Abstract Great Bahama Bank (GBB) stands behind many of the models used to illustrate depositional facies variation across flat-topped, isolated carbonate platforms. Such models have long served as subsurface analogs at a variety of scales. We have used Landsat TM and ETM+ imagery, and an extensive set of water depth measurements, to critically evaluate the magnitude and patterns of bathymetry across GBB. The refined bathymetric digital elevation model (DEM) and seafloor sample data were analyzed with eCognition to develop a map of depositional facies that is more robust than previous versions. 60%, or 61,400 km 2 , of GBB lies in 5 m or less of water. This includes carbonate sand accumulations where accommodation space is nearly filled, e.g., Tongue of the Ocean, Schooners, Exumas, Joulters, and the Cat Cay sand bodies, and also includes vast portions of the northern portion of GBB surrounding Andros Island and the New Providence Platform to the west of the Exuma Islands. The 40% of GBB lying in greater than 5 m of water occurs mainly in an east-west trending portion of the southern platform. These bathymetric patterns are important as a potential primary control over flooding history, filling (accommodation) history, and the resultant depositional facies patterns.

Abstract Great Bahama Bank (GBB) stands behind many of the models used to illustrate depositional facies variation across flat-topped, isolated carbonate platforms. Such models have long served as subsurface analogs at a variety of scales. We have used Landsat TM and ETM+ imagery, and an extensive set of water depth measurements, to critically evaluate the magnitude and patterns of bathymetry across GBB. The refined bathymetric digital elevation model (DEM) and seafloor sample data were analyzed with eCognition to develop a map of depositional facies that is more robust than previous versions. 60%, or 61,400 km 2 , of GBB lies in 5 m or less of water. This includes carbonate sand accumulations where accommodation space is nearly filled, e.g., Tongue of the Ocean, Schooners, Exumas, Joulters, and the Cat Cay sand bodies, and also includes vast portions of the northern portion of GBB surrounding Andros Island and the New Providence Platform to the west of the Exuma Islands. The 40% of GBB lying in greater than 5 m of water occurs mainly in an east-west trending portion of the southern platform. These bathymetric patterns are important as a potential primary control over flooding history, filling (accommodation) history, and the resultant depositional facies patterns. GBB is essentially a very grainy platform with muddier accumulations only in the lee of substantial island barriers; in this regard Andros Island, which is the largest island on GBB, exerts a direct control over the muddiest portion of the platform. Mudstones, wackestones, and mud-rich packstones cover 8%, 5%, and 14%, respectively, of the GBB platform top. By contrast, mud-poor packstones, grainstones, and rudstones account for 20%, 45%, and 3%, respectively. Of the 45% of the platform-top classified as grainstone, only 3% is composed of “high-energy” deposits characterized by the development of self-organized sandbar complexes that fill, or nearly fill, available accommodation. The most abrupt lateral facies changes are observed leeward of islands, areas which also hold the highest diversity in facies type. There is a clear trend that the widest portion of the platform, lying to the south of the Tongue of the Ocean and lacking islands, hosts the most continuous expanses of grainstone. The prevalence of rudstone increases from north to south in step with an increase in water depth.

