Inferring regolith history via in situ Rb-Sr dating, mineral mapping, and elemental analysis at the Avon River Critical Zone Observatory, Western Australia

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dc.contributor.authorSchultz, M.
dc.contributor.schoolSchool of Physical Sciencesen
dc.date.issued2022
dc.descriptionThis item is only available electronically. Whole thesis (as available).
dc.description.abstractThe critical zone is the interface between atmo-, bio-, hydro-, and lithospheres which supports all terrestrial life. Within this complex system, regolith forms as weathered bedrock products coalesce on the surface, providing anchorage and accessibility to essential nutrients and water for plants and associated microbiota. Productivity within the regolith therefore has significant implications for all heterotrophic lifeforms. Global establishment of Critical Zone Observatories concentrate efforts on understanding this system and the long-term response to anthropogenic influences. This study contributes to this cause, defining baseline geochemical and mineralogical compositions at bulk- and micro-scales for regolith within the Avon River Critical Zone Observatory. This study also addresses novel in situ Rb-Sr dating as a method to separate abiotic and biotic pedogenic mechanisms. Sodium peroxide fusion and ICP-OES is compared against acid digestion and ICP-MS methods to determine a viable immobile index element. Subsequent ‘normalised’ elemental concentration profiles are produced which account for volume changes and relative loss or gain of elements through vertical section. Elemental profiles reflect gradual, or near complete depletions of all elements, excluding Al, Si and Fe-Al metal-oxide species, that relate to a matured rudimentary mineral assemblage of kaolinite, quartz, and Fe-Al-oxide species. Subsequent Rb-Sr dating of clays (i.e., chlorite, illite), micas and feldspars indicate that biotite within the monzogranitic bedrock is of Neoarchean age (2673.4 ± 56.1 Ma (n = 21)) whilst bordering chlorite and feldspars reflect a younger ‘apparent’ age of 2400.5 ± 60.2 Ma (n = 60). Interestingly, Rb-Sr dating of illite also reflect this younger ‘apparent’ age within error across all lower regolith horizons, suggesting inheritance of (87Sr/86Sr)o ratios during authigenic weathering of feldspar and clay precursors. This concludes that pedogenesis in the lower regolith horizons was of abiogenic origin but absence of illite in the upper horizons does not entirely discount biotic involvement.
dc.description.dissertationThesis (B.Sc.(Hons)) -- University of Adelaide, School of Physical Sciences, YEAR
dc.identifier.urihttps://hdl.handle.net/2440/146277
dc.language.isoen
dc.provenanceThis electronic version is made publicly available by the University of Adelaide in accordance with its open access policy for student theses. Copyright in this thesis remains with the author. This thesis may incorporate third party material which has been used by the author pursuant to Fair Dealing exceptions. If you are the author of this thesis and do not wish it to be made publicly available, or you are the owner of any included third party copyright material you wish to be removed from this electronic version, please complete the take down form located at: http://www.adelaide.edu.au/legalsen
dc.subjectHonours
dc.subjectGeology
dc.subjectregolith
dc.subjectpedogenesis
dc.subjectRb-Sr dating
dc.subjectCritical Zone Observatory
dc.subjectAvon River
dc.subjectYilgarn Craton
dc.titleInferring regolith history via in situ Rb-Sr dating, mineral mapping, and elemental analysis at the Avon River Critical Zone Observatory, Western Australia
dc.typeThesis

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