BUT! You must be certain that the foresets belong to the SAME CROSSBED SET. In most cases, the direction of maximum foreset dip will be close to the paleoflow direction. Measure both plunge and bearings, and find the true dip using stereographic projection. In the example below, crossbed foresets are exposed in two rock faces of a joint block, presenting us with two apparent dips. The trick here is to look for nooks, crannies, joint or fracture faces that present a degree of three-dimensionality to the outcrop. In situations like this, the crossbed foresets are more likely to present an apparent dip direction, rather than true direction of flow. However, it is more common to find crossbed cross-sections in 2-dimensional exposures like cliffs and road-cuts. In such cases, measured bearings for individual bedforms provides a unique sense of flow. Identifying any of these is reasonably straight forward knowing what to measure can be a bit tricky.Īsymmetric current ripple and dune bedforms exposed on bedding planes can be measured by noting the facing direction of lee slopes (face down current – see the image above). It all begins with a humble crossbed, flute cast, or current aligned object. Knowing the direction of sediment transport will help you decipher paleoenvironments and sedimentary facies, paleoslope dip directions, possible sources of sediment, and the location of sediment sinks. Identifying sedimentary structures that indicate paleocurrent directions is an important task in any study of sedimentary rocks.
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