Messinian Erosional Surface Research Articles

New imaging of the salinity crisis: Dual Messinian lowstand megasequences recorded in the deep basin of both the eastern and western Mediterranean

Through several examples we show that following sea-level fall and marginal erosion during the Messinian salinity crisis (MSC), clastic inputs into the eastern and western Mediterranean Sea are not distributed evenly in space and time but are mainly limited to the lower section of the Messinian salinity crisis depositional megasequence. Significant similarities around the basin allow us to propose a Mediterranean Messinian salinity crisis depositional episode that can be divided into two seismic megasequences: the Messinian lower megasequence (MLM) and the Messinian upper megasequence (MUM). Their distinctive seismic facies correspond to systems tracts deposited during three main stages that represent a complete sea level cycle. (1) A falling stage systems tract including mass transport deposits and forced regressive clinoforms deposited in the early part of the falling stage, and related to the increasing rate of relative sea level fall. This stage is characterized by a marked shift in the depocenter towards the deep basins. (2) An early lowstand characterized by massive clastic inputs from major Messinian rivers (the Rhone, Nile, and Antalya Gulf rivers) or smaller river systems (offshore south Lebanon). These clastics were deposited in an oversaturated basin, as evidenced by the interfingering chaotic and transparent seismic facies of the Messinian lower megasequence (MLM). (3) A late lowstand, starting with rapid deposition of massive halite, with no detrital inputs into the deep basin. The upper part of the evaporites clearly onlaps the Messinian erosional surface at the margins and is evidence for a transition between a late lowstand stage and an early transgressive stage. These deposits belong to the Messinian upper megasequence (MUM). We interpret the transition between the two megasequences as the peak of the “salinity” crisis, the end of the relative sea level fall, and the maximum dispersal of sands into the deep Mediterranean basins.

The Messinian salinity crisis in Cyprus: a further step towards a new stratigraphic framework for Eastern Mediterranean

AbstractA revised stratigraphic framework for the Messinian succession of Cyprus is proposed demonstrating that the three‐stage model for the Messinian salinity crisis recently established for the Western Mediterranean also applies to the Eastern Mediterranean, at least for its marginal basins. This analysis is based on a multidisciplinary study of the Messinian evaporites and associated deposits exposed in the Polemi, Pissouri, Maroni/Psematismenos and Mesaoria basins. Here, we document for the first time that the base of the unit usually referred to the ‘Lower Evaporites’ in Cyprus does not actually correspond to the onset of the Messinian salinity crisis. The basal surface of this unit rather corresponds to a regional‐scale unconformity, locally associated with an angular discordance, and is related to the erosion and resedimentation of primary evaporites deposited during the first stage of the Messinian salinity crisis. This evidence suggests that the ‘Lower Evaporites’ of the southern basins of Cyprus actually belong to the second stage of the Messinian salinity crisis; they can be thus ascribed to the Resedimented Lower Gypsum unit that was deposited between 5.6 and 5.5 Ma and is possibly coeval to the halite deposited in the northern Mesaoria basin. Primary,in situevaporites of the first stage of the Messinian salinity crisis were not preserved in Cyprus basins. Conversely, shallow‐water primary evaporites deposited during the third stage of the Messinian salinity crisis are well preserved; these deposits can be regarded as the equivalent of the Upper Gypsum of Sicily. Our study documents that the Messinian stratigraphy shows many similarities between the Western and Eastern Mediterranean marginal basins, implying a common and likely coeval development of the Messinian salinity crisis. This could be reflected also in intermediate and deep‐water basins; we infer that the Lower Evaporites seismic unit in the deep Eastern Mediterranean basins could well be mainly composed of clastic evaporites and that its base could correspond to the Messinian erosional surface.

Messinian evaporite deposition during sea level rise in the Gulf of Lions (Western Mediterranean)

The Messinian Salinity Crisis resulted from desiccation of the Mediterranean Sea after its isolation from the Atlantic Ocean at the end of the Miocene. Stratal geometry tied to borehole data in the Gulf of Lions show that the pre-crisis continental shelf has been eroded during a major sea-level fall and that sediments from this erosion have been deposited in the basin. This detrital package is onlapped by high amplitude seismic reflectors overlain by the “Messinian Salt” and the “Upper Evaporites”. Towards the shelf, the transition between regressive deposits and overlying onlapping sediments is characterised by a wave-ravinement surface, suggesting that a significant part of the onlapping reflectors and overlying Messinian Evaporites were deposited during a relatively slow landward migration of the shoreline. The clear boundary between the smooth wave-ravinement surface and the subaerial Messinian Erosional Surface observed on the Gulf of Lions shelf and onshore in the Rhône valley is interpreted to have resulted from a rapid acceleration of the Mediterranean sea level rise at the end of the Messinian Salinity Crisis. Numerical simulation of this cycle of sea level change during the Messinian Salinity Crisis and of precipitation of thick evaporites during the slow sea level rise shows that this scenario can be modelled assuming a value of evaporation minus precipitation of 1.75 m3/m2/yr in the deep Mediterranean basins.

