Eolianite-Bearing Depositional Parasequences in the Ste. Genevieve Limestone of Indiana and Kentucky: Evidence for Mississippian Eustacy?
J. Robert Dodd, Ralph E. Hunter, and Patricia A. Merkley
Carbonate eolian deposits are interbedded with shallow marine limestones within the Ste. Genevieve Limestone in southern Indiana and northern Kentucky. Eolian grainstones occur in four intervals within the formation. Subaerial exposure surfaces, revealed by brecciation, rhizoliths, and calcrete are usually associated with the eolianites. Seven cycles or parasequences defined by marine-flooding surfaces occur in the Ste. Genevieve and upper St. Louis Limestones in this area. The base of a parasequence is marked by a flooding surface indicated by marine sediments above an eolian unit or exposure surface. Basal beds are typically carbonate mudstones or wackstones (commonly dolomitized) that probably formed in the deepest environment. These deposits typically are overlain by eolitic, skeletal, or peloidal marine grainstones or packstones that probably formed as shoal or beach deposits. These may be topped by an exposure surface. The upper unit in four of the parasequences is an eolian deposit that commonly has rhizoliths and calcrete stringers at the top or within the deposit. The upper boundary of the parasequence is marked by another marine-flooding surface. In some cases eolian deposits are missing from the parasequence, probably due to nondeposition. Individual sequences can be correlated along the outcrop belt for at least 50 km and for at least 20 km across the outcrop belt and in nearby cores. Eolianites and exposure surfaces formed during falls in relative sea level that may have been caused by eustatic changes related to the early stages of late Paleozoi glaciation, but local tectonism cannot be ruled out.
AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California