP 48, 06235 Villefranche-sur-Mer Cedex, France.
3: Jacques DEVERCHERE, Christian GORINI, Agnès MAILLARD, Jean-François MIRALLES, B. VENDEVILLE

Between 5.95 and 5.32 My. B.P., the Messinian Salinity Crisis (MSC) is known to have deeply reshaped the Mediterranean Sea margins by huge erosional episodes, and to have led, in the deepest part of the basin, to the deposition of a thick sequence of evaporites, which are divided into three distinct units, the “Lower Evaporites”, the “Salt”, and the “Upper Evaporites”. Although the main stages and timing of the MSC are nowadays broadly known, many aspects of this major event remain unresolved on the lower continental margins. In the deepest part of the margin, the age nature volume and extent of the messinian detritals accompanying the massive erosion of the continents during the second step of the MSC, described as the lower-stand stage (from ~5.60 to 5.32 My.) are badly constrained. The geometrical and chronostratigraphic relationships between this detritic material, the mobile salt and the Upper Evaporites are still enigmatic because: (1) there is no deep drilling going through the entire messinian sedimentary sequence; (2) bad quality of Seismic imaging due to the presence of salt. To better constrain the chronostratigraphic relationships between the Messinian detrital sequences and the evaporites, we recently started a new study at the the Provençal margin rise, offshore the Maures massif. This area is characterized by: (1) a small Plio-Quaternary sediment input (compared with the Gulf of Lion margin), (2) no major tectonic activity after the rifting stage of the Mediterranean except for the salt tectonics (compared to the other margins which were recently reactivated, such as the Ligurian margin) and all this lead to a better preservation and seismic imaging of the Messinian erosional surface and clastic deposits. All those elements should help to identify the sea-level lowering effects on the erosion and sedimentation processes. During the “MAURESC” cruise (R/V “TETHYS II”) conducted on the Provençal Margin slope and rise, in September 2003, we have collected 530 km of high resolution seismic lines. These profiles complete an older data set acquired during the “MESEA I” cruise (1990), which has been reinterpreted. New seismic processing has been used to increase the accuracy of our subsurface interpretations. This work focuses on the identification, characterization and distribution of the MSC-related sedimentary units and on the relationships between the detrital sedimentary bodies and the evaporites in the deep Provençal Basin.


38) - AN OVERVIEW ON THE MESSINIAN “LAGO-MARE” PALEONTOLOGICAL RECORD

Rocco GENNARI and Silvia M. IACCARINO

Department of Earth Sciences, Parco Area delle Scienze 157/A University of Parma, Italy

The «Lago-Mare» facies characterizes the latest Messinian of the Mediterranean area and is dominated by hypohaline deposits. It represents the period of time postdating the evaporitic phase and predating the re-establishment of open marine condition at the very base of the Pliocene. In fact, the most common faunal assemblage within this stratigraphic interval consists of molluscs (Melanopsis fauna of Ruggieri, 1958) and ostracods (Iaccarino & Papani, 1979; Bassetti et al 2003), indicating brackish-water environment. The foraminifers and calcareous nannofossils are at time abundant but because of their small and equidimensional sizes are considered by most of the researchers as rerworked. Among them Moruzzi & Follador (1973) described a foraminifer assemblage from the north-eastern Apennine, composed of «recrystallized Globigerinids rarely abundant in number, and frequently very small in size» (< 125 µm). Colalongo et al. (1976) reported the finding of an association of small or poorly preserved to broken planktonic and benthonic foraminifers. Iaccarino & Papani (1980) found a similar assemblage in the uppermost Messinian deposits of the north-western Apennine. All the authors agreed on the interpretation of these assemblages as resedimentation episodes. Iaccarino et al. (1998) documented at the very top of the Messinian “Lago-Mare” sequence at Site 975 (Leg 161, Balearic Basin) a paralic foraminifer assemblage which testifies the presence of marine waters before the Pliocene abrupt re-establishement of the open marine environment. Only very recently, on the basis of the calcareous nannofossil association , several authors (Snel et al. 2001, Popescu, 2003, Crescenti et al., 2002) suggested the presence of repetitive marine water incursions within the ”Lago Mare” facies. At present, on the basis of foraminifer assemblages, “Lago – Mare” deposits indicate typical brackish-water conditions. Even Cresenti et al. (2002) confirm that foraminifers are not clearly indicative of marine influxes because, as usual, they are very poor and badly preserved. Nonetheless the calcareous nannoplankton association is supposed to be authoctonous and therefore testifying marine influences prior to the base of the Pliocene. Recently, two ENI-AGIP survey were drilled in NE Apennine within the postevaporitic unit; both recovered a continuous record, the former (Campea) recovered 170m from a volcanoclastic horizon (5.50 Ma, Odin et al., 1997) down to the top of resedimented evaporite; the latter (Scab) started from about 50 m below the M/P boundary and spanned 60 m downward in the “Lago – Mare” deposits. Therefore they cover almost completely the post-evaporitic unit of the NE Apennine Messinian basin (Roveri et al.,1998, Ricci Lucchi et al., 2002). The stratigraphic interval spanned by CAMPEA well is not considered an actual «Lago-Mare» environment. In samples from this well ostracods are very rare, while foraminifers range from rare to abundant; P/B ratio is often major than one, but specimens are often very small and not recognizable; a few sample are devoid of organic component. In SCAB well foraminifers are very rare (can be abundant in <125 µm fraction) and badly preserved, while ostracods are more frequent. Ostracods are particularly well preserved, together with molluscs, in a thin horizon that overlies an organic-rich marsh deposit that, in turn, rest on a paleosoil.

