Author(s): Mei Liu (presenter), Paul Mann, University of Houston
We use regional gravity and magnetic maps to better define the crustal types and crustal structures of the area of recent, giant oil discoveries in Guyana and Suriname. The main crustal provinces include: 1) Precambrian craton of northeastern America that is 30 to 45 km thick and includes a prominent, near-right-angle in the area of the Orinoco delta; 2) a 134-km-wide area of thinned, continental crust that is characterized by two, parallel rift zones of inferred Triassic-Jurassic age which can be followed as semi-continuous features from the southern edge of the Orinoco delta to northernmost Brazil; we call these the Outer and Inner rifts; the more seaward, Outer rift is bounded to the northeast by a narrow high that also marks the continent-ocean boundary: recent giant oil discoveries occur in a passive margin sag above the Inner rift; 3) the Guyana basin is underlain by 6-9 km thick oceanic crust that exhibits faint, northeast-trending fracture zone trends and is buried by 8-10 km of sedimentary rocks; previous workers have inferred that this crust is late Jurassic in age based on its depth relations and opened in a NW-SE direction; and 4) the western Demerara is overlain by a ~10-km thick section of volcanic flows of inferred Jurassic age; these folds were folded during the Aptian opening of the Equatorial Atlantic. A sweet spot for giant discoveries is found on the southeastern end of the Inner rift that changes its strike and closes near the Suriname border. This feature also is seen to deepen in northwestern Guyana. We have also used the gravity map to map several basement arch in northern Guyana. None are obviously related to the peripheral bulge of the Eastern Venezuelan foreland basin which appears to terminate in the onland area to the west.
Mei Liu, University of Houston
Mei has her PhD in progress at the University of Houston. She currently is graduate research assistant, and is a member of AAPG, AGU, Houston geological society, Geophysical society of Houston and SPE.