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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 68 (1984)

Issue: 4. (April)

First Page: 467

Last Page: 467

Title: Upward-Shoaling Origin of an Eastern Gulf Coast Barrier Island: ABSTRACT

Author(s): Douglas E. Crowe, Richard A. Davis, Jr.


North Bunces Key is a narrow barrier island which has formed on the northern portion of the ebb-tidal platform of Egmont Channel which services Tampa Bay. The island first became supratidal in 1960. Since that time, it has grown to a length of 2 km (1.2 mi) with widespread vegetation and dunes which rise about 2 m (6 ft) above mean sea level.

Most investigators discount upward shoaling as a mechanism for barrier formation in favor of drowned beach ridges. A closely spaced sequence of aerial photos documents the origin of North Bunces Key from a subtidal shoal area without benefit of significant storm activity. Requirements for formation of the barrier appear to be (1) abundant sediment, (2) shallow, very gently sloping platform, and (3) low wave energy.

Vibracores taken from several traverses across the barrier show a general stratigraphic sequence of nearshore sediments successively overlain by foreshore, backbeach, and dune sediments. Cores immediately landward of the barrier contain muddy lagoonal sands containing fining-upward washover deposits. Absence of typical nearshore sediments landward of the barrier may result from low energy conditions which permitted mud to accumulate even prior to emergence of the shoal or reworking and addition of mud as pellets by benthic organisms.

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Copyright 1997 American Association of Petroleum Geologists