Unconformity on Shelf Road

Precambrian granite (about 1.6 billion years old), distinct to the practiced eye from Pikes Peak Granite, sits directly under the Ordovician Manitou Limestone (~ 450 million years ago), which has fossilized scales from jawless fishes. This contact represents over a billion years that’s missing from the geologic record (at this site). That means that the old granite probably had a series of overburdens that may have represented many events, but the evidence has all eroded away, leaving the nearly flat erosional surface, upon which the seafloor sediments accumulated that became the limestone. On Shelf Road you can put your finger on over a billion years of missing time.screen-shot-2017-03-04-at-10-18-49-pm.png

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Author: Samuel A. Johnson

This blog is about hiking, thinking, and writing.

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