CARBONATE LITHOFACIES AND FORAMINIFERS FROM A MIDDLE PERMIAN SEAMOUNT IN THE BAKER TERRANE, ELKHORN MOUNTAINS, EASTERN OREGON

A small exposure of isolated carbonate blocks is located within a volcanic complex in the Elkhorn Mountains northwest of Baker City, Oregon and within the Baker terrane. The least metamorphosed part of the outcrop area is a small knob of several isolated limestone bodies surrounded by metasediment (argillite), marble, and various volcanic rocks. Samples of the various carbonate lithofacies have been examined to identify their faunal constituents and possible paleodepositional environments. Carbonate textures are dominantly grainstone (biosparite) and packstone which suggest high energy depositional conditions. The absence of significant evidence of terrigenous input in these carbonate rocks suggests a depositional environment away from a continental margin, possibly on a seamount. Faunal diversity consists of foraminifers, dasycladacean alga (Mizzia), gastropod fragments, and crinoid remains. A shallow marine environment, possibly lagoonal is indicated. Small foraminifers present include: Geinitzina cf. G. senkinensis Sosnina, Hemigordius japonicus Ozawa, Eomarginulinella vulgaris Sosnina, Abadehella sp. and Pachyphloia sp. The fusulinid fauna includes Pseudodoliolina cf. P. pseudolepida (Deprat) Parafusulina cf. P. kaerimizensis Ozawa, and representatives of Neoschwagerina, Schubertella, Rauserella, and Chusenella. The genus Pseudodoliolina is common in Asiatic Tethyan fusulinid faunas, but has been reported from only a few localities in accreted terranes in the northwestern part of North America (Oregon, Washington, British Columbia, and the Kenai Peninsula of Alaska). The foraminiferal fauna found in these rocks strongly suggests a Middle Permian age. Several stages of fracturing and extensive recrystallization of the carbonate rocks make difficult the specific identification of fossil elements, especially the highly fractured fusulinaceans. Paleontological components show significant affinity to faunas found in similar aged strata in accreted terranes in Japan, China, and the far eastern part of Russia. These rocks from the Elkhorn Mountains locality could have originated as carbonate on a seamount located in a Panthalassan island-arc system that was later accreted to North America in the Mesozoic Era.