. Permian evaporites of the Castile Formation crop out over ~1,800 km2 in the western Delaware Basin (Eddy County, New Mexico and Culberson County, Texas, USA) with abundant and diverse karst manifestations. Epigene karst occurs as well-developed karren on exposed bedrock, while sinkholes dominate the erosional landscape, including both solutional and collapse forms. Sinkhole analyses suggest that more than half of all sinks are the result of upward stoping of subsurface voids, while many solutional sinks are commonly the result of overprinting of collapsed forms. Epigene caves are laterally limited with rapid aperture decreases away from insurgence, with passages developed along fractures and anticline fold axes. Hypogene karst occurs as diverse manifestations, forming the deepest and longest caves within the region as well as abundant zones of brecciation. Hypogene caves exhibit a wide range of morphologies from complex maze and anastomotic patterns to simple, steeply dipping patterns, but all hypogene caves exhibit morphologic features (i.e. risers, outlet cupolas and half-tubes) that provide a definitive suite of evidence of dissolution within a mixed convection (forced and free convection) hydrologic system. Extensive blanket breccias, abundant breccia pipes and numerous occurrences of calcitized evaporites indicate widespread hypogene speleogenesis throughout the entire Castile Formation. Although most cave and karst development within the Castile outcrop region appears to have hypogene origins, epigene processes are actively overprinting features, creating a complex speleogenetic evolution within the Castile Formation. Keywords: hypogenic caves, epigenic overprint, speleogenesis, evaporites, geomorphology Received 21 July 2007; Revised 16 October 2007; Accepted 8 November 2007Permian (Fig. 2) (Scholle et al, 2004). Limited studies on specific caves or local karst regions have been conducted within the evaporite facies of the Permian Basin, including karst studies in the San Andres Formation (Forbes & Nance, 1997) and Seven Rivers Formation (Stafford et al, 2007a;Land, 2006) of the Artesia Group, the Castile Formation (Sares, 1984;Nance, 1993), and the Salado and Rustler Formations (Hill, 1996). However, no studies have been conducted to evaluate the full range of cave and karst development within any of the evaporitic units of the region. Cave exploration has been conducted by the Gypsum Karst Project (GYPKAP) of the National Speleological Society throughout the evaporite karst regions of New Mexico (Eaton, 1987; Belski, 1992;Lee, 1996). Documentation of evaporite karst regions within Texas has been conducted by the Texas Speleological Survey (TSS) (e.g. Redell & Fiesler, 1977). Although all of the evaporite facies of the region deserve comprehensive study, it is beyond the scope of a single study; therefore, this research focuses specifically on karst development in one evaporitic unit, the Castile Formation because it is the largest continuous outcrop of a single evaporite formation in the Permian Basin...
The Monterrey metropolitan area (MMA) is the third greatest urban area and the second largest economic city of Mexico. More than four million people living in this megacity use groundwater for drinking, industrial and household purposes. Thus, major ion and trace element content were assessed in order to investigate the main hydrochemical properties of groundwater and determine if groundwater of the area poses a threat to the MMA population. Hierarchical cluster analysis using all the groundwater chemical data showed five groups of water. The first two groups were classified as recharge waters (Ca-HCO3) coming from the foothills of mountain belts. The third group was also of Ca-HCO3 water type flowing through lutites and limestones. Transition zone waters of group four (Ca-HCO3-SO4) flow through the valley of Monterrey, whereas discharge waters of group 5 (Ca-SO4) were found toward the north and northeast of the MMA. Principal component analysis performed in groundwater data indicates four principal components (PCs). PC1 included major ions Si, Co, Se, and Zn, suggesting that these are derived by rock weathering. Other trace elements such as As, Mo, Mn, and U are coupled in PC2 because they show redox-sensitive properties. PC3 indicates that Pb and Cu could be the less mobile elements in groundwater. Although groundwater supplied to MMA showed a high-quality, high mineralized waters of group 5 have NO3 − concentrations higher than the maximum value proposed by international guidelines and SO4 2−, NO3 −, and total dissolved solid concentrations higher than the maximum levels allowed by the Mexican normative.
Evaporite calcitization within the Castile Formation ofthe Delaware Basin is more widespread and diverse than originally recognized. Coupled field and GIS studies have identified more than 1000 individual occurrences of calcitization within the Castile Formation outcrop area, which includes both calcitized masses (limestone buttes) and laterally extensive calcitized horizons (limestone sheets). Both limestone buttes and sheets commonly contain a central brecciated zone that we attribute to hypogene dissolution. Lithologic fabric of calcitized zones ranges from little alteration of original varved laminae to fabrics showing extensive laminae distortion as well as extensive vuggy and open cavernous porosity. Calcitization is most abundant in the western portion of the Castile outcrop region where surface denudation has been greatest. Calcitization often forms linear trends, indicating fluid migration along fractures, but also occurs as dense clusters indicating focused, ascending, hydrocarbon-rich fluids. Native sulfur, secondary tabular gypsum (i.e. selenite) and hypogene caves are commonly associated with clusters of calcitization. This assemblage suggests that calcium sulfate diagenesis within the Castile Formation is dominated by hypogene speleogenesis.
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