A paper in "Geology" describe for the first time the occurrence of extensive Mn oxide stromatolites formed in the deep interior of a cave (El Soplao, Cantabria, Spain). The stromatolites are of decimeter thickness and kilometer extent and show features extremely similar to typical CaCO3 stromatolites. Their biogenicity is supported by the exceptional abundance of fossil microbes. The data support that the stromatolites were mainly induced by chemolithotrophic Mn-oxidizing microbes,




