A stage 7 marine interglacial record (the Grødeland Interglacial) on Jaeren, southwestern Norway; foraminiferal, stable isotopes and amino acid evidence

Foraminiferal biostratigraphy, stable isotopes and amino-acid diagenesis have been investigated in a 125 m (+ 1 to — 124 m a.s.l.) long core from Jæren, southwestern Norway. Two marine units, the 42 m thick Grødeland Sand and the 8 m thick Sunde Sand, were found between till beds. Based on the biostratigraphic data, nine foraminiferal assemblage zones are defined. The Grødeland Sand shows a development from an ice-proximal glacial environment in the lower part, through an arctic, possibly shallow-water, environment, into a full interglacial open-shelf regime (the Grødeland Interglacial). The Grødeland Interglacial sediments (zone 6 Cassidulina laevigata-Cibicides zone) were deposited at a water depth of 20 m, in an open, high-energy shelf environment with temperature conditions similar to those prevailing in the northern North Sea today. The interglacial sediments are followed by deposits characteristic of an arctic environment which become more ice proximal upwards. Superimposed on the Grødeland Sand is a diamicton interpreted as till. Above the till is the upper marine unit (the Sunde Sand), which in the lower part yielded a shallow-water arctic fauna replaced upwards by an ice-proximal facies. The upper part of the Sunde Sand is barren of foraminifera and is superimposed by an upper till. The Sunde Interstadial is defined as a climatostratigraphic event resulting in deglaciation of western Norway and deposition of the Sunde Sand. Based on amino acid geochronology and inferences from the biostratigraphy, the Grødeland Interglacial is assigned to oxygen-isotope stage 7, whereas the Sunde Interstadial is assigned to the Early Weichselian. Combined with existing data from the North Sea region and the Norwegian Sea, it is concluded that for stage 7, in addition to stages 1 and 5e, there must have been a strong influx of Atlantic water into the Norwegian Sea north of the British Isles. This circulation created a similar north-south gradient in water masses in the North Sea to that which occurred during the Eemian and the Holocene. In the Nordic Seas, however, the stage 7 warm influx was probably restricted to the eastern part of the basin, unlike the later warm periods. This led to the development of fully interglacial conditions in the North Sea region, even though the palaeoceanographic data from the central part of the Nordic Seas suggest relatively cooler conditions for oxygen-isotope stage 7.     

Lipid composition of phytoplankton from the Barents Sea and environmental influences on the distribution pattern of carbon among photosynthetic end products

The colonial algae Phaeocystis pouchetii and Dinobryon pellucidum dominated the phytoplankton crop at three stations in the Polar Front area of the Barents Sea.
Lipid extracted from the seawater containing the phytoplankton was dominated by neutral lipid classes, particularly triacylglycerols, and phospholipids were more abundant than galactolipids at all stations. Polyunsaturated fatty acids comprised between 15 and 26% of fatty acids of total lipid.
Of the carbon assimilated into lipid over 24 hours, 40% was located in the neutral lipid fraction. Phospholipids contained a smaller proportion of fixed carbon than galactolipids.
No defiinte relationships were observed between the distribution of fixed carbon in photosynthetic end products and the temperature or irradiance at which the phytoplankton was incubated. At a constant irradiance of 8.5 μmol m⁻²s⁻¹, the highest proportion of fixed carbon was recovered in protein at 4.5°C, but at −1.5°C most radioactivity was present in low molecular weight compounds. Regardless of incubation conditions, lipid always contained less than 30% of total assimilated carbon.     

Temperature variations recorded in Pinus tabulaeformis tree rings from the southern and northern slopes of the central Qinling Mountains, central China

The Qinling Mountain range constitutes a critical boundary for climate and vegetation distribution in eastern central mainland China owing to its importance as a geographic demarcation line. In this article, cores from 88 Chinese pines ( Pinus tabulaeformis ) from the southern (MW site) and northern (NWT site) slopes of the Qinling Mountains were used to reconstruct seasonal temperature variations. During the calibration period, significant correlations were found between ring width and the mean temperature from prior September to current April of 0.76 at the southern slope, and between ring width and the mean May–July temperature of 0.67 at the northern slope. The subsequent temperature reconstructions span 1760–2005 for the northern site and 1837–2006 for the southern site. Prior to the mid-20th century, low September–April temperatures were, in general, followed by high May–July temperatures, probably reflecting variations in the winter and summer monsoon. However, since the mid-20th century, both records show trends of a more pronounced increase in September–April temperature on the southern slope. The results provide independent support for the interpretation that recent warming is unusual in nature, coinciding with the observed record. The results compare well with tree-ring based reconstructions from the surrounding regions, suggesting regional signals in the Qinling Mountain reconstructions.     

