| Co-Investigator(Kenkyū-buntansha) |
KAWABE Tetsuya Department of Earth Sciences, Faculty of Science, Chiba University, 理学部, 助手 (60009389)
YANAGIDA Juichi Department of Earth and Planetary Sciences, Faculty of Science, Kyushu Universit, 理学部, 教授 (70037183)
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| Research Abstract |
In succession of our biostratigraphic study of the Paleozoic and Mesozoic Groups in Central Andes, which was started in 1980, more detailed field survey and re-examination were undertaken during late July to late August, 1990, and November 1991, on the Tarma Group (Middle Carboniferous) developed near Tarma City in Peru and the Copacabana Group (Upper Carboniferous to Lower Permian) developed near and around Titicaca Lake in Bolivia.
The aims of the present research are mainly as follows : 1) to complete our biostratigraphic study of the Upper Paleozoic (Carboniferous-Permian) in Central Andes with the conodonts as additional data, and 2) to make clear the boundary between the Carboniferous and Permian Systems in the Copacabana Group.
In Peru, the rock samples for conodont analysis were collected from the Tarma Group, but unfortunately no conodont could be found at all.
In Bolivia, the Copacabana Group developed in Yaurichamb, Ancoraimes, Matilde, Cuyavi and Yampupata were re-examined and
… More
collected some rock samples for conodont analysis, especially around the boundary between the Triticites Zone and Pseudoschwagerina Zone in the Copacabana Group. The Copacabana Group has been divided into three fusuline zones, namely, the Triticites, Pseudoschwagerina and Eoparafusulina Zones in ascending order, and all of which has been recognized to be the Lower Permian (Wolfcampian) in age by previous students since Dunbar and Newell (1946) and so on. Suarez-Riglos et al. (1987), however, divided it into four conodont assemblage zones. They are of the opinion that, the lower two assemblage zones, which have been recognized as the lowermost Permian Triticites Zone or Triticites nitens Subzone by the previous students including us, should be the uppermost Carboniferous (Virgilian) by tht conodont evidence. The first occurrences of Pseudoschwagerina are in the horizons at 25-40m from the base of the Copacabana Group in Yaurichambi, Ancoraimes and Matilde routes, and at 240-280m in Cuyavi and Yampupata routes.
Accordingly, at present, the correlation of stratigraphic sections is revised and the boundary between Carboniferous and Permian is tentatively placed at the base of Pseudoschwagerina Zone. Less
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