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Physiography, ecology, and sediments of two Bermudan lagoon reefs

Donald L. Smith, Peter Garrett, David Patriquin and Augustus O. Wilson
Physiography, ecology, and sediments of two Bermudan lagoon reefs
The American Association of Petroleum Geologists Bulletin (1970) 54 (5): 871


To provide a possible Holocene analogue for some ancient reefs, we studied the physiography, ecology, and sediments of two small reefs in Bermuda's north lagoon. Both are rough-topped "mesas" rising 18 m from the relatively featureless lagoon floor to within 1-2 m of sea level. On the reef top, irregular coral- and algae-covered knobs are separated by sediment-filled valleys and hollows. The central area of 1 reef, believed to be in a more advanced stage of development, is an atoll-like sandy plain with only scattered knobs. Scleractinian corals, principally Montastrea annularis and Diploria strigosa, are the most important reef-framework builders, as revealed in sections artificially constructed by blasting with dynamite. Coral growth is thought to be the major factor influencing the shape of reef cavities that are common throughout the reef mass. The walls of these cavities are covered with distinctive wall growths built by the skeletons of shade-loving organisms, principally encrusting red algae, pelecypods, a foraminifer, and ectoprocts. Sediments on the reef top are generally coarse to very coarse sand with good to moderate sorting. The particles, dominated by Halimeda, which is also common in lagoonal sediments, are derived entirely from the breakdown of reef-top organisms. These same reef-top sands are washed down the reef face to build a steep reef-sediment slope. Fine sediments are winnowed from the reef-top and settle from suspension to the near-reef lagoon floor, where they form a "halo" of fines around the reef.

ISSN: 0002-7464
Serial Title: The American Association of Petroleum Geologists Bulletin
Serial Volume: 54
Serial Issue: 5
Title: Physiography, ecology, and sediments of two Bermudan lagoon reefs
Pages: 871
Published: 1970
Text Language: English
Publisher: American Association of Petroleum Geologists, Tulsa, OK, United States
Summary: Y
Accession Number: 1970-019174
Categories: Sedimentary petrology
Document Type: Serial
Bibliographic Level: Analytic
N32°15'00" - N32°25'00", W64°49'60" - W64°40'00"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute.
Update Code: 1970
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