River terraces (tectonic–climatic interaction)
River terrace formation
Long-lived river (
Age of terraces
Time of incision versus time of aggradation
The ages of incision and flooding (
Dating of these abandoned terrace surfaces (treads) is possible using a variety of geochronologic techniques. The type of technique used, however, is dependent on the composition and age of the terraces. Currently used techniques are magnetostratigraphy, low temperature thermochronology, cosmogenic nuclides, radiocarbon, thermoluminescence, optically stimulated luminescence, and U-Th disequilibria. Additionally, if there is a succession of preserved fossils, biostratigraphy can be used.
Scale of observation
Scale of observation is always a factor when evaluating tectonic and climatic forcing. At a glimpse in geologic time, one of these forcing mechanisms may look to be the dominant process. Observations made on long geologic times scales (≥106
Climate and terraces
Rivers in continental interiors that have not experienced tectonic activity in the geological recent history likely record climatic changes through terracing. Terraces record natural, periodic variations driven by cycles such as the
Tectonic uplift and terraces
In contrast, coastal marine terraces can be preserved only by tectonism or a progressive lowering of sea level. The seismically active coastline of southern California, USA,[6] for example, can be considered an emergent coastline, where tectonism due to transpression provides uplift of shorelines formed during periods of relatively high sea level. Subsequent wave erosion along uplifted portions of the coastline produces an inset wave cut platform and terrace riser below the abandoned marine terrace surface that formed initially at sea level. Uplift can therefore lead to a sequence of marine terraces at a few distinct elevations along the coast. Although these surfaces formed at sea level maxima during interglacial periods, the landforms are preserved solely due to tectonic uplift.
Tectonic–climatic interactions and terraces
Tectonic uplift and climatic factors interact as a
The Himalayas act as an
Tectonic uplift during the creation of high mountainous regions can produce incredible surface elevations and therefore exposure of rocks to wind and water. High precipitation can drive enhanced erosion of the exposed rocks and lead to rapid denudation of sediment from the mountains. Buoyancy of the crust, or isostasy, will then drive further tectonic uplift, in order to achieve equilibrium, as sediment is continuously stripped from the top.[10] Enhanced uplift will then create higher topography, drive increased precipitation which will concentrate erosion, and further uplift.
See also
References
- ^ Leeder, M.R., and Mack, G.M., 2002, Basin-fill incision, Rio Grande and Gulf of Corinth rifts: Convergent response to climatic and tectonic drivers, in, Nichols, G., Williams, E., and Paola, C., eds., Sedimentary Processes, Environments and Basins: A tribute to Peter Friend: International Association of Sedimentologists Special Publication No. 38, p. 9-27.
- ^ Easterbrook, D.J., 1999, Surface Processes and Landforms: New York, New York, Prentice Hall, 546 p.
- ^ a b Blum, M.D., and Tornqvist, T. E., 2000, Fluvial responses to climate and sea-level change: a review and look forward: Sedimentology, 47, p. 2-48.
- ^ Schumm, S., 1979, The fluvial system: Blackburn Press, 338 p.
- ^ a b Einsele, G., Ricken, W., Sielacher, A., 1991, Cycles and events in stratigraphy: basic concepts and terms, in Einsele, G., Ricken, W., and Sielacher, A., eds., Cycles and events in Stratigraphy, New York, Springer-Verlag, pp 1-19.
- ^ Lajoie, K.R., 1986, Coastal Tectonics, in Active Tectonics: studies in geophysics: Washington, D.C., National Academy Press, 266 p.
- ^ Zisheng, A., Kutzbach, J. E., Prell, W. L., and Porter, S. C., 2001, "Evolution of Asian monsoons and phased uplift of the Himalayan–Tibetan plateau since Late Miocene times": Nature, 411, p. 62-66
- ^ Clift, P. D., and Plumb, R. A., The Asian Monsoon: Causes, history and effects: Cambridge, Cambridge University Press, 270 pp.
- ^ Clift, P. D., Tada, R., and Zheng, H., Monsoon evolution and tectonics-climate linkages in Asian:an introduction: Geological Society of London, Special Publications, 342, p. 1–4.
- ^ Pinter, N., and Brandon, M. T., 1997, "How erosion builds mountains": Scientific American, 1997, p. 74–79.