岷江上游叠溪古滑坡坝-堰塞湖研究进展

doi:10.13745/j.esf.sf.2020.9.2

摘要/Abstract

摘要：

四川岷江上游叠溪发育有一套厚度超过200 m、保存较为完整的湖相沉积,被定名为叠溪古堰塞湖相沉积,其形成于距今30 ka前,存活了约15 ka,因此记录了青藏高原东缘晚更新世—全新世(包括末次冰期)的重大地质与环境事件。现有研究初步揭示了古堰塞的沉积特征,但对叠溪古滑坡及古堰塞湖形成与演化的系统研究还十分不足。本文通过详细的野外调查,结合现代遥感测绘技术(无人机载LiDAR),构建叠溪古滑坡的三维地质模型,研究了其地质与地貌特征。同时,采用高密度电阻率法ERT,在滑坡体上布设2条长870 m和990 m的测线,探明了滑坡体内部结构特征。通过古堰塞湖相沉积露头和钻孔的调查,结合激光粒度测试,重建了古堰塞湖的范围、规模与沉积特征。在此基础上,通过对古湖相沉积坡面上多级阶地的分析,初步探讨了古堰塞湖的消亡及其对下游史前古聚落变迁的影响。研究结果表明,叠溪古滑坡不仅完全堵塞岷江而且还堵塞了对岸支沟,堆积体方量达到(1 400~2 000)×10⁶ m³。古堰塞湖在滑坡坝后向上游延伸26 km,所形成的最大湖面覆盖面积约21.4 km²,库容蓄水量约1 670×10⁶ m³。叠溪古滑坡-堰塞湖在岷江上游形成了陡峭的河道裂点(Knickpoint),对山区河道与地貌演化具有长期影响。

关键词: 地震, 古滑坡, 古滑坡坝-堰塞湖, 溃坝洪水, 史前聚落

Abstract:

A paleo-lacustrine deposit, more than 200 m thick, named the “Diexi paleo-landslide-dammed lake deposit” was found upstream of the Minjiang River in Sichuan Province. The paleo-lake was formed around 30 ka BP and the dam started to fail around 15 ka BP. Therefore, the paleo-lacustrine deposit could have recorded important geological and geoenvironmental events (earthquakes, paleo-climate changes, etc.) during the period from the late Pleistocene to Holocene. The formation and evolution of the Diexi paleo-landslide and the landslide-dammed lake are poorly understood. Through detailed field investigation and LiDAR measurements, we constructed a 3D geological model and found the geomorphological and geological evidence to determine the boundary and volume of the paleo-landslide that formed the Diexi paleo-lake deposit. Using geophysical measurements (ERT) and laser grain size analysis, we determined the internal structure of the landslide deposit. We then reconstructed and analyzed the extent, volume, and sedimentological features of the paleo-lake based on a survey of outcrops and boreholes, and discussed the possible failure processes of the paleo-dam and its implications for the migration of prehistoric settlements. The results indicate that the Diexi paleo-landslide not only completely blocked the Minjiang River but also blocked its upstream branches, with the deposit volume reaching 1400×10 ⁶-2000×10⁶ m³. The paleo-lake extended upstream to about 26 km behind the dam; the maximum surface area and volume of the lake was approximately 21.4 km² and 1670 × 10 ⁶ m³, respectively. The paleo-landslide caused a knickpoint that may have a long-term impact on the mountain landscape evolution in the region.

Key words: earthquake, paleo-landslide, paleo-landslide dam and dammed lake, dam-breach flood, prehistorical settlements

中图分类号:

P642.2

范宣梅, 戴岚欣, 钟育瑾, 李婧娟, 王兰生. 岷江上游叠溪古滑坡坝-堰塞湖研究进展[J]. 地学前缘, 2021, 28(2): 71-84.

FAN Xuanmei, DAI Lanxin, ZHONG Yujin, LI Jingjuan, WANG Lansheng. Recent research on the Diexi paleo-landslide: dam and lacustrine deposits upstream of the Minjiang River, Sichuan, China[J]. Earth Science Frontiers, 2021, 28(2): 71-84.

