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Mineralogical Constraints from Cenozoic Reservoir Provenance in the Northestern Margin of South America

Vincent, Hasley L.1; Wach, Grant D.2
1 Resource Management, Ministry of Energy and Energy Industries, Port of Spain, Trinidad and Tobago.
2 Earth Sciences, Dalhousie University, Halifax, NS, Canada.

Trinidad is the eastern-most exposure of the deformed passive continental margin across northern South America. It is widely believed that the Guyana Shield was the source for clastic reservoirs throughout the Cenozoic of this region and this has guided sediment-pathway and reservoir distribution reconstructions. This hypothesis is largely driven by the age and proximity of the Shield’s rocks and the assumption that the Orinoco River was an important pathway for sediments during the Neogene.

Detrital and heavy mineral analysis was applied to Cretaceous and Cenozoic sandstones to test this hypothesis. Guyana Shield mineralogical signatures are limited to Early Cretaceous feldspathic sandstones while the mature Late Cretaceous and Paleogene arenites were derived from low-relief, Orinoco-type, alluvial plains. An orogenic, metamorphic source was incipient during the Paleogene but became prominent by the Late Oligocene reflected in the sandstones of the dual-sourced Nariva Formation. Metamorphic lithics were sourced from the uplifted Caribbean Mountains-Northern Range to the west and north which bordered an asymmetric foreland basin by the Pliocene. This foreland basin received most of its detritus from this uplifted mountain belt.

The changes in mineralogy support sparse paleocurrent measurements which also suggest a change from southerly to westerly sources by Late Oligocene. The perception of a singular Guyana Shield-Orinoco source ignores potential sediment recycling during later tectonic episodes and may have been applied too liberally in the past. Detrital mineralogy provided important provenance constraints for clastic reservoirs in a region of limited exposures, and a complex structural history.


AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009