黔南七星洞石笋古气候变化记录及末次间冰期终止点的确定

当前在全球气候变化预测研究中,洞穴石笋的高分辨定年和碳、氧同位素组成的变化规律研究,为这个领域的突破和填补空白做出了巨大贡献。通过对贵州都匀七星洞 1号石笋进行 11件TIMS U系测年和 79件碳、氧同位素分析,获得了距今 10 9.0 0kaB.P.至 6 5.90kaB.P.的高分辨率古气候记录。石笋在大于 10 9.0 0kaB.P.前开始生长,于 6 5.90kaB.P.后停止生长,平均沉积速率为 4.5 8mm/ 10 0a,属晚更新世的沉积产物。七星洞 1号石笋剖面的研究揭示,其年龄和δ18O同位素的变化,可以与深海岩芯氧同位素记录所揭示的第五阶段中的 5a、5b、5c和第四阶段的早期进行对比。它的碳、氧同位素记录揭示,在 10 9.0～ 10 2.5kaB.P.和 86.6～ 78.92kaB.P.时段,显示受东亚夏季风影响较强,气温升高,降水增多,δ18O偏负,表现为温暖湿润的气候环境。在 10 2.5～ 86.6kaB.P.时段,显示受东亚夏季风影响强度减弱,受东亚冬季风影响强度增加,气温降低,大气降水减少,δ18O稍趋向偏正,表现为冷凉半湿润-温凉湿润的气候环境;而在 78.92～ 6 5.6kaB.P.时段,显示东亚冬季风强盛和受西北风影响较强,海表温度下降,大气温度降低,降水量较少,δ13O偏重,δ13 C偏正 (C4植物占 95 % ),表现为严寒     

Testing the accuracy of quartz OSL dating using a known-age Eemian site on the river Sula, northern Russia

Quartz optically stimulated luminescence (OSL) forms the basis for the chronology of Weichselian ice advances in Arctic Eurasia developed over the last few years. There is almost no age control on this chronology before 40 ka, except for some marine sediments correlated with marine isotope stage (MIS) 5e on the basis of their palaeofauna. Results from more southern latitudes have shown that dose estimates based on quartz OSL and the single aliquot regenerative (SAR) dose procedure may underestimate the age of MIS 5e deposits. Here we use the same method to date well-described marine sediments, thought to have been deposited during the very beginning of the Eemian interglacial at 130 ka, and exposed in two sections on the river Sula in northern Russia. Various quality-control checks are used to show that the OSL behaviour is satisfactory; the mean of 16 ages is 112±2 ka (σ=9 ka). This represents an underestimate of 14% compared to the expected age, a discrepancy similar to that reported elsewhere. In contrast to SAR, the single aliquot regeneration and added (SARA) dose procedure corrects for any change in sensitivity during the first OSL measurement. The SARA results are shown to be 10% older than those from SAR, confirming the geological age estimate and suggesting that SAR ages may underestimate older ages (larger doses), despite their good performance in the younger age range.     

Identification and significance of a visible,basalt‐rich Vedde Ash layer in a Late‐glacial sequence on the Isle of Skye,Inner Hebrides,Scotland

This paper reports the discovery of a visible, tephra horizon of Late‐glacial age from the site of Loch Ashik in the Isle of Skye, the Inner Hebrides, Scotland. Although the tephra shards have a bimodal geochemical composition identical to that of the Vedde Ash (a well known marker horizon within Late‐glacial sequences. The horizon at Ashik is dominated by basaltic shards and devitrified tephra shards, giving the layer its characteristic black colour. Only rhyolitic shards have previously been reported from Vedde Ash horizons in the British Isles. This new evidence raises some important questions about the factors that govern the distribution and accumulation of basaltic tephra, and about the methods used to detect ash shards in basins distal to centres of volcanic activity. Copyright © 2001 John Wiley & Sons, Ltd.     

萨拉乌苏河流域末次间冰期 古土壤化学风化与古气候

内蒙萨拉乌苏河流域米浪沟湾剖面末次间冰期发育5 层古土壤。对这5 层古土壤的形 态特征、粒度、扫描电镜及化学风化等分析结果表明: (1) 这些古土壤具有与华北现代褐土相 似的形态特征; (2) 粘化率中部高和石英颗粒表面硅质溶蚀-沉淀现象表明古土壤层中发生过 风化成壤作用; (3) 用K₂O/Na₂O、Al₂O₃/Na₂O、MnO/Al₂O₃、CIA 及A-CN-K 图解与华北现代 褐土作对比分析, 发现它们的化学风化特征极为相似; (4) 用气温及降水量与CIA 值的回归 关系方程, 得出5 层古土壤发育时期的水热状况确与华北现代的暖温带半湿润季风性气候大 致相同或更显暖湿。形态特征、粒度、石英颗粒表面特征和化学风化特征等多个方面具备了 与现代华北褐土类似的化学风化成壤特征, 证明这些古土壤是在与华北相似的暖温带半湿润 季风性气候条件下形成的。     

Closely-spaced recuperated OSL dating of the last interglacial paleosol in the southeastern margin of the Chinese Loess Plateau

