Flute casts preserved in a duster on the sole of an overturned Tae turbidite bed in the Cretaceous Franciscan Complex at Point St. George, California have outward-splaying, feather-like surface markings. These are interpreted to be casts of scours made by two oppositely rotating corkscrew vortices that were present in the fluid that eroded seafloor mud during flute formation. Their geometry is similar to the geometry of skin friction lines for narrow flutes, determined experimentally by J.R.L. Allen.

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