THE IDENTIFICATION, DETECTION AND ANALYSIS OF THROMBOLITES USING SPECTROSCOPY TO FURTHER UNDERSTAND THE EVOLUTION, ADAPTATIONS, AND PRESERVATION OF EARLY LIFE

Six thrombolite samples were collected in a transect at Schreiber Beach, Thunder Bay, ON. Laboratory analysis was conducted to determine the detection and characterization of thrombolites. Thrombolites are of interest because they consist of microbial communities bound to benthic sediments creating microfossils that provides insights into the evolution and adaption of past macroscopic life. Thrombolites found within the Schreiber Beach area were collected because of the old age of the chert matrix, ~1.9 billion years, and the uniquely adapted life, such as iron metabolizing organisms, being able to live in soil, as well as ammonia-rich, and anoxic environments.

These samples were analyzed by reflectance, Raman spectroscopy, and X-ray diffractometry (XRD), focusing on mineralogy and preserved organics. Raman detected carbon signatures such as graphitic G and D-bands. Major and minor mineralogy was determined by each instrument, Raman detected quartz, calcite, sulfides, and hematite. Reflectance spectroscopy was able to detect calcite, water absorption bands, and Fe (iron) related features. The XRD detected calcite and quartz as major components with hematite, salts, and sulfides as minor ones.

Raman was most useful in the search for preserved evidence of life, because of its ability to detect sp² bonded carbon, and identifying bulk mineralogy that could indicate thrombolite structures. Reflectance spectroscopy functioned to detect other bulk minerals and properties that were beyond the Raman’s ability, such as Fe oxidation state which is of interest because of life’s reliance and interaction with iron. The XRD was able to identify minerals that Raman and reflectance spectroscopy did not, such as the presence of salts. Through spectral analysis, samples found in the field that could indicate preservation of past life can be detected and collected for further and more thorough analysis. Spectral and x-ray analysis indicate that signs of past life can be detected as well as related mineralogy associated with the structures that preserve microfossils. Our results also show that these three analytical techniques are very complementary.

This study was supported by grants and contracts from the Canadian Space Agency (CSA), the Geological Society of America (GSA), MRIF, CFI, UWinnipeg, and NSERC.