古地理学报
古地理學報
고지이학보
JOURNAL OF PALAEOGEOGRAPHY
2005年
1期
79-97
,共19页
巴丹吉林沙漠%粒度分析%热发光测年%弱水河%风成
巴丹吉林沙漠%粒度分析%熱髮光測年%弱水河%風成
파단길림사막%립도분석%열발광측년%약수하%풍성
Badain Jaran Desert%granulometry analysis%thermoluminescence dating%Ruoshui River%aeolian
巴丹吉林沙漠位于中国内蒙古自治区的西部,是中国第三大沙漠.过去通常认为该沙漠中沙丘的可能沙源来自附近的各种沉积物和岩石,包括弱水河扇的沉积物,弱固结的二叠纪页岩、白垩纪砂岩和砾岩以及戈壁阿尔泰的古老岩石.根据对风成砂的粒度观测,有证据表明在沙漠内部的风成砂沉积朝东南方向具有较弱的但又确实的变细趋势.这与沙丘横脊线的SW-NE向排列以及坡面的南东指向是一致的.因此,可以认为西北部的弱水河冲积扇是巴丹吉林沙漠风成砂的最可能的沙源.在西北部风成床沙覆盖了较老弱水河扇起源的冲积物.这种沉积物的热发光测年范围在190～100 ka BP之间.由于测量中对沉积物漂白可能不完全以及对其中平均古水含量估算均存在不确定性,同时由于对沙漠该地区风成作用开始之前堆积的沉积物进行了测年,这一数据范围代表了最大的年龄.另外三个风成砂测年结果分别接近133.66和22 ka,代表有关巴丹吉林沙漠西北部风成作用开始的最小年龄.沙漠的沙丘高度平均为200～300 m,但在东南部偶尔可达450 m.一些学者曾提出风成床沙覆盖了一个陡峭岛山突起的假说,来解释这些异常的空间.本次研究发现,在研究区之下是一个产状水平的白垩纪扇砾岩和砂岩的台地,可以断定在沙漠东南部呈现台地地貌,但进一步向北该台地明显延伸到这些沙丘之下.因此现在可以认为巴丹吉林沙漠中高的沙丘是不同区域气候和地貌因素相互作用的结果,而不是覆盖一个陡峭的岛山突起.对弱水河冲积扇作为巴丹吉林沙漠的主要源区的证实强调区域环境的重要性.在全新世,沿河流的绿洲植被在某种程度上阻碍了冲积扇提供沙源.现在,河西走廊的农业用水量极大地危及沿河森林,因此沿着作为天然拦沙阱的弱水河,维持足够的河水流量来保护区域性密集的沙丘植被,一定会避免具有重大威胁的沙的活动性增加.
巴丹吉林沙漠位于中國內矇古自治區的西部,是中國第三大沙漠.過去通常認為該沙漠中沙丘的可能沙源來自附近的各種沉積物和巖石,包括弱水河扇的沉積物,弱固結的二疊紀頁巖、白堊紀砂巖和礫巖以及戈壁阿爾泰的古老巖石.根據對風成砂的粒度觀測,有證據錶明在沙漠內部的風成砂沉積朝東南方嚮具有較弱的但又確實的變細趨勢.這與沙丘橫脊線的SW-NE嚮排列以及坡麵的南東指嚮是一緻的.因此,可以認為西北部的弱水河遲積扇是巴丹吉林沙漠風成砂的最可能的沙源.在西北部風成床沙覆蓋瞭較老弱水河扇起源的遲積物.這種沉積物的熱髮光測年範圍在190～100 ka BP之間.由于測量中對沉積物漂白可能不完全以及對其中平均古水含量估算均存在不確定性,同時由于對沙漠該地區風成作用開始之前堆積的沉積物進行瞭測年,這一數據範圍代錶瞭最大的年齡.另外三箇風成砂測年結果分彆接近133.66和22 ka,代錶有關巴丹吉林沙漠西北部風成作用開始的最小年齡.沙漠的沙丘高度平均為200～300 m,但在東南部偶爾可達450 m.一些學者曾提齣風成床沙覆蓋瞭一箇陡峭島山突起的假說,來解釋這些異常的空間.本次研究髮現,在研究區之下是一箇產狀水平的白堊紀扇礫巖和砂巖的檯地,可以斷定在沙漠東南部呈現檯地地貌,但進一步嚮北該檯地明顯延伸到這些沙丘之下.因此現在可以認為巴丹吉林沙漠中高的沙丘是不同區域氣候和地貌因素相互作用的結果,而不是覆蓋一箇陡峭的島山突起.對弱水河遲積扇作為巴丹吉林沙漠的主要源區的證實彊調區域環境的重要性.在全新世,沿河流的綠洲植被在某種程度上阻礙瞭遲積扇提供沙源.現在,河西走廊的農業用水量極大地危及沿河森林,因此沿著作為天然攔沙阱的弱水河,維持足夠的河水流量來保護區域性密集的沙丘植被,一定會避免具有重大威脅的沙的活動性增加.