3D modelling of the Sorbas Basin (Spain): New constraints on the Messinian Erosional Surface morphology

The scenario of the Messinian Salinity Crisis (MSC) remains one of the most debated topics in the Mediterranean realm and especially in the Sorbas Basin, which is one of the type-localities of MSC-related deposits. After a recently improved chronostratigraphic framework of the Miocene and Pliocene deposits of the basin, this work is an attempt to image the morphology of the Messinian Erosional Surface (MES) at depth. We built a basin-scale 3D-model of the Miocene and Pliocene series that confirms the erosional character of the Messinian/Pliocene boundary, solving a long-standing and debated question. We tentatively also suggest that the fluvial system developed during the peak of the MSC was exiting the basin toward the south. This new geometrical model, showing a robust internal consistency, can be used as a basis for interpreting the Messinian Salinity Crisis in other sedimentary basins around the Mediterranean Sea. The return of marine conditions in the Early Pliocene on an erosional surface interferes with the continuous formation of the Sorbas Basin asymmetrical syncline, subsidence of the hinge, uplift of the limbs and gravitational sliding. The irregular shape of the MES is superimposed in the southern part of the basin by small-scale box-type folds with two oblique NNE–SSW and WNW–ESE fold axes directions. The architecture of these folds suggests gravitational sliding of post-evaporitic marine sediments during the progressive deformation of the basin during the Zanclean.

The Messinian Salinity Crisis: New seismic evidence in the West-Sardinian Margin and Eastern Sardo-Provençal basin (West Mediterranean Sea)

Abstract We processed and interpreted a newly acquired geophysical dataset (WS10 project) integrated with vintage seismic profiles to study the evolution of the Sardinian passive margin of the Sardo-Provencal basin. The most prominent features of the area of study are a consequence of the Messinian Salinity Crisis (MSC) which produced a thick salt layer in the deep basin. Complex halokinetic tectonics deformed the overlying Messinian Upper Unit (UU) and the Pliocene–Quaternary (PQ) sediments, sometimes also bending the sea bottom. A thinner autochthonous salt in the UU suggests at least one further low stand during the late MSC. The Messinian Erosional Surface (MES) separates the erosional truncation of the pre-Messinian sedimentary sequence from the overlaying Plio-Pleistocene sequence with a clear angular discordance, which almost completely masks possible earlier erosional events. The MES is present across the middle and upper slopes of the Sardinian margin and can be easily recognized down to the lower slope, where it interfingers with the Messinian evaporites which gradually thicken basinward. We propose a correlation between the main erosional surface of the lower slope and the salt layer recognized in the UU as a consequence of a falling stage during the last part of the MSC. The seismic profiles now available along the West Sardinian margin provide novel and crucial information to correlate the Messinian depositional units in the deep basin with those present in the lower continental slope and with the erosional surface of the middle and upper slopes. Our data and interpretation highlight the main units of the Messinian trilogy and further internal sequences that are probable related to cyclic fluctuations during their deposition.

Lago Mare and the Messinian Salinity Crisis: Evidence from the Alboran Sea (S. Spain)

This paper provides a new environmental, sedimentological and stratigraphic context of the Lago Mare deposits from the North Alboran region and clarifies their chronologic location with respect to the Messinian Salinity Crisis. We present new micropalaeontological data (dinoflagellate cysts, calcareous nannoplankton, planktonic foraminifers), correlated with field observations and offshore seismic interpretations. We show that the Lago Mare event known in three onshore localities (Río Mendelín near Malaga, Zorreras near Sorbas, Gafares near Níjar) follows the marine reflooding of the Mediterranean Basin which ended the Messinian Salinity Crisis. Chronologically, these Lago Mare deposits last from the latest Messinian to the early Zanclean. In fact, the first influx of Paratethyan organisms is revealed by the dinoflagellate cyst record from near Malaga within a Gilbert-type fan delta overlying the Messinian Erosional Surface. Invading molluscs and/or ostracods may have persisted in lagoonal coastal areas more or less affected by discontinuous marine influxes (Sorbas and Níjar). The Malaga area is convenient for a palaeogeographic and sedimentary reconstruction which shows the prevalent forcing of sea-level changes during the time-interval 5.600–5.332 Ma at the difference of the usually solicited prevalent tectonics. The studied Lago Mare event is the third episode resulting in such a palaeobiological assemblage in the Mediterranean region and corresponds to the final two-way water exchange at high sea level between the Mediterranean and the former Paratethys. It documents the onset of the modern marine circulation in the Mediterranean after the reflooding ending the Messinian Salinity Crisis.

