pg(s) 123-131 Karst
development in Permian Castile evaporites has resulted in
complex speleogenetic evolution with multiple phases of
diagenetic overprinting. More than 10,000 surficial features,
primarily sinkholes, occur throughout Culberson County, Texas,
and Eddy County, New Mexico, based on GIS-analyses where
laminated Castile sulfates crop out. Cave development is
largely the result of hypogene processes, where ascending
fluids from the underlying Bell Canyon Formation migrate near
vertically through the Castile Formation, creating caves up to
100 meters deep and over 500 meters long, which have been
breached through a combination of collapse and surface
denudation. Numerous small and laterally limited epigene
features occur throughout the region, as well as the
anomalously large Parks Ranch Cave System with more than 6.5
kilometers of cave development and multiple large, incised,
sinkhole entrances. Hypogene caves exhibit varying degrees of
epigenic overprinting as a result of surficial breaching. Water
resources in the Castile Formation are directly related to
karst development with extremely heterogeneous flow networks.
Most springs in the region discharge sulfate-rich waters,
contain high levels of hydrogen sulfide, and support
sulfate-reducing bacterial colonies. Isolated stream passages
in northern Culberson County provide locally significant water
resources that do not exhibit elevated hydrogen sulfide
concentrations. Local water tables vary greatly over the region
and few caves access base-level conditions. Upward migration of
hydrocarbons complicates regional hydrology and diagenesis,
resulting in extensive evaporite calcitization, which greatly
modifies both fluid / rock interaction and permeability
13TH SINKHOLE CONFERENCE NCKRI SYMPOSIUM 2 123 caves and rapidly evolving landscapes, all of which are coupled to a complex and poorly understood eastern New Mexico and far west Texas, with Castile strata outcrops limited to Eddy County, New Mexico, and Culberson County, Texas, along the western edge of the Delaware Basin (Figure 1). The region occurs within the northern portion of the Chihuahuan Desert with annual Annual precipitation averages 267 mm, with greatest summer monsoonal storms. Cave and karst development in far west Texas and southeastern New Mexico is extensive and widespread; however, most people envision the famous carbonate Lechuguilla Cave) when they think of this region, which overlooked and generally less studied, evaporite karst in the region is more extensive and widespread. In interbedded gypsum, carbonate, and clastic strata host extensive karst development in the Castile Formation, while strata overlying (Salado and Rustler formations) similar karst development (Stafford and Nance, 2009). Most research on evaporite karst associated with Permian deposition in the region has received little study, including geology (e.g. Forbes and Nance, 1997; Nance, Abstract Karst development in Permian Castile evaporites has resulted in complex speleogenetic evolution with multiple phases of diagenetic overprinting. More than throughout Culberson County, Texas, and Eddy County, Castile sulfates crop out. Cave development is largely from the underlying Bell Canyon Formation migrate near vertically through the Castile Formation, creating caves up to 100 meters deep and over 500 meters long, which have been breached through a combination of collapse and surface denudation. Numerous small and laterally limited epigene features occur throughout the region, as well as the anomalously large Parks Ranch Cave System with more than 6.5 kilometers of cave development and caves exhibit varying degrees of epigenic overprinting Water resources in the Castile Formation are directly related to karst development with extremely colonies. Isolated stream passages in northern Culberson Local water tables vary greatly over the region and few of hydrocarbons complicates regional hydrology and diagenesis, resulting in extensive evaporite calcitization, permeability structures. Introduction The arid southwestern United States hosts unique EVAPORITE KARST AND HYDROGEOLOGY OF THE Kevin W. Stafford Department of Geology, Stephen F. Austin State University, P.O. Box 13011, SFA Station, Nacogdoches, Texas, 75962-3011, email@example.com
