The
Guyana offshore basin is a passive, continental-margin-style sedimentary
accumulation. The sedimentary section is Mid-Cretaceous to Pliocene
in age. These sediments range from onlap of Precambrian basement
in the west to more than 29,000 ft of section to the east, before
thinning out in deep-water areas. The main tectonic element of the
basin is a major east-normal fault zone with more than 5,000 ft of
net throw occurring near the end of the Cretaceous. This faulting
formed the ancestral continental margin. Subsequent deposition has
prograded the continental margin over 30 miles NE along the basin
axis.
The
figure above shows the basin stratigraphy, and the figure below shows
a generalized cross-section near the basin's central axis. The basal
formation is the Stabroek, which is Cretaceous-Barremian in age and
is dominated by continental shales and sands deposited on the "Atlantic" Pre-Cretaceous
unconformity. Overlying the Stabroek is the Aptian-aged Potoco formation,
a carbonate that is the age equivalent of the productive Golden Lane
reef trend in Mexico. Recent seismic has illuminated the potential
for shelf-edge, reef-like features at depths of 26,000 ft. At the
end of the Potoco, a marine inundation begins and continues through
the Lower Maastrichtian age, interrupted only by the Berbice Unconformity.
The Cenomanian to Turonian interval contains the Canje formation,
which is the main hydrocarbon source rock in the basin.
