【作者】 盛海洋；

【导师】 李勇；

【作者基本信息】 成都理工大学 ， 第四纪地质学， 2007， 博士

【摘要】 若尔盖盆地晚新近纪沉积是研究青藏高原东北缘隆升演化历史及其周缘环境响应和高原东北缘水系变迁，黄土成因特征，古砂丘时空演化及现代草地沙化等的天然地质记录体，具有重要科学意义。论文以中国地质调查局项目“川滇黔资源与生态地质背景调查及数据更新，四川1：25万若尔盖县、红原县、炉霍县、马尔康县幅区域地质调查修测（项目编码1212010510304）”为依托，选择若尔盖盆地晚新近纪地质及其环境演化为研究课题。遵从以证据为代表的地质事件，重塑青藏高原东北缘若尔盖盆地的晚新近纪地质及其环境演化过程。通过野外地质填图、调查、系统取样，室内样品测试分析和遥感解译等工作方法和手段，利用地貌及第四纪地质学、多重地层学（岩石地层学、生物地层学、层序地层学、磁性地层学）、构造地质学、气候环境学、地球化学、遥感学、年代学、冰川学、沉积学、地理学等多学科知识，对研究区晚新近纪地层及其环境演化，新构造运动及盆地形成与构造演化，黄河古河道时空演变，全新世古沙丘时空特征及其变化，草地沙化调查分析，黄土的成因研究，地球化学元素分布特征，盆地地貌特征及其与泥炭地的关系等方面做了系统、全面、综合研究。论文的创新性工作在于：1．利用多学科理论，全面、系统地以新构造运动为背景，以岩石地层特征为基础，以古地磁、碳14(¹⁴C)、热释光（TL）、光释光（OSL）、电子自旋共振（ESR）等测年数据为依据，以生物化石种属与产出层位和气候地层为参考，按照多重地层划分观点对若尔盖盆地晚新近纪更新统及全新统岩石地层、生物地层、气候地层、年代地层、磁性地层的对比和划分做了深入的研究。提出了研究区晚新近纪年代地层的划分，进一步完善了若尔盖盆地晚新近纪地层层序及分布规律。并取得以下认识：黄河干流、白河支流、黑河支流水系的河道堆积岩石地层，在以新构造运动为背景下的更新统-全新统不同发展阶段具有不同的特征，相同时期不同水系沉积物也不尽相同，反映出盆地晚新近纪地层的发育过程及空间上的差异。冰川堆积除钻孔中见有较多的相当于中更新统的冰川堆积外，对地表主要出露在东北角木哈隆、东南角羊拱海山地和西北部年保也则山地冰川堆积终碛垄测年等研究反映出末次盛冰期和全新世中几次较强的寒冷事件。“阿坝砾石层”时代划归为早更新世。由泥炭孢粉剖面和RM孔孢粉资料揭示出晚冰期到冰后期以来，若尔盖地区的气候表现出极大的不稳定性，冷暖变化频繁。黄河干流、黑河和白河地层中所产古脊椎动物化石，地质时代为晚更新世。根据¹⁴C、TL、OSL、ESR等同位素测年资料，结合岩石、生物地层地质依据，提出测区晚新近纪年代地层划分年龄界线。由冰期与间冰期或干旱期与湿润期交替演进的气候地层可划分为中更新世4366高地冰期和公巴拉克冰期，晚更新世末次冰期早期的木哈隆冰阶、扎尔吉冰阶、羊拱海冰阶、希门错沟冰阶和末次冰期晚期的安纳尔冰阶，以及全新世冰后期气候地层单位等。2．通过对盆地黄土的粒度组分、石英砂的表面结构以及其它地质现象的综合研究，对若尔盖盆地黄土成因进行了探讨。在黄土的概率累计曲线上，跃进组分和悬移组分反映明显，以悬移组分为主，并采用矩阵法计算了黄土的粒度参数。对黄土扫描电镜观察和石英颗粒表面特征的统计分析，反映出气流搬运的特点，以发育碟形坑为其主要标志，具有风成环境的表面特征组合。黄土中孢粉稀少，并在邻区黄土层中发现有冰楔构造。根据上述特征分析出若尔盖盆地黄土应为冰缘风成黄土。以测年资料为依据，黄土形成年代主要为马兰期查针梁子黄土和离石期索克藏寺黄土。3．通过调查黄河古河道的地貌形态特征，结合卫片形迹分析，从宏观上肯定了黄河古河道的分布特征。对古河道和现代黄河沉积物中的矿物组成鉴定分析和粒度测试与粒度分布曲线对比分析，看出其蚀源区、沉积介质和沉积环境的一致性，从而获得黄河古河道存在的微观证据。以新构造运动为背景，以测年资料为依据，确定了黄河古河道的形成年代为晚更新世，黄河变迁的原因是盆地北部出现了短暂的回升，下降幅度最大的地方在盆地的中部唐克沉降中心附近以及白河袭夺黄河发生水系变迁的结果。4．利用区域化探扫面成果编制的若尔盖盆地数字地球化学图，研究发现Zn、Sb、Hg、Pb、As、Au、Ag等绝大多数化学元素在若尔盖盆地古湖区显示为明显的低背景分布，是川西典型的表生元素缺乏的地球化学区。大多数元素在盆地内的变化系数CV＜30％，呈分散状态，缺少后期地球化学作用的叠加。而具有显著不均匀分布特征的Hg、As、Sb、Mn、Au、Sr等元素的变化系数在50.5～92.8之间，反映出的集中分布趋势主要同金、铀等成矿作用有一定的关系。根据若尔盖盆地特殊的自然环境特征研究发现，影响元素分布特征的主要因素是气候条件中的温度与湿度以及沼泽、泥炭等有机质的强烈还原环境。5．通过野外调查、取样分析，探讨了若尔盖盆地全新世以来沙漠化过程。粒度、矿物分析和扫描电镜分析表明，若尔盖盆地的古（现代）风成砂的沙源来自黄河阶地和高原地区的冰水沉积，但在风力作用下，分选程度和极稳定矿物含量均有所提高。极稳定重矿物含量是现代风成砂＞古风成砂＞河流相砂，相对稳定的轻矿物石英和沙物质分选程度也大致反映出相同的顺序，表明沙物质随着外营力（风）作用的延长，不稳定—稳定矿物受到风化、分解，而极稳定矿物相对富集，分选程度也得到提高。晚全新世以来，本区沙漠化主要经历4个阶段。本区更早的活动沙丘年龄为距今47000a以前。6．通过1999年（前期）和2005年（本期）前人资料和野外调查与遥感图象分析对比得出若尔盖盆地潜在沙化土地减少了20189.4hm²。但沙化耕地、固定沙地、半固定沙地与流动沙地却分别增加了57.4hm²、3572.9hm²、194.2hm²与2816.3hm²。有明显沙化趋势的增加了3.6hm²。2005年与1999年相比，风成堆积增加了36204.9hm²，由此表明，本区风成堆积仍呈上升趋势。从1999年到2005年研究地区风成堆积变化情况来看，近些年来通过退耕还林与生态环境治理工程以及天然林保护工程等建设，潜在沙化土地、沙化耕地在逐年减少，但固定沙地、半固定沙地、流动沙地以及露沙地却在逐年增加。由此看出，研究地区沙化趋势呈局部好转，整体恶化的状态。结合野外调查，深入研究分析了草地沙化原因。在草地沙化过程中，自然因素与人为因素的影响作用几乎是同等的。在自然因素中，地质因素和气候变化是主要影响因素，地质因素是导致草地沙化的主要内动力影响因素，气候变化则是其主要的外动力影响因素；在人为因素中，最主要的原因是草地超载放牧、开渠排水、草地利用不合理影响、乱挖滥采活动的影响等。7．利用钻孔资料年代序列、沉积特征、岩性组合、旋回结构，以及沉积速率的变化，结合环境冷暖、干湿的组合特点，分辩出900ka以来高原东部3次明显的构造加速隆升时期和高原环境演变的三个阶段。探讨了高原不同隆升阶段下盆地自身断裂系统的活动性、构造演化和形成模式等特点。8．通过野外调查与遥感解译，研究了盆地地貌形态特征和泥炭地的地貌类型。研究发现泥炭地的产出均与负向地貌部位（湖盆洼地、平底宽谷、坳谷、麓前洼地、沟谷谷底等）有关，地貌作用与泥炭地形成、演变、赋存与分布有着密切的关系。地貌的解译有助于对泥炭成矿规律提供正确认识。这对研究区泥炭、资源远景评价有着重要的意义。更多还原

【Abstract】 The deposits of Zoig（?） Basin in Late Neogene is one natural geological record for thestudy on uplift evolution history of previous northeast margin and its surroundingenvironment response and water system change of Qinghai-Tibet Plateau, formationfeature of loess, space-time evolution of ancient sand hills, and modern grasslanddesertification etc. and has significant scientific meaning. Relying on the projects of ChinaGeology Investigation Bureau, Investigation and Data Update of Geological Backgroundof Resources and Zoology of Sichuan, Yunnan and Guizhou Provinces and RegionalGeology Investigation and Revision of 1: 250000 Zoig（?）, Hongyuan, Luhuo and MaerkangCounties （coded 1212010510304）, this paper selects geology in Late Neogene and itsenvironment evolution of Zoig（?） Basin as study project, which obeys geological eventswith supported evidences, and remodels geology and environment evolution process ofLate Neogene at northeast margin of Zoig（?） Basin of Qinghai-Tibet Plateau.Through several methods like field geological mapping, investigation and sampling, indoor sample test and analysis, and remote sensing interpreter etc., using landform andmulti subject knowledge including quaternary geology, multiple geology, tectonics, climate and environmental science, geochemistry, remote sensing, chronology, andglaciology etc., we have carried out fully, systematic and composite study upon divisionand contrast of late Neogene multiple stratigaphic and its environment evolution of thestudied region, structural evolution and formation mode of the basin, space-time evolutionof ancient channel of Yellow River, space-time feature and change of ancient sand hill ofHolocene Epoch, investigation of basin and grassland desertification, formationinvestigation upon basin loess, distribution features of geochemical elements of the basin, landform zoning features of the basin and its relationship with peat land etc. The mainachievements are showed as below: 1.Making use of multidisciplinary theory, completely and systemically takingneotectonic movement as the background, basing on paleomagnetism, ¹⁴C, thermoluminescence, optically stimulated luminescence dating data, referring tooryctocoenose species, original horizon, and climatostratigraphy, depending on multiplestratigraphic classification, we have carried out further study on the contrast andclassification upon lithostratigraphy, biostratigraphy climatostratigraphy, chronostratigraphy, magnetostratigraphy of Zoige Basin in Pleistocene series andHolocene series of late Neogene. We have put forward the stratigraphic classification oflate Neogene of the studied region, and further completed stratigraphic sequence anddistribution rule of late Neogene stratum of Zoige Basin. And we also learned thefollowing points.We also learned that accumulative statrum of the rock of the river courses of trunkstream of Yellow River, tributary stream of Bai River and tributary stream of Hei Riverhas different features in different developing stages from Pleistocene series to Holoceneseries under the background of neotectonic movement, and the deposits of different watersystems of the same period is not totally the same as one another, which shows thedifference of stratigraphic developing process and the spatial difference of late Neogene ofthe basin. Except glacial accumulative formation of equivalent Pleistocene series in boringholes, ground mainly outcrops at Muhalong in northeast corner, Yanggonghaimountainous area in southeast corner and Nianbaoyeze mountainous area in northwesternpart, and reflect several relatively intensive cold events of the last Glacial Epoch andHolocene Epoch of terminal moraine dating. The peat sporo-pollens profile and RM holesporo-pollens data shows that climate in Zoig（?） region displays extreme instability andtemperature rises and falls frequently from late Glacial Epoch to post Glacial Epoch.Geological period of vertebrate fossils at stratum of the trunk stream of Yellow River, HeiRiver and Bai River belongs to Late Pleistocene epoch. Age boundary of stratigraphicclassification of late Neogene of the investigated area is proposed according to dating dataof isotope of ¹⁴C, TL, OSL, ESR etc., combining with geological base of rock bed andbiostratigraphy. Climate stratum evolves alternatively between Glacial Epoch or inter Glacial Epoch or dry period and humid period that can be classified as Glacial Epoch ofhighland 4366 of mid Pleistocene epoch and Glacial Epoch of Gongbalake, Muhalong icestep, Zhaerji ice step, Yanggonghai ice step and Ximencuogou ice step of the early stageof last Glacial Epoch of Late Pleistocene