Browsing by Subject "Geology, Stratigraphic--Pennsylvanian"
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Item Community paleoecology of the Pennsylvanian Winchell Formation, north-central Texas(2003) Schneider, Christie Lynn; Sprinkle, James T.Item Depositional systems and shelf-slope relationships in uppermost Pennsylvanian rocks of the eastern shelf, north-central Texas(1970-12) Galloway, William E.; Brown, L. F. (Leonard Franklin), 1928-The Eastern Shelf was a constructional platform developed on the margin of the sediment-starved Midland Basin during Late Pennsylvanian and Early Permian time. A mixed terrigenous-carbonate sedimentary province characterized the shelf during most of its history. Sediments were derived from highlands to the east and northeast. Along the outcrop in Eastland, Stephens, Young, and Jack counties, uppermost Pennsylvanian beds compose the Harpersville Formation, a boundary-defined rock stratigraphic unit within the Cisco Group. Harpersville facies extend westward into the subsurface 50 to 60 miles, where they grade into equivalent shelf margin carbonate and slope terrigenous facies. Preserved relief between the shelf margin and basin floor ranges from 600 to 1100 feet with dips of up to five degrees. Three depositional systems are recognized on the basis of gross lithologic composition and position relative to the shelf edges. They are the Cisco fluvial-deltaic system, the Sylvester shelf edge bank systern, and the Sweetwater slope system. The Cisco fluvial-deltaic system is composed of dip-fed fluvial-deltaic facies and associated strike-fed interdeltaic embayment facies. Eight deltaic lobe complexes have been mapped. The Sylvester slope system is composed of several slope wedges or fans each of which includes shelf margin, slope trough, and distal slope sandstone facies, as well as slope mudstone facies. Terrigenous sediments were transported across the shelf by prograding fluvial-deltaic channels, which locally extended through the shelf edge bank system and onto the slope where submarine fans were constructed into the basin. The Eastern Shelf prograded into the Midland Basin by local upbuilding through fluvial, deltaic, and shelf edge bank deposition contemporaneous with outbuilding by slope fan deposition. Sites of shelf construction shifted through time in response to sedimentary and structurally controlled abandonment of delta lobes. Extrabasinal controls such as eustatic sea level changes were of secondary importance in developing the depositional fabric of the shelf.Item Depositional systems in the Pennsylvanian Canyon Group of North-Central Texas(1974-07) Erxleben, A. W.; Brown, L. F. (Leonard Franklin), 1928-The Canyon Group (Missourian Series) is a sequence of westward-dipping, genetically related carbonate and terrigenous clastic facies that crop out in a northeast-southwest belt across North-Central Texas. The section includes stratigraphic units between the base of the Palo Pinto Limestone and the top of the Home Creek Limestone. Surface and subsurface studies within thirteen counties indicate that terrigenous clastic rocks are principally component facies of high-constructive delta systems. The Perrin delta system repeatedly prograded westward and northwestward from source areas in the Ouachita Fold Belt. Algal-crinoid banks flanked the Perrin delta system on the northeast and southwest. A typical vertical deltaic sequence includes (upward) (a) organic rich, prodelta mudstone, devoid of invertebrate fossils; (b) thin, distal delta-front sandstone and mudstone, displaying graded beds, sole marks, and flow rolls; (c) thicker proximal delta-front sandstone, exhibiting contorted beds, flow rolls, and contemporaneous faults; (d) locally contorted distributary-mouth bar sandstone; and (e) distributary channel sandstone, containing abundant trough cross stratification and local clay-chip conglomerate. Thin, coal-bearing delta-plain deposits occur locally on top of deltaic sequences. All delta facies are rich in plant debris. During delta abandonment and destruction, shallow bay-lagoon environments developed. Destructional facies include bioturbated sandy mudstone, burrowed sandstone and thin, platy argillaceous limestone with abundant invertebrate fossils. Fossiliferous mudstone units grade upward into transgressive shelf carbonate units commonly composed of phylloid algal-crinoid biomicrudite and local intraclastic biosparite shoal facies. Shelf carbonate includes onlapping sheetlike deposits; thick elongate bank deposits, which stood above the sea floor with slight bathymetric relief; massive platform carbonate; and shelf edge reef-bank accumulations. The Henrietta fan-delta system, occurring exclusively in the subsurface of Montague, Clay, Wichita, Archer and Baylor counties, is composed of thick wedges of feldspathic sandstone and conglomerate that were deposited by high-gradient fluvial systems, which built southwestward into northern Texas from source areas in the Wichita-Arbuckle Mountains of southern Oklahoma.Item Swastika (Upper Pennsylvanian) shelf-margin deltas and delta-fed turbidites, Flowers "Canyon Sand" Field area, Stonewall County, Texas(1987-12) Neuberger, Daniel J.; Brown, L. F. (Leonard Franklin), 1928-Hydrocarbon producing, deep-water Cisco sands along the Eastern Shelf were studied in the vicinity of Flowers "Canyon Sand" Field to develop a depositonal model explaining their origin, geometry, and style of deposition. Regional correlations and subsurface mapping indicate that producing sands were deposited within the Swastika lithogenetic unit, which contains a network of shelf-margin fluvial/deltaic, slope, and basin depositional systems deposited between transgressive Gunsight and Ivan Limestones. The sands are not "Canyon", but Virgilian in age. During Swastika time a wedge of sediments up to 1100 feet thick was deposited in the study area in response to westward progradation of shelf-margin deltas. Standard mapping techniques and detailed correlations using nearly 700 well logs and the examination of 3 cores indicate that this wedge can be divided into three principal systems: (1) a sand-dominated turbidite, basin and lower slope system, which constitutes the reservoir facies, (2) a shale-rich prodelta/slope system punctuated by slope channel filled gullies, and (3) a sand-dominated shelf-margin fluvial/deltaic system. Ten deltaic lobes, averaging 2 miles in diameter, were recognized. These lobes may have been deposited during a lowstand of sea level. Elongate/lobate geometry and rapid shifting of lobes indicate high depositional rates. Shelf-margin instabilities associated with deltas led to prodelta/slope slumping, gully formation, and generation of turbidity currents. Turbidity currents generated by the earliest deltas to breach the shelf break were of sufficient magnitude to erode a broad, shallow inner-fan valley at the base of the slope. This valley initially focused turbidity currrents onto a base-of-slope terrace, which was mapped on top of the Gunsight Limestone, and formed by differential compaction over a subjacent Canyon delta or carbonate buildup. Low gradients associated with this terrace gave rise to a sediment trap. Nearly all existing production in Flowers Field is established above this terrace. Turbidites deposited within this phase of Swastika evolution display characteristics of an elongate/radial type fan deposit. Continued deltaic progradation filled the inner-fan valley. Once this valley was breached, a network of small channels originating as gullies along slopes in front of the advancing Swastika delta system transported sediment down the slope to form an aggrading/prograding wedge of turbidite and volumetrically less significant grain flow deposits. This change in depositional style led to superposition of what is best classified as an elongate/debris apron type system over the earlier elongate/radial deposits. A critical conclusion is that no single channel developed into a large canyon feeder system, which resulted in facies relationships that differ from commonly accepted models calling on a prolonged point source. Given the importance of turbidite sands in many petroliferous basins, application of the delta-fed model to appropriate turbidite systems can improve exploration strategies.