Mezen Bay—a key area for understanding Weichselian glaciations in northern Russia

Sediment successions in coastal cliffs around Mezen Bay, southeastern White Sea, record an unusually detailed history of former glaciations, interstadial marine and fluvial events from the Weichselian. A regional glaciation model for the Weichselian is based on new data from the Mezen Bay area and previously published data from adjacent areas. Following the Mikulinian (Eemian) interglacial a shelf‐centred glaciation in the Kara Sea is reflected in proglacial conditions at 100–90 ka. A local ice‐cap over the Timan ridge existed between 75 and 65 ka. Renewed glaciation in the Kara Sea spread southwestwards around 60 ka only, interrupted by a marine inundation, before it advanced to its maximum position at about 55–50 ka. After a prolonged ice‐free period, the Scandinavian ice‐sheet invaded the area from the west and terminated east of Mezen Bay about 17 ka. The previously published evidence of a large ice‐dammed lake in the central Arkhangelsk region, Lake Komi, finds no support in this study. Copyright © 2003 John Wiley & Sons, Ltd.     

Glacial rebound and sea-level change in the British Isles

Observations of sea levels around the coastline of the British Isles for the past 10,000–15,000 years exhibit a major regional variation and provide an important data base for testing models of glacial rebound as well as models of the Late Devensian ice sheet. A high-resolution rebound model has been developed which is consistent with both the spatial and temporal patterns of sea-level change and which demonstrates that the observations are the result of (i) the glacio-isostatic crustal rebound in response to the unloading of the ice sheet over Britain and, to a lesser degree, of the ice sheet over Fennoscandia, and (ii) the rise in sea-level from the melting Late Pleistocene ice sheets, including the response of the crust to the water loading (the hydro-isostatic effect). The agreement between model and observations is such that there is no need to invoke vertical crustal movements for Great Britain and Ireland of other than glacio-hydro-isostatic origin. The rebound contributions are important throughout the region and nowhere is it sufficiently small for the sea-level change to approximate the eustatic sea-level rise. The observational data distribution around the periphery as well as from sites near the centre of the former ice sheet is sufficient to permit constraints to be established on both earth model parameters specifying the mantle viscosity and lithospheric thickness and the extent and volume of the ice sheet at the time of the last glaciation. Preliminary solutions are presented which indicate an upper mantle viscosity of (3–5)10²⁰ Pas, a lithospheric thickness of about 100 km or less, and an ice model that was not confluent with the Scandinavian ice sheet during the last glaciation and whose maximum thickness over Scotland is unlikely to have exceeded about 1500 m.     

Morphological analysis of the drainage system in the Eastern Alps

We study the morphology of the major rivers draining the Eastern Alps to test whether the active tectonics of this part of the orogen is reflected in the shape of channel profiles of the river network. In our approach we compare channel profiles measured from digital elevation models with numerically modelled channel profiles using a stream power approach. It is shown that regions of high stream power coincide largely with regions of highest topography and largest uplift rates, while the forelands and the Pannonian Basin are characterised by a significantly lower stream power. From stream power modelling we conclude that there is young uplift at the very east of the Eastern Alps, in the Bohemian Massif and in the Pohorje Range. The impact of the Pleistocene glaciations is explored by comparing properties of rivers that drain in proximal and distal positions relative to the ice sheet during the last glacial maximum. Our analysis shows that most knick points, wind gaps and other non-equilibrium features of catchments covered by ice during the last glaciations (Salzach, Enns) can be correlated with glacial processes. In contrast the ice free catchments of the Mur and Drava are characterized by channels in morphological equilibrium at the first approximation and are showing only weak evidence of the strong tectonic activity within these catchments. Finally, the channel profiles of the Adige and the divide between the upper Rhine and Danube catchments differ significantly from the other catchments. We relate this to the fact that the Adige and the Rhine respond to different base levels from the remainder of the Eastern Alps: The Adige may preserve a record from the Messininan base level change and the Rhine is subject to the base level lowering in the Rhine Graben.     

