Browsing by Author "Bestland, EA"

Now showing 1 - 3 of 3
  • No Thumbnail Available
    Item
    Catchment-scale denudation and chemical erosion rates determined from 10Be and mass balance geochemistry (Mt. Lofty Ranges of South Australia)
    (Elsevier, 2016-10-01) Bestland, EA; Liccioli, C; Soloninka, L; Chittleborough, DJ; Fink, D
    Global biogeochemical cycles have, as a central component, estimates of physical and chemical erosion rates. These erosion rates are becoming better quantified by the development of a global database of cosmogenic radionuclide 10Be (CRN) analyses of soil, sediment, and outcrops. Here we report the denudation rates for two small catchments (~ 0.9 km2) in the Mt. Lofty Ranges of South Australia as determined from 10Be concentrations from quartz sand from the following landscape elements: 1) dissected plateaux, or summit surfaces (14.10 ± 1.61 t km− 2 y− 1), 2) sandstone outcrops (15.37 ± 1.32 t km− 2 y− 1), 3) zero-order drainages (27.70 ± 1.42 t km− 2 y− 1), and 4) stream sediment which reflect a mix of landscape elements (19.80 ± 1.01 t km− 2 y− 1). Thus, the more slowly eroding plateaux and ridges, when juxtaposed with the more rapidly eroding side-slopes, are leading to increased relief in this landscape. Chemical erosion rates for this landscape are determined by combining cosmogenic denudation rates with the geochemical mass balance of parent rock, soil and saprolite utilizing zirconium immobility and existing mass balance methods. Two different methods were used to correct for chemical weathering and erosion in the saprolite zone that is shielded at depth from CRN production. The corrected values are higher than uncorrected values: total denudation of 33.24 or 29.11 t km− 2 y− 1, and total chemical erosion of 15.64 or 13.68 t km− 2 y− 1. Thus, according to these methods, 32–40% of the denudation is taking place by chemical weathering and erosion in the saprolite below CRN production depth. Compared with other similar areas, the overall denudation and chemical erosion rates are low. In most areas with sub-humid climates and tectonic uplift, physical erosion is much greater than chemical erosion. The low physical erosion rates in these Mt. Lofty Range catchments, in what is a relatively active tectonic setting, are thought to be due to low rainfall intensity during the winter wet season, which inhibits physical erosion such as land-sliding and debris flows.© 2016 Published by Elsevier B.V.
  • No Thumbnail Available
    Item
    Catchment-scale groundwater-flow and recharge paradox revealed from base flow analysis during the Australian Millennium Drought (Mt Lofty Ranges, South Australia)
    (Springer Nature Limited, 2021-01-30) Anderson, TT; Bestland, EA; Wallis, I; Kretschmer, PJC; Soloninka, L; Banks, EW; Werner, AD; Cendón, DI; Pichler, MM; Guan, H
    Catchment-scale recharge and water balance estimates are commonly made for the purposes of water resource management. Few catchments have had these estimates ground-truthed. One confounding aspect is that runoff and soil-water inputs commonly occur throughout the year; however, in climates with strong dry seasons, base flow can be directly sampled. In an experimental catchment in the Mt. Lofty Ranges of South Australia, run-of-stream hydrochemical parameters were monitored. In this Mediterranean climate during the Millennium Drought (2001–2009), the stream was reduced to disconnected groundwater-fed pools. Two groundwater types were identified: (1) high-salinity type from meta-shale bedrock with thick, clayey regolith and (2) low-salinity type from meta-sandstone bedrock with sandy regolith. End-member mixing using silica and chloride concentrations and robust 87Sr/86Sr ratios reveal an apparent groundwater-flow paradox as follows. According to chloride mass balance and spatial distribution of hydrogeological units, the low-salinity groundwater type has seven times more recharge than the high-salinity type. Over the 28-year record, low-salinity groundwater contributed 25% of stream water, whereas high-salinity groundwater contributed 2–5%. During the drought year, however, annual stream flow from the high-salinity groundwater contributed 50%, whereas low-salinity groundwater contributed 18%. High-salinity groundwater dominated dry-season base flow during all years. The paradox can be resolved as follows: The meta-sandstone terrane drains quickly following wet-season recharge and therefore contributes little to dry-season base flow. Conversely, the meta-shale terrane drains slowly and therefore provides stream flow during dry seasons and drought years. © 2021 Springer-Verlag GmbH Germany, part of Springer Nature.
  • No Thumbnail Available
    Item
    Chronology, stratigraphy and palaeoenvironmental interpretation of a Late Pleistocene to mid-Holocene cave accumulation on Kangaroo Island, South Australia
    (Wiley-Blackwell, 2013-10-01) McDowell, MC; Bestland, EA; Bertuch, F; Ayliffe, LK; Hellstrom, JC; Jacobsen, GE; Prideaux, GJ
    Chronological, sedimentological and geochemical analyses of a clastic infill from Kelly Hill Cave (5K1), Kangaroo Island, document a palaeoenvironmental record that spans from the Late Pleistocene to the middle Holocene. We AMS radiocarbon-dated bone collagen and U-Th-dated speleothem to determine that fossiliferous sediments were deposited between >20ka and 7ka ago. Most of the 15 sedimentary layers are dominated by sand- and silt-sized quartz that is physically and geochemically comparable with surface soils in the Kelly Hill area. Late Pleistocene and Last Glacial Maximum strata are represented primarily by homogeneous, poorly sorted quartz-rich sediments that contain little organic matter, but include a thin layer composed largely of silt-sized clay pellets that resemble sediments deflated from playa lakes. Microstructures observed in petrographic slides indicate that, with the exception of one layer, all sediments experienced little reworking once deposited in the cave. Some layers display pedogenic microstructures such as redeposited clays and opaline silica infilling that indicate postdepositional modification; that is, cave-floor soil development. Overlying Holocene-aged sediments also consist mainly of quartz but have much greater organic matter content. Some of these sediments have been strongly influenced by re-precipitated organic matter that appears to have been transported into the cave via vadose drip water. The presence of dissolved organic matter in soil/vadose waters suggests a high vegetation density and acidic soils, which are congruent with the more equitable climatic conditions characteristic of the Holocene. The sediments described here provide a valuable palaeoenvironmental record that will facilitate future interpretation of associated vertebrate fossils. © 2013, Wiley-Blackwell.