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Middle-Late Volgian regression as it expressed in different depositional environments of Central Russian Sea
Elena Shchepetova, Mikhail A. Rogov, Dmitry Kiselev, Ivan Ukhov, Svetlana Maleonkina, Alexandra Khakhina, Valeria Churkina

Building: Muséum d'Histoire Naturelle de Genève
Room: Amphithéâtre
Date: 2018-12-05 03:50 PM – 04:10 PM
Last modified: 2018-12-01

Abstract


Middle-Upper Volgian deposits of the Russian Platform were investigated in Rybinsk, Moscow and Ul’yanovsk-Syzran regions of Central Russia. The results were obtained by sedimentological and biostratigraphical examinations of well-known and newly found exposures, supplemented by new core material, yielded from drilling in Moscow City.The objective was to create lateral transect, passing through sites of stable Late Jurassic marine sedimentation, from Moscow syneclise in the north-west to Ul’yanovsk-Saratov trough in the south-east, and target it for reconstruction of depositional systems and its evolution. Three general types of depositional environment were distinguished and in the studied regions and the main evolutional trends were recognized. In the Rybynsk region the sediments were accumulated within storms- and waves-dominated shoreface, prograding basinward , and in Moscow region seems to be accumulated in more offshore environment, subjected to weakened storms and progressively approaching to fairweather wavebase. In the Ul’yanovsk-Syzran region the sequence is substantially reduced in thickness due to effects of sediment starvation and amalgamation of numerous omission surfaces. The sediments are very-fine sandy and muddy, with high proportion of autochthonous basinal components (glauconite, shells and detrirus, siliceous sponge spicules). Depositional environment is suggested to be offshore-nearshore, around the Islands or submarine elevations, providing calm hydrodynamics, low siliciclastic influx and high nutrient availability. The general trend of regression is manifested in all types of studied sequences, and shows similar stepwise dynamics, expressed in subsynchronous impulses of progradation and its delays, recorded within transition Virgatus-Nikitini Zones, Nikitini Zone, and probably in the Catenulatum-Nodiger Zones transition.


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