Conference Agenda

The Messinian salinity crisis (MSC; 5.97-5.33 Ma) has been the object of numerous research projects targeting its sedimentary record. The scarcity of body fossils in the MSC depositional record makes the use of molecular fossils (lipid biomarkers) a very promising tool for the reconstruction of the paleoenvironmental conditions of this event. Recent studies focused on compound-specific carbon and hydrogen isotopes of n-alkanes and long-chain alkenones and on compound-dependent proxies (e.g. the TEX₈₆ and U^k₃₇ paleothermometers) with the aim to decipher regional climatic and hydrologic changes. Other studies documented the diversity of archaea and bacteria able to tolerate the harsh conditions assumed for the MSC, but also revealed that locally non-evaporitic conditions prevailed in surface waters during the deposition of the thick evaporitic sequence. Besides compounds derived from extremophilic microorganisms, represented for example by abundant isoprenoidal diether membrane lipids of halophilic archaea, other molecular fossils including phytoplankton-derived sterols and planktonic archaeal-derived isoprenoidal tetraethers (GDGTs) are common in the deposits of the first phase of the crisis in marginal basins. The distribution of the latter molecular fossils is indicative of normal marine surface water conditions, whereas some of the associated compounds such as tetrahymanol and isorenieratane suggest stratification of the water column. These findings disagree with an exclusively hypersaline water body and with the paradigm of the desiccation of the Mediterranean Sea. The Mediterranean Salt Giant is an ideal natural laboratory to be investigated with molecular fossils.

Between 5.97-5.33 Ma several kilometre-thick evaporite units were deposited in the Mediterranean Basin during the Messinian Salinity Crisis (MSC). The MSC reflects a period featured by a negative hydrological budget, with a net evaporative loss of water exceeding precipitation and riverine runoff. The contemporary changes in continental and marine circum-Mediterranean temperature are, however, poorly constrained. Here we reconstruct continental mean annual temperatures (MAT) using branched glycerol dialkyl glycerol tetraether (GDGT) biomarkers for the time period corresponding to MSC Stage 3 (5.55-5.33 Ma). Additionally, for the same time interval, we estimate sea surface temperatures (SSTs) of the Mediterranean Sea using isoprenoidal GDGTs based TEX₈₆ proxy. The excellently preserved organic biomarkers were extracted from outcrops and DSDP cores spread over a large part of the onland (Malaga, Sicily, Cyprus) and offshore (holes 124 and 134 from Balearic abyssal plane and hole 374 from Ionian Basin) Mediterranean Basin domain. The calculated MATs for the 5.55 to 5.33 Ma interval show values around 16 to 18 ºC for the Malaga, Sicily, and Cyprus outcrops. The MAT values calculated for DSDP Leg 13 holes 124, 134 and Leg 42A hole 374 are lower, around 11 to 13 ºC.

For samples where the branched and isoprenoid tetraether (BIT) index was lower than the 0.4 we could calculate TEX₈₆ derived SSTs averaging around 27 ºC for all sampled locations. Where available (i.e. Sicily), we compared the TEX₈₆ derived SSTs with alkenone based, U^k₃₇ derived SST estimates from the same samples. The TEX₈₆ derived SST values are slightly higher than the U^k₃₇ derived SST of 20 to 28 ºC. For the Mediterranean region, values between 19 and 27 ºC of the U^k₃₇ derived SSTs were calculated for the interval between the 8.0 and 6.4 Ma, close to our calculations for Sicily section (20 to 28 ºC). Independent of common pitfalls that may arise in using molecular biomarkers as temperature proxies, both SST estimates independently hint towards much warmer Mediterranean Sea water during the latest phase (Stage 3) of the MSC. These elevated temperatures coincide with higher δD values measured on alkenones and long chain n-alkanes (both records indicating for more arid and/or warmer conditions than today between 5.55 and 5.33 Ma). We therefore conclude that the climate between 5.55 to 5.33 Ma was warmer than present-day conditions, recorded both in the Mediterranean Sea and surrounding basin.

