| 江汉平原东北缘末次冰消期沉积物粒度特征及环境意义 |
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| 引用本文： | 张玉芬,李长安,赵举兴,毛欣,许应石,魏传义,李亚伟,张岱.江汉平原东北缘末次冰消期沉积物粒度特征及环境意义[J].沉积学报,2021,39(4):983-994. |
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| 作者姓名： | 张玉芬 李长安 赵举兴 毛欣 许应石 魏传义 李亚伟 张岱 |
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| 作者单位： | 1.中国地质大学（武汉）地球物理与空间信息学院，武汉 430074 |
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| 基金项目： | 国家自然科学基金41672355, 41671011, 41877292武汉市多要素城市地质调查示范项目WHDYS?2018?004, WHDYS?2018?007 |
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| 摘 要： | 麻城剖面位于江汉平原东北缘山地丘陵与平原过渡带半封闭的宽浅碟形洼地，是江汉平原北缘末次冰消期代表性沉积剖面。沉积环境主要由山麓坡洪积相和沼泽相组成，形成年代为距今18.00~8.60 ka。麻城剖面粒度组成主要以粉砂为主，达60.73%，其中，粗粉砂达40.83%。剖面粒度变化可划分为7个变化阶段。结合剖面的岩性与沉积环境特征等综合分析，发现末次冰消期气候环境经历了四个气候期:第一气候期17.90~17.02 ka B.P.，为冰盛期之后气候开始回暖升温期。此时降水相对较多，地表径流强度中等偏强。第二个时期17.02~12.02 ka B.P.，为快速升温期。总体暖湿多雨，是末次冰消期最显著暖湿期，在江汉平原北缘坡麓地带的洼地广泛发育了沼泽。粒度变化进一步表明气候存在波动，早、晚期降雨强度大，时有强降水发生，地表径流稳定性差；中期（14.47~12.64 ka B.P.）降水明显减少，但雨量相对均匀，地表径流变幅小，此与长江中下游地区石笋记录的冰消期气候特征是一致的。第三气候期12.02~10.80 ka B.P.，该期是新仙女木事件之后的快速升温期，平均粒径和分选系数为剖面最大。表明当时降雨量大，气候稳定性较差，强降雨时有发生。第四气候期10.80~8.60 ka B.P.，气候总体为偏温湿环境。地表径流较第三气候期明显降低，早期降水偏多，后期温湿程度降低，地表径流变小。剖面中有两个明显的气候事件记录，一是新仙女木事件，表现为第④层与第⑤层之间的短暂沉积间断和沼泽环境的结束；二是9.8~9.2 ka B.P.干旱期，为厚约15 cm的黄土状土的沉积。研究表明，长江和汉江洪泛影响不到的江汉平原边缘洼地沉积可能是记录本地区气候特征的良好载体。
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| 关 键 词： | 江汉平原 末次冰消期 粒度分析 地表径流 |
| 收稿时间： | 2020-02-25 |
Grain Size Characteristics and Climatic Environmental Significance of Sediments in the Northeastern Margin of the Jianghan Plain During the Last Deglaciation Period |
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| ZHANG YuFen,LI ChangAn,ZHAO JuXing,MAO Xin,XU YingShi,WEI ChuanYi,LI YaWei,ZHANG Dai.Grain Size Characteristics and Climatic Environmental Significance of Sediments in the Northeastern Margin of the Jianghan Plain During the Last Deglaciation Period[J].Acta Sedimentologica Sinica,2021,39(4):983-994. |
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| Authors: | ZHANG YuFen LI ChangAn ZHAO JuXing MAO Xin XU YingShi WEI ChuanYi LI YaWei ZHANG Dai |
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| Abstract: | The Macheng section is a semi?closed wide， shallow saucer?shaped depression located in the transition area between the Dabie Mountains and the Jianghan Plain. It is a typical section of deposition during the last deglaciation at the northern margin of the Jianghan Plain. The depositional environment of the area is made up of torrential floodplains and swamps， with a formation age between 18.00 and 8.60 ka. The major component of sediments in the Macheng section is silt， which represents 60.73% of the grain size， including a significant 40.83% of coarse silt. The grain size variation of the section is vertically divided into seven stages of change. Judging by the grain size composition and variation of sediment， combined with lithological and depositional environment analysis， it was found that the climate change during the last deglaciation was in four stages: the first was 17.90?17.02 ka B.P.， after the last glacial maximum， when a warm climate returned with increased precipitation； the intensity of surface runoff at this stage was medium to strong. The second stage， from 17.02 to 12.02 ka B.P.， was a period of rapid warming， generally warm and humid， when swamps were being developed along the torrential plains along the northern margin of the Jianghan Plain. The variation of grain size data indicates an unstable climate， with intense precipitation during the earlier and later phases of this stage， causing erratic surface runoff. In the metaphase （14.47?12.64 ka B.P.） precipitation was significantly reduced， but with a balanced stability， and the surface runoff was also relatively stable. During the later phase， precipitation intensified again and surface runoff became stronger. This stage is the most significant warm?humid period in the area during the last deglaciation， which is consistent with the stalagmite record of the middle and lower reaches of the Yangtze River. The third climatic stage was 12.02?10.80 ka B.P.， recognized as layer ④ of the Macheng section （depth 1.65?1.10 m）， with an obvious sedimentation break with its underlayer⑤， indicating the Younger Dryas （YD） event， followed by rapid warming. The values of average grain size and sorting coefficient are the largest in the entire section during this stage， which also indicates an unstable climate， but with rich precipitation. The fourth climatic stage was 10.80?8.60 ka B.P.， which was warm and humid in general， with less surface runoffs than the previous stage， but with heavy precipitation during the early phase， becoming the least intensive of both these phases in the later phase. The records of two climatic events are present in the Macheng section sediment: （1） the Younger Dryas event， represented by the short break in swamp facies deposition between layer ④ and layer ⑤； and （2） drought conditions from 9.80 to 9.20 ka B.P.， evidenced by a 15 cm loess?like depositional layer in the section. This study has shown that the sediment in the depressions along the northern margin of the Jianghan Basin， which was not affected by flooding of the Yangtze and Hanjiang Rivers， is a good indicator of climatic conditions in the Jianghan Plain region. |
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