Cretaceous Foraminifera from Hokkaido, Japan

概要

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The foraminiferal assemblages from isolated Cretaceous areas along the meridional zone of Hokkaido are described. In the sectioned areas, the vertical change in quality and quantity of the assemblage-species are determined, and in other areas their relationship to those in the sectioned areas. Applying the Japanese time scale to the foraminiferous horizons, the distributions of the assemblages are discussed. The characteristics of these assemblages are analysed with reference to their paleoecological significance. In Hokkaido, the Cretaceous deposits are nearly continuous marine sediments ranging from the Paleomiyakoan to Neohetonaian (correlated with standard Aptian to Maestrichtian). The Neohetonaian assemblage is not dealt with because of the insufficient materials. The Cretaceous assemblage is divided into the lower assemblage ranging from Paleomiyakoan to Neogyliakian (≒Aptian to Turonian), and the upper from Paleourakawan to Paleohetonaian (≒Coniacian to Campanian). The lower one of these assemblages is a product of a fluctuating stage and the upper is one of a stable stage, as described in the text. Furthermore, taking the major group or assemblage of characteristic species as a unit marker, both assemblages can be subdivided into minor units and they correspond to the respective stages and substages previously established. The intimate relationship between these discriminated assemblages and the previously established stratigraphic units can be recognized. From the correlation based upon field and laboratory work it is clear that the respective areas in which the Cretaceous deposits are distributed were subjected to similar histories in broad view, but reveal different features in detailed view. The differences are shown by the faunal elements and lithofacies of the respective areas together with their associated faunal facies. This paleoecological significance is reflected in the growth of the Cretaceous sedimentary basins. These differences reflect the progress in evolutionary trends in the minor and major assemblages from the respective areas, and indicate the migratory growth and development of the basins as related with the paleooceanographical conditions shown by the quanti-qualitative plankton constituent-frequency. Paleontological work is done systematically, both in sampling and in technique procedure as well as Paleontologically. Among the total of 25 families, 68 genera, 158 species and eight subspecies determined, two genera, 40 species and three subspecies are described as new to science. Thirty-four species are given letter designations because of their scarcity and unfavorable preservation. Subdivisions of the foraminiferal assemblages and their relation with the lithological units resulted in the establishment of a satisfactory correlation of corresponding time-stratigraphic units of foreign countries as described in detail in the text. This is the first detailed account of the Cretaceous Foraminifera of Hokkaido, and therefore it is considered basic for future research.
東北大学の論文
1960-11-28

Cretaceous Foraminifera from Hokkaido, Japan

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概要

東北大学 | 論文

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