2014 GSA Annual Meeting in Vancouver, British Columbia (19–22 October 2014)

Paper No. 108-5
Presentation Time: 8:50 AM

RADIOLARIAN FAUNAL TURNOVER AND PALEOPRODUCTIVITY CHANGES IN THE LATE TRIASSIC PANTHALASSA OCEAN: A POSSIBLE EFFECT OF LARGE IMPACT EVENT


ONOUE, Tetsuji1, SATO, Honami2, IKEHARA, Minoru3, TAKAYA, Yutaro4, NOZAKI, Tatsuo4, FUJINAGA, Koichiro5, KATO, Yasuhiro5 and UNO, Koji6, (1)Department of Earth and Environmental Sciences, Kumamoto University, 2-39-1 Kurokami, Kumamoto, 860-8555, Japan, (2)Department of Earth and Planetary Sciences, Kyushu University, 6-10-1 Hakozaki, Fukuoka, 812-8581, Japan, (3)Center for Advanced Marine Core Research, Kochi University, Nankoku, 783-8502, Japan, (4)Research and Development Center for Submarine Resources, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 2-15 Natsushima-cho, Yokosuka, 237-0061, Japan, (5)Frontier Research Center for Energy and Resources (FRCER), School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8656, Japan, (6)Graduate School of Education, Okayama University, Tsushimanaka 3-1-1, Okayama, 700-8530, Japan

Anomalously high platinum group element (PGE) concentrations in Upper Triassic (middle Norian) pelagic bedded chert in the Sakahogi section, central Japan, have been attributed to an extraterrestrial source and impact event that formed the 90-km-diameter Manicouagan crater in Canada. Previous osmium isotope studies have revealed that the anomalously high PGE abundances resulted from a large chondritic impactor (3.3–7.8 km in diameter). To evaluate the biotic and environmental effects of such an impact event, we report on new micropaleontological and geochemical data from the Sakahogi section across the middle Norian ejecta layer.

Three biostratigraphic radiolarian zones are recognized in the Sakahogi section; in ascending order, these are the Capnodoce–Trialatus zone, the Trialatus robustus–Lysemelas olbia zone, and the Lysemelas olbia zone. Detailed high-resolution sampling and biostratigraphic data showed that the ejecta layer occurs at the base of the Trialatus robustus–Lysemelas olbia zone. The biostratigraphc analysis revealed that no mass extinction of radiolarians occurred at the impact event horizon. However, major turnovers in radiolarians occur above the ejecta horizon, in the Trialatus robustus–Lysemelas olbia zone; this turnover is associated with deposition of a spicular chert, suggesting temporal changes in marine ecosystems after the impact event. Furthermore, significant negative excursions in paleoproductivity proxies (Ca, Ba, d13C) above the ejecta horizon may reflect a decrease in biological pelagic production in the Panthalassic Ocean after the impact event.

Session No. 108

T205. Major Evolutionary Events of the Early Mesozoic— Paleontology and Paleoecology from the Middle Triassic to the Late Jurassic
Monday, 20 October 2014: 8:00 AM-12:00 PM
220 (Vancouver Convention Centre-West)
Geological Society of America Abstracts with Programs. Vol. 46, No. 6, p.278
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