Jurassic-Lower Cretaceous siliceous rocks and black shales from allochthonous complexes of the Koryak-Western Kamchatka orogenic belt, East Asia

Abstract

ABSTRACT Composition, stratigraphic and structural position of Jurassic-Lower Cretaceous radiolarian-rich siliceous rocks and black shales are described within allochthonous lithotectonic complexes of the Koryak-Western Kamchatka orogenic belt of East Asia. Comparative lithological and stratigraphic analysis of sedimentary units exposed in imbricated tectonic slices over a distance of more than 1000 km helped to restore a continuous succession of siliceous rocks from Hettangian to Barremian. The Jurassic-Lower Cretaceous siliceous succession is composed of Hettangian and Aalenian-Barremian haematitic jaspers and Sinemurian-Toarcian radiolarian-bearing pyrite-bearing organic-rich black cherts and siliceous shales. Allochthonous Jurassic-Lower Cretaceous siliceous successions of the Koryak-Kamchatka orogenic belt likely accumulated in some open pelagic domains of the Paleo-Pacific within the Izanagi-Kula plate at different paleo-latitudes from high (southern boreal) to subequatorial (northern Tethys) paleo-latitudes. Depositional environments of Sinemurian-Toarcian organic-rich black shales were characterized by euxinic deep-water paleo-oceanic settings with poor water circulation. Accumulation of the Toarcian black shale succession corresponds in time to a global Toarcian oceanic anoxic event, while deposition of regionally occurring Sinemurian-Pliensbachian black shales was likely controlled by local factors. Hettangian, Middle Jurassic to Upper Jurassic-Barremian haematitic jaspers accumulated under aerobic conditions with well-circulated waters enriched with oxygen.