陕西蓝田公王岭黄土古土壤序列的磁组构特征及其古环境意义

对黄土高原南部边缘公王岭黄土剖面的磁组构的研究发现,该剖面与前人的研究结果有一些相似之处,但更具有其特殊性.几乎所有样品的磁面理值F都大于磁线理值L,各向异性度P与磁面理值F相关性较高,磁化率椭球体表现为压扁状.水成黄土的P、L和F值均大于典型黄土古土壤,而混合黄土或古土壤则介于这两者之间.且典型黄土的P、L和F值也比典型古土壤高.另一方面,水成黄土的最大磁化率主轴方向为SW方向,与现代灞河水系的方向一致,其次要的方向为NNW方向.典型黄土的方向表现为SWW方向,而典型古土壤则为NNW方向,这是由于秦岭山脉的阻隔作用造成的.混合黄土或古土壤受到季风和坡面流水的共同作用,其最大磁化率主轴方向表现为EW方向.不同类型沉积物代表了不同的古环境古气候条件,这一切都可能受控于秦岭山脉阶段性抬升等构造运动的影响.本研究结果也将为进一步了解蓝田直立人的生存环境提供新的方法.     

Late Weichselian and holocene sea-level history for a cross-section of western Norway

The postglacial sea-level history along a cross-section of western Norway has been studied in detail. Ten local sea-level curves were used to construct an equidistant shoreline diagram, covering the last 13000 years. This includes 76 radiocarbon dates, of which the majority represent lacustrine sediments at the marine/lacustrine boundary in cores from emerged lakes. The distance between the westernmost and easternmost sites is 170 km and the difference in total emergence along this profile is more than 200 m. The shorelines all dip westward with a decreasing gradient through time. The Late Weichselian lines are all slightly curved whereas the Holocene lines are apparently straight. After the formation of the uppermost shoreline by around 12 800 BP there was a rapid emergence that decelerated with time to a near standstill during the Younger Dryas. From about 10 300 there was again a rapid emergence followed by the Tapes transgression along the coast and a standstill in the most easterly areas. At the western end of this profile, the Tapes transgression started around 9000 and culminated approximately 6000 BP, when a gradual regression occurred. To the east the early Holocene regression minimum occurs at a younger date and the transgression maximum is up to 1500 years older.     

Climate changes during the last c. 7500 years as recorded by the degree of peat humification in the Lofoten region,Norway

Vorren, K.‐D., Jensen, C. E. & Nilssen, E. 2012 (January): Climate changes during the last c. 7500 years as recorded by the degree of peat humification in the Lofoten region, Norway. Boreas, Vol. 41, pp. 13–30. 10.1111/j.1502‐3885.2011.00220.x. ISSN 0300‐9483. Two peat cores from two neighbouring bogs in Lofoten, northern Norway were densely AMS dated and analysed for humification. The two cores have been influenced by human agricultural impact, especially c. 1600 cal. a BP, which may have affected the local hydrology of the bogs. From 7400 cal. a BP onwards, 19 distinct wet‐shifts are recorded in the two cores. Eight or nine of these correspond chronologically to periods of low solar activity. This correlation is most convincing during the last 2000 years. Some wet‐shifts are connected with a solar low‐activity period during the Subboreal/Subatlantic transition, which in central Europe is dated at 2750–2565 cal. a BP. For Lofoten, the corresponding Subboreal/Subatlantic transition – or the wet‐shift marking this transition – is dated at c. 2600 cal. a BP. Some wet‐shifts occur just before or just after solar low‐activity periods, but only four of the nineteen wet‐shifts are clearly not temporally connected with periods of low solar activity. Compared with the wet‐shifts in NW European (mainly British Isles) bogs, there are more frequent wet‐shifts in northern Norway. Compared with other peat cores in northern Norway, especially for the interval 6500–5000 cal. a BP, Lofoten deviates by its lack of wet‐shifts. As in England, Scotland and Ireland, there is regional variability in the temporal formation of wet‐shifts in northern Norway.     

