Stromatolite Provinces of Hamelin Pool, Western Australia

Hamelin Pool, Shark Bay, Western Australia, is home to the most extensive living stromatolite system in the world, providing an analog for Precambrian fossils that dominated the planet for over 80% of Earth’s history. Due to the remote location and restricted access of Hamelin Pool, which is a marine reserve within a World Heritage area, previous geospatial, microstructural and environmental studies in this area are limited in scope. Existing ground truth data comes mainly from the two iconic stromatolite locations located on the western margin (Flagpole Landing and Carbla Point). Additionally, many studies are out of date with current technology or simply inaccessible. As a result, there are significant gaps in knowledge regarding the distribution and morphogenesis of stromatolites throughout Hamelin Pool. This dissertation research has taken an innovative approach involving intensive in situ observations to characterize and thereby better understand the living stromatolite system lining the shoreline of Hamelin Pool. Contrary to traditional mapping approaches, which classified stromatolites primarily on the basis of surface mat type, we mapped structures based on morphology. Seven main facies divisions were identified, including: weakly lithified to non-lithified stratiform sheets, lithified discrete microbial buildups, pavements, sediments, beachrock, boulders and breccia. Each facies type was further divided into sub-facies. In particular, discrete microbial buildups were classified as individual and merged, elongate, elongate-nested, composite/segmented, sinuous, elongate-clustered, seif and tabular structures. A high-resolution map was generated showing the distribution of the newly identified facies. The new map is based on the most comprehensive ground truthing survey of Hamelin Pool to date. Mapping of structures revealed a unique distribution of morphologically distinct types of microbial buildups around the margins of the Pool. This result further led to the designation of eight Stromatolite Provinces, each with distinct patterns of stromatolite morphology and unique shelf physiography. Additionally, high-density depth soundings were collected and used with a new generation of 30 m resolution satellite imagery to create a high-resolution digital elevation model (DEM). The new DEM model reveals previously unknown large-scale complexity within the Hamelin Pool embayment. Regional-scale physiographic features were exposed, facilitating a better understanding of the interaction of microbial buildups and their associated facies with the environment (ie: shelf vs. ramp, headland vs. bight, grade of slope into the basin, the location relative to the Faure Sill, etc.). Finally, coupling the new high-resolution facies map and bathymetry model with three years of environmental monitoring data assisted in the interpretation of stromatolite growth and distribution. Recognition of discrete Stromatolite Provinces in Hamelin Pool, each with unique stromatolite morphologies that do not correspond to broad surface mat types, suggests that varying energy regimes, sediment bed loads, and substrates interact to control stromatolite structure at the macro-scale. These observations linking morphology to physiography and environmental conditions in a modern system provide strong evidence that stromatolite morphology can be a powerful and potentially quantitative paleoenvironmental recorder