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[The manuscript presents the first attempt to define the diagenetic conditions (burial and related paleo‐temperatures) for sulfur formation in relationship with the deposits generated by the Messinian salinit crisis. ​, Abstract Recent studies on the genesis of sedimentary native sulfur deposits indicate diagenetic mid‐low temperature Bacterial Sulfate Reduction (BSR) as the main process, involving organic compounds (kerogen/hydrocarbons), bacterial colonies and gypsiferous rocks. In the peri‐Mediterranean area (Southern Spain, Sicily, Northern Apennines, Israel), the main sulfur accumulations are always associated with late Miocene sulfates and organic‐rich successions encompassing the Messinian salinity crisis (MSC). In particular, the Messinian successions of the Apennine‐Adriatic foreland basin system, due to a large amount of high‐resolution stratigraphic data, represent a perfect case study for understanding the diagenetic conditions controlling the development of the BSR process during sedimentary basin evolution. In this work, thermal models performed in three sub‐basins in a sector of the Northern Apennines comprised of the Sillaro and Marecchia rivers (Italy), calibrated by means of organic and inorganic geothermometers, indicate a general thermal immaturity of the studied successions attained as a result of a constant heat flow similar to the present day one (ca. 40 mW/m2) since Late Tortonian and lithostatic loads between 615 and 1,710 m depending on different sub‐basins. These results suggest that the MSC deposits experienced maximum temperatures between about 39°C and 65°C. Temperatures derived from thermal models have been used to constraint occurrence of the diagenetic BSR associated with evaporitic deposits providing thermal constraints in sulfur genesis as well as new useful thermal‐constraints for basin analysis studies.]

The onshore–offshore correlation of sedimentary successions is a common problem in basin analysis, but it becomes critical for the full understanding of the Messinian salinity crisis (MSC), a complex array of palaeoenvironmental events which affected the Mediterranean basin at the end of the Miocene. The outcrop records show that the Messinian stratigraphic architectures may be highly complex as the deposits of the different MSC evolutionary stages can be lithologically similar and separated by erosional surfaces and/or morphostructural highs. The correct definition of the nature and stratigraphic position of Messinian deposits in offshore areas through seismic data may be almost impossible, especially where core data are sparse. To bridge the gap between onshore and offshore records, we have built synthetic seismic sections from well‐constrained outcrop successions. Our results provide useful insights and warnings for the interpretation of offshore data, pointing out that MSC units having different age, nature and depositional settings, may show similar seismic facies and geometries. Conversely, the same deposit may result in different seismic facies, either with parallel and high‐amplitude reflections or even transparent or chaotic due to interference patterns of seismic reflections related to dominant frequency. It follows that a correct interpretation of the nature and age of deep‐seated Messinian deposits can only be obtained through the integration of seismic and core data, and considering the onshore record. The application of our approach to the Balearic Promontory results in an alternative interpretation with respect to previous models. We show that this offshore area has good analogues in the onshore of the Betic Cordillera and includes both shallow and intermediate depth sub‐basins that underwent a strong post‐Messinian subsidence.

The Messinian primary gypsum sequence, formed during the first stage of the salinity crisis in the Caltanissetta basin (Sicily), is characterized by a high degree of disruption and deformation. The primary gypsum occurs as huge (up to 3 km large and up to 250 m high) tilted blocks, detached from their stratigraphic base, floating within a matrix of folded shales and clastic gypsum. This association represents a giant chaotic unit lying unconformably on the Gela Nappe, the youngest structural unit of the Maghrebian fold-and-thrust belt. The origin of the deformations affecting the Primary Lower Gypsum unit is still debated; in the past they have been related to intra-Messinian tectonics or to the collapse of primary gypsum platforms due dissolution of interbedded to halite. Our study on the distribution, size and bedding of the gypsum blocks reveals a pattern similar to that of modern giant submarine mass-transport deposits, which may have been triggered by a combination of active tectonics and sea-level change, and favored by the strong mechanical contrasts of the involved units. The chaotic unit shows a downslope evolution from the south, characterized by elongated blocks with their main axes parallel to the inferred slide headwall (NW-SE oriented), to intermediate and distal areas, where the blocks become progressively smaller in size with their main axes parallel to the flow (SW-NE). We identify the source area as either a shallow evaporitic basin above the Gela Nappe or on the Pelagian foreland ramp. A general implication for the Messinian salinity crisis is that no primary gypsum was deposited in deep water basins during the first stage; instead, during the second stage, large gypsum blocks collapsed from the basin margin and were mass-transported into a deeper water setting, where halite was depositing.

The lack of modern analogues for the thick primary selenite gypsum deposits formed in the Mediterranean area limits the understanding of the Messinian (Miocene) evaporitic systems and particularly of their lateral relationships, their evolution through time and their related ecosystems. Some complex stratigraphic relationships of these extreme environments are revealed in the Messinian Canos Formation along the northern flank of the Sierra Alhamilla at the southern boundary of the Sorbas Basin (southern Spain). Here, the bottom-grown selenite gypsum beds pinch-out against graded clastic carbonate beds (ooid grainstones, rudstones and mudstones) emplaced by gravity flows. We infer that these tabular bodies formed along a low gradient ramp, derived from the periodic erosion of coeval shallow-water to coastal carbonate factories located on top of the Sierra Alhamilla ridge. The carbonate deposits bear many similarities with the Terminal Carbonate Complex described in the northern, steeper margin of the basin; both deposits show a cyclical pattern given by the repetition of couplets consisting of coarser- and finer-grained deposits. This rhythmic facies organization recalls the precessional-controlled cyclic pattern of the gypsum unit. Clastic carbonates and gypsum were deposited during the same precessional hemicycle but appear to be mutually exclusive. In fact, the clastic carbonates represent the lateral equivalent of the gypsum beds, or are occasionally found at their base or at both their base and top, but never interstratified with them. Such an arrangement suggests that during the peak of the evaporitic phases a strong pycnocline acted as the top boundary for gypsum and the lower boundary for carbonate-bearing gravity flows, with the exception of debrites, high-density gravity flows and slumps. These facies architectures appear to be mainly controlled by the interplay between the variable depth of the pycnocline and the density of the brine within the evaporitic cycle.

We present a basin-wide correlation of the pre-evaporitic succession across the deep Levant basin, based on integrated bio- and cyclostratigraphy. The onset of Messinian salinity crisis (MSC) can be placed in all studied wells where foraminifers suddenly disappear and normal marine calcareous nannofossils are replaced by opportunistic assemblages. These changes mark the base of the Foraminifers Barren Interval (FBI), a 10s-of-m-thick (below seismic resolution), evaporite-free, shale unit that records the entire duration of the first stage. Moving towards the basin margin the FBI is progressively truncated on top by the Messinian erosional surface (MES), a regional-scale discontinuity sealed by a thin clastic evaporite units overlain by thick halite deposits. Our results confirm previous hypothesis suggesting that the crisis started in deep- as well as in shallow-water settings at 5.97 Ma and pointing to a synchronous onset of the MSC but diachronous deposition of evaporites. During stage 1 of the crisis, coeval with gypsum deposition in marginal basins, the salinity in deep basins progressively increased (with possible oxygen reduction) hindering the life of marine organisms. Then, at 5.60 Ma, when salinity in deep basins exceeded halite saturation, massive halite precipitation started, and a nearly 2-km-thick salt sequence accumulated in deep basins within a short period of 60 kyr. At that time (stage 2), sedimentation rate jumped by an order of magnitude reaching a few cm/yr. Similar sedimentation rates are inferred for the Realmonte salt mine (Sicily) and observed in the modern Dead Sea and artificial salinas.

