Evaluating lateral compaction in deepwater fold and thrust belts: how much are we missing from “nature’s sandbox”?

Deepwater fold and thrust belts offer unique opportunities for evaluating deformation in sedimentary successions with unrivalled seismic imaging of fold-thrust structures. A regional seismic line through the Orange Basin, offshore Namibia, reveals a classic paired, gravity-driven deformation system, over 100 km across, with extension high on the submarine slope and contraction toward the toe of slope. A mismatch between the minimum estimate of extension (44 km) and slip on thrusts (18–25 km) requires an additional longitudinal strain component of 18%–25% to be distributed across the system, most plausibly as lateral compaction and volume loss. Strains of this magnitude raise issues for understanding deformation in partially lithified strata, with implications for the applicability of theoretical fold-thrust models and the development of hydrocarbon resources in deepwater settings.