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Sedimentological re-interpretation of the early cretaceous oil reservoir in the Northern Bredasdorp Basin, offshore South AfricaAsiashu, Mudau January 2015 (has links)
>Magister Scientiae - MSc / This study was aimed at determining the sedimentary environment, its evolution and facies areal distribution of the Upper Shallow Marine (USM, Late Valanginian). The study was conducted in wells E-S1, F-AH4 and E-W1 in the Bredasdorp basin between E-M and F-AH fields, located in a basinwards transect roughly transverse to the palaeocoast. The wells were studied by logging all the cores in detail between the chosen intervals, followed by facies analysis. Each core log was tied with its respective gamma ray and resistivity well logs. The logs were then correlated based on their log signatures, trends and facies interpretation. The Gamma ray logs show a fining-upwards and coarsening-upwards trend (“hour-glass shape”) in E-S1 and F-AH4 while in E-W1 it shows more accommodation space. These trends are believed to have been influenced by relative sea level changes, such as transgression and regression. Facies analysis identified seven facies in the study area: Facies A, B, C, D, E, F and G. Facies A, B and C were interpreted as fair-weather and storm deposits of the offshore-transition zone, shoreface and foreshore respectively. Facies D was considered as lagoonal mud deposits, while Facies E and F were interpreted as tidal channel and tidal bar deposits respectively. Finally Facies G was considered as fluvial channel deposits. The facies inferred that the sedimentary environment of the study area is a wave-dominated estuary or an Island-bar lagoon system. This led to the production of a conceptual model showing the possible locations for the three wells in the Island bar-lagoon system. The conceptual model inferred the previous findings from PGS (1999) report, that the Upper Shallow Marine beds were deposited in a tidal/estuarine to shoreface setting. This model also supports the findings of Magobiyane (2014), which proposed a wave-dominated estuary for the Upper Shallow Marine reservoir between E-M and F-AH fields, located west of the study area.
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Fácies sedimentares e proveniência da Formação Bebedouro, Neoproterozóico (BA) / Sedimentary facies and provenance of the Bebedouro Formation, Neoproterozoic (BA)Felipe Torres Figueiredo 19 December 2008 (has links)
O registro sedimentar do final do Neoproterozóico tem sido alvo de intensas pesquisas desde a retomada dos modelos de glaciação extrema e rápidas mudanças climáticas, com destaque para a hipótese Snowball Earth. Esses modelos baseiam-se na identificação, em todos os continentes, de sucessões neoproterozóicas que compreendem diamictitos sobrepostos por carbonatos, interpretados, respectivamente, como depósitos glaciais e pós-glaciais. A fim de explicar o caráter global da distribuição dos diamictitos e sua aparente transição rápida para carbonatos, alguns autores propuseram hipóteses de que o planeta teria sofrido mudanças climáticas extremas, e de que estas teriam ocorrido na forma de três eventos glaciais durante o Criogeniano e o Ediacarano (Sturtian, Marinoan e Gaskiers). Outros autores consideram que a correlação global destes depósitos pode ser explicada pelo modelo Zipper-rift, que considera a existência de geleiras de altitude, condicionadas pelo soerguimento das ombreiras de sistemas de rifts, supostamente abertos durante a fragmentação do supercontinente Rodínia. Apesar de intensos esforços para correlacionar estas sucessões, ainda persistem dúvidas a esse respeito. Isto se deve, em parte, à ênfase dada ao estudo das sucessões carbonáticas sobrejacentes, em detrimento das pesquisas nos próprios diamictitos. Dentro desse contexto, o presente estudo tem como alvo a sucessão sedimentar inferior do Grupo Una, interpretada como representativa do evento Sturtian, localizada na porção norte do Cráton do São Francisco, Bahia, Brasil. Foram realizadas análises de fácies, de associações de fácies e de proveniência sedimentar com o objetivo de testar os modelos de dinâmica glacial propostos para o período e avaliar localmente o caráter da transição entre diamictitos e carbonatos. O Grupo Una apresenta área de afloramento de aproximadamente 16.000 km2 e compreende depósitos sedimentares isentos de metamorfismo, que se encontram distribuídos em três sinclinais (Salitre, Irecê e Una-Utinga). Na base, compreende arenitos, diamictitos e pelitos com clastos esparsos da Formação Bebedouro, interpretada em termos das associações de fácies (1) Transicional marinha influenciada por banquisas e/ou icebergs e (2) Marinha de plataforma continental. A passagem para a unidade de topo ocorre de forma brusca, em contato plano com dolomitos maciços a laminados com pseudomorfos de aragonita, sobrepostos por ritmitos de calcarenitos e calcilutitos com laminação planoparalela, laminação cruzada cavalgante, estromatólitos e slumps, dividos nas associações de fácies de (3) Plataforma carbonática rasa influenciada por ondas