STRATIGRAPHY AND CHRONOLOGY OF ALLUVIAL LANDFORMS IN THE LOWER KANSAS RIVER VALLEY: AN UNDERGRADUATE USGS EDMAP EXPERIENCE

This poster presents new data from a three-year USGS EDMAP project aimed at mapping and characterizing the stratigraphy and chronological evolution of alluvial terraces in the Kansas River valley. Terraces were mapped in a GIS environment using a combination of LiDAR imagery, historical maps, and field mapping along a 34-km reach of the Kansas River valley between Grantville and Rossville, Kansas. Sample sites were identified on each terrace, and stratigraphy was documented through outcrops, hand auguring and hydraulic coring. Numerical age data were derived from OSL and ¹⁴C samples collected at select sites.

Terrace morphology, stratigraphy and chronology in our study reach is consistent with that documented in other parts of the Kansas River valley. The Menoken terrace, oldest of the sequence, is characterized as a glacial-fluvial deposits dating to the Kansan Glacial period ~700–600 ka. Aeolian dunes mantle the Menoken terrace, and new OSL ages from our mapped region suggest their initial formation ranging between ~35 ka and ~48 ka. The Buck Creek is the next youngest terrace in the river valley, though only mapped at a few locations in the study reach. Terrace stratigraphy is divided into two discrete sedimentary units: an upper fine-grained silty-clay package overlaying a thick, sandy lower unit. Sedimentary data suggest the lower Buck Creek may be the sediment source of the dunes found through the river valley, and limited ¹⁴C ages indicate that the upper Buck Creek was abandoned ~15 ka. The Newman terrace is the second youngest terrace in the river valley and is widespread in this reach of the river valley. The Newman terrace is characterized by a thick basal soil that formed between ~14–10 ka, which is overlain by multiple packages of Holocene-age alluvial sands and fine-grained paleosols. The youngest terrace is the Holliday complex, a surface which primarily consists of abandoned meander scrolls. Stratigraphy of the Holliday terrace consists of a surface soil overlying thick deposits of cross bedded alluvial sands. Multiple OSL ages from the Holliday surface indicate lateral migration of the Kansas River beginning ~4 ka—this migration has continued in parts of the Kansas River valley through historic times.