VESSIGNY BEACH SAND COMPOSITION AND PROVENANCE IMPLICATIONS, SOUTHERN TRINIDAD (Invited Presentation)

Trinidad is situated on the northern edge of the South American plate, but close to the southern boundary of the Caribbean plate. Current research includes sample collection and subsequent laboratory work at York College (CUNY). Preliminary laboratory work includes grain size analysis, heavy mineral separation, and chemical analysis of beach sands by XRF. Sieve analysis data indicate that the sediments are well sorted, having an average standard deviation of 0.43 phi, with a near symmetrical distribution (average skewness -0.10). The sediments are leptokurtic, predominately medium to fine-grained sand (average Mean 1.24 phi). Initial heavy mineral separation reveals that sand is composed predominately of minerals of low specific gravity, such as quartz and feldspars. These minerals comprise 91-99%, by weight, of the sand grains. Traditional heavy mineral separation shows the presence of hornblende, zircon, epidote, pyrite, tourmaline, glauconite, magnetite and garnet. Such composition might indicate that the provenance is in close proximity to a mixed igneous, metamorphic, and reworked sedimentary source. Studies of recent geological map data have shown that surficial terrain is of sedimentary origin. Based on this, one might discern that the provenance of these coastal deposits is from the South American continent via the Orinoco River. In addition, trace amounts of heavy ultrastable minerals having well-rounded shape indicating that some, if not all of the sand, was reworked from older Tertiary and Quaternary marine and barrier island sediments. Trace elements such as Zr, Cu, Ni, Ti, Cr, and Ba also suggest winnowing of sediments by hydraulic sorting and ultimate enrichment of these elements in the sand. The deposition and winnowing of sand on the barrier island is apparently in equilibrium condition and final mineralogy of the beach sand reflects close interactions between coastal processes and weathering of recent and Neogene sedimentary rocks.