Further evidence for a turbidity current following the 1929 Grand banks earthquake

Abstract

Evidence has been obtained indicating that the uppermost layer of sediment of the abyssal plain south of the Grand Banks consists of silt and sand. The top layers of two piston sediment cores consist of 130 and 70 cm of graded silt and sand overlying foraminiferal clay of abyssal facies. Recent deposition of these graded layers is indicated by absence of abyssal sediment overlying them. At three additional coring stations nothing but a few grains of sand was obtained.The existence of this silt and sand layer constitutes a further line of evidence in support of the hypothesis of Heezen and Ewing (1952) that slumps initiated by the 1929 Grand Banks earthquake were transformed into a turbidity current which swept down slope, broke and carried away the submarine telegraph cables, destroyed bottom life and deposited a large quantity of sediments far out into the ocean basin.The thickness of the graded silt and sand layers in the cores is near to the 40–100 cm thickness predicted by Kuenen (1952).The existence of the layers of silt and sand is also further evidence for the hypothesis that the abyssal plains with their flat gently sloping surface were formed by ponded or otherwise spent turbidity currents.