珠江三角洲晚第四纪沉积的OSL和14C年龄探讨

提要：珠江三角洲第四纪沉积的年代测定在三角洲的发育演化、古海平面变化以及断裂活动性研究等方面具有重要意义。对东江平原的7个钻孔岩心进行了14C和OSL测年以及孢粉和微体古生物分析。与前人主要根据14C年龄得到珠江三角洲沉积小于4万年的认识不同,OSL测年结果显示下部地层的年龄值为4.7~13.5万年。本文对年龄的信度以及晚第四纪两次海侵旋回的地层年代框架进行了初步分析,提出珠江三角洲地区第一次海侵旋回可能发生于距今4~10万年期间;在晚更新世与全新世两次海侵之间,三角洲地区长期暴露地表,出现较大跨度的地层缺失。     

辽东湾LDD7孔晚更新世以来的沉积层序与古环境演化

对取自渤海辽东湾中部LDD7孔的300个沉积物样品进行了微体古生物分析,对196个样品进行了粒度分析,并选取8个层位的底栖有孔虫混合种进行了AMS¹⁴C测年,利用线形插值方法建立了该孔的年代地层框架。研究结果表明:自晚更新以来辽东湾中部保持了相对连续的沉积序列,LDD7孔记录了该区约60.85 cal.kaBP以来的沉积环境演化过程。根据垂向上微体化石组合和岩性的变化,将全长50.1 m的沉积物柱状样划分为9个沉积单元,分别代表晚更新世冰期旋回中随着海平面的变化,辽东湾中部区域在不同阶段分别处于海相、陆相或海陆过渡相沉积环境;LDD7孔中共识别出两次主要的海侵过程,分别对应着渤海中部Bc-1孔所记录的献县海侵与黄骅海侵;此次测年结果进一步明确了辽东湾中部两次海侵持续的确切时间,分别是45.84~27.66 cal.kaBP和10.64~0 cal.kaBP。此外,几个相关岩心的年代框架计算结果表明,献县海侵过程中辽东湾南部沉积速率低于中部,而献县海侵之后辽东湾南部的沉降总量和平均沉积速率都明显高于中部。     

渤海菜州湾第四纪晚期以来微体化石组合特征和沉积环境演化

对渤海莱州湾南岸央子镇YZ1钻孔取微体古生物样品18个，通过分析鉴定和地层对比，以及对微体古生物化石进行属种、丰度和分异度分析，共划分出4个化石组合层段。根据化石组合特征分析认为：第Ⅰ、第Ⅱ微体化石组合为全新世海侵的产物。第Ⅰ组合代表了海进序列，沉积环境为潮上带—潮间带；第Ⅱ组合为海退序列，沉积环境为潮间带—潮下带。第Ⅲ、第Ⅳ组合分别是晚更新世2次海侵的产物。第Ⅲ组合为晚更新世末期海侵的产物，海侵规模较大，沉积环境为滨海潮坪—潮间带；第Ⅳ组合海侵规模较小，陆相因素增大，沉积环境为河口—滨岸带或者为海陆交互相。     

珠江三角洲中部晚更新世以来的有孔虫记录与古环境演化*

珠江三角洲中部钻孔PRD20和PRD17晚第四纪以来的沉积记录较为完整,尤其是晚更新世海侵记录良好。以其为研究对象,对两孔的有孔虫微体动物群记录和沉积特征进行了分析和对比,并结合前人研究成果,重建珠江三角洲晚更新世以来的古环境演变,并着重分析了晚更新世海侵事件。约44500 cal a BP以前,研究区为河流环境,发育河道砂砾沉积。约44500—21300 cal a BP,发生晚更新世海侵,形成溺谷型河口湾,两孔沉积物中有孔虫的垂直分布记录了水体条件发生的多次变化,可辨识出2次海侵海退次级旋回;其中PRD20孔中有孔虫以滨岸广盐型占绝对优势,PRD17孔中以滨岸广盐型为主、海相—半咸水型有孔虫占有一定比例,表明研究区位于溺谷湾中径流与潮流共同作用的区域,且PRD20孔受径流影响更大。约21300 cal a BP后,受末次冰盛期海退影响,研究区暴露于地表遭受风化剥蚀,风化产物在PRD20孔表现为1层褐红色砂砾,在PRD17孔表现为1层花斑黏土。约8000 cal a BP,海平面回升导致河水滞留形成沼泽环境,PRD20孔发育1层泥炭层。约8000—5500 cal a BP,PRD20孔发育受径流影响较大的河口湾湾头沉积,仅在全新世海侵最盛时含有少量有孔虫记录。约5500 cal a BP后,研究区发育三角洲平原沉积。受构造抬升影响,PRD17孔地势较高,于约4700 cal a BP才开始重新接受沉积,零星出现潮水搬运而来的有孔虫。     

