Enhanced Terrestrial Weathering in the North American Interior across the Paleocene/Eocene Boundary

了解地球陆地地球化学储层过去对大气扰动的响应对于预测未来对现有环境的影响具有重要意义。“始新世初始热极大值”（IETM，约55 Ma）是一个短暂的（~100 - 200 kyr）全球变暖事件，由温室气体的突然增加所驱动，其时间尺度与当今的人为流入相似。这种涌入被认为是由于海洋天然气水合物释放了大量甲烷。随后大气温室气体[二氧化碳（CO2）和甲烷（CH4）]水平的增加对地球表面过程和生物地球化学循环的功能分配产生了全球性的影响。IETM的海洋记录清楚地记录了这种扰动引发的同位素和矿物学变化，而对地下暴露的陆地的反应却没有得到很好的理解。特别令人感兴趣的是这种气候超调的短暂性，它反映了负反馈（加速风化反应）的存在，通过减少大气中温室气体的水平来稳定气候。我们建议研究这种气候变暖对北达科他州西部威利斯顿盆地（WB）非常精细的沉积成员的沉积模式和风化速率的影响。这些单元包含保存完好的多代理信息（如：孢型/大型植物化石、自生矿物和古成因特征、保存完好的有机物质），具有良好的时空相互关系。本研究提出了这样的假设：WB的精细分辨率地层包记录了同位素轻的海洋甲烷水合物释放和随后的全球变暖的陆地信号/响应。为了验证这一假设，我们将使用1)整个沉积物组成，2)半定量粘土矿物学和3)稳定同位素地球化学来确定沉积过程的变化和速率以及对IETM期间假设的全球变暖气候的响应。我们的初步调查提供的证据表明，IETM的记录保存在WB内，并且沉积物地球化学在这一边界上有明确的转变。这一综合记录可以与邻近同时期内陆盆地（如怀俄明州的大角盆地）有充分记录的IETM记录联系起来，并将增强我们对中纬度次大陆对快速气候变化的响应的理解。更广泛的影响：从跨学科的角度将保存完好的多代地层记录与生物地球化学通量的热力学模型和估计的物理重建进行比较是很重要的。将我们的记录与大角盆地保存的记录联系起来，将有助于我们更好地理解次大陆对快速全球变暖的反应。主要研究人员将利用这些信息来加强古环境重建和古古生物学方面的新兴研究项目。本研究将成为研究生/本科生发展研究项目的机制。一旦调查工作产生了全面的数据集，将进行一次讨论会实地考察课程，参与者每周进行讨论，为西部内陆盆地（WIB）省（威利斯顿、波德河、大角、瓦萨奇和绿河流域）为期两周的实地考察做准备。这将为学生提供一个查看和综合次大陆尺度信息的机会。该项目的手稿将发表在公认的跨学科地球科学期刊上，并将建立一个专门用于WIB的链接网站，以特别关注本研究所包含的工作，供学术界访问。最后，这项研究的结果将被纳入威斯康星大学地质博物馆的公共推广计划。

It is important to understand the past responses of earth's terrestrial geochemical reservoirs to atmospheric perturbations in order to predict future impacts on the existing environment. The "initial Eocene thermal maximum" (IETM, ca. 55 Ma) was a short-lived (~100 - 200 kyr) global warming event driven by a sudden increase in greenhouse gases similar in temporal scale to present-day anthropogenic influxes. This influx was postulated to have been due to a massive release of methane from marine gas hydrates. The subsequent increased levels of atmospheric greenhouse gases [carbon dioxide (CO2) and methane (CH4)] had a worldwide impact on the earth's surficial processes and functional partitioning of biogeochemical cycles. Marine records of the IETM clearly document the isotopic and mineralogic shifts triggered by this perturbation, while the response on subaerially exposed landmasses is not as well understood. Of particular interest is the transient character of this climatic overshoot, which reflects the presence of negative feedbacks (accelerated weathering reactions) that stabilized climate by reducing atmospheric levels of greenhouse gases. We propose to study the influence of this climatic warming on sedimentation patterns and weathering rates within the remarkably fine-textured sedimentary members of the Williston Basin (WB) in western North Dakota. These units contain well preserved, multi-proxy information (i.e., palynomorph/ macrofloral fossils, authigenic minerals and paleopedogenic features, well-preserved organic materials) that lends itself well to temporal and spatial cross-correlation. This study poses the hypothesis that the fine resolution stratigraphic package in the WB records a sympathetic terrestrial signal/response to the release of isotopically-light marine methane hydrate and subsequent global warming. To investigate this hypothesis, we will use 1) whole sediment composition, 2) semi-quantitative clay mineralogy, and 3) stable isotope geochemistry to ascertain alterations and rates in sedimentary process and sub-aerial weathering intensity in response to the warmer global climate hypothesized to have prevailed during the IETM. Our preliminary investigations provide evidence indicating that a record of the IETM is preserved within the WB and that there is a definitive shift in sediment geochemistry across this boundary. This integrated record can be tied to well-documented IETM records in neighboring contemporaneous interior basins (e.g., Bighorn Basin of Wyoming) and will augment our understanding of mid-latitude sub-continental response to rapid climate change.Broader Impacts: It is important to compare the reality of a well-preserved multi-proxystratigraphic record to thermodynamic models of biogeochemical fluxes and estimated physical reconstructions from an interdisciplinary aspect. The linkage of our records to those preserved in the Big Horn Basin will build a stronger understanding of sub-continental land mass responses to rapid global warming. The principle investigators will utilize the information to strengthen fledgling research programs in paleoenvironmental reconstruction and paleopedology. This study will be a mechanism for graduate/ undergraduate students to develop research projects. Once investigative work has yielded a comprehensive data set, a colloquium field trip class will be conducted, with participants conducting weekly discussions in preparation for a two-week field excursion through the Western Interior Basin (WIB) province (Williston, Powder River, Bighorn, Wasatch, and Green River Basins). This will provide students an opportunity to view and synthesize sub-continental scale information. Manuscripts from this project will be published in recognized interdisciplinary earth science journals and a linked website devoted to the WIB with specific focus on the work encompassed by this study will be constructed for access by the academic community. Finally, results of this proposed research will be incorporated into a public outreach program at the University of Wisconsin Geology Museum.