西北地区晚第四纪沉积地层一元正脂肪酸酰胺分布特征及古气候意义     

蒲阳  张虎才  雷国良  常凤琴  杨明生  庞有智 《地球科学进展》2010,25(5):533-542

利用气相色谱质谱联用仪在中国西北地区晚第四纪沉积地层中检测出一类特殊的类脂物分子--一元正脂肪酸酰胺.根据其碳数分布特征及前人的研究成果,认为一元正脂肪酸酰胺来源于各种生物体,产生于生物的某些生理活动过程,而不是来源于石油残余物及各种可能的污染.通过对比3个不同区域相近时期古湖相及黄土沉积地层中的脂肪酸酰胺分布特征,认为柴达木盆地可能不是黄土沉积的主要物源区,而额济纳盆地及邻近区域对黄土堆积有着重要的贡献或具有相同的物源.典型黄土沉积地层中UFAA值(不饱和与饱和脂肪酸酰胺相对含量的比值)与粒度、磁化率等指标具有很好的可对比性,特别是在相对暖湿阶段UFAA值呈现了明显的低值.这一现象表明脂肪酸酰胺在沉积地层中的变化受控于气候变化所导致的成岩作用强度的变化,从而记录了气候变化信息.通过研究,认为生物生理活动过程中所产生的一元正脂肪酸酰胺与构成细胞膜的类脂物分子一样,可记录古气候变化.  相似文献   

青海南部杂多地区新建扎青组的地层层序及地质意义     

王毅智  叶占福  李琳业  宋泰忠  任二峰  祁生胜  王伟  裴生菊  许长青 《西北地质》2010,43(3):20-27

在青藏高原北羌塘盆地青海南部,青海省杂多县扎青乡地区的然者涌一带,发现以基性火山熔岩为主夹有中基性火山碎屑岩,具大陆板内裂谷拉斑玄武岩喷发特点的一套火山地层。该地层底部角度不整合接触覆盖在早中二叠世开心岭群诺日巴尕日保组、九十道班组之上,其上被晚三叠世结扎群甲丕拉组角度不整合覆盖。主要岩性为灰绿—灰紫色橄榄玄武岩、粗面玄武岩、玄武粗安岩及流纹岩、中基性火山角砾岩、角砾凝灰岩夹少量流纹岩和紫红色岩屑砂岩及细砾岩,其特征与峨眉山低钛玄武岩相似,具陆相喷发-沉积特征。区域对比在北羌塘地区具有独特地层特征,可与四川峨眉山玄武岩地层进行对比。而区域上该地区晚二叠世主要为一套海陆交互相含煤碎屑岩建造,未发现陆相火山岩出露,本文建立正式地层单位扎青组,以供参考,其时代暂归晚二叠—早三叠世。  相似文献   

松辽盆地反转期的界定   总被引：1，自引：0，他引：1  

陈骁  李忠权  陈均亮  李洪奎  张彤 《地质通报》2010,29(2)

松辽盆地的构造反转对油气生成、运移和聚集保存有明显的控制作用.以往的研究认为,松辽盆地晚期经历了嫩江组沉积末期、明水组沉积末期和古近纪的多期反转.通过对松辽盆地北部进行剖面与平面的构造演化分析,认为嫩江组沉积末期为南北向差异升降活动,未引起地层褶皱变形和构造格局的改变,该期形成了区域伸展不整合面;明水组沉积末期松辽盆地从区域拉张转为挤压,盆地表现为东西向缩短,构造格局发生了性质上的变化,形成了一系列反转构造,该期构造反转奠定了盆地现今的构造格局.构造物理模拟实验进一步证明,松辽盆地不同方向的反转构造带为明水组沉积末期形成的.  相似文献   

九江市蓼花剖面末次冰期中晚期沉积的粒度端元特征与气候变化     

李世乾  李志文  周万蓬  杜丁丁  黎武标 《热带地理》2023,43(1):135-143

鄱阳湖湖滨地区广泛分布着晚第四纪风沙沉积序列。在星子县沙岭沙山进行野外调查后选择蓼花剖面开展工作,测试了地质时代和粒度,对粒度结果使用端元分析模型进行研究,探讨该区域末次冰期中晚期的气候变化规律。结果显示：该剖面由湖相-古土壤-沙丘砂等沉积相叠覆堆积组成,形成于末次冰期中晚期（48.8—17.1 ka）。端元分析模型将粒度数据分解出3个不同的粒度端元,不同端元组分在垂向上呈峰谷交替的旋回变化,EM1代表粉砂端元组分,峰值对应湖相和古土壤发育时期;EM2和EM3代表中砂—粗砂端元组分,峰值对应沙丘砂发育期,这些峰谷交替变化的规律指示了末次冰期的季风演变以及气候波动变化,万年尺度上表现为LH10 (48.8—39.9 ka)和LH3～LH5 (28.1—17.1 ka)的冬季风强盛期,分别对应深海氧同位素的MIS3b和MIS2阶段。LH6～LH9 (39.9—28.1 ka)为温暖的夏季风时期,对应深海氧同位素的MIS3a阶段。这些变化与YZ洞石笋氧同位素以及格陵兰冰心有良好的对应,与全球气候变化基本一致。  相似文献   

“南音不幸而盛”:冯梦龙批评晚明剧坛析辨     

王小岩 《广东海洋大学学报》2014,(5):58-62

冯梦龙主张戏曲创作要"奇",且"调协韵严",基于此,他对晚明剧坛创作中存在的问题予以批评。这些批评从两个方面展开。在"曲"的方面,他批评了民间传奇创作、文人创新、汤显祖及其追随者等;在"戏"的方面,他提出"奇"的标准——"事奇"和"掀翻窠臼",并批评很多作品难以做到这两点。冯梦龙对晚明剧坛的批评原则立于对形式的推崇,故而有其局限性。  相似文献   

渤海莱州湾地区晚更新世以来有孔虫特征反映的古环境变化     

姚菁  于洪军  徐兴永  易亮  陈广泉  苏乔 《海洋学报(英文版)》2014,33(10):10-18

Controlled by climate changes, there were three large-scale transgressions and regressions around the Bohai Sea during the late Quaternary, which were accepted by most geologists. However, a big controversy still exists about the time when the transgressions occurred separately. In order to find out the process of the paleoenvironmental changes around the Bohai Sea in the late Quaternary, the foraminifera assemblages from a new borehole Lz908 in the southern coast of the Laizhou Bay were studied, and then the transgressive strata were indentified. Combined with accelerator mass spectrometry radiocarbon 14C（AMS14C） and optically stimulated luminescence（OSL） ages, the occurrence time of these transgressions were re-determined. The result showed that three major large-scale transgressions occurred separately at the beginning of marine isotopic stage 7（MIS7）, the last interglacial period（MIS5） and the Holocene. In addition, a small-scale transgression occurred in the mid-MIS6, and the corresponding transgressive stratum was deposited. The transgressive deposition of MIS3 was also discovered in this study. However, the characteristics of the foraminifera indicated the environment during this period was colder than that in the MIS5. By comparison with the global sea-level changes, the paleoenvironmental changes around the Bohai Sea in the late Quaternary can be consistent with the global climate changes.  相似文献   

Emplacement of the La Peña alkaline igneous complex,Mendoza, Argentina (33° S): Implications for the early Miocene tectonic regime in the retroarc of the Andes     

《Journal of South American Earth Sciences》2014

The La Peña alkaline complex (LPC) of Miocene age (18–19 Ma) lies on the eastern front of the Precordillera (32°41ʹ34ʺS, 68°59ʹ48″W, 1400–2900 m a.s.l.), 30 km northwest of Mendoza city, Argentina. It is a subcircular massif of 19 km² and 5 km in diameter, intruded in the metasedimentary sequence of the Villavicencio Formation of Silurian-Devonian age. It is the result of integration of multiple pulses derived from one or more deep magma chambers, which form a suite of silicate rocks grouped into: a clinopyroxenite body, a central syenite facies with a large breccia zone at the contact with the clinopyroxenite, bodies of malignite, trachyte and syenite porphyry necks, and a system of radial and annular dikes of different compositions. Its subcircular geometry and dike system distribution are frequent features of intraplate plutons or plutons emplaced in post-orogenic settings. These morphostructural features characterize numerous alkaline complexes worldwide and denote the importance of magmatic pressures that cause doming with radial and annular fracturing, in a brittle country rock. However, in the LPC, the attitude of the internal fabric of plutonic and subvolcanic units and the preferential layout of dikes match the NW–SE extensional fractures widely distributed in the host rock. This feature indicates a strong tectonic control linked to the structure that facilitate space for emplacement, corresponding to the brittle shear zone parallel to the N–S stratigraphy of the country rock. Shearing produced a system of discontinuities, with a K fractal fracture pattern, given by the combination of Riedel (R), anti-Riedel (R′), (P) and extensional (T) fracture systems, responsible for the control of melt migration by the opening of various fracture branches, but particularly through the NW–SE (T) fractures. Five different pulses would have ascent, (1) an initial one from which cumulate clinopyroxenite was formed, (2) a phase of mafic composition represented by dikes cross-cutting the clinopyroxenite, (3) a malignite facies that causes a small breccia in the clinopyroxenite, (4) a central syenite facies that develops breccias at the contact with the clinopyroxenite and, finally, (5) porphyry necks and a system of radial dikes intruding all units. At the moment of the emplacement different mechanisms would have acted, they summarized in: 1) opening of discontinuities synchronous to the magma circulation as the principal mechanism for formation of dikes and conduits; 2) stoping processes, that play an important role in the development of the breccia zone and enabling an efficient transference of material during the emplacement of the syenitic magma and 3) shear-related deformation (regional stress), affected the internal fabric of the facies, causing intracrystalline deformation and submagmatic flow, which is very evident in the central syenite intrusive. The kinematic analysis of shear planes allows proposing that emplacement of the LPC took place in a transtensive regime, which would have occurred in the back-arc of the Andes orogen, during a long period spanning from Miocene to the present, of the compressive deformation responsible, westward and at the same latitude, for the development of the Aconcagua fold and thrust belt.  相似文献   

虎头崖岩体地质地球化学特征及其对东昆仑祁漫塔格印支中-晚期构造环境的制约     

马圣钞 《地质学报》2014,88(1):72-82

虎头崖岩体位于青海东昆仑祁漫塔格成矿亚带,形成于中-晚三叠世,主要由黑云母二长花岗岩、正长花岗岩组成,局部含闪长质暗色包体。岩石高硅、高钾、富碱,SiO2含量为70.71%～77.67%;K2O含量平均为4.7%;Na2O K2O为7.86%～9.1%;K2O/Na2O平均为1.36。A/CNK比值为1.01,KN/A比值为0.86,属于高钾钙碱性系列的微过铝质I型花岗岩类。∑REE含量中等,平均为120.10μg/g;δEu值0.04～0.47;（La/Yb）值为1.52～8.06 ;稀土元素球粒陨石标准化曲线显示Eu负异常、HREE较平坦的右倾“V”型特征。岩体富集LIL和HFS元素,而Ba、Sr、Nb、Ti、P元素明显的负异常。结合区域地层岩性特征、A/MF-C/MF图解和岩体微量元素蛛网图,认为花岗岩是基性源区部分熔融和地壳物质混合的产物。结合地质特征、构造演化背景、元素判别图解等,认为包括虎头崖岩体在内的印支中晚期花岗岩形成于同造山阶段的后碰撞构造环境。印支中晚期花岗岩形成机制为：在二叠纪末-三叠纪初阿尼玛卿洋盆向北部昆仑微陆块俯冲碰撞造山并形成同碰撞/板内构造环境,期间发育与幔源岩浆底侵关系密切的源区基性岩浆岩;中-晚三叠世期,主碰撞之后挤压应力相对松弛,深部压力降低,因地壳增厚升温、岩石熔点降低而导致源区中-基性岩浆部分熔融,并在相对开放的环境下高侵位成岩  相似文献   

全新世温度研究回顾及对历史人地关系的启示     

饶志国  秦倩倩  魏士凯  郭海春  李云霞 《地理学报》2022,77(5):1169-1180

最新一些研究结果强调了全新世期间的长期增温趋势,综合全球平均海平面、大陆冰盖面积、大气温室气体和太阳辐射证据来看,这比传统观点所认为的全新世期间的长期降温趋势,更具有合理性。回顾历史,结合最新的一些研究进展,发现支持“中全新世大暖期”和“晚全新世降温趋势”的证据存在明显的不确定性,最核心的问题为晚全新世加强的人类活动对代用指标或者证据的强烈扰动,使得其不能准确地反映真实的气候变化过程。鉴于目前全新世温度历史争论的核心关键在于晚全新世,因此有必要加强晚全新世温度变化研究。在人类活动影响较小的地区,或者利用对人类活动不敏感的代用指标开展研究,有望可以获得更可靠的晚全新世温度历史重建结果,为准确认识中华数千年文明的长期温度变化背景,进而理解期间的“人地关系”演化历史,并最终客观认识现今面临的以全球变暖为主要特征的气候环境问题,提供一定的科学基础。  相似文献   

Vegetation in western Central Mexico during the last 50 000 years: modern analogs and climate in the Zacapu Basin     

A. Correa‐Metrio  S. Lozano‐García  S. Xelhuantzi‐López  S. Sosa‐Nájera  S. E. Metcalfe 《第四纪科学杂志》2012,27(5):509-518

The late glacial and the transition towards the Holocene marked a period of significant environmental change at a global scale. In western Central Mexico, few records span beyond the Holocene, and little is known about Pleistocene climatic and environmental variability. Here we report on the pollen record of a composite sequence made of three cores that cover the last 50 ka (thousands of calibrated radiocarbon years before present) in the Zacapu Basin, western Central Mexico (～1970 m asl). The conjunction of modern pollen rain from the area with the composite fossil pollen sequence from cores Cantabria, Cantabria 1 and CEMCA Point‐1 provided a detailed history of the vegetation of the area. Recognition of modern environmental patterns through individual modern pollen taxa proved difficult, but multivariate analysis separated different vegetation types. No‐modern‐analog communities relative to the modern vegetation cover of the area were evident, especially during periods of drought. Apparently, summer precipitation was significant before 40 ka and after the deglaciation. However, this moisture source declined from ～40 to 10 ka because tradewinds from the Gulf of Mexico were blocked by the eastern mountains of Central Mexico as a result of lower temperatures. By contrast, westerly and northerly winds were enhanced by maximum ice cover from ～19 to 17 ka, providing abundant winter precipitation and therefore preventing extreme drought in the area. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献