Stratigraphy and geologic age of the Middle Paleozoic strata in the Kuzuryu Lake-Upper Ise River area of the Hida-gaien Terrane, central Japan

Abstract

Middle Paleozoic tuffaceous clastic and carbonate rocks are well developed in the Kuzuryu Lake-Upper Ise River area of the Hida-gaien Terrane in central Japan and are lithologically subdivided into the Kagero, Shibasudani, and Kamianama formations. The Kagero Formation consists mainly of tuffaceous sandstone and tuffaceous shale, which sometimes alternate, and differs from the other Paleozoic formations by having well-stratified tuffaceous rocks and an overall abundance of calcareous grains. The Shibasudani Formation is subdivided into three parts. The lower and upper parts consist mainly of sandstone and shale, with alternating sandstone and shale containing siliceous shale intercalations. The middle part of this formation is characterized by limestone blocks that are inferred to be exotic inclusions. The Kamianama Formation, which is correlative with the Lower Devonian Fukuji Formation, consists of limestone, felsic tuff, and sandstone. Radiolarians clearly indicate that the Kagero and Shibasudani formations are early Early Silurian and Late Silurian to Early Devonian in age, respectively. Terrane-wide correlations clearly show that the Middle Paleozoic strata of the Kuzuryu Lake-Upper Ise River area strongly resemble those of the Fukuji-Hitoegane area in age, lithology, and assemblage of lithologic units, and just as strongly differ from strata in the Hongo-Arakigawa and Naradani areas. Both Lower Devonian shallow-marine carbonates and deep-water tuffaceous elastics are present in the study area. Their occurrence together implies the presence of a diverse sedimentary system in a differentiated Middle Paleozoic basin.