Die geodynamische Entwicklung der Thiersee- und der Karwendelmulde (Nördliche Kalkalpen)

Zusammenfassung Die Thiersee- und die Karwendelmulde in den Nördlichen Kalkalpen sind als zwei getrennte, E-W-verlaufende Synklinen entwickelt. Ihre Länge zwischen Kufstein und Mittenwald beträgt über 70 km.Systematische geologische Aufnahmen — Kartierung, Stratigraphie, Sedimentologie und Gefügekunde — ergaben, daß die Thierseemuide im Raum von Achenkirch nicht — wie früher vermutet wurde — in die Karwendelmulde umbiegt. Die Auswertung von mehr als 45 000 Gefügemessungen mit Hilfe eines EDV-Programms bewies vielmehr, daß Thierseemuide und Karwendelmulde zwei parallele, unabhängige Strukturen sind, die durch die komplizierte tektonische Zone von Achenkirch getrennt werden.Die paläogeographische Entwicklung und der Ablauf der Bewegungen werden im Überblick skizziert.

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Systematic geological survey showed that the Thiersee and Karwendel synclines in the Northern Calcareous Alps are two parallel structures, separated by a slightly folded intersection. The synclines do not turn into each other, as was presumed by earlier workers.The tectonic situation in the area of Achenkirch was cleared by evaluation of more than 45,000 field texture data by a computer program. Mapping as well as stratigraphical and sedimentological analysis supports the tectonic model. The paleogeographic development and tectonic history are briefly described.

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Résumé Les dépressions du «Thiersee» et du «Karwendel», dans les Alpes calcaires du Nord, sont deux synclinaux indépendants de direction Est-Ouest. Elles font 70 km de long entre Kufstein et Mittenwald.Des relevés géologiques systématiques — levés géologiques, stratigraphie, sédimentologie et structurologie — démontrèrent que, dans la région d'Achenkirch, la dépression du «Thiersee» ne contourne pas la dépression du «Karwendel» (comme on l'a longtemps supposé!). L'exploitation par ordinateur de plus de 45.000 mesures structurales révéla au contraire, que ces dépressions sont deux structures parallèles et indépendantes, séparées par la zone tectonique complexe d'Achenkirch.Le développement paléogéographique et le déroulement des mouvements font l'objet d'une vue d'ensemble.

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Albeluvisol development with time in loamy marine sediments of southern Norway

This paper reports a study on soil development in loamy marine sediments on both sides of the Oslofjord (Vestfold, Østfold). This region has been subject to steady glacio-isostatic uplift during the whole Holocene. Hence, land surface age continuously increases from the coast inland. Several sea level curves, based on radiocarbon datings, enable estimation of land surface age for all locations. Clay illuviation starts in less than 1650 years. E horizons become lighter with age, but their lower boundary stays around 40 cm for more than 10 000 years. Albeluvic tongues develop between 4600 and 6200 years. Initially, they form along intersections of cracks. As preferential flow and leaching along the cracks continues, the tongues increase in length and width, progressively consuming the prisms between the cracks in the upper Bt horizon. The Fe_d/Fe_t ratios (weighted means of the upper meter) show a clear linear increase with soil age and may be used for “pedo-dating”, i.e. for estimating the ages of non-dated land surfaces covered with similar sediments. In contrast, the logarithmic decrease of base saturation and pH, with rapid changes in the first time but only very slight changes between 2000 and 10 000 years, makes these parameters unsuitable for “pedo-dating”.     

Delimiting the eastern extent of the Altyn Tagh Fault: Insights from structural analyses of seismic reflection profiles

The Altyn Tagh Fault (ATF) serves as a key continental‐scale controlling structural element of the Tibetan Plateau. However, its eastward extent remains controversial. Here we use high‐resolution seismic reflection profiles to investigate the subsurface structures of the easternmost ATF and use these to delimit the easternmost extent of the fault. The structural analyses show an eastward geometric change from transpressional positive flower structures to compressional thrusts, with transpression‐induced shortening magnitudes decreasing eastwards from a maximum of ~5.3 km to being absent. Stratigraphic controls indicate that the deformation took place over the last ~<1.2 Ma. Our wider findings lead us to: (a) reject the suggestion that the ATF previously extended beyond the Kuantan Shan‐Hei Shan to link with the Alxa‐East Mongolia Fault; and (b) propose that the rigid block model used to describe the Tibetan Plateau crust is not consistent with the extent and structural details of the easternmost ATF.     

