Abstract

The recognition of large olistostromes is difficult unless outcrop is nearly complete over broad areas. A previously unrecognized olistostrome in the lower Pit Formation was exposed on the shores of Shasta Lake, California, at a time of low water level. Blocks as much as 1000–2000 m across of diverse volcanic and sedimentary rocks are set in an unsheared tuffaceous matrix. The olistostrome formed in response to a Middle Triassic disturbance, possibly involving rifting, and it disrupted volcanogenic massive sulfide deposits.

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