Browsing by Subject "Carbonate sedimentology"
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Item Anatomy, dimensions, and significance of the penultimate Yates tepee-shelf crest complex, G25 Hairpin HFS, Guadalupe Mountains, New Mexico and Texas(2016-05) Voorhees, Kristopher James; Kerans, C. (Charles), 1954-; Janson, Xavier; Fisher, William L.The steep-rimmed Permian Capitan platform in the Guadalupe Mountains has been studied in extensive detail to understand the effect of eustacy on platform architecture as seen in continuously exposed 700 m relief shelf-to-basin depositional profile. The Guadalupian Hairpin member (G25 High-Frequency Sequence) of the Yates Formation represents a major regional shelf marker and displays continuous 2.5 km dip-width exposures of the Capitan platform in McKittrick, Big, Double, Gunsight, Slaughter, Rattlesnake, and Walnut Canyons. Compared to the sequences above and below it, the G25 HFS is unique in that it reveals pronounced expansion of the shelf crest tepee-pisolite complex from an average of 1 km width to greater than 2 km. Tepee structures are 2-20 m diameter expansion megapolygons with compressional ridges formed by syndepositional expansive crystallization of micritic cement in arid to evaporitic supratidal settings. Increased dip-width of the shelf crest tepee-belt reflects a prolonged period where repeated cycles of wetting, evaporation, precipitation, and buckling of storm-ridge washover facies (grainy tidal flats/beaches) dominated the shelf. This study seeks to examine the role that eustacy/accommodation play in expansion of the shelf crest tepee complex by quantifying the dimensions of Capitan-equivalent shelf facies in McKittrick and Rattlesnake Canyons. Dip-oriented regional cross sections in Rattlesnake and McKittrick Canyons were created from 21 measured sections from 50-500 m spacing covering 30 to 70 m in thickness calibrated to 3 high-resolution gigapan photomosaics that are in turn constrained spatially using airborne lidar data. Cross sections in both canyons constrain facies tract dimensions as well as depositional topography and spatial distribution of the tepee complexes, allowing construction of a new tightly controlled depositional profile. 29 thin sections aid in grain identification, cement composition, and facies classification. Two main results of this study are (1) a new tightly constrained model for the Capitan shelf unequivocally showing that the tepee-belt is the topographic high-point of the profile, and (2) the Hairpin G25 highstand marks a period of prolonged supratidal exposure of the shelf and rapid volumetrically significant marine cementation from a supersaturated fluid, marking the first phase of silling of the Delaware Basin and onset of basinal restriction prior to end-Capitan Castile evaporite deposition.Item Carbonate platform demise and recovery at the Toarcian Oceanic Anoxic Event : high-resolution data from the Adriatic Carbonate Platform(2017-06-28) Ettinger, Nicholas Patrick; Martindale, Rowan C; Kerans, C. (Charles)The sedimentological, stratigraphic, and geochemical signature of the Toarcian Oceanic Anoxic Event (OAE) on the Bahamian-style, Adriatic Carbonate Platform of Southern Europe is examined here. New stratigraphic sections correlated to previously published data show that a healthy and diverse metazoan carbonate factory characterized the flat-topped platform prior to the onset of the OAE. Carbon isotopes of marine organic matter and bulk carbonate, as well as trace element data (V, Ni, Mo, Mn, Hg) were used to identify the stratigraphic location of the OAE on the outer platform. A negative organic carbon isotope excursion of -2.2‰ coincident with enrichments in Mo and Fe was used to correlate to time equivalent strata in both the inner platform and adjacent basin. The onset of the OAE heralded a carbonate factory collapse on the outer platform that was driven by deoxygenation, eutrophication, and possibly ocean acidification. At the same time, a shallow intrashelf basin developed, while the adjacent deep-water basin accumulated black shales. The cessation of carbonate production throughout the OAE yielded a significant drowning unconformity on the outer platform as sea-level continued to rise, while restricted, organic-rich mudstones accumulated on the inner platform under a euxinic regime. Recovery of carbonate production is characterized mainly by calcitic fauna and ooids. By the Middle Jurassic, ooids generated on the outer margin spilled into the adjacent basin forming a thick deep-water oolitic fan, and they prograded to the inner platform, reestablishing a flat-topped carbonate platform.Item Revised stratigraphic framework for the Cutoff Formation and implications for deepwater systems modified by large-scale inflections in slope angle below the shelf break(2016-05) Hurd, Greg; Kerans, C. (Charles), 1954-; Janson, Xavier; Mohrig, David; Flemings, Peter; Simo, ToniNear times of ocean anoxic events or the peaks of long-term transgressions, carbonate margins may be drowned below a backstepping platform, and preserved as a submarine edifice which demonstrates hundreds-of-meters of vertical relief above the