Investigating the controls of microbialite morphogenesis using GIS-based approaches

BRADLEY, A.; BEELER, S.; GOMEZ, F.J.

Indianapolis

Congreso; 6th Annual Midwest Geobiology Symposium; 2017

6th Annual Midwest Geobiology Symposium

Microbialites are sedimentary structures that arise from the interaction of microbial andgeological processes. These structures can record information regarding microbial evolutionand/or environmental changes through geologic time. A wide range of microbialite morphologieshave been recognized in the geologic record, however in most cases an understanding of thecontrols of this morphological variability is lacking. The hypersaline lake Laguna Negra(Catamarca Province, Argentina) contains a zone of carbonate precipitation consisting ofmorphologically diverse structures including those interpreted as microbialites whose abundancevaries across the lake edge. Gradients in physico-chemical conditions and the communitystructure of microbial mats and sediments associated with the carbonates occur across the zoneof carbonate association making it an ideal location to study the controls of microbialitemorphogenesis.We utilized an approach combining aerial imagery, geochemical measurements, and fieldobservation into a GIS-based data model to investigate the spatial distribution of and relationshipbetween environmental parameters and carbonate morphology. High resolution aerial images(1.76 cm/px resolution) were generated and utilized to map changes in the morphology,abundance, and size of carbonates at Laguna Negra as well as visual changes in microbialcommunities. Additionally, geochemical measurements and ground truth observations weretaken at locations across the lake edge. Integration of these results into a GIS data model inArcMap was performed to enable recogniton and statistical analysis of the spatial distribution ofcarbonates, geochemical parameters, and microbial communitiesSpatial analysis reveals that the occurrence of carbonate morphologies does vary acrossthe lake edge, but the contact between morphologies are gradational. Non-carbonate cobbles andboulders are also abundant within the zone of carbonate formation, and typically occur in areaswithout the presence of large carbonate structures. Morphologies interpreted as microbialiticwere more commonly associated with microbial mats than non-microbial carbonates and noncarbonatesconsistent with a microbial contribution to their formation. However, not allmicrobialites were associated with microbial mats and in some cases non-microbialites wereassociated with microbial mats confounding this interpretation. Large geochemical gradients dueto the mixing of waters, degassing, and evaporation were measured at the lake edge and are alsoassociated with the morphological changes. Ongoing work aims to better quantify therelationship between these environmental changes and morphology to develop a model formicrobialite morphogenesis at Laguna Negra as an analog for ancient examples.