长江河口地区晚更新世晚期以来沉积环境的变迁

本文所述长江河口地区,指河口附近的陆上部分,包括北部的三角洲平原,东部的滨海平原及西南部的冲积一湖积平原。全区除局部见有一些基岩山体以外,绝大部分为第四系覆盖区。整个第四系岩相层序比较复杂,反映沉积环境有过多次更替。     

渤海南部莱州湾晚更新世以来沉积演化特征

晚更新世以来渤海南部莱州湾发生了3次重要海侵-海退事件及沉积演化过程,渤海南部多源河流三角洲对莱州湾沉积环境改变作用明显。本文选择莱州湾剖面进行沉积地层对比,结合调查资料和测试数据,初步建立莱州湾沉积地层格架,分析晚更新世以来莱州湾沉积演化过程。研究发现,渤海南部中小河流与黄河泥沙为莱州湾沉积物的共同物质来源,二者在不同阶段分别对莱州湾沉积演化起主导作用。提出本区沉积地层具有分期性、分段性和相关性规律。在124.6~72.0 ka B.P.,60.0~24.4 ka B.P.和10.2~4.0 ka B.P.出现过3次暖湿期,分别对应沧州海侵、献县海侵和黄骅海侵,主要发育滨浅海相沉积,向南退积为三角洲/潮坪—河流沉积;由陆向海,短源河流沉积贡献降低,黄河沉积贡献增加。在72.0~60.0 ka B.P.和24.4~10.2 ka B.P.出现2次冷干期,分别对应玉木早冰期和玉木晚冰期,河流相发育,三角洲进积。受海陆交互作用影响,晚更新世以来渤海南部莱州湾大致经历了浅海相—三角洲—潮坪—浅海相—三角洲—陆相的沉积演化。     

河北三河晚更新世地层粒度特征分析

本文通过详细测量河北三河齐心庄一带第四纪剖面、采集光释光测年样品和粒度样品,分析该区地层形成年龄、沉积速率、各粒度样品粒度参数、频率分布曲线及概率累积曲线,进而推断其沉积环境。实测剖面显示地层可以分为20层,沉积物以细砂、粉砂和黏土为主。第2层光释光地质年龄为12.23±1.32ka,第19层光释光地质年龄为19.35±2.10ka,故实测剖面为晚更新世末期堆积,根据地层厚度及年龄测定结果测算出该区平均沉积速率为0.071cm/a。12个粒度样品频率分布曲线均为不对称的单峰态,表明沉积物成分单一,为相对稳定条件下形成。概率累积曲线分为两段式和三段式,滚动组分较少,总体为能量相对不高的沉积环境。地层自下而上呈现明显的旋回性沉积特征,存在两种韵律沉积模式:"中砂-细砂-粉砂"和"粉砂-黏土"。结合区域地质特征,综合分析结果显示河北三河晚更新世地层形成于相对稳定的低水能条件下的河流环境,进一步可细分为河流砂坝和泛滥平原沉积。本文研究结果对于探讨华北北部平原的形成与发展过程、潮白河下游的变迁历史、晚更新世末期的沉积速率提供了重要的基础资料和数据。实测剖面位于新夏垫断裂的下盘,本文测试结果对于研究新夏垫活断裂两盘的差异性活动和断裂性质提供了重要的资料。     

Late Pleistocene loess‐palaeosol sequences in the Vojvodina region,north Serbia

Late Pleistocene loess‐palaeosol sequences are widespread in the Vojvodina region, with thicknesses reaching a maximum of about 20 m. Our investigations include more than 40 of these loess sections. Geochronology of the last glacial loess‐palaeosol sequences, based on luminescence dating and amino acid racemisation, provides correlations between Upper Pleistocene loess‐palaeosol sediments in Vojvodina and comparable deposits at other European localities. Sedimentary logs of magnetic susceptibility, grain‐size measurements and carbonate content, combined with malacological evidence, indicate two main relatively cold and arid phases during the last glacial period, related to intensive accumulation of loess units L1L1 and L1L2, as well as many brief episodes of dry and windy climatic conditions, suggesting a possible relationship with cold events recorded in the North Atlantic region. Generally, late Pleistocene climate in the region was dry and relatively warm, compared with glacial period sites in central Europe, and was characterised by sharp differences between glacial and interglacial modes. New data and interpretations presented in this study emphasise the significance of loess‐palaeosol sequences in Vojvodina for the reconstruction of the temporal and spatial evolution of late Pleistocene palaeoclimate in this part of Europe. Copyright © 2007 John Wiley & Sons, Ltd.     

