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