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New Insight Into the Shark Bay Microbial System, Part 1: Stromatolite Provinces

Abstract

Hamelin Pool, a hypersaline embayment with 135 km of shoreline within the Shark Bay World Heritage Area, Western Australia, supports the most extensive and diverse system of living stromatolites and microbial mats in the world. A recent comprehensive mapping program, which mapped stromatolites based on morphology, yielded a detailed facies map displaying substantial structural diversity along the margin. Combined with a high resolution bathymetry model, these maps provide insight into the spatial distribution of microbial deposits in a modern actively growing system. Interrogation of facies maps, in conjunction with shelf physiography, revealed a unique geographic distribution of morphologically distinct buildups and associated facies around the margins of Hamelin Pool. This allowed the differentiation of eight distinct Stromatolite Provinces. The Hamelin Pool microbial deposits constitute a progradational system with similarities to Aptian microbialite sediments, which were deposited in post-rift, lacustrine sag basins during the opening of the South Atlantic and have become attractive exploration targets on the conjugate margins of South America and Africa. Both aggradational and progradational stratigraphic geometries and lateral facies distributions in the Aptian microbialite are believed to have been controlled mainly by relative lake-level fluctuations and extensional tectonics. As such, microbialite facies in the “pre-salt” often occur in accumulations of over 200m. Understanding the lateral heterogeneity of the Hamelin Pool system allows insight to the long-lived microbialite system that occurred in the Aptian. Understanding the general physiography of Hamelin Pool and the location and type of structures present along its margins not only helps us better understand the contemporary system, but also provides insight into factors controlling the distribution of microbial structures throughout the rock record.