Tansill Formation Research Articles

Diagenetic controls on the isotopic composition of carbonate‐associated sulphate in the Permian Capitan Reef Complex, West Texas

AbstractLate Palaeozoic‐age strata from the Capitan Reef in west Texas show facies‐dependent heterogeneity in the sulphur isotopic composition of carbonate‐associated sulphate, which is trace sulphate incorporated into carbonate minerals that is often used to reconstruct the sulphur isotopic composition of ancient seawater. However, diagenetic pore fluid processes may influence the sulphur isotopic composition of carbonate‐associated sulphate. These processes variously modify the sulphur isotopic composition of incorporated sulphate from syndepositional seawater in shelf crest, outer shelf, shelf margin and slope depositional settings. This study used a new multicollector inductively‐coupled plasma mass spectrometry technique to determine the sulphur isotopic composition of samples of individual depositional and diagenetic textures. Carbonate rocks representing peritidal facies in the Yates and Tansill formations preserve the sulphur isotopic composition of Guadalupian seawater sulphate despite alteration of the carbon and oxygen isotopic compositions by meteoric and dolomitizing diagenetic processes. However, sulphur isotopic data indicate that limestones deposited in reef and slope facies in the Capitan and Bell Canyon formations largely incorporate sulphate from anoxic marine‐phreatic pore fluids isotopically modified from seawater by microbial sulphate reduction, despite generally preserving the carbon and oxygen isotopic compositions of Permian seawater. Some early and all late meteoric calcite cements have carbonate‐associated sulphate with a sulphur isotopic composition distinct from that of Permian seawater. Detailed petrographic and sedimentary context for carbonate‐associated sulphate analyses will allow for improved reconstructions of ancient seawater composition and diagenetic conditions in ancient carbonate platforms. The results of this study indicate that carbonate rocks that diagenetically stabilize in high‐energy environments without pore fluid sulphate gradients can provide a robust archive of ancient seawater's sulphur isotopic composition.

Extensive, uplift-related and non-fault-controlled spar precipitation in the Permian Capitan Formation

With time, unlithified grains in sediments become cemented and eventually lithified to form sedimentary rocks. Sedimentary rocks of all ages, lithologies and depositional settings exhibit cements. The timing of cementation within a given sedimentary unit, however, is generally poorly constrained. The formation conditions of the youngest of cement generations are particularly difficult to characterize. Typically, traditional carbonate carbon (δ13Ccarb) and oxygen (δ18Ocarb) isotope analyses are used to characterize precipitation timing and environment. However, ambiguities associated with the interpretation of δ18Ocarb data lead to conflicting hypotheses. The Permian Capitan Formation is one of the most widely studied carbonate sequences and contains extensive calcite cements that have been interpreted to form across a range of diagenetic environments through δ18Ocarb analyses. Here, we present new and previously reported clumped isotope data from calcite spars of Capitan fore-reef slope and equivalent shelf facies (Tansill Formation) in order to constrain mineralization temperatures, provide previously unattainable information concerning precipitation environment, and explore the spatial extent of precipitation events. Spar precipitation temperatures range from ~30 to 75°C and show positive correlation with reconstructed pore water δ18O values, indicating rock-buffered behavior. Evaluation of the data using a simple water–rock model indicates that the fluid(s) involved in diagenesis must have had a significant meteoric component, exhibiting fluid δ18O values approaching −12‰ (VSMOW). These new data along with previously reported outcrop and core relationships indicate that spar precipitation occurred well after deposition of the Capitan Formation and likely during Tertiary uplift when fluids with such light isotopic signatures would have infiltrated the basin, and not during burial as generally assumed. The meteoric fluids responsible for spar precipitation may have been delivered locally through fracture networks, but also penetrated less fractured facies and produced extensive spar cements.

Stratigraphic Response Across a Structurally Dynamic Shelf: The Latest Guadalupian Composite Sequence at Walnut Canyon, New Mexico, U.S.A.

Abstract The uppermost Yates and Tansill formations (Late Permian), as exposed along Walnut Canyon in Carlsbad Caverns National Park, New Mexico, USA, provide a unique opportunity to document the depositional architecture of a progradational, oversteepened, and mechanically failure-prone carbonate platform. Detailed facies mapping permitted critical assessment of depositional processes operating along this structurally dynamic platform margin. At the shelf crest, thick (12 m), vertically stacked fenestral–pisolite–tepee complexes indicate a stable shoreline. Early lithification of sediments and extensive cementation fostered rapid vertical accretion and allowed the shelf crest to easily adjust to base-level oscillations by stepping landward, stepping seaward, or aggrading. This production imbalance—in combination with syndepositional brittle failure and down-to-the-basin tilting(

Middle Permian (Late Guadalupian) foraminifers from Dark Canyon, Guadalupe Mountains, New Mexico

