5:15 PM - 7:15 PM
[BPT04-P01] Redox condition in the pelagic Panthalassa during the end-Permian mass extinction, referred from the Ubara section, southwest Japan.
Keywords:mass extinction, oceanic anoxia, Permian, Triassic, pyrite, Ubara section
The largest mass extinction in Earth’s history occurred at the end of the Permian. The extinction is called the end-Permian mass extinction (EPME: 252 Ma). Global warming and widespread ocean anoxia associated with Siberian volcanism are considered as the environmental causes of the EPME. However, detailed oceanic environment changes across the EPME have been still debated in Panthalassa, which covered about 90% of the global ocean at that time. Geological records of this oceanic region are seen in the accretionary complex in Japan, New Zealand and Canada. According to previous study based on these records, ocean anoxia occurred in the low-latitude Panthalassa and spread in the southern middle-latitude Panthalassa (Takahashi et al., 2021). However, information on the spatial extent of anoxia in the Panthalassa Ocean has not been sufficient to discuss the global trend due to the limited number of continuous environmental records across EPME. To address this issue, this study aims to elucidate the environmental change in the Panthalassa in more detail using another continuous Permian-Triassic boundary section.
We focus on the Permian-Triassic boundary section namely the Ubara section which is located in Fukuchiyama-city, Kyoto Pref. Japan. This section belongs to the Tamba-Mino-Ashio Belt. Previous research of radiolarian and conodont biostratigraphy (Kuwahara et al., 1991; Yamakita et al., 1999) have been indicated the position of the Permian-Triassic boundary in this section. In this study, we conducted careful observation of the outcrop to reconstruct geological structure and stratigraphy. We then made detailed columnar section from the identified continuous strata and collected rock samples for in-room analysis.
Based on our outcrop observation, the lithofacies of the Ubara section consist of the following three lithofacies. It is upper Permian (Changhsingian) bedded chert (2 beds, total 0.30 m in thickness), the upper Permian siliceous claystone (24 beds, total 0.93 m in thickness), and the uppermost Permian to the earliest Triassic black claystone (2 beds, totally 0.26 m in thickness). In the black claystone, a 2 cm thick, grey-colored siliceous claystone bed is interbedded.
In this presentation, we will report results of the laminae preservation and pyrite presence based on our observations of outcrop and polished rock samples and discuss oceanic redox records during the latest Permian and the earliest Triassic across the EPME. According to previous research, pyrite has been found in the siliceous claystone and black claystone of the latest Permian, pyrite framboids also can be seen in the approximately same horizon (Algeo et al., 2011). This is suggestive to ocean anoxia in the pelagic Panthalassa. The parallel lamination appeared to be well preserved in these horizons due to limited benthos activity caused by the oxygen-poor bottom-water condition. During the day, we will generate our original data of lamination and pyrite presence at high resolution to show more detailed consequences of redox conditions across the EPME.
We focus on the Permian-Triassic boundary section namely the Ubara section which is located in Fukuchiyama-city, Kyoto Pref. Japan. This section belongs to the Tamba-Mino-Ashio Belt. Previous research of radiolarian and conodont biostratigraphy (Kuwahara et al., 1991; Yamakita et al., 1999) have been indicated the position of the Permian-Triassic boundary in this section. In this study, we conducted careful observation of the outcrop to reconstruct geological structure and stratigraphy. We then made detailed columnar section from the identified continuous strata and collected rock samples for in-room analysis.
Based on our outcrop observation, the lithofacies of the Ubara section consist of the following three lithofacies. It is upper Permian (Changhsingian) bedded chert (2 beds, total 0.30 m in thickness), the upper Permian siliceous claystone (24 beds, total 0.93 m in thickness), and the uppermost Permian to the earliest Triassic black claystone (2 beds, totally 0.26 m in thickness). In the black claystone, a 2 cm thick, grey-colored siliceous claystone bed is interbedded.
In this presentation, we will report results of the laminae preservation and pyrite presence based on our observations of outcrop and polished rock samples and discuss oceanic redox records during the latest Permian and the earliest Triassic across the EPME. According to previous research, pyrite has been found in the siliceous claystone and black claystone of the latest Permian, pyrite framboids also can be seen in the approximately same horizon (Algeo et al., 2011). This is suggestive to ocean anoxia in the pelagic Panthalassa. The parallel lamination appeared to be well preserved in these horizons due to limited benthos activity caused by the oxygen-poor bottom-water condition. During the day, we will generate our original data of lamination and pyrite presence at high resolution to show more detailed consequences of redox conditions across the EPME.