Browsing by Author "Swander, ZJ"

Now showing 1 - 2 of 2
  • No Thumbnail Available
    Item
    Buried, but not forgotten — reconciling climate dynamics with catchment evolution in the East Kimberley using 10Be & 26Al
    (Australian Geosciences Council, 2012-08-05) Swander, ZJ; Dosseto, A; Fink, D; Mifsud, C; Fujioka, T
    In the well entrenched bedrock rivers of northwest Australia, fluvial geomorphic processes rely both on intense energy pulses input to the hydrologic system, and the negation of bedrock choke points or “gates”. Established Quaternary paleoclimate records identify warm and wet interglacial conditions associated with catastrophic flood episodes along the inland Ord River during the Upper Pleistocene. Today, the “neo-Ord” cuts a jagged 600km mixed bed course through the semi-arid landscape of the East Kimberley, when seasonally inundated by monsoon. Beneath the Ivanhoe Plain near Kununnura, up to 30m of pre-Holocene aggraded valley fill obscure the river’s paleo-path to the Joseph Bonaparte Gulf, over 100km from present day mouth. By exploring the links between fluvial activity and monsoon variability, this project aims to constrain the chronology of bedrock channel migration in the transition from older to younger bedrock gates, and any associated incision. This was accomplished by quantifying 16 in situ bedrock minimum exposure ages from 5 study sites across varied lithologies. Terrestrial Cosmogenic Radionuclides (TCN), 10Be and 26Al, are the result of incoming cosmic radiation sparking spallation reactions penetrating ∼50cm of the the bedrock surface. Our results will test the hypothesis that multiple early interglacial intensifications of the regional monsoon, dating back to MIS 11, would provide the catalyst for trunk channel migration and a general disruption of the steady-state. Base level readjustment should manifest most clearly by rapid bedrock incision within gorges, and at back-cutting knickpoint retreats along unconstrained rock bars.
  • No Thumbnail Available
    Item
    Late quaternary fluvial incision and aggradation in the Lesser Himalaya, India
    (Elsevier, 2018-10-01) Dosseto, A; May, JH; Choi, JH; Swander, ZJ; Fink, D; Korup, O; Hesse, PP; Singh, T; Mifsud, C; Srivastava, P
    Reconstructing how rivers respond to changes in runoff or sediment supply by incising or aggrading has been pivotal in gauging the role of the Indian Summer Monsoon (ISM) as a geomorphic driver in the Himalayas. Here we present new chronological data for fluvial aggradation and incision from the Donga alluvial fan and the upper Alaknanda River, as well as a compilation of previous work. In addition to conventional OSL-SAR (Single-Aliquot Regenerative-Dose) dating method, we have tested and applied pulsed OSL (POSL) dating for quartz samples that include K-rich feldspar inclusions, which is expected to improve the applicability and validity of OSL ages in the Lesser Himalaya. For previously dated deposits, our OSL ages are shown to be systematically older than previously reported ages. These results suggest periods of aggradation in the Alaknanda and Dehradun Valleys mainly between ∼25 and 35 ka. This most likely reflects decreased stream power during periods of weakened monsoon. In addition, in-situ cosmogenic beryllium-10 was used to infer bedrock surface exposure ages, which are interpreted as episodes of active fluvial erosion. Resulting exposure ages span from 3 to 6 ka, suggesting that strath terraces were exposed relatively recently, and incision was dominant through most of the Holocene. In combination, our results support precipitation-driven fluvial dynamics, which regulates the balance between stream power and sediment supply. On a larger spatial scale, however, fluvial dynamics are probably not spatially homogeneous as aggradation could have been taking place in adjacent catchments while incision dominated in the study area. © 2018 Elsevier Ltd.