These strata were originally deposited horizontally

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Unformatted text preview: rata were originally deposited horizontally, but were later folded by tectonic forces. 2 1/25/2013 Superposition - earliest event at bottom In an undisturbed sequence of sedimentary rocks, and/or extrusive igneous rocks, we can assume that younger rocks sequentially overlie older rocks. Based on this principle, the law of superposition states that in any sequence of layered rocks, a given stratum (layer) must be older than any stratum (layer) on top of it. Younger upward Youngest stratum exposed Oldest stratum exposed Niagara Gorge Cross-Cutting Relationships Geologic features such as faults (cracks along which movement has occurred) and igneous intrusions are cut into pre-existing rock bodies. - faults must be younger - bottom is younger (cuts through other one) Based on this principle, the law of cross-cutting relationships states that a fault or intrusive igneous body must be younger than the rock through which it has cut. fault This fault (and associated movement) is younger the strata that it has cut into and displaced. These felsic dykes (igneous intrusions) are younger than the mafic volcanic rocks into which they have been intruded.(cut through) Fossil Succession Evolution is an irreversible processes. Thus, individual fossil species represent finite periods of time and occur in a specific sequence. The law of fossil succession states that fossils occur in a consistent vertical order in sedimentary rocks all over the world. Thus the relative age of “slices” of time represented in rocks can be determined from the fossil _______ content of rocks. - William Smith...
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