【摘要】：黃土作為記錄過(guò)去環(huán)境變化的重要信息載體,一直被用于全球變化中古氣候的演變研究,尤其是對(duì)末次盛冰期以來(lái)的氣候記錄更為關(guān)注。漢江上游地區(qū)地處秦嶺南側(cè),為北亞熱帶北緣,是氣候環(huán)境變化的敏感區(qū)域。區(qū)內(nèi)普遍分布著厚層風(fēng)成黃土覆蓋物,但對(duì)于該黃土沉積的研究很有限。本文選取鄖縣段漢江左岸彌陀寺黃土剖面(MTS)為研究對(duì)象,對(duì)沉積物樣品的理化性質(zhì)(粒度、化學(xué)元素組成等)、微結(jié)構(gòu)形態(tài)(石英顆粒形態(tài)、集粒形態(tài)、孔隙、粗顆粒、土壤生成物)等進(jìn)行了測(cè)試,用OSL方法獲得地層年齡,以這些實(shí)驗(yàn)數(shù)據(jù)為基礎(chǔ),對(duì)秦嶺南側(cè)漢江上游黃土的地層、組成結(jié)構(gòu)、風(fēng)化成壤特征以及對(duì)氣候變化的響應(yīng)等問(wèn)題進(jìn)行分析研究,獲得了以下主要結(jié)論：(1)漢江上游一級(jí)河流階地上黃土的地層序列自上而下依次為：表土層(TS)→全新世黃土(L0)→古土壤(S0)→過(guò)渡層黃土(Lt)→馬蘭黃土(L1)→黃土和砂交互層(JH)→河流相沉積(AL-1),結(jié)合OSL測(cè)年數(shù)據(jù),建立起漢江上游一級(jí)階地上黃土序列的年代框架,黃土和砂交互層底部年齡大約為55000 aB.P.,頂界年齡約為25000 aB.P.,馬蘭黃土L1的頂界年齡為11500aB.P.,古土壤S0底界年齡則為8500 aB.P.,頂界年齡為3100 aB.P.(2)MTS剖面黃土粒度組成、化學(xué)元素、微結(jié)構(gòu)形態(tài)等特征顯示漢江上游一級(jí)階地交互層以上穩(wěn)定沉積物質(zhì)為風(fēng)塵沉積,交互黃土層與上部馬蘭黃土組成相近,為風(fēng)塵堆積,而砂層與下部河流相組成類(lèi)似,為水成成因。各地層的沉積特征又存在差異,具體體現(xiàn)在：①各層粒度組成以粉砂為主,古土壤S0層相對(duì)于黃土層(L1/Lt/L0)粒級(jí)更細(xì),各層平均粒徑大小排序?yàn)镾0TSLtL0L1JH。②化學(xué)元素的變異系數(shù)均很小(除JH層外),體現(xiàn)同一區(qū)域黃土中成分一致且混合性強(qiáng),易遷移元素(Ca、Sr等)與穩(wěn)定元素(Al.Cu等)在剖面垂直方向上呈相反鏡像變化,易遷移元素在古土壤S0層中含量呈現(xiàn)低值,在黃土層(L1/L0)中含量則高,穩(wěn)定性元素則反之。③微結(jié)構(gòu)形態(tài)中石英顆粒以次棱-次圓為主,石英顆粒表面多為碟形坑、麻坑等風(fēng)成機(jī)械標(biāo)志,而交互砂中出現(xiàn)貝狀斷口、三角痕等水成標(biāo)志；從S0→Lt→L0→L1次棱狀-棱狀石英顆粒增多,磨圓度逐漸變差,古土壤S0中石英顆粒的機(jī)械標(biāo)志上疊加的硅質(zhì)沉淀、SiO2溶蝕刻蝕等化學(xué)成因特征明顯增多；剖面骨架顆粒之間的微結(jié)構(gòu)連接方式從TS→L0→S0→Lt→L1→JH-t→JH-s依次為絮凝膠結(jié)→微鑲嵌半膠結(jié)→凝塊膠結(jié)→鑲嵌半膠結(jié)→支架微膠結(jié)→支架微膠結(jié)→單顆粒接觸結(jié)構(gòu)；孔隙形態(tài)則多以復(fù)合堆疊狀態(tài)為主,多囊狀、氣泡狀孔隙,孔隙率排序?yàn)镾0LtL0L1；從S0→Lt→L0→L1粗顆粒依次增多,圓度變小,C/F10μm依次變大；彌陀寺剖面中土壤生成物在So層出現(xiàn)居多,以次生黏土鐵錳侵染和鐵錳凝團(tuán)為主,未見(jiàn)次生方解石。④MTS剖面在古土壤層150～190cm處色度、黏粒、100μm的中粗砂、化學(xué)元素等數(shù)據(jù)均顯示有異常變化值,與上下層古土壤層理化性質(zhì)有一定差異,微結(jié)構(gòu)形態(tài)也顯示其石英顆粒磨圓度變差,集粒間孔隙增多,之間的膠結(jié)狀態(tài)也變差,粗顆粒明顯增多,暗示該時(shí)段氣候發(fā)生變異,導(dǎo)致沉積物質(zhì)性狀有較大變化。(3)秦嶺南側(cè)漢江上游地區(qū)黃土處于由低等向中等化學(xué)風(fēng)化過(guò)渡階段,Ca、Na淋失嚴(yán)重,鉀長(zhǎng)石變化不大,風(fēng)化程度古土壤So過(guò)渡性黃土Lt全新世黃土L0馬蘭黃土L1,具體表現(xiàn)為：①磁化率與全鐵、游離鐵、晶質(zhì)鐵等鐵形態(tài)指標(biāo)變化均有良好的對(duì)應(yīng)關(guān)系,其值均在S0LtL0L1,反映古土壤S。風(fēng)化最強(qiáng)。②化學(xué)蝕變指數(shù)CIA和CPA均指示MTS黃土剖面整體處于由低等向中等化學(xué)風(fēng)化過(guò)渡階段,A-CN-K三角圖顯示彌陀寺黃土經(jīng)歷了以斜長(zhǎng)石風(fēng)化為主的風(fēng)化過(guò)程,次生風(fēng)化黏土礦物以蒙脫石、伊利石為主,尚未達(dá)到以高嶺石、水鋁石為主產(chǎn)物的強(qiáng)風(fēng)化階段。③K/Na、Fe/Mg、Rb、Sr三個(gè)化學(xué)風(fēng)化參數(shù)的值均呈TSS0 LtL0L1,而硅鋁系數(shù)Sa變化與上面四個(gè)指數(shù)相反,四者共同指示古土壤層風(fēng)化要強(qiáng)于黃土層。此外,磁化率、鐵形態(tài)、CIA、K、Na、Fe、MgRb、Sr及硅鋁系數(shù)等風(fēng)化指標(biāo)在剖面150～190cm處有變異值,指示該段古土壤發(fā)育出現(xiàn)弱風(fēng)化,反映出該時(shí)期古氣候有異常。(4)鄖縣漢江段MTS黃土的風(fēng)化成壤特征有效地反演了漢江上游一級(jí)階地在大約25000 aB.P.穩(wěn)定抬升以后古氣候演變的4個(gè)階段：末次冰期冰盛期(25000～11500aB.P.),全新世早期(11500～8500aB.P.),全新世中期(8500～3100aB.P.),全新世晚期(3100aB.P～至今),氣候狀況依次為冷干→涼干→暖濕→冷干,此外全新世大暖期期間存在多次氣候波動(dòng),MTS剖面古土壤中150-190cm的弱風(fēng)化層就是對(duì)全新世中期5.5ka冷事件的一次直接記錄。