--> ABSTRACT: Near-Surface Stratigraphic Evolution of Niger Shelf-Margin Delta/Upper Slope at OPL22O: Implications for Exploration Targets, by P. J. Bart, R. Keen, and R. Kooper; #91021 (2010)

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Near-Surface Stratigraphic Evolution of Niger Shelf-Margin Delta/Upper Slope at OPL22O: Implications for Exploration Targets

BART, PHILIP J., RICHARD KEEN, and ROBERT KOOPER

At OPL220, five near-surface regressive shelf-margin deltas have been identified on seismic data. From oldest to youngest these are referred to as the: (1) Orange, (2) Blue, (3) Red, (4) Green and (5) Purple units. Observations of the three-dimensional distributions of geologic features at these stratigraphic levels through time indicate cyclic deposition with depositional cycles consisting of shelf-margin delta (SMD) and upper-slope canyon stratigraphy. However, canyon development was distinctly magnified at Orange unit time. Throughout Orange unit time, a major shelf-margin counter-regional fault system was inactive relative to the rate of outbuilding of the Orange SMD, thus down-thrown expansion at the counter-regional faults did not contribute to sequestering of sediment on the shelf. Moreover, the Orange SMD had anomalously high progradation an lies (90). These high-angles of repose suggest high sand to shale ratio from the seismic stratigraphic analysis of the Orange unit and the other stratigraphic levels, SMDs with high-angle prograding foresets appear to have been more susceptible to major retrogressive failures. From the near-surface stratigraphic analysis the following five conclusions are relevant to upper-slope exploration targets of the Niger Delta depositional system: (1) inactive counter-regional faults do not effectively sequester sediments in the SMD; (2) SMDs with high-angle prograding foresets are susceptible to large-scale retrogressive failure; (3) retrogressive failure creates a broad base-of-slope canyon which parallels the trend of the offlap break; (4) sediments derived from the SMD are organized 5 kilometers basinward of the offlap break into well-defined incised canyons which extend more than 25 kilometers downslope and (5) beyond 30 kilometers, slope deposits include channel/levee strata. 

AAPG Search and Discovery Article #91021©1997 AAPG Annual Convention, Dallas, Texas.