Alkylammonium characterization of smectite alteration in the Tertiary basins of southeast Korea

The layer charge characteristics of smectite from the Tertiary basins in the Pohang area, Korea have been studied in detail using the alkylammonium method. On the basis of layer charges, the smectite in the Pohang area can be classed as normal and high-charge (hc) smectite. The layer charge of the normal smectite averages 0.3, and ranges from 0.25 to 0.38/half unit-cell. The hc-smectite collapses on K saturation to become illite-like material and shows 10 Å-series reflections on X-ray diffraction. The layer charge of the hc-smectite ranges from 0.5 to 1. The layer charges do not appear to be related to stratification or to basins of occurrence. The diagenetic trend that may have existed in the region was probably disturbed by later volcanic activity. A systematic change in layer charge and geochemistry of smectite in Waeup illustrates that the heat and solutions associated with the volcanic activity may have played a role in the development of layer charge.