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Speleogenesis and Morphologic Characterization of Secondary Gypsum Development in Amazing Maze Cave, Pecos County Texas

Bryan F. Byrd
Department of Geology, Stephen F. Austin State University
P.O. Box 13011, SFA Station Nacogdoches, TX 75962-3011

Amazing Maze Cave, in Pecos County, Texas is a rectilinear maze cave that appears to have been formed by hypogenic processes. The cave resides in Lower Cretaceous Fort Terrett limestone of Fredericksburg Group carbonates that have undergone varying degrees of dolomitization.

Several mineral species are found in the cave that indicate a H2S hypogenic dissolution processes, such as secondary gypsum, possible halloysite 10Å, carnotite, and manganese oxides. Most are spatially limited, but common throughout the cave are massive secondary gypsum forms filling passage floors near intersections and dominating the spatial volume of many larger rooms.

The angular maze shape of the cave, along with the appearance of speleogens such as cupolas, risers, and ceiling channels, are definitive characteristics of a morphometric suite of rising flow characteristic of mixed convection flow regimes associated with hypogene cavernous porosity development. Secondary minerals and morphological features in the cave support a sulfuric-acid hypogenetic model for speleogenetic origin with H2S likely originating from San Andres hydrocarbon reservoirs proximal to the study area.

Current studies focus on the gypsum massives utilizing GPR (Ground Penetrating Radar) and mapping for quantitative analyses and spatial extents. Also utilized are XRPD (X-Ray Powder Diffraction), Mass Spectroscopy, and SEM (Scanning Electron Microscopy) for qualitative analyses and better understanding of fluid chemical and flow dynamics forming the cave and the subsequent gypsum forms. These studies should provide better insight for the fluid chemical and fluid kinetics responsible for cavernous porosity and permeability development in carbonate environments decoupled from surficial influences.

AAPG Search and Discovery Article #90182©2013 AAPG/SEG Student Expo, Houston, Texas, September 16-17, 2013