下辽河平原晚更新世泥炭的发现及其古气候意义

位于沈阳市东部和西部的2个钻孔剖面均有晚更新世晚期泥炭发育。¹⁴C测年结果表明：东部钻孔泥炭层形成于玉木亚间冰期晚期,西部泥炭层形成于玉木亚间冰期结束之后。孢粉分析结果表明：东部钻孔剖面中的泥炭以暖温带落叶阔叶植物花粉为主,指示温暖湿润的气候环境;西部钻孔剖面中的泥炭以温带草本被子植物花粉为主,山地针、阔叶植物花粉为辅,指示温干偏湿的气候环境。定量古气候分析结果表明,玉木亚间冰期晚期沈阳地区与现今气候相当;玉木亚间冰期结束之后,沈阳地区的气候比现在稍冷。     

Late Oligocene-early Miocene evolution of the Lunpola Basin,central Tibetan Plateau,evidences from successive lacustrine records

Widespread Cenozoic sediments in and around the Tibetan Plateau (TP) are thought to have played an important role in explaining the process of the India-Asia collision as well as its interactions with global and regional paleoclimate. However, high-resolution temporal frameworks of sedimentary sequences and controls on geological and climatic events are still absent. To study the abovementioned issues, we investigate the Oligocene-Miocene lacustrine sequences (the Dingqinghu Formation) of the Lunpola Basin, central TP. In this work, cyclostratigraphic analyses are conducted with gamma ray log and pollen data to establish a high resolution temporal framework ranging from ca. 25.4 to 18.0 Ma for the sections. Along these sections, sediment accumulation rates are calculated with orbital signals to monitor clastic input of the lake basin; elemental, palynological, and isotopic data are summarized to depict the paleoclimate and paleoelevation evolution of this drainage system. Integrating all these clues together, we sort out a chronological list of events including lake basin, tectonics, and paleoclimate: regional uplift took place at 23.7 Ma; simultaneously, a distinct lake-basin transition characterized by accelerated sediment accumulation rate is recognized; about 0.2 Ma later at 23.5 Ma, catchment scale drought occurred and maintained to the end of the sections. Our results demonstrate that paleoclimate did not impose decisive influence on the late Oligocene-early Miocene evolution of the lake basin; instead, regional uplift and its associated accelerated exhumation of the source area resulted in the lake-basin transition and paleoclimatic drought. After reviewing the Oligocene-Miocene sedimentary records distributed in and around the TP, we argue that the 23.7 Ma geological event of the Lunpola Basin is probably not a single case but a regional effect of a dramatic tectonic transition of the plateau.     

西藏佩枯错盆地晚更新世以来的孢粉组合特征及其古气候意义

西藏佩枯错盆地晚更新世以来河湖相沉积剖面的孢粉分析显示,该地区在晚更新世早期的127—72 ka B.P.时期,气候温和湿润,植被以针阔叶混交林为主;至66—56 ka B.P.时期,气候转变为温凉略干,植被转为疏林草原;在56—49 ka B.P.时期,气候温凉潮湿,植被又转为针阔叶混交林为主的森林草原;而在49—46 ka B.P.时期,气候温和偏干,植被转为疏林草原;在46—31 ka B.P.时期,气候寒凉湿润,植被表现为温度进一步下降的疏林草原;在31—15 ka B.P.时期,环境向寒冷方向发展,植被转为高寒草原;自11 ka B.P.(全新世初期)开始,气候由温暖偏干转变为温凉偏湿,植被由灌丛草原转变为森林灌丛草原.这表明自晚更新世以来,该区气候环境是在逐渐变干的总趋势上,经历了多次明显的冷暖与干湿波动.     

宁晋泊晚更新世以来气候变化的正构烷烃分子记录

华北地区晚更新世以来气候变化研究具有重要的意义.选择宁晋泊地区开展河湖相沉积物的分子化石研究.结果表明,沉积物中正构烷烃碳数分布范围为C₁₅~C₃₃,高碳数奇碳优势明显,多以C₂₉和C₃₁为主峰的单峰分布,少量样品出现以C₁₇为次主峰的双峰分布,表明有机质以陆生植物和大型水生植物为主.结合正构烷烃参数,分析了宁晋泊地区晚更新世以来的气候演变过程,展现了"83~68 ka气候较为温和,湖泊水位较低;68~30 ka气候暖湿,湖泊扩张;30~22 ka气候冷干,湖泊萎缩;22~10 ka气候好转,湖泊水位上升;全新世气候温和适度,湖泊水位略有降低"的特征.区域对比分析表明,末次冰期以来宁晋泊地区与延庆盆地等地的气候变化基本一致,具有冰期-间冰期旋回特征,说明其主要受太阳辐射的控制.      

