大阪府,千里山丘陵の大阪層群中のオーソコーツァイト質礫

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Orthoquartzitic gravels were abundantly found in the basal part of the Osaka Group in the Senriyama Hills, Osaka Prefecture. These gravels were observed under the microscope to clarify their textural and compositional properties. The mineral composition of orthoquartzitic gravels consists of six components, that is, detrital quartz, secondary overgrown quartz, feldspar, rock fragments, accessory minerals and matrix. About three quarters of specimens belong to orthoquartzite, and about a quarter to feldspathic quartzite. The amount of detrital matrix ranges between 0.0 and 23.3% of the total components. One sample which contains large amount of matrix belongs to quartzose wacke. Some specimens from the Senriyama Hills have larger amount of rock fragments and/or matrix than those of the Muro Group. Matured specimens are composed of well-rounded or rounded quartz grains, and are moderately or well sorted, while most specimens from the Tetori Group contain ill-rounded quartz. These differences in lithologic characteristics between the orthoquartzitic gravels in the Senriyama Hills and those in the Muro Group or the Tetori Group, indicate that the source area of the orthoquartzitic gravels in the Senriyama Hills are not the same as those in the Muro Group or the Tetori Group. There are many kinds of color in orthoquartzitic gravels. And some specimens show bimodal grain size distribution. These facts indicate that some of the orthoquartzitic rocks were originally formed under dune environment.
日本地質学会の論文

大阪府,千里山丘陵の大阪層群中のオーソコーツァイト質礫

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