ERS120H5 Lecture Notes - Lecture 16: Xenolith, Absolute Dating, Stratigraphic Column
Document Summary
Telling time: geologic time and rock dating methods. We know that this dike cross cuts because the rocks are older than the rock that is cross cutting. Any piece of rock (inclusion or xenolith) included within another rock must be older than the rock in which it is incorporated. The sill has bits of pieces from the rocks above and below incorporated into it. The inclusion must be younger than the granite than is included in it. The oldest layer is at the bottom and the youngest layer is at the top. Only applies if there hasn"t been depervation. An unconformity is a rock interface which represents a gap in the geologic record, like pages missing from a book. Some of the old record gets removed (eroded) and new rocks starts being made. Sedimentary layers (and lava flows) are usually originally laid down horizontally. If they re not now horizontal, they have been deformed.
