关键词: 河流阶地, 黄河, 形成年代

Abstract:

Based on field work, four Quaternary terraces are found according to overlapped loess sequences at Pantang-Heiyukou area and its surroundings in northern Chinese Shanxi-Shaanxi Gorge. These four terraces, which are 12, 50, 80 and 130 m above present the Yellow River level respectively, are all rock-seated terraces. The thicknesses of overlapped loess from the lowest terrace to the highest Quaternary terrace are about 20, 33, 37 and 43 m respectively. ESR dating samples were collected from river sediments on T2, T3 and T4. ESR dating result reveals that the formation ages of these three terraces are 0.609, 0.876 and 0.97±0.107 Ma in turn from T2 to T4. In order to corroborate the dating results, powder samples and oriented samples were collected from sections on T3 and T4. Paleomagnetic result shows that section bottom on T3 does not reach the boundary of B/M (Brunhes/Matuyama), which means a formation age younger than 0.78 Ma. This age is younger than that gotten from ESR dating. The bottom age of T4 section reaches an age of 1.07 Ma, which is a bit older than ESR dating result but within its range. The formation ages of the terraces are in accord with other terraces in upper and lower reach of the Yellow River such as Lanzhou and Sanmenxia which suggests river terraces controlled by tectonic movement exist universally in the domain of the Yellow River. A Late Tertiary section was resampled and measured as an improvement to former works. The result is used to discuss the incision rate of different terraces in this region.

Key words: river terraces, the Yellow River, formation age