Episodic fluvial incision of rivers and rock uplift in the Himalaya and Transhimalaya

Abstract

Abstract: Seventeen strath terraces in northern India were dated using 10 Be surface exposure methods; ages range from c . 7 to c . 735 ka and provide fluvial incision rates of 0.02 ± 0.003 to 2.6 ± 1.9 mm a −1 . On the northern side of the Ladakh Range, incision rates are c . 1 mm a −1 ; in the northern Zanskar Range they are ≤0.06 ± 0.005 mm a −1 . New and published incision rates in southernmost Lahul range from 0.1 ± 0.02 to 13.2 ± 6.2 mm a −1 ; rates for ages >35 ka are ≤0.4 ± 0.2 mm a −1 . Across the Himalaya and Transhimalaya, Holocene fluvial incision rates range from c . 0.02 to c . 26.0 mm a −1 , whereas Pleistocene incision rates are ≤5 mm a −1 . Many of the Holocene incision rates exceed exhumation rates, whereas Pleistocene incision rates are comparable with exhumation rates. This suggests that long-term fluvial incision is in dynamic steady state with exhumation. The temporal pattern for rates of fluvial incision is probably controlled by episodic incision linked to significant precipitation changes throughout the Quaternary, suggesting that strath terraces with ages >35 ka can be used for assessing long-term rates of rock uplift. In contrast, rates of fluvial incision based on Late Glacial and Holocene strath terraces reflect changes in monsoon intensity and deglaciation events. By determining ages for multiple samples on flights of strath terraces, it is possible to document changes in incision rate, assess whether post-abandonment transient shielding has occurred, and help elucidate tectonic v. climatic controls on their formation. Supplementary material: Tables (DS1–4) for previously published data and recalculated ages for strath terraces, and figures (DS1 and DS2) showing plots of incision rates against time for the Himalaya and Transhimalaya are available at http://www.geolsoc.org.uk/SUP18454 .