Depositional environments and burial history of the Late Early Pliocene, Moruga Group, south coast, Trinidad, West Indies (Trinidad and Tobago)

The depositional style, biostratigraphy and burial history of the Late Early Pliocene, Moruga Group were studied in outcrop and the subsurface, along the south coast of Trinidad to determine its depositional environments, sediment sources, geologic age, and diagenetic history.; During Late Miocene to Early Pliocene time the northerly prograding, ancestral Orinoco delta transported large volumes of terrestrially derived subarkosic and sublitharenitic sand to the Northern Venezuela/Columbus Basin area. The influence of sea level, coupled with tectonics provided a depocenter which adjusted to accommodate more than 1600 meters of Late Early Pliocene sandstones, siltstone and mudstones of the Moruga Group.; The Moruga Group was deposited by gravity flows and turbidity currents which were very effective in resedimenting the originally deltaic sediments. Three distinct facies were identified on the basis of sandstone/mudstone ratio, sedimentary structures and bedding characteristics. The facies associations, together with the widespread occurrence of complete and truncated Bouma cycles, indicate deposition in a delta-fed submarine ramp environment, by high efficiency, turbidity currents and gravity flows. This system lacked some elements (e.g. canyons) of classic turbidity current models. The Moruga Group was deposited as viscous sheet gravity flows, (turbidites) which were mobilized downslope from a line source as unstable sediments piled up on the prograding delta slope.; Petrography and heavy mineral analyses indicate that the sediments were derived from a mixed igneous and metamorphic source and were the result of rapid erosion and transportation from the Andes and Guyana Shield areas.; The burial diagenetic history of the Moruga Group was evaluated using data from clay mineralogy, organic and inorganic geochemistry. A typical Gulf Coast type clay mineral assemblage was recognized. Evidence suggest that source and depositional environment might have been the major control on the diagenetic mineral association encountered. Rock Eval Pyrolysis indicate that very large amounts of the organic geochemical components are reworked, and cannot be used in source rock evaluation of these sediments. Where rock eval pyrolysis was possible the sediments were determined to be gas prone but immature. Stable isotope data suggest no relationship between carbon and oxygen isotopic compositions, indicating a complex diagenetic history. (Abstract shortened with permission of author.)...