Morphology and Dynamics of Carbonate Tidal Sand Ridges: Schooner Cays, Bahamas*
Eugene C. Rankey1, Stacy L. Reeder2, Scott Ritter3, and Paul M. Harris4
Search and Discovery Article #50134 (2008)
Posted November 20, 2008
*Adapted from oral presentation at AAPG International Conference and Exhibition, Cape Town, South Africa, October 26-29, 2008.
1 RSMAS/University of Miami, Miami, FL, USA; currently University of Kansas
2 Schlumberger-Doll Research, Cambridge, MA, USA
3 Brigham Young University, Provo, UT, USA
4 Chevron Energy Technology Company, San Ramon, CA, USA([email protected])
Understanding and modeling many carbonate reservoir systems requires knowledge of depositional trends, including links between geomorphology and granulometry. To further explore such trends in carbonate systems, this study explores Holocene ooid shoals of Schooner Cays, Bahamas.
In this area, sands occur in geomorphic forms including both parabolic bars and flow-parallel tidal sand ridges and channels between a rocky to skeletal-sand rich outer shelf (5-8 m deep) and the muddy peloidal platform interior (~4-6 m deep). Within this bar-and-channel belt, individual flow-parallel sand ridges are up to 13 km long and 1.5 km wide, and generally radiate outward. Sand ridge crests include bare, rippled sands, with superimposed sand waves of various orientations. The crest sediments are clean, moderately well-sorted oolitic sands, with mean grain size of ~ 600 μm and no mud or silt. In contrast, most bar flank and channel areas are burrowed and partly seagrass-stabilized sediments with moderately- to poorly-sorted peloid-skeletal-ooid sands and silts, with up to ~30% mud and silt. Within the channels, there is a trend of decreasing grain sizes, from oceanward to bankward. Measured depth-averaged current velocities reach a maximum of ~80 cm/sec in channels, whereas velocities decrease to < 40 cm/sec on shallow crests; current velocity generally decreases platformward within channels. Significant wave height is < 1 m, and waves are not powerful enough to initiate large-scale sand transport, although winds may drive some westward transport on the platform.
Collectively, the results illustrate geomorphic-sedimentologic links, driven by physical oceanographic controls. The quantitative information provides metrics and trends for developing more realistic geologic or simulation models.
Ability to reproduce “shapes” of object-based algorithms.
Speed, flexibility and easy data conditioning of variogram-based algorithms. The 3D training image is a rendering of the geological model that defines relative facies body dimensions and shapes, as well as associations between facies.
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Subparallel, elongate oolite bodies are typical of Carboniferous sequences in the Illinois Basin, the Mid-Continent, and the Appalachian Basin.
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