微体化石在海侵研究中的应用与错用

微体古生物分析已经证明是沿海平原和陆架海侵研究的最重要手段之一。由于我国第四纪海侵研究大量工作是在海陆过渡相地层中进行,而对于过渡相化石群古生态和埋葬学方面复杂性认识不足,往往会导致微体化石的错用。河口微体化石的溯流搬运,海岸带低pH环境下钙质壳体的溶解作用,氯化钠型盐湖中有孔虫的产出以及河床摆动造成与海侵、海退相似的化石序列,都可能引起微体化石在海侵研究中错误解释和应用。本文通过澳大利亚和中国的实例进行论证,并提出今后研究工作的建议。     

渤海湾西晚更新世以来3期海侵与古河道研究

通过对钻孔岩心详细的沉积特征、微体古生物、测年(AMS 14 C、OSL)等综合研究,表明研究区晚更新世以来受到区域性的3期海侵事件影响,多表现为边缘海滨海湖沼相沉积.同时,追踪了3期海侵最大影响边界:晚更新世早期最大海侵(第3海侵层)位于唐官屯-西长屯-梁头镇;晚期最大海侵(第2海侵层)位于大黄洼—三呼庄一带;全新世...     

基于沉积成因地化元素指标的闽北海湾晚更新世海侵地层辨识及其意义*

福建沿岸晚更新世地层中微体古生物化石较为缺乏,极大限制了对该区晚第四纪海侵过程的深入研究。针对这一问题,本研究以闽北2个海湾内的第四纪钻孔为研究对象,通过有孔虫化石以及沉积成因的地球化学元素(Sr/Ba、Mn/Fe)分析,结合三沙湾表层沉积物相应指标,探讨沉积成因的地球化学元素指示海侵地层的可行性。结果显示,2个海湾钻孔的晚第四纪地层中均发育3套疑似海相深灰色黏土层,其中开放海湾霞浦湾钻孔底部黏土层中缺失有孔虫,半封闭海湾三沙湾钻孔中有孔虫仅出现于顶部黏土层中。这3层黏土层的Sr/ Ba值远大于1,和现代潮滩—河口湾体系相近,且出现的海相沟鞭藻和自生黄铁矿为典型的海相地层特征。基于已有的OSL和AMS¹⁴C年龄框架,这3层海侵层分别对应于MIS5、MIS3和MIS1期,Sr/Ba和Mn/Fe均值从MIS5到MIS1期不断增大,结合现代潮滩-河口湾体系指标,表明从MIS5到MIS1期海侵强度的增加。由此可见,沉积成因地球化学元素指标可以有效辨识闽北海湾晚更新世海侵地层,这将有助于进一步了解该区晚第四纪海侵过程及其控制因素。     

渤海西缘YRD-1101孔晚更新世以来沉积物粒度特征及其环境变迁

对现代黄河三角洲地区YRD-1101孔上部岩心开展粒度分析,并结合AMS14C和光释光(OSL)年代学测试结果、沉积特征、微体古生物鉴定及周边钻孔对比,建立了MIS5期以来的地层框架,揭示出该地区主要经历了3个阶段的沉积环境演化过程:(1)晚更新世—早全新世河流与海相交替沉积,其中MIS5c阶段海侵水动力环境中等,MIS3期海侵水动力环境较弱,MIS2期河流沉积水动力较强;(2)全新世滨、浅海沉积环境,动力环境整体较强,相对比较稳定;(3)1855年至今形成的黄河三角洲沉积,水动力强度较弱到中等。海平面变化和构造沉降是影响研究区晚更新世以来沉积演化的主要因素,此外,黄河带来的大量泥沙对海侵强度也有显著影响。     