epoch, and Annaier ice step of the late stage oflast Glacial Epoch as well as post Glacial Epoch of Holocene Epoch.2.Loess origin of Zoig（?） Basin has been discussed basing on synthetic study in graincomposition of the loess, surface texture of quartz sand, as well as other geologicalphenomena. On the probability cumulative curve of loess, saltation mass and suspensionare obvious, and the later is dominant, and matrix method is adopted to compute grain sizeof the loess. The statistic analysis on quartz sand surface textures of loess throughscanning electron microscope shows the features of air transportation, the main symbol ofdeveloped dishing pit, and combined profile features of Aeolian environment. In addition, sporo-pollens are scarce in the loess and ice-wedges are discovered in the neighboringloess strata. As above, it appears that Zoig（?） Basin loess is Aeolian sediment in theperiglacial environment, loess formation age mainly are Chazhenliangzi loess of Malanperiod and Suokezang Temple loess of Lishi period.3.Through field investigation of landform features of ancient river course of YellowRiver （identified valley margin profile, relatively good valley slope remained locally, smoothly connection between two sides of ancient river course and terrace of gradeⅡofmodern Yellow River, unclogged and open ancient valley etc.）, combining with traceanalysis by satellite pictures （it presents obvious deep gray reverse ’S’ image features inplane pattern）, thus distribution features of ancient courses of Yellow River is confirmedmacroscopically. Through contrast and analysis of deposit grain size test and grain sizedistribution curve of ancient courses and present Yellow River, we can learn that itsdeposit media and deposit environment is coincident. Therefore we have achievedmicroscopic evidence for the existence of ancient courses of Yellow River from theconsistency of mineral constituents from the result of mineral constituent analysis（showing the consistency of their oxidation and deposit environment）. Taking neotectonicmovement as the background, depending on dating data, we have confirmed that ancient courses of Yellow River was formed in Late Pleistocene epoch. Variation of Yellow Riverresults from temporal uplift of the north of the basin, water system variation under theaction of bradyseism and stream capture of Bai River and Tangke settlement center thatlies at the severest settlement point of the basin.4.Combining with the digital geochemical map of Zoig（?） Basin based on 1: 200000regional geochemical exploration results, we learn that the overwhelming majority ofgeochemical elements including Zn, Sb, Hg, Pb, As, Au, Ag etc. shows obviouslow-background distribution in ancient lake zone of Zoig（e） Basin, which is one typicalgeochemical zone lack of surface genetic elements in the west of Sichuan province. InZoig（?） Basin, variation factor CV of most elements is less than 30%, in dispersed state, andlack of superposition of late geochemical action. However variation factor of obviousunevenly distributed elements including Hg, As, Sb, Mn, Au, Sr etc ranges from 50.5 to92.8, reflects concentrated distribution trend, and has certain relation with metallization ofgold, and uranium etc. According to special nature environment features of Zoig（?） Basin, we find out that main factor which can affect elements distribution features are: thetemperature and humidity of the climate and the intensive reducing environment oforganic substances like marsh and peat.5.Through field investigation and sample analysis, we have discussed desertificationprocess of Zoig（?） Basin since Holocene Epoch. Grain size and mineral analysis andscanning electron microscopy analysis shows that sand source of ancient （present） aeoliansand of Zoig（?） Basin comes from outwash drift of terrace of Yellow River and