185-8 Timescale and Mechanisms of Microbialite Mineralization in Mobile Microbialite Clasts from Great Salt Lake, Utah

Session: New Advances and Voices in Geobiology (Posters)

Presenting Author:

Authors:

Abstract:

Ancient microbialites represent some of the earliest geological evidence of life on Earth and are a key archive in reconstructing Earth’s history. To accurately interpret ancient microbialites and understand what kinds of information may be written into the rock record, we can use modern analogs to learn how microbialites form and are preserved. Previous analysis of modern microbialites forming in Great Salt Lake was used to formulate a microbialite mineralization model in which a local increase in pH due to photosynthesis drives the permineralization of extra-cellular organic matrix in the microbial biofilm by a poorly crystalline Mg-Si phase. This Mg-Si phase is then replaced by aragonite, which nucleates in association with sulfate reduction hotspots. In some cases, the aragonite can be partially replaced by dolomite in a final step. To expand upon these findings and understand how this model may apply to mobile microbialite grain morphologies (rather than the more commonly studied static microbialite mounds), we characterized samples of mobile microbialite clasts from two sediment cores from Great Salt Lake using light microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffractometry. We also analyzed a subset of samples for radiocarbon ages to define the timescale over which the mineralization process occurs.

We found that microbialite grains were significantly permineralized by Mg-Si, as described in the previous model, in under ~230 years, and grains were nearly completely mineralized by aragonite after ~2500 years. This data provides a quantitative timescale over which these processes occurred in these clasts. We did not observe authigenic dolomite in any of our samples, which we posit may be due to 1) a lack of intense microbial activity during the mineralization of these grains; 2) a reduced influence of microbial metabolic activity on local water chemistry experienced by mobile grains relative to in situ microbialite mounts; or 3) insufficient duration of time for dolomite formation. These findings help us more accurately understand modern microbialites and may aid their use as analogs for interpreting ancient microbialites in the rock record.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9273

© Copyright 2025 The Geological Society of America (GSA), all rights reserved.