杭州湾北岸更新世以来沉积环境记录及古气候变迁

文章通过对杭州湾北岸孔深为237.80 m的BZK04钻孔进行沉积物岩性、微体古生物、孢粉组合、粒度含量、古地磁和OSL测年的综合分析,讨论研究区更新世以来沉积环境演变及古气候变迁特征,建立第四纪多重地层划分对比框架。结果显示, BZK04孔岩心自下而上可分为基岩长河组碳质泥岩（Ech）和早更新世以来的嘉兴组（N-Qp1 j）、前港组（Qp2q）、东浦组（Qp3d）、宁波组（Qp3n）、镇海组（Qhzh）地层;有孔虫鉴定为11属17种,其中包括16种底栖有孔虫,1种浮游有孔虫;介形类鉴定为8属8种;孢粉分析显示含37种类型,其中木本植物花粉18种,草本植物花粉11种,蕨类孢子8种,孢粉组合中木本植物含量最高,约为85.1%,蕨类孢子次之,约为8.7%,草本植物花粉含量仅为6.3%。根据岩性分层特征、沉积相、孢粉、有孔虫及介形虫以及粒度分布频率曲线对钻孔的沉积环境进行综合分析,可将沉积环境记录划分18个孢粉组合带和七个古气候旋回变迁,其中早更新世为河流相和河湖相沉积,揭示第三暖期—第4冷期的两个古气候旋回;中更新世以河流相、湖泊相和河湖相为主,揭示第五暖期—第6冷期的两个古气候旋回;晚更新世以潮坪相、河口湾相、浅海相沉积为主,对应第七暖期—第8冷期的两个古气候旋回;全新世时期为潮坪相和河湖相沉积,对应大西洋期和亚北方期。研究结果为进一步掌握长江三角洲南翼更新世以来的第四纪沉积环境变化、地层划分和古气候演变等提供基础资料。     

东海陆架盆地第三纪海平面变化

东海陆架盆地是建立西太平洋新生代海平面变化的关键地区。本文以层序地层和沉积体系分析为基础,利用微体古生物带化石资料,建立了东海陆架盆地第三系相对精度较高的年代地层格架。通过古生态分析、成因相及特征沉积构造分析和反射地震剖面的海岸上超分析,辅以地球化学参数变化研究,首次编制了东海陆架盆地第三纪海平面变化曲线。自第三纪以来,能识别的长周期二级旋回海平面变化4次,短周期三级旋回变化26次,相对海平面变化幅度在0-150m.分析发现海平面变化具有不对称性,即海侵作用速度大于海退作用速度。与Haq曲线对比也有较大的差异。     

Late-Quaternary paleoenvironmental evolution of Lesina lagoon (southern Italy) from subsurface data

Integrated sedimentological and micropaleontological (foraminifers and ostracods) analyses of two 55 m long borehole cores (S3 and S4) drilled in the subsurface of Lesina lagoon (Gargano promontory—Italy) has yielded a facies distribution characteristic of alluvial, coastal and shallow-marine sediments. Stratigraphic correlation between the two cores, based on strong similarity in facies distribution and AMS radiocarbon dates, indicates a Late Pleistocene to Holocene age of the sedimentary succession.Two main depositional sequences were deposited during the last 60-ky. These sequences display poor preservation of lowstand deposits and record two major transgressive pulses and subsequent sea-level highstands. The older sequence, unconformably overlying a pedogenized alluvial unit, consists of paralic and marine units (dated by AMS radiocarbon at about 45–50,000 years BP) that represent the landward migration of a barrier-lagoon system. These units are separated by a ravinement surface (RS1). Above these tansgressive deposits, highstand deposition is characterised by progradation of the coastal sediments.The younger sequence, overlying an unconformity of tectonic origin, is a 10 m-thick sedimentary body, consisting of fluvial channel sediments overlain by transgressive–regressive deposits of Holocene age. A ravinement surface (RS2), truncating the transgressive (lagoonal and back-barrier) deposits in core S4, indicates shoreface retreat and landward migration of the barrier/lagoon system. The overlying beach, lagoon and alluvial deposits are the result of mid-Holocene highstand sedimentation and coastal progradation.     

