Latitude-Dependent Climatic Responses to Milankovitch Orbital Forcing and its Expression in Cretaceous Rocks of the Northern Hemisphere

米兰科维奇轨道强迫的纬度相关气候响应及其在北半球白垩纪岩石中的表达

• 批准号: 0001093
• 负责人: Bradley Sageman
• 金额: $ 15万
• 依托单位: Northwestern University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2000
• 资助国家: 美国
• 起止时间: 2000-09-01 至 2003-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0001093&HistoricalAwards=false
• 关键词: Latitude; Dependent; Climatic; Responses; Milankovitch

Latitude-Dependent Climatic Response to Milankovitch Orbital Forcing and its Expression in Cretaceous Rocks of the Northern Hemisphere Bradley B. SagemanEAR-0001093 The proposed research seeks to document and constrain changes in the behavior of the hydrologic cycle and atmospheric circulation patterns over North America during the mid-Cretaceous greenhouse. The key to this reconstruction is the preservation of orbital signals in hemipelagic deposits of the Western Interior basin. These deposits offer an opportunity to examine the effect of the same climatic changes on two fundamentally different pathways of sedimentation in the basin that are sensitive to changes in hydrologic and atmospheric conditions: detrital and biogenic. Because orbital forcing places predictable constraints on the behavior of these two pathways, a succession in which orbital parameters are quantified offers the possibility to deconvolve the relative roles of each. Ultimately, by placing processes like biogenic sedimentation within a quantified time series, greatly improves the ability to reconstruct biogeochemically significant events such as the flux of organic matter to sediments resulting from increased primary productivity. This component of the global carbon cycle, which has been inferred to play a major role in many critical events in Earth history, such as "oceanic anoxic events," is notoriously difficult to constrain in the ancient rock record. This project is based on recent quantitative documentation of orbital signals in rhythmic limestone-marlstone facies of Cenomanian-Turonian (C-T) age in the central Western Interior using spectral techniques. With that work as a foundation, PI will apply improved spectral methods to reconstruct detailed sedimentation rates for the C-T interval, and quantify changes in biomarker-type organic compounds based on the spectrally defined time scale. His data set will include samples from core comprising a paleolatitudinal transect of the basin. These two components will allow him to test the following key working hypotheses: (1) Does limestone-marlstone formation reflect climatic forcing of siliciclastic dilution, carbonate productivity, or a combination of both? (2) Does the unique pattern of bedding in the C-T deposits reflect latitude-dependent forcing of different orbital parameters through different depositional pathways? Specifically, does obliquity dominate detrital flux through forcing of the higher latitude hydrologic cycle, and precession dominate biogenic flux (carbonate) through forcing of lower latitude surface water conditions? and (3) How are the Milankovitch scale variations expressed in limestone-marlstone facies influenced by longer-term changes in the ocean-climate system, such as the global carbon burial and ocean anoxic event termed OAE II? Can he detect feedback in the carbon cycle-climate relationship via changes in latitude-dependent orbital forcing (i.e., did obliquity become more dominant due to carbon burial, CO2 drawdown, and climatic cooling)? The application of an integrated quantitative cyclostratigraphic-organic geochemical methodology represents a significant innovation in the study of ancient climate-ocean dynamics and will significantly advance knowledge of the Milankovitch climate-sedimentation linkage during the mid-Cretaceous greenhouse.

对米兰科维奇轨道强迫的气候响应及其在北方半球白垩纪岩石中的表现布拉德利B.该研究旨在记录和限制白垩纪中期温室期间北美水文循环和大气环流模式行为的变化。 这种重建的关键是保存轨道信号在半远洋沉积的西部内陆盆地。 这些沉积物提供了一个机会，研究同样的气候变化对盆地中两种根本不同的沉积途径的影响，这两种途径对水文和大气条件的变化很敏感：碎屑和生物。 由于轨道强迫对这两条路径的行为施加了可预测的约束，因此对轨道参数进行量化的连续性提供了对每个路径的相对作用进行解卷积的可能性。 最终，通过将生物沉积等过程置于量化的时间序列中，大大提高了重建生物地球化学重要事件的能力，例如由于初级生产力增加而导致的有机物质向沉积物的通量。 全球碳循环的这一组成部分被推断在地球历史上的许多关键事件中发挥了重要作用，例如“海洋缺氧事件”，但在古代岩石记录中很难约束。 该项目是基于最近的定量记录的轨道信号的节奏石灰岩-泥灰岩相的Cenomanian-Turonian（C-T）年龄在中西部内陆使用光谱技术。 以这项工作为基础，PI将应用改进的光谱方法来重建C-T间隔的详细沉降速率，并根据光谱定义的时间尺度量化生物标志物型有机化合物的变化。 他的数据集将包括来自岩心的样本，这些样本包括盆地的古纬度断面。 这两个组成部分将使他能够测试以下关键的工作假设：（1）石灰岩-泥灰岩的形成是否反映了硅质岩稀释，碳酸盐生产力或两者的组合的气候强迫？(2)C-T沉积物中独特的层理模式是否反映了不同轨道参数通过不同沉积路径的纬度依赖性强迫？ 具体来说，通过强迫高纬度水文循环，岁差主导碎屑通量和生物通量（碳酸盐）通过强迫低纬度地表水条件？以及（3）在石灰岩-泥灰岩相中，米兰科维奇尺度变化如何受到海洋气候系统长期变化的影响，如全球碳埋藏和被称为OAE II的海洋缺氧事件？ 他能否通过纬度依赖的轨道强迫的变化（即，由于碳埋藏、CO2下降和气候变冷，气候变化是否变得更占主导地位？ 综合定量旋回地层学有机地球化学方法的应用代表了古气候-海洋动力学研究的一个重大创新，并将大大推进对白垩纪中期温室期间米兰科维奇气候-沉积联系的认识。