Browsing by Subject "Hueco Bolson"

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Contributions to Geology, 1931
(University of Texas at Austin, 1931-01-01) University of Texas at Austin
Geomorphology of the Hueco Bolson in the Vicinity of the Proposed Low-Level Radioactive Waste Disposal Site, Hudspeth County, Texas
(1990) Baumgardner, Jr., Robert W.
The Fort Hancock study area is located 40 mi (65 km) southeast of El Paso, Texas, in the Hueco Bolson on an alluvial slope between the Diablo Plateau and the Rio Grande. The study area spans the drainage divide between Alamo and Camp Rice Arroyos. Since deposition of bolson fill ceased, the arroyos have incised, cutting down to expose the Fort Hancock and Camp Rice Formations in their floors and valley walls. Quaternary strata younger than the Camp Rice Formation underlying the study area can be divided into four units: a basal gravel, a middle sand, a petrocalcic horizon (Stage IV), and an upper sand. The petrocalcic horizon is interpreted to be the upper surface of the Madden Gravel, and, on the basis of its dense, laminated character, took 25,000 to 75,000 years to form. These Quaternary sediments range in thickness from 20 to 60 ft (6 to 18 m), thinning to the southwest across the study area and toward the edges of arroyos.
Ground Water Hydrochemistry in the Southeastern Hueco Bolson and Southwestern Diablo Plateau, Trans-Pecos Texas
(1990) Fisher, R. Stephen; Mullican, William F.
The hydrochemical history of groundwater in the arid southeastern Hueco Bolson and southwestern Diablo Plateau was investigated by collecting soil-moisture samples from unsaturated siliciclastic bolson-fill sediments and groundwater samples from the Diablo Plateau aquifer, the Hueco Bolson silt and sand aquifer, and the Rio Grande alluvial aquifer. Major, minor, and trace solutes, stable isotopic compositions, and activities of tritium and carbon-14 were measured in groundwater samples; major solute concentrations were determined in soil-moisture samples. Soil samples were collected to determine the type and amount of material that could be readily dissolved by recharge water. Core samples of Cretaceous carbonate and bolson-fill material were analyzed to determine the mineralogy of sediment and aquifer matrix. The Hueco Bolson and Diablo Plateau aquifers contain mainly sodium-sulfate groundwater that derived solutes by calcite, dolomite, and gypsum dissolution, coupled with exchange of aqueous calcium and magnesium for sodium on clay minerals and other ion-exchange sites. Rio Grande groundwater is dominated by sodium and chloride derived from dissolution of salts precipitated in irrigated fields during times of high evaporation. All groundwaters are inferred to acquire major compositional characteristics early in the flow history, principally through reactions in the unsaturated zone. Ages estimated from tritium and carbon-14 activities show that Rio Grande groundwaters are youngest, reflecting the short flow paths from the river to sampled wells following irrigation and percolation. Young groundwater is also found in the Diablo Plateau aquifer at wells both on the plateau and near the toe of the plateau escarpment. These are inferred to be recharge waters that rapidly moved along fractures to the water table. Other groundwater samples from the Diablo Plateau and Hueco Bolson aquifers are as much as 28,000 years old. Carbon-14 ages and tritium activities do not vary uniformly along a flow path. However, the oldest waters are found in wells near the center of the bolson pediment, and the distribution of carbon-14 ages generally conforms to the salinity distribution, suggesting a systematic relation between residence time, chemical and isotopic composition of groundwater, and regional hydrologic properties of the aquifers.
Ground Water Hydrochemistry in the Southeastern Hueco Bolson,Trans-Pecos Texas
(1989) Fisher, R. Stephen; Mullican, William F.
The hydrochemical history of groundwater in the arid southeastern Hueco Bolson was investigated by collecting soil-moisture samples from unsaturated siliciclastic bolson-fill sediments and groundwater samples from the Diablo Plateau aquifer, the Hueco Bolson silt and sand aquifer, and the Rio Grande alluvial aquifer. Major, minor, and trace solutes, stable isotopic compositions, and activities of tritium and carbon-14 were measured in groundwater samples, while major solute concentrations were determined in soil-moisture samples. Soil samples were collected to determine the type and amount of material that could be readily dissolved by recharge water. Core samples of Cretaceous carbonate and bolson-fill material were analyzed to determine the mineralogy of sediment and aquifer matrix. The Hueco Belson and Diablo Plateau aquifers predominantly contain Na-SO4 groundwater, derived from solutes through carbonate and gypsum dissolution, coupled with the exchange of aqueous calcium and magnesium for sodium on clay minerals and other ion exchange sites. Rio Grande groundwater is dominated by sodium and chloride, derived from the dissolution of salts precipitated in irrigated fields during periods of high evaporation. Major compositional characteristics of all groundwater types appear to be acquired early in the flow history, primarily through reactions in the unsaturated zone. Ages estimated from tritium and carbon-14 activities indicate that Rio Grande groundwater is the youngest, reflecting short flow paths from land surface following irrigation, infiltration, and deep penetration from the river to sampled wells. Groundwater from the Diablo Plateau and Hueco Bolson aquifers ranges in age from a few hundred to nearly 29,000 years. Carbon-14 ages and tritium activities do not vary systematically along a flow path; however, the oldest waters are found in wells near the center of the bolson pediment. The irregular distribution of carbon-14 and tritium suggests that the Bolson and Diablo Plateau aquifers are internally complex, and flow velocities are not readily predictable solely based on the potentiometric gradient and estimates of regional porosity and permeability data.
