Speleogenetic Evolution and Geological Remote Sensing of the Gypsum Plain, Eddy County, New Mexico

Permian evaporites of the Gypsum Plain region of the Delaware Basin host extensive karst phenomena, as well as unique diagenetic alterations of host strata. Because of the complex, poorly understood hydrogeologic system, little has been established concerning the relation and evolution of the overprinted, modern and ancient karst manifestations within the Gypsum Plain, as a whole. Through a combination of traditional field studies and the development of improved remote sensing methodologies, this study established the speleogenetic evolution of the Gypsum Plain in relation to the greater tectonic, stratigraphic, hydrogeologic and climatic history of the Delaware Basin. Emphasis was focused on a 100 km2 area of the Gypsum Plain in Eddy County, New Mexico, for the presence of all characteristic evaporite karst manifestations previously reported for the region, including epikarst, epigene caves, hypogene caves, intrastratal brecciation, calcitization and sulfur oxidation. Late Miocene uplift and tilting of the Delaware Basin tectonic block initiated development of dissolution and collapse of Castile strata, inducing an early phase of hypogene karsting. Renewed uplift and tilting during the latest Miocene, combined with increasing regional geothermal gradients, enabled hydrocarbon maturation, evaporite calcitization and additional hypogene porosity development. Pleistocene climate fluctuations increased denudation and exposed Castile evaporites to epigene development, while migration of the Pecos River across the area during the late Eocene enhanced karst processes. Karsting slowed with the Holocene shift to the current warm, arid climate, but solutional processes remain active with the general eastward migration of the hydrogeologic system. Traditional karst studies such as this are often costly and require months, if not years, of physical fieldwork. Preliminary identification of areas of interest through the careful evaluation of geologic maps offers a more efficient approach. However, published geologic maps of the Gypsum Plain feature little to no detail of lithologic variability, a vital attribute when dealing with phenomena dm2 to tens of m2 in area. Therefore,50 centimeter spatial resolution geologic maps were created through the classification of reflectance values of color infrared imagery of the study area in order to better constrain spatial variability in karst processes. Multispectral data was used for this purpose due to the high spatial resolution commercially/publicly available over that of hyperspectral sensor’s higher spectral resolutions and band combinations, deemed unnecessary because of the contrasting reflectance values of surface strata across the Gypsum Plain. Coupling of an improved speleogenetic evolution of the area with more accurate geologic mapping enables the development of better land management practices for karsted terrains such as the Gypsum Plain

Evaporite karst geohazards in the Delaware Basin, Texas: review of traditional karst studies coupled with geophysical and remote sensing characterization

Evaporite karst throughout the Gypsum Plain of west Texas is complex and extensive, including manifestations ranging from intrastratal brecciation and hypogene caves to epigene features and suffosion caves. Recent advances in hydrocarbon exploration and extraction has resulted in increased infrastructure development and utilization in the area; as a result, delineation and characterization of potential karst geohazards throughout the region have become a greater concern. While traditional karst surveys are essential for delineating the subsurface extent and morphology of individual caves for speleogenetic interpretation, these methods tend to underestimate the total extent of karst development and require surficial manifestation of karst phenomena. Therefore, this study utilizes a composite suite of remote sensing and traditional field studies for improved karst delineation and detection of potential karst geohazards within gypsum karst. Color InfraRed (CIR) imagery were utilized for delineation of lineaments associated with fractures, while Normalized Density Vegetation Index (NDVI) analyses were used to delineate regions of increased moisture flux and probable zones of shallow karst development. Digital Elevation Models (DEM) constructed from high-resolution LiDAR (Light Detection and Ranging) data were used to spatially interpret sinkholes, while analyses of LiDAR intensity data were used in a novel way to categorize local variations in surface geology. Resistivity data, including both direct current (DC) and capacitively coupled (CC) resistivity analyses, were acquired and interpreted throughout the study area to delineate potential shallow karst geohazards specifically associated with roadways of geohazard concern; however, detailed knowledge of the surrounding geology and local karst development proved essential for proper interpretation of resistivity inversions. The composite suite of traditional field investigations and remotely sensed karst delineations used in this study illustrate how complex gypsum karst terrains can be characterized with greater detail through the utilization of rapidly advancing technologies, especially in arid environments with low vegetation densities

Castile Evaporite Karst Potential Map of the Gypsum Plain, Eddy County, New Mexico and Culberson County, Texas: A GIS Methodological Comparison

