Triassic limestones from the Panthalassa Ocean: new insights on Hokkaido Island and Far East Russia

• Main Authors: Peyrotty, Giovan, Martini, Rossana
• Format: Book Part
• Language: English
• Published: 2018
• Subjects: info:eu-repo/classification/ddc/550; Triassic; Sedimentology of carbonates; Japan; Hokkaido; Far East Russia; Diagenesis; Biotstratigraphy; Sakhalin
• Online Access: https://archive-ouverte.unige.ch/unige:104004

In comparison with the well-known Tethyan domain, and despite of the amount of research already carried out, Upper Triassic limestones from the Panthalassa Ocean remain poorly known. Two of the best areas to study these carbonates are Hokkaido Island (north end of Japan) and Sikhote-Alin mountain range (Primorsky and Khabarovsk Kraïs, Far East Russia) where many different Triassic limestones outcrops are exposed. These two areas are part of the South—North continuity of Jurassic to Paleogene accretionary complexes, going from the Philippines to Sakhalin Island (Far East Russia). In Hokkaido Island, two major tectonic units have been accurately explored and extensively sampled: the Jurassic Oshima Belt (west Hokkaido), and the Cretaceous Sorachi-Yezo Belt (central Hokkaido). The same fieldwork approach has been applied to the Cretaceous Taukha Terrane (Sikhote-Alin, Far East Russia). Through a complete sedimentological, diagenetic and biostratigraphic study, these limestones allow us (1) to compare the depostional settings and biotic assemblages from Tethyan and Panthalassic domains, (2) to better understand the geodynamic evolution of central part of Hokkaido Island and (3) to propose a model of evolution of these carbonates from their deposit to their accretion. The initial microfacies analysis indicates that very similar facies characterise all the sampled blocks occuring on different tectonic units either in Hokkaido or in Sikhote-Alin. Furthermore, the lithology and the aspect of these limestones, as well as their biological composition, are closely related to the Triassic limestones observed in the southern part of Japan (i.e., Sambosan Accretionary Complex; Chablais et al., 20101; Peybernes et al., 20162). The microfacies are dominated by peloidal packstones-grainstones with aboundant microbial clasts and microproblematica. Oolitic grainstones and Megalodont patches are also very common. The diagenetic analysis, made on the best preserved limestone blocks, shows major events, from early marine diagenesis to accretion-related changes. These limestones underwent a continuous evolution, with no emersion, from an early cementation to a very low compaction imprint which is consistent for mid-oceanic limestones. The carbonates also record an event related to a partial dismantling of the system, marked by the presence of early breccias after shallow burial diagenesis.