The Belize margin revisited: 1. Holocene marine facies

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Belize is best known for its 260-km-long barrier reef and associated lagoon reef shoals, but also exhibits a complete transition from near-shore siliciclastics to pure carbonate deposits across a narrow shelf lagoon and, in addition, has three of the very few occurrences of Caribbean atolls. Published Holocene facies relationships on the Belize shelf have been semi-quantitative in that they are based on quantitative point count thin section data in the northern shelf lagoon and on qualitative estimates of thin section composition in the southern shelf lagoon. This contrast has been rectified by point counting southern shelf lagoon thin sections and incorporating the result with published point count data from the northern shelf, supplemented by additional information, to produce a modified factor analysis facies distribution for the entire shelf. The resulting nine facies are extended seaward to include previously published analysis of sediment on the three Belize off-shelf atolls, resulting in a total of 11 facies. In addition, the carbonate mud distribution has been mapped over both the shelf and atolls with the not unexpected result that, in places, the distribution pattern clearly indicates a barrier platform source of lagoon-deposited carbonate mud. Dunham's limestone classification terminology has been used as a basis for description to make these relationships more useful to those reconstructing ancient limestone depositional environments.