Effective mechanisms in the formation of pool-rimstone dams in continental carbonate systems: The case study of Huanglong, China

The tufa/travertine landscape is an important heritage and ecological wealth given to mankind by nature, of which rimstone dam limiting pools are important features that allow their development. This study explores the mechanisms influencing the formation of rimstone dams through the study of depositional behavior in the short-term under hydrodynamic action, hydrochemical changes, and biological characterization, independent from the long-term dynamics. Numerical simulations clearly show the complex flow regimes of the paired pool and rimstone dam. Differences in flow regime and particle transport distribution in different areas of the pool lead to differences in deposition at different areas of the pool. Hydrodynamic effects generate morphological changes of the pool-rimstone dam by promoting the deposition on the outer wall of the dam and causing no-deposition and remobilization (erosion in a broad sense) in the inner wall. Significant changes in the ion concentrations of Ca2+ and HCO3- occur at short distances in the external upper and lower parts of the dam, suggesting that the thin layer of water and high velocity conditions in the outer wall of the rimstone dam facilitate precipitation. Biological processes influence the development of rimstone dam and promote its thickening. The plant remains of leaves, branches, and roots provide the basic depositional framework and depositional template for rimstone dam growth. Besides, microorganisms affect the micro-morphology of calcite through their own metabolism. This study aims to clarify the mechanisms of pool-rimstone dam formation by exploring the interactions between abiogenic and biogenic controls within a hydrodynamic model.