Genetic implications of new lead isotope measurements on Schwarzwald vein and Upper Triassic sediment galenas

We report the results of a lead isotopic investigation of galena from vein deposits from the Southern Schwarzwald (33 samples) and from various localities (6) from the galena horizon of the South German Keuper. The total range of isotopic ratios for the veins and the Keuper leads is:18,29 <²⁰⁶Pb/²⁰⁴Pb < 18,97; 15,59 <²⁰⁷Pb/²⁰⁴Pb < 15,70; 38,42 <²⁰⁸Pb/²⁰⁴Pb < 38,90. The lead isotopic systems give anomalous ages when compared with lead evolution models ofHolmes (1946, 47)Houtermans (1946),Stacey &Kramers (1975) andCumming &Richards (1975). This indicates a more complex lead evolution than allowed for in these models.Small but significant variations in the isotopic ratios of lead were observed in galenas from within a number of veins and between veins. Also leads in galena from Hercynian veins within granitic host rocks in the Southern Schwarzwald were found to be more radiogenic than galena leads in veins found in gneisses in the Central Schwarzwald. These results strongly suggest a local influence on the lead isotopic compositions of the vein galenas and also place constraints on the age of the veins and models of vein formation.Galenas from Tertiary veins were found to have lower²⁰⁷Pb/²⁰⁴Pb ratios in comparison with ratios observed in Hercynian vein leads, suggesting that the Tertiary veins contain a compound of older retarded lead from a source not identified in the present study.The Keuper sedimentary galenas were found to have relatively homogenous lead isotopic ratios which fall within the range of isotopic compositions of the Hercynian vein leads. The galenas from the Upper Triassic (Keuper) are slightly more radiogenic than the more isotopically variable galena leads from the uppermost Permian (Kupferschiefer;Wedepohl et al. 1978).

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Zusammenfassung An Bleiglanzen von Gängen des mittleren und südlichen Schwarzwaldes (33 Proben) und von verschiedenen Lokalitäten (6) der Bleiglanzbank des süddeutschen Keupers wurden massenspektrometrische Blei-Isotopen-Untersuchungen durchgeführt.Die Werte fallen in die Bereiche: 18,29 <²⁰⁶Pb/²⁰⁴Pb < 18,97; 15,59 <²⁰⁷Pb/²⁰⁴Pb < 15,70; 38,42 <²⁰⁸Pb/²⁰⁴Pb < 38,90. Aus den Blei-Isotopenverhältnissen erhält man anomale Blei-Entwicklungsalter, wenn man die Modellevon Holmes (1946, 47),Houtermans (1946),Stacey &Kramers (1975) undCumming &Richards (1975) zugrunde legt. Das zeigt, daß die Entwicklung dieses Bleis komplexer ablief, als die genannten Modelle annehmen.Kleine aber signifikante Unterschiede in der Blei-Isotopenzusammensetzung wurden für Proben eines Gangsystems und zwischen den verschiedenen Gängen beobachtet. Das Blei aus Bleiglanzen von variscischen Gängen des St. Blasien-Granits (Südostschwarzwald) ist radiogener als das der Gänge in den Gneisen des Zentral-Schwarzwaldes. Diese Beobachtung zeigt, daß die Blei-Isotopenwerte mit der lokalen geologischen Situation verknüpft sind und ist von Bedeutung für die Diskussion der Alter und Entstehungs-modelle der Bleiglanze.Bleiglanz aus den als Tertiär angesehenen Gängen zeigt niedere²⁰⁷Pb/²⁰⁴-Verhältnisse als die variscischen Gang-Bleiglanze. Daraus kann man auf eine ältere zurückgebliebene Bleikomponente schließen, deren Quelle jedoch noch nicht gefunden wurde. Die Bleiglanze aus der Keuper-Bleiglanzbank ergaben relativ einheitliche Isotopenverhältnisse, welche in die Verteilung der Schwarzwälder Bleie fallen. Sie sind etwas radiogener als die isotopisch sehr variablen Bleiglanz-Isotopenwerte des Zechsteins (Kupferschiefer;Wedepohl et al. 1978).

