---

Authigenic carbonate crust archives a protracted seepage event of deep-seated methane sources.

Sadique M, Mazumdar A, Peketi A, Hasozbek A, Kumar TV, Babu EVSSK, Ghosh A, Verma S, Mishra S.

CHEMICAL GEOLOGY

https://doi.org/10.1016/j.chemgeo.2026.123416 

First high-resolution multiproxy record of methane seepage from a brecciated methane-derived carbonate crust recovered at 1463 m in the Mannar Basin spanning 14.8 ± 1.1 to 3.5 ± 0.1 kyr are provided as part of this study. Petrography and mineralogy reveal two aragonite phases: micritic aragonite clasts (75-90% aragonite, plus high-Mg calcite and pyrite) and nearly pure aragonite cements (>99%). Very negative carbonate δ13C values (-53.9 to -39.4‰ VPDB) confirm methane as the carbon source; organic δ13C (-45.4 ± 6.6‰ VPDB) records input from methanotrophic biomass. Positive aragonite δ18O (3.4-5.9‰ VPDB) points to 18O-enriched fluids, likely from clay dehydration in overpressured deeper strata and gas-hydrate dissociation. A three-stage formation model is proposed.

Cross section of the brecciated aragonite crust with microdrill points and U-Th ages and Bottom-Conceptual model illustrating the evolution of the brecciated aragonite crusts under the variable methane-flux regimes.

---