Vegetation patterns, recent pollen deposition and distribution of non-pollen palynomorphs in a polygon mire near Chokurdakh (NE Yakutia, NE Siberia)

Fine-scaled distribution patterns of vegetation and palynomorphs in a polygon mire in NE Siberia were studied in 31 × 31 plots of 1 m² (vegetation) and along a transect at intervals of 1 m (palynomorphs). Pollen and non-pollen-palynomorph contents clearly reflect differences between polygon ridges and centres. For most single pollen types, however, no unambiguous relation with actual plant abundances and distribution exists. High pollen values are restricted to the immediate vicinity of the pollen sources, which is attributed to the low height of the vegetation. For several plant taxa, high pollen values were found to be restricted to particular plant specimens in the population. High values of pollen ascribed to taxa currently absent at the relevant plot show that the sampled mosses contain a pollen signal of several years. Betula exilis produces two morphologically clearly distinct pollen types. The distribution of selected non-pollen palynomorphs correlates to microrelief, moisture regime and/or trophic conditions. The study shows that single palaeo-sections from arctic peatlands should not be over-interpreted with respect to their palaeoecological value. Local vegetation types and site conditions, however, can be accurately reconstructed from the total assemblages and from combined occurrences of specific palynomorph types.     

Modelling the formation of residual dune ridges behind barchan dunes in North-east Brazil

Residual dune ridges are often formed by vegetation growing along a line some distance upwind of the lower stoss slope of migrating dunes. This process is common in areas where vegetation germinates along the edge of the water during the rainy period when the water level is higher and interdune areas are flooded. The phenomenon occurs on a large scale in North‐east Brazil, because of the rise and fall in groundwater level at the end of the rainy season. Each residual dune ridge corresponds to the position of the dune during the wet period in each year. Therefore, variations in the distance between these residual dune ridges could be used potentially to monitor climatic fluctuations in rainfall and wind. To examine the potential use of these residual dune ridges for the reconstruction of past climatic fluctuations, a model that simulates them under varying conditions of wind, rainfall and evaporation rates was formulated. The model was tested for sensitivity to climatic variability in North‐east Brazil and validated against residual dune ridge displacements as measured in the field and from high spatial resolution satellite images. Based on the results, it is concluded that residual dune ridges may not form in North‐east Brazil in years which are exceptionally dry, as may happen during El‐Niño events. When this type of event happens, the distance between adjacent residual dune ridges corresponds to more than one year and, therefore, the correlation between dune displacements and wind power becomes weak or even disappears. Additionally, because of biotic, aeolian and hydrological processes, these arcuate residual dune ridges may not preserve their initial shape for long periods. The presence of residual dune ridges testifies to the temporary flooding which may or may not be seasonal. However, the potential for using residual dune ridges to reconstruct the palaeo‐climate of wind regime on a yearly basis or to identify past El‐Niño events seems to be limited.     

Ordovician conodonts from the Bulltinden Formation, Motalafjella, central-western Spitsbergen

Seven samples from the Limestone and Boulder Conglomerate Members of the Bulltinden Formation have yielded poorly preserved conodonts. On tentative identifications Periodon aculeatus Hadding and Prioniodus cf. P. alobatus Bergstrom at the base of the formation suggest an Ordovician lower Caradoc, or older age. This confirms that the Vcstgotabrcen Formation unconformably beneath underwent high-pressure mctamorphism during the Taconic and/or Finmarkian phases of the Caledonian orogeny. The conodonts show affinity to the North Atlantic Province suggesting a deeper water marine depositional environment. Conodont colour alteration indices of five indicate that the Bulltinden Formation was heated to temperatures in excess of 300°C, probably during the middle-upper Silurian main Caledonian uplift event.     

The N Variscan margin of the Ruhr coal district (Western Germany): structural style of a buried thrust front?

The Ruhr coal district represents part of an external fold and thrust belt of the Variscan orogen in central Europe. Extensive mining exposed molasse-type, coal-bearing clastic sequences of Upper Carboniferous age, deformed by folding and thrusting.Thrusts range in scale from decameters to 40 kilometers along strike but displacements are below 2.5 km. They are distributed in various stratigraphic levels and no regional detachment horizon is exposed. Displacement is mainly towards NW (towards the foreland) but also towards SE. The thrusts are bound to stockwerk-tectonics and die out towards depth frequently antithetic to the exposed strata.Folds vary in wavelength from decameters to more than 10 kilometers. Transitions from cylindrical or concentric to chevron-type folds are common. They have also been modelled in experiments. There, varying fold types compensate volume problems, created (e.g.) during concentric folding, without a major detachment.Another mechanism of compensating excess volume during folding is evident, where thrusts transport volume from fold hinge areas to fold limbs. Folds generally deform both footwall and hangingwall of thrusts. Numerous observations prove a contemporary development of thrusts in mechanic relation to the folding-process.Overall orogenic shortening decreases slowly from SE to NW, towards the foreland without a major break. The presented structural observations and experimental data point to the fact that orogenic shortening in the marginal fold and thrust belt of the Ruhr district may well be compensated by folding and minor thrusting without major detachment. Therefore, the buried tip line of a regional Variscan detachment horizon may be situated towards the internal parts of the orogen, southeast of the Ruhr district.

