Soil Evolution during the Past 30,000 Years In the Black Rock Desert, Utah, SW USA

Previous work in the western United States links the development of accretionary eolian mantles to the desiccation of pluvial lakes during the Pleistocene-Holocene climate transition. Lava fields as well as beach ridges have been identified as effective in trapping these sediments due to their rough surface.

The Black Rock Desert was flooded by Lake Bonneville at 20 ka BP and fell dry until 11.9 ka BP. Additionally the basin was volcanically active throughout the Quaternary. Lava fields of various ages and several levels of Lake Bonneville created a mosaic of surfaces with different maximum ages of soil evolution.

Based upon nine model hypotheses of soil evolution and implementing the results of field work and laboratory analyses, a sediment and soil stratigraphy has been developed. Six periods of soil evolution were differentiated, each characterized by changes in occurrence and intensity of typical processes of sediment genesis and/or soil development.

During the Bonneville period (28-14.5 ka BP) pedogenesis under humid conditions (i.e. clay dynamics) prevailed and Lake Bonneville transgressed into the basin. At about 14.5 ka BP the Bonneville flood lowered the lake level rapidly and caused erosion along the former lake margins and from parts of the former lake bed. During the Provo stage of Lake Bonneville (early Provo period 14.5-14.0 ka BP) the lake level stabilized. Cover beds lacking signs of eolian addition formed outside the lake. The late Provo period (14-10 ka BP) was characterized by numerous lake level oscillations prior to the lake's ultimate desiccation at about 11.9 ka BP, increased eolian input, and the formation of the Provo soil. During the Holocene (10 ka BP-1850) eolian activity remained at high levels. Holocene soils differ from the Provo soil in lacking significant clay accumulation. Eolian sediments of a modern period (1850-today) are identified by their higher sand content.