Soft-Sediment Deformation Structures in the Late Quaternary Lacustrine Sediments and Paleo-earthquake Studies in Tashkorgan, Northeastern Pamir, China

Soft-sediment deformation structures (SSDS) developed in the lacustrine sediments of paleo-dammed lakes in tectonically active regions contain significant information on fault activities. In this study, multiple SSDS were identified from the strata of late Pleistocene lacustrine sediments in the drainage of Tashkorgan River located in the northeastern Pamir. According to the driving mechanisms, the SSDS were classified into three types: gravity-induced SSDS (load and slide structures), sand liquefied SSDS (sand dykes, liquefied droplets, diapir and pillow structures), and composite SSDS (sand liquefaction-clay thixotropic structures and sand liquefaction-clay thixotropy-sliding combined structures). The regional tectonic setting and distribution of lacustrine strata indicated that the most probable trigger for the SSDS in lacustrine sediments was seismic activity, with an approximate earthquake magnitude of M > 6.0. The potential seismogenic fault is the southern part of the Kongur normal fault extensional system, such as Kongur fault, Muztagh fault, Taheman fault and Tashkorgan fault. AMS ¹⁴C dating data showed that the SSDS in the Tashkorgan lacustrine sediments were roughly formed between 25790±90 yr BP and 21270±80 yr B.P, implying intense fault activity in this region during the late Pleistocene. This study not only provided the understanding of fault activities and geodynamic process of Northeastern Pamir during the late Pleistocene, but also revealed reliable geological background for the anti-seismic design of Xiabandi Reservoir Construction in the downstream of Tashkorgan River.