Contract Reports

Permanent URI for this collection


Recent Submissions

Now showing 1 - 20 of 341
  • Item
    Coordination of Geological and Engineering Research in Support of the Gulf Coast Co-Production Program
    (1989) Jirik, Lee A.; Ambrose, William A.  ; Kerr, D. R.; Light, M. P. R.
    Shallow-marine sandstones in Northeast Hitchcock field having high porosities and permeabilities contain abundant authigenic kaolinite and have acted as preferential conduits for fluid migration. Authigenic clay creates fluid production problems because of its delicate structure. Dislodged clay will obstruct pore throats at high production rates. A maximum safe rate of fluid production will need to be determined for co-produced wells. Middle and lower Miocene barrier-island sands in Northeast Hitchcock field have the potential for receiving large volumes of co-produced brines. These sands have permeabilities in excess of 2,000 md, are internally homogeneous, and are laterally extensive in the field area. Detailed geologic analyses of two reservoirs in Seeligson field delineate heterogeneous, fluvial sandstones that probably contain isolated, undrained reservoir compartments. Zone 15 can be subdivided into at least four genetic sandstones, and Zone 18-C can be subdivided into two separate sandstones. Two new pool discoveries (Miocene) in Tom O'Connor field developed during growth-fault activity along the Vicksburg Fault Zone. Deposition of these sandstones, as part of an offshore system during initial parasequence deposition, was confined between the Vicksburg Fault Zone and the Tom O'Connor anticlinal crest.
  • Item
    Mined Lands Inventory, Industrial Minerals, South Texas
    (1989) Jackson, M. P. A.; Blodgett, Robert H.; Kaiser, W. R.
    The Bureau of Economic Geology, under an interagency cooperative contract with the Railroad Commission of Texas, conducted a comprehensive inventory of abandoned and active mining operations across 48 counties in South Texas. Project objectives were to characterize potential reclamation, or priority, sites, to create a surface-mining database of industrial minerals, and to provide data to meet future legislative and regulatory needs. Comprehensive procedures were established for identification and evaluation of mined lands using U.S. Geological Survey topographic maps, black-and-white and color-infrared aerial photographs, on-site surveys, and low-altitude flyovers. The site location, mineral commodity, and relative size were recorded on a Mined Lands Inventory Form (MLIF) for each site greater than 2 acres in size. Data on health, safety, and environmental aspects were recorded for all priority sites. All data were entered into the Texas Mined Land Database (TMLDB), a computer database that follows the format of the MLIF. Locations of all inventoried sites are shown on over 400 topographic maps.
  • Item
    Production Potential of Unrecovered Mobile Oil Through Infield Development: Integrated Geologic and Engineering Studies Overview
    (1989) Bureau of Economic Geology; ICF Resources Incorporated
    This report is part of a coordinated series of research efforts designed to prepare preliminary evaluations of important components of the domestic unrecovered oil resource. The specific resource of interest is the oil that is displacable by water and remains in the Nation's reservoirs after conventional production. Integrated geologic, engineering, and economic evaluations in this series estimate future reserve additions from this unrecovered mobile oil (UMO) resource under various circumstances. The individual studies (Volumes 2 through 5) consider the effects of changes in oil prices and advances in production technology on the economic recovery potential of the UMO resource. This report (Volume 1) discusses and compares the approaches and results of the individual studies. Several recovery technologies are evaluated, including the use of waterflooding in conjunction with infill drilling to displace and produce UMO at decreased well spacings. The overall analysis series was conducted in two separate, but coordinated, parts: at a detailed reservoir level and at a generalized regional level. At the reservoir level, detailed analyses of three individual Texas reservoirs fully delineated the resource and the potential for UMO recovery in each reservoir under a variety of development situations. Results of the individual reservoir evaluations were extrapolated to groups of reservoirs with common depositional histories, collectively known as "plays". At the regional level, reservoirs in three major oil producing states, Texas, Oklahoma, and New Mexico, were analyzed to determine the resource volume, potential recovery, and the costs and benefits associated with this recovery both in the individual states and for the region as a whole. This analysis relied on the geologic classification of individual reservoirs, specific rock and fluid properties, and production and development histories to quantify the resource and to assess its potential for UMO recovery potential. Coordination of the studies at two analytical levels proved advantageous -- the initial methods and results at both levels were compared in order to calibrate and to modify the final approach at each level and can now be used as a guide in future analyses. In addition to the specific results from the two analytical levels, several shorter issue and summary papers have also been prepared.