The Messinian salinity crisis is a dramatic hydrological and biological crisis that occurred in the Mediterranean basin at 5.97–5.33 Ma. The interpretation of the facies and stratigraphic associations of the Messinian salt deposits is still the object of active research because of the absence of modern depositional analogues of comparable scale. In this study, the spatial distributions of Na, Mg, S, O, Si, and Al in a potassic-magnesian salt and a halite layers of Messinian evaporites from the Realmonte mine on Sicily were determined using synchrotron based micro-X-ray fluorescence. The dominant molecular host site of Mg and S obtained by X-ray absorption near edge structure (XANES) is applied to specify the hydrochemistry of hypersaline brines and the presence of diagenetic minerals, thus shedding light on evaporative concentration processes in the Caltanissetta Basin of Sicily. Mg and S K-edge XANES spectra revealed the presence of highly soluble Mg-bearing sulfates. The massive halite layer “unit C,” contains less soluble minerals, thus did not exceed the stage of halite crystallization. We infer that as evaporative concentration increased, the density of the brine at the shallow margin of the basin increased as salinity increased to concentrations over 70 times the starting values, creating brines that were oversaturated with Mg-sulfate. Density stratification of the deep basin caused heavy brines to sink to the bottom and become overlain by more dilute brines. We propose lateral advection of dense Mg-sulfate brines that certainly affected marine biota.

This integrated study (field observations, micropalaeontology, magnetostratigraphy, geochemistry, borehole data and seismic profiles) of the Messinian–Zanclean deposits on Zakynthos Island (Ionian Sea) focuses on the sedimentary succession recording the pre‐evaporitic phase of the Messinian salinity crisis (MSC) through the re‐establishment of the marine conditions in a transitional area between the eastern and the western Mediterranean. Two intervals are distinguished through the palaeoenvironmental reconstruction of the pre‐evaporitic Messinian in Kalamaki: (a) 6.45–6.122 Ma and (b) 6.122–5.97 Ma. Both the planktonic foraminifer and the fish assemblages indicate a cooling phase punctuated by hypersalinity episodes at around 6.05 Ma. Two evaporite units are recognized and associated with the tectonic evolution of the Kalamaki–Argassi area. The Primary Lower Gypsum (PLG) unit was deposited during the first MSC stage (5.971–5.60 Ma) in late‐Messinian marginal basins within the pre‐Apulian foreland basin and in the wedge‐top (

In the late Miocene the Mediterranean Sea experienced a salinity crisis and thick sequences of evaporites precipitated across the deep and marginal basins. In this study we report Os isotopic records from Deep Sea Drilling Project and Ocean Drilling Project cores in the Mediterranean: the Balearic Sea (Site 372), the Tyrrhenian Sea (Site 654), the Ionian Basin (Site 374), and the Florence Rise (Sites 375–376), as well as Integrated Ocean Drilling Project Site U1387 in Gulf of Cadiz, North Atlantic. Pliocene-Pleistocene sediments at all sites show 187Os/188Os values close to that of the coeval ocean water, indicating that the Mediterranean was connected to the North Atlantic. Evaporitic sediments deposited during the latest Miocene, however, have 187Os/188Os values significantly lower than coeval ocean water values. The offset of the Mediterranean evaporite 187Os/188Os is attributed to limited exchange with the North Atlantic during the Messinian salinity crisis. The source of unradiogenic Os is likely to be weathering of ultramafic rocks (ophiolites) cropping out in the Mediterranean's drainage basins. Based on a box model we estimated the amount of unradiogenic Os and the Atlantic-Mediterranean exchange rate to explain this offset. Os isotopic ratios of the pre-evaporite sediments in the western Mediterranean are almost identical to that of the coeval ocean water. In contrast, equivalent sediments from the Florence Rise have significantly lower 187Os/188Os values. The offset in the Os isotopic ratio on the Florence Rise is attributed either to limited water exchange between eastern and western Mediterranean or to local effects associated with exhumation of the Troodos ophiolites (Cyprus).

The recent release of a large number of subsurface geological data by the Italian Minister of Economic Development, including boreholes and seismic profiles, provided the occasion for a new assessment of the deposits associated with the Messinian salinity crisis (MSC) in the Adriatic foreland basin system and a new integration with the outcropping successions of the Apennines. In particular, the study of the Messinian evaporites allowed to reconstruct a new detailed palaeogeographic and palaeobathymetric framework for all the stages of the crisis. We identified the largest evaporitic marginal basin ever described for the Mediterranean hosting the precipitation of the primary shallow-water gypsum deposits (PLG, Primary Lower Gypsum) during the first stage of the crisis. During the second and third stages of the crisis, the PLG basin underwent uplift and erosion and the evaporite accumulation moved to the deeper part of the basin and was characterized by the deposition of the Resedimented Lower Gypsum unit including clastic evaporites, recycling the PLG ones, primary halite and terrigenous deposits. The distribution of the different evaporitic facies, was the basis for an improved reconstruction of the upper Miocene tectonic evolution of the Apennines thrust belt. Our results show a clear separation between shallower depocenters, located in the wedge-top and in the Adriatic foreland basins and characterized by MSC stage 1 PLG deposition, and deeper-water ones, located in the Adriatic foredeep and close to the Calabrian Arc, where MSC stage 2 terrigenous and gypsum-bearing clastic deposits and primary halite accumulated.

An integrated micropaleontologic, magnetostratigraphic and cyclostratigraphic investigation of the Tokhni composite section (Southern Cyprus Island, Eastern Mediterranean) refines the previously published age model and paleoenvironmental interpretation particularly concerning its uppermost pre-Messinian Salinity Crisis interval (pre-MSC), between 6.46 and 5.97 Ma. This section is characterized by a precession-paced alternation of red shales and limestones, which correlate with insolation maxima and minima on the basis of their delta O-18 signatures and calcareous nannofossil assemblages. The planktonic foraminifer and magnetostratigraphic events permit the tuning of the sedimentary cycles to the 65 degrees N summer insolation curve and to the Mediterranean pre-evaporitic reference sections. The upper bathyal sedimentary succession of the Tokhni composite section records paleoceanographic changes at 6.4 and 6.1 Ma, indicating increasingly stressed conditions both at the sea floor and in the water column. Compared to the Western Mediterranean pre-MSC successions, we observe less severe sea floor anoxic conditions at times of insolation maxima and higher salinity surface and bottom waters at times of insolation minima. Moreover, from 6.1 Ma to the MSC onset we observe a progressively increase of continental-derived waters, which was likely caused by a tec-tonic pulse. The MSC onset at 5.97 Ma is marked by the deposition of clastic carbonates rather than primary evaporitic facies and is approximated by the last recovery of foraminifera, the abundance peaks of Helico sphaera carteri and Umbilicosphaera rotula and the decrease of the Sr-87/86. The MSC onset is recorded two cycles below the Messinian erosional surface (MES, 5.60 Ma) and the overlying clastic evaporites, suggesting a hiatus of approximately 350 kyr.

This research is focused on a complete reexamination of the evaporite facies present in all the cores that cut through the topmost deposits of the Messinian salinity crisis lying below the floor of the Mediterranean Sea (DSDP Legs 13 and 42A, ODP Legs 107 and 161). This review suggests that the uppermost evaporite units in both western and eastern deep Mediterranean basins consist mainly of clastic (gypsrudite, gypsarenite and gypsiltite) and fully subaqueous deposits (laminar gypsum, selenite and cumulate halite) that are partially affected by burial anhydritization and tectonic-induced recrystallization. No unequivocal evidence of shallow water or even supratidal (sabkha) deposition is in evidence, suggesting that at the very last phase of the salinity crisis the Mediterranean Sea did not experience desiccation, but that deposition took place under permanent subaqueous conditions.

