Geochemical transect through a travertine mount: A detailed record of CO 2 -enriched fluid leakage from Late Pleistocene to present-day – Little Grand Wash fault (Utah, USA)

International audienceActive and fossil endogenic travertine mounts scattered along the Little Grand Wash fault are studied asrecords of Quaternary CO2-enriched fluid leakage. This study focusses on a particular area where a fossilmount formed in a near-surface setting by successive circulation/sealing episodes from Late Pleistoceneto Mid-Holocene and where a modern surface travertine is still being formed by a CO2-enriched fluidsource. The fossil mount is composed of horizontal and vertical veins whereby the vertical veins recordednumerous cycles of circulation/sealing/dissolution events and were used as conduits for the CO2-enriched fluid circulation from the depth to the surface or along sub-horizontal fractures where successiveprecipitation events are recorded. The modern travertine is being built at the surface by successiveeruption of Crystal Geyser, an anthropic geyser active since the 1930's.d13C and d18O signatures and U/Th datings, ranging from 11.5 ky till present-day allows calibrating indetail the CO2 enriched fluid leakage along a single fault segment and in a post glacial context, as lastglaciations in the study area took place 15 ky ago. The dataset shows a high decrease of the oxygen stableisotope values till about 6 ky, then the variations reflect a constant range until present-day. This tends torestrain the period of local increase of the meteoric water input in the aquifer that is sourcing the CO2-enriched water.The fossil travertine represents a 7 ky-long record of CO2 leakage above a natural reservoir, from LatePleistocene to Mid-Holocene. The flux of CO2 leakage through time and the total escaping volume havebeen computed and appears to be low in comparison with an anthropogenic leak provoked, for instance,by a non-sealed well