Structural diversity of biogenic carbonate particles in microbial mats

Abstract

Non-skeletal carbonate particles in microbial mats were studied using thin sections and scanning electron microscopy. The microbial mats form biolaminated units (so-called potential stromatolites) in salterns. This study emphasizes the coexistence of different particle forms and makes a genetic connection between the heterogeneity of the organic substrate built by bacteria and diatoms and their extracellular polymeric substances (EPS). Whereas allochthonous particles are scarce, Lanzarote microbial mats provide various autochthonous surfaces for the attachment of cells and EPS, including sheaths and capsules of cyanobacteria, frustules of diatoms, metabolic products such as gas bubbles, liquid globules and faecal pellets, as well as the carbonate precipitates themselves. Morphologically different carbonate precipitates are: (i) calcified organic clumps (peloids), (ii) particles composed of concentric aragonite and biofilm laminae (ooids and oncoids), (iii) isolated particles floating in gel-supported mats and coated by rims of fibrous cement (cortoids), (iv) particles bound by cryptocrystalline matrices or cement, resulting in aggregate grains and (v) lobate cement which fills out spaces and pores and fixes the particles. Peloids are suggested to represent faecal pellets although microbial systems also generate cell clumps by non-faecal processes. Ooid and oncoid constructions clearly record alternating processes of biofilm accumulation and aragonite encrustation. Further characteristic features of carbonate particles generated within a microbial mat are: (i) an irregular distribution ranging from isolated particles floating within the gel-like matrix to closely packed particles, (ii) the amalgamation of different particle types (e.g. peloids and ooids) in aggregate grains, (iii) the heterogeneous nature of nuclei comprising bacterial clumps, intraclasts, individual cells, cell colonies and bubbles, (iv) the enrichment of remains, casts and imprints of cells within precipitates and (v) deformation (e.g. truncated cortices) of particles.

The accelerating effects of the microorganisms on biodeterioration of stone monuments under air pollution and continental-cold climatic conditions in Erzurum, Turkey

“…These chemicals were found to be trapped in the mineral matrices of the buildings. An investigation of the coexistence of dif- ferent particle forms of biogenic calcium carbonate deposits within the microbial biofilm was investigated by Gerdes et al (1994), who showed that aragonite accumulation occurs due to biologically induced physiochemical changes in the microenvironment of the interface. Hydration-dehydration cycles might exert a clear biogeophysical effect on the stone.…”

Microfacies Data: Matrix and Grains

“…130/3. 1 Microbial peloids. The clotted structure of the peloids and the occurrence as constituents of bindstones point to a microbially induced origin of the grains formed in situ within mats ('benthic peloids': Gerdes et al 1994;Kazmierczak et al 1996). Bedded lagoonal limestone.…”

“…In-situ growth of modern oncoids has been reported from lakes, lake margins and sabkhas (Jones and Wilkinson 1978), and rivers or streams (Freytet and Plaziat 1965; Hartkopf-Fröder et al 1989). Ancient in situ growth has been claimed for Tertiary lacustrine oncoids (Leinfelder and Hartkopf-Fröder 1990).Algal and cyanobacterial pellets formed in situ (benthic peloids) occur in microbial mats of salinas, saline lakes and intertidal settings (Gerdes et al 1994; Kazmierczak et al 1996). The rounded micritic grains as well as autochthonous micrite (Sect.…”

“…Nodule turning is facilitated by waves and tidal currents, a sloping surface, or bioturbation of the underlying surface by grazing herbivorous fish. The contribution of cyanobacteria and other bacteria to the formation of cyanoids and spongiostromate oncoids has generated a large number of publications in the last few decades that have clearly established the fundamental role played by cyanobacteria (Pentecost and Riding 1986;Gerdes et al 1994). These observations were reinforced by experiments that succeeded in creating calcite and aragonite biocrystals under laboratory conditions approximating natural conditions (Chafetz and Buczynski 1992; Knorre and Krumbein 1992; Castanier et al 1999).…”

“…They are dominated by cyanobacteria, colorless and purple sulfur bacteria, and sulfate-reducing bacteria. The driving force of most microbial mats is photosynthesis by cyanobacteria and algae.Microbial signatures in thin sections are in-situ formed benthic peloids and ooids (Chavetz 1986, Gerdes et al 1994 within mats, thrombolitic, clotted and fine-peloidal fabrics, laminated and stromatolitic fabrics, fossils interpreted as cyanobacteria (see Pl. 53) and microborings (Pl.…”