A3-size poster (PDF - 844 kb)


39) - WAS THE MESSINIAN EVENT RECORDED IN THE BLACK SEA? NEW INSIGHTS FROM BLASON HIGH RESOLUTION SEIMIC PROFILES

Hervé GILLET1-2, Gilles LERICOLAIS1, Jean-Pierre REHAULT2 and Corneliu DINU3

1: IFREMER, Centre de Brest, France (Herve.Gillet@ifremer.fr; Gilles.Lericolais@ifremer.fr).
2: UMR 6538 Domaines océaniques, IUEM, France (Jean-Pierre.Rehault@univ-brest.fr).
3: University of Bucharest, Faculty of Geology and Geophysics, Romania (dinuc@gg.unibuc.ro)

In the 70’s, the seismic reflection and DSDP drilling data revealed the presence of a thick layer of evaporites within the sediment pile of the deep Mediterranean basins. This discovery led to the famous hypothesis of the Messinian Salinity Crisis (MSC) (Ryan et al., 1973). In 1975, sediment cores from the DSDP program revealed in the Black Sea a thin evaporitic carbonates layer at the Miocene-Pliocene boundary (Ross et al, 1977). From this sampling and in the wake of the previous phenomenal Mediterranean discovery, Hsü suggested for the Black Sea, as for the Mediterranean Sea, a desiccation period at the end of the Messinian (Hsü and Giovanoli, 1979). As for the Mediterranean MSC hypothesis at the beginning, the Hsü‘s assumption was soon largely disapproved (Steininger and Papp, 1979; Kojumdgieva, 1983). Whereas the main topics of the MSC in Mediterranean Sea is now widely accepted, the debate about the Messinian desiccation of the Black Sea stayed until nowadays open. The analysis of the new High Resolution (HR) multi-channel seismic data acquired recently (BLASON 1 and 2 French-Romanian surveys) bring new elements to the scientific debate about the possible Late Miocene Black Sea desiccation hypothesis. On the northwestern margin of the Black Sea, these data were calibrated with Romanian exploration boreholes. In the southwestern part of the basin, they were correlated with the DSDP drillings. First, the correlation of the BLASON seismic data with the DSDP drillings at sites 380 and 381 on the Turkish slope, shows the top of the shallow water environment unit recognised in these drillings corresponding to an erosional surface on our seismic data. This is in agreement with the Hsü and Giovanoli proposition. On the other hand, several incisions of restricted spatial extension, have been underlined under the Romanian shelf sea floor and are dated from the late Pontian period. Most of the authors consider the regional Pontian stage as the equivalent of the Messinian stage. Thus, these incisions may be related to a Messinian Black Sea sealevel drop. However, the restricted lateral and upstream extension of these incisions is in contrast with the complete desiccation of the Black Sea proposed by Hsü. These new observations should involve a review of the Hsü ‘s hypothesis. We propose that the Messinian event in the Black Sea may correspond to a sea level drop but with a weaker amplitude than the one recognised in the Mediterranean Sea.
References:
Hsü, K.J. and Giovanoli, F. (1979) Messinian event in the Black Sea. Pal. Pal, Pal., 29, 75-93.
Kojumdgieva, E. (1983) Paleogeographic environment during the desiccation of the Black Sea. Pal. Pal, Pal., 43, 195-204.
Ross, D.A. (1978) Summary of results of Black Sea drilling. In: Initial Reports of the Deep Sea Drilling Project, 42 (part 2) (Eds. D. A. Ross and Y. P. Neprochnov), pp. 1149-1178. U.S. Govt. Printing Office, Washington,
D.C. Ryan, W.B.F., Hsü, K.J. et al. (1973) Initial Reports of the Deep Sea Drilling Project,13 (Part 1 & 2). U.S. Govt. Printing Office, Washington, D.C, 1447 pp.
Steininger, F.F. and Papp, A. (1979) Current biostratigraphic and radiometric correlations of Late Miocene Central Paratethys stages (Sarmatian s.str., Pannonian s.str., and Pontian) and Mediterranean stages (Tortonian and Messinian) and the Messinian Event in the Paratethys. Newsl.-Stratigr., 8(2), 100-110.


