Shallow perched groundwater, a flux of deep CO2, and near-surface water-rock interaction in Northeastern Jordan: An example of positive feedback and Darwin's “warm little pond”

Darwin's “warm little pond”, where he envisioned life began, was perhaps metaphorical. However, it included the notion of separation, just as the Galápagos Islands are separated from mainland South America. We have studied a location where simple life flourishes far from other abundant life, i.e., a permanently damp surficial zone that is surrounded by stark desert in NE Jordan. NE Jordan is a young basaltic plateau with fresh outcrops. However, a positive-feedback process has produced local weathering at Biyar el Ghussein in the Tulul al Ashaqif area. Calcite, smectites, and goethite occur with parent minerals. Water that is inducing this weathering has come from rainfall, but the isotopic composition of abundant carbonate veins reveals a deep source, i.e., volcanogenic CO2. A local coincidence of groundwater and rising CO2 is inducing a positive-feedback process, enhancing a weakly perched water table through weathering of basalt. Additional perched water dissolves more volcanogenic CO2, accelerating decomposition of the basalt, and enlarging the aquiclude.