塔里木盆地下志留统塔塔埃尔塔格组痕迹化石与海进期沉积及海进体系域

在层序地层学研究中,海进（transgrssion）常被认为是快速形成的,序列简单,并以少量沉积为特征。对塔里木盆地下志留统塔塔埃尔塔格组痕迹化石及沉积特征研究表明,海进期沉积及海进体系域比人们想象的要复杂,由三类沉积组成:（1）与海进侵蚀有关,包括海进滞留沉积,发育固底控制Glossifungites痕迹相;（2）与海进初期的海面缓慢上升或总体海进过程中的静止期有关,包括前滨和临滨砂泥岩,发育Skolithos痕迹相和近端Gruziana痕迹相;（3）与海面快速上升有关,包括滨外泥岩,发育远端Gruziana痕迹相。     

北京延庆第四纪盆地杨户庄剖面新信息——有孔虫与海相介形虫新发现

文中报道了在北京延庆杨户庄剖面,发现的第四纪有孔虫与海相介形虫化石。该化石产地以化石层位稳定、分布面积较广、化石丰富及地质时代较明确为特点。至于化石是否是“海侵”或“海泛”的产物?,或是由“生物传布的空中通道”而来,还是为“湖盆内盐度增高的水介质中生存的特殊生物相”?都正在研究与探讨之中。     

相对海平面变化与南海珠江深水扇系统的响应

根据微体古生物分析建立起来的珠江口盆地第三系相对海平面曲线,具有与全球海平面变化相一致的三级旋回和不一致的二级旋回。三级海平面升降导致了各沉积层序体系域在宽广陆架和陆坡之间的迁移,研究证实,位于南中国海北缘、珠江口外的陆坡深水区广泛发育第三系多层序叠置的南海珠江深水扇系统。区域性构造作用使得珠江口盆地二级海平面变化与全球海平面变化具有不一致性,并形成与全球海退趋势相反的海侵型海平面曲线。受相对海平面变化的控制,现今处于陆坡深水区的白云凹陷自32Ma南海扩张以来经历了三台阶式的海侵事件,形成了台阶式退积层序组合,具有下粗上细的沉积序列;造就了23.8Ma以前的浅水三角洲-滨岸砂泥岩沉积组合;23.8~10.5Ma的深水扇砂泥岩为主的沉积组合;以及10.5Ma以来主要为远端的细粒沉积为主。     

中国北方晚更新世哺乳类动物群的划分及其地理分布

<正> 新第三纪以来,由于青藏高原、喜马拉雅山脉与西部山脉的隆起,我国形成了西高东低的地形特点,导致了气候和环境的变迁,明显地影响了中国哺乳动物的分布。在晚更新世,中国南北动物群分化逐渐扩大,动物群更替尤为频繁。中国晚更新世地层及动物群的研究已有一段相当长的历史,发现了众多重要的遗址和化石地点,积累了丰富的资料。笔者综合有关资料,对我国北方晚更新世动物群,特别是猛犸象-披毛犀动物群的划分、地     

Sedimentary response to Late Quaternary sea-level changes in the Romagna coastal plain (northern Italy)

