SEDIMENTOLOGICAL AND PROVENANCE INSIGHTS FROM THE UPPER PATLANOAYA GROUP, SOUTHERN MEXICO: EVIDENCE OF THE EARLY INTERACTION BETWEEN THE OAXACAN AND ACATLÁN COMPLEXES DURING PANGEA ASSEMBLY
The Pangea assemblage was the most significant global tectonic event of the late Paleozoic time. This supercontinent was assembled through a diachronous process of continental convergence between Laurentia–Baltica and Gondwana, coupled with the gradual closure of the Rheic Ocean since the Early Carboniferous to the Permian time, leading to the development of an extensive orogenic system that includes the Variscan, Alleghanian, and Ouachita–Marathon–Sonora belts. During this period, several tectonic blocks were progressively accreted along the continental margins of the colliding landmasses, forming regional suture zones that record significant displacements and played a key role in shaping topography and controlling sedimentation in different regions. Such suture zones form the tectonic boundary among some terranes currently composing southern Mexico, which based on paleogeographic reconstructions for the late Paleozoic, were part of the peri-Gondwanan continental blocks located along the suture zone between Gondwana and Laurentia. The regional Caltepec Fault Zone juxtaposes the Acatlán and Oaxacan Complexes, the basements of two peri-Gondwanan blocks, and is considered a record of this tectonic process. The understanding of the Permian tectonic activity of this fault zone is fundamental to the geological evolution of the region. However, this suture is exposed only in a very limited area, which prevents a detailed comprehension of the timing of collision between these peri-Gondwanan blocks and a full assessment of the regional effects of their accretion.
The Upper Paleozoic Acatlán Complex preserves a key stratigraphic record of the tectonic processes associated with Pangea’s assembly. The Patlanoaya Group, of late Paleozoic age, corresponds to the only part of this complex that did not experience metamorphism and penetrative deformation. As such, this sedimentary Group represents one of the best-preserved and most stratigraphically continuous Paleozoic clastic successions in Mexico that can provide essential insights into the tectono-sedimentary evolution of the region during the late Paleozoic time. This succession has been previously studied by several authors due to its paleontological content, leading to numerous paleoenvironmental and paleogeographic reconstructions based solely on marine fossil evidence. Nevertheless, these proposed scenarios underestimate the existence of major tectonic events in southern Mexico associated with the Pangea’s assemblage. Despite its tectonic meaning, detailed sedimentological and provenance data remain limited.
In this work, we present new sedimentological, petrographic, geochronological, and paleontological data from the upper Patlanoaya Group, obtained within the framework of the PAPIIT-IA103125 and IN107924 projects. These results allow for a redefinition of the depositional environments of the upper Patlanoaya Group, revealing transitions from shallow- to deep-marine settings. Furthermore, provenance analysis indicates pre-Permian sediment supply from both the Oaxacan and Acatlán complexes, suggesting a tectonic proximity between them and the peri-Gondwanan blocks they belong to earlier than previously documented.