The PISCES IVsubmersible was used to investigate the upper continental slope around 44 ON, 56" W, near the epicentre of the 1929 Grand Banks earthquake. Four dives in water depths of 800-2000 m were undertaken to observe speci3c features identijied with the SeaMARC I sidescan system in 1983. Two dives were made in the head of Eastern Valley where pebbly mudstones ofprobable Pleistocene age were recognized outcropping on the seafloor. Constructional features of cobbles and boulders, derived by exhumation and reworking of the pebbly mudstone, were also observed. These include gravel/sand bedforms (transverse waves) on the valley floor. Slope failure features in semiconsolidated mudstone were recognized on two dives onto the St. Pierre slope. Exposures in these mudstones are rapidly eroded by intense burrowing by benthic organisms.
Center for Coastal and Ocean Mapping Affiliate
Geological Survey of Canada
Hughes Clarke, J., Mayer, L.A., Piper, D.J.W., and Shor, A.N, 1989, Pisces IV submersible dives in the epicentral region of the 1929 Grand Banks earthquake, in Piper, D.J.W., ed., Submersible studies off the east coast of Canada, Geological Society of Canada Special Paper no. 88-20, pp. 57-69.