The linear expression of pockmarks on continental slopes, oriented parallel to depositional dip, is linked with the formation of deep-water slope channel complexes. The pockmark locations lead to the development of ridges directly upslope that show rotational failure of the slope progressively up the deepening and widening channel axis, as well as lateral foundering from the steeper channel walls. As the pockmarks grow, failure leads to progressive excavation of the slope updip, new pockmarks form, and progressively stack upslope. When the channel cuts the shelf edge, it begins to capture downslope-moving gravity currents that continue to mold the pockmark-generated fairway. Sand ponds in the splash pools and larger-scale failure from the channel margins become more active during this phase of channel excavation because of undercutting of the channel walls. Nearby linear pockmark trains become abandoned as one slope channel complex captures most downslope sediment gravity flows in that area. This paper provides a new mechanism for the initiation of slope channel complexes.

Data from several modern continental slopes and subsurface examples are used to illustrate the mechanism. Seismic mapping of the basal Jubilee field, offshore Ghana reveals large circular features aligned parallel to the deep-water Turonian slope dip, along the same depositional fairway as the subsequent Jubilee feeder slope channel complex. These features are spaced ∼2 km (∼ 1.25 mi) apart, ranging in diameter from 400 m (0.25 mi) to 1.1 km (0.68 mi) and form part of the lower Jubilee reservoir section (MH1). Identified most prominently on three-dimensional seismic data, they show an amplitude response indicative of significant sand accumulation when calibrated to existing wells. The conceptual geological model recognizes isolated bodies interpreted as ponded frontal splays infilling irregular topography at the base of the Jubilee reservoir. The bodies are located off-axis to the main MH1 depositional fairway. They are penetrated by several wells that prove sand presence and quality and hydrocarbon charge. Older, similar circular features appear to be largely filled by muddy slumps. In dimension and orientation, giant pockmarks are found to be the most likely origin.

Empty and active seafloor pockmarks of the same dimension, spacing, and orientation are documented from offshore Ghana and Equatorial Guinea to show a progressive evolution from linked pockmark chains, to pockmark gullies, to through-going blindhead channels that appear to be stranded in midslope locations with no obvious upslope feeders, and finally, to fully evolved slope channel complexes linked to the continental shelf. The pockmark-generated mechanism produces slumps below the base of the channel complexes before the sand-prone active phases of channel bypassing, and several examples of outcropping and subsurface channel complexes are documented to show this often observed, although never fully explained, facies association.