OSTRACODES AS HYDROCLIMATIC INDICATORS IN PLIO-PLEISTOCENE AQUATIC DEPOSITS IN MEADE COUNTY, KANSAS

Nonmarine ostracodes are useful microfossils with hydroclimatic significance as proxies for past hydrologic conditions. This study presents a preliminary analysis of a database of fossil ostracode species assemblages collected from Pliocene and Pleistocene sites in Meade County, Kansas. The database consists of two historical collections (housed at Kent State U.) completed in the mid 20^th century by Ed Gutentag and Richard Benson (1962) and by Claude Hibbard (1950s). Historical collections were augmented by a third sampling campaign we conducted in 2019 including some of the same localities. We collected samples spanning about 4 million years of age, from the oldest sites in Fox Canyon (~4.4 my) to mid-Pleistocene Cudahy Ash (~0.7 my). The youngest Pleistocene locality in the database is Butler Springs, collected by Hibbard in the 1950s. Stratigraphy and chronology follow Lukens et al., (2019) and species biogeography was obtained from the Neotoma Paleoecology Database (www.neotomadb.org).

The ostracode fauna from the combined collections includes 32 species. Most are common North American freshwater species found in fen wetlands, streams, and flowing springs. Cudahy samples (~0.7 my) include Paracandona euplectella and Scottia pseudobrowniana, indicative of fen wetlands with TDS concentrations not exceeding about 350 mg/L (www.neotomadb.org). Sites with assemblages indicative of elevated salinities and bicarbonate-depleted solute chemistry are Pleistocene in age, and contain Cyprideis salebrosa, Fabaeformiscandona rawsoni, and Limnocythere staplini.

The Pliocene localities, Keefe Canyon (~3.5 my) and Fox Canyon (~4.4 my) have assemblages dominated by Pseudocandona stagnalis, Ilyocypris bradyi, Cyclocypris ovum, and Candona fluviatilis, indicative of wet meadows and flowing streams, with TDS concentrations that do not exceed about 1,000 mg/l.

Results from constrained cluster analysis and classic modern analog analysis using the Neotoma Database support the interpretation of Lukens et al., (2019): 1) that the Pliocene sites represent palustrine environments wetter than today; and 2) that Pleistocene episodes of drying produced shallow, evaporative saline ponds. Thus, the Pliocene samples and the mid-Pleistocene Cudahy samples are freshwater assemblages with modern analogs living today in the forested wetland and stream complexes of the northern Midwest, whereas the Pleistocene saline samples have modern analogs found today in small evaporative ponds and playas of the southwestern Great Plains.