GEOL 3233 Lecture Notes - Lecture 7: Turbidite, Sedimentary Structures, Debris Flow
11 Oct 2017
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Hummocky x-stratification-undulating sets of cross laminae both concave-up (swales) and convex-up (hummocks) produced by big storms waves. Wind/eolian saltation very important get many ripples and dunes. Plane bed lamination-wind velocity too high for ripples ) analogous to u. f. r. p. b. Grain flow cross strata over steepening of the dune lee slope and avalanching down. Coarse grains at top because of dispersive pressure and at the toe because they overrun fine sediment. Grain fall laminae initiated at zones of flow separation at the brink of the slipface where grains in saltation lose momentum and fall on lee slope hard to distinguish from subaqueous grain fall. Thicker, more laminae, fine upward thinner, fewer laminae, coarsen upward. Rather than just the fluid being important, in sediment gravity flows the fluid-sediment mixture is moved down slope under the force of gravity. Sediment gravity flows were first recognized when turbid river water flowed into lakes and reservoirs.
