Distribution and provenance of the Baginton Sand and Gravel in the Wreake Valley,northern Leicestershire,England: Implications for inter-regional correlation

The Baginton Sand and Gravel is traced along the lower Wreake Valley as a continuous water-laid stratum at the base of the drift succession. Its properties closely resemble those previously described from the proto-Soar valley, namely an upward fining sequence and a composition dominated by pebbles of Triassic and Carboniferous origin. Such a provenance is consistent with the idea that the proto-Soar once followed a route eastwards past Melton Mowbray, and that the drainage along the lower Wreake Valley has been reversed in the course of Pleistocene times. However, the slope of the sand and gravel train appears to be to the west rather than the east, and the rockhead relief is also inconsistent with an eastward-flowing proto-Soar. Until this enigma is resolved, it would be imprudent to use the Baginton Sand and Gravel as the basis for inter-regional correlations. The issue is further complicated by the preservation at Brooksby of earlier interglacial or interstadial deposits whose temporal affinities remain unclear.     

末次间冰期全球地表温度变化及物理机制的模拟研究

本研究基于第六次国际耦合模式比较计划(CMIP6)的末次间冰期模拟试验(lig127k)与工业革命前参照试验(piControl)数据, 利用气候反馈响应分析方法, 揭示了地球轨道参数改变引起的全球地表温度变化及其关键过程和机制。5个模式的分析结果表明: 1)与piControl相比, lig127k试验中地球轨道参数的改变主要影响了大气层顶入射太阳辐射的季节性差异, 其中北半球冬季大气层顶入射太阳辐射明显减少, 全球平均为-19.60W/m², 而夏季则显著增加, 为20.42W/m², 全年平均变化较小, 仅为-0.06W/m²; 2)lig127k的地表温度也表现为冬季(夏季)显著的降低(升高), 其中北半球冬季全球平均降温-0.61 K, 夏季增温0.67 K; 3)从物理过程分解来看, 北半球冬季(夏季)的降温(增温)均主要来自大气层顶入射太阳辐射的贡献, 其次来自水汽的正反馈贡献, 而云辐射效应则抵消了大部分降温(增温); 4)与工业革命前时期相比, 在末次间冰期, 海陆热力对比在北半球显著加强, 而在南半球显著减弱, 其中起正贡献的主要过程为陆地/海洋热输送和云辐射效应, 而太阳辐射强迫效应和地表湍流热通量则是主要的负贡献项。

     

Rock coast inheritance: an example from Galicia,northwestern Spain

A shore platform on the western coast of Galicia in northwestern Spain has been inherited from interglacial stages when sea level was similar to today. The wide, gently sloping intertidal platform is backed in places by supratidal rock ledges, and in other places by a steeper and narrower supratidal ramp. The gradient of the intertidal platform is consistent with the relationship between platform gradient and tidal range, but the slope of the ramp is much too high. The abandoned and degraded sea cliff is grass-covered along most of this coast, and the ledges and the ramp, which extend up to several metres above the highest tides, are covered by lichen and, in places, by salt-tolerant plants. Radiocarbon-dated sediments in the cliff, which range up to 36 000 years in age, lie on top of an ancient beach deposit. The former beach, remnants of which are found in situ on the ramp and rock ledges, as well as two caves that are filled with the dated sediments, are probably last interglacial in age. The morphological and sedimentary evidence suggests that the supratidal ramp and ledges were also formed during the last interglacial stage, whereas the wider intertidal platform is probably the product of several older interglacials, when sea level was generally similar to today. A general model is proposed for the inheritance of shore platforms in macro- and microtidal environments. Copyright © 1999 John Wiley & Sons, Ltd.     

