Cleats and fractures in southwestern Indiana coal scams are often filled with authigenic kaolinite and/or calcite. Carbon- and oxygen-stable isotope ratios of kaolinite, calcite, and coalbed CO2 were evaluated in combination with measured values and published estimates of PO of coalbed paleowaters that had been present at the time of mineralization. delta O-18 (mineral) and delta O-18(water) values jointly constrain the paleotemperature of mineralization. The isotopic evidence and the thermal and tectonic history of this part of the Illinois Basin led to the conclusion that maximum burial and heat-sterilization of coal seams approximately 272 Ma ago was followed by advective heat redistribution and concurrent precipitation of kaolinite in cleats at a burial depth of < 1600 m at similar to 78 +/- 5 degrees C. Post-Paleozoic uplift, the development of a second generation of cleats, and subsequent precipitation of calcite occurred at shallower burial depth between similar to 500 to similar to 1300 m at a lower temperature of 43 +/- 6 degrees C. The available paleowater in coalbeds was likely ocean water and/or tropical meteoric water with a delta O-18(water)similar to-1.25 parts per thousand versus VSMOW. Inoculation of coalbeds with methanogenic CO2-reducing microbes occurred at an even later time, because modern microbially influenced C-13- enriched coalbed CO2 (i.e., the isotopically fractionated residue of microbial CO2 reduction) is out of isotopic equilibrium with C-13- depleted calcite in cleats. (c) 2007 Elsevier B.V. All rights reserved.