Composition and Facies Formation Environments of Cherts in the Algan Terrane (Pacific Margin)

The article presents the results of petrographic, X-ray diffraction, and geochemical analyses of siliceous rocks forming tectonic slices among the Late Albian–Campanian tuff-terrigenous rocks of the Algan terrane. The trace-element distribution and mineral composition in cherts from different tectonic units are shown to differ, which can be explained by their accumulation in different facies environments: pelagic and near-continental. The Campanian pelagic cherts indicate the existence of an oceanic basin in the region up to this period.