Alan R. Dutton

Origin of Satin Spar Veins in Evaporite Basins

ABSTRACT Satin spar (fibrous gypsum) veins occur in rocks overlying evaporites in the Amadeus Basin, Australia; Appalachian Basin, USA; Cheshire Basin, England; Elk Point Basin, Canada; Palo Duro Basin, USA; Paradox Basin, USA, and Zechstein Basin, England. These antitaxial veins, which are characterized by central partings and near-vertical fibers, fill horizontal and inclined fractures. Most satin spar veins occur in highly fractured or brecciated clastic strata that overlie or are associated with bedded halite, anhydrite, and gypsum. Saline springs are commonly present, indicating that halite dissolution is active. The similarities in morphology and occurrences of these veins suggest a common genesis. Satin spar veins result from several simultaneously active processes. Recharge of low-salinity surface water results in dissolution of shallow ( 200 m to 750 m deep) halite, development of cavernous porosity, and formation of extensional fractures in the rock column overlying salt-dissolution zones. Greater solubility of anhydrite than gypsum at low temperatures and at salinities below halite saturation causes hydration of anhydrite to gypsum, which takes place without significant volume change. Once groundwater is saturated with respect to gypsum, any further anhydrite hydration and solution must result in supersaturation, and the excess CaSO4 carried by ground water flowin from dissolution zones precipitates as gypsum in open, high-permeability fractures.

Origin of brine in the San Andres Formation, evaporite confining system, Texas Panhandle and eastern New Mexico

Although regional hydrogeologic data and numerical models suggest that ground water flows downward through the evaporite-confining system in the Palo Duro Basin, new evidence of chemical and isotopic composition of brine from a carbonate bed in the Permian San Andres Formation suggests that post-Permian ground-water movement within the evaporite section has been negligible. Similarity between δD and δ 18 O of brine in San Andres carbonate rock and δD and δ 18 O of Permian fluid inclusions in halite beds implies that brine in the carbonate rock is connate and originated as Permian evaporatively concentrated sea water. Extensive rock-water reactions that account for chemical and isotopic composition of the brine by circulating meteoric ground water seem more complex and less substantiated than does diagenetic change of connate Permian brine. The conflict between hydrogeologic and chemical interpretations is reconciled if (1) there has not been enough time for flow of meteoric ground water to flush connate brine from the carbonate bed since a significant cross-formational gradient in hydraulic head developed, (2) present cross-formational flow of ground water is unevenly distributed between fractured and unfractured areas, and (3) composition of brine sampled at the test wells differs from that of brine in fractured zones that have not been sampled.

Isotopic evidence for paleohydrologic evolution of ground-water flow paths, southern Great Plains, United States

A confined aquifer in Triassic Dockum Group sandstone beneath the southern Great Plains was isolated from hypothesized paleorecharge areas in eastern New Mexico by Pleistocene erosion of the Pecos and Canadian river valleys and formation of hydrologic divides. Truncation of the flow system left meteoric water in the confined aquifer with mean {delta}D and {delta}{sup 18}O values that are 17{per thousand} and 2.0{per thousand}, respectively, lighter than those in the overlying High Plains aquifer. Thick upper Dockum mudstone retards downward flow from the High Plains aquifer, which has been recharged by isotopically heavy precipitation during the Holocene. Recharge to the confined aquifer occurred at altitudes of 1600 to 2200 m in proximal Dockum sandstone facies since eroded in eastern New Mexico, at a mean temperature 3 C cooler than present temperature across the southern High Plains. Effect of Pleistocene climatic change on isotopic composition of Dockum ground water could be superposed over geomorphologic effects.

Water-Level Declines in the Woodbine, Paluxy, and Trinity Aquifers of North-Central Texas

ABSTRACT Ground-water mining of the Woodbine, Paluxy, and Trinity aquifers has led to substantial water-level declines in North-Central Texas since the turn of the century. Water-level maps constructed from R. T. Hills 1901 well survey data show that water levels were initially above land surface before development. Numerous wells were drilled for water supply because the wells flowed at land surface. Water levels declined rapidly, and many of the wells around Fort Worth stopped flowing by 1914. Many of these wells were then abandoned, which slowed the rate of water-level decline. Since the turn of the century, water levels have declined nearly 850 ft in the Trinity aquifer in the Fort Worth area. As of 1990, water levels had declined about 400 ft in the Woodbine aquifer near Dallas and 450 ft in the Paluxy aquifer near Fort Worth. Maps drawn on the basis of water-level measurements in 1935, 1955, 1960, 1970, 1980, and 1990 show how the shape of potentiometric surfaces has evolved during the century. This great drawdown in water levels has increased pumping costs, reversed ground-water flow directions in the Dallas-Fort Worth and Sherman areas, and may have affected water quality. Land subsidence from water-level decline has not been observed in North-Central Texas, perhaps because of the structural stability of the geologic units or a consolidation time lag. Pumping costs and water-quality problems have caused many ground-water users to switch to surface sources of water. Consequently, the rate of water-level decline has decreased in some parts of the aquifers, and in the case of the Paluxy aquifer, this may have caused recent water-level recovery.

