Low‐latitude and Southern Hemisphere origin of Anisian (Triassic) bedded chert in the Inuyama area, Mino terrane, central Japan

Abstract

Paleomagnetic and paleontologic studies of Middle Triassic to earliest Jurassic radiolarian bedded chert in the Inuyama area, southern Mino terrane of central Japan, have shown that the chert was deposited in an equatorial region with a paleolatitude between 10°N and 10°S, and in particular, the lower to middle Anisian chert depositional basin was situated in the Southern Hemisphere. The chert has four characteristic components of remanent magnetization. The highest blocking temperature component, carried by hematite, shows positive fold and reversal tests and is regarded as the primary remanent magnetization acquired just after deposition. The other three components are interpreted as a present field overprint and two postfolding remagnetizations. The absolute, tilt‐corrected inclinations of the primary component are less than 20° for all the samples of Middle Triassic to earliest Jurassic age, with the mean inclination of the lower to middle Anisian chert being 11.0°±4.3°. Paleomagnetic polarity reversals observed for the lower to middle Anisian chert are well correlated with those of the European Triassic sections, under paleontologic age constraints using radiolarians and conodonts, provided that the Anisian chert in Inuyama was deposited in the Southern Hemisphere. This conclusion illuminates the paleogeographic evolution of the chert‐bearing accretionary complexes not only in Japan but along the eastern margin of Asia as well.