Geological Circulars

Permanent URI for this collectionhttps://hdl.handle.net/2152/121888

Peer-reviewed geoscience research summaries, targeted on Bureau project areas in Texas and other locations, 1965–2003.

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A numeric code for describing rocks in sedimentary basins
(University of Texas at Austin. Bureau of Economic Geology, 1974) Wermund, E. G.; Caughey, Charles A.
The purpose of this paper is to present a system of encoding rock data for multiple uses that include (1) mapping subsurface stratigraphy for economic exploration, (2) cataloging borings used in subsurface waste disposal, and (3) building a library of natural resource information. Regional surface and subsurface stratigraphic studies for exploration in sedimentary basins commonly require the handling of numerous columnar sections that display rock descriptions collected from both outcrop and borings. Data of the borings are core descriptions, logs of cuttings or ditch samples, and mechanical logs of physical properties such as self potential, resistivity, gamma, gamma-neutron, and others. It is not unusual in a regional problem for a geologist to use columnar data from 2,500 or more localities (Wermund and Jenkins, 1970; Galloway and Brown, 1972). One way of handling large stratigraphic data files is to describe the rocks in a computer-compatible format. Whenever lithofacies mapping or statistical analyses become a required means toward solving regional stratigraphic problems, a numerical encoding system to describe the rocks becomes valuable. Although there is a large literature on solving regional problems including various numerical (or lithofacies) mapping techniques, little has been written about methods for encoding rock data. At least, the writers are unaware of many published systems for encoding lithologic descriptions. There is considerable evidence (Galley, 1968) that the problem of disposing of man's wastes will increase in size and complexity and that waste disposal into deep wells will become more common than now. This will be especially true regarding disposal of radioactive wastes (Kubo and Rose, 1973). A catalog of possible deep disposal sites for which the lithologic sequence is encoded will be a valuable adjunct to decision making. Even for shallow pits at the surface which are more in demand the encoding of lithology will be useful. Related to the above needs, increased interest in the construction of environmental and natural resource inventories gives further impetus toward encoding rocks. This interest concerns ongoing active legislation to formulate land use policy and law. Government agencies at all levels, foreseeing their responsibilities in land management, actively discuss many kinds of classification and information systems, one of which is always a natural resources information system. Examples are land use classification (Anderson, Hardy, and Roach, 1972), the proposed nationwide RALI information system formulated by the U.S. Geological Survey (Clarke, 1973), and a Texas natural resources information system (Interagency Council on Natural Resources and Environment, 1973). Part of any natural resources information system requires the description of typical sections of rock in representative or critical geographic regions. If these natural resources systems are to be computer-compatible, then a lithologic encoding system will be an essential element.
A preliminary assessment of the geologic setting, hydrology, and geochemistry of the Hueco Tanks geothermal area, Texas and New Mexico
(University of Texas at Austin. Bureau of Economic Geology, 1981) Henry, Christopher D.; Gluck, James K.
The Hueco Tanks geothermal area contains five known but now inactive hot wells (50° to 71°C). The area trends north-south along the east side of Tularosa-Hueco Bolson astride the Texas-New Mexico border approximately 40 km northeast of El Paso. Because of its proximity to El Paso, geothermal water in the Hueco Tanks area could be a significant resource. Hueco Bolson is an asymmetric graben. Greatest displacement along boundary faults is on the west side adjacent to the Franklin Mountains. Faults, probably with less displacement, also form an irregular boundary on the east side of the bolson. Several probable faults may allow the rise of thermal waters from depth. Ground water in the central part of Hueco Bolson flows southward to the Rio Grande. However, four of the five hot wells occur in a ground-water trough along the eastern margin of the bolson. The trough may be bounded by one of the postulated faults serving as a barrier to ground-water flow. Data on permeability of potential reservoir rocks, including basin fill and fractured bedrock, suggest that they may be sufficiently permeable for development of geothermal water. The concentration of dissolved solids in the geothermal waters varies from 1,100 to at least 12,500 mg/L, but most waters show high concentrations. They are Na-Cl-(SO4) waters similar in composition to nonthermal waters in basin fill. The composition probably results from contact with evaporite deposits either in basin fill or in Paleozoic bedrock. Shallow reservoirs reach maximum temperatures of about 80° to 110°C. Available data are too limited to evaluate adequately the resource potential of geothermal water in the Hueco Tanks area. A complete exploration program, including geological, hydrological, and geochemical investigation, is recommended.
