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ABSTRACT: Miocene/Quaternary sequence stratigraphy of the Caspian Sea region: interplay of deltaic systems and climatic control on non-marine depositional sequences

Abreu, Vitor, Dag Nummedal, Dan Self, Paul Ware, and Roger Witmer , Unocal, Sugarland, TX

The interplay of the paleo-Volga, paleo-Amu Darya, and paleo-Kura deltas is the most important factor for lithology distribution in the southern Caspian. The three delta systems exhibit significant differences in depositional style. Strong progradation of the paleo-Amu Darya delta occurred from Pereryva to Surakhany (Lower Pliocene) on the Turkmenistan shelf during an overall rise in the Caspian lake level. During the same time interval, aggradation was the primary depositional pattern in the paleo-Volga delta at the Apsheron sill. In the Central Caspian, the paleo-Volga delta is marked by transgressive stratal patterns. In the paleo-Kura system, on the southeast margin of Azerbaijan, a transgressive trend occurred during the deposition of the Lower Productive Series to the mid-Balakhany (uppermost Miocene to Lower Pliocene), with onlap of these units over Miocene and Cretaceous rocks. A major downlap surface developed in the paleo-Kura during mid-Surakhany time. The downlap surface at the base of the paleo-Kura progradation correlates to the upper part of the progradational phase of the paleo Amu-Darya delta. Thus, the paleo-Amu Darya delta could have prograded during rising lake-level, similar to the progradation of the Mississippi delta during the Holocene transgression, controlled primarily by the sediment supply.

Climatic fluctuations exert a dominant control on the style of sedimentation in the South Caspian basin, along with sediment supply. The entire Productive Series reflects the Pliocene "golden climate" when the earth overall was much warmer than today. On a shorter time scale, the stratification pattern is controlled by high-frequency climatic cycles. Climatic cycles of 400, 100 and 20 thousand years seem to be the most important factor controlling the depositional systems in the Caspian Sea during the Pliocene.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia