Differential effects of base-level, tectonic setting and climatic change on Quaternary alluvial fans in the northern Great Basin,

Abstract: Mountain-front alluvial fans in the northern Great Basin were affected by interactions between the t ctonic setting, late Quaternary climatic hanges and climatically induced base-level changes through fluctuations inpluvial ake levels. Four fan groups were studied on the margins of and near pluvial Lake Lahontan with varying eology and tectonic settings. All fans were affected by climatically ed variations in sediment supply, but only those on steep mountain fronts adjacent to deep lakes were affected by base-level changes during lake desiccation. Relationships between fan segments and dated lake shorelines, augmented by soil and desert pavement characteristics, have enabled fan segments older and younger than the lake highstands to be identified. Major periods of fan aggradation occurred prior to the last glacial maximum and during the Holocene, with little or no fan deposition occurring during and after the last glacial maximum, at the time of high lake levels. The interactions between tectonics, climate and base-level change have produced istinctive fan geometric relationships between older and younger fan segments, also expressed inthe morphometric properties of the fans. Tectonics primarily influence the fan setting, particularly the accommodation space, and interact with sediment supply rates partly related to source-area geology. Theclimatic signal is present in all four groups of fans, but i