Magnetic Properties of Red Cherts with Special Reference to the Associated Greenstone, in Southwest Japan : A Rock Magnetic Approach

An experimental approach to the study of Fe-Ti minerals originally contained in Paleozoic to Mesozoic red cherts from the Tamba, Mino and Shimanto terrains in Southwest Japan has been made. The main purpose of the study is to establish a foundation for the paleomagnetic reliability of cherts to support paleomagnetic results which were already reported by the author and his collaborators. (SHIBUYA and SASAJIMA, 1980; KATSURA et al., 1980). Thermomagnetic analyses combined with some heating experiments under an appropriate vacuum condition, lend an effective way to recover the original ferromagnetic mineral assemblage of these cherts. As the results, the possible ferromagnetic minerals (β phase) of the red cherts, which are found in stratigraphic sequences that contain greenstones, show an affinity with that of tholeiitic basalt (x=0.62±0.05), suggesting that the primary ferromagnetic minerals in the red cherts were probably derived from related submarine basaltic tuffs. If we accept a view that red cherts underwent submarine weathering or hydrothermal alteration almost the same time as the greenstones associated with them, a closed system with respect to Fe-Ti minerals and consequently blocking of their remanent magnetization as well, was maintained after an uncertain diagenetic event: this condition presumably related to the time of crystallization of major silica of the chert

Paleoniagnetism Study of Pliocene to Pleistocene Volcanic Rocks in Southwest Japan

目次のタイトル"Paleoniagnetism of Pliocene to Pleistocene Rocks in Southwest JapanThe directions of natural remanent magnetization of about 300 volcanic rock specimens collected from Southwest Japan of which ages range from Pliocene to Pleistocene were measured. The mean pole positions calculated from the results agree with the present geographic north pole within an oval of 95% confidence. This fact suggests that there were no considerable movement of paleomagnetic pole position during Pliocene and Pleistocene in Southwest Japan, and that Southwest Japan did not change its geographical situation since Pliocene epoch. Furthermore, the volcanic rocks of remote localities used in the study can be correlated much more exactly with one another by the aid of comprehensive knowledges, such as their stratigraphy, absolute age determined by isotope method and the paleomagnetic polarity change of their remanent magnetization

A General Report of the Geological and Palaeontological Survey in Maragheh Area, North-West Iran, 1973

The present article is a general report on the excavation of the bone beds in Maragheh area, N. W. Iran. The excavation has been done at four sites in Dareh-e Gorg, near Mordagh, in autumn of 1973. Many fossil bones were sampled and those dispositions were recorded. The fossil materials excavated in this time were listed, including many cranial and postcranial bones of Hipparion, Antelope, and other Bovidae, Carnivores, Choerolophodon, etc. The fossil bone was obtained from the sediments of 130 m thick in Mordagh area, consisting mainly of the alternations of tuffaceous sandstone and mudstone. Those are assignable to the lower part of the Maragheh Formation. The six tephra were recognized as the distinct marker beds in those sediments. Then, the sedimentary environment is presumed. Directions of natural remanent magnetization of 9 sites were measured. Six pyroclastics including one ash flow of basement were dated by fission-track method and the age of the Maragheh fauna was considered as 6.6 to 6.9 my