Acid and neutral saline lake and groundwater systems on the Yilgarn Craton in southern Western Australia represent a rare modern extreme environment type. These natural systems are characterized by waters with a pH range from 1.5 to 10.5 and diverse chemical composition, as well as by an unusual assemblage of depositional and diagenetic minerals, and novel extremophilic microorganisms. PIs will conduct a drilling project that will provide the first intact and complete samples of Quaternary and late Tertiary sediments from these extreme environments. Past surface and subsurface histories will be interpreted from sedimentological, mineralogical, and palynological studies of these cores. Temperatures, pHs, and chemical compositions of past surface water and groundwater will be determined by fluid inclusions in bedded and displacive halite and gypsum and stable isotopes in gypsum, alunite, and jarosite. Identification of palynomorphs and dating of organic-rich siliciclastics and diagenetic minerals will constrain ages. Any suspect microbial remains will be described and will undergo preliminary study. Data from ten cores from throughout the Yilgarn Craton will yield: (1) past depositional environments; (2) past lake water and groundwater chemistry and pH; and (3) past surface water temperatures, which serve as surface air temperature proxies, through the Quaternary for southern Western Australia. This research will document the evolution of these acid saline waters and their response to and from local, regional, and global geological processes. The recognition of past extreme environments in the rock record of Earth and Mars will be evaluated with this work. Finally, PIs will use these results to make predictions about the future evolution of acid saline waters in Western Australia, where it threatens farming, ranching, and even human habitation.
Southern Western Australia contains lakes and groundwaters with amongst the Earth’s most extreme waters in terms of acidity and salinity. The goal of this project was to trace the history of environments, including water chemistry, as well as climate and life to gain an understanding of how such extreme acid saline regional water systems develop. We drilled ten cores in and near acid saline lakes and retrieved approximately 200 meters of sediment in this poorly explored region of Australia. We determined the ages, mineralogy, sedimentology, and paleontology of the subsurface sediments. The deepest core is ~60 meters deep and records the past approximate 40 million years. The other nine cores are shorter and record more recent time. Radiocarbon dating and microfossil studies allowed for age dates to be placed on individual sediment layers. The base of the deepest core contains sediments characteristic of wetlands, freshwater perennial lakes, and humid climate soils, indicating that Western Australia was humid approximately 40 million years ago. The topmost ~20 meters of sediment consist of saline lake, dry soil, and wind-blown sediments, all suggestive of a dry climate. This information documents a long-term drying trend over the past ~40 million years. The complexity of the mineralogy in the Western Australian cores reflects the complex, heterogeneous, and highly unusual composition of modern and past lake and ground waters there. The highly unusual mineral assemblage is a result of the weathering of local igneous rocks, chemical precipitates that formed in acid saline lakes, and crystals that grew from acid saline groundwater. The mineral assemblages vary locally due to localized differences in extreme water chemistry. The alteration overprint from the modern acid saline groundwaters is ubiquitous and in many areas masks original sediment textures. The paleontological study of the core sediments is among the first studies of pollen, spores, and algae for inland Australia. The modern sediments at acid saline lakes contained diverse, generally well-preserved pollen, spores, non-marine algae, and dispersed organic matter (palynodebris). The identification of specific genera has allowed for interpretations of ages of sediment and environmental conditions. The preservation condition of these microfossils was used to determine if they were physically reworked. Microfossil data support the depositional and climate interpretations suggested by the sedimentology and mineralogy. For example, freshwater alga was found in the older sediments of the cores, and salt- and arid-tolerant pollen and alga were found in the more recent sediments. Outreach to the public and educational training were part of this project, as was collaboration with the Geological Survey of Western Australia. Multiple graduate and undergraduate students at three universities in three states have conducted original research as part of their PhD dissertations, masters theses, and bachelors degrees. University courses and workshops for preK-12 schools, Girl Scout troops, senior citizen groups, and university seminars have used the samples and data from this project. An art exhibit at a library, a museum exhibit at the St. Louis Science Centre, and displays at Purdue University and the core lab at the Geological Survey of Western Australia have also involved samples and data from this project.
