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dc.contributor.authorOrme, A. R.-
dc.descriptionTechnical Report-
dc.description.abstractIn late Pleistocene time, Lake Thompson rose to 710 m above sea level and covered 950 km² of the western Mojave Desert, California. During Holocene time, the lake desiccated and is today represented mainly by Rogers, Rosamond, and Buckhorn Dry Lakes, which cover 200 km2 of Edwards Air Force Base. Elsewhere the former lake basin is characterized by exposed lake beds and beach ridges or mantled by aeolian and fluvial deposits. This study reports on the spatial and temporal components of former Lake Thompson. The spatial dimension identifies seven major geomorphic and lithostratigraphic units within the former lake basin, of which the most important are the modern playa, former lake system, Aeolian mantle, interfingering fluvial deposits, and various bedrock outcrops. These units and their subdivisions are presented on a map entitled Geomorphology and Quaternary Geology of Lake Thompson within Edwards Air Force Base, California. The temporal component is represented by a chronology of Lake Thompson based on accelerator mass spectrometry dating of the stratigraphic sequence. Although a former deep lake beneath the modern dry lakes had long been inferred from borehole data, its age and development remained unknown. The present study recovered four cores for stratigraphic and sediment analysis and dating. Ages for the deep lake range from 30,000 to 17,000 BP, a humid interval typified by frequent inputs of fluvial sediment. After 17,000 BP, the lake began to desiccate, and its exposed floor was lowered by deflation. However, shallow perennial lakes returned during latest Pleistocene and early Holocene time, prior to the present phase of desiccation. Clay minerals from the cores support this scenario. High smectite values reflect deposition in a large lake under humid conditions around 30,000 BP, followed by diminishing smectite as conditions became drier. A more saline, alkaline lake existed under drier climatic conditions before 30,000 BP. The later phases of lake devolution during Holocene time have seen lake segmentation as shallow-water waves and currents generated a sequence of beach ridges around contracting lakes. These ridges became mantled with aeolian sand, but as fluvial sediment inputs diminished, these dunes were degraded and their sand removed downwind. The roots of these dunes survive as yardangs. Understanding this complex system provides a valuable tool for management of the lake basin, including its flood hazards, groundwater resources, blowing dust potential, subsidence problems, and ecology.-
dc.description.sponsorshipEdwards Air Force Base (Calif.)-
dc.publisherCold Regions Research and Engineering Laboratory (U.S.)-
dc.publisherEngineer Research and Development Center (U.S.)-
dc.relation.ispartofseriesERDC/CRREL ; TR-04-1.-
dc.subjectGeology, Stratigraphic-
dc.subjectPleistocene-Holocene boundary-
dc.titleLake Thompson, Mojave Desert, California : a desiccating late quaternary lake system-
Appears in Collections:Technical Report

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