Abstract The Ambergris Shoal at the southeast end of the Caicos Platform is approximately 25 km long and composed of ooids. Ooids with nuclei of quartz grains were found in one sample. The coatings are up to 0.05 mm thick. Quartz does not occur naturally on the surface in Caicos. Therefore, coatings on quartz nuclei probably formed in the last 500 years when humans may have transported quartz sand to the platform. The quartz-cored ooids have radially-oriented crystals in their cortex, in contrast to tangentially-oriented needles in other ooids on the shoal. An “island” in the Caicos Mid-Platform Shoals is approximately 500 m long by 100 m wide and is now at sea level. Lithified Holocene grainstone beds along the margins of the “island” dip away from the middle of the “island” similar to beach deposits. Those dipping beds were truncated at sea level, and have fibrous cements similar to beachrock and other marine cements. The middle of the island also contains lithified grainstones at and slightly below sea level; however those grainstones have equant calcite cements supporting an interpretation that they precipitated from freshwater. The presence of freshwater cements suggests that eolian dunes covered the entire island in the past. A large storm (hurricane) apparently removed poorly lithified eolian sands above the water table, leaving meteoric-cemented rocks in the middle and marine-cemented rocks around the margins of the island.

Abstract Observations of the Caicos Platform indicate that shallow-marine and eolian carbonate sediments have equilibrated to sedimentological perturbations caused by Hurricane Donna in 1960 over a geologically short period of time (40 years). The north side of the Caicos Platform has several Holocene islands between the Pleistocene islands of North Caicos and Providenciales. In 1960, Hurricane Donna cut a channel ~700 m wide in one of the Holocene islands, Water Cay. For the next 35 years, tidal currents flowed on and off the platform through Donna Cut mixing platform interior sediments with open-marine sediments (coral, coralline algae, and other bioclasts). As a result, deposition of cross-bedded tidal bars composed of bioclasts and ooids immediately began to fill in the accommodation space created by the hurricane. By 1999, beach deposits had migrated laterally and completely filled Donna Cut from both sides of the channel. The depositional system is now apparently at steady state and characterized by meter high eolian dunes behind the beach.

Abstract Dark organic material from two sites on the Caicos Platform, a tidal flat in the middle of Little Ambergris Cay and the Great Salina on West Caicos Island, was analyzed for source-rock potential. The sample from Little Ambergris Cay was a filamentous cyanobacterial mat, whereas the West Caicos sample was a gelatinous material. The Little Ambergris Cay sample had a total organic carbon (TOC) content of 7.32 wt % and a hydrogen index (HI) of 677 mg/g. The Great Salina sample had a TOC of 4.05 wt % and HI of 694 mg/g. With burial and upon entering the oil window, both of these samples would have excellent potential for generating crude oil.

Abstract Accurate estimates of depositional porosity and in particular permeability are critical initial inputs for process-based models used to predict diagenesis in carbonate reservoirs. Unfortunately, the depositional porosity and permeability of modern carbonate sediments have rarely been measured. In this study, porosity and permeability, using Kozeny-Carman and Lattice-Boltzman algorithms, were calculated on simulated grain packs built from grain-size analyses of carbonate sediments. Five depositional environments on the Caicos Platform were sampled: Tidal Flat, Lagoon, two different Shoals, and Beach. Sediments were analyzed for texture, composition, mineralogy, grain size, and sorting. The depositional environments sampled have a characteristic grain-size distribution and the mean grain size for individual sample locations was relatively uniform. Porosities calculated for grainstones (0.39 to 0.42) were lower than those measured in a separate study on the Great Bahama Bank (0.5 to 0.53). Porosity calculated for tidal-flat sediments (0.31) is significantly lower than measured values (0.61 to 0.78) because intragranular porosity is not calculated. Depositional permeability calculated for grainstones with Lattice-Boltzman (290 to 531 darcies) was greater than with Kozeny-Carman (137 to 285 darcies). Values of permeability for ooid grainstones measured on the Great Bahama Bank (16 to 57 darcies) are an order of magnitude lower, but those sediments are also finer grained (200 versus 700 microns mean grain size).

