Deep structure and margins of the Kurai Basin (Gorny Altai), from controlled-source resistivity data

The deep structure of the Kurai basin and its junction with the flanking mountains has been studied by controlled-source resistivity surveys (vertical electric sounding and transient electromagnetic methods). According to the data processing results, the basin is the deepest along its northern, southern, and eastern margins. The sedimentary fill comprises two resistivity units corresponding to two sequences deposited at different stages of the basin history. The lower, less resistive unit consists of Paleogene–Neogene lacustrine clay and the higher-resistivity upper unit represents coarser Quaternary deposits. In Paleogene–Neogene time, the basin formed by the left-lateral pull-apart mechanism. The earliest Quaternary strike-slip faulting in the setting of overall compression produced the Central Kurai basin within the northern Kurai basin, while the flanking ranges and fault blocks thrust upon the basin transforming it into a ramp. Thus, piedmont steps rose along the basin margins, and the marginal grabens became ramps and half-ramps.