THE ROLE OF ENVIRONMENTAL CONDITIONS IN THE FORMATION OF THE MESOSTRUCTURE AND MICROSTRUCTURE OF THROMBOLITES

Thrombolites are non-laminated, clotted microbialites that are likely formed by the lithification of microbial communities (e.g., through mineral precipitation). This precipitation is highly controlled by the so-called “alkalinity engine”, which receives inputs from both extrinsic (environmental) and intrinsic (microbial) factors. By better understanding the environments in which thrombolites currently exist, it is possible to gain insight into their formation, structures, and processes through geologic time.

Living thrombolites are found around the world in various climates and conditions, including the Bahamas, northern New York, and Western Australia. By characterizing these contemporary, thrombolite-forming, macroenvironments using hydrochemical and physical data such as water chemistry, temperature, salinity, light, and sediment supply, it may be possible to understand the environmental factors that inhibit or induce microbialite formation. Intrinsic factors are also important to consider as the microbial community metabolism generally plays a pivotal role in changing the mineral saturation. Microbes are affected by the environmental conditions and they can influence precipitation location, mineralogy, and morphology.

Characterization of the thrombolite structure at each of these environmental locations is done using thin sections and scanning electron microscopy. Analysis of the thrombolitic mesostructure and microstructure is based on classification of trapped and bound sediment and the nature of precipitation within the different environments. By categorizing these structures and linking the environments in which they are forming it is possible to understand 1) the different environmental systems in which thrombolites are currently forming; 2) the environmental (extrinsic) controls of the alkalinity engine; 3) the role of microbial (intrinsic) activity in thrombolitic precipitation; and 4) extrinsic factors that are affecting structural formation of thrombolites.

Further research may provide a link to the fossil record if similar structures can be seen in fossilized thrombolite samples. If this is the case, thrombolitic structure could potentially be used an indicator for past environmental conditions.