THE LOWER PATLANOAYA GROUP: SEDIMENTOLOGICAL AND PETROGRAPHIC PERSPECTIVES ON THE EVOLUTION OF THE PANGEA ASSEMBLAGE IN SOUTHERN MEXICO
During the Late Paleozoic time, the oldest rocks in Mexican territory were located on the periphery of Gondwana, making Mexican territory largely influenced by the tectonic processes involved in the assembly of Pangea. This global tectonic event is recorded in the Paleozoic metamorphic rocks of the Acatlán Complex, which preserves the stratigraphic record of the Patlanoaya Basin, developed in southern Mexico during the Late Paleozoic time. The Patlanoaya Group, exposed in Puebla, is notable for its low deformation and minimal recrystallization. Although the Patlanoaya Group has been the subject of various paleontological studies in recent decades, no detailed sedimentological analysis has been conducted for each formation within the group. Consequently, environmental reconstructions have mainly relied on fossil content, leaving the evolution of sedimentary environments within this unit poorly defined from a sedimentological perspective.
Some researchers attribute the detrital-carbonate nature of this succession to sea-level fluctuations or climatic changes, but such interpretations downplay the significance of major tectonic events in southern Mexico during the assembly of Pangea. Within this tectonic context, some suggest that the Patlanoaya Group was deposited in a compressive tectonic setting due to the collision between Laurentia and Gondwana. Others associate it with an extensional basin linked to the exhumation of high-pressure rocks from the Acatlán Complex in a supra-subduction setting. It is also proposed that the succession resulted from the erosion of the Oaxacan and Acatlán Complexes. As a result, the origin and significance of the variation between siliciclastic and carbonate sedimentation throughout the Patlanoaya Group succession remain subjects of important debate.
In the framework of the PAPIIT IN107924 project, this work shows the reconstruction of the tectono-sedimentary evolution of the lower Patlanoaya Group by integrating sedimentological, petrographic, and U-Pb detrital geochronological data. Our findings suggest that the lower Patlanoaya Group was deposited in an Early Mississippian basin, beginning with debris flow deposits from small-scale reliefs composed of low-grade metamorphic rocks, followed by deposits from an NNE-trending axial fluvial system derived from low-grade metamorphic rocks in a mylonitic zone. Therefore, the deposition of the lower Patlanoaya Group was controlled by an NNE-oriented mylonitic shear zone associated with the formation of a supradetachment basin and the progressive exhumation of high-pressure rocks during a significant extensional event in the Early Mississippian time.