沉积与特提斯地质2024，Vol.44Issue(4)：809-825,17.DOI:10.19826/j.cnki.1009-3850.2024.06001
上扬子地区奥陶纪—志留纪转折期古气候演化与有机碳同位素变化成因
Paleoclimate evolution and origin of organic carbon isotope variations during the Ordovician-Silurian transition in the Upper Yangtze area
摘要
Abstract
The Ordovician-Silurian transition is an important period in Earth's history,marked by drastic changes in paleoclimate and the well-known Hirnantian isotope carbon excursion(HICE)in the Late Ordovician.However,the causes of paleoclimate changes and carbon isotope excursions,as well as their correlations,are still unclear.Based on the analysis of the total organic carbon(TOC)contents,organic carbon isotopes(δ13Corg),as well as major and trace elements,the chemical index of alteration(CIA)values of the Wufeng-Longmaxi Formation black shales of Well JY4 in Jiaoshiba area in the upper Yangtze region were calculated.Combined with biostratigraphy,it is found that the paleoclimate conditions of WF2-WF4 members gradually changed from warm and humid to cold and arid.The paleoclimate of LM1-LM4 members remained cold and arid,with an increasing trend upward in chemical weathering.The LM5 Member marked a gradual transition back to warm and humid climate environment,while the paleocimate conditions of LM6-LM7 and their above members showed an episodic fluctuation to cold and arid.The elemental geochemical proxies indicate that the sedimentary environment of the WF2-WF4 members shifted from oxic to anoxic conditions,with a rapid increase in oxygen content in Guanyinqiao Formation.The shales of LM1-LM3 members were deposited in an extremely anoxic and sulfidic environment,with oxygen content gradually increasing upward in the LM4 Member,transitioning from anoxic to suboxic,hypoxic,and finally oxidized conditions.The"positive drift"of δ13Corg in Guanyinqiao Formation is likely related to the burial and oxidation of organic carbon,with enhanced nutrient input from chemical weathering also playing a role.The subsequent"negative drift"in the black shale of Longmaxi Formation may be associated with the return of 12C to the marine carbon pool due to large-scale transgression.关键词
五峰—龙马溪组/古气候/碳同位素/古环境/地球化学Key words
Wufeng-Longmaxi Formation/paleoclimate/carbon isotope/paleoenvironment/geochemistry分类
天文与地球科学引用本文复制引用
杜梧槚,高平,蔡益栋,刘若冰,曹刚杉..上扬子地区奥陶纪—志留纪转折期古气候演化与有机碳同位素变化成因[J].沉积与特提斯地质,2024,44(4):809-825,17.基金项目
国家自然科学基金项目(42272140,U19B6003-03-01) （42272140,U19B6003-03-01）
