压实作用与磁倾角变化的实验研究   总被引：1，自引：0，他引：1  

邓云山  孟自芳  郑彦鹏 《沉积学报》2001,19(2):306-308

库车坳陷上新统库车组古地磁资料表明,泥岩组样品的平均磁倾角最小,从泥质粉砂岩、砂岩到粉砂岩其平均磁倾角依次递增,相应的古纬度值从泥岩、泥质粉砂岩到粉砂岩依次增高。为了研究这一现象,我们选取了 48个库车组样品作了一系列实验。实验结果表明,压实作用引起的体积变化与磁倾角降低呈线性关系.  相似文献   

Pliocene sedimentation in a shallow, cool-water, estuarine gulf, Murray Basin, South Australia     

Peir K. Pufahl  Noel P. James  Yvonne Bone†  Jeff J. Lukasik‡ 《Sedimentology》2004,51(5):997-1027

The Pliocene Norwest Bend Formation is a well‐preserved succession of terrestrial and shallow‐marine deposits in the Murray Basin, South Australia. Sediments in this unit consist of two discrete terrigenous clastic‐rich, decametre‐scale sequences, or informal members, which record episodes of marine incursion during the Early and Late Pliocene respectively. The base of each sequence is a transgressive lag and/or strandline deposit that is transitional upwards into a highstand, subtidal, terrigenous clastic and cool‐water carbonate sediment accumulation. The top of each sequence is incised by fluvial channels that are filled by river deposits which formed as relative sea‐level fell and terrestrial environments prograded basinward. Sedimentological data suggest that gross stratigraphic architecture was primarily determined by glacioeustasy. Differences in sedimentary style between these two sequences, however, reflect a major climatic change that took place in southern Australia during the mid‐Pliocene. The lower quartzose sand member is formed of siliciclastic sediment derived from prolonged, deep, subaerial weathering and contains a bivalve‐dominated, cool‐temperate, open‐marine mollusc assemblage. These sediments accumulated under an equitable, relatively warm, humid climate. The Murray Basin during this time, because of high fluvial discharge, was a salt‐wedge estuary with typical estuarine circulation. In contrast, the upper, oyster‐rich member is typified by large monospecific oyster buildups that grew in restricted coastal environments. Strandline deposits contain a warm‐temperate skeletal assemblage. Contemporaneous aeolian sediments accumulated under warm, semi‐arid climatic conditions. Well‐developed ferricrete, silcrete and calcrete horizons reflect cyclic conditions of rainwater infiltration and evaporation in the seasonally dry climate that typifies southern Australia today. Highly seasonal rainfall produced an estuary that fluctuated annually from being well to partially mixed. These Pliocene sediments support the notion that mollusc‐rich facies are the signature of cool‐water carbonate accumulations in inboard neritic environments. Unlike bryozoans that dominate the outer parts of Cenozoic cool‐water carbonate shelves, molluscs evolved to exploit an array of coastal ecosystems with wide salinity variations and variable sedimentation rates.  相似文献   

山西榆社盆地上新世植物群及其环境意义   总被引：11，自引：0，他引：11       下载免费PDF全文

曹家欣  崔海亭 《地质科学》1989,6(4):369-375

山西榆社盆地,上新世河湖相地层十分发育,植物化石丰富。上新世早—中期的代表性植物有:Magnolia Liquidambar, Platycarya和Tsuga等,说明当时的榆社地区为北亚热带森林景观,但已有向干冷方向发展的趋势。上新世晚期,榆社地区为暖温带落叶阔叶林景观,同现在华北南部的植被相似。河湖的广泛分布和植被的特征表明,上新世的榆社地区属于季风气候,一年之中季节性的干湿变化和冷暖变化十分明显。  相似文献   

用磁性地层学方法讨论西域组的时代   总被引：9，自引：0，他引：9  

滕志宏  岳乐平 《地质论评》1996,42(6):481-489

通过对塔里木盆地及其周缘地区西域组砾岩的野外调查和磁性地层学研究，及相关层位的安山玄武岩同位素年龄测定等综合分析研究表明：西域组上段记录了松山负极性带下段， ２．５－１．６Ｍａ，上界大约位于奥尔都维正极性事件层位，年龄为１．６７－１．７６Ｍａ。上覆高阶地砾岩层及其下火山岩层年龄为１．４－１．６Ｍａ，西域组下段记录了高斯正极性  相似文献   

上新世～早更新世云杉属和冷杉属在华北地区的发展及其气候指示意义   总被引：1，自引：1，他引：1  

石宁 《第四纪研究》1996,(4)

华北地区的云杉属和冷杉属在早上新世就有大量的发展。榆社盆地在４．４ＭａＢＰ．时，云杉属在孢粉植物群中的含量达５０％一７０％，与云杉属同时发现的还有一些喜暖植物。根据化石和孢粉学证据、沉积条件、古地形及欧洲的旁证材料推测，上新世云杉属和冷杉属的生态习性与现代生活在寒冷地带的云杉、冷杉不同，它们是一些可以生长在相对暖湿气候条件下的种类。上新世以森林为主的植被在２．３ＭａＢ．Ｐ．时转变为疏林草原，亚热带植物基本迁离榆社盆地。云杉属和冷杉属不仅在孢粉植物群中大量减少，在木本植物中也降为次要组分。古植物的演化和迁移历史反映了冰期气候和东亚季风气候发展的历程。  相似文献   

重论真马(Equus属)首次出现可作为第四纪下限的标志   总被引：1，自引：0，他引：1  

邓涛  薛祥煦 《地层学杂志》1997,(2)

真马（Ｅｑｕｕｓ属）首次出现曾被作为第四纪下限标志，近年来不断受到怀疑、甚至否定。然而，根据目前公认的２．５ＭａＢ．Ｐ．的第四纪下限，则真马在欧亚大陆的首次出现正与此界线吻合，从欧洲维拉方动物群、中国北方泥河湾地层、南方元谋盆地，以及其他剖面得到的证据都证明了这一点。真马首次出现事件与２．５ＭａＢ．Ｐ．的许多重大地质事件同时，如古地磁高斯期与松山期界线，中国黄土开始堆积、北极冰盖出现、新构造运动第一次强化等。真马首次出现于２．５ＭａＢ．Ｐ．是由于北极冰盖出现所伴随的海平面下降，导致白令海峡露出水面，欧亚大陆和北美大陆得以连通，在北美起源并在进化上取得成功的真马迅速扩散至欧亚大陆等地。因此，真马首次出现可以作为这些地区第四纪下限的一个显著标志，尤其是在欧亚大陆。  相似文献   

Bimodal back-arc alkaline magmatism after ridge subduction: Pliocene felsic rocks from Central Patagonia (47°S)     

Felipe Espinoza  Diego Morata  Mireille Polv  Yves Lagabrielle  Ren C. Maury  Christle Guivel  Joseph Cotten  Herv Bellon  Manuel Surez 《Lithos》2008,101(3-4):191-217

Volumetrically minor microsyenites, alkali microgranite and related trachytic dykes intrude early Pliocene OIB-like alkali basaltic and basanitic flows of the Meseta del Lago Buenos Aires in Central Patagonia (47°S–71°30′W), and occur together with scarce trachytic lava flows. Whole-rock K–Ar ages between 3.98 and 3.08 Ma indicate that the emplacement of these felsic rocks occurred more or less synchronously with that of the post-plateau basaltic sequence that they intrude, during a bimodal mafic–felsic magmatic episode devoid of intermediate compositions. Chemically, these rocks have A₁-type granitoid affinities and are characterized by high silica and alkali contents (60–68 wt.% SiO₂; 8.7–10.8 wt.% Na₂O + K₂O), major and trace elements patterns evidencing evolution by low-pressure fractional crystallization, and Sr and Nd isotopic signatures similar to those of coeval basalts ((⁸⁷Sr/⁸⁶Sr)_o = 0.70488–0.70571; (¹⁴³Nd/¹⁴⁴Nd)_o = 0.512603–0.512645). Nevertheless, some of them have the most radiogenic Sr values ever reported for a magmatic rock in the Meseta and even in the whole Neogene Patagonian Plateau Lavas province ((⁸⁷Sr/⁸⁶Sr)_o = 0.70556–0.70571; (¹⁴³Nd/¹⁴⁴Nd)_o = 0.512603–0.512608). In addition, very high contents of strongly incompatible elements in the most evolved rocks, together with Sr isotopic ratios higher than those of coeval basalts, suggest the occurrence of open-system magmatic processes. Continuous fractional crystallization from a primitive basaltic source, similar to post-plateau coeval basalts, towards alkali granites combined with small rates of assimilation of host Jurassic tuffs (AFC) in a shallow magmatic reservoir, best explains the geochemical and petrographic features of the felsic rocks. Therefore, A₁-type magmatic rocks can be generated by open-system crystallization of deep asthenospheric melts in back-arc tectonic settings.

In Central Patagonia, these  3–4 Ma old alkaline intrusions occur aligned along a  N160–170 trending lineament, the Zeballos Fault Zone, stacking the morphotectonic front of one segment of the Patagonian Cordillera. Intrusion along this fault zone occurred during the onset of a new transtensional or extensional event in the area, related to major regional tectonics occurring in possible relation with the collision of one segment of the Chile Spreading Ridge with the trench.  相似文献   

四川攀枝花昔格达组下伏砾石层成因和时代探讨与古金沙江河谷发育   总被引：12，自引：0，他引：12  

赵希涛  胡道功  张永双 《地球学报》2008,29(1):1-12

本文主要描述和讨论了四川省攀枝花市沿金沙江分布、并以炳草岗地龙箐剖面为代表的昔格达组湖相沉积下伏的砾石层的沉积特征及其河流相成因.根据前人对昔格达组湖相沉积的磁性地层学研究结果,为4.2/3.28～2.6/2.12/1.78 MaBP的上新世中、晚期或至早更新世早期,表明其下伏厚达50 m的砾石层的形成时代约为4.2～4.5/5 MaBP的上新世早期.早上新世金沙江河流相砾石层在接近金沙江谷底位置的发现,表明金沙江很早就已经从青藏高原主夷平面下切了2000 m以上、已在接近其现今谷底的位置上存在.这对于探讨古金沙江的河谷发育及其与青藏高原隆升的关系,具有重要的指示意义.  相似文献   

Paleophytochemical Constituents from the Pliocene Fossil Wood of Pinus Armandii from Longling,Yunnan     

ZHAO Youxing  LI Chengsen  YI Tiemei  LUO Xiaodong  ZHOU Jun 《《地质学报》英文版》2008,82(6):1146-1151

Specimens of fossil wood preserved lignified in Pliocene brown coal and identified as Pinus armandii Francher come from an opencast coalmine at Longling in western Yunnan Province, China. Phytochemical investigation of the fossil wood isolated using liquid column chromatography seven compounds （1-7） including a new fluorene derivative named 11,11-dimethyl-11H-benzo[b]fluorene. A further 28 volatiles were detected by gas chromatography-mass spectrometry （GC-MS）. Spectroscopic investigation methods, including MS and 1D and 2D-NMR techniques elucidated the structure of the seven compounds. Two types of natural products, isopimara and stilbene commonly occuring in extant and Pliocene fossil P. armandii indicate phytochemical fidelity during burial under certain circumstances in sediments. Discovery of stilbenes that can inhibit the activities of wood-destroying fungi in the Pliocene P. armandii prompts the assumption that the chemical preservation of this Pliocene fossil wood of P. armandii in brown coal might contribute to the presence of inner natural inhibitors against wood-destroying fungi.  相似文献   

Paleophytochemical Constituents from the Pliocene Fossil Wood of Pinus Armandii from Longling, Yunnan     

ZHAO Youxing  LI Chengsen  YI Tiemei  LUO Xiaodong  ZHOU Jun 《《地质学报》英文版》2008,82(6)

Specimens of fossil wood preserved lignified in Pliocene brown coal and identified as Pinus armandii Francher come from an opencust coalmine at Longling in western Yunnan Province,China. Phytochemical investigation of the fossil wood isolated using liquid column chromatography seven compounds(1-7)including a new fluorene derivative named 11,11-dimethyl-11H-benzo[b]fluorene.A further 28 volatiles were detected by gas chromatography-mass spectrometry(GC-MS).Spectroscopic investigation methods,including MS and 1D and 2D-NMR techniques elucidated the structure of the seven compounds.Two types of natural products,isopimara and stilbene commonly occuring in extant and Plincene fossil P.armandii indicate phytochemical fidelity during burial under certain circumstances in sediments.Discovery of stilbenes that can inhibit the activities of wood-destroying fungi in the Pliocene P.armandii prompts the assumption that the chemical preservation of this Pliocene fossil wood of P.armandii in brown coal might contribute to the presence of inner natural inhibitors against wood-destroying fungi.  相似文献