摘要
岱海盆地位于鄂尔多斯周缘断裂系的东北角,总体走向NEE,南北两侧均由断裂控制。岱海盆地南缘分布两条平行于边界断裂的地貌陡坎,延伸方向65°,总长约20km,形似断层陡坎。本文用开挖探槽、分析地层沉积过程的方法,查明了这两条地貌陡坎均为全新世形成的湖岸阶地的前缘陡坎,不是断裂活动错断地表的结果。结合全新世的气候资料,分析了湖岸阶地的形成时间和过程。一级陡坎形成于2115±80aB.P.之后,记录了最后一次高湖面的位置;二级陡坎形成于10000aB.P.至6165±105aB.P.之后,即全新世暖期开始之后的第一次湖侵至岱海第二次大的湖侵期。二级陡坎地层沉积记录了两次大的湖进湖退过程,第一次湖进时间为10000aB.P.,湖退时间9450±1260aB.P.;第二次湖进时间6700aB.P.,湖退时间6165±105aB.P.,其间有一次级湖退过程,时间为7620±930aB.P.。两级阶地前缘陡坎的形成时间与孢粉等记录的中国北方全新世温度变化相对应。
Daihai basin locates in the northeast corner of active fauh system around Ordos Massif. It is a young basin on the Inner Mongolian Plateau, which formed with the basalt eruption since the Miocene. The strike of its microaxis is NEE. Both the north and south sides are controlled by faults. There are two parallel surficial scarps with a length of 20 kilometers lie in the south of basin. They own the strike of 65 ° and are similar to the scarps caused by the activity of faults. However, besides the activity of faults, scarps in the unconsolidated deposit are also caused by some Earth＇ surface reforming process. Such as the erosion of the running water, differential settlement of the ground, and even the solidification process of sand caused by plants. Through this research, with the method of trench observations and the analysis of sediment in layers, we find out that both the two scarps are not caused by fault activity but the front edges of lacustrine terraces formed since the Holocene. We carry out the research in different ways. First, with the detailed field survey we measured the different height and shape of the two surficial scarps. It shows that the height of the first scarp is 1.0 - 5.5m and the second scarp is 2 - rim,the elevation of the first scarp is 1230m and the second scarp is 1240m. Each of the two scarps lies on the same contour line. A few section of the scarps are destroyed by the river-erosion. Second,we studied the stratum of basion and the area in the front of mountain. To find out the sediment form of the two scarps and the layer under the scarp, we separately excavated two trench across the first scarp and the second scarp in Xishaliang village and Baimiaozi village. The size of the trenches is about 22m long,5m wide,and 6.5m deep. The stratigraphic section exposed in the trench across the first scarp shows that, the sediment of the first scarp environment. And the layers are continuous, horizontal, and is sil.ty clay which indicates deep lake depositional straight. So, it indicates that the formation of first scarp is influenced little by the change of water level near the lakeshore. It was formed during the latest large-scale lacustrine regression. The stratigraphic section exposed in the trench across the second scarp shows that,the bottom of the second scarp is silty clay which indicates deep lake depositional environment. The continuous layers shows no active faults. But the upside sections of the leading edge and the trailing edge are not continuous. The sediment of leading edge is sand mixed with small spiral shell fossils which indicates depositional environment of lakeshore. The sediment of trailing edge shows two period loess and between them there are lacustrine clay mixed with spiral shell fossils and gravel layer. The pattern of loess and the sediments above it indicates a period of lacustrine advance and lacustrine regression. So two large-scale lacustrine advance and regression could be seen from the sediments. Third, with the reference of the climate information since the Holocene,we discussed the formation time and depositional model of the lacustrine terraces. And with the optically stimulated luminescence method （OSL） , we dated some of the geologic sections. The first terrace formed after 2115±80aB. P., recording the last high lake-level. The second terrace formed during 10000an. P. to 6165± 105an. P., that is since the first lacustrine transgression after the Holocene warm period to the second large scale lake transgression. The layer sediment of the second surficial scarp records two large scale lake-level fluctuations. The first lacustrine transgression happened in 10000an. P. and the first lacustrine regression happened in 9450± 1260aB. P. The second lacustrine transgression happened in 6700an. P. and the second lacustrine transgression happened in 6165±105aB. P. Besides, there is a subordinate lacustrine regression in 7620±930aB. P. during the two lake-level fluctuations. The formation time of two surficial scrapes are corresponding to the Holocene temperature fluctuations in North China recorded by palynological sequence.
出处
《第四纪研究》
CAS
CSCD
北大核心
2013年第3期445-460,共16页
Quaternary Sciences
基金
中国地震重点监视防御区活动断层地震危险性评价项目(批准号:1521044025)
国家自然科学基金项目(批准号:40971013和41171001)共同资助
关键词
地貌陡坎
岱海南缘断裂
湖岸阶地沉积过程
全新世气候
surficial scarps
the south edge fault of Daihai basin
lacustrine terrace
sedimentary model
Holocene climate
