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:
GE0-3112 Sedimentary processes and products Lecture 6. Rivers Geoff Corner Department of Geology University of Tromsø 2006 Literature: - Leeder 1999. Ch. 17. Rivers.
RiversGEO-3112 2006 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-3112 2006 ► 1) Rivers are : erosive agents conduits for sediment transport to lacustrine and marine basins.
RiversGEO-3112 2006 ► 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-3112 2006 ► 3) Fluvial deposits are sensitive palaeoenvironment indicators: tectonic slope changes sourceland geology climate sea-level change Postglacial fluvial terraces at Porsanger, N. Norway
RiversGEO-3112 2006 Fluvial channels ► Size and gradient ► Shape (form) ► Processes ► Bedforms and internal structures
RiversGEO-3112 2006 Bankfull width ► Channel size is measured as bankfull width. Channel width Bankfull Normal
RiversGEO-3112 2006 Channel size ► Size varies by four orders of magnitude: <2 m (small streams) >20 km (Brahmaputra, Ganges).
RiversGEO-3112 2006 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-3112 2006 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-3112 2006 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-3112 2006 Downstream changes: Amazon R.
RiversGEO-3112 2006 W E Tectonic disturbance of river profiles across the Himalayan front.
RiversGEO-3112 2006 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-3112 2006 Channel belts Palaeochannels of the Holocene Rhine-Meuse. Stacking patterns – fluvial architecture.
RiversGEO-3112 2006 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-3112 2006 Fluvial incision and knickpoints ► Fall in relative sea-level causes upstream knickpoint migration.
RiversGEO-3112 2006 Depositional architecture and stacking patterns
RiversGEO-3112 2006 Depositional architecture and stacking patterns at Tana Masjok, Tana
RiversGEO-3112 2006 Fluvial architecture
RiversGEO-3112 2006 Ancient fluvial deposits
RiversGEO-3112 2006 Further reading ► Cf. Colloquim literature on fluvial deposits.