The Devonian-Carboniferous Boundary Deposits in the Central Magnitogorsk Zone of the South Urals

In the Central Magnitogorsk Zone (Magnitogorsk Megasynclinorium; eastern subregion of the South Urals), the Devonian-Carboniferous boundary beds are represented by volcanics, volcaniclastics (Shumilino Formation), and carbonates (Gora Magnitnaya Formation). The carbonate rocks contain diverse fossils, of which ammonoids are the most stratigraphically significant, allowing the succession of geological events in this region to be reconstructed. This includes a series of major tectonic events in the Late Devonian when the eastern border of Laurussia collided with the Magnitogorsk volcanic arc. In the center of the Magnitogorsk Megasynclinorium, the Devonian-Carboniferous boundary deposits crop out in accordance with the topography resulting from post-subductional rifting and break-up of the arc when it was accreting to the eastern margin of Laurussia. The carbonates in these successions vary in composition depending on their distance from the Magnitogorsk-Bogdanovskoe rift-graben which was superimposed on the arc. A model of a syn-rift isolated carbonate platform, developed on the volcanic arc edifice in the late Devonian-Early Tournaisian, and drowned during rift volcanism that increased in the Late Tournaisian, was proposed.