Climatic variability in the Late Copper Age: stable isotope fluctuation of prehistoric Unio pictorum (Unionidae) shells from Lake Balaton (Hungary)

Geochemical records of bivalve shells have been increasingly studied in the last decade to obtain information on climate conditions. In this paper we present stable isotope compositions of living and prehistoric shells of freshwater mussels (Unionidae) and their relationships with climate conditions in a shallow lake environment of Lake Balaton, West-Central Hungary. Physical conditions and stable oxygen isotope compositions of lake water samples were monitored where living bivalves were collected. Comparisons between seasonal variations in ambient temperature, water composition and within-shell isotopic variations indicate that the shells of Unio pictorum do reflect local changes at high resolution and thus can be used to study past conditions. Additionally, shells covering the last two decades were gathered at several locations along the lake in order to determine spatial and temporal variations in the shells’ isotopic compositions as a function of weather conditions. As an application, prehistoric shells collected in archaeological excavations were analysed in order to study past environmental variations. Climate variations during the Late Copper Age (5460–4870 cal. yr BP) have been assumed on the basis of geomorphological and archaeozoological observations at the site Balatonkeresztúr-Réti-dűlő (south of Lake Balaton), that suggested increasing humidity as a cause of changes in settlement location and domestic livestock husbandry. Stable carbon and oxygen isotope compositions of prehistoric bivalve shells were analyzed from excavations representing five archaeological subphases (Boleráz subphase, 5460–5310 cal. yr BP; two transitional subphases around 5310 cal. yr BP; Early Classic subphase, 5310–5060 cal. yr BP; Late Classic subphase, 5040–4870 cal. yr BP). The analyses revealed significant negative C and O isotope shifts in the transitional subphases relative to the earlier and later subphases. The isotopic variations indicate that the local climate became relatively wet and possibly cold around 5310 cal. yr BP, then it returned to drier (and likely warmer) conditions during the Classic subphases. This interpretation is in agreement with previous studies on climate changes related to the “5.3 ky event” in the European continental area and the North Atlantic Region, indicating an Atlantic influence in the Carpathian Basin.     

Old, Low-Mass, Metal-Rich (SMR) Stars

The authors of this paper try to disentangle the many problems arisen from a new enlarged sample of nearby low-mass,metal-rich-stars. These stars have reliable absolute magnitudes, deduced from Hipparcos parallaxes, precise bolometric corrections, effective temperatures and metal abundances from high resolution detailed spectroscopic analyses. Their ages have been derived from a grid of isochrones calculated with up to date physics. The main goal of this paper is to determine the ages of the slightly evolved SMR stars. Among those with well determinated ages about 80% of them have intermediate ages of (2 to 5 Gyr), but only 20% have ages of 8 Gyr or more. Nevertheless, the existence of very old metal-rich stars is confirmed. This revised version was published online in July 2006 with corrections to the Cover Date.     

A ‘mathematical’ spider living on gravel plains of the Namib Desert

In certain areas of the Namib gravel plains a new Ariadna sp. was discovered. It rims its vertical burrow with a stone circle, made on average of seven quartz stones. Some mathematical relationships between hole diameter, stone sizes and weight, and animal size were studied. A correlation was found, and stone selection by this spider postulated. Different hypotheses on the adaptive value of stone circle are suggested.     

Geochemical processes in a Mediterranean Lake: a high-resolution study of the last 4,000 years in Zoñar Lake,southern Spain

