A high‐resolution pollen and geochemical analysis of late Holocene human impact and vegetation history in southern Cumbria,England

The historic era, which in Cumbria begins with the Roman invasion of AD 71, is a frequently neglected period in palaeoecological research, but its study can bring benefits in improving knowledge of landscape history and in understanding the significance and limitations of palaeoecological records. Pollen and geochemical data are presented for late Holocene records from Deer Dyke and Hulleter Mosses in southern Cumbria. The records show initially low levels of anthropogenic impact, followed by a phase of forest clearance and mixed agriculture from the 7th to 11th centuries AD. The timing of these clearances suggests that they were initially Anglo‐Saxon in origin, rather than Norse. Further clearances in the 16th century AD are interpreted as a response to monastic dissolution and late Tudor population pressures; the landscapes reached their contemporary form following extensive clearances in the 17th century AD. Silicon and titanium concentrations at Deer Dyke Moss were used to reconstruct past levels of atmospheric dust loading, which is broadly related to soil erosion. Geochemical influx was found to peak during periods of landscape transition rather than from established land use. This relationship with pollen data is thought to reflect the predominantly low levels of anthropogenic impact in the region, which changes as substantial woodland clearances during the 16th century AD and continuous land use pressure since then have greatly increased the supply of airborne dust. Copyright © 2008 John Wiley & Sons, Ltd.     

Late Pleistocene deposits at Block Fen,Cambridgeshire, England

Organic sediments in a gravel quarry at Block Fen, Cambridgeshire, form a sheet dividing lower from upper gravels. Analyses of pollen, macroscopic plant remains and molluscs from these organic sediments are presented. They indicate the presence of temperate freshwater and slightly brackish fine floodplain sediments, which, on the basis of the palaeobotany, are correlated with the temperate Ipswichian Stage. The freshwater sediments, ascribed to Ipswichian substage IIb, occur at ca. ?3 m OD. Marine-influenced tidal sediments, ascribed to Ipswichian substage III, occur at ca. ?6 m OD. No evidence was found for the presence of more than one temperate stage in the sequence. The lower gravels are then correlated with the cold Wolstonian Stage and the upper gravels with the cold Devensian Stage. In contrast to the woodland environments indicated by the palaeobotany of the Ipswichian organic sediments, post-Ipswichian pollen diagrams and macroscopic plant remains in the upper suite of sands and gravels indicate open tree-less vegetation typical of the cold Devensian Stage. They also contain a typical cold-stage mollusc fauna. The sediments containing these floras and faunas are associated with thermal contraction cracks, indicating the presence of permafrost. The final sand and gravel aggradation in the Devensian forms the Block Fen Terrace, near 0 m OD. The evidence indicates that it is younger than the lacustrine sediments resulting from the blocking of the Fenland at the Wash by Late Devensian ice at ca. 18.5 ka BP. The sequence at Block Fen is related to nearby Ipswichian and Devensian sediments at Chatteris, March, Wimblington and Mepal, and to deposits at Wretton on the east margin of Fenland. The correlation permits an outline reconstruction of the history of the valley carrying the River Great Ouse between the Isle of Ely and the Chatteris and March ‘islands’ from the time of a gravel aggradation before the Ipswichian to the Flandrian. The reconstruction shows the time and level of the Ipswichian marine incursion into the Middle Level of Fenland and the extent of aggradation and erosion in the Devensian.     

碱性环境对油松花粉保存影响实验研究

孢粉是恢复古植被、古气候的重要代用指标。然而,即使是同一时代的地层,不同地点、不同岩性提取出的花粉量差异很大,造成这些差异的原因很多,其中花粉在不同沉积环境中的保存差异是重要原因之一。本研究是在实验室内模拟自然条件下碱性环境对油松花粉(Pinus tabulaeform is)的破坏情况:煮水5小时,泡10%NaOH溶液10天,煮10%NaOH溶液5小时对油松花粉破坏都很小;煮20%和30%NaOH溶液1小时对油松花粉影响也不明显;煮40%NaOH溶液1小时,油松花粉壁出现蚀变,加热时间增至5小时,蚀变现象进一步加深。表明油松花粉具有很强的耐碱,耐高温能力。更强碱或更长时间情况下花粉蚀变情况,有待进一步研究。     