NCKRI SYMPOSIUM 2 13TH SINKHOLE CONFERENCE 124 a complex and evolving hydrogeologic system. Study Area The Castile Formation crops out over approximately 1800 km 2 in Eddy County, New Mexico, and Culberson in the north to the Apache Mountains in the south (Figure 1). The western portion of the Castile Formation truncation associated with the uplifted Delaware Mountains. To the east, the Castile Formation dips into the subsurface beneath younger strata where it reaches a maximum thickness of 480 meters (Kelley, 1971). Intrastratal speleogenesis and diagenetic alterations occur throughout the eastern portion of the Delaware Basin where Castile evaporites are exposed at the land surface (Stafford et al., 2008a). Permeable siliciclastics of the Bell Canyon and Cherry Canyon formations underlie the Castile Formation throughout the Delaware Basin; the carbonate reef facies of the Capitan Formation (Figure 2) (Lee and Williams, 2000). The Castile Formation was deposited in the Ochoan, Reef, which is now exposed at the surface in the at the end of the Permian (Kirkland and Anderson, 1970; halite. Sulfates are hydrated to gypsum near the surface in the deeper subsurface. Similarly, halite interbeds are with limited reporting associated with karst inventories (e.g. Eaton, 1987; Belski, 1992; Lee, 1996). In the last in an attempt to characterize its speleogenetic and Stafford et al., 2008a, 2008b). Castile evaporites host a complex history that includes phases of hypogene and epigene cave development, high rates of landscape denudation, extensive evaporite calcitization, and a Figure 1. Castile Formation outcrop area showing relationship to major depositional features of the Delaware Basin and geomorphic features. Small inset shows relationship of Delaware Basin to the Orogrande Basin (OB), Val Verde Basin (VB) and Midland Basin (MB) (from Stafford et al., 2008c). Figure 2. Simplified stratigraphic section of Permian strata in the Delaware Basin region (adapted from Scholle et al., 2004).
13TH SINKHOLE CONFERENCE NCKRI SYMPOSIUM 2 125 bedrock, with typical varieties associated with the slope of the rock surface they are developed upon (Stafford et al., 2008b). Deeply incised rillenkarren form long and length of rillenkarren increasing proportionally from moderately dipping surfaces to near vertical surfaces. apexes of dipping rock surfaces and converge through dendritic channels into rillenkarren. Kamenitzas form on algal crusts that hydrate during monsoonal storms. In addition to the normal karren forms, tumuli commonly limited to more deeply buried portions of the Castile Formation where they have not been removed by intrastratal dissolution (Kelley, 1971). Calcite laminae fabrics have been diagenetically altered since deposition, creating irregularly laminated, massive, nodular, and Throughout the Castile Formation, evaporite calcitization is common and widespread. Stafford et al. (2008c) documented more than one thousand regions of calcitized evaporites exposed at the surface across the into calcitization associated with vertical breccia pipes and calcitization associated with intrastratal dissolution Kirkland and Evans (1976) attributed these calcitized evaporites to bacterial sulfate reduction; however, isotope analyses by Stafford et al. (2008c) showed that differentiate the calcitization as being the result of bacterial sulfate reduction or thermal sulfate reduction. These extensive calcitized evaporites have formed along gases delivered from the underlying Bell Canyon and Cherry Canyon formations have migrated through Castile strata (Stafford et al, 2008c). Associated with most of the calcitized evaporites, intrastratal dissolution and recrystallization of microcrystalline sulfate into macrocrystalline sulfate (selenite) is common, as well as native sulfur, which is limited due to high rates of oxidation in near surface calcitized zones. Surficial-Karst Development crops out is widespread and diverse, ranging from large sinkholes to small karren developed on exposed bedrock (Stafford et al., 2008b). The Castile Formation has been 2 ) of the surface area is composed of exposed bedrock and less than one percent is calcitized evaporites. Alluvium associated with Quaternary gravels commonly occurs along incised drainages, while residual outcrops of the Rustler Formation occur as patchy remnants across the Figure 3. Castile Formation outcrop area geomorphic map, delineating zones of exposed bedrock, gypsite, calcitized evaporites, and karst features.
