Comparison of Shallow-Marine Shelf Carbonate Mounds of Fort Payne Formation (Lower Mississippian) of Tennessee with Waulsortian Mounds of Western Europe: ABSTRACT

Abstract

Although Fort Payne and Waulsortian carbonate mounds are similar, differences in sedimentary and diagenetic environments account for the development of porosity, permeability, and emplacement of petroleum in producing Fort Payne mounds. Waulsortian-type mounds, including the Fort Payne mounds, are characterized by: (1) similar mound morphology and alignment of mound trends, (2) distinctive microfacies and limited faunal diversity, and (3) limited stratigraphic and widespread geographic occurrence. European Waulsortian mounds, exposed on the surface, range up to 300 m thick, are not generally porous, and contain little evidence of hydrocarbons. They occur on relatively rapidly subsiding shelf margins, at intermediate water depths, and were not subaerially exposed during buildup. Fort Payne limestone mounds are low relief features (30 m thick) with initial dips less than 1°, containing primary and secondary porosity in bryozoan grainstones in multiple zones within dominant mud-supported microfacies. Mounds formed on a shallow slowly subsiding shelf (ramp) during transgression. Variation in rate of subsidence or eustatic sea-level changes are recorded either by minor zones bearing normal marine fauna or by zones bearing shallow-marine dolomite and evaporites. Periodic subaerial exposure and descending, dissolving, meteoric water probably enhanced secondary porosity development. Minor, but complex, synsedimentary solution collapse, fracturing, and brecciation during mound compaction occurred above evacuated evaporites, solution seams, and stromatactis cavit es. After burial by Warsaw Formation clastics, subsurface (mesogenetic) diagenesis is documented by postlithification compaction features including stylolites, microstylolites, and multiple-fractured breccias. Pore-fill spar occlusion of some porosity, and emplacement of petroleum in permeable reservoirs were late mesogenetic events. End_of_Article - Last_Page 743------------