40) - PARATETHYAN OSTRACOD IMMIGRANTS IN ITALY DURING LATE MIOCENE

Elsa GLIOZZI, Maria Elena CECI, Francesco GROSSI, and Silvia LIGIOS

Dip. Scienze Geologiche, Univ. Roma Tre, L.go S. Leonardo Murialdo, 1 – 00145 Roma, Italy. (gliozzi@uniroma3.it)

During Serravallian, the emersion of the Carpathians and of the Alpine foreland domain closed the northern connection between the western and the eastern Tethys. In the late Miocene this latter became subdivided into several basins (Vienna Basin, Pannonian Basin, Dacic Basin, Ponto-Euxinic Basin and Caspian-Aral Basin) which, due to the freshwater input from several important rivers, were progressively characterised by brackish waters. The connection via the present Dardanelli straight was still open but the different salinity between western and eastern Tethys represented an ecological barrier, preventing the faunistic exchanges and causing the onset of two different Late Miocene bioprovinces: the Paleomediterranean bioprovince to the west and the Paratethyan bioprovince to the east. Notwithstanding the Late Miocene isolation of Paleomediterranean from Paratethys, during Late Tortonian-early Messinian it is possible to recognise in Italy few brackish and freshwater ostracods with Paratethyan affinity. The palaeogeography of the area prevents to suppose a normal aquatic migration, and, indeed, the distribution of several Paratethyan genera seems disjuncted. In this case, only a passive dispersal by aquatic birds can be claimed. Paratethyan genera transported in Italy are Camptocypria (Sirmiella), Bakunella, Propontoniella, Labiatocandona, Zalanyiella (all included in the Subfamily Candoninae), Loxoconchissa s.s. and Loxoconchissa (Loxocaspia), included in Family Loxoconchidae and Amnicythere (and may be Chartocythere and Mediocytherideis) included in Family Leptocytheridae. During the latest Messinian lago-mare event, the closure of the Atlantic-Mediterranean connection and the subsequent humid global climate phase caused a salinity lowering of the Paleomediterranean waters. The ecological barrier between Paleomediterranean and Paratethys was disrupted and an important contingent of Paratethyan ostracods migrated westwards colonising the Paleomediterranean, whose endemic fauna was severely impoverished by the Messinian salinity crisis and the following water dilution. The Italian (and Paleomediterranean) latest Messinian lago-mare deposits are characterised by Paratethyan species such as Caspiocypris pontica, Lineocypris cf. L. fossulata, Lineocypris cf. L. hodonensis, Pontoniella pontica, Zalanyiella venusta, Amnicythere accicularia, Amnicythere anormalis, Amnicythere cellula, Amnicythere costata, Amnicythere idonea, Amnicythere pontica, Amnicythere lata, Amnicythere litica, Amnicythere multituberculata, Amnicythere palimpsesta, Amnicythere propinqua, Amnicythere cf. A. rosalinae, Amnicythere subcaspia, Euxinocythere (Maeotocythere) praebaquana, Euxinocythere (Maeotocythere) bosqueti, Loxoconcha (Loxoconcha) eichwaldi, Loxoconcha (Loxoconcha) muelleri, Loxoconcha rhombovalis, Loxoconcha cf. L. schweyeri, Loxocorniculina djafarovi, Pseudocythere limata, Cytherura pyrama, Tyrrhenocythere ruggierii, Tyrrhenocythere pontica.

