Clay mineral origin and distribution on Astoria Fan

Graduation date: 1967Clay minerals from sediment samples obtained on Astoria Fan\ud were analyzed by X-ray diffraction. Clay minerals are defined for\ud the purpose of this study as crystalline phyllosilicates less than two\ud microns in equivalent settling diameter. The clay minerals are subdivided\ud into the five common families: montmorillonite, chlorite,\ud vermiculite, illite, and kaolinite. One X-ray scan of a magnesium\ud ion saturated, ethylene glycol treated sample was sufficient for the\ud identification of all the clay minerals.\ud A typical Recent hemipelagic sediment contains about 40 percent\ud montmorillonite, 30 percent illite, and 30 percent chlorite. Neither\ud kaolinite nor vermiculite is detectable in these samples. These concentrations\ud are similar to those reported for Columbia River sediments.\ud The surface sediments have an identical clay mineral assemblage\ud from the head of Astoria Canyon to the outer edge of the fan\ud approximately 250 kilometers offshore. All of the Recent sediments\ud in piston cores from Astoria Fan are the same as the surface sediments\ud on the fan. This similarity indicates an unchanging source\ud during Recent time and a lack of any visible marine diagenesis after\ud burial.\ud X-ray traces of Pleistocene clay minerals are distinctly different\ud from those of the Recent. One can use this change in clay mineralogy\ud as a time marker across the fan. Presumably the Pleistocene\ud clays were formed under different weathering conditions caused\ud by different climatic conditions