e (4) Rampa carbonática influenciada por escorregamentos. Dados de contagem de litotipos em clastos e seções delgadas indicam variação lateral de proveniência, com fontes particulares para cada uma das áreas investigadas. Essa variação é interpretada como resultado de aporte de geleiras de vale ou do tipo outlet na margem glacio-marinha, indicando a presença de altos topográficos. A datação U-Pb SHRIMP de seixos revelou predomínio de fontes próximas, com contribuição local de fontes mais distantes, sugerindo alguma deposição a partir de icebergs provenientes da margem oposta da bacia, talvez a mais de 150 km à leste, sobre os Blocos Jequié ou Itabuna-Salvador- Curaçá. Datações de cristais de zircão detrítico da matriz dos diamictitos confirmam os dados obtidos a partir de seixos, e permitem a identificação de uma fonte jovem, de fora do cráton, com cerca de 850 Ma. Esse dado limita a idade máxima da unidade. Ainda que a proveniência da Formação Bebedouro indique a existência de altos topográficos adjacentes à bacia, a ausência de controles tectônicos na sedimentação, evidenciada pela grande persistência lateral de sistemas deposicionais com pouca variação de espessura, não corrobora o modelo de desenvolvimento das geleiras neoproterozóicas em margens de sistemas de rifts. / The sedimentary record of Neoproterozoic age has become a major subject of research since the rebirth of the models of extreme glaciation and rapid climatic changes for the period, including the Snowball Earth hypothesis. These models are founded on the identification, in all continents, of Neoproterozoic diamictites directly overlain by carbonates, which are interpreted respectively as glacial and post-glacial deposits. In order to explain the global distribution of diamictites and their apparently rapid transition to carbonates, some authors have proposed hypothesis of extreme climatic change related to three glacial episodes during the Cryogenian and the Ediacaran (Sturtian, Marinoan e Gaskiers). On the other hand, some authors consider that the global correlation of these deposits is the consequence of altitude-nucleated glaciers formed on the shoulders of rift systems during the breakup of the Rodinia Supercontinent, in what is called the Zipper-rift model. Despite the efforts to establish a chronological correlation among the several successions, many questions still persist, in part due to the great emphasis on the study of the carbonate successions and the scarce work on the diamictites. The present work aims at studding the lower section of the Una Group, interpreted as related to the Sturtian glacial event and located in the northern region of the São Francisco Craton, Bahia, Brazil. Facies, facies associations and clastic provenance analysis were performed in order to test the current models on the Neoproterozoic glacial dynamics and to locally evaluate the passage from diamictites to carbonates. The Una Group crops out in a area of approximately 16,000 km2 and is composed of sedimentary deposits without metamorphism, preserved in three synclinal folds (Salitre, Irece e Una-Utinga). At its base, the unit comprises sandstones, diamictites and mudstones with dropstones grouped into the Bebedouro Formation. This formation comprises two facies associations: (1) Marine transitional deposits influenced by ice-shelves and/or icebergs and (2) Continental platform marine deposits. The passage to the upper unit is marked by a sharp planar surface above which lay two facies associations: (3) Wave influenced shallow carbonatic platform deposits, comprising massive to laminated dolomites, locally with aragonite pseudomorph crystals, overlain by (4) Carbonatic ramp influenced by slumps, composed of calcareous grainstones and mudstones with plane-parallel lamination, climbing ripples, slump structures and locally stromatolites. Pebble lithology and thin section compositional data indicate great spatial variation of provenance, with specific sources for each of the investigated areas. This variation is interpreted as the consequence of valley or outlet glaciers feeding the glaciomarine margin, thus indicating the presence of topographically elevated areas near the basin. U-Pb SHRIMP dating of selected pebbles reveals the dominance of nearby sources, with the local contribution of far-traveled clasts, suggesting mixing with sediments deposited from icebergs which came from the opposite basin margin, as far as 150 km to the east. U-Pb SHRIMP dating of detrital zircon grains from the matrix of the diamictites confirmed this model and lead to the identification of a source from outside the craton with approximately 850 Ma. This data constraints the maximum depositional age of the Bebedouro Formation. Despite provenance from the Bebedouro Formation indicates the presence of topographically elevated areas near the basin, the absence of tectonic controls on the sedimentation, evidenced by the great lateral continuity of the depositional systems and their small thickness variation, does not confirm the model of development of neoproterozoic glaciers over the shoulders of rift systems.
