Anatomy of the grainstone shoal facies of the Salem Limestone (Mississippian) of southern Indiana
- Indiana Univ., Bloomington, IN (United States)
- Indiana Geological Survey, Bloomington, IN (United States)
In 1990 M.A. Brown described the middle Mississippian (Valmeyeran) Salem Limestone exposed on the eastern side of the Illinois Basin as consisting of a massive grainstone shoal facies behind which developed a sand flat, an open lagoon, and a restricted lagoon facies. Smaller intrashoal channels provided limited exchange between lagoon and open ocean. The authors have made detailed studies of sedimentary structures and petrography of the shoal facies in three settings: the shoal proper, an intrashoal channel, and an intershoal channel. The shoal and channel facies consists of tabular-planar and trough cross-stratified beds of grainstone containing echinoderm and fenestrate bryozoan grains as their primary constituents. Prominent hardgrounds that have up to 1 m of erosional relief occur in two of the sections. Despite the apparent uniformity of composition of the shoal, porosity and especially permeability varies over a wide range, suggesting a range of cementation patterns within the shoal. Most of the cement in the shoal consists of syntaxial overgrowths on echinoderm grains. Cementation is less and thus porosity and permeability greater, in portions of the shoals containing a lower concentration of echinoderm grains and grains with thick micrite envelopes. However, some portions of the intershoal channel facies that contain a high percentage of ooids have reduced porosity and permeability due to crushing of ooids, producing micrite that clogged the pores. Primary sedimentary features of the shoal facies were produced predominantly by storm reworking of carbonate grains produced in situ and perhaps in part washed in from surrounding environments.
- OSTI ID:
- 5018899
- Report Number(s):
- CONF-9303210-; CODEN: GAAPBC
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Vol. 25:3; Conference: 27. annual Geological Society of America (GSA) North-Central Section meeting, Rolla, MO (United States), 29-30 Mar 1993; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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