BPT27-P01

Room:Convention Hall

Time:May 24 18:15-19:30

Spongy parenchyma found in meta-tuff of Hitachi Cambrian Akazawa Formation
TAGIRI, Michio1∗ ; HANAWA, Katsutoshi2 ; OIKAWA, Akira2
1Hitachi City Museum, 2 Geonet Hitachi

Hitachi Cambrian meta-tuffs containing spongy parenchyma occur as gravels in the Miyata River and the Ayukawa River.
Spongy parenchyma consists of siliceous sphere with several layers and dark matrix. This texture is not like to siliceous oolite,
pisolite, and spherulite, but to silicified sponge.
Keywords: Hitachi Cambrian, meta-tuff, spongy parenchyma, sphere

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BPT27-P02

Room:Convention Hall

Time:May 24 18:15-19:30

Middle-Late Ordovician biodiversification and relevant environmental changes in Estonia
SHIMATSUKA, Momoko1∗ ; ISOZAKI, Yukio2 ; KANI, Tomomi3 ; ISHIKAWA, Akira41

Department of Earth and Planetary Science - Graduate School of Science, The University of Tokyo, 2 Department of Earth
Science and Astronomy, Multi-disciplinary Sciences - General Systems Studies, Gr, 3 Department of Earth and Environmental
Sciences, Kumamoto University, 4 Department of Earth Science and Astronomy, The University of Tokyo

Following up the ’Cambrian explosion’ , marine biodiversity increased dramatically during the Ordovician, as known as the’Great Ordovician Biodiversification Event’ (GOBE). Estonia in central Batoscandia provides excellently continuous Ordovician
sedimentary package for detailed analysis. We are analyzing the drilled core samples of the Middle-Upper Ordovician strata (ca.
150 m-thick) collected from Velise in central Estonia, in order to clarify litho-, bio-, and isotope stratigraphy of C and Sr, and toreveal the cause and processes of the GOBE. We will report on our preliminary results.
Keywords: Ordovician, Baltscandia, GOBE, stratigraphy, drilled core

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BPT27-P03

Room:Convention Hall

Time:May 24 18:15-19:30

Organic geochemical evidences for smoke clouds induced by an asteroid impact at theCretaceous-Paleogene boundary
KAIHO, Kunio1∗ ; FUJIBAYASHI, Megumu1 ; SAITO, Ryosuke1
1Tohoku University

An asteroid impacted the continental shelf of Mexico 66 Myr ago. Although the resulting ejecta containing asteroidal andterrestrial materials in the stratosphere caused acid rain, darkness, and a mass extinction, the mechanisms of the extinction
remain under debate. We demonstrate that the impact caused the ejection of combusted fossil oil into the stratosphere, forming
a smoke plume that remained for several years. The absorption of solar radiation by the smoke led to the devastation of plants,
causing the extinction of the dinosaurs and some marine invertebrates at the end of the Cretaceous. Combusted organic molecules
containing coronene are concentrated in the microspherule-dominated coarse deposits and the superjacent fine layer containing
iridium derived from the asteroid in Haiti. The coronene percentage in the completely combusted organic molecules and δ 13 Cvalues in the ejected layers show similar values in the coarse deposits and the iridium layer in the proximal site and also in
the iridium layer in a distal site (Spain) for the impact crater, implying that the combusted organic molecules remained in thestratosphere globally for several years. The carbon preference index values of n -alkanes in the coarse ejected layers indicate thatthe n -alkanes were primarily sourced from oil. The stable carbon isotope ratio values of short-chain n-alkanes in Haiti show
devastation of marine life occurred within a year after the impact. The δ 13 C profile of long-chain n -alkane implies devastationof land vegetation by darkness. Therefore, we suggest that these smoke clouds contributed to the mass extinction.
Keywords: coronene, Cretaceous, Paleogene, smoke clouds, stable carbon isotope ratio

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BPT27-P04

Room:Convention Hall

Time:May 24 18:15-19:30

Euxinic conditions at Three Gorges area as opposed to global oxidation event, around
PC/C boundary
SAWAKI, Yusuke1∗
1Tokyo Tech

It is widely accepted that the Neoproterozoic was a transitional period to modern Earth in terms of oceanic redox condition.
Some geological evidences, including carbon and sulfur molybdenum isotopic data, support this idea, and fossils of large multicellular animal have been discovered from Neoproterozoic strata throughout the world. In contrast, some of the fossils werediscovered from anoxic sediments and iron speciation analyses indicate existences of ferruginous and euxinic conditions in somepoints.
Three Gorges area, South China, is one of the best places to decipher surface environmental changes during the Ediacaran andCambrian due to the successive deposition on Yangtze platform. Our group conducted on-land drilling at the Three Goregs tocollect fresh and continuous rock samples. The age range of the core samples is from the beginning of the Ediacaran to the endof the early Cambrian. I measured molybdenum concentration of the core samples by XRF analysis using glass bead. The resultshows that molybdenum concentrations of organic carbon-rich black shale layers deposited at ca. 560 Ma and 525 Ma are up to800 ppm. Same horizons contain high levels of rhenium, approaching 3 ppm, and TOC, more than 10 %. Abundant pyrites arealso included in the black shale, and all of these evidences suggest that euxinic conditions occurred at Three Gorges during theseperiods.
In modern Black Sea, surface layer is oxic but bottom layer is euxinic because of down-welling of organic matter. As referringto this concept, euxinic conditions of Three Gorges area might imply both onset of effective burial of organic material and oxic
surface layer around PC/C boundary.
Keywords: Three Gorges, molybdenum, euxinic

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