Inputs of dissolved and particulate 226Ra to lakes and implications for 210Pb dating recent sediments

Gamma spectroscopy was used to measure radioisotope (²¹⁰Pb, ²²⁶Ra, ¹³⁷Cs) activities in sediment cores from 20 lakes and a wetland in Florida, USA. Nine profiles display relatively low (<5 dpm g^–1) and constant ²²⁶Ra activities, whereas 12 show high (>5 dpm g^–1) and variable ²²⁶Ra activities. In the latter group, most display up-core increases in activity. Upper sediments from two lakes (Round and Rowell) possess very high (>20 dpm g^–1) ²²⁶Ra activities that exceed total ²¹⁰Pb activities, clearly illustrating disequlibrium between ²²⁶Ra and supported ²¹⁰Pb. Supported ²¹⁰Pb activity is generally thought to come from in situ, ²²⁶Ra-containing detrital mineral particles, and is typically assumed to be in secular equilibrium with ²²⁶Ra activity. Since 1966, Round Lake has been augmented hydrologically with ²²⁶Ra-rich (6.2 dpm L^–1) groundwater pumped from the local deep aquifer. Adsorption of dissolved ²²⁶Ra to recent Round Lake sediments probably accounts for the high measured ²²⁶Ra activities and the pronounced disequilibrium between ²²⁶Ra and supported ²¹⁰Pb in topmost deposits. We suspect that many Florida waterbodies receive some ²²⁶Ra-rich runoff and seepage from groundwater pumped for irrigation, residential use, industrial applications, and mining. This may account for up-core increases in ²²⁶Ra activity measured in sediment cores from some Florida lakes. Significant groundwater pumping began within the last century, and there has been insufficient time for supported ²¹⁰Pb to come into equilibrium with adsorbed ²²⁶Ra in uppermost deposits. Input of ²²⁶Ra-rich groundwater to lakes may occur in any geographic region where local bedrock contains ²³⁸U and its daughters. When dissolved ²²⁶Ra adsorbs to recent sediments, it complicates accurate estimation of supported ²¹⁰Pb activity, and confounds calculation of unsupported ²¹⁰Pb activity that is used in dating models.     

青南高原树轮年表的建立及与气候要素的关系

根据青海南部曲麻莱、治多地区树木年轮样本,建立了青海南部高原(下称青南高原)树木年轮年表序列,系统地与所在地区气候资料进行了综合分析。通过响应函数,计算得出该年表对青南高原春季(4～6月)的最高温度和蒸发量的反映更为敏感。并重建了青南高原春季最高温度序列。     

非水溶剂中电解质溶液活度系数的测定:NaCl在1,2-丙二醇中活度系数的测定

应用钠离子选择性电极和Ag-AgCl电极组成可逆电池,通过测定电池的电动势,应用Debye H櫣ckel极限公式,计算了不同温度下NaCl在1,2-丙二醇非水溶剂中的活度系数,并根据电解质溶液的溶剂化理论对NaCl的活度系数的某些变化规律进行了讨论。     

Mobility of a remobilised parabolic dune in Kennemerland, The Netherlands

A parabolic dune in the Netherlands was remobilised in December 1998 by removing vegetation and soil. The main aim of the experiment was ecological: to investigate whether permanent rejuvenation at the landscape scale is possible by restoration of natural processes. If processes can be reactivated at coarse scale, periodic rejuvenation of the landscape over the long term is possible, without the need for managers to interfere further. The experiment provides the opportunity to address another important question: can large parabolic dunes in the Netherlands be mobile in the present climate? Mobility of the dune is investigated by means of erosion pins, aerial photography and measurement of cross sections. Activity indices are derived from erosion pin recordings and correlated to weather conditions. From 1999 to 2001, displacement of the dune ranged from 0 to 12 m in east–northeasterly direction. Activity of the dune is related to wind conditions, but the relationship is strongly influenced by precipitation and therefore differs for wet and dry periods. Periods with extreme wind speeds resulted in much less geomorphic change than expected.     

