Interplay of abiotic, biotic, and environmental controls on travertine formation: Insights from Baishuitai (White Water Terraces), Southwest China

Abstract

Travertines, striking carbonate formations created by mineral-rich spring waters, develop through an interplay of abiotic and biotic processes. Yet, the roles and interactions of these processes across travertine systems remain unclear. In this study, we investigated the Baishuitai, a large, active travertine in Southwest China, using geochemical and petrographic methods to explore how abiotic and biotic processes interact and drive travertine deposition and decipher the environmental factors controlling them. The results show that the travertines are precipitated by waters issuing from springs that have relatively low temperatures (∼10.8 °C) and are highly enriched in Ca²⁺ and HCO₃⁻ (∼200 mg/L and 770 mg/L, respectively) and CO₂ (∼10^−0.9 atm). Geochemical data (e.g., δ¹³C_DIC: −0.1 ‰) confirm that these waters originate from a mix of meteoric recharge and deep-seated CO₂ transported via neotectonic faults. Owing to the enrichment of CO₂ in spring water, significant calcite precipitation occurs primarily through abiotic processes that are driven by rapid CO₂ degassing along the flow path. Additionally, microbial biofilms greatly modulate the deposition by creating localized zones for mineralization, providing crystal nucleation sites, and trapping particles with their mucilage. The interplay of abiotic and microbially influenced processes varies in different depositional environments and is mainly governed by water chemistry dynamics, topography-driven flow conditions, biological growth pattern, and seasonal climate changes. The study illuminates the primacy of abiotic processes, the subtle yet crucial role of microbes, and the environmental controls sculpting travertine in low-temperature, CO₂-rich systems, which has significance to the full understanding of the development of travertine formations.