Analysis of paleoclimate during OAE2. with world-highest resolution

白垩纪海洋缺氧事件2（OAE 2）是地质历史上研究最多的海洋缺氧事件之一。为了以世界上最高的分辨率对西北太平洋OAE 2时期的古环境进行解码，首次在<13>Tappu地区（Tappu剖面）的Yezo群层序中建立了数千年分辨率的碳同位素（δ^ C）地层，并与英国世界参考剖面进行了对比。在<13>参考剖面中观测到的δ^ C事件到OAE 2的所有阶段都在塔普剖面中找到。在此基础上，对Tappu剖面进行了对比，确定了欧洲剖面中记录最强缺氧和CO_2从海洋-大气系统中提取导致冷却的时间段。然后，我们通过该层段（约70 m厚）进行了详细取样。使用引擎切割机从河床上切割出几乎连续的样品，并从 ...更多信息 m，然后编制1/5地质柱。这种描述使我们能够在收集子样品进行分析时排除再沉积或相当大的生物扰动的材料。Tappu剖面的碳同位素地层模式与英国参考剖面基本一致，但在该剖面上出现了2.7‰的负偏移，这是本剖面所特有的，并被命名为NEMO事件。NEMO之下的层序显示δ^<13>C模式，样品间变化很小，而NEMO之上的δ^<13>C模式在几个相邻样品内明显具有较大的变化。这可能意味着地表碳循环的重建（出现kyr-order波动）。NEMO事件可能是解释这种碳循环重建的关键事件。基于分辨率和与参考剖面对比的准确性，我们分析了浮游生物微体化石和生物标志物，用于古环境重建。两次消失的整个浮游有孔虫从沉积物中观察到与OAE 2的早期阶段。这些生物事件不是溶解等次生效应的结果，因为在距离塔普剖面100多公里的奥汤巴里地区也观察到了同样的事件。生物标志物显示，陆地分子的相对丰度发生了显著变化。这可能表明植物的周转超过了耶佐集团的种源。目前，这些古环境分析的时间地层分辨率还没有赶上世界上最高的δ^<13>C地层分辨率。我们继续通过放大的策略（选择几个重要的间隔作为NEMO并进行集中分析）来实现OAE 2期间古环境的超高分辨率分析。少

Cretaceous Oceanic Anoxic Event 2 (OAE2) is one of the most well studied oceanic anoxic event through the geologic history. Objective of this study is to decode paleoenvirorment in northwestern Pacific during the OAE2 with world-highest resolution.We firstly establish carbon isotope (δ^<13>C) stratigraphy in a resolution of several kyr through the Yezo Group sequence in the Tappu area (Tappu section) and compared it with world reference section in UK. All phases of δ^<13>C event through OAE2 observed in the reference section was found in the Tappu section. Based on this result, the interval that records strongest oxygen deficiency and associated cooling derived from CO_2 withdrawal from ocean-atmosphere system recognized in European sections was correlated and identified in the Tappu section. Then we performed detailed sampling through the interval (about 70m thick). Nearly continuous samples were cut out from river floor using engine cutter and full-scaled sketches were taken from the … More m, then 1/5 geologic column was compiled. Such description enables us to exclude material of re-deposition or considerable bioturbation when collecting sub-samples for analyses. Ultra-high resolution sampling was then successfully performed with time interval of several hundreds years.Carbon isotope stratigraphy of the Tappu section shows generally comparable pattern with that of the reference section in UK ; however, conspicuous 2.7‰ negative excursion that was peculiar to our section was observed and named as NEMO event. The sequence below the NEMO showsδ^<13>C pattern with little sample-to-sample variation whereas theδ^<13>C pattern above the NEMO apparently have larger variation within several adjacent samples. This potentially suggests re-establishment of surface earth carbon circulation (appearance of kyr-order fluctuation). NEMO may be a key event to elucidate such re-establishment of carbon circulation.Based on the resolution and the accuracy of correlation with the reference section, we analyzed plankton microfossils and biomarkers for paleoenvironmental reconstruction. Twice disappearance of entire planktonic foraminifera from sediments was observed associated with the early phase of OAE2. These biotic events were not resulted from secondary effect such as dissolution, for identical events were also observed in the Oyubari area, more than 100km away from the Tappu section. Biomarkers show a remarkable change in relative abundance of terrestrial molecules. It may suggest floral turnover over the provenance of the Yezo Group. At this moment, time-stratigraphic resolution of these paleoenvirormertal analyses has not caught up with the world-highest resolution ofδ^<13>C stratigraphy. We keep working through a strategy of zooming-in (selecting several inportant intervals as NEMO and perform concentrated analyses) to achieve ultra-high resolution analyses of the paleoenvironment during OAE2. Less