Tufas are freshwater carbonate rocks that form in continental environments through
a combination of physical, chemical, and biological processes. This study investigates
the role of microorganisms in the precipitation of Quaternary tufa deposits in the
Serra da Bodoquena Formation, in the Bonito region. Two sites along the Mimoso River,
named Taíka and Mimosa, characterized by the pool–barrage–cascade depositional subenvironment,
were selected for this study. Four distinct facies were identified: stromatolitic
boundstones, phytoherm boundstones of algae, phytoherm boundstones of bryophytes,
and phytoclastic rudstones. These facies were observed in diverse hydrological settings,
including fast-flowing waters, such as waterfalls and cascades, as well as slow-flowing
areas, such as pools and dams. The δ 18 O depletion indicated a meteoric origin for
the fluid involved in carbonate precipitation. The low δ 13 C values were attributed
to photosynthetic processes and the contribution of light carbon-enriched groundwater.
The presence of Oocardium stratum and calcified organic mucilage from extracellular
polymeric substance (EPS) corroborates the significant role of microorganisms in tufa
formation, particularly in stromatolitic boundstones and phytoherm boundstones of
algae. Rapid CO 2 degassing significantly contributes to mineralization in fast-flowing
waters. Micro-CT results offer detailed insights into the relationship between mechanical
processes and biological influences in shaping porosity characteristics. The findings
of this study significantly enhance our understanding of the role of microorganisms
in tufa formation, highlighting the complex interplay between biotic and abiotic processes
in the development of different tufa facies. Moreover, the insights gained from this
study provide valuable implications for interpreting tufa deposits worldwide.