Late Miocene sedimentary architecture of the Ebro Continental Margin (Western Mediterranean): implications to the Messinian Salinity Crisis

The Messinian Salinity Crisis (MSC) resulted from a significant multi-phase drop and subsequent reflooding of the Mediterranean Sea from 5.96 to 5.33 Ma. Well-developed drainage networks, characterized by step-like profiles and abrasion platforms, are associated to this event. The Ebro Continental Margin (Western Mediterranean) presents an additional complexity since the capture of the drainage of the adjacent subaerial Ebro Basin took place sometime prior to the Messinian stage. Using 3D seismic reflection data, this work provides new insights into the origin of the step-like profile of the Messinian erosional surface (MES) and timing of the capture of the subaerial Ebro Basin. The results obtained indicate a sedimentary-active continental slope and delta progradation during Middle-Late Miocene, in a normal regressive context associated to a pre-Messinian proto-Ebro River. The mature development attained by the Messinian Ebro River network during the MSC corroborates that the capture of the Ebro Basin occurred prior to the MSC. The configuration of the clinoforms below the MES suggests that deltaic sediments of the Messinian Paleo-Ebro River deposited during the Tortonian and initial Messinian sea-level drawdown. The MES formed at the top of the Tortonian Highstand, where a fluvial network was deeply carved, and in the topset region of the Messinian Falling Stage Systems Tract, where minor erosion occurred. Fluvial deposits are outstandingly preserved on the main valleys of the MES. Therefore, the step-like profile of the MES was not created during Zanclean inundation, but during the latest stages of the main Messinian sea-level fall and lowstand.

The “Brecciated Limestones” of Maiella, Italy: Rheological implications of hydrocarbon-charged fluid migration in the Messinian Mediterranean Basin

The upper Messinian “Brecciated Limestones” of the Maiella area (Central Italy) reveal clues to the rheological behavior of the sedimentary column during fluid migration processes, as well as the timing of a major phase of methane release. Seep limestones have been studied worldwide in ancient and present-day settings. However, investigations of the complex rheologic behavior shown by the wide array of brecciated facies have received less attention. In this work special emphasis was placed on fabric and facies analyses, comparisons of the various scales of observation, and integrated stable isotope analyses (δ18O and δ13C), all within the context of the precisely-dated stratigraphy of the late Messinian sediments of the Mediterranean Basin.Above the basin scale Messinian Erosional Surface (MES), widespread brecciated limestone buildups and minor concretions constitute microbial carbonate bodies laterally embedded or passing to a marly-pelitic succession. In situ fluid-driven brecciation, together with the occurrence of fluid migration paths, are interpreted to represent vestiges of a mud volcano feeder system. However, chaotic textures testify to complex rheological behavior, where brittle and plastic responses in the same micro-environments co-occurred during fluid migration through a partially lithified sedimentary column.Different patterns of tar-bearing facies and degrees of brecciation, coupled with a geochemical dataset yielding wide ranges of δ18O (from +4 to −10‰ PDB-1) and δ13C values (from +4 to −40‰ PDB-1), point to two distinct stages of ascending hydrocarbon-charged fluids: in an earlier phase, fluids were mostly typified by low-molecular-weight hydrocarbons and induced widespread brecciation in the sedimentary column; in a later phase, fluid migration was accompanied by crude oil migration. During the early phase, fluid migration through the sedimentary column developed both: (a) with large vigorous fluxes, creating neoformed feeder channels and causing high degrees of brecciation; and (b) via slow seepage, favouring authigenic carbonate precipitation in the host sediment and causing negligible brecciation.In our proposed scenario, the Maiella area witnessed a hydrocarbon-rich fluid migration event (mainly methane) during the late Messinian, accompanied by authigenic carbonate precipitation and widespread brecciation. We suggest that this event was triggered by the sudden depressurization induced by the major drawdown of the Mediterranean Sea in late Messinian times.

Separating human and climatic impacts on Mediterranean forests: a combined dynamic modeling/palynological approach

