Oakville Sandstone Research Articles

Stratigraphic Architecture and Depositional History of Lower Miocene, Planulina Zone, Southern Louisiana: ABSTRACT

The Planulina zone is a wedge of clastic sediment positioned between the Anahuac shale below and the Oakville sandstone interval above. Planulna sediments were deposited on an erosional surface, during a general rise in the sea level, and formed a retrogradational wedge. Within the study area, the Planulina zone consists of two large depositional complexes: the Mud Lake complex in west Cameron Parish, Louisiana, and the East Cameron complex in east Cameron Parish. The lowermost depositional sequence in the East Cameron complex is preserved in a network of submarine canyons that were eroded into the upper slope. Framework sands were deposited in channel systems confined to the axis of the canyons, and the sands are encased in marine shale containing benthonic foraminifera indicative of an upper to middle slope paleoenvironment. Two younger depositional sequences overlie the submarine canyon facies and were deposited by deltaic systems that prograded basinward. A zone of expansion extends east to west through the Planulina interval and is named the ''Planulina flexure.'' The flexure is a large fault located at the relict shelf edge and soles out downdip inn the Anahuac shale. Several thousand feet of sediment downthrown on the flexure is equivalent to several hundredmore » feet upthrown, and the flexure represented the boundary dividing updip deltaic processes from downdip slope processes during the beginning of Planulina deposition. The Planulina depositional history and stratigraphic architecture are directly related to the displacement along the flexure and the structural deformation of the underlying Anahuac shale.« less

Ore petrography of a sedimentary uranium deposit, Live Oak County, Texas

Samples from the McLean 5 open-pit uranium mine, a small high-grade deposit located along a normal fault in the Miocene Oakville sandstone of Live Oak County, Texas, have been studied for uranium abundance, distribution, and nature of occurrence on the microscopic level. The host sandstone is composed of quartz, feldspars, and volcanic rock fragments, cemented by sparry calcite. Authigenic minerals include iron disulfide minerals (dominantly pyrite and some marcasite) and small amounts of clays, Ti oxides, and opal. High-grade ore (to 3% U) occurs along the fault, decreasing to less than 1,000 ppm within 10 m from the fault. The ore mineral is amorphous pitchblende and exhibits botryoidal morphology.The microscopic occurrence of uranium, documented by fission-track mapping of petrographic thin sections, is presented in detail. Uranium occurs abundantly as grain coatings and fillings in intergranular spaces in samples with high uranium content, where calcite cement has been partially or totally leached as mineralization proceeded. Lesser amounts are adsorbed onto leucoxene (microcrystalline anatase), mud clasts, and altered igneous rock fragments. Adsorbed uranium is the major mode of occurrence in samples, with lower uranium contents farther from the orebody.Textural relations indicate that iron sulfides formed both before and after mineralization. Initial mineralization was by adsorption onto aggregates of fine particles of Ti oxide and clay minerals of various origins. With dissolution of cement and continued uranium influx, uranium precipitated as grain coatings and pore fillings.

Role of fluid mixing and fault-related sulfide in the origin of the Ray Point uranium district, South Texas

The Lamprecht and Felder deposits are two of many roll-type uranium deposits hosted by the Miocene Oakville Sandstone in the Ray Point (south Texas) uranium district. The deposits in this district are aligned parallel to or are intersected by the Oakville fault which suggests control by the faults on their origin and/or preservation. The Lamprecht and Felder deposits show fundamentally similar patterns of geochemical zonation and of distribution of authigenic iron disulfide (FeS/sub 2/) minerals. Distribution of U, Mo, and Se are typical of roll-type deposits that result from invasion of geochemically reduced rock by oxygenated uranium-bearing solutions. Sulfur content of these deposits is high (as much as 9%), with almost all sulfur occurring as FeS/sub 2/ minerals. Organic carbon is virtually absent. Four distinct stages of FeS/sub 2/ mineral formation are recognized: (1) a generation of isotopically light (delta/sup 34/S 0%o), and (4) a yet later generation of marcasite with isotopically light sulfur close to the values of stages 1 and 2. The alteredmore » tongue in these deposits is anomalous in that it contains FeS/sub 2/ minerals in contrast to other Texas and Wyoming roll-type deposits which typically have an oxidized (ferric iron-bearing) altered tongue. The dominant FeS/sub 2/ mineral in the altered tongue is isotopically heavy pyrite (stage 3) with subordinate amounts of late marcasite (stage 4).« less

