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

9820511 Montanez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洋碳酸盐中记录了中生代已知最大的碳同位素偏移之一（18 C值偏移高达+5%）。并被定义为SPICE事件。 在强烈的对比，大多数耦合的正碳同位素偏移和动物群的危机记录在中生代的岩石记录，启动SPICE事件被解释为同步的海洋无脊椎动物的大规模灭绝，而不是postdate的碳同位素偏移的开始。 这种推断的因果关系表明，大规模灭绝与碳循环的重大变化有关。 由于PI的NSF支持的与大卫Osleger博士和杰伊班纳对北美中晚寒武世早期碳酸盐岩的综合层序地层和Sr同位素分析的合作研究，我们已经在大盆地南部和加拿大落基山脉南部的几个剖面中确定了SPICE事件的基底部分，这表明SPICE事件作为年代地层学工具具有很大的潜力，前所未有的全球相关性解决方案。 然而，值得注意的是，我们的研究结果（1）确定了推断的海平面变化，海洋87 Sr/86 Sr和（18 C）值与三叶虫灭绝之间的关系，这与SPICE事件发现者提出的结果有很大不同，（2）暗示了产生三叶虫大灭绝的过程。 此外，我们的初步数据表明，在下寒武统晚期至中寒武统早期的碳酸盐岩中可能记录到类似于SPICE量级的正同位素漂移，并且这种同位素漂移表现出与海洋87 Sr/86 Sr值、海平面以及可能与我们对早期SPICE事件的研究所定义的类似的早期生物区边界的关系。这是PI目前由NSF资助的研究的直接产物，（CHN-9628382）的研究表明，寒武纪生物、化学和物理现象之间存在着复杂的关系，并导致三个研究目标：（1）更全面地阐述SPICE事件、三叶虫大灭绝、海平面波动、（2）在早寒武世晚期至中寒武世早期，在记录了与SPICE峰值相似的海平面下降幅度并在其底部包含生物群边界的地层区间内，测试碳同位素正偏移的程度，（3）利用不同的地球化学代用指标，建立物理、生物和化学“事件”之间的相关系和相对大小，并严格评价和约束可能联系寒武纪物理、生物和化学现象的潜在地球化学过程。 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解决，其中大部分的初步数据来自这些地点，并且可以获得最大数量的生物地层控制。 耦合稳定的（13 Ccarb和（13 Corg）和放射成因（87 Sr/86 Sr）同位素数据的地层分布将与微量元素数据耦合，以便最好地实现研究目标。 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地球化学过程的性质，并进一步开发寒武纪正同位素漂移事件作为全球对比和确定寒武系主要分支的高分辨率年代地层工具的潜力。通过为她提供额外的“动手”经验，在解开复杂的古环境记录，并提供研究经验和指导有前途的妇女和/或少数民族本科生的教学和专业目标。 拟议的研究通过与杜邦少数民族教育奖潜在的成本分摊纳入了几个暑期实习;实习将提供给有前途的女性和/或少数民族本科生，他们将由PI从整个北美的地质学项目中招募。

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.