Castile Formation gypsum crops out over ,1,800 km2 in the western Delaware Basin where it forms the majority of the Gypsum Plain. Karst development is well recognized in the Gypsum Plain (i.e., filled and open sinkholes with associated caves); however, the spatial occurrence has been poorly known. In order to evaluate the extent and distribution of karst development within the Castile portion of the Gypsum Plain, combined field and Geographic Information System (GIS) studies were conducted, which enable a first approximation of regional speleogenesis and delineate karst-related natural resources for management. Field studies included physical mapping of 50, 1-km2 sites, including identification of karst features (sinkholes, caves, and springs) and geomorphic mapping. GIS-based studies involved analyses of karst features based on public data, including Digital Elevation Model (DEM), Digital Raster Graphic, (DRG) and Digital Orthophoto Quad (DOQ) formats. GIS analyses consistently underestimate the actual extent and density of karst development, based on karst features identified during field studies. However, DOQ analyses coupled with field studies appears to produce accurate models of karst development. As a result, a karst potential map of the Castile outcrop region was developed which reveals that karst development within the Castile Formation is highly clustered. Approximately 40% of the region effectively exhibits no karst development (,1 feature/km2). Two small regions (,3 km2 each) display intense karst development (.40 features/km2) located within the northern extent of the Gypsum Plain, while many regions of significant karst development (.15 features/km2) are distributed more widely. The clustered distribution of karst development suggests that speleogenesis within the Castile Formation is dominated by hypogenic, transverse processes

Physical and Chemical Controls on Suffosion Development in Gypsic Soil, Culberson County, Texas

In the Gypsum Plain, suffosion processes have encouraged road failure through dissolution and transport of gypsic soils; however, no prior research has been conducted within the Delaware Basin in regard to these processes. These phenomena were evaluated in both field and laboratory settings in order to assess the parameters of suffosion development associated with Ranch to Market (RM) 652 in Culberson County, Texas, where infrastructure extends across Castile and Rustler strata. Field studies simulated surficial ponding in various gypsic soils and correlated suffosion potential with soil composition and thickness. Soluble fractions of gypsic soils were delineated through geochemical analyses, further expanding upon the soil descriptions published in the Culberson County Soil Survey (USDA, 2013). Suffosion modeling replicated processes observed in the field through repeated infiltration of Dellahunt and Elcor soils—soil piping and subsidence were induced within suffosion models. Lineaments inferred as solutional fractures were delineated using color infrared (CIR) images to determine regional suffosion potential. Results obtained from this research were used to form a conceptual model of suffosion development in order to better mitigate damage imposed on infrastructure in evaporite karst terrains. Regions with thick, heterogeneous soils of low to moderate gypsum content (10-70%) and moderate fracture densities (100-800 m/km2) are optimal for suffosion development. This model should be considered for future projects in not only the Gypsum Plain, but for other arid environments with significant evaporite karst and gypsic soils as well

Soil Gypsum Content Analysis of the Proposed Road Route Extension of FM 2185 in the Gypsum Plain, Culberson County, Texas

Soils serve as the underlying substrate on which foundations for most structures are built. The properties of a soil type are therefore an important consideration in building engineered structures. Gypsic soils are problematic for construction of such structures. One of the main problems with gypsic soils is dissolution. Gypsum (CaSO4·2H2O) in soils dissolves easily creating voids which can be detrimental to the integrity of engineering structures. To mitigate this, it is important to determine the amount of gypsum present in soils, before construction is initiated. In this study, three methods were employed in the determination of gypsum content in soils along a proposed road route in the Gypsum Plain, Culberson County, Texas: the wet chemical method, the X-ray fluorescence method and the thermogravimetric method. Results showed no significant difference in gypsum concentrations using the varying methods on samples obtained at the same point in a location but showed a significant difference in the concentration of samples obtained at different depths in a location. Gypsum contents along the approximately ninety-kilometer road route was predominantly relatively low, with about 65% of sample locations having gypsum content of less than 10%. About 11% of sampling locations, together totaling about three miles of the route, had high gypsum contents of over 70%

Speleogenesis and Delineation of Megaporosity and Karst Geohazards Through Geologic Cave Mapping and LiDAR Analyses Associated with Infrastructure in Culberson County, Texas

The Gypsum Plain region of the Delaware Basin hosts approximately 1800 km2 of the Castile Formation outcrop. A myriad of karstic developments from closed sinkholes to large multi-kilometer cave systems have been documented within the region. Karst studies on the distribution and speleogenetic evolution within Castile strata began within the last decade with ever increasing data resolution. In this study, a combination of both physical field surveys and analyses of high resolution (~30 cm accuracy) LiDAR data was used to create a theoretical model for karst development across the region. This idealized model considers speleogenetic formation type variations (hypogene and epigene), the density of karstic features based on lithology variations, and the connection between the local hydrostratigraphic setting and the regional hydrogeological framework. Field studies included physical mapping of 20 km2 of the Gypsum Plain from the Castile’s western outcrop to where it dips into the subsurface to the east. These surface surveys involved the recording of all surfically-expressed karstic phenomena and the mapping of all enterable caves so that the speleogenetic evolution could be analyzed. The way in which hypogene and epigene caves are surfically expressed across the region indicates that many of the caves have been affected by either multi-stage epigenetic development or multi-stage hypogenetic development with epigenetic overprinting. Through the use of the methods outlined above, surficial karst manifestations vary across the region, from hypogenetic exposures in the west and epigenetic phreatic / vadose exposures in the east. Additionally, supplementary LiDAR data was used to create digital elevation models (DEM) so that the effectiveness of physical field surveys versus remote sensing techniques could be determined. Previous works in the area by Stafford et al., (2008b) determined that remote sensing preserved only 36% of all karstic features found through physical field surveys. Given today’s advancements in remote sensing accuracy, this study determined that on average LiDAR analysis identifies almost seven times more karstic features than physical surveys over a given area

