Groundwater tracing with nucleogenic 36Cl in West Canning Basin, Western Australia

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dc.contributor.authorWilcken, KMen_AU
dc.contributor.authorCendón, DIen_AU
dc.contributor.authorMeredith, KTen_AU
dc.contributor.authorSimon, KJen_AU
dc.contributor.authorStopic, Aen_AU
dc.contributor.authorPeterson, MAen_AU
dc.contributor.authorHankin, SIen_AU
dc.date.accessioned2022-01-25T01:27:04Zen_AU
dc.date.available2022-01-25T01:27:04Zen_AU
dc.date.issued2017-04-26en_AU
dc.date.statistics2022-01-11en_AU
dc.description.abstractChlorine-36 has been used over the past 20-30 years as a groundwater tracer in many hydrological studies and is a well-established dating technique. Given the half-life of 301 kyr it is well suited for dating of ‘old’ groundwater between 50 kyr - 1 Myr. A challenge associated with utilising 36Cl as a tracer is that it can be produced via three different pathways that will influence the result based on the unique hydrogeological setting of a study area. Typically the dominant source of 36Cl in groundwater is atmospheric 36Cl that is produced at troposphere and stratosphere via interaction of cosmic-ray protons and secondary neutrons with Ar. However, the secondary cosmic-ray neutrons can similarly produce 36Cl in surface rocks particularly at high elevations. Also nucleogenic production of 36Cl at subsurface environments can become significant, especially if U and/or Th concentrations are high. Delineating and quantifying these processes is essential when using 36Cl as a groundwater dating tool. In contrast to a conservative situation where atmospheric 36Cl dominates, we present a study in the West Canning Basin located in the Pilbara region of Western Australia, where the 36Cl/Cl ratio increases from 30 10-15 near the recharge zone to 100 10-15 over a 60 km of flow path within a confined aquifer. Additional isotopic evidence (14C and 87Sr/86Sr) in groundwater, mineralogy (X-Ray diffraction) and elemental analysis (Neutron Activation) of whole-rock powder samples from the aquifer and overlying geological units, is used to establish an interpretation that nucleogenic 36Cl production is effectively the only potential process to explain the data. Nucleogenic production can influence the groundwater 36Cl content in two different ways: (1) as an additional input of Cl with a 36Cl/Cl ratio that reflects the neutron flux within the particular mineralogy; or (2) via “in-situ” production of 36Cl directly in the groundwater from the dissolved 35Cl where the rate is dictated by the neutron flux in the aquifer and the residence time. For this study, the whole-rock elemental composition is used to calculate the nucleogenic production within the aquifer and confining units of the groundwater system. This effectively ruled out both the Wallal sandstone aquifer and the overlying confining unit of the Jarlemai clay aquitard as the sources of 36Cl. Here we explore the idea that the underlying granite is the most likely source of 36Cl. © Author(s) 2017. CC Attribution 3.0 License.en_AU
dc.identifier.citationWilcken, K., Cendón, D. I., Meredith, K., Simon, K., Stopic, A., Peterson, M., & Hankin, S. (2017). Groundwater tracing with nucleogenic 36Cl in West Canning Basin, Western Australia. Paper presented at the European Geosciences Union General Assembly 2017, Vienna, Austria, 23–28 April 2017. Retrieved from: https://meetingorganizer.copernicus.org/EGU2017/EGU2017-6848en_AU
dc.identifier.conferenceenddate28 April 2017en_AU
dc.identifier.conferencenameEuropean Geosciences Union General Assembly 2017en_AU
dc.identifier.conferenceplaceVienna, Austriaen_AU
dc.identifier.conferencestartdate23 April 2017en_AU
dc.identifier.journaltitleNuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atomsen_AU
dc.identifier.otherEGU2017-6848en_AU
dc.identifier.otherHS8.2.7en_AU
dc.identifier.urihttps://meetingorganizer.copernicus.org/EGU2017/EGU2017-6848.pdfen_AU
dc.identifier.urihttps://apo.ansto.gov.au/dspace/handle/10238/12720en_AU
dc.language.isoenen_AU
dc.publisherEuropean Geosciences Unionen_AU
dc.subjectGround wateren_AU
dc.subjectTracer techniquesen_AU
dc.subjectWestern Australiaen_AU
dc.subjectAustraliaen_AU
dc.subjectCarbon 14en_AU
dc.subjectTroposphereen_AU
dc.titleGroundwater tracing with nucleogenic 36Cl in West Canning Basin, Western Australiaen_AU
dc.typeConference Abstracten_AU
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