The ratio of total organic carbon to total nitrogen (TOC:TN) and the stable carbon isotope ratio of organic matter (δ13Corg) are widely applied for inferring the origin of organic matter (OM) in Quaternary marine sed...The ratio of total organic carbon to total nitrogen (TOC:TN) and the stable carbon isotope ratio of organic matter (δ13Corg) are widely applied for inferring the origin of organic matter (OM) in Quaternary marine sediments. A plot of TOC:TN vs. δ13Corg is useful for such studies but is strongly based on qualitative constraints. This study is based on the qualitative characterization of the source of Quaternary OM via analysis of TOC:TN and δ13Corg signatures, but also proposes a probability parameter, which combines both signatures, to infer the amount of Terrestrial OM Input (TOMI). This index provides a method for quantifying the proportion of terrestrial OM vs. marine OMin a more comprehensive manner. The TOMI index concept was applied to a study area in theJoetsuBasin, eastern margin of theJapanSea, where previous studies have characterized theOMfrom the Last Glacial Maximum (LGM) to the present. The upwards increase in TOC indicates thatOMproduction during the Holocene was higher than during the LGM. The enriched δ13Corg signature upwards and decrease in TOC:TN suggest predominantly marine phytoplankton OM during the Holocene. Throughout the LGM, low OM production with depleted δ13Corg values and high TOC:TN values in the sediments suggest a predominantly C3 terrestrial plant source for the OM. Using these data, it was possible to calculate a proxy for a sea level variation curve during that period and to investigate the influence of the proximity of the coastal line to the continental slope on the input of terrestrial material to the basin. The proposal provides information for the application of sequence stratigraphic concepts. The TOMI index could confirm that the proximity to the shoreline and shelf break has a strong influence on the input of terrestrial material during lowstand periods.展开更多
本文利用碳酸盐岩风化剖面土壤中Rb/Sr值、有机碳氮的稳定同位素值（δ^（13）C_（org）和δ^（15）N_（org））并结合^（14）C定年结果,讨论了贵州黔西南喀斯特地区晚更新世以来的植被和气候变化情况。结果表明：（1）晚更新世以来,研...本文利用碳酸盐岩风化剖面土壤中Rb/Sr值、有机碳氮的稳定同位素值（δ^（13）C_（org）和δ^（15）N_（org））并结合^（14）C定年结果,讨论了贵州黔西南喀斯特地区晚更新世以来的植被和气候变化情况。结果表明：（1）晚更新世以来,研究区气候在千年尺度上经历了多个冷热、干湿循环过程,植被以C4植物为主;（2）研究区在14 750 a BP时期可能发生过较为极端的气候事件;（3）Rb/Sr值和δ^（13）C_（org）值可以用来指示古环境变化情况,高Rb/Sr值和高δ^（13）C_（org）值指示湿热气候,低Rb/Sr值和低δ^（13）C_（org）值指示干冷气候。展开更多
The Mid-Miocene Climatic Optimum （MMCO; 15-17 Ma） was one of the short-term climatic warm events that punctuated the Cenozoic long-term cooling trend. Because there are very few terrestrial records of this event, m...The Mid-Miocene Climatic Optimum （MMCO; 15-17 Ma） was one of the short-term climatic warm events that punctuated the Cenozoic long-term cooling trend. Because there are very few terrestrial records of this event, most of our understanding comes from marine cores. In this report, we first present new palaeomagnetic data that revises the dating of our 400 m-thick lacustrine section in Wenshan （Yunnan）, previously thought to be Late Mio- cene. These new data suggest an older age, ca. 15.2-16.5 Ma, coinciding with the MMCO. We measured δ13C on bulk organic matter （3 Corg）, total organic carbon （TOC）, total nitrogen （TN） and C/N ratios at a high sample resolution to： （1） reconstruct the palaeoenvironmental changes in the lake catchment area, and （2） infer mechanisms responsible for these changes. Our results show that all four geochemical parameters demonstrate that a strong environmental change occurred around the middle of the section, shortly after the C5Cn/C5Br geomagnetic reversal and the Early/Middle Miocene boundary at 15.97 Ma. We propose that the environmental shift may be due to a combination of a change in climate, which became cooler, together with a change in organic matter cycling within the lake. This study provides a new insight into the MMCO and demonstrates that although the MMCO was generally a warm event, it was also a time of climatic instability and abrupt environmental changes.展开更多
文摘The ratio of total organic carbon to total nitrogen (TOC:TN) and the stable carbon isotope ratio of organic matter (δ13Corg) are widely applied for inferring the origin of organic matter (OM) in Quaternary marine sediments. A plot of TOC:TN vs. δ13Corg is useful for such studies but is strongly based on qualitative constraints. This study is based on the qualitative characterization of the source of Quaternary OM via analysis of TOC:TN and δ13Corg signatures, but also proposes a probability parameter, which combines both signatures, to infer the amount of Terrestrial OM Input (TOMI). This index provides a method for quantifying the proportion of terrestrial OM vs. marine OMin a more comprehensive manner. The TOMI index concept was applied to a study area in theJoetsuBasin, eastern margin of theJapanSea, where previous studies have characterized theOMfrom the Last Glacial Maximum (LGM) to the present. The upwards increase in TOC indicates thatOMproduction during the Holocene was higher than during the LGM. The enriched δ13Corg signature upwards and decrease in TOC:TN suggest predominantly marine phytoplankton OM during the Holocene. Throughout the LGM, low OM production with depleted δ13Corg values and high TOC:TN values in the sediments suggest a predominantly C3 terrestrial plant source for the OM. Using these data, it was possible to calculate a proxy for a sea level variation curve during that period and to investigate the influence of the proximity of the coastal line to the continental slope on the input of terrestrial material to the basin. The proposal provides information for the application of sequence stratigraphic concepts. The TOMI index could confirm that the proximity to the shoreline and shelf break has a strong influence on the input of terrestrial material during lowstand periods.
