Holocene evolution of the Erickson Creek basin, Story County, Iowa; Geological Society of America, 2000 annual meeting

Holocene-age alluvial deposits of the DeForest Formation are preserved within the Erickson Creek basin, a tributary of the South Skunk River in central Iowa. Terrace remnants and alluvial fans within the basin document multiple depositional and erosional events during the Holocene. Nineteen radiocarbon ages and detailed soil geomorphic analyses of cutbank exposures and cores provide a chronologic and stratigraphic framework for reconstructing the basin's postglacial development. Entrenchment of the South Skunk River occurred ca. 13,500 yr BP, initiating the headward expansion of Erickson Creek. Entrenchment of the lower part of the basin was complete before 10,000 yr BP, when the valley floor began to aggrade. Prior to 8,000 yr BP. deposition ceased and soils began to form on the floodplain. Episodic aggradation of alluvial fans began at the mouths of tributary streams ca. 8,000 yr BP, burying soils developed in older alluvial deposits, and continued until ca. 6,500 yr BP when a valley-wide period of relative stability occurred. Entrenchment took place in the lower basin ca. 3,600 and 3,000 yr BP. During this interval, headward expansion began in the middle and upper portions of the basin. Stability and soil formation occurred soon after this period and continued until the time of Euroamerican settlement when changes in land-use practices resulted in floodplain instability and the removal of older Holocene deposits. Some Holocene geomorphic events in the Erickson Creek Basin coincide with vegetation and climatic changes documented in upland pollen sequences from central Iowa, while other evidence suggests that at least part of the postglacial development of the basin is related to a complex response. No single causal mechanism can be proposed for all of the geomorphic events recognized within the Erickson Creek basin. The complex record of erosion, deposition, and stability preserved within the valley appears to have resulted from factors both extrinsic and intrinsic to the system.