Abstract

The late Miocene–Holocene deep-water fold-and-thrust belt of offshore northwestern Borneo displays one of the most acute angles recorded for a submarine critical-taper wedge. The very low surface (1°–2.5°) and basal detachment (2°–5°) dips require basal pore-fluid pressures near lithostatic pressure for the wedge to propagate at such angles. In the deep-water environment, sedimentary processes act against the wedge attaining critical taper. In places of lower sedimentation rates, the fold-and-thrust belt extends to the base of the slope and dips ∼1.5°–2.5°. In areas of the highest sedimentation rates (Baram Delta), the slope has a lower angle (1°) and the slope continues beyond the limit of the fold-and-thrust belt. Slope morphology changes along the margin from concave up (relatively low sedimentation rate, low shortening rate), to convex up (relatively high sedimentation rate, low shortening rate), to stepped (relatively low sedimentation rate, high shortening rate).

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