Defining the timing and controls of alluvial fan aggradation in an extreme continental-interior setting in the Basin of Great Lakes, western Mongolia

Quaternary geomorphic processes in western Mongolia's Basin of Great Lakes (BGL), one of the most continental regions on Earth, are predominantly controlled by a neogene tectonic setting and climate cyclicity. Here, Lake Khyargas presents the terminal water and sediment sink of a cascading lake system draining the adjacent Altai and Khangai mountains. Well-preserved sequences of shorelines and associated landforms provide evidence of multiple pronounced lake level highstands since the mid-Pleistocene in response to orbitally-driven climate cyclicity and widespread glacier melt in the broader catchment following the local last glacial maximum (Wolf et al., 2025,  https://doi.org/10.1016/j.quascirev.2025.109373).        
The Khankhukhii Range, reaching peak elevations of 2,928 m asl, separates the endorheic catchments of Lakes Khyargas and Uvs along the westernmost expression of the geomorphic prominent active Bulnay fault system. There is no evidence of former glaciations in the Khankhukhii Range, however, widespread periglacial impact is evident. The southern slopes of the Khankhukhii Range are inclined towards Lake Khyargas, where mesoscale alluvial fans form the interface between the mountain system and the terminal lake basin. Analyzing the timing of alluvial fan formation will promote the understanding of the coupling between climate cylicity and geomorphic processes in this highly continental region. The timing of alluvial fan aggradation and incision phases is determined using morphostratigraphic mapping of fan surfaces and their relationship with previously dated shoreline features. We combined surface-exposure dating using ¹⁰Be depth profiles, and sediment age pIRIR luminescence dating. Our approach reveals two preserved aggradational fan-surface generations corresponding to the transitions from MIS 6 to MIS 5 (~130 ka) and from MIS 4 to MIS 3 (minimum pIRIR age of 47 ka), and ongoing incision since the Pleistocene to Holocene transition. We discuss the suitability of investigating sedimentary archives of alluvial fan response to climate cyclicity in this setting that is modified by (1) tectonic uplift and (2) autogenic adjustments of the drainage network across the catchment, as well as (3) significant Late Pleistocene to Holocene hydrostatic changes in base level and accommodation space.