Stratigraphic response to basin formation: Jeanne d’Arc Basin, offshore Newfoundland

Using seismic reflection and exploratory well data, the stratigraphic response of the Jeanne d’Arc Basin to early Cretaceous extension was examined. The Jeanne d’Arc Basin, located c. 300 km east-southeast of St John’s, Newfoundland, is a large asymmetric half-graben, which trends north-northeast. The border faults delineating the western limit of the basin are eastward dipping. The structure and geometry of the border faults and transbasinal faults engendered by the early Cretaceous extension influenced the drainage and therefore, the sedimentation patterns in and around the Jeanne d’Arc Basin. In order to assess the stratigraphic response to basin formation and its spatial variation, it was necessary to establish a chronostratigraphic framework with which to examine the effects of the extensional deformation on the preserved stratigraphy. Time surfaces determined by sequence stratigraphy in conjunction with detailed palynology from wells have allowed correlation of time-equivalent coarse-grained proximal facies to the fine-grained distal facies within the Jeanne d’Arc Basin. Correlations among seismic reflection, sedimentological and biostratigraphic data reveal that the stratigraphic response to extensional basin formation varies spatially on both a local and regional scale. The local response was controlled by the small-scale basin architecture (i.e. border/transfer fault interaction) whereas the more regional response was governed by the pre-existing axial drainage networks that enter the basin along the southern basin-bounding transfer zone. The locally-derived sediments were allowed access to the basin near the transfer zones that segment the border faults possibly because of the diminished footwall uplift. These locally derived sandstone units correlate with prograding seismic reflectors that downlap onto the late Barremian rift-onset unconformity producing a wedge-shaped geometry. The wedge is thickest near the border fault and tapers basinward. Away from these locally-derived prograding wedges (i.e. fan delta deposits), the late Barremian rift-onset unconformity, defined from stratal patterns in seismic reflection data, correlates to a flooding surface within the basin depocentres where marine sandstones onlap on to restricted marine/lagoonal and non-marine subaerially-exposed shales. These shales are iron-stained and commonly contain abundant root structures, evidence for pedification, and sideritic concretions. The overlying marine sediments predominantly sourced from the southernmost transfer zone, infilled the basin longitudinally, are more regionally persistent, and onlap onto the locally-derived prograding wedge. Exploratory well data from the Jeanne d’Arc Basin suggest that the regionally derived sediments that infill the basin longitudinally are better hydrocarbon reservoirs than the locally-derived prograding wedges because of better sediment sorting and greater regional extent.