Palynological studies are considered as an excellent tool for palaeoaltitude estimates as sedimentary basins receive abundant pollen grains from surrounding uplands, especially through riverine detritic inputs. Here, we provide new evidence for estimating the palaeoaltitude of the Northern and Central Apennines (Italy) during the late Neogene (from the late Tortonian to the early Zandean), based on vegetation data derived from pollen analysis of five sections (Trave, Legnagnone, Cava Li Monti, Maccarone and Stirone). The past vegetation changes reflect shifts in the vegetation belts on the nearby massifs. The climate reconstruction realised on these sites, at sea-level, suggests that mean annual temperatures were higher than today at the end of the Neogene. Therefore, the different vegetation belts occurred at higher elevation than at present to compensate for the higher temperatures. The results obtained in our study suggest that the Northern and Central Apennines were uplifted as early as the Tortonian attaining significant minimum altitudes around 1350 m up to 1500 m at the end of the Miocene in the Central part, a minimum altitude around 1900 m during the Messinian and around 2150 m during the early Zandean in the Northern part. (C) 2014 Elsevier B.V. All rights reserved.

The Sorbas basin is a reference sector of the Mediterranean basin for the definition of the onset of the Messinian salinity crisis straddling the transition from the open marine deposits (Abad marls) to the Primary Lower Gypsum (Yesares Formation) during the first stage of the crisis, between 5.97 and 5.60 Ma. Because of its proximity to the Atlantic gateway, the Sorbas basin is pivotal for the study of the oceanographic evolution that led to the most dramatic environmental event in the Mediterranean Sea. We measured the carbon (delta C-13), oxygen (delta O-18) and strontium (Sr-87/Sr-86) isotope ratio of 50 samples of planktonic foraminifera, mollusk shells, gypsum and carbonate sediments from the Abad and Yesares Members (Tune and Canos Formation) in the Perales, Hueli, Los Yesos and Rio de Aguas sections. Our results show a long-term trend with most of the values plotting within the range of the global ocean strontium isotope curve and distinct short-term fluctuations on precessional time scale. The investigated geochemical proxies suggest that these oscillations reflect significant input of continental waters into the basin during the humid phase of a single precessional cycle. This implies that the Western Mediterranean did not experience a main disconnection from the global ocean water before and during the first stage of the Messinian salinity crisis and that different Milankovitch forcings played a significant role in determining the seawater geochemistry. (C) 2016 Elsevier B.V. All rights reserved.

The salt giant beneath the deep Mediterranean seafloor is the impressive record of the “Messinian salinity crisis,” a dramatic event that occurred about 6 Ma ago following the reduction of the connections with the Atlantic Ocean. According to the shallow-water deep-basin model, developed for these deposits (Hsu and others, 1973a, 1973b, 1978a, 1978b), the Messinian evaporites formed in a deep but desiccated Mediterranean, while shelves and slopes underwent subaerial erosion due to fluvial rejuvenation triggered by a 1500 m sea level drawdown. Deeply incised Messinian canyons in the continental slopes surrounding the Mediterranean are the main argument supporting this scenario. Using a state of the art model and idealized but realistic numerical simulations, here we demonstrate that the activation of downslope flows of hypersaline, dense waters, in a process similar to present-day “dense shelf water cascading,” but much more energetic, may account for both slope erosion and progressive salinity rise leading to the formation of deep-seated supersaturated brines. Our findings support a deep-water deep-basin model (Schmalz, 1969, 1991; De Benedetti, 1976, 1982; Dietz and Woodhouse, 1988), thus implying that evaporite deposition may have occurred in a non-desiccated basin with strongly reduced ocean connections.

In natural resource exploration, Ca–Cl basinal brines are important for understanding the origin and spatial and temporal distribution of hydrocarbons and sedimentary ore deposits. Little attention has been paid to the possible connection between fossil basinal brines and paleo-seawaters and to the implications for reconstructing paleo-seawater compositions. Secular variations of Ca/Mg and Ca/Sr ratios in seawater have been documented mainly using fluid inclusions in halite, calcareous fossils and mineral analyses. However, brines and other sedimentary records connected to paleo-seawater or its evaporated residues may be chemically affected by burial diagenesis or the effects of continental waters of meteoric origin, thus complicating interpretations of the analytical results. To investigate these effects on fluids and minerals related to the Messinian salinity crisis of the Mediterranean basin, we re-evaluate published data from: (1) brackish-to-brine waters from onshore (Northern Apennine foredeep; Levantine basin) and offshore (porewaters from the Deep Sea Drilling Project); (2) Messinian parental seawater deduced from calcareous fossils, fluid inclusions and sulfate minerals; (3) meteoric waters dissolving evaporites. The compositional trends related to seawater evaporation, diagenesis and mixing that affect the Ca/Mg and Ca/Sr molar ratios of the basinal brines are effectively discriminated on a binary plot depicting the proper fields for seawater and meteoric-derived fluids. Brines showing stronger dolomitization start from Ca/Mg and Ca/Sr molar ratios of Messinian seawater deduced from the published analysis of fluid inclusions and open ocean fossils, that are therefore here validated ex post.

A 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 situ evaporites 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.

A recent paper by Caruso et al. (2015) dealing with the Calcare di Base of Sicily and Calabria reintroduced an earlier idea that onset on the Messinian salinity crisis is diachronous. The paper provided a stratigraphic correlation of five sections together with the reference section of Falconara and Gibliscemi (Sicily) in order to establish the diachronous nature of restricted saline conditions. In our opinion their conclusions are not supported by the data, and the paper contains some stratigraphic errors that depend on a flawed presentation of the main stratigraphic concepts provided over the past few years covering the deposits of the Messinian salinity crisis in Sicily. In this discussion we challenge the stratigraphic conclusion of Caruso et al. (2015) holding that: a) they did not fully consider the different types of deposits included in the Calcare di Base unit and consequently did not recognize the large scale unconformity at the base of the brecciated limestone (Calcare di Base type 3); b) they did not provide univocal criteria for the definition of the onset of the Messinian salinity crisis; c) they hold the idea that the onset of the salinity crisis must be coincident with the onset of the evaporites, concept which is not necessarily true; d) they arbitrarily correlated different evaporitic deposits formed during different stages of the MSC; e) they provided a stratigraphic correlation of the study sections and their tuning with the insolation curve that lacks of reliable stratigraphic constraints. Consequently, they have presented an unreliable schematic evolution of the Caltanissetta basin.

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.

A petrological investigation has been carried out on the Late Miocene (around 5.5 Ma) volcaniclastic layer interbedded in the uppermost Messinian deep-water sediments of the Northern Apennines foredeep basin. The studied samples derive from five sections located on a 200 km long area and reveal that the volcaniclastic layer corresponds to centimetric- to metric-thick turbiditic sequence, essentially composed of lapilli to ash-sized glass shards and scarce (

