Abstract: Geochemistry of Cenomanian-Turonian Anoxic Depositional Environments: a Comparison Between Brazil and West Africa

Telnaes, Nils - Norsk Hydro; Mello, M.R. - Petrobras/Cenpes; Requejo, Adolfo G. - Geochemical Solutions

The Cenomanian-Turonian was a time during which extensive source rocks were deposited in most of the West African offshore basins. This paper presents geochemical evidence for similarities in depositional environment and organic facies in these West African basins and their analogues along the Brazilian margin. Bulk geochemical, biological marker and kinetic data from a Cenomanian to Turonian sequence in an offshore Namibia well bear a strong resemblance to those determined in a similar sequence penetrated in the Pelotas Basin, offshore southern Brazil. The section in Namibia is immature but very well developed, with Rock-Eval S2 values in excess of 60 kg/t in some intervals and TOC values over 20%. Similar organic-richness and thermal maturity levels are evident in the Pelotas age-equivalent section. These units, where mature, would represent an important contributor to South Atlantic petroleum reserves. Similar correlations are evident in Cenomanian-Turonian sediments from the Kwanza and Congo Basins in West Africa and the analogous Brazilian basins.

These similarities are reflected not only in kerogen type and hydrocarbon source potential, but also in the molecular properties of hydrocarbons generated during laboratory simulations (MSSV and pyrolysis GC-MS). The results illustrate how geochemical characterization of source rock depositional environments in West Africa might be used to predict potential source facies in unexplored regions of the offshore Brazilian basins.

AAPG Search and Discovery Article #90933©1998 ABGP/AAPG International Conference and Exhibition, Rio de Janeiro, Brazil