Some Precambrian carbonate rock bodies host economic petroleum reserves. Here, we present a case study of the deeply buried (>5 km) upper Ediacaran Dengying Formation (ca. 551–541 Ma) to document the formation of a microbialite gas field. Detailed petrological and geochemical data are presented and placed in context with porosity and permeability analyses. This approach leads to a better understanding of Ediacaran microbialite textures, diagenetic pathways, and reservoir properties in general. Microbialite facies yield a positive correlation between sorting coefficient and porosity. Compared with other microbial fabrics, thrombolites have well-connected pore networks and large pore-throat radii. Fibrous dolomite cement was precipitated in a marine pore water environment at an early diagenetic stage. Maximum porosity (∼4%–6%) and permeability values (∼0.01–10 md) are established in spatially confined stratigraphic intervals. Meteoric diagenesis correlates with transient subaerial seafloor exposure and affects carbonates. Meteoric diagenesis is typified by dolostone with low δ13C (∼−2‰ to 0‰) and δ18O values (∼−11‰ to −8‰). Silica phases were subsequently precipitated from hydrothermal fluids, whereas reflux and burial dolomitization increased reservoir performance. In the deep-burial regime, late-stage hydrothermal fluids resulted in the generation of secondary pores. Along hydrothermal pathways, fluid-inclusion temperatures, Sr contents, and radiogenic 87Sr/86Sr ratios of saddle dolomite decrease in parallel, whereas the salinity of fluid inclusion in saddle dolomites increases. One-dimensional numerical models support the increase in porosity as a response to meteoric and hydrothermal diagenesis. The data shown here are relevant for those concerned with petroleum exploration in ancient, deeply buried microbialite reservoirs.

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