(5)對(duì)比秦嶺南北黃土的地層序列、粒度特征、化學(xué)元素以及風(fēng)化程度,得出秦嶺南北兩側(cè)黃土的幾點(diǎn)異同：①兩地區(qū)的剖面地層序列一致,自上向下都為T(mén)S→L0→S0→Lt→L1,區(qū)別在于漢江上游馬蘭黃土L1下部為黃土和砂的交互層以及河流相沉積,而關(guān)中地區(qū)馬蘭黃土L1下部仍為黃土,兩剖面的年代框架也一致,L1頂界和S0發(fā)育年齡相同。②兩地粒度均以粉砂尤其是粗粉砂為主,且二者土壤質(zhì)地均屬粉質(zhì)黏土亞黏土；漢江上游古土壤S0層顆粒要比關(guān)中地區(qū)黃土古土壤都要細(xì),而馬蘭黃土中顆粒要粗些,這與漢江上游黃土混入近源物質(zhì)有關(guān)。③兩地黃土中的化學(xué)元素變異系數(shù)都比較小,組成一致且均一,秦嶺南側(cè)漢江上游黃土中活動(dòng)性元素(Ca、Mg、Sr等)要比北側(cè)關(guān)中地區(qū)黃土的有所減少,穩(wěn)定元素(Ca、Mg、Sr等)相對(duì)增多,反映出秦嶺南側(cè)黃土中不穩(wěn)定成分淋失較多,經(jīng)歷風(fēng)化淋溶作用更強(qiáng)。④兩地區(qū)黃土中磁化率、化學(xué)蝕變指數(shù)(CIA)、元素比值(K/Na、 Ca/Mg、Rb/Sr)、淋溶系數(shù)以及殘積指數(shù)等相關(guān)風(fēng)化指標(biāo)均顯示在古土壤層風(fēng)化要強(qiáng)于黃土層,說(shuō)明秦嶺南北兩側(cè)黃土經(jīng)歷了相似的沉積發(fā)育過(guò)程,但漢江上游地區(qū)黃土中風(fēng)化指數(shù)更高,風(fēng)化程度更強(qiáng),說(shuō)明秦嶺南側(cè)古氣候更為暖濕。
[Abstract]:Loess, as an important information carrier for recording past environmental changes, has been used to study the evolution of paleoclimate in global change, especially since the last glacial maximum. In this paper, the physicochemical properties (grain size, chemical element composition, etc.) and microstructure (quartz grain shape, aggregate shape, pore, coarse grain, soil product) of the sediment samples from the Mituosi loess section (MTS) on the left bank of the Hanjiang River in Yunxian were studied. Based on these experimental data, the stratigraphic age of the Loess in the upper reaches of the Hanjiang River on the southern side of the Qinling Mountains is obtained by OSL. The main conclusions are as follows: (1) The stratigraphic sequence of the Loess in the upper reaches of the Hanjiang River is from top to bottom. The following sequence is: surface soil (TS) Holocene loess (L0) paleosol (S0) transitional loess (Lt) Malan loess (L1) loess and sand interaction layer (JH) fluvial facies deposition (AL-1). Combined with OSL dating data, the chronological framework of loess sequence on the first terrace of the upper Hanjiang River is established. The age of loess and sand interaction layer is about 55 000 aB.P. The top age is about 25 000 aB.P., the top age of Malan Loess L1 is 11500 aB.P., the bottom age of Paleosol S0 is 8500 aB.P., and the top age is 3100 aB.P. (2) The characteristics of loess grain size, chemical elements, microstructure and morphology in MTS section show that the stable sediments above the first terrace in the upper reaches of Hanjiang River are aeolian-dusty sediments and interactive loess. The sedimentary characteristics of each layer are different. The grain size composition of each layer is mainly silt, and the grain size of Paleosol S0 layer is finer than that of loess layer (L1/Lt/L0). The average grain size of each layer is in the order of S0TSLtL. The variation coefficients of chemical elements (except JH layer) are very small, indicating that the composition of loess in the same region is consistent and strong mixing, and the content of migrable elements (Ca, Sr, etc.) and stable elements (Al. Cu, etc.) in the vertical direction of the section is opposite mirror