A valley crossing in Pleistocene deposits

Sauer, E. Karl, 1977. A valley crossing in Pleistocene deposits. Eng. Geol., 11:1–21.Proglacial meltwater channels are of considerable importance in geotechnical engineering in Southern Saskatchewan. Dams, roads, bridges and urban development are major projects involving these channels. The Arm River crossing illustrates the types of problems that can occur in highways constructed across these channels, including instability, groundwater control and excavation through a boulder pavement. This discussion demonstrates how these problems can be resolved by establishing the geology of the sites and designing to preclude geotechnical problems. The investigation involved rotary drilling, geophysical logging, installation of piezometers and engineering analysis.     

Review: the environmental status and implications of the nitrate time lag in Europe and North America

The efficacy of water quality policies aiming to reduce or prevent nitrate contamination of waterbodies may be constrained by the inherent delay or “time lag” of water and solute transport through unsaturated (soil) and saturated (groundwater) pathways. These delays must be quantified in order to establish realistic deadlines, thresholds and policy expectations, and to design effective best management practices. The objective of this review is to synthesise the current state of research on nitrate-related time lags in both the European and North American environmental and legislative contexts. The durations of time lags have been found to differ according to climatic, pedological, landscape and management scenarios. Elucidation of these driving factors at a watershed scale is essential where water quality is impaired or at risk. Finally, the existence of time lags is increasingly being acknowledged at a policy level and incorporated into the development of environmental legislation. However, the full impact of these time lags is not yet fully understood or appreciated, and continued outreach and education in scientific, public and policy venues is still required.     

Channel incision by headcut migration: Reconnection of the Colorado River to its estuary and the Gulf of California during the floods of 1979–1988

The macrotidal Colorado River Delta at the northern end of the Gulf of California in Mexico is hydrologically complex. We review historical accounts, data, field notes and photographs to evaluate the hydrological processes active on the delta prior to the advent of upstream dams. We also employ satellite imagery as well as recent LIDAR data to illustrate the critical role played by headcut erosion in restoring the river's fluvial/tidewater connection during the 1979–1988 floods. Prior to human manipulation, the river's contribution of fresh water to the Gulf was periodically interrupted by natural overflowing, avulsing, and flooding into the sub-sea level Salton Sink on the north slope of the delta plain. River flow south towards the Gulf was also subject to occasional overflow into Laguna Salada, another sub-sea level basin. In the mid-20th century, the Delta was disconnected from its fluvial supply following installation of upstream dams and reservoirs. A tidal sediment obstruction developed in the estuary channel, forming a final barrier to fluvial connectivity. Release of Colorado River floodwaters into Mexico between 1979 and 1988 provided a natural experiment on the hydrological response of a long-disconnected macrotidal delta to restoration of fluvial supply.     

Identification and classification of transient pulses observed in magnetometer array data by time-domain principal component analysis filtering

A method for identification of pulsations in time series of magnetic field data which are simultaneously present in multiple channels of data at one or more sensor locations is described. Candidate pulsations of interest are first identified in geomagnetic time series by inspection.Time series of these ‘‘training events' ' are represented in matrix form and transpose-multiplied to generate timedomain covariance matrices. The ranked eigenvectors of this matrix are stored as a feature of the pulsation. In the second stage of the algorithm, a sliding window(approximately the width of the training event) is moved across the vector-valued time-series comprising the channels on which the training event was observed. At each window position, the data covariance matrix and associated eigenvectors are calculated. We compare the orientation of the dominant eigenvectors of the training data to those from the windowed data and flag windows where the dominant eigenvectors directions are similar. This was successful in automatically identifying pulses which share polarization and appear to be from the same source process. We apply the method to a case study of continuously sampled(50 Hz) data from six observatories, each equipped with threecomponent induction coil magnetometers. We examine a90-day interval of data associated with a cluster of four observatories located within 50 km of Napa, California,together with two remote reference stations-one 100 km to the north of the cluster and the other 350 km south. When the training data contains signals present in the remote reference observatories, we are reliably able to identify and extract global geomagnetic signals such as solar-generatednoise. When training data contains pulsations only observed in the cluster of local observatories, we identify several types of non-plane wave signals having similar polarization.     

