Carbonate-cement stratigraphy of Burlington Limestone (Osagean) of Iowa: evidence for Eh gradients in a regional Mississippian Paleo-groundwater system
Cathodoluminescent petrography of calcite overgrowth cements in crinoidal grainstones from the Burlington Limestone reveals compositional zoning, which suggests that a chemical gradient was effective during cementation. These syntaxial calcite cements have as many as 7 luminescent zones. On the basis of these zones, a regional cement stratigraphy has been established among 22 measured sections within a 5000 mi/sup 2/ area in southeastern Iowa. Overgrowths are interpreted as freshwater phreatic-zone precipitates. Comparison of the characteristic luminescent signature of Burlington calcite cements with cements in underlying Kinderhookian and overlying Meramecian limestones suggest the Burlington formed during, or before, the regional mid-Meramecian (sub St. Louis Limestone) hiatus. Early nonferroan calcite cements show a pronounced basinward change in luminescent zoning. Updip cements consists of 4 distinct compositional zones. In contrast, downdip cements contain only a single luminescent zone. Zonal distribution may have formed when cementation occurred along an Eh gradient within a fresh or phreatic-water system during exposure in mid-Meramecian time. Updip recharge areas were characterized by alternating oxidizing and reducing conditions, resulting in a sequence of luminescent (low Eh) and nonluminescent (high Eh) cement zones. Downdip, away from recharge areas, contemporaneous cements have only a single luminescent zone, which formed under continuously reducing conditions. The recognition of Eh gradients that were effective during carbonate cementation enables paleoflow paths to be determined, and aids in the prediction of diagenetic trends.
- Research Organization:
- Sohio Petroleum Co., San Francisco, CA
- OSTI ID:
- 6000505
- Report Number(s):
- CONF-850322-
- Journal Information:
- Am. Assoc. Pet. Geol., Bull.; (United States), Journal Name: Am. Assoc. Pet. Geol., Bull.; (United States) Vol. 69:2; ISSN AAPGB
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
020200* -- Petroleum-- Reserves
Geology
& Exploration
ALKALINE EARTH METAL COMPOUNDS
CALCITE
CALCIUM CARBONATES
CALCIUM COMPOUNDS
CARBON COMPOUNDS
CARBONATE MINERALS
CARBONATE ROCKS
CARBONATES
DEPOSITION
FEDERAL REGION VII
FOSSILS
GEOLOGIC AGES
GEOLOGY
IOWA
LIMESTONE
MINERALS
MISSISSIPPIAN PERIOD
NORTH AMERICA
OXYGEN COMPOUNDS
PALEOZOIC ERA
RESERVOIR ROCK
ROCKS
SEDIMENTARY ROCKS
STRATIGRAPHY
USA