School of Geography - Theses

Permanent URI for this collection

http://hdl.handle.net/11343/208041

Filters

1994 1
Reset filters

Settings
Statistics
Citations
Type: PhD thesis × Start date: 1980 × End date: 1999 × Author: Fabel, Frederik Gysbert ×

Search Results

Now showing 1 - 1 of 1
  • Item
    Thumbnail Image
    Denudation along a passive margin: a study from southeastern Australia
    Fabel, Frederik Gysbert ( 1994)
    This thesis reports the results obtained and conclusions made regarding research into the isostatic effects of denudation and deposition on the post-rifting morphological evolution of the southeast Australian margin. The temporal and spatial variation of denudation since 125 Ma is quantified using geomorphological and apatite fission track analysis (AFTA) data. Depositional data for the Gippsland Basin is derived from isopach maps. Reference surfaces for the volumetric calculations of material removed and deposited are based on 2 x 2 km gridded data. On the basis of modelling the thermal and mechanical effects of denudation on the thermal structure of the lithosphere it is assumed that rifting related thermal overprinting did not occur in the AFTA samples. Hence the estimated thicknesses of crustal section removed by denudation are maxima. The denudation and deposition data are used as applied loads in one- and twodimensional continuous elastic plate models to determine the isostatic response of the margin. Results on the spatial and temporal variation of denudation indicate that from 125 Ma to 60 Ma a maximum of 3.6 km of crustal section has been removed from the southeast Australian margin. The amount of material removed generally decreases from the coast inland, supporting a model of margin evolution where the morphology of the margin is largely the result of the retreat of a major erosional escarpment. Rates of denudation have varied considerably in the last 125 Ma, suggesting that previously argued post Cretaceous landscape stability for the area is incorrect. The isostatic response of the margin suggests that within the limitations of the model used, the morphological evolution of the margin can be explained without the need for postrifting tectonic surface uplift. The maximum amount of surface uplift generated by the escarpment retreat model is in the order of 500 m along the boundary between the elevated tablelands and the escarpment. Deposition in the Gippsland Basin does not significantly change the amount of predicted surface uplift, however, it does change the spatial distribution of the uplift. Evidence from the Towamba and Snowy River valleys suggests that escarpment retreat has been slowed considerably since the early Tertiary. This may be due to changes in the drainage pattern of the margin associated with the uplift of the Kosciusko Block and river capture. The results provide some answers to contentious issues raised by geomorphologists and thermochronologists about the timing of uplift and overall morphological evolution of the southeast Australian margin. These conflicts appear to be largely due to differences in terminology and definitions, as well as extrapolations of results beyond the constraints of the data.