DEPOSITIONAL SETTING AND PALEOECOLOGY OF THE BOWDEN SHELL BEDS, SOUTHEASTERN JAMAICA

The Bowden shell beds, upper-Pliocene (3.5. Ma) Layton Formation, southeastern Jamaica, contain one of the most diverse Cenozoic fossil assemblages in the Antillean Caribbean. Despite the rich and well-preserved faunal assemblage, paleoenvironmental and ecological interpretations for the Bowden shell bed have been difficult owing to the mixture of fossils from different environments (terrestrial – pelagic) it contains. These “jumbled shell beds” have been interpreted as representing multiple turbidity flows triggered by tectonic activity or hyperpycnal plumes sourced from the narrow island shelf and ultimately deposited in deep (100-250 m) channels or submarine fan systems. We collected 14 bulk samples from different locations within the Bowden shell beds containing ~10,000 benthic mollusks. All bivalves have been identified to the generic level, with a total of 86 genera identified (compared to Woodring’s 112 identified genera and subgenera). Bivalve assemblages appear to represent typical tropical shallow water communities. However, ordination of bivalve assemblages collected from different shell beds within the Bowden Member shows variation in the assemblages among shell beds as well as within the main channel deposit itself, suggesting discrete depositional events. In addition, a MANOVA of the bulk samples based on the 5 most abundant bivalve taxa also reveals a significant difference among shell beds. These results suggest that the Bowden shell beds represent discrete events and may be sourced from slightly different communities. We therefore caution against ecological analysis of the Bowden Member as a whole (e.g. using museum collections) and suggest that best paleoecological practice should take stratigraphic context into account.