Complex-mixing dolomitization of supratidal deposits, Ambergris Cay, Belize, Central America
Extensive dolomitization of Holocene sediments is occurring on humid supratidal flats adjoining lagoons in the interior of Ambergris Cay. One such flat (Tomas Savannah) caps 3 discrete emergent beach-ridge and washover-swale sand and mud systems that prograded over an irregular, karstic surface of Pleistocene limestone. The Scytonema-covered sediments of the flats are dominantly Mg-calcitic peneroplid (foram) sands and micrites, with subordinate amounts of aragonite from cerithids and bivalves. The relict beach ridges stand as much as 30 cm above mean sea level, whereas adjoining swales are nearly perennially bathed in waters of varying salinity. The most-landward swale occupies a bowl on the Pleistocene surface and is the locus of dolomitization on the flats. The sediments of the swale are a 0.7 m thick section of graded sandy muds in which 3 superposed dolomitic crusts (each 10-15 cm thick) are present; the middle and upper crust are dated at 1700 and 905 yr B.P. (+/- 130), respectively. The volume of dolomite on this one flat alone is 17,000 m/sup 3/, which formed at a startling rate of 14 cm/1000 yr. Each crust grades downward to an equal thickness of unconsolidated deposits. The upper crust contains 64-68% protodolomite, the remainder is Mg-calcite micrite and altered peneroplids; most of the skeletal aragonite has been removed by dissolution. The dolomite is microcrystalline and has selectively replaced the host micrite of the sediments. Average porosities and permeabilities of the crusts are 45-52% and 5.9-7.2 darcys, respectively.
- OSTI ID:
- 5867017
- Report Number(s):
- CONF-850322-
- Journal Information:
- Am. Assoc. Pet. Geol., Bull.; (United States), Vol. 69:2; Conference: American Association of Petroleum Geologists annual meeting, New Orleans, LA, USA, 25 Mar 1985
- Country of Publication:
- United States
- Language:
- English
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