Physical constraints on dolomite crust formation, Ambergris Cay Belize

Conference · Tue May 01 04:00:00 EDT 1990 · AAPG Bulletin (American Association of Petroleum Geologists); (USA)

OSTI ID:6857872

Birdwell, B A; Bischoff, W D; Mazzullo, S J ^[1]

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1. Wichita State Univ., KS (USA)

Dolomitic crusts forming on a peritidal flat on Ambergris Cay, Belize, occur beneath surface sediment adjacent to, but not within, small saline (60-90 ppt) ponds. Upper crusts, 2-12 cm thick forming at or slightly below the water table (approximately equivalent to lagoon water level) are areally restricted by (1) ponds where sediment lies below 20-50 cm of water, (2) high and relatively dry areas where sediment accumulation of more than 15 cm above water level supports diverse vegetation, and (3) low areas affected by mangrove encroachment where preexisting crusts are perforated by roots and displaced. The lower crusts occur immediately above the Pleistocene in lows beneath the Holocene sediment and on exposed Pleistocene surfaces. Estimates from x-ray diffraction analysis indicate 80-100% dolomite content within the upper crusts and 50-60% dolomite content in the lower crusts. Unlithified sediment above and below the upper crust contain up to 80% dolomite. Compositions range from Ca{sub 56}, Mg{sub 44} in the upper crusts to Ca{sub 60} Mg{sub 40} in the lower crusts. There is no correlation between stoichiometry and ordering in the dolomites; all are poorly ordered as indicated by very weak (015) and (021) superstructure peaks. Where crusts are not 100% dolomite, the dolomite is evident as euhedral cements within pores, especially within foraminiferal tests, and as micrite along algal laminations and walls of burrows. However, preliminary examinations with scanning electron microscopy and energy dispersive x-ray mapping show that magnesium enrichment is pervasive within these crusts and may represent Mg-enrichment of calcite as an intermediate stage in dolomite formation.

• OSTI ID: 6857872
• Report Number(s): CONF-900605--
• Conference Information: Journal Name: AAPG Bulletin (American Association of Petroleum Geologists); (USA) Journal Volume: 74:5
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
020200* -- Petroleum-- Reserves
Geology
& Exploration
58 GEOSCIENCES
580000 -- Geosciences
ALKALINE EARTH METAL COMPOUNDS
BELIZE
CALCIUM CARBONATES
CALCIUM COMPOUNDS
CARBON COMPOUNDS
CARBONATE MINERALS
CARBONATES
CENTRAL AMERICA
COHERENT SCATTERING
DIAGENESIS
DIFFRACTION
DOLOMITE
LATIN AMERICA
MAGNESIUM CARBONATES
MAGNESIUM COMPOUNDS
MINERALS
ORIGIN
OXYGEN COMPOUNDS
SCATTERING
X-RAY DIFFRACTION