运城盆地栲栳塬晚更新世地层序列及地质意义

古汾河改道是运城盆地新生代时期一次重要的地表巨变过程,对于古汾河改道时限目前仍存在着中更新世和晚更新世2种观点,尚未有统一的定论。研究以运城盆地栲栳塬晚更新世沉积序列为调查对象,在光释光测年的基础上,厘定了沉积序列转换的关键时限;结合碎屑锆石U-Pb同位素测年,分析了栲栳塬晚更新世沉积序列的成因及地质主控因素。研究认为：运城盆地栲栳塬晚更新世沉积序列具有双层结构的特点,下部为一套河流相砂体,上部为一套风成相黄土,二者之间的界限大约在7.6～6.3万年;碎屑锆石年龄序列对比分析认为,栲栳塬晚更新世早期的河流相沉积与运城盆地汾河古河道的沉积特征基本一致,晚更新世中期,由于峨眉台地的区域性抬升,古汾河发生改道进而退出运城盆地,栲栳塬早期的河流相沉积之上开始接受持续的风成相沉积;运城盆地晚更新世中期的构造抬升事件在鄂尔多斯盆地周缘均有响应,预示着青藏高原在该时期存在一期明显的构造隆升,其远程效应是造成汾河改道退出运城盆地的主要动力。该研究成果从沉积角度为运城盆地古汾河的改道时限提供了新的证据。     

Magnetostratigraphy and Pliocene-Pleistocene boundary in Italy

Analysis of some sedimentary series near Rome and comparison with other series in northern and southern Italy give evidence that Arctica islandica, considered a marker species for the beginning of the Pleistocene, appears during the Re´union paleomagnetic event (about 2 my ago). A period of erosion, called the Aullan erosional phase, is evident in the lower part of the late Villafranchian (= early Pleistocene, Olivola faunal unit).     

Stratiform gold mineralization in palaeosol and ironstone of early Proterozoic age,Transvaal Sequence,South Africa

An early Proterozoic palaeosol, developed on basalt and the basal part of an overlying transgressive marine sedimentary sequence, contains pyrite which is auriferous in places. The mineralization is stratiform and continuous over a distance of several hundred kilometres. Although this mineralization can be explained by a number of genetical models the author concluded that the mineralization took place during pedogenesis and/or diagenesis. Gold is considered to have been leached from the basalt and from the B horizon of the palaeosol by sulphide-rich groundwater and was then precipitated by the effect of the lowering of the HS^– activity. The latter is thought to have been caused by atmospheric oxidation and by reaction with Fe-rich leachate from the A horizon, and pyritization of pre-existing iron oxide minerals may also have contributed. It is concluded that a pedogenic gold protore may explain the origin of at least some of the gold of the Witwatersrand type of deposit.     

Monte Verde,South-Central Chile: Stratigraphy,climate change,and human settlement

Two sedimentary units are recognized by means of stratigraphic and sedimentological analyses at Monte Verde, a late Pleistocene archeological site with stone tools and well-preserved wood artifacts and botanical remains, that lies southwest of Lago Llanquihue and north of the Golfo de Reloncavi in the southern end of the Chilean Central graben. the geological evidence shows that at no time after 33,000 yr B.P., and perhaps since the first Llanquihue advance (before 56,000 yr B.P.), was the Monte Verde area covered by ice. Influences of two glacial advances at 20,000 and 15,000-14,500 yr B.P. are recognized at the site; effects of the Varas Interstade, however, are not identified. Rapid climatic change took place after the end of the Llanquihue Glaciation. It was shortly interrupted by a cool, wet period around 10,000 yr B.P., after which a well-documented Hypsithermal (8270-4750 yr B.P.) accompanied by pyroclastic vulcanism followed. The evidence indicates that around 13,000 yr B.P. 1) the site occupants settled on the sandy point bars and beaches of the old creek channel and 2) the area was habitated during cool and wet conditions similar to those that prevail in the area today. Evidence for reconstruction of the paleo-environment and climate of the terminal Pleistocene and the preliminary implications of these findings for understanding the human occupation at Monte Verde are discussed.     