A revision of Taylor nomenclature, Upper Cretaceous, Central Texas
(University of Texas at Austin. Bureau of Economic Geology, 1965) Young, Keith, 1918-2004
Since the days of R. T. Hill (1901) two Upper Cretaceous lithic units have been used as formations but have remained unnamed. These two units have usually been called the "Lower Taylor Marl" and the "Upper Taylor Marl". If Taylor is used as a group, both of these formations belong in the Taylor Group. If one uses Hill's division system of classification, the "Upper Taylor Marl" belongs to the Taylor Division but the "Lower Taylor Marl" belongs to the Austin Division, since it is a claystone lithosome interfingering with the type Austin Chalk and is genetically part of the Austin. Schuchert (1943, p. 900) may have been aware of some of the problems and some of the confusion rising out of this nomenclatural muddle when he applied the term "unnamed formation" to the unit generally termed "Lower Taylor Marl". The "Lower Taylor" and the "Upper Taylor" are separated by the Pecan Gap Formation (Stephenson, 1918) so that the lithic sequence is claystone, chalk (or marly limestone), and claystone. In more detailed maps of the greater area of Austin, Texas, the Pecan Gap is omitted by faulting in some areas, leaving the two claystone formations in fault contact. To eliminate confusion, it is imperative that the two unnamed claystone units be named.
Asbestos in the Allamoore Talc District, Hudspeth and Culberson Counties, Texas
(University of Texas at Austin. Bureau of Economic Geology, 1973) Rohrbacher, R. G.
The Allamoore district of Hudspeth and Culberson counties, Texas, has become one of the most significant talc-producing areas of the United States. Exploitation of talc deposits in the district began in 1952 with a cumulative production of 120,000 tons through 1957 (Flawn, 1958). With continued growth, annual production exceeded 160,000 tons in 1968, making the district second only to New York State in national output, Moderate- to large-sized deposits have been developed with near-surface parts inexpensively extracted. Talc reserves are estimated in the tens of millions of tons. Long-fiber asbestos was first found in association with talc deposits of the Allamoore district in 1960 during exploratory drilling of what became the Buck claim, Small amounts of asbestos were noted in subsequent development of this large talc deposit. Later, small amounts of white asbestos were encountered in the T. & P. No. 1 mine and... at the Neal-Mann prospect (fig. 1). Early in 1971, Albert Gregory of Van Horn, Texas, discovered an asbestos deposit now known as the Diablo prospect. Subsequently, the Van Horn Soapstone and Talc Corporation was formed and preliminary exploratory work at the prospect indicated the possible presence of commercially exploitable amounts of asbestos. This evaluation of asbestos deposits is based on a current study of the stratigraphy, structure, and mineral deposits of the talc district.
Bloating characteristics of east Texas clays
(University of Texas at Austin. Bureau of Economic Geology, 1965) Fisher, W. L. (William Lawrence), 1932-; Garner, L. E.
Incidence of bloating among approximately 600 clay samples from East Texas, ranging in age from Gulfian (Late Cretaceous) to Recent, correlates principally with clay mineralogy-and pH--together an indication of bulk composition--and to a lesser extent with texture, loss on ignition, and content of nonclay refractory minerals. Clay-mineral and pH data permit prediction of bloating with an accuracy of about 80 percent. Montmorillonitic and illitic clays are the best bloaters; bloating occurs in more than 80 percent of clays consisting of less than 30 percent kaolinite, more than l 0 percent illite, and between 20 and 90 percent montmorillonite. Only 10 percent of the high-alumina clays (more than 50 percent kaolinite) bloat; these generally are plastic and carbonaceous. Value of pH is an index of the amount of certain flux and gas-forming materials in clays; accordingly, bloating incidence generally increases with increase in pH. Incidence of bloating also increases slightly with decrease in grain size, increase in plasticity, increase in loss on ignition, and decrease in content of nonclay refractory minerals.
Calderas and mineralization: volcanic geology and mineralization in the Chinati Caldera complex, trans-Pecos Texas
(University of Texas at Austin. Bureau of Economic Geology, 1981) Duex, Timothy W.; Henry, Christopher D.
This report describes preliminary results of an ongoing study of the volcanic stratigraphy, caldera activity, and known and potential mineralization of the Chinati Mountains area of Trans-Pecos Texas. Many ore deposits are spatially associated with calderas and other volcanic centers. A genetic relationship between calderas and base and precious metal mineralization has been proposed by some (Albers and Kleinhampl, 1970) and denied by others (McKee, 1976, 1979). Steven and others (1974) have demonstrated that calderas provide an important setting for mineralization in the San Juan volcanic field of Colorado. Mineralization is not found in all calderas but is apparently restricted to calderas that had complex, post-subsidence igneous activity. A comparison of volcanic setting, volcanic history, caldera evolution, and evidence of mineralization in Trans-Pecos to those of the San Juan volcanic field, a major mineral producer, indicates that Trans-Pecos Texas also could be an important mineralized region. The Chinati caldera complex in Trans-Pecos Texas contains at least two calderas that have had considerable postsubsidence activity and that display large areas of hydrothermal alteration and mineralization. Abundant prospects in Trans-Pecos and numerous producing mines immediately south of the Trans-Pecos volcanic field in Mexico are additional evidence that ore-grade deposits could occur in Texas.
Cotton Valley (Upper Jurassic) and Hosston (Lower Cretaceous) depositional systems and their influence on salt tectonics in the East Texas Basin
(University of Texas at Austin. Bureau of Economic Geology, 1984) McGowen, Mary K.; Harris, David W.