basin floor and forms a large-scale inflection (LSI) in slope angle. This study uses outcrops in the Guadalupe Mountains Region of West Texas, a robust suite of subsurface data from the northern Delaware Basin, and previously published literature in order to illustrate how LSIs influence patterns of sediment dispersal and accumulation in carbonate systems. Outcrops of the Lower – Upper Permian Cutoff Formation reveal that processes of channelization, bypass, and slope failure associated with a drowned carbonate margin (LSI) contributed to a dramatic thickening of carbonate, shale, and sandstone strata in the basinward direction. Correlation of this unit to the equivalent shelf system reveals that bedrock channels incising the LSI served as conduits for turbidity currents throughout the transgression and much of the ensuing highstand of a 2-4 m.y. composite sequence (PCS9). In the latest highstand, an increase in the production of carbonate mud by the active shelf system contributed to the complete filling of bedrock channels and the accumulation of carbonate mud-dominated mass-transport deposits basinward of the LSI. Correlation of this shelf-to-slope framework to basinal strata of the Bone Spring and Avalon trends in the subsurface reveals a landward shift in the locus of deposition downdip of the LSI across the northern Delaware Basin which was concomitant with the transition to patterns of sediment dispersal dominated by mass-transport events. Strata associated with turbidite systems accumulate mainly near the center of the basin, and demonstrate basinward-stepping geometries along shallow slope gradients downdip of the LSI, while demonstrating aggradational geometries along steep slopes. Strata associated with mass-transport deposits accumulate near the LSI on both shallow and steep slopes. Previous studies in other basins have documented LSIs which exhibit dimensions and stratal patterns comparable to the relict platform margin in the Delaware Basin. Insights developed from this study can help to improve exploration activities in the Delaware Basin, and other basins with analogous deepwater systems.Item The sedimentology and stratigraphy of the Arab D Reservoir, Qatif Field(2011-08) Al-Nazghah, Mahmoud Hasan; Steel, R. J.; Kerans, C. (Charles), 1954-; Smith, Langhorne Bullitt, 1961-The Late Jurassic Arab D Formation in Saudi Arabia hosts the some of the world’s largest hydrocarbon reservoirs including Ghawar, the world’s largest oil field, and Khurais, the world’s largest supergiant to come into production in the last 5 years. Despite the vast oil reserves within the Arab D, and the central role of this reservoir at Ghawar in making up short-falls in global production, our understanding of the much fundamental characterization work both in terms of modern sequence stratigraphic reservoir frameworks and linked structural/fracture characterization. This study of Arab D reservoir at Qatif, immediately to the north of Ghawar, provides one of the first looks at a modern sequence analysis of this producing interval and illustrates that porosity zonations, and ultimately flow unit architecture may be substantially different than currently in use. The Arab D of the Arabian Plate is a carbonate ramp system of exceedingly low angle (<1o) developed during a low-eustatic-amplitude greenhouse Milankovitch setting. Combined macroscopic and petrographic data analysis allowed recognition of nine depositional facies: 1) spiculitic wackestone, 2) Planolites-burrowed wackestone, 3) bioturbated skeletal-peloidal packstone, 4) pelletal packstone, 5) peloidal-skeletal grain dominated packstone, 6) peloidal-skeletal grainstone, 7) skeletal-ooids grainstone, 8) cryptalgal laminites and 9) anhydrite. The depositional facies defined are used to interpret three facies tracts from deep to shallow across the ramp profile: 1) low energy sub-storm wave base (SWB) dominated facies that may illustrate disaerobic tendencies, 2) high energy within-fair-weather-wave-base ramp-crest or mid-ramp facies including foreshore and upper shoreface oolitic and skeletal grainstones that define one of the key reservoir pay zones and 3) back-barrier tidal flats consisting of cryptalgal laminites, sabkha-type anhydrites, and salina-type anhydrites. Three high frequency sequences are defined: QSEQ 1 is asymmetrical, dominated by subtidal lithofacies; and QSEQ 2 and QSEQ 3 are symmetrical and record a complex history of the fill on an intrashelf basin. Detailed cycle-scale correlations using core-based cycles and wireline log patterns allowed a cycle-scale correlation framework to be established that illustrates a north to south progradation of the Arab D reservoir strata, building landward from the Rimthan Arch. Diagenetic features observed in the Arab D reservoir include fitted fabric (chemical compaction), dolomitization, and cementation. These features play a major role altering reservoir quality properties as they essentially control fluid flow pathways which ultimately alter primary porosity and permeability.Item Shelf-to-basin architecture and facies variability of a Cretaceous intrashelf basin in the northwest Gulf of Mexico(2015-12) Sitgreaves, Jeffrey Robert; Kerans, C. (Charles), 1954-; Loucks, Robert G; Fisher, William LThe geomorphic expression of intrashelf basin systems (ISBs) and their associated facies patterns is extremely subtle, with shelf-to-basin dip angles that can average 0.3° across the slope profile. This presents an issue to stratigraphers working to understand facies variability at the reservoir-scale because the changes in stratal geometries at the shelf-to-basin transition will occur beneath the resolution of conventional subsurface datasets. Exposures along the Pecos River Canyon provide a unique opportunity to observe the transition from grain-dominated facies of the ramp crest into planktonic foraminifera mudstones/wackestones of the intrashelf basin. For this study, 475 m of detailed sections were collected at five localities and integrated with a high-resolution 3D digital outcrop model (DOM) to document the relationship between vertical facies successions and stratal geometries of the intrashelf basin profile. The high-resolution DOM provides the ability to accurately interpret the subtle depositional dips of the shelf-to-ISB profile that range from less than 0.1° to 0.7°. The development of the differential topography and facies changes associated with the formation of the Maverick ISB is attributed to differential sediment accumulation rates between active rudist-skeletal shoal formation versus deeper-water foraminiferal mudstones of the basin-center. Rudist bank deposition early in the Albian 6 Composite Sequence formed the positive topographic relief (1-3m) that led to the localization of rapid shallow-water sediment accumulation. After the development of subtle topographic expression, ensuing changes in relative sea-level promoted the development of ISB margins that were dominated by rudist faunal assemblages. The development of the ISB margin increasingly led to the differentiation between the grain-dominated facies along the margin and deposition of globigerinid mudstones in the basin-center. The extensive and largely undeformed exposures along the lower Pecos River Canyon and adjacent Amistad Reservoir provide clear evidence of the constructional differential-accumulation-driven formation for the Maverick ISB. Similar constructional models are likely for the East Texas and Fort Stockton ISBs on the Texas Comanche Shelf. Similar constructional progressions have been called on for the Bab intrashelf basin and the Natih-E Formation in the Cretaceous of the Middle East.Item Wolfcampian carbonate platform sequence stratigraphy of the southwestern Delaware Basin : Wylie Mountains, Van Horn, TX(2018-09-14) Canada, Taylor Wayne; Kerans, Charles, 1954-The Wolfcamp unconventional play in the Permian Basin is currently one of the most active drilling targets in North America. Despite its economic importance, the Early Permian Wolfcampian interval in the Delaware Basin lacks a detailed understanding of the linkage between carbonate platform sedimentation and basinal deposits. Previous studies on Wolfcampian platform carbonates in the Permian Basin and Orogrande Basin from outcrop and subsurface work have interpreted variable sequence frameworks, which suggests antecedent topography, local to regional tectonic activity, and/or other localized depositional controls likely have significant influence on sequence architecture. This study presents a stratigraphic framework from the Hueco Formation in the Wylie Mountains near Van Horn, Texas that records middle to late Wolfcampian deposition in the southwestern Delaware Basin. These inner ramp carbonate strata correlate with outer ramp to basinal deposits to the northwest in the Sierra Diablo Mountains on the western shelf of the Delaware Basin. This combined data set allows for the recognition of both eustatic and tectonic controls on carbonate platform sequence architecture during the Wolfcampian. Eleven partial measured stratigraphic sections totaling 1450 m were used to generate a 300 m composite section for the Hueco Formation exposed in the Wylie Mountains, which records middle to late Wolfcampian carbonate sedimentation overlying the early to middle Wolfcampian Powwow Formation siliciclastics. Nine depositional facies are recognized from field observations and petrographic analysis. These facies are grouped into four depositional facies tracts, including outer ramp, low energy inner ramp, high energy inner ramp, and tidal flat facies tracts. Three sequences were interpreted based on 1D and 3D facies and cycle stacking pattern analysis, including two middle Wolfcampian sequences and one late Wolfcampian sequence. The late Wolfcampian sequence backsteps relative to the middle Wolfcampian sequences, consistent with observations of Hueco Formation sequence architectures in outcrop around the Diablo Platform and in the subsurface. The top of the Hueco Formation in the Wylie Mountains is bounded by an unconformity caused by a relative sea level of fall of at least 40-45 m at the end of the Wolfcampian which was succeeded by an influx of siliciclastics in the early Leonardian. Additionally, extensive brecciation and deformation have been documented in the lower two sequences. This deformation