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Zusammenfassung Das Ruhrkarbon ist Teil des externen Falten- und Überschiebungsgürtels der Varisziden in Mitteleuropa. Ausgedehnte Bergbauaufschlüsse geben hier Einblick in die gefaltete und zerblockte, molasseartige Schichtenfolge des Oberkarbons.Die aufgeschlossenen Überschiebungen erreichen hier eine streichende Länge von maximal 40 km, die Schubweiten aber allerhöchstens 2.5 km. Die Überschiebungen treten in unterschiedlichen stratigraphischen Niveaus auf; ein regionaler Abscherhorizont ist nicht aufgeschlossen. Die Schubbewegungen sind vorwiegend nach NW in Richtung auf das Vorland gerichtet, es treten aber auch zahlreiche Überschiebungen auf, die nach SE gerichtet sind. Das Auftreten der Überschiebungen ist an ein bestimmtes tektonisches Stockwerk gebunden. Sie laufen zur Tiefe hin häufig antithetisch zur Schichtung aus.Die Spannweite der Falten reicht von Zehnermetern bis zu über 10 km. Übergänge zwischen zylindrischen oder konzentrischen Falten zu Knickfalten sind allgemein verbreitet. Sie lassen sich auch experimentell nachbilden, wobei die verschiedenen Faltentypen Volumenprobleme lösen, die bei konzentrischer Faltung auftreten, ohne daß eine größere Abscherung erfolgt.Eine andere Möglichkeit Volumenüberschüsse abzubauen, ist dort verwirklicht, wo Überschiebungen Material von den Faltenkernen zu den Faltenflanken transportieren. Im allgemeinen setzen sich die Faltenachsen über die Überschiebungen hinweg fort, so daß Hangend- und Liegendscholle gleichartig verfaltet sind. Dies und zahlreiche andere Beobachtungen zeigen, daß die Überschiebungen zeitgleich mit und in mechanischer Abhängigkeit von der Faltung entstanden sind.Die generelle orogene Einengung nimmt im Ruhrkarbon allmählich von SE nach NW, d. h. in Richtung auf das Vorland ab, ohne daß eine sprunghafte Änderung dieses Gradienten eintritt.Die dargelegten Beobachtungen und experimentellen Ergebnisse zur Strukturgeologie deuten darauf hin, daß die orogene Einengung des Ruhrkarbons allein durch Faltung und untergeordnete Überschiebungstektonik erfolgt sein dürfte, ohne daß die Annahme eines größeren Abscherhorizontes erforderlich wäre. Aus diesem Grunde kann mit dem Auftreten großregionaler varistischer Abscherhorizonte im Untergrund erst südlich vom Ruhrgebiet, also näher am internen Bereich des Orogens, gerechnet werden.

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Résumé Le Carbonifère de la Ruhr fait partie de la zone externe plissée et charriée du tectogène hercynien en Europe occidentale. La série stratigraphique du Carbonifère supérieur, de type molassique, plissée et fracturée, est bien connue grâce aux nombreuses exploitations minières.Les chevauchements peuvent y être suivis en direction sur 40 km au maximum, mais leurs rejets ne dépassent pas 2.5 km. Ces failles se rencontrent dans des niveaux stratigraphiques différents. Aucun décollement d'importance régionale n'a été décelé. Le transport est surtout dirigé vers l'avant-pays (vers le nord-ouest), mais il existe aussi de nombreux chevauchements vers le sud-est. La présence des chevauchements est liée à un certain étage tectonique. Vers la profondeur, ils se terminent souvent dans une position antithétique par rapport à la stratification.Les plis sont décamétriques à plurikilométriques (> 10 km). Des transitions entre des plis isopaques et des plis aigus de type «en chevron» sont fréquentes. La coexistence de ces diverses formes de plis, réalisée aussi expérimentalement, permet d'éliminer les problèmes de volume soulevés par un plissement uniquement isopaque, sans faire intervenir un décollement important. Un autre mécanisme d'élimination des excédents de volume est représenté par des chevauchements qui transportent des matériaux depuis les zones de charnières vers les flancs des plis. En général, les surfaces axiales se poursuivent à travers ces failles dont le toit et le mur ont été plissés de la même façon. Cette disposition, jointe à d'autres observations, indique que les chevauchements ont été contemporains du plissement et en interdépendance mécanique avec celui-ci.Dans le Carbonifère de la région de la Ruhr, le raccourcissement orogénique diminue du sud-est vers le nord-ouest, c'està-dire vers l'avant-pays, de manière progressive, sans variation brusque.En conclusion, le raccourcissement orogénique du Carbonifère de la région de la Ruhr a été réalisé par les plis et les chevauchements mineurs associés, sans décollement d'importance régionale. Pour cette raison, l'existence de tels décollements en profondeur ne peut être envisagée qu'au sud de la région de la Ruhr, donc dans une zone plus interne de l'orogène.

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