本文選題：晚第四紀(jì)　切入點(diǎn)：沙漠-黃土邊界帶　出處：《蘭州大學(xué)》2017年碩士論文　論文類型：學(xué)位論文

【摘要】：我國黃土高原堆積有巨厚的黃土沉積,為不同尺度的古氣候?qū)Ρ妊芯刻峁┝酥匾年懴嘤涗�。目前為�?有關(guān)黃土沉積空間范圍的研究相對較少,然而黃土沉積空間范圍的變化可能直接影響到黃土物質(zhì)的堆積過程與代用指標(biāo)古氣候意義解釋。沙漠-黃土邊界帶風(fēng)成沉積地層多表現(xiàn)為風(fēng)成砂、砂質(zhì)黃土與砂質(zhì)古土壤的互層沉積,有效地記錄了區(qū)域風(fēng)沙活動和粉塵堆積歷史,為研究我國黃土沉積范圍變化與北方沙漠演化提供了重要的地層資料。選取黃土高原西北邊緣的風(fēng)成沉積為研究對象。風(fēng)成剖面包括位于騰格里沙漠南部香山北坡香山剖面(XS-A和XS-B)以及共和盆地東南部卡加剖面(KJ)。通過分析風(fēng)成沉積巖性變化以及粒度組成、元素含量、磁化率和燒失量等代用指標(biāo),結(jié)合光釋光(OSL)測年結(jié)果,探討了中更新世以來我國黃土高原沉積范圍的變化及其潛在的區(qū)域氣候環(huán)境意義。主要結(jié)論如下:1、沙漠-黃土邊界帶3個(gè)風(fēng)成剖面中的黃土沉積與黃土高原典型黃土沉積特征一致,而風(fēng)成砂為含有一定粉砂組分的亞砂土沉積。香山剖面顯示該區(qū)典型黃土沉積至少出現(xiàn)在240 ka之前,并持續(xù)到42.5 ka,甚至25.4 ka前后;共和盆地東南部典型黃土沉積至少在在中更新世已經(jīng)出現(xiàn),并階段性地持續(xù)到末次盛冰期之前。2、沙漠-黃土邊界帶氣候由冷干轉(zhuǎn)向暖濕時(shí),研究區(qū)發(fā)育草原或者干草原植被,風(fēng)成沉積類型由風(fēng)成砂逐漸向典型黃土沉積過渡,沉積連續(xù),黃土沉積的范圍向北、向西擴(kuò)張。氣候由暖濕轉(zhuǎn)向冷干時(shí),地表風(fēng)力侵蝕加劇。沉積地層出現(xiàn)沉積間斷,形成假整合接觸面,表現(xiàn)為由黃土沉積向風(fēng)成砂沉積的快速過渡,黃土沉積的范圍向南收縮。3、至少中更新世以來,黃土高原北部黃土沉積區(qū)域遠(yuǎn)大于現(xiàn)在的范圍,可能到達(dá)騰格里沙漠南部以及鄂爾多斯盆地大部分地區(qū)。黃土高原西部黃土堆積的范圍至少到達(dá)共和盆地東南部的貴南地區(qū),甚至更西的位置。受風(fēng)蝕、水蝕作用的影響,黃土地層曾被風(fēng)力或流水侵蝕,上覆的風(fēng)成砂沉積指示了典型黃土在研究區(qū)存在沉積間斷,代表黃土沉積范圍收縮。4、盡管中更新世以來騰格里沙漠、木格灘沙地可能存在一定規(guī)模的擴(kuò)張,然而,其擴(kuò)張范圍遠(yuǎn)沒有達(dá)到現(xiàn)在的位置。研究區(qū)末次盛冰期沙漠/沙地的擴(kuò)張,奠定了現(xiàn)代沙漠/沙地的基本格局。5、中更新世以來黃土沉積范圍變化伴隨的風(fēng)蝕過程,意味著下風(fēng)向黃土沉積可能有部分粉塵物質(zhì)源自黃土本身。這種過程或許解釋了黃土記錄中某些時(shí)段粒度組成變化較小時(shí),粉塵通量增加的現(xiàn)象。
[Abstract]:There are very thick loess deposits on the Loess Plateau in China, which provide an important continental record for the comparative study of paleoclimate on different scales. So far, there have been relatively few researches on the spatial range of loess deposits. However, the variation of the spatial range of loess deposition may directly affect the accumulation process of loess material and the interpretation of paleoclimate meaning of the proxy index. The aeolian sedimentary strata in the desert loess boundary zone are mostly represented as aeolian sand. The interbedded deposits of sandy loess and sandy paleosol have effectively recorded the regional aeolian activity and dust accumulation history. It provides important stratigraphic data for studying the variation of loess sedimentary range in China and the evolution of the northern desert. The aeolian deposits on the northwest margin of the Loess Plateau are selected as the objects of study. The aeolian profiles include those located in the northern part of Xiangshan Mountain in the south of Tenggri Desert. The XS-A and XS-B of the Poxiangshan section and the KJJ of the Kaga section of the southeastern Gonghe basin are analyzed by analyzing the lithologic changes and granularity composition of the aeolian sediments. Element content, magnetic susceptibility and burning loss, etc., combined with the results of OSL dating, The variation of sedimentary range of loess plateau in China since the Middle Pleistocene and its potential regional climatic and environmental significance are discussed. The main conclusions are as follows: 1, loess deposits in three eolian sections of desert loess boundary zone and typical loess plateau. The sedimentary characteristics of loess are consistent. The Xiangshan section shows that the typical loess deposits in the area appeared at least before 240 ka and lasted until 42.5 ka or even 25.4 ka. The typical loess deposits in the southeast of Gonghe Basin appeared at least in the Middle Pleistocene and lasted periodically until the last glacial peak. When the climate of the desert loess boundary zone changed from cold to dry to warm and wet, grassland or steppe vegetation was developed in the study area. The type of aeolian deposits is gradually transitioning from aeolian sand to typical loess deposits, with continuous deposition, the range of loess deposits extending northward and westward. When the climate changes from warm and wet to cold and dry, the surface wind erosion intensifies, and sedimentary strata occur sedimentary discontinuity. The formation of pseudo-integrated contact surface is characterized by a rapid transition from loess deposition to aeolian sand deposition, and the extent of loess deposition shrinks to the south. At least since the Middle Pleistocene, the loess sedimentary area in the northern part of the Loess Plateau is much larger than the present one. Possibly reaching the southern part of the Tenggri Desert and most of the Ordos Basin. The loess accumulation in the western part of the Loess Plateau is at least as far as the southern part of the Gonghe Basin, or even further west. Affected by wind and water erosion, Loess layers have been eroded by wind or income, and the overlying aeolian sand deposits indicate that there are sedimentary discontinuities in typical loess in the study area, representing the shrinking of loess sedimentary range, although since the Middle Pleistocene, the Tenggri Desert, Mug beach sandy land may have a certain scale of expansion, however, its expansion scope is far from its present position. The last glacial period desert / sandy land expansion in the study area, The basic pattern of modern desert / sandy land. 5. The process of wind erosion associated with the variation of loess sedimentary range since the Middle Pleistocene. This process may explain the increase of dust flux due to the small change of particle size composition in some periods in loess records.
【學(xué)位授予單位】：蘭州大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：P512.2;P532

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