Effects of deglacial sedimentation pulse, followed by incision: A case study from a catchment in the Northern Calcareous Alps (Austria).

Im Einzugsgebiet des ‘Giessenbaches’ (Nördliche Kalkalpen, NKA) lagerte sich eine mächtige Sedimentabfolge während bis wenig nach dem Zerfall des hochglazialen Eispanzers ab. Das Einzugsgebiet liegt auf gestörten, geklüfteten triassischen Dolomitgesteinen. Die quartäre Abfolge besteht aus, (a) aufgearbeitetem Till mit Leitgeschieben des Letzten Glazialen Maximums (LGM), (b) alluvialen Kiesen, die vom Dolomitgesteins-Untergrund gespeist wurden, (c) Decklagen von Flusssedimenten auf Terrassen, und (d) grossen Schutthalden. Die ehemalige (Vor-LGM) obere Hälfte des Giessenbach-Laufs ist noch heute ein trockenes, erhöhtes Tal das wesentlich durch spätglaziale bis holozäne Sedimente verfüllt ist. Der heutige Giessenbach zeigt ein konvexes Längsprofil mit einer Klamm im Unterlauf; diese Klamm war wahrscheinlich teilweise durch Toteis versperrt während die Sedimentation der Eiszerfallsphase bereits eingesetzt hatte. Außer glazial überformten Felsflächen und ehemaligen Nunatakkern ist die heutige Morphologie des Einzugsgebiets im wesentlichen bestimmt durch (a) einen ‚Schub‘ sehr rascher Sedimentation vom Eiszerfall bis ins ?frühe Spätglazial, gefolgt von (b) Hangstabilisierung durch Bewachsung, und Einschneiden von Gerinnen. Die rasche Sedimentation wurde durch den Untergrund aus tektonisch verformtem Dolomitgestein gefördert, das unter reichlicher Schuttbildung abwittert. Ähnliche Verläufe von rapider Sedimentation vom Eiszerfall bis zum Spätglazial hin zu einem längeren Zeitabschnitt vorwiegend mit Einschneiden von Gerinnen sind in den NKA weit verbreitet.researc

Subaqueous conglomerates above pre-LGM basal till: Another element of the ‘classic’ interglacial mountain-flank succession (Hötting Breccia Auct.) north of Innsbruck, Austria

The “Hötting Breccia” near Innsbruck is a classic interglacial mountain-flank succession mainly comprising lithified alluvial fans and scree slopes. Directly NW of Innsbruck, a pre-LGM (Riss?) basal till >20 m in thickness overlies a plucked rock surface that records eastward ice flow. The till is dominated by clasts of carbonate rocks from the Northern Calcareous Alps; index clasts of the LGM ice stream are absent. The basal till is overlain by a package of conglomerate nearly 1 km in preserved lateral extent that dip at 20–30° South and show the same clast spectrum as the underlying till. The conglomerate – hitherto assigned to the Hötting Breccia – accumulated from fan deltas and/or scree slopes shed into a standing water body; it is overlain by younger, unlithified LGM to Holocene deposits. We suggest the following scenario: During decay of the ice stream that formed the basal till, the conglomerate package was deposited by paraglacial reworking of till into a lake or ice-marginal lake. The alluvial fans of the Hötting Breccia accumulated independently from the conglomerate package, and from a distinct alluvial-fan system. The age relation of the till/conglomerate package to the main part of the Hötting Breccia is unclear. Our results demonstrate that the rocks hitherto summarized as Hötting Breccia represent a compound of lithosomes of different origins and ages.researc

Early Holocene (8.6 ka) rock avalanche deposits, Obernberg valley (Eastern Alps): Landform interpretation and kinematics of rapid mass movement

In the Obernberg valley, the Eastern Alps, landforms recently interpreted as moraines are re-interpreted as rock avalanche deposits. The catastrophic slope failure involved an initial rock volume of about 45 million m³, with a runout of 7.2 km over a total vertical distance of 1330 m (fahrböschung 10°). 36Cl surface-exposure dating of boulders of the avalanche mass indicates an event age of 8.6 ± 0.6 ka. A 14C age of 7785 ± 190 cal yr BP of a palaeosoil within an alluvial fan downlapping the rock avalanche is consistent with the event age. The distal 2 km of the rock-avalanche deposit is characterized by a highly regular array of transverse ridges that were previously interpreted as terminal moraines of Late-Glacial. ‘Jigsaw-puzzle structure’ of gravel to boulder-size clasts in the ridges and a matrix of cataclastic gouge indicate a rock avalanche origin. For a wide altitude range the avalanche deposit is preserved, and the event age of mass-wasting precludes both runout over glacial ice and subsequent glacial overprint. The regularly arrayed transverse ridges thus were formed during freezing of the rock avalanche deposits.ISSN:0169-555xISSN:1872-695

A global review on ambient Limestone-Precipitating Springs (LPS): Hydrogeological setting, ecology, and conservation

Springs are biodiversity hotspots and unique habitats that are threatened, especially by water overdraft. Here we review knowledge on ambient-temperature (non-geothermal) freshwater springs that achieve sufficient oversaturation for CaCO3 -by physical CO2 degassing and activity of photoautotrophs- to deposit limestone, locally resulting in scenic carbonate structures: Limestone-Precipitating Springs (LPS). The most characteristic organisms in these springs are those that contribute to carbonate precipitation, e.g.: the mosses Palustriella and Eucladium, the crenophilous desmid Oocardium stratum, and cyanobacteria (e.g., Rivularia). These organisms appear to be sensitive to phosphorus pollution. Invertebrate diversity is modest, and highest in pools with an aquatic-terrestrial interface. Internationally, comprehensive legislation for spring protection is still relatively scarce. Where available, it covers all spring types. The situation in Europe is peculiar: the only widespread spring type included in the EU Habitat Directive is LPS, mainly because of landscape aesthetics. To support LPS inventorying and management to meet conservation-legislation requirements we developed a general conceptual model to predict where LPS are more likely to occur. The model is based on the pre-requisites for LPS: an aquifer lithology that enables build-up of high bicarbonate and Ca2 + to sustain CaCO3 oversaturation after spring emergence, combined with intense groundwater percolation especially along structural discontinuities (e.g., fault zones, joints, schistosity), and a proper hydrogeological structure of the discharging area. We validated this model by means of the LPS information system for the Emilia-Romagna Region (northern Italy). The main threats to LPS are water diversion, nutrient enrichment, and lack of awareness by non-specialized persons and administrators. We discuss an emblematic case study to provide management suggestions. The present review is devoted to LPS but the output of intense ecological research in Central Europe during the past decades has clearly shown that effective conservation legislation should be urgently extended to comprise all types of spring habitats

Animals in a bacterial world, a new imperative for the life sciences.

International audienceIn the last two decades, the widespread application of genetic and genomic approaches has revealed a bacterial world astonishing in its ubiquity and diversity. This review examines how a growing knowledge of the vast range of animal-bacterial interactions, whether in shared ecosystems or intimate symbioses, is fundamentally altering our understanding of animal biology. Specifically, we highlight recent technological and intellectual advances that have changed our thinking about five questions: how have bacteria facilitated the origin and evolution of animals; how do animals and bacteria affect each other's genomes; how does normal animal development depend on bacterial partners; how is homeostasis maintained between animals and their symbionts; and how can ecological approaches deepen our understanding of the multiple levels of animal-bacterial interaction. As answers to these fundamental questions emerge, all biologists will be challenged to broaden their appreciation of these interactions and to include investigations of the relationships between and among bacteria and their animal partners as we seek a better understanding of the natural world