Abstract
The clay mineral composition in five sediments holding the fossils of dinosaur from the Early Cretaceous Tetori Group was discussed under the results of X-ray diffraction, thermal analyses and infrared absorption spectroscopy. The outline of the results is as follows:
Illite and chlorite were dominant in all samples from the Itoshiro and Akaiwa Subgroups. These clay mineral phases were classified into the type III stage, the Late Anadiagenesis to the Epidiagenesis, according to Aoyagi (1987). The iron contents in the octahedral layers of both illite and chlorite were higher in the minerals from the Itoshiro Subgroup than the Akaiwa's, presupposing these minerals constracted from almost ideal structure.
A small amount of kaolin minerals was found in each sediments from the Akaiwa Subgroup, but not in the Itoshiro Subgroup. Considerable amounts of quartz, feldspars, calcite, and organic materials were determined in all sediments samples.
