地质论评2025，Vol.71Issue(5)：1517-1533,17.DOI:10.16509/j.georeview.2025.01.032
应用沉积有机质单体正构烷烃分子碳同位素定量重建古降雨量的方法及研究实例
Ancient precipitation reconstruction method and example by applying carbon isotopic composition of individual n-alkanes from marine sedimentary organic matters
摘要
Abstract
Objectives:The wet and dry changes in paleoclimate is an important research content in study and reconstruction of paleoenvironments during geological history,while the paleo-precipitation is an important indicator of wet and dry zonation of the land surface climate.According to global and Chinese modern plant leaf carbon isotopes(δ13Cleaf)data,it is believed that the δ13Cleaf values of the C3 plant are controlled by the magnitude of precipitation,with positive δ13Cleaf in arid zones and negative δ13Cleaf in humid zones,and it is straightforward to calculate mean annual precipitation(MAP)by using logarithmic equations of δ13Cleaf versus MAP.This paper proposes and substantiates a method for quantitatively reconstructing ancient precipitation levels using δ13C values of higher terrestrial plants,which holds significant scientific importance for exploring terrestrial paleoclimatic conditions throughout geological history. Methods:Previous studies shows that the nC27,nC29,and nC31 spectral peaks in the saturated hydrocarbon chromatograms are typical markers for the identification of organic matter from terrestrial plants sources in sedimentary strata,and the δ13C of these n-alkanes(δ13Cn_alkanes)records the carbon isotopic signals of the leaf of the plants(δ13Cplant),therefor it is possible to calculate and reconstruct the terrestrial plant leaf carbon isotopes(δ13Cleaf)after calibrating the effect of pedogenesis and diagenetic.Finally,based on the isotopic fractional coefficient(Δ‰=δ13CCO2-δ13Cplanr)between paleo-atmospheric CO2(δ13CCO2)and the plant(13Cplant),and by using the fitting equations of Δ‰ values to MAP(mm/a)which was established in this paper,we quantitatively calculated the paleo-precipitation and delineated the dry/wet changes of the paleoclimate during the deposition process of the section,and we also discuss the influence of latitude,altitude,and temperature on the reconstruction results. Results:In this paper,we reconstructs the variation curves of paleo-precipitation correspond to the succession from Eocene upper member of Xiaganchaigou Formation to the Quaternary Qigequan Formation of the Fengxi 104 wells(4514～530 m)in the Qaidam Basin.The result showed that during the deposition of the Oligocene Shangganchaigou Formation,the Qaidam Basin received the least amount of precipitation of only 250 mm/a,while during the deposition of Pliocene Shizigou Formation,the Qaidam Basin received the maximum precipitation which is up to 1200 mm/a. Conclusions:The climate and environment of the Neogene period in China have undergone significant changes.It is hypothesized that the replacement of planetary wind systems and monsoon wind systems is the cause of the changes in precipitation.关键词
陆地古植物/长链正构烷烃/碳同位素/古降水量/新生代/气候干湿/柴达木盆地Key words
terrestria plants/long-chain n-alkanes/carbon isotope/paleo-precipitation/drought and humid climate/Cenozoic/Qaidam Basin引用本文复制引用
伊海生,伊帆,田康志,石宇翔..应用沉积有机质单体正构烷烃分子碳同位素定量重建古降雨量的方法及研究实例[J].地质论评,2025,71(5):1517-1533,17.基金项目
本文为国家自然科学基金资助项目(编号:42172121)和甘肃省油气资源研究重点实验室开放课题基金项目(编号:SZDKFJJ2022002)的成果. This study was financially supported by Project of the National Natural Science Foundation of China(No.42172121)and Open Project Fund of Gansu Provincial Key Laboratory of Oil and Gas Resources Research(No.SZDKFJJ2022002) （编号:42172121）
