Paleoenvironmental evolution of a Carboniferous marine succession during active volcanism in southern Mexico and its implications in the western Pangea margin configuration

Carboniferous units in southern Mexico consist of mixed carbonate-volcaniclastic facies representing shallow marine environments, from the middle ramp to shallow subtidal environments in the inner ramp. The Tournaisian-Visean Santiago Formation is characterized by the dominance of mixed clastic and bioclastic sediments in a mid-ramp setting without a supply of volcanic material within the basin. Instead, the newly reported locality of the Mississippian-Pennsylvanian Ixtaltepec Formation is a mixed succession of volcaniclastic and carbonated sediments deposited under a tidal influence in the middle to the inner ramp. The age is determined to be late Visean and early Serpukhovian (∼333-325 Ma) based on the presence of Actinoconchus lamellosus, Syringothyris sp., and Punctospirifer sp. and corroborated by geochronological data. This study provides new evidence of Carboniferous volcanism in the sediment-sources area in southern Mexico. Volcanic activity in the area is linked to the subduction of the oceanic crust of the Rheic Ocean, which resulted in the formation of magmatic arcs on the Gondwanan realm and the assembly of Pangea. During the Early Mississippian to early Permian, extensive areas of the northwest of South America and southwest of North America were covered by epicontinental seas. Sedimentation in the area was mainly characterized by shallow clastic-carbonate-dominated environments and deep marine settings, where basins within the peri-Gondwana Terranes received volcanic detritus from the North Gondwana and western Pangea arcs.