In the present study, we investigate the Mediterranean–Paratethys connection during the late Miocene in Strymon Basin (North Aegean, northeastern Mediterranean) and compare this onshore sequence with the adjacent offshore Prinos-Nestos sequence, before, during, and after the Messinian Salinity Crisis (MSC). Strymon Basin was a peripheral shallow-water basin during the first MSC stage. The Akropotamos sections expose a clastic sequence with gypsum intercalations, which is dated in the Messinian based on the ostracod and calcareous nannofossil assemblages. This sequence records the Primary Lower Gypsum deposition in a shallow marine environment and its passage via the Messinian erosional surface to a brackish environment with changing salinity conditions similar to the Paratethyan depositional environments. The sequence is capped by a travertine marker horizon observed across the entire Strymon Basin indicating freshwater environment. The Miocene–Pliocene transition is characterized by salinity changes caused by the interaction between Atlantic-Mediterranean and Paratethyan waters, predating the marine reflooding at the end of the MSC, which is attested by the overlying Pliocene open marine deposits. The offshore Prinos-Nestos basin incorporates the Nestos intermediate basin and the Prinos intermediate-deep basin. Borehole and seismic profile data from the offshore Prinos-Nestos oil field reflect a thick clastic sequence, topped by turbidites, and followed by an evaporitic unit deposited during the Messinian. In the Nestos slope area, the evaporite unit consists of anhydrite-shale alternations. Toward the basin's depocenter (Prinos Basin), anhydrite is replaced by halite. The sequence is overlain by Pliocene–Holocene deltaic prograding deposits. Sedimentologic and biostratigraphic data show that the thick halite-shale couplets in the deepest part of the offshore Prinos-Nestos Basin were deposited under permanent marine conditions, suggesting no desiccation before, during, and after the MSC. Conclusively, the present results indicate that a connection between the Mediterranean and the Paratethys was occasionally established before the Pliocene reflooding and favor the non-desiccation MSC model for the deep marine evaporite deposition.

Post-Messinian evolution of the Florence Ridge area (Western Cyprus Arc), Part I: Morphostructural analysis

The Florence Ridge, part of the western Cyprus arc, is a compressional relief that was eroded during the Messinian salinity crisis while deposition of salt occurred North (Antalya basin) and South (Herodotus abyssal plain). In order to better assess the impact of salt-tectonics in the Florence Ridge region deformations, we conducted a morpho-structural analysis of available multibeam and seismic data (Simed and Prismed II campaigns). It is indeed a crucial issue to distinguish crustal and gravity driven structures in the compressional to strike-slip belts of the eastern Mediterranean.Along the Antalya basin, we mainly observed multi-directional tectonic rafts typical of gravity gliding above salt. On the Florence Ridge itself, the base of salt evolves laterally to a Messinian erosional surface that erodes a series of stacked nappes. This surface is involved in recent faulting. South of the Florence Ridge, a nearly 100km wide fold belt characterizes the Herodotus abyssal plain. Three different zones parallel to the Florence Ridge appear within this fold belt. Those are respectively from North to South zones A, B and C. Zone A is characterized mainly by small-wavelength folding and faulting. Approaching Zone B, a long extensional graben deforms the seafloor. Zone B stands ~100 to 200m higher than zones A and C. There, salt welding seems common. In the easternmost zone B deep sub-circular bathymetric depressions are associated with extremely thick and fan-shaped depocenters probably emplaced in relation with active sub-salt thrusts. Many evidences suggest post-Messinian uplift in this zone. Zone C shows medium to high wavelength salt-cored folds. Wavelength of those folds increase approaching the distal Nile deep-sea fan. Within zone C, a nearly undeformed domain exists approaching the Eratosthenes seamount. ‘En echelon’ folds bound this flat domain suggesting lateral salt extrusion at the junction between zone C and the distal Nile deep-sea fan.To conclude, numerous evidences argue for a post-Messinian reactivation of the pre-Messinian Florence Ridge accretionary wedge (numerous folds, uplifted zones). The salt, as on the nearby Mediterranean Ridge, decouples deep and surface deformations and even allow the development of isolated grabens and associated salt ridges in the heart of the Florence compressional zone. We propose in this case that local basal slope of salt increase related to basement fault activity triggered gravity gliding and thus extensional deformation despite the regional compressional regime. Finally, this study shows that the eastern Nile deep-sea fan, submitted to extremely vigorous salt tectonics seems to have collided with the Florence Ridge fold belt and to have generated a “salt extrusion” zone.

