Changing sediment supply during glacial-interglacial intervals in the North Atlantic revealed by particle size characterization and environmental magnetism

The Pliocene-Pleistocene transition is characterized by an abundance of Ice-Rafted Debris (IRD) in the North Atlantic basin. One of the regions affected by IRD during this period is the Gardar Drift, where the DSDP Leg 94 Hole 611A is located. This region received sediments from different sources during the glacial and interglacial intervals (e.g., Iceland and Greenland). We analyzed grain size and particle-size specific magnetic properties of sediments for their provenance characterization between ∼2.64 and 2.52 Ma. Our results show that major proportion of bulk sediments during both glacial and interglacial periods were made up of basaltic-rich Icelandic sediments, whereas only during intense glacial periods (Marine Isotope Stages 100 and 104), a small proportion of non-basaltic sand compositions were identified, possibly sourced from Greenland and other non-basaltic provenance. The non-basaltic sand fractions during the intense glacial periods were likely supplied as IRDs. In addition, a new level of coarse lithics (38 pcs. of >1 mm) composed of different rocks types (e.g., basalt, granite, granodiorite etc.) were identified in DSDP 611A Hole during the end of MIS 104 glacial period. The coarse lithic fragments showed distinctive magnetic properties than rest of the particle sizes and were classified as Iceberg-Rafted Debris (IBRD). Overall, our results show that higher sand percentage was found during the intense glacial episodes, and their magnetic grain size analysis could help in distinguishing their provenance. We elaborate that particle size specific magnetic measurements of sand fractions could help in rapidly characterizing the glacial episodes in the subpolar North Atlantic

The dire straits of Paratethys: gateways to the anoxic giant of Eurasia

A complex interplay of palaeoclimatic, eustatic and tectonic processes led to fragmentation and dis-sipation of the vast Tethys Ocean in Eocene–Oligocene times. The resulting Paratethys Sea occupied the northern Tethys region on Eurasia, grouping water masses of various sub-basins, separated from each other and from the open ocean through narrow and shallow gateways and land bridges. Changes in marine gateway configu-ration and internal connectivity affected regional hydrology, shifting most Paratethyan basins to extreme car-bon-sink anoxic environments, anomalohaline evaporitic or brackish conditions, or even endorheic lakes. Paratethys gateway restriction triggered the onset of a long-lasting (c. 20 myr) giant anoxic sea, characterized by stratified water masses and anoxic bottom-water conditions, resulting in thick hydrocarbon source rocks. Here, we review the geological evolution of the ‘dire straits’ of Paratethys that played a crucial role in the Eocene–Oligocene connectivity history of the Central Eurasian seas and we show that the main anoxic phases (Kuma and Maikop) correspond to restricted connectivity with the global ocean and a period of CO2 depletion in the atmosphere. Paratethys represents one of the largest carbon sinks in Earth’s history and may thus have played a prominent role in global climate change

Changing seas in the Early-Middle Miocene of Central Europe : a Mediterranean approach to Paratethyan stratigraphy

The Miocene palaeogeographic evolution of the Paratethys Sea is still poorly constrained. Here, we use modern Mediterranean biochronology to provide an up-to-date overview of changing seas in Central Europe. Instead of a Paratethys that waxed and waned with fluctuating global sea levels, we show that the development of different seas was mainly controlled by tectonic phases. The Early Miocene “Ottnangian Sea” (~18 Ma) was connected to the Mediterranean via the Rhône valley, while the “Karpatian Sea” (~16.5 Ma) was initiated by a tectonically induced marine transgression through the Trans-Tethyan gateway. In most Central European basins, the establishment of the “Badenian Sea” (<15.2 Ma), triggered by subduction-related processes in the Pannonian and Carpathian domain, is significantly younger (by ~1 Myr) than usually estimated. The updated palaeogeographic reconstructions provide a better understanding of the concepts of basin dynamics, land–sea distribution and palaeoenvironmental change in the Miocene of Central Europe

Changing seas in the Early-Middle Miocene of Central Europe : a Mediterranean approach to Paratethyan stratigraphy

The Miocene palaeogeographic evolution of the Paratethys Sea is still poorly constrained. Here, we use modern Mediterranean biochronology to provide an up-to-date overview of changing seas in Central Europe. Instead of a Paratethys that waxed and waned with fluctuating global sea levels, we show that the development of different seas was mainly controlled by tectonic phases. The Early Miocene “Ottnangian Sea” (~18 Ma) was connected to the Mediterranean via the Rhône valley, while the “Karpatian Sea” (~16.5 Ma) was initiated by a tectonically induced marine transgression through the Trans-Tethyan gateway. In most Central European basins, the establishment of the “Badenian Sea” (<15.2 Ma), triggered by subduction-related processes in the Pannonian and Carpathian domain, is significantly younger (by ~1 Myr) than usually estimated. The updated palaeogeographic reconstructions provide a better understanding of the concepts of basin dynamics, land–sea distribution and palaeoenvironmental change in the Miocene of Central Europe

Changing seas in the late Miocene Northern Aegean: A Paratethyan approach to Mediterranean basin evolution

The Northern Aegean region evolved during the Miocene as a restricted land-locked basin with small ephemeral connections to both the Eastern Paratethys (former Black Sea) and Mediterranean. Its biostratigraphic data show mixed Paratethys-Mediterranean components, but the Paratethys 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 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, indicate a middle Messinian (late 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 palaeoenvironmental 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 domain do not reflect the classic Mediterranean MSC sequences, but are more likely related to older (Badenian or Maeotian) salinity incursions

Changing seas in the late Miocene Northern Aegean: A Paratethyan approach to Mediterranean basin evolution

The Northern Aegean region evolved during the Miocene as a restricted land-locked basin with small ephemeral connections to both the Eastern Paratethys (former Black Sea) and Mediterranean. Its biostratigraphic data show mixed Paratethys-Mediterranean components, but the Paratethys 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 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, indicate a middle Messinian (late 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 palaeoenvironmental 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 domain do not reflect the classic Mediterranean MSC sequences, but are more likely related to older (Badenian or Maeotian) salinity incursions

The Badenian-Sarmatian Extinction Event in the Carpathian foredeep basin of Romania : Paleogeographic changes in the Paratethys domain

The Badenian-Sarmatian boundary interval is marked by a major extinction event of marine species in the Central Paratethys. The exact age of the boundary is debated because many successions in marginal basins show erosional features and fauna reworking at the boundary level. Here, we selected the Tisa section in the Carpathian foredeep basin of Romania, which is continuous across this Badenian-Sarmatian Extinction Event (BSEE). Quantitative biostratigraphic records of planktic and benthic foraminifera and calcareous nannofossils allow to accurately locate the Badenian-Sarmatian boundary and indicate a major paleoenvironmental change from open marine to brackish water conditions. Magnetostratigraphic results reveal a polarity pattern that uniquely correlates to the time interval between 12.8 and 12.2. Ma. Interpolation of constant sedimentation rates determines the age of the BSEE in the Carpathian foredeep at 12.65. ±. 0.01. Ma, in good agreement with several earlier estimates. We conclude that the extinction event took place in less than 10. kyr, and that it was most likely synchronous across the Central Paratethys. It corresponds to a major paleogeographic change in basin connectivity with the Eastern Paratethys, during which the nature of the Barlad gateway switched from a passive to a full connection

A greigite-based magnetostratigraphic time frame for the Late Miocene to recent DSDP Leg 42B Cores from the Black Sea

