Biostratigraphy and depositional facies of the Cretaceous in the upper reaches of the Haboro River, Hokkaido.

Abstract

The Cretaceous deposits yield abundant animal fossils from many levels, and inoceramids exceed 90% in number at most localities. The Cretaceous sequence of this area can be divided into 5 Inoceramus Zones; hobetsensis, teshioensis, uwajimensis-mihoensis, amakusensis and japonicus. They range from Middle Turonian in age. The Cretaceous deposits of this areea are extraordinarily thick, nearly two to five times as thick as those of the same ages or in other areas of the Meridional Zone of Hokkaido. This is largely due to the influx of a large amount of muddy sediments in addition to the incurrence of gravity-induced turbidites and debris-flow deposits. The lateral facies and thickness changes suggest that the sediment supply was from the west of this area. from English summary