Pleistocene patch reefs and Holocene swamp morphology, Grand Cayman Island, West Indies

Patterns of mangrove and non-mangrove species mosaics within the mangrove swamps of Salt Creek, Grand Cayman Island, West Indies, are related to substrate topography and geology. Non-mangrove vegetation is localized on emergent 'dry cays' within the swamp. Both lithological and palaeontological evidence suggests that these bedrock protrusions may be interpreted as a series of Pleistocene patch reefs which were initially slightly elevated above a sandy and silty lagoon floor. The Pleistocene bedrock is overlain by a laminated crust of subaerial origin, above which are Holocene sediments. The Holocene sediments consist of a localized basal orange mud and an overlying cover of mangrove- derived peat. This sequence from subaerial to intertidal sediments records the Holocene marine transgression of the area. Pleistocene patch reefs are at present emergent features, but would be submerged and covered by sediments if the transgression were to continue. It is suggested that this situation is equivalent to an early stage in a similar transgression already identified on the submerged coastal shelf of Belize, central America.

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