Collaborative Research: A Molecular Isotope Perspective on the Processes of Organic Matter Preservation in Fossils

对化石中残余有机质稳定同位素记录的解释，需要从根本上认识生物合成、成岩作用和保存过程中碳氮元素库的形成和转化。提出了一系列的实验来阐明生物合成和成岩作用对生物成因矿物和沉积物中有机质分子和稳定同位素组成的影响。将与Howard Spero博士合作进行两种浮游有孔虫（Orbulina universa和Globigerina bulloides）的生长研究，比较壳蛋白氨基酸成分与饲料中氨基酸成分的稳定碳和氮同位素组成。除了可能识别必需氨基酸外，还将评估与营养相互作用相关的同位素分馏量。对来自化石的生物成因信号进行现实的评估，需要对成岩作用期间可能发生的同位素分馏的极限进行评估，并制定明确的标准来评估组分与保存基质的可能交换。拟开展模拟实验，评价成岩作用对化石和沉积物中有机质稳定同位素组成的影响。具体地说，将尝试评估水解和腐殖化引起的稳定碳和氮同位素分馏的大小。在保存方面，一个主要的关切仍然是区分本地有机化合物和外源重叠物的能力。气相色谱/燃烧/同位素比值质谱（GC/C/IRMS）在化石氨基酸对映体稳定氮同位素分析中的进一步发展，将为验证氨基酸对映体稳定碳同位素分析提供一种独立的方法。用于稳定氮同位素分析的GC/C/IRMS的发展依赖于建立能够氧化和还原卤代氨基酸衍生物的同位素可重复的燃烧技术。该方法的一项重要测试是对白垩纪样品中单个氨基酸的D-和L-对映体进行分子稳定碳和氮同位素分析，这些样品将包括恐龙蛋和相关的胚胎骨骼成分。这些罕见的样品是由Dale Russell博士和Jack Horner博士从北美和中国的一些地点提供的。如果同位素信号证实了原生性，就有可能使用分子稳定同位素来确定产蛋的成虫的身份和营养水平。据我们所知，这项研究还将首次直接比较来自同一化石生物的壳和骨的氨基酸成分的分布和稳定同位素组成。另外一组来自西撒哈拉的白垩纪恐龙样本也由戴尔·拉塞尔提供，用于对有机物保存和古生态学的详细调查。

9417836 Macko Interpretations of the stable isotope record of residual organic matter in fossils requires a fundamental appreciation of the formation and transformation of the elemental pools of carbon and nitrogen during biosynthesis, diagenesis and preservation. A series of experiments are proposed to elucidate the effects of biosynthesis and diagenesis on the molecular and stable isotope composition of organic matter in biogenic minerals and sediments. Growth studies involving two species of planktonic foraminifera (Orbulina universa and Globigerina bulloides) will be conducted in collaboration with Dr. Howard Spero to compare the stable carbon and nitrogen isotope compositions of amino acid constituents of the shell protein to those of the diet. In addition to potentially identifying essential amino acids, the magnitude of isotope fractionations associated with trophic interactions will be assessed. A realistic assessment of biogenic signals from fossils requires an appraisal of the limits of isotope fractionation that can occur during diagenesis and the development of unambiguous criteria for evaluating the possible exchange of components with the preserving matrix. Simulation experiments are planned to evaluate the effects of diagenesis on the stable isotope composition of organic matter in fossils and sediments. Specifically, attempts will be made to assess the magnitudes of stable carbon and nitrogen isotope fractionations resulting from hydrolysis and humification. With respect to preservation, a major concern continues to be the ability to distinguish indigenous organic compounds from exogenous overprints. The further development of gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS) for stable nitrogen isotope analysis of amino acid enantiomers in fossils will provide an independent method for verifying the stable carbon isotope analysis of amino acid enantiomers, the development of GC/C/IRMS for stable nitrogen isotope analysis is dependent upon e stablishing isotopically reproducible combustion techniques capable of oxidation and reduction of halogenated derivatives of amino acids. An important test of this method involves molecular stable carbon and nitrogen isotope analysis of D- and L- enantiomers of individual amino acids in Cretaceous age samples, which will include dinosaur eggs and associated embryonic skeletal components. These rare samples are being provided from sites in North America and China by Dr. Dale Russell and Dr. Jack Horner. If the isotopic signals verify indigeneity, it may be possible to use molecular stable isotopes to establish the identities and trophic levels of the adults that produced the eggs. This study will also provide, to the best of our knowledge, the first direct comparison of the distribution and stable isotope composition of amino acid constituents of shell and bone from the same fossil organisms. An additional sample set of Cretaceous age dinosaurs from the western Sahara is also being provided by Dale Russell for a detailed investigation of organic matter preservation and paleoecology.