LAB4_cross_sections - Structural Geology Lab 5 Part I. More...

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21 Structural Geology Lab 5 Part I. More on Geologic Maps and Cross-Sections I. The Nature of Geologic Contacts A. Depositional Geologic Contacts 1. sedimentary or volcanic rocks deposited in stratigraphic succession according to the laws of layer-cake geology a. Conformable Contact: (1) no evidence of erosion or break in stratigraphic succession (i.e. each successive layer becomes sequentially younger in age) (2) Geologic contact mapped as solid line showing break between rock formation or rock type b. Unconformities (1) Successive layers show evidence for significant erosion or non-deposition (i.e. there is a significant break in the stratigraphic record = "missing time") (2) Types of Unconformities (a) Nonconformities = sedimentary rocks deposited on crystalline rocks (e.g. igneous, metamorphic) (b) Angular Unconformities = sedimentary layers deposited on deformed and eroded older sedimentary layers i) erosional surface cross-cuts bedding planes of older sedimentary layers (c) Disconformities = sedimentary layers deposited on undeformed, but eroded older sedimentary layers B. Structural contacts 1. Fault Contacts a. structural discontinuity between rock and/or bedding planes (1) fault gouge, slickenlines, offset beds, etc. b. Can result in angular discontinuities, or stratigraphic discontinuities just like an unconformity
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22 C. Igneous Intrusive Contacts 1. Intrusive Contacts a. intrusive, hypabyssal igneous rocks cross-cut younger sedimentary beds (1) dikes = transverse to bedding planes at some angle (2) sills = parallel to bedding planes at some angle
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This note was uploaded on 10/02/2011 for the course GEOLOGY 406 taught by Professor Taylor during the Spring '11 term at Western Oregon University.

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LAB4_cross_sections - Structural Geology Lab 5 Part I. More...

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