Toward a new paradigm for the Great Artesian Basin: hydrologic mixing, partitioned subbasins, and mantle influences on groundwater quality.
Andrew Love, Flinders University, Adelaide Australia
Laura Crossey, University of New Mexico, Albuquerque NM, USA
Karl Karlstrom, University of New Mexico, Albuquerque NM, USA
David Hilton, Scripps
Brad Wolaver Flinders University, Adelaide Australia
Pauline Rousseau-Gueutin Flinders University, Adelaide Australia
Abstract
The Great Artesian Basin (GAB) underlies 22% of the Australian continent and is one of
the largest groundwater basins in the world. Of great national and societal significance for
Australia, the GAB is also an iconic example of a continental-scale artesian groundwater system
and of international scientific importance as sustainable groundwater management is emerging as
one of the great global scientific challenges of the new millenium. Existing models involve
recharge in Eastern Australia, relatively simple flow paths, and discharge in springs and bores in
the western GAB. New geochemical and hydrologic data suggest these may need modification.
Our hypothesis, based on new geochemical data, is that endogenic fluid inputs into the J-K
aquifer system leak up faults from below the aquifer and cause degradation of water quality. It
has long been known that elevated 3He/4He values are present in groundwater from eastern
Australia (3 RA at Mount Gambier corresponding to 37% mantle helium and 0.81 RA in eastern
GAB, 10% mantle helium). New 3He/4He data from mound springs in the western GAB also
indicate mantle inputs. Warburton Spring has RA= 0.16 (2% mantle helium) with X=30, and
CO2/3He= 9x109; Bubbler Spring has RA= 0.72 (9% mantle helium) with X=3.2 and CO2/3He=
2x1010. These fluids are also rich in CO2, Cl, metals, and radiogenic Sr. Additional studies are
underway as part of an Australian National Water Commission project to evaluate complexities
of mixing models, variable flow rates, variable water quality, and tectonic influences in different
sub-basins of the Great Artesian Basin at different time scales. 1) Hydrologic modeling will
quantify recharge from western and northern sources, 2) CO2/3He values can be used to resolve
asthenospheric, lithospheric, and surface system CO2 contributions, 3) hydrochemical modeling,
stable isotope studies, and 87Sr/86Sr will elucidate contributions from radiogenic basement, 4)
paleohydrology will be approached via modeling of changes in equipotential surface through time
as constrained by U-Series dates from the travertine record, 5) neotectonic studies involve scales
ranging from the mound springs fault line to the Australian plate. New understandings of the
Great Artesian Basin will require holistic models that merge these hydrologic, geochemical, and
tectonic perspectives.