_05A_Basin_RangeTwo

_05A_Basin_RangeTwo - GEOLOGY 20 - LECTURE 5A - BASIN &...

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1 GEOLOGY 20 - LECTURE 5A - BASIN & RANGE: Part 2 California During the Paleozoic (Ch. 7, 1 & p.483-490 in Harden - read selectively!) Interpreting the early geologic history of California from rocks in the Basin and Range Province (p. 487-490 in textbook) You know that the current Basin and Range landscape that we see today is a product of extensional tectonics that occurred during the latest Cenozoic. But how and when did the rocks of the Basin and Range get there? What do those old rocks that we now see uplifted in young mountain ranges represent? Most of the sedimentary rocks comprising the ranges in the B/R of California were originally deposited during the Paleozoic Era (540-250 m.y.). (Remember that these old rocks were deformed into tilted fault blocks much later, beginning about 16 m.y. and continuing to today. The age of the rocks is much older than the age of the mountains. ) - rocks older than about 600 m.y. are relatively rare in California, but they do exist in a region stretching south from Death Valley toward the San Bernardino Mtns. We’re not going to discuss these older rocks in this class. - geologists describe and interpret the sedimentary rocks exposed in the Basin & Range to reconstruct what the past environments must have looked like when these rocks were originally deposited Fossils reveal two important clues about the rock in which they’re found: 1) fossils tell us the age of the rock because of progressive evolutionary change - fossil species of plants and animals continually change in younger and younger rocks – e.g., we know that many of the rocks exposed in the Basin & Range are Paleozoic because they contain trilobites that only lived between 540 and 250 m.y. ago.
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_05A_Basin_RangeTwo - GEOLOGY 20 - LECTURE 5A - BASIN &...

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