Microbially induced cementation of carbonate sands: are micritic meniscus cements good indicators of vadose diagenesis?

Abstract

Characteristic fabrics such as micrite envelopes, calcified filaments and micritic grain‐to‐grain bridges are observed in a modern subtidal firmground (Wood Cay, Bahamas) and in a variety of firm‐ and hardgrounds of Lower Cretaceous and Upper Jurassic platform carbonates (Swiss and French Jura Mountains). Their similarity to microbial fabrics described in grapestones and in intertidal to continental vadose environments suggests that microbial activity played an important role in the initial stabilization and cementation of carbonate sands. ‘Meniscus‐type cements’ (to distinguish them from vadose meniscus cements), which clearly formed in subtidal environments, are related to filament calcification, trapping of percolating micrite and microbially induced carbonate formation. Such meniscus‐type cements are commonly micritic, but meniscus‐shaped precipitation of fibrous aragonite or sparitic calcite around organic filaments is also observed. Therefore, an interpretation of vadose early diagenesis should not be based on meniscus cements alone. Similarly, subtidally formed filamentous structures can strongly resemble alveolar septal structures and be interpreted incorrectly as related to subaerial exposure.

Depleted dissolved organic carbon and distinct bacterial communities in the water column of a rapid-flushing coral reef ecosystem

“…However, increased aggregation should be reflected in elevated concentrations of particulate organic carbon on the reef (which is not observed; Supplementary Figure S2) unless aggregates are rapidly consumed by metazoans within the reef. DOM adsorbtion to the high-porosity carbonate sands common in the backreef habitats of Moorea is another abiotic removal process that may be important and has been demonstrated in similar environments (Suess, 1970;Hillgärtner et al, 2001). However, this process is difficult to distinguish from heterotrophic reef sediment biofilms that can remove DOM (Wild et al, 2004(Wild et al, , 2006.…”

Lower Carboniferous peritidal carbonates and associated evaporites adjacent to the Leinster Massif, southeast Irish Midlands

“…Grain aggregation by 'meniscus-type' micritic grain-to-grain bridging ( Figure 5I) found in Mesozoic and Recent carbonates was interpreted by Hillgärtner et al (2001) as firm-to hardgrounds, formed within a subtidal environment. Fibrous biofilm, similar to that in Figure 5H, was interpreted as the result of microbial activity and sulphate reduction by MacIntyre et al (2000), Reid et al (2000) and Visscher et al (2000).…”

First note on marine-like cementation of Late Holocene beachrock, Iznik Lake (Turkey)

“…Several previous studies have been made on the precipitation of meniscus cement from carbonate-rich meteoric waters (Friedman, 1964;Scoffin and Studdart 1983;Spurgeon et al, 2003;Rey et al, 2004). However, the bridges in this study are composed solely of micritic aragonite crystals, which could therefore also be related to precipitation around organic filaments by trapping of percolating micrite (Hillgärtner et al, 2001). The third kind of cement is made up of isopachous aragonite rims, consisting of randomly-orientated aragonites, which range from 10 µm to 50 µm in length (Fig.…”