Research Article| January 01, 2006 Middle Permian (Late Guadalupian) foraminifers from Dark Canyon, Guadalupe Mountains, New Mexico Galina P. Nestell; Galina P. Nestell Department of Earth and Environmental Sciences, University of Texas at Arlington, Arlington, TX 76019, USA, email: gnestell@uta.edu; nestell@uta.edu Search for other works by this author on: GSW Google Scholar Merlynd K. Nestell Merlynd K. Nestell Department of Earth and Environmental Sciences, University of Texas at Arlington, Arlington, TX 76019, USA, email: gnestell@uta.edu; nestell@uta.edu Search for other works by this author on: GSW Google Scholar Author and Article Information Galina P. Nestell Department of Earth and Environmental Sciences, University of Texas at Arlington, Arlington, TX 76019, USA, email: gnestell@uta.edu; nestell@uta.edu Merlynd K. Nestell Department of Earth and Environmental Sciences, University of Texas at Arlington, Arlington, TX 76019, USA, email: gnestell@uta.edu; nestell@uta.edu Publisher: Micropaleontology Press Received: 11 Nov 2005 Accepted: 25 Jan 2006 First Online: 09 Mar 2017 Online ISSN: 0026-2803 Print ISSN: 1937-2795 © 2005 The Micropaleontology Project, Inc. Micropaleontology (2006) 52 (1): 1–50. https://doi.org/10.2113/gsmicropal.52.1.1 Article history Received: 11 Nov 2005 Accepted: 25 Jan 2006 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Galina P. Nestell, Merlynd K. Nestell; Middle Permian (Late Guadalupian) foraminifers from Dark Canyon, Guadalupe Mountains, New Mexico. Micropaleontology 2006;; 52 (1): 1–50. doi: https://doi.org/10.2113/gsmicropal.52.1.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyMicropaleontology Search Advanced Search Abstract Late Capitanian foraminifers are described from two cores taken by Amoco on the north side of the entrance of Dark Canyon. The Amoco #1 core (400ft) penetrates proximal forereef debris of the Tansill Formation and bottoms in massive Capitan reefal limestone. The Amoco #2 core (468ft) penetrates proximal backreef lagoonal deposits of the upper Yates Formation and the Tansill Formation.Foraminifers are very diverse and abundant in these cores. Based on the fusulinid distribution, the Codonofusiella extensa (upper part of the Yates Formation), Yabeina texana, Paradoxiella pratti and Reichelina lamarensis zones (lower and middle Tansill Formation) are present in the Amoco #2 core. Among small foraminifers, the first appearance of the genera Sengoerina and Crescentia are recorded at the base of the Y. texana Zone and they disappear at the top of the P. pratti Zone. The genus Baisalina appears at the base of the R. lamarensis Zone and disappears at the top of that zone. The Ocotillo Silt Member and upper dolomitized part of the Tansill Formation do not contain foraminifers. The Ocotillo Silt Member is present in the Amoco #2 core at a depth of from 88 to 112ft and, because of its regional dip of approximately six degrees, would possibly project below the base of the Amoco #1 core, thus correlating the Capitan and Tansill formations in the Amoco #1 core with the upper Tansill Formation of the Amoco #2 core. The lower part of the Amoco #1 core (from 110 to 370ft) contains fusulinacean species of the Paraboultonia splendens Zone. The assemblage of small foraminifers is dominated by species of nodosariids and hemigordiopsids. Four new genera and sixteen new species of foraminifers are described from both cores. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Syndepositional deformation of the Permian Capitan reef carbonate platform, Guadalupe Mountains, New Mexico, USA

