The Namuskluft and Dreigratberg sections in southern Namibia (Kalahari Craton,Gariep Belt): a geological history of Neoproterozoic rifting and recycling of cratonic crust during the dispersal of Rodinia until the amalgamation of Gondwana

This paper presents combined U/Pb, Th/U and Hf isotope analyses on detrital and magmatic zircon grains together with whole-rock geochemical analyses of two basement and eight sedimentary rock samples from the Namuskluft and the Dreigratberg in southern Namibia (Gariep Belt). The sedimentary sections evolved during the Cryogenian on the SW part of the Kalahari Craton and where therefore deposited in an active rift setting during the break-up of Rodinia. Due to insufficient palaeomagnetic data, the position of the Kalahari Craton within Rodinia is still under discussion. There are possibilities to locate Kalahari along the western side of Australia/Mawsonland (Pisarevski et al. in Proterozoic East Gondwana: supercontinent assembly and break-up, Geological Society, London, 2003; Evans in Ancient Orogens and modern analogues. Geological Society, London, 2009; and others) or together with the Congo-Sao Francisco and Rio de la Plata Cratons (Li et al. in Prec Res 45: 203–2014, 2008; Frimmel et al. in Int J Earth Sci (Geol Rundsch) 100: 323–354, 2011; and others). It is sill unclear which craton rifted away from the Kalahari Craton during the Cryogenian. Although Middle to Upper Cryogenian magmatic activity is known for the SE Kalahari Craton (our working area) (Richtersveld Suite, Rosh Pinah Fm), all the presented samples show no U/Pb zircon ages younger than ca. 1.0 Ga and non-older than 2.06 Ga. The obtained U/Pb ages fit very well to the exposed basement of the Kalahari Craton (1.0–1.4 Ga Namaqua Province, 1.7–2.0 Ga Vioolsdrif Granite Suite and Orange River Group) and allow no correlation with a foreign craton such as the Rio de la Plata or Australia/Mawsonland. Lu–Hf isotopic signatures of detrital zircon point to the recycling of mainly Palaeoproterozoic and to a smaller amount of Archean crust in the source areas. εHf(t) signatures range between ?24 and +14.8, which relate to T_DM model ages between 1.05 and 3.1 Ga. Only few detrital zircon grains derived from magmas generated from Mesoproterozoic crustal material show more juvenile εHf(t) signatures of +14, +8 to +4 with T_DM model ages of 1.05–1.6 Ga. During Neoproterozoic deposition, only old cratonic crust with an inherited continental arc signature was available in the source area clearly demonstrated by Hf isotope composition of detrital zircon and geochemical bulk analysis of sedimentary rocks. The granodiorites of the Palaeoproterozoic basement underlying Namuskluft section are ca. 1.9 Ga old and show εHf(t) signatures of ?3 to ?5.5 with T_DM model ages of 2.4–2.7 Ga. These basement rocks demonstrate the extreme uplift and deep erosion of the underlying Kalahari Craton at its western margin before general subsidence during Cryogenian and Ediacaran time. The sedimentary sequence of the two examined sections (Namuskluft and Dreigratberg) proposes the presence of a basin and an increasing subsidence at the SW part of the Kalahari Craton during the Cryogenian. Therefore, we propose the initial formation of an intra-cratonic sag basin during the Lower Cryogenian that evolved later to a rift basin at the cratonic margin due to increasing crustal tension and rifting together with the opening of the Adamastor Ocean. As the zircons of the sedimentary rocks filling this basin show neither rift-related U/Pb ages nor an exotic craton as a possible source area, the only plausible sedimentary transport direction providing the found U/Pb ages would be from the E or the SE, directly from the heart of the Kalahari Craton. Due to subsidence and ongoing sedimentation from E/SE directions, the rift-related magmatic rocks were simply covered by the input of old intra-cratonic material that explains the absence of Neoproterozoic zircon grains in our samples. The geochemical analyses show the erosion of a continental arc and related sedimentary rocks with an overall felsic provenance. The source area was a deeply eroded and incised magmatic arc that evolved on continental crust, without any evidence for a passive margin. All of this can be explained by the erosion of rocks related to the Namaqua Belt, which represents one of the two major peaks of zircon U–Pb ages in all analysed samples. Therefore, the Namaqua Belt was well exposed during the Cryogenian, available to erosion and apart from the also well-exposed Palaeoproterozoic basement of the Kalahari Craton one potential source area for the sedimentary rocks in the investigated areas.     

Potentials of monitoring rock fall hazards by GPR: considering as example the results of Salzburg

A part of the IUGS-UNESCO research project "Landslide Hazard Assessment and Cultural Heritage" (IGCP-Project No. 425) includes testing the application of geophysical methods for assessing hazard risks to people and cultural assets. In this work, Austria contributed with a study on the assessment of rock-fall hazards. As the Old Town of Salzburg is a prime example of such hazards, systematic GPR-measurements were made on major rock surfaces. The aim of the exploration with GPR was to assess the potential of the method for monitoring rock walls. That is, whether structures in the rock mass which could become important when considering the risk of a rock fall, can be imaged. To manage this problem successfully, moving the antenna over the rough rock surface was made as regular as possible. The effects of vegetation lifting the antenna from the rock surface and of overhanging regions could not be avoided. Due to the loss of coupling of the antenna and the change of radiation pattern, some interference of the records occurred. Thus, only after processing could it become clear which reflections came from within the rock. A three-dimensional survey of discontinuities in the rock requires accurate mapping of the rock surface by photogrammetric methods, to get a digital terrain model for the analysis of the GPR records. The results of repeated measurements have proved to be of essential relevance. They have shown that it is possible to reveal changes with time. For the interpretation of such observations, modeling is a very useful tool.     

Using embodied HANPP to analyze teleconnections in the global land system: Conceptual considerations

Geografisk Tidsskrift—Danish Journal of Geography 109(2):119–130, 2009

In our rapidly globalizing world economy activities in one region have increasingly important effects on ecological, economic or social processes elsewhere, an effect which we here denote as ‘teleconnections’ between different regions. Biomass trade, one of the causes behind such teleconnections, is currently growing exponentially. Integrated analyses of changes in the global land system are high on the agenda of sustainability science, but a methodological framework for a consistent allocation of environmental burdens related to the consumption and production of biomass between regions has not been put forth to date. The concept of the ‘embodied human appropriation of net primary production’ (abbreviated ‘embodied HANPP’ or ‘eHANPP’) allows for the assessment of the ‘upstream’ effects on ecosystem energetics associated with a particular level of biomass consumption or with a given biomass-based product. This concept is based on HANPP and its two components: (1) productivity changes resulting from land conversion (ΔNPP_LC), and (2) harvest of biomass in ecosystems (NPP_h). HANPP, defined as the sum of ΔANPP_LC and NPP_h in any given territory, is indicative of the intensity with which humans use the land for their purposes. eHANPP is defined as the NPP appropriated in the course of biomass production, encompassing losses along the production chain as well as productivity changes induced through land conversion or harvest. By making the pressure exerted on ecosystems associated with imports and exports visible, eHANPP allows for the analysis of teleconnections between producing and consuming regions. This article puts forward the eHANPP concept, illustrates its utility for integrated socioecological land-change research based on top-down data on global HANPP and biomass consumption, and discusses the possibilities and challenges related to its quantification in bottom-up approaches.     

The historical and palaeoflood record of Katherine river,northern Australia: evaluating the likelihood of extreme discharge events in the context of the 1998 flood

The discharge regimes of the large rivers of northern Australia are characterized by the occurrence of extreme flood events with far‐reaching environmental and societal impacts. In January 1998 the largest flood ever recorded on the Katherine River, northern Australia, resulted in widespread inundation and resultant damage to the town of Katherine. The occurrence of the flood emphasized the unreliability of the then available flood probability estimates and prompted a palaeoflood approach to estimate the recurrence interval of the event. The location of Katherine is ideal for such a study, as the town is located immediately downstream from Katherine Gorge, which provides the necessary bedrock‐confined channel required for such an approach. In addition, previous work in Katherine Gorge had demonstrated that the gorge sections hold suitable deposits for palaeoflood stage reconstruction. The results of the present study show that at least two flow events with discharges similar to the 1998 flood have occurred within the last 600 years, and that high‐magnitude floods are a general feature of the discharge record of the Katherine River over the last c. 2000 years. Furthermore, because the study was undertaken within a few months of the occurrence of the 1998 flood, it provided the opportunity to evaluate the previously obtained flood discharge estimates and draw attention to the general uncertainties associated with palaeoflood studies. Our results emphasize that palaeoflood stage estimates based on slackwater deposits need to be treated as conservative estimates only. More specifically, with respect to the 1998 event, our study demonstrates that the controls of flood peak were more complex than simply flood routing through the gorge sections. It is clear that the areas downstream from Katherine Gorge made an important contribution to the flood peak of the 1998 event. Copyright © 2005 John Wiley & Sons, Ltd.     

