ABSTRACT

The environment of deposition and diagenetic changes of some of the Late Pennsylvanian and Early Permian limestones of the Glass Mountains, Texas, are closely reflected in their field relations and in their texture and particle composition as determined by thin section investigations.

From analysis of stable carbon isotopes the fine grained, light colored, algal limestones indicative of an oxidizing environment have distinctly positive C¹³ values, whereas fine grained, dark colored, fetid limestones indicative of reducing environments have markedly negative C¹³ values. The coarse grained limestones having abundant sparry calcite cement have C¹³ values near zero, that is, a C¹³/C¹² ratio near the standard, Chicago PDB, a belemnite. These C¹³ values suggest that the source of the sparry calcite cement is at least in part from CO₂ produced by methane fermentation of organic material in the substrata.