The environmental conditions under which the youngest Salt Giant of our Planet – the late Messinian Mediterranean Salt Giant – formed are debated to date, since most evaporites are buried beneath the modern Mediterranean seafloor and the accessible marginal successions contain scarce or no body fossils. To shed light on the environmental conditions characterizing the advent and the earliest phase of the formation of the Mediterranean Salt Giant during the so-called Messinian salinity crisis (MSC), we investigated the Govone section from the Piedmont Basin (NW Italy). The Govone section archives the onset of the MSC (5.97 Ma) in a succession of organic-rich shales and dolomite-rich marls, which we investigated applying a multidisciplinary approach including organic geochemical, petrographic and carbon and oxygen stable isotope analyses. The studied interval spans about 150 ka (6.07 – 5.92 Ma), with the MSC part of the succession representing the deep-water (200 – 1000 m) equivalent of shallow water (<200 m) marginal sulphate evaporites deposited during the first phase of the crisis (5.97 – 5.60 Ma). The onset of the MSC was marked by an intensification of water column stratification, rather than the establishment of widespread hypersaline conditions. The water column was typified by a stagnant, oxygen-depleted bottom layer separated through a chemocline from an oxygenated, upper seawater layer influenced by freshwater inflows. We suggest that vertical oscillations of the chemocline associated to temporal and spatial variation of the water masses with different redox chemistries controlled the stratigraphic architecture of the sediments deposited during the first stage of the MSC.

The Northern Aegean region evolved during the Miocene as a restricted land-locked basin with ephemeral small connections to both the Eastern Paratethys (former Black Sea) and Mediterranean. Biostratigraphic data show a predominant Paratethys component, but this fauna has generally been neglected for chronologic reconstructions. Here, we review this biostratigraphic data from a Paratethyan perspective and present revised paleogeographic reconstructions of the Northern Aegean region throughout the late Miocene. In the Tortonian, all sub-basins show mainly fluvio-deltaic terrestrial environments with a series of scattered lakes that are predominantly fed by local rivers and short-lived Paratethys connections. The first persisting marine conditions, still alternating with brackish Paratethyan environments, converge to a middle Messinian (upper Maeotian) age (6.9-6.1 Ma), when the region formed a semi-isolated (Egemar) sea with multiple marine influxes. The termination of marine conditions is very well documented by a marked paleoenvironmental change to the brackish water environments that correlate to the Maeotian/Pontian boundary (6.1 Ma) in Eastern Paratethys. During the Messinian Salinity crisis (5.97-5.33 Ma), the northern Aegean was a brackish water system (Lake Egemar) that formed a passageway for Paratethyan overspill waters towards the Mediterranean. We conclude that the thick evaporites of the Northern Aegean region do not reflect the classic Mediterranean MSC sequences, but are likely related to Maeotian salinity incursions.

The late Miocene is a period of environmental transition for the entire Eurasian continental mass including its hydrologic system governed by the presence of the Paratethys. For the Eurasian continental interior, the late Miocene is marked by fragmentation and redistribution of the water masses.

Here we reconstruct the climatic conditions from a section in Taman Peninsula (Russia)-Cape Panagia, between 12.8 to 7.6 Ma, from combined proxies such as SST’s, δ²H, δ¹³C, MAT’s, charcoal and pollen, focusing on the interval between 9.6 to 7.6 Ma, which corresponds to the end of Bessarabian and Kersonian East Paratethys sub-stages.

Our results show a possible connection to a different basin between 9.75-9.66 Ma (Bessarabian-Khersonian limit) when SSTs increase from 10.2 to 31 °C, temperatures that remain high for the next 1ky. The temperatures remain high for the rest of Kersonian, but a second interval with marked high temperatures occurs between 7.81-7.66 Ma, followed by the famous Maeotian transgression at 7.66 Ma. The 2 high temperature intervals correlate with extremely high values of δ²H_C37alkenones (up to −126.2 ‰) and shifts in δ¹³C_{n-alkanes ,} from C₃ dominated to C₄ dominated plant assemblages. The same intervals show an increase in poaceae charcoal and the appearance of chenopodiaceae species pollen, reflecting dramatic changes in vegetation and hydrology.

The event from 9.66 marks the sudden occurrence of Coccolithus pelagicus, an open marine lover which is the main producer of alkenones, chemical components that were not registered in the basin before, supporting the presence of a marine connection.

