Browsing by Subject "Pennsylvanian"
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Item Analysis of the effects of carbonate mounds on associated stratal geometry and fracture development, Sacramento Mountains, New Mexico, USA(2016-12) Tinker, Nathan Scott; Janson, Xavier; Zahm, Christopher Kent; Kerans, Charles; Fisher, William LThe objective of this research is an integrated structural‐stratigraphic analysis of compaction‐related fracturing in carbonate mounds and associated cover strata. The influence of early-cemented carbonate mounds on subsequent sediment deposition (such as creation of hard substrates and topographic relief) is relatively well-understood. The effect of early-cemented carbonate mounds during burial, however, has not been studied in detail. Early marine cementation of mounds enhances mechanical rigidity, which reduces mound compaction during burial as compared to less-resistant sediments surrounding and overlying the mound. This rigidity difference facilitates differential compaction of sediments overlying the mound, which are warped over the inflection point created by the mound topography. This study hypothesizes that there is a measurable increase in fracture intensity associated with differential compaction above early-lithified carbonate mounds. Thus, this work analyzes and quantifies the effects of differential compaction on stratal geometry, mechanical stratigraphy, and fracture development in Mississippian strata overlying carbonate mounds which are well-exposed in the Sacramento Mountains in southeast New Mexico. Methods employed in this study are drawn from structural geology, sedimentology, petrography, and remote sensing in an effort to adequately determine facies, examine fracture characteristics (e.g. size, orientation, and intensity), and to better understand which process(es) most directly control those characteristics (e.g. host rock facies type, diagenesis, bed thickness, mound proximity, mound size). Innovative methods of outcrop characterization such as high-resolution gigapan photography and unmanned aerial vehicle (UAV) photography were combined with photogrammetric techniques to create photo-realistic 3D outcrop models. The resulting models enabled a cost-effective, more detailed, less-distorted, and more comprehensive interpretation compared to previous methods, and improved understanding of the relationship between stratigraphy, rock mechanical evolution, and structural deformation in carbonate mound systems. Field work documented facies, stratal geometries, folds, faults, and fracture sets which validated observations and characterizations made using high-resolution field photographs and 3D outcrop models. Results of this work show that paleotopographic relief which has been early lithified (in this instance, Mississippian carbonate mounds) directly controls fracture development and overlying stratal geometry, in that there is a significant increase in tension fracture (mode 1) intensity above pre-existing rigid structures and over-steepening of bed dips beyond an expected and reasonable angle of repose. Additionally, this work outlines a multi-stage tectonostratigraphic sequence of the development of the stratigraphically complex Teepee Mound assemblage based on field observations of facies, fractures, stratal geometries, and diagenetic effects (e.g. cementation, compaction, and chertification), which includes new evidence of late-Mississippian tectonic compression. This result emphasizes the importance of understanding both syndepositional and post-depositional processes in outcrop characterization. Specifically, syndepositional processes establish the original mechanical stratigraphy and control the formation and propagation of early mechanical discontinuities, which in turn set up the fabric of weaknesses preferentially utilized by later fracture development. Post-depositional mechanical and diagenetic processes alter mechanical stratigraphy and rock brittleness, and thus influence fracture propagation through time.Item Biogeochemical Evolution of the Western Interior Basin of North America during a Kasimovian Highstand and Regression(2012-02-14) Banerjee, SikharThe purpose of this study is to identify and analyze the geochemical facies of the Hushpuckney Shale using XRF scanning data and the bioturbation indices, which will contribute to a better understanding of the biogeochemical environment prevalent during the deposition of the Hushpuckney Shale. The Hushpuckney Shale Member of the Swope Formation (Kasimovian Stage) preserved in KGS Spencer core 2 - 6, consists of a black shale submember overlain by bioturbated gray shale. Millimeter-scale core description and analysis of XRF scanning data enables identification of geochemical facies within the study core and contributes to understanding the environment of shale deposition. The XRF spectrometer produces X-ray image of the core and abundance values of selected major and trace elements, including iron (Fe), calcium (Ca), sulfur (S), molybdenum (Mo), zinc (Zn), vanadium (V), chromium (Cr), copper (Cu), nickel (Ni), titanium (Ti), zircon (Zr), potassium (K) and phosphorous (P). Canfield and Thamdrup's (2009) classification of geochemical environments is used to recognize oxic/aerobic, manganous-nitrogenous, ferruginous and sulfidic facies within the black shale submember. A modification of Droser and Bottjer's (1986) semi-quantitative field classification of bioturbation is used to identify facies variations within the gray shale submember. Abundance of apatite nodules and lamina in the black shale submember of the study core suggest that black shale sediments accumulated slowly in a sediment-starved basin. A high abundance of sulfide-scavenged elements, including Mo, Zn, V, Ni and Cr, identifies the sulfidic facies in the black shale submember, and indicates deposition in an oxygen-depleted environment with a high concentration of hydrogen sulfide. The overlying ferruginous facies has lower abundances of sulfide-scavenged elements and lacks cryptic Fe-laminations. The uppermost black shale submember facies, the manganous-nitrogenous facies, has cryptic Fe laminations and a relatively high P/Ca ratio. Abundance of cryptic iron laminations and apatite nodules and lamina indicates the syngenetic deposition of iron and phosphate due to Fe-P coupling mechanism. The gray shale submember is burrowed, indicating deposition under oxygenated conditions. Bioturbation indices reveal the variations in the intensity and nature of burrows within the gray shale, which corresponds to the changes in the depositional environment that may be related to the rise and fall of sea-level.Item Conodonts of the Desmoinesian (middle Pennsylvanian) Lost Branch Formation, Oklahoma and Kansas(2005-05) Rosscoe, Steven J.; Barrick, Jim; Chatterjee, Sankar; Lehman, ThomasThe Lost Branch Formation of Oklahoma and Kansas was deposited during the last Desmoinesian (Middle Pennsylvanian) transgressive-regressive cycle of the Midcontinent Sea. The regression of the Midcontinent Sea during Lost Branch deposition records the final occurrences of the conodont genera Neognathodus and Swadelina as well as numerous ammonoids, the Desmoinesian brachiopod Mesolobus, the fusulinid Beedina, and some sponges and palynomorphs. The Lost Branch Formation begins at the top of the Dawson Coal in a sandy shale deposit of the Upper Holdenville Shale. The transgression of the Midcontinent Sea is recorded in the Upper Holdenville Shale, the Homer School Limestone, and the Nuyaka Creek Black Shale Bed. The regression of the Midcontinent Sea is recorded in the “offshore” Upper Holdenville Shale, the Glenpool Limestone, and the upper sandy shale deposit of the Upper Holdenville Shale. The lower outside shale is characterized by a conodont fauna of Idiognathodus species A, Adetognathodus lautus, and Idioprioniodus. As the transgression progressed there was further diversification of the fauna. The Homer School Limestone has the first appearance of Neognathodus dilatus dilatus, N. expansus expansus, and Hindeodus minutus. Specimens of I. expansus, Swadelina nodocarinata, N. dilatus bifurcatus, N. roundyi, N. expansus subspecies B, Gondolella magna, G. denuda, grooved morphotypes of I. expansus, and rounded and nodose morphotypes of Sw. nodocarinata are found in the overlying Nuyaka Creek Shale. The Nuyaka Creek Shale is the only interval where G. magna, G. denuda, and the rounded and nodose morphotypes of Sw. nodocarinata are recovered. The regression of the Midcontinent Sea is reflected in the conodont fauna by a loss of diversity. In the offshore shale of the Upper Holdenville Shale the conodonts Swadelina nodocarinata and Hindeodus minutus are absent. The Glenpool Limestone lacks the grooved morphotype of Idiognathodus expansus, Neognathodus dilatus dilatus, N. dilatus bifurcatus, N. roundyi, N. expansus expansus, N. expansus subspecies B, and Idioprioniodus. The only species found in the upper outside shale are I. expansus, I. species A, and Adetognathodus lautus. A paleoecological model for the Lost Branch Formation is presented that shows species tolerant of turbid waters living in the surface waters of the sea, and species preferring clear waters appearing only in the deeper offshore intervals. Gondolella and Swadelina dominate in clear-water assemblage, while Idiognathodus dominates in turbid waters. The well-preserved conodont fauna and easy clay-shale processing of the Lost Branch Formation provided an opportunity to study conodont Pa element function as it relates to microwear and element morphology. The original texture of blade denticles is fibrous, while the bar of the blade is smooth and featureless. The original texture of the platform forms a polygonal texture on the oral surface and a smooth texture on the aboral surface. Abrasive microwear removes original texture from the elements. Reshaping microwear takes element features, like denticles and ridges, and reshapes them into asymmetric surfaces indicative of their functional significance. By comparing the morphology of an element with the areas