Fluvial and tectonic geomorphology of orogenic plateaux

Abstract

Geomorphology is an expression of processes acting upon an area. The links between driving processes and the resulting geomorphology are far from being fully understood. This thesis investigates controls on the dynamics and behaviour of fluvial systems from the interior of orogenic plateaux to the tectonically active plateaux margins. Orogenic plateaux provide a good study area by juxtaposing different tectonic and climatic settings that are served by the same sediment transport systems, allowing for observation of different variables on the same or similar fluvial systems. This is the first time that rivers draining orogenic plateaux have been extensively investigated.
The Turkish-Iranian and Tibetan plateaux are the study areas. Forms of rivers draining from plateaux interiors, through the plateaux margins are analysed, along with alluvial fans within both the plateaux interior and plateaux margins. Plateau draining rivers act as the major route for material leaving the plateau region and a first-order control on erosive processes retarding plateau growth. Alluvial fans redistribute material within the plateau interior, enhancing the low relief topography diagnostic of a plateau.
It is found that rivers draining plateaux show a sigmoidal form associated with the edge of the plateaux. High gradients and curvatures occur within the mountain ranges at the plateaux margins, while low values are present within the plateau interiors. Modelling work demonstrates that such forms to be likely responses for all plateau-draining rivers, but are most sensitive to the effects of precipitation upon a river’s ability to incise in-to the underlying sedimentary cover and bedrock lithologies.
Alluvial fans in orogenic plateau regions are larger and with a lower surface gradient within the plateau interior than those nearer the active tectonic margins. It is theorised that this is due to the lack of lateral control on the accommodation space of alluvial fans within the plateau interior.