The eastern side of the Guadalupe Mountains, located in New Mexico and west Texas, represents an erosional profile along the Capitan reef margin. A complete shelf-to-basin exposure of the Upper Permian Capitan shelf margin is found on the north wall of North McKittrick Canyon, which is nearly perpendicular to the Capitan reef margin. An excellent 2-D sequence stratigraphic framework for upper Permian backreef facies has been developed by previous workers for North McKittrick Canyon (Tinker, 1998) and Slaughter Canyon (Osleger, 1998), forming the basis for observations in this study. The goal of this study is to describe the sequence stratigraphic architecture of the Yates Formation, focusing on the Y4-Y6 high-frequency sequences (HFSs) found in the middle to outer shelf depositional systems, and to illustrate the use of airborne lidar data to quantitatively map at the cycle-scale. Seven measured sections were taken in North McKittrick Canyon. From airborne lidar, 3-D geometries of key sedimentary and structural features were mapped in Polyworks, in addition to the sequence boundaries delineating the Yates 4-6 HFSs. In general, major cycles exhibit asymmetry and shoal upward. Cycle boundaries are sometimes hard to delineate due to amalgamation, particularly in the shelf crest. High-frequency sequences are commonly asymmetric; they deepen and thicken upward toward the maximum flooding surface, and the boundaries between HFSs are usually marked by thick siltstones. Major HFS boundaries can be mapped across the entire dataset, and some component cycles can be observed for minimum distances of one kilometer in an updip-downdip direction. Also, some facies tract dimensions can be estimated directly from the lidar data. Measured sections indicate that the shelf crest facies tract shifts seaward with each successive HFS, while the outer shelf facies tract steps landward. Future work that could be done with the Y4-Y6 HFSs includes 8-10 more measured sections, collection of samples for thin sections, and tracing out of contacts between facies tracts. Extensive lidar data interpretation needs to be done so that digital outcrop models demonstrating facies distributions can be produced. This would enable the development of an outcrop analog model to mixed carbonate-siliciclastic reservoirs, which would be unprecedented in this area. / text

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published_or_final_version / Earth Sciences / Master / Master of Philosophy

This thesis attempts to interpret the metamorphic condition and fluid composition experienced by metacarbonates on Utö, located in the south-eastern parts of the Stockholm archipelago. Utö is a part of the Svecofennian domain, and the area Bergslagen, that has hosted several mines over the last millennia. The bedrock in this area has been dated by the U-Pb technique to 1.90-1.87 Ga, placing it in the Paleoproterozoic era (Allen et al. 1996, Lundström et al. 1998). The rocks, of the studied area on the island of Utö, are mainly metacarbonates with a varying purity and thin layers of volcanic ash. These rocks become more felsic towards the north-western coast as the layers of felsic ash become more dominant. To determine the P-T-XCO2 of metamorphism, metacarbonates were examined, in the field, in thin sections and mineral chemistry was determined by SEM analysis. Three samples were collected along a 1km transect, along which the assemblage calcite + dolomite + quartz + tremolite + diopside was observed. Petrographic and SEM analysis were performed to gather chemical data from coexisting calcite and dolomite in order to calculate temperature using the calcite-dolomite geothermometer. Chemical data from the SEM analysis were also run with AX and THERMOCALC together with pressure data received from a study by Engström (2011) of the adjacent island, Persholmen, to generate a T- XCO2 diagram. Pressure was estimated to 3.1 +/- 1.3 kbars, temperature calculated to 442°C 30°C and XCO2 to range from 0,00067-0,0038 with the standard deviation taken in to account. These results record equilibration with a CO2-bearing hydrous fluid at greenschist facies conditions. / Metamorphic map of Sweden

No description available.

<p>Sandstone and shale samples were selected within the systems tracts for laboratory analyses. The sidewall and core samples were subjected to petrographic thin section analysis, mineralogical analyses which include x-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and stable carbon and oxygen isotopes geochemistry to determine the diagenetic alteration at deposition and post deposition in the basin. The shale samples were subjected to Rock-Eval pyrolysis and accelerated solvent extraction (ASE) prior to gas chromatographic (GC) and gas chromatographic-mass spectrometric (GC-MS) analyses of the rock extracts, in order to determine the provenance, type and thermal maturity of organic matter present in sediments of the Orange Basin. The results revealed a complex diagenetic history of sandstones in this basin, which includes compaction, cementation/micritization, dissolution, silicification/overgrowth of quartz, and fracturing. The Eh-pH shows that the cements in the area of the basin under investigation were precipitated under weak acidic and slightly alkaline conditions. The &delta / 18O isotope values range from -1.648 to 10.054 %, -1.574 to 13.134 %, and -2.644 to 16.180 % in the LST, TST, and HST, respectively. While &delta / 13C isotope values range from -25.667 to -12.44 %, -27.862 to -6.954% and -27.407 to -19.935 % in the LST, TST, and HST, respectively. The plot of &delta / 18O versus &delta / 13C shows that the sediments were deposited in shallow marine temperate conditions.</p>