内蒙东风金矿勘查地球化学特征与深部预测

东风金矿位于华北地台北缘，赤峰-朝阳金矿化集中区中部老哈河拗断带内的局部断块隆起中。矿化类型主要是少硫化物的蚀变岩型。矿脉中Hg、Ba、As、Sb、(As Hg)/(Mo Pb)、(Hg/Mo)100、F2因子得分值等参数的高值和Mo、Co、Ni、Fl因子得分值等参数的低值存在是矿体上部或前缘标志。反之，则是矿体下部或无矿的标志。根据上述标志，8^#脉63800-64200线之间的十中段以下深部可能有新的工业矿化存在；8^#脉63700线附近的金矿体的勘探重点应放在六、七中段；2^#脉的工业矿化在64000线以西向三中段以下有进一步延深，但由于被主成矿期后的断所切，其深部的规模不大。     

香港-大亚湾近岸海域表层沉积物的孢粉分布规律

对香港大亚湾近岸海域表层沉积物的孢粉分析结果表明．蕨类孢子占绝对优势，其次是木本植物花粉，而草本植物花粉含量较少，这一结果总体上与岸区丘陵低地植被受人为干扰破坏后的表土孢粉组合特征一致。大亚湾和大鹏湾的孢子沉积离岸越近含量越高，湾内的沉积规律与海流和沉积粒度的分布有关。香港海域则在靠伶仃洋一侧孢子含量较高，反映了蕨类孢子以径流搬运为主。此外，木本植物和草本植物花粉总量离岸越远含量越低，松属在木本植物中占优势．其相对含量向外海增加。     

海桑属花粉在南海晚第四纪地层中的分布及其意义

海桑属(Sonneratia)植物是热带滨海特有的盐滩植物,是气候和环境的指示植物,其花粉可作为滨海相沉积的重要标志。此属花粉在南海南部晚第四纪地层中分布较广,在南海中部的深海盆地,由于海流的影响,也有少量的断续分布,而处于南海北部的香港地区,在晚更新世中晚期的地层中,曾大量出现过。分析海桑属花粉在晚第四纪地层中的分布,对深入研究南海海区的物质来源、古环境和古气候等有着重要的意义。     

霞浦No.1孔晚第四纪古气候因子的定量估算

本文使用孢粉图式、最优分割、对应分析和Q型聚类分析方法，将福建霞浦No.1孔的孢粉划分为8个孢粉组合带，并由此推论出8个植被演替阶段。依据对应分析结果和一系列热力学计算公式，本文估算了该孢粉所反映的古气候因子。它们包括年平均温度、相对温度、绝对湿度、水汽压、年蒸发量、干燥度、年降水量。并依据之些古气候因子，认为该孔孢粉反映的该地区晚第四纪古气侯有7个阶段。     

孢粉稳定碳同位素研究进展

由于植物的光合作用途径不同,C3和C4植物的δ13C值有明显不同的分布范围,这可以用来研究环境的变化。花粉的碳同位素分析结果显示其δ13C值与植物的δ13C值变化规律一致,也能很好地反映植物的光合作用途径,进而间接反映其所处的气候环境条件。相比于植物体,化石花粉颗粒组成成分较单一,而其生成时间短,因而其碳同位素或许能较好地反映植物开花期时的环境条件,如雨水、大气CO2等的性质,为更精确的环境重建提供可能。初步的研究结果也显示花粉的δ13C值与开花期的温度存在线性关系。高精度结果的取得依赖于实验技术和仪器设备的改进,研究表明传统孢粉的醋酸酐处理过程中存在碳同位素污染,采用浓H2SO4浸泡可达到相同的去除纤维素的目的而避免污染。另外,通过对质谱仪的改进——装配旋转镍丝等进样系统(SWiM-IRMS),使实验所需的测试量大大减少,对单粒花粉进行测定也已经成为可能,但实验的精度还待进一步提高。     

巴里坤湖孢粉浓缩物~(14)C测年可行性研究

14C测年是湖泊沉积物定年的主要方法之一,随着对过去气候环境变化的深入研究,对于湖泊样品中的年代要求更高,而不同的测年物质的14C定年结果,会有不同的误差。通过对巴里坤湖部分样品,分别进行块状样有机质、陆生高等植物残体以及孢粉浓缩物定年比较,以探讨干旱区湖泊中14C定年的方法。测试结果表明:孢粉浓缩物与陆生高等植物残体的测年值极为接近,在西北干旱区湖泊测年过程中,孢粉浓缩物有望成为一种可靠的测年材料。在探讨湖泊沉积物年代的碳库效应时,孢粉浓缩物定年可能会成为一种有效的方法。