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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 68 (1984)

Issue: 4. (April)

First Page: 528

Last Page: 529

Title: Fluid Inclusions in Burlington Limestone (Middle Mississippian)--Evidence for Multiple Dewatering Events from Illinois Basin: ABSTRACT

Author(s): F. D. Smith, R. J. Reeder, W. J. Meyers

Abstract:

Syntaxial calcite cements and dolomite from crinoidal limestones in the Burlington formation, southeastern Iowa and western Illinois, contain 2-phase fluid inclusions which represent samples of the diagenetic fluids. A U.S. Geological Survey-type heating/freezing stage was used to determine the homogenization temperatures, bulk salinities, and major dissolved salt compositions of the inclusions. The calcite- and dolomite-hosted inclusions have mean homogenization temperatures of 85°C (185°F) and 109°C (228°F), respectively. Mean bulk salinities are

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19.4 wt. % total salts for calcite-hosted inclusions and 20.0 wt. % for dolomite-hosted inclusions. Eutectic and intermediate melting data indicate that NaCl and CaCl2 are the principal brine components. The significantly higher mean homogenization temperature for dolomite-hosted inclusions suggests that the dolomitizing fluids were warmer than the fluids from which calcite cement precipitated. Petrographic relationships shown dolomitization preceded calcite cementation. The presence of high-temperature, high-salinity fluids conflicts with previously proposed low-temperature, freshwater diagenetic conditions. The shallow (< 1,500 ft, 450 m) burial history of the Burlington sediments is incompatible with the generation of elevated temperature and salinity fluids intraform tionally, and suggests a more deeply buried source, such as the Illinois basin. Cathodoluminescent cement stratigraphy and fluid temperatures indicate that the diagenetic history of the Burlington Limestone was complex, with several generations of hydrothermal brine migration into the porous Burlington carbonates along the northwestern edge of the basin. Two basinal brine expulsion models can account for the temperature variations seen during diagenesis, either an episodic, compaction-driven flow system or a gravity-driven ground-water flow system.

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