Formation and Demise of Late Carboniferous to Early Permian Carbonate Platforms on the Southern Margin of the Central Asian Orogenic Belt

Carbonate platforms have significant implications for the ancient marine environment. During the Late Carboniferous to Early Permian, continuous deposited carbonate strata were widely distributed on the southern margin of the Central Asian Orogenic Belt. However, these rock units lack precise age constraints and systematic correlation, thus limiting further discussions on their paleogeographic and paleoenvironmental significance. This study reports the stratigraphic sequence of the "Amushan Formation" measured sections on the northern margin of the Alxa Block and provides zircon U-Pb isotope ages from volcanic intercalations, precisely constraining the age and distribution of the carbonate platforms. The results indicate that the "Amushan Formation" north of the Engerwusu Fault Zone should be revised to the "Gegenaobao Formation," which is dominated by clastic rocks and dates to the Kasimovian to Asselian (＜296.1 Ma). South of the fault zone, the carbonate platform of the Amushan Formation is characterized by continuously deposited and fusulinid-rich limestone with ages from the Gzhelian to Asselian (303.2～295.3 Ma). Based on high-resolution stratigraphic correlations with areas such as Beishan in Gansu and central Inner Mongolia, this study proposes that the carbonate platforms at the southern margin of the Central Asian Orogenic Belt were a product of global Late Carboniferous transgression and the subtropical climate of the southern margin of the Paleo-Asian Ocean. The rifting during the Early to Middle Permian was the primary reason for the demise of these carbonate platforms.