Bank erosion of legacy sediment at the transition from vertical to lateral stream incision

Streambank erosion is a primary source of suspended sediments in many waterways of the US Atlantic Piedmont. This problem is exacerbated where banks are comprised of fine sediment produced by the intensive land use practices of early European settlers. A stream in this region, Richland Creek incises into banks comprised of three stratigraphic layers associated with historic land use: pre‐European settlement, early European agriculture and development, and water‐powered milldam operation. This study aims to identify the bank processes along a reach of Richland Creek that is eroding towards its pre‐disturbance elevation. The volume of material that has eroded along this stream since the milldam breached was calculated by differencing a reconstructed surface of the pond bed and an aerial lidar digital terrain model (DTM). Immediately downstream from the study reach, the channel is floored by bedrock and immediately upstream the rate of channel erosion approximately doubled along the longitudinal profile of Richland Creek, which indicate that the study reach spans the transition from a channel dominated by vertical incision in the upstream direction to horizontal widening in the downstream direction. The combined hydrometeorological conditions and dominant processes causing reach‐scale cut bank erosion were investigated with analyses of stream stage, precipitation, and streambank volumetric and surfaces change that was measured during nine terrestrial lidar surveys in 2010–2012. The spatial variability of erosion during a simulated precipitation event was examined in a field‐based experiment. Erosion was greatest where mill pond sediment columns detached along vertical desiccation and horizontal seepage cracks. This sediment accumulated on the bank toe throughout the study and was a source of readily‐entrained fine sediment contrary to the upper reaches where depositional accommodation space is more limited. Findings suggest that hotspots of sediment excavation progress upstream, indicating that restoration efforts should focus upon stabilizing banks at these locations. Copyright © 2015 John Wiley & Sons, Ltd.     

Hillslope response to knickpoint migration in the Southern Appalachians: implications for the evolution of post‐orogenic landscapes

The southern Appalachians represent a landscape characterized by locally high topographic relief, steep slopes, and frequent mass movement in the absence of significant tectonic forcing for at least the last 200 Ma. The fundamental processes responsible for landscape evolution in a post‐orogenic landscape remain enigmatic. The non‐glaciated Cullasaja River basin of south‐western North Carolina, with uniform lithology, frequent debris flows, and the availability of high‐resolution airborne lidar DEMs, is an ideal natural setting to study landscape evolution in a post‐orogenic landscape through the lens of hillslope–channel coupling. This investigation is limited to channels with upslope contributing areas >2.7 km², a conservative estimate of the transition from fluvial to debris‐flow dominated channel processes. Values of normalized hypsometry, hypsometric integral, and mean slope vs elevation are used for 14 tributary basins and the Cullasaja basin as a whole to characterize landscape evolution following upstream knickpoint migration. Results highlight the existence of a transient spatial relationship between knickpoints present along the fluvial network of the Cullasaja basin and adjacent hillslopes. Metrics of topography (relief, slope gradient) and hillslope activity (landslide frequency) exhibit significant downstream increases below the current position of major knickpoints. The transient effect of knickpoint‐driven channel incision on basin hillslopes is captured by measuring the relief, mean slope steepness, and mass movement frequency of tributary basins and comparing these results with the distance from major knickpoints along the Cullasaja River. A conceptual model of area–elevation and slope distributions is presented that may be representative of post‐orogenic landscape evolution in analogous geologic settings. Importantly, the model explains how knickpoint migration and channel–hillslope coupling is an important factor in tectonically‐inactive (i.e. post‐orogenic) orogens for the maintenance of significant relief, steep slopes, and weathering‐limited hillslopes. Copyright © 2011 John Wiley & Sons, Ltd.