SEEKING SIGNS OF LIFE THROUGH THE LENS OF DIAGENESIS IN SILICEOUS HOT SPRING DEPOSITS

To be able to more confidently interpret the biogenecity of samples we need to understand the morphological and chemical changes that happen to biosignatures after deposition. This data can be used as a tool to distinguish less-than well preserved fossils from non-biologic mimics. Decades of research in siliceous hot springs on Earth have shown that biosignatures, such as organic content, body fossils, and biofabrics, are captured and preserved in the silica minerals that precipitate from hot spring waters. Therefore, hot spring deposits are prime targets for the search of life in other planets, like Mars. While it is generally agreed that rapid mineralization of microorganisms and biofabrics is essential for their preservation, mineralization often begins with the precipitation of a metastable silica phase that, over time, undergoes diagenetic transformation to a more stable, ordered phase(s). In general, sinter diagenesis involves systematic structural transformation of amorphous opal-A, to Opal-CT, to Opal-C, to the stable phase, quartz. Because of this, hot springs provide a natural laboratory to study the progressive degradation of biosignatures over time. One question I will address in this study is: How are biosignatures modified during mineral diagenesis? I hypothesize that there is progressive degradation of body fossils and biofabrics, as well as, loss of sinter total organic carbon associated with the mineral diagenetic recrystallization of opal-A, to opal-CT, opal-C and quartz. To address this question, 30 samples with palisade fabric were collected from Puchuldiza hot springs in Chile. X-ray powder diffraction shows that the samples we collected span the full silica diagenetic sequence from opal-A to quartz. The morphological and compositional characteristics of body fossils and biofabrics, and their diagenetic modifications, will be determined by thin-section petrography, Scanning Electron Microscopy, Electron Microprobe Analyzer, Raman spectroscopy and total organic carbon analysis. These established methods will provide the data sets needed to test my hypothesis. By documenting morphological and chemical changes that occur to biosignatures during diagenesis we will build a framework to better interpret the fossil record on Earth and potentially, Mars.