Groundwater calcrete deposits in Australia some observations from Western Australia

Microbial influence on dolomite and authigenic clay mineralisation in dolocrete profiles of NW Australia

Dolomite (CaMg(CO3 )2 ) precipitation is kinetically inhibited at surface temperatures and pressures. Experimental studies have demonstrated that microbial extracellular polymeric substances (EPS) as well as certain clay minerals may catalyse dolomite precipitation. However, the combined association of EPS with clay minerals and dolomite and their occurrence in the natural environment are not well documented. We investigated the mineral and textural associations within groundwater dolocrete profiles from arid northwest Australia. Microbial EPS is a site of nucleation for both dolomite and authigenic clay minerals in this Late Miocene to Pliocene dolocrete. Dolomite crystals are commonly encased in EPS alveolar structures, which have been mineralised by various clay minerals, including montmorillonite, trioctahedral smectite and palygorskite-sepiolite. Observations of microbial microstructures and their association with minerals resemble textures documented in various lacustrine and marine microbialites, indicating that similar mineralisation processes may have occurred to form these dolocretes. EPS may attract and bind cations that concentrate to form the initial particles for mineral nucleation. The dolomite developed as nanocrystals, likely via a disordered precursor, which coalesced to form larger micritic crystal aggregates and rhombic crystals. Spheroidal dolomite textures, commonly with hollow cores, are also present and may reflect the mineralisation of a biofilm surrounding coccoid bacterial cells. Dolomite formation within an Mg-clay matrix is also observed, more commonly within a shallow pedogenic horizon. The ability of the negatively charged surfaces of clay and EPS to bind and dewater Mg2+ , as well as the slow diffusion of ions through a viscous clay or EPS matrix, may promote the incorporation of Mg2+ into the mineral and overcome the kinetic effects to allow disordered dolomite nucleation and its later growth. The results of this study show that the precipitation of clay and carbonate minerals in alkaline environments may be closely associated and can develop from the same initial amorphous Ca-Mg-Si-rich matrix within EPS. The abundance of EPS preserved within the profiles is evidence of past microbial activity. Local fluctuations in chemistry, such as small increases in alkalinity, associated with the degradation of EPS or microbial activity, were likely important for both clay and dolomite formation. Groundwater environments may be important and hitherto understudied settings for microbially influenced mineralisation and for low-temperature dolomite precipitation.

Two new subterranean ameirids (Crustacea : Copepoda : Harpacticoida) expose weaknesses in the conservation of short-range endemics threatened by mining developments in Western Australia

The discovery of two new non-marine ameirids from the southern Yilgarn region significantly extends the geographic range for this group in Australia and exposes weaknesses in the conservation and environmental impact assessment (EIA) of subterranean species potentially threatened by mining developments. Megastygonitocrella embe, sp. nov. differs from seven previously described Australian congeners by the armature of the second leg endopod and absence of spinules on the somites. A key to world species of Megastygonitocrella is presented. Phylogenetic analysis based on 57 morphological characters and 30 species belonging to the Stygonitocrella s.l. group suggests that Antistygonitocrella pardalotos, gen. et sp. nov. has no close relatives anywhere in the world. Superficial similarities between the two new species are either plesiomorphies or homoplasies. The habitats of these new short-range endemic species are fractured-rock aquifers developed in Archaean greenstone, where the groundwater is characterised by acid conditions, high salinity and low dissolved oxygen. The population of A. pardalotos is threatened by a mining development. Despite the advanced level of environmental protection policy in Western Australia, our taxonomic study highlights limitations in EIA practices and discusses potential improvements which have global relevance in regions where short-range endemics coincide with extraction of mineral resources.

Phylogeography of the ancient Parabathynellidae (Crustacea:Bathynellacea) from the Yilgarn region of Western Australia

The crustacean order Bathynellacea is a primitive group of subterranean aquatic (stygobitic) invertebrates that typically inhabits freshwater interstitial spaces in alluvia. A striking diversity of species from the bathynellacean family Parabathynellidae have been found in the calcretes of the Yilgarn palaeodrainage system in Western Australia. Taxonomic studies show that most species are restricted in their distribution to a single calcrete, which is consistent with the findings of other phylogeographic studies of stygofauna. In this, the first molecular phylogenetic and phylogeographic study of interspecific relationships among parabathynellids, we aimed to explore the hypothesis that species are short-range endemics and restricted to single calcretes, and to investigate whether there were previously unidentified cryptic species. Analyses of sequence data based on a region of the mitochondrial (mt) DNA cytochrome c oxidase 1 gene showed the existence of divergent mtDNA lineages and species restricted in their distribution to a single calcrete, in support of the broader hypothesis that these calcretes are equivalent to closed island habitats comprising endemic taxa. Divergent mtDNA lineages were also observed to comprise four new and 12 recognised morphospecies. These results reflect the findings of previous studies of stygobitic arthropods (beetles, amphipods and isopods) from the Yilgarn region and reinforce the usefulness of using DNA-sequence data to investigate species boundaries and the presence of cryptic species.

Rising from Down Under: developments in subterranean biodiversity in Australia from a groundwater fauna perspective

Over the last two decades, Australia has undergone a renaissance in studies of subterranean biology. This paper sets these recent developments into context from the perspective of groundwater fauna. Owing to its obligate subterranean life, typical local endemicity and the geological persistence of subterranean habitats, stygofauna is an excellent subject for biogeographic study. Groundwater containing diverse faunas range from freshwater to marine salinities in both coastal and continental locations. They occur in typical karst, alluvial, and fractured rock aquifers, but also in novel matrices formed during the hydrogeochemical evolution of groundwater (goethite pisolites and groundwater calcretes) in the Tertiary. This range of habitats, water quality and the diverse origins of the fauna (Gondwanan, Pangaean and Tethys) support a phylogenetically highly diverse fauna. Several taxa, notably among the Podocopida, Bathynellacea, Amphipoda, and Dytiscidae show remarkable species diversity. Typically there is fine spatial scale endemicity of species associated with local aquifers, but there are inexplicable regional differences, such as the change of fauna between the Yilgarn and Pilbara, contiguous areas on the long emergent Western Shield. The anchialine taxa representing higher taxa are highly disjunct from their congeners in the North Atlantic. The emerging species richness, the fine scale patchwork of endemicity, and the distinct regional differences, respectively, contribute to a substantial increase in α, β and γ diversity of the aquatic fauna, especially in arid Australia. This diversity is posing challenging issues for proponents and regulators of mineral development because much of this diversity has emerged in the two most mineraliferous provinces of Australia. The scientific capacity to respond is challenged by the sheer scale of the emerging issues.