Sedimentologic and Diagenetic Controls on Aquifer Properties, Lower Cretaceous Edwards Carbonate Aquifer, Texas: Implications for Aquifer Management

ABSTRACT The distribution of water in the Edwards aquifer was assessed using a core and log-based study. Porosity distribution reflects both depositional fabric and subsequent diagenesis. Vertical facies stacking patterns influence the depositional porosity as well as dolomitization and diagenetic porosity modification. Subtidal facies deposited during sea-level highstands are generally undolomitized and exhibit low porosity (5 to 10 percent); platform grainstones commonly have high depositional porosity and significant solution enhancement (20- to 42-percent porosity). Dolomitized subtidal facies in tidal-flat-capped cycles have very high porosity (20 to 40 percent) because of selective dolomite dissolution in the fresh-water aquifer. Porosity in former evaporite beds is high in some areas because of dissolution and collapse, but it is low where gypsum was replaced by calcite cement. Low-energy subtidal and evaporitic units in the Maverick Basin have porosities that are generally less than 15 percent. The overlying basinal packstones and grainstones have solution-enhanced porosities of 25 to 35 percent. Mapped average porosity also shows nonstratigraphically controlled variations. Diagenesis associated with fluctuations in water chemistry near the saline/fresh-water interface may be one cause. Other complex patterns of high and low porosity are attributed to structurally and hydrologically controlled porosity enhancement and cementation. Three-dimensional mapping of porosity trends provides data for improved aquifer management. Only about 3 percent of the water stored in the aquifer during a year of average water level lies above the water table at which natural spring flow is diminished. An average specific yield of 42 percent in the unconfined aquifer is determined from total porosity, changes in the water-table elevation, and changes in estimated recharge and discharge. Average storativity of 2.6 10-4 in the confined Edwards is estimated using average porosity and barometric efficiency calculated from comparing water-level hydrographs and atmospheric-pressure changes.

Abandoned SSC Site can provide underground facility for geoscience research

By the time Congress terminated the Superconducting Super Collider (SSC) project in October 1993, the Department of Energy and the state of Texas had sunk

CENSUS AND STATISTICAL CHARACTERIZATION OF SOIL AND WATER QUALITY AT ABANDONED AND OTHER CENTRALIZED AND COMMERCIAL DRILLING-FLUID DISPOSAL SITES IN LOUISIANA, NEW MEXICO, OKLAHOMA, AND TEXAS

2 billion into the project. Now closure and remediation of the disturbed surface and subsurface lands are underway with a budget of

ANALYSIS OF SOIL REMEDIATION REQUIREMENTS OF ABANDONED CENTRALIZED AND COMMERCIAL DRILLING

22 million, according to a recent agreement between the DOE and Texas. Rather than chalking up the creation of the large, expensive hole in the ground to failure, however, some are hailing the site as an excellent test-bed for geoenvironmental and geotechnical research (Figure 1). They hope to use the sites tunnel, exploratory shaft, and test wells to identify new and improved methods for investigating subsurface fluid flow and transport processes, to characterize physical properties of weak and fractured rock through geophysics and geomechanical testing, and to test model predictions through large-scale experiments conducted underground.

Groundwater Isotopic Evidence for Paleorecharge in U.S. High Plains Aquifers

Commercial and centralized drilling-fluid disposal (CCDD) sites receive a portion of spent drilling fluids for disposal from oil and gas exploration and production (EP five percent were land treatment facilities. A typical disposal-pit facility has fewer than 3 disposal pits or cells, which have a median size of approximately 2 acres each. Data from well-documented sites may be used to predict some conditions at abandoned sites; older abandoned sites might have outlier concentrations for some metal and organic constituents. Groundwater at a significant number of sites had an average chloride concentration that exceeded nonactionable secondary drinking water standard of 250 mg/L, or a total dissolved solids content of >10,000 mg/L, the limiting definition for underground sources of drinking water source, or both. Background data were lacking, however, so we did not determine whether these concentrations in groundwater reflected site operations. Site remediation has not been found necessary to date for most abandoned CCDD sites; site assessments and remedial feasibility studies are ongoing in each State. Remediation alternatives addressed physical hazards and potential for groundwater transport of dissolved salt and petroleum hydrocarbons that might be leached from wastes. Remediation options included excavation of wastes and contaminated adjacent soils followed by removal to permitted disposal facilities or land farming if sufficient on-site area were available.

Origin, distribution, and movement of brine in the Permian Basin (U.S.A.): A model for displacement of connate brine

During this reporting period our project focused on (1) review of case studies of remediation of centralized and commercial drilling fluid disposal (CCDD) sites in Texas, and (2) information transfer with preparation of a proceedings paper and a workshop/short course. Texas remediation of certain drilling-fluid disposal sites includes examples at CCDD sites as well as commercial oil reclamation sites and saltwater disposal sites that also disposed of drilling fluids in pits. Site investigations range from qualitative visual inspection and assessment to comprehensive hydrodynamic, chemical, and geophysical analyses of wastes and groundwater. A range of techniques has been used to evaluate waste material, soil, groundwater, and surface water for potential contamination with hydrocarbons, chemicals, saltwater, and naturally occurring radioactive materials (NORM). Most constituents of concern measured in these studies are below regulatory action levels and established guidelines. A proceedings paper summarizes results presented in this and previous semi-annual progress reports will be part of the Transactions of the Gulf Coast Association of Geological Societies (GCAGS). A technology transfer workshop also was prepared as part of that Annual Meeting of the GCAGS to be held in November 2002.