The Facies Architecture of Manzanilla Formation, Trinidad – How Tides and Tectonics Created a Reservoir

Huggins, Georgia¹, Ronald J. Steel² (1) The University of Texas at Austin, Austin, TX (2) University of Texas-Austin, Austin, TX

In studying the Late Miocene-Early Pliocene Manzanilla Formation of Trinidad we examined the interaction between tectonics and sedimentation using the depositional facies and sandbody architectures (processes and sub-environments) during a crucial time in Trinidad's geological history. The formation records the interaction between the southwards thrusting of the Caribbean Plate onto northern Trinidad and the sediment influx of the palaeo–Orinoco delta system from the southwest.

The Manzanilla Formation was deposited in the northern of two basins on the island. This 1,500m thick succession consists of the San Jose Calcareous Siltstone, the Montserrat Glauconitic Sandstone and the Telemaque Sandstone members, which were deposited in a tidally influenced basin. This contrasts the time equivalent south Trinidad sub-delta systems of the Columbus Basin, which suffered open ocean swell and the dominance of waves.

We examine the dispersal patterns of the sub-delta deposits of the Manzanilla Formation, the role of syn-sedimentary tectonics in the growth of its deltas, the delta regime, architecture and the reservoir properties of the sandstones of the Manzanilla Formation.

Preliminary results suggest: (1) the Manzanilla sub-delta deposits were dispersed from the palaeo- Orinoco delta in the west-southwest, into a relatively protected (Central and Northern Range uplifts) Northern Basin, (2) the distal deltaic deposits were interbedded with coarser –grained material from fans of the tectonically active Northern Range, (3) the Northern Basin was tectonically stable during the L. Miocene – E. Pliocene, and (4) the Central Range had a smaller uplift at this time, which created southerly ‘protection' for the delta system and caused the Manzanilla deltas to be tidally dominated. (5) The tidal nature of this reservoir is the key to understanding hydrocarbon distribution.