Remnant Grasslands of the Fayette Prairie, Texas

Twenty-five remnant grasslands from across the Fayette Prairie of SE Texas were sampled for species frequency and basal cover as well as selected soil and topographic properties. Polar ordination was used to elucidate stand and species patterns and plant-environmental interrelationships. Three major topo-edapho-vegetation complexes were defined. Upland clay soils (Vertisols and Mollisols) were characterized by Andropogon gerardii var. gerardil, Bouteloua curtipendula var. curtipendula and Carex microdonta. Upland sandy clay loam and clay loam soils (Alfisols) had Paspalum plicatulum, Coelorachis cylindrica and Fimbristylis puberula var. puberula as characteristic species. Schizachyrium scoparium var. frequens and Sorghastrum nutans were ubiquitous dominants or codominants in all upland communities. Panicum virgatum and Tripsacum dactyloides dominated lowland clay soils (Vertisols). The Fayette Prairie should be classified as a southern extension of the True Prairie Grassland Association. INTRODUCTION The Fayette Prairie is located in SE Texas (Fig. 1). It is isolated from the Blackland Prairie to the N and the Coastal Prairie to the S by narrow strips of Post Oak Savanna. To the E it borders on the southeastern Evergreen Forest (Braun, 1950) and to the W it grades into the South Texas Plains (Godfrey et al., 1970). It once contained approximately 1.5 million ha of native grassland (Godfrey et al., 1970), but little undisturbed vegetation remains (Johnson, 1931; Launchbaugh, 1955). No quantitative analysis of the vegetation exists for the area and, as a result, available data are insufficient to adequately describe or classify the prairie. The purpose of this study is to: (1) provide a quantitative ecological analysis of remnant vegetation and soil; (2) relate differences in vegetational composition to edaphic and topographic factors, and (3) evaluate ecological affinities and determine the appropriate classification of the prairie. STUDY AREA The Fayette Prairie is characterized by a flat to gently rolling topography. Two rivers, the Brazos and the Colorado, cross the area. Uplands were historically prairie although Quercus stellata and Q. virginiana occurred occasionally as scattered individuals or in small clumps. Lowlands were dominated by stands of hardwood forest including Q. stellata, Ulmus crassifolia, Fraxinus spp. and Carya illinoiensis. Current land use is primarily for native and tame pasture with limited cropland. Geologically, the Fayette Prairie consists of material deposited in the middle to upper Miocene (Geol. Atlas Tex., 1974). Three major formations occur: the Fleming, Oakville Sandstone and Cook Mountain (Fig. 1). The Fleming formation underlies most of the area except the western margin. Laid down in the upper Miocene, it consists of a 400-m-thick layer of calcareous silty clay sediment with some medium to coarse grained sandstone. The Oakville Sandstone is slightly older. It is found as a narrow strip on the NW side and in the S-central portion of the prairie, and consists of a

Groundwater prospecting for sandstone-type uranium deposits: a preliminary comparison of the merits of mineral-solution equilibria, and single-element tracer methods

Groundwater quality data was collected from published sources and estimated when necessary for three sandstone-type uranium deposits in Texas and Wyoming. The purpose of the study was to compare the merits of using the computed saturation state of the groundwater with respect to uranium minerals, to that of single-element tracers in groundwater for geochemical prospecting. The uranium minerals considered were carnotite and tyuyamunite within oxidized deposits in the Catahoula Tuff in southern Texas, and uraninite and coffinite in reduced deposits within the Oakville Sandstone in southern Texas, and Wasatch Formation in northeast Wyoming. Groundwater chemical maps and profiles were constructed for the three sites, showing locations of known and probable uranium mineralization. The single tracer elements and parameters considered in the comparison were pH, Fe, SO 4, V, U, Ra, As, Mo and Se. Mineral-saturation results were the most dependable evidence for uranium mineralization, and showed systematic trends towards saturation at distances as great as 300 m from the ore. In general, the next best indicators of ore were uranium concentrations, and vanadium concentrations in the oxidized deposit. Single tracer species As, Mo, Se and V were at or below detection in groundwaters near the reduced deposits, and except for V, provided ambiguous information in the oxidized deposit. Because of its high mobility, radium was displaced from the mineralization in the direction of groundwater flow at the Oakville Site, although its success as an ore pathfinder was equal to that of dissolved uranium at the Wasatch Site.

