Pedosediments of karstic sinkholes in the eolianites of NE Yucatلn: A record of Late Quaternary soil development, geomorphic processes and landscape stability

The pedogenetic and geomorphic processes controlling soil development in tropical karstic landscapes, are still poorly understood. We have discovered and studied thick pedosediments in karst pockets, developed in Late Pleistocene lithified calcareous dunes (eolianites), in the NE coast of the Yucatán peninsula. The morphological geochemical and mineralogical characteristics of the pocket fills, were interpreted as a record of pedogenesis and geomorphic dynamics, that shaped the soil mantle during the Holocene. Sand fraction mineralogy and the Zr/Ti ratio, indicated a mixed origin of the soil parent material; volcanic and granitic/metamorphic components, redeposited in the lithoral and coastal environments were identified. Within the soil matrix, primary minerals were transformed by weathering and caused desilicification, accumulation of clay (hydroxy-interlayered vermiculite and kaolinite) and dithionite–citrate–bicarbonate extractable iron oxides (Fed). Reworked pedofeatures indicative of clay illuviation and redoximorphic processes were observed. This set of processes points to a continuous phase of humid pedogenesis, several thousand years long in the Early–Middle Holocene. However, the development of thick recalcified pedosediments in the pockets, contrasting with the thin background Rendzinas requires active soil redeposition, during a late phase of geomorphic activity. The available Accelerator Mass Spectrometry (AMS) radiocarbon date indicates that the switch of the erosion/sedimentation processes could be related to ancient Maya land-use impact.