Paleogeographic Implications of High Latitude and Middle Latitude Affinities of the Ammonoid Uraloceras

SPINOSA, CLAUDE, Boise State University, Boise, ID, WALTER W. NASSICHUK, Geological Survey of Canada, Calgary, WALTER S. SNYDER and DORA M. GALLEGOS, Boise State University, Boise, ID

The ammonoid genus Uraloceras characterized a Lower Permian Boreal paleogeographic realm. Reported Lower Permian Pangaean Uraloceras occurrences have a Boreal or high-latitude distribution. Additional Lower Permian occurrences in Alaska, dominated by Boreal species, are compatible with and reinforce the Boreal distribution of the genus. In contrast, a new Uraloceras species from Nevada and from the Yukon, as well as representatives of the genus from Nei Monggol, inhabited regions of lower latitudes. The latter

ammonoid faunas, geographically and paleoecologically transitional between boreal and equatorial realms, include the genus Uraloceras as well as abundant other ammonoid taxa and representatives of equatorial perinitid ammonoids.

The lower assemblage of Wrangellia terrane in eastern Alaska, consisting of the Lower Permian Mankomen Group (Slana Spur and Eagle Creek formations), contains abundant Uraloceras and Paragastrioceras of high-latitude affinities. These are overlain by allochthonous Triassic chert, limestone, the Nikolai Greenstone and younger rock. Published paleomagnetic data indicate that the Nikolai Greenstone is of equatorial origin, with paleolatitudes 10 to 17 degrees. The Nikolai Greenstone seems to have a far-traveled history incompatible with ammonoid evidence suggesting cool-water setting on the Pangaean continental shelf. Published data for the Nabesna area demonstrate that lower and upper Wrangellia assemblages are not structurally juxtaposed.

A reinterpretation for the origin of Wrangellia or its magnetic signature may be in order. Alternative hypotheses suggest that the Eagle Creek Uraloceras-Paragastrioceras Boreal fauna was scraped off the craton at higher latitudes (possible 30-45 degrees ) and carried with Wrangellia to its present location.

AAPG Search and Discovery Article #91009©1991 AAPG-SEPM-SEG-SPWLA Pacific Section Annual Meeting, Bakersfield, California, March 6-8, 1991 (2009)