Sedimentology and biostratigraphy of upper Triassic atoll-type carbonates from the Dalnegorsk area, Taukha terrane, far East Russia

Contrary to their Tethyan counterparts, and despite substantial research, Upper Triassic shallow-water limestone from the Panthalassa Ocean remain poorly known. Their understanding is yet crucial to better constrain past depositional, ecologic, geographic and geodynamic conditions out of the Tethyan domain, and to better assess life evolution and recovery following the greatest Permo-Triassic biological crisis. The Taukha terrane, located in a poorly studied area of the Sikhote-Alin mountain range (Primorsky and Khabarovsk Kraya, Far East Russia) is a key Panthalassan terrane. Near Dalnegorsk City, North-East of Vladivostok, on the northern part of the Taukha terrane, Upper Triassic marine carbonates abound. They show a clear affinity with Panthalassan terranes of both Japan and North America. There, eleven new localities have been extensively sampled, described and interpreted. Based on field observations and facies analysis, eight major fades, corresponding to specific depositional environments within a carbonate platform, have been established. A conceptual depositional model corresponding to a mid-oceanic atoll-type system composed of well-developed lagoon, fringing patch reefs and oolitic shoals is proposed. The foraminiferal assemblages allow refining the age of the carbonate system to the Norian, and locally, exclusively to the lower/middle and the middle parts of the Norian.