PRELIMINARY STUDY OF A MIDDLE MISSISSIPPIAN (LATE OSAGEAN, EARLY VISÉAN) FORT PAYNE CARBONATE MUD-MOUND COMPLEX, CUMBERLAND COUNTY, SOUTH-CENTRAL KENTUCKY
To provide a more contextual understanding of mound genesis, we mapped the distribution of facies in two dimensions, analyzed petrographic samples along a vertical section, and did stable-isotope analyses (δ13Ccarb and δ18Ocarb) on a series of samples. Facies mapping and petrographic analyses indicate that each of the superimposed mounds began with a bed of rudstone, packstone or grainstone that formed a firm mound substrate. On top of this, smaller, organic, carbonate buildups, indicated by clotted micrite with a laminar aspect, developed. The clotted texture reflects algal-produced carbonate mud interspersed with fragmented megafossils and underlying voids filled by early radiaxial fibrous calcite cement. This facies pattern was repeated in each period of mound growth. The δ13Ccarb values (ranging from 2.5 to 4.5‰ VPDB) reflect those from Mii et al. (1999) and others for the Illinois Basin and are thought to represent changes in the dissolved inorganic carbon content of the oceans at the time. Two cycles recording concurrent decreases in δ13Ccarb and δ18Ocarb values correspond with each of the superimposed mounds and suggest possible glacioeustatic control on mound growth. The mounds appear to nucleate on debris-flow deposits at peak glaciation and expand following minor increases in sea level. The analyses conducted herein will aid future studies in understanding the role regional tectonics, paleoclimate and paleoceanography on carbonate mud-mound evolution.