The Upper Gypsum unit of the Caltanissetta Basin (Sicily) records the last phase of the Messinian salinity crisis comprising the so-called ‘Lago Mare’ event. A new facies analysis study recognizes nine to ten depositional cycles consisting of seven rhythmically interbedded primary gypsum bodies, and two to three sandstone bodies separated by marly terrigenous horizons showing laterally persistent vertical organization. A basal thin gypsum bed is overlain by a cluster of five thicker gypsum bodies. A marly interval containing two distinct sandstone horizons separates this cluster from the overlying uppermost (seventh) gypsum body. The terrigenous Arenazzolo Formation, in turn followed by the lower Pliocene Trubi Formation, is considered here to form the uppermost part of the Upper Gypsum unit. The rhythmic alternation in the sandy marls and gypsum/sandstone bodies records the response of sediments from shelfal to deltaic systems to precession-driven arid-wet climate fluctuations causing cyclical changes of both base-level and water concentration. During wet climate phases (at insolation maxima) marl and sandstone were deposited in a hypohaline environment as suggested by: (i) the typical Lago Mare faunal assemblage and (ii) the negative δ18O values. During arid phases (at insolation minima) the reduced meteoric supply, recorded by higher δ18O values in the carbonate, caused the development of a negative hydrological budget leading to evaporite precipitation. At a basinal scale the Upper Gypsum unit unconformably overlies a mainly clastic evaporite unit containing carbonate breccia (the so-called ‘Calcare di Base’) and/or clastic gypsum. Towards the basin centres, where the basal contact becomes conformable, a primary gypsum cumulate horizon is present. This layer is interpreted as a possible lateral equivalent of the Halite unit present only in the deepest depocentres. Based on astronomical calibration of the depositional cycles, the Upper Gypsum unit, including the Arenazzolo Formation, spans the interval between 5·33 and 5·53 Ma. This new age calibration allows the deposition of the Halite unit to be dated between 5·6 Ma (top of the Lower Evaporites) and 5·55 Ma (base of the Upper Evaporites) corresponding to isotopic stages TG12 and/or TG14.

Controversies around the Messinian salinity crisis (MSC) are because of the difficulties in establishing genetic and stratigraphic relationships between its deep and shallow-water record. Actually, the Sicilian foreland basin shows both shallow and deep-water Messinian records, thus offering the chance to reconstruct comprehensive MSC scenarios. The Lower Gypsum of Sicily comprises primary and resedimented evaporites separated in space and time by the intra-Messinian unconformity. A composite unit including halite, resedimented gypsum and Calcare di Base accumulated between 5.6 and 5.55 Ma in the main depocentres; it records the acme of the Messinian Salinity Crisis during a tectonic phase coupled with sea-level falls at glacials TG14-TG12. These deposits fully post-date primary gypsum, which precipitated in shallow-water wedgetop and foreland ramp basins between 5.96 and 5.6 Ma. This new stratigraphic framework results in a three-stage MSC scenario characterized by different primary evaporite associations: selenite in the first and third stages, carbonate, halite and potash salt in the second one associated with hybrid resedimented evaporites.

The ‘Vena del Gesso’ (Gessoso-Solfifera Fm, Messinian) is a 227 m-thick ridge along the western Romagna Apennines (Italy) consisting of up to 16 selenite cycles separated by shales and minor carbonate. The total organic carbon values of these deposits range between 0.087–0.016% (gypsum) and 3% (shales). Organic matter is dominated by black debris associated with continental debris. Algae and dynocysts are rare (,1%). The amount of amorphous organic matter is low but it may reach up to c. 40%. The Sr/Sr of gypsum and carbonate vary from 0.708890 to 0.709024, yielding non-oceanic values with several exceptions that plot within error of coeval oceanic values only in the upper part of the section (from the 68 bed). The sulphur isotope composition of gypsum range between dS 1⁄4þ21.8 and þ23.7‰ and may represent precipitation of dS-enriched gypsum due to the fractionation effect or recycling of coeval gypsum with contributions of brine-sediment redox variations. The isotope values of carbonates show a large variability (26.4 , dO , þ6.05‰; 214.68 , dC , þ2.5‰), suggesting a complex origin by mixing of marine and non-marine waters with a significant contribution of reduced organic matter. These data point to an evaporite basin dominated by continental waters which received significant phases of marine recharge in the upper part together with a marked facies change. Because seawater recharges and a similar facies change are present in other Messinian sections, it follows that we have new possible geochemical and facies markers to correlate the Lower Evaporites across the Mediterranean. Isotope stratigraphy represents a fundamental tool in palaeoenvironmental and palaeoclimate reconstruction, especially for evaporite sediments. The integration of geochemical data is imperative in facies interpretation, as the peculiar and restricted setting of evaporite deposition makes the use of geochemical data problematic. This is because brine composition may be the result of a mixture of marine and continental water, and sediment composition may be strongly influenced by recycling of older sediments, biologic activity and diagenesis. These uncertainties may be overcome only with the integration of geochemical data in a detailed stratigraphic and facies framework. This integration is particularly needed for the Messinian evaporites in the Mediterranean, because their origin is still debated and because many of the available isotope data are scattered and commonly obtained from sections whose stratigraphy is not well constrained in the regional framework. The information provided by such scattered data is very difficult to interpret if its significance is not correctly placed into the salinity crisis framework. This is probably one of the reasons why the debate still exists and even is growing. This paper illustrates the geochemistry of the Vena del Gesso evaporites (Northern Apennines), which represent the most significant example of detailed facies stratigraphy for the Lower Evaporites in the Mediterranean. The aim is to discuss new possible stratigraphic markers to correlate the elusive evaporite sediments across the Mediterranean during the Messinian salinity crisis. From: SCHREIBER, B. C., LUGLI, S. & BĄBEL, M. (eds) Evaporites Through Space and Time. Geological Society, London, Special Publications, 285, 179–190. DOI: 10.1144/SP285.11 0305-8719/07/$15.00 # The Geological Society of London 2007. Geological setting and stratigraphy The Romagna Apennines extends from the Sillaro valley to the west and to the Marecchia valley to the east (Fig. 1). This portion of the chain can be subdivided into two minor basement-detached units affected by fold-and-thrust structures (Barchi et al. 1998): (1) a lower and older one composed of Mesozoic to Cenozoic carbonates; and (2) an upper one, up to 3500 m-thick, consisting of a lower Miocene–Quaternary siliciclastic wedge representing the deep-water to continental infill of successive foredeep basins progressively migrating toward the NE, ahead of the advancing Apennines thrust belt (Ricci Lucchi 1986). According to Roveri et al. 2003, the upper unit of the Romagna Apennines can be subdivided into four formations ranging from Langhian to Pliocene (Vai 1988): (1) The Marnoso-arenacea Formation (Langhian–Messinian) mainly consists of deepwater siliciclastic turbidites representing the sedimentary infill of the Adriatic foredeep. In the upper part a clayey unit, mainly consisting of slope mudstones (‘ghioli di letto’) contains minor turbiditic sandstones and chaotic bodies; these deposits are capped by a thin horizon of cyclically interbedded organic-rich laminites and mudstones, informally named ‘euxinic shales’ (upper Tortonian–lower Messinian). The welldefined biomagnetostratigraphic events recognized within this unit (Vai 1997; Krijsman et al. 1999) allow a detailed correlation with other pre-evaporitic successions of the Mediterranean (Tripoli Formation of Sicily and Spain). The euxinic shales unit, recording the palaeoceanographic changes that affected the whole Mediterranean area before the Messinian Salinity Crisis, contains the Tortonian– Messinian boundary and spans a 1.5 million year time interval. (2) The Gessoso-solfifera Formation (Messinian) is made up of both primary (Vena del Gesso, Vai & Ricci Lucchi 1977; Table 1) and clastic, resedimented evaporites with interbedded organic-rich shales (eastern Romagna and Marche area), deposited during the evaporitic and post-evaporitic Fig. 1. Schematic geological map of the Romagna Apennines. S. LUGLI ET AL. 180

A large consensus has been reached on a three-stage evolutionary model of the Messinian salinity crisis (MSC), each of them characterized by a peculiar association of evaporitic deposits, which record changes in the Mediterranean basin hydrology. However, a general agreement on what actually happened during the MSC, and particularly in the deepest settings of the Mediterranean basin, is still far from being obtained and several scenarios of the crisis have been proposed, with different implications for hydrocarbon exploration. The current MSC paradigm - the “shallow-water deep-basin” model - implying high-amplitude sea-level oscillations (>1500 m) of the Mediterranean up to its desiccation, is often considered as a fact. Actually, the different MSC scenarios so far proposed should be considered as theories needing to be proved. In recent times the desiccation theory has been questioned on its main arguments. We suggest an alternative, deep-water, non-desiccated scenario implying the permanence of a large water body in the Mediterranean throughout the whole MSC with strongly reduced Atlantic connections. The model has important implications for the exploration of the deep Mediterranean and the assessment of its hydrocarbon systems. In particular, its impact for a better definition of source rock generation and distribution, as well as of the magnitude of water unloading processes and their effects on hydrocarbon accumulations, should be carefully considered and evaluated.

