CHARACTERIZATION OF MODERN STROMATOLITES BY MICROSCALE FEATURES: HAMELIN POOL, AUSTRALIA AND EXUMA CAYS, BAHAMAS

Stromatolites, microbially-constructed sedimentary structures, provide a record of life on Earth for more than 3 billion years, across a variety of aquatic environments. Stromatolites can serve as a record of the environment in which they formed; a thorough understanding of the formation process is vital to interpreting this record. Modern marine stromatolites are rare but are potentially key for interpreting their ancient counterparts. Evidence thus far indicates that modern stromatolite growth patterns differ significantly from growth patterns of ancient stromatolites, which could significantly limit their utility as analogs. This study principally focuses on determining whether the two localities of modern marine stromatolites are similar enough to each other to comprise a temporal data point regarding modern stromatolites or whether they represent a spectrum of stromatolite growth patterns. A further aim of the study is to evaluate the hypothesis that modern and ancient stromatolites have fundamentally different modes of construction.

This study characterizes stromatolites from Hamelin Pool, Australia and Exuma Cays, Bahamas at micro-, meso-, and macroscales. Morphological analysis and optical microscopy were applied to a suite of samples to determine the relation between microfabric and final morphology of the stromatolites and to assess whether such correlations persist across localities in the modern world. Fabric percentages for each sample were calculated using the thresholding tool on ImageJ, then compiled and compared based on macrostructure. Hamelin Pool stromatolites show a notable diversity of microfabrics in stromatolites across a range of macro- and mesostructures. Stromatolites from Exuma Cays have a similar suite of microfabrics, but the proportions are strikingly different from stromatolites in Hamelin Pool.

The stromatolites from these two modern locations have previously been individually studied; this is the first study to compare microfabrics directly between each locality. This analysis provides a basis for comparison with ancient microfabric diversity and represents a first step in determining whether modern stromatolites are robust analogues for ancient forms.