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Using Facies Analysis and Reservoir Characterization of the Albian-Cenomanian Nanushuk Formation to Assist in Better Understanding Interactions Between Shoreface, Deltaic, and Fluvial Systems on the North Slope, AlaskaSmoot, Andrea 16 December 2021 (has links)
The Albian-Cenomanian Nanushuk Formation located on the North Slope of Alaska is the result of fluvial, deltaic, and shoreface processes and has been the focus of recent petroleum exploration activity in the Colville Basin. The Nanushuk and underlying Torok formations together contain an estimated 8.7 billion barrels of oil and 25 trillion cubic feet of natural gas reserves within the resource-rich North Slope. The Nanushuk Formation is composed of sediment sourced from the Chukotka Peninsula to the west and deposited axially within the Colville Basin. High sedimentation rates led to rapid progradation of shoreface and deltaic systems, which effectively filled the entire basin during the Cretaceous. Resulting in a thick stratigraphic succession of marginal to deep marine sandstones and mudstones. However, considerable facies variation within the basin has led to a previous lack of understanding of the spatial distribution of depositional elements. Integration of outcrop photogrammetry, detailed measured sections, core interpretations, hand samples, and thin section microscopy from the Colville Basin in this study reveal the distribution of litho- and depo-facies within the Nanushuk Formation. Three key outcrop locales along the northern flank of the Brooks Range expose ~200 to ~1000 feet of mudstone, silty sandstone, and sandstone that record the transition from distal shoreface sedimentation to deltaic and fluvial processes over time. Progradationally-stacked parasequences are clearly identifiable in both outcrop and core, recording rapid axial progradation to the east. While shoreface processes do exist in the Nanushuk, outcrop observations show a dominance of deltaic processes, consistent with the highly progradational nature of the strata. Further, there is a trend towards more fluvially-dominated deltaic processes in the more axial part of the Colville syncline, as shown by core, compared to more wave-dominated deltaic facies associations along the margins of the axial basin where outcrops were described. These trends, both vertically and spatially, have important implications for understanding the geologic evolution of the formation and for targeting areas for further exploration within this evolving hydrocarbon play.
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Modelo evolutivo para la sucesión sedimentaria depositada entre la Cuenca de Post Rift y la Cuenca de Antepaís de MagallanesSoto Riveros, Angélica Isabel January 2018 (has links)
Memoria para optar al título de Geóloga / La sucesión sedimentaria que se deposita entre el Barremiano-Cenomaniano, en la cuenca de Magallanes, Chile, es respuesta de mecanismos depositacionales complejos, estudiados por numerosos autores en los afloramientos de la faja plegada. Sin embargo, el subsuelo de la zona oriental sólo se ha estudiado a través de la información de pozos. Estos depósitos se generan previos a la cuenca de antepaís de Magallanes y con posterioridad a la ruptura cortical que originó la cuenca marginal (Cuenca de Rocas Verdes) en una etapa de subsidencia termal, manifestada como una extensa transgresión marina diacrónica.
Desde un punto de vista sedimentológico el estudio de las facies más distales, conformada por la Formación Lutitas con Ftanita y la Formación Margas, permite atribuir cuatro facies a la Formación Lutitas con Ftanitas: (1) wacka/fangolita biogénica, (2) fangolita con laminaciones de limolita, (3) laminación ondulítica de fangolita-limolita y (4) argilita. Mientras que la Formación Margas se puede agrupar de igual forma en cuatro facies, pero con mayor contenido de carbonatos: (1) fangolita, (2) mudstone bioturbado con intercalación de caliza, (3) wackestone con fragmentos de pelecípodos y (4) wackestone biogénico con laminaciones calcáreas.
