The Early Triassic was a period of ecological restoration for the earth＇s system after the end-Permian mass extinction. Geochemical records linked to the variations in marine ecosystems during this period have attrac...The Early Triassic was a period of ecological restoration for the earth＇s system after the end-Permian mass extinction. Geochemical records linked to the variations in marine ecosystems during this period have attracted the interest of geologists for many years. Based on petrographic analysis of samples and evaluations of their reliability as proxies for original seawater, this study investigated the carbon and oxygen isotopic compositions of 350 carbonate rock samples from the Lower Triassic （and adjacent strata） in the southern Longmenxia section of Guang＇an, eastern Sichuan Basin. The results indicate that the Triassic carbonate rocks from the southern Longmenxia section favorably preserved the original seawater＇s δ13C signal. Furthermore, carbon and oxygen isotopic compositions are found to be poorly correlated, with a determination coefficient as low as 0.0205 and only 44 rock samples show results of Mn/Sr〉2 and/or 6180〈-6.5%0. The complete carbon isotopic curve for the Lower Triassic is established using the data from the remaining 306 samples with MrdSr〈2 and/or 6180〉-6.5%o. This curve presents favorable comparability on a global scale, specifically in the δ13C minima near the Permian-Triassic boundary, at the top of the Jial and within the the Jia3, as well as in the δ13C maxima at the tops of the Yel and Ye4, at the base of the Jia2 and at the top of the Ye3. The peaks and troughs corresponding to these maxima and minima all reflect global signals. By comparing these results to previous research on coeval carbon isotopic curves established within the chronostratigraphic framework, the ages of these critical evolution points are determined. The results show that the Yel roughly corresponds to the Griesbachian substage; the Ye2 through Ye4 correspond to the Dienerian substage; Jial corresponds to the Smithian substage; from the Jia2 to the lower part of the Jia4 correspond to the Spathian substage; and the middle and upper parts of the Jia4 belongs to the Aegean Substage of the Middle 展开更多
A 36CI peak was found in the predicted section of Guliya ice core, from the Qinghai-Tibetan Plateau, at about 37 kaBP. This cannot be interpreted by means of changes in the accumulation rate, but by the enhanced cosmo...A 36CI peak was found in the predicted section of Guliya ice core, from the Qinghai-Tibetan Plateau, at about 37 kaBP. This cannot be interpreted by means of changes in the accumulation rate, but by the enhanced cosmogenic isotope production rate in the atmosphere. Compared with the records of 10Be and 36CI in the other regions, the peaks of the cosmogenic isotopes are global and can be considered as time marks. An intriguing fact is that the peaks coincided with cold periods.展开更多
地缘关系研究是地理学中的一个重要研究领域,基于大数据的地缘关系的定量研究是对传统定性地缘关系研究的必要补充。利用全球事件、语言与语调(global database of events,language,and tone,GDELT)新闻数据库获取中国与缅甸、老挝、越...地缘关系研究是地理学中的一个重要研究领域,基于大数据的地缘关系的定量研究是对传统定性地缘关系研究的必要补充。利用全球事件、语言与语调(global database of events,language,and tone,GDELT)新闻数据库获取中国与缅甸、老挝、越南、泰国和柬埔寨5个国家之间的交互事件,通过定量统计和空间制图、构建交互网络、时空热点分析等方法,对中国与这5个国家的地缘关系进行剖析。并以中缅为例分析两国地缘关系变化的原因,提出相应合作建议。结果表明,事件主要发生在各国政治经济文化较为活跃的地区;中国与越南和泰国的地缘交互较多,与越南的关系最为复杂;中国与五国的交互热点主要分布于越南、泰国、柬埔寨,除越南外,中国与另外4个国家的合作水平呈增强态势。展开更多
基金supported by the National Natural Science Foundation of China(Grant No.41272130)
文摘The Early Triassic was a period of ecological restoration for the earth＇s system after the end-Permian mass extinction. Geochemical records linked to the variations in marine ecosystems during this period have attracted the interest of geologists for many years. Based on petrographic analysis of samples and evaluations of their reliability as proxies for original seawater, this study investigated the carbon and oxygen isotopic compositions of 350 carbonate rock samples from the Lower Triassic （and adjacent strata） in the southern Longmenxia section of Guang＇an, eastern Sichuan Basin. The results indicate that the Triassic carbonate rocks from the southern Longmenxia section favorably preserved the original seawater＇s δ13C signal. Furthermore, carbon and oxygen isotopic compositions are found to be poorly correlated, with a determination coefficient as low as 0.0205 and only 44 rock samples show results of Mn/Sr〉2 and/or 6180〈-6.5%0. The complete carbon isotopic curve for the Lower Triassic is established using the data from the remaining 306 samples with MrdSr〈2 and/or 6180〉-6.5%o. This curve presents favorable comparability on a global scale, specifically in the δ13C minima near the Permian-Triassic boundary, at the top of the Jial and within the the Jia3, as well as in the δ13C maxima at the tops of the Yel and Ye4, at the base of the Jia2 and at the top of the Ye3. The peaks and troughs corresponding to these maxima and minima all reflect global signals. By comparing these results to previous research on coeval carbon isotopic curves established within the chronostratigraphic framework, the ages of these critical evolution points are determined. The results show that the Yel roughly corresponds to the Griesbachian substage; the Ye2 through Ye4 correspond to the Dienerian substage; Jial corresponds to the Smithian substage; from the Jia2 to the lower part of the Jia4 correspond to the Spathian substage; and the middle and upper parts of the Jia4 belongs to the Aegean Substage of the Middle
文摘A 36CI peak was found in the predicted section of Guliya ice core, from the Qinghai-Tibetan Plateau, at about 37 kaBP. This cannot be interpreted by means of changes in the accumulation rate, but by the enhanced cosmogenic isotope production rate in the atmosphere. Compared with the records of 10Be and 36CI in the other regions, the peaks of the cosmogenic isotopes are global and can be considered as time marks. An intriguing fact is that the peaks coincided with cold periods.
文摘地缘关系研究是地理学中的一个重要研究领域,基于大数据的地缘关系的定量研究是对传统定性地缘关系研究的必要补充。利用全球事件、语言与语调(global database of events,language,and tone,GDELT)新闻数据库获取中国与缅甸、老挝、越南、泰国和柬埔寨5个国家之间的交互事件,通过定量统计和空间制图、构建交互网络、时空热点分析等方法,对中国与这5个国家的地缘关系进行剖析。并以中缅为例分析两国地缘关系变化的原因,提出相应合作建议。结果表明,事件主要发生在各国政治经济文化较为活跃的地区;中国与越南和泰国的地缘交互较多,与越南的关系最为复杂;中国与五国的交互热点主要分布于越南、泰国、柬埔寨,除越南外,中国与另外4个国家的合作水平呈增强态势。
