A Turbidite Fan without Distributary Channels and Fed from a Dispersed Line Source is Imaged by 3D Seismic Data in an Upper Slope Setting, Nigeria
Commonly cited models of submarine fans (or lobes) share the following characteristics: (1) sediments are funneled into deep water via a submarine canyon; (2) sediments are delivered to the canyon via a fluvial or deltaic system; (3) the delivered sediments are heterolithic, consisting of clay-rich mud to coarse sand or gravel; (4) sediments are transported to the depositional fan via a single channel complex; (5) sediments are dispersed across the fan via distributary channels; (6) and the fan grows as a result of avulsions or bifurcations at diverse positions along the distributary channel pathways.
Although fans that fit this description are common on the continental slope of Nigeria, some fans are very different. Within the uppermost 150 meters of sediment on the upper slope, two fans are illustrated from high quality industry-standard 3D seismic data. One fan is consistent with the characteristics listed above whereas the other fan is interpreted to lack all of the characteristics listed above. The anomalous fan has the following characteristics: (1) it is constructed of sediments derived from multiple points along the shelf edge (a line source) without evidence of a submarine canyon; (2) the line source is interpreted to reflect transport by littoral drift; (3) fan deposits lack any resolvable levees suggesting that the delivered sediments are extremely sand-rich with minimal accompanying mud; (4) the delivered sediments are transported from the shelf edge to the fan via multiple channel complexes that are focused by slope topography toward the fan location; (5) no distributary channel system is visible within the fan; (6) avulsions are recognizable only at the head of the fan, and channel forms are poorly developed within the fan.
AAPG Search and Discovery Article #90162©2013 Pacific Section AAPG, SPE and SEPM Joint Technical Conference, Monterey, California, April 19-25, 2013