Las facies mencionadas de la Formación Lutitas con Ftanita, por el abundante contenido de material fino o matriz y baja madurez composicional permite atribuirla a un ambiente de baja energía dominado por procesos de decantación en una plataforma externa. Asimismo, la presencia de pirita y preservación de laminación delgada en las formaciones son evidencias de ambientes depositacionales anóxicos, condición adecuada para la preservación de la materia orgánica. Las facies presentes en la Formación Margas corresponderían en parte a facies depositadas en una plataforma más somera, constituyendo los últimos depósitos de la cuenca marginal.
Ambas formaciones son asociadas a la sección distal de flujos turbidíticos de grano fino evidenciada por la abundancia de fragmentos fósiles. Además, la presencia de líticos volcánicos podría ser indicio de la existencia de actividad volcánica coetánea en el periodo de depositación.
El análisis e interpretación de la información existente, aunque todavía escasa, permite definir los elementos necesarios para la caracterización de rocas y la definición de un proyecto de exploración petrolera, enfocado en la Formación Lutitas con Ftanitas, la cual tiene favorables condiciones para ser considerado un reservorio no convencional de hidrocarburos debido a la estimación de hidrocarburos a partir de perfiles eléctricos de pozos y datos geoquímicos.
. Adicionalmente las mismas rocas de reservorio en el límite occidental de la plataforma tendría las condiciones geomecánicas adecuadas para ser estimuladas a partir de fracturamiento hidráulico. / ENAP-SIPETROL
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Geochemické studium jezerních sedimentů v oblasti zaniklého Komořanského jezera / Geochemical study of the lacustrine deposits of the extinct Komořany LakeValentová, Daniela January 2011 (has links)
Komořany Lake, regarded as one of the most important sites of the Czechoslovak Quaternary, was situated at the southern foot of the Krušné hory Mountains, northwest from the Starý Most town, between the villages of Souš, Komořany, Ervěnice, Dřínov, Albrechtice, Černice and Dolní Jiřetín. Due to its size, Komořany Lake belonged to the largest bodies of water in the Czechoslovak Republic (25 km2 ) and due to the quantity of organogenic sediments get into the focus of paleoecologists. Gyttji sediments which occupy comparatively thick position in the lake infilling, formed a continuous record from the Last Glacial period to the Subatlantic period and up to now have been processed mainly from the paleoecological point of view. In this work the organogenic sediments are studied from the sedimentary record using modern geochemical methods (TOC/TN and d13C) for the first time in Komořany Lake history. The work was based on profiles (PK-1-C, PK-1-Ch, PK-1-I and PK-1-W) which were taken between 1977-1983 before a complete exploitation of Komořany Lake sediments as a result of coal mining in the Most Basin in the 1980's.
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Provenance and depositional environments of early cretaceous sediments in the Bredasdorp Sub-basin, offshore South Africa: an integrated approachHendricks, Mogammad Yaaseen January 2020 (has links)
>Magister Scientiae - MSc / Southern offshore basins of South Africa are well known as potential provinces of hydrocarbon exploration and production. The complex nature of the Bredasdorp sub-basin’s syn-rift architecture (transform fault system) can have adverse effects on reservoir distribution due to periodic local and regional uplift of horsts and grabens. This present investigation focusses on an integrated approach of the 1AT1-V horizon or early Cretaceous sediments in the Bredasdorp sub-basin to identify the depositional environment and provenance of these sediments as well as their role in regionally complex compositional heterogeneities associated with the late stage rifting of Gondwana break-up.
