Presentation on theme: "GE0-3112 Sedimentary processes and products Lecture 6. Rivers Geoff Corner Department of Geology University of Tromsø 2006 Literature: - Leeder 1999. Ch."— Presentation transcript:
GE Sedimentary processes and products Lecture 6. Rivers Geoff Corner Department of Geology University of Tromsø 2006 Literature: - Leeder Ch. 17. Rivers.
RiversGEO Importance of fluvial systems ► 1) Rivers are major erosive and sediment transport agents. ► Fluvial sediments are mostly transient but may form thick deposits in several settings. ► Fluvial deposits are sensitive palaeoenvironment indicators.
RiversGEO ► 1) Rivers are : erosive agents conduits for sediment transport to lacustrine and marine basins.
RiversGEO ► 2) Fluvial sediments are mostly transient but form thick deposits in several settings: coastal plains intermontane basins tectonic forelands Modern and Holocene terraced fluvial deposits at Tana, N. Norway.
RiversGEO ► 3) Fluvial deposits are sensitive palaeoenvironment indicators: tectonic slope changes sourceland geology climate sea-level change Postglacial fluvial terraces at Porsanger, N. Norway
RiversGEO Fluvial channels ► Size and gradient ► Shape (form) ► Processes ► Bedforms and internal structures
RiversGEO Bankfull width ► Channel size is measured as bankfull width. Channel width Bankfull Normal
RiversGEO Channel size ► Size varies by four orders of magnitude: <2 m (small streams) >20 km (Brahmaputra, Ganges).
RiversGEO Channel size vs. discharge ► Discharge increases with increasing width, depth and velocity. ► Discharge, width, depth and velocity all increase downstream. Q = whu Discharge Channel width Channel depth Mean flow velocity
RiversGEO Width vs depth ► Depth (h) increases with increasing width (w). ► W/h ratios are higher in low-sinuosity rivers. High sinuosity (low w/h ratios) Low sinuosity (high w/h ratios) NB: Symbols erroneously reversed
RiversGEO Long profile ► Downstream changes (in effluent streams): Discharge increases. Gradient decreases (the flow is more efficient; with increased discarge the gradient must decrease to maintain equilibrium). Graded river: concave long- profile.
RiversGEO Downstream changes: Amazon R.
RiversGEO W E Tectonic disturbance of river profiles across the Himalayan front.
RiversGEO Avulsion and channel belts ► Sudden shift in channel reach (bend cutoff) or whole channel belt. ► Controlled by internal (autocyclicity) or external factors (base-level, climate, tectonics). ► Diversion more likely during extreme flood events or fault movement.
RiversGEO Channel belts Palaeochannels of the Holocene Rhine-Meuse. Stacking patterns – fluvial architecture.
RiversGEO Incision – aggradation cycles ► Regional cycles of incision and aggradation may occur on the scale of decades or more. ► Causes may be ’intrinsic’ or extrinsic, e.g: water and sediment discharge variations controlled by climate and catchment characteristics (e.g. ENSO). eustatic sea level changes. tectonics.
RiversGEO Fluvial incision and knickpoints ► Fall in relative sea-level causes upstream knickpoint migration.
RiversGEO Depositional architecture and stacking patterns
RiversGEO Depositional architecture and stacking patterns at Tana Masjok, Tana
RiversGEO Fluvial architecture
RiversGEO Ancient fluvial deposits
RiversGEO Further reading ► Cf. Colloquim literature on fluvial deposits.