層状チャートの堆積リズムによる地層の対比

その他

Upper Triassic bedded cherts are good example of recorded depositional cycles corresponding to the Milankovitch cycles, 100,000 years and 400,000 years, because radiolarian blooming was effected by nutrient supply in high-stand of sea level. Thus reading these cycles in bedded chert sequence by combination of thicker chert beds (activated radiolarian blooming and rapid deposition) and following thinner chert beds (weakened blooming) could be a new method for global correlation. This cycles clearly can be read in the Upper Triassic especially upper Carnian to lower Norian of relatively oceanic regression, while in the Middle Triassic, chert beds were deposited steady and evenly because of less effect of geologic cycles to radiolarian blooming at the time of relative transgression.