COLLABORATIVE RESEARCH: Presaging Paleoproterozoic Global Change: Geobiology of the Late Archean Eon

该项目将对2004年夏季新采集的太古宙沉积物钻取岩心进行地质、古生物学和地球化学检查。这个长度约1000米的连续岩心将对西澳大利亚皮尔巴拉克拉通的哈默斯利盆地过去约2.5亿年的太古宙地层进行采样。采样的岩性将包括玄武岩、碳酸盐、燧石和几个干酪质黄铁矿页岩单元。这一提议之所以成为可能，是因为与美国宇航局天体生物学研究所的天体生物学钻探计划（ADP）合作的前所未有的机会。ADP将为收购该核心提供资金。NSF基金将用于岩心材料的初步表征，包括对干酪质沉积物的古生态和古环境的详细研究。重要的是，核心回收将由PI Buick监督，并专门针对拟议的研究。学术价值：提出研究的总体动机是表征太古宙晚期，即大气中氧气增加前不久的生命性质及其环境。许多工作者正在研究这种氧化还原转变的时间及其与同期气候波动（可能包括全球冰河期）的关系。这个团队的兴趣，有点不同，但互补，是了解太古代生物圈是如何为这种独特的环境转变奠定基础的。具体而言，该项目的一个主要目标是表征太古宙晚期海洋环境中不同类型微生物的相对重要性，并通过岩相关系研究环境对其分布的控制。这一目标将通过对干酪质沉积物中烃类分子标志物、氧化还原指标和生物地球化学循环的综合检测来实现。清洁的钻井方法、即时的取样和及时的分析将使我们能够明确地确定甾烷和三萜碳氢化合物是否是这些岩石的原生分类诊断。这些化合物在现存的、保存较差的哈默斯利盆地岩心中含量丰富，如果不是污染物，它们是真核生物和蓝藻的最早生物标志物。此外，对新岩心的分析应该使我们能够在环境背景下检查这些化合物的相对丰度和同位素组成，从而获得有关生态关系的信息。其他目标是表征太古宙晚期主要生物地球化学旋回的状态，并通过对整个岩心进行沉积学和生物地球化学侦察，为未来的调查提供坚实的基线。总的来说，这项工作将验证一个假设，即产氧蓝藻和需氧微生物存在于太古宙生态系统中，这些微生物的环境印记在它们起源后的数亿年里一直保持沉默。更广泛的影响：有三个更广泛的影响领域。首先，约6名研究生将参与一个跨越6所主要研究型大学的不同寻常的综合多学科研究项目。虽然每个学生都将扎根于项目的一个方面，但这些学生将有大量的机会在跨学科和机构之间架起桥梁。其次，由于计划中的岩心最终将根据ADP章程公开提供，因此这项工作将为更广泛的研究界提供有利于岩性和化学地层学的框架。第三，希望这次NSF-NASA的合作将为其他研究人员未来的努力提供一个积极的先例，最终可能演变成一个更广泛的机构间“深时间钻探计划”。

Project will integrate geological, paleobiological and geochemical examination of a freshly-collected Archean sediment drill-core that will be obtained in the summer of 2004. This continuous core, ~ 1000 m in length, will sample the last ~ 250 million years of Archean stratigraphy in the Hamersley Basin of the Pilbara Craton, Western Australia. Sampled lithologies will include basalt, carbonate, chert and several kerogenous pyritic shale units.This proposal is possible because of an unprecedented opportunity for collaboration with the Astrobiology Drilling Program (ADP) of the NASA Astrobiology Institute. The ADP will fund acquisition of this core. The NSF funds will be used for initial characterization of core materials to include a detailed study of paleoecology and paleoenvironment in kerogenous sediments. Importantly, core recovery will be over-seen by PI Buick and is geared specifically toward the proposed research.Intellectual Merit: The general motivation of the proposed research is to characterize the nature of life and its environment in the late Archean, shortly before the rise of atmospheric oxygen. Many workers are examining the timing of this redox transition and its relationship to contemporaneous climatic oscillations that may include global ice ages. The team's interest, somewhat different but complementary, is to understand how the Archean biosphere set the stage for this singular environmental transformation. Specifically, a major goal of this project is to characterize the relative importance of different types of microbes in late Archean marine environments and, through lithofacies relationships, to study the envi-ronmental controls on their distributions. This goal will be achieved through integrated examination of hydrocarbon molecular biomarkers, redox indicators and biogeochemical cycling in kerogenous sediments.Clean drilling methods, immediate sampling and prompt analysis will allow us to unambiguously deter-mine if taxonomically diagnostic sterane and triterpenoid hydrocarbons are indigenous to these rocks. These compounds are abundant in existing, poorly-preserved Hamersley Basin drill core and, if not contaminants, constitute the earliest biomarkers of eukaryotes and cyanobacteria. Further, analysis of the new core should permit us to examine the relative abundances and isotopic compositions of such compounds in an environmental context, yielding information about ecological relationships. Additional goals are to characterize the status of major biogeochemical cycles in the late Archean and generate a robust baseline for future investigations by conducting sedimentological and biogeochemical reconnaissance of the entire core. Collectively, this work will test the hypothesis that oxygen-generating cyanobacteria and aerobic microorganisms were present in Archean ecosystems and that the environmental imprints of these me-tabolisms remained muted for hundreds of millions of years after their origins.Broader Impact: There are three areas of broader impact. First, ~ 6 graduate students will participate in an unusually integrative and multi-disciplinary research project spanning six major research universities. While each will be rooted in a single aspect of the program, these students will have substantive opportunities to bridge across subdisciplines and institutions. Second, because the planned drill core will ultimately be openly available in accordance with the ADP charter, this work will provide a lithological and chemostratigraphic framework of benefit to the wider research community. Third, it is hoped that this NSF-NASA collaboration will provide a positive precedent for future efforts by other investigators that might ultimately evolve into a broader inter-agency "Deep Time Drilling Program".