Multivariate Analyses of Trace Fossil Distribution from an Early Mississippian Oxygen-Deficient Basin, Central Appalachians

The Early Mississippian Appalachian foreland basin was oxygen deficient. The Price Formation constitutes a deltaic sedimentary wedge that prograded westward into the foreland basin following a major transgression. Shallow-shelf facies are preserved in north-central West Virginia (Riddlesburg Shale Member) and basinal facies are preserved farther south (Sunbury Shale Member). An overturned section near Bluefield preserves basinal submarine fan, fan-slope and outer-shelf facies that grade upsection to shoreline facies. High organic contents in outer shelf shales and abundant, large phosphate nodules indicate that upwelling took place offshore of the Price deltaic complex. A paleodepth of 150 m can be estimated for the Sunbury Shale based on stratigraphic thickness at the Bluefield section. The lateral and vertical distribution of oxygen-deficient bottom water was controlled by surficial wave and current mixing in the aerobic layer that extended to depths of approximately 60-75 m. Distributary channel-fill facies are not preserved in the Bluefield sequence and significant clastic influx and dilution of the density-stratified water column did not occur in the area. Abundant and diverse deposit-feeding and grazing traces of the Nereites Ichnofacies occur in outer shelf silty shales and sandstone tempestites. The basin-to-shoreline facies transition at Bluefield is paralleled by gradation from the Nereites to the Skolithos Ichnofacies with no transitional Cruziana Ichnofacies between. Oxygen-deficient bottom water appears to have been limiting to trace-makers with diverse ethologies characteristic of the Cruziana Ichnofacies. R-mode and Q-mode cluster analyses, minimum spanning trees and multidimensional scaling have been used to define environmental gradients expressed by trace fossils from the Bluefield section and in a larger data set comprising the entire Price Formation. Cluster analysis has defined two major trace-fossil assemblages in the Price that constitute Cruziana and Nereites Ichnofacies. A Skolithos Ichnofacies is defined by ichnogenera excluded from the two major assemblages.