The Messinian "Calcare di Base" (Sicily, Italy) revisited

Research Article| January 01, 2011 The Messinian “Calcare di Base” (Sicily, Italy) revisited Vinicio Manzi; Vinicio Manzi † 1Dipartimento di Scienze della Terra, Università degli Studi di Parma, Via G.P. Usberti, 157/A, 43100 Parma, Italy4Alpine Laboratory of Paleomagnetism (ALP), Via Madonna dei Boschi 76, 12016 Peveragno (CN), Italy †E-mail: vinicio.manzi@unipr.it Search for other works by this author on: GSW Google Scholar Stefano Lugli; Stefano Lugli 2Dipartimento di Scienze della Terra, Università degli Studi di Modena e Reggio Emilia, Piazza S. Eufemia 19, 41100 Modena, Italy Search for other works by this author on: GSW Google Scholar Marco Roveri; Marco Roveri 1Dipartimento di Scienze della Terra, Università degli Studi di Parma, Via G.P. Usberti, 157/A, 43100 Parma, Italy4Alpine Laboratory of Paleomagnetism (ALP), Via Madonna dei Boschi 76, 12016 Peveragno (CN), Italy Search for other works by this author on: GSW Google Scholar B. Charlotte Schreiber; B. Charlotte Schreiber 3Department of Earth and Space Sciences, University of Washington, P.O. Box 351310, Seattle, Washington 98195, USA Search for other works by this author on: GSW Google Scholar Rocco Gennari Rocco Gennari 1Dipartimento di Scienze della Terra, Università degli Studi di Parma, Via G.P. Usberti, 157/A, 43100 Parma, Italy4Alpine Laboratory of Paleomagnetism (ALP), Via Madonna dei Boschi 76, 12016 Peveragno (CN), Italy Search for other works by this author on: GSW Google Scholar GSA Bulletin (2011) 123 (1-2): 347–370. https://doi.org/10.1130/B30262.1 Article history received: 29 Jan 2010 rev-recd: 03 May 2010 accepted: 05 May 2010 first online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Vinicio Manzi, Stefano Lugli, Marco Roveri, B. Charlotte Schreiber, Rocco Gennari; The Messinian “Calcare di Base” (Sicily, Italy) revisited. GSA Bulletin 2011;; 123 (1-2): 347–370. doi: https://doi.org/10.1130/B30262.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Three different types of carbonate deposits are included within the “Calcare di Base,” commonly envisaged to record the Messinian salinity crisis onset: type 1 consists of sulfur-bearing limestones, representing the biogenic product of bacterial sulfate reduction after original gypsum; type 2 comprises dm-thick, laminated dolomitic limestones interbedded with diatomites, sapropels, and marls found at the top the Tripoli Formation; type 3, the most common variety, consists of m-thick, brecciated limestones interbedded with shales and clastic gypsum.Type 3 shows sedimentary features suggesting a clastic origin and deposition from high- to low-density gravity flows; thus, these deposits can be regarded as an end-member of a large variety of evaporite-bearing, gravity-flow deposits, with a dominant carbonate component.The genetic and stratigraphic characterization of these carbonates has strong implications for a better comprehension of Messinian events; the three types of Calcare di Base seem to have formed during different stages of the Messinian salinity crisis (MSC). Type 2 formed in the first stage (5.96–5.60 Ma), and is the only type that can be regarded as the Lower Gypsum time-equivalent. Type 3 was deposited in the second stage (5.60–5.55 Ma), and its base is associated with a regional-scale hiatus and erosion (Messinian erosional surface). Type 1 formed even later, likely in post-Messinian time, through diagenetic processes affecting resedimented gypsum deposited during the second stage of the MSC.It follows that not all the Calcare di Base deposits record the onset of the Messinian salinity crisis, as commonly thought. Thus, a detailed facies characterization of these carbonate deposits is fundamental for both stratigraphic reconstructions and a better comprehension of Messinian events. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Erosion of continental margins in the Western Mediterranean due to sea-level stagnancy during the Messinian Salinity Crisis

High-resolution multi-channel seismic data from continental slopes with minor sediment input off southwest Mallorca Island, the Bay of Oran (Algeria) and the Alboran Ridge reveal evidence that the Messinian erosional surface is terraced at an almost constant depth interval between 320 and 380 m below present-day sea level. It is proposed that these several hundred- to 2,000-m-wide terraces were eroded contemporaneously and essentially at the same depth. Present-day differences in these depths result from subsidence or uplift in the individual realms. The terraces are thought to have evolved during one or multiple periods of sea-level stagnancy in the Western Mediterranean Basin. According to several published scenarios, a single or multiple periods of relative sea-level stillstand occurred during the Messinian desiccation event, generally known as the Messinian Salinity Crisis. Some authors suggest that the stagnancy started during the refilling phase of the Mediterranean basins. When the rising sea level reached the height of the Sicily Sill, the water spilled over this swell into the eastern basin. The stagnancy persisted until sea level in the eastern basin caught up with the western Mediterranean water level. Other authors assigned periods of sea-level stagnancy to drawdown phases, when inflowing waters from the Atlantic kept the western sea level constant at the depth of the Sicily Sill. Our findings corroborate all those Messinian sea-level reconstructions, forwarding that a single or multiple sea-level stagnancies at the depth of the Sicily Sill lasted long enough to significantly erode the upper slope. Our data also have implications for the ongoing debate of the palaeo-depth of the Sicily Sill. Since the Mallorcan plateau experienced the least vertical movement, the observed terrace depth of 380 m there is inferred to be close to the Messinian depth of this swell.