Correct interpretation of the effect of basin infilling on salt mobilization is critical to understanding salt dome growth and stability. The size of salt structures in the East Texas Basin is determined by the original thickness of the underlying Louann Salt (Middle Jurassic). That is, salt structures distinctly increase in size toward the interior of the basin. Initial movement of salt apparently occurred in the marginal areas of the basin during Smackover (Late Jurassic) deposition. This movement seems to have resulted from downward creep induced by the loading of carbonate units and was enhanced by basinward tilting. During a major shift from carbonate to clastic sedimentation in the Late Jurassic, salt movement became more extensive. This salt migration was caused by uneven sediment loading of fluvial-deltaic systems in the Cotton Valley Group (Upper Jurassic) and the Hosston Formation (Lower Cretaceous). Erosion source areas on the west and north persisted throughout Cotton Valley and Hosston time. Clastics were delivered to the East Texas Basin by many small streams, rather than by one major stream, because a mature drainage system had not yet formed. The Cotton Valley Group, thought to be a fan-delta system, can be subdivided into three types of facies: prodelta deposits, delta-front deposits, and braided fluvial deposits. Fan deltas, supplied by braided streams, prograded from the north, northwest, and west. Dip-oriented sandstone trends dominate in the northwestern part of the basin and change basinward to northeast to southwest strike-oriented trends. During Hosston time, sedimentation in the northwestern part of the basin was predominantly fluvial. The depositional characteristics of sediments in this area are typical of braided streams. In the study area, parallel net-sandstone and sediment chucks are clearly defined in the distal part of the Cotton Valley but are not as well defined in the Hosston. This suggests that most deltaic sedimentation during Hosston time occurred basinward of the study area. A major transgression at the end of Hosston time resulted in the deposition of the Pettet Limestone. Apparently, the location of salt domes and salt anticlines was controlled by the position of the Smackover-Gilmer carbonate platform. This platform impeded local subsidence to the extent that fan-delta sediments of the Cotton Valley Group spread laterally across the shelf rather than stacked vertically. Sediment depocenters formed preferentially basinward of the platform, resulting in migration of the underlying salt into ridges that fronted the prograding sediment wedge. As the salt was depleted under these depocenters, subsidence slowed and thereby allowed the fan deltas to override the salt ridges. This resulted in a basinward progradation of deltaic depocenters and produced younger depocenters toward the interior of the basin. Further salt migration and differentiation of salt ridges produced the present complex array of salt domes and anticlines in the East Texas Basin. Seismic and gravity data clearly demonstrate the existence of these salt ridges and intervening sediment thicknesses.
Cretaceous paleogeography: implications of endemic ammonite faunas
(University of Texas at Austin. Bureau of Economic Geology, 1972) Young, Keith, 1918-2004
Endemic ammonite faunas evolved from cosmopolitan faunas in a series of successive episodes over about 35 million years of the Cretaceous of the Gulf Coast of the United States. During basin-basin-margin tectonic adjustments the Cretaceous barrier reef was inundated or circumvented so that a cosmopolitan fauna entered the back-reef area. Gradual isolation of the fauna behind the barrier produced endemism. With the next basin adjustment the endemic fauna became extinct, and a new cosmopolitan fauna migrated into the back-reef area, likewise evolving into an endemic fauna in its turn. Six cosmopolitan-endemic cycles have been identified. Geological evidence suggests two or three additional cycles.
Depositional systems and oil-gas reservoirs in the Queen City Formation (Eocene), Texas
(University of Texas at Austin. Bureau of Economic Geology, 1972) Guevara, Edgar H.; García, Roberto
Regional surface and subsurface studies indicate that thick deltaic (Queen City Formation) and thin shelf (Reklaw and Weches Formations) sequences compose the stratigraphic interval between the top of the Carrizo Sand and the base of the Sparta Formation. In East Texas, the Queen City Formation accumulated as part of a high-constructive, lobate delta system; and in South Texas, as part of a high-destructive, wave-dominated delta system. In South Texas, principal facies are meanderbelt sand, lagoonal mud, stacked coastal barriers, and prodelta shelf mud facies. In East Texas, delta plain, delta front, and prodelta facies are dominant; and in Central Texas, the principal facies are strandplain sands originated by southwestward longshore drift of sediments from the high-constructive delta system. Facies distribution, composition, and size of the deltas in East Texas are similar to lobes of the Holocene high-constructive Mississippi delta system and to ancient deltas in the lower part of the Wilcox and m the Jackson Groups of the Gulf Coast Basin. Deltaic sediments of South Texas are comparable to Pleistocene high-destructive, wave-dominated facies on the Surinam coast, to the Holocene Rhone delta system, and to ancient deltas in the upper part of the Wilcox Group. Queen City deltas prograded gulfward over shelf muds and glauconites of the Reklaw Formation; they are overlain by comparable shelf facies of the Weches Formation. In East Texas, deltaic facies wedge out eastward. Terrigenous elastics of the high-destructive deltas extend southward into Mexico. Hydrocarbons are produced from thin strike-oriented sands downdip from the belt of maximum sand thickness of the high-destructive deltas in South Texas; only a minor amount of oil and gas has been obtained from delta front and distributary channel sands of the high-constructive deltas in East Texas.
