RUIZ, CLAUDIA
Royal Holloway University of London: currently at BP Exploration Colombia, Bogota

Abstract: Tectono-Stratigraphic Evolution and Development of Raft Structures in the Northern Rio Muni Basin, Offshore Equatorial Guinea, West Africa

The Rio Muni Basin is a narrow passive margin, formed during the opening of the South Atlantic in the ?Barremian-Early Aptian, probably in a transtensional oblique rift system.

Two Megasequences were identified in the basin: Aptian-Early Albian synrift-transitional megasequence and Albian to Holocene postrift megasequence. The synrift transitional megasequence consists of Aptian lacustrine turbidites and shales, and Aptian-Albian evaporites and shales. The postrift magasequence is divided into three sequences 1) Albian-rafted sequence formed by Albian carbonates and Cenomanian syngliding strata; 2) Turonian-?Paleocene transgressive sequence formed probably by marine turbidites and shales; and 3) Miocene-Holocene progradational sequence formed by deep water shales and submarine fans.

Four major tectonic events shaped the Northern Rio Muni basin: 1) ?Barremian-Aptian rift tectonics in a transtensional setting, 2) Albian-Cenomanian thin-skinned, gravity-gliding extension; 3) Santonian transpression and basin inversion; and 4) a Miocene uplift present only in the northern region, probably related to the emplacement of the Cameroon Volcanic line. These events resulted in the superposition of three structural styles in the basin: rift structures, a thin skinned extensional fault system formed by gravity sliding on a salt decollement, and inversion structures.

The rift structures trend NE-SW and WNW-ESE, while the overlying raft structures trend N-S. The gravity sliding was controlled mainly by the palaeoslope. However the rafting detachment conserved the imprint of the underlying rift topography.

Two petroleum system are postulated: 1) Apto-Albian turbidite/carbonate reservoirs with Aptian lacustrine source rocks; 2) Tertiary turbidite sandstones-with Miocene shaly source rocks.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas