MICROENDOLITHIC STRUCTURES FROM THE FORT PAYNE FORMATION (LOWER MISSISSIPPIAN), KENTUCKY AND TENNESSEE: IMPLICATIONS FOR THE PALEOENVIRONMENT OF CARBONATE MUD-MOUNDS

Resin cast embedment and naturally occurring internal molds have revealed for the first time an assemblage of microendoliths from the Early Mississippian Fort Payne Formation. Heterotrophic microendoliths Orthogonum lineare, O. giganteum, and Saccomorpha clava dominate this unit, as well as the phototrophic traces Ichnoreticulina elegans and Fascichnus dactylus, a chlorophyte (Ostreobium quekettii) and cyanobacteria (Hyella caespitosa), respectively, that were found within a variety of fossil substrates, including solitary corals, bryozoans, brachiopods, and gastropods, with a notable absence in all echinoderms. The Fort Payne from the Lake Cumberland/Dale Hollow region of southern Kentucky-northern Tennessee contains a suite of fossiliferous green shale deposits with isolated locations of enigmatic carbonate mud-mounds. The latter, commonly referred to as ‘Waulsortian’ mounds, have been the center of much speculation in the past few decades. Paleoenvironmental parameters in which formation occurred have only been indirectly inferred. Using the aforementioned microendoliths, a sense of the light availability within the Illinois Basin can be determined. The ichnofaunal assemblage uncovered is representative of light conditions spanning from dysphotic to aphotic. Using previously constrained depth parameters that indicate a depth of no more than 100m, a dysphotic environment suggests that the water column was eutrophic, presumably due to high productivity within the Illinois Basin. This would seem to corroborate several other inferences about the Early Mississippian, including the growing number of suspension feeding echinoderms, in addition to the restructuring of phytoplanktonic communities and increased nutrient flux from a developing terrigenous floral weathering regime in the Early Mississippian.