Facies and diagenesis of upper Tertiary-Pleistocene platform carbonates in a 300m borehole, southern Ambergris Caye, Belize
- Wichita State Univ., Wichita, KS (United States)
Well cuttings from an [approx]300 m-deep borehole drilled by the Belize government on Ambergris Caye were examined for inferred depositional environments, mineralogy, and stable oxygen-carbon isotopic compositions. The recovered section composes carbonates of the Barton Creek and ( )Sand Hill Formations, presumably of upper-most Tertiary to Pleistocene age. Location of the wellbore to the west of the exposed Pleistocene and superposed Holocene platform margin reef suggests continuous platform deposition. Comparison to modem facies indicates that the entire section is, in fact, mostly outer-shelf reef and immediate back-reef facies. Four unconformities are recognized in the upper 150 m of section on the basis of microbreccias and calcretes, and they truncate stacked, shallowing-upward cycles within the section. Depleted [delta][sup 18]O and [delta][sup 13]C compositions of whole-rock samples from the upper 150 m, which are highly porous and LMC-dominated, range from -2.5 to -5 [per thousand] and -3 to -7 [per thousand] (PDB), respectively. Unconformities are therefore believed to be subaerial exposure surfaces. Dolomite (replacive and cement) occurs below 150 m within HMC-dominated limestones that also contain aragonite. Dolomite generally increases with depth from 8-28%, its composition varies from Ca[sub 51-57], and its mean isotopic composition is [delta][sup 18]O = 3.2 [per thousand] and [delta][sup 13]C = 2.5 o/oo. There are no depth-related trends in dolomite stoichiometry or isotopic composition. Although the timing and site of dolomitization are not known, available data suggest formation from circulating marine fluids of near-normal composition.
- OSTI ID:
- 6589414
- Report Number(s):
- CONF-960527-; CODEN: AABUD2
- Journal Information:
- AAPG Bulletin, Vol. 5; Conference: Annual convention of the American Association of Petroleum Geologists, Inc. and the Society for Sedimentary Geology: global exploration and geotechnology, San Diego, CA (United States), 19-22 May 1996; ISSN 0149-1423
- Country of Publication:
- United States
- Language:
- English
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