plateauregion, however under the action of wind, sorting degree and extreme resistant mineralcontent is enhanced more or less. In term of extreme resistant mineral, present aeoliansand＞ancient aeolian sand＞fluvial faces sand, relative resistant light mineral quartzand sand sorting approximately shows same sequence, and this displays that non resistantand resistant minerals of sand are weathered and decomposed with prolonged deflation, however extreme resistant minerals are accumulated and sand well sorted. Since lateHolocene Epoch, desertification at the studied region shows fluctuant development undergeneral situation of global environment variation, and it is basically consistent with Chinese climatic changes and desertification process of west neighboring region, andmainly experienced four periods. Ages of active sand dunes in much older time of thisregion includes 5000-7000a, 11500-15400a, and before 47000a.6.Through the field investigation and remote sensing image analysis and contrast of1999 （previous stage） and 2005 （present stage）, we can learn that potential desertificationland of Zoige region has reduced 20189.4hm², however, desertification farmland, stabilized sand, semi-stabilized sand and wandering sand have increased 57.4hm².3572.9hm², 194.2hm² and 2816.3hm² respectively, and land with obvious desertificationtrend has increased 3.6hm². Comparing with 1999, Aeolian accumulation of 2005increases 36204.9hm². From this, it can be seen that Aeolian accumulation at Hongyuan-Zoig（?） region is still in a rising trend. From Aeolian accumulation variation of the studiedregion from 1999 through 2005, we can learn that potential desertification land anddesertification farmland are reducing year after year through returning farmland to forestry, ecological environment treatment projects and natural forestry reserve projects, however, stabilized sand, semi-stabilized sand, wandering sand, and naked sand are increasing yearafter year. From this, it can be seen that desertification trend at the studied region ischanging from overall deterioration state to local improvement. Grassland desertificationcauses are analyzed through combing with field investigation. Nature factors play oneequivalent role as human factors in the process of grassland desertification. Geologicalfactors and climate change are dominant in nature factors;geological factor is the maininternal element leading to grassland desertification, and climate change is the mainexternal element; human factor mainly comes from oversized cattle population, channeling and discharging, unreasonable grassland utilization, exploitation abuse, etc.7.On the basis of chronosequence, deposit features, lithology combination and cyclestructure of boring data, as well as variation of deposit rate, combining with combinationfeatures of cold-warm and dry- humidity environment temperature, we can identify threeobvious structural accelerated uplift periods （namely 800ka, 360ka, 160ka） at the east ofthe plateau and three stages of plateau environment evolution after 900ka. And we alsohave studied features of lower basin self rupture system at different uplift stages of the plateau including activity, structural evolution and formation mode.8.Through the field investigation and remote sensing interpreter, we have studiedbasin landform subzone and morphological feature, geomorphologic type of peat. Welearn that peat formation all have relation with negative geomorphology （lake basindepression, dale with flat bed, valley, piedmont depression, and cleuch floor etc.）, andgeomorphologic process has close relation with peat formation, evolution, occurrence anddistribution. Geomorphology interpreting is helpful to offer correct comprehension uponpeat metallographic rules. And this is meaningful for the prospect evaluation of peat andresources in the studied region.更多还原