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Résumé Une étude isotopique du plomb a été effectué sur des galènes provenant de filons de la Forêt Noire Centrale et du Sud (33 échantillons) et de différentes localités (6) de l'horizon à galène du Keuper du Sud de l'Allemagne.Les valeurs de plomb se situent dans les intervalles suivants: 18,29 <²⁰⁶Pb/²⁰⁴Pb < 18,97; 15,59 <²⁰⁷Pb/²⁰⁴Pb < 15,70; 38,42 <²⁰⁸Pb/²⁰⁴Pb < 38,90.Les rapports isotopiques du plomb indiquent des âges d'évolution de plomb anormaux, si l'on prend pour base les modèles d'évolution deHolmes (1946, 47),Houtermans (1946),Stacey &Kramers (1975) etCumming &Richards (1975). Cela montre que l'évolution du plomb s'est déroulée d'une façon plus complexe que ne le supposent les modèles mentionnés. Des différences minimes mais significatives ont été observées dans la composition isotopique du plomb, pour des échantillons d'un système filonien et entre différents filons. Le plomb des galènes des filons hercyniens du granite de St. Blasien (Forêt Noire du Sud Est) est plus radiogénique que celui des filons trouvés dans les gneiss de la Forêt Noire Centrale. Cette observation montre que la composition isotopique du plomb est liée à la situation géographique locale et est d'une grande importance pour la discussion des âges et des modèles de formation des galènes.Les rapports²⁰⁷Pb/²⁰⁴Pb des galènes des filons considérés comme d'âge tertiaire sont moins élevés que ceux des galènes d'âge hercynien, ce qui permet de supposer une composante de plomb plus âgée, «retardée» dont on n'a pu jusqu'ici déceler la source. Le plomb des galènes du Keuper a une composition isotopique relativement homogène, qui se trouve dans la gamme de celle observée pour le plomb des galènes de la Forêt Noire. Leur plomb est légèrement plus radiogénique que celui des galènes du Zechstein qui a une composition isotopique très variable (Kupferschiefer;Wedepohl et al., 1978).

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— (33 ) (6 ) - . : 18,29 <²⁰⁶Pb/²⁰⁴Pb < 18,97; 15,59 <²⁰⁷Pb/²⁰⁴Pb < 15,70; 38,42 <²⁰⁸Pb/²⁰⁴Pb < 38,90. , Holmes'a, 1946; Houterman'a, 1946, Stacey & Kramer'a, 1975 Cumming & Richard'a, 1975, . , , , ., , . St. Blasien (- ) , . , , . ²⁰⁷Pb/²⁰⁴Pb, . , . , . , , .

     

An ostracod-conductivity transfer function for Tibetan lakes

About 145 freshwater to hypersaline lakes of the eastern Tibetan Plateau were investigated to develop a transfer function for quantitative palaeoenvironmental reconstructions using ostracods. A total of 100 lakes provided sufficient numbers of ostracod shells. Multivariate statistical techniques were used to analyse the influence of a number of environmental variables on the distributions of surface sediment ostracod assemblages. Of 23 variables determined for each site, 19 were included in the statistical analysis. Lake water electrical conductivity (8.2%), Ca% (7.6%) and Fe% (4.8%, ion concentrations as % of the cations) explained the greatest amounts of variation in the distribution of ostracod taxa among the 100 lakes. Electrical conductivity optima and tolerances were calculated for abundant taxa. A transfer function, based on weighted averaging partial least squares regression (WA-PLS), was developed for electrical conductivity (r ² = 0.71, root-mean-square-error of prediction [RMSEP] = 0.35 [12.4% of gradient length], maximum bias = 0.64 [22.4% of gradient length], as assessed by leave-one-out cross-validation) based on 96 lakes. Our results show that ostracods provide reliable estimates of electrical conductivity and can be used for quantitative palaeoenvironmental reconstructions similarly to more commonly used diatom, chironomid or pollen data.     

