Larisa Golovina

Abstract Various hypotheses exist on the age and origin of the so-called “Pebbly Breccia” unit in the deep-sea record of DSDP Hole 380A of the Euxinian (Black Sea) Basin. Here, we present a detailed study of diatom and nannofossil assemblages of Hole 380A. Our diatom records show a characteristic sequence of appearance of markers species, which we can correlate to the recently established bio-magnetostratigraphic time frame of the Zheleznyi Rog section on the Black Sea coast of the Taman Peninsula (Russia). It shows that the Pebbly Breccia is sandwiched between Upper Maeotian deposits, and must have been deposited at an age between 6.7 and 6.3 Ma. The appearance of nannoplankton and the marine diatom association at above the Pebbly breccia (Unit IVc) suggests a short-term incursion of marine conditions. The age of Unit IVc, based on diatom data, is 6.3–6.1 Ma. The nannoplankton record is mainly represented by species that do not have stratigraphic value. The previously reported presence of Ceratolithus acutus in the Black Sea is explained by misinterpretation of destructed elements of ascidian spicules. We conclude that the Pebbly Breccia is not related to a desiccated Black Sea at Messinian Salinity Crisis times, but it corresponds to a late Maeotian episode of gravitational instability in the SW Black Sea region.

Abstract The Black Sea and Caspian Sea are the present-day remnants of a much larger epicontinental sea on the Eurasian continental interior, the Paratethys. During the late Miocene Messinian Salinity Crisis (MSC), a unique oceanographic event where 10% of the salt in the world's ocean got deposited in the deep desiccated basins of the Mediterranean, the Paratethys Sea was connected to the Mediterranean Sea. Unlike the Mediterranean, no salt is known to have been deposited in the Paratethys region at this time, yet a similar mechanism of deep desiccation (with a water level drop of up to 2 km occurring at 5.6 Ma) has been proposed in the past to explain the late Miocene and Pliocene Paratethys basin evolution. Here, we review the basin evolution, stratigraphy and subsurface data of the four main Paratethyan sub-basins to investigate the response to the Mediterranean Messinian event. We show that hypotheses of a Paratethys-wide desiccation synchronous to the Messinian Salinity Crisis climax at 5.6 Ma do not hold. Determinations of the magnitude of the sea level drop appear to have regularly been overestimated by speculative basin-to-margin interpretations, and often been disproven by increased age model resolution. In the Euxinian (Black Sea) Basin, the most recent estimates for the magnitude of sea level drop vary between 50 and 500 m, yet the timing is debated. Marginal outcrops in the Dacian Basin highlight multiple switches from shallow basinal to littoral and fluvial environments during the MSC interval, but no major water level drop coincides with the 5.6 Ma event. The Paleo-Danube deposits filling in the Pannonian Basin do not indicate any influence by the MSC and show prograding patterns into the deepwater lake Pannon. The dramatic expansion of the Paleo-Volga delta in the Caspian Sea is shown to be younger than the MSC, while estimates of the amount of water level drop vary widely due to the poorly understood contribution of tectonic processes. These changing perspectives and decreasing estimates of water level lowering are not surprising given the vast northern drainage of the Paratethys region. Precipitation and runoff from the Eurasian continent ensures a much more positive hydrological budget under isolated conditions than the vast negative hydrological budget of the Mediterranean Sea which requires constant compensation by inflowing oceanic waters.

Abstract Marine gateways prove to be important factors for changes in the ecology and biochemistry of marginal seas. Changes in gateway configuration played a dominant role in the Middle Miocene paleogeographic evolution of the Paratethys Sea that covered Central Eurasia. Here, we focus on the connection between the Central (CP) and Eastern Paratethys (EP) to understand the paleoenvironmental changes caused by the evolution of this marine gateway. We first construct an integrated magneto-biostratigraphic framework for the late Langhian-Serravallian (Chokrakian-Karaganian-Konkian-Volhynian) sedimentary record of the eastern domain, which allows a correlation to the well-dated successions west of the gateway. The magneto-biostratigraphic results from the Zelensky-Panagia section on the Black Sea coast of Russia show that the Chokrakian/Karaganian boundary has an age of 13.8 Ma, the Karaganian/Konkian boundary is dated at 13.4 Ma, and the Konkian/Volhynian boundary at 12.65 Ma. We identify three major phases on gateway functioning that are reflected in specific environmental changes. During the Karaganian, the EP turned into a lake-sea that supplied a unidirectional flow of low-salinity waters to the west, where the CP sea experienced its Badenian Salinity Crisis. This configuration is remarkably similar to the Mediterranean during its Messinian Salinity Crisis. The second phase is marked by a marine transgression from the west, reinstalling open-marine conditions in the CP and causing marine incursions in the EP during the Konkian. The Volhynian is characterized by a new gateway configuration that allows exchange between CP and EP, creating unified conditions all over the Paratethys. We hypothesize that a density driven pumping mechanism is triggered by the increase in connectivity at the Konkian/Volhynian boundary, which simultaneously caused major paleoenvironmental changes at both sides of the gateway and led to the Badenian-Sarmatian extinction event in the CP.

