安中-富岡地域ベントナイト鉱床に関する被熱履歴の推定

概要

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The Miocene sedimentary strata are widely distributed in the Annaka-Tomioka area, northwestern Kanto. Workable several bentonite deposits that are interbedded in the middle Miocene sequence are formed by physical and chemical activities during burial diagenesis. The middle Miocene sequence provides evidence of stratigraphical data, biohorizontal investigation and paleobathymetrical data. From these analytical research, the sedimentary age and paleoseadepth of these workable T-7, T-11 and T-14 bentonite beds are regarded as 13.5Ma/-175m, 15.2Ma/-500m and 15.8Ma/-200m respectively. In this normal basin, which are consisted of mainly clastic sedimentary rocks and not effected by any volcanic activity or assuming thermal anomaly, equation (2) can be applicable to temperature estimation in each stratum. For the first input parameter, the heat now has been held constant (87.9mW/m^2) from burial age to present. For the second input parameter, the thermal conductivity of sandstone and mudstone depends on the porosity. Therefore, it can be made use of the data to calculate the primary thermal conductivities. For the third input parameter, the thicknesses of all burial strata are used thicknesses to restored at that age. In this paper, the method to restored have been adopted an exponential porosity-depth relationship. Thermal history modeling of the main bentonite deposits during diagenesis can be determined by this system.
日本粘土学会の論文
2004-03-12