Shanwan Pond Sediment Characteristics and Evolutionary History at Wanzhou City in the Three Gorges Reservoir
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摘要: 万州特有的阶梯状地貌特征是万州地区河流地貌演化及水平地层特殊地质环境共同作用的结果，通过系统的野外地质调查、勘探和资料收集，结合2008年堰塘的湖中钻探，对该堰塘沉积物进行系统取样与分析，并进行了沉积物年龄与成分的测定.结果表明山湾陡崖的崩塌与阶地抬升及区域构造运动一致.绘制了山湾滑坡崩塌堆积物各期次沉积剖面，共分为10个崩塌旋回.结合沉积物测年，研究了山湾滑坡体沉积物沉积速率，得出了山湾危岩陡崖后退速率为0.31~0.37 m/ka.Abstract: The interaction of fluvial geomorphology evolution and special geological environment in horizontal formation in Wanzhou district resulted in its unique stepladder geomorphic feature. Based on a systematic field investigation, exploration and data collection, combining with the drilling at Shanwan pond in 2008, we conducted a comprehensive study of its sediment for the first time, systematically collecting sediment samples, doing analysis to determine its age and composition. It shows the consistency of Shanwan cliff collapse and the regional tectonism. The sediment profile of Shanwan landslide collapse deposit at each stage is presented and it is divided into 10 cycles of failure. Combining with the sediment dating, the deposition rate of Shanwan landslide sediment is researched, and the recession rate of Shanwan cliff is proposed as 0.31-0.37 m/ka.
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Key words:
- nearly horizontal formation /
- deposition rate /
- cliff /
- recession rate /
- sediments /
- engineering geology
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表 1 山湾滑坡沉积物分层
Table 1. Sediment layer of Shanwan landslide
分段描述 沉积物分层序号及说明 深度(m) 厚度(m) 备注 粉质粘土(淤泥) 1.人工填土：主要为碎石和粉质粘土，碎石成分为砂质泥岩 0.00~0.50 0.50 2.粉质粘土：褐色，软塑状，含植物根系及腐殖质，有腥臭味 0.50~1.00 0.50 3.淤泥：褐色，软塑状，粘粒含量高，含植物根系及腐殖质，有腥臭味 1.00~4.65 3.65 4.粉质粘土：褐色，由浅到深，由软塑状逐渐过渡为可塑、硬塑状，4.65~9.20 m为软塑状态 4.65~11.20 6.55 测年 碎石土块石交互 5.砂岩块石：13.00~16.40 m为紫红色泥质粉砂岩块石，锤击可碎，块径0.5~24.0 cm，可见层面倾角为42° 11.20~16.40 5.20 6.碎石土：红褐色，密实饱和，碎石成分主要为泥岩、砂质泥岩 16.40~18.10 1.70 7.块石：暗红色细砂岩，柱长0.5~19.0 cm 18.10~19.70 1.60 8.碎石土：红褐色，密实饱和，碎石成分主要为暗红色细砂岩 19.70~20.30 0.60 9.块石：成分主要为暗红色细砂岩，层面倾角为21°，块径0.9~21.5 cm 20.30~22.30 2.00 10.细砂-粉质粘土：红褐色，含中-细砂约60%，另含灰白色砂质团块 22.30~23.60 1.30 测年 11.碎石土：紫红色，稍密，碎石成分主要为棕褐色砂岩，含量约30%~40% 23.60~25.50 1.90 12.块石：为紫红色泥质粉砂岩，弱风化，块状构造，可见层面倾角45° 25.50~26.99 1.49 13.碎石土：褐色，稍密-密实，碎石为灰色、青灰色泥质粉砂岩 26.99~28.15 1.16 14.粉砂岩：灰褐色粉砂岩，泥质含量较低，不均匀风化 28.15~29.20 1.05 15.碎石土：灰褐色，较密实，饱和，碎石成分主要为粉砂质泥岩 29.20~29.85 0.65 16.块石：29.85~30.90 m主要为紫红色泥质粉砂岩，块状构造 29.85~32.55 2.70 17.泥质粉砂岩：紫红色，夹少许青灰色砂质泥岩，块状构造，柱长39 cm 32.55~32.94 0.39 18.碎石土：紫红色，密实，碎石主要为青灰夹紫红色砂质泥岩 32.94~35.30 2.36 19.泥质砂岩：为紫红色泥质粉砂岩，夹少量青灰色砂质泥岩 35.30~37.35 2.05 20.碎石土：灰褐色，密实，碎石主要为强风化的细砂岩、泥质粉砂岩 37.35~39.45 2.10 测年 21.砂质泥岩：紫红色，可见层理倾角57°、65°，节理倾角80° 39.45~40.00 0.55 22.碎石土：灰褐色，夹少许青灰色，较密实，蒙脱石含量较高 40.00~40.35 0.35 破碎岩 23.细砂岩：青灰色夹紫红色，弱风化，轻度破碎 40.35~43.02 2.67 24.泥质砂岩：紫红色，中-弱风化，柱长30 cm，下部泥质含量较低 43.02~44.22 1.20 25.泥岩：紫红色，弱风化，较坚硬，柱长13 cm 44.22~45.11 0.99 26.细砂岩：青灰色夹紫红色，弱-微风化，坚硬，柱长9~62 cm 45.11~48.86 3.75 27.泥质砂岩：紫红色，中-弱风化，较坚硬 48.86~49.63 0.77 28.细砂岩：青灰色，较破碎，坚硬，柱长6 cm 49.63~51.98 2.35 29.粉砂质泥岩：紫红色夹青灰色，弱风化，柱长3~30 cm 51.98~54.05 2.07 30.粉砂岩：青灰色夹紫红色，强-弱风化，坚硬，柱长为14 cm，可见节理，倾角为36°.其中54.95~55.82 m为碎石土 54.05~57.44 3.39 31.泥质细砂岩：紫红色夹青灰色，弱风化，坚硬 57.44~61.47 4.03 完整基岩 32.泥质细砂岩：紫红色夹少许青灰色，弱风化，坚硬，柱长为80 cm，十分完整，泥质含量高，层面近水平 61.47~63.37 1.90 
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表 2 山湾滑坡钻孔沉积物测年结果
Table 2. Age-dating results of drilling sediments in Shanwan landslide
样品编号 NL-05 NL-08 NL-10 取样深度(m) 9.07~9.14 23.36~23.45 39.29~39.39 对应高程(m) 239.4 225.1 209.2 测年结果(ka) 32 85 126
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表 3 山湾滑坡典型剖面崩塌堆积物统计
Table 3. Statistics of colluvial deposits in the typical profile of Shanwan landslide
旋回期 钻孔深度(m) 测年结果(ka) V1 V2 1 40.00 126 1 381.1 2 37.35 1 631.3 250.2 3 32.94 2 048.0 416.7 4 29.20 2 401.2 353.2 5 26.99 2 687.4 286.2 6 23.60 85 3 202.8 515.4 7 19.70 3 814.7 611.9 8 16.40 4 278.3 463.6 9 12.60 4 821.8 543.5 10 11.20 32 5 160.0 338.2 注：V1.典型剖面崩塌堆积物单位总体积(m3)；V2.崩塌旋回期沉积单位体积(m3).
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