A Study of the Origin and Significance of Pyrite Ooids

黄铁矿鲕体的起源及意义研究

• 批准号: 9706178
• 负责人: Juergen Schieber
• 金额: $ 9.9万
• 依托单位: University of Texas at Arlington
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1997
• 资助国家: 美国
• 起止时间: 1997-08-01 至 2001-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9706178&HistoricalAwards=false
• 关键词: Study; Origin; Significance; Pyrite; Ooids

9706178 Schieber Pyrite ooids are sedimentary grains of up to 4mm diameter that show concentric pyrite laminae around a core of variable composition. First mention of such grains was made by Hayes (1915), and since then they have sporadically been mentioned in the literature (e.g. Kalliokoski, 1966; Gorter, 1991; Taylor, 1949; Kearsley, 1989). In all these references, pyrite ooids are found in association with oolitic ironstones, are summarily described in a few sentences, and interpreted as diagenetic alterations of chamositic or goethitic ooids. Hayes (1915) and Carozzi (1972) are the lone exceptions in considering pyrite ooids as of primary origin. My interest in pyrite ooids stems from my first encounter with these enigmatic grains in the Chattanooga Shale of Tennessee. In a sedimentary sequence that was supposedly deposited under anoxic conditions in comparatively deep water (Potter et al., 1982; Ettensohn et al., 1988; Woodrow et al., 1988; Leventhal et al., 1987), these grains, with their implication of agitation and wave reworking, seemed to be oddly out of place. Since then I have become aware of other occurrences of pyrite ooids, and was able to acquire material from two of them. Samples and polished thin sections from the Chattanooga Shale, the Decorah Shale (Cambrian of Iowa), and the Powers Steps Formation (Wabana iron ores, Ordovician of Newfoundland) were examined with petrographic and electron microscopes (reflected/transmitted light; SEM and BEI mode; EDAX). This preliminary study showed features that suggest that pyrite ooids may indeed be primary intrabasinal grains, and also indicates that there are several types of pyrite ooids that may well be reflective of paleoceanographic conditions at the time of deposition. Funds are requested for a detailed comparative study of pyrite ooids from a variety of depositional settings and time periods. The aim of the study is (1) to verify that primary pyrite ooids do indeed exist, (2) to show that primary pyrite ooids ar e a more widespread phenomenon than typically appreciated, (3) to determine the conditions for their formation, (4) to understand the various pathways for pyrite ooid formation, and (5) to derive information about paleoceanographic parameters, such as presence or absence of anoxia, energy level of the environment, water depth, chemical conditions at the seafloor and in the surface sediment, and rate of deposition.

9706178个席伯黄铁矿泥粒是直径达4毫米的沉积颗粒，在不同成分的核心周围显示出同心的黄铁矿纹层。这种谷物最早是由Hayes(1915年)提出的，从那时起，它们就零星地在文献中被提及(例如，Kalliokoski，1966；Gorter，1991；Taylor，1949；Kearsley，)。在所有这些文献中，黄铁矿类蛇绿岩都是与橄榄铁矿伴生的，用几句话概括地描述，并解释为混铁岩或针铁矿类蛇绿岩的成岩蚀变。Hayes(1915)和Carozzi(1972)是唯一的例外，认为黄铁矿类物质是原生成因。我对黄铁矿卵母的兴趣源于我在田纳西州查塔努加页岩中第一次遇到这些神秘的颗粒。在一个被认为是在相对较深的水中缺氧条件下沉积的沉积序列中(Potter等人，1982；Ettensohn等人，1988；Woodrow等人，1988；Leventhal等人，1987)，这些颗粒，以及它们所暗示的搅动和波的再加工，似乎奇怪地不在适当的位置。从那时起，我发现了其他的黄铁矿泥粒产状，并从其中的两个中获得了材料。对查塔努加页岩、Decorah页岩(爱荷华州寒武纪)和Power Steps地层(纽芬兰奥陶系Wabana铁矿)的样品和抛光薄片进行了岩相学和电子显微镜(反射/透射光；扫描电子显微镜和BEI模式；EDAX)的研究。这一初步研究表明，黄铁矿类物质可能确实是主要的盆地内颗粒，并表明有几种类型的黄铁矿类物质可能很好地反映了沉积时的古海洋条件。需要资金对不同沉积环境和时间段的黄铁矿泥粒进行详细的比较研究。这项研究的目的是：(1)证实原生黄铁矿黑云母确实存在，(2)表明原生黄铁矿黑云母是一种比通常想象的更为普遍的现象，(3)确定其形成条件，(4)了解黄铁矿黑云母形成的各种途径，以及(5)得出有关古海洋学参数的信息，例如是否存在缺氧、环境能级、水深、海底和表层沉积物的化学条件以及沉积速度。