Abstract

The North Coast Marine Area (NCMA) extends across approximately 7000 km² (4300 mi²) of the northern Trinidad and Tobago shelf in water depths between 50 and 200 m (165–655 ft). In 2009, the NCMA had two exploration blocks under active oil and gas exploration with gas production from the NCMA totaling approximately 1.1 tcf since 2002. The NCMA is located within a complex, tectonic environment characterized by oblique, right-lateral–strike-slip displacement between the Caribbean and South American plates moving at a rate of about 20 mm/yr. This study analyzes two Pleistocene, fourth-order, shelf, and shelf-edge stratigraphic sequences (sequences B and C) deposited over the past approximately 500 k.y. in the western part of the NCMA. Micropaleontologic well data through Sequences B and C constrain the basal deposition to have initiated at ∼500 k.y. and ∼125 k.y., respectively. The lithologic interpretation from well log analysis tied to the seismic data shows these sequences composed of sand, shale, and thin limestone. Seismic interpretation allows division of both Sequences B and C into eight system tracts, which include (1) lowstand, (2) transgressive, (3) highstand, and (4) falling stage. The Sequences B and C lowstand systems tracts are characterized by subaerial or subaqueous delta top deposition from the paleo-Orinoco River as it prograded northward through the narrow region known as the Dragon’s Mouth on the northwestern side of Trinidad. The falling stage systems tract of Sequence C consists of a package of approximately 20–45-m (65–150 ft)-high, 0.1°–0.25°-inclined, and northeastward-prograding muddy, shelf-deltaic clinoforms whose northward termination marks the paleoshelf edge. Normal and strike-slip faults deform Sequence B and produced accommodation space to thieve sediment, and inhibit the extent of progradation and subsequent gravity deposition off the delta front. Faults do not penetrate into overlying Sequence C whose deposition was more eustatically controlled. These Pleistocene sequences provide an analog for underlying Miocene and Pliocene age sequences and reservoirs that form the most productive, NCMA gas fields.