41) - DRILLING IN THE NORTHERN PROVENCE BASIN THROUGH MESSINIAN EVAPORITES AND A THICK MIOCENE COVER: THE NORTHERN PROVENCE BASIN TRANSITIONAL CRUST

Christian GORINI1, Alain MAUFFRET2, Jean-Louis OLIVET3, Louis GELY3, Pol GUENNOC4, Jean-Pierre REHAULT5, Georges CLAUZON6 and Jean-Pierre SUC7

1: Université de Lille 1, Laboratoire P.B.D.S. (UMR 8110), SN5 F, 59 655 Villeneuve d'Ascq Cedex, France.
2: Université Paris et Marie Curie (Paris VI), Paris, France.
3: IFREMER, Brest, France.
4: Avenue Claude Guillemin, 45060 Orléans cedex 02, France.
5: IUEM-U.B.O, UMR 6538 "Domaines Océaniques" Place Nicolas Copernic 29280 Plouzané, France.
6: CEREGE, Aix en Provence, France.
7: PEPS (UMR 5125 CNRS), Université Cl. Bernard – Lyon 1, 27-43 boulevard du 11 Novembre, F-69622 Villeurbanne Cedex, France.

The deep Northwestern Mediterranean (Provence) Basin lies between the Valencia Trough to the southwest, the Gulf of Lions to the north, the Catalan Margin to the west, and the Ligurian Sea to the northeast. This area is characterised by a Neogene extensional rift, within a context of regional compression between the European and African plates in the back-arc area of Calabrian subduction. Although the timing of this rifting event has been determined by indirect methods (cores from the edges of syn-rift Oligocene basins, kinematic reconstructions), the deep basin crust itself has never been sampled. Rifting came to an end during the Middle Aquitanian (23 Ma). The break-up unconformity is coeval with onset of the first oceanic crust in the Provence Basin, which opened during the Burdigalian (20.5 to 19 Ma) as a result of southeastward drifting of Corsica and Sardinia. The extent of oceanic crust is still the subject of debate due to an ambiguous magnetic pattern, which has led to the proposal of many different hypotheses. From the northwest to the southwest, the transition between the slope and the central basin may be associated with a crustal discontinuity. A major change in crustal velocity occurs between ESP 203 (6.2 km/s, slope base,GLP2) and ESP 204 (6.6 km/s), coinciding with the T reflector high. This area corresponds to a zone of deformed, thinned, and presumably continental, basement. It also corresponds to a zone of listric faulting affecting the Late Messinian, as well as the Pliocene-Quaternary. Southeast of ESP 205, the sedimentary layer between the Late Burdigalian marker and the acoustic basement is relatively thick, but the basement reflector here is flatter and smoother, and no syn-rift sediments are identified. The crust has a homogeneous velocity structure, and is probably a highly extended crust or an intermediate crust, related to progressive lithospheric thinning from the end of rifting to the beginning of ocean spreading. The crustal nature in this area can be regarded as a fossil example of the transitional realm at the continent-ocean boundary. The salt layer is not disturbed and the Miocene succession is complete. Drilling in this area will provide significant information concerning not only Mediterranean history (rifting and spreading constraints, Messinian event), but also thinning processes, lithospheric/asthenospheric interactions during continental breakup, thermal state of the lithosphere, etc. Two longstanding and controversial geological issues relating to this area, namely the Messinian event in the Mediterranean Sea and the process of lithospheric extension, could be resolved by an ultra-deep drilling programme in this Mediterranean domain of the Provence Basin.

