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 End_Page 528------------------------------ 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 ( End_of_Article - Last_Page 529------------
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