Figure 1

(a) Simplified map of major tectonic boundaries and Tertiary faults in the Northeastern Tibetan Plateau (after Dai et al., 2006); (b) Morphologic characteristics of the NETP derived from Aster Global Digital Elevation Model data"

Figure 2

Terrace sequence along a schematic section in the Xining basin (modified after Lu et al., 2004a, and Vandenberghe et al., 2011)"

Figure 3

Histogram of De distribution for typical samples in Menyuan basin using small aliquots (after Wang et al., 2013)"

Figure 4

Schematic diagram illustrating the geomorphologyical evolution of the Xining basin and the formation of the relict surface (modified after Wang et al., 2012). Firstly, the tectonic basin was formed before the Mesozoic (I). Then, the surrounding mountains eroded and the basin was filled (II,i). As a last stage in this step, limited and very local erosion in the basin might have slightly lowered the surface formed in II (i), ultimately resulting in the formation of a peneplain surface (II, ii). Finally, tectonic uplift caused the Huangshui to incise vertically into the surface, producing a terrace sequence (III)."

Figure 5

Sedimentologic character of the erosion terrace (a) and the accumulation terrace (b) in the Huangshui catchment"

Figure 6

The formation model of the terrace in Huangshui catchment (modified after Wang et al., 2010). Firstly, the fluvial balance state is crossed because of climatic change or tectonic and the river incisions, until reaching to a new balance state; Secondly, the tectonic subsidence happens in the blocks, and an intensified erosion in upstream while a huge volume of sediments supplied deposit quickly in the subsidence depression. Finally, the river incises in the whole catchment, caused by climatic changes such as increasing of the precipitation and the reducing of the sediment load caused by the relevant development of the vegetation cover or tectonic uplift, and the accumulation terraces are formed in the subsidence depressions while the erosion terraces or no terrace are formed in upstream blocks."

Figure 7

DEM of the Minhe subsided block with the transition to the Laoya gorge in the left upper corner"

Figure 8

Fault scarp at the boundary between the Laoya block composed of hard rock and the Minhe depression underlain by soft sediments"

Figure 9

Terrace sequence at the exit of the Laoya gorge and the transition to the western most part of the Minhe basin, and the relation to fault activities (modified after Vandenberghe et al., 2011). Firstly, incision occurred from 271 to 197 m, due to regional tectonic uplift. Secondly, uplift continued in the Laoya block, while the Minhe block subsided, leading to the accumulation of 30 m gravel (terrace at +200 m). Subsequently, uplift was dominant everywhere, resulting in the formation of a series of erosion terraces in the Laoya block between +197 and 100 m; while only one erosional terrace was preserved in the tectonic depression at +100 m. Finally, the recent fault activity, resulted in sharp vertical erosion in Laoya block, while subsidence prevailed in Minhe depression, leading to the formation of two accumulation terraces at 60 and 44 m."

Figure 10

Characteristic sedimentary sequences of terraces: (a) Planar sheets of gravel alternating with finer grained, shallow, trough cross-bedded channels of 44 m terrace above present floodplain in Ledu basin; (b) inter-bedded layers of horizontally-laminated silt reworked soil filling shallow channels; (c) aggradation sequence of -40 m terrace above present floodplain in the eastern part of the Minhe depression; (d) horizontally laminated silts occasionally containing gravel strings of limited extent of 22 m terrace above preset floodplain at east Minhe depression"

Figure 11

(a) Terrace distribution in the confluence region of the Huangshui and Huanghe rivers (modified after Wang et al., 2014). (b) A selected topographic section from Figure 11a, illustrating a typical terrace sedimentary sequence. U1, U2, U3 are the sedimentary units of the terraces (U1: stacked fluvial gravels of varying thickness with inter-bedded sand lenses, U2: cross-stratified sands, U3: inter-bedded layers of horizontally-laminated silt and sands.)"

Figure 12

Comparison of the age of terraces (T2, T3, T4, T5, T6 and T7) and periods of fluvial deposition (at top) with climatic evolution recorded by the grain-size record of loess deposits at GL (gray) (Sun et al., 2012) and YZ (red) (Lu et al., 2004b) in the NETP (modified after Wang et al., 2015). Green, black and blue codes of ages and errors (2σ error bars at top) correspond to sedimentary units (U1, U2, and U3, similar to that in Figure 11), respectively. Numbers indicate marine isotope stages and substages. Age of loess deposit sequence is based on 20 OSL datings of GL by Sun et al. (2012) and correlation to marine isotope stages in YZ (Lu et al., 2004b)."

Figure 13

Schematic diagram illustrating the terrace formation in response to climatic change in the confluence of Huangshui and Huanghe. U1, U2, U3 are the sedimentary units of the terraces, similar to that in Figure 11."