Data from 17 continuously cored boreholes, 40–170 m deep, reveal the subsurface stratigraphy of the Romagna coastal plain. Sedimentological and microfaunal data allow the distinction of eight facies associations of Late Pleistocene–Holocene age, including 18 lithofacies and 16 faunal associations. Ten ¹⁴C dates provide the basis to establish a sequence stratigraphic framework for the succession corresponding to the upper part 35 ky BP of the last glacio-eustatic cycle. The eight facies associations can be grouped into lowstand, transgressive and highstand systems tracts. The upper part of the lowstand systems tract consists of alluvial plain deposits. These accumulated during the Late Pleistocene when the shoreline was ≈250 km south of its present-day position. A pronounced stratigraphic hiatus (between 25 and 8·8 ky BP) is invariably recorded at the upper boundary (transgressive surface) of these Pleistocene, indurated and locally pedogenized alluvial deposits. The succeeding postglacial history is represented by a well developed transgressive–regressive cycle. Transgressive deposits, interpreted to reflect the rapid landward migration of a barrier–lagoon system, include two wedge-shaped, paralic and marine units. These thicken in opposite directions and are separated by a ravinement surface. Above the transgressive deposits, the maximum flooding surface (MFS) marks the change from a transgressive barrier–lagoon complex to a prograding, wave-dominated delta system (early Po delta). The MFS can be traced landwards, where it constitutes the base of lagoonal deposits. An aggradational to progradational stacking pattern of upper delta plain (marsh), lower delta plain (lagoon/bay), and delta front (beach ridge) deposits reflects the progressive increase in the sediment supply/accommodation ratio during the following highstand. The alluvial deposits capping the sequence accumulated by the 13th century AD, in response to an avulsion event that caused abandonment of the former Po delta lobe and the northward migration of the Po River towards its present position.     

Pleistocene mammal faunas of Eastern Europe

Systematic studies of the Pleistocene mammal assemblages of Eastern Europe have been carried out for more than a century, and they elucidated evolutionary changes and ascertained chronological sequence of the faunas. The available evidence on fossil mammals from Eastern Europe allows differentiation of 7 complexes of large mammals. These complexes represent 15 assemblages and their phases distinguished for small mammals. The appearance of new taxa of different rank provides the basis for identification of the principal stages in mammal evolution. Multi-disciplinary studies of fossil mammal localities have made it possible to correlate theriological data with the main events of the Pleistocene (such as glacials and interglacials) by comparison between geological, geochronological and palaeontological data.Interglacial and periglacial mammal faunas of different age have been defined on the basis of their structural characteristics and geographical distribution. Two types of mammal assemblages are recognised: zonal interglacial and periglacial assemblages specific to glacial periods. In the first type, each zonal assemblage is dominated by a single ecological group of mammals. A distinctive feature of the second type is the co-existence of animals belonging to different ecological groups and inhabiting different natural environments.     

腾格里沙漠西北缘青土湖中更新世晚期以来沉积环境变迁

以腾格里沙漠西北缘青土湖钻孔ZK1为研究对象,通过对钻孔沉积物的光释光年代、粒度、磁化率等研究,揭示了该湖泊自中更新世晚期以来的环境变迁。研究结果表明：该地区中更新世晚期经历了干冷→暖湿两个阶段,晚更新世经历了湿暖→干冷两个阶段,与深海氧同位素的末次间冰期、末次冰期气候旋回特征吻合,全新世主要经历了干冷→暖湿的气候波动。反映了腾格里沙漠西北缘晚第四纪的气候波动变化特征,特别是为本区中更新世晚期以来的气候环境变化的研究提供了依据。     

Revised age of deglaciation of Lake Emma based on new radiocarbon and macrofossil analyses

Previous radiocarbon ages of detrital moss fragments in basal organic sediments of Lake Emma indicated that extensive deglaciation of the San Juan Mountains occurred prior to 14,900 yr B.P. (Carrara et al., 1984). Paleoecological analyses of insect and plant macrofossils from these basal sediments cast doubt on the reliability of the radiocarbon ages. Subsequent accelerator radiocarbon dates of insect fossils and wood fragments indicate an early Holocene age, rather than a late Pleistocene age, for the basal sediments of Lake Emma. These new radiocarbon ages suggest that by at least 10,000 yr B.P. deglaciation of the San Juan Mountains was complete. The insect and plant macrofossils from the basal organic sediments indicate a higher-than-present treeline during the early Holocene. The insect assemblages consisted of about 30% bark beetles, which contrasts markedly with the composition of insects from modern lake sediments and modern specimens collected in the Lake Emma cirque, in which bark beetles comprise only about 3% of the assemblages. In addition, in the fossil assemblages there were a number of flightless insect species (not subject to upslope transport by wind) indicative of coniferous forest environments. These insects were likewise absent in the modern assemblage.