Galeacysta etrusca complex: Dinoflagellate cyst marker of paratethyan influxes to the Mediterranean sea before and after the peak of the messinian salinity crisis

More than one thousand specimens of a morphological complex including Galeacysta etrusca Corradini & Biffi 1988 from 11 Upper Miocene and Lower Pliocene localities of the Paratethyan and Mediterranean realms have been studied using a biometric approach in part relating to the degree of separation between endocyst and ectocyst. Four stable biometric groups have been distinguished statistically, the occurrence or prevalence of which appears closely linked to environmental conditions irrespective of the realm. Group ‘a’ is related to brackish conditions, group ‘b’ to marine conditions, group ‘c’ to freshwater, and group ‘d’ to high nutrient levels. Based on an accurate chronology provided by calcareous nannoplankton bioevents and recognition of the Messinian Erosional Surface, this study reveals: 1. the high sensitivity of the Galeacysta etrusca complex for reconstructing paleoenvironments and discriminating phases of connection and isolation of basins; 2. the detailed history of this species complex which originated in the Pannonian Basin at ca. 8 Ma before invading the Dacic Basin during the interval 6–5.60 Ma, then migrating into the Mediterranean during high sea‐level connections (the ‘Lago Mare’ events just before and after the peak of the Messinian Salinity Crisis, i.e. at 5.60 Ma and during the interval ca. 5.46–5.278 Ma, respectively), and finally into the Black Sea at ca. 5.13 Ma; 3. an improved paleogeography for the Mediterranean and Paratethyan realms with focus on the location of corridors and the timing of when they were active. Based on field observations and dinoflagellate cyst data, we propose that the reflooding of the Mediterranean Basin by Atlantic waters occurred at ca. 5.46 Ma, about 130 kyr before the Zanclean GSSP (5.332 Ma).

GALEACYSTA ETRUSCA COMPLEX: DINOFLAGELLATE CYST MARKER OF PARATETHYAN INFLUXES TO THE MEDITERRANEAN SEA BEFORE AND AFTER THE PEAK OF THE MESSINIAN SALINITY CRISIS

More than one thousand specimens of a morphological complex including Galeacysta etrusca Corradini & Biffi 1988 from 11 Upper Miocene and Lower Pliocene localities of the Paratethyan and Mediterranean realms have been studied using a biometric approach in part relating to the degree of separation between endocyst and ectocyst. Four stable biometric groups have been distinguished statistically, the occurrence or prevalence of which appears closely linked to environmental conditions irrespective of the realm. Group ‘a' is related to brackish conditions, group ‘b' to marine conditions, group ‘c' to freshwater, and group ‘d' to high nutrient levels. Based on an accurate chronology provided by calcareous nannoplankton bioevents and recognition of the Messinian Erosional Surface, this study reveals: 1. the high sensitivity of the Galeacysta etrusca complex for reconstructing paleoenvironments and discriminating phases of connection and isolation of basins; 2. the detailed history of this species complex which originated in the Pannonian Basin at ca. 8 Ma before invading the Dacic Basin during the interval 6–5.60 Ma, then migrating into the Mediterranean during high sea-level connections (the ‘Lago Mare' events just before and after the peak of the Messinian Salinity Crisis, i.e. at 5.60 Ma and during the interval ca. 5.46–5.278 Ma, respectively), and finally into the Black Sea at ca. 5.13 Ma; 3. an improved paleogeography for the Mediterranean and Paratethyan realms with focus on the location of corridors and the timing of when they were active. Based on field observations and dinoflagellate cyst data, we propose that the reflooding of the Mediterranean Basin by Atlantic waters occurred at ca. 5.46 Ma, about 130 kyr before the Zanclean GSSP (5.332 Ma).

Messinian deposits and erosion in northern Tunisia: inferences on Strait of Sicily during the Messinian Salinity Crisis

AbstractOutcrops, offshore wells, electric logs and seismic profiles from northern Tunisia provide an opportunity to decipher the Messinian Salinity Crisis in the Strait of Sicily. Messinian deposits (including gypsum beds) near the Tellian Range reveal two successive subaerial erosional surfaces overlain by breccias and marine Zanclean clays, respectively. In the Gulf of Tunis, Messinian thick evaporites (mostly halite) are strongly eroded by a fluvial canyon infilled with Zanclean clays. The first erosional phase is referred to the intra‐Messinian tectonic phase and is analogous to that found in Sicily. The second phase corresponds to the Messinian Erosional Surface that postdates the marginal evaporites, to which the entire Sicilian evaporitic series must refer. The Western and Eastern Mediterranean basins were separated during deposition of the central evaporites.

