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Sedimentary Structures in Modern Carbonate Sands of the Bahamas

John Imbrie
John Imbrie
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Hugh Buchanan
Hugh Buchanan
Financial support for field work and for developing and testing coring techniques came from two sources: a grant made to Columbia University jointly by Pan American Petroleum Corporation and Phillips Petroleum Company, and a National Science Foundation Grant (NSK-GP 1243). Field studies in the vicinity of Bimini, B.W.I., were made possible by boats and shore facilities of the Lerner Marine Laboratory, a field station of the American Museum of Natural History. Part of the cost of laboratory analysis was paid by a grant from the American Petroleum Institute (Grant-in-Aid 167).Most of the field work was carried out with the assistance of cooperating investigators working on other problems. In particular the authors are grateful to the following geologists, who shared the discomforts and hazards of smaJI-boat survey work in remote stretches of shoal water: Robin Bathrust, Barry Cameron, N. D. Newell, G. R. Orme, E. G. Purdy, John Sanders, Richard Scalan, S. S. Streeter, and Willis Tyrrell. Information given by M. M. Ball, of the Shell Oil Company, made it possible for us to study a hurricane deposit in Florida Bay.We extend our thanks also to N. D. Newell, who introduced the authors to Bahamian geology and ecology, and whose knowledge of the region provided essential background. Finally, we acknowledge the stimulus of Edward Klovan, who convinced the senior author in 1960 that data on primary structures in recent carbonate sediments were urgently needed, and whose box-type coring device was used to take many of the cores described here.
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January 01, 1965


Sedimentary structures in carbonate sands of portions of the Great Bahama Bank are described and interpreted using data from air photographs, visual inspection of the bottom, echo-sounding traverses, and 50 box-cores impregnated with epoxy resin. Surface forms described include: avalanche ripples, with angle-of-repose lee slopes; accretion ripples, with lee slopes less than the angle of repose; flat, swash surfaces; large-scale current lineations on the order of 1000 feet long; bars; and irregular shoals. Strata are classed as avalanche deposits if they are cross-strata dipping at the angle of repose with coarser particles concentrated down their dip; accretion deposits if they are cross-strata less than the angle of repose without down-dip assortment; and sheet deposits if they are flat or gently dipping strata approximately parallel to underlying truncation surfaces From hydrodynamic theory and field observations the conclusion is reached that avalanche deposits form where the current separates from the bed on the lee side of avalanche ripples and other migrating embankments; that accretion deposits form where a traction carpet is moving down the lee side of an accretion ripple or other embankment with a significant component of tangential fluid flow; and that sheet deposits are formed in the upper flow regime on beaches, and on level-bottom areas by rare, high velocity currents. Meta-ripples and cross-ripples are described. Biogenic structures, including biolaminites and bioturbites, dominate deposits in intertidal and sheltered subtidal areas of the shelf-lagoon where bottom traction is small compared to the rate of organic activity.

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Figures & Tables


SEPM Special Publication

Primary Sedimentary Structures and Their Hydrodynamic Interpretation

Gerard V. Middleton
Gerard V. Middleton
McMaster Ulliversity
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SEPM Society for Sedimentary Geology
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Publication date:
January 01, 1965




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