East Texas Embayment Research Articles

A new pachyrhizodontid fish (Actinopterygii: Teleostei) from the Tarrant Formation (Cenomanian) of the Upper Cretaceous Eagle Ford Group in Texas, USA

SMU 76938 is a nearly complete skeleton of a fossil bony fish, about 1.2 m in total length, housed in Southern Methodist University in Dallas, Texas, USA. It was collected from the Tarrant Formation (middle Cenomanian) of the Upper Cretaceous Eagle Ford Group in Tarrant County, Texas, an area where it was near the East Texas Embayment of the Western Interior Seaway during the Late Cretaceous. Our phylogenetic analysis indicates that it is a pachyrhizodontid crossognathiform fish, and comparisons with previously reported pachyrhizodontids suggest that the fossil fish belongs to a new genus and species within Pachyrhizodontidae, Polcynichthys lloydhilli gen. et sp. nov.. With a fusiform body, a large symmetrical caudal fin, and a mouth with numerous small conical teeth suited for grasping, the new taxon is interpreted to be a fast swimming, open-ocean predator that likely pursued smaller squid, crustaceans, and other fishes. Vertebral growth rings suggest that the individual was possibly about 14 years old at the time of its death, and our vertebra-based theoretical growth model indicates that the species could have reached up to about 1.8 m TL and lived up to 37 years old in age.

A tidal origin for coarsening-upward sequences above two Wilcox lignites in East Texas

Conventional palaeogeographic reconstructions show a large river system occupying the East Texas Embayment during the deposition of the Wilcox Group. Coarsening-upward sequences above Wilcox lignites in East Texas have been interpreted as floodplain splays. However, the bedding types, sedimentary structures and shallow scour surfaces in a coarsening-upward sequence above the main seam at the Martin Lake Mine in Panola County indicate deposition in water stirred by tidal and wave activity. The bedding types include sand streaks in mud and lenticular, wavy and flaser bedding. The sedimentary structures include abundant wave-ripple lamination and large-scale crossbeds with thin, closely-spaced mud drapes. These crossbeds suggest traction currents of short duration alternating with periods of slack water. Pollen from broadleaf hardwood trees is the most common element of the palynoflora from the coarsening-upward sequence at the mine. The upper reaches of riverine estuaries along the SE coast of the United States provide a modern analogue for the environment of deposition of the Wilcox sediments at the Martin Lake Mine. Here tidal currents extend inland to places where freshwater aquatic plants and forests border the estuaries. The same bedding types and sedimentary structures that occur in the sediments at the Martin Lake Mine occur in a coarsening-upward sequence above a lignite at the Big Brown Mine in Freestone County. Recognition of the tidal origin of the coarsening-upward sequences suggests an embayed coast or a shoreline within the East Texas Embayment during the deposition of the strata above the lignites.

Geology of Dallas, Texas, United States of America

Dallas, the seventh largest city in the United States and the second largest city in Texas, lies within the Blackland Prairie physiographic province. The modern city, born on a “hardrock” crossing in the Trinity River in 1845, was also the site of many earlier Indian settlements dating to 11,000 B.C. The city is located on the updip edge of the Gulf Coastal Plain at the northwestern limit of the East Texas Embayment. A wedge of 610–1,372 m of Cretaceous age sedimentary rocks underlies the city. Paleozoic rocks of undetermined thickness are encountered below these units. Surficial deposits include, in ascending order, the Eagle Ford Shale, the Austin Chalk, the Ozan Formation (Taylor Marl) of Cretaceous age, and terraced alluvial deposits of Quaternary age. Soils consist of residual clays and silty clays (CH-CL) over bedrock and transported silty and sandy clays and gravels in terraced alluvial deposits and recent alluvium. Only three major constraints were identified in Dallas: expansive soils and bedrock, slope instability, and flooding. Most damage due to expansive soils is concentrated in areas of lightly loaded structures. Here techniques such as “pre-wetting,” lime stabilization and engineered slabs or pier and beam foundations systems are being utilized. Heavily loaded structures are usually tied into bedrock below the zone of seasonal moisture variation through means of drilled-shaft foundations. Most slope instability and flooding problems are administered through avant-garde hillslope and flood-plain ordinances. Dallas9s water supply is projected to be adequate through the year 2050. While surface water reservoirs are the major source of water, ground water, considered an emergency water source by the city, is being mined by private industry and surrounding municipalities at rates faster than apparent recharge. Solid waste is managed through a 4 km 2 landfill operation and is projected to be adequate for the next 50–75 years. Hazardous waste is transported to the Texas Gulf Coastal depositories.