渤海湾盆地中原地区古地温梯度恢复研究

渤海湾盆地中新生代具有叠合盆地多期叠加演化的特点,不同地质时期地温场的恢复具有多解性和不确定性。应用包裹体测温、磷灰石裂变径迹分析、Barker温度函数法、EASY%Ro模拟等方法,通过不同构造单元的最高古地温的恢复,进行不同地质时期的地温梯度恢复。研究表明:(1)包裹体测温、磷灰石裂变径迹分析、Barker温度函数等方法仅适用于欠补偿沉积区古地温及古地温梯度恢复;(2)Barker法计算的地温梯度偏高;(3)而EASY%Ro热史模拟方法是补偿-近补偿沉积区古地温梯度恢复的有效方法;(4)三叠纪、侏罗—白垩纪、古近纪是影响上古生界烃源岩演化的关键时期,地温梯度分别为3.3℃/100 m、4.5℃/100 m和4.0℃/100 m。     

Seasonal distribution and variability of atmospheric freeze/thaw cycles in Norway over the last six decades (1950–2013)

This study focused on atmospheric freeze/thaw cycles in Norway and presents the results of processing daily thermal data from 20 Norwegian meteorological stations for the period 1950–2013. Its two major aims were: (i) to provide long‐term time series of atmospheric freeze/thaw cycle data for Norway, and (ii) to analyse their trends over the last six decades. The study highlights the spatial and temporal modalities of the distribution of freeze/thaw cycles in Norway. The differences in the seasonal distributions of cycles and their mean annual number are because of the geographical location of the stations (coastal or inland stations, lowland or mountainous stations) and result from the combined effects of oceanity, continentality, latitude and elevation. The annual average number of freeze/thaw cycles is similar in the north (90) and south of Norway (84) but shows notable differences between coastal stations (27) and inland and/or mountainous stations (114). Since the 1950s, prolonged periods of several years characterized by increasing numbers of cycles have given way to periods of decreasing freeze/thaw frequency. This cyclicity is linked with the Northern Atlantic Oscillation (NAO). Strong positive or negative phases of the NAO since the 1950s have induced marked increases (or decreases) in atmospheric freeze/thaw cycle frequency in Norway.     

A 70-year groundwater recharge record from sandy loess in northwestern China and its climatic implications

The processes and rates of groundwater recharge in arid and semiarid environments are highly related to local climate parameters, particularly precipitation. The chloride profile of an unsaturated zone in an arid and semiarid region can be used to infer the recharge history and past changes in climate, by extension. In this study, a 17-m chloride profile was collected from the sandy loess in the northwestern Chinese Loess Plateau, which also lies in the transition zone between desert and loess. A 71-year groundwater recharge history was reconstructed using the chloride mass balance method with an annual Cl^? input of 0.84 g/m²/year. The reconstructed history revealed a long-term decline in recharge with multiple shorter-term oscillations. Five recharge stages between 1938–1946, 1947–1955, 1956–1975, 1976–2000, and 2001–2008 AD were identified, where the lowest average recharge value was 25.1 mm/a in 1976–2000 AD and the highest was 71.7 mm/a in 1947–1955 AD. Climate conditions during these five periods were also inferred based on the reconstructed recharge rates with the knowledge that high recharge corresponds to more humid climates. The climate over the past 71 years generally became drier in the study area, despite some fluctuations. The reconstructed recharge rates, calculated from 1/Cl^? in the profile, exhibited the same variability as annual precipitation measured in the region, both in long- and short-term oscillations over the period from 1955 to 2008. The chloride concentration variations in the profile, indicating changes in recharge flux, also well correlated with annual precipitation anomalies in the region to the east of 100°E in China for the whole study period. These comparisons verified that it is feasible to study not only groundwater recharge, but also past climate change using a chloride profile from the sandy loess area. The results suggested that unsaturated zones of sandy loess may be valuable archives for reconstructing recharge history and regional paleoclimate changes in the region.     

