Abstract <p>New data on the composition of Upper Jurassic sandstones formed the base of the Kameshkov depression on the southwestern edge of the Chukchi Terrane are presented. The rock-forming components include fragments of cleaved terrigenous rocks and volcanic material such as altered pyroclastic and glass components, angular quartz crystalloclasts, and unrounded felsite fragments. The U–Pb isotopic dating of detrital zircon revealed the presence of the young population with the unimodal distribution and a peak of 145.6 Ма, which corresponds to the age of the deposits determined by the findings of <i>Buchia piochii</i> (Gabb). Other age populations are typical for the Triassic rocks of the Chukchi Terrane. The studied sediments have been accumulated on the southwestern margin of the Chukotka microcontinent under the shallow marine conditions due to erosion of the underlying deformed Triassic sequences in the immediate vicinity of an active volcanic source. The similarity of the Tithonian–Berriasian deposits composition in most Upper Jurassic–Lower Cretaceous depressions of the Chukchi Terrane and sharp change in the provenances at the Kimmeridgian–Tithonian boundary was traced. We interpreted the strike-slip setting of the formation of sedimentary basins on the Chukotka margin in the Late Tithonian, associated with the accretion of the Kulpolney ensimatic arc.</p>