H.Y. Baik¹, A. Richtmyer², N.B. Asafu-Adjaye³, N. Adzei-Akpor³, T. Manu³
(1) Nuevo Energy Company, Houston, TX
(2) Nuevo Energy Company
(3) Ghana National Petroleum Company, Tema, Ghana

Abstract: Tectono-Stratigraphy and Hydrocarbon Potential of an Active Transform Margin Basin: Offshore Accra/Keta Basin, Ghana, West Africa

The offshore Accra/Keta basin, a sub-basin of the larger Ghana Coast Basin, developed as a part of the transform margin along the Romanche Fracture Zone as Africa separated from South America beginning in the Early Cretaceous. To unravel the complex structural and stratigraphic framework related to this transform margin basin, our study has focused on the regional structural trend and associated trap type, and on the development of deepwater canyon-fan systems across the continental slope and rise. These differences related to the basin’s [transform] evolution directly influenced the depositional systems active across the shelf and slope into the deep water environment.

Nuevo Energy and its partner, Ghana National Petroleum Company, are current lease holders for Accra-Keta concession, encompassing approximately 11,000 square kilometers (2.7 million acres) in offshore Ghana. This offshore block is situated in the eastern portion of the larger Saltpond basin, which has historically been considered primarily a Paleozoic frontier basin. Across the shelf (less than 200 m), the Lower Cretaceous and Paleozoic sequences are encountered at relatively shallow depths north of the Romanche fault zone. This fault zone separates the deformed shallow water platform to the north from a gradually subsiding deepwater basin to the south. Significant right lateral displacement along the Romanche fault zone has resulted in an entirely different sedimentary regime from that found shoreward. The orientation and morphology of the Upper Cretaceous deepwater canyons identified in the concession were predominantly influenced by the combination of active strike-slip movement of the Romanche fracture zone and the distribution of the Upper Cretaceous drainage system along the eastern Ghana shelf.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana