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

北半球白垩纪岩石对Milankovitch轨道强迫的依赖于纬度的气候响应及其在白垩纪岩石中的表达Bradley B.SagemanEAR-0001093拟议的研究旨在记录和限制白垩纪中期温室期间北美上空水文循环和大气环流模式的行为变化。这种重建的关键是保存西部内陆盆地半深海沉积物中的轨道信号。这些沉积物提供了一个机会，可以研究同样的气候变化对盆地中两条根本不同的沉积路径的影响，这两条路径对水文和大气条件的变化很敏感：碎屑和生物成因。由于轨道作用力对这两条路径的行为施加了可预测的约束，轨道参数被量化的序列提供了去卷积每一条路径的相对作用的可能性。最终，通过将生物沉积等过程置于量化的时间序列中，极大地提高了重建生物地球化学重大事件的能力，例如由于初级生产力增加而导致的有机质向沉积物的通量。这一全球碳循环的组成部分，被推断在地球历史上的许多关键事件中发挥着重要作用，如“海洋缺氧事件”，在古代岩石记录中是出了名的难以限制。该项目基于最近使用光谱技术对中西部内陆塞诺马尼亚-图罗尼亚(C-T)韵律石灰岩-泥灰岩相(C-T)轨道信号的定量记录。在这项工作的基础上，PI将应用改进的光谱方法重建C-T间隔的详细沉积速率，并基于光谱定义的时间尺度量化生物标志物类型有机化合物的变化。他的数据集将包括来自岩心的样本，其中包括盆地的古纬度横断面。这两个组分将使他能够检验以下关键的工作假说：(1)石灰岩-泥灰岩的形成是否反映了硅屑稀释、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的沉积路径与纬度有关的强迫？具体地说，倾角是否通过迫使较高纬度的水循环来支配碎屑通量，而岁差是否通过强迫较低纬度的地表水条件来支配生物通量(碳酸盐)？以及(3)石灰岩-泥灰岩相表现的米兰科维奇尺度变化如何受到海洋气候系统的长期变化的影响，例如全球碳埋藏和海洋缺氧事件被称为OAE II？他能否通过改变依赖于纬度的轨道作用力(即倾角是否由于碳埋藏、二氧化碳减少和气候变冷而变得更加重要)来探测碳循环-气候关系中的反馈？综合定量旋回地层学-有机地球化学方法的应用代表了古代气候-海洋动力学研究的一项重大创新，并将极大地促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。

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.