The importance of the sedimentary record of Messinian events in the Apennines foredeep is due to its geological and structural settings, which allow the reconstruction of the relationships between marginal and basinal settings and provide fundamental insights into some important issues. A geologic–stratigraphic model of the Messinian Apennine foredeep indicating a possible solution for closing the last ‘Messinian gap’ is here presented. Moreover, the establishment of a preliminary high-resolution stratigraphy for the terminal Lago Mare stage allows us to attempt Mediterranean-scale correlations across different structural settings. The Messinian evolution of the Apennine foredeep and some considerations of adjacent areas suggest the great importance of tectonic deformation in controlling Messinian events. The intra-Messinian unconformity is a common feature of the marginal basins of the Mediterranean, and it is associated in many cases to the collapse and resedimentation of primary evaporites. The genesis of such unconformity seems to be strictly related to a general tectonic reorganization of the Mediterranean area. Preliminary observation on the stratigraphy of the Lago Mare stage suggest that the high-frequency lithological cyclicity observed in the non-marine deposits of this stage, as well as the superimposed transgressive trend, are common to many Mediterranean basins. These characteristic features might reflect the interplay between a longer-term tectonic trend and higher-frequency, precession-related, climatic changes; this could represent a fundamental tool for establishing a high-resolution stratigraphic framework of the latest Messinian allowing long-distance correlations between terrestrial and marine ecosystems and hence more accurate palaeoenvironmental studies.

A new genetic facies model for deep-water clastic evaporites is presented, based on work carried out on the Messinian Gessoso-solfifera Formation of the northern Apennines during the last 15 years. This model is derived from the most recent siliciclastic turbidite models and describes the downcurrent transformations of a parent flow mainly composed of gypsum clasts. The model allows clearer comprehension of processes controlling the production and deposition of clastic evaporites, representing the most common evaporite facies of the northern Apennines, and the definition of the genetic and stratigraphic relationship with primary shallow-water evaporites formed and preserved in marginal settings. Due to the severe recrystallization processes usually affecting these deposits, petrographic and geochemical analyses are needed for a more accurate interpretation of the large spectrum of recognized gravity-driven deposits ranging from debrisflow to low-density turbidites. Almost all the laminar ‘balatino’ gypsum, previously considered a deep-water primary deposit, is here reinterpreted as the fine-grained product of high to low-density gravity flows. Facies associations permit the framing of the distribution of clastic evaporites into the complex tectonically controlled depositional settings of the Apennine foredeep basin. The Messinian Salinity Crisis occurred during an intense phase of geodynamic reorganization of the Mediterranean area that also produced the fragmentation of the former Miocene Apennine foredeep basin. In this area, primary shallow-water evaporites equivalent to the Mediterranean Lower Evaporites, apparently only formed in semi-closed thrust-top basins like the Vena del Gesso Basin. The subsequent uplift and subaerial exposure of such basins ended the evaporite precipitation and promoted a widespread phase of collapse leading to the resedimentation of the evaporites into deeper basins. Vertical facies sequences of clastic evaporites can be interpreted in terms of the complex interplay between the Messinian tectonic evolution of the Apennine thrust belt and related exhumation–erosional processes. The facies model here proposed could be helpful also for better comprehension of other different depositional and geodynamic contexts; the importance of clastic evaporites deposits has been overlooked in the study of other Mediterranean areas. Based on the Apennine basins experience, it is suggested here that evaporites diffused into the deeper portions of the Mediterranean basin may consist mainly of deep-water resedimented deposits rather than shallow-water to supratidal primary evaporites indicative of a complete basin desiccation.

The integration of field and subsurface data permits a substantial revision of the sedimentary evolution of the Vena del Gesso basin, a thrust-top basin in the Northern Apennines where shallow-water primary gypsum deposits related to the Messinian salinity crisis were well developed and preserved. As inferred from lateral and vertical facies changes within the underlying deep-marine turbidites of the Marnoso-arenacea Formation, evaporite precipitation occurred in a basin bounded to the north and to the east by a thrust-related anticline actively growing since the late Tortonian. Both gypsum deposition and subsequent deformation were strongly controlled by evolving paleobathymetry driven by tectonics. Primary gypsum precipitated in a shallow, silled basin, while in the adjacent deeper and larger foredeep basin, organic-rich shales were deposited. Gypsum deposits underwent severe postdepositional deformation related to large-scale gravitational collapse, as a result of a regional uplift event, also coincident with the end of the evaporitic phase. Along the inner, shallower-dipping limb of the anticline bounding the basin, large-scale, poorly deformed gypsum slabs moved downslope along a detachment surface developed at the contact with the underlying euxinic shales, forming both extensional and compressional features and showing an overall southwestern vergence. The identification of a south-southwest–dipping paleoslope, here pointed out for the first time, suggests that the deformational features affecting the gypsum unit were probably driven by gravity and not by active thrusting, as thought up to now. The steeper frontal limb of the anticline promoted the transformation of gypsum slides into debris flows and turbidite currents that deposited their load in the adjacent deeper basin. This gravitational deformation was sealed by postevaporitic upper Messinian Lagomare deposits. The sedimentary history of the Vena del Gesso basin suggests that the Messinian salinity crisis in the Apennine foredeep, as well as in the Balearic, Tyrrhenian, Sicily, and Eastern Mediterranean Basins, was tightly linked to tectonic processes. The large-scale, postdepositional collapse of primary evaporitic deposits is a widespread feature in the Mediterranean basins, and it may have altered the original stratigraphic relationships in some places. This finding has potentially important implications for a correct paleoenvironmental reconstruction of the onset of the Messinian salinity crisis.

During the first stage of the Late Miocene Messinian salinity crisis (5.97–5.60 Ma), deposition of sulfates (the Primary Lower Gypsum) occurred in shallow silled peripheral subbasins of the Mediterranean undergoing restricted water exchange with the Atlantic Ocean. Fluid inclusions in Messinian selenite crystals from the Piedmont Basin (northwest Italy) have surprisingly low salinities (average of 1.6 wt% NaCl equivalent), suggesting that parent waters were depleted in Na + and Cl – compared to modern seawater. Modern gypsum from a Mediterranean salt work, in contrast, contains fluid inclusions with elevated salinities that match the normal evaporation trend expected for seawater. The salinity data indicate that the Messinian sulfate deposits from the Piedmont Basin formed from hybrid parent waters: seawater mixed with Ca 2+ and SO 4 2– enriched freshwaters that dissolved coeval marginal marine gypsum. Such mixed parent waters and complex recycling processes should be taken into account when explaining the genesis of other Messinian gypsum deposits across the Mediterranean Basin.

