Abstract

At the western margin of Jamaica, emergence and submergence caused by positive and negative vertical tectonic movements and glacio-eustatic sea-level change have initiated several phases of carbonate, clastic, and organic sedimentation from Neogene to Recent time. Subaerial exposure of a mid-Tertiary carbonate platform in the late middle Miocene resulted in vadose solution of the emerged limestones, creating hummocky karst topography. Estimates derived from limestone erosion rates and extrapolated rates of displacement of last-interglacial high–sea-level features indicate that down-faulting of an extensive coastal block commenced in the late Pliocene. River systems developed across the block subsequent to downfaulting, depositing clay and limestone gravel in valleys incised across the platform surface.

During the last-interglacial high sea-level stand, a cliff and notch were cut into the western edge of the block, and reefal sediments accumulated on the terrace below. Continued downfaulting subsequent to the last interglacial lowered the block by as much as 24 m in places, although variable depths along the notch suggest intra-block faulting. In contrast, rapid uplift of an adjacent block to the south has brought bathyal Miocene sediments to emergent levels, during the course of which interaction with sea level at various times has resulted in the formation of at least four marine terraces. With the last-postglacial transgression, a sill reef began to develop on a break of slope seaward of the cliff, but it appears to have been drowned by a combination of rapid eustatic sea-level rise and the introduction of reworked terrigenous detritus washed from the shelf surface by the encroaching sea. Inland, a wetland began to form at about 8500 yr B.P. in response to flooding of the downfaulted platform by the rising sea, and subsequent to complete Holocene submergence, a peat deposit as much as 18 m thick has formed. A carbonate sand beach migrated eastward over the wetland during the later stages of the Holocene transgression, but the remainder of the submerged shelf seaward of the beach is notably lacking in Holocene carbonate accumulation.

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