Travertine- depositing mound springs of South Australia

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Jack Cade
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Travertine- depositing mound springs of South Australia: key for characterizing
groundwater mixing and paleohydrology in the Great Artesian Basin
Laura Crossey, University of New Mexico, Albuquerque NM, USA
Andrew Love, Flinders University, Adelaide Australia
Karl Karlstrom, University of New Mexico, Albuquerque NM, USA
David R. Hilton
Geosciences Research Division,
Scripps Institution of Oceanography,
La Jolla,
California 92093-0244
USA
Phone: 1 858 822 0639 (office); 822 0716 (lab)
Fax: 1 858 822 3310
[email protected]
Mark Keppel
School of Chemistry, Physics and Earth Sciences
Flinders University
GPO Box 2100, Adelaide, South Australia
AUSTRALIA 5001
Tel:
61-8-82012020 (International) 82012020 (local)
Fax:
61-8-82015635 (International) 82015635 (local)
E-mail:
[email protected]
Geochemistry of water and gas in mound springs provides a window into groundwater mixing in
the GAB. Elevated 3He/4He gas values, termed “xenowhiffs”, provide unequivocal evidence for
deep fluid sources that have been introduced into the groundwater system in the last several
million years and hence an active mantle-to-groundwater fluid linkage. Evaluating fluid and gas
mixing requires use of multiple tracers. We estimate the external (deeply derived) CO2 in water
samples from both travertine (a.k.a. tufa) mound springs and artesian bores using water chemistry
and C isotope data. Contributions from dissolution of carbonate in the aquifer (Ccarb=Ca+MgSO4) is distinguished from contributions from biological/organic sources (d13C= -28) versus
mantle sources (d13C= -5). Of the external C, mixing models using CO2/3He values of 9 x 109
(Warberton Spring) to 2 x 1010 (Bubbler Spring) can be used to model contributions of CO2 from
the asthenospheric mantle (MORB end member taken as 2 x 109) versus lithosphere. Elevated
87
Sr/86Sr values at Dalhousie Spring indicate fluid-rock interactions in granitic crust and small
volume, but geochemically potent, crustal contributions to the endogenic fluids. U-Series dates
indicate persistent deposition of travertine mound springs (conceptualized as “chemical
volcanoes”) at discrete vent sites for millions of years. Travertine- depositing springs are
windows into active and heterogeneous groundwater mixing. Major ion chemistry suggests
different highly variable water chemistry spring to spring, different endmember endogenic fluids,
and variable mixing proportions in different subbasins. Travertine mound springs, coupled with
the associated mound and platform travertine rock record, thus collectively provide a rich record
that can be used to link the present hydrologic system to paleohydrology of the GAB over the last
several million years. Microbiology sampling of springs is underway to also evaluate niches for
Archea and Bacteria associated with these springs. The overall goal is to test a model for
interactions between mantle and deep crustal fluid inputs, neotectonic pathways, groundwater
mixing, groundwater quantity and quality, and unique microbiology in the near-surface
hydrologic systems.
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