Poster Presentation Australasian Groundwater Conference 2017

Age and nature of calcrete accumulations in fluvial sediments: implications for regional groundwater dynamics and landscape evolution (#49)

John W Magee 1 , Ken C Lawrie 1 , Chris Harris-Pascsal 1
  1. Geoscience Australia, Symonston, AUSTRALIAN CAPITAL TERRITORY, Australia

In this study, petrographic and geomorphic analysis of unconsolidated river bank sediments was carried out to provide new insights into groundwater dynamics and lateral bank processes in the Lower Darling Valley. Quaternary geomorphology was mapped in 3D using LIDAR, AEM and temporal Landsat, validated by drilling and field observations. Riverbank calcrete distribution was mapped using boat-mounted photography; petrographic analysis used standard optical microscopy; calcrete ages were determined by radiocarbon dating. Three-dimensional mapping of the Quaternary fluvial systems has demonstrated that calcrete accumulations occur where the river incises relatively coarser-grained sediments in abandoned meander point bars, aeolian dunes or buried paleochannels. Petrographic study suggests that calcrete forms during groundwater discharge localised at river bank sites. Solutional features in calcrete and overprinting relationships with oxides and oxyhydroxides indicate that these discharge sites may also act as recharge sites for the alluvial aquifer. This supposition is supported by bore hydrograph data (Lawrie et al., 2012). The age of calcrete accumulations cluster in periods of river migration identified by OSL dating of quartz grains. This study of the distribution of calcrete in the landscape demonstrates that groundwater-surface water interactions are discontinuous. This has implications for groundwater processes. Calcrete ages cluster in phases of river migration due to the greater likelihood of relatively coarser-grained sediments being exposed on the riverbank during periods of channel migration. Due to the resistance of calcrete to erosion, calcrete formation may play a significant role in controlling the morphology of the Darling River. The relationship between river morphology and calcrete accumulation in the river bank may assist in mapping and predicting sites of lateral bank recharge and groundwater discharge.

  1. Lawrie, K., Brodie, R.S.1, Dillon, P.2, Tan, K.P.1, Gibson, D.1, Magee, J.1, Clarke, J.D.A.1, Somerville, P.1, Gow, L1., Halas, L.1, Apps, H.E.1, Page, D.2, Vanderzalm, J.2, Abraham, J.3, Hostetler, S.4, Christensen, N.B.5, Miotlinski, K.2, Brodie, R.C.6, Smith, M.1 and Schoning, G. 2012 Assessment of conjunctive water supply options to enhamce the drought security of Broken Hill, regional communities and industries. Geoscience Australia record 2012/15
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  • We are offering awards for Career and Early Career presentations and posters. Please indicate length of time since highest degree completed.: 0 to 5 Years or currently studying