Upper Cretaceous Mass Transport Systems Above the Wyandot Formation Chalk, Offshore Nova Scotia

Abstract

Interpretations from 18 contiguous 3-D seismic surveys, covering more than 17,000 km2, show a wide variety of diagnostic geomorphic elements that indicate mass wasting was an important process in shaping the top surface of the Wyandot Formation, an Upper Cretaceous chalk unit deposited across wide areas off the coast of Nova Scotia. These geomorphic elements include a series of clearly defined ~80 m high head scarps extending more than 100 km across the margin, multiple 20 to 80 m high side scarps defining up to 40 km long failure corridors, and an irregular planform fabric above areas interpreted to correspond to bedding plane detachments, variably modified by overlying deformed strata. The latter morphology includes large >1 km wide slide blocks or erosional remnants. In addition, multiple intervals of chaotic seismic facies are recognized directly above the top Wyandot Formation seismic marker. These geomorphic features are attributed to a complex history of slope failure originating from a series of shelf-perched delta systems located 40 to 60 km landward from the paleo-continental slope break. These deltas prograded over the Wyandot Formation in the Late Cretaceous through early Paleogene. This study indicates that significant quantities of resedimented chalk may have been deposited on the outer shelf and upper slope. Such deposits could form important gas reservoirs, as demonstrated in the North Sea (e.g. Ekofisk field). However, the degree to which overlying prodelta muds were mixed with the Wyandot chalk during failure is unclear and likely has a direct bearing on the reservoir potential of resedimented chalks off Nova Scotia.