Two biologically and lithologically distinct realms of carbonate deposition characterized mid-Tertiary Jamaica. After a latest Cretaceous to Paleocene orogenic episode, complete submergence of insular paleo-Jamaica accompanied the strike-slip or extensional faulting associated with the formation of the Cayman Trench on the north. Differential subsidence along a series of peripheral subsea escarpments (Duanvale-Wagwater escarpment) produced relief of more than 2,000 m by the middle Eocene. The slowly subsiding Cornwall-Middlesex platform was covered by shoal-water limestones which ended the supply of clastics to sea-bottoms north and east of the escarpment,

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where contemporaneous planktonic-foraminiferal pelagites accumulated. Middle Eocene to middle Miocene carbonate rocks deposited in the deep-sea realm represent a distinctive lithogenetic unit herein united as the Montpelier Group.

The preponderance of globigerinid and radiolarian tests typifies lower Montpelier (late Eocene to early Miocene) microfossil assemblages. Dominant benthic forms include Melonis pompilioides, Fontbontia wuellorstorfi, and species of Stilostomella and Pleurostomella. Available faunal criteria including assemblage parameters, depth preferences for extant species, and convergent-ecologic morphologies suggest that abyssal (below 2,000 m) paleodepths prevailed at the depositional site on a sediment apron at the base of the Duanvale-Wagwater escarpment. Middle Eocene to early Miocene subsidence computed from inferred paleodepth and estimated sedimentary thickness totals 2,800 m. Biostratigraphic and paleoecologic evidence does not support the concept of a regional unconformity within the Mon pelier, as has been proposed.

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