CaCO3, organic carbon, and nitrogen at DSDP Hole 93-603B

Contents of organic carbon and carbonate carbon were determined on the same set of Cretaceous samples from DSDP Hole 603B in three different laboratories in order to assess the degree of comparability of organic carbon and carbonate values obtained by different labs using the same or different methods. We report the results of analyses for organic carbon using two different CHN analyzers, LECO, and Rock-Eval II and for carbonate carbon by CHN (total C minus C after acidification), the carbonate bomb technique, and CaCO3 calculated on the basis of total calcium obtained from X-ray fluorescence and induction-coupled plasma techniques. In addition, total nitrogen was obtained by two different labs using a CHN analyzer, but different bases for calculation were used. The various techniques for organic carbon analysis yielded comparable results, with the exception of those obtained by one of the CHN analyses of acid-treated samples. The calculation of organic carbon values and comparison on a whole-rock basis is very sensitive to errors in determination of carbonate contents, and this factor explains most, but not all, of the disparities between the data sets. The carbonate bomb technique gives CaCO3 values that correspond well with those calculated from total calcium concentrations (XRF and ICP analyses), whereas the CaCO3 calculated from CHN total carbon minus acid-soluble carbon consistently overestimated CaCO3. Total nitrogen and C/N results from the two different CHN analyses are not comparable and are subject to more error than the factor related to error in estimation of CaCO3.为评估不同实验室采用相同或不同方法测得的有机碳与碳酸盐碳数据的可比性，研究人员针对取自深海钻探计划（Deep Sea Drilling Project，DSDP）603B钻孔的同一套白垩纪样品，在三家不同实验室开展了相关测定。本次分析中，有机碳的测定采用了两台不同的CHN元素分析仪（CHN analyzer）、力可（LECO）仪器以及热解分析仪II（Rock-Eval II）；碳酸盐碳的测定则通过三种方式完成：一是CHN法（总碳减去酸化后残留碳），二是碳酸盐弹法，三是基于X射线荧光光谱法（X-ray fluorescence，XRF）与电感耦合等离子体法（induction-coupled plasma，ICP）测得的总钙含量计算碳酸钙（CaCO3）。此外，两家不同实验室通过CHN元素分析仪测定了总氮，但采用了不同的计算基准。 各类有机碳分析方法所得结果具有较好的可比性，仅经酸化处理样品的其中一组CHN分析结果除外。以全岩基准计算有机碳数值并开展对比时，对碳酸盐含量的测定误差极为敏感，该因素可解释数据集间绝大多数（但非全部）的差异。碳酸盐弹法所得碳酸钙数值与基于总钙浓度（XRF与ICP分析）计算得到的结果吻合度较高，而通过CHN总碳减去酸溶碳计算得到的碳酸钙则持续偏高。两家不同实验室的CHN分析所得总氮及碳氮比（C/N）结果不具可比性，且其误差幅度大于与碳酸钙估算误差相关的误差因素。