New 87Sr/86Sr data from DSDP–ODP Messinian cores from deep Mediterranean basins suggest that the usually envisaged correlation of offshore Upper Evaporites with onshore Upper Gypsum deposits of Sicily, Cyprus and Crete recording the stage 3 (5.53–5.33 Ma) of the Messinian salinity crisis may be not entirely correct. High-resolution stratigraphic calibration of Sr isotope data indicates that only a very thin unit (commonly

The recognition of peculiar laminated layers atypically rich in a biogenic intrabasinal component in the mudstone intervals from the Messinian (late Miocene) Primary Lower Gypsum unit (5.97–5.60 Ma) of the Piedmont basin (NW Italy) provides information on the palaeoenvironmental evolution at precessional insolation maxima. These cyclic layers consist of irregular alternation of cm-thick grey terrigenous laminae and whitish composite packets; the latter is in turn composed of sub mm-thick wrinkled dolomite-rich laminae that alternate with terrigenous ones. Two types of layers can be distinguished: i) peloidal layers, composed of faecal pellets and irregular diatom-rich aggregates, interpreted as marine snow floccules; and ii) filament bearing layers, composed of interwoven filaments up to 150 μm across, corresponding to remains of Beggiatoa -like giant sulphide-oxidising bacteria. By comparison with present-day settings, the peloidal layers are interpreted as flocculent layers, deposited on anoxic sea bottoms, following episodes of phytoplankton bloom in the upper water column. The filament-bearing layers are considered as chemotrophic microbial mats, growing on dysaerobic sea bottoms. The uncommon preservation of both kinds of layers is the result of extensive dolomite precipitation in the shallow subsurface, induced by bacterial sulphate reduction. The laminated layers are the first reported example of a high frequency climate-driven cyclicity in the non-evaporitic portion of the Primary Lower Gypsum unit. Their stacking pattern within the mudstone intervals reflects the gradual increase of the oxygen content of bottom waters during the humid precessional hemicycle, culminating with gypsum deposition at the onset of the arid phase.

Η λεπτομερής χαρτογράφηση των Νεογενών αποθέσεων της Ζακύνθου δείχνει ότι οι λεκάνες πρωτογενούς Μεσσήνιας εβαποριτικής απόθεσης, που σχηματίστηκαν πάνωεβαποριτικών διάπειρων (δυτικά της Μεσσήνιας ενότητας γύψου Καλαμάκι-Αργάσι). Η μετα-Μειοκαινική εξωτερική Ιόνια επώθηση τοποθετείται δυτικά αυτών των Τριαδικών διάπειρων. Βιοστρωματογραφική ανάλυση των συναθροίσεων πλαγκτονικών τρηματοφόρων στα Νεογενή ιζήματα δείχνει ότι η συσσώρευση πρωτογενούς εβαπορίτη έλαβε χώρα πιθανά κατά το πρώτο στάδιο της κρίσης αλμυρότητας του Μεσσηνίου (5.96-5.60 Εκατ.χρ.), στα αβαθέστερα τμήματα της λεκάνης προχώρας, η οποία σχηματίστηκε πάνω στο Προ-Απούλιο και Ιόνιο αλπικό υπόβαθρο. Ο σχηματισμός των περιβαλλόντων ιζηματογένεσης, πριν από την Ιόνια επώθηση, πιθανά οφείλεται στις ιδιαιτερότητες της λεκάνης προχώρας, η οποία εκείνο το διάστημα εκτείνονταν από την εξωτερική Ιόνια ως την εσωτερική Προ-Απούλια ζώνη. Νέα δεδομένα υπαίθρου, σε συνδυασμό με τη βιοστρωματογραφία, τα στοιχεία γεωτρήσεων και μία διαθέσιμη σεισμική τομή δείχνουν ότι τα Νεογενή ιζήματα πάνω στο Προ-Απούλιο υπόβαθρο αντιστοιχούν στον τμήμα της λεκάνης προχώρας, από το προβύθισμα (foredeep) ως την πρόσθια ανύψωση (forebulge), όπως αυτό διαπιστώνεται από την χωρική κατανομή του πάχους τους. Αντίθετα, τα Νεογενή ιζήματα πάνω στο Ιόνιο υπόβαθρο αντιστοιχούν στο τμήμα της λεκάνης προχώρας που βρίσκεται πάνω στο μετωπικό πρίσμα της ορογένεσης (wedge top), το οποίο βυθίζονταν λιγότερο όπως συνάγεται από το ελαττωμένο πάχος των ιζημάτων. Ο μικρότερος ρυθμός βύθισης οφείλεται στις διαπειρικές κινήσεις των Τριαδικών εβαποριτών. Στη Νεογενή ακολουθία, που βρίσκεται πάνω σε Προ-Απούλιο υπόβαθρο (περιοχή Άγιος Σώστης), παρεμβάλλονται επανιζηματοποιημένα μπλοκ δεκαμετρικού πάχους αποτελούμενα από σεληνίτη μικρού βάθους απόθεσης. Προς νότο, αυτή η βαρυτικά μεταφερόμενη μάζα της Μεσσήνιας γύψου μεταπίπτει κυρίως σε τουρβιδιτική γύψο. Στην περιοχή Καλαμάκι-Αργάσι που βρίσκεται πάνω σε Ιόνιο υπόβαθρο, το αβαθές περιβάλλον οδήγησε στην απόθεση της παρατηρούμενης πρωτογενούς γύψου. Η διάβρωση της πρωτογενούς γύψου τόσο της πρόσθιας ανύψωσης όσο και του μετωπικού πρίσματος επώθησης τροφοδότησαν το προβύθισμα της λεκάνης προχώρας με τουρβιδίτες γύψου., Detailed mapping of the Neogene deposits on Zakynthos Island shows that the Messinian primary evaporite basins, formed over Ionian basement, are delimited by the westernmost outcrop of the Triassic evaporitic diapirs, located west of the Kalamaki-Argasi Messinian gypsum unit. The post-Miocene external Ionian thrust is emplaced west of the Triassic diapirs. Planktonic foraminifera biostratigraphy indicates that primary evaporite accumulation took place probably during the first stage of the Messinian salinity crisis (5.96-5.60 Ma), in shallower parts of a foreland basin, formed over the Pre-Apulian and the Ionian zone basement. Establishment of these depositional environments, before the Ionian thrust emplacement, was probably due to the particularities of the foreland basin, which extended from the external Ionian to the internal Pre-Apulian zone. Field observations, borehole data and an onshore seismic profile show that the Neogene sediments over the Pre-Apulian basement correspond to the foredeep through forebulge domain of the foreland basin, as it is documented from their spatial thickness distribution. In contrast, the Neogene sediments over the Ionian basement correspond to the wedge top of the foreland basin, which was less subsiding, as it is deduced by their reduced thickness. This lower subsidence rate was the result of the concurrent diapiric movements of the Ionian Triassic evaporites. In Agios Sostis area, located over Pre-Apulian basement, the Neogene sequence is intercalated by decametre-thick resedimented blocks consisting of shallow water selenite. To the southeast, this mass-wasting Messinian gypsum passes to mainly gypsum turbidite. In Kalamaki-Argasi area, located over Ionian basement, the shallow water environment led to the deposition of the observed primary gypsum. Erosion of the primary gypsum of both forebulge and wedge top supplied the foreland basin’s depocenter with gypsum turbidites.