渤海湾西沧县隆起第四纪以来沉积差异性研究

沧县隆起是渤海湾盆地的重要组成部分。通过对沧县隆起上施工的350m深ZKT1钻孔沉积特征、测年(AMS14C和OSL)及磁性地层研究,并与CGZ5、BZ2孔磁性地层及海侵层对比,结果发现:沉积岩层M/G(松山/高斯,Matuyama/Gauss)极性带界线埋深存在较大沉积差异,B/M(布容/松山,Brunhes/Matuyama)极性带界线趋于一致,3期海侵层基本稳定;早更新世沧县隆起不同部位存在沉积差异,继承了古近纪以来的断陷沉积;中更新世-晚更新世沧县隆起准平原化,整体处于同一稳定下沉的沉积演化环境;晚更新世以来,发生三期区域性层位较稳定的海陆交互作用,形成滨海冲积平原。本文可为渤海湾地区新构造活动性研究及区域古地理恢复与地质演化提供参考。     

Vegetation and climates in southern Tasmania since the last glaciation

Enclosed basins (glacial and nonglacia) of Tasmania contain the most comprehensive record in Australia of trends in a regional vegetation and climate since the late Pleistocene. Seven pollen sequences, each continuous and extending back at least 10,000 years, are used to reconstruct the history of postglacial vegetation and climate in Southern Tasmania (42°S–43°30′S). Interpretations are supported by a study of the modern pollen rain. Postglacial climates in Tasmania were characterized by a strong west-to-east decrease in precipitation. During the late Pleistocene, climates were markedly colder and drier than at present, and the vegetation was largely devoid of trees. A major rise in temperature between ca. 11,500 and 9500 yr B.P., accompanied by rising effective precipitation, resulted in the expansion of Eucalyptus, then other trees, across Tasmania. This warming trend may have been temporarily reversed during the early postglacial. Dry climates delayed the development of forest in inland eastern Tasmania until after ca. 9500 yr B.P. There is no evidence for a major change in climate since this temperature rise. Two broad phases of development have occurred within the postglacial forests. The first was an early Holocene phase during which Nothofagus cunninghamii cool temperate rain forest developed in western Tasmania and on the slopes of mountains in central and southeastern Tasmania. Eucalyptus sclerophyll forests developed in eastern Tasmania and have remained dominant there since. By ca. 7800 yr B.P. rain-forest communities were established beyond present-day limits. The second phase was a mid to late Holocene phase during which forests and alpine vegetation became more open in structure, leading to the re-expansion of Eucalyptus and shade-intolerant species. During the early to mid Holocene, climates in Southern Tasmania were wetter and (? then) warmer than at present. Maximum and minimum dates for this “optimum” are 8000 and 5000 yr B.P. Since then, climates have become increasingly rigorous, possibly through an increased incidence of inequable “weather types” leading to an increase in the frequency of drought and frost. Structural changes in the postglacial vegetation of Southern Tasmania closely parallel those at equivalent latitudes in New Zealand and Chilean South America, hence are likely to reflect the same primary cause.     

Paleoclimatic reconstruction in northern Oman based on carbonates from hyperalkaline groundwaters

A paleoclimatic reconstruction for the past 35,000 years for northern Oman is based on an unusual approach using travertines and fracture calcites associated with hyperalkaline springs. High-pH groundwaters (pH up to 11.9) discharge from the mantle sequence of the Oman Ophiolite as the product of modern, low-temperature serpentinization. Under arid climatic conditions, hyperalkaline discharge occurs at the surface. Uptake of atmospheric CO₂ precipitates characteristic laminated travertines, accompanied by strong kinetic depletion of ¹³C and ¹⁸O. Pluvial climates supporting a shallow bicarbonate-groundwater flow system and vegetation are recorded by fracture calcites with equilibrium stable isotope contents and calcite-replaced roots and stems. All such carbonates have modern initial ¹⁴C contents, allowing radiocarbon dating and paleoclimatic reconstruction for the late Pleistocene and Holocene. Our reconstruction shows a dominantly wet late Pleistocene up to 19,000 yr B.P., when a phase of climatic deterioration began, leading to a period of hyperaridity which dominated from ca. 16,300 to 13,000 yr B.P. The early Holocene pluvial occurred from 12,500 to ca. 6500 yr B.P. and was followed by renewed climatic deterioration and the current phase of hyperaridity. Comparison of this paleoclimatic reconstruction with that for lacustrine deposits from the A'Rub al Khali of central Saudi Arabia and the summer insolation-driven monsoon record of east Africa and the Arabian Sea is remarkably good.     

