Analysis of paleoclimate during OAE2. with world-highest resolution

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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