Journal
CHEMICAL GEOLOGY
Volume 401, Issue -, Pages 1-14Publisher
ELSEVIER
DOI: 10.1016/j.chemgeo.2015.02.021
Keywords
Nitrogen isotope; Carbon isotope; Tournaisian; Late Paleozoic Ice Age; South China
Categories
Funding
- 973 program [2011CB808800]
- National Natural Science Foundation of China [41290260, 41303001]
- Ministry of Science and Technology Foundation Project
- 111 project [B08030]
- State Key Laboratory of Paleobiology and Stratigraphy, Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences [133108]
- Simons Foundation
- Sedimentary Geology and Paleobiology program of the U.S. National Science Foundation
- NASA Exobiology program
- State Key Laboratory of Geological Processes and Mineral Resources at the China University of Geosciences-Wuhan [GPMR201301]
- Directorate For Geosciences
- Division Of Earth Sciences [1053449] Funding Source: National Science Foundation
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Carbonate carbon (delta C-13(carb)) and bulk nitrogen (delta N-15) isotopic variation during the mid-Tournaisian was analyzed in the Malanbian and Long'an sections of South China. Their C-isotope profiles document a large positive excursion, herein termed the 'mid-Tournaisian carbon isotope excursion' (TICE), during the Siphonodella isosticha conodont Zone, although its magnitude differed between the two sections (>6 parts per thousand at Malanbian versus similar to 3 parts per thousand at Long'an). The TICE event coincided with sedimentologic and oxygen-isotopic evidence of climatic cooling and glaciation during the mid-Tournaisian. It was probably triggered by an increase in organic carbon burial rates linked to changes in global-ocean circulation. The study sections also document a large positive shift in delta N-15, from 1.7 parts per thousand to 4.2 parts per thousand at Malanbian and from 1.5 parts per thousand to 3.8 parts per thousand at Long'an. The N-isotope shift shows no termination within the study sections and is likely to mark the onset of an extended interval of N-15-enriched marine nitrate that lasted for the duration of the Late Paleozoic Ice Age. Its initiation coincided with TICE and thus may have been linked to ocean-circulation changes that resulted in intensified upwelling and an increase in water-column denitrification. The continuation of the N-isotope shift over millions of years may have been linked to glacio-eustatic fall and a long-term shift in the locus of denitrification from continental-shelf sediments to continent-margin oxygen-minimum zones. The TICE event thus marks the onset of sustained continental glaciation during the Late Paleozoic Ice Age. (C) 2015 Elsevier B.V. All rights reserved.
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