GEOLOGIC STRUCTURE AND KARST DYNAMICS OF THE THREE RIVERS REGION: UNVEILING THE FOUNDATIONS OF THE BAJO LANDSCAPE

This paper considers the geological backdrop for the Maya region’s anthropogenic geomorphology, namely the built capital of terraces, wetland fields, and other agricultural features. We focus here on the Three Rivers Region, straddling northeast Guatemala and northwest Belize, which showcases a complex geologic terrain characterized by normal faults, half-grabens, and karst landforms. These geologic elements have been pivotal in shaping the region into a landscape of alluvial-filled structural depressions and fluviokarst, forming the foundation for seasonal wetlands locally known as bajos. Our study delineates the southern Yucatán Peninsula into structural provinces, each marked by distinct geologic styles and boundaries. At the heart of the peninsula lies the Petén Plateau, which was raised through isostatic rebound resulting from the convergence of the Caribbean Arc and North America during the Middle Eocene. The Rio Hondo Fault Zone, characterized by northeast trending normal faults and half-grabens, stretches from the plateau's eastern margin to the Caribbean coast, formed subsequently during late-stage extension of the offshore Yucatan Basin. Long non-linear faults, including notably the Buenavista and Rio Hondo faults, initially formed as smaller fault segments linked by relay ramps which gradually merged over time as the ramps were breached. Linkage of the faults created interconnected depressions that served as depocenters for alluvial sediments. The fluviokarst landscape which covers much of the region is characterized by karst landforms such as karst valleys, dolines, swallow holes, intermittent streams, and residual pools. Using near infrared satellite data, we have interpreted the extent of the seasonal wetlands and validated these through ground truthing and the use of prior regional ecological surveys. These seasonal swamps make up 25.7% of the 6750 km² study area but can also be subdivided by structural provenance or landscape illustrating how they are influenced by the underlying geology. This synthesis elucidates how these structural and karst features underpin the seasonal bajo landscape, which the ancient Maya civilization adapted to, allowing them to thrive within this unique ecological and geological setting.