Mineral Chemistry and Geochemistry of the Bentonites Intercalated within the Basal Conglomerates of the Tertiary Sediments in Korea and Their Stratigraphical Implication

제3기층 기저역암에 협재되는 벤토나이트의 광물학, 지화학적 연구 및 층서적 적용

  • 이종천 (영국 임페리얼칼리지) ;
  • 이규호 (연세대학교 지구시스템과학과) ;
  • 문희수 (연세대학교 지구시스템과학과)
  • Published : 2001.02.01

Abstract

Bentonite layers are intercalated within the basal conglomerates in the Tertiary sedimentary basins of Kampo, Janggi and Pohang, southeastern Korea. Eighteen samples of the bentonites went through X-ray diffraction, scanning electron microscopy, heavy mineral analyses, chemical analyses and oxygen, hydrogen stable isotope analyses to define the mineralogical characters of the bentonites. Heavy minerals such as zircons, apatites, amphiboles and biotites separated from bentonites show clean and euhedral surfaces, which are the characteristic features of volcanic origin. But biotites from the Chunbook Conglomerate are found as altered and heavily broken flakes which implies longer transportation of these bentonites. $TiO_{2}/Al_{2}O_{3} ratios of <2 $\mu$m particle fractions (the Chunbook Conglomerate 0.031; Janggi 0.029; Kampo 0.025) suggest that those are originated from volcanic tuffs. That is, the higher the value is, the more mafic in chemical compositions of the original tuffs. Authigenic montmorillonite and zeolite minerals were observed by SEM, which indicates diagenesis origin of bentonites. But the samples from the Chunbook Conglomerate showed only chaotically packed clay flakes in the matrix of sands or conglomerates, which implies detrital influence, not authigenic origin. The structural formulae of montmorillonite from these basins reflects their environment of formation. Fe (Ⅵ) can show the redox condition of its past environment and much lower $Fe^{2+}(Ⅵ)/Fe^{3+}(Ⅵ)$ ratios in montmorillonite of the Chunbook Conglomerate imply the greater oxidizing influence. Calculated burial depths from oxygen stable isotope data of the samples from the Chunbook Conglomerate generally fall to the range of 929~963 m whereas the real burial depth of this area is only 530~580 m. This could be explained as the bentonites of the Chunbook conglomerate had not been formed in situ. Discriminant analyses with the data from chemical analyses and structural formulae of montmorillonites show that bentonites from three different basins could definitely be distinguished with each other. This result arises from the different chemical compositions of original volcanic ashes and the difference of sedimentary environments.

References

  1. 광산지질 v.10 영인지역, 제3기 심광화대의 광물학적 특성, 성인 및 그 잠재성에 관한 연구 김수진;노진환
  2. 동력자원연구소 조사연구보고 no.10 3기층지역 불석 및 벤토나이트, 산성백토광상 연구 김종환;문희수;유장한;김용욱
  3. 광산지질 v.19 3기층에 배태된 벤토나이트의 산 소 및 수소동위원소 연구 문희수
  4. 지질학회지 v.18 한국 어일분지의 제3기 층서 윤선
  5. 동력자원연구소 연구보고 한국 동남부지역 제3기 퇴적분지의 지체구조 발달 및 퇴적환경 연구 한종환
  6. Clays and Clay Min. v.37 Oxidatin state og iron in giaucontinite from oxidation and reduced zones of soil-geologic columns Fanning .D.S.;Rabenhost, N.C.;May, Leoplo;Wagner, D.P.
  7. Ceochim. Cosmochim. Acta v.35 Deutrium and oxigen correlation: Clay minerals and hydroxides in Quaternary soils compared to meteoric waters Lawrence, J.R.;Taylor, H.P.
  8. Geochim. Cosmochim. Acta. v.36 Hydrogen and oxygen isotope systematics in weathering profiles Lawrence J.R.;Taylor H.P.
  9. Clay MIn. Bull. v.1 The hydration of montmorillonite Mackenzie, J.R.
  10. Geochim. Cosmochim. Acta. v.43 Oxigen isotopic frationation in the system quartzalbite-another-water Matsuhisa, J.R.;Goldsmith, J.R.;Claton, R.N.
  11. Geochim. Cosmochim. Acta. v.40 Ma,Ca and ? exchange in the sediment-pore water system Perry, E.A.;Geiskes, J.M.;Lawrence, J.R.
  12. Nature v.423 Adsorption of the silver-thiourea complexes in montmorillonite clay Playsier, J.;Cremers, A.
  13. Chem. Soc. Faraday Trans. Ⅰ. v.71 Stability of silver-thiourea complexes in montmorillonite clay pleysier, J.;Cremers, A.
  14. Geophysical Monograph Isotopic pateerns in modern global precipitation Rozanski, K;Arguas-Arguas, L.;Gonfiantini, R.
  15. In Handbook of environment isotpe geochemistry Oxygen and hydrogen isotope effects in low temperature mineral water interaction Savin, S.M.;Fritz, P.(ed.);Fontes, J.Ch.(ed.)
  16. Sedimentology v.26 A geochemical and mineralogical investigation of some British and other European tonsteins Spear D.A.;Kanaris-Sotiriou
  17. Soil Sci. Soc. Amer. J. v.41 Oxidation-reduction mechanism for structual iron in nontronite Stucki, J.W.;Roth, C.B.
  18. Geologic Atlas of chosen no.2 Tateiwa
  19. Natural zeolites Properties of natural zeolites Vaugan, D.E.W.
  20. J. Sed. Petrol. Interpretative value of heavy minerals from bentonites Weaver, C.E.