High-resolution geochemical analysis of a 6-m-long sediment core from Zoñar Lake, southern Spain, provides a detailed characterization of major changes in lake and watershed processes during the last 4,000 years. Geochemical variables were used as paleolimnological indicators and complement Zoñar Lakes’s paleoenvironmental reconstruction based on sedimentological and biological proxies, which define periods of increasing allochthonous input to the lake and periods of dominant autochthonous sedimentation. Chemical ratios identify periods of endogenic carbonate formation (higher Ca/Al, Sr/Al and Ba/Al ratios), evaporite precipitation (higher S/Al, Sr/Al ratios), and anoxic conditions (higher Mo/Al, U/Th ratios and Eu anomaly). Higher productivity is marked by elevated organic carbon content and carbonate precipitation (Mg/Ca). Hydrological reconstruction for Zoñar Lake was based on sedimentological, mineralogical and biological proxies, and shows that lower lake levels are characterized by Sr-rich sediments (a brackish lake with aragonite) and S-rich sediments (a saline lake with gypsum), while higher lake levels are characterized by sediments enriched in elements associated with alumino-silicates (Al, K, Ti, Fe, trace and rare earth elements), reflecting fresher conditions. Geochemical indicators also mark periods of higher detrital input to the lake related to human activity in the watershed: (1) during the Iberian Roman Humid Period (650 BC–AD 300), around the onset of the Little Ice Age (AD 1400), during the relatively drier Post-Roman and Middle Ages (AD 800–1400), and over the last 50 years, due to mechanized farming practices. Heavy metal enrichment in the sediments (Cu and Ni) suggests intensification of human activities during the Iberian Roman Period, and the use of fertilizers during the last 50 years.     

Toroidal versus poloidal magnetic fields in Sun-like stars: a rotation threshold

From a set of stellar spectropolarimetric observations, we report the detection of surface magnetic fields in a sample of four solar-type stars, namely HD 73350, HD 76151, HD 146233 (18 Sco) and HD 190771. Assuming that the observed variability of polarimetric signal is controlled by stellar rotation, we establish the rotation periods of our targets, with values ranging from 8.8 d (for HD 190771) to 22.7 d (for HD 146233). Apart from rotation, fundamental parameters of the selected objects are very close to the Sun's, making this sample a practical basis to investigate the specific impact of rotation on magnetic properties of Sun-like stars.
We reconstruct the large-scale magnetic geometry of the targets as a low-order  (ℓ < 10)  spherical harmonic expansion of the surface magnetic field. From the set of magnetic maps, we draw two main conclusions. (i) The magnetic energy of the large-scale field increases with rotation rate. The increase in chromospheric emission with the mean magnetic field is flatter than observed in the Sun. Since the chromospheric flux is also sensitive to magnetic elements smaller than those contributing to the polarimetric signal, this observation suggests that a larger fraction of the surface magnetic energy is stored in large scales as rotation increases. (ii) Whereas the magnetic field is mostly poloidal for low rotation rates, more rapid rotators host a large-scale toroidal component in their surface field. From our observations, we infer that a rotation period lower than ≈12 d is necessary for the toroidal magnetic energy to dominate over the poloidal component.     

Sur quelques concentrations plombo-zinciferes du devonien inferieur du massif schisteux rhenan

