An Investigation of the Relation Between Mio-Pliocene Sea Level Changes and Dolomitization Events Imprinted on a SouthPactific Carbonate Platform

中新世海平面变化与南太平洋碳酸盐台地白云石化事件关系的研究

• 批准号: 9304661
• 负责人: Paul Aharon
• 金额: $ 17.62万
• 依托单位: Louisiana State University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1993
• 资助国家: 美国
• 起止时间: 1993-07-01 至 1997-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9304661&HistoricalAwards=false
• 关键词: Investigation; Relation; Between; Mio; Pliocene

We will undertake isotopic, elemental chemistry, and petrographic studies of the massive dolomites and host reef carbonates in the Neogene section at Niue, a raised coral atoll in the South Pacific. Recent studies in the Bahamas and Barbados have suggested that dolomitization may be mediated by sea water and/or sea water derived fluids, may be episodic, and may be related to eustatic fluctuations. Cores recently drilled at Niue have extended the known section there from the Upper Pliocene to probably the Lower Miocene and have revealed stratigraphically and temporary discrete dolomites coexisting with multiple and distinct imprints of sea level falls and rises. Niue's pre-Pleistocene tectonic history of simple subsidence, a groundwater system limited to marine and meteoric waters, and a lithologic system limited to clean carbonates offers minimal tectonic and chemical interference to the study of how and when massive dolomites form. The objectives of this proposed investigation are to determine with higher confidence than previously achieved (1) the exact nature of the fluids involved in the replacive dolomitization; (2) the degree of water-rock interaction during the dolomitization; (3) the stratigraphic position of the dolomites with respect to the fossil water table; (4) the timing and duration of dolomitization vis-a- vis deposition, and (5) whether there is a relation between dolomitization episodes and eustatic fluctuations. 18O/16O, 13C/12C, and 87Sr86Sr ratios, Ca, Mg, Sr, and trace element concentrations, XRD crystal chemistry analysis, and petrographic and SEM studies of the dolomites, the host carbonates, co-existing calcite-dolomite pairs, and coeval dolomites and phreatic calcite cements will be the chief techniques used in this study. The results emerging from this investigation will provide a closely dated section of Neogene dolmites and host carbonates which have an important bearing on the more fundamental problem of the origin of synsedimentary dolomitization and implications concerning the relation between periodic sea level changes and dolomite episodicity. It will also evaluate to what degree synsedimentary dolomites preserve the geochemical imprint of the fluids involved in dolomitization vis-a-vis the imprint of the host carbonates and therefore contribute to the question of dolomites' utility as monitors of past surficial processes. In addition, the sea level imprints documented on this mid-oceanic carbonate platform will allow a detailed reconstruction of the sea level record during the Mio-Pliocene time, thus providing additional constraints to the Vail-Haq sea level record obtained rom onlap/offlap imprints on continental margins.

我们将对纽埃岛（南太平洋凸起的珊瑚环礁）新近纪部分的块状白云岩和主礁碳酸盐进行同位素、元素化学和岩石学研究。 巴哈马和巴巴多斯最近的研究表明，白云石化可能是由海水和/或海水衍生流体介导的，可能是间歇性的，并且可能与海平面波动有关。 最近在纽埃钻探的岩心将那里已知的部分从上新世延伸到了可能的下中新世，并揭示了地层上和临时离散的白云岩，与海平面下降和上升的多种不同印记共存。 纽埃更新世前的简单沉降构造历史、仅限于海洋和大气水的地下水系统以及仅限于清洁碳酸盐的岩性系统，为研究块状白云岩如何和何时形成提供了最小的构造和化学干扰。 这项拟议调查的目标是比以前实现的更有信心地确定 (1) 替代白云石化作用中涉及的流体的确切性质； (2)白云石化过程中水岩相互作用的程度； (3)白云岩相对于化石地下水位的地层位置； （4）白云石化与沉积的时间和持续时间，以及（5）白云石化事件与海平面波动之间是否存在关系。 18O/16O、13C/12C 和 87Sr86Sr 比率、Ca、Mg、Sr 和微量元素浓度、XRD 晶体化学分析以及白云石、主体碳酸盐、共存方解石-白云石对以及同时期白云石和潜水方解石胶结物的岩相学和 SEM 研究将是本研究使用的主要技术。 这项调查的结果将提供新近纪白云岩和宿主碳酸盐的密切年代部分，这对同沉积白云石化起源的更根本问题以及有关周期性海平面变化和白云岩幕式性之间关系的影响具有重要影响。 它还将评估同沉积白云岩在多大程度上保留了白云石化过程中涉及的流体的地球化学印记（相对于主体碳酸盐的印记），从而有助于解决白云岩作为过去地表过程监测器的实用性问题。 此外，在这个大洋中部碳酸盐台地记录的海平面印记将允许详细重建Mio-上新世时期的海平面记录，从而为从大陆边缘上重叠/非重叠印记获得的Vail-Haq海平面记录提供额外的约束。