The objective of this study is to construct a numerically dated chronology of the last interglacial paleosol (S₁) in Chinese loess using luminescence dating. The recuperated optically stimulated luminescence (ReOSL) dating approach was applied to 18 closely-spaced (20 cm intervals) samples, with 15 of these collected from the S₁ unit at the Weinan site, which is located at the southeastern margin of the Chinese Loess Plateau (CLP). By using the multiple-aliquot regenerative-dose (MAR) approach, 18 fine-grained quartz ReOSL equivalent dose (D_E) values, spanning about 249–466 Gy, were obtained. The validity of ReOSL MAR protocol was checked by dose recovery measurements and recycling ratio tests. By comparison of the dose-response curves of all the samples, we found that it is feasible to construct a standardized growth curve (SGC) for the ReOSL signal at the Weinan site. Considering the effects of pedogenesis of the S₁ unit during formation, the dose rate during the last interglacial was corrected, which should be beneficial for constructing a more reliable chronology. Finally, a detailed chronology of the S₁ unit was established. The results show that S₁ was deposited between approximately 76–127 ka, which confirms the early suggestion that the S₁ unit in Chinese loess corresponds to the whole marine oxygen-isotope stage (MIS) 5. The detailed ReOSL chronology of S₁ indicates the consistency of the substrata of S₁ with MIS 5a-e, but cannot determine whether they are exactly coeval. According to the present ReOSL age results, it is suggested that dust deposition is continuous at timescales larger than 14.1 ± 11.8 ky during the last interglacial and there is no hiatus longer than 4.4 ± 13.0 ky at the L₂/S₁ transition. Further work, e.g. minimizing the errors on ages and reducing the luminescence sampling intervals, is needed to understand the more detailed dust deposition conditions during the last interglacial in Chinese loess.     

Late Quaternary paleoenvironments and paleoclimatic conditions in the distal Andean piedmont, southern Mendoza, Argentina

The Andean piedmont of Mendoza is a semiarid region covered by extensive and partially vegetated dune fields consisting of mostly inactive aeolian landforms of diverse size and morphology. This paper is focused on the San Rafael plain (SRP) environment, situated in the distal Andean piedmont of Mendoza (34° 30′S), and reports the sedimentology and OSL chronology of two representative exposures of late Quaternary deposits, including their paleoenvironmental and paleoclimatic significance. Eleven facies, including channel, floodplain, fluvio–aeolian interaction, and reworked pyroclastic and aeolian deposits, were described and grouped into two facies associations (FA1 and FA2). FA1 was formed by unconfined sheet flows, minor channelized streams and fluvial–aeolian interaction processes. FA2 was interpreted as aeolian dune and sand-sheet deposits. OSL chronology from the SRP sedimentary record indicates that between ca. 58–39 ka and ca. 36–24 ka (MIS 3), aggradation was governed by ephemeral fluvial processes (FA1) under generally semiarid conditions. During MIS 2, the last glacial maximum (ca. 24–12 ka), a major climatic shift to more arid conditions is documented by significant aeolian activity (FA2) that became the dominant sedimentation process north of the Diamante–Atuel fluvial system. The inferred paleoenvironmental conditions from the SRP sections are in broad agreement with regional evidence.     

柴达木盆地大浪滩130ka BP以来的孢粉组合与古气候

应用柴达盆地西部大浪滩梁ZK02孔岩芯,依据铀系年龄数据,选择130 ka BP(90.5 m以上)的含石膏粉砂淤泥层中34个样品进行孢粉分析研究,依据其孢粉组合特征,将该孔深90.5m以浅的孢粉百分比图式从下至上划分6个区域性孢粉带,进而分析了该区末次间冰期(130 ka BP)以来的古植被状况,结果表明,山地主要由...     

Geological note: Pyro‐intrusive veins in the northeastern Sydney Basin

Stratigraphic and sedimentological investigation of the interglacial succession within the Cryogenian-aged Umberatana Group of the Northern and Central Flinders Ranges reveals a complex array of sedimentary successions lying between the Sturtian and Marinoan glacial deposits. The Sturtian–Marinoan Series boundary was first defined from the Adelaide area at the uppermost contact of the Brighton Limestone. In the Northern Flinders Ranges the Sturtian–Marinoan Series boundary has been positioned at the uppermost contact of the Balcanoona Formation, which is thought to correlate with the Brighton Limestone. In the Northern Flinders Ranges a major unconformity separates the Sturtian and Marinoan-aged sedimentary successions (Nepouie–Upalinna Subgroups). In moderately deep marine depositional settings, this submarine unconformity is located at the base of the Yankaninna Formation where erosion has deeply incised (up to 300 m) into the underlying Tapley Hill Formation. In shallower marine settings the unconformity is found at the base of the Weetootla Dolomite. In very deep water depositional settings this unconformity is not recognised, and the Yankaninna Formation appears to conformably overlie the Tapley Hill Formation suggesting that this erosional feature is restricted to shallow and moderately deep depositional settings. This unconformity presents a regionally persistent chronostratigraphic marker horizon, which reliably marks the Sturtian–Marinoan Series boundary at the base of the Yankaninna Formation from shallow shelfal to deep-water basinal settings throughout the Northern Flinders Ranges. In the Central Flinders Ranges the post-Sturtian glacial stratigraphy records a very similar depositional record to that observed in the Northern Flinders Ranges. In the Central regions the Tapley Hill Formation is overlain by deep-marine carbonates and calcareous shales of the Wockerawirra Dolomite and Sunderland Formations, respectively. The base of the Wockerawirra Dolomite is found to be in erosional contact with the underlying Tapley Hill Formation. This stratigraphic relationship, together with lithological similarities, indicates the Wockerawirra Dolomite and Sunderland Formation of the Central Flinders Ranges are lateral correlatives of the Yankaninna Formation of the Northern Flinders Ranges. The regional nature of the Sturtian–Marinoan unconformity in the Adelaide Geosyncline suggest the possible existence of a glacio-eustatic event that may correlate with glacials/glaciation elsewhere on the Earth during the Cryogenian.