Exceptional preservation in Quaternary Atacama Desert Tufas: Evidence for increased groundwater and surface water in the Calama Basin, Atacama, Chile

Exceptionally well-preserved tufas located west of Calama, Atacama Desert, Chile, designated Santa Juana tufas, record episodic wetter conditions, relative to today, over the past 500,000 years. Globally, tufa architecture and depositional details are poorly understood as most described have been degraded by weathering erosion. In hyperarid Atacama, post-depositional alteration is negligible, therefore, exceptional preservation documented in this study provides new information about facies their complex interactions. include microbial stromatolites, phytoherms, cascadestone, flowstone porous limestone. Phytoherms, consisting former plant stems coated with calcite, developed channels, within pools, along spring discharge aprons. Cascadestone, representing waterfalls, preserves filaments delicate V-shaped calcite crystals. Flowstone lines shallow subvertical subhorizontal sites rapidly sluicing water flow. Porous limestone, containing sparse and/or gypsum anhydrite cement crystals, represents detrital accumulations. Stable isotope results, coupled U/Th ages, show that Quaternary, Neogene, groundwater was less supercharged volcanogenic CO2 so degassing moderated. The δ18O ratios from Miocene–Pliocene palustrine lacustrine freshwater carbonates underlie indicate significant evaporation, but signal indicates a evaporative trend due shorter atmosphere exposure time. Biological fractionation δ13C largely masked region's carbon footprint, although petrography shows laminations. range ages there were time periods drainage basin headwater area late Pleistocene early Holocene, aridity hyperaridity became established. lack diagenesis or has minimal rainfall since deposition.