Late Pleistocene to Holocene vegetation and climate changes in northwestern Chukotka (Far East Russia) deduced from lakes Ilirney and Rauchuagytgyn pollen records

This paper presents two new pollen records and quantitative climate reconstructions from northern Chukotka documenting environmental changes over the last 27.9 ka. Open tundra- and steppe-like habitats dominated between 27.9 and 18.7 cal. ka BP. Betula and Alnus shrubs might have grown in sheltered microhabitats but disappeared after 18.7 cal. ka BP. Although the climate was rather harsh, local herb-dominated communities supported herbivores as is evident by the presence of coprophilous spores in the sediments. The increase in Salix and Cyperaceae ~16.1 cal. ka BP suggests climate amelioration. Shrub Betula appeared ~15.9 cal. ka BP, and became dominant after ~15.52 cal. ka BP, whilst typical steppe communities drastically reduced. Very high presence of Botryococcus in the Lateglacial sediments reflects widespread shallow habitats, probably due to lake level increase. Shrub Alnus became common after ~13 cal. ka BP reflecting further climate amelioration. Simultaneously, herb communities gradually decreased in the vegetation reaching a minimum ~11.8 cal. ka BP. A gradual decrease of algae remains suggests a reduction of shallow-water habitats. Shrubby and graminoid tundra was dominant ~11.8–11.1 cal. ka BP, later Salix stands significantly decreased. The forest-tundra ecotone established in the Early Holocene, shortly after 11.1 cal. ka BP. Low contents of green algae in the Early Holocene sediments likely reflect deeper aquatic conditions. The most favourable climate conditions were between ~10.6 and 7 cal. ka BP. Vegetation became similar to the modern after ~7 cal. ka BP but Pinus pumila came to the Ilirney area at about 1.2 cal. ka BP. It is important to emphasize that the study area provided refugia for Betula and Alnus during MIS 2. It is also notable that our records do not reflect evidence of Younger Dryas cooling, which is inconsistent with some regional environmental records but in good accordance with some others.     

河北安固里淖孢粉记录的晚冰期以来的植被演替与气候变化

河北安固里淖地处东南季风的边缘地区,是研究古气候环境演化的理想地区之一。文章以安固里淖的沉积岩芯（长18.4 m）为研究对象,利用AMS ¹⁴C测年和孢粉数据,重建了安固里淖湖区14.3 cal.ka B.P.以来的植被与气候演化历史。结果表明：14.3~11.0 cal.ka B.P.期间,湖区以疏林草原植被为主,气候偏干;11.0~6.0 cal.ka B.P.以森林草原植被为主,气候湿润;6.0~3.2 cal.ka B.P.以疏林草原植被为主,气候偏湿;3.2~0 cal.ka B.P.以荒漠草原植被为主,气候干旱。总体而言,自晚冰期以来安固里淖的气候经历了由干变湿再逐渐变干的过程,全新世适宜期出现在早中全新世。通过区域对比发现,安固里淖揭示的晚冰期以来东南季风的气候演化特征与西南季风的演化具有很大的相似性,表明晚冰期以来东南季风与西南季风在轨道尺度上的演化并无太大差异,太阳辐射是二者演化的共同驱动力。

     

The influence of climate on water chemistry states and dynamics in rivers across Australia

