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

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. Plain Language Summary: The generally NW‐SE‐trending thrusts developed north of the Kunlun Range are the most prominent morphological feature in the western Qaidam Basin, NE Tibet. These folds have played a key role in the Miocene‐Quaternary uplift of the region. However, little is known about the long‐term rupture behavior of this active thrust zone due to the absence of an extended paleoseismic record. Our understanding of earthquake history is still limited by short seismological and historical records. A continuous lacustrine sedimentary sequence (∼33‐1.6 Ma) accumulated in the Qaidam paleolake which may have sequentially recorded the development and activities of the underlying folds and thrusts. Here, we present a unique record of disturbance spanning 2‐Myr based on a deep core drilled on the crest of one such fold in the western Qaidam Basin. The disturbances comprise micro‐faults, soft‐sediment deformation, slumps, and detachment surfaces. We interpret the four types of disturbance as seismites. The 2‐Myr‐long seismite sequence records five paleoseismic clusters that occurred between 3.6 and 2.7 Ma, suggesting episodic late Pliocene deformation in the western Qaidam Basin, NE Tibet. Key Points: We interpret micro‐faults, soft‐sediment deformation, slumps, and detachment surfaces as paleoearthquake/tectonic indicatorsThe core records five seismite clusters between 3.6 and 2.7 Ma, revealing episodic thrusting in relation to intense regional deformationDuring the clusters, regional deformation was concentrated more in the fold‐and‐thrust system than along regional major strike‐slip faults [ABSTRACT FROM AUTHOR]