Abstract
Stromatolites are critical evidence of the earliest traces of life on Earth, yet consensus has not yet been reached regarding the mechanisms by which stromatolites form. Understanding the significance of Rare Earth Element (La-Lu), Yttrium, and Thorium (REY + Th) records in stromatolites may represent a breakthrough in the understanding of the processes by which stromatolites form and provide insight into the ancient depositional environments in which the stromatolites formed. This study aimed to analyze and interpret previously collected REY data using various extraction techniques (bulk digestion, sequential leach with various acids, and laser ablation ICP-MS (LA-ICP-MS) in order to determine the most effective method of extraction. Samples from the Ediacaran in China, ooids from the Bahamas, low-TOC stromatolite from the Bahamas formed through trapping and binding, and a high-TOC stromatolite from Hamelin Pool, Shark Bay, WA formed through microbial precipitation were tested using eight extraction methods included bulk dissolution, laser ablation, and sequential leaches using nitric acid with and without H2O2, hydrochloric acid with and without H2O2, and acetic acid with and without H2O2. The results of this study indicate that the method of REY+Th extraction and measurement from stromatolites influences the quality of extracted data. A nitric acid sequential leach with H2O2 was found to be the most effective in terms of completely digesting the samples and providing a consistent REY+Th pattern across each sequential leach; this method is therefore recommended for future studies analyzing REY+Th data in stromatolites.Ongoing work is focused on applying this extraction technique to different morphologies of the stromatolites in order to understand the REY+Th patterns within the 8 stromatolite provinces of Hamelin Pool, which is anticipated to hold implications for understanding the significance of REY+Th signatures collected from microbialites throughout the geological record.