Carbon isotopic compositions of pore and matrix carbonates in carbonate nodules, and origin of carbonate formation  

作　　者：LIU Lian YIN QiuZhen WU HaiBin GUO ZhengTang 

机构地区：[1]Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China [2]Graduate University of the Chinese Academy of Sciences, Beijing 100049, China [3]Institut d'Astronomie et de Geophysique G. Lemaitre, Universite catholique de Louvain, Chemin du Cyclotron 2, 1348 Louvain-la-Neuve, Bel gium

出　　处：《Chinese Science Bulletin》2010年第26期2926-2929,共4页

基　　金：supported by the National Basic Research Program of China (2010CB950200);the Knowledge Innovation Program of the Chinese Academy of Sciences (KZCX2-YW-117);the National Natural Science Foundation of China (40730104)

摘　　要：Carbon isotopes of pedogenic carbonate are often used to study paleoenvironments, but the existence of detrital carbonate changes the carbon isotopic composition. To develop an experimental method to determine existence of detrital carbonate in carbonate nodules, and to avoid it during isotope analysis, 23 pedogenic carbonate nodules in Miocene loess from the Loess Plateau of China were studied through micromorphology and carbon isotope analysis. The difference in carbon isotopic composition between matrix carbonate (B) and pore carbonate (A) (δ 13C(B-A)) ranges from 0.27‰ to 0.44‰ in nodules containing detrital carbonate and -0.16‰ to 0.13‰ in nodules where detrital carbonate is absent. The latter is within measurement error, but the former is beyond it. Here we propose an isotopic approach to determine if nodules contain detrital carbonate: if δ 13C(B-A) is within the measurement error, the nodules do not contain detrital carbonate, and vice versa. We suggest that it is better to analyze pore carbonate instead of matrix carbonate when using carbon isotope of carbonate nodules to reconstruct paleoenvironments.Carbon isotopes of pedogenic carbonate are often used to study paleoenvironments, but the existence of detrital carbonate changes the carbon isotopic composition. To develop an experimental method to determine existence of detrital carbonate in carbonate nodules, and to avoid it during isotope analysis, 23 pedogenic carbonate nodules in Miocene loess from the Loess Plateau of China were studied through micromorphology and carbon isotope analysis. The difference in carbon isotopic composition between matrix carbonate （B） and pore carbonate （A） （δ^13C（B_A）） ranges from 0.27‰ to 0.44‰ in nodules containing detrital carbonate and -0. 16‰ to 0.13‰ in nodules where detrital carbonate is absent. The latter is within measurement error, but the former is beyond it. Here we propose an isotopic approach to determine if nodules contain detrital carbonate： if δ^13C（B_A） is within the measurement error, the nodules do not contain detrital carbonate, and vice versa. We suggest that it is better to analyze pore carbonate instead of matrix carbonate when using carbon isotope of carbonate nodules to reconstruct paleoenvironments.

关 键 词：碳同位素组成 碳酸盐结核 核基质 中国黄土高原 碳同位素分析 起源 测量误差 同位素方法 

分 类 号：P736.211[天文地球—海洋地质] P588.245[天文地球—海洋科学]