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Nanoballs appear as 50 to 200 nm in diameter spheroidal features, which are closely associated to mineral precipitations in sedimentary rocks. In fact, they are encountered in various environments ranging from rocks to present-day environments and living organisms, i.e., terrigenous and carbonate rocks, seawater, and living organisms within which they form pathogenic calcifications. Recent experiments of Schieber and Arnott (2003) on tissue decay suggest that nanoballs are an early organic degradation product. These authors used experimental conditions comparable to those found in Earth's surface sediments, and diagenetic mineralization of these spheroids may be a common process for preservation of nanoballs observed in the rock record.
The research presented here focuses on the nanostructuration of organic matter (OM) using an atomic force microscope (AFM) with a resolution down to 10 nm. Optical observations require the preliminary destruction of the mineral fraction through HCl and HF. Studied samples have been selected according to various degrees of interaction with microbes, i.e., in oxic/dysoxic environments (cyanobacteria) and in anoxic conditions where early diagenetic processes occur (recent lacustrine OM, peat bog and hypersaline microbial mat). Comparisons have been made with well-known sedimentary rocks (Cretaceous black shales and Kimmeridgian bituminous laminites).
In the recent samples, results indicate a close association between the occurrence of nanoballs and the degree of microbial activity. Anoxic samples show a wide occurrence of nanoballs, associated with the degradation of organic substrates. They seem to indicate a low level of OM degradation in the diagenetic processes. In fossil samples, a wide occurrence of nanoballs has been observed in environments where OM had been previously defined as well-preserved (Pacton et al., 2006).
It can be concluded that nanoballs are another proof of microbial activity associated with well-preserved OM and its formation in anoxic conditions.
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