  • Item
    Volcanic Geology of the Davis Mountains, Trans-Pecos Texas: Second Year Report
    (1989) Henry, Christopher D.
    This report describes the results of the second year of mapping of the volcanic rocks of the Davis Mountains, Trans-Pecos Texas. The Davis Mountains (fig. 1) constitute a major part of the eastern, alkalic belt of the Trans-Pecos volcanic field (Barker, 1977; Price and others, 1986). Yet, because of their volcanic and stratigraphic complexity, the Davis Mountains remain the most poorly mapped and least understood part of the field. Published geologic maps of the area (the Fort Stockton and Marfa sheets of the Geologic Atlas of Texas (McKalips and others, 1982; Twiss, 1979)) are based on regional, aerial photographic extrapolation of formations established in a few detailed studies.
  • Item
    Mineral Resource Assessment. Big Bend RanchState Natural Area, Presidio and Brewster Counties, Texas - Final Report
    (1989) Henry, Christopher D.; Raney, J. A.; Rubin, Jeffrey N.; Standen, Allan R.
    The Big Bend Ranch State Natural Area has a diverse geology reflecting nearly 600 million years of geologic evolution. Major geologic events include (1) deposition of elastic sedimentary rocks during the Paleozoic and their deformation (folding and faulting) at the end of the Paleozoic; (2) deposition of limestone and elastic rocks during the Cretaceous and their deformation during the early Tertiary; (3) intense extrusive and intrusive igneous activity during the middle Tertiary; and (4) major normal faulting during the late Tertiary. Almost all mineral potential of the area is associated with mid-Tertiary igneous activity. The only significant mineral production within the Ranch area was from the Fresno Mine in the western part of the Terlingua mercury district, one of the largest mining districts in Texas. This mine produced approximately 3500 flasks of mercury, mostly during World War II. Other production was minor and included some additional mercury from localities near the Fresno Mine, as well as silver-lead ore containing minor gold from a small mine in the Solitario.
  • Item
    Paleontologic Survey of the Superconducting Super Collider Site
    (1989) Garner, L. E.; DuBar, Jules R.
    The Superconducting Super Collider (SSC) Paleontological Resource Study aimed to identify potential unique fossils and offer background information on the distribution of fossils within the SSC Project area. This report presents a survey of published literature documenting fossil presence in the region and synthesizes data obtained from examining core samples from the SSC Project area. The project commenced on October 2, 1989, under a subcontract between the Bureau and the Texas National Research Laboratory Commission. Laboratory investigations concluded on November 15, 1989.
  • Item
    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.
  • Item
    Hydrogeologic Description of Pressure Chambers and Application to Enhanced Oil and Gas Recovery - Final Technical Report
    (1989) Dutton, Alan R.
    This study aimed to identify geologic and hydrologic characteristics that delineate compartmentalized reservoirs in oil and gas fields, thereby enhancing our understanding of the hydrocarbon resource potential and facilitating improved recovery methods from such reservoirs. Compartmentalized reservoirs represent significant phenomena as they constitute major hydrocarbon reservoirs. The investigation focused on the Chocolate Bayou field in eastern Brazoria County on the upper Texas Gulf Coast. The methodology comprised three primary steps: (1) describing reservoir architecture using geologic data (structural and stratigraphic features, facies description), (2) characterizing hydrology (pressure distribution, reservoir depletion with production), and (3) assessing produced and unproduced reserves and undrained sections. The concept of compartmentalized reservoirs in sedimentary basins was introduced by Amoco Oil Company in the 1970s. These reservoirs are hydrocarbon-bearing and are bounded by pressure seals, which are low-permeability envelopes surrounding the reservoirs. They can be conceptualized as "pressure chambers" with well-defined boundaries, typically exhibiting abnormally high pressures. Lateral seals, separating the abnormally pressured compartments from adjacent normally pressured ones, are characterized by vertical seals. Three types of seals are identified: basal, lateral, and top. Basal seals define the bottom of abnormally pressured compartments and usually follow a stratigraphic horizon, while lateral seals are typically associated with faults. Top planar seals may parallel or cut across time-stratigraphic boundaries and can develop in any lithology. Sedimentological, mechanical, and chemical factors contribute to compartmentalization.
  • Item
    Description and Quaternary History of the Campo Grande Fault of the Hueco Basin, Hudspeth and El Paso Counties, Trans-Pecos Texas
    (1989) Collins, Edward W.; Raney, J. A.
    The Hueco Basin of Trans-Pecos Texas and Chihuahua, Mexico, formed in response to Basin and Range extensional tectonism that began about 24 million years ago and continues to the present. The southeastern arm of the basin is asymmetrical, with the thickest sediments deposited along the fault-bounded basin axis near the southwestern flank. Approximately 45 kilometers long and striking northwestward, the Campo Grande fault is 12 kilometers from the northeastern basin edge; it divides the downthrown central part of the basin (with over 2,000 meters of fill) from the shallower (175 meters) northeastern flank. Another major northwest-striking fault dips northeastward and bounds the southwestern basin margin in Mexico. The Campo Grande fault trend is composed of at least 17 en echelon fault strands that are 1.5 to 10 kilometers long, with strikes of N25° to 75°W. Dips range between 60 and 90° southwest. Displacements decrease near the terminations of strands. Grooves on fault planes indicate mostly dip-slip movement. Fault scarps have been modified by erosion of the footwall and deposition on the hanging wall. Erosion-resistant caliche (stages IV to V) at the surface aids in preserving scarp heights ranging from 1.5 to 11.5 meters and scarp slopes of 4 to 17°.
  • Item
    Deep Well Injection: Chemical Wastes Disposed and Their Subusrface Reactions
    (1989) Capuano, Regina M.; Kreitler, Charles W.
    More than half of the liquid hazardous waste disposed of annually in the United States is disposed of by deep well injection. Little is known, however, about the chemical compositions of these wastes or about the subsurface reactions that could degrade hazardous compounds within them. This study presents the compositions of waste streams disposed of into Class I wells in Texas and their degradation processes. These Texas waste streams, which constitute 60 percent of the industrial waste disposed of annually by deep well injection in the United States, are probably representative of such injection nationwide. Phenols, chlorinated organics, cyanide, nickel, nitriles, and ketones-aldehydes compose 92 to 95 percent of the acute hazardous and toxic wastes disposed of annually. Biodegradation, if it occurs in deep injection aquifers, is probably the most effective degradation process because it causes nearly complete consumption of the organic nutrient and can degrade the widest range of hazardous organic compounds. Hydrolysis, chemical interactions, sorption, and oxidation-reduction are other possible degradation processes. Degradation in the deep subsurface probably changes with distance from the wellbore. Oxidation and hydrolysis are likely near the wellbore, where solutions are oxidized and have extremely low or high pH values, whereas anaerobic microbial activity probably dominates in an outer zone where toxic compounds are more dilute, the solution is reduced, and pH conditions are near neutral. All compounds in the waste solution must be considered when waste degradation processes are predicted. For example, generally nonhazardous carboxylic acids and their derivatives, present in 30 of the 98 waste streams studied, are highly reactive, and their presence in solution significantly affects the solution pH and hydrolysis and sorption reactions of hazardous compounds. Because carboxylic acids are generally favored as a primary substrate, their presence may either inhibit biodegradation of other primary substrates in the waste solution or enhance degradation of secondary substrates. Another common component in the organic waste streams, cyanide, is generally toxic to microbes and therefore inhibits biodegradation of other hazardous compounds. Field experiments backed up by laboratory experiments and numerical simulations are the best method for verification of waste degradation reactions. Waste-stream compositions could be altered before injection to enhance degradation and discourage unfavorable reactions using the relationships predicted from this type of experiment. This report was submitted in fulfillment of Cooperative Agreement CA-814056-01-0 by the Bureau of Economic Geology under the sponsorship of the U.S. Environmental Protection Agency. This report covers a period from August 1, 1987, to July 31, 1988, and work was completed as of July 31, 1988.