Historical Comparison of Fish Community Structure in Lower Chesapeake Bay Seagrass Habitats

Seagrass beds provide important habitat for fishes and invertebrates in many regions around the world. Accordingly, changes in seagrass coverage may affect fish communities and/or populations, given that many species utilize these habitats during vulnerable early life history stages. In lower Chesapeake Bay, seagrass distribution has contracted appreciably over recent decades due to decreased water clarity and increased water temperature; however, effects of changing vegetated habitat on fish community structure have not been well documented. We compared fish community composition data collected at similar seagrass sites from 1976–1977 and 2009–2011 to investigate potential changes in species richness, community composition, and relative abundance within these habitats. While seagrass coverage at the specific study sites did not vary considerably between time periods, contemporary species richness was lower and multivariate analysis showed that assemblages differed between the two datasets. The majority of sampled species were common to both datasets but several species were exclusive to only one dataset. For some species, relative abundances were similar between the two datasets, while for others, there were notable differences without directional uniformity. Spot (Leiostomus xanthurus) and northern pipefish (Syngnathus fuscus) were considerably less abundant in the contemporary dataset, while dusky pipefish (Syngnathus floridae) was more abundant. Observed changes in community structure may be more attributable to higher overall bay water temperature in recent years and other anthropogenic influences than to changes in seagrass coverage at our study sites.     

Palaeoenvironmental change recorded in the palaeodunefields of the western Murray Basin,South Australia – New data from single grain OSL-dating

This study is concerned with the reconstruction of the palaeoenvironmental history of southeastern Australia for the last ～300 ka by establishing a luminescence chronology of dune sand deposition in the western Murray Basin (South Australia). In the study area, vast fields of palaeodunes, stabilised by vegetation, provide evidence of past environmental change. In total 98 samples were collected from dune sand layers at 13 different dune sections. The time of their deposition was determined using optically stimulated luminescence dating of single quartz grains, accounting for the impact of post-depositional mixing by the use of a finite mixture model. The oldest depositional phase demonstrates that dune sand layers of great antiquity are preserved in the western Murray Basin, ranging up to at least 380 ka. Phases of substantial dune sand deposition were identified for the periods 18–38 ka and 63–72 ka. Older depositional phases also exist, but are poorly resolved due to relatively large errors of the luminescence ages. Aeolian deposition during the last termination and the Holocene is relatively limited, with a slight clustering of ages at the time of the Antarctic Cold Reversal and from 5–8 ka. Two modern ages give evidence of very recent dune sand deposition. Comparison with other palaeoclimate records from the region suggests that phases with high aeolian sedimentation coincide with more arid conditions and breaks in the dune record with more humid phases. Thus, although dune records are often discontinuous and their interpretation in palaeoclimatic terms is not always straightforward, the palaeodunes of the western Murray Basin show a good preservation of phases of aeolian activity and provide useful information for palaeoenvironmental reconstruction.     

Amino acid ratios in Quaternary molluscs and foraminifera from western Norway: correlation, geochronology and paleotemperature estimates

Isoleucine epimerization (alle/Ue) ratios in the pelecypod Mya truncata and benthic foraminifer Cibicides lobalulus from emerged marine units in western Norway allow construction of a regional relative chronostratigraphy for the Ecmian and Weichselian. Two in situ interglacial sections are considered correlative by the similar biostratigraphy and alle/Ile ratios in C. lobalulus. Overlying sediments at the two sites are of both marine and glacial origin. Neither site contains a complete Weichselian record, but allelic ratios, lithostratigraphy and fauna! changes suggest at least four stadial and three interstadial events occurred along the western Norwegian coast during Early and Middle Weichselian time. Kinetic data defining the relationship between the isoleucine epimerization rate constant and temperature for the species studied allow the estimation of paleotemperatures for samples of known age. Accepting published age estimates for the Eemian interglacial beds, the average Weichselian temperature in western Norway is calculated to have been ca. 4°C below the average Holocene temperature, whereas the last interglacial was 1 to 2°C warmer that the Holocene. The limited temperature depression over this region during the Weichselian implies that coastal western Norway was ice-covered only about 30% of this period, and that Atlantic water, although not necessarily in a warm surface current as today, entered the Norwegian Sea during much of marine isotope stage 5 and intermittently during stage 3. Interpolated amino acid ages date interstadial events at ca. 94 ka, 78 ka and 52 ka, B.P., whereas glacial events are dated ca. 103 ka and bracketed by limiting dates between 78 and 89 ka, between 52 and 63 ka and less than 36 ka B.P.     