Permian shelf strata equivalent to the Capitan reef are cut by at least 13 closely spaced syndepositional dip-slip faults in Slaughter Canyon, Guadalupe Mountains, New Mexico, USA. The control of five of these faults on platform development, architecture, stratigraphy and diagenesis is revealed by an integrated stratigraphic, sedimentological and structural framework within a 500-m-wide and 200-m-high outcrop window. Here, faulting and fault-related deformation acted as a primary control on changes in thickness, facies and stratal geometry, and resulted in the local steepening, shallowing and even the reversal of dip in shelf strata. The role of primary depositional relief in controlling changes in thickness and stratal geometry was of secondary importance. The relationship between geopetal fabrics (average dip=12° towards 141°) and bedding shows that during deposition of the Yates Formation fault growth was concurrent with down-to-the-basin tilting (and rotation?) of at least 6–8°. This tilting appears to have been the main control on the down-dip expansion of shelf strata towards the basin. A further 4–6° of basinward tilt occurred after fault growth, during deposition of the Tansill Formation and later. The syndepositional faults reported here have a maximum displacement of 24 m. Most tip-out below asymmetric growth folds and have high displacement-distance gradients typical of growth faults and faults cutting unlithified strata. The average rate of fault displacement (0.021 m/ka) and the maximum rates of fault propagation (0.088–0.123 m/ka) were normally less than the platform accumulation rates (0.053–0.336 m/ka). Thus, the faults were normally blind and rarely broke the platform top so that slumps and fault-scarp degradation breccias are rare. The fault zones were substantially modified by diagenesis during platform development. They are up to 9 m wide, taper both up and downward, have irregular margins and complex fills mainly of sedimentary origin. Their margins and fill were subject to extensive modification by karstic(?)/mixing zone dissolution, gravitational collapse and dolomitising fluids. Consequently, tectonic fabrics and kinematic indicators are rare. Preserved tectonic fabrics consistently indicate a normal and reverse dip-slip sense of movement. Previously, these faults were mistaken for ‘neptunian’ dykes and fissures, so that the Seven Rivers and Yates 1–2 HFS shelf stratigraphy has been miscorrelated across them. It is apparent that the stratal relationships exposed in the Guadalupe Mountains do not simply preserve the original depositional morphology of the Capitan-equivalent shelf. The subsidence history, stratigraphy and development of the platform succession is more complex than previously thought. The study has important implications for many aspects of the Capitan system, including: (i) shelf-reef correlations, (ii) the controls on platform architecture and development, (iii) Capitan reef palaeobathymetry, (iv) diagenesis, and (v) the amplitude of sea-level changes affecting the platform's stratigraphic development.

Sequence architecture and sea-level dynamics of Upper Permian shelfal facies, Guadalupe Mountains, southern New Mexico

ABSTRACT A 3.2 km profile of mixed carbonates and clastics is superbly exposed in Slaughter Canyon in the Guadalupe Mountains of southern New Mexico and provides a seismic-scale panorama of stratal architecture and cyclic facies relationships across the Upper Permian shelf margin of the Delaware basin. The upper Seven Rivers and Yates Formations exposed in the mapped profile behind the Capitan reef margin are characterized by extreme seaward thickening and strongly progradational architecture. Meter-scale cycles exhibit systematic lithofacies changes in a seaward direction, spanning pisolitic shelf-crest to skeletal outer-shelf facies tracts. Retrogradational, aggradational, and progradational stacking patterns of meter-scale cycles in the Yates define four complete high-frequency sequences (Y1-Y4) and the lower half of a fifth (Y5) that continues into the overlying Tansill Formation. Individual Yates high-frequency sequences are fundamentally macroscale versions of Yates meter-scale cycles, on the basis of comparable internal arrangements of lithofacies and their seaward-thickening geometry. The evolution of the Yates-Capitan shelf margin from Y1 through Y4 is expressed by systematic trends in downdip thickness changes, lateral extent of facies tracts relative to the Capitan reef margin, aspect ratios of facies tracts, progradation:aggradation ratios and derived offlap angles, and progradation rates. These trends reflect the position of individual high-frequency sequences in the larger scale Yates-Tansill composite sequence. Long-term changes in aspect ratios record the progressive seaward migration and lateral expansion of the shelf-crest facies tract from Y1 through Y4 and the reciprocal seaward-stepping architecture and lateral contraction of the outer-shelf facies tract. The four Yates high-frequency sequences in Slaughter Canyon are characterized by an average offlap angle of 3.6°, whereas the corresponding average growth angle for the time-equivalent Capitan reef is 5.2°. The higher reef growth angle reflects the greater amount of accommodation available near the outer shelf-to-reef transition as well as limitations to seaward growth imposed by the steepness of the reef front. The Yates shelf prograded at an average rate of 2.1 m/k.y., whereas the time-equivalent Capitan reef prograded at a rate of 1.7 m/k.y. The strongly progradational architecture of the Yates shelf resulted in a progressive decrease in the depth of the Capitan reef through time from a maximum of ~ 65 m during early Yates time to near sea level during the latest stages of the Yates platform. The abrupt seaward expansion within each Yates high-frequency sequence occurs directly above the terminal reef margin of the preceding high-frequency sequence. The underlying reef likely acted as a foundation to localize the basinward shift in deposition associated with sea-level fall along high-frequency sequence boundaries, contributing to the seaward thickening and progradational step-out of the outer shelf. Architectural changes controlled by the interaction between relative sea level and antecedent depositional topography may be a fundamental characteristic of many progradational shelf margins.

Brachiopod mounds not sponge reefs, Permian Capitan-Tansill Formations, Guadalupe Mountains, New Mexico

Small bioherms in the uppermost Tansill Formation and Capitan Limestone in the northern Guadalupe Mountains, New Mexico, have been informally interpreted as sponge reefs by past workers. Samples collected during the present cycle of field work in 1993 and 1994 suggest that some of these isolated carbonate mounds have a different origin. Guadalupe Mountains complexes have been recognized for many years as outstanding models for interpretation of reefs, reef facies, and reef faunas (for example, King, 1948; Newell et al., 1953; Achauer, 1969; Yurewicz, 1976, 1977; Babcock, 1977; Kirkland et al. 1993).

