Seasonality in low latitudes during the Oxfordian (Late Jurassic) reconstructed via high-resolution stable isotope analysis of the oyster Actinostreon marshi (J. Sowerby, 1814) from the Kachchh Basin, western India

A high-resolution stable isotope (δ¹⁸O, δ¹³C) analysis of a specimen of the oyster Actinostreon marshi (J. Sowerby, 1814) from the Lower Oxfordian of the Kachchh Basin in western India was used to reconstruct average seasonal temperatures over a consecutive time interval of 10 years. The recorded temperatures during this period varied around a mean of 13 °C (maximum: 15.1 °C; minimum: 11.4 °C) with a generally low seasonality between 1 and 3 °C. Such weak seasonal changes can be expected from a subtropical palaeolatitude between 25° and 30°S. However, the low average temperatures are in contrast to studies on broadly contemporaneous fossils from Europe and the southern Malagasy Gulf which point to much warmer conditions in these areas. It is therefore proposed that the low temperatures in the Kachchh Basin are caused by upwelling currents which influenced the north-western coast of India during the Late Jurassic.     

The Berchtesgaden National Park (Bavaria, Germany): a platform for interdisciplinary catchment research

The Berchtesgaden National Park (Bavaria, Germany), a study site of the UNESCO Man and the Biosphere program in the catchment of Berchtesgadener Ache, is introduced as a platform for interdisciplinary research. As the investigation of how human activities affect the natural resources in the park area, which has been defined a main aim of the program, naturally requires expertise from different scientific fields, interdisciplinary research has been fostered in the national park plan since the very beginning of the Man and the Biosphere program in 1981. To analyze the complex interactions and mutual dependencies between socio-economic and natural systems, a variety of monitoring programs have been initialized in different disciplines (e.g. climate sciences, zoology, botany) that are addressed in this paper. As a result of these research efforts, the park offers a profound data basis to be used in future studies (e.g. land cover classifications, maps of geological and soil conditions). Detailed information is provided on a climate monitoring network that has been installed in the park starting in the year 1993. The network has been continuously extended over the years and now provides extraordinary comprehensive information on meteorological conditions in the park, setting the basis for current as well as for potential future climate-related studies. A special characteristic of the station network is the fact that it covers a large range of elevations from 600 m a.s.l in the valleys to 2,600 m a.s.l in the summit regions and is therefore able to capture altitudinal gradients in meteorological variables as typical for Alpine regions. Due to the large number of stations in high elevations (15 stations are in elevations higher than 1,500 m a.s.l) the network provides information on the complex hydrometeorological conditions in summit regions which are often insufficiently represented in observation networks due to the increased costs for maintenance of climate stations in these locations. Beside the various monitoring programs, a variety of numerical models have been (further) developed for application in the park area that make extensive use of the different data collected and therefore largely benefit from the comprehensive data pool. The potential and necessity of the climate monitoring network for modelling studies is demonstrated by utilizing the meteorological recordings in the framework of a hydrometeorological simulation experiment. Further examples of environmental modelling efforts are shortly described together with preliminary model results.     

Upper Jurassic record of Polyphylloseris (Egypt, Northern Sinai)

Genus Polyphylloseris is a scleractinian colonial coral that has been established by d’Orbigny (1849) from the Neocomian of Yonne, France. The genus is characterized by having elevated domal calices that are mammillar or craterlike in shape and with porous confluent septa. Columella is absent or rudimentary, and the lower surface of the corallum is covered with a thick and wrinkled holotheca. Specimens having the above-mentioned characteristics have been collected from the Upper Jurassic Arousiah Member of the Masajid Formation (Callovian–Oxfordian) of Gebel Maghara, Northern Sinai, Egypt. They are characterized by having a cupolate colonial form and porous pennulate septa which reach 40–50 in number. Based on these characters and other characters such as density of septa, height, and width of mammillar calices, the studied material is attributed to a new species named Polyphylloseris magharensis. The new species is a first undoubted record of Polyphylloseris in the Jurassic. Previously recorded undoubted ages of the genus are Early and Late Cretaceous. The fewer number of septa and the smaller-sized and closer mammillar calices allow differentiation of the species from other species such as Polyphylloseris icaunensis d’Orbigny and Polyphylloseris convexa d’Orbigny.     

GEOCHRONOLOGY OF ~(Ar)/~(39)Ar DATING IN THE BASEMENT ROCKS IN EASTERN KUNLUN MOUNTAINS AND ITS TECTONIC IMPLICATIONS

GEOCHRONOLOGY OF ~(Ar)/~(39)Ar DATING IN THE BASEMENT ROCKS IN EASTERN KUNLUN MOUNTAINS AND ITS TECTONIC IMPLICATIONS     

Observations of some sedimentary processes acting on a tidal flat

In order to examine sedimentary processes acting on tidal flats, eighteen foot valves were “plumbed” into a small tidal cove in southern New Hampshire. Transport of suspended sediment was determined by comparing concentrations (determined by filtering) at 15 and 30 cm above the tidal flats throughout a tidal cycle. In general, sediment resuspension occurs more readily on the flood tide than the ebb. The concentration of suspended sediment follows the water mass distribution and is affected to a lesser degree by tidal currents and small amplitude waves. Deposition occurs during slack water shortly after high tide primarily in the bottom regime (15 cm); it is probably related to coarser particle sedimentation. The water mass distribution was not a simple rise and fall perpendicular to the bottom contours, but rather followed a slow clockwise gyre. The net effect on the suspended sediments was to impart a “longshore” component of drift to the suspended load during the tidal cycle.     

