| 23 Apr 2026
Challenges of initial Thorium and Approaches to Robust Speleothem Age Models: A case study from the Yucatán peninsula, Mexico
Abstract. Speleothems, such as stalagmites and flowstones, are invaluable archives of past environmental and climatic conditions due to their layered growth and suitability for precise 230Th/U dating. These natural formations record hydroclimatic variability over time, offering insights into how environmental changes have influenced ecosystems and human societies. In the context of Mesoamerica, speleothem records provide an opportunity to explore potential links between climate variability and sociopolitical transformations during Maya cultural evolution. Paleoclimate archives from this region document severe dry conditions during the Terminal Classic Period (∼800–1000 AD), a time marked by societal decline and urban abandonment among the Maya. Yet, existing records often suffer from limited chronological precision, and high-resolution multi-proxy datasets from the area remain scarce. This study presents extensive 230Th/U dating of several speleothems from Áaktun Kóopo Cave, Yucatán, revealing continuous carbonate deposition over the past 2.7 kyr, encompassing the entire era of Maya cultural evolution, as well as evidence of speleothem growth during earlier glacial and interglacial periods. High uranium concentrations in the speleothems (averaging 1 ppm) enabled precise dating, despite challenges from elevated and variable detrital thorium contamination. These challenges were addressed by combining multiple techniques, including isochron analysis, stratigraphic approaches, and annual layer counting, to constrain elevated and initial (230Th/232Th) activity ratios. Notably, we infer a high and largely unsystematic variability of high initial (230Th/232Th) activity ratios in space and time, with values spanning between 4 and 68. Still, our approach yields stalagmite chronologies from Áaktun Kóopo Cave that provide a robust foundation for detailed multi-proxy reconstructions of hydroclimate and vegetation changes over the past 2.7 kyr. These chronologies address a critical gap in high-resolution data for this region and enable future studies to better resolve environmental conditions throughout Maya history.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Geochronology.
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