Zusammenfassung The Lower Devonian of the Rhine Schist Massif is characterized by a fine detrital sedimentation which reflects a coastal plain environment located between the Old Red Sandstone continent in the N and the marine Bohemian Facies in the SE. Mineralisations are located within these coastal-plain sediments, especially in fractured horizons topped by pelitic and floored by sandy sediments of Sieg Emsian age. The mineralised localities occur in three zones: the districts of Bensberg, Eitorf and Mayen. The Lüderich locality (Bensberg) is the most important having approximately one million tons of Zn and Pb metal. It is localised within a zone having marked sedimentary characteristics since the Siegenian. Mineralisation occurs as penecontemporaneous lenses, fracture fillings etc, formed at abnormal contacts between lithological units having different competance during Siegenian and Lower Emsian deformation. However, locally there is lateral transition between the upper units of the sandy channel series and the lower units of the pelitic swamp facies. Vertical extension of mineralisations is strictly limited to the tectonic contact zone between the Odenspiel Sandstone and the Bensberg pelites. Study of mineralisations at various levels (mapping, morphology, structure, paragenetic and geochemical) leads to the formulation of a genetic model requiring complex fracturation at the contact between contrasting lithologies and preferential drainage through these fractured zones; metals are trapped on the sandstone floor, the pelitic roof trapping the vadose hydrothermal solutions. These basic controls seem to apply throughout the Bensberg, Eitorf and Mayen districts. On a more regional scale the age variations of the gangue sediments reflects a lateral displacement of red/grey facies limits due to coastal evolution. Thus one may demonstrate a type of mineral occurrence whose model may be that of epigenetic reconcentration within fractures affecting syngenetic geochemical anomalies.Zusammenfassung Das Unterdevon des Rheinischen Schiefergebirges wird durch eine feinkörnige detritische Sedimentation gekennzeichnet. Die Verteilung dieser detritischen Sedimente widerspiegelt eine flache Küstenlandschaft zwischen dem Kontinent des Unterrotliegenden im Norden und des Meeres mit der Böhmischen Fazies im Südosten. In diesen Schichten befinden sich gangförmige Vererzungen, die in Bruchzonen auftreten, die ein pelitisches Hangendes und ein sandsteinreiches Liegendes vom Siegen-Ems Alter haben. Die Lagerstätten kommen in drei Bezirken vor: Der Bensberger Bezirk, der Bezirk Eitorf und der Bezirk Mayen. Die Lagerstätte Lüderich (Bensberger Revier) ist die größte (ungefähr eine Million Tonnen Metall Zink+Blei). Sie befindet sich in einer Zone, in der schon in der Siegen-Stufe bemerkenswerte sedimentäre Strukturen auftreten. Die Vererzung tritt als penekonkordante Linsen, Gänge, Stockwerke in tektonischen Kontaktzonen auf. Diese Kontaktzonen befinden sich zwischen 2 verschiedenen sedimentären Einheiten, deren Gesteinseigenschaften sehr verschieden sind. Es handelt sich um Pelite mit Sandstein-Einschaltungen einerseits, die zur unteren Emsstufe gehören sollen und um fluviatile Sandsteine andererseits, die zur oberen Siegenstufe gehören sollen. Lokal ist ein lateraler Übergang durch Faziesänderung von den oberen Sandsteinen in die unteren Pelitschichten jedoch nicht unmöglich. Die Sandsteine vertreten einen fluviatilen Sedimentationsbereich, die Pelite einen sumpfigen Sedimentationsbereich. Die Vererzung (mit einer vertikalen Ausdehnung ungefähr von 300 m) tritt nur im Bereich der Kontaktzone zwischen den Odenspieler Sandsteinen und den Peliten der Unteren Bensberger Schichten auf. Die Resultate der Kartographie, der morphologischen Studie der Erzkörper, der Struktur und der Paragenese führen zu einem genetischen Modell. Dabei spielt die Anwesenheit einer Bruchstruktur an der Grenze zwischen 2 Bereichen mit verschiedenen lithologischen Eigenschaften eine Hauptrolle für die Konzentration der im Hangenden fein verteilten Metalle. Die hydrothermalen Lösungen kommen demnach nicht von der Teufe, sondern aus dem Nebengestein. Im ganzen Bensberger Erzrevier wie in der Gegend von Eitorf und in der Gegend von Mayen finden wir dieselben Leitfäden für die Vererzung in den Lagerstätten und Vorkommen. Beobachtet man die ganze Provinz, dann merkt man, daß die Altersverschiedenheiten in den Nebengesteinen der verschiedenen Lagerstätten eine geographische Wanderung der Faziesgrenze zwischen rot und grau in dieser küstennahen Ebene Widerspiegeln. Die verschiedenen Vorkommen und Lagerstätten treten immer in unmittelbarer Nähe dieser Grenze auf. Die Eigenschaften dieser Lagerstätten weisen auf eine Bildung durch eine epigenetische Umlagerung in eine gangförmige Bruchstruktur hin.     

Relationships between Holocene sea-level variations,trophic development,and climatic change in Negra Lagoon,Southern Uruguay

Paleolimnological data are presented on trophic development, climatic change and sea level variations in Negra Lagoon, a 142 km² coastal lagoon in southern Uruguay. Using a sediment core that extended to the early Holocene, analyses of organic matter, carbonate, diatoms and opal phytoliths allowed us to track changes in trophic state and paleosalinity levels, which were closely related to Holocene sea level variation, temperature and humidity. Diatom Association Zones (DAZ) corresponding to transgressive events were dominated by marine/brackish taxa and relatively low organic matter values, while those DAZ corresponding to regressive events showed increases in brackish/freshwater diatoms and organic matter. Opal Phytoliths Association Zones (OPAZ) also were identified, temperature and humidity indices were calculated, and climatic trends were inferred. During the middle Holocene (i.e., ~5000–4000 yr BP), cool–dry climatic conditions were established. After ~4000 yr BP, a transition from cool to warm–humid conditions was observed, but fully warm humid conditions established only after ~1700 yr BP. Such climatic amelioration led to increases in trophic state.     

