BIOSTRATIGRAPHIC AND PALEOGEOGRAPHIC SIGNIFICANCE OF NEW CAMBRIAN FAUNAS FROM THE JONES RIDGE LIMESTONE, YUKON STABLE BLOCK, EASTERN ALASKA

Re-sampling of the thick (ca. 500m) platform margin to upper slope carbonate package mapped as the Jones Ridge Limestone in eastern Alaska yielded numerous new faunal collections from the Millardan and Ibexian Series. Collecting at Jones Ridge over the past few years produced macrofossils from more than fifty horizons in a single measured section through the formation, as compared to ten or fewer in four partial sections in previous studies. Among the trilobite genera added to the known fauna are a few (e.g. Idiomesus, Bowmania) whose species display restricted ranges elsewhere, offering potential for refined correlation into other Laurentian shallow water successions. A substantial increase in the number of recovered agnostoid arthropods improves correlation into deep-water units such as the Rabbitkettle Formation in northwestern Canada. More than fifteen horizons have now yielded agnostoids that represent at least four genera. The Ibexian part of the formation yielded trilobite collections from eight horizons through 65m of strata here assigned to the Symphysurina Zone, a Laurentian biozone characterized by rapid turnover of highly endemic/regionalized species. These collections reveal a vertical succession of different faunas that include four or more species of Symphysurina as well as Highgatella, and at least two hystricurine genera. Conodonts from this interval will provide critical constraints for comparison of the succession of faunas at Jones Ridge with similar Symphysurina-dominated species successions documented through the Symphysurina Zone in the Snowy Range Formation in Wyoming-Montana and the Bliss Formation in New Mexico. These Symphysurina Zone collections thus provide a biostratigraphic transect along the full length of the northern Laurentian platform. Among the conodonts already recovered (the first Cambrian conodonts reported from Jones Ridge) is Eoconodontus notchpeakensis, an important species whose FAD (First Appearnance Datum) defines the base of the Eoconodontus Zone on multiple continents. All faunal collections are tied in precisely to a suite of Carbon isotope samples collected at 1-5m resolution through the formation, providing a non-paleontological tool to augment the biostratigraphy in constraining correlations along the northern margin of the paleocontinent.