三紀層에 胚胎된 벤토나이트의 酸素 및 水素同位元素 硏究

Hydrogen and oxygen isotopic compositions of tertiary montmorillonites in Southern Korea

Hydrogen and oxygen isotope ratios of thirteen of the under 2 micron size fraction of the montmorillonites were measured. The oxygen isotopic compositions of these samples range from +17.0 to +25.1 permil and the hydrogen isotope compositions range from -47.5 to -65.8 permil with an average standard deviation of 0.7 and 2.7 permil, respectively. The oxygen isotope compositions show a positive relationship with stratigraphy whereas the hydrogen isotope compositions do not. It suggest that the montmorillonite attained isotopic equilibrium at the maximum burial depth and ratained their oxygen isotope composition on subsequent uplift. Possibilities of montmorillonite formation by weathering or hydrothermal alteration of volcanic material are eliminated by the δD and δ¹⁸O values of these samples. Calculated formation temperature lie between 29 to 80℃.