Abstract: The Paraspirifer Acuminatus Biofacies: Paleoecological Analysis of a Fossil Assemblage Relative to Flooding Surfaces within a Middle Devonian Sequence
LEONARD, KARL W., Department of Geological Sciences, Indiana University, Bloomington, IN 47405
A paleoecological analysis of the Paraspirifer acuminatus biofacies in the middle part of the Muscatatuck Group (Middle Devonian of Indiana) carried out relative to a parasequence boundary has helped to delineate a subtle paleoenvironmental gradient. The principle limitation to previous paleoecological studies has been the lack of temporal and spatial control. Traditional biostratigraphic and lithostratigraphic methods can provide only limited temporal and spatial resolution so traditional methods for the study of benthic paleocommunities can provide only general information. These method do not allow for the recognition of minor changes in taxonomic composition relative to paleoenvironmental gradients. Recognition of these small taxonomic changes is, however, crucial for an accurate reconstruction of paleocommunities and paleoenvironments. Sequence stratigraphic techniques can provide the temporal and spatial resolution required to conduct a detailed paleoecological and gradient analysis.
Bulk limestone samples were collected along a north-south transect which represents a probable depth gradient from the lower part of the Paraspirifer acuminatus biofacies directly above a marine flooding surface. The northernmost locality lies directly over a basement structure that manifested itself as a paleotopographic high during the Middle Devonian. Peritidal facies are present below the flooding surface at the base of the parasequence containing the Paraspirifer acuminatus biofacies at this locality. The parasequence boundary at the base of this biofacies in the south overlies a shallow subtidal facies. Relative abundance and diversity of macrofossils and microfossils increases progressively from south to north, and multivariate statistical analyses of the relative abundance and presence/absence data also suggest a south to north shallowing trend.
AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah