Geomorphic history of Lake Manix, Mojave Desert, California: Evolution of a complex terminal lake basin

Pluvial lake deposits in the Basin and Range province have long been exploited for records of hydrologic and climatic change. To obtain the most accurate reconstructions, a thorough understanding of the geomorphic evolution of such lake basins must be grounded in field stratigraphy and mapping, which are often lacking or are not well integrated with core studies. We conducted extensive stratigraphic investigation, mapping, and dating of exposed strata in the Lake Manix basin, former terminus of the Mojave River, California, during the Pleistocene to provide such a background and to supplement interpretations from a 45-m-long core. In this paper, we emphasize the geomorphic and tectonic processes that shaped the evolution of the Manix basin after the arrival of the Mojave River in the early-middle Pleistocene. The main processes include (1) sedimentary infilling of the lake basin, (2) interaction among the subbasins as controlled by internal sills and sill failures, (3) tectonics, and (4) climate change. From about 500 to 190 ka, Lake Manix was confined to its western subbasins, and fluctuated in response to climate change and perhaps to brief diversions of the river into the upstream Harper Lake basin. During this time, about 24 m of sediment accumulated near the confluence of the Mojave River and Manix Wash, and a 15-km-long clastic wedge built into the western basins, gradually filling the accommodation space. Two basin-integration events subsequently occurred, both caused by failure of sills that lay on sheared deposits along the Manix fault zone. When Lake Manix rose at the onset of glacial marine isotope stage 6, the sill on the south flank of Buwalda Ridge failed and triggered a catastrophic flood that entered the new, lower elevation, previously endorheic Afton subbasin. Subsequent lake-level changes affected both subbasins, but the thickest deposits after the flood are preserved in the Afton subbasin. The area upstream of Buwalda Ridge was only submerged during relatively high lake levels. Thus, sediment records interpreted from the core site and nearby outcrops in part reflect a geomorphic event (basin integration) rather than climatic conditions. The sill of Lake Manix after the integration event lay at the northeast end of the Afton subbasin, athwart strands of the Manix fault zone. At about 25 ka, this eastern sill was rapidly incised, and the river advanced to terminate in Lake Mojave in the Soda and Silver Lake basins. Recognition and dating of integration events, common for lake-river interactions in active tectonic settings, provide important context for interpreting paleoclimate records from sediments and provide temporal and spatial constraints on the biogeography of aquatic species. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).