Quaternary time scales for the Pontocaspian domain: interbasinal connectivity and faunal evolution

The Pontocaspian (Black Sea - Caspian Sea) region has a very dynamic history of basin development and biotic evolution. The region is the remnant of a once vast Paratethys Sea. It contains some of the best Eurasian geological records of tectonic, climatic and paleoenvironmental change. The Pliocene-Quaternary co-evolution of the Black Sea-Caspian Sea is dominated by major changes in water (lake and sea) levels resulting in a pulsating system of connected and isolated basins. Understanding the history of the region, including the drivers of lake level and faunal evolution, is hampered by indistinct stratigraphic nomenclature and contradicting time constraints for regional sedimentary successions. In this paper we review and update the late Pliocene to Quaternary stratigraphic framework of the Pontocaspian domain, focusing on the Black Sea Basin, Caspian Basin, Marmara Sea and the terrestrial environments surrounding these large, mostly endorheic lake-sea systems

Mediterranean-Paratethys connectivity during the late Miocene to Recent : Unraveling geodynamic and paleoclimatic causes of sea-level change

The Black Sea and Caspian Sea are the present-day remnants of the former Paratethys, a large epicontinental sea that spanned large parts of continental Eurasia. Hydrological interactions between these seas in the Eurasian continental interior and with adjacent seas (e.g. Mediterranean Sea) are determined by the hydrological budget and connectivity through shallow marine gateways. The high sensitivity of these seas to changes in the hydrological budget has resulted in a very dynamic sea-level history. This has resulted in frequent changes in salinity and especially in the Caspian Sea, large variations in surface area. However, a process-based understanding of forcing mechanisms and environmental impacts of these major sea-level variations is severely hampered by a lack of high-resolution age constraints. We use high-resolution geochronology together with integrated stratigraphy and paleomagnetism to unravel the internal (geodynamics, tectonic uplift, basin infill) from external (climate, glacio-eustatic sea-level change) forcing factors. In this thesis, we will extend and refine the chronostratigraphic framework of the Eastern Paratethys region for the last 6 Myrs in order to better constrain the main connectivity changes in the Mediterranean-Paratethys region. The study can be divided into two parts. Part one focuses on the Plio-Pleistocene evolution of the Paratethys and on the impact of the change from global warm conditions in the Pliocene to global cold conditions in the Pleistocene. High global sea levels during the warmest moment of the Pliocene, the Mid-Pliocene Warm Period (MPWP) resulted in a rise of the sea level in the Black Sea which flooded the at that time freshwater Dacian Basin. The onset of glaciations on the northern hemisphere changed the hydrological setting of the Paratethys region. Large sources of fresh water were introduced on the northern margin of continental Eurasia. Part of the water that became available while melting these ice sheets was directed southwards into the Paratethys region and through the Paratethys outflow into the Mediterranean Sea. The second part of this thesis focuses on the late Miocene to Pliocene of the Paratethys, with the main focus on the Pontian regional stage, the time equivalent of the Messinian salinity crisis (MSC). The MSC (5.97-5.33 Ma) is an outstanding paleoceanographical event, known for the massive deposition of gypsum and salt throughout the Mediterranean Sea. Prior to the MSC, a connection is formed between the Mediterranean Sea and the Paratethys, including the Caspian Sea. Therefore, the Pontian phase of connectivity represents the maximum size of Paratethys at a time of minimum Atlantic-Mediterranean connectivity. The Caspian Sea became an isolated lake during the MSC and during the Pliocene large volumes of sediment were deposited, determined by large variations in the surface area of the Caspian Sea. These deposits form the main oil-reservoirs of the South Caspian Basin and using magnetostratigraphy we provide an improved age model

Quantitative analysis of Paratethys sea level change during the Messinian Salinity Crisis