An integrated seismic, sedimentological (including petrography and geochemistry) and ichnologic analysis of the 1AT1-V horizon sediments showed an overall lower regressive element complex assemblage set and an upper transgressive element complex assemblage set that occurred as a >120m thick succession. The analysis identified a mixed-energy deltaic succession followed by an estuarine succession. The 1AT1-V interval (late syn-rift) consisted of nine sedimentary facies associations (and associated petrofacies) on a dipslope setting with variations occurring along the strike and the downdip depositional slope areas. Two overall sequences were identified as a lower regressive and upper transgressive sequence (Element complex assemblage sets). The regressive sequence consisted of middle to distal delta front lobe fringes, hyperpycnal event beds (sourced from basement highs), offshore migrating tidal bars (and associated inter-bar regions), distal mouth bars, terminal distributary channels (and associated inter-terminal distributary regions). The distal delta plain to proximal delta front consisted of interdistributary bays, distributary channels, crevasse splay sub-deltas, mouth bars, tidal flats and offshore embayments. In the laterally isolated depocenter, these deposits also consisted of basement high slopes with upliftment of the basement highs leading to proximal/central embayment to regressive shoreface/foreshore environments. These sequences consisted generally of low diversity and intensities (impoverished abundances) of trace fossils. The paleoclimate inference from this sequence indicates a humid climate with intermediate degrees of weathering intensities (possibly fluctuating arid-humid conditions). The transgressive sequence consisted of estuarine sedimentation with the occurrence of tidal sand ridges and compound dune fields, embayment facies and tidal bars. These sequences consisted of relatively higher ichnodiversities and intensities than their relative regressive sequences. The paleoclimate inference during these times consisted of more arid to semi-arid settings with low degrees of weathering in the source terrain. Local tectonic upliftment and subsidence, with exposed basement highs, gave rise to differential process regimes (tidal, wave and fluvial) and hence depositional facies in the diachronous updip/downdip areas (spatial) and within-stratigraphic (temporal) variations. There are several modern analogues that are similar to the 1AT1-V horizon sequence and they are the Mahakam, Ganges-Brahmaputra, Po, Burdekin deltaic and Satpara lake environments Compaction and dissolution diagenetic features as well as transportation were responsible for the major compositional heterogeneities concerning the reservoir quality and distribution. Proximal and distal sources were identified with first cycle and polycyclic sediments being deposited in the northern and southern part of the basin during the late stages of rifting in the Bredasdorp sub-basin.
The provenance lithology has been identified as recycled sedimentary rocks (and their meta-equivalents) with an ultimate source terrain that was largely felsic in nature (Cape granite suite). The northern part of the studied section is suggested to have received sediments from the main metasedimentary rocks of the Cape fold belt (including the Table Mountain Group and Bokkeveld Group) whereas the southern sections received more sediments from the basement highs (recycled Malmesbury Group (and Pre-Cape sediments) and Cape granite suite), which is further supported by seismic data. Provenance analysis revealed that the Cape Fold belt (most recent collision) was possibly a provenance terrain but overprinting of several collisions are also acknowledged. The tectonic setting was envisaged to be of a rifted margin during the break-up of Gondwana. This compositional heterogeneity due to facies and provenance-related terrains had major consequences to the reservoir quality and distribution from the northern part to the southern part of the studied section
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Sequence Stratigraphy of the Middle Cambrian Marjum Formation: Response of Sedimentary Facies and Biota to Sea-level ChangesSmith, Douglas D. 01 May 2007 (has links)
Research on the Marjum Formation provides insight into facies transitions in the House Range embayment of southwestern Utah during the Middle Cambrian. Sections of the Marjum Formation and equivalents were measured in strata representing shallow- (Drum Mountains), intermediate- (Wheeler Amphitheater), and deep-ramp (Marjum Pass) environments. This traverse across the embayment reveals strong litho- and biofacies changes. The Drum Mountains strata (343 m thick) are dominated by thickbedded shallow-water limestone facies containing polymerid trilobites and stromatolites. The Wheeler Amphitheater locality (392 m thick) provides an example of intermediate deposits between deep-water and shallow-water environments and is characterized by limestone and subordinate shale facies containing polymerid and agnostid trilobites, brachiopods, and sponge spicules. The Marjum Pass locality (424 m thick) contains equal parts shale and limestone facies with abundant fossils that include polymerid and agnostid trilobites, sponge spicules and soft bodied algae, representing deep-water environments. Migration of litho- and biofacies observed within Marjum Formation sections across the embayment shows carbonate ramp build-up and progradation from the Drum Mountains to the Swasey Peak, Wheeler Amphitheater area. Lateral migration of deepwater shale and rhythmite-producing turbidite facies can also be observed on a larger timescale from the Drum Mountains, during the early Bolaspidella time (Wheeler Formation deposits), to the Marjum Pass area (Marjum Formation deposits) by late Bolaspidella time. The Marjum Formation records two, third order shoaling-upward sequences. Fourth, fifth, and higher-frequency (rhythmite) cycles superimposed on these third order sequences can also be identified within the formation and are best preserved within the relatively deep-water deposits at Marjum Pass. Identification of sampled trilobites allowed correlation of known fauna! turnovers found by Robison and Vorwald with observed strata and systems tracts from this study. Stratigraphic locations of trilobite fauna! turnovers were found to be associated with transgressive systems tracts in the Drum Mountains and Marjum Pass localities. Fauna! turnover associated with significant sea-level events within these systems tracts suggests change in water depth altered the local environment forcing extinction and/or migration of organisms. Peak values of total organic carbon (TOC) at each measured section were also found to have a close relationship with maximum flooding zones. Associations of peak TOC values and fauna! turnovers with significant sea-level events demonstrate the value of these tools for correlation across the embayment.
