Molecular fingerprinting of microbial consortia in late Oligocene microbialite architectures from a freshening Junggar paleolake, Central Asia

Abstract

Microbialites preserve crucial records of early life and geobiological processes, yet interpreting their formation mechanisms remains challenging. Here we analyze Oligocene oncolites from the Junggar Basin that retain exceptional lipid biomarkers due to limited diagenetic alteration. These spheroidal structures exhibit alternating calcite-rich laminae with Fe-Mn coatings, revealed through petrographic and elemental mapping. Lipid analysis identifies prokaryote-dominated communities, particularly phototrophs and heterotrophs, with carbonate-associated biomarkers indicating continuous microbial activity during growth. The release of saturated fatty acid derivatives through acid treatment further confirms exceptional organic preservation. We demonstrate that oncoid formation involved complex microbial consortia mediating calcification. These deposits correlate with accelerated Tianshan Mountain uplift, which triggered lake shallowing and turbulent conditions that enhanced benthic microbial productivity prior to Central Asian aridification. Our findings establish microbialites as sensitive indicators of coupled tectonic and environmental changes during the Oligocene-Miocene transition. (Figure presented.)