Depositional systems and structural controls of Hackberry sandstone reservoirs in southeast Texas
(University of Texas at Austin. Bureau of Economic Geology, 1984) Ewing, Thomas E.; Reed, Roneé S.
Deep-water sandstones of the Oligocene-age Hackberry unit of the Frio Formation contain significant quantities of oil and gas and remain potentially one of the most productive exploration targets in southeast Texas. The Hackberry is a wedge of sandstone and shale containing bathyal fauna that separates upper Frio barrier-bar - strandplain sandstones from lower Frio neritic shale and sand. Major Hackberry sandstones lie atop a channeled unconformity that forms the base of the unit. Sandstones in a typical sand-rich channel at Port Arthur field grade upward from a basal, confined channel-fill sandstone to more widespread, broad, fan-channel deposits, Topmost are proximal to medial fan deposits and overbank turbidite deposits. The sequence suggests that Hackberry sandstones were laid down by an onlapping submarine canyon-fan complex deposited in canyons that eroded headward into the contemporaneous Frio barrier system. Regional maps and seismic interpretations outline a network of sand-filled channels extending from the barrier toward the southeast. The earliest structural activity of the Port Arthur area is lower Oligocene (Vicksburg) faulting associated with continental-slope sedimentation. Small growth faults of late Oligocene (Frio) age displace the Hackberry section less than 500 ft and extend upward into Miocene strata. Isopach and isolith maps indicate that the Orange, Port Neches, and Fannett salt domes were active uplifts during Frio and Anahuac (Lower Miocene) deposition. Near Spindletop dome, however, only a north-south-trending salt-cored ridge is present. The Hackberry channels are in part located in salt-withdrawal basins, but major channel axes extend across the uplifts. Time versus depth plots of water depth and sediment thickness indicate that most of the Hackberry Embayment in Texas could have been formed by normal subsidence during the later Oligocene if the embayment were cut off from its supply of muddy sediment. Thick, sandy, lower Hackberry deposits filled deep canyons eroded into the retreating shelf margin. The Hackberry contains two hydrocarbon plays. The updip play is relatively shallow and oil-rich and lies near the updip limit of deep-water deposition. Some of the fields in this play produce from barrier-bar - strandplain Frio sandstones erroneously correlated with the Hackberry. The downdip play is gas-rich and generally geopressured. The reservoirs lie either within or on the flanks of the major channel systems and are commonly bounded updip by small growth faults, Understanding the component depositional environments represented by the discontinuous and complex lithofacies of these sandstones will improve hydrocarbon exploration and production.
Depositional systems in the Jackson Group of Texas: their relationship to oil, gas, and uranium
(University of Texas at Austin. Bureau of Economic Geology, 1970) Fisher, W. L. (William Lawrence), 1932-; Proctor, Jr., C.V.; Galloway, William E.; Nagle, J. Stewart (James Stewart), 1889-1952
Five main depositional systems of the Jackson Group in Texas are delineated through regional outcrop and subsurface investigation. Dominant element in the central and eastern Texas Gulf Basin is the Fayette fluvial-delta system (bounded by Guadalupe River on the south and Neches River on the east) consisting of dip-oriented, lobate wedges of sands, muds, and lignites. Vertical sequence in updip subsurface and outcrop grades upward from marine muds through delta facies into fluvial sands and muds, reflecting net regression and progradation of the system. Longshore drift of sediments from the delta system contributed to the South Texas strandplain-barrier bar system, consisting of strike-trending sand bodies interbedded with marine and lagoonal muds. Landward of the strandplain-barrier bar system and extending into outcrop is a lagoonal-coastal plain system consisting of muds, local lignites, and minor, dip-oriented channel sand units. Gulfward of the strike-trending strandplain system is the South Texas shelf system, formed of marine muds derived largely from the delta system to the northeast. Beneath the South Texas strandplain-barrier bar and Fayette delta systems and extending eastward into Louisiana and Mississippi is the Yazoo-Moodys Branch shelf system consisting of marine, fossiliferous muds and minor glauconitic marls. Texas Jackson delta and associated systems are comparable to depositional systems of other Eocene units (Lower Wilcox and Yegua) of the Gulf Basin as well as the Holocene Mississippi delta and related systems of the northwestern Gulf of Mexico. Delineation of depositional systems and component facies facilitates definition of significant mineral trends (oil, gas, lignite, and uranium) that show the relationship between existing and potential areas of production.
Depositional systems in the Paluxy formation (Lower Cretaceous), northeast Texas-oil, gas and groundwater resources
(University of Texas at Austin. Bureau of Economic Geology, 1977) Caughey, Charles A.
