Abstract

Sandstone beds intercalated with thick shale of the upper member of the Haida Formation (Albian-Turonian) in the Queen Charlotte Islands, British Columbia, Canada, show thinly laminated graded bedding. The sandstones generally are present as successions of more than a few tens of inversely to normally graded thin beds. The beds at the base of each succession contain much coarser detritus than the beds at the top. Each succession of graded beds shows a lens-shaped channel geometry. Wavy bed forms similar in shape to the hummock-and-swale topography that is thought to form hummocky cross-stratification (HCS) characterize the uppermost part of the succession. However, grain fabric and spacing of the bed forms indicate that they are of antidune origin. It is concluded that the successions of multiple laminated sandstone beds were produced by high-density turbidity currents that were probably associated with a gravity transformation, in which a successive freezing of traction carpets took place. Lack of shale in the succession together with the common presence of antidunes suggest that each succession was the product of one sedimentation event without decrease in stream power.

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