The use of microphytoplankton and chitinozoans for interpreting transgressive/regressive cycles in the Rapid Member of the Cedar Valley Formation (Middle Devonian), Iowa

With only minor exceptions, the paleoenvironmental interpretations using microphytoplankton diversity and microphytoplankton/spore ratios are in agreement with previous ecological and depositional interpretation for the Rapid Member (Middle Devonian, upper Givetian) exposed at the River Products Conklin Quarry, Johnson County, Iowa. Analyses of acritarch morphotype variability, fluctuations in acritarch species diversity and the ratio of microphytoplankton (acritarchs and prasinophytes) to spores were compared to known paleoenvironmental interpretations based on sedimentology and megafossil content. The greatest microphytoplankton diversity occurs in the lower 14 m of the Rapid Member, suggesting deposition in a near- to offshore marine environment; whereas, the increase in relative abundance of spores in the upper 6 m suggests a closer proximity to the paleoshoreline. Chitinozoan diversity trends (greater diversity in 'deeper-water' depositional settings) indicates the same shallowing trend. The combined palynomorph (microphytoplankton, chitinozoan and spore) data appear to provide a fine resolution for paleoecological interpretation of the Rapid Member, particularly in relation to paleoshoreline fluctuations. The acritarch assemblage consists of 40 species distributed among 28 genera. The new genus Luscinisphaera Wicander et Wood, gen. nov. and the new species Ammonidium iowaensis Wicander et Wood, sp. nov., Cymatiosphaera cladora Wicander et Wood, sp. nov., ?Gorgonisphaeridium adjunctum Wicander et Wood, sp. nov., G. parvipinosum Wicander et Wood, sp. nov., Luscinisphaera indistincta Wicander et Wood, sp. nov., Multiplicisphaeridium segregatum Wicander et Wood, sp. nov., Solisphaeridium laevigatum Wicander et Wood, sp. nov. and Villosacapsula compta Wicander et Wood, sp. nov. are established. The chitinozoan assemblage consists of ten species, including Ancyrochitina fruticosa Wicander et Wood, sp. nov.