The Paluxy Formation is a stratigraphic unit which is composed of sandstone and shale and extends across the northern part of the East Texas embayment. Paluxy deposits were derived from sedimentary rocks to the north, and they accumulated in shoreface and coastal plain environments associated with an irregular southward regression of the shoreline. Preserved in the sedimentary mass are three major depositional systems: a centrally located delta system, a fluvial system in the north, and a strandplain system in the west. The delta system is wave dominated, composed largely of marine-influenced sediments aligned along depositional strike. Sand isolith maxima, associated with stacked coastal barrier deposits, outline the cuspate shape of the delta system. Two principal delta lobes are recognizable; these are centered in Hunt and in Wood Counties. The fluvial system consists of a broad, sandy meanderbelt facies which thins northward into discrete channel complexes separated by floodbasin deposits. The strandplain system blankets the western embayment margin with coalescent beach ridge and associated shoreface and coastal lake deposits. Strandplain sands provide small to moderate quantities of groundwater that are generally suitable for uses other than irrigation. Fluvial system deposits furnish local areas with water for irrigation and for domestic and municipal supply. Major oil and gas accumulations occur in deltaic coastal barrier and fluvial meanderbelt facies.
Depositional systems in the Sparta Formation (Eocene): Gulf coast basin of Texas
(University of Texas at Austin. Bureau of Economic Geology, 1977) Ricoy, Jose Ulises; Brown, L. F. (Leonard Franklin), 1928-
Three principal depositional systems were defined within the Sparta Formation of Texas using surface and subsurface data: high-constructive delta system in east Texas; strandplain-barrier bar system in central Texas; and high-destructive, wave-dominated delta system in south Texas. Principal facies constituents of the high-constructive delta include upper delta plain in outcrop and lower delta plain, delta front, and prodelta in subsurface. Five major deltaic lobes in the Sparta Formation are similar to various lobes of the Eocene Queen City Formation, Lower Wilcox Group, Jackson Group, and Yegua Formation of Texas. The Sparta high constructive delta system is present from Fayette and Colorado counties in Texas, eastward into Louisiana, Mississippi, and Arkansas. The Sparta strandplain-barrier bar system of central Texas is basically composed of a single multistory barrier bar unit. It was constructed with sand transported along strike by longshore currents from reworked sediments of the high-constructive delta system in east Texas. This system extends from Fayette and Colorado counties westward to Atascosa and Live Oak counties. A Halocene analog is the Texas barrier island system. Eocene analogs are the strandplain-barrier bar system of the Eocene Jackson Group, Yegua Formation, Lower Wilcox Group, and Queen City Formation. A high-destructive delta system in south Texas is composed essentially of coastal barriers and associated lagoonal facies in outcrop; and coastal barrier, lagoon, and prodelta shelf facies in the subsurface. This wave-dominated delta system is present from Atascosa and Live Oak counties southward to the Rio Grande, and it extends into northern Mexico. Eocene analogs occur in the south Texas Wilcox Group, Yegua Formation, and Queen City Formation. Oil and gas have not been found in the Sparta Formation, in part because little growth faulting was associated with the thin Sparta delta front sandstone and prodelta shale facies. Water chemistry variations are closely related to depositional systems within the Sparta Formation. A bicarbonate province is related to updip areas (major fluvial influence) of the high-constructive delta system of east Texas; a sulfate province occurs in updip areas (barrier bar/lagoon influence) associated with the high destructive delta system of south Texas and central Texas; and a chloride province is associated with downdip marine sandstone facies of barrier and deltaic origin. Flushing by fresh water has quantitatively but not qualitatively altered the initial water distribution within the various Sparta sand facies.
Depositional systems in the Wilcox Group of Texas and their relationship to occurrence of oil and gas
(University of Texas at Austin. Bureau of Economic Geology, 1967) Fisher, W. L. (William Lawrence), 1932-; McGowen, J. H.
Regional investigation of the lower part of the Wilcox Group in Texas in outcrop and subsurface indicates seven principal depositional systems. These include: (1) Mt. Pleasant Fluvial System developed updip and in outcrop north of the Colorado River;(2) Rockdale Delta System, present primarily in subsurface, chiefly between the Guadalupe and Sabine Rivers; (3) Pendleton Lagoon-Bay System in outcrop and subsurface largely on the southern flank of the Sabine Uplift; (4) San Marcos Strandplain-Bay System, occurring in outcrop and subsurface mainly on the San Marcos Arch; (5) Cotulla Barrier Bar System in subsurface of South Texas; (6) Indio Bay-Lagoon System developed updip and in outcrop of South Texas; and (7) South Texas Shelf System, an extensive system entirely within subsurface of South Texas. The Rockdale Delta System, consisting of large lobate wedges of muds, sands, and carbonaceous deposits, is the thickest and most extensive of the lower Wilcox depositional systems. It grades updip to the thinner terrigenous facies of the Mt. Pleasant Fluvial System. Deposits of the Rockdale Delta System were the source of sediments redistributed by marine processes and deposited in laterally adjacent marine systems. Delineation of depositional systems and, more specifically, delineation of component facies of the various systems, permits establishment of regional oil and gas trends which show relationship of producing fields and distribution of potentially producing trends.
Depositional-episodes: their relationship to the Quaternary stratigraphic framework in the northwestern portion of the Gulf Basin
(University of Texas at Austin. Bureau of Economic Geology, 1974) Frazier, David E.