Vulkanogene Glasscherben-Relikte in Kohlentonsteinen des Saar-Lothringer Oberkarbons sowie Herkunft und Menge der Pyroklastika

Zusammenfassung Obwohl Kohlentonsteine aus dem Saar-Lothringer Oberkarbon seit etwa 170 Jahren bekannt sind, gelang erst in jüngster Zeit der Nachweis und die Identifikation vulkanogener Relikte im petrographischen Stoffbestand. Diese befinden sich in Kohlentonsteinen des Stefan A: KTst 0=950; Westfal D: KTst 1=700; Westfal C: KTst 3 =400, KTst 4a=330, KTst 4aß=322, KTst 4=320, KTst 5=300 und im KTst 6=270. Das entspricht einem Anteil von ca. 18 % an der Gesamtzahl der in diesem limnischen Steinkohlenrevier beobachteten Kohlentonsteine, die hier große praktische und wissenschaftliche Bedeutung besitzen. Die pseudomorphen Relikte bestehen aus kleinen Splittern, kleinen und größeren Fragmenten mit teilweise gut erhaltenem blasigen Gefüge von Vitroklasten — sie zeigen die für Aschenschmelztuffe typisch verschweißte Scherbentextur. Die Glassubstanz ist meist zu mikrokristallinem Kaolinit devitrifiziert. Der eindeutige Nachweis dieser Relikte ist für die Genese bedeutungsvoll, liefern sie doch nun den sicheren Beweis, daß der primäre Stoffbestand aus aerisch abgelagertem pyroklastischen Material bestand, das intensive chemische Verwitterungs- und diagenetische Umbildungsprozesse erfahren hat. Für die 43 Kohlentonsteine des Saar-Lothringer Oberkarbons wird eine pyroklastische Eruptionsmenge von mindestens 8,2 km³ Festvolumen bzw. 20,5 km³ Lokkervolumen angenommen. Die Eruptionen erfolgten vermutlich aus der in der Nähe befindlichen Metz-Hunsrück-Südrand-Tiefenstörung, die nach Reflexionsseismik bis unter die Moho reicht.

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Tonsteins in the Carboniferous of the Saar-Lorraine basin are known since about 170 years. Volcanic glass remains, however, have been proven as constituents of the tonstein only recently. They occur in tonsteins of Stephanian A: KTst 0=950; Westphalian D: KTst 1=700; Westphalian C: KTst 3=400, KTst 4a=330, KTst 4aß= 322, KTst 4=320, KTst 5=300 and KTst 6=270. Tonsteins with volcanic glass fragments amount to 18% of the total tonsteins observed in the limnic Saar-Lorraine basin. They are important to applied geology, e.g. for seam identification and correlation, as well as for scientific reasons, namely for the determination of provenance and genesis of tonsteins.The volcanic remains consist of tiny glass splinters, glass fragments, and of fragments with well preserved gasbubble texture. The welded splinter texture is typical of welded pyroclastic ash deposits. Much of the glass has been devitrified to microcrystalline kaolinite. The indisputable evidence of volcanic remains is essential when considering the genesis of tonsteins, as they provide proof that tonsteins are primarily composed of eolian pyroclastic constituents which were altered by chemical weathering and diagenesis.For the 43 horizons of the coal tonsteins found in the Upper Carboniferous of the Saar-Lorraine basin, a pyroclastic eruption quantity of at least 8.2 km³ of solid volume or 20.5 km³ of bulk volume is assumed. The eruptions possibly took place along the nearby deep-seated Metz fault at the southern rim of the Hunsrück. This fault, reaches below the Moho according to reflection seismic.