  • Item
    Petrography and Diagenesis of the Travis Peak (Hosston) Formation, East Texas
    (1985) Dutton, Shirley P.
    Petrographic studies of the Travis Peak Formation in East Texas were used to interpret the diagenetic history of Travis Peak sandstones and to relate the diagenetic history to permeability variations within the formation. Travis Peak sandstones are fine to very fine-grained quartzarenites and subarkoses that were derived from sedimentary, metamorphic, and igneous rocks exposed in a large area of the southwestern United States. The originally high depositional porosity in matrix-free sandstones was reduced by compaction and precipitation of authigenic cements, particularly quartz, ankerite, illite, and chlorite. In addition, reservoir bitumen, a high molecular weight hydrocarbon residue, occludes porosity in some zones near the top of the Travis Peak. Porosity and permeability have a wide range of values at the top of the formation, but both the range of values and the maximum values decrease with depth below the top of the Travis Peak. Dissolution of orthoclase and plagioclase has formed most of the secondary porosity. Porosimeter-measured porosity is the best predictor of permeability, and there is a significant inverse correlation between the total volume of cement and permeability.
  • Item
    Morphometry of Major Arroyos in the Vicinity of Low-Level Radioactive Waste Area, Hudspeth County, Texas
    (1989) Baumgardner, Jr., Robert W.
    The area in Hudspeth County under consideration for disposal of low-level radioactive waste lies within the drainage divides of two watersheds: Alamo and Camp Rice Arroyos. The recent geomorphic history of these arroyos has been dominated by incision. Downcutting on the major arroyos caused upslope expansion of drainage networks and an increase in drainage density where clayey sediments of the Fort Hancock Formation crop out. However, alluvium fills the upper reaches of some tributaries and extends upslope onto the alluvial slope where drainage density values are relatively low.
  • Item
    Preliminary Investigation of Selected Samples of Varnished Rock from the Baluco Surface, Vicinity of Proposed Low-Level Waste Site Near Ft. Hancock, Texas
    (1989) Avakian, Arten J.  
    This report summarizes work conducted from March to June of 1989 in the preliminary investigation of varnished rock samples under consideration for AMS radiocarbon dating (Dorn, in press). The report is divided into three sections: (1) description of samples, (2) summary of discussions with Dr. Ronald I. Dorn, Arizona State University, and (3) summary of total organic carbon (TOC) determinations. Ultimately, it was concluded that the varnish on these samples is not well enough developed to yield reliable results, and as a result, the work was terminated.
  • Item
    Surface Water Hydrology ofProposed Low-Level Radioactive Waste Isolation Site
    (1989) Akhter, M. Saleem; Dutton, Alan R.
    The purpose of surface-water hydrology studies at the proposed low-level radioactive waste isolation site in Hudspeth County, Texas, was to define the flooding potential as interpreted from the applicable regulatory requirements. Federal Emergency Management Agency Report 37 (FEMA, 1985), which details guidelines and specifications for flood insurance studies, and other published reports (Texas Department of Water Resources, 1979a-c) were used as the primary source to develop the scope of field reconnaissance and hydrologic evaluation of the study area. The scope of this project included: (1) Delineation of drainage basins and identification of drainage divides and potential surface-water pathways on and near the study area. (2) Collection of rainfall and surface runoff data from the study area. (3) Development and evaluation of a hydrologic model to determine the extent of flooding at the site due to actual and potential storms. (4) Definition of a 100-year floodplain for the study area by determining depth, velocity, and extent of surface runoff resulting from a hypothetical 100-year rainstorm. The approach adopted to meet these objectives consisted of estimating soil properties, monitoring rainfall and surface-water runoff rates, matching simulated flows to observed data on surface-water runoff, and predicting flow characteristics based on calibrated computer models. Two methods were used to evaluate the flooding potential. The first method treated the study area as an active alluvial fan: this analysis indicates that the study area lies within a 100-year floodplain. This method excluded the topographic features and the hydraulic storage in the existing channels. The second method incorporated computer models to determine flood elevations for a 100-year flood: this analysis indicates that runoff from such an event would be mostly contained within the existing channels, leaving large sections in the middle of the study area uninundated.
