POWRE: Cambrian Extinction Event and Carbon Cycling: An Integrated Isotopic Approach to Unraveling Biogeochemical Processes Linking Cambrian Phenomena

9820511最近在澳大利亚、中国、哈萨克斯坦和北美的晚寒武世早期海相碳酸盐岩中记录了显生宙中已知最大的碳同位素偏移（18C值偏移达+5%）的montanezone。并被定义为SPICE事件。与显生宙岩石记录中记录的大多数耦合的正碳同位素偏移和动物危机形成鲜明对比的是，SPICE事件的开始被解释为与海洋无脊椎动物大灭绝同步，而不是晚于碳同位素偏移的开始。这种推断的因果关系表明，大灭绝与碳循环的主要变化有关。由于PI的nsf支持的合作研究与博士。David Osleger和Jay Banner对北美中至晚寒武世早期碳酸盐岩的综合层序地层学和Sr同位素分析表明，我们在大盆地南部和加拿大南部落基山脉的几个剖面中发现了SPICE事件的基底部分，表明SPICE事件具有作为全球对比的空前分辨率的年代地层工具的巨大潜力。然而，值得注意的是，我们的研究结果(1)定义了推断的海平面变化、海洋87Sr/86Sr和（18C）值与三叶虫灭绝之间的关系，这与SPICE事件的发现者提出的关系有很大不同；(2)表明产生三叶虫大规模灭绝的过程。此外，我们的初步数据表明，下寒武统晚期至中寒武统早期碳酸盐岩可能记录到类似SPICE的正同位素偏移，并且这种同位素偏移与海洋87Sr/86Sr值、海平面以及可能更早的生物群落边界有关，这与我们研究的早期SPICE事件相似。这些初步的观察结果是科学科学小组目前在美国国家科学基金会资助下进行的研究（EAR-9628382）的直接结果，表明寒武纪生物、化学和物理现象之间存在着复杂的关系，并导致了三个研究目标：(1)更全面地探讨SPICE事件、三叶虫大灭绝、海平面波动与推断的中寒武纪晚期至晚寒武纪早期海水87Sr/86Sr值变化之间的时间关系；(2)在一个记录了与SPICE峰值相关的海平面下降幅度相似且底部包含生物群落边界的地层区间内，检验早寒武统晚期至中寒武统早期的碳同位素正偏移在多大程度上发生；(3)利用不同的地球化学指标建立物理、生物和化学“事件”的相对相关系和相对量级；以及批判性地评估和限制潜在的生物地球化学过程，这些过程可能将这些寒武纪的物理、生物和化学现象联系起来。这些目标将通过研究大盆地南部的四个地点和加拿大落基山脉南部的两个地点来实现，这些地方提供了大量的初步数据，并提供了最多的生物地层控制。稳定同位素（13Ccarb和13Corg）和放射性成因同位素（87Sr/86Sr）数据的耦合地层分布将与微量元素数据进行耦合，以最好地完成研究目标。该研究将有助于更好地约束寒武纪生物、物理和化学现象之间的生物地球化学过程的性质，并进一步开发寒武纪正同位素偏移事件作为全球对比和定位寒武纪主要分支的高分辨率年代地层工具的潜力。这个计划中的项目通过为PI提供额外的“动手”经验来解开复杂的古环境记录，并为有前途的女性和/或少数民族本科生提供研究经验和指导，有助于实现PI的研究、教学和职业目标。拟议的研究包括几个暑期实习，通过潜在的成本分摊与杜邦少数民族教育奖；PI将从北美各地的地质学项目中招募有前途的女性和/或少数族裔本科生，并为他们提供实习机会。

9820511MontanezOne of the largest known carbon isotope excursions in the Phanerozoic (up to +5% shift in (18C values) has been recently documented in early Late Cambrian marine carbonates in Australia, China, Kazakhstan and North America. and has been defined the SPICE event. In strong contrast to most coupled positive carbon isotope excursions and faunal crises documented in the Phanerozoic rock record, initiation of the SPICE event is interpreted to be synchronous with mass extinction of marine invertebrates rather than postdate the initiation of the carbon isotope excursion. This inferred causal relationship suggests that mass extinction was associated with the cause of the major change in carbon cycling. As a consequence of the PI's NSF-supported collaborative research with Drs. David Osleger and Jay Banner on integrated sequence stratigraphic and Sr isotope analysis of Middle to early Late Cambrian carbonates of North America, we have identified the basal portion of the SPICE event in several sections from the southern Great Basin and southern Canadian Rockies suggesting that the SPICE event has great potential as a chronostratigraphic tool of unprecedented resolution for global correlation. Significantly, however, the results of our study (1) define a relationship between inferred sea-level changes, marine 87Sr/86Sr and (18C values, and the trilobite extinction that differs significantly from that proposed by the discoverers of the SPICE event, and (2) implies that the Processes that produced the trilobite mass extinction. Additionally, our preliminary data suggest that a positive isotope excursion of similar magnitude to SPICE may be recorded in latest Lower Cambrian to early Middle Cambrian carbonates, and that this isotope excursion exhibits a relationship with marine 87Sr/86Sr values, sea-level and possibly an earlier biomere boundary that is similar to that defined by our study for the early SPICE event.These initial observations, which are a direct outgrowth of the PI's currently NSF-funded research (EAR-9628382), indicate that a complex relationship exists between Cambrian biologic, chemical and physical phenomena, and lead to three research objectives: (1) to more fully address the nature of the temporal relationship between the SPICE event, the trilobite mass extinction, sea-level fluctuations, and inferred changes in seawater 87Sr/86Sr values during the late Middle to early Late Cambrian, (2) to test to what degree a positive carbon isotope excursion occurs in the latest Early Cambrian to early Middle Cambrian within a stratigraphic interval that records a similar magnitude sea-level fall to that associated with peak SPICE values and contains a biomere boundary at its base, and (3) to use different geochemical proxies to establish phase relationships and relative magnitude of physical, biologic and chemical 'events' relative to each other, as well as to critically evaluate and constrain the potential biogeochemical processes that could have linked these Cambrian physical, biologic and chemical phenomena. These objectives will be addressed by studying four localities in the southern Great Basin and two localities in the southern Canadian Rockies from which much of the preliminary data come, and for which the greatest amount of biostratigraphic control is available. The stratigraphic distribution of coupled stable ((13Ccarb and (13Corg) and radiogenic (87Sr/86Sr) isotope data will be coupled with trace element data in order to best accomplish the research objectives. This study should contribute significantly towards better constraining the nature of the biogeochemical processes linking Cambrian biologic, physical and chemical phenomena, as well as further developing the potential of Cambrian positive isotope excursion events as high-resolution chronostratigraphic tools for global correlation and for locating major subdivisions of the Cambrian Systems.The proposed project contributes to the fulfillment of the PI's research, teaching and professional goals by providing her with additional 'hands-on' experience in unraveling complex paleoenvironmental records, and providing research experience and mentoring to promising women and/or minority undergraduate students. The proposed research incorporates several summer internships through potential cost-sharing with a DuPont Minority Educational Award; internships will be offered to promising women and/or minority undergraduates who will be recruited by the PI from geology programs throughout North America.