Arakura Formation and Arakuran Age

NAKAZAWA Keiji

doi:10.15080/agcjchikyukagaku.1958.36_19

Bibliographic Information

Other Title

三疊系荒倉層及び荒倉期について
舞鶴地帯の層序と構造-7-
マイズルチタイノソウジョトコウゾウ 7
舞鶴地帯の層序と構造-その7
A Study on the Stratigraphy and Geologic Structure of the "Maizuru zone" Part 7.

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Description

The Arakura formation, composed mostly of black shales and sandy shales more than 70m thick, is overlain disconformably by the Sakawan (≒ Carnian) Nabae group. The Arakura is referred to be earliest Carnian or Ladino-Carnian in age by the following animal fossils and from the stratigraphical view point: "Monophyllites" arakurensis NAKAZAWA MS., Monophyllites? sp., Halobia? sp., Palaeoneilo sp., Nuculopsis (Palaeonucula?) sp., Psioidea spp. α, β, Spiriferina sp.. "Monophyllites" arakurensis belongs probably to a new genus derived from the Monophyllites-stock like Mojsvarites. Psioidea sp. α resembles especially P. conjuncts (HECTOR) from the Oretian (≒ lower Carnian) in New Zealand. The Arakura is surely later in age than the Zohoin group, the type of the Fujinohiran, which is characterized by typical Ladinian molluscs such as Daonella kotoi, D. sakawana, Monophyllites cf. wengensis and Protrachyceras aff. archelaus, although the stratigraphical relation between the two cannot be ascertained. Therefore, the Arakura formation represents the new stage between the Fujinohiran and the Sakawan. Here, the Arakuran age (= earliest Carnian or Ladino-Carnian) is proposed.

Journal

Earth Science (Chikyu Kagaku)

Earth Science (Chikyu Kagaku) 1958 (36), 19-21, 1958

The Association for the Geological Collaboration in Japan