ICE 2022


The first entrant of Orinoco sands into the Columbus Basin, Trinidad, was deposited by the 3rd order Pliocene Forest/ Moruga/ Mayaro clastic wedge. This clastic wedge is strongly segmented by both syn-depositional growth faults, and syn- and post- transpressional events associated with the eastward migration of the Caribbean plate, making it challenging to correlate strata across the basins. 130 wells and outcrop exposures across the Southern and Columbus basins were integrated to reconstruct a sub-regional dip correlation, defining 11, 4th order, clinoform topsets (F10 - F110) across the shelf margin and some of their earliest clinoforms (F10 - F20). The oldest sub-wedge (Forest-Gros Morne sands, (F10 – F40) shows the development of at least four topset clinoforms and records some of the fastest progradation rates for the Trinidad Orinoco wedges (up to 25 m/ ky), extending the shelf margin ~40 km eastwards in the early Pliocene. This sub-wedge is dominated on the outer-shelf by coarsening upward successions of well-developed mouth bar sands and hyperpycnal flows, indicating the overall fluvial dominance of the delta. This characteristic may have been controlled by the southward growing thrust on the margin, which created an embayment and hindered reworking by waves. The focused sedimentation of the fluvial deltas on the outer-shelf initiated growth faults resulting in impressive over-thickening of these topsets across the margin, from 600 to 1500 ft on the inner- to mid-shelf, and > 7,500 ft towards the shelf edge. The subsequent topsets (F50-F110) show a mixed fluvial-wave influence and the development of double clinoforms on the mid-shelf. However, as the delta lobes prograded across active growth faults on the shelf margin, the increased accommodation not only resulted in a reduction of their forward growth but also led to a longer period of wave reworking on the delta.