The Greater Antilles Mesozoic-early Tertiary orthogeosyncline originally was either a basin between the Bahamas platform on the north and a land-mass on the south (on the site of the present Caribbean), or an island-arc system between the Bahamas-Turks and Caicos-Atlantic Ocean basin on the north, and an oceanic basin (modern Caribbean Sea) on the south. The Greater Antilles was not continuous with, or a part of, the Lesser Antilles arc, which is a younger, independent tectonic unit. The oldest Greater Antillean rocks may be Paleozoic, and are present mainly in central and western Cuba. They consist of metamorphosed graywacke, argillite, tuff, mafic igneous extrusive flows, mafic sills, and carbonates. The oldest rocks dated paleontologically are Early and Middle Jurassic terrigenous clastic strata and evaporites in Cuba. The Greater Antilles orthogeosyncline formed in latest Jurassic-Early Cretaceous time from Cuba to the Virgin Islands, and persisted until Eocene time. Locally 10 to 12 km of mafic to silicic igneous rocks and clastics accumulated. In Cuba and the Bahamas, 6 to 7 km of carbonates and evaporites were deposited. A Cretaceous foredeep trough occupied northeastern Jamaica. This trough faced the western Jamaica Paleozoic(?) “backland,” which the writers interpret to be an eastward extension of the Paleozoic-Tertiary Northern Central American orogen. Since Eocene time, isolated basins developed in which carbonate sedimentation was dominant, and the Greater Antilles no longer was a tectonically active arc. Orogeny and related crustal movements have been almost continuous since the Jurassic. Wrench-type and vertical block faulting, beginning locally in middle Cretaceous or earlier time, gradually fragmented the once-continuous orthogeosyncline. Granodioritic intrusions, having radiometric dates ranging from 180 to 46 m.y., are scattered through the orthogeosynclinal sequence. Tectonism—not of the island-arc type—continues today.

Abstract Geologic modeling of zones of early cavernous porosity development in carbonate reservoirs can be especially challenging beyond existing well control. As a result, dolines on Providenciales, Turks and Caicos Islands, were analyzed to evaluate the spatial density and metrics of these early diagenetic features, as well as their relationship to local fracture orientations. Dating of the adjacent host rock material indicates that these diagenetic features are well established in rocks deposited ~122,000 ybp (U/Th). In the dataset of 116 dolines, mean length is 5.16 ± 4.38 m, width = 3.40 ± 2.72 m, and area = 21.27 ± 32.57 m2. Regression analyses of aspect ratios reveal a good, predictable relationship between doline length and width. Approximately 60% of the dolines are less than 10 m2 in area. Numerical modeling of observed dolines using “change of support” spatial statistics establishes a density of 1.13 dolines/acre; a testament to the abundance of small heterogeneities in carbonates that can potentially impact fluid flow. Bivariant plots of area versus exceedance probability indicate three doline populations (0.1 to < 4 m2, 4 m2 to 44 m2, and > 44 m2), and calculations of associated fractal dimensions indicate some degree of scale invariance. Analyses of doline long axis azimuth reveal strong directional controls on doline development within the area of study, thereby establishing an early diagenetic anisotropy template. Early cavernous porosity development preserved in ancient carbonate successions is likely more widespread than would be resolved by traditional seismic methods, and the bulk of fluid flow may be controlled by relatively numerous, small dissolution features.

