SILICICLASTIC-CARBONATE TRANSITIONS ALONG SHELF TRANSECTS THROUGH THECAYOS-COCHINOS ARCHIPELAGO, HONDURAS

The Honduran Caribbean shelf possesses all of the conditions necessary for deposition of both carbonate and siliciclastic sediments within a relatively limited area. However, what is revealed in two cross shelf transects through the Cayos Cochinos Archipelago is not a simple shor e to shelf edge gradual transition between siliciclastic and carbonate shelf environments. Rather there is lateral as well as cross-shelf va riability, in addition to variability in the nature of the sediments w ithin both the siliciclastic and carbonate settings. Strong terrestria l influence is restricted to a narrow nearshore siliciclastic belt les s than 10 Km in width, with abundant organic-rich siliciclastic mud, a nd a low proportion of biogenic, predominantly molluscan, carbonate gr ains. At the outer edge of this belt, there is a transition zone of co arse siliciclastic sands that are likely the result of longshore trans port. The mid and outer shelf areas have carbonate bottom sediments, w here biogenic material is mostly derived from reef coral fragments and Halimeda flakes in varying proportions. Results from this study and o thers in the area indicate that the transition between siliciclastic a nd carbonate shelf environments is rather complex, with lateral and cr oss-shelf variability related to the effects from the freshwater disch arge from rivers, the wind/wave-driven longshore currents, and the geo morphology and topography of the shelf.