文摘本文利用碳酸盐岩风化剖面土壤中Rb/Sr值、有机碳氮的稳定同位素值（δ^（13）C_（org）和δ^（15）N_（org））并结合^（14）C定年结果,讨论了贵州黔西南喀斯特地区晚更新世以来的植被和气候变化情况。结果表明：（1）晚更新世以来,研究区气候在千年尺度上经历了多个冷热、干湿循环过程,植被以C4植物为主;（2）研究区在14 750 a BP时期可能发生过较为极端的气候事件;（3）Rb/Sr值和δ^（13）C_（org）值可以用来指示古环境变化情况,高Rb/Sr值和高δ^（13）C_（org）值指示湿热气候,低Rb/Sr值和低δ^（13）C_（org）值指示干冷气候。
基金The authors are grateful to two anonymous reviewers for their constructive comments, which significantly improved the manuscript. The authors thank fellow members of staff of the Palaeoecology group in Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences for assistance during sample collection and productive critical discussions Professor Yun Fu from the Central Laboratory of Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences for assistance during the TN mea- surements+1 种基金 Dr. Olesya V. Bondarenko, from the Russian Academy of Sciences, Vladivostok, for her help and support during sample preparation Yi-Min Tian from the Faculty of Land Resource Engi- neering, Kunming University of Science and Technology, for her assistance when preparing and observing thin sections. The authors are grateful to Dr. Andrea Kern from the USGS and Dr. Dayou Zhai from Yunnan University for fruitful discussions and suggestions to improve the manuscript. This study was supported by National Nat- ural Science Foundation of China （U1502231）, the CAS 135 Program （XTBG-F01）, and a grant from the China Scholarship Council to J. Lebreton Anberr6e （2013GCX606）. Shihu Li and Chenglong Deng acknowledge support from the National Natural Science Foundation of China （41404056）, and the State Key Laboratory of Lithospheric Evolution （11431780）. Shu-Feng Li was supported by the Foundation of the State Key Laboratory of Paleobiology and Stratigraphy, Nanjing Institute of Geology and Paleontology, CAS （15310）. This work is part of the NECLIME （Neogene Climate of Eurasia） network.
文摘The Mid-Miocene Climatic Optimum （MMCO; 15-17 Ma） was one of the short-term climatic warm events that punctuated the Cenozoic long-term cooling trend. Because there are very few terrestrial records of this event, most of our understanding comes from marine cores. In this report, we first present new palaeomagnetic data that revises the dating of our 400 m-thick lacustrine section in Wenshan （Yunnan）, previously thought to be Late Mio- cene. These new data suggest an older age, ca. 15.2-16.5 Ma, coinciding with the MMCO. We measured δ13C on bulk organic matter （3 Corg）, total organic carbon （TOC）, total nitrogen （TN） and C/N ratios at a high sample resolution to： （1） reconstruct the palaeoenvironmental changes in the lake catchment area, and （2） infer mechanisms responsible for these changes. Our results show that all four geochemical parameters demonstrate that a strong environmental change occurred around the middle of the section, shortly after the C5Cn/C5Br geomagnetic reversal and the Early/Middle Miocene boundary at 15.97 Ma. We propose that the environmental shift may be due to a combination of a change in climate, which became cooler, together with a change in organic matter cycling within the lake. This study provides a new insight into the MMCO and demonstrates that although the MMCO was generally a warm event, it was also a time of climatic instability and abrupt environmental changes.