is interpreted to be related to dissolution of interbedded evaporites associated with tidal flat deposition in the upper portion of the lowermost sequence. Structural data suggests that late Wolfcampian tectonism may also have influenced deformation in this stratigraphic interval. The primary contribution of this study is improved resolution of Wolfcampian platform sequence stratigraphy and relative sea level change in the southwestern Delaware Basin. Identifying periods of sea level lowstand in the platform record is important because these periods are often associated with siliciclastic bypass of the shelf and increased sedimentation to the basin. Due to the generally low porosity and permeability of the basinal Wolfcamp Formation, these bypass events are critical for the development of coarse grained or siliciclastic sand rich units that can serve as highly productive Wolfcamp oil and gas reservoirs. The end-Wolfcampian sea level fall and associated conglomeratic unit documented in this study at the top of the Hueco Formation suggests a period of siliciclastic bypass in the earliest Leonardian in the southwestern Delaware Basin.Item Wolfcampian shelf-to-basin stratigraphic framework of the Central Basin Platform and Midland Basin, Andrews County, Texas(2019-09-12) Draper, Cody Hale; Kerans, C. (Charles), 1954-Despite collection of extensive subsurface data, the icehouse climatic forcing and tectonic modification of the Wolfcampian Hueco carbonates have frustrated attempts to adequately link shelfal and time-equivalent basinal depositional patterns. This study attempts to create a stratigraphic framework for correlating eastern Central Basin Platform Hueco shelfal carbonates and Wolfcamp Shale basinal stratigraphy by generating core-based vertical facies successions, wireline log and seismic-derived stratal architecture and sedimentation patterns, and isopachs along a contemporaneous shelf-to-basin depositional profile. Where available, fusulinid biostratigraphic control from the Midland Farms field area, provided by Dr. Greg Wahlman, constrained correlations, as did basinal palynologic data collected by Fasken Oil and Ranch. A total of 1,569 ft of core was described from the Midland Farms Deep Unit132, 101, 135, and 74 wells, the Midland Farms Unit 37 and AX-5, the Midland Farms Operating 3, and the Fasken Fee AL-910 and BI-307 wells. Thirteen depositional facies are recognized, which are grouped into seven facies tracts. Two depositional sequences were interpreted on the basis of 1D core lithofacies stacking patterns and were linked to selected shelf-to-basin log sections and seismic stratigraphic relationships. Shelf-to-basin correlations were made using a volume of nearly 2000 well-logs and 500 sq mi of 3D seismic data. The two major composite sequences recognized are termed the Lower Hueco and the Upper Hueco. The transgressive systems tract (TST) of the Lower Hueco Sequence LW-1 is characterized by phylloid algal patch reefs and associated bioclastic-oolitic grainstones that transition around the maximum flooding surface to skeletal packstones. The highstand systems tract of LW-1 records a shallowing-upward succession of slope, outer platform, and shelf crest facies. The LW-1 tract is capped by paleosols overlying shelf crest facies. The shelfal LW-1 is correlative to interbedded sediment-gravity flows and organic-rich siliciclastic mudstones in the Midland Basin, which represent platform shedding in conjunction with hemipelagic sedimentation. Despite the significant exposure recorded at the top LW-1, the mid-Wolfcamp unconformity is not identified as a significant erosive surface in this study, as suggested in other studies. The correlative mid-Wolfcampian interval in the adjacent basin is a stacked gravity flow complex that might represent a period of shelfal erosion related to exposure and/or tectonism. The transgressive systems tract of the Upper Hueco sequence UW-1 shows aggradation over the upper LW-1. The transgressive facies tract deepens to skeletal wackestone and is overlain by a thicker shallowing upward highstand systems tract that culminates in a large accumulation of grain-dominated packstone to grainstone facies which show evidence of subaerial exposure at the top Wolfcamp sequence boundary. This Wolfcampian-Leonardian unconformity is expressed by uppermost Hueco grainstones overlain by Leonardian deepwater basinal mudstones and gravity flows. Contemporaneous basinal sedimentation is mostly organic-rich siliciclastic mudstone with scarce sediment-gravity flow deposits. This study contributes an integrated model for the shelf-to-basin stratigraphic architecture of the Wolfcampian Hueco Group on the Central Basin Platform and the equivalent Wolfcamp Shale of the adjacent Midland Basin. Identifying controls on basinal sedimentation is important because allochthonous carbonate debris flows in the western Midland Basin can act both as drilling hazards and as reservoirs. Understanding the connections between the Hueco Group shelfal carbonate facies and sequences to the adjacent basinal stratigraphy could greatly improve reservoir prediction and development in the adjacent Wolfcamp Shale play.