At the time of the Messinian Salinity Crisis in the Mediterranean Sea (i.e., the Pontian stage of the Paratethys), the Paratethys sea level dropped also. Evidence found in the sedimentary record of the Black Sea and the Caspian Sea has been interpreted to indicate that a sea level fall occurred between 5.6 and 5.5 Ma. Estimates for the magnitude of this fall range between tens of meters to more than 1500 m. The purpose of this study is to provide quantitative insight into the sensitivity of the water level of the Black Sea and the Caspian Sea to the hydrologic budget, for a scenario in which the Paratethys is disconnected from the Mediterranean. Using a Late Miocene bathymetry based on a palaeographic map we quantify the fall in sea level, the mean salinity, and the time to reach equilibrium for a wide range of negative hydrologic budgets. By combining our results with (i) estimates calculated from a set of recent global Late Miocene climate simulations and (ii) reconstructed basin salinities, we are able to rule out a drop in sea level of the order of 1000 m in the Caspian Sea during this time period. In the Black Sea, however, such a large sea level fall cannot be fully discarded

A magnetostratigraphic time frame for Plio-Pleistocene transgressions in the South Caspian Basin, Azerbaijan

The isolation of the Caspian Sea took place in the latest Miocene coinciding with a significant lowering of sea level and the deposition of a massive lowstand deltaic system. This so-called Productive Series is the main reservoir unit of the SouthCaspian oil-province. The Productive Series is overlain by marine clays from the Akchagylian and Apsheronian regional stages. During the Plio-Pleistocene, the Caspianbasin experienced several short periods of intermittent connectivity with other marine basins. This work aims to create integrated, high-resolution, bio-magnetostratigraphic dating of these regional transgressions in key sections of the SouthCaspianBasin in Azerbaijan. We sample two long sections, the Lokbatan section in the Palaeo-Volga delta and the Xocashen section in the Kura Basin. Palaeoenvironmental reconstructions are derived from characteristic ostracod species. Rock magnetic analyses combined with thermal demagnetisation data indicate that the magnetic signal is carried dominantly by the iron oxide magnetite in the Productive Series of Lokbatan section and in the Xocashen section. The marine Akchagylian and Apsheronian of Lokbatan are characterised by the iron sulphide greigite, which appears to be of (near-) primary origin. The most logical correlation of the magnetic polarity patterns to the Geomagnetic Polarity Time Scale dates the Akchagylian transgression at ~ 3.2 Ma, a major transgression during the Apsheronian at ~ 2.0 Ma and the Bakunian transgression at 0.85–0.89 Ma. Ostracod assemblages indicate increasing salinities during these transgressions, from fresh water lacustrine to brackish-marine species. This implies that marine connections have been created with an adjacent basin that has a higher salinity, most likely the Black Se

NEW GEOCHEMICAL INSIGHTS INTO CENOZOIC SOURCE ROCKS IN AZERBAIJAN: IMPLICATIONS FOR PETROLEUM SYSTEMS IN THE SOUTH CASPIAN REGION

The Maikop Group and the Diatom Formation constitute the two main source rocks in the South Caspian Basin and onshore Azerbaijan where large-scale oil production began more than 150 years ago. However, the stratigraphic distribution of the source rocks and the vertical variation of source-rock parameters are still poorly understood. The aim of the present paper is therefore to investigate in high resolution the source-rock distribution in the Perekishkyul and Islamdag outcrop sections, located 25 km NW of Baku, which provide nearly complete middle Eocene and lower Oligocene to upper Miocene successions. Bulk geochemical parameters of 376 samples together with maceral, biomarker and isotope data were analysed. In addition, new Re/Os data provide independent age dating for the base of the Upper Maikop Formation (30.0 ± 1.0 Ma) and the paper shale within the Diatom Formation (7.2 ± 2.6 Ma). The presence of steradienes in high concentrations demonstrates the thermal immaturity of the studied successions, limiting the application of some biomarker ratios. Intervals with high TOC contents and containing kerogen Type II occur near the top of the middle Eocene succession. However, because of the low net thickness, these sediments are not considered to constitute significant hydrocarbon (HC) source rocks. The Maikop Group in the Islamdag section is 364 m thick and represents lower Oligocene (upper Solenovian) to middle Miocene (Kozakhurian) levels. Samples are characterized by moderately high TOC contents (∼1.8 wt.%) but low hydrogen index (HI) values (average ∼120 mgHC/gTOC) despite a dominance of aquatic organic matter (diatoms, methanotrophic archaea and sulphate-reducing bacteria). Rhenium-osmium chronology suggests low sedimentation rates (∼25 m/Ma), which may have had a negative impact on organic matter preservation. Terrigenous organic matter occurs in variable but typically low amounts. If mature, the Maikop Group sediments at Islamdag could generate about 2.5 tHC/m2. The Diatom Formation includes a 60 m thick paper shale interval with high TOC contents (average 4.35 wt.%) of kerogen Type II-I (HI up to 770 mgHC/gTOC). The source potential is higher (∼3 tHC/m2) than that of the Maikop Group. The organic matter is dominated by algal material including diatoms. High TOC/S ratios suggest deposition under reduced salinity conditions. Strictly anoxic conditions are indicated by the presence of biomarkers for archaea involved in methane cycling. For oil-source correlations and a better understanding of the petroleum system, it will be necessary to distinguish oil generated by the Maikop Group from that generated by the Diatom Formation. This study shows that these oils can be distinguished based on the distribution of specific biomarkers e.g. C30 steranes, C25 highly branched isoprenoids (HBIs), and the C25 isoprenoid pentamethylicosane (PMI)