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Reservoir Characterization and Outcrop Analogs to the Navajo Sandstone in the Central Utah Thrust Belt Exploration PlayDalrymple, Ashley 07 July 2007 (has links) (PDF)
Reservoir heterogeneity plays an important role in oil field economics and completion strategies. We herein characterize the reservoir heterogeneity of the Early Jurassic Navajo Sandstone in the Justensen Flat/Devils Canyon area of the San Rafael Swell, Utah. These outcrops are located approximately 60 kilometers (45 mi) east of the recently discovered Covenant oil field which is located in the central Utah thrust belt exploration play. The reservoir for the Covenant field is the Navajo Sandstone. This study can serve as an outcrop analogue for this developing play and other eolian reservoirs worldwide. There are eight facies within the Navajo Sandstone in the Justensen Flat/Devils Canyon area based on differences in primary and secondary sedimentary structures, sedimentary texture, petrology, porosity/permeability, and other macro-scale features of the outcrop. Three facies were deposited by eolian dunes. These serve as the primary reservoir facies of the Navajo in the Justensen Flat/Devils Canyon area, displaying relatively high porosity and permeability (approximately 28 percent porosity and 100 mD of permeability). Five interdune facies display finer grain size, more abundant cement, and relatively lower porosity and permeability (approximately 18 percent porosity and 29 mD of permeability). Four of the five inderdune facies have variable porosity and permeability or are not laterally extensive (tens of meters). These four facies act as baffles to fluid flow within the reservoir. One interdune facies, the Wavy Algal Matted facies (WAM), displays very low porosity (10 percent) and permeability (0.265 mD) based on 4 samples, and is laterally extensive in the field area (greater than 1 km2). There are nine facies in the Wolverine Federal 17-3 core from the Covenant Field, four of which are tidally influenced. This is unique compare to the Justensen Flat/Devils Canyon outcrop. Tidal influence was apparently present in western Utah but did not have a direct influence on sedimentation 60 kilometers (45 mi) to the east. The Large Trough Cross-stratified (LTC) facies, which serves as the primary reservoir of the Navajo Sandstone, was observed in both outcrop and core. The laterally extensive, low permeability WAM facies was also present in both core and outcrop, suggesting the possibility of reservoir partitioning within oil fields having eolian reservoirs similar to the Navajo Sandstone.