Impact of dust aerosol on glacial-interglacial climate

The temperature anomaly and dust concentrations recorded from central Antarctic ice core records display a strong negative correlation. The dust concentration recorded from an ice core in central Antarctica is 50-70 times higher during glacial periods than interglacial periods. This study investigated the impact of dust aerosol on glacial-interglacial climate, using a zonal energy balance model and dust concentration data from an Antarctica ice core. Two important effects of dust, the direct radiative effect and dust-albedo feedback, were considered. On the one hand, the direct radiative effect of dust significantly cooled the climate during the glacial period, with cooling during the last glacial maximum being as much as 2.05℃ in Antarctica. On the other hand, dust deposition onto the ice decreased the surface albedo over Antarctica, leading to increased absorption of solar radiation, inducing a positive feedback that warmed the region by as much as about 0.9℃ during the glacial period. However, cooling by the direct dust effect was found to be the controlling effect for the glacial climate and may be the major influence on the strong negative correlation between temperature and dust concentration during glacial periods.     

Glacial and palaeoenvironmental history of the Cape Chelyuskin area, Arctic Russia

Quaternary glacial stratigraphy and relative sea-level changes reveal at least two glacial expansions over the Chelyuskin Peninsula, bordering the Kara Sea at about 77°N in the Russian Arctic, as indicated from tills interbedded with marine sediments, exposed in stratigraphic superposition, and from raised-beach sequences mapped to altitudes of at least up to ca. 80 m a.s.l. Chronological control is provided by accelerator mass spectrometry ¹⁴C dating, electron-spin resonance and optically stimulated luminescence geochronology. Major glaciations, followed by deglaciation and marine inundation, occurred during marine oxygen isotope stages 6–5e (MIS 6–5e) and stages MIS 5d–5c. These glacial sediments overlie marine sediments of Pliocene age, which are draped by fluvial sediment of a pre-Saalian age, thereby forming palaeovalley/basin fills in the post-Cretaceous topography. Till fabrics and glacial tectonics record expansions of local ice caps exclusively, suggesting wet-based ice cap advance, followed by cold-based regional ice-sheet expansion. Local ice caps over highland sites along the perimeter of the shallow Kara Sea, including the Byrranga Mountains and the Severnaya Zemlya archipelago, appear to have repeatedly fostered initiation of a large Kara Sea ice sheet, with the exception of the Last Glacial Maximum (MIS 2), when Kara Sea ice neither impacted the Chelyuskin Peninsula nor Severnaya Zemlya, and barely touched the northern coastal areas of the Taymyr Peninsula.     

地面沉降根源分析与防治对策

地面沉降是普遍存在的一种地质灾害。人类经济社会的发展,尤其是城市化进程日趋加快,一些人类不合理的活动导致了地面沉降频繁发生,给生产、建设和人民生活造成极大的危害。要防治地面沉降发生,必须认清其产生的根源,方能收到药到病除的效果。本文采用归纳分析的方法,将地面沉降划分为5种类型,依据其产生的不同根源,有针对性地提出了预防和治理的措施。     

Middle Pleistocene interglacial deposits at Barling,Essex, England: evidence for a longer chronology for the Thames terrace sequence

Results are presented from a multidisciplinary study of fossiliferous interglacial deposits on the northern side of the Thames estuary. These fill a channel cut into London Clay bedrock and overlain by the Barling Gravel, a Thames–Medway deposit equivalent to the Lynch Hill and Corbets Tey Gravels of the Middle and Lower Thames, respectively. The channel sediments yielded diverse molluscan and ostracod assemblages, both implying fully interglacial conditions and a slight brackish influence. Pollen analysis has shown that the deposits accumulated during the early part of an interglacial. Plant macrofossils, particularly the abundance of Trapa natans, reinforce the interglacial character of the palaeontological evidence. A beetle fauna, which includes four taxa unknown in Britain at present, has allowed quantification of palaeotemperature using the mutual climatic range method (T_max 17 to 26 °C; T_min ?11 to 13 °C). A few vertebrate remains have been recovered from the interglacial deposits, but a much larger fauna, as well as Palaeolithic artefacts, is known from the overlying Barling Gravel. The age of the interglacial deposits is inferential. The geological context suggests a late Middle Pleistocene interglacial, part of the post‐diversion Thames system and therefore clearly post‐Anglian. This conclusion is supported by amino acid ratios from the shells of freshwater molluscs. The correlation of the overlying Barling Gravel with the Lynch Hill/Corbets Tey aggradation of the Thames valley constrains the age of the Barling interglacial to marine oxygen isotope stages 11 or 9. The presence of Corbicula fluminalis and Pisidium clessini confirms a pre‐Ipswichian (marine oxygen isotope substage 5e) age and their occurrence in the early part of the interglacial cycle at Barling precludes correlation with marine oxygen isotope stage 11, as these taxa occur only later in that interglacial at sites such as Swanscombe and Clacton. Thus by process of elimination a marine oxygen isotope stage 9 age would appear probable. Copyright © 2001 John Wiley & Sons, Ltd.     

