Browsing by Author "Spencer, J"

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    Differentiating recharge mechanisms and groundwater inputs in a carbonate aquifer (NW-Queensland, Australia)
    (18th INQUA Congress, 2011-07-21) Van der Ley, M; Cendón, DI; Graham, IT; Spencer, J
    The NW of Queensland is a remote pristine and sparsely populated region with minimal groundwater monitoring infrastructure. This is a semi-arid climatic region with monsoonal fronts between December and March being the main source of precipitation. While yearly rainfall averages 580 mm, evaporation can reach 3000 mm. Only a limited number of streams flowing north into the Gulf of Carpentaria sustain flow through the year. These are exclusively maintained by groundwater discharge during the dry season. Furthermore, all perennial streams share the same headwater lithology, consisting of an ∼80 m thick Cambrian marine-platform carbonate sequence. A number of water samples have been collected from perennial spring discharges and available wells downstream. Preliminary results suggest the presence of several aquifer systems operating at different time scales. The shallow system has short residence times as indicated by 35S activities in stream waters. The very low SO4 concentrations of stream waters (∼1 mg/L) suggests that most sulfur in the shallow system is marine derived and related to the last monsoonal rainfalls events. Intermediate systems discharge into perennial springs with longer residence times, where no 3H activity is detected and 14C activities suggest sub-modern groundwater. The comparison of 87Sr/86Sr and REEs of local lithologies and water samples show the interaction between water, carbonates and Proterozic metasediments. This proves intermediate systems either expand into underlying metasedimentary formations or mix with other sources prior to discharging in the springs. The deepest regional system contains palaeowaters (ca. 9000 a) that may have been partially recharged through carbonate lithologies but mostly flow through underlying Proterozoic metasediments, generally increasing in age towards the N but also mixing with younger waters along deep faults and other regional structural controls such as the Riversleigh impact structure.
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    Hydrogeochemical processes in a monsoon dominated karst environment, NW Queensland
    (Australian Geosciences Council, 2012-08-05) Van der Ley, M; Cendón, DI; Graham, IT; Spencer, J
    The Lawn Hill region, NW Queensland Australia, is host to perennial streams fed by springs from a large karstic aquifer with sub-modern (>50 y) groundwater, developed in Cambrian carbonate lithologies. NW Queensland is subject to semi-arid monsoon climates, and consequently the modern ground and surface waters and their interactions are greatly dependent on seasonal variability of rainfall. We have used a range of techniques to evaluate hydrogeochemical processes including geochemical analysis of host rocks, and a range of isotopic and chemical analyses of ground and surface waters. Samples were collected over multiple sampling campaigns, including during the wet season. Surface waters and groundwaters from carbonate terrains were found to be similarly Ca(Mg) HCO3 type waters as expected from interactions with the karst carbonates, which were found to be composed of primarily dolomite and minor chert. However, there are many indicators (14C, 3H and others) of a more complex system with different temporal scales. Surface waters, while showing dolomitic interactions, have compositions which suggest interaction with underlying silicic lithologies before forming springs. Also, variability in the strength and timing of the monsoon appears to have an effect on activation of different springs and groundwater flow. Additionally, there are groundwaters with much longer residence times (∼6000 a) and chemistries indicative of interaction with silicic and underlying Proterozoic sedimentary units.