Niger Delta Growth Faults and Growth Stratigraphy - The Interaction between Delta Tectonics and Sedimentation

Fazli Khani, Hamed ¹; Back, Stefan ¹
(1) Geological Institute, RWTH Aachen University, Aachen, Germany.

This study examines syn-depositional faults and syn-tectonic sediments in the western Niger Delta offshore Nigeria on three-dimensional (3D) seismic data. Seven medium- to large-scale regional and one counter-regional growth fault divide the study area into five major fault blocks. The initiation, lateral growth or retreat, activity or quiescence, and the decay of faulting around these blocks can be monitored by analyzing series of time-structure and isopach maps through time. The syn-depositional activity of the studied growth faults is expressed either by thickening of sediments on the hanging wall into the active fault plane generating a depositional wedge, by the development of a significant difference of the thickness of contemporaneous strata on the footwall and hanging wall of active faults, or by lateral changes of the length of growth faults between successive horizon levels. Based on the above analyzes, the study area can be subdivided into three zones, (1)a northwestern zone that is characterized by the presence of a major counter-regional growth fault in the deep subsurface. This deep-seated structure is superposed by an array of younger, regional growth faults displacing a kilometer-thick sedimentary overburden that accumulated on the former footwall; (2) a central to eastern zone that seems largely unaffected by young deltaic faulting; this zone is characterized by the thinnest sedimentary record of the study area; and (3) a southeastern zone that is dominated by a large, listric, regional master fault-zone associated with a kilometer-scale rollover anticline. Combined structure-stratigraphy analyzes document a strong interrelation between syn-depositional fault activity and syn-tectonic sedimentation in that phases of significant fault activity, lateral fault growth and fault migration coincide with major depositional phases; in turn, areas and intervals characterized by least sediment accumulation also record the lowest fault activity. A particularity of the studied system is that it exhibits during certain depositional intervals a contemporaneous landward backstepping and seaward progression of faults bounding adjacent depocentres; this structural variability seems to exert a primary control on the development of sedimentary systems and associated reservoir facies within the study area.

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.