Proper motion surveys in the infrared

Current and future wide field surveys in infrared passbands present opportunities for ultra low‐mass stellar sample selection via proper motions, as well as or instead of purely photometric techniques. Furthermore, proper motion measurements yield additional clues as to candidate membership of cluster or field (kinematic) populations. In this paper we review some recent results and speculate as to the possibilities afforded by the next generation of wide‐field infrared surveys. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Strontium and oxygen isotope evidence relating to the petrogenesis of the Kangerdlugssuaq alkaline instrusion,East Greenland

The Kangerdlugssuaq intrusion, East Greenland, consists of quartzsyenites, syenites, pulaskites and foyaites. The age and petrogenesis of the intrusion has been investigated by strontium and oxygen isotope analyses of the major rock types (and some separated minerals) and the surrounding country rocks. Crystallization and rapid cooling of the intrusion close to 50 m.y. ago is indicated by concordance of an Rb-Sr mineral isochron (49.9±1.0 m.y.) and an Rb-Sr whole-rock isochron (50.0±1.9 m.y.) with previously published mineral dates. The feldspathoid-bearing rocks of the intrusion, which were the last to crystallize, have uniformly depleted oxygen (¹⁸O = +3.9, SMOW) and homogeneous initial ⁸⁷Sr/⁸⁶Sr ratios (0.70450±7). This is ascribed to equilibration of the magma prior to the crystallization of these rocks with about 10% by weight of meteoric ground water. The concommittant increase of to about 1 Kb (the lithostatic load pressure) would depress the liquidus surfaces in the system Ne-Ks-Qz by about 200 ° C, allowing the magma to evolve continuously down temperature from oversatuated to undersaturated compositions. The chemical mechanism responsible for this trend has not been uniquely identified, but probably involved reduction of SiO₂ content in an open system. The outer, quartz-normative, rocks of the intrusion have ¹⁸O values ranging up to +5.5 and initial ⁸⁷Sr/⁸⁶Sr ratios ranging up to 0.7095. This is due to interaction of the solid rocks, down to temperatures approaching 500 ° C, with ground water which had been enriched in ¹⁸O and ⁸⁷Sr by previous exchange with the Precambrian country rocks. Minimum water/rock ratios are lower than in certain other known cases of interaction in the North Atlantic Tertiary Igneous Province.     

Performance‐based design using structural optimization

A new methodology for seismic design is proposed based on structural optimization with performance‐based constraints. Performance‐based criteria are introduced for the seismic design of new buildings. These criteria are derived from the National Guidelines for Seismic Rehabilitation of Buildings (Reference [19], Federal Emergency Management Agency (FEMA), ‘NHERP Guidelines for seismic rehabilitation of buildings’, Report Nos 273 and 274, Washington, DC, 1997) for retrofitting existing structures. The proposed design methodology takes into account the non‐linear behaviour of the structure. The goal is to incorporate in the design the actual performance levels of the structure, i.e. how much reserve capacity the structure has in an earthquake of a given magnitude. The optimal design of the structure minimizes the structural cost subjected to performance constraints on plastic rotations of beams and columns, as well as behavioural constraints for reinforced concrete frames. Uncertainties in the structural period and in the earthquake excitation are taken into account using convex models. The optimization routine incorporates a non‐linear analysis program and the procedure is automated. The proposed methodology leads to a structural design for which the levels of reliability (performance levels) are assumed to be quantifiable. Furthermore, the entire behaviour of the structure well into the non‐linear range is investigated in the design process. Copyright © 2000 John Wiley & Sons, Ltd.