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<p>This study presents a detailed petrographic, microanalytical, and isotopic investigation of Neoarchaean stromatolites from the Kumsi mine, Joldhal Formation (&gt; 2638 ± 66&#xa0;Ma), Karnataka, India. The stromatolites preserve distinct micritic lamination and associated fine-grained chert horizons containing minute spheroidal carbonaceous microstructures. FESEM imaging reveals isolated spheroidal microstructures dispersed within the chert matrix. The EDX elemental mapping indicates localized carbon enrichment associated with these microstructures. The small size range of the spheroids suggests possible affinities with picoplankton-sized microbial communities inhabiting Archaean shallow marine environments under predominantly low-oxygen conditions. Organic carbon isotope analysis shows lighter δ<sup>13</sup>C values (−&#xa0;31‰ to −&#xa0;29‰), aligning with signatures from cyanobacteria, anoxygenic phototrophs, and methanogenic bacteria. The occurrence of these spheroidal microstructures in stromatolitic cherts with biologically consistent carbon isotopic signatures reveals one of the least known types of microbial life from the Neoarchaean Era and support a biologically influenced genesis for the Kumsi stromatolites.</p>

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Microfossil-like structures and biologically consistent carbon isotopic signatures from stromatolitic cherts of the Neoarchaean Dharwar Craton, India

  • 期刊论文

  • 发表日期：

    2026年7月13日

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  • Yogmaya Shukla,
  • Arif Husain Ansari,
  • Mukund Sharma

摘要

This study presents a detailed petrographic, microanalytical, and isotopic investigation of Neoarchaean stromatolites from the Kumsi mine, Joldhal Formation (> 2638 ± 66 Ma), Karnataka, India. The stromatolites preserve distinct micritic lamination and associated fine-grained chert horizons containing minute spheroidal carbonaceous microstructures. FESEM imaging reveals isolated spheroidal microstructures dispersed within the chert matrix. The EDX elemental mapping indicates localized carbon enrichment associated with these microstructures. The small size range of the spheroids suggests possible affinities with picoplankton-sized microbial communities inhabiting Archaean shallow marine environments under predominantly low-oxygen conditions. Organic carbon isotope analysis shows lighter δ13C values (− 31‰ to − 29‰), aligning with signatures from cyanobacteria, anoxygenic phototrophs, and methanogenic bacteria. The occurrence of these spheroidal microstructures in stromatolitic cherts with biologically consistent carbon isotopic signatures reveals one of the least known types of microbial life from the Neoarchaean Era and support a biologically influenced genesis for the Kumsi stromatolites.