Middle Miocene to Pleistocene sedimentary record of rift evolution in the southern Albert Rift (Uganda)

This study presents an almost complete Middle Miocene to Pleistocene sequence of synrift sediments in the western branch of the East African Rift. The studied succession is exposed in several patches on an eastward tilted block between the northern tip of the Rwenzori Block and the eastern shoulder of the Albert Rift. In this position, it reaches a maximum thickness of 600 m of which 350 m have been logged systematically by analysing lithofacies and sediment architecture. Stratigraphic subdivision of the succession relies on published biostratigraphic data of endemic mollusc associations and their correlation across East Africa. The synrift sediments encountered are siliciclastics ranging from clay to coarse gravel with gypsum and ferrugineous interlayers or impregnations. Lithofacies and architectural analysis indicate alluvial plain, delta plain, nearshore, delta front, or lacustrine depositional environments. Based on the vertical stacking pattern, prograding and retrograding trends of the depositional environments, and climatic indicators (e.g. conservation of feldspar, gypsum, and/or iron hydroxide precipitation), four evolutionary phases can be distinguished: (i) a first phase between ca. 14.5 and 10.0 Ma is characterised by bedload-dominated fluvial environment with massive sandy to gravelly bedforms, feldspar-rich sands, rare iron impregnations and relatively low accommodation space. This phase is interpreted as pre- and early synrift sedimentation under a semiarid climate. (ii) From ca. 10.0 to 4.5 Ma predominantly fine-grained siliciclastics were deposited in a distal fluvial plain to lacustrine setting characterised by limited accommodation space. Fluctuation of thin beds, dominance of clay and frequent iron impregnations point to a more humid climate with seasonality and weak tectonic activity. (iii) During the third phase between 4.5 and 2.0 Ma delta plain and nearshore deposits with frequent ferrugineous impregnations and rich mollusc associations occurred, indicating a humid period with lake-level highstands and accelerated subsidence. (iv) During the final sedimentary interval between 2.0 and 1.5 Ma gravel units reoccurred with less iron- but more carbonate and gypsum impregnations, and arkosic sandstones. This phase recorded a general aridisation trend most probably caused by the upcoming rain barrier of the Rwenzori Mountains together with accelerated rift-flank uplift and strong subsidence of the rift floor. The results of this study are of particular importance for delineating key controls on sedimentation in the Albert Rift.     

Late Eocene-early Miocene palaeogeographic evolution of central eastern Anatolian basins,the closure of the Neo-Tethys ocean and continental collision

In central eastern Anatolia which is located between Eurasia and Africa, the study of basin developments between late Eocene and early Miocene is of great importance for understanding the process of the closure of the Neo-Tethys Ocean and the formation of strike-slip faults and regional uplift. To study these, three basins were selected: the Sivas-Erzincan, Gürün-Akkisla-Divrigi (GAD), and Malatya basins. The study proposes that the opening of the GAD basin played a key role in the formation of the Ecemis fault, which started developing at the end of early Miocene, and in mountain uplift. All these basins are situated on continental blocks and oceanic crust, arranged from north to south as the Sakarya continent, the Izmir-Ankara-Erzincan ocean (Northern Neo-Tethys), the Kirsehir continent, the inner Tauride ocean, the Munzur-Binboga block, the Maden (=Berit) ocean, the Bitlis-Pütürge block, the Çüngüs ocean and the Arabian continent.The findings indicate that late Eocene-early Miocene successions in these basins were not deposited in foreland basins formed in front of the thrust faults associated with the closure of the ocean, as stated in previous studies. Rather, they were deposited in forearc and backarc basins related to the subduction which was effective until the end of early Miocene. The Sivas-Erzincan and Malatya basins, located on the inner Tauride and Maden (=Berit) oceans, were forearc basins, while the GAD basin situated on the Munzur-Binboga block was a backarc basin. These basins have parallel developments up to the end of early Miocene. While marine sediments were deposited in the Malatya and Sivas-Erzincan basins between late Eocene and early Miocene, terrestrial units began to settle in the GAD basin from the late Eocene and the deposition there is continuous until the end of the early Miocene.Collision of the Arabian and the Anatolian plates at the end of early Miocene (16-18 Ma) produced the left-strike slip Ecemis fault zone, which caused the lateral slip of sedimentary units in the Sivas-Erzincan and GAD basins over hundreds of kilometers. This event produced the first westward tectonic escape of the Anatolian plate prior to the north Anatolian fault (NAF) and the east Anatolian fault (EAF). The Gürün region located in the GAD basin was exhumed in late Miocene and this basin was broken. The Gürün region, which remains on the rising part of the Munzur-Binboga block, is not a different basin as stated earlier, but it is a part of the GAD basin, representing the central part of the GAD basin lake, as indicated by the fine grained deposits (limestones and clay) that occur in the Gürün area.     

