Gravity flow deposits in Mesozoic sediments of Chukotka microplate (North-East Russia)

Abstract

In the Mesozoic succession of the Anyui–Chukotka fold system (North-East Russia), five stratigraphic intervals were recognised that have an abundance of gravity flow deposits. These are the Olenekian (Lower Triassic), Upper Carnian, Upper Norian, Oxfordian–Kimmeridgian and Valanginian. The Triassic gravity flow deposits formed on the south-facing, passive margin of the Chukotka microplate and consist of greywackes and lithic arenites. Palaeocurrent data indicate that the flows were directed towards the south-east. The Olenekian gravity flow units consist of clast-rich sandstone deposited on the continental slope, and clast-poor sandstone deposited at the base of the slope. Upper Carnian mud-poor sandstones were deposited at the base of the slope and the Norian thin-bedded turbidites were upper to mid-slope deposits. The continental margin was affected by tectonism and was uplifted in the latest Triassic–earliest Jurassic, possibly due to the initiation of the southward translation of the Arctic Alaska–Chukotka microplate. Following an Early–Middle Jurassic uplift of the area, sedimentation resumed in the Late Jurassic and earliest Cretaceous. Several syn-orogenic depressions (Rauchua, Pegtymel, Pevek, Myrgovaam and Kytepveem) developed on the south-western margin of the Chukotka microplate, and deposition in these basins included gravity flow deposits at various times. In both the Oxfordian–Kimmeridgian and Valanginian successions, gravity flow deposits included arkosic and subarkosic sandstones with a northern source area of granitoid complexes and deformed Triassic strata. The intervening Tithonian–Berriasian gravity flow deposits consisted mainly of thin-bedded turbidites. These sediments had a southern source, which included a volcanic arc that had accreted to the southern margin of the Chukotka microplate.