Formation and Transformation of Clay Minerals in the Noma Formation, Chita Peninsula

Abstract

The Pleistocene Noma formation is distributed along the western coast of Chita Peninsula, Aichi Prefecture. It is composed of marine sediments, mainly sandy, of Riss/Würm Interglacial in age. Clay mineral composition of these sediments was determined by the X-ray diffraction, differential thermal, and electron microscopic methods. The results are summarized as follows.
1) The clay fraction of the lower sand member and that of the middle silt member are composed of metahalloysite, illite, montmorillonite, and others; this mineralogy is in harmony with the marine environment of sedimentation.
2) The clay fraction of the upper sand member is mainly composed of a mixture of halloysite of various degree of hydration, which is considered as a product of weathering by percolating meteoric water.
3) The Noma formation is covered by acid, reddish-brown soil, the clay fraction of which is composed of metahalloysite, Al-vermiculite, gibbsite, and others. Gibbsite concretions are often found beneath the soil. It is inferred that aluminum was leached out from the soil and migrated downward to the horizon where the concretions were formed.