Browsing by Subject "Facies (Geology)--Texas"
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Item Deposition of prograding carbonate sand shoals and their subsequent diagenesis, lower Glen Rose (Cretaceous), South Texas(1980) Bay, Annell Russell; Debout, D. G.; Folk, Robert L.The Glen Rose Formation is a thick (300 to 900 m), carbonate unit that was deposited on a broad, shallow-marine shelf during the early Cretaceous. Three cyclic, shoal-water complexes of the lower Glen Rose Formation developed over the Pearsall Arch in Frio and Medina Counties of South Texas. These complexes, consisting of high-energy grainstone and coral-stromatoporoid-caprinid boundstone and packstone, trend east-west for at least 125 km and are located approximately 80 km inland of the Cretaceous shelf edge and 70 km seaward of the Cretaceous shoreline. Three major, depositional environments have been recognized within the lower Glen Rose of South Texas: open shelf, shoal-water complex, and protected lagoon. The facies and their respective depositional environments, from the base to the top of the upward-coarsening sequences are (1) sandy mudstone/wackestone, fossiliferous quartzarenite, mollusc-miliolid wackestone, and echinoid-mollusc wackestone deposited in an open-shelf environment; (2) echinoid-mollusc and oncolite-caprinid packstone deposited in intertidal shoals and subtidal grainflats; (3) coated-grain and echinoid-mollusc grainstone deposited in sandflats, tidal channels, spits, and bars; (4) coral-stromatoporoid-caprinid boundstone and packstone deposited as patch reefs and associated flanking debris. Toucasiid-oyster-miliolid wackestone, toucasiid boundstone, and burrowed and laminated mudstone deposited in shallow-water, protected lagoons and tidal mudflats interfinger with upward-coarsening sequences on the landward side. The lagoonal deposits overlying the shoal-water sequence indicate the seaward progradation of the complex. Eventually each complex was transgressed by open-shelf facies and the cycle began again. The patch reefs and associated biostromes may have prograded out across the shelf and formed the initial build-up of the Stuart City shelf margin. A petrographic study of grainstone diagenesis indicates there are four gradational phases of diagenesis: (1) early submarine, (2) early mixing-zone and meteoric, (3) late meteoric-to-early subsurface, and (4) late subsurface. Early cementation in the marine environment is evidenced by micrite envelopes and isopachous crusts around some allochems. Subaerial exposure of bars and spits allowed early invasion of meteoric and mixing-zone water as indicated by aragonite dissolution or neomorphism to calcite; precipitation of finely crystalline, equant, isopachous cement; syntaxial cement; and medium crystalline, nonferroan, equant, calcite cement. During early burial of the rocks coarser crystals of nonferroan, equant calcite precipitated, indicating continual flushing with meteoric water. Later burial of rocks to the subsurface lead to the growth of zoned ferroan and nonferroan calcite, replacement of mollusc shells by lutecite and megaquartz, precipitation of euhedral quartz overgrowths, anhydrite precipitation and replacement, precipitation of baroque dolomite, and stylolitization. Petrography of the mud-supported facies indicates there is replacement of micrite by both limpid and inclusion-rich dolomite. The limpid dolomite is interpreted to form in a schizohaline environment whereas the inclusion-rich dolomite formed in both schizohaline and hypersaline environments.Item Depositional systems and natural resources of the middle Eocene Yegua Formation, south and central Texas coastal plain(1981) Van Dalen, Stephen Craig; Not availableA regional investigation of the Yegua Formation, using both surface and subsurface data, permits delineation of two genetic units beneath the south and central Texas coastal plain. The lower pro-gradational Yegua unit is composed of a series of wave-dominated delta systems. The principal deltaic complex, the Falcon delta, is located in Webb County and is believed related to the deposition of an ancestral Rio Grande. Facies within the delta include: channel-fill/channel mouth bar; coastal barrier; lagoonal/marsh/floodbasin; prodelta; and transgressive/destructional. The upper Yegua unit consists of stacked barrier bar and lagoonal systems in south Texas. This unit was deposited following abandonment of the Falcon delta, upon avulsion of the Rio Grande and its shift into northeastern Mexico. As the delta foundered, it was replaced by a barrier system supplied with strike-fed sediments from the Mexican delta located to the south. In central coastal Texas, both the upper and lower Yegua consist of a series of small wave-dominated to lobate deltas. The Yegua Formation contains important oil and gas reservoirs in this area. Most production is from the upper genetic unit. Hydrocarbons are accumulated along a trend between the barrier bar and lagoonal systems, where minor structural features combine with pinchouts of barrier sands to provide stratigraphic traps. Another important area of production is along the Mirando-Provident City fault system, where faulted coastal barrier and deltaic sands serve as reservoirs. Because of highly mineralized ground water, the Yegua Formation is not an important aquifer. Commercial deposits of lignite or sedimentary uranium have not been recognized within the study area and sedimentological analysis indicates that discovery of these deposits is very unlikelyItem Depositional systems in the Sparta Formation (Eocene), Gulf Coast basin of Texas(1976) Ricoy, José Ulises, 1948-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.