The Pliocene-Pleistocene transition in the Kura Basin: Environmental and climate reconstruction of basin margin sediments

Abstract

During the Neogene, the Caspian Sea experienced major fluctuations in lake-level as a result of climate change and (dis)connections with adjacent basins. A five-fold increase in Caspian Sea surface area is reported to have occurred during the Akchagylian flooding (Plio-Pleistocene). This largest and last flooding is increasingly better understood through research in the Paleo-Kura Basin, a former embayment of the Caspian Sea. These studies focused on the distal and interior parts of the Kura Basin however, leaving the exact expression and timing of the Akchagylian flooding at the basin margin unresolved. This study aims to determine the expression of this flooding and drivers of environmental change in the westernmost extent of the Kura Basin across the Plio-Pleistocene transition. Environmental reconstructions using facies analysis and grainsize distribution limit the maximum westward extent of the Caspian Sea to the location of the studied sections. The muddy, vegetated, and protected coast remained at a relatively constant location by balanced (sub)basin subsidence and sediment supply. An exploratory climate reconstruction using clay mineralogic proxy’s for humidity and temperature allows for the identification of three regional to global cooling-warming cycles that might correspond to obliquity-scale orbital forcing. Warm and humid periods increased the deposition of coarser sand-rich sediments, while cold and arid phases are dominated by the deposition of fine-grained mudstones. Tectonic activity of the Kura fold-thrust belt seems to become increasingly more important in controlling sedimentation from the start of the Pleistocene Insights from this study on basin margin sedimentology and clay mineralogy contribute to a better understanding of environmental change in semi-enclosed basins during climate variability, by providing a detailed reconstruction of the largest flooding in the history of the largest ‘lake’ in the world.