42) - THE LATE MESSINIAN SALINITY CRISIS AND LATE MIOCENE TECTONISM: INTERACTION . CONSEQUENCES ON THE PHYSIOGRAPHY AND POSTRIFT EVOLUTION OF THE GULF OF LIONS MARGIN

Christian GORINI1, François BACHE1, Antonio Tadeu DOS REIS2, Johanna LOFI1, Pol GUENNOC3, Jean-Louis OLIVET4, Serge BERNE4, Marina RABINEAU1, Alain MAUFFRET5 and the SEASAME6 team

1:Université de Lille 1, Laboratoire P.B.D.S. (UMR 8110), SN5 F, 59 655 Villeneuve d'Ascq Cedex, France.
2: Universidade do Estado do Rio de Janeiro, Departamento de Oceanografia, Rio de Janeiro, Brazil.
3: BRGM, 3, Avenue Claude Guillemin, 45060 Orléans cedex 02, France.
4: IFREMER, DRO/GM Technopôle Brest- Iroise, B.P. 70, 29 280 Plouzané, France.
5: Laboratoire de Tectonique (UMR 7072), Université Pierre et Marie Curie - Paris 6, 75 252 Paris Cedex 05, France.
6: Virginie GAULLIER (LEGEM, Univ. de Perpignan), Jacques DEVERCHERE (UBO-IUEM, CNRS-UMR6538, Plouzane), Agnès MAILLARD (LMTG, Univ. de Toulouse)
.

This study supports the interpretation of numerous industrial and high-resolution seismic profiles taken in the Gulf of Lions by the petroleum industry (RM96 LIGO et HR Total profiles) and by IFREMER (Marion and Calmar campaigns). Seismic profiles have revealed that in the Gulf of Lions, the Late Miocene platform is offset by normal faults associated with latest Miocene - earliest Pliocene extension. The origin of this extension has yet to be clearly identified, but it is thought to be associated with uplift in the east of the Pyrenees (Alberes and Canigou massifs). The interpretation of the seismic profiles, the accurate mapping of all the structural features affecting the Miocene cover, and study of the Messinian river profiles on the platform made it possible for us to develop a structural model for the top of the eroded Miocene of the Gulf of Lions platform. The latest Miocene extension could have been caused by gravity-driven destabilization of the platform associated with base-level lowering at the onset of the Messinian salinity crisis. Exposed during dessication, margin collapsed and was heavily eroded. In the deep basin of the Gulf of Lions, salt is gradually replaced upsection by chaotic seismic units, which overlies the Messinian erosion surface, and which is interpreted as Messinian detritus (Lofi, 2001; Dos Reis, 2000).The geometries at the upper Miocene paleo slope show a thick prograding unit characterized by steep clinoforms (oblique progradation), whose upper limit is an erosive top lap. Its equivalent on the platform is a by-pass surface, associated with erosion. In the basin, its equivalent is a thick seismic unit, beneath the Messinian salt, characterized by high frequency reflectors and high seismic velocities, the signification of this unit is discussed.