CHARACTERIZATION AND DELINEATION OF POTENTIAL EVAPORITE GEOHAZARDS USING ELECTRICAL RESISTIVITY METHODS ALONG FM 2185, CULBERSON COUNTY, TEXAS

Extensive karst development within the Delaware Basin of West Texas and southeastern New Mexico poses a significant geohazard threat to infrastructure. Dissolution of regional evaporite strata have led to manifestations of karst geohazard phenomena including sinkholes, subsidence features, and caves. The study area is located within the Gypsum Plain in Culberson County, Texas, and includes outcrops of Castile and Rustler strata that host gypsum karst geohazards. Land reconnaissance surveys conducted during the summer of 2019 documented numerous surficial manifestations of karst features proximal to Farm to Market Road 2185 (FM 2185). In combination with traditional survey techniques, electrical resistivity methods were used to delineate karst features along a 48-kilometer segment of FM 2185. Capacitively-Coupled Resistivity (CCR) and Direct-Current Resistivity (DCR) methods were used to characterize evaporite karst features that do not manifest surficially but pose potential geohazard concerns. CCR data was acquired using the Geometrics OhmMapper G-858 resistivity system, which uses a dipole-dipole configuration composed of five receivers connected by 2.5-meter coaxial cables and a transmitter offset of 2.5 meters. In combination with the medium analyzed, this geometric configuration enabled resistivity soundings up to 5 meters deep. DCR data was collected with a SuperSting (R8/IP) multi-electrode earth resistivity meter using 112 electrodes with 2-meter spacing and a dipole-dipole array configuration. This enabled a depth of investigation of up to 73 meters. Data was processed using AGI’s (Advanced Geometrics Inc.) EarthImager 2D software and used to delineate and characterize karst-related geohazards in the shallow subsurface within the study area

GEOPHYSICAL DELINEATION OF MEGAPOROSITY AND FLUID MIGRATION PATHWAYS FOR GEOHAZARD CHARACTERIZATION WITHIN THE DELAWARE BASIN, CULBERSON COUNTY, TEXAS

ABSTRACT Differential dissolution of gypsum karst within the Delaware Basin poses a significant threat to infrastructure that society depends on. The study area is located in Culberson County, Texas and traverses a distance of approximately 54 kilometers along RM 652 within the Gypsum Plain which is situated on the northern margin of the Chihuahua Desert and includes outcrops of Castile and Rustler strata that host karst geohazards. Regions of karst geohazard potential have been physically surveyed proximal to the study area in evaporites throughout the Castile Formation outcrop; minimal hazards, in comparison to the Castile Formation, have been documented in the Rustler Formation. A TR-5 OhmMapper capacitively-coupled resistivity meter was used to acquire resistivity data for geohazard characterization. This study utilized a traditional dipole-dipole array, with an electrode spacing of 2.5 meters between receivers, and a transmitter offset of 2.5 meters. This geometric configuration combined with the medium analyzed, allowed for resistivity readings to be recorded up to approximately 5 meters deep. Data acquisition was recorded with the OhmMapper attached to a vehicle moving at approximately 3 kilometers per hour and transmitting and receiving once per second (approximately three feet per sample). Resistivity data was processed using AGI’s EarthImager 2D inversion software. Capacitively-coupled resistivity has shown to be effective in locating karst geohazards in the shallow subsurface

Intensive Survey Of The Proposed Aragorn Solar Farm On University Lands, Culbertson County, Texas

IP Aragorn LLC plans to develop a solar farm on a 1,765-acre tract on University Lands (UL) in Culberson County, Texas. In March and April 2018, Turpin and Sons Inc. (TAS) assessed the potential for significant cultural resources under the authority of Texas Antiquities Permit 8374 issued to UL, Aragorn and TAS with Jeff Turpin acting as Principal Investigator. The project area is a barren extent of interfluvial gypsum plain between the Rustler Hills on the east and the Delaware Mountains on the west. One previously recorded site, 41CU558, barely extends to the access road on the northeastern end of the tract, with the majority of the cultural remains outside the boundary. Although the Texas Historical Commission had at one time declared the site eligible for the National Register of Historic Places (NRHP), neither the first recording nor two subsequent revisits found anything of significance on the site. One newly recorded site, 41CU862, is a scatter of fire-cracked rock and lithic debris that is equally insignificant with no potential for buried or intact deposits. Neither 41CU862 nor the portion of 41CU558 in the Aragorn tract meet eligibility criteria for listing on the NRHP or merit designation as a State Antiquities Landmark (SAL). No further work nor avoidance measures are recommended in the Aragorn tract

Hypogene Calcitization: Evaporite Diagenesis in the Western Delaware Basin

Evaporite calcitization within the Castile Formation of the 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 speleogemesis