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Résumé Bien que des tonstein du Carbonifère supérieur de SarreLorraine soient connus depuis 170 ans c'est seulement il y a peu de temps que des fragments de verre volcanique y ont été identifiés. Ces fragments ont été rencontrés dans les niveaux de tonstein suivants: Stephanien A: KTst 0=950; Westphalien D: KTst 1=700; Westphalien C: KTst 3=400, KTst 4a=330, KTst 4aß=322, KTst 4=320, KTst 5=300 et KTst 6=270. Ces niveaux représentent une proportion de l'ordre de 18% dans le total des couches de tonstein carbonifère rencontrées dans ce bassin houiller limnique où elles présentent un grand intérêt tant au point de vue pratique que scientifique. Les verres se présentent en esquilles et en fragments de tailles diverses, montrant parfois une structure bulleuse bien conservée; ils présentent également les structures d'agglomération propres aux tufs soudés à chaud. Le verre est le plus souvent dévitrifié en kaolinite microcristalline. La présence de ces fragments est d'un intérêt particulier pour la genèse du dépôt puisqu'elle fournit la preuve que celui-ci était constitué de matériaux primaires pyroclastiques sédimentés dans l'air, matériaux qui ont subi ensuite des altérations chimiques et des transformations diagénétiques intenses.Pour l'ensemble des 43 horizons de tonstein du Carbonifère supérieur de la Sarre-Lorraine, on admet un volume de matières pyroclastiques d'au moins 8,2 km³ (volume à l'état monolithique) ou de 20,5 km³ (volume à l'état fragmenté). Ces éruptions ont probablement pour origine la faille de Metz, située à proximité, qui forme la limite sud du Hunsrück et que la sismique-réflexion permet de prolonger jusqu'au Moho.

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Das Thema dieser Arbeit war Gegenstand des KurzvortragesBurger &Wolf (1987) auf dem XI. ICC in Peking (31. 8. bis 4. 9. 1987). Vorliegende Bearbeitung stellt die originäre Fassung dar.     

Three-dimensional model and late stage warping of the Plattengneis Shear Zone in the Eastern Alps

The Plattengneis shear zone is a 250–600 m thick, flat lying, Cretaceous, eclogite facies, mylonitic shear zone, with north-over-south transport direction, that is exposed over almost 1000 km² in the Koralpe region along the eastern margin of the Alps. Although the shear zone is one of the largest in the Alps, its role in the Eoalpine metamorphic evolution and the subsequent exhumation of the region, remain enigmatic and its large-scale geometry is not well understood. The outcrop pattern suggests that the shear zone is made up of a single sheet that is folded into a series of open syn- and antiforms with wavelengths of about 10 km. Eclogite bodies occur above, within and below the shear zone and there is no metamorphic grade change across the shear zone. In the south, the fold axes strike east–west and plunge shallowly to the east. In the north, the fold axes are oriented in north–south direction and form a dome shaped structure of the shear zone. Total shortening during this late stage warping event was of the order of 5%. Indirect evidence constrains this folding event to have occurred between 80 and 50 Ma and the fold geometry implies that the final exhumation in the Koralpe occurred somewhat later than further north. Interestingly, the shear zone appears to strike out of the topography in the south and dip into the topography in the north, so that north of the shear zone only hanging-wall rocks are exposed and south of it only foot-wall rocks. Possibilities for the geometric relationship of the Plattengneis shear zone with the surrounding south dipping detachments are discussed.     

Gneiss-Water Interaction and Water Evolution During the Early Stages of Dissolution Experiments at Room Temperature

Gneiss-distilled water interaction at room temperature was investigated with batch-reactors to study water-rock reaction and geochemical evolution of the aqueous phase with time. The ion concentrations in water were controlled not only by the dissolution of primary minerals, but also by the precipitation of secondary minerals. The decreasing fraction sizes of gneiss could favor dissolution and precipitation simultaneously. Ca^2 and K^ were the major cations, and HCO3^- was the major anion in water. All the ions except Ca^2 increased in concentration with time. The Ca^2 release from the rock to the aqueous phase was initially much faster than the release of K^ , Na^2 and Mg^2 . But after about 5 - 24 hours, the Ca^2 concentrations in water decreased very slowly with time and became relatively stable. During the experiment, the water varied from the Ca-( K)-HCO3-type water to the K-Ca-HCO3-type water, and then to the K-(Ca, Na)-HCO3-type water. The water-gneiss interaction was dominated by the dissolution of Kfeldspar in the solution. The remaining secondary minerals were mainly kaolinite, illite and K (Mg) -mica.     