43) - MESSINIAN GEOLOGY AND STRUCTURE OF THE CORSICAN MARGINS: A REGIONAL SYNTHESIS

Pol GUENNOC1, Jean-Pierre REHAULT2, Isabelle THINON1 and Jean FERRANDINI3

1: BRGM, CDG/MA 3 Claude Guillemin BP6009 45060 Orléans cedex 2, France. (p.guennoc@brgm.fr; i.thinon@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 Corsican margins have been the subject of a lot of scientific studies within the framework of the collaboration between the University of Corsica, the BRGM and the IUEM (Brest) for many years. Several thousands kilometres of seismic profiles have been collected and interpreted on the basis of the new geological data, then digitised to build a Messinian map on a Corsican scale. The Messinian geological map underlines the present dissymmetry of two Corsican margins: the western margin together with the North Ligurian margin bounds the oceanic saliferous ligurian area. The eastern margin edges the endoreic Messinian Corsican Basin. The morphology of the Messinian western margin seems close to the present morphology. It is large and cut by some important canyons where the basement outcrops evenly. The sourthern part is characterised by an important volcanism dated from the Lower-Middle Miocene epochs extending those of Sardinian rift. The numerous volcanic structures attest all the post-rift evolution of the margin. Immediately in the North, very thick Miocene units cover the basement that deepens rapidly at the foot of the continental slope. The Miocene series of the continental rise are almost totally covered with a detritic sedimentary prism at the foot of the continental slope, dated from the Final Miocene to Lower Pliocene epochs. In the northern Corsica, the extension of numerous continental structures have been observed among which the large Miocene Saint-Florent basin in the West. The deep structures of the western margin are underlined by the presence of various volcanic systems which controlled the Messinian evaporitic deposition distribution. On the contrary, the morphology of the Messinian eastern margin seems to be very different from the present morphology owing mainly to an important Plio-Quaternary sedimentation. The study of this margin (cf Thinon et al.) shows the influence of the tectonic heritage until the Messinian period and the absence of the Miocene shelf s.s. except for the Aleria zone in the centre area and the eastern Bofinacio margin in the South. Along the Cap Corse Region, the Messinian continental slope is straight and the residual reliefs suggest that the morphology of the nowadays margin is little different to that of the Messinian margin. This steep margin reflects the likely structure of the south areas before the installation of the Plio-Quaternary sedimentary shelf. The eastern Corsican margin is bounded by the shallow Messinian Corsican Basin. The nature of the Messinian deposition and the morphological context of this basin show its endoreic character of the Messinian epoch. The detailed study of the Messinian evidence - incision networks well drawn, uplifted and limited to the southern part of the basin where the connection has been obstructed by a magmatic structure - shows the active tectonic and magmatic context of the Pianosa Ridge of the Later Miocene epoch, the Plio-Quaternary periods and notably during the Messinian phase.

44) -THE MESSINIAN PALEOMARGIN OF THE WESTERN BONIFACIO STRAITS: A WHITNESS OF A MULTIPLE RIFTING HISTORY BETWEEN CORSICA AND SARDINIA

Pol GUENNOC1, Jean FERRANDINI2, Jean-Pierre REHAULT3 and Isabelle THINON1

1: BRGM, CDG/MA 3 Claude Guillemin BP6009 45060 Orléans cedex 2, France. (p.guennoc@brgm.fr; i.thinon@brgm.fr)
2: Université de Corse, Sciences de la Terre - BP . 52 – 20250 Corte, France. (jferrand@univ-corse.fr)
3: IUEM-U.B.O, UMR 6538 "Domaines Océaniques" Place Nicolas Copernic 29280 Plouzané, France. (rehault@univ-brest.fr)

The margin of the Western Bonifacio Straits between Corsica and Sardinia is characterised by a large and wide outer margin and the absence of a continental hinterland. Previous studies have shown the presence of large magnetic anomalies in the outer part of the margin and deep Miocene basins in the inner part. Kinematic recontructions are still assuming some differential movements between Corsica and Sardinia that may explain some of these deep features. However, geological observations are arguing against any large movements between the two islands in the Straits of Bonifacio. Despite various researches the history of this key section of the Corsican-Sardinian block was rather poorly known. Then, several recent studies have been conducted in order to decipher the Neogene history of the Western Bonifacio Straits margin. On the outer part, geophysical studies and new geological observations made during Marco and Cylice cruises have demonstrated the importance of the Mid-Miocene (c.a. 17 - 16 Ma) volcanic stage on the South-western Corsican margin in the prolongation of the central Sardinian rift. More recent studies have been focused on the Bonifacia platform itself during three cruises (Bocca 99, 2000, Geocorse 2003) and a dense grid of high resolution seismic profiles and some new geological sampling have been acquired. These studies have demonstrated the complex structure of this platform area and as a major result, the discovery and detailed mapping of a Messinian paleoslope in the central part of the present shelf. Indeed, on the contrary to other adjacent margins, this Messinian paleoslope is located well inland of the present-day shelf edge. This paleoshelf displays a complex shape with large canyons and secondary canyons that may be controlled by deep structures. This paleoslope sharply delimits the innermost area where a rather close relationship can be established between the Miocene series of the Bonifacio on land and the offshore Miocene seismic units that display a very low westward dipping. The offshore units are undeformed and only some minor flexures have been observed demonstrating the absence of significan brittle tectonics in that area since Mid- Miocene and confirming the observations made on land series. The Miocene cover is present over the whole inner shelf and very near to the land granitic basement areas along the whole coastline, which thus represents an erosional boundary. The Messinian paleoslope is presently buried westwards under a thick sedimentary succession about 500 to 800 metres high. Although it has not been proved by sampling and dating, this infilling is Plio-Quaternary in age as a continuous sediment architecture can be seen in the southernmost part of the shelf offshore Northern Sardinia. At the North-western edge of the present shelf the structure of the shelf edge is controlled by the presence of various magmatic structures (volcanic flows or sills, intrusive bodies...) that have uplifted and tilted the pre-existing lower Miocene series to the East. These Mid-Miocene volcanic and tectonic events are linked to the "second" rifting stage of the Central Sardinia-SW Corsican margin and have controlled the Neogene evolution of the Western Bonifacio margin.