The effect of river dynamics induced by the Messinian Salinity Crisis on karst landscape and caves: Example of the Lower Ardèche river (mid Rhône valley)

The karstic canyon of Lower Ardèche is located in the Middle Rhône valley, which is directly tributary to the Mediterranean Sea. The Rhône River is emblematic of the Messinian Salinity Crisis (MSC) impact on landscape morphology. Along the edge of the Saint-Remèze Plateau, the Rhône valley displays four benchmark levels generated by the MSC: the Pre-evaporitic abandonment surface (1), the Messinian erosional surface (2), the Marine/non-marine surface of the Pliocene ria (3) and the Pliocene abandonment surface (4). The study of these benchmark levels allows us to reconstruct the evolution of the regional base level over the last 6 Ma. We obtain a curve for base-level evolution that provides a geodynamic reference, which is used to investigate the morphogenesis of the Saint-Remèze karstic plateau. The Ardèche River downcuts the Saint-Remèze Plateau in a deep canyon, from Vallon-Pont-d'Arc to the West, to its confluence with the Rhône to the East. Several abandoned valleys are present along the western edge of the Saint-Remèze Plateau at the inlet of the Ardèche canyon. In these abandoned valleys, the fluvial deposits are related to several periods, from the Pliocene onwards. They provide important insights into the fluvial dynamics: a 160 m-thick aggradation sequence infilled the Ardèche canyon during the Pliocene. This aggrading river caused the first lateral shifting, as an aggradation epigenesis. This first infilling shows that the Ardèche canyon already existed before the Pliocene. Secondly, it has been demonstrated that the Ardèche Canyon is downcut into the Pre-evaporitic surface of the Saint-Remèze Plateau, dated to 5.45 Ma [Martini, J., 2005. Etude des paléokarsts des environs de Saint-Remèze (Ardèche, France): mise en évidence d'une rivière souterraine fossilisée durant la crise de salinité messinienne. Karstologia 45–46, 1–18]. Consequently, the canyon downcutting is entirely due to the MSC, and occurred during a time span of only 100 000 years. Based on these observations, it is possible to elucidate the curve of the regional base-level evolution. Hence, we are able to propose a new interpretation of the geomorphological evolution of the Saint-Remèze karstic plateau and its cave levels for the last 6 Ma. The cave levels consist in underground short-cuts of the surface meanders. They mainly developed during the Pliocene aggradation cycle. The Chauvet Cave, famous for its Palaeolithic paintings, corresponds to one of these underground short-cuts. The aggradation period ends at the end of the Pliocene with long high-level riverbed stability. It favours the development of large low gradient surfaces as pediments. The complete Messinian–Pliocene eustatic cycle is responsible for the downcutting of the Ardèche canyon and its infilling during the Pliocene. Consequently, karst developed according to the base-level oscillations, as low gradient surfaces and as cave levels. For the study of the peri-Mediterranean caves and karst areas, we propose to apply the Lower Ardèche valley evolution model, based on the base-level oscillations during and after the MSC.

Messinian event in the black sea: Evidence of a Messinian erosional surface

In 1975, sediment cores from leg DSDP 42b (sites 380A and 381) revealed a thin sediment layer in the Black Sea basin which points to a shallow water environment at the Miocene-Pliocene boundary. With these facts and in the wake of hypothesis of the Messinian Salinity Crisis (MSC), it was proposed that the Black Sea, like the Mediterranean Sea, suffered a desiccation period at the end of the Messinian (Hsü, K.J. and Giovanoli, F., 1979. Messinian event in the Black Sea. Palaeogeography, Palaeoclimatology, Palaeoecology, 29: 75–93). Whereas the main topics of the MSC in the Mediterranean Sea is now widely accepted, the lack of evidence for a Messinian erosional surface in the Black Sea left the debate about the Messinian desiccation of this basin open until today. The analysis of high resolution multi-channel seismic data acquired during the BlaSON surveys brings important new elements for this scientific debate: (1) Down the slope offshore the Bosporus, we show a clear erosional surface correlated to the top of the Upper Miocene shallow water environment unit of site DSDP 381. The overlying Lower Zanclean unit inevitably dates this erosional surface of the Messinian event. (2) A wide intra-Pontian erosional surface (IPU) is evidenced on the Romanian shelf. The IPU is characterized by a sharp decrease in the incision rate from outer (deep canyons) to inner shelf (superficial incisions network). According to the most recent Paratethyan and Mediterranean stratigraphic scale correlations, the IPU erosional surface is considered as the analogue to the Messinian erosional surface described down the slope offshore the Bosporus. In addition to recently discovered inland erosional signature, the wide regional erosional surface we underline on the Western Black Sea margins validates the Black Sea Messinian desiccation hypothesis. We also demonstrate that evaporative draw-down of the Black Sea implied the installation in the basin of a negative hydrologic budget during the Messinian. The lack of a major Messinian Danube canyon on the Romanian shelf supports the hypothesis of a Messinian Danube trapped in the Dacic basin. However, the presence of a Messinian superficial incision network connecting the location of the modern Danube delta to deeply incised Messinian canyons on the outer shelf (IPU) makes the hypothesis of a Danube reaching the partially desiccated Black Sea still possible.