Middle and Late Pleistocene fluvial systems in central Poland

This reconstruction of the fluvial palaeogeography of central Poland is based on an exhaustive and critical review of the published and archival data for the Middle and Late Pleistocene sediments of the area. The Warsaw Basin in central Poland was a major confluence area during the Middle and Late Pleistocene. The fluvial watersheds have been only slightly modified since that time. The past river systems resembled the contemporary one, therefore indicating rebuilding during successive interglacials, at least since the Holsteinian when the sea undoubtedly occupied the southern Baltic Basin. The Weichselian fluvial system was strongly influenced by the Scandinavian ice sheet, especially by meltwater runoff in the extraglacial area and ice-damming in the Warsaw Basin where a large proglacial lake developed. The Weichselian fluvial sediments form up to three terraces in the valleys of the Vistula and its tributaries. The most contentious issue is the mutual relation of the ice-dammed lake and ice marginal spillways in the Warsaw Basin, both being important fragments of a widespread drainage network in the Central European Lowland.     

Late Pleistocene raised beaches of coastal Estremadura,central Portugal

We present new stratigraphic, sedimentological, and chronological data for a suite of tectonically raised beaches dating to Marine Isotope Stages 5, 4, and 3 along the Estremadura coast of west-central Portugal. The beach deposits are found in association with ancient tidal channels and coastal dunes, pollen bearing mud and peat, and Middle Paleolithic archaeological sites that confirm occupation of the coastal zone by Neanderthal populations. The significance of these deposits is discussed in terms of the archaeological record, the tectonic and geomorphic evolution of the coast, and correlation with reconstructions of global climate and eustatic sea-level change. Direct correlation between the Estremadura beach sections is complicated by the tectonic complexity of the area and the age of the beach deposits (which are near or beyond the limit of radiocarbon dating). Evidence from multiple sites dated by AMS radiocarbon and optical luminescence methods suggests broad synchroneity in relative sea-level changes along this coast during Marine Isotope Stage 3. Two beach complexes with luminescence and radiocarbon age control date to about 35 ka and 42 ka, recording a rise in relative sea level around the time of Heinrich Event 4 at 39 ka. Depending on assumptions about eustatic sea level at the time they were deposited, we estimate that these beaches have been uplifted at rates of 0.4–4.3 mm yr^?1 by the combined effects of tectonic, halokinetic, and isostatic processes. Uplift rates of 1–2 mm yr^?1 are likely if the beaches represent sea level stands at roughly 40 m below modern, as suggested by recent eustatic sea level reconstructions. Evidence from coastal bluffs and the interior of the study area indicates extensive colluvial, fluvial, and aeolian sedimentation beginning around 31 ka and continuing into the Holocene. These geomorphic adjustments are related to concomitant changes in climate and sea level, providing context that improves our understanding of Late Pleistocene landscape change and human occupation on the western Iberian margin.     