45) - BIOSTRATIGRAPHY OF THE MESSINIAN: STATE OF THE ART

Silvia M. IACCARINO1, Rocco GENNARI1 and Fabrizio LIRER2

1: Dipartimento di Scienze della Terra – Università di Parma, Parco Area delle Scienze 157/A, 43100 Parma, Italy.
2: Istituto per l’Ambiente Marino Costiero (IAMC) – CNR, Geomare di Napoli, Calata Porta di Massa, Interno porto di Napoli, 80133 Napoli, Italy.

The Messinian Stage represents the standard chronostratigraphic unit for the uppermost Miocene and is widely known because of the «salinity crisis» occurred in the Mediterranean at that time. The up-to-date biostratigraphic results related to the Messinian Stage from the base up to the early Pliocene Stage are presented. The base of the stage is well defined biochronologically (7,25 My) after the formal definition of the Global Stratigraphic Section and Point (GSSP) located at Oued Akrech (Rabat, Morocco). The Messinian sediments predating the deposition of the evaporites are biostratigraphically well documented in the Mediterranean area. The paleontological record of the deposits overlying the evaporites is, on the contrary, poorly documented because of the poor microfossil content and therefore its meaning is still debated. Most of the researches carried out in the past led to the interpretation that these sediments were deposited in brackish paleoenvironments and therefore the only fossils occurring in these sediments are representative of this environment. Recent researches suggest the occurrence of “marine” intercalations within this brackish-water facies (Lago-Mare so-called event). We stress the occurrence of these levels and suggest a different interpretation of their source.

46) - MEDITERRANEAN GEODYNAMICS IN THE CENOZOIC, FROM THE MANTLE TO POST-OROGENIC SEDIMENTARY BASINS

Laurent JOLIVET1, Romain AUGIER1 and Claudio FACCENNA2

1: Laboratoire de Tectonique, UMR 7072, Université Pierre et Marie Curie, T 46-00 E2, case 129, 4 Place Jussieu, 75252 Paris cedex, France. (laurent.jolivet@lgs.jussieu.fr)
2: Dipartimento di Scienze Geologiche, University of Roma 3, Largo San Murialdo 1, 00146 Rome, Italy. (faccenna@uniroma3.it)

The Cenozoic period in the Mediterranean region was characterized by a sharp change in the subduction dynamics some 30-35 Ma ago, from generalized compressional subduction, leading to the formation of Alpine mountain belts, to extensional subduction and the formation of backarc basins, from the Alboran Sea to the Aegean Sea. Backarc extension was thus associated with collapse of the mountain belts formed before this Oligocene revolution. Sedimentary basins evolved in connection with the reactivation of thrust faults as extensional detachments or the creation of new detachments. From the Aegean Sea to the Tyrrhenian Sea and the Alboran Sea we have analysed onshore the kinematic and P-T evolution of the deep crust exhumed by extension and the transition from ductile to brittle conditions and the relations between deep deformation and the formation of basins. We also have reconstructed the behaviour of the deep subducted slabs using kinematic reconstructions and tomographic models. We show two different types of evolution, in the eastern Mediterranean where subduction had been engaged in the Early Mesozoic, and in the Central and Western Mediterranean where it started only in the late Cretaceous or Early Cenozoic. We tentatively propose a scheme explaining how the interactions between the subducting slab and the mantle control the basal shear below the upper plate and the geometry and distribution of detachments and the associated sedimentary basins. The example of the Betic Cordillera and the Rif orogen, where the direction of stretching where different in the lower and the upper crust and changed through time, is discussed and we proposed a scenario of evolution from the Eocene to the Messinian salinity crisis.