  • Item
    Marsh Sedimentation Colorado and Trinity River Deltas Texas Gulf Coast
    (1988) White, William Allen, 1939-; Calnan, Thomas R.
    The most extensive losses in coastal wetlands in the United States over the last two decades have occurred along the Gulf Coast. Wetlands are disappearing at the alarming rate of more than 100 km2 per year (39 sq mi/yr) on the Mississippi River Delta, indicating a reversal in the trend of net progradation of the delta that characterized much of the past 5,000 years (Gagliano and others, 1981). The loss rates have accelerated geometrically during the 20th century, apparently as a result of natural and artificial processes. The latter include artificial levees and control structures that have harnessed the Mississippi River and virtually eliminated the deltaic sedimentation processes of overbank flooding, crevassing, and upstream diversion. Extensive canalization and accelerated subsidence related to mineral extraction compound the problem (Gagliano and others, 1981). Investigations of marsh losses in Louisiana indicate that marsh aggradation (vertical accretion) rates are not keeping pace with relative (apparent) sea-level rise (Delaune and others, 1983; Hatton and others, 1983; Baumann and others, 1984; Boesch and others, 1984).
  • Item
    Fluvial-Estuarine Sedimentation Texas Gulf Coast
    (1988) White, William Allen, 1939-; Calnan, Thomas R.
    Deltaic and associated alluvial areas located at the mouths of rivers that flow into the bay-estuary-lagoon system along the Texas coast serve as habitats for extensive salt, brackish, and fresh-water marshes, which are crucial components of biologically productive estuarine ecosystems. These bay-head depositional systems are predominantly formed by fluvial sediments transported and deposited by the major rivers that discharge into the estuarine waters. The loss of over 10,000 acres of wetlands in the alluvial and deltaic areas of the Neches and San Jacinto Rivers underscores the necessity to closely examine the processes that establish, sustain, and degrade these vital natural resources along the Texas coast.
  • Item
    Mississippian Depositional History of the Texas Panhandle: A Reappraisal
    (1988) Ruppel, Stephen C.
    Recent lithostratigraphic and biostratigraphic studies of subsurface Mississippian rocks in the Texas Panhandle suggest that previous interpretations of the sequence and timing of depositional events in the area require revision. During the Early Mississippian period (Kinderhookian to Osagean), deposition in the area was limited to the northeastern Panhandle (Anadarko Basin), while the Texas Arch, a Devonian structure, remained positive, preventing sediment accumulation in the rest of the area. It wasn't until the Meramecian stage that a significant inundation occurred in the southern Panhandle. Shallow platform conditions developed in the submerged area around the Texas Arch, with carbonate buildups forming locally on the outer ramp along the previous margin of the Arch. This marine transgression corresponds to the drowning of platform margins across the midcontinent region. The Texas Arch intermittently controlled deposition until the end of the Mississippian Period.
  • Item
    Stratigraphy and Depsoitional Systems of the Lower Cretaceous Travis Peak Formation East Texas Basin
    (1988) Tye, Robert S.
    The Travis Peak Formation has been stratigraphically divided into five units through well-log correlations. A depositional system tract characterized by fluvial-deltaic-paralic-shelf environments was interpreted based on analyses of sedimentological and stratigraphic data from each unit, along with well-log and core data. During the early development of the Travis Peak Formation, braided streams deposited sediments such as channelbelt, floodplain, and overbank deposits across most of the study area. Towards the downdip regions of the braided streams, deltas extended southward and southeastward over a shallow and stable shelf. As the braided streams migrated and expanded, the location of deltaic deposition moved southward and expanded northeastward. Estuaries formed in areas between the centers of deltaic deposition where sediment supply was relatively low. Seaward of the deltas, shelf sandstones accumulated due to sediment-gravity processes induced by high sediment loads and rapid deposition in the deltas. The late evolution of the Travis Peak Formation is characterized by shoreline transgression and the development of coastal-plain and paralic environments. Fluvial systems transported a sediment load rich in mud and transitioned from sinuous-braided to meandering forms. Channelbelts traversed a coastal plain with extensive floodplains and lakes, feeding small retrogradational deltas. Estuaries grew larger and became prominent coastal features as the coastal plain continued to submerge. With ongoing transgression, marine limestone of the Sligo Formation overlapped the Travis Peak Formation.
