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

Abstract

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.