Middle and Late Triassic radiolaria from Kotel’nyi Island (New Siberian Islands, Russia, Arctic) and their paleobiogeographical significance

Kotel’nyi Island is located in the Arctic Ocean near to the prolongation of Southern Anyi ophiolite suture zone which is supposed to be remnant of southern Anyi Paleo-ocean located between Eurasian and North American plates. Therefore the information on Early Mesozoic faunas of this area and their paleobiogeographic affinities represent high interest for paleogeography and paleotectonics. Triassic of Kotel’nui Island is represented by all three series that are well characterized by ammonites, nautiloids, coleoids, bivalves and radiolarians. Section is characterized by predominance of soft clays. Radiolaria are present in the Middle and Upper Triassic, from Upper Anisian to Middle Norian.
   The Middle Triassic is represented by Anisian black clays with interlayers of bituminous shales, clayey limestones and phosphatic concretions with total thickness 30 - 140 meters. Ladinian is composed of similar clays with thickness 6 - 15 meters. Radiolaria were found in the Upper Anisian together with ammonites Indigirophyllites popowi Konstantinov. They are represented by Glomeropyle clavatum Bragin, sp. nov., G. boreale Bragin and others (11 species). Next radiolarian assemblage was found in the Upper Ladinian (with bivalvs Daonella sp. ex gr. D. frami Kittl.): Muelleritortis firma (Gorican), M. kotelnyensis Bragin, sp. nov., and others (10 species). Upper Triassic is represented by Carnian clays with siderite and phosphatic concretions (100 m) and Norian clays with siderite and phosphatic concretions (up to 500 m). Radiolaria are present in the Lower Carnian (with ammonoids
Discophyllites taimyrensis Popov): Pentactinocarpus colum Bragin, sp. nov., Glomeropyle cuneum Bragin, sp. nov., and others (12 species); Upper Carnian (with ammonoids Yakutosirenites yakutensis (Kiparisova): Pseudostylosphaera glabella Bragin, sp. nov., P. gracilis Kozur et Mock, and others (34 species); and in the Lower Norian (with ammonoids Striatosirenites kinasovi Bytschkov): Pseudostylosphaera glabella Bragin, sp. nov., P. gelida Bragin, sp. nov., and others (10 species). Each radiolarian assemblage includes several forms know from low-latitude regions as Mediterranean and Japan. These taxa constitute from 25 to 40 % of all species present in assemblage/
   These results allow making several conclusions:
   1) The sections include several radiolarian assemblages ranging from late Anisian to the early Norian. Taxonomic diversity of the assemblages increases at the stratigraphic levels rich in phosphorites and bituminous shales, which probably correspond to transgression episodes and well correlate with intervals of abundance of cephalopods.
   2) Triassic radiolarian assemblages from Kotel’nyi Island significantly differ from the coeval radiolarians of Pacific and Mediterranean. They are characterized by domination of genus Glomeropyle Aita et Bragin which is present only in Northern Siberia and in the New Zealand and displays bipolar distribution pattern. Triassic radiolarian assemblages of these regions display clear affinity. Radiolarians can serve as paleoclimatic indicators for the Triassic.
   3) The Middle Triassic radiolarian assemblages from Northern Siberia and regions of Mediterranean and Pacific include a number of common species (25-40 %). Using them, we can correlate Triassic deposits. This approach is helpful for solving the basic problem of correlation between Triassic deposits accumulated in the high- and low-latitude zones.
   4) The presence of low-latitude species in radiolarian assemblages is well correlative with constant presence of low-latitude taxa among cephalopods. Their assemblages include several species known from Mediterranean and North America. These facts can be explained as results of marginal position of Kotel’nyi Island in the Boreal Realm and well connections between basins. We can interpret the appearance of warm-water taxa by the influence of warm current coming from Pacific via suspected North Anyi Paleo-ocean.