Tectonism: the dominant factor in mid-Cretaceous deposition in the Jeanne d'Arc Basin, Grand Banks

Abstract

The development of stratigraphic sequences has been demonstrated to be controlled by a set of factors including variations in subsidence, sediment input, eustatic sea level and physiography. Well and seismic data from the Jeanne d'Arc Basin, Grand Banks indicate that mid-Cretaceous tectonism controls at least three of these factors, namely subsidence, sediment input and physiography. North Atlantic rift tectonism was therefore the dominant factor in controlling the migration of coastal to shallow marine environments and the development of sequence stratigraphy in this basin during the mid-Cretaceous. The Avalon Formation respresents a mainly Barremian to Early Aptian regressive phase of clastic, marine to marginal marine sedimentation. This followed the deposition of a thick sequence of mainly marine limestones and shales of the Whiterose Formation above a mid-Valanginian sequence-bounding unconformity. The increased clastic input and northward progradation of coastal environments represented by the Avalon Formation occurred during uplift of a basement arch to the south with subsidence of the basin increasing to the north, accompanied by only relatively minor faulting. These features indicate that a period of epeirogenesis was initiated during the Barremian. Continuing uplift over an expanding area at the southern end of the basin is interpreted to have resulted in the development of an angular unconformity with incised valleys. This mid-Aptian unconformity defines the top of the Whiterose/Avalon sequence. Initiation of brittle fracturing of the sedimentary package and underlying basement (i.e. rifting) in mid-Aptian times resulted in rapid fault-controlled subsidence and fragmentation of the Jeanne d'Arc Basin. This great increase in subsidence rate caused retrogradation of coastal environments across the previously developed sequence-bounding unconformity, despite continuing high rates of sediment input from the uplifted basin margins. The transgressive, siliciclastic Ben Nevis Formation comprises two separate but related facies associations. A locally preserved basal association represents interfingering back-barrier environments and is herein defined as the Gambo Member. An upper, ubiquitous facies association comprises tidal-inlet channel, shoreface and lower shoreface/offshore transition sandstones. This upper facies association onlapped marine ravinement diastems above the laterally equivalent back-barrier facies. The rapid fault-controlled subsidence and high sediment input rate of this mid-Aptian to late Albian rift period resulted in the accumulation and preservation of very thick shoreface sandstones. The transgressive sandstones were buried by laterally equivalent offshore shales of the Nautilus Formation. Flooding of the basin margins induced by the onset of thermal subsidence in latest Albian or early Cenomanian times marks the top of the Ben Nevis/Nautilus syn-rift sequence.