Prolific Overton Field Gas Reservoirs Within Large Transverse Oolite Shoals, Upper Jurassic Haynesville, Eastern Margin East Texas Basin: ABSTRACT

Late Triassic rifting along a northeast-southwest spreading center in east Texas resulted in basement highs along the eastern margin of the East Texas basin that became sites of extensive ooid shoal deposition during Late Jurassic time. Reservoirs within oolite facies at Overton field contain over 1 tcf of natural gas. These large shoals, each approximately 15 mi (24 km) long and 3 mi (4.8 km) wide, trend north-south as a group and northeast-southwest individually. They are oblique to the basin margin but parallel with Jurassic diffracted tidal currents within the East Texas embayment. Modern Bahamian ooid shoals of similar size, trend, and depositional setting occur at the terminus of the deep Tongue-Of-The-Ocean platform reentrant. Overton field reservoirs are in ooid g ainstone shoal facies and in transitional shoal margins of skeletal-oolitic-peloidal grainstones and packstones. Adjacent nonreservoir facies are peloidal-skeletal-siliciclastic wackestones and mudstones. Early diagenesis of grainstone reservoir facies included meteoric dissolution and grain stabilization, resulting in abundant chalky intraparticle porosity and equant and bladed calcite cements filling interparticle porosity. Subsequent burial diagenesis resulted in intense solution compaction and coarse equant calcite and saddle crystal dolomite that occluded remaining interparticle porosity. Whole-rock trace element analysis indicates greatest diagenetic flushing (less magnesium, strontium) in porous zones. Stable isotopes for grains and cements show strong overprint of later burial diagenesis, with greater depletion of ^dgr18O in reservoir facies. However, hydrocarbons were emplaced prior to late cementation, and unlike other Jurassic Gulf Coast reservoirs, deep burial iagenesis provided no late-stage formation of porosity. End_of_Article - Last_Page 257------------

Coarsening-Upward Tidal Sequences in Wilcox Group in East Texas: ABSTRACT

Most exploration concepts for the Wilcox Group are based on paleogeographic reconstructions derived from maps of net sand or sand percent. Coarsening-upward tidal sequences exposed in the highwalls of two lignite mines in east Texas show the shortcomings of these reconstructions. In the past, the coarsening-upward sequences have been interpreted as prograding floodplain splays because they occur in an area of supposed fluvial sedimentation (conventional paleogeographic reconstructions show a large river system occupying the East Texas embayment during the deposition of the Wilcox Group). Recognition of the tidal origin of the coarsening-upward sequences suggests an embayed coast or a shoreline within the East Texas embayment at the time the coarsening-upward sequences wer deposited--information which has exploration implications. Paleogeographic reconstructions based on maps of net sand or sand percent show time-averaged conditions. The search for the subtle trap requires paleogeographic maps based on smaller stratigraphic intervals than present reconstructions provide. These intervals can be defined by using the principles of sequence stratigraphy and tracing unconformities in the subsurface. End_of_Article - Last_Page 142------------

Geology of North Part of Corsicana Shallow Oil Field, Ellis and Navarro Counties, Texas: ABSTRACT