For effective water quality management and policy development, spatial variability in the mean concentrations and dynamics of riverine water quality needs to be understood. Using water chemistry (calcium, electrical conductivity, nitrate-nitrite, soluble reactive phosphorus, total nitrogen, total phosphorus and total suspended solids) data for up to 578 locations across the Australian continent, we assessed the impact of climate zones (arid, Mediterranean, temperate, subtropical, tropical) on (i) inter-annual mean concentration and (ii) water chemistry dynamics as represented by constituent export regimes (ratio of the coefficients of variation of concentration and discharge) and export patterns (slope of the concentration-discharge relationship). We found that inter-annual mean concentrations vary significantly by climate zones and that spatial variability in water chemistry generally exceeds temporal variability. However, export regimes and patterns are generally consistent across climate zones. This suggests that intrinsic properties of individual constituents rather than catchment properties determine export regimes and patterns. The spatially consistent water chemistry dynamics highlights the potential to predict riverine water quality across the Australian continent, which can support national riverine water quality management and policy development.     

A late Quaternary lake record from the Qilian Mountains (NW China): evolution of the primary production and the water depth reconstructed from macrofossil, pollen, biomarker, and isotope data

The history (45–0 ka BP) of the aquatic vegetation composition of the shallow alpine Lake Luanhaizi from the NE Tibetan Plateau is inferred from aquatic plant macrofossil frequencies and aquatic pollen and algae concentrations in the sediments. C/N (range: 0.3–100), δ¹³C (range: −28 to −15‰), and n-alkane measurements yielded further information on the quantitative composition of sedimentary organic matter. The inferred primary production of the former lake ecosystem has been examined in respect of the alternative stable state theory of shallow lakes [Scheffer, M., 1989. Alternative stable states in eutrophic, shallow freshwater systems: a minimal model. Hydrobiological Bulletin 23, 73–83]. Switches between clear and turbid water conditions are explained by a colder climate and forest decline in the catchment area of Lake Luanhaizi. The macrofossil-based reconstruction of past water depth and salinity ranges, as well as other organic matter (OM) proxies allowed climatic inferences of the summer monsoon intensity during the late Quaternary. Around 45 ka BP, conditions similar to or even moister than present-day climate occurred. The Lake Luanhaizi record is further evidence against an extensive glaciation of the Tibetan Plateau and its bordering mountain ranges during the Last Glacial Maximum. Highest lake levels and consequently a strong summer monsoon are recorded for the early Holocene period, while gradually decreasing lake levels are reconstructed for the middle and late Holocene.     

Comparing Eulerian and Lagrangian eddy census for a tide-less,semi-enclosed basin,the Baltic Sea

Ocean Dynamics - Eddies in the global and coastal ocean play a key role in mixing and transport processes. Here, we present an eddy census for the Baltic Sea covering the years 2008–2010. The...     

Biolaminoid facies in a peritidal sabkha: Permian Platy Dolomite of northern Poland

The Platy Dolomite, a carbonate unit in the Zechstein Formation (Upper Permian) of the Leba Elevation, Poland, was deposited in a semi-closed or completely separated back-barrier sabkha environment. This arid, hypersaline zone is comparable to the recent Gavish Sabkha, Sinai. The processes which formed the modern Gavish Sabkha are similar to those responsible for the biolaminoid formation in the Platy Dolomite series. The deposition of this Platy Dolomite was mainly the result of microbial activity building extensive microbial mats. The Platy Dolomite is characterized by loosely packed microbial biolaminoids (a less significantly laminated build-up of biogenetic sediments) with horizontally or obliquely to vertically orientated filaments. Intermediary coated grains occur. Densely packed, flat laminated stromatolitic rocks, pure oolites, and bioclastic sedimentary strata are rarely intercalated with the biolaminoid beds. Laboratory and field investigations indicate that carbonate formation was induced by the chemoorganotrophic bacterial decay of cyanobacterial mats. Magnesium was bound and absorbed by organic matter and later liberated by anaerobic decay. Early diagenetic processes formed Mg²⁺- and Ca²⁺-enriched solutions in which carbonates precipitated biologically and chemically. A system of biogenic carbonate formation of the Platy Dolomite microbiolite series is proposed and supported by the results of microbiological laboratory studies.