QUATERNARY GROWTH FOLDS IN THE JIUXI BASIN AT THE NORTHEASTERN MARGIN OF THE QINGHAI—XIZANG PLATEAU

QUATERNARY GROWTH FOLDS IN THE JIUXI BASIN AT THE NORTHEASTERN MARGIN OF THE QINGHAI—XIZANG PLATEAUgrants 49732 0 90and 496 0 2 0 36fromtheNSFofChina     

Das Problem Akmit-Ägirin

Zusammenfassung In der vorliegenden Arbeit wurde erneut die Frage nach dem Zusammenhang zwischen der Farbe der Natriumeisenpyroxene und ihrer chemischen Konstitution aufgeworfen. Da die früheren Versuche, diese Frage auf analytischem Wege zu lösen, nicht zum Ziele geführt hatten, wurde hier das reine Endglied NaFe^IIIISi₂O₆ synthetisch hergestellt; in weiteren Versuchen wurden Na und Fe³⁺ durch andere Ionen zu einem kleinen Teil ersetzt und der Einfluß auf die Farbe ermitteltEs wurden Versuche durchgeführt, bei denen Na durch Ca oder Cd, Fe³⁺ durch Mg, Mn²⁺, Fe²⁺, Co, Ni oder Zn ersetzt wurde; bei weiteren Versuchen wurde anstelle von Fe³⁺ zu einem kleinen Teil sowohl eines der obengenannten 2wertigen Ionen als auch Ti⁴⁺ oder Zr⁴⁺ eingebaut. Die erhaltenen Mischkristalle wurden optisch und röntgenographisch untersucht.Zur näheren Charakterisierung dieser Mischglieder wurde in einer Reihe von Schliffen das Absorptionsspektrum in verschiedenen kristallographischen Richtungen bestimmt und mit den ebenfalls aufgenommenen Absorptionskurven von natürlichen Ägirinen verglichen.Auf Grund der synthetischen Versuche werden folgende Definitionen vorgeschlagen: Die Namen Akmit und Ägirin sollen weiterhin für Natriumeisenpyroxen nebeneinander beibehalten werden, wobei die Abgrenzung gegenüber Ägirinaugit gemäß dem Vorschlag vonTröger (2) vorgenommen werden kann. Für die Unterscheidung der beiden Varietäten soll gemäß den bisherigen Gepflogenheiten die Farbe maßgebend sein.Das reine Endglied NaFe^IIISi₂O₆ ist braun und muß deshalb als Akmit bezeichnet werden.Ferner sind mit Akmit die Mischkristalle zu bezeichnen, bei denen das Fe³⁺ durch Mn ersetzt ist, da auch diese Glieder braune Farbe aufweisen; die Ansicht vonGrout konnte also durch synthetische Versuche bestätigt werden.Die grüne Farbe der Ägirine in RichtungX undY wird durch die gleichzeitige Anwesenheit von 2- und 3wertigem Eisen hervorgerufen, so daß als Ägirin diejenigen Mischkristalle zu bezeichnen sind, bei denen 3wertiges Eisen durch zwertiges ersetzt ist. Der Einfluß des 2wertigen Eisens überwiegt dabei gegenüber dem Einfluß anderer Ionen.Das häufigere Auftreten des Ägirin gegenüber Akmit hat also seine Ursache darin, daß in der Natur 2wertiges Eisen praktisch stets vorhanden ist.Die Gitterkonstanten von Akmit und Ägirin sind im Bereich der hier erzielten Meßgenauigkeit gleich und wurden wie folgt bestimmt:a = 9,66 Åb = 879 Åc = 5,26 Å = 72,7 °Die Arbeit wurde gefördert durch eine Spende keramischen Materials zum Bau der Versuchsöfen, wofür ich auch an dieser Stelle der Fa. Stemag in Lauf meinen Dank aussprechen möchte.Der Fa. Elchem in Nürnberg danke ich für die Durchführung der Spektralanalysen sowie für die Anfertigung einer Aufnahme mit der Guinier-Kammer.Ferner danke ich dem Institut für Anorganische Chemie der Universität Erlangen für Überlassung, bzw. Anfertigung einiger Substanzen.