A Paleoseismic Record Spanning 2‐Myr Reveals Episodic Late Pliocene Deformation in the Western Qaidam Basin, NE Tibet

Abstract

The western Qaidam Basin, NE Tibet contains numerous NW‐SE‐trending thrusts that extend over a distance of ∼300 km along the Altyn Tagh Fault and north of the Kunlun Range. However, little is known about the long‐term seismo‐tectonic evolution of this active thrust zone due to the absence of an extended paleoseismic record. We present a 2‐Myr‐long disturbance record established from a core drilled on the crest of a thrust‐cored anticline. Based on detailed sedimentological analysis, the disturbances (micro‐faults, soft‐sediment deformation, slumps, and detachment surfaces) are interpreted as paleoearthquake/tectonic indicators. The core records five seismite clusters which occurred at 3.6‐3.5, 3.4‐3.2, 3.15‐3.1, 3.0‐2.9, and 2.8‐2.75 Ma. This suggests the rate of tectonic strain accommodated by the folds and thrusts in the region varies and thus reveals episodic local deformation. During the clusters, regional deformation is concentrated more in the fold‐and‐thrust system than along regional major strike‐slip faults.

Recognising surface versus sub-surface deformation of soft-sediments: Consequences and considerations for palaeoseismic studies

“…The direction of slumping is supported by anisotropy of magnetic susceptibility (AMS) fabrics (Weinberger et al, 2017). This collective movement of sediment from the basin margins towards the centre results in the Lisan Formation being three times thicker in the depocentre where drill cores penetrate numerous MTDs (Lu et al, 2017(Lu et al, , 2021aKagan et al, 2018).…”