Oil was discovered at Corsicana, Texas, in 1894 during the drilling of a city water well. The boom which followed led to the development of the first commercial rotary method of drilling, the use of gas engines to pump wells, and the first regulatory efforts of oil and gas by the state of Texas. Two other booms occurred in the early 1950s and late 1970s because of waterflooding and an increase in the price of oil. Corsicana Shallow field consists of four producing horizons: Durango Sand, Wolfe City Sand, Pecan Gap Chalk, and Nacatoch Sand. The northern part of the field produces from the Wolfe City Sand of Campanian age within the Taylor Group. The sand can be divided into separate sand zones with independent oil-water contracts. As the sand zones are traced north and west, each thins and grades into shale. Corsicana field is located on the western edge of the East Texas embayment between the Balcones and Mexia-Talco fault zones. In the north part of the field, two fault trends are present, a N5°W up-to-the-coast fault zone and a N55°E trend of both up-to-the-coast and down-to-the-coast faults. Displacement along major faults ranges from 50 to 140 ft at the Wolfe City horizon. Product on techniques varied in Corsicana field with most wells being completed open hole with 2-in. tubing used for casing during the early 1950s. After 1959, most wells were completed by perforating through casing and mechanically fracturing the pay sand. New production techniques employed in the early 1980s involved the use of salt-water mud systems, selective perforating and treating of individual sand zones, and cement bond logs and radioactive tracer surveys. A polymer injection project in progress southeast of the city of Corsicana may provide additional means of oil recovery if the pilot project proves successful. End_of_Article - Last_Page 145------------

Deltaic Sedimentation in Nacatoch Formation (Late Cretaceous), Northeast Texas: ABSTRACT

The terrigenous clastics of the Nacatoch Formation are a record of short-lived progradational phases within the major Late Cretaceous transgression in the East Texas embayment. Progradation was achieved by deltaic out-building from three fluvial feeder systems along the north and northwest margins of the basin. It is probable that additional was derived from a major sediment dispersal system east of the Nacatoch deltas. The deltaic package of the Nacatoch (131 m, 430 ft) is composed of roughly equal proportions of sandstones and mudstones, with the sandstones ranging from very fine-grained, poorly sorted, and mud-rich, to fine-grained and well-sorted. The sandstones have a feldspathic litharenite and subfeldspathic litharenite composition with increasing compositional maturity in the well-sorted examples. Some of the muddy sandstones are highly bioturbated and carbonaceous. Vertical and lateral lithofacies changes in the Nacatoch deltas were determined by means of electric-log (resistivity) interpretation and well core data, with support from limited outcrop studies. Dip- and strike-oriented cross sections delineated three major coarsening-upward sandstone units which could be correlated in a shore-parallel direction for 42 km (25 mi). Each sandstone shows evidence of reworking by wave-induced processes and redistribution by longshore currents. The lower two sandstones are separated by a thick mudstone interval interpreted as a minor transgressive event. The highly bioturbated, carbonaceous, mud-rich intervals between the other sandstone units are interdistributary bay fills. The Nacatoch deltas are lobate and developed in response to moderate input, moderate to low wave-energy flux, and significant longshore current action. Southwest longshore transport from the Nacatoch deltas gave rise to extensive shelf sands in the western margin of the East Texas basin. These well-sorted sandstones are petroleum reservoirs at shallow depths. The similar well-sorted sandstones of the Nacatoch deltas have the same potential as petroleum reservoirs, given the same structural influence. End_of_Article - Last_Page 496------------

Subsurface Glen Rose Reef Trend in East Texas and West-Central Louisiana: ABSTRACT