History of Sulfidization of South Texas Roll-Type Uranium Deposit: ABSTRACT

Studies of the mineralogy, sulfur isotope geochemistry, and uranium-lead isotope geochronology of a roll-type orebody in the Felder deposit, south Texas, have indicated important constraints on the genesis of this deposit. Post-mineralization sulfidization of the host Oakville Sandstone (Miocene) resulted in precipitation of pyrite and marcasite in the altered tongue that differ in relative abundance and in isotopic composition from pyrite and marcasite elsewhere in the host rock. The altered tongue is characterized by a predominance of pyrite over marcasite and by heavy ^dgr34S values (-5.2 to +20.6 per mil), whereas reduced-barren and mineralized rock is characterized by abundant ore-stage marcasite and by light ^dgr34S values (-29.9 to -47.7 per m l). In reduced-barren and mineralized rock, two generations of pyrite are present: (1) pre-ore pyrite grains that are commonly enclosed by ore-stage marcasite; and (2) post-ore pyrite that is genetically equivalent to pyrite in the altered tongue. Resulfidization of the deposit by hydrogen sulfide-bearing solutions introduced along one or more nearby faults is indicated by the similarity in isotopic compositions of pyrite in the altered tongue to that of sour gas in the underlying Edwards Limestone (Cretaceous). The time of this resulfidization is probably indicated by the unusually precise 207Pb/204Pb-235U/204Pb isochron age of 5.09 ± 0.11 m.y. The lack of significant scatter of the points on the isochron diagram must reflect the immobili y of uranium and lead over the last 5 m.y. due to the continued presence of hydrogen sulfide. The 5-m.y. isochron age indicates that no significant roll-forming processes have occurred in the Felder deposit since this time. End_of_Article - Last_Page 772------------

Oxidation-Reduction in Oakville Sandstone of South Texas--Implications for Uranium Mineralization: ABSTRACT

Three distinct oxidation-reduction zones have been identified within the uranium-bearing Oakville aquifer. An oxidizing zone with Eh values greater than 300 mv and with measurable dissolved oxygen occurs in areas of recharge and extends to depths as great as 800 ft (244 m). An intermediate zone with Eh values between 110 and 10 mv occurs downdip from the oxidizing zone. Eh in these waters may be controlled by ferrous-ferric mineral reactions. About half of the intermediate Eh waters contain low but detectable concentrations of hydrogen sulfide. In east Texas the deepest wells sampled (1,600 ft; 488 m) penetrate this intermediate zone. A reducing zone with Eh less than -40 mv and dissolved H2S occurs in deepest parts of the Oakville in south Texas and also at sh llow depths (300 ft; 91 m) associated with faults, which apparently provided conduits for the discharge of reducing, sulfide-rich waters from deeper formations. Present-day Eh is controlled by either the continued discharge of reducing water or the presence of pyrite formed by previous reduction. Thermodynamic calculations show that uranium and selenium phases may precipitate within the intermediate zone, but that molybdenum and arsenic require more reducing conditions for precipitation. All four elements should occur together only where the oxidizing and reducing zones are adjacent without an intervening intermediate zone. Such areas can occur (1) where fault discharge has superimposed reducing, sulfidic conditions on an otherwise normal Eh gradient or (2) where a sharp Eh gradient separates highly permeable oxidized sediment from less permeable reduced sediment. Where oxidizing and reducing zones are not adjacent, uranium and selenium only should accumulate within the intermediate zone, and mineralization may be diffuse. End_of_Article - Last_Page 722------------

Hydrostratigraphic Framework and Flow Dynamics of Uraniferous Aquifer-Oakville Sandstone of South Texas Coastal Plain: ABSTRACT

