女川層のいわゆる硬質頁岩の組成

概要

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The mudstone of the Onnagawa formation of Miocene age in the oil field of northeastern Honshu is characterized by very hard, siliceous and well stratified rock, so it has been nicknamed hard shale by field geologists. The hard shale can be subdivided into three types on the basis of compositional research by optical, X-ray and scanning electron microscopic techniques. The seare: (1) clastic hard shale, (2) diatomaceous hard shale, and (3) tuffaceous hard shale. X-ray diffractometer pattern of the whole rock sample of type (1) is characterized by the existence of quartz, however, type (2) and (3) show the X-ray reflection of α-cristobalite (opal-CT). The d(101) spacing of cristobalite of type (2) is obviously different from type (3). The value of type (2) (4.11-4.13 Å) is slightly larger than type (3) (4.07-4.09 Å). The morphology of opal-CT lepispheres, framboidal pyrite and potash feldspar (adularia) in the hard shale are also shown by SEM photographs.
日本地質学会の論文
1978-11-30