Abstract The Exuma Islands and surrounding carbonate sand bodies of Great Bahama Bank are an important training venue, an area of interest to researchers of modern carbonates, and a valuable modern analog for understanding carbonate sand bodies in the subsurface. We hope to promote this interest by making readily available a set of processed satellite images, offshore/onshore digital elevation model (DEM), and interpretation maps organized into a GIS, along with examples of how this data can be visualized and used for geological interpretation. The clearest satellite images of the Exumas 1972 to 2005 were acquired and processed. Image processing was undertaken to maximize apparent water penetration and delineate submerged features. The primary images are 28.5-m Landsat TM, 15-m ASTER, and 0.6 m Quickbird. The processed scenes were georeferenced to a base image in GIS, creating a stack of co-registered images that can be effectively used for change detection. Masks were created for water and land to enable integration of different images and maps. A digital bathymetric map was created from water depths estimated from the spectral characteristics of a Landsat TM image. This offshore depth map was integrated with an onshore DEM derived from NASA Space Shuttle elevation data (SRTM) for the islands. The overall distribution of carbonate sands, i.e., total sand body, was interpreted primarily with the offshore DEM and satellite imagery. By selecting different water depth intervals, different portions of the total sand body were highlighted for visual analysis and extracted for morphometric measurements. A water depth interval termed the “shallowest sands” (0–1.8 m water depth) revealed geologically-reasonable patterns of deposition and accounted for 37% of the total sand body in the subarea studied. Forty-eight out of the 617 shallowest sand bodies have areas larger than 100,000 m 2 . An evaluation of the shape of these shallow sand bodies using the Form Factor shape parameter of Russ (1999) suggests larger sand bodies are relatively more irregular compared with smaller sand bodies. The total sand body was also divided into flood tidal delta lobes, ebb tidal delta lobes, and sand flats/island-attached sands - flood tidal delta lobes comprise 85% of the total sand body. The average distance from any portion of the flood tidal delta to the channel opening along an ebb-flood dividing line was 2.7 km ± 1.5 km (with a range from 0 to 7.3 km). Fifty-two active tidal channels, either terminating within the tidal delta lobes or open to the east toward the open ocean, were interpreted from the Landsat image and offshore DEM. Channel lengths average 2.9 km and range between ∼ 0.5 and 8.2 km, whereas their depth averages 5.4 ± 2.7 m and ranges from 0 to 13 m. Sediment was deposited in the flood delta lobes up to ∼ 4400 m from the tidal channels and averages 900 m ± 650 m from them. Interpreting Pleistocene and Holocene ridges from enhanced satellite imagery of one key island (Hawksbill Cay) indicated 38% of the island is Pleistocene at the surface, and the Holocene ridges were deposited around the Pleistocene topography in a complex fashion. Integrating elevations with the interpretation map indicated that Holocene ridges have elevations from near sea level to 12 m (mean elevation of 7.7 ± 2.5 m) while Pleistocene landforms have elevations from near sea level to 19 m (mean elevation of 9.3 ± 3 m). Spectral classification of a key island (Shroud Cay) dominated by tidal flats reveals a consistent pattern of depositional environments related to subtle elevation differences. Changes between 1967 and 2005 in channels and emergent sand bars/beaches between Shroud Cay and Hawksbill Cay show the area was relatively stable throughout the 40-year period, but one portion showed a significant increase of emergent sand bars/beaches. Our application of spatial analysis techniques to the Exumas and its carbonate sand bodies provides new insights into this modern carbonate setting and potentially provides data that can have value as an analog in reservoir characterization and modeling. To increase accessibility, improve learning, and promote spatially accurate feedback, the stack of images, color-coded DEM, and geologic maps were exported out of GIS into easier and more flexible viewing programs such as GeoPDFs, GoogleEarth, and Animations.

Abstract The Exumas Islands and surrounding carbonate sand bodies of Great Bahama Bank are an important training venue, an area of interest to researchers of modern carbonates, and a valuable modern analog for understanding carbonate sand bodies in the subsurface. This DVD makes readily available a set of processed satellite images, offshore/onshore digital elevation model (DEM), and interpretation maps organized into a GIS, along with several examples of how this data can be visualized and used for geological interpretation.

Abstract Driven by requests to provide carbonate analogs for subsurface hydrocarbon exploration in rift settings, we have identified and described select examples, summarized them from a carbonate perspective, and assembled them into a GIS database. The analogs (Fig. 1 ) show a spectrum of sizes, shapes and styles of deposition for lacustrine and marginal marine settings, wherein the types of carbonates inferred in the subsurface from seismic and cores (emphasis on microbialites and tufas) can be illustrated. This introductory chapter and overviews of each analog provide the basic descriptions of the analogs and their potential application. The analog examples are grouped as Early Rift Lakes , Other Lakes , and Marine Basins . The Early Rift Lake examples are all from East Africa and include: Lakes Turkana, Bogoria, Natron and Magadi, Manyara, and Tanganyika. Other Lakes includes four examples 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). The Marine Basins are Shark Bay from Australia and the Red Sea. Landsat images and DEMs for each analog delineate present and past lake/basin margins, and for several examples the shorelines representing different lake levels can be compared to illustrate changes in size, shape, and configuration that may impact the presence of carbonates. A subset of the examples illustrates the location and various styles of carbonate deposition within lacustrine and marine settings. Links

Abstract Driven by requests to provide carbonate analogs for subsurface hydrocarbon exploration in rift settings, we have identified and described select examples, summarized them from a carbonate perspective, and assembled them into a GIS database. The analogs show a spectrum of sizes, shapes and styles of deposition for lacustrine and marginal marine settings, wherein the types of carbonates inferred from seismic and cores (emphasis on microbialites, tufas, and travertines) can be illustrated.

