A Paleogeographic Model of a Cenomanian–Turonian Anoxic Event in Central and East Black Sea Regionsстатья

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[1] Badulina N. V., Gabdullin R. R., Kopaevich L. F. A paleogeographic model of a cenomanian–turonian anoxic event in central and east black sea regions // Moscow University Geology Bulletin. — 2009. — Vol. 64, no. 6. — P. 337–345. The paper presents the sedimentological and geochemical characteristics of the Cenomanian– Turonian oceanic anoxic event (OAE2) based on eight sections in the Central and East Black Sea Regions.A series of paleogeographic models of the OAE2 is suggested based on Crimean and Caucasian sections. A sedimentological investigation of rocks in Crimean sections revealed a tendency toward a decrease in the calcium carbonate concentration up the section up to the bituminous interlayer where (in the AksuDere section) two peaks of organic carbon concentration were detected. Sections in the North west Caucasus show evidence of turbidite sedimenta tion on the slope and floor of the deepsea trough and influence of a local volcanic center and the Pontian–Transcaucasian volcanoplutonic belt. Geochemical investigations showed that kerogen of types II and III is preponderant in rocks from the OAE2 interval and that Corg concentrations increased at the expense of its greater supply from continent. The rocks found above and below the black interlayer accumulated in an oxic environment, while sediments accumulated during the OAE2 event under conditions of hydrogen sulfide contamination and warmernearsurface water (data of isotope geochemistry). The sedimentation rate slowed during the OAE2 event and varied from 0.403 (AksuDere Ravine) to 1.36 (Mt Belaya) cm/ka and later increased again. The sedimentation rate was minimal in the AksuDere section with a maximum concentration of organic matter. The accumulation rate of late Cenomanian sediments in the Gamburtsev2 well was higher by an order of magnitude than in the Crimea, while that in the Caucasus was close to the rate in Crimean sections. The sedimentation rate in the trough increased during the early Turonian. The accumulation of organicrich black interlayers in the Crimea took place during a shortterm regression in the basin approximately 500 m deep and a sea level decline by 50 m, which was accompanied by the formation of smallscale normal faults. Locally, the conditions of hydrogen sulfide contamination gave place to oxic environment with intensification of hydrodynamic processes and occurrence of microupwellings. Similar events took place during OAE2 on the slope and floor of the deepsea trough in the Northwest Caucasus, possibly when the carbonate compensation level declined under conditions of a shortterm regression. Organicrich sediments accu mulated above, and even below, this level. [ DOI ]

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