The subsurface Glen Rose trend in east Texas and west central Louisiana (Lower Cretaceous Comanchean) is a regressive carbonate complex deposited on a broad shallow water shelf. The major structural influences on deposition were the East Texas basin and the northwest Louisiana basin, separated by the Sabine uplift. The Glen Rose trend can be differentiated into two separate reef tracts that prograded seaward over a slowly subsiding shelf. The Upper and Middle tracts overlap within the East Texas embayment and diverge over the southern flank of the Sabine uplift eastward into Louisiana. The trend appears to be located midway between the shoreline and shelf edge. It remains to be seen whether the Glen Rose are actual framework reefs or mounds of transported material. Cores through the massive limestones reveal porous buildups of varying compositions. Reef facies include poorly sorted caprinid-coral grainstones, moderately sorted peloid and oncolite packstones and grainstones, and well-sorted, very fine grained skeletal grainstones. Coated grains, abraded skeletal fragments, scoured bedding surfaces, and minor cross-beds are evidence for deposition of the facies in a high-energy shoal setting. The reefal buildups grade laterally into low-energy shallow water wackestones and mudstones containing toucasids, orbitolinids, and serpulid burrows. Porosities associated with the reefal buildups appear facies controlled. Caprinid-coral packstones and grainstones exhibit intraparticle, moldic, and vuggy porosities of 10 to 15%. Pinpoint End_Page 410------------------------------ microporosity of 5 to 10% are found within the finegrained skeletal grainstones. Fracture porosity enhances permeability in several facies. Moldic and vuggy porosity types are generally secondary whereas intraparticle porosity may be preserved primary. Pinpoint microporosity is probably matrix related secondary porosity. Coarse equant calcite commonly occludes intraparticle, moldic, vuggy, and fracture porosities. Dolomitization within the reef limestones may have acted to create or preserve porosities. Poor production from the Glen Rose trend has been attributed to the lack of structural closure. Use of all available electric logs and sample logs in conjunction with extensive core and thin section analysis should provide new insight on carbonate diagenesis and the relationship to porosity-permeability trends within the Glen Rose trend. End_of_Article - Last_Page 411------------

The practicality of vertical cephalopod shells as paleobathymetric markers

The depth to which an intact coiled cephalopod shell will sink with its plane of symmetry vertical is related to shell geometry. Equations that relate shell geometry to physical constants of pressure, sea-water density, and gravity yield the maximum depth of stable verticality of a shell. Water depths calculated from the geometries of vertical shells of Cymatoceras hilli (Shattuck), Drakeoceras drakei Young, and Mortoniceras wintoni (Adkins) from the Fort Worth Formation (Upper Cretaceous, Albian) of north-central Texas are used to reconstruct a portion of the paleobathymetry of the East Texas Embayment during late Fort Worth time. The maximum water depth to which shells with these geometries would have sunk with the plane of symmetry vertical range from 1.6 m for the least stable shell geometry ( D. drakei ) to 2.6 m for the most stable shell geometry ( C. hilli ). Water depths were deeper than 2.6 m at localities where no vertical shells were observed and shells with the plane of symmetry horizontal showed no evidence of being reworked from the vertical orientation.

Depositional Systems in Nacatoch Sand (Upper Cretaceous), East Texas Basin and Southwest Arkansas: ABSTRACT

End_Page 1563------------------------------The Nacatoch Sand, the middle formation of the Navarro Group, consists of marine sandstones and mudstones derived largely from a source area to the north and northeast of the east Texas embayment. Terrigenous clastics were supplied to the Nacatoch basin by two major dispersal systems: (1) a bifurcating northwestern and northern system in southern Hunt and southern Delta Counties, and (2) a northeastern system originating in southwestern Arkansas. Five facies are recognized in surface exposures of southwestern Arkansas: tidal flat, tidal channel, tidal inlet association, shoreface, and shelf facies. In northeast Texas, a deltaic sequence is recognized in southcentral Hunt County, and shelf sandstones and mudstones are present in Navarro and Kaufman Counties. Nacatoch sandstones in the East Texas basin are significant shallow oil and gas reservoirs. Production of hydrocarbons from the Nacatoch is restricted to the shelf-sand facies. Hydrocarbon occurrence is perhaps more a function of structural closure than depositional facies. Hydrocarbon production is associated with the Van salt dome in Van Zandt County and coincident with the Mexia fault system trend along the western margin of the basin. End_of_Article - Last_Page 1564------------

Queen City Formation in East Texas Embayment--Record of Riverine, Tidal, and Wave-Dominated Processes: ABSTRACT