The Oligocene Brac Formation is the oldest part of the Bluff Group that is exposed on Cayman Brac. Sediments of the Brac Formation were deposited on a small, open bank in shallow marine waters. Today, the formation is composed of limestone, finely crystalline dolostone, and coarsely crystalline sucrosic dolostone. The Pollard Bay member, defined herein, comprises the sucrosic dolomite that is exposed only on the south coast of Cayman Brac. Changes in sea level and subsequent groundwater chemistry mediated a complex diagenetic evolution that is responsible for the lithological heterogeneity that now characterizes the formation. Field, petrographic, and geochemical analyses indicate that dolomitization was probably mediated by normal to slightly modified seawater. Multiphase dolomite crystals represent different stages of textural and geochemical maturity, and attest to time-transgressive dolomitization processes that evolved in various hydrologic regimes through time.

Small back-barrier sand islands are poorly known in terms of hydrogeology and have been overlooked in more extensive studies of coastal groundwater systems that include larger barrier island complexes. This study employs a three-fold sequential approach to aquifer characterisation in a back-barrier sand island. A three-dimensional stratigraphic model forms the foundation framework, being derived from a multidisciplinary approach to sedimentary analysis and the construction of a depositional chronology. A conceptual hydrostratigraphic model is formulated based on the translation of sedimentary facies to hydrofacies, combined with density dependent flow calculations and tidal oscillation measurements. Groundwater hydrochemical data and mineral geochemistry are integrated with the resulting hydrogeological model to examine water-rock interaction and solute transport mechanisms. The study area is Toorbul Island, a small back-barrier sand mass of ~5 km2 with a maximum surface elevation of ~3.5 m AHD, located in the Pumicestone Passage of Southeast Queensland. The island hosts a dual aquifer system consisting of an unconfined island freshwater lens, underlain by a semi-confined palaeovalley-fill aquifer. Groundwater in the semi-confined aquifer is hyper-saline, carrying high concentrations of dissolved metals, with iron, in particular, ranging from 40 to < 200 mg l-1. This is of significant interest for both human health and environmental management, because iron is an important nutrient source for toxic algal bacteria such as Lyngbya majuscula. Conceptual modelling demonstrates that iron oxides and hydroxides are the main source of iron in the semi-confined aquifer, with a contribution from ferruginous chlorite dissolution. Aqueous manganese and a proportion of the aqueous iron are derived from the dissolution of manganoan ilmenite. Ferric iron minerals also contribute a significant proportion of dissolved iron in the deeper regions of the unconfined aquifer. Aqueous iron in the shallow unconfined groundwater is limited by iron sulphides, which also regulate acidity and indirectly limit dissolved aluminium concentrations. Groundwater redox state governed by seasonal climatic fluxes is the most significant control on iron-bearing mineral phase stability. Transport of dissolved metals to the surrounding estuary and the adjacent barrier island groundwater system is limited by the rate of ion diffusion across transition zone boundaries. The overall conclusions derived from this research show that back-barrier islands should be evaluated as discrete hydrogeological entities. The stratigraphic complexity that may be apparent within these island landforms should not be underestimated and the model domain should not necessarily be treated as a homogeneous system. This complexity is exemplified by the relationship between the upper and lower aquifers on Toorbul Island and the associated distribution of groundwater compositional heterogeneity. The complex stratigraphy within the sedimentary pile is derived from the presence of a sub-surface palaeovalley and the sedimentary response to changing sea-level over time. Considering the current widespread distribution of estuarine systems, complex hydrogeology as exhibited by Toobul Island, may be common in many small back-barrier island groundwater systems. The aquifer characteristics and their influence on solute transport and delivery can have significant ramifications for the exploitation of the adjacent coastal plain and barrier island aquifers. The potential influence on the latter is of particular concern due to the pressure imposed on potable groundwater supplies by increasing population densities in coastal areas.

