Abstract

A new type of submarine unconformity is identified in actively deforming basins, referred to as a hinged-margin drowning unconformity, recording high accommodation–high supply conditions on tilted clastic shelves characterized by a scalloped morphology. In contrast to drowning unconformities occurring in carbonates, and to transgressive surfaces onlapped by healing phase wedges, such discontinuities are tied to angular unconformities developed during tectonically generated relative sea-level rise. They also involve regional tilting and morphostructural reorganization. Three types of hinged-margin drowning unconformities are recognized, linked to specific structural styles. Such unconformities are recorded by networks of deep water incisions, 30–350 m deep and 50–7500 m wide, leaving remnants of a drowned shelf unconformably overlain by deeper-water facies. The unconformity passes laterally into a paraconformity of regional extent with stratigraphic lacunae ranging from some hundreds of thousands of years to a few million years. The above-grade slope created by tectonic tilting provides instability and huge sediment remobilization, testified by sedimentation rates >1m/k.y. in the depocenters. Changes in the paleowater depth reach up to 1 km, greater than is common in the classical sequence stratigraphy paradigm. The sediments removed from drowned and ravined deltas feed intra-shelf, intra-slope, and basin-floor turbidites during the regional transgression driven by increasing but laterally changing accommodation on hinged shelves. These new concepts are of great importance not only to interpret the accommodation succession and predict sediment delivery to deep water, but also for the inverse problem of reconstructing the timing of deformation.

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