Late Quaternary ostracodes as indicators of salinity conditions and paleohydrology in a mid-continent wetland, Cheyenne Bottoms, Kansas

An understanding of prehistoric hydrologic conditions of mid-continent lakes is needed to characterize changes in fresh-water recharge to wetlands resulting from anthropogenic activities. Salinity-dependent, fresh-water ostracode species from a 13.8 m sediment core were used to interpret the paleohydrology of one such wetland. Ostracode microfossils and sediment core analysis enabled the reconstruction of local water salinities and flow regimes. The core was divided into sixty-six samples based on visual description and hand texturing. Fossil assemblages and soil morphologic features indicate a transition at a depth of 6.0 m from wetland below to drier grassland conditions above. Ostracodes were found from the bottom section of the core upward to 6.0 in and indicate a range of salinity conditions. Throughout this section, mixosaline ostracodes, particularly Fabaeformiscandona rawsoni and Limnocythere ceriotuberosa, are abundant. Between 12.6 and 8.7 m the mixosaline assemblage occurs with several episodes of the additional species, Cyprideis salebrosa and Limnocythere staplini. This suggests a transition upward from hypersaline to extreme hypersaline conditions, indicating a long-standing diminished wetland. Between 6.9 m and 6.0 m the abundance of oligosaline species Fabaeformiscandona caudata and Limnocythere itasca indicates rare fresher-water conditions. Here, also, the presence of Cypridopsis vidua suggests an environment of sub-aquatic vegetation with shallow ground-tivater influx and/or additional fresh-water recharge. Cretaceous foraminifera weathered from nearby outcrops are present throughout the ostracode-bearing sediments. The lack of ostracodes in the upper part of the core implies the absence of standing water and is in agreement with interpretations of a Late Pleistocene---Holocene unconformity and Holocene climate change cited by others.