Age, origin, and palaeo-ecological evidence of blanket bogs in Nord-Trøndelag, Norway

Pollen diagrams, ¹⁴C-datings, and peat stratigraphy are presented from 3 sites in the Forradal sub-oceanic area in Nord-Trøndelag, a moorland complex of flat and sloping fens and blanket bogs lying 400–500 m above sea-level, ca. 40 km E of the Trondheimsfjord. The vegetational and climatic history during the last 8500 years is described, together with a survey of present-day conditions. The origin of the blanket-bog areas is shown to agree generally, in both time and mode of genesis, with similar bog types in Scotland and N England. Dates are given for the expansion of both alder and spruce, the latter occurring more than 1000 years later than in SE Norway. The possible role of provenance formation and Roman Iron Age amelioration of the climate is discussed in this connection. The course of the alder pollen curve indicates a drier and probably colder type of climate at ca. 3000–2400 B.C.     

Thermal Backstripping from Vitrinite Reflectance Profiles in Comparison with an Extensional Model for Passive Continental Margin Basins on Northern Continental Shelf of South China Sea

INTRODUCTIONVitrinitereflectance(R.)canprovideagreatdealinfor-mationonthermalhistoryofabasin.Itisafunctionofmaximumpaleotemperatureandeffectiveheatingtime,inotherwords,afunctionofdepositionalrateandgeothermalgradientwithirreversiblecharacteristics.Butitalsohasacumulativeeffectthroughoutgeothermalevents.Paleotemperaturesaremainlycontro1ledbythebasalheatflowandheatgenerationfromradioactivesourceswithinthecrust.Themodelforde-terminingpaleoheatflowoflinearchangewithtimefr0mvitri-nitereflecta…     

Streamflow reconstruction for the Guxiang River,eastern Tien Shan (China): linkages to the surrounding rivers of Central Asia

Based on the high correlation of the tree-ring widths of larch and spruce trees with the actual streamflow variations, the streamflow reconstruction of the Guxiang River was developed for the period 1680–2009, with the low and high streamflow periods identified. The reconstruction model accounts for 41.1 % of the instrumental streamflow variance during the period 1957–2007. Some significant cycles (18.1, 8.1, 3.8, 2.9, 2.6, 2.4 and 2.1 years) are found using the multi-taper spectral analysis. The significant correlations with the gridded SPEI dataset revealed that the streamflow reconstruction also represents the drought variation for a large area of the eastern Tien Shan. The streamflow reconstruction of the Guxiang River shows the decreasing trend since the 1970s, and compares well with high and low streamflow periods of the Selenge River previously estimated from tree-ring records. The synoptic climatology analysis reveals that there is the relationship between anomalous atmospheric circulation and extreme hydrological events in the Guxiang River basin.     

Flandrian sea-level changes in the Fenland. II: Tendencies of sea-level movement,altitudinal changes,and local and regional factors

Stratigraphic, micropalaeontologic and radiocarbon data show that since c. 6500 BP the Fenland has been influenced by 7 periods of positive sea-level tendencies and by 6 periods of negative sea-level tendencies. Despite the numerous problems associated with the reconstruction of past altitudes of sea level the periods of positive sea-level tendencies were clearly characterised by a rise in sea level, the development of transgressive overlaps and a landward movement of the coastline. The periods of negative sea-level tendencies were characterised by the development of regressive overlaps, a seaward movement of the coastline and a reduced or negative rate of sea-level rise. The various altitudinal errors do not permit the incontrovertible distinction of periods of falling sea levels. All changes within the Fenland were not synchronous and local factors influenced the exact nature of each sea-level indicator. Dominant regional and local factors have been identified for different areas and different time periods. The chronological and spatial characteristics of the sequences within the Fenland are best explained by a palaeocoastline without supratidal barriers controlling sedimentation. The data indicate an average crustal subsidence in the Fenland of 0.9m/1000 years since c. 6500 BP and the pattern of positive and negative tendencies of sea-level movement is also seen in the chronologies for north west England and north east Scotland.     

