Life And Death Around Acid-Saline Lakes

Salt is a contradiction in itself. Halite requires a specific set of environmental conditions for growth, yet it is fairly common. It is extremely soluble, but many well-preserved examples are known from the rock record. It has been used by people for centuries as a food preservative, yet traditionally has been considered a poor fossilizer of other organisms. Recent studies have shown, however, that halite may be an excellent source for microfossils (e.g., Vreeland et al., 2000; Fish et al., 2002; Mormile et al., 2003; Schubert et al., 2005). A few organisms thrive in and near hypersaline environments. Flamingos, brine shrimp, halophilic algae and bacteria, and even the Death Valley pupfish are well known to most evaporite sedimentologists and saline-lake ecologists. But what life, if any, lives in or near lakes that are not only hypersaline and ephemeral, but also extremely acid? Do these organisms play any role in the unusual chemistry of their environment? Most importantly, do they become preserved in the fossil record? Natural acid-saline lakes are relatively rare. Two known modern settings, in Western Australia and Chile, host lakes and groundwaters with salinities of 100‰–300‰ TDS (total dissolved solids) and a pH of 1.5–4. There are hundreds of ephemeral, acid-saline lakes, and regional acid-saline groundwater, as well as nearby neutral-hypersaline lakes on the highly weathered Archean rocks of the Yilgarn Craton in the southern part of Western Australia (Mann, 1988; McArthur et al., 1991; Benison et al., 2007). In the Chilean Andes, at elevations of …