Existing facies models of rift basin evolution are biased towards humid climatic regimes. This study uses geomorphic and sedimentologic observations from the actively extending, arid to semi-arid Basin and Range Province, Western U.S.A., to critically assess the applicability of the existing models to dryland regions. This was achieved by documenting the range of landscape responses to extensional tectonism in drylands, with the subsequent development of a revised, dryland specific, extensional basin facies evolution model. The geomorphic and sedimentologic character of six representative modern basins was mapped, and their facies proportions calculated. Key observations are the rarity of well-integrated exogenic fluvial systems and the resulting dominance of sediments issuing out of transverse catchments. The landscape maturity of the basins was quantified in order to compare their facies distributions within an evolutionary framework, serving as a proxy for rift phase. Syn to post rift facies evolution is characterised by: 1) a progression with drainage evolution from mixed debris and stream flow to stream flow dominated processes in marginally derived alluvium; 2) the inundation of playa facies as marginal facies prograde into increasingly central positions; 3) the resultant loss of facies asymmetry; 4) increasingly homogenised basinal facies, as longer sediment residence times at the surface allow for greater potential reworking; 5) a reduction in marginal catchment relief. Observations from the modern basins were tested against the Miocene to Recent post rift basin fill of the Virgin River Depression. Existing models suggest the dominance of axial fluvial sedimentation throughout the life of extensional basins. Findings of this study show that longitudinal fluvial sedimentation in dryland basins is, however, limited and if present, more likely to be restricted to the later, post rift stages of basin evolution.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:439986 |
| Date | January 2006 |
| Creators | Fordham, Alexandra M. |
| Publisher | University of Aberdeen |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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