Fold growth in the South Caspian Sea Basin: mechanisms and interaction with deep-water lacustrine sediments

Abstract

Growth strata analysis, finite element modelling and mapping of a lacustrine turbidite channel network utilizing a high-quality 3D seismic reflection dataset have been used to explore the Plio-Pleistocene growth history of the Shafag – Asiman fold structure, within the centre of the South Caspian Basin. For the first time, I document the amplification of fold growth in response to shortening and sediment loading of a mobile shale in the South Caspian Basin. 2D finite element modelling results suggest that atypical growth strata geometries can be explained by tectonic shortening and sediment loading of a mobile visco-plastic layer (Maykop shale) with a viscosity of 1018 Pa.s and a porosity of 30%. Fold geometries are controlled by the distribution of sediment between the crest and flanks of the fold structures, determined by the relative amounts of shortening and sediment input. The location and initial growth of the fold structure is controlled by a deep basement fault. However, detailed growth strata analyses record anti-clockwise rotation of the fold axes through the Pleistocene as the structures formed in response to transpressive dextral shear above the mobile shale. Shortening and subsequent transpression is caused by the relative NNW and SW motion of the basin with respect to Eurasia and Iran. The interaction of deep-water lacustrine turbidites with growing fold structures is documented for the first time, revealing the alternating dominance of the Shafag and Asiman fold crests on seafloor topography through the Pleistocene to recent times. Novel growth strata analysis, defined as sediment accumulation indices, and lacustrine turbidite channel mapping demonstrate the complex interaction of the channel network and growing fold structures. Channel characteristics such as density, sinuosity and avulsion points are controlled by the interaction of the channels with the growing structures. The results show that sediment accumulation indices have the potential to be applied as a predictive tool for other deep-water sedimentary systems.