From rising fluids to multi-stage landslide emplacement: reconstructing the formation of the Cape Fear Slide Complex offshore North Carolina, US

The Cape Fear Landslide Complex offshore North Carolina is the largest and most-voluminous mass transport complex on the Eastern North American Margin. Despite its scale, preconditioning factors, trigger mechanisms, and emplacement processes responsible for its formation remain poorly constrained. Previous studies have proposed gas hydrate dissociation or salt diapirism as primary triggers, but these interpretations are largely based on spatial correlations rather than direct causal evidence.

Here, we use 2D multichannel seismic data collected on R/V Marcus G. Langseth in 2023 to reconstruct the processes that led to the formation of the Cape Fear Slide Complex. The data reveal vertical fluid migration pathways originating in Jurassic sediments within the thermogenic production zone, terminating directly below the uppermost landslide headwall on the continental slope. Seismic bright spots and amplitude-versus-offset responses indicate the presence of gas within and around these vertical fluid migration pathways, consistent with higher-order hydrocarbon anomalies in Ocean Drilling Program drill cores.

We propose that sustained vertical fluid migrations led to overpressure in shallow sediments, reducing effective stress and critically preconditioning the slope prior for failure. Furthermore, we identify multiple, spatially separated depositional lobes on the abyssal plane downslope from the headwall. This geometry suggests that the Cape Fear Slide Complex formed through distinct progradational and retrogradational phases rather than in one catastrophic failure event. This multi-phase emplacement style implies different magnitudes and recurrence characteristics for landslide-generated tsunami than previously assumed.