Identification of Quaternary tephras by thermomagnetic properties of ferromagnetic minerals

For identificate and correlate the Quaternary tephras, the thermomagnetic properties of ferromagnetic minerals contained in the Daisen tephra formation re analysed by means of thermomagnetic balance. The investigates outcrop is 16km northeast of the Daisen volcano. At the outcrop, ten pumice fall layers and eight ash fall layers are exposed. Almost all these tephra layers are very thin and remarkably weatherd because the outcrop is situated apart from their disrutibution axes.The results of the thermomagnetic analysis show that these thin and weathered tephras are completely corelated to thick and more fresh tephras of their main distribution area. The thermomagnetic properties of ferromagnetic minerals including the Curie temperature are effective indicators for identification of tephra layers

Vertical variations of heavy mineral assemblage and thermomagnetic property of ferromagnetic minerals in the Daisen Kurayosh Pumice

The vertical variations of heavy mineral assemblage and thermomagnetic property of ferromagnetic minerals were examined on the Daisen Kurayoshi Pumice(DKP). The DKP is a late Pleistocene widespread tephra in Japan. At the eastern foot of Mt.Daisen apart 17 km from eruption center, 3.5 m thick DKP were divided into twelve horizons and specimens were corrected from each horizon. At the investigated outcrop, the DKP is accompanied by thin volcanic ash layer at its base and covered by volcanic soil(loam). In this volcanic soil, the Nh volcanic sand layer and a layer of pumice grains reworked from the DKP are intercalated. The specimens of all these layers were also corrected and examined. The DKP has biotite, hornblende, orthopyroxene, titanomagnetite and hemoilmenite as heavy mineral components. Modal composition is unique in the DKP except its lowest part. From the thin volcanic ash layer to the main part of DKP through the lowest part of DKP, the systematic modal variation is recognizable, the decrease in hornblende and increase in orthopyroxene. The Curie temperatures of titanomagnetite (429±4℃) and hemoilmenite (108±10℃) measured by thermomagnetic balance are also unique in the DKP except its uppermost part. In the uppermost part of DKP, the Curie temperatures of both titanomagnetite and hemoilmenite are systematically varied to higher temperature;446℃ and 147℃respectively. There are no correspondance between veriation of heavy mineral assemblage and that of thermomagnetic property

Nature of the Karakawa moor, Iwami-cho, Tottori Prefecture : topography, geology and vegetation

The Karakawa moor situated in the mountainous area of eastern part of Tottori Prefecture west Japan was investigated geologically and vegetationaty as the basic study for conservation of natural environments. The 26 hand orger drillings revealed the buried topography under the moor. There are small ridge and two shallow valleys under the moor. The formation of moor was promoted by deposition of dam upped sediments at the junction of these two valleys, The sediments are composed of gravel, silt and clay, volcanic ash and black organic soil (peat) in ascending order. The volcanic ash is considered as secondary deposits and identified as mixture of Aira Tn ash (ca.25ka) and Daisen Uh ash (ca.20 ± α ka) by means of thermomagnetic and also EDX analyses. From the results of fossil pollen analysis, the black organic soil is divided into three pollen zones in ascending order as follows; A zone (145-130 cm depth: Castanea & Castanopsis, Taxodiaceae &Cupressaceae, Betula, Cryptomeria), B zone (130-90 cm depth: Castanea & Castanopsis, Taxodiaceae & Cupressaceae, Cyclobalanopsis, Aesculus), C zone (90-35 cm depth: Taxodiaceae & Cupressaceae, Castanea & Castanopsis, Aesculus, Tsuga). the vegetation of the moor was inbestigated phytosociologically in 1980-1981 and 1988-1989. As the result of the studies, 5 communities were recognized. The following 3 communities with 2 sub-communities as a typical moor vegetation among them were discussed with the comparison of a secular change. 1) Eriocaulon miquelianum - Rhyncospora fauriei community 2) Hosta montana - Arundinella hirta community 　(2-1) Rhynchospora fauriei - A.hirta sub-community 　(2-2) Carex dispalata - A.hirta sub-community 3) Lythrum anceps - C.dispalata community (1) is an oligotrophic community favored by pudding water flowing from percolating underground water. (3) is an eutrophic community confined to the area near the stream

Nature of the Asanabewashigasen Houbutsusan Mountainous Region, Western Tottori Prefecture : Topography, Geology and Vegatation

The Asanabewashigasen-Houbutsusan area, western Tottori Prefecture, is a mountainous highland with elevation over one thousand meters. Saved from recent artificial reformation, the natural environment there is well preserved. The area consists geologically of lower to upper Mesozoic (meta-)sedimentary rocks, upper Cretacous to Paleogene volcano-plutonic rocks and uppermost Cenozoic sediments. The fairly restricted distributions of the latter sediments indicates the the mountainous area has been subjected to uplifting and subaerial erosion through late Cenozoic time. The climate type of Japanese Islands is divided into three, i.e., the Japan Sea, the Pacific Ocean and the transitional climate types. The transitional one is called also the Semi-Japan Sea climate type, based on less amounts of winter snowfall. The investigated area is of the the Semi- Japan Sea climate type. In addition, the present investigation suggests that the southwestern limit of Ilex leucoclada and Sasa kurulensis, characteristic of the Japan Sea climate type, locates between Mt. Kenashiyama and Mt. Houbutsusan. Many plants including scarce ones such as Erytronium japonicum, Galium kinuta, Tripterygium regelii, Lepisorus ussuriensis var. disrans and so on have survived in the Aasanabewashigasen-Houbutsusan area, but not in the Daisen volcanic area to the north, where a Pleistonce volcanism forms a big cone 30km across. This fact suggests that the flora in the latter area is still immatured probably due to the geological youthfulness of the volcanic area