Dolomitic Mottling in Palliser (Devonian) Limestone, Banff and Jasper National Parks, Alberta

Beales, F. W.

doi:10.1306/5ceadd8e-16bb-11d7-8645000102c1865d

Cited by 14 publications

(1 citation statement)

References 7 publications

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“…As an important type of partial or selective dolomitization, it is attracting increasing academic and industry research interest. Dolomitized burrows feature special morphologies and different fill textures from matrices; previous studies referred to burrow‐dolomitized carbonates as pseudobreccia limestones (Wallace, 1913), mottled limestones (Beales, 1953; Hattin, 1971; Kendall, 1977; Pak et al ., 2001; Yang et al ., 2022a), nodule limestones (Corlett & Jones, 2012; and references therein) and vermicular limestones (Jaglarz & Uchman, 2010; and references therein). For the origin of burrow dolomites, early scholars emphasized the effects of physical alteration of the substrate by burrowers on selective‐dolomitization and ascribed preferential dolomitization of burrows to their potential to act as preferential migration pathways for high salinity seawater in the near‐surface realm (Morrow, 1978; Jones et al ., 1979; Saller & Yaremko, 1994; Zenger, 1996a).…”

Section: Introductionmentioning

confidence: 99%

High‐magnesium calcite skeletons provide magnesium for burrow‐selective dolomitization in Cretaceous carbonates

Liu,

Shi,

Liu

et al. 2023

Sedimentology

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The source and pumping mechanism of magnesium play crucial roles in dolomitization. The preferential dolomitization of burrows has been extensively documented in geological archives. Although burrows are abundantly preserved in Cretaceous carbonates, burrow‐selective dolomitization is uncommon in normal salinity marine environments due to low Mg/Ca ratio of seawater. However, burrow‐selective dolomitization occurred in the Cenomanian Rumaila Formation carbonates of the Arabian Platform providing an excellent example to further clarify the mechanism and explore other potential Mg sources of burrow‐elective dolomitization. Integrated studies of petrography, stable isotope geochemistry and laser ablation‐inductively coupled plasma‐mass spectrometry‐based in situ element geochemistry were conducted. It was found that the burrow‐selective dolomitization exclusively occurred in echinoderm fragments‐filled Thalassinoides networks occurred as Glossifungites ichnofacies. Burrow dolomites showed fine to medium crystalline and planar subhedral to euhedral textures with cloudy centres and clear rims. They exhibited relatively greater Mn, lower Sr and Fe concentrations, no or very weak negative Ce anomaly and middle rare earth element‐bulge patterns, and are slightly enriched with occasionally depleted δ13C and comparable δ18O relative to the surrounding calcite matrix. The initial high‐Mg calcite echinoderm fragments in burrows have been stabilized to low‐Mg calcite, and echinoderm syntaxial overgrowth calcite cement was practically nonexistent. Echinoderm fragments were frequently replaced by dolomite in part or whole. Undolomitized echinoderms have negative Ce anomaly and seawater‐like rare earth element patterns, as well as very low Mn, Fe and relatively greater Sr concentrations. These suggest that echinoderm stabilization occurred in fluid unsaturated with respect to high‐Mg calcite driven by aerobic decomposition of organic matter in oxic seawater near sediment‐water interface, meanwhile, Mg ions were liberated into pore water. This process predated the dolomitization allowing the Mg derived from echinoderm to raise the Mg/Ca ratio of burrow interstitial water. The dolomites in burrows were generated by initial replacement and subsequent overgrowth cementation associated with bacterial sulphate reduction and methanogenesis in low‐temperature and suboxic to anoxic fluids in near‐surface realm, and faintly recrystallized as burial depth increased. This study sheds light on the echinoderm stabilization process, links the early diagenesis of skeletons to burrow dolomitization, and proposes a conceptual model illustrating that high‐Mg calcite skeletons could act as a major Mg source for burrow‐selective dolomitization, which compensates for the deficiency of Mg in normal low Mg/Ca ratio Cretaceous seawater. This study implies the interaction effect and element cycle among components in early diagenetic systems, and verifies that high‐Mg calcite is indeed a non‐negligible potential Mg source for partial or elective dolomitization.

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