Self-sedimentation of phytoplankton blooms in the geologic record

Understanding the formation of laminated, organic-rich sediments is an essential topic for researchers interested in fossil fuels, biogeochemical cycles, Earth's environmental history and global change. Biologists have very recently demonstrated that some marine phytoplankton blooms actively govern their own sedimentation by the formation of sticky transparent gels that facilitate rapid aggregation, accelerated sinking and efficient export flux. Here we present fossil evidence of unfragmented, low-diversity phytoplankton assemblages preserved as sedimentary laminae and irregular flocs that are attributable to a similar phytoplankton-driven sedimentary mechanism we term ‘self-sedimentation’. The geological evidence suggests that self-sedimentation precludes significant heterotrophic grazing, propels the formation of some conspicuous hemipelagic sedimentary laminae and results in efficient carbon and opal flux to the sediments. We suggest that the self-sedimentation phenomenon may have broad implications for the geological history of biogeochemical cycling, oceanic ecological dynamics, and abrupt atmospheric/environmental change. Broader recognition of the self-sedimentation phenomenon as explicitly defined here is a prerequisite to testing these unconventional hypotheses.     

Bristen granite: a highly differentiated,fluorite-bearing A-type granite from the Aar massif,Central Alps,Switzerland

Bristen granite is a body of fine-grained leucogranite occurring in the Gotthard rail base tunnel in the Central Alps. During construction of the tunnel, Bristen granite (Brgr) has been drilled along a 600 m long section. The aplite-granite belongs to the suite of Variscan granitoid intrusions of the Aar massif and contains a variety of accessory minerals typical of highly differentiated granites. Rock forming fluorite, partly enriched in yttrium (Y) and rare earth elements (REE), is intergrown with the late Y- and REE-bearing carbonate mineral synchysite. The granite contains a variety of Ti- and Y-REE-niobates, thorite, and zircon. Compared with the calc-alkaline central Aar granite (cAgr), Bristen granite is strongly depleted in Ti, P, Mg, Sr, and Ba and shows a remarkable enrichment in incompatible elements such as Rb, Th, U, Nb, Y, HREE and F. Bristen granite is the most evolved granitoid rock of the Aar massif. The composition of Brgr is typical of post-collisional reduced (ferroan) A-type granites. The Brgr melt formed in the lower crust and crystallized from a highly differentiated melt at the cotectic point in the quartz-feldspar system close to 100 MPa and 700 °C. The Brgr intruded as a small isolated stock pre-Variscan gneisses with sharply discordant contacts. The primary igneous host of Nb, Ta, Y, U, Th and REE is biotite in addition to minor amounts of allanite, and zircon. The presence of Y-REE-fluorite, synchysite, parisite and Y- and Ti-niobates and other REE-minerals can be related to reaction of igneous biotite and primary fluorite with hydrothermal fluids. The reaction is associated with alpine metamorphism, because Y-bearing fluorite and synchysite have been reported from Alpine fissures. The transformation of primary biotite to chlorite and muscovite released the heavy metal oxides under lower greenschist facies conditions that formed the Alpine diagnostic mineral stilpnomelane at about 300 °C.     

Diatom assemblages from Costa Rican lakes: an initial ecological assessment

We compared the distributions of 59 diatom species in surface sediments of 25 Costa Rican lakes with 21 environmental variables using canonical correspondence analysis (CCA). The distribution of taxa was related to the chemical and physical characteristics of the lakes. The most influential chemical variables were cation concentrations (especially magnesium) and related variables such as water hardness, pH, and temperature. Lake area and lake depth were among the most important physical variables.A number of taxa were identified as potential environmental indicators. The diatoms Brachysira serians var. brachysira and Frustulia rhomboides seem to be associated with low values of alkalinity, hardness, Ca, Mg, and SiO2. Cymbella minuta var. silesiaca is associated with low to moderate values of alkalinity, hardness, Ca, and Mg. Nitzschia cf. amphibia may be an indicator of moderate-to-high concentrations of Mg. Pinnularia braunii var. amphicephala seems to prefer low values of hardness, Ca, Mg, and SiO2.In many closed lakes, these environmental variables (Mg/Ca/hardness/alkalinity) increase with effective evaporation. Consequently, these diatoms may be indirectly tracking P:E ratios. Results from this initial, small data set indicate the potential of diatoms for inferring lake paleochemistry, and perhaps P:E ratios, in Costa Rica.