Gravitationally unstable vertical gradients of bulk density can arise during the re-sedimentation of water-logged normally graded sand beds following liquidization, even though the density gradient imposed on the beds by the depositional process was originally stable. Convolute lamination, found chiefly in turbidites, is therefore capable of being formed under a wider range of circumstances than was formerly appreciated, and the presence of an unstable bulk density gradient dating from the time of deposition is not necessary for the manifestation in sediments of this type of Rayleigh–Taylor instability. Although the analysis promoting these conclusions cannot at present be tested experimentally because of practical difficulties, a laboratory study of the analogous sudden heating of a layer of viscous liquid from below affords some evidence in its support.

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