PALEONTOLOGICAL AND PETROLOGICAL STUDY OF LIMESTONES IN THE PERMIAN-TRIASSIC BOUNDARY

1994 Fiscal Year Final Research Report Summary

• Project/Area Number: 05454002
• Research Category: Grant-in-Aid for General Scientific Research (B)
• Allocation Type: Single-year Grants
• Research Field: Stratigraphy/Paleontology
• Research Institution: YOKOHAMA NATIONAL UNIVERSITY
• Principal Investigator: KOIKE Toshio YOKOHAMA NATIONAL UNIVERSITY.FACULTY OF EDUCATION PROFESSOR, 教育学部, 教授 (80037283)
• Co-Investigator(Kenkyū-buntansha): IGO Hisaharu TOKYO GAKUGEI UNIVERSITY.FACULTY OF EDUCATION ASSISTANT PROFESSOR, 教育学部, 助教授 (70014818) ; ARIMA Makoto YOKOHAMA NATIONAL UNIVERSITY.FACULTY OF EDUCATION PROFESSOR, 教育学部, 教授 (10184293)
• Project Period (FY): 1993 – 1994
• Keywords: PERMIAN-TRIASSIC BOUNDARY / CONODONT FOSSILS / FUSULINID FOSSILS / TEXTURE AND COMPONENTS OF LIMESTONE

Research Abstract

A drilling (50 m in depth. 70 mm in diameter) was performed in 1994 for the purpose of getting information about the Permian-Triassic boundary in the Taho Limestone exposed in Tahokamigumi. Shirokawa-cho. Higashiuwa-gun. Ehime Prefecture. As a result of investigation of the drilling core, there occures the lower Triassic Griesbachian conodont Hindeodus minutus. H.parvus. and? Isarcicella isarcica from the dark gray dolomitic limestone in the level of 22.80 m to 23.45 m and permian fusulinid Staffella sp. from the light gray dolomitic limestone at the level of 23.50 m below the grand surface. We propose the Taho Formation for the Triassic limestone and the Shirokawa Formation for the Permian Limestone. The boundary between the formations is conformable.
The boundary between the Upper Permian Mitai Formation and the Triassic Kamura Formation exposed in Shioinosou. Takachiho-cho. Nishiusuki-gun. Miyazaki Prefecture. We confirmed the occurrence of Hindeodus minutus. H.parvus. Isarcicella is arcica. and Neogondolella carinata from the dark gray limestone with small gastropods in the basal 3 m of the Kamura Formation. The Permian Mitai Formation conformably underlies the Kamura Formation. The uppermost part of the Mitai Formation is usually strongly dolomitized and unfossiliferous but Permian fusulinid Staffella sp. occurs in the weakly dolomitized limestone with foraminifers and calcareous algae near the boundary.
As mentioned above we could confirm the Griesbachian in the Shirokawa and the Kamura Formation. This is the first confirmation of the Griesbachian deposited on the submarine volcanic island which accreted to the Yangtze continent in Jurassic. It is quite interesting that the Griesbachian limestone and Upper Permian limestone represent close similarity in lithofacies between two sections. Taho and shioinousou. The dark gray micritic limestone of the Griesbachian deposited in low energy and anoxic environment and light gray micritic limestone of the Upper Permian (Changxingian) sedimented in low energy and oxic environment. The dolomitization occured during the Late Permian and Early Triassic.