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U.S. Geological Survey
Open-File Report 2004-1094
Version 1.0

Map Showing Fossil Localities of the Rattlesnake Creek, Western and Eastern Hayfork, and North Fork Terranes of the Klamath Mountains

By William P. Irwin, and Charles D. Blome

2004

Significant collections of fossils from the Rattlesnake Creek, Western and Eastern Hayfork, and North Fork terranes (rocks known collectively as the western Paleozoic and Triassic belt (or TrPz)(Irwin, 1972)) of the Klamath Mountains were first made by J.S. Diller of the U.S. Geological Survey in the company of T.W. Stanton and James Storrs in 1902 (see Diller, 1903). These collections augmented a few earlier collections by Diller and Storrs. Some of these collections variously contained Chaetetids (corals or spongiomorphs?) and ammonites that were originally thought to be Devonian in age: A Devonian age for the Chaetetids now seems doubtful, and the ammonites are now known to be Triassic in age (Silberling and Irwin, 1962). These fossils were from discontinuous bodies of limestone in the Rattlesnake Creek terrane that were referred to by Diller (1903) as the "southwestern Devonian belt". Discontinuous limestone bodies in the Eastern Hayfork and North Fork terranes, east of the so-called "southwestern Devonian belt", yielded late Paleozoic fossils and were referred to by Diller (1903) as the "southwestern Carboniferous belt".

Much additional sampling and paleontologic work has been done since Diller's time, and the Paleozoic of the TrPz is now thought to be represented mainly by scattered small limestone bodies that contain late Paleozoic microfossils. These limestones are present in all the terranes except the Western Hayfork. Some of the late Paleozoic microfossils in the limestones of the Eastern Hayfork and North Fork terranes are of Tethyan faunal affinity and attest to the allochthonous and far-traveled nature of the terranes. Two limestone localities (105 and 108) in the Eastern Hayfork terrane contain Waagenophyllid corals that also are considered Tethyan. Conodonts also are found in many of the limestone bodies of the TrPz and in some of the chert. The color alteration index (CAI) of the conodonts in the TrPz ranges from 5 to 7, which indicates they have been heated to temperatures of 300° to 500°C (Irwin and others, 1983).

The advent of modern radiolarian studies, pioneered by Emile Pessagno and others in the late 1960's, quickly followed the discovery of simple laboratory techniques for extracting radiolarians from chert. During the following decades, many chert localities in the terranes of the TrPz were sampled for radiolarians by various geologists and students. The TrPz chert has been found to be predominantly Triassic or Jurassic (or Mesozoic) in age and less commonly Paleozoic. The least sampled terrane, the Western Hayfork, contains four sampled radiolarian localities, three of which were identified as Mesozoic and one as Late Triassic to Early Jurassic. All of the other terranes of the TrPz contain chert with some Triassic and/or Jurassic radiolarian faunas, although the presence of Jurassic radiolarians in the Eastern Hayfork terrane is questionable. Chert with late Paleozoic radiolarians is sparsely present in the Eastern Hayfork and North Fork terranes, but is absent in the Rattlesnake Creek terrane. The oldest radiolarians recognized in the TrPz are Permian in age; the youngest are Early or Middle Jurassic. Chert containing Pliensbachian (Early Jurassic) radiolarians occurs in the North Fork terrane, and, interestingly, is also found in some Franciscan terranes of the Coast Ranges (see Blome and Irwin, 1983).

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For questions about the content of this report, contact Porter Irwin

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Maintained by: Michael Diggles
Date created: April 5, 2004
Date last modified: October 24, 2006 (mfd)