of intense microwear it was determined that the Pa element of Idiognathodus expansus served a food-processing and a food-transport function. The blade of the element pushed large food particles onto the ventral platform for crushing. The blade may also have sliced larger food particles. The ventral platform served a crushing and bruising function. The dorsal platform of the element pushed food back to the ventral platform for further processing.Item Conodonts of the Desmoinesian Lost Branch Formation, Oklahoma and Kansas(Texas Tech University, 2005-05) Rosscoe, Steven J.; Barrick, James E.; Chatterjee, Sankar; Lehman, ThomasThe Lost Branch Formation of Oklahoma and Kansas was deposited during the last Desmoinesian (Middle Pennsylvanian) transgressive-regressive cycle of the Midcontinent Sea. The regression of the Midcontinent Sea during Lost Branch deposition records the final occurrences of the conodont genera Neognathodus and Swadelina as well as numerous ammonoids, the Desmoinesian brachiopod Mesolobus, the fusulinid Beedina, and some sponges and palynomorphs. The Lost Branch Formation begins at the top of the Dawson Coal in a sandy shale deposit of the Upper Holdenville Shale. The transgression of the Midcontinent Sea is recorded in the Upper Holdenville Shale, the Homer School Limestone, and the Nuyaka Creek Black Shale Bed. The regression of the Midcontinent Sea is recorded in the “offshore” Upper Holdenville Shale, the Glenpool Limestone, and the upper sandy shale deposit of the Upper Holdenville Shale. The lower outside shale is characterized by a conodont fauna of Idiognathodus species A, Adetognathodus lautus, and Idioprioniodus. As the transgression progressed there was further diversification of the fauna. The Homer School Limestone has the first appearance of Neognathodus dilatus dilatus, N. expansus expansus, and Hindeodus minutus. Specimens of I. expansus, Swadelina nodocarinata, N. dilatus bifurcatus, N. roundyi, N. expansus subspecies B, Gondolella magna, G. denuda, grooved morphotypes of I. expansus, and rounded and nodose morphotypes of Sw. nodocarinata are found in the overlying Nuyaka Creek Shale. The Nuyaka Creek Shale is the only interval where G. magna, G. denuda, and the rounded and nodose morphotypes of Sw. nodocarinata are recovered. The regression of the Midcontinent Sea is reflected in the conodont fauna by a loss of diversity. In the offshore shale of the Upper Holdenville Shale the conodonts Swadelina nodocarinata and Hindeodus minutus are absent. The Glenpool Limestone lacks the grooved morphotype of Idiognathodus expansus, Neognathodus dilatus dilatus, N. dilatus bifurcatus, N. roundyi, N. expansus expansus, N. expansus subspecies B, and Idioprioniodus. The only species found in the upper outside shale are I. expansus, I. species A, and Adetognathodus lautus. A paleoecological model for the Lost Branch Formation is presented that shows species tolerant of turbid waters living in the surface waters of the sea, and species preferring clear waters appearing only in the deeper offshore intervals. Gondolella and Swadelina dominate in clear-water assemblage, while Idiognathodus dominates in turbid waters. The well-preserved conodont fauna and easy clay-shale processing of the Lost Branch Formation provided an opportunity to study conodont Pa element function as it relates to microwear and element morphology. The original texture of blade denticles is fibrous, while the bar of the blade is smooth and featureless. The original texture of the platform forms a polygonal texture on the oral surface and a smooth texture on the aboral surface. Abrasive microwear removes original texture from the elements. Reshaping microwear takes element features, like denticles and ridges, and reshapes them into asymmetric surfaces indicative of their functional significance. By comparing the morphology of an element with the areas of intense microwear it was determined that the Pa element of Idiognathodus expansus served a food-processing and a food-transport function. The blade of the element pushed large food particles onto the ventral platform for crushing. The blade may also have sliced larger food particles. The ventral platform served a crushing and bruising function. The dorsal platform of the element pushed food back to the ventral platform for further processing.Item Description of Alethopteris from the Williamson #3 Mine, Lucas County, Iowa: anatomical variation, diversity, paleoecology(Texas A&M University, 2004-09-30) Slone, Elizabeth Dunbar JonesFor more than 100 years, Pennsylvanian permineralized peats have been studied for their exceptionally preserved plant remains. Late Atokan-early Desmoinesian coal balls from the Williamson # 3 deposit in south-central Iowa were preserved by the permineralization of soluble carbonate into pores in the peat and plant cells creating carbonate nodules. These nodules, referred to as coal balls, protect the plant remains from the compaction associated with coal allowing for the analysis of anatomically preserved plants from