Deep seismic-reflection data show the fundamental importance of major basement faults in controlling continental lithosphere extension and in forming major extensional sedimentary basins. These major basement faults extend down into the lower crust, where faulting gives way to distributed plastic deformation. A mathematical model has been constructed of the geometric, thermal, and flexural isostatic response of the lithosphere to extension by faulting (simple shear) in the upper crust and to plastic distributed deformation (pure shear) in the lower crust and mantle. This coupled simple-shear/pure-shear model of lithosphere deformation has been used to predict extensional sedimentary basin geometry, subsidence history, and crustal structure. Basin geometry and subsiden e history are controlled by fault geometry, the amount of fault extension, the depth of transition from simple- to pure-shear (detachment depth), the relative lateral position of the pure shear and the simple shear, and the flexural rigidity of the lithosphere during synrift and postrift stages of basin formation. Lithosphere extension on both listric and planar faults is considered.

The fundamental building block of extensional sedimentary basin formation is a localized rift basin in the hanging wall of a major basement fault overlain by a broader and thinner postrift thermal subsidence basin. Major extensional basins created by extension on several major basement faults are formed by the superposition of several of these fundamental building blocks.

The mathematical model of extensional sedimentary basin formation has been applied to the origin of the Jeanne d'Arc basin, Grand Banks, offshore eastern Canada. The Jeanne d'Arc basin formed by rifting that began in the Triassic and continued through into the Early Cretaceous. The mathematical model predicts the observed thicknesses of synrift and postrift sequences within the Jeanne d'Arc basin and indicates that only a few hundred meters at most of synrift and postrift sediments were lost through the Aptian "breakup" unconformity. The erosion of footwall uplift leading to regional uplift through the flexural response of the lithosphere provides a possible mechanism for the generation of this unconformity.

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