Comparative Petrology of Cores from Two Test Wells in the Eastern Part of the Edwards Aquifer, South-Central Texas

摘要

The report presents the results of a study that compared zones of cavernous porosity where dolomite has been removed by alteration and zones where stratigraphically equivalent strata still contain dolomite in order to determine the causes of dedolomitization in the Edwards aquifer. The comparison is based on detailed sampling of well-documented, continuous core from the two wells. Enough information is available to place these samples in a regional paleogeographic and diagenetic context so that the results of this comparison are applicable to major parts of the rocks containing the Edwards aquifer. In addition to changes in carbonate lithology, the dedolomitization reactions involved changes in noncarbonate minerals, stable carbon-isotope ratios, and minor and trace elements. In an effort to define these changes, comparative data from x-ray diffraction, mass spectrometry and emission spectroscopy of stratigraphically equivalent samples are presented in the report, along with preliminary interpretation.