Cuencas piggy-back de Limón Sur, Costa Rica

A morphotectonic analysis of the piggy-back basins of southern Limón, Costa Rica, is presented to evaluate their geomorphic evolution and relationship with active tectonic deformation. Seven basins were analyzed using geomorphic metrics derived from digital elevation models, including basin area, elevation, mean slope, local relief, and the normalized channel steepness index (ksn), complemented by drainage network analysis. The basins are distributed along a ~150 km-long belt parallel to the Caribbean coast and display marked morphological variability. Basins located toward the north-northwest are smaller and more strongly confined by structural highs associated with the Matama Range and the Siquirres–Matina fault system, whereas those toward the southeast are larger and exhibit more homogeneous internal topography. The Sixaola River basin is the largest continental basin (103.04 km²) and records the lowest mean slope (2.33°) and local relief (37.75 m), in contrast to the Río Blanco basin, which covers only 4.71 km² and exhibits a mean local relief of 100.45 m and ksn values approaching 200 associated with the Río Blanco Fault, indicating strong tectonic control on the drainage network. The highest local relief and ksn values are concentrated along the Matama Range, the Senosri Anticline, and the Río Blanco Fault, whereas relict surfaces in the southwestern sector exhibit low values for both metrics. In addition, braided river systems, coalescent alluvial fans, and a downstream transition to meandering channel patterns within the Telire–Sixaola fluvial system were identified, reflecting variations in sediment supply and topographic gradient. The results are consistent with the syntectonic evolution of a piggy-back basin system developed within a compressional tectonic setting and provide new geomorphic evidence for evaluating the tectonic models proposed for southern Caribbean Costa Rica, particularly those interpreting the region as either a retroarc foreland basin or the expression of an incipient subduction zone.