The stratigraphic record yields evidence that each episode of clastic silicate deposition has been of limited duration and that each has been preceded and followed by a significant hiatus. Evidence for alternations of deposition and nondeposition is readily apparent in the landward portions of Pleistocene deposits along the Gulf Coast, due to the glacio-eustatic changes in sea level; evidence of alternations, although elusive, exists also in the basinward portions of these deposits. The concept of depositional-episodes explains the significance and relationship of these alternating conditions throughout the basin. The strata attributed to each depositional episode are a composite of several discrete facies sequences and are referred to in this paper as a depositional-complex. Each facies-sequence represents either a single delta lobe within a deltaic progression, or one of the several repetitive sequences deposited in an interdeltaic environment. Each depositional-complex records and defines a depositional-episode and indicates three phases of development. Deposits of the initial phase record a stillstand of the sea during which each of the several rivers entering the basin prograde a succession of delta lobes and interdeltaic facies sequences across the shelf. The second phase of development (which is penecontemporaneous with the first) is recorded by the intercalation of clastic and organic flood-plain deposits which accumulate on the newly formed coastal plain, and by the deep-water hemipelagc basin sediments which are secondarily derived from unstable sediments deposited in the outermost shelf and uppermost slope environments. The terminal phase is evidenced by sediments deposited during a period of instability when a marine transgression either continuously or intermittently forces estuarine conditions on the rivers entering the basin. Throughout the terminal transgression, the finite zone of active deposition adjacent to the shoreline is shifted landward. Basinward of this active zone of deposition, hiatal conditions are imposed and at the instant of maximum transgression, when the depositional-episode is terminated, all points on the hiatal surface are synchronous. The bounding surfaces of depositional complexes represent natural stratigraphic breaks over the entire basin and are related to hiatal conditions imposed by marine transgressions. Within the Quaternary section, the repetitive alternation of depositional-episodes and significant hiatuses is due to the glacio-eustatic fluctuations of sea level: as a result, worldwide correlations of the Quaternary depositional complexes and hiatal surfaces may be possible.
Distribution and significance of coarse biogenic and clastic deposits on the Texas inner shelf
(University of Texas at Austin. Bureau of Economic Geology, 1980) Morton, Robert A.; Winker, C. D.
Sediments of the Texas inner shelf are generally fine grained; coarse clasts ( > 0.5 mm) are uncommon (< 1%) over much of the area. Higher concentrations of coarse material, however, occur in discrete areas that apparently represent positions of foyer deltas. Coarsest constituents are predominantly whole shells and shell fragments with subordinate amounts of lithic clasts. The calcareous skeletal debris represents a mixture of extant shelf fauna and relict brackish-water molluscs includingRangia spp. and Crassostrea uirginica. Rounded sandstone, limestone, and mudstone clasts up to 7 cm long and caliche nodules are common in some areas. Maps showing 1) coarse fraction percent, 2) distribution of brackish-water molluscs, and 3) rock fragments show similar trends outlining ancestral Rio Grande, Brams-Colorado, and Trinity deltas; a patchy, arcuate trend between Pass Cavallo and Aransas Pass is enigmatic. Criteria used to determine postdepositional history and possible sources of shell debris for each of the four trends are degree of abrasion, fragmentation, etching, boring and discoloration. Possible explanations for concentration of coarse material include high biological productivity, low rates of terrigenous clastic sedimentation, selective deposition by modern shelf processes, and reworking of locally shelly relict deposits exposed on the seafloor during the Holocene transgression. Of these possibilities, no single explanation adequately accounts for areal variations in coarse material. Reworking of delta-plain and estuarine deposits during and after sea-level rise is characteristic of areas that are now receiving insignificant amounts of coarse-sediment. The Sabine-Bolivar trend is interpreted as a transgressive lag derived from erosion of a late Pleistocene Trinity delta. In contrast, Brazos-Colorado and Rio Grande trends are interpreted as compound strandline features associated with subsidence, erosion, and retreat of Holocene deltas.
