Abstract
Microorganisms may play an important role in the aggregation of sediments and the formation of sedimentary structures. Biofilms are microbial aggregates that, in a mature stage, can develop into microbial mats, fibrillar networks that irreversibly bind filaments of cyanobacteria and sediments, inside which it has been identified a stratification with functional groups of microorganisms that coexist, generate symbiotic relationships and potentially modify the characteristics of sediments and sedimentary rocks, particularly in extreme environments. In this work, filamentous cyanobacteria from biofilms of a lacustrine environment with intervals of flooding/desiccation and a saline environment, and a microbial mat from the Agua Caliente Thermal, El Rosal, Cundinamarca, are identified. In the biofilms, most cyanobacteria were found to belong to the Orden Oscillatoriales, while in the microbial mat cyanobacteria of the order Orden Nostocales were also recognized. Two rock samples isolated from the thermal which genesis was possibly influenced by the activity of cyanobacteria are described and classified. One of them, named R-1, is a calcareous rock inside which it was possible to differentiate biolaminations and an apparent dominance of biomineralization processes. This sample was both classified as a travertine and a microbial framestone with stromatolitic and thrombolytic texture. The second one, called R-2, is a siliciclastic rock classified as a mudstone and a microbial boundstone. Finally, a comparison between the sedimentary structures identified in those rocks with similar structures in the formations La Luna, Paja and Tetuán and the microbially-induced sedimentary structures (MISS) described in the literature is performed. Based on morphological resemblance, fibrillar networks identified locally in those formations are interpreted as possible biolaminations originated from the activity of cyanobacteria.
Highlights
The surface adhesion of microorganisms by means of extracellular polymeric substances (EPS) favors the formation of thin organic laminae known as biofilms (Marshall, 1992; Costerton et al, 1995)
The detailed observation of organic matter laminae in sedimentary geologic units, mainly in marine settings, has allowed the reinterpretation of some of these as potential microbial mat features. Most of these structures manifest themselves as continuous biolaminations, inside which a fibrillar mesh produced by the filaments of cyanobacteria can be differentiated, related to biomineralization and sediment binding
Diagenetic effects can alter the integrity of lithified microbial mats, which, together with the characteristics of the depositional environment, could account for the differences between the structures observed in the modern and the Cretaceous microbial mat features
Summary
The surface adhesion of microorganisms by means of extracellular polymeric substances (EPS) favors the formation of thin organic laminae known as biofilms (Marshall, 1992; Costerton et al, 1995) These structures may grow to form thick stratified layers called microbial mats (Castenholz, 1994; Gerdes, 2010), fibrillar networks that often irreversibly bind filaments of cyanobacteria and sediments. The interaction between EPS and sediments, either calcareous or siliciclastic, allows the preservation of characteristics that provide evidence of the presence of microorganisms Those microbially-induced sedimentary structures (MISS) have been categorized into 17 different types and can be found in current environments and in the lithological record (Noffke, 2009). Both MISS and microbial mats are considered biosignatures, chemical or physical evidence of biological activity (Farmer and Des Marais, 1999; Summons et al, 2011; Westall and Cavalazzi, 2011)
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