Ochoan (Upper Permian) Stratigraphy and Age Determinations, Southeastern New Mexico and West Texas: ABSTRACT

Upper Permian strata, which are the stratotype of the Ochoan State (Series), have an extensive subsurface distribution and limited outcrop area in southeastern New Mexico and west Texas. The oldest strata are alternating laminae of anhydrite and calcite of the Castile Formation and are as much as 700 m thick. The closely related and overlying Salado Formation is a much as 600 m thick and is mostly halite and argillaceous halite with minor anhydrite. The overlying Rustler Formation is as much as 150 m thick and consists of anhydrite, red silty shale and magnesian limestone. Overlying red beds are the Quartermaster Formation (Dewey Lake Formation is a synonym, as is the term Pierce Canyon red beds), which is as much as 106 m thick and consist of fine sandstones, siltstones, and minor gypsum. The Castile rests disconformably on the Capitanian (middle Permian) Lamar Limestone Member of the Bell Canyon Formation and its equivalent, the Tansill Formation of the Artesia Group. Counting of Castile-Salado laminae and their posited relationship to astronomical cycles suggests that Castile-Salado deposition took only 200,000-300,000 yr. Limited assemblages of brachiopods and conodonts from the Rustler Formation indicate a Late Permian age, but are no more precise agemore » indicators. A small assemblage of bivalves, K-Ar ages and magnetostratigraphy indicate a late Permian age for the Quartermaster Formation. There is no evidence to support a Triassic age assignment for the Quarter-master; it is disconformably overlain by the Upper Triassic (Carnian) Chinle group. Most workers us the Ochoan as a Late Permian Stage-Age, although its typical strata generally lack good age indicators and may represent relatively short and sporadic intervals of the Late Permian. We prefer recognition of the Ochoan as a lithostratigraphic unit (group) without regional or global geochronologial significance.« less

Silicification of Evaporites in Permian (Guadalupian) Back-Reef Carbonates of the Delaware Basin, West Texas and New Mexico

ABSTRACT Outcrops of the Seven Rivers, Yates, and Tansill Formations contain widespread evaporites replaced by quartz and calcite. The original evaporites consisted of discrete horizons, scattered nodules, enterolithic layers, and individual crystals or crystal fragments of gypsum and/or anhydrite within a finely crystalline dolomite matrix. Based on field and petrographic observations, silicification of evaporites proceeded from the exterior to the interior of the nodules. The earliest replacement was by euhedral, black megaquartz that contains abundant fluid inclusions (water and hydrocarbons) and solid inclusions (mainly anhydrite and dolomite). The siliceous replacements were followed by precipitation of equant, blocky calcite spar, which filled pores left by latestage dissolution of evaporites. The fluid inclusions in the replacive megaquartz are primary, and many contain both hydrocarbons and water. Daughter minerals of halite, gypsum, or possibly antarcticite (CaCl2·6H2O) are also found within the aqueous inclusions. Homogenization-temperature data for hydrocarbon and aqueous fluid inclusions average 67.7°C and 67.1°C, respectively. Hydrocarbonbearing and aqueous inclusions are thus interpreted to have formed simultaneously from the same fluids. Eutectic melting and final melting temperatures for aqueous inclusions indicate that the fluids were concentrated brines consisting of CaCl2 and NaCl. Oxygen-isotope values for the megaquartz replacements averaged 28.4 (SMOW), indica ing precipitation from evaporative waters with an isotopic composition of +2.9 (SMOW). Evaporite silicification was coeval with or slightly postdated hydrocarbon migration. The fluid-inclusion data provide a record of the fluid temperatures and compositions that prevailed during silica precipitation. These data, coupled with regional stratigraphy and published geothermal gradients, suggest a burial depth of approximately 1.3 km during silicification. The source of the silica for evaporite replacement is problematic. We postulate, however, that silica may have been derived from dissolution of siliciclastics in back-reef units. Organic acids that form from breakdown of hydrocarbons increase the solubility of quartz by bonding with silicic acid. As these products (and associated brines) moved into cooler oxidizing zones, the organic acids broke down, releasing silica into solution. This organically mobilized silica eventually precipitated as megaquartz replacements of preexisting evaporites.

