Changes in Permian marine ostracode faunas during regression, Florena Shale, northeastern Kansas

The Florena Shale (Permian, Wolfcampian) of the Midcontinent of North America was deposited in a restricted marine basin. Shifting environments due to marine regression caused a gradual change in the ostracode fauna. Cluster analysis and ordination by nonmetric multidimensional scaling of data on ostracode relative abundances revealed three ostracode assemblages, each characteristic of a different environment. The Cryptobairdia seminalis assemblage from the lowest Florena Shale is characteristic of deeper water, offshore, marine environments with only minor influx of terrigenous mud. The Amphissites centronotus assemblage found above the C. seminalis assemblage occupied a similar environment, but with greater influx of terrigenous mud and intervals of increased turbidity. The Knightina texana assemblage occurs stratigraphically highest and probably represents a quiet-water, very shallow, nearshore, marine environment. Although protected from strong wave and current activity, the water mass was occasionally turbid. Species diversity of ostracodes is high both at the base of the Florena Shale, which was deposited in the most offshore position, and again at the top of the lower part of the Florena Shale, which was deposited nearer to the shore. In contrast to diversities of assemblages of ostracodes from similar environments in other stratigraphic units, the K. texana assemblage has an anomalously high diversity. This is due in part to time averaging of adjacent ostracode assemblages and a strong taphonomic overprint.