Pennsylvanian. The Williamson #3 deposit is unusual because it is dominated by a diverse assemblage of gymnosperms. Other deposits of similar age in Iowa are dominated by a mixture of cordaitalean gymnosperms, tree-ferns, and medullosan gymnosperms; while, other North American deposits are dominated by lycopsids with tree-ferns and seed-ferns as the subdominant vegetation. Because vegetation types differ with environment, analysis of the Alethopteris pinnules from the Williamson #3 Mine provides insight into the ecology of a peat-producing swamp during the Pennsylvanian, and allows for the comparison of this deposit to others in North America. The focus of this study is the description of a distinct morphotype of Alethopteris from the Williamson #3 Mine. Alethopteris pinnules described from other mines were used to compile a traits list and compare measured and descriptive characteristics. The objective of this study is to gain a better understanding of changes in swamp vegetation during the Pennsylvanian, and the effect of environmental variation on the dominant vegetation in peat swamps.Item High-Resolution Carbon Isotope Stratigraphy, Pennsylvanian Snaky Canyon Formation, East-Central Idaho: Implications for Regional and Global Correlations(2012-07-16) Jolley, CaseyNearly 550 samples of fine grained carbonates, collected every 0.5 to 1.0 m from the Bloom Member of the Snaky Canyon Formation at Gallagher Peak, Idaho, were analyzed to determine the high-resolution carbon isotope stratigraphy. To constrain for diagenesis, thin sections were petrographically analyzed and viewed using cathodoluminescence microscopy. Chemical analyses were performed using an electron microprobe. Average delta18O and delta13C values from the Bloom Member are -4.5% +/- 1.6% (1 sigma) and 2.1% +/- 1.1%, respectively. Maximum delta13C values are about 1% higher for the Desmoinesian and Missourian than the Morrowan and Atokan, similar to results from the Yukon Territory. delta18O and delta13C values are lowest for crystalline mosaic limestones and siltstones, moderate for packstones, wackestones, and mudstones, and highest for boundstones and grainstones. The delta13C profile from Gallagher Peak consists of high frequency 1% oscillations with several larger excursions. No large delta13C increase at the base of the section suggests the Mid-Carboniferous boundary is in the underlying Bluebird Mountain formation. delta13C of Gallagher Peak and Arrow Canyon, NV, correlate well from 318 to 310 Ma, but correlation becomes more difficult around 310 Ma. This may result from increased restriction of the Snaky Canyon platform beginning in the Desmoinesian. Most of the short term (<1 Ma) isotopic excursions are the result of diagenesis. Two of the largest negative excursions at Gallagher Peak correlate with two large negative excursions at Big Hatchet Peak, NM, possibly due to sea level lowstands of the Desmoinesian. Phylloid algal mounds at Gallagher Peak are associated with positive excursions because of original aragonite composition and increased open marine influence. Positive excursions related to other facies characteristics also result from increased marine influence. The delta13C curve for the upper half of Gallagher Peak contains three repeated cycles of increasing delta13C over 1-1.5 Ma, which are possibly related to long-term sea level fluctuations. Given the complexity of each local environment, without detailed biostratigraphy, detailed rock descriptions, and analysis of the various rock components, delta13C stratigraphy of whole rocks can be misinterpreted.Item Idiognathodus and Streptognathodus species from the lost branch to Dewey sequences (middle-upper Pennsylvanian) of the midcontinent basin, North America(Texas Tech University, 2008-08) Rosscoe, Steven J.; Barrick, James E.; Holterhoff, Peter; Lehman, Thomas; Chatterjee, Sankar; Asquith, George B.A function-based taxonomic method was developed to revise Idiognathodus and Streptognathodus species from the Lost Branch Sequence (latest Desmoinesian) to the Dewey Sequence (Middle Missourian). The new method relies on characters significant to the food-processing function of the P1 element. The chief controls over food processing efficiency are surface area and surface roughness. The two primary morphological features affecting surface area are the shape and size of the rostral lobe and the shape and size of the caudal lobe. Ornamentation of the ventral and dorsal platform affects surface roughness. Use of these three features as the major characters to discriminate species resulted in the description of twenty-four species of Idiognathodus and five species of Streptognathodus. A regional zonation for the Midcontinent Basin (North America; Barrick et al. 2004) was revised based on the new taxonomic scheme for Swadelina, Idiognathodus and Streptognathodus. Five zones and five subzones were erected within the study interval. The Swadelina nodocarinata zone of Barrick et al. (2004) includes the Lost Branch Sequence. The new Idiognathodus sulciferus zone