Relative Sea Level Record of Yates and Tansill Formation Shelf Facies, Permian Reef Geology Trail: Implications for Platform Development

Relative Sea Level Record of Yates and Tansill Formation Shelf Facies, Permian Reef Geology Trail: Implications for Platform Development

Calcitization and Silicification of Evaporites in Guadalupian Back-Reef Carbonates of the Delaware Basin, West Texas and New Mexico

Outcrop of the Seven Rivers, Yates, and Tansill formations contain numerous examples of evaporites that have been replaced by both quartz and calcite. The original evaporites consisted of discrete horizons, scattered nodules, enterolithic layers, and individual crystal laths of gypsum and/or anhydrite within a predominantly dolomitic matrix. Based on field and petrographic observations, evaporite replacement proceeded from the exterior to the interior of the nodules. The earliest replacement was by euhedral, black megaquartz containing abundant hydrocarbon inclusions. Calcite replacement followed silicification and consists of coarse, equant, blocky spar. Isotopic analyses of these calcites form two distinct groups: the first group ranges from -10.9 to -20.1{per thousand} (average -16.4{per thousand}) {delta}{sup 13}C and -6.4 to -13.8{per thousand} (average -10.9{per thousand}) {delta}{sup 18}O; the second group ranges from +1.4 to 5.8{per thousand} (average -2.4{per thousand}) {delta}{sup 13}C and -6.2 to 14.1{per thousand} (average -9.2{per thousand}) {delta}{sup 18}O. Evaporite silicification was coeval with hydrocarbon migration as indicated by the inclusion data. Calcitization, however, was associated with mid-Tertiary block faulting that uplifted the area causing deep groundwater circulation. The isotopically very light calcites resulted from the mixing of meteoric fluids and hydrocarbon-rich pore fluids, probably during early uplift while these strata were still atmore » significant depth. The calcites with heavier isotopic values were produced somewhat later by meteoric fluids that had little or no contact with hydrocarbons. Evaporite diagenesis in the Delaware basin is an ongoing process that started during hydrocarbon migration, continued over millions of years, and has the potential to significantly change the porosity of these units.« less

Occurrence and Significance of Magnesite in Upper Permian (Guadalupian) Tansill and Yates Formations, Delaware Basin, New Mexico (1)

Magnesite (MgCO[3]) occurs pervasively in a 270-ft (82-m) cored interval of Upper Permian (Guadalupian) shelf deposits from the northern rim of the Delaware basin portion of the Permian basin, New Mexico. In our core example, magnesite is found in tidal flat/lagoon and pisolite shoal dolomites and siltstones of the Tansill and uppermost Yates formations. The interval is overlain by magnesite-bearing anhydrite and a thick halite section of the (Ochoan) Salado Formation. The basinwide extent of magnesite is unknown. The texture of magnesite in core slabs, thin sections, and SEM (scanning electron microscope) mounts is nearly identical to that of dolomite. The magnesite consists of anhedral to euhedral crystals ranging in size from 1 to 4 mm. Within the dolomite intervals of the core, magnesite occurs in three forms: (1) patches of crystals and as replacement of allochems, both in an otherwise dolomite matrix, (2) pervasive replacement of host dolomudstone and peloidal and pisolitic dolowackestone/packstone, and (3) discrete layers interbedded with anhydrite. Magnesite rarely fills pore spaces in dolomite, but within siliciclastic beds, magnesite occurs both as a first-generation cement and as a replacement of carbonate grains. Magnesite and dolomite are mutually exclusive in siliciclastic beds wi hin the core, and magnesite occurs only where anhydrite is abundant. Magnesite may have formed either (1) during Ochoan deposition or thereafter, after burial of the Tansill and Yates formations, from dense brines originating from the overlying Salado evaporites; or less likely, (2) syndepositionally with the Tansill and Yates sediments. Preliminary measurements of stable carbon and oxygen isotopes for magnesite yield normal Permian values for (sigma){13}C averaging +6.84 parts per mil (PDB) and slightly evaporitic values for (sigma){18}O averaging +1.04 parts per mil (PDB); corrected {87}Sr/{86}Sr isotope composition averages 0.70687. Because a high content of associated uranium in the magnesite-rich part of the core causes large gamma-ray deflections similar to those for shale, and because the density of magnesite is close to that of anhydrite, the presence of magnesite could lead to improper evaluation of lithology and porosity from logs and could ultimately result in failure to recognize potential reservoir zones.

Occurrence and Significance of Magnesite in Upper Guadalupian Shelf Strata, Delaware Basin, New Mexico: ABSTRACT

