Earth Sciences 1022A/B Lecture Notes - Lecture 4: Geologic Time Scale, Unconformity, Metamorphic Rock
14 Jan 2016
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Relative time: tells us whether a rock is younger or older than another, based on: Superposition: in undeformed, horizontal sedimentary rocks, each bed is older than the one above, and younger than, youngest on top, oldest on the bottom. Original horizontality the one below: layers of sediment tend to be deposited in a horizontal position. Cross-cutting relations: a fault is younger than the rock it cuts, a rock is younger than the rock it cuts, inclusions are older than the rock containing them. Unconformities: missing rocks (due to nondeposition or erosion) Between flat and tilted, eroded beds within rock sequences: angular unconformity, disconformity. Hard to see time break: nonconformity. Between flat beds on eroded igneous, metamorphic. Correlation rock: matching similar rock type, position, especially fossils in the rock record based on fossil succession as organisms evolved through earth"s history; with index fossils can correlate over long distances, fossil succession. Organisms evolved along distinct pathways through geologic time, left index fossils.
