Eolianite-Bearing Depositional Cycles in the Ste. Genevieve Limestoneof Indiana and Kentucky: Evidence for Mississippian Eustasy
J. Robert Dodd, Ralph E. Hunter, Patricia A. Merkley, 2001. "Eolianite-Bearing Depositional Cycles in the Ste. Genevieve Limestoneof Indiana and Kentucky: Evidence for Mississippian Eustasy", Modern and Ancient Carbonate Eolianites: Sedimentology, Sequence Stratigraphy, and Diagenesis, F. E. (Rick) Abegg, David B. Loope, Paul M. (Mitch) Harris
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Carbonate eolian deposits are interbedded with shallow-marine limestones in the Ste. Genevieve Limestone in southern Indiana and northern Kentucky. Eolian grainstones can be distinguished from marine grainstones on the basis of sedimentary structures and petrographic characteristics. Eolian grainstones occur in four separate intervals in the formation. Subaerial exposure surfaces, as revealed by brecciation, rhizoliths, and calcrete, are usually at the tops of eolianites. Some exposure surfaces are not accompanied by eolian deposits, indicating that eolianites are discontinuous.
At least seven shoaling-upward cycles (0 to 12 m thick) bounded by marine-flooding surfaces occur in the Ste. Genevieve and upper St. Louis Limestones in this area. Individual cycles can be correlated along the outcrop belt for at least 50 Ion and for at least 20km across the outcrop belt and in nearby cores. The base of a cycle is marked by a flooding surface as indicated by marine sediments above an eolian unit or exposure surface. The basal beds are typically carbonate mudstones or wackestones (in some cases dolomitized), which probably formed in the deepest envLronment. These micrite-ricb deposits typically are overlain by oolitic, skeletal, or peloidal marine grainstones or packstones, which probably formed as shoal or beach deposits. These are in many cases topped by an exposure surface as indicated by brecciation, rhizoliths, and rare calcrete stringers. The upper unit in four of the cycles is an eolian deposit that commonly has rhizoliths and calcrete stringers at the top and in some locations within the deposit. The upper boundary of the cycle is marked by another marineflooding surface. In some cases eolian deposits are missing from the cycle, probably because of nondeposition.
Eolianites and exposure surfaces formed during falls in relative sea level. Sea-level fluctuation may have been caused by eustatic changes related to the early stages of late Paleozoic glaciation, but local teclonism cannot be disproved. Eolian deposits reach their maximum known thickness of about 6 m in the Corydon area and gradually thin to zero to the west and north.
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Carbonate eolianites had long been considered to be limited to the Quaternary, but a number of Mesozoic and Paleozoic examples have been documented in the past 15 years. Thus, an increased awareness of carbonate eolianites is required to properly interpret the rock record and to assess their spatial and temporal distribution. The papers of this volume will help geologists to: (1) recognize carbonate eolianites and understand their preservation potential—recognitional criteria for most carbonate environments are common knowledge, but this is less true for carbonate eolianites; (2) understand their sedimentologic and diagenetic variability—diagenesis of carbonate eolianites has important economic considerations. Whereas Quaternary eolian limestones are commonly porous, Paleozoic and Mesozoic examples are typically tight owing to compaction; (3) understand the Psilionichnus (marginal marine) and Scoyenia (nonmarine) Ichnofacies—carbonate eolianites are not devoid of trace fossils; (4) interpret them in a sequence stratigraphic framework—interpretations of relative sea level during eolian deposition can be difficult, as differences between transgressive, regressive, and deflationsourced eolianites are subtle. Thus, the placement of sequence boundaries within interbedded eolian and subtidal carbonate successions is not entirely straightforward.