LATE-QUATERNARY LANDSCAPE EVOLUTION AND GEOARCHAEOLOGY OF THE COTTONWOOD RIVER BASIN, FLINT HILLS, KANSAS

This paper presents a basin-wide investigation of late-Quaternary landscape evolution in the Cottonwood River valley, located in the Flint Hills of Kansas. Subsurface information gleaned from the inspection of cores and cutbank exposures was used to determine lithostratigraphy and soil-stratigraphy of landform sediment assemblages (LSAs). Radiocarbon assays, alluvial stratigraphic information, and δ¹³C analyses provide the data to reconstruct the temporal and spatial patterns of late-Quaternary landscape evolution and correlate geomorphic responses to environmental change in the basin. Furthermore, these data provide the basis for predicting where buried cultural deposits are likely to occur in the basin. Data indicate that most small valleys (< fourth-order) were zones of net sediment erosion during the early Holocene, and zones of net sediment storage during the late Holocene. Late-Holocene aggradation was punctuated by a major period of landscape stability in small valleys at ca. 500 ¹⁴C yr B.P. By contrast, large valleys (> third-order) were zones of net sediment storage during the early and late Holocene. Aggradation in large valleys in the early Holocene was punctuated by a major period of landscape stability at ca. 10,500 ¹⁴C yr B.P., followed by multiple periods of stability in the early Holocene. Another period of landscape stability is recorded at ca. 2,500 ¹⁴C yr B.P. in large valleys. Late-Holocene sediments in the larger valleys dating to the past ca. 4,000 ¹⁴C yr B.P. grade into younger late-Holocene deposits dating to the past ca. 3,000 ¹⁴C yr B.P. in the smaller valleys. Few middle-Holocene ages have been recorded in the basin, suggesting the entire basin may have been a zone of net sediment erosion during the middle Holocene. These patterns of erosion, deposition and stability are attributed to major climatic changes during the late Wisconsinan and Holocene.