Note #3 GEOL 201 - 001
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This 8 page Class Notes was uploaded by ach0261 on Saturday September 26, 2015. The Class Notes belongs to GEOL 201 - 001 at University of Wisconsin - Eau Claire taught by `Lori D. Snyder in Fall 2015. Since its upload, it has received 25 views. For similar materials see Geology of Our National Parks and Monuments in Geology at University of Wisconsin - Eau Claire.
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Date Created: 09/26/15
Geology 201 Note 3 How do we infer the relative ages of events EON ERA PERIOD EPOCH Fossils allow us to compare ages of different rock layers and to construct the geologic timescale 76 N id J 1 S De Hjbliocen i in Ersiesambiri n 1 Principles Original horizontality if layers are no longer horizontal some event affected the layers after they found Principle of superposition a layer of sediment is deposited any rock unit on which it rests must be older When a rock or deposit forms it may incorporate pieces or clasts of older rock Cross cutting relations when rocks are crosscut by fractures so the rocks were there before the fractures formed Contact effects magma is younger than the rocks that were altered How do we infer the age of landscape surface The age of a landscape surface must be younger than any rocks on which it is carved A landscape surface is older than any rock that is deposited on top of the surface What is the significance of an unconformity Erosion surfaces can be buried and preserved beneath later deposit These buried erosion surfaces called unconformities can represent large intervals of time missing from a rock sequence Unconformities nonconformities disconformities Unconformity Erosion surfaces formed in the past can be buried and preserved within a sequence of rocks f underlying rocks are titled before formation of the erosion surface the unconformity is an angular unconformity Nonconiormity Some erosion surfaces form on top of rocks that are not layered ike granite this type of unconformity is especially igneous rocks I called a nonconformity NONCONFORMITY Disconformity If rock layers are not titled before they are overlapped by younger layers but the boundary still represents millions of years of time the contact is a disconformity A disconformity can involve erosion orjust a long time period with little or no deposition Disconformities may be overlooked because they are parallel to rock layers DISCONFORMITY
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