Throughout the Late Neogene, the Black Sea experienced large paleoenvironmental changes, switching between (anoxic) marine conditions when connected to the Mediterranean Sea and (oxic) freshwater conditions at times of isolation. We create a magnetostratigraphic time frame for three sites drilled during Deep Sea Drilling Project (DSDP) Leg 42B to the Black Sea (drilled in 1975). At the time, magnetostratigraphic dating was impossible because of the presence of the little understood iron sulfide mineral greigite (in sediments a precursor to pyrite) as magnetic carrier. Our rock-magnetic results indicate that only anoxic conditions result in poor magnetic signal, likely as a result of pyrite formation in the water column rather than in the sediment. The magnetostratigraphic results indicate that Hole 379A, drilled in the basin center, has a continuous sedimentary record dating back to 1.3 Ma. Hole 380/380A is subdivided into three consistent intervals, 0–700 mbsf, 700–860 mbsf, and 860–1075 mbsf. The top unit covers the Pleistocene but the magnetostratigraphy is likely compromised by the presence of mass transport deposits. The middle unit spans between 4.3 and 6.1 Ma and records continuous deposition at ∼10 cm/kyr. The lower unit lacks the independent age constraints to correlate the obtained magnetostratigraphy. Hole 381 is drilled on the Bosporus slope and as a result, hiatuses are common. A correlation to the nearby Hole 380/380A is proposed, but indicates deposits cannot straightforwardly be traced across the slope. Our improved age model does not support the original interpretation based on these cores of a desiccation of the Black Sea during the Messinian salinity crisis

A greigite-based magnetostratigraphic time frame for the Late Miocene to recent DSDP Leg 42B Cores from the Black Sea

Throughout the Late Neogene, the Black Sea experienced large paleoenvironmental changes, switching between (anoxic) marine conditions when connected to the Mediterranean Sea and (oxic) freshwater conditions at times of isolation. We create a magnetostratigraphic time frame for three sites drilled during Deep Sea Drilling Project (DSDP) Leg 42B to the Black Sea (drilled in 1975). At the time, magnetostratigraphic dating was impossible because of the presence of the little understood iron sulfide mineral greigite (in sediments a precursor to pyrite) as magnetic carrier. Our rock-magnetic results indicate that only anoxic conditions result in poor magnetic signal, likely as a result of pyrite formation in the water column rather than in the sediment. The magnetostratigraphic results indicate that Hole 379A, drilled in the basin center, has a continuous sedimentary record dating back to 1.3 Ma. Hole 380/380A is subdivided into three consistent intervals, 0–700 mbsf, 700–860 mbsf, and 860–1075 mbsf. The top unit covers the Pleistocene but the magnetostratigraphy is likely compromised by the presence of mass transport deposits. The middle unit spans between 4.3 and 6.1 Ma and records continuous deposition at ∼10 cm/kyr. The lower unit lacks the independent age constraints to correlate the obtained magnetostratigraphy. Hole 381 is drilled on the Bosporus slope and as a result, hiatuses are common. A correlation to the nearby Hole 380/380A is proposed, but indicates deposits cannot straightforwardly be traced across the slope. Our improved age model does not support the original interpretation based on these cores of a desiccation of the Black Sea during the Messinian salinity crisis

Severe late Miocene droughts affected western Eurasia

A large and highly dynamic aquatic system called Paratethys governed important elements of the middle and late Miocene (15.97–5.33 Ma) hydrology in western Eurasia. So far, the impact of the vast Paratethys water body on the Eurasian climate, however, is not yet understood. Here we apply biomarker analyses coupled to compound-specific hydrogen and carbon isotope data to track changes in sea surface temperature, mean annual air temperature, hydrological budget and vegetation changes to reconstruct long-term western Eurasian climate conditions between 12.7 and 7.65 Ma in the Black Sea region. Biomarker data from Panagia (Russia) indicate the presence of three exceptionally evaporative intervals peaking at 9.65, 9.4 and 7.9 Ma. These peaks in evaporation relate to aridity, parallel increasing fire activity and are associated with changes in vegetation. Carbon isotope and pollen data support the evidence of an increase in C4 plants associated with these dry intervals. At 9.66 Ma, alkenone producing algae appear in the basin and thrive for the subsequent two million years. Cumulative fluctuations in both hydrology and surface temperature of Paratethys might have enhanced rainfall seasonality in western Eurasia as a response to changes in evaporation over the Paratethys basin. Our combined data suggest a strong regional imprint on overall climate patterns, dominated by basin dynamics causing Paratethys volume and surface reduction. Collectively, the presented biomarker results provide evidence of severe droughts affecting the late Miocene circum-Paratethys region, leading to a direct impact on the evolution of biota in the basin and its surroundings