Coarse-Clastic Rocks in Northeastern Kamchatka: Morphology, Material Composition, and Formation Settings

The results of studying the conditions of occurrence, morphological features, and material composition of coarse-grained rocks in the Cenozoic molasse of the Olyutorsky terrane (northeastern Kamchatka) are considered. The obtained data allows us to suggest the paleogeological conditions of their formation. Morphological studies revealed that conglomerates are usually medium-sized rocks, with fairly well-sorted and rounded pebbles. However, during the transition from marine to continental deposits, their dimension increases slightly, but the sorting and roundness deteriorate. Gravelites are medium-gravel sediments in marine deposits and coarse-gravel sediments in continental deposits. The gravel is marked by good sorting and roundness. Analysis of the obtained data shows that sediments of the Alugin and Pakhacha formations were deposited in narrow intermontane troughs in a shallow sea; sediments of the Korf Formation, in continental environments. The sediments were delivered from mountains surrounding the basins. A huge amount of coarse-clastic material was transported by ephemeral and permanent watercourses. The material composition of the psephite clasts indicates that the sediments were delivered mainly from local sources composed of the molasse-underlying volcanogenic-siliceous and terrigenous rocks. The secondary sources, which supplied the basin with clasts of feldspar–quartz sandstones and ancient siliceous and granite-metamorphic rocks, were represented by the Cretaceous–Paleocene turbidites of the Ukelayat terrane and the Late Paleozoic–Early Mesozoic rocks of the Koryak folded region located to the north.