Abstract: Geometry and Sequence of "Exploding Anticlines" and Toe Thrusts in the Deep-Water Niger Delta, Western Africa

E. A. Griffin, A. A. Imhof, C. F. Kluth

Recent, very high-quality seismic data in the deep-water Niger Delta in West Africa permit the analysis of compressional features at the toe of the delta. These features are part of a system of shortening which is related, in a complex way, to the extensional structures typical of the Niger Delta. The shortening structures are thrust faults and folds that include overpressured(?), buoyant shales in their hanging walls. As displacement increases along strike on the thrusts, more of the shales are carried into the structures. When a critical volume threshold of shale within the structure is reached, the shale becomes diapiric and explodes through the crest or the backlimb of the anticline. The folds and thrusts grew during sedimentation, so that a record of the growth history is recorde in the sedimentary architecture. The seismic data indicate that parts of earlier anticlines are preserved and rotated to high angles on the flanks of several diapirs in the thrust belt. The evidence indicates unequivocally that some of the thrusts formed out of the normal, younger in the direction of transport sequence. The location, the structural style and the sequence of thrusting of the fold and thrust belt can be related to the thickness variations in the mobile shale and a change in the dip of the underlying basement. These structures are analogous in some ways to structures in the distal part of the Mississippi River Delta in the Gulf of Mexico.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994