Vegetation cycles in a disturbed sequence around the Cobb-Mountain subchron in Catalonia (Spain)   总被引：1，自引：0，他引：1  

Suzanne A. G. Leroy 《Journal of Paleolimnology》2008,40(3):851-868

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Integration of reflection seismic and sediment grain-size data from Lake Khubsugul (Northern Mongolia): a reply to Prokopenko and Kendall   总被引：1，自引：0，他引：1  

A. P. Fedotov  M. De Batist 《Journal of Paleolimnology》2008,40(4):1193-1199

Prokopenko and Kendall (J Paleolimnol doi:, 2008) criticise the work presented in Fedotov et al. (J Paleolimnol 39:335–348, 2008), and instead propose an alternative interpretation for the grain-size evolution recorded in the KDP-01 core, retrieved from the central part of Lake Khubsugul. Their interpretation is based (i) on a seismic-stratigraphic re-interpretation of sparker seismic profile khub012 (which they copied from Fedotov et al. (EOS Trans 87:246–250, 2006)), (ii) on the presupposition that changes in lake level are the dominant control on facies distribution in Lake Khubsugul, and (iii) on the invalidation of our age-depth model. In this reply to their comment, we demonstrate that they interpreted seismic artefacts and geometries caused by changes in profile orientation as true stratigraphic features and that the lake-level reconstruction they derive from this interpretation is therefore incorrect. We also demonstrate that their grain-size predictions, which they consider to be predominantly driven by changes in lake level, are inconsistent with the measured sulphate concentration, which is a demonstrated proxy of lake level in Lake Khubsugul, and with the measured grain-size record. Finally, we point out that even if there would be a problem with the age-depth model, this problem would not affect the part of the sedimentary sequence discussed in Fedotov et al. (J Paleolimnol 39:335–348, 2008).  相似文献   

太行山南缘晚更新世以来河流阶地的发育及其新构造运动意义     

张蕾  张绪教  武法东  何泽新  田珺  于航  王春林  刘江红 《现代地质》2013,27(4):791-798

太行山南缘的武家湾河流经太行山与华北平原两大地貌单元的过渡地带,较太行山内部其他水系对新构造运动的响应更为敏感,能较好地记录区域地壳抬升历史。以武家湾河下游平甸河为研究重点,通过野外河流阶地级序及沉积特征的调查并结合光释光（OSL）测年结果,厘定了平甸河4级河流阶地,T4、T3、T2及T1阶地河拔高度分别为61～96 m、35～54 m、19～43 m、3～5 m,分别形成于974 kaBP、739 kaBP、483 kaBP、23 kaBP,根据对阶地成因的探讨,认为T4、T3、T2阶地为构造阶地,T1阶地为气候阶地,阶地资料揭示晚更新世（Qp3）太行山南缘经历3次间歇性构造抬升后至少隆升了90 m: 第一次抬升26～42 m、抬升速率111～179 mm/a,第二次抬升11～27 m、抬升速率043～105 mm/a,第三次抬升16～39 m、抬升速率035～085 mm/a。本研究为河流阶地对新构造运动的响应研究提供了实际材料,对晚更新世太行山的形成及演化研究具有较重要的参考价值。  相似文献   

大九湖钻孔记录的神农架地区中更新世晚期以来的气候环境变化   总被引：2，自引：0，他引：2  

郑秋凤  张茂恒  李吉均  舒强  陈晔  萧家仪  赵志军 《地理研究》2014,33(6):1167-1177

运用孢粉浓缩物AMS ¹⁴C测年和氨基酸测年方法结合气候地层对比,建立神农架地区大九湖盆地DJH-2 孔的地层年代序列。依据孢粉分析结果并结合沉积环境,将大九湖盆地中更新世晚期以来的植被演替和古气候演化划分为六个阶段：① 275.0-188.0 ka,寒冷偏干,寒温带针叶林、高山草甸;② 245.0-188.0 ka,暖湿偏干,常绿、落叶阔叶混交林;③ 188.0-129.0 ka,冷干,寒温带针叶林为主,过渡为高山草甸为主;④ 129.0-71.8 ka,暖湿,暖温带落叶阔叶林;⑤71.8-15 ka,冷干,寒温带针叶林与高山草甸间隔发育,中间有喜暖种属增多的迹象;⑥ 15.0-1.0 ka,暖湿,亚热带常绿、落叶阔叶林。孢粉组合特征及单种属特征所显示的盆地气候变化反映了良好的全球冰期、间冰期气候旋回。孢粉浓度特征反映大九湖盆地气候变化受北半球高纬冰量与低纬太阳辐射的双重控制。  相似文献   

重庆穿洞遗址大马蹄蝠化石发现及其意义     

武仙竹  王运辅  王超 《热带地理》2014,34(1):1-8

2008年,重庆穿洞遗址发掘出一具保存较好的晚更新世大马蹄蝠（Hipposideros armiger）化石,这是中国发现的第5个大马蹄蝠化石地点,同时,也是迄今为止所发现保存最为完整的标本。对该地点化石材料观测显示：大马蹄蝠在与其他翼手目标本进行形态对比时,可以根据其个体大小、颅骨形状及齿式特征等进行多项有效鉴别。在大马蹄蝠演化方面,从化石材料上观察,更新世晚期大马蹄蝠桡骨长度与现生标本基本一致,这反映出大马蹄蝠在更新世晚期其飞翔能力与现生标本相似（桡骨长度增大,这是翼手目与一般哺乳动物相比在演化方面的特化现象）。穿洞大马蹄蝠化石的发现,对研究长江三峡地区第四纪古环境具有重要意义。它证明了更新世晚期时三峡地区有温暖湿润的气候和繁茂的森林植被,并且分布有为翼手目提供居址栖息的大型岩溶洞穴;晚更新世时期,出现于中国其他地区的冰期气候等恶劣环境现象,未曾对长江三峡地区动、植物生存环境造成影响。  相似文献   

库木库里背斜活动性初步研究          下载免费PDF全文

孙浩越  何宏林  付碧宏  杨顺虎  白濱吉起  池田安隆  狩野谦一  越後智雄 《地震地质》2014,36(1):1-13

库木库里盆地位于青藏高原北缘,与柴达木盆地一山之隔,是二者的过渡地带,也是高原主体部分向NE扩展的前缘地区;现今构造表现为被3条大型活动构造带(走滑的阿尔金断裂带、东昆仑断裂带和逆冲的祁漫塔格褶皱逆冲系)所夹持。因此,该盆地对于研究青藏高原北缘的构造活动性、活动历史,探讨高原的扩展模式具有十分重要的意义。虽然库木库里盆地南、北两侧均发育活动性很强的大型走滑断裂,但是在盆地中央发育1条大型背斜,走向NWW-SEE,与祁漫塔格褶皱逆冲系和柴达木盆地内的褶皱构造走向一致,说明盆地目前遭受NNE向的挤压。通过对盆地地形横、纵剖面和阶地展布形态的分析,得出背斜有自西向东扩展变形的特征;野外调查和测年结果显示,背斜东段冰川融水形成了大型冰水扇,形成年龄为(87.09±2.31)~(102.4±3.7)ka,进而获得背斜东段自晚更新世以来平均隆升速率的最大值为(2.78±0.28)~(3.28±0.28)mm/a。库木库里盆地整体的活动性很强,在构造上与其北边的柴达木盆地类似,都受控于阿尔金断裂南侧的NNE向的区域挤压作用。  相似文献   

Towards a detailed distal tephrostratigraphy in the Central Mediterranean: The last 20,000 yrs record of Lago Grande di Monticchio     

Sabine Wulf  Michael Kraml  Jörg Keller 《Journal of Volcanology and Geothermal Research》2008

A detailed compilation of distal tephrostratigraphy comprising the last 20,000 yrs is given for the Central Mediterranean region. A total of 47 distinct ash layers identified in the maar lake sediments of Lago Grande di Monticchio (Basilicata, Southern Italy) are compared with proximal and distal terrestrial-marine tephra deposits in the circum-central Mediterranean region. The results of these studies provide valuable information for reconstructing the Late Pleistocene and the Holocene dispersal of pyroclastic deposits from south Italian explosive volcanoes, in particular Somma-Vesuvius, the Campi Flegrei caldera, Ischia Island and Mount Etna. Prominent tephras are discussed with respect to their reliability as dating and correlation tools in sedimentary records. Ashes from Plinian eruptions of Somma-Vesuvius (i.e. Avellino, Mercato, Greenish, Pomici di Base), for instance, are well-defined by their distribution patterns and their unique composition. The widespread Y-1 tephra from Mount Etna, on the other hand, derived most likely from two distinct Plinian events with changing wind conditions, and therefore becomes a less reliable stratigraphic marker. Statistical–numerical calculations are presented in order to discriminate between Holocene tephras from the Campi Flegrei caldera (i.e. Astroni 1–3, Agnano Monte Spina, Averno 1, Lagno Amendolare), since these ashes are characterized by an almost indistinguishable chemical fingerprint. As a highlight, numerous Campanian eruptions of proposed low-intensity have been identified in the distal site of Monticchio suggesting a revision of existing tephra dispersal maps and re-calculation of eruptive conditions. In summary, the tephra record of Monticchio is one of the key successions for linking both, terrestrial records from Central-southern Italy and marine sequences from the Tyrrhenian, Adriatic and Ionian Seas.  相似文献   

The microtine distribution and its environmental significance since the Middle Pleistocene in Zhangping Caves of the Qinling Mountains     

Li YongXiang  Xue XiangXu 《中国科学D辑(英文版)》2008,51(2):294-299

Three microtine species are recovered from the Zhangping Caves of the Qingling Mountains, namely Microtus oeconomus, Caryomys inez and Caryomys eva. They are climate-sensitive ones with different ecological habits, therefore their distribution well corresponds to environmental variations. Statistical comparison of the distribution of fossil microtines and their counterparts nowadays displays that the climate variation of the studied area and its contiguity since the middle Pleistocene are: warm and humid at 493 ka ago, cool and humid at 259 ka ago―cold and humid at 205 ka ago―cool and humid at 28 ka ago, and warm and dry at present.  相似文献   

High-harmonic geoid signatures related to glacial isostatic adjustment and their detectability by GOCE     

L.L.A. Vermeersen  H.H.A. Schotman   《Journal of Geodynamics》2008,46(3-5):174

The Earth’s asthenosphere and lower continental crust can regionally have viscosities that are one to several orders of magnitude smaller than typical mantle viscosities. As a consequence, such shallow low-viscosity layers could induce high-harmonic (spherical harmonics 50–200) gravity and geoid anomalies due to remaining isostasy deviations following Late-Pleistocene glacial isostatic adjustment (GIA). Such high-harmonic geoid and gravity signatures would depend also on the detailed ice and meltwater loading distribution and history.ESA’s Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellite mission, planned for launch in Summer 2008, is designed to map the quasi-static geoid with centimeter accuracy and gravity anomalies with milligal accuracy at a resolution of 100 km or better. This might offer the possibility of detecting gravity and geoid effects of low-viscosity shallow earth layers and differences of the effects of various Pleistocene ice decay scenarios. For example, our predictions show that for a typical low-viscosity crustal zone GOCE should be able to discern differences between ice-load histories down to length scales of about 150 km.One of the major challenges in interpreting such high-harmonic, regional-scale, geoid signatures in GOCE solutions will be to discriminate GIA-signatures from various other solid-earth contributions. It might be of help here that the high-harmonic geoid and gravity signatures form quite characteristic 2D patterns, depending on both ice load and low-viscosity zone model parameters.  相似文献   

New insights into Late Pleistocene explosive volcanic activity and caldera formation on Ischia (southern Italy)   总被引：2，自引：1，他引：1  

Richard J. Brown  Giovanni Orsi  Sandro de Vita 《Bulletin of Volcanology》2008,70(5):583-603

A new pyroclastic stratigraphy is presented for the island of Ischia, Italy, for the period ∼75–50 ka BP. The data indicate that this period bore witness to the largest eruptions recorded on the island and that it was considerably more volcanically active than previously thought. Numerous vents were probably active during this period. The deposits of at least 10 explosive phonolite to basaltic-trachyandesite eruptions are described and interpreted. They record a diverse range of explosive volcanic activity including voluminous fountain-fed ignimbrite eruptions, fallout from sustained eruption columns, block-and-ash flows, and phreatomagmatic eruptions. Previously unknown eruptions have been recognised for the first time on the island. Several of the eruptions produced pyroclastic density currents that covered the whole island as well as the neighbouring island of Procida and parts of the mainland. The morphology of Ischia was significantly different to that seen today, with edifices to the south and west and a submerged depression in the centre. The largest volcanic event, the Monte Epomeo Green Tuff (MEGT) resulted in caldera collapse across all or part of the island. It is shown to comprise at least two thick intracaldera ignimbrite flow-units, separated by volcaniclastic sediments that were deposited during a pause in the eruption. Extracaldera deposits of the MEGT include a pumice fall deposit emplaced during the opening phases of the eruption, a widespread lithic lag breccia outcropping across much of Ischia and Procida, and a distal ignimbrite in south-west Campi Flegrei. During this period the style and magnitude of volcanism was dictated by the dynamics of a large differentiated magma chamber, which was partially destroyed during the MEGT eruption. This contrasts with the small-volume Holocene and historical effusive and explosive activity on Ischia, the timing and distribution of which has been controlled by the resurgence of the Monte Epomeo block. The new data contribute to a clearer understanding of the long-term volcanic and magmatic evolution of Ischia.  相似文献