图/表 14

图1 四川岷江上游叠溪古滑坡坝-堰塞湖研究区位置图 a—巴颜喀喇断块及研究区位置;b—研究区地质图。

Fig.1 (a) Tectonic map of the Qinghai-Tibet Plateau showing the location of the study area, and (b) geological map of the study area showing the locations of the Diexi paleo-landslide dam and lake upstream of the Minjiang River, Sichuan

图2 叠溪古滑坡地貌及堆积特征 a—叠溪古滑坡全景照片;b—左岸滑坡源区全景照片;c—叠溪古滑坡坝地貌解译详图;d—叠溪区域古滑坡群解译图;e—右岸龙池村平台的大块石岩屑堆积物;f—滑坡坝下游的溃坝堆积体。蓝色箭头指示现今岷江河流方向。

Fig.2 Geomorphological and depositional features of the Diexi paleo-landslide

图3 叠溪古滑坡纵剖面图剖面位置见图2c。

Fig.3 Geological profile of the Diexi paleo-landslide

图4 叠溪古滑坡坝体高密度电阻率法物探及湖相沉积物钻孔 a—高密度电阻率法布线与钻孔分布图;b—龙池平台滑坡堆积体电阻率E1剖面图;c—较场平台湖相沉积物高密度电阻率E2剖面图。钻孔(2009)资料据文献[3];钻孔ZK1-ZK3(2018)为本文作者团队2018年沉积取心钻孔。

Fig.4 Geophysical measurements (a) and ERT profile (b, c) of the Diexi paleo-landslide dam

图5 叠溪古堰塞湖范围重建 a—基于湖相沉积物分布重建的古堰塞湖范围;b—湖相沉积物钻孔揭露的古堰塞湖横剖面。a包括古湖相沉积出露位置与取样点分布;b中剖面线位置与钻孔信息见图4a。

Fig.5 Reconstruction of the Diexi paleo-lake

图6 古湖相沉积物粒度从坝址到上游库尾的空间变化图

Fig.6 Grain size distributions in the paleo-lacustrine deposit from the dam site to the end of the lake

图7 古湖相沉积物的粒度特征 a—三角分类图;b—C-M图。

Fig.7 Grain size variations in sediment samples collected from the dam (blue square), mid-lake (green square) and lake-end (red square) sections of the Diexi paleo-lake deposit

图8 古堰塞湖的沉积特征 a—库尾河湖交汇相;b—中游段沉积剖面;c—库首段沉积剖面;d—交错层理结构。

Fig.8 Sedimentologic characteristics of the Diexi paleo-lake deposit

图9 叠溪古堰塞消亡过程形成的河流相阶地(c图中阶地14C测年数据引自文献[3]) a—团结村发现的7级阶地;b—太平村发现的3级阶地;c—阶地露头沉积相划分和测年结果复合剖面示意图。

Fig.9 Fluvial terraces embedded in the Diexi paleo-lake deposit. 14C data adapted from [3].

图10 河流相阶地沉积特征

Fig.10 Sedimentologic characteristics of the fluvial terraces

图11 1933年叠溪地震复活的古滑坡体(a据文献[39]) a—尔尼斯特·亨利·威尔逊拍摄于1910年8月30日的叠溪老照片,拍摄地点见图11c;b—基于三维可视化模型获取的叠溪2018年景观(与图11a取景一致);c—1933年叠溪地震中复活的古滑坡体解译图。

Fig.11 The paleo-landslide reactivated by the 1933 Diexi earthquake. Photo in (a) adapted from [39].

图12 叠溪段裂点、陡峭系数和汇水面积复合河道纵剖面

Fig.12 Longitudinal profile of the Minjiang River around the Diexi paleo-landslide dam, showing the knickpoints (star), steepness indexes (circle), and upstream catchment contribution area

图13 ZK1(2018)钻孔岩心照片 a—ZK1(2018)钻孔从孔顶至孔底方向31.17~31.88 m段取心照片;b—枕状构造、负载构造、球状构造;c—负载构造;d—碟状构造;e—碟状构造、液化变形构造;f—微断层;g—纹层。

Fig.13 Photos of the ZK1 (2018) core (a) and core sections showing various core structural features (b-g)

图14 岷江上游古堰塞湖与史前聚落分布图(古堰塞湖分布据文献[2],史前聚落分布据文献[49])

Fig.14 Distribution of the dammed paleo-lakes (adapted from [2]) and prehistoric settlements (adapted from [49]) in the upstream catchment of the Minjiang River

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