Magnesite (MgCO/sub 3/) occurs pervasively in a 270-ft cored interval of Upper Permian (Guadalupina) shelf deposits from the northern rim of the Delaware basin, New Mexico. The texture of magnesite in core slab, thin section, and SEM is almost identical to that of dolomite. Because the density of magnesite is close to that of anhydrite and a high associated uranium content causes large gamma-ray deflections similar to that of shale, magnesite could lead to improper evaluation of lithology and porosity from logs and ultimately results in failure to recognize potential reservoir zones. In the authors' core example, magnesite is found in tidal flat and evaporative lagoon dolomites of the Tansill and uppermost Yates Formations. The interval is overlain by Tansill anhydrite and a thick halite section of the Ochoan Salado Formation. The magensite consists of anhedral to euhedral crystals ranging in size from 1 to 4 ..mu..m. Within the dolomite intervals, magnesite occurs in three forms: (1) patches and discrete grains floating in dolomite matrix, (2) pervasive replacement of host dolomudstoen and pelodial and pisolitic dolowackestone or packstone, and (3) discrete layers interbedded with anhydrite. Mangesite rarely fills pore spaces in dolomite, but within siliciclastic beds, magnesite occurs as amore » first generation cement and as a replacement of former carbonate grains. Magnesite and dolomite are mutually exclusive in siliciclasted beds, and magnesite occurs only when anhydrite is abundant. Preliminary measurements of stable carbon and oxygen isotopes yield normal Permian values for deltaC/sup 13/, averaging +6.84 o/00 and slightly evaporitic values of deltaO/sup 18/, averaging +1.04; corrected Sr/sup 87//Sr/sup 86/ isotopic composition averages 0.70687.« less

Permian (Guadalupian) Shelf Deposition and Diagenesis: Tansill Formation of Cheyenne Field, Winkler County, Texas: ABSTRACT

Cheyenne field, Winkler County, Texas, produces oil from shelf-margin lithofacies of the Tansill Formation of late Guadalupian age. The Tansill Formation encountered in the Cheyenne field compares favorably with basin-margin outcrops found in the Guadalupe Mountains of New Mexico and Texas. The Delaware basin margin consisted of (1) outer shelf ooid shoals and back-shoal green-algal flats, (2) a shelf-crest pisoid-tepee complex, and (3) inner shelf evaporitic, stromatolitic, and peloidal sediments during the late Guadalupian. The Cheyenne field reservoir exhibits varied lithologies and porosites in the Tansill Formation. Fresh-water phreatic diagenesis created moldic porosity in the outer shelf, green-algal lithofacies. Fresh-water vadose conditions existed during low sea level stands preserving intergranular porosity in the pisolitic lithofacies of the shelf-crest tepee complex. Fresh-water vadose diagenesis also helped form burrow-moldic porosity and fenestral porosity in the inner shelf peloidal lithofacies. Periodic hypersaline vadose conditions occluded some porosity with evaporites and aragonitic cements. Dolomitization of the Tansill Formation occurred in the mixing zone between a seasonal fresh-water lens in the shelf-crest sediments and the saline waters of the Permian sea and inner shelf lagoon. s sea level fluctuated the mixing zone migrated laterally. In this way, much of the Tansill Formation was dolomitized, forming finely crystalline dolomite that preserved textural details well but did little to enhance porosity. Porosity is best developed in the thin beds of the outer shelf, green-algal lithofacies. More importantly, the 194 ft (59 m) of pay in the Cheyenne field results from favorable diagenesis of lithofacies on the shelf margin that were interbedded with the shelf-crest lithofacies by fluctuations of sea level. The arid climate at the time of deposition was essential in maintaining porosity created by early diagenesis and for the absence of abundant vadose cements in the Tansill Formation. The trap in Cheyenne field is depositionally controlled by updip, nonporous, and impermeable sediments of the inner shelf lagoon. Anhydrites of the overlying Salado Formation provide an excellent seal. Interbedded End_Page 118------------------------------ lithologies of the Cheyenne field average 8% porosity and 1 md permeability. The field has recovered 499,950 bbls of oil as of May 1983, with estimated total recoverable reserves of 1,744,987 bbls of oil. End_of_Article - Last_Page 119------------

Extensive Coniatolite-Pelagosite Diagenetic Sedimentation in Marine Limestones, Tansill Formation (Permian), New Mexico: ABSTRACT

Pelagosites (calcareous crust formed in splash zone) and coniatolites (supratidal tufa) composed of inorganic precipitates of aragonite and some high-Mg calcite have been described from Holocene deposits along the western Persian Gulf and elsewhere. Such diagenetic deposits are believed to be restricted to intertidal and supratidal environments, and are only rarely encountered in ancient carbonate rocks. Laminated encrustations, coated grains, and pseudostromatolites of presumed former aragonite mineralogy, all associated to some extent with encrusting marine fossils, are the dominant if not exclusive components of shallow-marine limestones in the Tansill Formation (back-reef facies of the Capitan) in New Mexico. These deposits occur in shallow back-reef environments of possible hypersaline character. In landward directions, they are replaced by peritidal dolomites. The vertical and lateral occurrence of particular coniatolite-pelagosite structures is related to the hydraulics of the depositional environment in a manner somewhat similar to that which controls algal laminite and stromatolite distributions in modern and ancient deposits. Internally, the laminae of crystalline calcite in these deposits are interlayered with the alga Archaeolithoporella and encrusted by Tubiphytes. Petrographically, this crystalline calcite consists of square-tipped crystal ghosts and divergent fan-druses in neomorphic sparry mosaics identical to altered aragonites described from other ancient carbonates. These deposits are similar to the coniatolites and pelagosites described from the Holocene, but represent the first reported occurrence of extensive diagenetic sedimentation of this type in ancient shallow-marine carbonate rocks. End_of_Article - Last_Page 602------------