The Dardanelles region has formed a key gateway connecting the Paratethys and the Aegean/Mediterranean since the late Miocene. Its sedimentary sequences contain crucial information about connectivity, but so far lack unambiguous age constraints. Here, we apply an integrated stratigraphic approach and use the recently established chronostratigraphy for the Eastern Paratethys to re-evaluate the faunal assemblages and paleoenvironments of the Seddülbahir and İntepe sections that allegedly played a crucial role in the geodynamic evolution of the Dardanelles during the Messinian. The Paratethyan ostracods and mollusks, however, clearly indicate that these sections correspond to the middle Tortonian. Nannofossil assemblages are dominated by a mixing of reworked taxa from the late Eocene and Oligocene and no age diagnostic taxa have been observed. Dinoflagellate analyses are also hampered by reworking and mainly reveal non-marine (fresh to oligohaline) aquatic conditions. Fossil mammal remains in the Seddülbahir section confirm the presence of terrestrial intervals. Strontium (⁸⁷Sr/⁸⁶Sr) isotope data of the anomalohaline ostracods are significantly below open ocean values, and similar to values obtained from Khersonian ostracods of Bulgaria. Fresh water assemblages reveal much higher ⁸⁷Sr/⁸⁶Sr values, which are interpreted to reflect the composition of local rivers. We conclude that in late Miocene times the Dardanelles region was a fresh to anomalohaline embayment, ephemerally connected to the Eastern Paratethys. We found no evidence for a major Messinian erosional surface nor for marine fossils indicative of the early Zanclean as has been postulated elsewhere.

Landlocked basins like the Caspian Sea are highly sensitive to changes in their hydrological budget, especially at times of disconnection from the global oceans. Here we reconstruct hydrological and environmental changes in the Caspian Sea basin, using compound-specific hydrogen isotope (δ²H) data on excellently preserved long chain n-alkanes and alkenones. Additionally, the reconstructed mean annual air temperature (MAT) data and the source of the organic matter based on the relative distribution of branched and isoprenoid glycerol dialkyl glycerol tetraethers (BIT). These biomarkers were extracted from Pliocene to Pleistocene successions, including the Productive Series, Akchagylian and Apsheronian (as in the regional Caspian Basin nomenclature). Terrestrial plant wax long chain n-alkanes δ²Hvalues reflect continental hydrological changes in the region surrounding the Caspian Sea. δ²Hvalues of long chain alkenones, in contrast, are derived from haptophyte algae within the basin water column and typically reflect changes in δ²H of Caspian Sea water. The δ²H valuesof the terrestrial long chain n-alkanes show a variation of 55‰ from as high as -142 ‰ at the base of the sampled section (at ~ 3.55 Ma) to as low as -175 ‰, in the youngest part (at ~ 2.1 Ma). The change towards constant δ²H_n-alkane values around -179 ‰ appears to be correlated with the occurrence of alkenones with δ²H values of around -190 ‰ in the sampled section suggesting a newly installed connection of the Caspian Sea with a marine basin at that time, most likely the Black Sea. The newly established connection permitted the influx of Black Sea endemic biota into the newly occupied basin around Akchagylian/Apsheronian boundary, at ~2.13 Ma. New MAT and BIT data show that, prior to this Black Sea connection, the so-called Akchagylian transgression at 2.6±0.1 Ma marked by influx of marine biota into the Caspian Basin, originated a cold region of the open ocean, namely the Arctic domain.

The Caspian Sea, the largest isolated basin worldwide, experienced substantial lake-levels fluctuations throughout the Quaternary, driving major landscape evolution and faunal turnover events. Understanding the external forcing mechanisms of the Caspian Sea lake-level variability is of great importance as it provides valuable information regarding changes in interbasinal connectivity and large-scale regional climatic changes over the Eurasian continental interior. Yet the mechanistic pathways of these external forcing factors are not well constrained. This study proposes an integrated sedimentological-isotopic-faunal-climate modelling approach in order to unravel the drivers of lake-level, isotopic and biotic changes occurring in the Caspian Sea during the Early Pleistocene Apsheronian regional stage. The Caspian Sea records frequent lake-level highstands covalent with heavier stable oxygen and carbon isotope ratios with in some cases the appearance of marine foraminifera. These highstands repeatedly alternate with lake-level lowstands characterized by lighter stable oxygen and carbon isotope ratios and the disappearance of marine foraminifera. Although these changes might independently be explained by climatic conditions modelled over the catchment area of the Caspian Sea throughout the obliquity and precession cycles, their synchronicity points towards episodic connections between the Caspian Sea and an adjacent marine basin, likely the Black Sea. These findings provide unprecedented insights into the Caspian Sea and Black Sea evolution and offer large ramifications for understanding their faunal development during the Quaternary.