The Stable Isotope and Minor Element Geochemistry of Iron- Rich Chemical Sediments

富铁化学沉积物的稳定同位素和微量元素地球化学

• 批准号: 9003108
• 负责人: Crayton Yapp
• 金额: $ 11万
• 依托单位: University of New Mexico
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1990
• 资助国家: 美国
• 起止时间: 1990-06-15 至 1992-11-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9003108&HistoricalAwards=false
• 关键词: Stable; Isotope; Minor; Element; Geochemistry

Chemical sediments dominated by iron(III) oxides are a manifestation of the unique combination of abundant free oxygen and liquid water found in the surface and many near-surface environments of Earth. Research performed in this laboratory has shown that the stable isotope ratios of oxygen, hydrogen and carbon in certain iron(III) oxides contain information on ancient temperatures, sources of water and organic contributions to aqueous carbonate systems associated with iron(III) oxide precipitation. In addition trapped CO2 abundance data from geothites may be related to ambient CO2 partial pressures at the time of mineral formation. The oxygen isotope systematics of ubiquitous phosphate-iron(III) oxide pairs will be studied to determine if they contain information on paleotemperatures. Knowledge obtained from this and our previous studies of iron(III) oxides will be applied to isotopic, chemical and attendant petrographic investigations of Phanerozoic oolitic ironstones, recent bacterially mediated iron(III) oxide precipitate and Late Precambrian banded iron formation(BIF). Fe(III) carbonate abundance and carbon-13 variations in a Late Ordovician weathering surface could provide knowledge of ambient CO2 partial pressures and the role of organic matter in this ancient environment. Oxygen, hydrogen and carbon abundance and isotopic data from tropical oolitic ironstones that date from global "greenhouse" and "icehouse" intervals in the Phanerozoic will be obtained. The ancient tropical temperatures and sources of water will be compared for the deposits that represent these putative global climatic extremes. Oxygen isotopic measurements of a Late Precambrian quartz-hematite BIF should provide insight into the depositional environment of this deposit. Paleoclimatic data of the type to be obtained in this research are essential to an ultimate understanding of the possible link between global tectonics and the types of climatic regimes that could produce apparent tropical continental ice sheets in the Late Precambrian or polar ice sheets in the Late Ordovician.

以铁(III)氧化物为主的化学沉积物是在地球表面和许多近地表环境中发现的丰富的游离氧和液态水的独特组合的表现。该实验室进行的研究表明，某些铁(III)氧化物中氧、氢和碳的稳定同位素比率包含有关古代温度、水源和与铁(III)氧化物沉淀有关的碳酸盐水相体系的有机贡献的信息。此外，地质岩捕获的二氧化碳丰度数据可能与成矿时的环境二氧化碳分压有关。将研究普遍存在的磷酸盐-铁(III)氧化物对的氧同位素系统，以确定它们是否包含古温度信息。从这项研究和我们以前对铁(III)氧化物的研究中所获得的知识将被应用于显生宙蚝粒铁矿、新近细菌介导的铁(III)氧化物沉淀和晚前寒武纪条状铁形成(BIF)的同位素、化学和伴随的岩石学研究。晚奥陶世风化面中Fe(III)碳酸盐丰度和碳13的变化可以提供环境二氧化碳分压和有机质在这个古老环境中的作用的信息。将获得来自显生界全球“温室”和“冰库”区间的热带橄榄铁石的氧、氢和碳丰度和同位素数据。古热带温度和水源将与代表这些假定的全球气候极端的沉积物进行比较。通过对晚前寒武纪石英-赤铁矿BIF的氧同位素测量，可以了解该矿床的沉积环境。这项研究中将获得的这种类型的古气候数据对于最终了解全球构造与可能在晚前寒武纪产生明显热带大陆冰盖或在晚奥陶世产生极地冰盖的气候制度类型之间的可能联系是至关重要的。