--> Eastern Guyana Shelf Margin Stratigraphic Architecture

AAPG/SEG International Conference & Exhibition

Datapages, Inc.Print this page

Eastern Guyana Shelf Margin Stratigraphic Architecture

Abstract

Abstract

The Guyana margin is part of the Equatorial Atlantic continental passive margin. This was affected by two rifting episodes; the first one in Late Triassic-Early Jurassic time associated with the southward propagation of the central Atlantic rifting into the area, and a second rifting episode in the Early Albian inherited from the opening of the South Atlantic, occurring along a pre-existent fracture zone. A subsequent plate rearrangement in the Middle Albian resulted in a counterclockwise rotation of Africa with respect to South America. This rotation induced contraction, uplifting and structural inversion along the entire margin followed up by a period of tectonic quiescence driven by thermal subsidence.

In this tectonic scenario, the shelf, from the Albian to Maastrichtian, was dominated by proximal fluvial-deltaic-to-offshore depositional environments. In this study the Cretaceous-to-Tertiary sedimentary succession of Guyana's shelf is dissected into 9 low-order depositional sequences: sequence 1 (Aptian-Albian) rests unconformably on Jurassic clastic and volcanic rocks. It consists of shales and carbonates (foraminiferal limestone), which show an onlapping-aggrading stacking pattern, and undifferentiated volcanic rocks.

Sequences 2, 3 and 4 are encased in the Berbice paleo-incised valley. This is the largest depositional feature on the shelf, which acted as a conduit allowing sediments to reach deep-water areas. All sequences are bounded by sequences boundaries and a maximum flooding surface with progradational, retrogradational and progradational stacking patterns from bottom up. These are interpreted as lowstand, transgressive and late highstand system tracts respectively. Sequences 2 and 3 consist of fluvial-deltaic-to-shallow marine sandstones and marine mudstones respectively. The latter is equivalent to the Canje Formation, which is a proven source rock in the area. Sequence 4 consists of interbedded sandstones and shales in a prograding pattern.

Sequences 5 and 6 exhibit an agrading-prograding staking pattern. These appear detached from the Berbice; however their depositional environment is similar, a fluvial-deltaic system. Sequences 7 and 8 are characterized by carbonates and mudstones, which are part of a widespread carbonate platform in the area. The top sequence (Pliocene) consists of mudstones and siltstones with a prograding geometry.