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Which way is up? Knowledge of the fundamental principles of stratigraphy (as in chapter 1) is especially important for correctly reading and interpreting sedimentary strata. The principle of superposition, where sedimentary layers are deposited in a time sequence, with the oldest on the bottom and the youngest on the top, uses way-up criteria to establish whether beds are in normal position or upside down because of tectonic movements (Fig. 1). Every time a sedimentologist observes inclined strata we ask ourselves, are these rocks the correct way up or overturned?

The blue colour in this thin section is stained epoxy resin infilling pore space. B) Ventifacts are pebbles and cobbles that are abraded, pitted, etched, grooved, or polished by wind-driven sand. When ancient ventifacts are preserved without being moved or disturbed, they may serve as palaeo-wind indicators. 2 the large-scale cross-bedding and the absence of finer-grained sediments (see Fig. 14). Ancient desert dune sandstones are usually highly porous, so make excellent reservoirs for both water and hydrocarbons.

9B). The delta front is the region where sediment carried by the distributary channels is deposited. Most delta fronts are dominated by sands with crossbedding, ripples and some bioturbation. g. Fig. 9C). 9 A) The subenvironments of a delta. B) Graphic log of the typical sedimentary succession and facies for a delta. C) Mississippi River delta with fine-grained Coal sediment plume at the delta front supplying Distributary sediment to the pro-delta. The sediment channel - C Delta - top/plain plume from the Mississippi River is at the right, and the plume from the Atchafalaya River can be seen at the left.