ERS120H5 Lecture Notes - Lecture 18: Gneiss, Unconformity, Xenolith
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Relative age: ordering events in the sequence in which they happened, without taking the actual date into mind. Numerical age: not only ordering events in which they occur, but also dating them and focusing on when specifically they happened. In order of creation (think of the principle of superpositioning, but remember it is not always present: erosion, basalt i, basalt ii, conglomerate, breccia, erosion, tilting, limestone, sandstone, erosion, gneiss. Any feature which cuts across other rocks or features must be younger. The oldest layer is at the bottom and the youngest layer is at the top. An unconformity is a rock interface which represents a gap. If you have the rocks meeting an angle, with sedimentary rocks below and above, it is referred to as angular unconformity. If there are igneous rocks below and sedimentary rocks above, it is called a nonconformity.