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Deepwater Fold and Thrust Belts in Passive Margin Deltas and Contractional Terranes—4-D Evolutionary Patterns


Modern high-resolution seismic data across deepwater fold and thrust belts has provided new insights into their geometries, fault-fold structures and how they form in space and time. These fold and thrust belts form critically-Previous HittaperedNext Hit Coulomb wedges and display dynamic interactions with both syntectonic sedimentation as well as syntectonic erosion. In delta terranes such as offshore Nigeria are characterised by a number of wide, low-taper fold belts formed on an over-pressured shale detachment unit. They are characterised by tight, variably spaced detachment folds commonly with faulted front and back limbs. High syntectonic sedimentations rates have lead to the burial of these folds with the formation of fanning growth wedges on both the front and back-limbs of the folds. In contractional terranes such as in accretionary wedges or on compressive margins critically-Previous HittaperedTop Coulomb wedges are characterised by regularly space thrust-fold systems. In the Makran accretionary prism offshore Iran and western Pakistan the fold and thrust belt is detached on an over-pressured shale sequence and consists on an imbricate fan of thrust faults with tip-line fault-propagation folds. Syn-tectonic sedimentation rates are low and the thrust-related folds are emergent on the sea floor such that gravitational collapse of the frontal limbs of the folds is common. Similar fold-thrust systems are found in the deepwater Sulawesi thrust and fold belt. Analyses and reconstructions of the deepwater fold and thrust belts have lead to new models for the development of thrust-related folds in these systems. The implications for petroleum exploration in these terranes is discussed.