Sedimentary Facies, Depositional Environments, and Paleosols of the Upper Tertiary Fort Hancock Formation and the Tertiary Quaternary Camp Rice Formation, Hueco Bolson, West Texas
(1990) Gustavson, Thomas C.
The Hueco Bolson is a segment of the Rio Grande Rift, which formed as a result of late Tertiary Basin and Range deformation. The upper Tertiary Fort Hancock Formation and the upper Tertiary-Quaternary Camp Rice Formation compose the basin fill except in the deepest (western) parts of the bolson. Five lithofacies make up the Fort Hancock Formation: (I) gravel; (II) sand, sandy mud, or sandy silt and gravel; (III) sand, sandy mud, and sandy silt; (IV) clay and sandy clay; and (V) clay, mud, sandy mud, and gypsum. These lithofacies represent the textural gradation from basin margin to basin center of proximal to transitional to distal alluvial fans (lithofacies I through III) to ephemeral lakes (IV) to saline playas (V). In cores from beneath the study area, these same lithofacies are present in a 230-meter-thick (700-ft) upward-fining sequence. The sequence records the lacustrine expansion that occurred over basin-margin alluvial fans as the basin filled. The Fort Hancock Formation is separated from the overlying Camp Rice Formation by a regional unconformity. The unconformity records a period of extensive erosion that marks the integration of the ancestral southern and northern segments of the Rio Grande approximately 2.25 million years ago. Fluvial, lacustrine, and eolian sediments accumulated above the unconformity as the Camp Rice Formation. Five lithofacies also make up the Camp Rice Formation: (1) sand and locally derived gravel, which was deposited by tributaries to the Rio Grande; (2) sand and exotic gravel (derived from north of the study area), which was deposited by a through-flowing stream, the Rio Grande; (3) sand, which was deposited as a dune complex; (4) coarse silt and very fine sand, which was deposited as loess; and (5) clay, sandy clay, and gypsum, which was deposited in ephemeral lakes with central playas.
Unsaturated Flow Along Arroyos and Fissures in the Hueco Bolson, Texas
(1990) Scanlon, Bridget R.
Unsaturated flow in the Chihuahuan Desert of Texas was analyzed to evaluate the suitability of this region for low-level radioactive waste disposal because thick unsaturated zones that have low moisture fluxes in arid regions are considered suitable for radioactive waste disposal. The principal study area was instrumented with neutron-probe access tubes and psychrometers to monitor moisture content and water potential, respectively. The absence of temporal variations in moisture content monitored in deep (41 meters [135 feet]) profiles indicated that recharge pulses are not moving through the system. Penetration of moisture after rainfall was restricted to the uppermost meter of the unsaturated zone because of the low degree of saturation of the surficial sediments. Water potentials were as low as -15.6 megapascals (MPa) near the land surface in the summer. Except in the shallow subsurface after precipitation events, water potentials generally decreased upward, indicating primarily upward flow under isothermal conditions, probably controlled by evapotranspiration. The computer code, TRACRN, was used to evaluate various unsaturated-flow processes in this system. Numerical simulations of upward flow indicated that small variations in water content result in large variations in water potential in dry unsaturated zones. One-dimensional simulation of infiltration was calibrated using chlorine-36 (36Cl) data. Sensitivity analyses suggested that applied flux and initial water potential are the most critical factors in controlling the propagation of the wetting front. Analyses of potential leakage from the base of a possible facility indicated that the direction as well as the net rate of water movement is controlled by lithologic layering in the system. Simulations of downward leakage rates that are similar to the saturated hydraulic conductivity of the deep clays showed that a saturated zone will develop at the contact between the shallow coarse material and underlying clays.