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Harris P.M.,Chevron | Purkis S.J.,Nova Southeastern University | Ellis J.,Ellis GeoSpatial
Journal of Sedimentary Research | Year: 2011

Three carbonate sand bodies on Great Bahama Bank, which show a range of depositional facies patterns typifying modern deposits as well as their ancient counterparts, are quantitatively interrogated to broaden our perspective of the types of information that can be derived from studies of modern environments. Rimming the southern end of Tongue of the Ocean (TOTO) is the broadest expanse of "high-energy" sands found in the Bahamas, characterized by narrow sandbars separated by wide, deep channels and a lack of islands. A variation of the tidal-bar motif with broader and more irregular sandbars, relatively narrow channels, and few small islands occurs at the northern end of Exuma Sound (Schooners). Sands associated with tidal channels and the numerous islands of the Exumas chain along the western edge of Exuma Sound occur primarily as flood tidal deltas. The geometry of sandbars that inhabit the three sand bodies is quantified using Landsat remote sensing and assembled, along with optically derived bathymetric surfaces, into a GIS. This database is quantitatively examined using a suite of morphometric tools to compare and contrast geometric character of sandbars within and between the three sand bodies. Considered are properties such as the size, shape, complexity, distribution, orientation, and topography of the individual sandbars. Profiles and spatial analysis tools enable sandbar and channel spacing, position relative to the platform margin, connectedness, separation distances, and density to be characterized. As has been previously reported for reef-dominated environments, certain aspects of the geometry of the three systems are found to behave in a systematic and hence predictable manner, though important mathematical differences are revealed between the scaling of reefal landscapes and the grainy geobodies considered by this study. Because the three sand bodies are disparate in their overall extent and depositional settings (e.g., orientation, prevalence of islands), this predictable behavior has the potential to impart considerable insight to the characterization of grainstone systems. Copyright © 2011, SEPM (Society for Sedimentary Geology).

Purkis S.J.,Nova Southeastern University | Harris P.M.,Chevron | Ellis J.,Ellis GeoSpatial
Journal of Sedimentary Research | Year: 2012

Patterns of sedimentation in the Red Sea offer a contemporary analog for carbonate deposition in marine rift settings. Covering 20u of latitude, the sea is sufficiently long to display pronounced climate differences and the clear tropical waters support vigorous coral reef growth and associated production of carbonate sediment. Six focus areas within the Red Sea, each covering exactly 1,600 sq. km, illustrate the variability of spatial patterns in reefal and other carbonates in this rift setting. Five of the focus areas are located on a north-south transect along the western margin of the sea: (1) Gubal Straits (Egypt), (2) Shalatayn (Egypt), (3) Trinkitat (Sudan), (4) Dahlak (Eritrea), and (5) Halib (Eritrea); and one is from the eastern margin: (6) Farasan Banks (Saudi Arabia). Using Landsat imagery, water depth and two marine facies classes, "reefal frameworks" and "sediments," were mapped. Lumping these two classes define "carbonate bodies" that were analyzed for trends in orientation, relation to local fault networks, and size-frequency distribution. Fault lineaments digitized from the literature are closely related to the orientation of carbonate bodies with areas exceeding 5 sq. km. Smaller bodies do not preferentially align with fault trends.Water depth and the occurrence of reefal frameworks and sediments for the six focus areas are not systematically related. Used as an analog, these data from the contemporary Red Sea may provide insight into the orientation and scale of accumulation of carbonates in subsurface marine rift settings. Copyright © 2012, SEPM (Society for Sedimentary Geology).

Harris P.M.M.,Chevron | Harris P.M.M.,University of Miami | Purkis S.J.,Nova Southeastern University | Ellis J.,Ellis GeoSpatial | And 2 more authors.
Sedimentology | Year: 2015

Satellite imagery and an extensive set of water-depth measurements have been used to map and critically evaluate the magnitude and patterns of bathymetry across Great Bahama Bank. Descriptions of previously collected sediment samples were combined with satellite imagery to map and refine the interpreted distribution of surficial carbonate sediments (depositional facies). Data reveal that 60% of Great Bahama Bank lies in 5 m or less of water. The deep portion occurs mainly in a generally east-west trending area in the southern portion of the platform. The re-evaluation of the facies reveals that Great Bahama Bank is essentially a very grainy platform with muddier accumulations primarily in the lee of Andros Island. This area of Great Bahama Bank also experiences currents related to an excursion of the Florida Current onto the platform top possibly enhancing sediment mud production through the generation of whitings. Sediment equivalents to mudstones, wackestones and mud-rich packstones cover 8%, 5% and 14%, respectively, of the platform top, whereas sediment equivalents to mud-poor packstones, grainstones and rudstones account for 20%, 45% and 3% of the surface area. Boundstones (reefs) were not specifically mapped in this study due to the resolution of the mapping. There is a poor relationship between the occurrence of the depositional texture and water depth, in that the grainier sediment types are abundant across the full range of water depths. The most abrupt lateral facies changes portrayed on the facies maps are observed leeward of islands, areas which also hold the highest diversity in facies type. The majority of the islands on the platform align with the north-west/south-east strike of the platform margin and these islands, in turn, exert control on the shape and orientation of facies belts that develop in proximity to them. For this reason, regions of the platform that contain principal islands host facies belts that align with the principal axis of the platform, whereas for regions lacking islands, the facies belts adopt an east-west trend consistent with prevailing winds and currents. There is a clear trend that the wide southern portion of the platform hosts the most continuous expanses of grain-rich sediments. Journal compilation © 2015 International Association of Sedimentologists.

Harris P.M.,Chevron | Ellis J.,Ellis GeoSpatial | Purkis S.J.,Nova Southeastern University
AAPG Bulletin | Year: 2013

Select lacustrine and marine depositional settings show a spectrum of styles of carbonate deposition and illustrate the types of carbonates, with an emphasis on microbialites and tufa, to be expected in early rift settings. Early rift lake examples examined in this review article are all from East Africa: Lakes Turkana, Bogoria, Natron and Magadi, Manyara, and Tanganyika. Other lake examples include four from the western United States (Great Salt Lake and high lake level Lake Bonneville, Mono Lake and high lake level Russell Lake, Pyramid Lake and high lake level Lake Lahontan, and Searles Lake) and two from Australia (Lakes Clifton and Thetis). Marine basin examples are the Hamelin Pool part of Shark Bay from Australia (marginal marine) and the Red Sea (marine rift). Landsat images and digital elevation models for each example are used to delineate present and past lake-basin margins based on published lake-level elevations, and for some examples, the shorelines representing different lake levels can be compared to evaluate how changes in size, shape, and lake configuration might have impacted carbonate development. The early rift lakes show a range of characteristics to be expected in lacustrine settings during the earliest stages of continental extension and rifting, whereas the Red Sea shows well advanced rifting with marine incursion and reef-skeletal sand development. Collectively, the lacustrine examples show a wide range of sizes, with several of them being large enough that they could produce carbonate deposits of potential economic interest. Three of the areas-Great Salt Lake and high lake level Lake Bonneville, Pyramid Lake and high lake level Lake Lahontan, and the Red Sea-are exceedingly complex in that they illustrate a large degree of potential depositional facies heterogeneity because of their size, irregular pattern, and connectivity of subbasins within the overall basin outline. Copyright © 2013.

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