The recognition of large clastic sulfate deposits in the Miocene Messinian onshore of the Mediterranean Basin appears to be in contrast with the hypothesis of a complete desiccation as a consequence of the salinity crisis. Below the sea floor the evaporite facies are virtually unknown, but the detailed review of the cores from onshore Israel cutting through the evaporite filling of the marginal canyons in the Levant Basin (Mavqi'im Formation) reveal exclusively clastic sulfate facies. The rocks are graded gypsrudite and gypsarenite associated with laminar and cross-bedded gypsarenite–gypsiltite and shale, whereas no primary, in situ evaporites are present. The clastic facies association is interpreted to have been deposited by subaqueous gravity flows sourced from dismantled selenite rocks originally located eastward and updip of the canyons. The absence of supratidal evaporites suggests that no pronounced sea-level drop can be inferred during the salinity crisis because the presence of the evaporite layers at different elevations along the canyons cannot mark oscillations in sea level, but instead is the result of subaqueous mass-wasting phenomena. These findings indicate that the other ancient canyons described around the Mediterranean Basin may not be necessarily related to a base-level drop due to basinwide desiccation. On the contrary, the widespread presence of clastic evaporites suggests that a water body persisted even during the acme of the salinity crisis. The clastic deposits onshore Israel are the first direct evidence that the widespread Lower Evaporite Unit lying below the floor of the Mediterranean may actually consist of deep-water resedimented evaporites and that one of the primary sources was originally located on the upper margin of the Levant Basin. If this hypothesis is correct, then the Mediterranean Basin may host the largest clastic sulfate deposit in the world.

We propose a revised age calibration of the Messinian salinity crisis onset in the Mediterranean at 5.971 Ma based on the recognition of an extra gypsum cycle in the transitional interval of the Perales section (Sorbas basin, Spain) and the revision of the magnetostratigraphy of the Monticino section (Vena del Gesso basin, Italy). This age re-calibration allows to state more accurately that: (i) the interval encompassing the MSC-onset is continuous, thus ruling out any erosional feature or stratigraphic hiatus related to a major sea-level fall affecting the Mediterranean; (ii) the first gypsum was deposited during the summer insolation peak at 5.969 Ma associated with an eccentricity minimum and roughly coincident with glacial stage TG32; (iii) the MSC-onset was preconditioned by the tectonically-driven reduction of the hydrological exchanges with the Atlantic Ocean and finally triggered by glacial conditions in the northern hemisphere and by arid conditions in northern Africa.

The Legnagnone section (North-eastern Apennines) represents one of the few shallow water records of the onset of the Messinian salinity crisis. Here we present a detailed description of a ~ 200 kyr time interval encompassing the pre-/syn-evaporitic transition based on a multidisciplinary approach, integrating sedimentological, bio-magnetostratigraphical, palaeontological and stable isotope data. Such a shallow water setting is potentially more sensitive to the palaeoenvironmental change leading to the MSC than the more often studied deeper Mediterranean basin. The aquatic palaeoenvironmental reconstruction proposed here is based on the study of foraminifer, ostracod and mollusc assemblages. It depicts a change from infralittoral (20–50 m) to inner circalittoral environment (60–100 m) that, since 6.12 Ma, was progressively affected by a reduction of oxygen at the sea floor punctuated by short-lived anoxic events. At least three cooling events have been recognized on the basis of relative abundance data in mid to high altitude pollen, which, before 6.03 Ma, are in phase with abundance peaks of Turborotalia spp., a taxon indicating eutrophic and cool surface waters. The absence of stress-tolerant benthic foraminifers during these peaks points to strong ventilation episodes triggered by a generally cooler climate. The proximity of a deltaic system and the consequent riverine input probably caused a salinity decrease of the surface waters, hindering the proliferation of planktonic foraminifers in the water column, which prevalently occur in short influxes and disappear at ca. 6 Ma. Our results suggest that the onset of the crisis occurred during a phase of relative sea level high stand, whereas no evidences of sea level drop can be envisaged. The palaeoclimatic reconstruction based on palynological data indicates the dominance of a “subtropical humid forest” vegetation type, where fresh water swamps are well represented. From 6.03 Ma onward, the transition to the salinity crisis is marked by more pronounced cyclical expansions of the temperate broad-leaved deciduous forest, along with herbaceous taxa. The establishment of the strongly evaporative condition at the crisis onset is not associated with major vegetational changes towards drier conditions, but linked to a sudden increase of δ18O and the disappearance of benthic foraminifers just prior to the deposition of the 1st laminated carbonate, which represents the base of the Primary Lower Gypsum unit.

The seven Messinian microbial carbonate-rich layers cropping out in the Pollenzo section (Tertiary Piedmont Basin, NW Italy) are interbedded with a precession-related cyclic succession composed of euxinic shale/marl couplets and straddle the onset of the Messinian salinity crisis (MSC). A sharp change of sedimentological, compositional and geochemical characteristics was observed from the onset of the MSC onward, suggesting strong differences in the mechanisms responsible for carbonate precipitation. Pre-MSC beds are mainly composed of dolomite and are interpreted as the product of early diagenesis, formed by bacterial sulphate reduction in the shallow subsurface along the sulphate–methane interface. Dolomite precipitation was temporarily enhanced by an upward flux of methane-rich fluids, possibly sourced by gas hydrate destabilisation. Conversely, from the onset of the MSC onward, carbonate beds are thinly laminated and show abundant filaments interpreted as Beggiatoa -like bacteria, while calcite (and aragonite) are the dominant authigenic phases. These beds are interpreted as microbialites, resulting from the lithification of chemotrophic bacterial mats dominated by sulphide-oxidizing bacteria. The carbonate necessary for their preservation was provided by bacterial sulphate reduction. These microbialites, that appear as the deeper water counterpart of bottom-grown selenite layers deposited in the marginal part of the basin, formed on an anoxic sea bottom under a density stratified water column. The high sulphate concentration in the pore waters, related to the presence of concentrated brines and to the regeneration of sulphate by sulphide-oxidizing bacteria, is considered as the driving factor controlling the mineralogical change from dolomite to calcite and aragonite. Finally, the sharp shift towards negative δ 18 O values of carbonates, observed from the onset of the MSC onward, was probably related to fractionation processes operated by sulphate-reducing bacterial communities in the pore waters. This suggests that care must be taken, when dealing with microbial carbonates, in the interpretation of the oxygen isotope values in terms of fluctuating salinity condition of the water mass. In conclusion, this study suggests that the onset of the MSC had a strong impact on microbial populations governing carbonate precipitation, in a sector of the basin dominated by depositional conditions not suitable for gypsum precipitation.

The deposition of varved sedimentary sequences is usually controlled by climate conditions. The study of two Late Miocene evaporite successions (one halite and the other gypsum) consisting of annual varves has been carried out to reconstruct the paleoclimatic and paleoenvironmental conditions existing during the acme of the Messinian salinity crisis, ~ 6 Ma, when thick evaporite deposits accumulated on the floor of the Mediterranean basin. Spectral analyses of these varved evaporitic successions reveal significant periodicity peaks at around 3-5, 9, 11-13, 20-27 and 50-100 yr. A comparison with modern precipitation data in the western Mediterranean shows that during the acme of the Messinian salinity crisis the climate was not in a permanent evaporitic stage, but in a dynamic situation where evaporite deposition was controlled by quasi-periodic climate oscillations with similarity to modern analogs including Quasi-Biennial Oscillation, El Ni\~no Southern Oscillation, and decadal to secular lunar- and solar-induced cycles. Particularly we found a significant quasi-decadal oscillation with a prominent 9-year peak that is commonly found also in modern temperature records and is present in the contemporary Atlantic Multidecadal Oscillation (AMO) index and Pacific Decadal Oscillation (PDO) index. These cyclicities are common to both ancient and modern climate records because they can be associated with solar and solar-lunar tidal cycles., Comment: 13 pages, 10 figures, 1 Table

