GEOLOGICAL HISTORY OF THE DEMERARA RISE GUYANA MARGIN IN CRETACEOUS TIMES
S. GOUYET
University de Pau et des Pays de l'Adour, BP 576, 64010 Pau Cedex, France & Societe Nationale Elf-Aquitaine,
avenue Larnbau,
BP 65, 64018 PAU Cedex, France
P. UNTERNEHR
University de Pau et des Pays de l'Adour, BP 576, 64010 Pau Cedex, France
A. MASCLE
Institut Francais du Petrole, BP 311, 92506 Rueil Malmaison Cedex, France
Several wells were drilled in the 1970's, on and around the Demerara Rise, during a first phase of hydrocarbon
exploration. The oldest sediments encountered so far have been dated as Valanginian. Seismic reflection data however
suggests that an older series of Jurassic age may exist.
The Jurassic and early Cretaceous sediments are believed to represent the southern extremity of the Central Atlantic
Rift and ocean which extended from western Europe to the north to the present northeast corner of South America
to the south. Sedimentation on the Demerara Rise at that time, occurred principally on the inner shelf, with significant
continental influxes.
In the Middle Albian, shallow marine to open marine environments of deposition prevailed as a response to the opening
of the east-west oriented equatorial ocean and margins. The initiation of these margins along a dextral shear zone
between South America and Africa in Barremian to Albian times have resulted in the formation of a few en-echelon
folds, unconformable overlain by Albian to younger sediments.
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