EARLY CENOZOIC CARIBBEAN CORAL COMMUNITIES FROM THE MIDDLE EOCENE CHAPELTON FORMATION OF JAMAICA

Caribbean coral faunas from the early Cenozoic are almost non-existent. Paleocene-early Eocene assemblages from the region are comprised of isolated small colonies or solitary corals, but by the late Eocene, corals and build-ups are common and conspicuous across the entire Caribbean/Western Atlantic region. Thus, the middle Eocene represents a little-known transitional phase on Caribbean reefs. The present study focuses on the Middle Eocene Chapelton Formation of Jamaica to examine this interval in the early establishment of reefs and coral communities in the Cenozoic of the Caribbean.

Large collections from exposures across central and western Jamaica were used to examine paleoecology, species richness, relative abundance and coral growth fabric in different facies in the Jamaican Middle Eocene. Over 2000 coral specimens have been identified from 20 localities. The corals are chiefly thin, ramose and dendroid forms found in shallow water marls and bioclastic limestones that also contain a diverse fauna of large benthic foraminifera, echinoids and molluscs. Colonies are generally not in growth position, though there are scattered, small (<1m) patches of coral growth fabric in the form of coral thickets or small low-relief knolls. Over 26 species have now been recognized from the Chapelton Formation. Ordination and cluster analysis of coral abundance reveal no distinct clusters that could be considered biofacies or coral assemblages. Instead, variation between samples appears chiefly related to differences in species richness with lower diversity found in more marly sediments. Common robust colony forms and patches of growth fabric are found only in purer carbonate facies. Most of these patterns in coral distribution and growth appear to have been governed by variation in substrate stability, sedimentation and turbidity.

A mix of likely zooxanthellate and azooxanthellate taxa was found at all sampled sites. This mix of reefal and non-reefal species throughout the Chapelton assemblages contrasts markedly with patterns seen in shallow water coral faunas from younger units. This suggests that the middle Eocene Jamaican coral community possessed a trophic structure distinct from later reef building faunas. Wider sampling is needed to determine if this pattern can be seen across the Caribbean as a whole.