This article examined the use of the <sup>40</sup>Ar/<sup>39</sup>Ar incremental heating and K/Ar analyses to date dolerites located in the extreme north region in Brazil. The material used for...This article examined the use of the <sup>40</sup>Ar/<sup>39</sup>Ar incremental heating and K/Ar analyses to date dolerites located in the extreme north region in Brazil. The material used for dating was whole rock and separated minerals（plagioclases,pyroxene or/and amphibole）in 6 samples of dykes and sills from Roraima.The dolerites yield plateau ages ranging from 1955±17 Ma to 1179±10 Ma.The reason展开更多
Demonstrating the biogenicity of presumptive microfossils in the geological record often requires supporting chemical signatures, including isotopic signatures. Understanding the mechanisms that promote the preservati...Demonstrating the biogenicity of presumptive microfossils in the geological record often requires supporting chemical signatures, including isotopic signatures. Understanding the mechanisms that promote the preservation of microbial biosignatures associated with microfossils is fundamental to unravelling the palaeomicrobiological history of the material. Organomineralization of microorganisms is likely to represent the first stages of microbial fossilisation and has been hypothesised to prevent the autolytic degradation of microbial cell envelope structures. In the present study, two distinct fossilisation textures(permineralised microfossils and iron oxide encrusted cell envelopes)identified throughout iron-rich rock samples were analysed using nanoscale secondary ion mass spectrometry(NanoSIMS). In this system, aluminium is enriched around the permineralised microfossils, while iron is enriched within the intracellularly, within distinct cell envelopes. Remarkably,while cell wall structures are indicated, carbon and nitrogen biosignatures are not preserved with permineralised microfossils. Therefore, the enrichment of aluminium, delineating these microfossils appears to have been critical to their structural preservation in this iron-rich environment. In contrast,NanoSIMS analysis of mineral encrusted cell envelopes reveals that preserved carbon and nitrogen biosignatures are associated with the cell envelope structures of these microfossils. Interestingly, iron is depleted in regions where carbon and nitrogen are preserved. In contrast aluminium appears to be slightly enriched in regions associated with remnant cell envelope structures. The correlation of aluminium with carbon and nitrogen biosignatures suggests the complexation of aluminium with preserved cell envelope structures before or immediately after cell death may have inactivated autolytic activity preventing the rapid breakdown of these organic, macromolecular structures.Combined, these results highlight that aluminium may play an important role in the preservation of microorganisms within the rock record.展开更多
文摘This article examined the use of the <sup>40</sup>Ar/<sup>39</sup>Ar incremental heating and K/Ar analyses to date dolerites located in the extreme north region in Brazil. The material used for dating was whole rock and separated minerals（plagioclases,pyroxene or/and amphibole）in 6 samples of dykes and sills from Roraima.The dolerites yield plateau ages ranging from 1955±17 Ma to 1179±10 Ma.The reason
基金support from the Vale S.A.-UQ Geomicrobiology initiative and the Australian Research Council Linkage Program(LP140100805) to G. Southam and P. Vasconcelos
文摘Demonstrating the biogenicity of presumptive microfossils in the geological record often requires supporting chemical signatures, including isotopic signatures. Understanding the mechanisms that promote the preservation of microbial biosignatures associated with microfossils is fundamental to unravelling the palaeomicrobiological history of the material. Organomineralization of microorganisms is likely to represent the first stages of microbial fossilisation and has been hypothesised to prevent the autolytic degradation of microbial cell envelope structures. In the present study, two distinct fossilisation textures(permineralised microfossils and iron oxide encrusted cell envelopes)identified throughout iron-rich rock samples were analysed using nanoscale secondary ion mass spectrometry(NanoSIMS). In this system, aluminium is enriched around the permineralised microfossils, while iron is enriched within the intracellularly, within distinct cell envelopes. Remarkably,while cell wall structures are indicated, carbon and nitrogen biosignatures are not preserved with permineralised microfossils. Therefore, the enrichment of aluminium, delineating these microfossils appears to have been critical to their structural preservation in this iron-rich environment. In contrast,NanoSIMS analysis of mineral encrusted cell envelopes reveals that preserved carbon and nitrogen biosignatures are associated with the cell envelope structures of these microfossils. Interestingly, iron is depleted in regions where carbon and nitrogen are preserved. In contrast aluminium appears to be slightly enriched in regions associated with remnant cell envelope structures. The correlation of aluminium with carbon and nitrogen biosignatures suggests the complexation of aluminium with preserved cell envelope structures before or immediately after cell death may have inactivated autolytic activity preventing the rapid breakdown of these organic, macromolecular structures.Combined, these results highlight that aluminium may play an important role in the preservation of microorganisms within the rock record.
