PALEOECOLOGY OF THE UPPER MISSISSIPPIAN AVIS LIMESTONE, MIDDLE HINTON FORMATION: EVIDENCE FOR DROWNING EVENTS IN THE APPALACHIAN BASIN

Evidence for 3^rd and 4^th -order drowning events resulting from rapid marine transgression of glacio-eustatic and tectono-eustatic origin is recorded by condensed sections represented by fossiliferous limestones and black shales within the Avis Limestone member of the late Mississippian (Chesterian) Middle Hinton Formation. Two stratigraphic sections were constructed with the view of deciphering the paleoenvironmental conditions of the Avis Limestone member using both sedimentological and paleontological approaches. Seven major lithofacies consisting of subaerial red beds, coastal plain calcareous siltstone, shallow marine muddy carbonates (mudstones and wackestones), restricted marine calcareous shales, tidal bar grainstones, and open marine packstones have been identified within the study interval. These facies define upward-coarsening parasequences separated by flooding surfaces. Description of the facies within a sequence stratigraphic framework shows that lowstand systems tracts are poorly developed. Transgressive systems tracts are carbonate-prone or dolomitic, whereas highstand systems tracts are dominantly interbedded units that are deposited during deltaic progradation and subsequent basin shallowing. Sequence boundaries are erosional discomformities on top of previous highstand that overlies shallowing-upward carbonate units. Sedimentary structures and faunal content in these rock units provided insights into probable sedimentary processes and paleoecological factors like sedimentation rates, oxygen levels, salinity, turbidity, depositional energy, temperature and water depth. Multivariate analyses including cluster analysis, non-metric multidimensional scaling (NMDS) and correspondence analysis revealed patterns in the fossil occurrences for the different locations and overall depositional conditions of the Avis Limestone.