RELATIONSHIPS BETWEEN MICROSTRUCTURE AND MORPHOLOGY IN LACUSTRINE STROMATOLITES

Stromatolites are widely used as records of early Earth marine environments, but are less well known as records for continental deposits. However, numerous modern and ancient lakes contain stromatolites as dominant features of their chemical sedimentary record. These lacustrine stromatolites can serve as biological, sedimentary, and chemical archives for continental systems, sometimes at a high resolution. An understanding of the factors that produce and preserve them proves vital to reading this archive.

The morphology and microstructure of stromatolites varies greatly, even within a single deposit. The relationship between these scales is complex and poorly documented, particularly for lacustrine stromatolites. Microscale features (crystal organization, lamina structure, and grain size), in aggregate, produce meso- to macroscale structures (observable morphology). It is less clear whether the factors that control microscale features also control large-scale features, or whether altogether different processes shape the large-scale morphology of the stromatolite, regardless of microscale features. Unraveling the relationship between scale of process and scale of feature is key to understanding the degree to which stromatolites are interpretable environmental archives of the lakes they formed in.

In this study, samples from Proterozoic, Cenozoic, and Recent lacustrine stromatolites are characterized at micro- to macroscales using morphological analysis, cathodoluminescence microscopy, and optical microscopy to determine the degree to which microstructure shapes the final morphology of the stromatolite and to assess whether such correlations hold across time and space.

Initial results show that morphology is not uniquely predicted by microstructure. However, a more complex interplay across scales may be detectable. While the presence of any one microstructure does not decide the large-scale form, the dominance of particular microstructures or specific microstructure combinations may correlate with stromatolite morphology and record environmental change during stromatolite growth.