ABSTRACT: Sedimentological resonse to climate cycles during the Pliocene of the South Caspian Basin

Sedimentological and paleontological studies of outcrops within the Paleo-Volga province of the Productive Series in the Kirmaku Valley north of Baku, Azerbaijan reveal a distinctive cyclicity inferred to record 20-ky to 100-ky cycles in lake level and climate of the Caspian basin. Typical small sequences range from 10 to 20 m in thickness. SBs lie at the base of thick sandstones or are expressed as mud-cracked surfaces (locally with paleosols) within mudstones, recording subaerial exposure.

Overlying the sequence boundary is either a sharp-based (proximal) or gradationally-based (distal), cross-bedded and rippled sandstone with abundant mudclasts. It is inferred to have accumulated as a lowstand systems tract (LST) during a phase of slow rise in lake level. The sandstones are overlain by dark, clay-rich mudstones with an ostracod fauna suggestive of a maximum water depth of about 50 meters. Mud deposition is inferred to occur during lake level rise, highstand, and fall. There is no sandstone between these TST/HST mudstones and the next overlying exposure surface implying that lake level fall was not associated with renewed progradation.

The number of Pliocene sequences recorded is consistent with an average duration of about 20-ky per sequence. The global dO18 curve for the Pliocene demonstrates a strong 20-ky (precession) climate cycle. We infer that the sedimentation pattern record a climate pattern of dry, hot periods characterized by Caspian lowstands, alternating every 20-thousand years with episodes of cool, wet highstands. Sand entered the region of the Kirmaku Valley only during intervals of slow lake level rise following absolute lowstand.

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