Allochthonous Mesozoic marine sequences of northeastern Asia and western North America: Correlation of the stratigraphic levels and geodynamic depositional settings

The problem of correlating the isolated outcrops of allochthonous Middle Mesozoic deposits developed in northeastern Asia and western North America includes several aspects: (1) the stratigraphic subdivision of the sequences using the radiolarian assemblages and taking into account the complex nappe-thrust structure of the region; (2) the analysis of their facies composition with reconstructing the geodynamic depositional settings; (3) the search for features in common (with respect to the previous two aspects) in all these localities. The first widely applied radiolarian analysis revealed that the Middle Mesozoic marine rocks from separate nappes and slices of tectono-stratigraphic sections in East Asia enclose 20 different-age (Norian to Hauterivian) radiolarian assemblages. The correlation of these assemblages revealed the wide lateral distribution of their host Middle Mesozoic marine sequences in the regions under consideration. The significance of the presented materials is determined by the following facts: (1) using the radiolarian analysis, the Middle Mesozoic marine sequences of northeastern Asia are first subdivided into stage and substage units with defining their analogs in western North America; (2) despite the discrete distribution of Mesozoic allochthons, it is shown that the defined stratigraphic units are widespread in northeastern Asia; (3) it is established that these allochthons consist of rocks formed in different geodynamic depositional settings: ocean floor, island arc, fore-arc, and marginal-sea domains. This spectrum of heterogeneous rocks is traceable practically through the entire northeastern Asia region.