Collaborative Research: Interbasinal Applications of Newly- Resolved Middle to Late Cambrian Sr Isotope Stratigraphy: North American Cordilleran Margin

本研究的主要目的是对加拿大南部落基山脉中下寒武统碳酸盐岩进行层序地层学和Sr同位素的协调研究。本项目是将沉积成因模式与Sr同位素地层学相结合的大盆地南部同世地层研究工作的自然延伸。大盆地研究取得了以下成果：1)显生宙Sr同位素海水曲线中部分最不明确的区间得到了相当程度的细化；2)证明了过去2世纪以来海水87Sr/86Sr值最高的时期可能出现在中寒武纪晚期至晚寒武纪早期的海洋；3)这一时期的年代地层分辨率可能有所提高；4)表明温室时代海水沉降与海水87Sr/86Sr之间存在机制联系。5)可能限制寒武纪造山事件的时间和规模。本提案中提出的研究的最终目标是进行一项盆地间试验，以评估温室时期海水中87Sr/86Sr与海水游动之间可能的联系。该合作提案正在与NSF VPW计划的平行提案一起提交，该提案列出了完成和扩展大盆地研究的时间范围的计划。将用于执行拟议工作的方法涉及两个阶段。首先，将在加拿大南部的落基山脉测量三个暴露最完整、生物地层控制程度最高的剖面，重点是怀特山到下莱尔地层。三个剖面的数据将使用层序地层学的基本前提进行解释，所得的成因模型将用于构建可容纳史。在将所有可用的生物地层学信息整合到成因地层学中之后，将尝试与同期的Bonanza King地层进行相关性，以评估调节事件之间的同步性程度。在三个测量剖面中，采集样品的岩石学和地球化学分析最高的剖面。所有样品将通过平面光、阴极发光和外荧光进行检查，以证明再结晶、微结构和微观结构的保存、发光特性以及在样品溶解过程中可能产生放射性87Sr的非碳酸盐包裹体的存在。对符合岩石学标准的样品进行地球化学指标分析，以评估其成岩改造状态，作为选择最小蚀变组分进行Sr同位素分析的额外先决条件。最后，样品将通过预处理技术进行处理，该技术是根据先前对大盆地南部样品的测试而改进的。拟议的盆地间项目的最终目标是评估一个新的模式，该模式表明温室时期海水中87Sr/86Sr与海水游动之间存在机制联系。早期在大盆地南部的研究表明，Sr同位素地层学与长期海侵和海退之间存在相关性，这些海侵和海退影响了可用于风化的大陆表面积。该模型以及长期海水同位素曲线需要在完全不同的盆地中进行测试，以评估其科学有效性。如果加拿大南部落基山脉的结果证实了时间海水87Sr/86Sr的趋势，以及海水87Sr/86Sr与海水的联系，那么古生代Sr同位素曲线的分辨率将达到一个全新的水平。这对寻找106年尺度的古生代海水87Sr/86Sr曲线变化趋势具有重要意义。在更广泛的范围内，该综合研究的87Sr/86Sr数据将为与冈瓦纳组合相关的广泛的寒武纪造山作用、寒武纪生物辐射和灭绝，以及寒武纪被动边缘沉积序列的广泛发展提供重要信息。

9628535 Banner The proposed research has one primary objective: to carry out a coordinated sequence stratigraphic and Sr isotope study of Middle to lower Upper Cambrian Carbonates exposed in the southern Canadian Rocky Mountains. This project is a natural extension of related work on coeval strata in the southern Great Basin that integrated a genetic model of deposition with Sr isotope stratigraphy. The Great Basin research has resulted in 1) considerable refinement of a portion of the most poorly-defined interval of the Phanerozoic Sr isotope seawater curve, 2) evidence that the highest seawater 87Sr/86Sr values over the past 2 b.y. likely occurred in latest Middle to earliest Late Cambrian oceans, 3) potential for enhanced chronostratigraphic resolution in this time interval, 4) suggestion of a mechanistic link between eustasy and seawater 87Sr/86Sr during greenhouse times, and 5) potential for placing constraints on the timing and magnitude of Cambrian orogenic events. The ultimate goal of the research laid out in this proposal is to perform an interbasinal test to evaluate the possible connection between eustasy and seawater 87Sr/86Sr during greenhouse times. This collaborative proposal is being submitted in conjunction with a parallel proposal to the VPW Program at NSF that lays out plans for completing and extending the temporal range of the research in the Great Basin. The methods that will be used to carry out the proposed work involved two phases. First, three sections with the most complete exposure and highest degree of biostratigraphic control will be measured in the southern Canadian Rockies, focusing on the Mt. Whyte through lower Lyell Formations. Data from the three sections will be interpreted using the fundamental premises of sequence stratigraphy, with the resulting genetic model used to construct an accommodation history. After all available biostratigraphic information is integrated into the genetic stratigraphy, correlations with the coeval Bonanza King Formati on will be attempted to assess the degree of synchroneity between accommodation events. Of the three measured sections, the one section with the highest petrographic and geochemical analysis of collected samples. All samples will be examined by plane-light, cathodoluminescence, and epifluorscence for evidence of recrystallization, preservation of microfabrics and microstructures, luminescence characteristics, and presence of noncarbonate inclusions which could contribute radiogenic 87Sr during sample dissolution. Samples that meet petrographic criteria will be analyzed for geochemical indicators to assess their state of diagenetic modification as an additional prerequisite to selection of least-altered components for Sr isotope analysis. Finally, samples will be run through pretreatment techniques that have been refined as a result of previous testing on samples from the southern Great Basin. The ultimate goal of the proposed interbasinal project is to evaluate a new model that suggests a mechanistic link between eustasy and seawater 87Sr/86Sr during greenhouse times. Earlier work in the southern Great Basin suggests a correlation between the Sr isotope stratigraphy and long-term transgressions and regressions that affect the amount of continental surface area available for weathering. This model, as well as the secular seawater isotope curve, need to be tested in a completely different basin to assess their scientific validity. If the results from the southern Canadian Rocky Mountains confirm the temporal seawatep 87Sr/86Sr trend and the connection between eustasy and seawater 87Sr/86Sr, then an entirely new level of resolution in the Sr isotope curve for Paleozoic time will have been attained. This may spur further research into searching for trends in the Paleozoicseawater 87Sr/86Sr curve at the 106 year scale that may be related to eustatic variation. On a broader scale, the 87Sr/86Sr data from this integrated study will contribute critical information regarding the widespread Cam brian orogenesis associated with the assembly of Gondwana, Cambrian biotic radiations and extinctions, and perhaps about the extensive development of Cambrian passive margin depositional sequences.