Evaluation of sanitary landfill sites, Texas coastal zone: geologic and engineering criteria
(University of Texas at Austin. Bureau of Economic Geology, 1972) Brown, L. F. (Leonard Franklin), 1928-; Fisher, W. L. (William Lawrence), 1932-; Malina, Joseph F., 1935-
Basic geologic, hydrologic and engineering criteria on which selection of sanitary landfill sites should be based include (1) thickness, excavation characteristics, permeability, solution-holding capacity, and reactivity of host and cover materials; (2) hydrologic properties including depth to water table, season variation in position of water table, and rate of liquid movement; and (3) nature of terrain in terms of slope, topography, and surface drainage. Evaluation of these features must be based initially on adequate mapping and inventory of surface and near-surface earth materials-both bedrock and surficial soils. Solid wastes include a broad spectrum of residues of municipal and industrial activities. These waste solids include refuse from residential areas, sludges from water and wastewater treatment, plant trash, organic and inorganic chemicals, toxic materials, manures, oils, and other materials which are not discharged into surface waters or into the atmosphere. Basic environmental mapping recently completed in an 18,000-square-mile area of the Texas Coastal Zone, an area embracing nearly one-third of the State's population and industry, shows the distribution of 130 substrate and landform map units. Map units are grouped into four main landfill suitability groups. Of these groups, only one is entirely suitable for landfill sites, two constitute very poor site areas, and one can be utilized only locally and with proper engineering design. Principal landfill suitability groups in the Texas Coastal Zone include (1) clays and muds with low permeability, high water-holding capacity, high compressibility, high to very high shrink-swell potential, low internal drainage, level to depressed surface relief, low shear strength, and high plasticity-such clays and muds provide secure landfill sites; (2) sands with high to very high permeability, low water-holding capacity, low compressibility, low shrink-swell potential, high internal drainage, high shear strength, and low plasticity-these sands are very poor landfill sites; (3) wetlands (marshes and swamps) with very low permeability, high water-holding capacity, high to very high compressibility, high shrink-swell potential, very poor internal drainage, depressed surface relief, and permanently high water table - these wetlands are poor landfill sites; and (4) clayey sands and silts with moderate to low permeability, moderate water-holding capacity, moderate compressibility, low to moderate shrink-swell potential, moderate internal drainage, and high shear strength - these sands and silts are marginal for solid-waste disposal but can be used locally with proper engineering design and control. Of the approximately 100 in-ground solid-waste disposal sites currently in operation in the Texas Coastal Zone, only 20 percent are geologically and hydrologically secure sites. Thirty percent are in substrates that are insecure, potential or active pollution areas. The remaining 50 percent of the sites occur within highly marginal areas with at least some degree of active or potential pollution. Clearly, geologic and hydrologic criteria have not been used in the selection of most existing sites. The Texas Coastal Zone is not unique; in far too few landfill areas are adequate geologic and land-suitability maps available to the planner. Within the Texas Coastal Zone and in most other areas, immediate economic considerations outweigh fundamental geologic and hydrologic suitability in site selection. For example, in the heavily populated and industrialized upper Texas Coastal Zone, the most secure and suitable substrates for solid-waste disposal also support the most valuable agricultural lands; by contrast, geologically and hydrologically insecure sites, such as wetlands and permeable sands, generally constitute less expensive land. Abandoned sand and gravel pits, for example, provide inexpensive, generally available, and ready-made sites, yet due to high substrate permeability, extensive pollution can result when these abandoned pits are used as solid-waste disposal sites. As in most other areas, the bulk of solid waste in the Texas Coastal Zone is disposed of in open dumps; only a small part of the total solid waste is incinerated or disposed of in a sanitary landfill. Under present conditions, properly managed landfills provide the most adequate manner of waste disposal and are naturally far superior to open dumps. However, unless selection of the site is based on geologic and hydrologic criteria, sanitary engineers will be severely handicapped in their efforts to prevent unacceptable environmental pollution.
Facies patterns and depositional history of a Permian sabkha complex -- Red Cave Formation, Texas Panhandle
(University of Texas at Austin. Bureau of Economic Geology, 1980) Handford, C. Robertson; Fredericks, Paul E.
The Red Cave Formation (Permian, Leonard Series) in the Texas Panhandle consists of cyclic, red-bed clastic and carbonate-evaporite members that reflect deposition in extensive coastal sabkhas. These environments were bounded on the north by a desert wadi plain and on the south by a carbonate inner shelf that bordered the northern Midland Basin. Evaporite members were deposited in carbonate evaporite coastal sabkhas, and clastic members were deposited in mud-rich coastal to continental sabkhas that passed inland to wadi-plain environments. Inner shelf dolomites include slightly fossiliferous, faintly laminated to burrowed mudstone and pellet wackestone. These lithofacies are overlain by and interfinger northward with dolomite and anhydrite deposited in coastal sabkhas. Oolitic or pellet packstone and grainstone with well-developed cross-lamination suggest shallow subtidal to intertidal deposition. Supratidal facies include dolomitic mudstone with algal laminations and some intraclasts. Sabkha sequences are commonly capped with nodular anhydrite; mud-rich sabkha sequences culminate with red to green mudstone and anhydrite. Carbonate and evaporite facies pinch out generally toward the northwest and northeast into wadi-plain red beds. These facies include ripple-drift, cross-laminated siltstone and sandstone, adhesion-rippled siltstone, and red to green mudstone. Desiccation features, intraclasts, root zones, and paleosol horizons cap braided fluvial deposits and attest to subaerial exposure and probable non-marine conditions. Partial modern analogs to Red Cave sabkha depositional elements include coastal mud flats and alluvial fans in the northwestern Gulf of California, tidal flats and the Wooramel ephemeral stream delta in Gladstone Embayment, Shark Bay, Australia, and Trucial Coast sabkhas in the Persian Gulf. Each setting has certain facets that are remarkably similar to interpreted paleoenvironments and lithofacies of the Red Cave Formation.
Fault tectonics of the East Texas Basin
(University of Texas at Austin. Bureau of Economic Geology, 1982) Jackson, M. P. A.