NCKRI SYMPOSIUM 2 13TH SINKHOLE CONFERENCE 126 Subsurface Karst Development Cave development in the Castile Formation is diverse and widespread, but not uniform. The spatial distribution of caves mimics that of sink development delineated cave development scattered amongst regions of poor cave development. Caves exhibit varying degrees of structural control, with many features being purely developed along fracture planes, while others show no distinct correlation to structural deformation (Stafford et al., 2008b). Cavernous porosity includes hypogene caves and intrastratal breccias, epigene caves, and hybrids that have resulted from epigenic overprinting of hypogene systems (Figure 6). resulting in a buckling of the local land surface over regions up to several meters. In regions where karren bedrock as a result of dissolution and reprecipitation of gypsum at the land surface (Stafford et al., 2008b). et al. (2008a) predict that more than 10,000 individual closed depressions exist across the study area based on on length to width ratios, and it was determined that at least 55% of the closed depressions were collapse structures while the remaining 45% were a mix of purely where surface denudation has enabled collapse features of subsurface voids that may not have been originally The widespread occurrence of collapse sinks and year investigation of surface denudation across the region utilizing standard gypsum tablets. Their data fall monsoonal season, with rates generally increasing northward away from the Apache Mountains to the southern and northern margins of the outcrop area, respectively (Shaw et al., 2011). When compared with the distribution of karst development assessed through sinkhole delineation (Figure 4), a similar trend is observed; however, sinkhole distribution is highly localized and occurs more frequently towards the western portion of the Castile outcrop area where total Castile thickness is reduced on the updip side of strata. Figure 4. Distribution of closed depressions across the Castile outcrop area derived from GIS analyses (modified from Stafford et al., 2008b).
13TH SINKHOLE CONFERENCE NCKRI SYMPOSIUM 2 127 humanly impassable within a few tens of meters as a result of the rapid solution kinetics associated with calcium sulfate (Klimchouk, 2000). Zombie Cave (Figure 6A) and Dead East Cave (Figure 6B) are the largest purely epigene caves that have been documented within the 41 meters, respectively. Although exceptionally large for epigene caves in the Castile Formation, they exhibit typical characteristics, including: 1) narrow apertures developed along dominant fractures; 2) laterally of secondary fractures proximal to the main conduit development. Most epigene features are developed in laminated, massive, and nodular facies; however, they occasionally develop in tabular (selenite) gypsum along crystal planes and in gypsite soils along zones of permeability contrast. extensive and deep cave systems within the Castile systems and isolated solutional chambers (Stafford et al., features, including risers, cupolas, wallchannels, and ceiling channels, often connected in series that show the complete suite of morphological features created (Klimchouk, 2007). Unlike epigene caves, hypogene features do not show rapid decreases in aperture width but instead exhibit zones of increasing pore volume beneath permeability boundary horizons. While hypogene caves do still exhibit passage correlation with fracture planes, they do not show speleogenetic dominance along preferential planes, but instead anticlinal structures and fracture planes with complex interconnected passages at multiple levels, while Bee Line Cave (Figure 6E) is largely a single solutional dome room in an ascending series of cupolas that have been overprinted by meteoric processes. Crystal series with interconnected ceiling and wall channels, in which the lowest portions of the cave descend below the current water table and are developed in selenite. Other hypogene caves in the study area (e.g. Black Dog Cave) exhibit inverse dendritic patterns where multiple Most caves within the Castile outcrop area are small and laterally limited epigene features (Figures 6A & 6B), having formed as either local groundwater recharge features or shallow bypass features proximal to incised arroyos. Epigene caves exhibit scalloped walls, are developed along fracture planes, and can be associated with solutional sinkholes that cover several hectares and routinely pass through these features, likely associated with extensive runoff during monsoonal storm events (Stafford et al., 2008b). Epigene cave apertures rapidly decrease away from entrance areas, generally becoming Figure 5. Average surface denudation for the Castile outcrop area based on standard tablet studies (modified from Shaw et al., 2011).
