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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
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
_______ content of rocks. - William Smith...
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- Fall '14