LATE PLIOCENE REEF CORAL ASSOCIATIONS FROM THE HOPEGATE FORMATION OF NORTHERN JAMAICA

The late Pliocene is a time of significant faunal turnover in the Caribbean reef-coral community. There are numerous coral bearing sites of this age throughout the region that document this turnover event with faunas composed of a mixture of extant and extinct species. Unfortunately, many Pliocene coral collections sample faunas that have undergone some degree of down-slope transport and/or come from silici-clastic and impure carbonate units. Records from true reefal carbonates of Pliocene age are rare in many parts of the Caribbean, making it difficult to interpret paleoecologic relationships between different parts of the ‘turnover’ fauna. The late Pliocene Hopegate Formation of Jamaica, however, is nearly unique in the northern Caribbean in that it is a shallow water carbonate unit with abundant in situ reef corals. This provides an excellent opportunity to examine associations between extinct and extant scleractinian species in the Pliocene fauna.

We used large new exposures in the Hopegate Formation to make detailed collections of >1000 coral specimens. Through ordination of presence/absence and relative abundance data, we can recognize distinct coral associations. These can be referred to reef crest, shallow and deep forereef and backreef environments based on lithologic characteristics, lateral facies relationships and based on the established ecology of those modern coral species present in the Hopegate fauna.

Our results show that the same species of Acropora and Montastraea that dominate modern Caribbean reefs also appear abundantly as in situ components of wave-washed reef crest and shallow forereef communities in the Hopegate. Regionally extinct forms, such as species of the branching coral Stylophora, appear almost exclusively in ‘off-reef’ facies in this Pliocene unit. This suggests that post Pliocene extinctions in the northern Caribbean were more significant away from true reef environments. It also implies that reef core communities had achieved an essentially modern aspect by the late Pliocene and experienced little species origination or extinction afterward.