153 / 2025-04-10 20:51:31

Microbial Gardening and Selective Dolomitization in Thalassinoides Burrows: Evidence from the Mantou Formation, North China Block

burrow-selective dolomitization；,intertidal sabkha environment,Microbial dolomite,T. paradoxicus

Theme 5: Life-Mineral Interaction and Evolutions > Session 5a: Microbe-mineral Interactions and Their Biosignatures: Integrating Laboratory Data with Field Insights

The Mantou Formation Member I (Cambrian Stage 4) in the southern North China Block hosts abundant Thalassinoides paradoxicus burrows within dolomitic micrite limestone. These burrows form complex and irregular networks, incorporating secondary shafts and blind tunnels. Sedimentary and geochemical indicators—including desiccation cracks, halite pseudomorphs, and REE signatures—are indicative of a hypersaline sabkha environment formed under arid and highly evaporative palaeoclimatic conditions.

Microscopic and geochemical analyses show that the burrow fills are predominantly composed of low-temperature, microbially induced dolomite, accompanied by minerals typically associated with dysoxic to anoxic conditions, including glauconite, euhedral pyrite, and siderite. These assemblages, together with kerogen-rich dolomite and enrichments in trace metals (Fe, Cu, Zn), suggest that the burrow microenvironments were enriched in dissolved organic matter and experienced persistent reducing conditions (e.g. Haley et al., 2004).

Rather than representing a simple fodinichnial or domichnial trace, T. paradoxicus is interpreted as an agrichnial trace reflecting a chemosymbiotic gardening strategy (e.g. Ekdale & Bromley, 2003). The burrowing organisms likely cultivated microbial consortia—particularly sulphate-reducing bacteria (SRB)—within the sediment, establishing mutualistic systems that influenced both redox conditions and nutrient cycling (e.g. Gingras et al., 2004; Corlett & Jones, 2012).

These microbial ‘gardens’, maintained within oxygen-depleted, organic-rich niches, provided favourable conditions for dolomite precipitation. The metabolic activity of SRB altered the porewater chemistry by consuming sulphate, releasing bicarbonate and Mg²⁺, and elevating both pH and alkalinity—thereby promoting dolomite nucleation within the burrow systems (e.g. Gingras et al., 2004). This study presents integrated mineralogical, sedimentological, and geochemical evidence for a biologically mediated model of burrow-selective dolomitisation, with broader implications for understanding early diagenetic processes in marginal marine environments.





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Ekdale, A. A., & Bromley, R. G. (2003). Paleoethologic interpretation of complex Thalassinoides in shallow-marine limestones, Lower Ordovician, southern Sweden. Palaeogeography, Palaeoclimatology, Palaeoecology, 192, 221–227.

Gingras, M. K., Pemberton, S. G., Muelenbachs, K., & Machel, H. (2004). Conceptual models for burrow-related, selective dolomitization with textural and isotopic evidence from the Tyndall Stone, Canada. Geobiology, 2, 21–30.

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Liu, H., Shi, K., & Liu, B. (2024). High-magnesium calcite skeletons provide magnesium for burrow-selective dolomitization in Cretaceous carbonates. Sedimentology, 71, 383–418.