  • Item
    Hydrogeology of Formations Used for Deep-Well Injection, Texas Gulf Coast
    (1988) Kreitler, Charles W.; Akhter, M. Saleem; Donnelly, Andrew C. A.; Wood, Warren Theodore, 1962-
    This research program was conducted to investigate fluid migration potential, fluid direction, and velocities in the regional hydrologic environment of the Texas Gulf Coast Tertiary formations in the context of deep-well injection of hazardous chemical wastes. The study focused on the Frio Formation due to its significant waste injection and the availability of a large database on formation pressures and water chemistry in the Frio. Pressure data collected from drill-stem tests and bottomhole pressure measurements in onshore oil and gas wells were used to evaluate pressure regimes. Pressure-depth profiles and potentiometric surfaces constructed from this data revealed three hydrologic regimes: a shallow section with fresh to moderately saline water in the upper 3,000-4,000 ft, an essentially saline hydrostatic section 4,000-5,000 ft thick, and a deeper overpressured section with moderate to high salinities. The hydrologic complexity is further compounded by extensive depressurization in the 4,000-8,000 ft depth interval, likely resulting from the production of over 10 billion barrels of oil equivalent and associated brines over the past 50 years. It was not possible to construct a composite potentiometric surface of the entire Frio to determine "natural" flow gradients or "natural" points of discharge. Potentiometric surfaces representing discrete depth intervals were mapped, and these values, along with flow gradients determined from potentiometric surfaces and published permeability and porosity data, were used to compute linear fluid flow velocities ranging from 0.01 ft/year to 105 ft/year in the lateral direction. The potential for vertical fluid migration was investigated using equivalent environmental hydraulic head maps. The presence of widespread pockets of depressured formations significantly affects the direction and value of fluid gradients, as these depressured oil and gas fields may become potential sinks for the injected chemical wastes. Published water chemistry data were supplemented by field sampling of waters from 32 oil fields. Active recharge of the Frio by continental waters does not seem to be occurring. All sampled waters appear to be in isotopic equilibrium with the rock matrix. Salt dome dissolution is the primary reaction controlling water chemistry in the northern section, while brines from the deeper geopressured section may be leaking into the hydrostatic section of the central and southern Gulf Coast Frio. The absence of organic acids and the alteration of Frio oils from samples shallower than approximately 7,000 ft suggest biodegradation, which has useful implications for the degradation of injected chemical wastes. A detailed analysis of the localized hydrodynamics in Victoria County, Texas, as a case study demonstrates the applicability of the developed techniques to injection facility siting and monitoring processes, particularly where depressurization was observed on a local, county-size scale.
  • Item
    Preliminary Assessment of Nonfuel Minerals on the Texas Continental Shelf
    (1988) Paine, Jeffrey G.; Morton, Robert A.; White, William Allen, 1939-
    As part of a passive continental margin with a long depositional history, the Texas continental shelf has been richly endowed with mineral resources. Exploitation of oil and gas resources on the shelf extends back decades, and the economic value of these deposits has long been recognized. The depositional setting that made the Texas offshore so rich in hydrocarbons has left it barren of exotic nonfuel minerals such as those found in active tectonic settings near Hawaii and at the Juan de Fuca Ridge along the Pacific Northwest. Nonetheless, there are significant accumulations of potentially economic nonfuel minerals in the Texas Exclusive Economic Zone (EEZ). The most promising of these are sand and gravel deposited on the continental shelf during the sea-level fluctuations of the late Pleistocene and Holocene. Requirements for sand and gravel, created by the burgeoning Texas coastal population and the need for compatible sands for beach nourishment projects, such as those contemplated for rapidly eroding beaches at North Padre Island, the Brazos delta, and Galveston Island, combined with the depletion of nearby onshore sand and gravel resources, could make shelf mining operations economically feasible in the future. Before economic feasibility can be determined, however, the local, size, and character of potentially economic shelf deposits must be assessed.