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Facies Analysis and Reservoir Characterization of Subtidal, Intertidal, and Supratidal Zones of the Mudstone-rich Entrada Sandstone, South-Central UtahHicks, Tanner Charles 04 March 2011 (has links) (PDF)
Understanding thickness variation and facies transitions in the mudstone-rich part of the Upper Middle Jurassic (Callovian) Entrada Sandstone depositional system is critical for constraining the paleogeography and evaluating the economic potential of Utah's Entrada Sandstone. Facies of the Entrada Sandstone in south-central Utah are dominated by mudstone-rich intertidal facies that were widespread within the Jurassic seaway. Intertidal deposits interfinger basinward with subtidal ooid-bearing shoals and bars, and landward supratidal sabkha, and erg-margin eolian deposits. Three sections were measured to improve understanding of the lateral and vertical facies transitions. Variations in thickness indicate the rate of developing accommodation space was high along the southwestern shoreline and relatively low along the northeastern shoreline during Callovian time. Although accommodation space was highest in the west, sediment supply from the west kept pace with, and eventually outpaced subsidence. In the east, sediment supply was significant but at one time was outpaced by subsidence, creating a complete range of facies, from subtidal to supratidal deposits. Along this eastern shoreline, erg-margin coastal dunes associated with the larger erg to the east eventually prograded westward. The variation in subsidence, sediment supply, and sediment source makes sequence stratigraphic correlation difficult. Reservoir-quality sandstones are associated with muddy sections of the Entrada Sandstone within the San Rafael Swell. Porosity and permeability of the facies in this area indicate excellent reservoir potential in three of eight facies that were studied. Porosities of these potential reservoirs ranged from 11-22%, with permeabilities ranging from 44-430md. These high quality reservoir facies are surrounded by muddy, low reservoir-quality rocks, creating conditions amenable to the development of stratigraphic hydrocarbon traps. Based on further study and a modern analog at the north of the Gulf of California, Hicks and others' (2010) depositional model for the Entrada Sandstone of south-central Utah has been modified to include newly interpreted facies. This improved depositional model may have predictive power in exploring for stratigraphic and combination traps within the Entrada system of Utah and analogous depositional systems throughout the world.
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Insights Into the Stratigraphic Evolution of the Early Pennsylvanian Pocahontas Basin, VirginiaGrimm, Ryan P. 05 January 2011 (has links)
Early Pennsylvanian, coal-bearing, siliciclastic strata of the Breathitt Group within the Pocahontas Basin, southwestern Virginia, define a southeasterly thickening clastic wedge deposited in continental to marginal marine environments influenced by recurring, high-magnitude relative sea-level fluctuations and low-frequency changes in tectonic loading. A robust dataset of >1200 well logs, cores and numerous outcrops allowed a unique review of the Central Appalachian lithologic record during both the Late Paleozoic Ice Age and onset of the Alleghanian Orogeny.
The tropical depositional landscape produced stacked deposits of braided-fluvial channels, broad alluvial plains, tidally-influenced estuaries and small deltas. Trends in facies associations allowed development of a high-resolution sequence stratigraphic architecture based on regional flooding surfaces and bounding discontinuities. Analysis of vertical stacking patterns of lithofacies on regional cross-sections identified 15 widespread, unconformity-bounded depositional sequences with an average duration of ~80 kyr based on available geochronology.
Glacioeustatic control on stratigraphic architecture is supported by corresponding sequence duration within the short-eccentricity periodicity of the Milankovitch band, as well as the magnitude and extent of rapid facies shifts, suggesting that far-a-field variations in overall Gondwanan ice-sheet size and volume impacted base-level changes in the tropical basin. The progressive increase in magnitude of transgressions, as indicated by brackish-marine ichnofacies and other faunal indicators within regional high-frequency transgressive system tracts, indicate extrabasinal trends in ice-volume and eustasy.
High-frequency eustatic sequences are nested within four asymmetric composite-sequences, attributed to low-frequency variations in tectonic accommodation. Evidence for tectonic forcing on foreland-basin accommodation is based on abrupt facies shifts, angular stratal terminations and wedge-shaped composite-sequence geometries. Spatial and temporal trends in facies associations within composite-sequences reveal episodic variation in tectonic loading overprinted by recurring high-frequency eustatic events.
Petrology and detrital-zircon geochronology indicates that sediment was derived from low-grade metamorphic Grenvillian-Avalonian terranes and recycling of older Paleozoic sedimentary rocks uplifted as part of the Alleghanian orogen towards the southeast and, in part, from the Archean Superior Province to the north.
Applications of the observed facies distribution and petrophysics of these coal-bearing sedimentary rocks indicate numerous confining intervals within regional mudstones overlying coalbeds, suggesting the potential for beneficial geological storage of CO2 through enhanced-coal-bed-methane recovery. / Ph. D.
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