Comparative depositional geometries and facies within windward rimmed platform and carbonate ramp sequences

Conference · Wed Jan 01 04:00:00 EST 1992 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:5936538

Boss, S K; Rasmussen, K A; Neumann, A C ^[1]

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1. Univ. of North Carolina, Chapel Hill, NC (United States)

Northern Great Bahama Bank (NGBB) combines geomorphic aspects of rimmed platforms and carbonate ramps in a windward (high-energy) environment. Analysis of Holocene sediment cores, seismic reflection mapping of the Holocene-Pleistocene unconformity and transgressive Holocene deposits and petrographic study of excavated Holocene submarine-cemented horizons provides an integrated view of evolving depositional geometries within both rimmed platform and ramp settings. Cores display gross textural and compositional homogeneity; all sediments are medium to coarse sands comprised of composite peloids, Halimeda sp., benthic foraminifera and molluscs. Three-dimensional seismic mapping reveals that this basal unconformity exhibits variation in topographic relief related to both constructional and erosional processes; rimmed portions of the platform are associated with topographic plateaus'' with fringing eolianite ridges or (rarely) reefs. These plateaus'' are separated by a somewhat deeper (ca. 5m deep) trough'' exhibiting little relief, but sloping seaward to form a ramp. Multiple intrasequence cemented horizons are a common feature of the thinner deposits of the NGBB ramp where tidal exchange is vigorous and sediment deposition is episodic or in dynamic balance with sediment export. Thus, rimmed carbonate platform facies are thick marine sands with relatively little submarine cementation while open, unsheltered ramp facies are characterized by thin sediment sequences containing numerous, discontinuous submarine-cemented horizons. In the absence of other obvious facies or geomorphic indicators (e.g. preserved reefal rims), the preservation of similar depositional features in ancient limestones may serve as a useful discriminant of rimmed platform versus carbonate ramp settings.

• OSTI ID: 5936538
• Report Number(s): CONF-921058--
• Conference Information: Journal Name: Geological Society of America, Abstracts with Programs; (United States) Journal Volume: 24:7
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
BAHAMA ISLANDS
CARBONATE ROCKS
CONTINENTAL MARGIN
CONTINENTAL SLOPE
DEPOSITION
DEVELOPING COUNTRIES
DRILL CORES
GEOLOGIC HISTORY
GEOLOGIC STRUCTURES
GEOLOGY
GEOPHYSICAL SURVEYS
ISLANDS
MAPPING
PETROGRAPHY
ROCKS
SEDIMENTARY BASINS
SEDIMENTARY ROCKS
SEDIMENTS
SEISMIC SURVEYS
SURVEYS
WEST INDIES