THE MID-MIOCENE CLARKIA LAKE: A TERRESTRIAL LAKE ANALOG FOR PALEOLAKES ON MARS

The confirmed extensive ancient lacustrine deposits on Mars opened exciting opportunities to study past hydrological cycle, climatic conditions, and possible life on the red planet. To better understand the origin and evolutionary history of lakes on Mars as well as their potentials to address both geological and astrobiological questions, one of the most efficient methods is to study analogous lakes on Earth, particularly ancient lakes experiencing the entire process of origin, development, and termination cycle with remarkably well-preserved biomolecules and biomarkers. The world renowned Middle Miocene (~15 million years) Clarkia Lake located in Idaho, USA fits this requirement, offering unique opportunities for comparative analysis of sedimentary architecture, mineral composition, and in situ preservation of biosignatures. The Miocene Clarkia Lake was formed through the damming of the proto–St. Maries River by the Columbia River Basalt creating a deep lake with stratified water body, which facilitated the preservation of extraordinary fossils and biomarkers. The deep lake phase was ended abruptly through a sudden physical geological event, likely associated with another volcanic eruption, which resulted in a rapid fall of lake water level. This catastrophic shallowing event played a key role in switching the mode of organic preservation. The extraordinary preservation of ancient biomolecules and biomarkers in the Clarkia deposits of various stratigraphic levels has attracted multi-disciplinary efforts to test various cutting edge biotechnologies applicable to ancient samples at all molecular levels such as the polymerase chain reaction (PCR) on DNA, amino racemization on protein, compound-specific carbon and hydrogen isotope analyses on in situ and sedimentary molecules, and glycerol dialkyl glycerol tetraether (GDGT) analysis on lipids. As direct characterization of preserved biosignatures is identified as a new approach of searching for life and studying paleolakes on Mars, we believe that the unique Clarkia Miocene Lake deposits with their association with basaltic volcanic terrains provide an ideal analog for paleolakes on Mars whose samples will be explored by landed missions, such as the upcoming Mars 2020 rover, and brought back to Earth in future Mars sample return missions.