Faunas of Mississippian Oolitic Limestones: Evidence from Salem Limestone, Southern Indiana

Howard Randall Feldman

In the Salem Limestone of southern Indiana, a correlation exists between the faunal assemblage and abundance of grains with superficial oolitic coatings in grainstones. Coarse, poorly sorted fossiliferous grainstones are dominated by an echinoderm-bryozoan-brachiopod assemblage of fossils with few mollusks. The presence of large whole fossils, such as articulated crinoid calyces, suggest limited transport of skeletal components. Grainstones, dominated by grains with superficial coatings, and foraminifers tend to contain a diverse mollusk-dominated assemblage of gastropods, bivalves, rostroconchs, chitins, and scaphopods. These fossils are disarticulated, but generally are not fragmented even though many of them are thin and delicate. Echinoderms, brachiopods, and bryozoan are represented in the mollusk-dominated assemblage almost exclusively by well-rounded and coated fragments, suggesting that they are not in situ. The presence of similar molluscan assemblages in other Mississippian coated-grain grainstones from Alabama (the Monteagle Limestone) and Oklahoma (an unnamed limestone) indicates that the assemblage may have been widespread. Mississippian grainstones dominated by oolites (which are not prominent in the Salem) generally have very few fossils.

The development of oolitic coatings probably corresponds roughly to the amount of reworking of carbonate coarse clastic substrates. Sediment that was not frequently reworked supported sessile attached benthos such as brachiopods, bryozoans, and echinoderms, many of which probably could not survive shallow burial. Moderately reworked substrates supported mobile benthos dominated by mollusks, and intensely reworked substrates supported little or no shelly benthic fauna.

AAPG Search and Discovery Article #91023©1989 AAPG Eastern Section, Sept. 10-13, 1989, Bloomington, Indiana.