NCKRI SYMPOSIUM 2 13TH SINKHOLE CONFERENCE 128 Figure 6. Simplified plan and profile maps of Castile Formation caves, including epigene caves (A,B), hypogene caves (C,E,G), stream caves (D), collapse structures that breach the water table (F) and the deepest cave in the study are which intersects the water table (G).
13TH SINKHOLE CONFERENCE NCKRI SYMPOSIUM 2 129 the incised valley, indicating that this spring location is the result of downward cutting of the incised valley and conduit breaching. Parks Ranch Cave appears to contain minor hypogene components that have been connected and heavily overprinted by epigene processes, forming a complex, hydrologically active system. Water Resources Water resources in the Castile outcrop area are scarce and limited to occasional springs, seeps, and caves that breech conduits. Most springs and seeps in the study area exhibit high total dissolved solids, primarily sulfate, as a result of the rapid saturation of waters passing through gypsum facies (Stafford et al., 2008b). solids to support diverse ecological systems, including several species of arthropods and healthy, riparian zones rich and relatively fresh water resources, are utilized by ranchers for livestock. Many of the springs provide perennial discharge and degas elevated hydrocarbons that provide source material for current evaporite calcitization in the subsurface and represent upward leakage of active hypogene processes to the land surface (Stafford et al., 2008b). China Mine, subsurface; however, these patterns are not common in the study area. While hypogene caves are the largest features in the study area, they are not the dominant cave type documented (Stafford et al., 2008b). This is likely a sampling bias because of the nature by which these caves form from hypogene features exhibit strong correlation with regions of evaporite calcitization and diagenetic recrystallization of original gypsum fabrics into tabular fabrics (Stafford et al., 2008c). Therefore, it is logical to assume that the development and evaporite calcitization were utilized by both ascending waters and hydrocarbons from the underlying Bell Canyon and Cherry Canyon Formations (Figure 7).The largest individual cave currently documented in the Castile Formation is Parks Ranch Cave with over 6.5 kilometers of surveyed passage (Figure either hypogene or epigene karst and likely represents a incised solutional sinkholes contribute meteoric runoff to the system which primarily discharges to Chosa Draw, a locally incised valley. Most passages exhibit exist that are effectively scallop free and contain minor (Stafford et al, 2008b). The current discharge point in Chosa Draw is a bisected cave passage and continues as Figure 7. Simplified paleohydrology diagram associated with evaporite calcitization and upward migration of hypogene fluids (adapted from Lee and Williams, 2000). White arrows show migration paths of meteoric waters; blue areas show migration paths of upward migrating, hydrocarbon-rich fluids.
