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

9628535旗帜拟议的研究有一个主要目标：对加拿大落基山脉南部出露的中、下寒武统碳酸盐岩进行层序地层学和锶同位素研究。该项目是大盆地南部同时代地层相关工作的自然延伸，该工作将沉积成因模式与锶同位素地层学相结合。大盆地研究的结果是：1)显生界锶同位素海水曲线最模糊区间的一部分得到了相当大的精确度；2)证据表明，在过去的2 b.y.年中，海水的87Sr/86Sr值最高。可能发生在最晚的中寒武世至最早的晚寒武世大洋，3)在这一时间间隔内提高年代地层分辨率的潜力，4)温室时期海平面与海水87Sr/86Sr之间的机械联系，以及5)限制寒武纪造山事件的时间和规模的可能性。这项提议中提出的研究的最终目标是进行一项盆地间测试，以评估温室时期海平面上升和海水87Sr/86Sr之间可能存在的联系。这项合作提案与NSF的VPW计划的平行提案一起提交，该方案列出了完成和扩大大盆地研究的时间范围的计划。将用于开展拟议工作的方法包括两个阶段。首先，将在加拿大落基山脉南部测量三个暴露最完整、生物地层控制程度最高的区段，重点是芒特山。怀特通过莱尔下部地层。三个区段的数据将利用层序地层学的基本前提进行解释，所产生的成因模型将用于构建可容纳历史。在所有可用的生物地层学信息被整合到成因地层学之后，将尝试与同时代的Bonanza King Formati On进行对比，以评估住宿事件之间的同步性程度。在三个测量剖面中，采集样品的岩相学和地球化学分析最高的一个剖面。所有样品都将通过平面光、阴极发光和荧光光谱进行检查，以寻找再结晶的证据、显微组构和微结构的保存、发光特征以及样品溶解过程中可能贡献放射性成因的非碳酸盐包裹体的存在。将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，以此作为选择变化最小的组分进行锶同位素分析的额外先决条件。最后，样品将经过前几次对大盆地南部样品的测试而改进的前处理技术。拟议的盆地间项目的最终目标是评估一种新的模型，该模型表明在温室时期海平面上升和海水87Sr/86Sr之间存在机械联系。大盆地南部早期的工作表明，锶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供风化的大陆表面积。这一模型以及长期的海水同位素曲线需要在一个完全不同的盆地进行测试，以评估它们的科学有效性。如果加拿大南部落基山脉的研究结果证实了海平面的时间变化趋势以及海平面与海水之间的联系，那么古生代锶同位素曲线的分辨率将达到一个全新的水平。这可能会促进进一步的研究，寻找可能与海平面变化有关的106年尺度上古海水87Sr/86Sr曲线的变化趋势。在更广泛的范围内，这项综合研究的~(87)Sr/~(86)Sr数据将有助于提供与冈瓦那拼接、寒武纪生物辐射和生物灭绝有关的广泛的凸起造山作用的关键信息，也可能有助于寒武纪被动边缘沉积序列的广泛发展。

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.