The deep-water counterpart of the Messinian Lower Evaporites in the Apennine foredeep: The Fanantello section (Northern Apennines, Italy)

A possible deep-water non-evaporitic unit equivalent of the Messinian Lower Evaporites has been recognised in the Northern Apennine foredeep. This unit, whose existence is implicitly admitted in the two-step model of the Mediterranean Messinian salinity crisis is documented here for the first time; it occurs throughout the Apennine foredeep basin below a thick horizon of resedimented gypsum deposits, usually ascribed to the Lower Evaporites. Actually, the Lower Evaporites of the Apennine foredeep basin include both shallow-water, in situ precipitated facies and deep-water, resedimented facies deposited in distinct depocenters. The usually envisaged coeval nature of the two deposits has been recently challenged in several works based on a) physical–stratigraphic considerations about the downbasin correlation of the Messinian erosional surface cutting on top the in situ evaporites with the sharp base of the resedimented evaporites unit and b) the common occurrence of a barren unit below the resedimented evaporites which has no obvious equivalents in pre-evaporitic successions underlying the in situ precipitated evaporites. In this work a multidisciplinary study has been carried out on a 140 m-thick composite section (Fanantello section) to definitely assess the age and palaeoenvironmental characteristics of the unit underlying the resedimented gypsum deposits. The topmost part of the section comprises a 60 m-thick succession of barren euxinic shales falling entirely within a reversed polarity chron and characterised by a) the complete disappearance of Foraminifera, b) the occurrence of high salinity tolerant thecosomatous pteropods ( Creseis sp.) c) the abundance peaks of the calcareous nannofossil Sphenolithus abies (interpreted as related to highly stressed likely hyperhaline conditions), d) the appearance of hyperhaline and/or stratified water molecular indicators (gammacerane, < 0.2 pristane/phytane ratio, < 1 n-alkanes odd–even predominance). Based on a multidisciplinary integrated stratigraphic approach this barren interval, is here proposed to be a deeper-water time-equivalent of the in situ primary Lower Evaporites, thus allowing to assess the events connected to the onset and the first phase of the Messinian salinity crisis from a basinal perspective. These data lend support to the hypothesis that the resedimented evaporite deposits of the Apennine foredeep basin postdate the in situ evaporites, thus implying that the term Lower Evaporites actually comprises rock bodies with different origins and separated in time and space by the Messinian erosional surface and its correlative conformity. This could be true also for other Mediterranean basins where the stratigraphy of deep-water successions should be carefully re-examined.

La microflore de diatomées au passage mio-pliocène en Corse

The “Aleria formation”, described in northeastern Corsica, consists of siliciclastic deposits referred to a deltaic environment and comprises diatomitic lenses exposed at Casabianda. The Aleria formation fills a depression of the Messinian erosional surface and is overlain by Early Pliocene sediments in several places. This suggests a late Messinian-earliest Pliocene age. Diatom microflora is well-preserved and contains 59 species. Pennates indicate a very large diversity with 54 species, while Centrics are represented only by five species. Diatom assemblages show a relative constant composition along the studied interval. The species Aulacoseira granulata is the dominant taxon with about 90% in all samples. Taxa are of different salinity classes and different modes of life (planktic, tychoplanktic, benthic, epiphytic…), suggesting multiple environmental factor interactions. The environmental model suggested by sedimentological and biological data led as to assume a pond-like coastal receptacle common in deltaic system. This receptacle was slightly influenced by the close marine waters and was supplied by permanent freshwaters from continental run-off and alluvial sheet. This model based on diatom assemblages provides new data for palaeoenvironmental and chronological interpretations of the so-called Messinian Lago-Mare deposits.

The Northwestern (Maghreb) boundary of the Nubia (Africa) Plate

A study of the present compressional deformation of the Northwestern (Maghreb) Nubia (Africa) margin is derived from the analysis of more than 20,000 km of seismic profiles. In the western part the compression is distributed in a large zone with on-land compression in Algeria, mainly strike-slip deformation on the Algerian margin and folds and strike-slip faulting in Eastern Spain. In the middle of the Algerian margin, around Algiers, the evidences of compression become more obvious. In this area a ridge trending N–S that is interpreted as a middle to late Miocene spreading center interacted with the transpressional margin that trends E–W. North of the location of the Boumerdes–Zemmouri earthquake the oceanic crust is deformed by blind thrusts up to 60 km from the coast. These thrusts are south dipping and with the northward dipping thrusts located onshore form a wedge that maybe a positive flower structure at a crustal scale related to the right-lateral transpression of the margin. In the eastern part of the Northwestern (Maghreb) Nubia (Africa) Deformed Belt, off eastern Algeria and Tunisia, the deformation is more intense but limited to the north by the continental slope. Large late Miocene Tortonian folds are cut by the Messinian erosional surface but the present deformation is also evident. It is suggested that the deformation with a double vergence may be followed up to the north of Sicily. After the docking (18 Ma) of the Kabylies to the Africa Plate, the crust has been thinned and the Algerian Basin opened during the middle-late Miocene with an E–W direction. From the late Miocene to the Present the margin has been rethickened by transpression and uplifted.