includes the Hepler Sequence. The I. eccentricus zone comprises the Shale Hill and Hertha sequences. The revised I. cancellosus zone (two subzones) includes the Swope, Mound Valley, and Dennis sequences. The S. gracilis zone (three subzones) comprises the Hogshooter, Cherryvale, and Dewey sequences. The merit of three proposals for levels characteristic of the boundary between the global Moscovian and Kasimovian Stages are discussed. The first level is the traditional base of the Missourian (near the traditional base of the Kasimovian) based on the disappearance of the last species of Swadelina. The second level is based on the first appearance of I. sagittalis (not found in the Midcontinent Basin), which can be approximated using the appearance of distinctive forms of I. swadei, I. turbatus, or I. eccentricus (near the redefined base of the Missourian). The third level is at the highstand in the Swope Sequence and marks the first co-occurrence of I. cancellosus and I. biliratus, two of the few species that may have had global distribution.Item Lithofacies and stacking architecture of a middle Pennsylvanian inner platform, bug scuffle member, gobbler formation, Fresnal Canyon, New Mexico(2007-12) LaPeter, Danielle; Holterhoff, Peter; Lehman, Thomas; Barrick, James E.The Bug Scuffle Member of the Gobbler Formation is part of an extensive Middle Pennsylvanian carbonate platform that accreted on the western edge of the Pedernal Uplift. A section exposed in Fresnal Canyon of the Sacramento Mountains, New Mexico occupies an inner platform position kilometers from the platform margin. The uppermost 173m of the Bug Scuffle was examined in two continuous sections to identify the lithofacies and stratal architectures of this inner platform icehouse system. Two composite sequences were identified based on facies and bedset thickness trends and a sandstone filled incised valley representing the greatest fall in sea level. Only the three uppermost high frequency sequences (HFS) of the lower composite sequence are exposed. These sequences are comparatively thick (20-30m) and are bounded by weak to well developed exposure surfaces. Parasequences and parasequence sets are poorly developed, with lithofacies dominated by deep to high - energy shallow marine lithofacies. The upper composite sequence is composed of at least 11 HFS. Contrary to many described icehouse platforms, exposure surfaces are not developed between the lower HFS such that they might be better described as parasequence sets (PSS). The lowest PSS is dominated by a deep platform crinoidal lithofacies and is considered the Transgressive Sequence Set. The overlying parasequence sets are dominated by phylloid algal and diverse skeletal lithofacies. These thick (15-20m) PSS are overlain by packages of distinctly different lithofacies and architecture that are composed of a phylloid unit, capped by a peloidal - coated grain grainstone and/or a distinctive gastropod lithofacies, and bounded by well developed exposure surfaces. These thin (2-10m) packages represent classic icehouse HFS. This evolution from thick PSS dominated by open marine facies to thin HFS containing significant restricted marine facies with well developed exposure surfaces reflects the long – term loss of accommodation space on the platform and represents the transition from early to late Highstand Sequence Set. This example highlights that a range of stratal motifs may characterize Late Paleozoic icehouse platforms and that classic icehouse HFS may be just one end member within a given platform.Item Lithofacies, depositional environments, and sequence stratigraphy of the Pennsylvanian (Morrowan-Atokan) Marble Falls Formation, Central Texas(2013-08) Wood, Stephanie Grace; Ruppel, Stephen C.; Loucks, R. G.The Pennsylvanian Marble Falls Formation in the Llano Uplift region of the southern Fort Worth Basin (Central Texas) is a Morrowan-Atokan mixed carbonate-siliciclastic unit whose deposition was influenced by icehouse glacioeustatic sea-level fluctuations and foreland basin tectonics. Previous interpretations of the Marble Falls Formation focused on outcrop data at the fringes of the Llano Uplift. This study uses a series of 21 cores to create a facies architectural model, depositional environmental interpretation, and regional sequence stratigraphic framework. On the basis of core data, the study area is interpreted to have been deposited in a ramp setting with a shallower water upper ramp area to the south and a deeper water basin setting to the north. Analysis of cores and thin sections identified 14 inner ramp to basin facies. Dominant facies are: (1) burrowed sponge spicule packstone, (2) algal grain-dominated packstone to grainstone, (3) skeletal foraminiferal wackestone, and (4) argillaceous mudstone to clay shale. Facies stacking patterns were correlated and combined with chemostratigraphic data to improve interpretations of the unit’s depositional history and form an integrated regional model. The Marble Falls section was deposited during Pennsylvanian icehouse