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Arienti, Luci M.1, Marco A. S. Moraes2, Valter R. Etgeton3, Ricardo T. Castellani3, Jair R. de S. Soares3
(1) Petrobras Research Center (CENPES), Rio de Janeiro, Brazil
(2) Petrobras Research Center (CENPES),
(3) Petrobras International - E&P, Rio de Janeiro, Brazil

ABSTRACT: Stratigraphic Framework and Architectural Evolution of Channel and Lobe Complexes – West Africa /Nigeria

This work relates the stratigraphic framework to the architectural evolution of turbidite channel and lobe complexes in an area offshore Nigeria. Evolution from lobe-dominated to channel-dominated 3rd-order sequences is mainly a function of slope progradation. In addition, structural control plays an important role since extremely linear Northwest-Southeast compressive folds cause turbidite ponding within interfold areas. These general trends can be refined by better defining the internal characteristics of the 3rd-order sequences.
Architectural elements defined by seismic geometries and stacking patterns include: (a) discrete channel fills; (b) overbank deposits; (c) lateral accretion packages; and (d) frontal lobes. Main channel architectural styles are: (a) amalgamated laterally-accreted channels; (b) discrete laterally-accreted channels; and (c) laterally to obliquely-accreted channels. Vertically, a common evolution of channel complexes is from highly amalgamated laterally-accreted channels at the base to discrete laterally-accreted channels, and from these to obliquely-accreted channels towards the top. Five 3rd-order sequences were identified within the area and interpreted as lowstand systems tracts. Each 3rd-order sequence is subdivided in a series of lobe or channel complexes, which seem to be related to 4th-order cyclicity.
The 3rd-order sequences show a change in their internal organization and geometry from lobe-complex dominated (Sequence I/Sequence II) to a transition from lobe to channel-complexes (Sequence III) to channel-complex dominated (Sequence IV and Sequence V). The documentation of such trends, and the higher order internal evolution within the sequences, which also include mass wasting complexes, condensed intervals, and by-pass phases, permit a significant refinement of sequence stratigraphic models.

 

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004