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Understanding Geological Principles: Analyzing Rock Outcrops and Geological Events

This resource explores fundamental geological principles used to analyze rock outcrops, focusing on the principles of uniformitarianism, superposition, original horizontality, cross-cutting relationships, inclusions, and baked contacts. It highlights the order of geological events, emphasizing how sedimentary, igneous, and metamorphic rocks can be interpreted in terms of their geological history. The principles assist in determining the relative ages of geological formations, enhancing understanding of Earth's history—particularly how climate, tectonics, and biota have evolved over time.

MikeCarlo
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Understanding Geological Principles: Analyzing Rock Outcrops and Geological Events

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  1. http://paleo.cortland.edu/tutorial/Timescale/Timescale3.GIF

  2. Figure F7. Cenozoic events in climate, tectonics, and biota vs. d18O and d13C in benthic foraminiferal calcite (after Zachos et al., 2001). VPDB = Vienna Peedee belemnite http://odp.pangaea.de/publications/207_IR/chap_01/c1_f7.htm#60367

  3. http://www.ruf.rice.edu/~leeman/GeoTimeSpiral.gif

  4. “Outcrop” or cross section view • Types of rocks based on geometry? (sedimentary, igneous, metamorphic) • Order of events? http://serc.carleton.edu/quantskills/methods/quantlit/DeepTime.html

  5. Guiding principles geologist use when examining a rock outcrop to determine order of events • principle of uniformitarianism: • physical processes acting today also acted in the past at comparable rates • -- the present is the key to the past; • principle of superposition: • younger sedimentary rocks overlie older rocks because a layer of sediment cannot • accumulate unless there is already a substrate on which it can collect • principle of original horizontality: • sedimentary rocks are deposited relatively horizontally because they settle out of fluid in • a gravitational field -- folds and tilted beds indicate deformation that postdates deposition; • principle of original continuity: • sedimentary rock units accumulate in continuous sheets, a layer exposed on one side of • a canyon likely spanned the canyon at one time; http://serc.carleton.edu/quantskills/methods/quantlit/DeepTime.html

  6. Guiding principles geologist use when examining a rock outcrop to determine order of events • principle of cross-cutting relationships: • a feature that cuts across another is younger than that which it cuts; • principle of inclusions: • igneous and sedimentary rocks that contain inclusions of other rocks must be younger • than the rocks they include • principle of baked contacts: • an igneous intrusion "bakes" the rock surrounding it. http://serc.carleton.edu/quantskills/methods/quantlit/DeepTime.html

  7. In this image, A is younger than C (superposition), C is younger than I (inclusions, cross cutting), I is younger than D, E and B (cross-cutting), D (the fault) is younger than E and B (cross-cutting), H, F, K and J have been tilted or folded (original horizontality), G is younger than B, H, F, K and J (baked contacts). In order from youngest to oldest, the sequence is as follows: A, C, I, D (faulting), E, G, B, tilting, H, F, K. J. http://serc.carleton.edu/quantskills/methods/quantlit/DeepTime.html

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