Herrera Sandstones in the Southern Basin Area, Trinidad: Evidence of Hyperpycnites Deposited Away From Ancient Oficina Delta Systems in Eastern Venezuela

Gamero Díaz, Helena¹, Jo Reader², Chris Izatt², Carlos Zavala³, Carmen C. Contreras F¹ (1) Schlumberger Venezuela, Caracas, Venezuela (2) BG Trinidad and Tobago, Port Of Spain, Trinidad and Tobago (3) IADO-CONICET; Universidad Nacional del Sur, Bahía Blanca, Argentina

The Lower Miocene Herrera sandstones is a prolific hydrocarbon producer in the Trinidad Southern Basin, and has traditionally been interpreted as being deposited by a sand-rich turbidite fan system sourced from the north. Classical turbidite systems are related to surge-type turbidite flows originating from slope failures due to shelf margin instability. Many authors have stated the existence of controversial opinions concerning the origin of the Herrera sandstones, either from the north, particularly the Central and Northern Ranges, indicating a southward depositional direction, or whether the sands were derived from the west, that is from Venezuela. Core and borehole image descriptions show an abundance of bed load-, suspended load- and lofting-related lithofacies suggesting an origin related to a river-fed long-lived and quasi-steady turbidite flow. The paleocurrent indicators interpreted from borehole images show a paleotransport direction from Venezuela. Lignite material indicates an ultimate source from a terrestrial deltaic environment, which probably developed in Venezuela (Oficina Formation). During the early Miocene, S-N oriented rivers draining the Guayana craton developed huge delta systems in the coastal areas of the Eastern Venezuelan Basin. During humid climate periods, high magnitude floods generated hyperpycnal discharges from the flood-dominated river deltas that dramatically increased the sediment flux into the Maturín and Southern Trinidad basins. An increasing amount of data supports that hyperpycnal flows can travel up to 1000 km basinward. Flows originating in Venezuela could thus travel to Trinidad as submarine (hyperpycnal) channels. This change in facies models increases the exploration potential both in Trinidad and Venezuela basins.