change. The content of migrable elements in the S0 layer of Paleosol is low, but in the L1/L0 layer is high. In the microstructure, the quartz grains are mainly sub-edge-sub-circle, and the surface of quartz grains is mostly dish-shaped pits, pits and other wind-forming mechanical indicators, while in the interactive sand, shellfish-like fracture and triangular marks appear; from S0 Lt L0 L1 prismatic-prismatic quartz grains increase, the roundness gradually deteriorates, and the stones in the paleosol S0 appear hydrological indicators. The chemical origin of the siliceous precipitation and SiO2 etching on the mechanical markers of the British particles increased obviously, and the microstructure of the cross-section skeleton particles was in turn from TS L0 S0 Lt L1 JH-t JH-s to flocculation micro-mosaic semi-cementation mosaic semi-cementation scaffold micro-cementation scaffold micro-cementation scaffold micro-cementation scaffold micro-cementation The pore morphology is mainly composed of composite stacking, multi-cystic, bubble-like pores, and the porosity ranks as S0LtL0L1; coarse particles from S0 Lt L0 L1 increase in turn, roundness decreases, and C/F10 micron increases in turn; soil products in the Mituosi section appear mostly in the SO layer, with secondary clay Fe-Mn infection and Fe-Mn coagulation. Fourthly, MTS profiles showed abnormal variations in chroma, clay, 100-micron medium-coarse sand, chemical elements and other data at 150-190 cm of paleosols, which were different from the physical and chemical properties of upper and lower layers of paleosols. Microstructure and morphology also showed that the roundness of quartz particles became worse, the porosity between aggregates increased, and the cementation between them. (3) Loess in the upper reaches of the Hanjiang River in the south of Qinling Mountains is in the transitional stage from low to moderate chemical weathering, Ca and Na leaching is serious, K feldspar has little change, weathering degree of Paleosol so transitional loess Lt Holocene L0. Malan Loess L1, the specific performance is: 1) magnetic susceptibility and total iron, free iron, crystalline iron and other iron morphological indicators have a good corresponding relationship, the values are in S 0LtL0L1, reflecting the strongest S. weathering paleosol. 2 Chemical alteration index CI A and CPA indicate that the overall MTS loess profile is in the transition from low to moderate chemical weathering stage, A-CN-K triangle. The map shows that the main weathering process of Miduosi loess is plagioclase weathering. The secondary weathering clay minerals are mainly montmorillonite and illite, but have not reached the stage of strong weathering with kaolinite and diaspore as the main products. In addition, magnetic susceptibility, iron morphology, CIA, K, Na, Fe, MgRb, Sr and Si-Al coefficients have variation values at 150-190cm of the section, indicating that Paleosols in this section