The last 750 ka in loess–palaeosol sequences from northern France: environmental background and dating of the western European Palaeolithic

This study presents an overview of Middle Pleistocene loess–palaeosol sequences (LPS) in northern France and discusses the palaeoclimatic significance of the pedosedimentary record in the context of western European LPS and of global climatic cycles for the last 750 ka. In this area, the oldest loess deposits (early Middle Pleistocene) are preserved in sedimentary traps (leeward scarps of fluvial terraces and dissolution sinkholes). They result from local deflation processes reworking Pleistocene sandy fluvial deposits or relicts of Tertiary sands. A large extension of typical calcareous loess over the landscape, the Loess Revolution, is then observed during MIS 6, with heavy mineral assemblages testifying to long-distance transport from the polar desert area of the dried eastern Channel. A correlation scheme is proposed between the global records of northern France in continental environments and both global palaeoclimatic records and other main western European LPS. After 30 years of research, northern France LPS stand as a fundamental archive of the impact of interglacial–glacial climatic cycles as well as millennial events. Finally, these works provide a robust chronoclimatic framework for the study of the western European Late Acheulean and Middle Palaeolithic and for the relative dating of the various fluvial terraces that they fossilise.     

Investigation of high-level glaciofluvial terraces and re-evaluation of the established soil stratigraphy for Early and Middle Pleistocene surfaces, central Yukon, Canada

Palaeosols developed on the highest Yukon River glaciofluvial terraces were investigated in order to reconstruct the Plio-Pleistocene evolution of the river valley beyond Late Pleistocene glacial limits. A record of at least two pre-Reid (> 311 kyr) glaciations is chronicled by the presence of two populations of glaciofluvial terraces within the study area. The populations of pre-Reid terraces were identified based on their degree of soil development and elevation. Pre-Reid terraces 200–250 m above river level have preserved morphological and mineralogical features of the Wounded Moose palaeosol, a palaeosol previously associated with pre-Reid surfaces in central Yukon. Clay mineralogy and colour indicate that the Wounded Moose palaeosol developed in part during warm and sub-humid as well as temperate and humid interglacials. A second set of pre-Reid terraces between 110 and 30 m above river level are characterized by the presence of the less-developed Diversion Creek palaeosol, a palaeosol previously associated with only Reid-aged (< 311 kyr) surfaces in central Yukon. In contrast to the Wounded Moose palaeosol, the Diversion Creek palaeosol developed during comparatively cool and humid interglacial conditions. The presence of Diversion Creek palaeosols on pre-Reid outwash terraces suggests that a transition from dominantly warmer to cooler interglacial conditions occurred prior to 311 kyr in Yukon Territory. In addition, the presence of a Diversion Creek palaeosol cannot be used to differentiate stable Reid and stable pre-Reid surfaces across central Yukon.     

渭北黄土台塬全新世地层高分辨率研究

在野外观测研究的基础上 ,对陕西扶风新店村全新世黄土剖面作了详细的地层划分。通过磁化率、粒度、TOC、全铁和碳酸盐含量测定分析 ,进一步揭示渭北黄土台塬全新世季风气候变化的规律。同时 ,阐明了“全新世大暖期”的气候有明显的波动变化 ,尤其是在 6 0 0 0— 5 0 0 0 a B.P.发生了一个干旱气候事件 ,形成黄土堆积 ,使得全新世古土壤分裂成为两层 ,表现为多周期土壤。从 3 10 0 a B.P.开始至今气候变得干旱 ,风尘堆积旺盛 ,形成了现代黄土和表土层     

青藏高原北缘银石山地区地貌年代学初步研究

青藏高原北缘银石山地区可划分出7类一级地貌类型：强抬升断块区、弱抬升断块区、低丘区、早期夷平面残留区、晚期准夷平面分布区、冲洪积平原、残积缓丘区等。通过相关沉积物的光释光和石英电子自旋共振年龄以及覆于早期夷平面、后期山丘、夷平低地或堆积台面等之上的火山岩年龄测年,重塑了晚新生代以来的地貌演化过程：中新世中晚期—上新世中期为主夷平面发育时期,上新世晚期(3．7Ma)主夷平面解体,强(弱)抬升断块区和低丘山地等开始形成。早更新世早期在低丘区中形成夷平低地或堆积台面,中后期抬升断块区与低丘区相间的地表形貌特征进一步强化。中更新世早期(0．64Ma)残积缓丘区形成,中期(0．43Ma)嵩华山北面形成一级冰斗,中后期(0．365Ma)低丘区主要斜坡地貌成型,末期(0．178Ma)强抬升断块区的主要沟谷地貌基本成型。晚更新世以来主要河流阶地形成,其间在0．037Ma前后冲洪积平原形成。     

