Biostratigraphy of Marine Triassic in Northern Alaska: ABSTRACT

Abstract

Marine Triassic sedimentary rocks crop out in northern Alaska at scattered localities in a belt that extends from Cape Thompson and the DeLong Mountains on the west, eastward along the north front of the Brooks Range across the drainages of the Colville and Sagavanirktok rivers, and then northeastward to the and Romanzof Mountains of northeasternmost Alaska. Respective parts of this outcrop belt are designated as western (W), central (C), or eastern (E). Although highly condensed, especially on the west, the Triassic is nearly completely represented. From study of the U.S. Geological Survey collections, distinctive successive ammonoid and pectenacid bivalve faunas, with their ages and stratigraphic occurrences, are: (1) Otoceras of early Griesbachian and Ophiceras and Claraia stachei of late Griesbachian age, lower Ivishak Member of Sadlerochit (E); (2) Euflemingites romunderi fauna of early Smithian age, upper Ivishak Member of Sadlerochit (E) and shale member of formation (C); (3) Leiophyllites fauna of probable early Anisian age, shale member of (C and W?); (4) Daonella frami and/or D. degeeri of early Ladinian age, lower (E) and lower chert member of (C and W); (5) Leptochondria nationalis fauna of probably early Karnian age, middle of (E), correlative in part with Halobia cf. H. zitteli occurrences in chert member of (C and W); (6) Arctosirenites canadensis fauna of late Karnian age, middle of (E), correlative in part with Halobia cf. H. ornatissima occurrences in chert member of (C and W); (7) Monotis typica of early (?) and early middle Norian age, Shublik formation (W); (8) Monotis pinensis, M. obtusicostata, and/or Halobia fallax of middle Norian age, upper (E) and limestone member of (C and W); (9) Monotis ochotica ochotica and/or M. subcircularis of late Norian age, upper (E) and limestone member of (C and W); and (10) Monotis ochotica pachypleura of late Norian or younger Triassic age, uppermost Shublik formation (C and W). These faunas have much in common with those from along the Yukon River in east-central Alaska and from the Canadian Arctic Archipelago and eastern Asia, but they contrast strongly with Triassic faunas of southern Alaska and the Pacific margin of North America. End_of_Article - Last_Page 2504------------