陆生蜗牛化石与中国黄土古环境研究

陆生软体动物蜗牛是黄土地层中重要的环境指标,在黄土地层成因和古环境与古气候研究方面具有独到的优势。文章总结了近10多年来中国黄土陆生蜗牛化石研究的成果,包括黄土蜗牛化石的研究方法、蜗牛典型种属及组合的地理分布与生态环境等,侧重介绍了黄土高原不同时间尺度的蜗牛记录及陆生蜗牛化石在黄土古环境和古气候研究中的新进展。     

Saalian to Weichselian stratigraphy and sedimentation along the Lågjæren – Høgjæren escarpment,southwest Norway

Quaternary sediments along a profile crossing the southern part of the Jæren escarpment, southwestern Norway, have been investigated with regard to their glacial history and sea-level variations. Deposits from at least three glaciations and two ice-free periods between Oxygen Isotope Stage 6 and the Late Weichselian have been identified. Subglacial till directly overlain by a glaciomarine regressional succession indicates a deglaciation, and amino acid ratios in Elphidium excavatum between 0.083 and 0.118 date this event to Oxygen Isotope Stage 6. Sea-level dropped from 130 to below 110 m a.s.l. Subsequently, a short-lived ice advance deposited a marginal moraine and a sandur locally on the escarpment. Stratigraphical position and luminescence dates around 148 ka BP suggest deposition during the final stage 6 deglaciation. A Late Weichselian till covers most of the surface of Jæren. In addition to a well documented westerly ice flow, glaciotectonic indications of ice flow towards the north have been found. Ice flow directions and a hiatus between Oxygen Isotope Stage 6 and the Weichselian indicate enhanced erosion along the escarpment and the influence of a Norwegian Channel ice-stream. Copyright © 1999 John Wiley & Sons, Ltd.     

Amino acid diagenesis in the marine bivalve Arctica islandica Linné from northwest European sites: Only time and temperature?

Collections of the molluscan species Arctica islandica from seven sites in Norway, Scotland and the North Sea, ranging in age from recent to Early Pleistocene, have been sampled for amino acid analyses. The shells were sampled in profiles through the valves at different distances from the umbo. In the fossil material a general trend of increasing degree of isoleucine (lle) epimerisation and decreasing amino acid concentrations were found going from the inner part of the valve to the outer. Although less pronounced, there is a similar trend from the central part of the valve to the margin. As the concentration of alloisoleucine (alle) remains nearly constant, the observed changes in alle/lle ratios are a result of variations in the amount of isoleucine. The amino acid composition is fairly uniform in recent shells and the observed gradients are established in mid-Holocene samples. Therefore, it is suggested that the gradients are established during rapid early degradation of the protein, possibly due to microbiological activity. Differences in alle/lle ratios observed in molluscs from sites of the same age and same thermal history could be explained by differences in the exposure to amino-acid-consuming microorganisms during the very early stage of diagenesis.     

Late Holocene high resolution palaeoclimatic reconstruction inferred from Sebkha Mhabeul, southeast Tunisia

Relations between climate change and landscape evolution during the last two millennia in southeastern coastal Tunisia have been documented using high-resolution reconstruction of flood history and fire activity in the Sebkha Mhabeul core. The age model, based on tephrochronology, indicates that the core extends from Roman to modern times and encompasses the well-defined climatic periods of the last two millennia. This record provides a first palaeoecological/palaeoclimatic high resolution reconstruction in North Africa using a cross-disciplinary approach with both physical (grey-scale intensity, quartz particles) and biological (charcoal and pollen) indicators. The flood history shows four wet/dry cycles (ca. AD 550-950, 950-1300, 1300-1570 and 1570-1870) of different duration. Major hydrological instabilities are concentrated during the Medieval Climate Anomalies and the early Little Ice Age, between AD 1000 and 1550. Direct correlation between climate and fire cannot be established suggesting that the fire history of the Sebkha environment is mainly influenced by human activity. This study demonstrates the great value of sebkhas as palaeoenvironmental archives.     

