Depositional Constraints of Sand-like Calcium Carbonate Particles in the High-Calcium Cold Springs of Huanglong, China: Insights from Mineralogy, Geochemistry, and Hydrodynamics

Wuyang He¹Fudong Wang^1*Carlos Pérez-Mejías²Enrico Capezzuoli³Shi Chen¹Yanwen Wang⁴Yuyin Zhu¹Xueqin Zhao¹Faqin Dong¹Qingming Zhang⁵Xinze Liu⁶

• ¹School of Environment and Resources, Southwest University of Science and Technology, Mianyang, China
• ²Institute of Global Environmental Change, Xi’an Jiaotong University, Xi’an, China
• ³Department of Earth Sciences, University of Florence, Florence, Italy
• ⁴China Earthquake Administration Institute of Geology, Beijing, China
• ⁵Huanglong National Scenic Spot Administration, Songpan, China
• ⁶Sichuan Geological Environment Survey and Research Center, Chengdu, China

Calcium carbonate particles are found everywhere in different environments around the world, and their characteristics and deposition mechanisms have been extensively studied and debated. Due to the variety of sedimentary environments, these particles exhibit significant variations in their petrographic, mineralogical, and geochemical features, as well as their genetic mechanisms. In the Huanglong travertine system, Sichuan, China, unique calcium carbonate particles, resembling sand grains, have been identified and are referred to as sandlike particles (0.5-3.0 mm). This study systematically investigates the mineralogical, petrographic, and geochemical characteristics of these particles. The particles form in a high-Ca²⁺ cold spring environment (Ca²⁺＞3.00 mM, T＜13°C) through an exceptional aggregationcementation-accretion-compaction process involving both detrital fragments and newformed calcite crystals. The particle growth is primarily controlled by hydrodynamic fluctuations and microbial mediation, with extracellular polymeric substances (EPS) templating calcite nucleation while kinetic disequilibrium drives rapid crystallization. These composite particles preserve distinct microtextural signatures of multiple diagenetic phases, offering new insights into non-classical carbonate formation. This study highlights the complexity and diversity of localized travertine deposition, bridging the gap between macroscopic sedimentary frameworks and localized depositional processes. The Huanglong system represents a unique natural laboratory for studying carbonate sedimentation under hydrochemical gradients. This research provides fundamental insights into the complex interplay between inorganic processes (hydrochemical precipitation driven by high Ca²⁺ and CO₂ degassing) and organic mediation (microbial activity and extracellular polymeric substances) in these unique high-calcium aquatic systems. This not only elucidates the diversity of carbonate deposition mechanisms in Huanglong's environment, but also holds significant implications for understanding the establishment of similar coupled physicochemical-biological systems in other high-altitude, calcium-rich spring environments worldwide.