Objective utilization of data from DSDP Site 380 (Black Sea) Speranta-Maria Popescu, Mihaela Carmen Melinte-Dobrinescu and Jean-Pierre Suc GeoBioStratData.Consulting, 385 Route du Mas Rillier, Rillieux la Pape 69140, France; National Institute of Marine Geology and GeoEcology, 23-25 Dimitrie Onciul Street, Bucharest 70318, Romania; Sorbonne Universit es, UPMC Universit e Paris 06, CNRS, Institut des Sciences de la Terre Paris, Paris F-75005, France

The initially obtained data characterize organic-walled phytoplankton (dinocysts), nannoplankton, spores, and pollen from the Upper Argun, Alkun, and Lower Assa deposits of the Fiagdon and Mairamadag sections situated on the southeast of North Ossetia (North Caucasus) in the Alkun Formation stratotype area. The lithology of the formation is described, and its position in the Oligocene-Miocene succession is considered. According to the analyzed data on organic-walled phytoplankton from the Fiagdon and Mairamadag sections, the transitional late Oligocene-early Miocene dinoflora from the top of the Argun Formation and the lower part of the Alkun Formation is in general of the Miocene aspect. Based on the dinocysts, deposits from the upper part of the Alkun Formation coupled with the Assa Formation are attributed to the lower Miocene. The entire interval of the studied deposits corresponds to the acme subzone Def of the Ebu Zone in the Mediterranean dinocyst zonation by D. Zevenboom, where it spans the top of the Chattian and lower part of the Aquitanian Stage. Nannoplankton assemblages from the Alkun deposits are tentatively correlated with the nannoplankton assemblage of Zone NN1 in the standard zonation by E. Martini. It is impossible to date precisely the Alkun Formation based on nannoplankton, as the respective deposits are lacking index species and characteristic taxa of the standard zonation. The dominance of the cosmopolitan species Cyclicargolithus floridanus is a peculiar feature of nannoplankton assemblages from the Alkun Formation. Palynological data are used to consider the dynamics of the evolution of the vegetation cover and climate. Four episodes of relative cooling are distinguished against a background of warm-temperate climatic conditions in general. The most significant episodes occurred in the mid-Alkun time and during the early phase of the Assa time.

The stratigraphy of the Taman Peninsula is defined using the sections at Zelensky Hill—Panagia, Popov Kamen, Taman and Zheleznyi Rog. The stratigraphy is constructed from distribution of mollusks, foraminifers, nannofossils, diatoms, and organic-walled ...

The problems related to age of the lower part of the Caucasian regional stage (Alkun Formation) and Paleogene-Neogene boundary in the North Caucasus and Ciscaucasia are discussed with analysis and generalization of the data on nannoplankton and dinocyst assemblages from Alkun sediments in their different areas. The new data obtained from the section of the Alkun Formation in the stratotypical area of the Caucasian regional stage (valley of the Kuban River middle reaches, Karamurzinskii village), including finds of the index species Triquetrorhabdulus carinatus and typical species of the zonal nannoplankton assemblage, confirm the belonging of Alkun sediments to Zone NN1. The composition and peculiar features of the Karamurzinskii nannoflora and dinocyst assemblages indicate their Neogene age. It is established that the Alkun sediments in the Kuban, North Ossetia, and Belorechensk areas are characterized by similar nannoplankton and dinocyst assemblages, which implies their synchronism in these localities. The dinocyst assemblages from the Alkun Formation exhibit significant similarity with their counterparts from the uppermost part of the “lower Krosno Subformation” and lower part of the “upper Menilite Subformation” of the Ukrainian Carpathians and from lower layers of the “Chernobaevka Formation” of the northern Black Sea region. The analysis of available data reveals that the Paleogene-Neogene boundary in the North Caucasus and Ciscaucasia corresponds to a narrow interval spanning from the upper layers of the Batalpasha Formation and its analogs to the lower layers of the Alkun Formation. Thus, it is shown that the Caucasian regional stage belongs practically in its entire volume, probably except for its basal layers, the age of which needs to be specified, to the lower Miocene. New data on hydrology and bionomy of the basin, vegetation, and climate of the Alkunian time are also considered.