Carbonate Facies Variation on Guadalupian Shelf Crest (Upper Yates and Lower Tansill Formations), Guadalupe Mountains, New Mexico: ABSTRACT

End_Page 501------------------------------The Guadalupian shelf crest provides a unique setting for the study of changing carbonate-shelf environments. Previous works by King, Newell, Dunham, Smith, Pray, and others have provided models and interpretations to define a generalized morphology of the carbonate facies for the Guadalupian shelf, behind the Capitan Limestone. Detailed field studies of about 50 m of carbonate units within the upper Yates and lower Tansill Formations reveal significantly different facies patterns and suggest changing shelf profiles and environments through time. Alternating carbonate and sandstone units are apparent as the product of cyclic shelf sedimentation. Major carbonate units within the stratigraphic interval studied are informally named (Hairpin dolomite, Triplet dolomite, and basal Tansill dolomite). Recognition of five major carbonate lithofacies within the three identified carbonate units at the shelf crest (the paleotopographic high of Dunham's marginal mound) indicates variance in deposition owing to highly restricted water conditions as well as more normal marine water circulation. The three carbonate units differ in the following respects: the Hairpin dolomite is dominated by fenestral peloid grain-supported, pisolite-rich facies, and is associated with erosion surfaces and abundant tepee structures. Carbonate facies in the Hairpin dolomite repeatedly grew to fill level, and the shelf crest extended at least 3 km perpendicular to the Capitan Limestone. The Triplet dolomite is composed primarily of peloidal grainstones with abundant admixed siliciclastic grains. Shelf-crest features, that is, pisolites, tepees, and fenestral strata, are uncommon, suggesting an absence of a nearly emergent paleotopographic high and a more continuous basinward sloping shelf. The basal Tansill dolomite contains abundant skeletal grains, that is, dasycladacean algae, ostracods, ga tropods, and foraminifers, suggesting a deeper shelfward penetration of more open marine water than for the other two units. Erosion surfaces common at the upper boundaries of the identified major carbonate units are most common and traceable horizontally 0.5 to 3 km behind the Capitan front, locally 50 m behind the Capitan Limestone. Simple progradation of the shelf-crest facies with the Capitan Limestone through time does not explain the change of facies within the three major carbonate units. End_of_Article - Last_Page 502------------

Diagenesis of Back-Reef Carbonate Rocks--Example from Capitan Complex: ABSTRACT

The lower Tansill Formation (Permian) in the vicinity of Carlsbad Caverns, New Mexico, is a basinward prograding sequence of back-reef carbonate rocks equivalent to the Capitan reef. Toward the north (shelfward), the facies tract consists of outer-shelf skeletal-intraclast grainstone, shelf-crest pisolite, and lagoonal pelletal dolomite. Diagenesis occurred by means of four phases that reflect the changing hydrologic regime. Square-ended ray cement (phase I), now calcite or dolomite, but originally aragonite, was the product of marine waters. Calcitized ray cement from the reef has retained up to 3,500 ppm strontium and has a relatively heavy carbon and oxygen isotopic composition. Back-reef examples are lower in strontium and lighter isotopically, reflecting neomorphism nder more open conditions by meteoric water. Soon after deposition, outer-shelf and shelf-crest sediment was periodically exposed to fresh water (phase II). Calcite cement that is the product of this early meteoric-schizohaline regime is nonluminescent, has low or variable magnesium content, and has an intermediate isotopic composition. Contemporaneous diagenetic processes include solution, conversion of aragonite to calcite, and schizohaline dolomitization. Perhaps reflecting its genesis, the strontium content of Tansill dolomite increases shelfward from the shelf crest, which was the area of meteoric recharge. As back-reef carbonate deposits became buried, meteoric conditions became more stable in the shallow subsurface (phase III). Phase III calcite cement is luminescent, uniformly low in magnesium, and has a relatively light isotopic composition. Upon erosion of the overlying sediment, the rocks were subjected to near-surface meteoric flushing, resulting in solution and minor cementation (phase IV). End_of_Article - Last_Page 519------------

Sedimentation of Upper Artesia (Guadalupian) Cyclic Shelf Deposits of Northern Guadalupe Mountains, New Mexico