末次间冰期以来黄土-古土壤序列的磁组构特征及其指示的古风向

黄土高原粉尘物质的搬运、沉积过程与来自中高纬度地区的季风密切相关。研究冬季风演化历史将有助于深入理解全球变化背景下,东亚地区气候变化的动力机制。通过对黄土高原的磁组构研究发现:1)各向异性度(P)与磁面理度(F)相关性较高,因此各向异性主要由磁面理引起,磁化率椭球体为压扁状;2)磁面理大致水平,K3近垂直于水平面;3)黄土平均磁面理为1.007,古土壤为1.004,古土壤层的磁面理与各向异性度均要低于其下伏的母质黄土层。成土作用在某种程度上破坏了黄土的原生磁组构;4)P,F和粉尘粒度间具有一定内在联系,一般而言冬季风越强,搬运的粉尘颗粒越粗,从而导致在沉积过程中形成较高的磁面理;5)K1方向的等面积赤平投影图和玫瑰花图解表明,末次间冰期以来该地区的主导风向为NW向冬季风。     

Variations in seawater osmium isotope composition since the last glacial maximum: A case study from the Japan Sea

Concentrations of Re and Os, and the isotopic composition of Os have been measured in the Japan Sea sediments to assess the response of the Japan Sea to glacial–interglacial climate change and associated weathering fluxes. The osmium concentrations in the sediment samples analyzed vary from 59 to 371 pg/g, and ¹⁸⁷Os/¹⁸⁸Os from 0.935 to 1.042. Only ¹⁸⁷Os/¹⁸⁸Os of sediment samples from dark laminations deposited under suboxic to anoxic conditions and having elevated concentrations of Re and Os, and with ≥ 80% hydrogenous Os are explained in terms of seawater composition. Lower ¹⁸⁷Os/¹⁸⁸Os were observed for sediments deposited during the last glacial maximum (LGM) when planktonic foraminifera from the Japan Sea recorded lighter oxygen isotopic composition. Decrease in dissolved Os fluxes from continents and/or change in the composition of the dissolved load to the Japan Sea are suggested as the driving mechanisms for the observed lower LGM ¹⁸⁷Os/¹⁸⁸Os. The results of this study, coupled with lower ¹⁸⁷Os/¹⁸⁸Os during the last glacial observed at other sites from ocean basins with different lithology and contrasting sediment accumulation rates, suggest that this trend is characteristic of the global oceans.

Data from this study show that the Japan Sea recorded higher ¹⁸⁷Os/¹⁸⁸Os during the current interglacial coinciding with excursions of oxygen isotopic compositions of planktonic foraminifera to heavier values. This is explained in terms of preferential release of ¹⁸⁷Os during deglacial weathering and/or higher continental Os flux driven by warm and wet climate. This study demonstrates that Os isotopic composition of reducing margin sediments has immense potential to track variations in the seawater composition. In addition, ¹⁸⁷Os/¹⁸⁸Os of reducing sediments may be used to draw inferences about local paleoceanographic processes in semi-enclosed basins such as the Japan Sea.