BUILDING THE WESTERN CORDILLERAN TERRANE COLLAGE: FOSSILS, PALEOMAGNETISM, AND FACIES FROM THE KLAMATH SUPERTERRANE (CALIFORNIA) TO THE ALEXANDER AND FAREWELL TERRANES (ALASKA)

In the late Neoproterozoic, Klamath Trinity ophiolite began forming in a post-Rodinian ocean basin ~7° N or S paleolatitude, with a paleopole 105° CCW from the Laurentian paleopole, while Antelope Mtn. Quartzite formed on a Siberian or Baltic continental shelf, colonized by Ediacaran White Sea-type cyclomedusoids (~555 Ma), but isolated from Avalon-type biota. Ordovician, Silurian, and Early Devonian fossils from Klamath to Alexander terranes suggest one or more island chains in the Uralian Seaway with Alaskan terranes separated from Klamath terranes but not isolated from them. The intraoceanic island chain(s) had strong faunal links to Siberia and/or Baltica but were isolated from Laurentia through the early Paleozoic. Paleomagnetic data suggest the island chain occupied by nascent Klamath terranes was oriented subparallel to latitude with equatorial to temperate faunas. The Middle Devonian Klamath paleopole increased to ~110° CCW from Laurentia with a paleolatitude of 31.1º ± 5º ― probably northern hemisphere based on faunas, suggesting that the island chain was moving away from Laurentia.

Early Permian faunas of the McCloud Limestone (Klamath: Redding subterrane) comprise a distinct biogeographic province in Northern Sierra and Eastern Klamath terranes. In the Mississippian, faunal links extend into the Grindstone terrane of Oregon. These endemic, tropical, shelly faunas suggest that these terranes formed a linear island chain subparallel to latitude, isolated from Laurentia by an ocean basin 2000-3000 km wide or by other elements that blocked migration of shallow-water faunas. The island chain remained ~110° CCW from North America through the Late Triassic (paleopole: Mankinen & Irwin, 1990).

In the Jurassic, the Klamath terranes rotated clockwise from ~95° to ~30° relative to Laurentia, coinciding with accretion of North Fork, Hayfork, Rattlesnake Creek, and Western Klamath terranes—intraoceanic accretionary complexes of arc, ophiolitic, and marine sedimentary rocks that successively collided with the southwestern edge of the Klamath superterrane nucleus as it approached North America. The Klamath-Alexander island chain did not accrete to North America until Early to mid-Cretaceous.