Depositional history of Devonian and Mississippian rocks from southern Mongolia: Stratigraphic and sedimentologic framework of a volcanic arc system

Abstract This report provides a detailed description of Devonian and Carboniferous formations in the Shinejinst area, southern Mongolia and places them into a regional context. Based on more than 120 thin sections, polished slabs, and field observations a detailed sedimentological/facies study provides information on the depositional development of an island arc system. This study forms a more detailed survey of the same section as our recent overview publication, which contained an updated conodont biostratigraphy of the Shinejinst area. The Shinejinst region is compared with rocks of the coeval Bayankhoshuu Ruins section further in the east. Both sections exhibit differences in the rock record, which can be explained by facies differences due to different settings, but both sections show similarities and interactions, which are mainly driven by regional tectonics and eustatic sea-level changes. Whereas the eastern section (Bayankhoshuu Ruins section) records more deep-water environments, the western section (Shinejinst section) is characterised mainly by shallow-water carbonate ramp successions. In the eastern section subduction started in the Early Devonian and volcanic activity had its most productive phase during the Givetian and lasted in both sections into the Mississippian, when final amalgamation of the arc system with an unknown arc or microcontinent took place. Both sections likely belong to the same island arc terrane, the Mandalovoo Terrane. This area is characterised by very complex geology, and these results will provide a useful framework for any future geologic mapping of the region. This publication is a contribution to the Special Series on “The Central Asian Orogenic Belt (CAOB) during Late Devonian: New insights from southern Mongolia” published in this journal.