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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 68 (1984)

Issue: 4. (April)

First Page: 539

Last Page: 539

Title: Shallowing-Upward Sequence in a Pleistocene Coral Reef and Associated Facies, San Salvador, Bahamas: ABSTRACT

Author(s): Brian White, Karen A. Kurkjy, H. Allen Curran, Kimberly A. Besom


Excellent exposures of a well-preserved Pleistocene coral reef (dated 120 to 140 thousand years B.P.) extend along the shore northwest of Cockburn Town on the island of San Salvador, which lies at the eastern edge of the Bahamas platform 600 km (375 mi) east-southeast of Miami, Florida. The reef was buried sequentially by nearshore marine and terrestrial carbonate sands during a lowering of sea level. This shoaling produced a vertical sequence of carbonate rocks that represents a progressive change from shallow subtidal through beach to dunel environments.

Acropora palmata, A. cervicornis, Diploria sp., and Montastrea annularis are found in growth position up to 2 m (6 ft) above present mean sea level (MSL). Coral rubble, composed principally of A. cervicornis and A. palmata, commonly occurs subjacent to, adjacent to, and up to 80 cm (31 in.) above the in-situ corals. Gullies in the coral rudites are filled by coarse skeletal calcarenites, which in some places contain well-preserved, irregular boxworks of Ophiomorpha sp. and Skolithos linearis burrows. The calcarenites extend upward and outward from the gullies to overlie the corals and coral rudites; lowermost beds commonly have trough cross bedding extending up to 3.6 m (12 ft) above MSL. Upward, the calcarenites become finer grained, skeletal, intraclastic, peloidal, and oolitic, wit gently seaward dipping planar cross beds and beachrock clast breccias occurring up to 4 m (13 ft) above MSL. Fine-grained eolianites with abundant rhizocretions and some paleosols occur higher than 4 m (13 ft) above MSL, and this elevation marks the maximum height of sea level during the development of the Cockburn Town reef. Following this high stand, lowering of sea level produced this fine Pleistocene example of a shallowing-upward carbonate sequence.

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