Indigenous microbial communities as catalysts for early marine cements: An in vitro study

Abstract

Early marine cementation is a fundamental process for many characteristics of carbonates, like the stabilisation of steep slopes. The genesis of early cements is often attributed to physicochemical processes but there is evidence for microbial mediation. To elucidate the role of microbes and associated organic material, in vitro experiments were undertaken in the presence and absence of indigenous microbiota in ooids from Schooner Cays, Bahamas and compared with native grapestones from Joulter Cays, Bahamas. Microscopic examinations by stereomicroscopy, scanning electron microscopy and thin section analysis of in vitro incubations with native flora document rapid grain fusion, resulting in the formation of grapestones within 30-60 days. The initial binding of the grains is primarily facilitated by exudates of extracellular polymeric substances and microbial communities acting as catalysts in the formation of micritic bridges, cements and encrusted aggregates. In vitro grapestones are similar to native grapestones from Joulter Cays with intergranular areas infested with extracellular polymeric substances, microbes, micritic cements, amorphous calcium carbonate nanograins and micritised outer surfaces. These similarities suggest that incubations with native flora follow similar mineralisation mechanisms as in the natural environment. In contrast, sterilised grains remain loose with little crystal formation after 60 days and are devoid of microbes and organic exudates. Owing to the near absence of precipitates, abiotic precipitation is not the driving force promoting early cements. In contrast, grain fusion is microbially mediated via both a passive mechanism, where extracellular polymeric substances and cell surfaces function as templates for crystal nucleation and generation of micritic cements, and through an active mechanism by which biofilm heterotrophs and autotrophs induce chemical alterations of a local environment, facilitating precipitation. This study underscores that microbially mediated cementation can occur at fast rates and that firmground to hardgrounds and slope stabilisation take place shortly after deposition of carbonate grains.

Deep marine diagenesis, offshore Hawaii and Enewetak, with implications for older carbonates

“…In addition, microbial organisms and reactions involving organics at or near the sediment–water interface can also affect carbonate precipitation and dissolution. The presence of microbial material in sediment has been shown to greatly increase rates of precipitation of calcium carbonate cements in sea water (Diaz et al, 2022; Silva‐Castro et al, 2015). Reactions involving sulphate‐reducing bacteria have also been shown to stimulate dolomite precipitation in altered sea water (Vasconcelos et al, 1995; Sánchez‐Román et al, 2009).…”

“…Commonly organics and oxidation of organics play a key role in that early diagenesis (Pederson et al, 2021; Swart, 2015; Walter & Burton, 1990). Microbial mediation also has a large effect on sea water diagenesis (Diaz et al, 2022). The potential effect of deep sea water diagenesis on development of reservoir porosity is shown nicely by Teillet et al (2019).…”

Carbonate diagenesis: A celebration of the work of John Anthony Dawson (Tony) Dickson

“…This section contains three papers (Diaz et al, 2023; Dickson, 2023; Immenhauser et al, 2023). The paper by Immenhauser et al (2023) shows spectacular images that elucidate the formation of helictites that represent a bizarre form of carbonate precipitate.…”

“…Diaz et al (2023) use experiments with and without indigenous microbial flora to evaluate the precise role of microbial communities in precipitating carbonate and forming aggregate grains, carbonate components that cover vast areas of the present‐day Bahamas. Diaz and co‐workers employ Scanning Electron Micrographs of samples with the attendant microbial biota to show significant alteration within 30–60 days, including binding of the grains by extracellular polymeric substances and the formation of micritic bridges, cements and encrusted aggregates, linked to heterotrophic and autotrophic microbial processes.…”

Insights into the growth morphology of calcite cement

“…Seeding is the process that seamlessly connects cement to substrate crystals; any substrate crystal can act as a seed when at least some of its crystal planes are continued into the cement. Some early marine cements are catalysed microbially leading to the precipitation of amorphous calcium carbonate (ACC) (Diaz et al, 2022); however, the cement discussed here is thought to precipitate entirely as crystalline calcite. The choice between nucleation and seeding is, primarily, controlled by fluid saturation; experimental precipitation of calcite shows seeding occurs at lower saturation states than nucleation (Tang et al, 2000).…”