Time scales across the Cretaceous-Tertiary boundary: A new approach

跨越白垩纪-第三纪边界的时间尺度：一种新方法

• 批准号: 0345670
• 负责人: Sujoy Mukhopadhyay
• 金额: --
• 依托单位: Harvard University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2004
• 资助国家: 美国
• 起止时间: 2004-08-01 至 2009-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0345670&HistoricalAwards=false
• 关键词: Time; scales; across; Cretaceous; Tertiary

ABSTRACTCyclical variations in the carbonate content, represented by limestone-marl bedding couplets, in Late Cretaceous-Early Tertiary sediments may be related to the Earth's precessional period of ~20-24 thousand years (kyr). However, do all bedding couplets really represent ~20-24 kyr? If so, did orbital forcing produce these variations by driving fluctuations in carbonate production in the ocean or was continental weathering equally important? Answering these questions would provide important checks on timescales derived using cyclostratigraphy, such as the pace of events across the Cretaceous-Tertiary boundary, and the response of continents and oceans to Milankovitch forcing. However, there are few available tools that can be utilized to accurately constrain events on timescales of a few thousand years. Accumulation rates of interplanetary dust particles (IDPs) may provide a new tool with which to investigate sedimentation rates at such high resolution. Prior work has shown that the accretion rate of IDPs across the K-T boundary is constant. Therefore, the concentration of these particles in sediments will be governed by sedimentation rates. Implantation of helium by the solar wind tremendously enriches IDPs in 3He compared to terrestrial rocks. By using 3He as a tracer of the IDP concentration in sediments, sedimentation rates at a resolution of 1000 years, and perhaps down to a hundred years, can be determined.Intellectual Merit: The two primary goals of this proposal are: 1) use 3He-based sedimentation rates to estimate durations of limestone-marl couplets across the K-T over a sufficient number of cycles to verify the claim that they represent precessional cycles and, more importantly, quantify variability in sedimentation rates within a carbonate cycle. Independent knowledge of the distribution of time within a bedding couplet will enable fluxes to be calculated quantitatively on sub-Milankovitch timescales, crucial pieces of information required to investigate causal mechanisms driving sedimentary cycles. 2) use 3He-based sedimentation rates to constrain the pace of climate and productivity changes recorded within the K-T clay, and estimate the duration of important biostratigraphic zones (such as P1A, P1B) to characterize the biological/ecological recovery in the first 100 kyr following the K-T impact. Hence, the proposed research will provide a precise chronological framework for testing models for biotic recovery and evolutionary dynamics. To assess the distribution of time in sediments deposited following the K-T impact event, the well-studied stratigraphic sections exposed in southeast Spain (Agost and Caravaca) will be sampled for helium measurements. To test the hypothesis that Milankovitch forcing induces carbonate cyclicity in Late Cretaceous-Early Tertiary sediments, 3He-based sedimentation rates will be used to determine duration of well-recognized limestone-marl beds in sediments from DSDP cores (site 516F on the Rio Grande Rise and sites 528 and 529 on the Walvis Ridge) and from Agost (Spain).Broader Impact: The proposed work will provide an important calibration between two techniques: 3 He and cyclostratigraphy. Because 3He is preserved in the geological record for at least 480 Myrs, a detailed study will illustrate the potential of applying 3He-based sedimentation rates over a large fraction of the Phanerozoic to probe timescales of climate changes, mass extinctions events, and the biological recovery following mass extinction events. The proposed research also incorporates graduate student education and involves them in research with goals that are of societal significance. Involvement in exciting research is important for recruiting and retaining talented individuals in the earth sciences. Such individuals are needed to address the growing environmental challenges facing humankind.

在晚白垩世-早第三纪沉积物中，以石灰岩-泥灰岩层理对为代表的碳酸盐含量的周期性变化可能与地球20-24千年的岁差周期有关。然而，所有的床上对联真的代表~20-24千？如果是这样的话，轨道强迫是通过驱动海洋中碳酸盐生成的波动来产生这些变化的，还是大陆风化同样重要？研究这些问题将对使用旋回地层学得出的时间尺度提供重要的检查，例如跨越古陆-第三纪边界的事件的速度，以及大陆和海洋对米兰科维奇强迫的反应。然而，几乎没有可用的工具可以用来精确地将事件限制在几千年的时间尺度上。行星际尘埃粒子（IDPs）的积累率可能提供一个新的工具，以这种高分辨率调查沉积速率。先前的工作表明，跨K-T边界的IDP的吸积速率是恒定的。因此，这些颗粒在沉积物中的浓度将取决于沉积速率。与陆地岩石相比，由太阳风注入的氦极大地富集了3 He中的IDPs。通过使用3 He作为沉积物中IDP浓度的示踪剂，可以确定分辨率为1000年甚至100年的沉积速率。知识价值：本提案的两个主要目标是：1）使用3 He基沉积速率来估计跨K-S的石灰岩-泥灰岩偶层的持续时间。T在足够数量的周期，以验证声称，他们代表岁差周期，更重要的是，量化的变化，在一个碳酸盐循环的沉积速率。独立知识的时间分布在一个床上的对联将使通量进行定量计算的子米兰科维奇时间尺度，调查驱动沉积周期的因果机制所需的关键信息。2)使用3 He基沉积速率来限制K-T粘土中记录的气候和生产力变化的速度，并估计重要生物地层带（如P1 A，P1 B）的持续时间，以表征K-T影响后前10万年的生物/生态恢复。因此，拟议的研究将提供一个精确的时间框架，用于测试生物恢复和进化动力学模型。为了评估K-T撞击事件后沉积的沉积物的时间分布，将对西班牙东南部（Agost和Caravaca）暴露的经过充分研究的地层剖面进行取样，进行氦测量。为了检验米兰科维奇强迫在晚白垩世-早第三纪沉积物中诱导碳酸盐旋回性的假设，将使用基于3 He的沉积速率来确定DSDP岩心沉积物中公认的石灰岩-泥灰岩床的持续时间（格兰德河海隆的516 F站点和沃尔维斯海岭的528和529站点）和Agost（西班牙）。建议的工作将提供两种技术之间的重要校准：3 He和旋回地层学。由于3 He在地质记录中保存了至少4.8亿年，因此详细的研究将说明在中生代的大部分地区应用3 He沉积速率来探测气候变化、大规模灭绝事件和大规模灭绝事件后的生物恢复的可能性。拟议的研究还包括研究生教育，并让他们参与具有社会意义的目标的研究。参与令人兴奋的研究对于招募和留住地球科学人才非常重要。需要这些人来应对人类面临的日益严重的环境挑战。