Abstract For the past 30 some years, Caicos Platform has been an important area for studies of Holocene and Pleistocene carbonate successions and a destination for numerous geoscientists interested in learning about modern carbonate sedimentary systems. During the past few years there has been a renewed interest in understanding the geology of the platform, stemming in large part from recognition in the petroleum industry that more refined reservoir models of carbonate systems are needed both in exploration and development. The impetus for this workshop and this volume was a desire to bring together both present and past Caicos Platform workers with those not familiar with the Platform to share knowledge on the Holocene to Pleistocene sedimentology, diagenesis, platform evolution, and the applicability of the platform as an analogue for ancient isolated carbonate platforms. This volume includes a broad array of papers and is divided into five sections Introduction Holocene, Platform-Scale Surficial Sediment and Facies Distribution Holocene Subsurface Studies Holocene Sedimentology, Reservoir and Source-Rock Potential Pre-Holocene Platform Evolution Sedimentology, and Diagenesis In the Introduction section, Lloyd et al. ( How It All Began: The Early Days of the Turks and Caicos Field Seminars ) recount their search for carbonate seminar locations in the 1970s, prompted by logistical and security issues associated with the classic locations of the Florida Keys and Bahamas, and their identification of Caicos Platform as a new seminar destination. They also describe their early work sampling and documenting the major depositional environments. Larger-scale observations on Holocene sediment distribution and

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.

Abstract In the late 70s it was becoming increasingly difficult to run modern carbonate-sediment seminars in the classic locations of the Florida Keys and the Bahamas. Logistics had always been difficult moving the class from one location to another and weather often controlled the schedule (e.g., if it was stormy on the Florida Reef day it had to be skipped because there was a plane to catch to the Bahamas). The Cat Cay ooid shoals and Three Creeks tidal flat locations in the Bahamas were usually visited using seaplanes chartered from Chalks Flying Service. Increased commercial scheduling by Chalks made it difficult to schedule charters and the planes themselves were getting old and unreliable for field use. Drug traffic passing through the Bahamas also added a security risk. At the same time that field trip logistics were becoming more difficult there was an increased demand for modern carbonate seminars from the oil and gas industry. We decided to look for alternative locations. Mike Lloyd recalled that, in the early 60s, while returning from a field trip in Bonaire on a commercial flight from Curacao to Miami, the plane flew over the Caicos Bank on a very clear day. He remembered that, at 30,000 feet, he could recognize all of the familiar depositional facies on the bank (reefs, tidal flats, Pleistocene islands, grainstone bars, etc.) in a very compact setting. At the time, he viewed it as an interesting curiosity and contrasted it with Inagua Island to the west, an almost totally

Abstract Outcrop and marine field work on the NW part of the Caicos platform illustrates Pleistocene-Holocene accretion of the Providenciales and West Caicos Islands, the effects of the Holocene transgression on the flooded substrate, and the differentiation of sedimentary provinces in relation to prevailing current direction and inherited topography. A marine field study of 2D seismic (CHIRP) sub-bottom profile data and surface sediment sampling on the shelf north of Providenciales and North Caicos, and on the platform interior south of Providenciales provide an image of the top-Pleistocene surface, the thickness of Holocene sediments, and the present distribution of facies, biogenic components, and grain sizes. A pronounced difference in the composition and grain sizes of Holocene sediments exists between the open shelf north and the platform interior south of Providenciales, but maximum thicknesses of approximately 2 meters are similar. On the back-reef shelf, peloidal nearshore sands grade seaward to coarse skeletal sands, rocky bottoms and reefs. On the platform interior, the sediments are peloidal and skeletal on or near beaches, coarse skeletal grains and rubble near patch reefs, and peloidal grainstones and mud-lean packstones elsewhere in the subtidal environment. Outcrop mapping and Uranium-Thorium age dating of carbonate material from Providenciales and West Caicos provide constraints on island growth and sequence development during the Pleistocene and Holocene. Providenciales has two discontinuous core ridges of eolian and subtidal deposits with ages ranging between 160 and 302 Ka. Cutting the island core and prograding away from it are shingles (up to 4 parasequences) of marine and eolian sediments deposited during 140-90 Ka representing the transgression and high stand of isotopic stages 5e and c. Comparison of the elevation of Pleistocene marine deposits (> 12 m) and published sea level curves for the area indicates the need for uplift or higher sea levels for the island. Holocene eolian ridges, beaches, and strandplains form a discontinuous outer shingle on the island. West Caicos is cored by two eolian cores with similar age sediments (219-136 Ka), followed by reef and beach growth (120-130 ka) and younger Holocene eolian ridges making up the east and northeast extension of the island.