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Figure F7. Cenozoic events in climate, tectonics, and biota vs. d 18 O and d 13 C in benthic foraminiferal calcite (after Zachos et al., 2001). VPDB = Vienna Peedee belemnite
Types of rocks based on geometry? (sedimentary, igneous, metamorphic) Order of events? “Outcrop” or cross section view
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 Guiding principles geologist use when examining a rock outcrop to determine order of events 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;
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. principle of cross-cutting relationships: a feature that cuts across another is younger than that which it cuts; Guiding principles geologist use when examining a rock outcrop to determine order of events
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.