Siliceous ferrihydrite speleothems with microbial imprints in a volcanic tube (Buracos cave, Terceira, Azores)

Located in the Malha Grande lava field (with probable eruptive centers at Galiarte cone area), Gruta dos Balcões is the longest cave on Terceira island. Isolated parts of the main lava tube of Gruta dos Balcões includes the Gruta dos Buracos (Pereira et al., 2004).The paper present here results of morphological, mineralogical and petrological investigations realized in the iron speleothems of the Buracos cave (¿Gruta dos Buracos¿) and offer an assessment of biological and non-biological mechanism that could have formed these speleothems.Peer Reviewe