Microbially Mediated Intracellular Barite Mineralization: Evidence From an Early Ediacaran Microfossil in the Doushantuo Formation of South China

Abstract Barite serves as a key proxy for reconstructing paleo‐oceanic productivity and chemistry in modern and ancient marine sediments. Although contemporary barite precipitation involves biological mediation, the mechanisms responsible for ancient barite formation remain unclear. Here, we report the first evidence of microbially mediated intracellular barite, preserved within Archaeophycus yunnanensis microfossils from the Ediacaran Doushantuo Formation. Two mineralization patterns were identified: (a) barite‐apatite assemblages with micron‐scale barite frameworks encapsulating poorly crystallized apatite, and (b) cells solely composed of well‐crystallized apatite. Barite's spatial association with organic residues and specific intracellular localization suggest microbially mediated processes. Crucially, the intracellular barite exhibits an extremely light Ba isotope composition (δ 138 Ba = −0.88‰), significantly lower than coeval marine carbonates. We propose that this microbial intracellular biomineralization drives strong Ba isotope fractionation, providing a key mechanism to explain the light Ba isotope signatures in post‐Marinoan carbonates. This reveals a novel microbially mediated pathway in the Ediacaran marine Ba cycle.