鲜水河断裂带色拉哈段中谷村一带的最新地表破裂讨论

鲜水河断裂带色拉哈段是2014年康定M_S6.3地震的发震断裂段, 其最新一次地表破裂事件(1725年康定7级地震)的离逝时间较长, 是最可能发生7级以上地表破裂型大震的危险地段之一。获得色拉哈段最新地震地表破裂的展布范围对确定断裂带的地震活动历史、评估断裂带的未来地震危险性以及防震减灾具有重要意义。然而, 迄今色拉哈段最新地表破裂的北西端位置仍存有较大争议。对此, 在以往资料认为没有同震地表破裂的中谷村一带开挖了探槽组, 获得了这一带的破裂历史, 其最新一次事件(E6)的限定年代为A.D.746±51之后。综合探槽剖面证据和附近的断错地貌特征以及历史地震资料, 探槽揭露的最新事件E6可能对应1725年康定7级地震, 色拉哈段的地表破裂北西端至少已延伸到中谷村一带。      

西南河流源区径流量变化规律及其未来演变趋势

采用统计学方法及集合经验模态分解、小波分析、水文模型等多种方法,在对气象水文、湖泊岩芯、树木年轮、气候模式数据进行深入分析的基础上,研究了西南河流源区径流变化规律与历史丰枯规律及其驱动机制,分析了未来气候变化影响下的径流演变趋势。结果表明:三江源地区的径流近50 a整体表现为上升趋势,雅鲁藏布江流域除尼洋河外的其他区域年径流量整体呈不显著下降趋势,气候变化是导致三江源、雅鲁藏布江和怒江流域径流变化的主要原因,其中降水是引起径流变化最关键的因子;主要河流径流不同时间尺度的丰枯演变规律为,雅鲁藏布江中游全新世洪水事件呈现出早晚全新世频繁、中全新世相对较少的特征,近500 a怒江流域重建径流序列存在10个丰水期和10个枯水期,丰枯序列变化主要受季风环流和厄尔尼诺-南方涛动(ENSO)活动的影响;在未来15~60 a,全球持续增温将使西南河流源区平均年径流深相比近30 a增加6%~14%,而极端径流呈现出“干更干、湿更湿”的变化特征,同时生态因子对径流变化的影响不可忽视。     

商末气候变化对于稻作农业的影响——基于济南大辛庄、刘家庄遗址商代植物遗存观察

气候变化影响着农作物的生长。文章通过对比济南大辛庄遗址中、晚商时期的植物遗存和济南刘家庄遗址商末周初的植物遗存,发现两个遗址主要农作物均包括粟(Setaria italica (L.)Beauv.)、黍(Panicum miliaceum L.)、大豆(Glycine max(L.)Merr.)和小麦(Ttiticum aestivum L.),大辛庄遗址水稻(Oryza sativa L.)绝对数量较多,但刘家庄遗址未发现水稻。综合本地区其他遗址的植物考古研究结果,可以发现山东地区岳石文化时期、商代水稻仍是主要粮食作物之一,但到商末周初水稻数量急剧减少。同时,邻近的中原地区和关中地区,多处商周时期遗址水稻种植也普遍出现萎缩。多项地质记录表明,商末(3000 a B.P.前后)东亚夏季风快速减弱,降水量显著下降。山东地区受东亚季风影响,这一时期降水量减少,难以保证稻作农业所需的持续充足的水源,从而影响到水稻产量和种植规模。因此,商末气候变化很可能是刘家庄遗址商末周初水稻缺失以及山东地区商末周初水稻数量骤降的主要原因之一,也同时影响到整个黄河中下游这一时期的稻作农业。