Late Guadalupian carbonate rocks and other deposits of the northwest shelf of the Delaware basin exhibit a wide variety of primary and secondary features indicative of sedimentary environments ranging from extensive evaporite-bearing coastal sabkhas in the north and west to longshore bars and marginal reefs in the south and east. Detailed examination of outcrops of the Seven Rivers, Yates, and Tansill Formations in the hilly area west and southwest of Carlsbad, New Mexico, reveals that the known cyclicity of these deposits stems from more than 250 oscillations of relative sea level, spread over a period roughly estimated to have exceeded 5 m.y. Many or most of these oscillations appear to have been of a few meters only, but, because of the low relief of the shelf and the roximity of its surface to sea level, they were accompanied by shifts of up to scores of kilometers in the various depositional environments. These shifts were most marked in gently shelving littoral zones, which, at different times, appear to have ranged from the shelf margin to as much as 50 to 60 km farther west and northwest. They are least marked where contemporary relief was greatest, as at the shelf margin and on longshore bars which appear to have separated inner and outer parts of the shelf during much of upper Artesia deposition. Relative sea-level oscillations of glacio-eustatic origin offer a possible cause of major rhythmicity such as that at formation level, but the absence of smaller scale cycles in some other approximately contemporaneous shelf deposits elsewhere in the w rld argues in favor of a local or regional cause, such as varying rates of epeirogenic subsidence.

Proposed Surface Reference Section for Yates Formation, Eddy County, New Mexico: GEOLOGICAL NOTES

The Yates Formation of Guadalupian (Permian) age, named for the Yates oil field, Pecos County, Texas, is a subsurface clastic unit. It extends over the Central Basin platform and onto the Northwestern shelf of New Mexico, within the interval between the Seven Rivers and Tansill Formations of the Artesia Group. Subsurface type sections have been designated for both Texas and New Mexico. This paper proposes that an outcrop of the Yates Formation in lower Dark Canyon (Secs. 26, 27, T23S, R25E), Eddy County, New Mexico, be adopted as the surface reference section. The Yates of this locality is well exposed as an intermittent cliff- and slope-forming unit between the cliff-forming Tansill and Seven Rivers Formations. The section totals 313 ft of interbedded siltstone, sandstone, and carbonate rocks. The upper contact is the top of a well-defined buff to ocher calcareous siltstone from 3 to 5 ft thick. The lower contact is not clearly defined, but is the base of the first buff sandy calcareous unit above the predominantly gray limestone of the Seven Rivers.

The Control of Ground–Water Occurrence by Lithofacies in the Guadalupian Reef Complex near Carlsbad, New Mexico

The occurrence and movement of water in the Guadalupian reef complex of southeastern New Mexico is controlled primarily by lithofacies. Major Guadalupian lithofacies which affect water occurrence are: (1) a basin facies of very low permeability which confines ground water, (2) a reef-zone facies of very high permeability, (3) a shelf-carbonate facies ranging from very high permeability near the reef zone to low permeability near the shelf-evaporite facies, and (4) a shelf-evaporite facies of moderate permeability. Major Johnson Springs and Indian Big Springs occur at the contact of the shelf-evaporite and shelf-carbonate facies because of a large decrease of permeability in the latter facies. The greatest amount of solution and highest permeabilities in the shelf-carbonate facies occur along joints in coarser-textured carbonates rather than in fine-grained carbonates, and in the calcareous rather than in the dolomitic subfacies. A zone of exceedingly high permeability, extending from the reef-zone facies into the calcareous subfacies of shelf-carbonates, forms the Limestone aquifer, and a zone of much lower permeability, occupying most of the shelf-carbonate and shelf-evaporite facies, forms the Shelf aquifers. The boundaries of the Limestone aquifer and Shelf aquifers extend across formational and time boundaries but conform to major lithologic facies. Water in the Shelf aquifers takes two divergent paths; in the San Andres Formation it moves northeastward into the Roswell basin, whereas in the stratigraphic interval from the Tansill Formation through the Grayburg Formation it moves eastward into the Limestone aquifer. The Limestone aquifer which parallels the Reef Escarpment is about 20 miles long and 5 to 6 miles wide. Downward movement of water in the aquifer is prevented by underlying massive sandstone of the Cherry Canyon Formation, and lateral movement eastward is prevented by impermeable anhydrite of the Castile Formation. The poorly permeable and impermeable barriers divert water to move in a northeasterly direction parallel to the Reef Escarpment and to the axis of the Capitan reef zone. The ultimate discharge area for most water in the Limestone aquifer is Carlsbad Springs, located north of Carlsbad, New Mexico. Knowledge of hydrology of the Guadalupian reef complex has aided geologic analyses in the subsurface location of lithofacies and in understanding the geomorphic history of the Guadalupe Fault Block. The presence of potable water west of the Pecos River in Guadalupian rocks and highly mineralized water east of the river in similar rocks suggests that the Guadalupe and Sacramento Fault Blocks were uplifted and trenched by the Pecos. The circulation of water through the Limestone aquifer has caused extensive solution and caverns, of which Carlsbad Caverns are a part. Shallow oil deposits occur in some anticlinal structures east of the Pecos River, but they do not occur in similar structures west of the river because circulating ground water from the west has flushed out the oil deposits and highly mineralized water.