Variations of Clay Mineral Assemblage, Colour, and Microfossil Abundance in the Tertiary Sediments from the Pohang Area During Chemical Weathering

포항지역(浦項地域) 제(第)3기층(紀層) 퇴적암(堆積岩)중 화학적풍화작용(化學的風化作用)이 결토광물조성(結土鑛物組成), 화학조성(化學組成), 암색(岩色) 및 미화석(微化石) 산출빈도(産出頻度)에 미치는 영향

  • Published : 1990.04.30

Abstract

Mineralogy, chemistry, physical property, and fossil abundance have been studied for the samples collected from three weathering profiles, two from the Duho Formation and one from the Hagjeon Formation in the Tertiary sediments in the Pohang area. The mineralogy of the samples from the Duho Formation shows somewhat different from that of the Hagjeon Formation. Kaolinite is more abundant and shows higher crystallinity in samples from the Duho Formation than those in the Hagjeon Formation, but clay mineral assemblage in each weathering profile remain fairly constant with depth. This difference in mineral distribution seems to be inherited from original source materials. It indicates that little or not severe leaching has been taking place in these three weathering profiles. Weathering indicies indicate different degrees of susceptibility to chemical weathering in these two formations. The Duho Formation has a higher degree of susceptibility to weathering than that of the Hagjeon Formation which is mainly due to differences in clay mineral assemblages in both formations. A noticeble colour difference between oxidized and unoxidized zones in each profile can be easily recognized which is definetely due to different decomposition rate organic carbon by various oxidation state from surface to bottom of the profile. Weathering process have also intensively influenced microfossil preservation about up to 7-10 m in depth in the Duho Formation. Consequently, characteristics observed at weathering surface should be used as a subsidiary tool in setting geologic boundary or establishing formation. Great care must be taken to choose sampling site for microfossil study.

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Acknowledgement

Supported by : Korea Research Foundation