파단길림사막위우중국내몽고자치구적서부,시중국제삼대사막.과거통상인위해사막중사구적가능사원래자부근적각충침적물화암석,포괄약수하선적침적물,약고결적이첩기혈암、백성기사암화력암이급과벽아이태적고로암석.근거대풍성사적립도관측,유증거표명재사막내부적풍성사침적조동남방향구유교약적단우학실적변세추세.저여사구횡척선적SW-NE향배렬이급파면적남동지향시일치적.인차,가이인위서북부적약수하충적선시파단길림사막풍성사적최가능적사원.재서북부풍성상사복개료교로약수하선기원적충적물.저충침적물적열발광측년범위재190～100 ka BP지간.유우측량중대침적물표백가능불완전이급대기중평균고수함량고산균존재불학정성,동시유우대사막해지구풍성작용개시지전퇴적적침적물진행료측년,저일수거범위대표료최대적년령.령외삼개풍성사측년결과분별접근133.66화22 ka,대표유관파단길림사막서북부풍성작용개시적최소년령.사막적사구고도평균위200～300 m,단재동남부우이가체450 m.일사학자증제출풍성상사복개료일개두초도산돌기적가설,래해석저사이상적공간.본차연구발현,재연구구지하시일개산상수평적백성기선력암화사암적태지,가이단정재사막동남부정현태지지모,단진일보향북해태지명현연신도저사사구지하.인차현재가이인위파단길림사막중고적사구시불동구역기후화지모인소상호작용적결과,이불시복개일개두초적도산돌기.대약수하충적선작위파단길림사막적주요원구적증실강조구역배경적중요성.재전신세,연하류적록주식피재모충정도상조애료충적선제공사원.현재,하서주랑적농업용수량겁대지위급연하삼림,인차연착작위천연란사정적약수하,유지족구적하수류량래보호구역성밀집적사구식피,일정회피면구유중대위협적사적활동성증가.
The Badain Jaran Desert(巴丹吉林沙漠),located in the western part of Inner Mongolia,is the third largest desert in China.A variety of sediments and sedimentary rocks in the vicinity of the Badain Jaran Desert ranging from sediments of the Ruoshui River (弱水河) fan to slightly consolidated Permian shales,Cretaceous sandstones and conglomerates and ancient rocks of the Gobi Altay mountains (壁阿尔泰山) have been suggested to be possible sand sources for the dunes of the desert in previous years.According to a granulometric survey of aeolian sands,there is evidence for a slight but distinct aeolian fining towards the southeast within the desert which is in agreement with the SW-NE alignment of the transverse dune ridges and slope faces pointing towards the southeast.Therefore the alluvial fan of the Ruoshui River in the northwest of the desert has to be considered as the most probable source area for the aeolian sands of the Badain Jaran Desert.In the northwestern part of the desert the aeolian bedforms cover alluvial sediments of an older Ruoshui fan generation.Results of thermoluminescence dating of such sediments range between approximately 190 ka and 100 ka BP which represent maximum ages due to uncertainties related to the dating of probably incompletely bleached sediments and the estimation of the palaeo-mean water content of the sediments and due to the dating of deposits which were accumulated prior to the onset of aeolian processes in this part of the desert.Three additional datings of aeolian sands yielded ages of approximately 133,66 and 22 ka BP respectively which represent minimum ages for the onset of aeolian processes in the related north-western part of the Badain Jaran Desert.The dunes of the desert are between 200 and 300 m high in average but attain elevations up to 450 m in the southeastern part occasionally.A steep inselberg relief which is covered by the aeolian bedforms was proposed by several authors to explain the extraordinary dimensions (Petrov,1966; Zhu et al.,1986;Yang,1991;Jkel,1996).As a result of this study,the part of the desert under consideration was found to be underlain by a platform topography of Cretaceous fanglomerates and sandstones which rest generally more or less horizontally.This platform morphology is pronounced in the southeastern vicinity of the desert but obviously extents further to the north under the dunes of the desert.Therefore it is assumed now that the high dunes of the Badain Jaran Desert are the result of the interaction of different regional climatic and geomorphologic factors rather than covering a steep inselberg relief.The verification of the alluvial fan of the Ruoshui River as the main source area of the Badain Jaran Desert emphasizes the environmental importance of this region.During the Holocene,sand supply from the alluvial fan was probably hampered to some degree by oasis vegetation along river courses.At present,the riverine forests are greatly endangered by water withdrawal for irrigation purposes in the Hexi Corridor (河西走廊).Therefore,a threatening significant increase in sand mobilization has to be avoided by maintaining a sufficient river discharge to preserve the locally dense vegetation along the Ruoshui River acting as a natural sand trap.