Use of targets to track 3D displacements in highly vegetated areas affected by landslides

Monitoring landslides with terrestrial laser scanning (TLS) is currently a well-known technique. One problem often encountered is the vegetation that produces shadow areas on the scans. Indeed, the points behind a given obstacle are hidden and thus occluded on the point cloud. Thereby, locations monitored with terrestrial laser scanner are mostly rock instabilities and few vegetated landslides, being difficult or even impossible to survey vegetated slopes using this method with its classical non-full wave form. The Peney landslide (Geneva, Switzerland) is partially vegetated by bushes and trees, and in order to monitor its displacements during the drawdown of the Verbois reservoir located at its base, an alternative solution has been found. We combined LiDAR technique with 14 targets made of polystyrene placed at different locations inside and outside the landslide area. The obtained displacements were compared with classical measurement methods (total station and extensometer), showing good resemblance of results, indicating that the use of targets in highly vegetated areas could be an efficient alternative for mass movements monitoring.     

The color of pumice: case study on a trachytic fall deposit, Meidob volcanic field, Sudan

 This paper examines the cause of color variations of trachytic pumices which are essentially uniform in chemical composition and proposes a geological model for their formation. A pyroclastic sequence of distinct subunits with brown, buff, and black pumices was deposited during the 5000-B.P. eruption of a tuff ring in the central Meidob volcanic field (Sudan). Subunits of buff pumices locally contain minor amounts of streaky pumice with pale-gray and dark-gray domains. The combined evidence of petrographic studies, chemical analyses of whole pumices and groundmass separates, electron microprobe analyses, optical spectroscopy, transmission electron microscopy, and magnetic susceptibility measurements show that color variations of the pumice clasts are related to the size and distribution of Fe³⁺-rich oxide microcrysts. Buff pumice and light-gray domains of streaky pumice have a colorless, transparent groundmass with very few microcrysts. Dark-gray domains of streaky pumice contain abundant hematite and/or magnetite microcrysts visible in thin section within a transparent, colorless glass groundmass. The groundmass of the black pumice clasts is brown in thin section which is most likely caused by submicroscopic magnetite microcrysts. Brown pumice clasts have a mixed groundmass consisting of brown domains and domains with opaque microcrysts in transparent glass. Variations in the eruption dynamics have been inferred from lithological observations. Subunits of black pumices are related to eruption pulses with low magma discharge and high water/magma mass ratio, whereas subunits of buff pumice were deposited during eruption pulses with high magma discharge and low water/magma mass ratio. Brown pumices represent the top part of the magma body, and the initial stage of the eruption probably had a low magma discharge. Streaky pumices are interpreted as the product of syn-eruptive mixing of Fe³⁺-rich oxide microcryst-bearing magma and microcryst-free magma. Received: 3 February 1997 / Accepted: 28 July 1997     

Tectonic significance of Triassic mafic rocks in the June Complex,Sanandaj–Sirjan zone,Iran

This study concentrates on the petrological and geochemical investigation of mafic rocks embedded within the voluminous Triassic June Complex of the central Sanandaj–Sirjan zone (Iran), which are crucial to reconstruct the geodynamics of the Neotethyan passive margin. The Triassic mafic rocks are alkaline to sub-alkaline basalts, containing 43.36–49.09 wt% SiO₂, 5.19–20.61 wt% MgO and 0.66–4.59 wt% total alkalis. Based on MgO concentrations, the mafic rocks fall into two groups: cumulates (Mg# = 51.61–58.94) and isotropic basaltic liquids (Mg# = 24.54–42.66). In all samples, the chondrite-normalized REE patterns show enrichment of light REEs with variable (La/Yb)_N ratios ranging from 2.48 to 9.00, which confirm their amalgamated OIB-like and E-MORB-like signatures. Enrichment in large-ion lithophile elements and depletion in high field strength elements (HFSE) relative to the primitive mantle further support this interpretation. No samples point to crustal contamination, all having undergone fractionation of olivine + clinopyroxene + plagioclase. Nevertheless, elemental data suggest that the substantial variations in (La/Sm)_PM and Zr/Nb ratios can be explained by variable degrees of partial melting rather than fractional crystallization from a common parental magma. The high (Nb/Yb)_PM ratio in the alkaline mafic rocks points to the mixing of magmas from enriched and depleted mantle sources. Abundant OIB alkaline basalts and rare E-MORB appear to be linked to the drifting stage on the northern passive margin of the Neotethys Ocean.     

Bemerkungen zu W. Dammann „Untersuchung über Schwankungen der Winterniederschläge in Deutschland”

Zusammenfassung An der Methode wird die physikalische Unwirklichkeit der Zusammenfassung der Monate Januar, Februar, März und November und Dezember des gleichen Kalenderjahres als Winter und die Unterdrückung wesentlicher Zusammenhänge mit dem Sonnenfleckenzyklus durch Bildung übergreifender Fünfjahresmittel bemängelt. Hinsichtlich des Ergebnisses wird die behauptete Ähnlichkeit der erhaltenen Kurven mit der Sonnenfleckenwelle widerlegt.

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Summary It is shown that the practice to define the months of January, February, March and November, December of the same calendar year as winter is not justifiable, from a physical point of view. By using running 5-yearly means important relations to the cycle of sun-spots are suppressed. A proposed similarity of the curves obtained byDammann with the solar cycle is disproved.

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Résumé L'auteur montre que l'hiver défini par la période de janvier à mars et de novembre à decembre de la même année est une irréalité physique et que l'emploi de la moyenne mobile de cinq ans masque le cycle des taches solaires; les courbes obtenues parDammann ne correspondent pas rythme des taches.