Pliocene uplift of the northern Tibetan Plateau

Neogene redbeds passing upward into upward-coarsening conglomerate and debr is-flow deposits at the foot of the Kunlun Mountains record the change in p aleoslope related to uplift of the surface of the northern Tibetan Plateau. Detailed magnetostratigraphy of a 4.5 km section near Yecheng in the weste rn Kunlun Mountains shows that the change from deposition on distal alluvia l plains to proximal alluvial fans occurred during the Gilbert reversed chr on (4.5-3.5 Ma). The change in depositional facies was accompanied by an in crease in sedimentation rate from an average similar to 0.15 mm/yr between the earliest Oligocene and the earliest Pliocene to 1.4 mm/yr in the Gauss normal chron (3.6-2.6 Ma). We interpret the change in depositional facies a nd increase in sedimentation rate as indicating that the main uplift of the northwestern Tibetan Plateau began ca. 4.5 Ma.