developed weakly weathered, reflecting the abnormal paleoclimate during this period. The paleoclimatic evolution of the first-order terrace in the upper reaches of the Hanjiang River has been effectively inverted in four stages: the last glacial glacial maximum (25 000-11 500 aB.P.), the early Holocene (11500-8500 aB.P.), the middle Holocene (8500-3100 aB.P.), and the late Holocene (3100 aB.P-present). The weak weathering layer of 150-190 cm in the MTS section is a direct record of 5.5 Ka cold event in the middle Holocene. (5) By comparing the stratigraphic sequence, grain size characteristics, chemical elements and weathering degree of the Loess in the north and south of Qinling Mountains, the Loess in the north and south of Qinling Mountains can be obtained. Some similarities and differences are as follows: 1) The stratigraphic sequence of the two sections is the same, and the upper and lower parts of the Malan Loess L1 in the upper reaches of the Hanjiang River are the interbeds of loess and sand and fluvial deposits, while the lower part of Malan Loess L1 in the Guanzhong area is still the loess, and the chronological framework of the two sections is the same, the top boundary of L1 and the development age facies of S0 are the same. Similarly, the grain sizes of the two places are mainly silt, especially coarse silt, and both of them belong to silty clay subclay. The grain size of S_0 layer of Paleosol in the upper reaches of Hanjiang River is finer than that in the Loess of Guanzhong area, while the grain size in Malan loess is thicker, which is related to the mixing of loess in the upper reaches of Hanjiang River with near-source materials. The variation coefficients are relatively small and the compositions are uniform. The active elements (Ca, Mg, Sr, etc.) in the Loess of the upper reaches of the Hanjiang River in the south of Qinling Mountains are less than those in the north of Guanzhong Mountains, and the stable elements (Ca, Mg, Sr, etc.) are relatively increased, reflecting that the Loess in the south of Qinling Mountains leached more unstable elements and experienced stronger weathering and leaching. The weathering indexes such as medium susceptibility, chemical alteration index (CIA), element ratio (K/Na, Ca/Mg, Rb/Sr), leaching coefficient and residual index showed that the weathering of Paleosol layer was stronger than that of Loess layer, indicating that the Loess in the north and south sides of Qinling Mountains experienced similar sedimentary development process, but the weathering index in the upper reaches of Han River was higher and the weathering degree was higher. Stronger, indicating that the southern side of Qinling Mountains is more warm and humid.
【學(xué)位授予單位】：陜西師范大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2015
【分類(lèi)號(hào)】：S151;P539

【參考文獻(xiàn)】

相關(guān)期刊論文 前7條

1 雷祥義;秦嶺黃土的粒度分析及其成因初步探討[J];地質(zhì)學(xué)報(bào);1998年02期

2 陳駿,汪永進(jìn),陳e，

本文編號(hào)：2219162