西藏阿里札达盆地下更新统香孜组地层厘定与层序地层划分

根据札达盆地香孜组河湖相地层剖面的接触关系、沉积旋回、沉积体系和岩相岩性特征,可将札达盆地下更新统香孜组河湖相地层划分为2个沉积相、3个岩段。香孜组一、二岩段为一套砾岩夹砂岩的粗碎屑岩,属典型的冲（洪）积扇沉积物;第三岩段为砾岩与砂岩互层,属冰水冰缘相沉积。ESR法和古地磁法测年结果表明,札达盆地香孜组河湖相地层的形成时代为早更新世早期（2．68—1．36Ma）。札达盆地为一同生断陷盆地,在后期重新复活的过程中,盆地只经历了冲积体系域和水进体系域。冲积体系域形成于札达盆地早更新世早期重新复活层序发育的早、中期,水进体系域形成于札达盆地早更新世早期重新复活层序发育的晚期。     

末次间冰期以来沙漠－黄土边界带的环境演变

沙漠-黄土边界带地处东亚季风边缘,这一地区的风成沉积即古风成砂-黄土-古土壤序列很好地反映了东亚季风环流的演变历史。末次间冰期的沉积（S1）由三层古土壤和夹于其间的两层黄土组成,可与深海氧同位素阶段5的五个亚阶段（a-e）则很好对比。末次冰期的沉积（L1）由三层古风成砂和夹于其间的两层黄土构成,由此反映了与上述三层古风成砂对应的阶段2、阶段4及阶段3的中期是沙漠-黄土边界带冬季风活动加剧、沙漠扩大的时期。全新世的沉积是由一层草原上（S0）和其上的流沙组成,但这层流沙是在最近两千年来不合理的人类活动和当地特定风场条件的共同作用下形成,已不具备明显的气候指示意义。     

宁夏清水河盆地晚更新世两期湖相沉积物的形成时代、沉积环境及构造背景

为了解宁夏清水河盆地晚更新世以来的沉积、构造演化规律,采用钻探、粒度分析、光释光测年等技术,对盆地中部发现的2期晚更新世湖相地层进行了沉积学、年代学研究。结果表明,下部湖相地层萨拉乌苏组的形成时代为76~63 ka,上部湖相地层水洞沟组形成时代为25~11 ka,二者之间存在明显的侵蚀面。根据沉积证据和粒度分析结果,将萨拉乌苏组自下而上划分为4个沉积阶段,构成了一个完整的湖进-湖退序列,代表了一期温暖湿润的气候环境;而水洞沟组为干冷环境下形成的浅湖。构造、环境对比分析表明,清水河盆地2期古大湖的形成、消亡指示该地区晚更新世经历了拉张-挤压-拉张的构造转换。两次拉张作用是萨拉乌苏湖和水洞沟湖形成的主要因素,古大湖发育的间断期存在的强烈构造隆升事件是导致萨拉乌苏湖消亡的根本原因,末次冰期MIS4和MIS2晚期的异常寒冷气候也是古湖衰退的原因之一。清水河盆地2期古湖的演化规律,为研究青藏高原周缘晚更新世古大湖形成与演化、古气候变迁及青藏高原的隆升提供了重要的证据。     

山西晋中盆地晚新生代地层划分、沉积环境及其先秦以来气候和湖泊演化

【研究目的】晋中盆地位于汾渭断陷盆地带的中部,新生代最大沉积厚度超过3800 m,建立晋中盆地精确地层年代框架和高分辨率沉积层序对于理解汾渭断陷盆地带的演化、华北地区气候变化具有重要意义。【研究方法】本文对晋中盆地东北部晚新生代标准孔ZK01（钻孔深度870.5 m）岩心开展了年代学和沉积学研究。【研究结果】将ZK01孔揭示的松散沉积物分为6个岩性组。首次通过磁性地层学研究,划分出13个正极性时段和12个负极性时段,建立了ZK01孔地层年代框架。晋中盆地新生代沉积物底部最老年龄约8.1 Ma,将晋中盆地活动的起始时间从前人一般认为的上新世初期,确定为中新世晚期,提前了约3 Ma。区内晚新生代地层划分为新近系中新统灞河阶（N₁⁴）和保德阶（N₁⁵）,上新统高庄阶（N₂¹）和麻则沟阶（N₂²2）,第四系下更新统泥河湾阶（Qp¹）,中、上更新统和全新统。【结论】构造活动与气候变化是盆地沉积环境的主要控制因素,共同导致了上新世早期和早更新世中晚期的两次湖泊大规模发育。全新世时期,早中期即先秦（约2.5 ka以前）,盆地中仍是河湖共存阶段;晚期（2.5 ka以来）,出现湖消河长的局面,直至明、清时期湖泊全部消失,气候变化和人类活动影响是盆地中湖泊最终消失的主要原因。创新点：首次通过磁性地层学将晋中盆地发育时间确定为中新世晚期约8.1 Ma;盆地的湖泊发育早期主要受构造和气候控制,全新世以来气候变化和人类活动造成湖泊最终消亡。