An ecological response to the Eocene/Oligocene transition revealed by the delta(13)G(TOC) record, Lanzhou Basin, NE Tibetan Plateau

Author:	Wu, F.L., Zhao, Y., Fang, X.M., Meng, Q.Q.
Abstract:	The Eocene/Oligocene (E/O) transition, corresponds to an abrupt global cooling, thought to have been one of the greatest temperature changes in the mid-Cenozoic Earth's history. Sparse studies have successfully reconstructed the terrestrial ecological response to this temperature change. Here, we report results from the study of organic carbon isotopes (delta C-13(TOC)), together with n-alkanes biomarker analysis, in the Yongdeng Section, Lanzhou Basin, Northwest China, and discuss changes in delta C-13(TOC) and their mechanisms. The results show that between 35.3 Ma and 31.0 Ma, delta C-13(TOC) ranged from- 26.72 parts per thousand to- 21.27 parts per thousand. The main change occurred at 33.4 Ma, when 813Groc became heavier by 3 parts per thousand. At this time the long-chain n-alkane members (C-27, C-29 and C-31) were dominant, suggesting the most likely sources of organic matter were terrestrial plants. Combining these results with existing measurements of plant delta C-13(TOC) and sporopollen data in adjacent areas, we infer that this change at 33.4 Ma might have been caused by an increase in gymnosperm content especially coniferous trees adapted to cold climates, which have a heavier delta C-13(TOC) than that of the angiosperms, this would have been a response to the global cooling characteristic of this period.
Contact the author:
Page number:	74-80
Issue:
Subject:
Authors units:
PubYear:	2018
Volume:	159
Publication name:	Journal of Asian Earth Sciences
Abstract:	The Eocene/Oligocene (E/O) transition, corresponds to an abrupt global cooling, thought to have been one of the greatest temperature changes in the mid-Cenozoic Earth's history. Sparse studies have successfully reconstructed the terrestrial ecological response to this temperature change. Here, we report results from the study of organic carbon isotopes (delta C-13(TOC)), together with n-alkanes biomarker analysis, in the Yongdeng Section, Lanzhou Basin, Northwest China, and discuss changes in delta C-13(TOC) and their mechanisms. The results show that between 35.3 Ma and 31.0 Ma, delta C-13(TOC) ranged from- 26.72 parts per thousand to- 21.27 parts per thousand. The main change occurred at 33.4 Ma, when 813Groc became heavier by 3 parts per thousand. At this time the long-chain n-alkane members (C-27, C-29 and C-31) were dominant, suggesting the most likely sources of organic matter were terrestrial plants. Combining these results with existing measurements of plant delta C-13(TOC) and sporopollen data in adjacent areas, we infer that this change at 33.4 Ma might have been caused by an increase in gymnosperm content especially coniferous trees adapted to cold climates, which have a heavier delta C-13(TOC) than that of the angiosperms, this would have been a response to the global cooling characteristic of this period.
The full text link: