Download Depositional Sedimentary Environments: With Reference to by Professor Dr. Hans-Erich Reineck, Dr. Indra Bir Singh PDF

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Cases are known where shell and mud pebbles accumulations on the intertidal flats are reformed in the shape of megaripples. Megaripples show an increase in length with increasing shear stress of the bed. In finer sand, megaripples achieve greater lengths at relatively lower shear stress values than in coarser sand. With increasing shear stress, the height of mega- Current Ripples ripples gradually increases. However, its dependence on grain size is rather obscure. Even so, in fine sand megaripples acquire, as a rule, greater height at lower shear stress values than in coarse sand.

1. 8. 5 mm are known only as asymmetrical wave ripples. Moreover, symmetry of successive ripples of a ripple train of wave origin can vary in direction. The crests of asymmetrical wave ripples (and symmetrical wave ripples) show repeated bifurcations in the shape of a tuning fork (REINECK and WUNDERLICH, 1968a) and the profile of crests is rather regular (Fig. 29). Small ripples of current origin do not show such bifurcations. However, one does find crests which terminate and are replaced by other crests, and this may give a false impression of biofurcation.

Anyway, the first two processes are probably most important and effective in the development of foreset laminae. JOPLING (1966) gives a list of useful indices of foreset laminae which may serve as a qualitative guide in determing the current strength in modern or ancient sediments. 1. Maximum Angle of Dip of Foreset Laminae. At low velocities the angle of dip may slightly exceed the static angle of repose (angle about 30°), whereas at high velocities the angle is less than the static angle (up to 20°).