Upper Carboniferous ostracode assemblages from a mixed carbonate–terrigenous-mud environment

The Upper Carboniferous Beil Limestone Member (Lecompton Formation; Virgilian) from the Midcontinent of North America was deposited in a tropical, shallow-marine environment in which varying amounts of terrigenous mud were mixed with carbonate sediment. Shallowing of the sea occurred during deposition so that the upper part of the Beil was deposited much nearer to shore than the lower part. Mean relative abundances of 24 species of ostracodes in 51 samples differed among three stratigraphical subdivisions of the Beil and allowed recognition of two assemblages. Most species of the Cryptobairdia seminalis–Bairdia pompilioides assemblage, characteristic of the lower part of the Beil, were negatively correlated with percent terrigenous mud. On the other hand, abundant species of the Moorites minutus–Bairdia beedei assemblage, consisting of the C. seminalis and the Cavellina nebrascensis subassemblages, respectively, of the middle and upper parts, were positively correlated with percent terrigenous mud. Ordinations by non-metric multidimensional scaling showed similar groupings of species. Species diversity was negatively correlated with content of terrigenous mud.