Late Cretaceous pollen and spore floras of northern Japan : Composition and interpretation

Abstract

For the establishment of floristic sequences, pollen and spore fioras from the Late Cretaceous sediments ranging from Cenomanian to Maestrichtian of northern Japan are studied.Four areas where the Late Cretaceous sediments are typically weli developed are selected: the Ishilcari coal field (the Campanian-Maestrichtian Hakobuchi Group), Saku area (the Cenomanian-Campanian Middle and Upper Yezo Groups), the Kuji goal field (the early Senonian Kuji Group) and the 3oban coal field (the early Senonian Futaba Group).Nine pollen and spore fioras two of which had been studied by previous investigators, are discussed.Based on fioristic composition and components, the four floras of Cenomanian-Turonian, Early Senonian, Campanian and Maestrichtian ages are distinguishable.The oldest fiora is characterized by diverse pteridophytes, particularly Schizaeaceous spores, and by less diversified angiosperms containing few porate pollen.The second has still the relic of Mesophytic appearance: pteridophytes are more or less superior to angiosperms in taxonomic diversity, containing commonly Schizaeaceou's and Gleicheniaceous spores.Of gymnosperm pollen Cycadopites, Monosulcites, Araucariacites, Rugubivesiculites and Classopollis are common.Angiosperm are composed predominantly of tricolpate pollen, but are represented by few porate pollen.The third is characterized by the predomint angiosperms and also by diverse species of Aquilapollenites.Pteridophytes are sparsely represented in Schizaeaceous spores.The youngest flora is composed of a predominant porate pollen, which occupies a majority of angiosperm pollen.This flora is characterized also by diverse pollen of uncertain taxonomic position such as Aquilapollenites, "iodehouseia and Ocellipollis.These fioristic sequences in northern Japan shows thqt pteridophytes and gymnosperms forming the major constituents during Cenomanian-Turonian times were gradually replaced by angiosperms towards Maestrichtian time.Late Cretaceeus floristic changes of northern Japan are very similar to those of Eastern Siberia, especialiy of the Zeya-Bureya basin.