Factors controlling the hydrochemistry of Louie Creek, a travertine-depositing stream in the seasonally wet tropics of northern Australia

Abstract

Relationships among wet-season recharge, hydrochemistry and the distribution of travertines at Louie Creek were investigated from water samples collected during four campaigns between April 1993 and November 1997. pH, temperature and major cation and anion data reveal that the springs feeding the creek rise with high concentrations of CO2 and dissolved calcium carbonate. The pattern of downstream changes in hydrochemistry was similar during each campaign: rapid outgassing of CO2 over the ˜1.3 km of surface flow increases calcite saturation, triggering extensive travertine deposition over ˜1.5 km. At low discharge, the creek sinks then re-emerges at the downstream limit of travertine deposition in a more CO2-rich state. Together with a low stream gradient and high magnesium concentrations, this chemical change arrests the evolution of the waters and inhibits further accumulation of travertine downstream. Significant wet-season recharge dilutes spring water concentrations and retards their downstream evolution, resulting in a downstream shift of the reach of deposition. Following a wet season of low magnitude, the spring waters rise with higher concentrations of dissolved carbonate and evolve to a supersaturated state over a shorter distance. This results in an upstream migration of the travertine reach. These results have significance for the interpretation of fossil Quaternary travertines at Louie Creek.