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The Influence of Salinity on Microbial Activity and Carbonate Precipitation in Microbialites

John Warden
The University of Texas at Austin, Department of Geological Sciences, Austin, TX, USA
[email protected]

The formation of lacustrine microbial carbonates has received recent interest after the discovery of microbialite-associated hydrocarbon reservoirs in pre-salt basins off Africa and South America. Organic matter preservation in lacustrine microbial carbonates is controlled by the depositional factors that influence microbial activity, carbonate buildup, and later diagenesis. Lake Clifton, Western Australia contains modern microbialite structures, ranging from several centimeters to one meter in height, which are primarily thrombolytic in texture and known to be associated with cyanobacteria. Unicellular and filamentous cyanobacteria were isolated from thrombolite-associated microbial mats in Lake Clifton to investigate salinity’s influence on microbial activity and geochemical reactivity. Lake Clifton is a hypersaline lake; total dissolved solids ranged from 5-7% in samples collected June, 2011 and August, 2012. Microorganisms employ varying strategies to survive osmotic stress in high salt environments. Some species of cyanobacteria increase exopolysaccharide (EPS) production as a salt tolerance mechanism. EPS affects the carbonate saturation state in microbial mats by binding and releasing calcium and other metals. The isolated cyanobacteria will be used in controlled, replicated culturing experiments to monitor both EPS production and carbonate precipitation in response to salt stress. The manner in which microbial communities produce EPS and induce carbonate precipitation is important for understanding organic matter preservation in microbial carbonate reservoirs. This work aims to advance understanding of how solution salinity influences microbial activity during carbonate precipitation in lacustrine microbialites.

AAPG Search and Discovery Article #90183©2013 AAPG Foundation 2013 Grants-in-Aid Projects