Late Ordovician Shelf Deposition in Northern Gorny Altai: Lithology, Faunas, and Paleogeography

––New and revised previous data based on detailed description of sections have provided better constraints on fauna taxonomy, lithology, and stratigraphy, as well as on biostratigraphic ages of sediments. The lithology and stratigraphy of several key Upper Ordovician sections in the northern Gorny Altai area show that the local units of Sandbian and Katian Savelieva and Bulukhta formations can be used as reference for the regional Ordovician division. It is suggested to include a newly distinguished Bulukhta facies zone, an area of Late Ordovician coarse clastic deposition, into the mapped Ordovician deposits of Gorny Altai. According to paleogeographic reconstructions, the deposition occurred in a large sea gulf surrounded with elevated landmasses exposed to erosion.