Tuff-sandstones of Perekatnaya Formation: composition, genesis, sources of demolition (Ust’-Belsky Mountains, Koryak Highland)

Research subject. In this work, we set out to investigate the petrographic, mineralogical and granulometric composition of tuff-sandstones in the Perekatnaya formation (Albian-Turonian).

Materials and methods. The work was based on the materials obtained during the course of fieldwork in the Ust-Belsky Mountains (Koryak Highlands) undertaken in 2011 and 2016 by researchers from the Geological Institute of the Russian Academy of Sciences. The collected samples of sedimentary rocks were comprehensively studied using granulometric and mineralogical analysis based on the petrographic method.

Results. The tuff-sandstones under study were represented by quartz-feldspar, feldspar and proper greywacke. The lithoclast composition was dominated by acidic and intermediate rock fragments. Specimens with a high lithoclast content value were characterized by a lower amount of quartz and feldspars, as well as by a larger grain size. An increase in the proportion of lithoclasts and the coarsening of grains are shown to occur from the southeast to the northwest. This fact has allowed us to establish the direction of material migration from the source area, which was located in the northwestern part of the region. According to the results of granulometric and mineralogical studies, the sediments appear to have been formed by high-speed turbidity currents under moderately deep marine conditions and at a relatively little distance from the coast, where the rivers (their deltas) provided sufficient amount of clastic material.

Conclusion. The obtained data confirm the assumptions about the evolution of the Perekatnaya formation under marine conditions on a continental margin (slope). The conditions for the sedimentation of the tuff-sandstones under study can be compared with those typical of areas in the vicinity of river deltas and/or prodelts. The sedimentation occurred concurrently with volcanism, which was associated with the existence of an active continental margin (Okhotsk-Chukotka volcanoplutonic belt).

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