Abstract:

Clay minerals in 29 samples of surface sediments and core Sll in the northwestern sea off the Antarctic Peninsula are analyzed to determine their distribution pattern and to decipher their origin and source. The clay fraction of less than 2 microns in the samples are studied by X-ray diffraction. The result indicate that the clay minerals consist mainly of montmorillonite, illite, chlorite and kaolinite and that change in their abundance is remarkable. The maximum content of montmorillonite, 45% in average, is found in the shallow zone around the South Shetlands, whereas the minimum content of montmorillonite (27%) is found in a zone nearby the northwestern side of the Antarctic Peninsula. The distribution pattern shows that relative abundance of montmorillonite gradually decreases from north to south in the sea area studied. However, the distribution trend of illite is just opposite to that of montmorillonite. For example, relative abundance of illite is 48% in a zone nearby the northwestern side of the Antarctic Peninsula and 32% m the shallow zone around the south Shetlands. Analysis of core Sll indicates that clay minerals are primarily composed of the same as above-mentioned. Among them illite is predominant. A relative abundance of montmorillonite decreases with depth of the core, whereas the abundance of illite and chlorite in creases with the depth, but content of kaolinite does not sharply vary. The variation indicates that montmorillonite has its highest concentration in the interglacial sediments, and illite and chlorite have their highest concentration in the glacial sediments.