Geological basins are one of the two most common places inland which collect sediment (the other is lakes). The type of rocks which form there tell about the palaeoclimate of the continent. The geology is of interest to oil prospectors, hydrologists and palaeontologists.
Causes[change | change source]
- One cause is stretching of the lithosphere (crust + upper mantle). Examples: North Sea; Nevada basin; Death Valley; Red Sea.
- Overthrusting of a continental plate, at a plate boundary, causes the plate to flex. Part goes up, and part goes down. The downward part becomes a foreland basin. Examples: the Ebro basin next to the Pyrenees in Spain; the Molasse and Po River basins next to the Alps.
- Rifting can cause basins, as with the Dead Sea rift.
Death Valley example[change | change source]
Starting around 16 million years ago in the Miocene, and continuing into the present, a large part of the North American Plate has been stretched by being pulled apart.p611 The result has been the creation of a large and still-growing region of relatively thin crust; the region grew an average of 1 inch (2.5 cm) per year initially and then slowed to 0.3 inches (0.76 cm) per year in the last 5 million years. Geologists call this region the Basin and Range Province.
Sediment[change | change source]
Because the basin is low-lying, it collects sediment. Rivers may run down into the basin from surrounding mountains. Floods or lakes may form with no outlet to the sea. Evaporation occurs; more sediment arrives, and so on. The strata which forms gives clues as to the palaeoclimate.
Drainage[change | change source]
Most basins, however, are drainage basins with rivers bringing their water into the sea. Many such rivers meander through a web of islands at the river delta, and bring along a huge amount of sediment in the form of mud, clay and sand. The Amazon and the Mississippi river systems are like this. The strata which form are quite different from inland basin lakes.
References[change | change source]
- Harris, Ann G.; Tuttle, Esther; Tuttle, Sherwood D. 1997. Geology of National Parks. 5th ed, Iowa: Kendall/Hunt Publishing. ISBN 0-7872-5353-7
- Collier, Michael 1990. An introduction to the geology of Death Valley. Death Valley Natural History Association. LCN 90-081612.
- "Hydrologic Unit Geography". Virginia Department of Conservation & Recreation. Retrieved 21 November 2010.
- "drainage basin". www.uwsp.edu. Retrieved 2008-02-21.
- Lambert, David (1998). The field guide to geology. Checkmark Books. pp. 130–13. ISBN 0-8160-3823-6.