宁夏清水河中上游发现末次冰期最盛期冰缘遗迹群  

Discovery of Periglacial Phenomena in the Late Stage of Last Glacial Maximum at the Upper to Middle Reaches of Qingshuihe River,Ningxia,China

作　　者：董晓朋[1,2] 李振宏 崔加伟[1,2] 黄婷 马兆颖 寇琳琳 DONG Xiao-peng;LI Zhen-hong;CUI Jia-wei;HUANG Ting;MA Zhao-ying;KOU Lin-lin(Institute of Geomechanics,Chinese Academy of Geological Sciences,Beijing 100081,China;Key Laboratory of Paleomagnetism and Tectonic Reconstruction of Ministry of Natural Resources,Beijing 100081,China;School of Earth Sciences and Resources,China University of Geosciences,Beijing 100083,China)

机构地区：[1]中国地质科学院地质力学研究所,北京100081 [2]自然资源部古地磁与古构造重建重点实验室,北京100081 [3]中国地质大学(北京)地球科学与资源学院,北京100083

出　　处：《地球科学与环境学报》2022年第3期524-534,共11页Journal of Earth Sciences and Environment

基　　金：国家自然科学基金项目(41972119);中国地质调查局地质调查项目(DD20190018,DD20221644);中国地质科学院院所长基金项目(DZLXJK202104)。

摘　　要：冰缘遗迹对重建一定区域和时间段的气候状况以及划定多年冻土边界具有重要意义。在宁夏清水河中上游(36°22′5″N~36°25′53″N)发现末次冰期最盛期冰缘遗迹群,包括古冰楔和融冻褶皱。其中,在唐堡村剖面发现有4处古冰楔,其形态呈楔形,上宽下窄;楔壁不平直,楔体周围地层中发育垮塌前形成的裂隙;楔体中充填有周围地层碎块和棕红色粉砂。在三岔河村剖面发现有两层连续的融冻褶皱,褶皱轴面倾向产状杂乱,无统一指向;褶皱轴部无明显加厚或减薄,翼部未发生层间滑动,褶皱层顶部未发育截切现象;层间褶皱未发育层间逆冲或正断裂。根据光释光测年和^(14)C测年结果,古冰楔形成于14.06~11.45 ka B.P.,融冻褶皱形成于13500~11570 a B.P.。受新仙女木事件影响,清水河流域在末次冰期最盛期发育大面积多年冻土,分布范围至少到达36°22′5″N以南。末次冰期中国北方中纬度约20 ka以来冻土南界西段可以向南推移至少约52′(径向上距离约97 km)。这一发现为末次冰期中国北方多年冻土南界的划分提供了新的证据。Periglacial phenomena are of great significance for reconstructing the paleo-climate in a certain stage or area,and depicting the southern limit of latitudinal permafrost.Periglacial phenomena,including cryoturbations and ice wedge pseudomorphs,formed during the late stage of Last Glacial Maximum,were discovered in the valley at the middle to upper reaches of Qingshuihe River,Ningxia,China(36°22′5″N-36°25′53″N).Four ice wedge pseudomorphs were discovered in the Tangbaocun section(36°22′5″N,106°8′25″E).The ice wedge pseudomorphs in the Tangbaocun section are characterized by wedges with wider top and narrower bottom.The wedge wall is irregular,and clasts of wall sediments and brown-red silt lacking of stratifications were filled in the wedges.Adjacent to the wedge wall,there are a series of fractures formed before the collapse of wall sediments.In the Sanchahe section(36°25′53″N,106°8′34″E),there developed two layers with a series of cryoturbations.As for the cryoturbations in the Sanchahe section,the inclinations of axial planes varied irregularly;the axis did not grow thicker or thin significantly;there was no interlayer sliding in the limbs;the wedge top had not been truncated,and there was no interlayer thrust or normal fault in the interlayer folds.The ice wedge pseudomorphs and cryoturbations might be triggered by the same single cold climate event during the period of~14 to~11 ka B.P.The presence of ice wedge pseudomorphs(14.06-11.45 ka B.P.)and cryoturbations(13500-11570 a B.P.)during the last stage of Last Permafrost Maximum(LPMax)indicates that the development of permafrost at the upper to middle reaches of Qingshuihe River,Ningxia has significantly lowered paleo-temperature and close relationship with Younger Dryas.Moreover,the southern limit of latitudinal permafrost could have reached as far south to 36°22′5″N.Therefore,the west part of southern limit of latitudinal permafrost since~20 ka B.P.in North China at mid-latitudes may have moved southwards by~52′in latitu

关 键 词：末次冰期 冰缘遗迹 古冰楔 融冻褶皱 清水河流域 新仙女木事件 冻土南界 宁夏 

分 类 号：P56[天文地球—构造地质学] P66[天文地球—地质学]