LATE PLEISTOCENE TO EARLY HOLOCENE CLIMATIC CHANGE RECORDED IN FILL OF A DISSOLUTION COLLAPSE FEATURE WITHIN THE CENTRAL GREAT PLAINS

Big Basin is the largest dissolution collapse feature in Kansas at nearly 2km diameter and over 35m deep. It is situated along the dissolution front of subcropping Permian salt beds in southwestern Kansas. Within the feature are several smaller collapse basins formed at various times and subsequently filled with sediments delivered from small, fourth-order drainages on the north and northeast sides and from the basin flanks. One recent depression yielded a radiocarbon age of 1630 yrs BP (~1525 cal yr BP) from organic muck at 6.8m depth. Another small internal collapse basin dated to the Pleistocene—Holocene transition: basal mollusk shell (4.6m) dated to 12,730 yr BP (~15,090 cal yr BP), and bulk humates from two welded, buried soils dated from 10,690 yr BP (~12,693 cal yr BP; 2.15m) to 9660 yr BP (~10,985 cal yr BP; 1.7m). A series of analyses were used to characterize the sedimentary record: particle size, elemental composition, clay mineralogy, carbon content (organic, carbonate, total), magnetic susceptibility, stable carbon and nitrogen isotopes, and biogenic opal analysis. Particle size fines upward; elements and weathering ratios transition within the buried soil zone; clay mineralogy remains relatively unchanged except in the welded soil zone; organic carbon distribution reflects the buried soils; and magnetic susceptibility increases in both magnitude and in variance above the buried soils. Carbon isotope and phytolith analyses indicate the Pleistocene—Holocene transition beginning about 3m depth, from cooler and wetter conditions (C3 plant dominance and abundant diatoms) to drier and warmer conditions (C4 grass dominance). Based on modern analogs, present temperature appear warmest and available moisture least of the record, though the Holocene record is abbreviated and fragmental.