As an introduction to using detailed techniques of X-ray diffractometry for estimating clay minerals in sediments, clay-sized fractions of two North Atlantic cores collected between the Faeroe and the Shetland Islands were examined. Molybdenum sulphide was used as internal standard. The relative quantities of the different clay minerals, based on peak heights, were measured and corrected at 50% and 100% relative humidities. Crystallinity of the swelling clay minerals was measured as width at halfpeak height. One core (NA81-5) appeared to be disturbed and comes out with confusing relations between the climatic periods on one hand, as determined from carbonate curve, and the X-ray parameters and CaCO3 content on the other. The results core NA81-10, however, are highly significant and interesting. In this core, the glacial period is uniformly marked by low contents of well crystalline combined swelling minerals, low amounts of vermiculite and high concentrations of smectite, while these values are uniformly the opposite in the warmer Holocene and interglacial periods. This pattern with regard to the climatic periods is also clearly reflected in the concentrations of kaolinite, chlorite and mica/illite, again with almost no exception. Similar patterns are also displayed by the CaCO3 content, but with more exceptions. However, the two factors mutually support each other, thus affirming the validity and importance of the X-ray diffraction parameters in delineating the different climatic periods. |