47) - UNRAVELLING THE PRE-MESSINIAN: INTEGRATED MICROFOSSIL DATA FROM THE LATE MIOCENE PISSOURI SECTION (CYPRUS)

Tanja KOUWENHOVEN1, Simona GIUNTA2, Caterina MORIGI2, Alessandra NEGRI2, Wout KRIJGSMAN3 and Jean-Marie ROUCHY4

1: Faculty of Geosciences, Utrecht University, Utrecht, the Netherlands.
2: Dipartimento di Scienze del Mare, Università Politecnica delle Marche, Ancona, Italia.
3: Paleomagnetic Laboratory Fort Hoofddijk, Utrecht, the Netherlands.
4: CNRS-UMR 5143, Département Histoire de la Terre, Géologie, Muséum National Histoire Naturelle, 43 rue Buffon, 75005 Paris, 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). As such this section holds important information concerning the onset of the evaporative (“Messinian”) phase at upper epibathyal depths. With the present accuracy of integrated dating methods (bio-, cyclo- and magnetostratigraphy) we have the opportunity to place important bio-events within a well-constrained time frame. In this study integrated microfossil data (planktonic and benthic foraminifera, calcareous nannofossils) are compared in order to add more detail to the emerging picture of changes affecting the eastern Mediterranean Basin towards the MSC. These microfossil data reveal a stepwise development towards an increasingly restricted paleoenvironment. The nannoflora shows a twofold distribution: starting from the bottom of the section to 6.6 Ma the surficial assemblage is typical of normal marine conditions whereas after this point it shows frequent, extreme fluctuations in abundance and in some cases oligotypic communities (e.g. consisting of 99% sphenoliths) Benthic foraminifera indicate a rather well ventilated open marine bottom-water environment until ~7.2 Ma. Subsequently, increasing restriction becomes evident, with a time-step around ~6.7 Ma. The planktonic foraminifera assemblage is well diversified until ~6.7 Ma, and mainly consists of Globigerina decoraperta, Globigerinoides spp. and Globorotalia genera. The simultaneous presence of surface-dwellers (Globigerinoides spp.) indicative of oligotrophic, stratified waters and deep dwellers as Globorotalia spp. indicative of mixing water, could indicate a strong seasonal contrast. After ~6.4 Ma, rapid and repeated changes in both pelagic and benthic productivity are indicated by the foraminifera. The low-diversity benthic faunas are dominated by stresstolerant taxa (buliminids, bolivinids). Samples barren of planktonic foraminifera alternate with samples with a low diversified planktonic assemblage where Neogloboquadrinids dominate. This taxon is supposed to flourish in spring when eutrophicated waters follow deep winter mixing, and their fluctuation in abundance suggests pulsing of the surficial productivity. Although constriction of the portals towards the Atlantic (Betic and Rif corridors) is by now more or less accepted as a cause of the MSC, we suspect and find indications for a superimposed effect of astronomically driven climate cycles.

48) - THE MESSINIAN SALINITY CRISIS OF THE MEDITERRANEAN: STATE OF THE ART

Wout KRIJGSMAN and co-workers

Paleomagnetic Laboratory Fort Hoofddijk, Utrecht University, The Netherlands. (krijgsma@geo.uu.nl)

The Messinian salinity crisis (MSC) is widely regarded as one of the most dramatic episodes of oceanic change of the past 20 or so million years. Earliest explanations were that extremely thick evaporites were deposited in a deep and desiccated Mediterranean basin that had been repeatedly isolated from the Atlantic Ocean, but elucidation of the causes of the isolation – whether driven largely by glacio-eustatic or tectonic processes – have been hampered by the absence of an accurate time frame. During the last decade significant progress has been made on the chronology of the Messinian deposits and accurate time scales have been developed for marine, lacustrine and continental realms. Here we will present the state of the art of the chronological data regarding the Messinian Stage. This will (hopefully) help us to solve, elucidate and discuss many of the long-standing problems and controversies related to the causes and consequences of the deposition of the so characteristic evaporite and Lago Mare facies of the Mediterranean Messinian.


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