times in a part of the Fort Worth Basin with active horst and graben structures developing in response to the Ouachita Orogeny. The resulting depositional cycles reflect high-frequency sea-level fluctuations and are divided into 3 sequences. Sequence 1 represents aggradational ramp deposition truncated by a major glacioeustatic sea-level fall near the Morrowan-Atokan boundary (SB1). This fall shifted accommodation basinward and previously distal areas were sites of carbonate HST in Sequence 2 deposition following a short TST phase. Sequence 3 represents the final phase of carbonate accumulation that was diachronously drowned by Smithwick siliciclastics enhanced by horst and graben faulting. These findings contribute to our understanding of the depositional response to glacioeustatic sea-level changes during the Pennsylvanian and can also form the basis for constructing a sedimentological and facies analog for Morrowan to Atokan shallow- to deepwater carbonates in the Permian Basin and the northern Fort Worth Basin.Item Paleoclimate and geochemical variation of the Stark Shale Member, Dennis Formation (Missourian), Mid-continent North America(2008-08) Akanbi, Oluwatosin T.; Holterhoff, Peter; Asquith, George B.; Barnes, Calvin G.The Upper Pennsylvanian Stark Shale is the core shale of the Dennis cyclothem. Bottom-water oxygenation is an important control on the preservation and quality of sedimentary organic matter and may influence the enrichments of trace elements (TEs). Detailed sample intervals were collected from four cores of the Stark Shale from Nemaha Uplift in Kansas (uplift cores) to the Forest City Basin in Missouri (basin cores). The samples were analyzed for major and trace elements, organic carbon and clay mineralogy. X-ray diffraction showed that illite, quartz and pyrite are the predominant minerals. Detrital elements (Si, Al, Zr and Ti) showed higher abundances of clay in the basin compared to the uplift. The weathering index and chemical index of alteration both indicate that source minerals of the shale were highly weathered. The basin core showed a more mature source compared to the uplift cores. Core shales were deposited during maximum transgression and may have high or low TOC depending on bottom-water oxygen levels. In high TOC cores (TOC > 10 %), abundances of V, Zn, Cr, Ni and Mo showed a moderate to strong correlation with TOC in the basin cores. The Heinen core (uplift) showed no significant correlation with the above elements at high TOCs. Low TOC shale (Emery core) showed no significant correlation with all trace elements (TEs). TEs enrichments were classified into TEs of euxinic affinity (V, Mo) and TEs associated with organic matter (Cu, Ni, Zn). Covariation of TEs of strong euxinic affinity with TOC were observed to be stronger in the basin core. Redox geochemical ratios V/Cr, TEs, V/ (V+Ni) and V-Mo covariation indicate euxinic conditions in the basin. Anoxic ¡V oxic conditions seem dominant in the uplift cores. Rock eval data showed a mixture of type I and II kerogen indicating terrestrial and marine organic matter. These data suggest that the controlling factors in the distribution of elements regionally and stratigraphically within the Stark Shale are: -Degree of weathering before deposition -Paleoredox conditions in the depositional environment -The composition of the organic -Settling time of detrital influx -Paleoclimate and paleogeographic conditions during deposition.Item Paradox Basin source rock, southeastern Utah : organic geochemical characterization of Gothic and Chimney Rock units, Ismay and Desert Creek zones, within a sequence stratigraphic framework(1995-08) Tischler, Keith Louris; Kirkland, Brenda Lee, 1959-The Chimney Rock and Gothic units of the Pennsylvanian Paradox Formation have long been considered source rocks for the rich hydrocarbon fields of southeastern Utah. Fundamental questions about these units include: source and nature of the organic material, source rock character, and position of the source rocks in the existing sequence stratigraphic framework. The Chimney Rock and Gothic, historically referred to as shales, are composed of calcareous mudstone, dolomudstone, and calcareous sandstone. High total organic carbon (TOC) values are more closely linked to sequence stratigraphic position than lithology. In the Gothic, TOC values decrease upwards. Terrestrial maceral content increases upwards in both the Gothic and the Chimney Rock as determined through point-count and qualitative observation. Pyrolysis indicates that greater than anticipated terrestrial influence is present and is consistent for all wells. No distinct difference in geochemical character exists between the two units. Sequence stratigraphic boundaries appear to be as good as, or better, than traditional lithostratigraphic boundaries for determining high TOC occurrence and source rock location. Within repetitive major sea level transgressions the organic matter that fed the basin evolved from a marine-dominated signature to a terrestrial-dominated signature.