Carbonate petrography of the Burlington/Keokuk contact in southeastern Iowa
- Kansas State Univ., Manhattan, KS (United States). Geology Dept.
The top of the Burlington Formation (Mississippian, Osagean Series), a dominantly skeletal packstone/grainstone unit in southeastern Iowa, is defined by a regionally persistent bone bed horizon and is overlain by the lower Keokuk Formation, a dominant skeletal wackestone and chert. A thin gray-green shale at some localities at the contact is interpreted as a condensed section that corresponds to a deepening event during the beginning of the Keokuk deposition. Both units represent similar carbonate bank settings deposited during rapid, uninterrupted progradation of carbonate sediments during changing sea levels. The upper Burlington facies consists dominantly of crinoids and has the highest biotic diversity (i.e., bryozoan, corals, and brachiopods) during the most open marine conditions. In thin section most crinoid grains show moderate abrasion and some evidence of early fragmentation. Frequent winnowing during storm events resulted in relatively clean packed calcarenite fabrics. Both formations acted as a single paragenetic unit during the induration process, characterized by multiple episodes of cementation, dolomitization, and compaction. Crinoidal syntaxial overgrowths and crushed bryozoan matrix make up most of the packstone/grainstone fabrics in both formations. The presence of mashed bryozoans suggests that some compaction may have preceded complete stabilization of the sedimentary mass by crinoidal syntaxial overgrowth cements. Staining revealed at least three generations of syntaxial overgrowth cements which probably formed in a meteoric phreatic environment during a relatively short period of geologic time.
- OSTI ID:
- 6002231
- Report Number(s):
- CONF-9303212-; CODEN: GAAPBC
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Vol. 25:1; Conference: 27. annual Geological Society of America (GSA) South-Central Section meeting, Fort Worth, TX (United States), 15-16 Mar 1993; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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