TY - JOUR
T1 - Tracking the redox history and nitrogen cycle in the pelagic Panthalassic deep ocean in the Middle Triassic to Early Jurassic
T2 - Insights from redox-sensitive elements and nitrogen isotopes
AU - Fujisaki, Wataru
AU - Sawaki, Yusuke
AU - Yamamoto, Shinji
AU - Sato, Tomohiko
AU - Nishizawa, Manabu
AU - Windley, Brian F.
AU - Maruyama, Shigenori
N1 - Funding Information:
Prof. Thomas J. Algeo and two anonymous reviewers provided many helpful comments, which greatly improved our manuscript. We thank Prof. Yukio Isozaki for fruitful discussions and comments on this manuscript. Field work was carried out with Shoko Ito, Hisahiro Ueda, Hikaru Sawada, Hisashi Asanuma, Yoshiaki Endo, Kaoru Mishima, Shinnosuke Aoyama, Konomi Suda, Kazue Suzuki, Takuya Saito, Kazumi Yoshiya, Tomohiro Kimura, Kenji Kawai, Hiroko Miyahara, Ryuho Kataoka, Hiroki Ogasa, Yusuke Chikaraishi and Fumiko Nakane, who are gratefully acknowledged. We wish to thank Drs. Shuichi Yanai and Yoshimitsu Akahori for their help in outsourcing the whole-rock geochemistry, and Drs. Yohei Matsui and Akiko Makabe for their assistance (EA-IRMS) in the acquisition of analytical data. This work was partly supported by JSPS grants (No. 23224012 , 24340102 , 21109006 and 15J11148 ) from the Ministry of Education, Culture, Sports, Science and Technology of Japan.
PY - 2016/5/1
Y1 - 2016/5/1
N2 - In order to clarify the redox history of the central Panthalassic Ocean in the Middle Triassic (Anisian) to Early Jurassic (Toarcian), we determined the abundances of major, trace and rare earth elements, and organic carbon and total nitrogen isotopes from well-exposed shales interbedded with deep-sea cherts from Inuyama, southwest Japan. A distinct positive Ce anomaly accompanying high Mn and weak Mo enrichments was detected in the transitional sequence across the Tr-J boundary, which indicates deposition under a more oxic condition than at any other period in the study section. The oxic period lasted for 130-170 kyr, and coincided with a faunal turnover at the end of the Triassic. On the other hand, strong enrichments of U, V, Mo, TOC and TN in Anisian and Toarcian black shales suggest deep ocean anoxia in both intervals. Highly concentrated Mo contents in some black shales indicate euxinia in the pelagic Panthalassic deep ocean. δ15NTN values are low, down to -2.0 ‰, in such black shales enriched in redox-sensitive elements, compared with other shales. This low δ15NTN values during recurrent oceanic euxinic events in the Anisian may indicate strong assimilation of ammonium, but the possibility of enhanced nitrogen fixation cannot be ruled out especially for the Toarcian anoxic event. This work provides the first documentation of the long-term redox history in the pelagic Panthalassic deep ocean, from the Middle Triassic to the Early Jurassic, based on redox-sensitive elements in shales, and it reveals probable links between oceanic redox changes and biological activity.
AB - In order to clarify the redox history of the central Panthalassic Ocean in the Middle Triassic (Anisian) to Early Jurassic (Toarcian), we determined the abundances of major, trace and rare earth elements, and organic carbon and total nitrogen isotopes from well-exposed shales interbedded with deep-sea cherts from Inuyama, southwest Japan. A distinct positive Ce anomaly accompanying high Mn and weak Mo enrichments was detected in the transitional sequence across the Tr-J boundary, which indicates deposition under a more oxic condition than at any other period in the study section. The oxic period lasted for 130-170 kyr, and coincided with a faunal turnover at the end of the Triassic. On the other hand, strong enrichments of U, V, Mo, TOC and TN in Anisian and Toarcian black shales suggest deep ocean anoxia in both intervals. Highly concentrated Mo contents in some black shales indicate euxinia in the pelagic Panthalassic deep ocean. δ15NTN values are low, down to -2.0 ‰, in such black shales enriched in redox-sensitive elements, compared with other shales. This low δ15NTN values during recurrent oceanic euxinic events in the Anisian may indicate strong assimilation of ammonium, but the possibility of enhanced nitrogen fixation cannot be ruled out especially for the Toarcian anoxic event. This work provides the first documentation of the long-term redox history in the pelagic Panthalassic deep ocean, from the Middle Triassic to the Early Jurassic, based on redox-sensitive elements in shales, and it reveals probable links between oceanic redox changes and biological activity.
KW - Japan
KW - Mass extinction
KW - Oceanic anoxic event
KW - Sediment geochemistry
KW - Shales
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U2 - 10.1016/j.palaeo.2016.01.039
DO - 10.1016/j.palaeo.2016.01.039
M3 - Article
AN - SCOPUS:84960172254
VL - 449
SP - 397
EP - 420
JO - Palaeogeography, Palaeoclimatology, Palaeoecology
JF - Palaeogeography, Palaeoclimatology, Palaeoecology
SN - 0031-0182
ER -