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Permian-Triassic Relationships and Faunal Changes in the Eastern Tethys
The stratigraphy and faunal sequences of the Upper Permian and Lower Triassic are described from nearly complete sections in Japan, south China and Indochina. The uppermost Permian is represented by the Paleofusulina sinensis Zone or the Pseudotirolites asiaticus Zone and the Lower Triassic by beds containing Claraia wangi or Ophiceras, Otoceras, or Glyptophiceras. The systemic boundary is marked in most areas by a disconformity, and in other areas by an unconformity, indicating a widespread recession of the sea and epeirogenic emergence, partly due to orogenic movements, at the end of the Permian. There are, however, other sections, mostly of eugeosynclinal facies, which are considered to exhibit a conformable sequence. Further studies are needed in these sections, however.
Observations are made on the faunal changes during the Late Permian, based on phyla or classes. No species apparently ranging from Permian to Triassic have been found. Extinctions and rates of decline are variable within organic groups and areas, but significant faunal changes were apparently much influenced by changes of geography and local sedimentary conditions, and particularly by the extensive regression of the sea. In the eastern Tethys, corals and bryozoans greatly declined in the early part of the Late Permian; while brachiopods and foraminifers, including small fusulinids in great numbers, continued to the close of the Permian. Bivalves and ammonoids, including ancestors of Triassic forms, flourished in the Late Permian, especially the former group in Japan, and the latter group in China. The great predominance of bivalves, especially Pteriaceans and Pectinaceans, among the lowest Triassic faunas is presumably a result of their adaptation to newly-vacated niches left by the abrupt extinction of Permian brachiopods.
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