Knowledge Resource Center for Ecological Environment in Arid Area
| 兰坪-思茅盆地与呵叻盆地含盐系/下伏地层碎屑岩沉积特征及其物源联系：对区域成盐背景的指示 | |
| 其他题名 | Sedimentary Characteristics and Source Links between Lanping-Simao and Khorat basins, based on the analysis of Clastic Rocks of Salt-bearing/underlying stratas：Implication for regional salt-forming setting |
| 苗卫良 | |
| 出版年 | 2017 |
| 学位类型 | 博士 |
| 导师 | 马海州 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 兰坪-思茅盆地是我国目前唯一发现有古代固体钾盐沉积的区域，然而经过多年的的调查研究，在钾盐勘查上一直没有取得更大的突破。而基于其南部老挝-泰国呵叻盆地内赋含丰富钾盐资源的事实，关于兰坪-思茅盆地成钾潜力及其与呵叻盆地成盐聚钾物源联系方面的问题便一直成为广大科技工作者极为关注的难题。本文从兰坪-思茅-呵叻盆地系中生代红层沉积充填物入手，以含盐系地层及其下伏砂岩地层为研究对象，在区域不整合面等时框架制约的基础上，重点分析该盆地系岩石序列组成、沉积环境、砂岩粒度分布特征及元素地球化学特征等，从沉积地质学的角度对研究区成盐基底盆地及成盐地层的物源属性特征、沉积环境特征及成盐期前后盆山格局等方面提供新的更全面、更直接的信息和认识。 研究区成盐基底盆地由区域上岩性极为均一的扒沙河组砂岩组成，含盐系地层与其在区域上普遍呈不整合接触关系，因此该不整合面可作为研究区进行物源关系探讨的等时参考面。此外也暗示了研究区成盐前较为稳定的陆内海（湖）环境。而含盐系地层主要由棕红色细碎屑岩与蒸发岩组成，在兰坪-思茅范围内呈西高东低，北高南低之势，反映了研究区晚白垩世时湖盆沉积中心的分布特征。 扒沙河组砂岩粒度的分析表明整个研究区域该套砂岩的矿物学特征极为相似，且具有较高的成分成熟度和结构成熟度，表明了这一时期较为稳定的沉积环境和相似的物源属性特征。通过粒度参数分析后认为在扒沙河组沉积期兰坪-思茅-呵叻盆地整体沉积环境应为滨海（湖）沙丘沉积，而石英颗粒的表面形貌特征分析也确认了该套地层兼具了沙漠环境和水下环境的共同典型特征。 通过物源属性分析认为，勐野井组及其下伏扒沙河组地层的主要物源类型均为长英质火山物源，所不同的是前者有显著的古老沉积物再循环沉积的影响，而后者则有基性物源参与的迹象。此外，多元素交叉对比分析表明勐野井组与扒沙河沉积时均具有相对稳定的大地构造背景，且二者间的不整合沉积间段期间并未发生显著改变研究区物源输入的构造活动事件，而各次级成盐洼陷间也并无山脉阻隔，是互相连通的。化学风化作用研究表明勐野井组物源区母岩经受的化学风化作用要显著低于扒沙河组沉积期，可能是勐野井组沉积期研究区汇水面积扩大使物源区母岩剥蚀物未能充分经受化学风化作用便沉积了下来；而老挝地区样品在两个时期均表现出较低的化学风化作用程度，则意味着呵叻地区较兰坪-思茅地区更为靠近物源区。综合前人的研究成果，认为哀牢山古隆起可能为兰坪-思茅-呵叻盆地系提供了长英质物源，而扬子古陆则提供了古老沉积物物源。 含盐系地层粘土矿物的分析表明，研究区粘土矿物组合主要受控于区域气候条件、物源输入类型及盐湖卤水介质的后期改造作用。成盐成钾段粘土矿物组合在勐野井钾盐矿区与泰国呵叻盆地类似，均以伊利石+绿泥石组合为主，而前者在碎屑层段还有高岭石出现，表明了区域暖干的基本气候环境。富Mg绿泥石含量在成钾段含量的升高表明了浓缩卤水对粘土矿物改造作用的加深，因此伊利石+绿泥石组合、绿泥石与MgO含量的高值可有效指示成盐成钾作用的演化程度。 通过沉积环境、大地构造背景、物源属性及区域气候条件等方面的分析，认为兰坪-思茅盆地与呵叻盆地在成盐期前有着统一稳定的成盐基底，而含盐系地层发育期间整个区域亦未发生可改变物源输入的重大构造事件，其物源属性、矿物组合及成盐背景条件等方面均具有可比性，因此现今钾盐资源储量的差异悬殊应主要归因于喜马拉雅期大规模的构造活动破坏所致，未来找钾的主要目标应以区域内构造相对稳定的部位为主，兼以各类成盐成钾指标辅助。 |
| 英文摘要 | Lanping-Simao Basin is the only one place where we found the ancient solid potash deposition in China. While after decades of investigation, there are still no more progress on potash exploration in this area. Based on the fact that the Khorat Basin which located in the south of Lanping-Simao Basin is rich in potash resources, the sylvite-forming prospect of Lanping-Simao Basin and the source relationship of salt-forming between these two basins have always been concerned. Based on the constraint of regional unconformity isochronous framework, the salt-bearing strata and its underlying sandstone formation are used as the research object to analyze the characteristics of rock sequences, the sedimentary environment, the grain size features of sandstone and the geochemical characteristics and so on. From the point of view in sedimentary geology, we try to discuss the characteristics of the source, the sedimentary environment and the pattern of basins and mountains before and after salt-forming stage and bring them more comprehensive and direct informations. The basement of salt-forming basin is composed of Pashahe formation sandstone which are homogeneous in lithology throughout the region. Which may means a stable sedimentary environment of intracontinental sea (lake). Generally, the salt-bearing strata is unconformity contact with Pashahe formation in the whole region. So the unconformity interface could be used as a isochronous reference for provenance research in study area. While the salt-bearing strata is composed of brown-red microclastic rocks and evaporites. As a reflection of depocenter of paleolake, the thickness of salt-bearing strata show high in western and northern and low in eastern and southern in Lanping-Simao Basin. The results from the petrographical study indicate that the mineralogical characteristics of Pashahe sandstone are very similar, and have a high compositional maturity and texture maturity. This also means a relatively stable sedimentary environment and similar provenance input during this period. And the grain-size analyses also show that the depositional environment of Lanping-Simao-Khorat basins should be coastal (lakeside) desert environment during the deposition of Pashahe formation. While the surface textural analysis of quartz grains also confirmed the existence of typical eolian-desert environment together with the features of water environment. Felsic source is the main source for both Mengyejing and Pashahe formation based on the geochemical analysis, but the former obviously affected by the ancient sediment recycling, while a small amounts of basic source involved in the latter provenance. Additionally, multi-element analysis indicate that the tectonic setting are stable during both Mengyejing and Pashahe deposition stage. Furthermore, no significant tectonic events which may change the source input of study area occurred during the stratum hiatus period. And the secondary salt-forming sags are connected with each other during salt-forming stage. The weaker degree of chemical weathering during Mengyejing Fm. deposition stage than Pashahe Fm. deposition stage may means that the weathering products from source area of Mengyejing Fm. were deposited before enough transformation by chemical weathering process because of the expand of catchment area during the stage of Mengyejing Fm. deposition. While the samples from Laos have a relatively low degree of chemical weathering, which may mean that the source region is close to these sample location. Based on the achievements of predecessors, we believe that the Felsic souce may come from the Ailaoshan paleouplift, while the ancient sediment source may come from the Yangtze block. The analysis of clay minerals in salt-bearing strata shows that the clay mineral assemblage of study area are mainly controlled by regional climate conditions, provenance and the modification of concentrated brine. The clay mineral assemblage in salt-forming stage are all dominated by illite + chlorite combination in the Mengyejing Potash Deposit and Khorat basin of Thailand. Combined with the emergence of kaolinate in the clastic layers of core SHK4 in Mengyejing Potash Deposit, which may indicates that the regional climate condition is mainly warm and dry. The increasing of Mg-rich chlorite in the sediments of sylvite-forming stage may indicates the deepening transformation of clay minerals by concentrated brine. Therefore, the clay assemblage of illite + chlorite, combined with the high content of chlorite and MgO in sediment could be used as a effective indicator to show the degree of salt-forming evolution. Generally, based on the analysis of sedimentary environment, tectonic background, provenance characteristics and region paleoclimate condition, we believe that there is a unified and stable basement before the formation of salt in the basin. And the source, mineral assemblage and salt-forming conditions are comparable in the whole region because of no significant tectonic events which could affect the source input of the basin have occurred during the development of salt-bearing strata. So the current disparities of potash resources between Lanping-Simao Basin and Khorat Basin should be mainly attributed to the damage effect caused by the Himalayan movement. While the main goal of potash exploration in Lanping-Simao Basin should mainly be tectonic stable part, and combined with various indicators for sylvite-forming. |
| 中文关键词 | 兰坪-思茅-呵叻盆地系 ; 盆地分析 ; 物源属性 ; 地球化学 ; 砂岩粒度特征 ; 粘土矿物 |
| 英文关键词 | Lanping-Simao-Khorat basins， Basin Analysis， Provenance Geochemistry， Characteristics of Grain Size Distribution of Sandstone， Clay Mineral. |
| 语种 | 中文 |
| 国家 | 中国 |
| 来源学科分类 | 地球化学 |
| 来源机构 | 中国科学院青海盐湖研究所 |
| 资源类型 | 学位论文 |
| 条目标识符 | http://119.78.100.177/qdio/handle/2XILL650/287836 |
| 推荐引用方式 GB/T 7714 | 苗卫良. 兰坪-思茅盆地与呵叻盆地含盐系/下伏地层碎屑岩沉积特征及其物源联系：对区域成盐背景的指示[D]. 中国科学院大学,2017. |
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