Five distinct facies are recognized in Queen City exposures between the Trinity River valley and Louisiana boundary. These facies (fluvial, deltaic, tidal flat, barrier, and tidal delta) display distinctive suites of physical and biogenic structures, with substantial differences in paleocurrent pattern. Fluvial influx was mainly from the northwest, possibly with minor contributions from the Sabine uplift on the east. A marginal alluvial plain was transected by sandy braided streams and sinuous mixed-load channels. Very small, high-constructive shoal-water deltas and crevasse subdeltas developed mainly along the northwestern embayment margin, prograding rapidly across the shallow shelf. Barriers may have originated as destructive components of delta abandonment or as contemporaneous strike-fed features marginal to the main delta complex in the west. In either event, barriers are poorly preserved, possibly because of transgressive ravinement, but more likely because they were never developed on a major scale. Flood-tidal deltas formed at the mouths of microtidal estuaries. Like some mo ern analogs, they are significantly larger than comparable mesotidal features. They also exhibit features reflecting storm processes. Extensive back-barrier or bay-margin intertidal and subtidal flats and shoals reflect the interplay of tidal and wave-generated processes, leaving a characteristic record of variable physical energy and flow patterns. Regional depositional patterns were largely controlled by (1) location of the east Texas embayment with respect to the major deltaic depocenter, resulting in an eastward decrease in sediment supply; (2) configuration of the broadly funnel-shaped embayment which may have augmented tidal range; and (3) transition from overall progradational character, with local transgressions, to a major marine transgression that culminated in shelf sedimentation of the overlying Weches Formation. End_of_Article - Last_Page 1603------------

Depositional History of Gulfian Cretaceous of East Texas Embayment

Regional aspects of the depositional environment of Gulfian Cretaceous rocks in the East Texas embayment have been investigated by a combined stratigraphic and paleontologic approach. Only readily available information from electrical and sample logs and simply made paleontologic determinations have been employed. Almost 3,000 wells were used for control. The program provided structure, isopach, three-end-member lithofacies, sandstone-shale-ratio, number-of-discrete-sandstone bodies, shale-color, and biofacies maps. This approach revealed essential continuity of structural behavior throughout the Gulfian, but showed a major change in the direction of the source of terrigenous clastics from northeasterly in early Gulfian time to westerly during the remaining Gulfian. Biofa ies and lithofacies data indicate that the seaward edge of the Gulfian Cretaceous continental slope lay in the position of the Angelina-Caldwell flexure, and that on the south, deep open ocean existed. North of this flexure lay an epicontinental sea crossed by various current systems. Evidence suggests that marine deposition occurred westward for a considerable distance beyond areas in which Gulfian Cretaceous rocks are preserved. It is proposed that the black shales characterizing parts of the Gulfian Cretaceous within the area owe their color to postdepositional reducing conditions caused by low permeability related to fine grain size. The Sabine uplift episodically changed its position with respect to sea level, resulting in varying effectiveness as a barrier to sediment and water tra sport. During part of early Late Cretaceous time the uplift apparently was slightly emergent and served as a minor source of sediment. The simple parameters studied delineated the areas now known from drilling to produce hydrocarbons as prospective for production of hydrocarbons.

Lower Cretaceous Rocks in Gulf Coastal Plain of United States: ABSTRACT

Rocks of Early Cretaceous (Comanchean) age underlie most of the Gulf coastal plain. Their thickness varies from zero at the updip subsurface pinchout in the eastern region and less than 2,000 ft at the outcrop in central Texas to about 7,000 ft at the downdip limit of control. Carbonates make up most of the section west of the East Texas embayment; alternating carbonates, terrigenous clastics, and some anhydrite compose the section in eastern Texas and adjacent parts of Louisiana and Arkansas; and sandstone and shale, with some beds of limestone and anhydrite, represent the Lower Cretaceous in the eastern region. The percentage of carbonates increases seaward in all segments of the Gulf Coast. Deposition was in shallow open-sea to restricted marine, deltaic, coastal-interdeltaic, and coastal-plain End_Page 358------------------------------ environments. Subsidence was generally at the same rate as sedimentation, and all sediments were deposited near sea level. The shoreline fluctuated greatly in the eastern clastic province but shifted little in the western carbonate region after the Early Cretaceous transgression. Deltas were constructed in several segments of the Gulf Coast during earliest Cretaceous, and in the central and eastern regions during several later regressive intervals. The tectonic-sedimentation history of the Gulf Coast Lower Cretaceous was optimum for the development and preservation of abundant organic matter adjacent to deltaic sandstone and porous carbonate rocks, creating favorable conditions for petroleum occurrence. End_of_Article - Last_Page 359------------