Magneto-biostratigraphic age constraints on the palaeoenvironmental evolution of the South Caspian basin during the Early-Middle Pleistocene (Kura basin, Azerbaijan)

The sedimentary record of the Caspian Basin is an exceptional archive for the palaeoenvironmental, palaeoclimatic and biodiversity changes of continental Eurasia. During the Pliocene-Pleistocene, the Caspian Basin was mostly isolated but experienced large lake level fluctuations and short episodes of connection with the open ocean as well as the Black Sea Basin. A series of turnover events shaped a faunal record that forms the backbone of the Caspian geological time scale. The precise ages of these events are still highly debated, mostly due to the lack of well-dated sections. Here, we provide an integrated magneto-biostratigraphic age model for two sections from the Kura Basin e Goychay and Hajigabul. Our results reveal several major intervals with elevated salinity, associated with mesohaline faunas, and propose the following age constraints: 1) The Productive Series-Akchagylian boundary is marked by a marine transgression from the open ocean that occurred around the Gauss-Matuyama reversal (~2.7e2.6 Ma); 2) The Akchagylian-Apsheronian transition is characterized by a regression event and introduction of a new, “Pontocaspian” mollusc assemblage, dated within the Reunion subchron (~2.13 Ma). The ostracod assemblages of the two sections do not show a major faunal turnover here; 3) The early Bakunian transgression occurs after the upper Apsheronian lowstand (0.85e0.83 Ma). We conclude that major transitions in the age-indicative mollusc groups sometimes occur at different time intervals (i.e. diachronic) and are highly depended on the local depositional environments. A highresolution interdisciplinary approach on sections outside the Kura Basin is required to better understand the potential diachroneity of these turnover events in the entire Caspian Basin

Paratethys pacing of the Messinian Salinity Crisis: Low salinity waters contributing to gypsum precipitation?

During the so-called Messinian Salinity Crisis (MSC: 5.97-5.33 Myr ago), reduced exchange with the Atlantic Ocean caused the Mediterranean to develop into a “saline giant” wherein ∼1 million km3 of evaporites (gypsum and halite) were deposited. Despite decades of research it is still poorly understood exactly how and where in the water column these evaporites formed. Gypsum formation commonly requires enhanced dry conditions (evaporation exceeding precipitation), but recent studies also suggested major freshwater inputs into the Mediterranean during MSC-gypsum formation. Here we use strontium isotope ratios of ostracods to show that low-saline water from the Paratethys Seas actually contributed to the precipitation of Mediterranean evaporites. This apparent paradox urges for an alternative mechanism underlying gypsum precipitation. We propose that Paratethys inflow would enhance stratification in the Mediterranean and result in a low-salinity surface-water layer with high Ca/Cl and SO4/Cl ratios. We show that evaporation of this surface water can become saturated in gypsum at a salinity of ∼40, in line with salinities reported from fluid inclusions in MSC evaporites