Methane seepage and associated authigenic carbonates are important archives for reconstructing subseafloor carbon cycling, fluid migration, and sediment instability under greenhouse climate conditions. However, whether seismically induced sand liquefaction can provide effective conduits for methane-rich fluids remains insufficiently documented in ancient marine successions. Here we report authigenic carbonate occurrences from the Gucuo II and Wolong East sections in the Tingri area, southern Tibet, which were deposited along the northern passive margin of the Indian continent during the Early Aptian. These two sections have previously been investigated for sandstone dikes and biostratigraphy, providing a stratigraphic framework for evaluating the relationship between sediment liquefaction, fluid migration, and methane seepage.
We integrate field relationships, petrography, SEM–EDS observations, stable carbon and oxygen isotope analyses of carbonate phases, in situ sulfur isotopes of pyrite, and detrital zircon U–Pb geochronology to evaluate the origin of these carbonates and their linkage to sand injection structures. The carbonates occur as irregular, non-stratiform bodies spatially associated with sandstone dikes and fractures. Petrographic observations reveal micrite–sparite fabrics, banded/botryoidal carbonate cements, ammonite-shell infillings, tube structures, and sand-sized to granule-sized siliciclastic grains mutually cemented with carbonate phases. Stable C–O isotope compositions of the carbonate phases provide additional constraints on carbon sources, carbonate-forming fluids, and precipitation conditions during seep-related authigenesis. SEM–EDS analyses further identify multiple generations of pyrite, including framboidal, overgrowth, and euhedral forms. In situ pyrite δ³⁴S values show a large range from −38.50‰ to +17.96‰, suggesting variable sulfur cycling involving organoclastic sulfate reduction and sulfate-driven anaerobic oxidation of methane(SD-AOM) near the sulfate–methane transition zone. Detrital zircon U–Pb age spectra from the authigenic carbonates yield Early Aptian youngest populations around 125 Ma and are comparable to reported ages of associated sand-injection or volcaniclastic materials, supporting a close temporal relationship between sand liquefaction, fluid migration, and carbonate precipitation.
We propose that Early Aptian magmatic–tectonic perturbations promoted paleoearthquake-related sand liquefaction, which created high-permeability pathways for methane-rich fluids. Subsequent methane seepage and redox reactions at or below the seafloor drove authigenic carbonate precipitation. This study provides a new geological record linking regional tectono-magmatic activity, sediment liquefaction, methane seepage, and carbon burial in an Early Cretaceous greenhouse ocean.

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