Paleomagnetic age and palaeobiological significance of hominoid fossil strata of Yuanmou Basin in Yunnan

The Yuanmou area in Yunnan Province is a fa-mous place for origin of mankind. Qian Fang et al. found tooth fossils of Yuanmou man in Shangnabang Village of Yuanmou in 1965. Jiang Nengren et al. identified the hominoid teeth from animal fossils un-earthed near Zhupeng Village in the Xiaohe Basin which were delivered by the local peasants. Hominoid fossils were also found in Leilao Village of Yuanmou afterward. These great discoveries have aroused ex-tensive concern in academic circle[1,2…     

C chronology for ice retreat and inception of Champlain Sea in the St. Lawrence Lowlands, Canada

AMS radiocarbon cross-dating of plant debris and marine shells trapped in a lake basin on Mount St. Hilaire (Québec, Canada) provides a direct assessment of a reservoir effect totaling ca. 1800 ¹⁴C years during the early stage of Champlain Sea. Pollen-based extrapolation of bottommost ages on terrestrial plant macrofossils in sediments of this lake, and of another lake nearby support an estimate of 11,100 ± 100 ¹⁴C yr B.P. for marine invasion in the Central St. Lawrence River Lowlands. Results indicate a 400–1000 years younger regional chronology of ice retreat, now congruent with the one inferred from the New England varve chronology. This is a summary of a longer paper to be published in French.     

Late Quaternary glacial and climate history of the Pamir Mountains derived from cosmogenic Be exposure ages

Moraines southwest of Lake Yashilkul, Pamir, Tajikistan, were dated using ¹⁰Be exposure ages of boulder surfaces. We found evidence for (1) an extensive glaciation ∼60,000 yr ago; (2) a less extensive glacial advance, which deposited a characteristic hummocky moraine lobe with exposure ages ranging from ∼11,000 to 47,000 yr, probably deposited at or before 47,000 yr ago; and (3) lateral moraines with exposure ages of ∼40,000 yr, 27,000 yr and 19,000 yr, respectively. Increasing aridity in the Pamir is most likely responsible for the progressively limited extent of the glaciers during the Late Pleistocene.     

Pleistocene and Holocene aeolian facies along the Huelva coast (southern Spain): climatic and neotectonic implications

The stratigraphic relationships, genesis and chronology, including radiocarbon dating, of the Quaternary sandy deposits forming the El Asperillo cliffs (Huelva) were studied with special emphasis on the influence of neotectonic activity, sea-level changes and climate upon the evolution of the coastal zone. The E-W trending normal fault of Torre del Loro separates two tectonic blocks. The oldest deposits occur in the upthrown block. They are Early to Middle Pleistocene fluviatile deposits, probably Late Pleistocene shallow-marine deposits along an E-W trending shoreline, and Late Pleistocene and Holocene aeolian sands deposited under prevailing southerly winds. Three Pleistocene and Holocene aeolian units accumulated in the downthrown block. Of these, Unit 1, is separated from the overlying Unit 2 by a supersurface that represents the end of the Last Interglacial. Accumulation of Unit 2 took place during the Last Glacial under more arid conditions than Unit 1. The supersurface separating Units 2 and 3 was formed between the Last Glacial maximum at 18 000 ¹⁴C yr BP and ca. 14 000 ¹⁴C yr BP, the latter age corresponding to an acceleration of the rise of sea level. Unit 3 records wet conditions. The supersurface separating Units 3 and 4 fossilised the fault and the two fault blocks. Units 4 (deposited before the 4th millennium BC), 5 (> 2700 ¹⁴C yr BP to 16th century) and 6 (16th century to present) record relatively arid conditions. Prevailing wind directions changed with time from W (Units 2–4) to WSW (Unit 5) and SW (Unit 6).     

丹巴地区变玄武岩年代学的初步研究及其地质意义

川西丹地区变玄武岩中单颗锆石的207Pb/206Pb年龄为736～800Ma，它近似代表其原岩的喷发时间；变玄武岩的Rb-Sr矿物等时线年龄为150.2±0.3Ma，它代表导该区变玄武岩形成的最主要的一次区域动热变质事件年龄。