Natural controls of fluvial denudation rates in major world drainage basins

Abstract

We present a new compilation of estimates of modern rates of mechanical and chemical denudation for externally drained basins exceeding 5×105 km2 in area. These estimates are based on sediment and solute load data selected in order to represent natural rates as far as possible. Chemical denudation rates have been calculated by deducting the nondenudational component of solute load. Mechanical denudation rates range from 1 mm kyr−1 for the St. Lawrence and Dnepr basins to 670 mm kyr−1 for the Brahmaputra basin. Chemical denudation rates vary from 1 mm kyr−1 (Kolyma, Niger, Nile and Rio Grande basins) to 27 mm kyr−1 (Chiang Jiang basin). The Kolyma basin has the lowest (4 mm kyr−1), and the Brahmaputra basin the highest, overall rate of denudation (688 mm kyr−1). Relationships between denudation rates and a range of morphometric, hydrologic, and climatic variables are investigated through correlation and regression analysis. Morphometric variables, such as mean local relief, are accurately calculated for large basins for the first time by using the National Geophysical Data Center 10‐minute topographic database. Variables expressing basin relief characteristics and runoff are found to be most strongly associated with both mechanical and chemical denudation rates, with more than 60% of the variance in total denudation being accounted for by basin relief ratio and runoff. Basin area, runoff variability, and mean temperature, however, are only weakly associated with rates of denudation. Although direct comparisons cannot be made, it appears that rates of basin denudation derived from present‐day mass flux estimates are not, overall, significantly different from estimates of long‐term rates based on sediment volume and thermochronologic data. It therefore appears that the key factors identified as controlling denudation rates here are also applicable to the geological time spans relevant to the interaction between tectonic and denudational processes.

Crustal redistribution, crust–mantle recycling and Phanerozoic evolution of the continental crust

“…The global study of Meybeck (1976) estimated that dissolved loads were only 20% of the solid fluvial transport load, which we estimate below at 1.8 km 3 /a, implying dissolved transport rates of only around 0.36 km 3 /y. This overall budget has been largely confirmed by more recent studies (Summerfield and Hulton, 1994). More recent studies of weathering of arc crust in the Lesser Antilles Arc argue for lower chemical weathering transport of this type of crust.…”

“…Studies of rivers in more stable continent regions, such as Siberia (Huh and Edmond, 1999) and even in more tectonized Venezuela (Tosiani et al, 2004) would also support rather lower values of dissolved material flux than suggested by Lee et al (2008). As a result we use a value of 0.4 km 3 /a in our mass balance calculations, following the 20% estimate of Meybeck (1976) and Summerfield and Hulton (1994), while recognizing the uncertainties involved in this.…”

South Atlantic continental margins of Africa: A comparison of the tectonic vs climate interplay on the evolution of equatorial west Africa and SW Africa margins

“…Analyses of alterites in Equatorial Africa indicate long term evolution from tropical climate during the late Cretaceous and Paleocene, toward more humid equatorial climate during Neogene (Tardy and Roquin, 1998), culminating in the Congo catchment during the Quaternary, with annual precipitation of 1600 mm. Such elevated precipitation rate induces high runoff values (> 40 litres per seconds) that favours mechanical and chemical weathering (Summerfield and Hulton, 1994). Increasing continental erosion throughout the Oligocene to Present is independently documented by the Strontium isotopic ratio: it increases when continental radiogenic granitoids are eroded and transferred to the oceans (Fig.…”

Analysis of longitudinal profiles along the eastern margin of the Qinghai-Tibetan Plateau

“…In particular the lower reaches of the Yarlung Tsangpo, Nu, Lancang, Yangtze and Yalong Rivers are characterized by extreme relief at the margins of the QTP. Based upon studies elsewhere (Binnie et al 2007;Harrison 2000;Milliman and Syvitski 1992;Montgomery and Brandon 2002;Summerfield and Hulton 1994), this suggests that landscape attributes such as slope or drainage density dynamically adjust to increased tectonic forcing or impact. These changes could potentially Figure 9 A synthesis of the trunk channel longitudinal profiles and their associated erosion patterns draining the eastern margin of the QTP.…”