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

9628382 Osleger 拟议的研究有一个主要目标：对加拿大落基山脉南部暴露的中下寒武统碳酸盐岩进行协调序列地层学和 Sr 同位素研究。 该项目是大盆地南部同期地层相关工作的自然延伸，将沉积成因模型与锶同位素地层学相结合。 大盆地研究已取得以下成果：1) 对显生宙 Sr 同位素海水曲线中定义最不明确的区间的一部分进行了相当大的改进，2) 证据表明过去 2 年海水 87Sr/86Sr 最高值在可能发生在最迟的中至最早的晚寒武世海洋，3）在该时间间隔内增强年代地层分辨率的潜力，4）温室时期海平面与海水 87Sr/86Sr 之间的机械联系的建议，以及 5）对寒武纪造山事件的时间和强度施加限制的潜力。 本提案中提出的研究的最终目标是进行跨盆地测试，以评估温室期间海平面稳定与海水 87Sr/86Sr 之间可能存在的联系。 该合作提案与 NSF VPW 计划的并行提案一起提交，该提案制定了完成和扩展大盆地研究时间范围的计划。 用于开展拟议工作的方法涉及两个阶段。 首先，将在加拿大落基山脉南部测量三个暴露最完整和生物地层控制程度最高的部分，重点关注怀特山和莱尔地层下部。 来自三个部分的数据将使用层序地层学的基本前提进行解释，并使用所得的遗传模型来构建住宿历史。 将所有可用的生物地层信息整合到遗传地层中后，将尝试与同时代的 Bonanza King 组进行相关性评估住宿事件之间的同步程度。 在三个测量剖面中，对收集的样品进行岩相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、阴极发光和落射荧光进行检查，以了解再结晶、微结构和微结构的保存、发光特性以及是否存在非碳酸盐夹杂物（这些夹杂物可能在样品溶解过程中产生放射性 87Sr）。 将分析符合岩相学标准的样品的地球化学指标，以评估其成岩作用状态，作为选择用于锶同位素分析的最小改变成分的附加先决条件。 最后，样品将通过预处理技术进行处理，这些技术是根据之前对来自大盆地南部的样品进行测试而改进的。 拟议的跨盆地项目的最终目标是评估一个新模型，该模型表明温室时期海平面稳定与海水 87Sr/86Sr 之间存在机械联系。 大盆地南部的早期工作表明，锶同位素地层学与影响可用于风化的大陆表面积的长期海侵和海退之间存在相关性。 该模型以及长期海水同位素曲线需要在完全不同的盆地进行测试，以评估其科学有效性。 如果加拿大落基山脉南部的结果证实了海水 87Sr/86Sr 的时间趋势以及海平面与海水 87Sr/86Sr 之间的联系，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。 这可能会促使人们进一步研究寻找 106 年尺度的古生代海水 87Sr/86Sr 曲线的趋势，这些趋势可能与海平面变化有关。 在更广泛的范围内，这项综合研究的 87Sr/86Sr 数据将提供有关与冈瓦纳大陆组装、寒武纪生物辐射和灭绝相关的广泛寒武纪造山作用的关键信息，或许还涉及寒武纪被动边缘沉积序列的广泛发展。

9628382 Osleger 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 Format ion 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 seawater 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 Ca mbrian orogenesis associated with the assembly of Gondwana, Cambrian biotic radiations and extinctions, and perhaps about the extensive development of Cambrian passive margin depositional sequences.