Synthesis of geologic, hydrochemical, and hydrologic data for the Oakville Sandstone provides a framework for effective hydrochemical exploration, leach mine planning, and evaluation of mining impact. Quantitative lithofacies maps were combined with structural and well-pump test data to produce a regional Oakville transmissivity map. Interpreted groundwater flux patterns within the resultant three-dimensional transmissivity framework were mapped, and quantitatively illustrate several hydrodynamic principles. (1) The complete groundwater system includes meteoric, elisian (compactional), and thermobaric connate zones. Boundaries separating zones are dynamic and evolve through time. (2) Recharge of meteoric systems occurs directly at outcrop by seepage through overlying confining units, and by seepage from underlying aquifers. (3) Flow occurs within a hierarchy of cells, ranging from unconfined local (n × 10 sq mi) to intermediate confined (n × 103 sq mi) to regional confined (n × 104 sq mi) flow cells. Shallow groundwater may move in any direction with respect to dip. (4) Discharge occurs by direct groundwater flow upward to the water table and by vertical seepage, commonly localized by fault zones, into adjacent aquifers. (5) Topography and the three-dimensional permeability framework localize recharge and discharge zones and control flow direction. Recharge occurs in topographically high areas; discharge in lowest areas. Groundwater flux in the Oakville is highly complex. Major uranium deposits occur within the realm of local (Ray Point district), intermediate (George West district), and regional (Duval County) flow cells. Extant flow direction commonly does not agree with geochemically-inferred mineralization-front polarity. End_of_Article - Last_Page 711------------

Field Relations and Petrology of Catahoula Formation in Parts of Lavaca, Gonzales, and Fayette Counties, Texas: ABSTRACT

The Catahoula Formation is unique in that it records the last significant influx of volcanic detritus supplied to Gulf Coast sediments. The study area is situated on the northeast flank of the San Marcos arch in Lavaca, Gonzales, and Fayette Counties, Texas. The Catahoula Formation was mapped and subdivided into a basal Chita Sandstone Member (fluvial channel facies) and an overlying and/or laterally contiguous Onalaska Clay Member (floodplain and levee facies). The basal unit of the Chita sandstone is typically a channel deposit of light-gray, conglomeratic sandstone lying unconformably on limonitic claystones and very fine-grained sandstones of the upper Eocene Whitsett Formation. The basal Chita sandstone unit consists of graded to poorly laminated beds containing lag eposits of silicified wood and/or mudstone clasts. Chita sandstone units grade laterally and vertically into tuffaceous, very fine-grained sandstone, siltstone, and claystone units of the Onalaska Clay Member which is conformably overlain by channel deposits of upper Miocene Oakville Sandstone. The Oakville Sandstone is comprised of lenses of coarse-grained calclithite beds (sandstone containing an abundance of carbonate rock fragments). The Oakville calclithite beds record an episode of early Miocene uplift of the Edwards plateau along the ancestral Balcones fault zone. Chita units consist of well-sorted to poorly sorted, silty fine-grained to pebbly coarse-grained, lenticular sandstone exhibiting fining-upward cycles of festoon cross-beds, plane beds, and ripples. A volcanic provenance contribution is suggested by (1) abundant volcanic quartz (22% of total quartz); (2) lithic fragments consisting mostly of silicic shards, felsite clasts, and tuffaceous clay clasts; (3) fresh sanidine (sanidine/orthoclase ratio = 1.2); and (4) a heavy-mineral suite dominated by euhedral, elongated zircons. Onalaska clay units consist of tuffaceous mudstone and clay-ball litharenite beds. Differing heavy-mineral suites and quartz-feldspar-lithic modes in the Catahoula Formation and coeval Gueydan Formation support the hypothesis that the San Marcos arch was a drainage divide in middle Tertiary time. In the study area north of the San Marcos arch Catahoula sandstones contain a mean Q:F:L ratio of 80Q:5F:15L and a zircon-tourmaline-rutile index of 90%. South of the San Marcos arch (data from Lindemann and McBride) Gueydan sandstones contain a mean Q:F:L ratio of 31Q:28F:41L and a zircon-tourmaline-rutile index of 33%. Abundant Ca-montmorillonite, reworked biomicrite clasts, montmorillonite rim cement, caliche beds, and wood replaced by length-slow chalcedony in the Catahoula Formation all support an alkaline diagenetic environment. Pervasive opal and chalcedony pore-filling cements are restricted to surficial outcrops and reflect Pleistocene and/or Holocene leaching of volcanic ash under alkaline conditions. It is likely that leaching of volcanic ash in the Catahoula Formation could result in uranium mineralization in Catahoula channel and overbank facies. End_of_Article - Last_Page 1607------------

