--> Abstract: New Insights into the Regional Structure of the Offshore Niger Delta, by Christopher D. Connors, Barbara J. Radovich, Al Danforth, and Sujata Venkatraman; #90072 (2007)

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New Insights into the Regional Structure of the Offshore Niger Delta

Christopher D. Connors1, Barbara J. Radovich2, Al Danforth3, and Sujata Venkatraman4
1Washington and Lee University, Lexington, VA
2Silver Grass Enterprises, Sugar Land,
3 Independent Consultant, Houston, TX
4GX Technology, Houston, TX

We present a new regional synthesis of the structure of the offshore Niger Delta from interpretation of the new NigeriaSpan regional 2D seismic survey, acquired and processed by GX Technology. These data have optimal characteristics (long-offset, long-recording time, prestack-depth migrated) that provide advanced imaging of the previously enigmatic mobile shale structures, as well as deep imaging of the prodelta stratigraphy, structural timing and relationships to the underlying basement geometry. On the shelf we recognize the soling out of syndepositional, listric normal faults along a unambiguous detachment surface at over 11 km subsea. This detachment sits near the base of the Tertiary. In the contractional toe of the delta this fundamental detachment shallows to about 7 km subsea rather uniformly in the upper Eocene section. The inner slope is both translating and accommodating shortening from updip extension, and exhibits a more ductile and complex shale response. Structures here have been poorly imaged by previous seismic data, and have sometimes been referred to as diapiric structures. Based on improved NigeriaSpan imaging we interpret these as primarily contractional, asymmetric, sometimes thrusted, detachment folds with mobile, Eocene-Oligocene prodelta and marine shale chaotically deformed in the cores of these structures. The structures appear long-lived with growth commencing in the late Oligocene. The contractional toe is primarily a brittle fold-and-thrust belt with variations in style from imbricate fault-bend and fault-propagation folds to shear fault-bend folds and shale-cored detachment folds. Here relatively systematic break-forward thrusting began in the late Miocene and continues to the present the day.

 

AAPG Search and Discovery Article #90072 © 2007 AAPG and AAPG European Region Conference, Athens, Greece