大凌河河口地区中更新世晚期以来沉积环境演化

大凌河河口地区LZK06孔40m以浅岩心的沉积学、古生物学和年代学等综合研究以及该地区LZK02-04钻孔资料,揭示了研究区中更新世晚期以来经历了两次海侵-海退旋回,依次形成了中更新世晚期湖相/河流相→晚更新世海相-湖相/河流相→全新世海相-河流相地层。全新世早中期由于物源供给很少,研究区处于长达约10ka的饥饿滞留相沉积环境,平均沉积速率仅约0.02～0.05cm/a。全新世晚期约1500a cal BP以来,由于人类活动导致水土流失,河流输砂量增加,研究区开始了快速加积过程,平均沉积速率约0.9～1.2cm/a,下辽河平原被快速充填,开始成陆。与全球海面变化时空分布特征的对比,推断辽东湾的第II海相层发育于MIS 5-MIS 3早期,第I海相层发育于MIS 1阶段高海面时期。晚更新世以来频繁的海面升降是辽东湾泥质海岸带地层和环境演化的主要控制因素。     

南黄海西北部晚更新世以来的沉积环境演化

利用在南黄海西北部陆架获得的3500 km高分辨率浅地层剖面资料,结合3口地质钻孔的岩芯资料,建立了研究区晚更新世以来的沉积地层格架,厘定了地层地质年代。研究表明,过孔的浅地层剖面与钻孔岩芯的沉积地层有很好的对应关系。浅地层剖面可划分出5个主要不整合面(T5～T1)和6个主要地震单元(SU6-SU1),相应的钻孔岩芯可划分出6个主要的沉积单元(DU6-DU1),反映了大约128 ka以来的地层结构和沉积环境演化。钻孔沉积物岩性相特征、测年数据和地层反射特征表明研究区氧同位素5期(MIS5)发育了滨浅海相和三角洲相沉积,MIS 4发育了河流湖泊相沉积,MIS 3发育了三角洲相沉积,MIS 2发育了河流和河口相沉积,MIS 1发育了近岸水下楔形沉积。晚更新世以来,南黄海构造相对稳定,影响沉积环境演化的主要因素是海平面变化和沉积物物源。本文的研究对于深入了解南黄海西北部陆海相互作用过程、地质环境演化以及揭示全球变化的区域响应具有重要的科学意义。     

The late Miocene to Pleistocene ice-rafting history of southeast Greenland

Analysis of a Miocene-Pleistocene ice-rafted debris (IRD) record from the western Irminger Basin provides evidence for the initiation and long-term behavior of the SE portion of the Greenland Ice Sheet. In the late Miocene (~7.3 Ma), IRD supply to Ocean Drilling Program site 918 increased significantly indicating that glaciers large enough to reach sea level were present in SE Greenland long before the onset of widespread Northern Hemisphere glaciation. IRD accumulated at this site throughout the Pliocene and Pleistocene, supporting the hypothesis that SE Greenland was a key nucleation area for the formation of the Greenland Ice Sheet. Since glacial onset, the western Irminger Basin IRD record is characterized by a succession of episodes with high IRD mass accumulation rates (MARs). The site 918 IRD record indicates that greatest iceberg production in SE Greenland occurred during major climatic transitions (e.g. widespread Northern Hemisphere glacial expansion at 2.7 Ma and the mid-Pleistocene climate shift at 0.9 Ma), and that SE Greenland sometimes also led the northern North Atlantic region in glacial response to climatic forcing (e.g. glacial intensification at ~4.8 and, along with NE Greenland, at ~3.5 Ma).     

藏南吉隆盆地中新世—早更新世沉积演化

位于喜马拉雅北麓的吉隆盆地中新统旦增竹康组,为冲积扇-辫状河沉积。沃马组沉积演化自下而上依次为扇三角洲-滨浅湖-扇三角洲,总体上表现为进积-退积-进积的沉积旋回。沃马剖面在10～7.4Ma期间,古流向主体为SEE向;7.4～1.67Ma,古水流方向主体为SWW向,说明7.4Ma以后,吉隆盆地古地理格局发生显著变化,古地势由原来的西高东低转变为后期的东高西低。根据沉积学、磁性地层学、年代学等方面的研究资料,将10Ma以来吉隆盆地的湖盆演化大致划分为3个阶段:10～7.4Ma,湖盆裂陷形成期;7.4～3.6Ma,湖盆扩展与稳定发展期;3.6～1.67Ma,湖盆萎缩消亡期,代表了盆地周围喜山的3次隆升期,即10～7.4Ma、7.4～3.6Ma和3.6～1.67Ma,其中3.6～1.67Ma为强烈隆升期。     

Glacial drainage towards the Mediterranean during the Middle and Late Pleistocene

To a varying degree the Middle and Late Pleistocene ice sheets in northern Eurasia redirected the drainage of major catchments in Europe and western Siberia from the North Sea and Arctic Ocean south to the Caspian, Black Sea, and ultimately the Mediterranean. During the Late Weichselian, glacial meltwater reached the Mediterranean through the Dniepr and Don catchments and to a minor extent through the Danube. During the Warthe Substage of the Saalian, meltwater from the Volga was most likely added. During the Drenthe Substagc of the Saalian the watershed shifted Par to the east, and meltwater reached the Mediterranean also from the Oh. Irtysh, Yenisei, and Tunguska catchments in Siberia. Depending on the extent of the ice sheets, the increase in freshwater supply during deglaciations resulted in reductions of Mediterranean overflow into the North Atlantic. Such overflow reductions may have reduced vapour transport to the ice sheets and thus accelerated wastage.     

Middle to Late Pleistocene palaeoenvironmental evolution of the southeastern Alpine Valeriano Creek succession (northeastern Italy)

The Middle–Late Pleistocene alluvial and lacustrine succession of Valeriano Creek (southeastern Alpine foothills, 190 m a.s.l.) documents the environmental evolution of the piedmont plain before the onset of the Last Glacial Maximum (LGM). The sedimentary record was investigated by multidisciplinary stratigraphical and sedimentological studies coupled with petrographic and palaeobotanical analysis. A chronology has been provided by luminescence, radiocarbon dating and pollen biochronology. The succession developed at the valley mouth of a small catchment and is confined in the piedmont plain by the alluvial fans of major rivers. The oldest deposits were formed during a cold phase during the late Middle Pleistocene. This part of the piedmont plain was generally stable until Termination II, when it was trenched more than 15 m deep by watercourses. The infilling succession of the trench, mostly by low‐energy alluvial sediments interbedded with mire and peat deposits, documents, for the first time on the southern side of the Alps, the relationships between fluvial activity, vegetation and climate change at the foothills piedmont plain during late Marine Isotope Stage (MIS) 5. The stadial–interstadial climate forcing implies a local reorganisation of fluvial dynamics and of forest composition, although substantial plant cover persisted even during cooler stadials. In accordance with coeval alluvial and speleothem records from the northern side of the Alps, this environmental evolution supports a very restricted Alpine glaciation of the main fluvial catchments of the southeastern Alps during MIS 5a–d. Copyright © 2009 John Wiley & Sons, Ltd.     

Late Pliocene to late Pleistocene environments preserved at the Palisades Site, central Yukon River, Alaska

The Palisades Site is an extensive silt-loam bluff complex on the central Yukon River preserving a nearly continuous record of the last 2 myr. Volcanic ash deposits present include the Old Crow (OCt; 140,000 yr), Sheep Creek (SCt; 190,000 yr), PA (2.02 myr), EC (ca. 2 myr), and Mining Camp (ca. 2 myr) tephras. Two new tephras, PAL and PAU, are geochemically similar to the PA and EC tephras and appear to be comagmatic. The PA tephra occurs in ice-wedge casts and solifluction deposits, marking the oldest occurrence of permafrost in central Alaska. Three buried forest horizons are present in association with dated tephras. The uppermost forest bed occurs immediately above the OCt; the middle forest horizon occurs below the SCt. The lowest forest bed occurs between the EC and the PA tephras, and correlates with the Dawson Cut Forest Bed. Plant taxa in all three peats are common elements of moist taiga forest found in lowlands of central Alaska today. Large mammal fossils are all from common late Pleistocene taxa. Those recovered in situ came from a single horizon radiocarbon dated to ca. 27,000 ¹⁴C yr B.P. The incongruous small mammal assemblage in that horizon reflects a diverse landscape with both wet and mesic environments.     

西藏阿里孔雀河晚更新世以来的阶地发育特征

一直以来,喜马拉雅山河流阶地发育的控制因素广受讨论。本研究选取了喜马拉雅山北坡的孔雀河作为分析对象,通过详细的野外考察和精确定年,探究了气候变化和构造运动对阶地发育的影响。结果表明孔雀河共发育了5级河流阶地,且均为基座阶地。阶地面砾石的¹⁰Be暴露测年揭示了T5~T1阶地分别形成于88.8±5.8 ka、约18.7~16.8 ka、14.5±1.3 ka、11.9±1.2~11.2±1.1 ka和1.9±0.5 ka;对比青藏高原气候变化资料以及恒河、印度河上游阶地研究成果,表明轨道尺度的气候变化或千年尺度的快速气候变化导致河流堆积下切过程快速转换,形成多级河流阶地。在降水较少的冷期,河道水动力条件减弱,河道堆积;在印度季风增强的暖期,侵蚀能力增强,河道快速下切。研究区晚更新世至末次冰盛期（LGM）期间的河流下切过程稳定,下切速率约为0.5 mm/a;LGM以来,孔雀河下切速率加快,约为1.0~1.8 mm/a。

     

Morphology and post-Chaudian (Late Pleistocene) evolution of the submarine Danube fan complex

The Danube deep sea fan in the northwestem Black Sea has a lateral dimension of over 150 km and stretches from several hundred metres water depth down to the abyssal plain. Eight seismic sequences have been recognized in the fan complex. Each sequence consists of channel, levee and overbank deposits, as well as mass transport units. The Danube and the Ukrainian rivers have aggraded two surficial channel-levee systems which diverge and decrease in volume downfan. The channels of these systems have a low sinuosity, implying young age, steep gradients and/or limited sediment supply. Significant channel migration occurred in the course of fan development, which could be largely controlled by relative sea-level changes. The six youngest sequences mapped have been correlated to sea-level fluctuations from the post-Chaudian regression to the present day.     

Drainage evolution in south and east England during the Pleistocene

Two major river systems operated in southern and eastern England throughout the Pleistocene: the river Thames and the Solent river. Both rivers are axial streams of comparable size draining major basinal structures comprising similar Tertiary and Mesozoic rocks. Although the modem Thames flows broadly W-E in the London Basin, upstream of Reading it flows from the north to drain the south Midlands. It was diverted to its present course through London by glaciation in the Anglian (Elsterian) before which it flowed across East Anglia into the southem North Sea. The Solent river no longer exists since most of its course was drowned by eustatic sea-level rise during the Flandrian Stage (Holocene). Previously, it flowed eastwards across SE Dorset and S Hampshire as an extension of the modem river Frome in the Hampshire Basin. During periods of low sea-level (cold stages) it was a tributary of the 'Channel River'. Fluvial aggradations provide evidence of the former courses of these substantial rivers and their tributaries. The facies and sedimentary structures indicate that the bulk of the deposits in both systems accumulated in braided river environments under periglacial climates. Fossiliferous sediments provide biostratigraphical frameworks. During temperate periods the rivers adopted singlethread courses. Evolution of both rivers reflect their responses to climatic change, local geological structure and long-term tectonic activity. Both rivers are undoubtedly of considerable antiquity, their records potentially extend from the Early Pleistocene or Late Pliocene, but they may have originated in the early Tertiary.     

晚更新世江苏海岸带沉积分布模拟研究

中国边缘海大陆架在晚更新世时期曾是海岸平原,在古长江、古黄河泥沙填充下形成了陆架堆积体,并在全新世发育了南黄海辐射沙脊群、废黄河三角洲和长江三角洲。根据点状的地质钻孔分析和重建,对南黄海-江苏海岸的沉积体系的分布和变化机制尚不明了。作为动力机制探讨,基于气候-海面-沉积系统,根据气候水文学、沉积学原理以及泥沙沉积面的动态高程计算,构建了气候冰川驱动-东黄海地海系统响应-河流沉积建造的数值模式,模拟了14万年、4万年和1万年不同时间尺度江苏海岸线和长江三角洲沉积的变化过程和分布,进而对冰川气候、构造沉降、沉积压实等复杂效应下的海面特征、陆源泥沙沉积和海岸线进行分析。模拟结果与地质钻孔资料揭示的层序和埋深能够进行对比。