<p>In the community of La Playa, Manuel Doblado, Quaternary microbialite deposits have been identified in inactive hot springs disconnected from the underground system due to intensive groundwater extraction 2 decades ago. Geomorphological analysis reveals fluctuating water levels, reflected in the morphology, growth rates, and preservation states of these deposits. Calcareous tufa formations extend from former spring heights to the valley floor, forming stepped carbonate slopes. A detailed study, including fieldwork, X-ray diffraction (XRD), X-ray fluorescence (XRF), and morphometric analysis via petrology and scanning electron microscopy (SEM), identified four facies: calcareous tufa, stromatolite, thrombolite, and dendrolitic facies, distributed along different geomorphological zones. Calcareous tufa occur at higher elevations, marking past water discharge points, while stromatolitic, thrombolytic, and dendrolitic facies distributed at different depths within the springs. Stromatolites are found in the upper sections, where water remained stable for prolonged periods, allowing laminated structures to develop. Thrombolites dominate intermediate depths, forming in fluctuating conditions with periodic exposure. Dendrolitic facies occur in the lower sections where water turbulence and infiltration influenced their branched morphology. Various microbialite morphologies were observed, reflecting contrasting environmental conditions during their formation. Vertical domes and columnar structures, rich in calcite and magnesium, are linked to stable groundwater flows and are associated with well-laminated stromatolitic facies. In contrast, spongy and porous textures composed of calcite, plagioclase, gypsum, and clinochlore suggest environments marked by abrupt water-level fluctuations, typically associated with thrombolitic and dendrolitic facies. These morphologies point to dynamic fluid–rock interactions with basaltic substrates and active biogeochemical processes. The deposits also contain trace amounts of rare-earth elements (yttrium, dysprosium, europium, ytterbium), radioactive elements (radium, uranium), and transition metals (rhenium, tungsten), underscoring their complex geochemical composition. Additionally, stable isotope analyses (δ¹³C and δ¹⁸O) of carbonate microbialite samples revealed values ranging from −0.95‰ to + 1.70‰ for δ¹³C and from −9.36‰ to −6.84‰ for δ¹⁸O. These results indicate that microbialite formation was influenced by biological activity and high-temperature waters, providing additional evidence of the complex interplay between microbial processes, thermal spring dynamics, and hydrological fluctuations.</p> Graphical Abstract <p>Quaternary microbialites in dry hot spring</p> <p></p>