JEG100H1 Chapter 12: Geologic Time
17 Nov 2016
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Uniformitarianism: physical, biological, chemical laws of today also operated in geologic past. Therefore, must understand present day processes to understand past. Cannot accurately say geologic processes of today are the same as those of past. Different relative importance, different rate, not currently observable. Stratigraphy: description of strata and their organization and relationship through space and time in order to establish age. If rock layers folded, must have been moved by crustal disturbances after deposition. Sedimentary beds originate in all directions until they grade into different type of sediment, or thin out at edge of basin. Geologic features cutting across formed after rock they cut through. Long period where deposition ceased, erosion removed previously formed rocks. Uplift and erosion followed by subsidence and renewed sedimentation. Tilted, folded rock overlain by younger, flatter strata b. Sea level falls, no sedimentation; sea level rises again, new sediment beds. Hard to identify, since new and old beds parallel c.
