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

晚白垩世-早第三纪沉积中以灰岩-泥灰岩层理组合为代表的碳酸盐含量的周期性变化可能与地球进动周期约为2万~24000年(KYR)有关。然而，所有的床品对联真的代表着20-24韩元吗？如果是这样的话，轨道强迫是通过推动海洋碳酸盐产量的波动来产生这些变化，还是大陆风化同样重要？回答这些问题将为利用旋回地层学得出的时间尺度提供重要的检查，例如跨越白垩纪-第三纪边界的事件速度，以及大陆和海洋对米兰科维奇强迫的响应。然而，几乎没有可用的工具可以用来准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)的累积速率可能为研究如此高分辨率的沉积速率提供新的工具。先前的工作表明，境内流离失所者跨越K-T边界的增长速度是恒定的。因此，这些颗粒在沉积物中的浓度将由沉降率决定。与陆地岩石相比，太阳风注入的氦极大地丰富了3He中的IDPs。通过使用3He作为沉积物中IDP浓度的示踪剂，可以确定分辨率为1000年，甚至可能低至100年的沉积速率。该建议的两个主要目标是：1)使用基于3He的沉积速率来估计横跨K-T的石灰岩-泥灰岩耦合在足够数量的旋回中的持续时间，以验证它们代表进动旋回的说法，更重要的是，量化碳酸盐旋回内沉积速率的变异性。对层理内时间分布的独立了解将使通量能够在米兰科维奇以下的时间尺度上进行定量计算，这是研究驱动沉积旋回的因果机制所需的关键信息。2)使用基于3He的沉积速率来限制K-T粘土中记录的气候和生产力变化的速度，并估计重要的生物地层带(如P1a、P1b)的持续时间，以表征K-T影响后前100KYR的生物/生态恢复。因此，拟议的研究将为测试生物恢复和进化动力学的模型提供一个精确的时间框架。为了评估K-T撞击事件后沉积的沉积物中的时间分布，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抽样，以进行氦测量。为了验证Milankovitch强迫在晚白垩世-早第三纪沉积物中诱导碳酸盐旋回的假设，基于3He的沉积速率将被用于确定来自DSDP岩心(里奥格兰德隆起的516F站点和Walvis Ridge的528和529站点)和来自Agost(西班牙)的沉积物中公认的石灰岩-泥灰岩层的持续时间。由于3He在地质记录中至少保存了480年，一项详细的研究将阐明在显生宙的很大一部分地区应用基于3He的沉积速率来探索气候变化、大规模灭绝事件和大规模灭绝事件后的生物恢复的时间尺度的可能性。拟议的研究还纳入了研究生教育，并让他们参与具有社会意义的目标的研究。参与激动人心的研究对于招募和留住地球科学领域的人才非常重要。需要这样的人来应对人类面临的日益严峻的环境挑战。

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.