NCKRI SYMPOSIUM 2 13TH SINKHOLE CONFERENCE 130 fresh. These features along with other isolated caves across the study area provide windows into the current hydrologic system, which are distinctively different microbial communities. glimpse into the extremely heterogeneous hydrogeologic system. Fluid chemistry varies rapidly over distances of several kilometers, with water tables that appear hydrogeologic system couples components of shallow that often exhibit a minor thermal component, high total dissolved solids, and host complex bacterial colonies. with aquifer compartmentalization. Conclusions The Castile Formation crops out in the western Delaware Basin in Eddy County, New Mexico, and Culberson County, Texas, and hosts extensive karst development. Surface denudation is rapidly modifying the landscape at breaching of numerous caves throughout the region. More than ten thousand individual sinkholes have been three thousand documented. Sinkholes provide windows into the complex speleogenetic evolution of the region, where hypogene caves form deep and complex systems that are being actively overprinted by epigene processes. Associated diagenetic alteration of the Castile sulfates has produced widespread regions of evaporite calcitization in association with ascending hydrocarbons from underlying clastic strata. The Castile Formation records the evolving hydrogeologic history of the Delaware Basin as multiple strata, creating a system that is continuing to be overprinted by current and active processes. Initial Castile Formation studies indicate a complex hydrogeologic system that couples ascending transverse chemistries have resulted in an extremely heterogeneous system in which perched water tables and a high an early 20 th century sulfur mine in northern Culberson secondary sulfur deposition but does not exhibit spring discharge (Stafford et al., 2008c); however, it is likely that it is a nonaqueous version of the smaller hydrogen structure approximately 15 meters in diameter that drops approximately 10 meters to water which forms a lake 15 to 20 meters deep (Figure 6F). The feature degasses occur throughout the lake. While this feature does not discharge to the surface as a spring, it does provide a window into the local water table, while a nearby water well descends over 50 meters to the local water table. Several caves in the area are vadose conduits, where subsurface. Brantley Stream Cave (Figure 6D) contains over 100 meters of cave passage with an active stream that sumps in regions and discharges to the Delaware River, a perennial stream in northern Culberson County. Similarly, a series of collapse sinkholes intersect a separate conduit system in Sinkhole Flat approximately 20 kilometers southeast of Brantley Stream Cave on the opposite side of the Delaware River. These collapse sinks provide windows into a relatively freshwater conduit system approximately 10 meters beneath the land surface with no obvious surface connections; however, the stream exhibits low total dissolved solids. In the southern portion of the study area, Crystal Cave Figure 8. Simplified plan view map of Parks Ranch Cave with entrances labeled (e). Note that the easternmost entrance was formed by conduit truncation as Chosa Draw entrenched, while the western entrances are associated with sinkholes (from Stafford et al., 2008a).
13TH SINKHOLE CONFERENCE NCKRI SYMPOSIUM 2 131 Park. In: Land L, Lueth V, Raatz B, Boston P, Love D, editors. Caves and karst of southeastern Alamogordo (NM): Southwestern Region of the National Speleological Society. Lee MK, Williams DD. 2000. Paleohydrology of the Delaware Basin, western Texas: overpressure development, hydrocarbon migration, and ore genesis. Bulletin of the American Association of a study of denudation in gypsum karst, Chosa Draw, University of Northern Colorado. 82 p. development of a low relief evaporite karst drainage basin, southeastern New Mexico [MS Thesis]. Albuquerque (NM): University of New Classic upper Paleozoic reefs and bioherms of west Texas and New Mexico. Socorro (NM): New Mexico Institute of Mining and Technology. Delaware Basin, southeastern New Mexico and far west Texas. In: White WB, editor. Proceedings of the 15th International Congress of Speleology. 2008a. Epigene and hypogene karst manifestations of the Castile Formation: Eddy County, New Mexico and Culberson County, Texas, USA. 2008b. Castile evaporite karst potential map methodological comparison. Journal of Cave diagenesis in the western Delaware Basin. degree of aquifer partitioning are prevalent in aquifer system. Future studies should focus on delineating this compartmentalization and unraveling geochemical creates a continuously evolving system that can pose continues to breach the system. References Albuquerque (NM): Southwestern Region of the National Speleological Society. Alamogordo (NM): Southwestern Region of the National Speleological Society. Forbes J, Nance R. 1997. Stratigraphy, sedimentology, and structural geology of gypsum caves in east central New Mexico. Carbonates and Evaporites Basin Section of the SEPM. Studies 62 (2). southeastern New Mexico. Socorro (NM): New Mexico Bureau of Mines and Mineral Resources. outcrop examination of the Capitan shelf margin, Kirkland DW, Anderson RY, 1970. Microfolding in the Castile and Todilto evaporites, Texas and New Kirkland DW, Evans R. 1976. Origin of limestone Klimchouk A. 2000. Speleogenesis in gypsum. In: Klimchouk A, Ford DC, Palmer AN, Dreybrodt W, editors. hydrogeological and morphometric perspective. Carlsbad (NM): National Cave and Karst Research Institute.
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