Principal fault systems in the East Texas Basin were examined in terms of their distribution, geometry, displacement history, and possible origins. All the faults studied are normal and moved syndepositionally over approximately 120 Ma (million years); some have listric shapes and associated rollover anticlines. The faults formed by processes associated with gravitationally induced creep of the Louann Salt, such as gliding over a salt decollement zone, crestal extension and collapse over salt pillows and turtle structures, and salt withdrawal from beneath downthrown blocks. None of the fault zones were caused by marginal flexure of the basins or salt diapirism; there is little evidence of basement control. Paucity of data prevents a reliable interpretation of the Mount Enterprise Fault, but our data suggest that none of the fault zones in this basin pose a seismic threat to a hypothetical nuclear-waste repository in the Gulf Coast area.
Flood hazards along the Balcones escarpment in central Texas; alternative approaches to their recognition, mapping, and management
(University of Texas at Austin. Bureau of Economic Geology, 1975) Baker, Victor R.
The public tends to dismiss floods as somewhat unreal catastrophes or occasional inconveniences that usually affect others. When a flood disaster strikes at the local level, the magnitude of the event is appraised in terms of the damage to human works on the river-valley floor or, in some cases, in terms of the loss of life. Resources are mobilized to combat the disaster, and discussions ensue concerning flood control plans and projects. The affected communities may then learn that they have experienced a "100-year flood," or a flood discharge that has a "1 percent probability of being equalled or exceeded in a given year." They may further learn that the unpleasantness of this event can be prevented and controlled by various combinations of levees, dikes, dams, reservoirs, and channels. Rarely does the public hear that floods are a natural part of a river's activity, really an essential part of a river's long-term task of conveying water and sediment down gradient from an evolving landscape to a base level, such as the Gulf of Mexico. Flooding is a great natural hazard because people occupy river-valley bottoms, flood plains, and other flood-prone areas. The term "flood" is variously defined depending on the concerns of its user. To all, it is an overflow of a stream channel that exceeds certain limits. To the flood-plain manager, these limits are those at which life and property are damaged or threatened. To the hydrologist, the limits are arbitrarily defined on the basis of magnitude-frequency studies of stream flow. The geomorphologist and the geologist view floods relative to the natural features associated with the stream or river. Clearly, the study of floods and the mapping of their potential occurrence require an interdisciplinary approach. The accelerating demand for flood-plain information makes desirable an evaluation of alternative techniques to standard engineering flood line and regional flood analyses (Wolman, 1971). Different mapping techniques may be appropriate to different localities depending on the local hydrologic regime, the level at which planning is being performed, and the funds available to finance the study. A geologic approach to flood hazard mapping can be used effectively at the state or regional scale to provide interim flood hazard information prior to detailed hydrologic and hydraulic studies on a local basis. If included within an overall program of regional environmental geological mapping, morphological flood-plain mapping can provide a relatively inexpensive byproduct of a general program of environmental inventory. It is a well-known fact that, despite immense public expenditures for flood protection, flood losses remain substantial, potentially costing an average of $2 billion (1966 dollars) per year nationally (U.S. Water Resources Council, 1968). Assuming established trends in the increased use and development of hazardous flood plains, this figure will increase to $5 billion by 2020. In 1966 the estimated annual flood damage for Texas rivers draining more than 250,000 acres, exclusive of the Rio Grande, was $28.2 million (U.S. Water Resources Council, 1968). Total damage to smaller basins was estimated at $55.9 million. Despite the current total investment of over $400 million in flood control works, the total damage figures are projected to rise to $59.3 and $125.3 million respectively by the year 2000. An increasing percentage of the annual national flood loss is the result of so-called catastrophic floods (Holmes, 1961), i.e., floods which either (1) have a return period of 100 years or more, or (2) cause failure of a flood protection project by exceeding the project design flood. The average amount of flood loss from floods of moderate frequency is decreasing relative to these catastrophic events. The estimated $3 billion damage produced by Hurricane Agnes flooding in the eastern United States during the summer of 1972 may represent the pattern for most future flood losses. Approximately 40 percent of the damage from Agnes flooding occurred in areas which had received federally funded flood protection benefits. The message for Texas, where flooding occurs because of what is perhaps the most catastrophic rainfall regime in the conterminous United States, is that flood-plain managers must consider alternative approaches to reservoirs, levees, floodwalls, and channels. Flood-plain management requires that an all-out effort be made to (1) increase basic knowledge of floods and flood hazards, (2) define and outline major flood areas, and (3) improve methods of flood-frequency analysis (U.S. Congress, 1966, p. 18-19). White (1964) has shown that from the theoretically broad range of choice for the flood-plain manager, only a few choices are generally considered in decision-making. This results in far less efficiency than could be achieved by considering the whole range of possible choices. Two main factors seem to limit choice: the flood-plain manager's perception of the nature and magnitude of the flood problem, and his perception of alternative responses. This report is a preliminary attempt to describe the flood problems of Central Texas, to suggest alternative approaches to their evaluation, and to relate these scientific goals to the managerial goals of the State and of local communities.

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