PALEOGEOGRAPHIC LINKS BETWEEN YREKA TERRANE (KLAMATH MOUNTAINS, NORTHERN CALIFORNIA) AND ALASKA'S NIXON FORK AND ALEXANDER TERRANES

Certain fossils from the Yreka terrane (Yt) of northern California's Klamath Mountains are similar to fossils in Alaska's Nixon Fork and Alexander terranes, especially early Paleozoic gastropods, brachiopods, and sphinctozoan sponges described in the literature. These similarities, plus species of shelly fauna endemic to the Yt, suggest that it was partially isolated in the Ordovician and Silurian but partially connected with tectonic elements that evolved into Alaskan accreted terranes. Other faunal affinities suggest early Paleozoic links with Laurentia, Siberia, Uralian terranes, and Baltica.

Where did these terranes develop? The Yt provides a Neoproterozoic starting point. Over 250 cyclomedusoid fossils of the Ediacaran biota include Ediacaria and Beltanella sp., recovered from argillites interbedded with the upper part of the Antelope Mountain Quartzite (AMQ). These fossils exhibit closest affinities to Ediacaran cyclomedusoids from Finnmark in northern Baltica, and from NW Laurentia; work by B. Waggoner also suggests ties to Australia and Siberia. AMQ provenance is continental but probably not the Laurentian craton (Bond and Devay, 1980). AMQ detrital zircons (E.T. Wallin and colleagues) are diverse but include Archean (3.20-2.60 Ga) through Proterozoic (2.53-1.3 Ga) with most being 1.9-1.8 Ga; a partial Laurentian source is permitted but other, cryptic sources are implied. These data suggest that the AMQ was deposited on a continental shelf following the breakup of Rodinia ca. 580-560 Ma, between the microcontinents of Baltica, Australia, Siberia, and Laurentia. The AMQ was later accreted to a series of island chains that eventually became the Klamath and Alaskan terranes. Paleolatitudes published by Mankinen et al. (2002) place the Yt at 7ºN or 7ºS ca. 580-570 Ma, and 31ºN or S in mid-Devonian.