PHYSICAL AND BIOLOGICAL DRIVERS OF REGIONAL VARIATION IN PENNSYLVANIAN-PERMIAN MARINE INVERTEBRATE PALEOCOMMUNITIES OF THE MIDCONTINENT, USA

Explaining variation in diversity at global, regional, and local scales is a fundamental question of biology. Marine environments present a gradient of depth-associated habitats that vary concurrently in grain size, oxygenation, light penetration, wave energy, and other physical factors. The composition of resident ecological communities varies along this gradient as taxa track their preferred habitats. Within a depth zone, communities may also vary due to small-scale physical heterogeneity, positive or negative interactions between organisms, or simply stochastic fluctuation in the taxa that happened to establish at a location. Thus, regional diversity can be partitioned into a patchwork of local communities that vary for a variety of reasons.

The late Pennsylvanian and early Permian rocks of the American Midcontinent present an opportunity to study the variation between communities and how it contributes to regional diversity. Strata of this time interval are composed of regionally continuous meter-scale cycles of shale and limestone. This study traces two of these cycles, sampling invertebrate communities from north to south across eastern Kansas along a 300-km transect which roughly parallels the very shallow depositional dip of the original epicontinental platform. This study characterizes and explores the differences between individual communities within the region and the contributions of these local communities to regional diversity. Possible causes of variation may include aspects of the physical environment such as relative position offshore or oxygenation of sediment, in line with previous work on brachiopods; partitioning of local habitat into niches by exploiting different life modes, investigated using a theoretical ecospace; or engineering of the sedimentary environment by the organisms (phylloid algae and fusulinid foraminifera) responsible for the bioherms which are present in the carbonate units of both cycles examined.