Abstract Processed satellite images, derived bathymetry (Digital Elevation Models), and sand body interpretation maps of three key areas of modern carbonate sand deposition on Great Bahama Bank (GBB) are organized into a GIS to develop morphometric data that hopefully will stimulate further studies of modern carbonates. 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. Collectively, these three sand deposits occur along a belt paralleling the platform edge and show a range of depositional facies patterns. Each carbonate sand body and subdivisions of it based on common sandbar patterns are analyzed for size, and then further differentiated by selecting different water depth intervals to define sandbars and bar crests. The TOTO sand body covers 3120 km 2 with sandbars extending onto the shallow platform up to 27 km, whereas that of Schooners covers 716 km 2 with sandbars up to 17 km long. The part of the Exumas examined here is a 450 km 2 linear belt with flood tidal delta lobes extending up to 8 km onto the platform. The portion of each sand body that is occupied by sandbars varies from ∼ 15% - 20%. Sandbar percentage varies between domains in each of the three sand bodies, and can comprise as much as 25% of a particular domain. Size (e.g., length, width, perimeter, and area), shape (using Form Factor, Sinuosity, Aspect, and Roundness), centerlines, and centroids are measured or calculated for the sandbars and analyzed spatially for interrelationships. Profiles and spatial analysis tools enable sand body and channel spacing, position relative to the platform margin, connectedness, and density to be characterized. Relationships are identified that link the size and shape of sandbars, their depths with regard to proximity to the platform edge, and mean separating distances between adjacent bars. For example, small sandbars tend to be rounded, whereas large ones (> 1 km 2 ) are exclusively elongate. However, there is no pronounced change in complexity with increasing area; more complex sandbars do not have a significant likelihood of being large or small. The size of a sandbar has no bearing on the separating distance to the nearest neighbor; however, more separated sandbars have a distinctly lower variance in water depth. More rounded sandbars, as quantified by their Form Factor, are found within close proximity to one another, while those separated by great distance have a propensity to be elongate. There is also a clear trend such that the sandbars with the roughest surfaces (i.e., most thickness variation) tend to be of greatest area. TOTO and Schooners, the two sand bodies without islands, have very similar sandbar centerline density (32% and 35%, respectively), whereas the island-rich Exumas has a relatively lower centerline density (21%). Centerlines at Schooners and TOTO have almost identical complexity, but Exumas centerlines are considerably less complex. All three sand bodies show a similar pattern wherein simple centerlines are by far the most prevalent while each site displays a small number of highly complex/convoluted bar lines (< 50, or ∼ 25% of total). That is, the propensity for the formation of sinuous and intricate centerlines is similar between the sand bodies, suggesting similar formative mechanisms at play in each setting. The results of the sand body and sandbar interrogation imply that certain architectural properties of high-energy sand deposits are generic. We think such results broaden our perspective of the types of information that can be derived from studies of the modern.

Abstract Geochronology, Time Scales, and Global Stratigraphic Correlation - The last decade has witnessed significant advances in analytic techniques and methodologic approaches to understanding earth history. This publication is a well-constructed geochronologic framework that allows estimation of rates of geologic processes, correlation of stratigraphies, and placement of discrete events in temporal order. Resulting from a research symposium at the 67th Annual SEPM meeting in New Orleans, Louisiana, April 1993, the 16 papers of this volume represent a broad spectrum of approaches to understanding earth history and the passage of geologic time.

Abstract The Caicos Platform has proven to be an area of continuing interest to researchers of modern carbonates, an important training venue, and a valuable modern analog for understanding facies patterns of subsurface isolated platforms. We hope to promote this interest by making readily available a set of processed satellite images and an offshore/onshore digital elevation model (DEM), along with examples of how this data can be visualized and used. The clearest satellite images of Caicos Platform from 1972 to 2005 were acquired and processed. Image processing was undertaken to maximize apparent water penetration and delineate submerged features. The primary images are 30-m Landsat TM complemented by older 57-m Landsat MSS, 15-m ASTER, and 0.6 m Quickbird. The processed scenes were georeferenced to a base image in GIS, creating a stack of co-registered images that can be effectively used for change detection. Masks were created for water and land to enable integration of different images and maps. Soundings, together with estimated water depths based on the spectral characteristics of a Landsat TM image from earlier work, were used to create a digital bathymetric map. This offshore depth map was integrated with an onshore DEM derived from NASA Space Shuttle elevation data (SRTM) for the islands. Drainage and possible offshore sediment flow were modeled using the onshore-offshore DEM—this new drainage map can be used for environmental and geological applications. Various satellite images and maps can be draped on the DEM within the GIS to provide perspective views. The transparency of draped layers can be modified, enabling different images and maps to be viewed together. To increase accessibility, improve learning, and promote spatially accurate feedback, the stack of images, color-coded DEM, and geologic maps were exported out of GIS using TerraGo’s GeoPDF for viewing with free Adobe Acrobat. Users of these GeoPDFs can annotate and interpret features, and then export their maps (points, lines, and polygons) as shapefiles for loading into a GIS. In addition, GIS layers were imported into GoogleEarth for global distribution and display as kmz files.