ABSTRACT
Seismic reflection profiles from the middle Laurentian fan show that the western fan valley has an abrupt eastward (leftward) hook at its terminus. The right-hand levee of this valley has been built across an older depositional surface in which numerous south-trending channels developed before the abrupt bend formed. This older channeled surface probably represents a complex depositional lobe deposit. Eastward deflection of turbidity-current flow occurred after debris-flow or slide deposits partly obstructed the valley near its termination or after aggradation of the lobe deposits. This deflection produced an abrupt change in the valley trend. Through time, the eastward-growing part of the levee has migrated northward toward the axis of the channel; this northward migration confines turbidity-current flow against the levee of another valley immediately upfan.
This study documents progradation of muddy facies over sandy lobes thus providing conditions for an effective seal for any hydrocarbons accumulated in the lobe sands. Updip migration of hydrocarbons through valley-fill sands that are contiguous with the lobes could be blocked locally by thick debris-flow units or by fine-grained turbidite fill in abandoned channels.