Microscopic Distribution of Uranium in Oakville Sandstone, South Texas: ABSTRACT

End_Page 475------------------------------When uranium ore is mined and processed in the conventional crushing plant there is little urgency to know what mineral contains the uranium and how that mineral is distributed within the ore. However, solution mining techniques depend for their success on bringing the dissolving solutions into contact with the uranium-bearing mineral and dissolving it. With that requirement in mind, a study was undertaken to help understand the character and location of the uranium-bearing mineral in the Oakville Sandstone of south Texas where solution mining is being carried out. Thin-section and electron-microprobe analyses were conducted on a sample of high concentration ore to confirm that uranium was located in the space between framework sand grains. Moreover, uranium was not uniformly distributed throughout the silt and clay intergranular matrix material. The disaggregated and fractionated sandstone showed the highest concentration of uranium to be in the silt-size fraction. Further separation of the ore was carried out by heavy liquids and magnetic fractionations. The uranium-bearing mineral was concentrated along with dense and magnetic minerals. Openwork intergrowths of pyrite crystals made up most of this fraction. In spite of having concentrated uranium in excess of 43,000 ppm U3O8, it was still not possible to identify any ura ium-bearing mineral by X-ray diffraction. This suggests that uranium may be held in the sandstone as an amorphous oxide. End_of_Article - Last_Page 476------------

South Texas Uranium Deposits

The demand for uranium to fuel the nation's nuclear generators will reach a very high level in the early 1990s. The South Texas coastal plain will furnish a significant part of the needed uranium. The uranium deposits of South Texas are in tuffaceous, zeolitic sandstone and mudstone beds that strike northeastward and dip gently southeastward. These host rocks are included in the Whitsett Formation of late Eocene age, Frio Clay of Oligocene(?) age, Catahoula Tuff and Oakville Sandstone of Miocene age, and Goliad Sand of Pliocene age. Uranium is produced from three uranium-mining areas--Karnes, Live Oak, and Duval--named for the counties in which they principally lie. In each area the host rock is different. Marine-beach sandstone of the Whitsett Formation is the primary host rock in the Karnes area, but some ore has been taken from crosscutting fluvial channels also in the Whitsett. This ore is in a down-dropped block between the Falls City fault on the northwest and the Fashing and Hobson faults on the southeast. The ore in this area is divided between a belt of updip oxidized deposits within a few feet of the surface and a belt of downdip unoxidized deposits, for the most part at a depth of 80 to 100 ft (24 to 30 m). The unoxidized deposits are mainly in ore rolls. Most of the ore in the Live Oak mining area is in unoxidized ore rolls in the Oakville Sandstone. One oxidized deposit in this area was found in the Frio Clay (Oligocene?). The ore in the Duval area is found principally in unoxidized ore rolls in sandstone parts of the Catahoula Tuff. One exceptional deposit is in the Goliad Sand that lies above Palangana salt dome. The Catahoula Tuff is believed by many authors to be the principal source rock for uranium and other elements in the deposits. The uranium apparently was leached from this rock during periods of dry-climate weathering, transported through permeable rocks in aqueous solution, and deposited in a chemically reducing environment. The reducing agents were probably hydrogen sulfide or methane gas that seeped from accumulations of petroleum in the subsurface, and carbonaceous material that is found in some of the rocks.

Miocene Formations and Vertebrate Biostratigraphic Units, Texas Coastal Plain

There is reasonable doubt that a collection of vertebrate fossils listed by Dumble and quoted by later authors came from the Oakville formation in southwest Texas. Vertebrate fossils low in the Fleming formation have been collected between Burkeville and George West, Texas, extending the Fleming formation vertebrate faunas into the upper Oakville of Renick and the emended Lagarto of Plummer. It is recommended that both be included in the Fleming formation, and the Oakville sandstone be restricted to beds from the top of the Catahoula to the top of the Moulton sandstone member, Oakville formation of Renick. The vertebrate fauna found at Cold Spring is appreciably younger than that found at Navasota. The former is in the Fleming formation and the latter in the Oakville formation. Vertebrate remains of the same age as those found at Cold Spring within the Fleming formation are also found at the type section of the emended Lagarto formation (Plummer, 1933). Traceable biostratigraphic units herein called faunas, are used to correlate and identify Miocene formations along the Texas Coastal Plain. Arikareean, Hemingfordian, Barstovian, and Pliocene biostratigraphic units are recognized.