Micromorphology, mineralogical and microbiological characterization of silica speleothems in Cerro Colorado Breccia, Sierras Australes (Buenos Aires, Argentina)

SILVIA CRISTINA GRILL

Revista de la Asociación Geológica Argentina

Buenos Aires : Asociación Geológica Argentina

Lugar: Sanj Juan; Año: 2023 vol. 80 p. 634 - 650

1851-8249

Micromorphological, mineralogical and microbiological characterization of siliceous speleothems from the Cerro Colorado Breccia, Sierras Australes (Buenos Aires, Argentina). The micromorphological, mineralogical and microbiological analysis of silica speleothems developed in the Breccia Cerro Colorado Formation (Northwest of the Sierras Australes) allowed for a new contribution on the environmental conditions and genesis of these deposits. The origin of the planar, cylindrical, concretions and peloids speleothems investigated was related to general and specific mechanisms that control water circulation (gravity, capillarity, surface tension), microenvironmental conditions (relative humidity (RH), temperature, evaporation and insolation) and biological activity. The microforms present inside the tafoni formed under significant humidity conditions (RH > 60%, water steam condensation, slow water circulation) which would have favored the formation of planar and cylindrical speleothems with thicknesses less than 20 mm, compact textures, and gypsum/calcite microcrystals at their free ends. On the other hand, those found in fractures and outside the tafoni (significantly less humid environments) were associated with moreporous microforms (gours and peloids) and smaller dimensions (< 5 mm thickness). The mineralogical analysis allowed the identification of opal – A, Quartz, Plagioclase, Illite, Chlorite and Hematite. Opal-A was associated with the dissolution/precipitation process of quartz (linked to water and biological activity). Clays are the product of weathering of silicates and moscovite, chlorite, and plagioclases are part of the BCC (Venega et al. 2022). The presence of fungi, lichens, diatoms (among others) allowed for inferring biological mediation in the development of the speleothems. The low thickness of the speleothems, the presence of opal-A, and the recordedpollen associations limited their age to recent times (Late Holocene?).