Bouldery deposits along the Kherlen fault, Central Khentey, Mongolia: implications for paleoseismology

The assumed Jargalant rockslide is located in Khentey Upland of Mongolia, an area undergoing active tectonic deformation and seismogenic activity but where geomorphic research that connects rock slope failure and long-term paleoseismic events has yet to be conducted. We present the first reconnaissance study on this topic, which demonstrates the possibility of cosmogenic ¹⁰Be dating of landslide-induced bouldery deposits to date the timing of the assumed seismic events. We performed integrated geomorphic analysis (geomorphic mapping, topographic profile analysis, and surface trenching) and ¹⁰Be surface exposure dating (boulder and bedrock scar) to document the recurrence interval of the assumed paleoseismic events by determining the recurrence of rock slope failures in Jargalant River valley. We identified four geomorphic surfaces and units identified based on their morphology, the distribution of quartzite boulders, and their ages. The geomorphic units are as follows: (1) outburst flood fan (S1), (2) remnant landslide-dam deposit (S2), (3) surviving rockslide body (S3), and landslide scar (S4). Bedrock quartzite outcrops only in the assumed headscarp, while most of the upland is composed of schist. The average ¹⁰Be age of quartzite boulders of S1 to S3 is 283.4, 138.8, and 48.4 ka, respectively, and that of the landslide scar (inner and outer edge) are 44.5 and 193.5 ka. Based on the morphology, depositional characteristics, quartzite provenance, and separated and clustered ¹⁰Be exposure age, we hypothesize that at least three catastrophic rock slope failures could occur at 283 ka, 138 ka, and 48 ka, likely being triggered by earthquakes associated with active Kherlen fault.