Possible microbial effects of stable carbon isotopes in hot-spring travertines

摘要: Recent and older (early Holocene to Pleistocene) hot-spring travertine carbonates from central Italy have two distinctive macrofabrics, crystalline crusts shrubs. Crystalline are laminated slope deposits that formed abiotically following CO 2 degassing spring water. The formation of shrub travertine--irregular, dendritic precipitates pool environments--is controversial has been attributed both abiotic microbial processes. Oxygen isotope variation in our travertines can be explained by processes, mainly degassing. In contrast, carbon data cannot wholly invoked earlier studies. Because photosynthesis is known preferentially remove 12 C, leaving ambient waters enriched 13 this fractionation should recorded delta C values microbially influenced travertine. Our between 0.5 per thousand 6.0 larger than for associated precipitates, difference probably caused activity. These support previous visual evidence some fabrics influenced.