Insights from the Talysh of Azerbaijan into the Paleogene evolution of the South Caspian region

The age and mode of formation of the South Caspian Basin are disputed. An similar to 10-km-thick, predominantly middle Eocene clastic and volcanic succession is exposed in the Talysh mountains of Azerbaijan at its western margin. Here, high-K alkali basalts pass laterally to the east and southeast into volcanogenic sandstone-dominated turbidity current and debris-flow deposits. These southeasterly directed depositional systems accumulated in water depths generally greater than 200 m and fed directly into the western South Caspian Basin. New Ar-Ar ages cluster around 39 Ma, with an upper, 1400-m-thick volcanic interval being deposited in 2.2 +/- 0.2 m.y. We interpret that this rapid deposition and magmatism records a major back-arc extensional/transtensional event in the Talysh, north of the north-dip-is recognized across much of southwest Asia and may indicate a period of significant basin formation within the adjacent South Caspian Basin. A transition into Upper Eocene-Lower Oligocene strata, dominated by fine-grained turbidity current and hemipelagic sediments with slope instability features, is interpreted to mark the end of rifting and voleanism in the Talysh and the start of the Arabia-Eurasia collision. Overlying Oligocene coarse clastic rocks are interpreted as the erosional products of localized topography created by the further propagation of compressional deformation into the Talysh region.