Glauconitic bryozoan shells in shelf sediments of Western Kamchatka

Resumo

Glauconite segregations in Oligocene–Miocene shelf sediments of Western Kamchatka (Kakert and Gakkha horizons) are studied. Glauconite occurs in the studied samples as morphologically different grains, finely dispersed cement, and pseudomorphoses after organogenic structures (siliceous sponge spicules, diatom algae frustules, and others). In addition, samples of the clasts of bryozoans, volcanic glass, and terrigenous grains revealed for the first time traces of the boring algae similar to recent species of genus Hyella and, possibly, Dalmatella, whose tubules are sometimes filled with the finely dispersed glauconite. Our data based on the detailed petrographic studies and SEM investigations confirm and supplement the opinion of several researchers about an important role of microbiota on the glauconite formation. The paper discusses different stages of the glauconite formation in sediments of the Kakert and Gakkha horizons and the possible setting of glauconite infilling in the algal borer trails and holes.