Despite increasing computer power, the requirement to upscale 3D geological models for dynamic reservoir simulation purposes is likely to remain in many commercial environments. This study established that there is a relationship between sandbody size, cell size and changes to predictions of reservoir production as grids are upscaled. The concept of a cell width to sandbody width ratio (CSWR) was developed to allow the comparison of changes in reservoir performance as grids are upscaled. A case study of the Flounder Field in the Gippsland Basin resulted in the interpretation of three depositional environments in the intra-Latrobe reservoir interval. The sandbody dimensions associated with these depositional environments were used to build a series of 3D geological models. These were upscaled vertically and horizontally to numerous grid cell sizes. Results from over 1400 dynamic models indicate that if the CSWR is kept below 0.3 there will be a strong correlation between the average production from the upscaled grids compared to those of a much finer grid, and there will be less than 10% variation in average total field production. If the CSWR is between 0.3 and 1, there could be up to 30% difference, and once the CSWR exceeds 1.0 there is only a weak relationship between the results from upscaled grids and those of finer grids. As grids are upscaled the morphology of bodies in facies models changes, the distribution of petrophysical properties is attenuated and the structure is smoothed. All these factors result in a simplification of the fluid flow pathways through a model. Significant loss of morphology occurs when cells are upscaled to more than a half the width of the reservoir body being modelled. A simple rule of thumb is established — if the geological features of a model cannot be recognised when looking at a layer in the upscaled grid, the properties of the upscaled grid are unlikely to be similar to those of the original grid and the predictions of dynamic models may vary significantly from those of a finer grid. This understanding of the influence of sandbody size on the behaviour of upscaled dynamic models can be used in the planning stages of a reservoir modelling project. Two simple charts have been created. The first chart is for calculating the approximate number of cells in a model before it is built. The second chart is for comparing the proposed cell size against the CWSR, so that the predicted discrepancy between the ultimate production from the upscaled grid and one with much smaller cells can be assessed. These two charts enhance discussion between all interested disciplines regarding the potential dimensions of both static and upscaled dynamic models during the planning stage of a modelling project, and how that may influence the results of dynamic modelling. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1375309 / Thesis (Ph.D.) - University of Adelaide, Australian School of Petroleum, 2009

Despite increasing computer power, the requirement to upscale 3D geological models for dynamic reservoir simulation purposes is likely to remain in many commercial environments. This study established that there is a relationship between sandbody size, cell size and changes to predictions of reservoir production as grids are upscaled. The concept of a cell width to sandbody width ratio (CSWR) was developed to allow the comparison of changes in reservoir performance as grids are upscaled. A case study of the Flounder Field in the Gippsland Basin resulted in the interpretation of three depositional environments in the intra-Latrobe reservoir interval. The sandbody dimensions associated with these depositional environments were used to build a series of 3D geological models. These were upscaled vertically and horizontally to numerous grid cell sizes. Results from over 1400 dynamic models indicate that if the CSWR is kept below 0.3 there will be a strong correlation between the average production from the upscaled grids compared to those of a much finer grid, and there will be less than 10% variation in average total field production. If the CSWR is between 0.3 and 1, there could be up to 30% difference, and once the CSWR exceeds 1.0 there is only a weak relationship between the results from upscaled grids and those of finer grids. As grids are upscaled the morphology of bodies in facies models changes, the distribution of petrophysical properties is attenuated and the structure is smoothed. All these factors result in a simplification of the fluid flow pathways through a model. Significant loss of morphology occurs when cells are upscaled to more than a half the width of the reservoir body being modelled. A simple rule of thumb is established — if the geological features of a model cannot be recognised when looking at a layer in the upscaled grid, the properties of the upscaled grid are unlikely to be similar to those of the original grid and the predictions of dynamic models may vary significantly from those of a finer grid. This understanding of the influence of sandbody size on the behaviour of upscaled dynamic models can be used in the planning stages of a reservoir modelling project. Two simple charts have been created. The first chart is for calculating the approximate number of cells in a model before it is built. The second chart is for comparing the proposed cell size against the CWSR, so that the predicted discrepancy between the ultimate production from the upscaled grid and one with much smaller cells can be assessed. These two charts enhance discussion between all interested disciplines regarding the potential dimensions of both static and upscaled dynamic models during the planning stage of a modelling project, and how that may influence the results of dynamic modelling. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1375309 / Thesis (Ph.D.) - University of Adelaide, Australian School of Petroleum, 2009