The Late Messinian fill of the Nijar Basin (Betic Cordillera, southeastern Spain) mainly consists of clastic deposits of the Feos Formation that at basin margins rest unconformably above the primary evaporites of the Yesares Formation, the local equivalent of the Mediterranean Lower Gypsum. The Feos Fm. records the upward transition towards non-marine environments before the abrupt return to fully marine conditions at the base of the Pliocene. The Feos Fm. is clearly two-phase, with \\\'lower\\\' and \\\'upper\\\' members, which exhibit substantial differences in terms of facies, thickness, depositional trends and cyclical organization. These members record two distinct sedimentary and tectonic stages of Nijar Basin infilling. A high-resolution, physical-stratigraphic framework is proposed based on key beds and stratigraphic cyclicity and patterns that differ largely from those of most previously published studies. The predominant influence on stratigraphic cyclicity is interpreted to be precessionally driven climate changes, allowing their correlation to the Late Messinian astronomically calibrated chronostratigraphic framework. Detailed correlations suggest a phase of enhanced tectonic activity, possibly related to the Serrata-Carboneras strike-slip fault zone, during the first stage (\\\'lower\\\' member), resulting in a strongly articulated topography with structural lows and highs controlling sediment thickness and facies variation. Tectonic activity decreased during the second stage (\\\'upper\\\' member), which is characterized by (1) a progressively dampened and homogenized, (2) overall relative base-level rise and (3) gradual establishment of hypohaline environments. Facies characteristics, overall stacking patterns and depositional trends of the Feos Fm. are analogous with uppermost Messinian successions of the Northern Apennines, Piedmont Basin and Calabria. Despite minor differences related to the local geodynamic setting, these basins experienced a common Late Messinian history that supports the development of a single, large Mediterranean water body characterized by high-frequency, climatically-driven changes in sediment flux and base-level.

The Alba succession (Tertiary Piedmont Basin, NW Italy) preserves the northernmost record of the Messinian salinity crisis (MSC) and was deposited on the southern margin of a wide wedge-top basin, related to the involvement of the Piedmont Basin in the Apennine compressional tectonics. Pre-MSC sediments consist of a cyclic succession of marine euxinic shales and calcareous marls, deposited under the influence of precession-modulated climate changes, and document the progressive restriction of the basin prior to the onset of the MSC. They are followed by the Primary Lower Gypsum unit (PLG), deposited during the first MSC stage (from 5.96 to 5.60 Ma). These sediments show a clear precession-related cyclic stacking pattern and record the lateral transition from a shallow water marginal setting in the SW to a deeper one in the NE. In marginal settings, six PLG cycles are recognised, truncated by an erosional unconformity placed at the base of the post-evaporitic sediments. The lowermost five cycles are composed of massive and banded selenite beds separated by thin shale intervals. A sharp change, evidenced by the appearance of the branching selenite facies, is recorded by the 6th gypsum bed that represents a distinctive marker bed, here called Sturani key-bed, that can be mapped throughout the study area. Basinward, the lower PLG cycles are transitional to decimetre-thick carbonate-rich layers interbedded to euxinic shales, that are overlain by the Sturani key-bed. Above the marker bed, other seven PLG cycles are present. The gypsum beds form thinner bodies compared to the Sturani key-bed and are characterised by a greater amount of fine-grained terrigenous fraction, suggesting an increase of continental runoff related, in turn, to humid climate conditions at the end of the first MSC stage. PLG cycles are followed by slumped mudstones and clastic gypsum beds that correspond to the resedimented and chaotic facies (Resedimented Lower Gypsum), deposited in the Mediterranean basins during the second MSC stage (from 5.60 to 5.55 Ma). They are in turn overlain by continental and brackish water facies with Lago Mare fossil assemblages, recording the final stage of the MSC. The Messinian succession of Alba provides the opportunity to reconstruct the lateral facies transition between marginal and distal settings and to shed new light on the deep water MSC sedimentary record. Moreover, the appearance of the branching selenite facies from the 6th PLG cycle upward provides a tool for properly placing the Piedmont record in the MSC chronostratigraphic framework, allowing us to investigate the influence of climate gradients on the sedimentary response to the Mediterranean salinity crisis.

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

At the foothills of the north-western Apennines, the Cortemaggiore Wedge-Top Basin (CWTB) is bounded by the buried and arcuate Cortemaggiore anticline, to the north, and by the polyphased and complex Salsomaggiore tectonic window, to the south. The CWTB started to form in response to a late Tortonian tectonic pulse that uplifted the Cortemaggiore anticline and established euxinic conditions. A major intra-Messinian tectonic pulse further shortened the CWTB and triggered the emplacement of gravity-driven mass-wasting deposits above which turbiditic, shelfal deposits evolve upward to fluvio-deltaic deposits. The former, Late Messinian hypohaline succession, is characterized by a well-developed cyclical pattern which falls in the range of astronomically-controlled climate changes with precessional periodicity modulated by obliquity and eccentricity periodicity. Tectonic and climate controls on sedimentary succession of the CWTB act at different frequencies. Based on the refined and highresolution late Miocene chronostratigraphy of coeval Mediterranean sedimentary succession, it is possible to time constrain the tectonic and climatic events and their cyclicity. Tectonics control acts at low frequency (order of 2 Myr) and produces major and fast morphologic changes of the basin. Climate acts at variable higher frequency (order of 20–100 kyr); it both distributes laterally and stacks vertically and cyclically the sediment supplied to transport by erosion of tectonically uplifted rocks. The tectonic and climatic controls should have acted concomitantly over the entire Northern Apennines foreland basin system and the Mediterranean area, because cyclicity and depositional characters of late Miocene succession present common features. Tectonic uplift causes basin-wide hydrologic and hydrogeologic changes that might induce increased evaporation; in the CWTB, two drier climate events, corresponding to the lower and upper evaporites of the Mediterranean region, are closely preceded by tectonic pulses. However, during late Miocene, climate changes occurred also outside the Mediterranean region. Thus, it is argued that the 2 Myr is a periodicity common both to tectonics pulses and climate changes; it is a low-frequency cyclicity that, related to astronomical forces, drives simultaneous action of tectonic pulses and climate changes within the CWTB.

The post-evaporitic Messinian in the northern sector of the Adriatic foredeep is characterized by the occurrence of abundant terrigenous deposits which have been subdivided into two allostratigraphic units (p-ev1, p-ev2) separated by an erosional unconformity of regional importance. The p-ev1 consists of basal complex of resedimented evaporites overlain by monotonous succession of mudstone/siltstone alternations (thin bedded turbidites) with an overall coarsening and shallowing upwards trend. It is possibly related to the rapid basin infill after the end of the salinity crisis. The upper unit (p-ev2) shows, in the most marginal areas, a clear cyclical stacking pattern made up of three fining-up sequences with fan-delta conglomerates at the base of each cycle. Here, a peculiar feature of the p-ev2 deposits is the occurrence of three distinct laminated limestone horizons (termed colombacci) interbedded with fine grained, varved mudstones. These limestones are abiotic, despite the occurrence of abundant Ostracod assemblages (Lago–Mare fauna) in the interbedding pelites, and are interpreted as inorganically precipitated, deposited in a relatively deep-water environment, possibly anoxic and related to permanent stratification of water mass events during periods of lake level maxima. The combination of petrographical and geochemical observations on carbonate layers reveals that they correspond to events characterized by significant variations of environmental conditions. However, δ18O (−5.30/+0.2) and δ13C (−9.28/+1.68) signatures suggest that the precipitation of low-Mg calcite often occurred in a non-marine environment and that meteoric water input had a considerable influence on late Messinian sedimentation. Moreover, the limestones have a uniform 87Sr/86Sr composition (0.70864–0.70875) in the range of other Lago–Mare sediments from elsewhere in the Mediterranean, suggesting that some of the major Mediterranean basins were likely interconnected during the Lago–Mare phase. A strongly reduced rate of hydrological exchange with the ocean is also possible, but the possibility of marine influence during this stage is not completely excluded.