Geological Society of America

T108 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

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

Paper number: T108-6
Program: Technical Sessions
Time: 8:50 AM – 9:05 AM

Authors

Tetsuji Onoue Presenting Author
Kumamoto University, Kumamoto, N/A
Honami Sato
Kyushu University, Fukuoka, N/A
Minoru Ikehara
Kochi University, Nankoku
Yutaro Takaya
Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka, N/A
Tatsuo Nozaki
Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka
Koichiro Fujinaga
The University of Tokyo, Tokyo, N/A
Yasuhiro Kato
The University of Tokyo, Tokyo
Koji Uno
Okayama University, Okayama, N/A

Abstract

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.