Tectonism and sedimentation in the Jeanne d'Arc Basin, Grand Banks of Newfoundland
The Jeanne d'Arc Basin, offshore eastern North America, is ideally situated to allow an assessment of the rifting history of the North Atlantic borderlands. Structures and the sedimentary fill of this basin record the occurrence of three main episodes of Mesozoic rifting. During the first episode in Late Triassic to Early Jurassic times, series of NE-SW trending, en echelon, normal faults formed in the Grand Banks of Newfoundland area. A second episode of tectonism began in the latest Oxfordian, while rifting of the upper crust characterized by the growth of northerly-trending faults occurred from the Tithonian to the Early Valanginian. The third tectonic episode began during the Barremian, while mid-Aptian to late Albian rifting resulted in growth of NW-SE-trending ("trans-basin") normal faults. A few major faults of this latter age and orientation, such as the Spoonbill fault and part of the Egret fault, are continuous from the pre-Mesozoic basement through Upper Triassic to Lower Cretaceous strata. The Spoonbill fault acted as a headwall fault, marking a southern limit to crustal extension of the Grand Banks area during this third rift episode. Transpressional and transtensional structures developed during mid-Aptian to late Albian rifting at restraining and releasing bends. These fault bends were created by oblique-slip reactivation and linkage of the previously-formed NE-SW-trending, en echelon faults in response to a ninety degree rotation of extensional stress axes between the first and third Mesozoic rift episodes. Similar lithostratigraphic architectures observed in the Jeanne d'Arc, Porcupine (Irish Continental Shelf) and Outer Moray Fifth (North Sea) basins support a regional model of sedimentation controlled by progressive changes in subsidence during the most widely recognized extensional episode, that which spanned the Late Jurassic to Early Cretaceous boundary. Subsidence rates began to vary across broad areas but without significant fault block rotation during a latest Oxfordian through Kimmeridgian "onset warp" phase, resulting in deposition of a lower interval of organic-rich source rocks. Conglomerates and/or sandstones were widely deposited at the start of rift deformation during the early Tithonian, while palaeoenvironments ranged from alluvial and braid plain to submarine fan. These basal sediments fine up a second layer of commonly organic-rich shales and marlstones. Sediments from all three basins show evidence of decreasing water depth, increasing oxygen levels and increasing grain size on basin margins during the final stages of this rift episode. Syn-rift subsidence rates are interpreted to have increased from the time of fault initiation to amid-rift peak. Subsidence is considered to have then slowed during the latest phase of this syn-rift episode, resulting in development of a base Late Valanginian break-up unconformity.