The role of long‐term human impact on avulsion and fan development

This study aims to understand (mainly qualitatively) the long‐term role of human impact on avulsion processes and the development of fluvial (mega‐) fans in semi‐arid environments. In this paper we refer to human impact as the direct influences of actions on the river's hydraulics (i.e. flow regulation, flow diversion and channel engineering). In five case‐studies drawn from the Khuzestan plains in southwest Iran we have analysed the setup and triggering conditions of specific avulsions that occurred in the past (timescale of millennia) and identified the role of human interference in their causation. Our analysis is based on the integration of historical, archaeological, geomorphological and geological data. Through this study we demonstrate that avulsions in the Khuzestan plains are the result of long‐term and complex interplay between multiple human‐induced and natural causes. In similar ways human‐induced actions may play important roles during different phases of avulsion development. The ‘success‘ of an avulsion in the post‐triggering phase may be defined by human‐induced setup causes as well as morphodynamic processes. We suggest that present‐day flood events may be partly inherited from long‐term human alterations of the natural processes. These finding could have implications for any fluvial system (e.g. distributive fluvial systems, deltas) where avulsion plays a major role in their development and research tends to emphasize on natural mechanisms. Copyright © 2016 John Wiley & Sons, Ltd.     

A study of presolar material in hydrated lithic clasts from metal-rich carbonaceous chondrites

We report on the investigation of presolar grain inventories of hydrated lithic clasts in three metal-rich carbonaceous chondrites from the CR clan, Acfer 182 (CH3), Isheyevo (CH3/CB_b3), and Lewis Cliff (LEW) 85332 (C3-un), as well as the carbon- and nitrogen-isotopic compositions of the fine-grained clast material. Eleven presolar silicate grains as well as nine presolar silicon carbide (SiC) grains were identified in the clasts. Presolar silicate abundances range from 4 to 22 parts per million (ppm), significantly lower than in pristine meteorites and interplanetary dust particles (IDP), and comparable to recent findings for CM2s and CR2 interchondrule matrix. SiC concentrations lie between 9 and 23 ppm, and are comparable to the values for CI, CM, and CR chondrites. The results of our investigation suggest similar alteration pathways for the clast material, the interchondrule matrix of the CR2 chondrites, and the fine-grained fraction of CM2 chondrites. Fine-grained matter of all three meteorites contains moderate to high ¹⁵N-enrichments (~50‰ ≤ δ¹⁵N ≤ ~1600‰) compared to the terrestrial value, indicating the presence of primitive organic material. We observed no correlation between ¹⁵N-enrichments and presolar dust concentrations in the clasts. This is in contrast to the findings from a suite of primitive IDPs, which display in several cases enhanced bulk ¹⁵N/¹⁴N ratios and high presolar grain abundances of several hundred or even thousand ppm. The bulk ¹⁵N/¹⁴N ratios of the clasts are comparable to the range for primitive IDPs, suggesting a nitrogen carrier less susceptible to destruction by aqueous alteration than silicate stardust.     

The chronology of a large ice-dammed lake and the Barents–Kara Ice Sheet advances, Northern Russia

Beach and shoreface sediments deposited in the more than 800-km long ice-dammed Lake Komi in northern European Russia have been investigated and dated. The lake flooded the lowland areas between the Barents–Kara Ice Sheet in the north and the continental drainage divide in the south. Shoreline facies have been dated by 18 optical stimulated luminescence (OSL) dates, most of which are closely grouped in the range 80–100 ka, with a mean of 88±3 ka. This implies that that the Barents–Kara Ice Sheet had its Late Pleistocene maximum extension during the Early Weichselian, probably in the cold interval (Rederstall) between the Brørup and Odderade interstadials of western Europe, correlated with marine isotope stage 5b. This is in strong contrast to the Scandinavian and North American ice sheets, which had their maxima in isotope stage 2, about 20 ka. Field and air photo interpretations suggest that Lake Komi was dammed by the ice advance, which formed the Harbei–Harmon–Sopkay Moraines. These has earlier been correlated with the Markhida moraine across the Pechora River Valley and its western extension. However, OSL dates on fluvial sediments below the Markhida moraine have yielded ages as young as 60 ka. This suggests that the Russian mainland was inundated by two major ice sheet advances from the Barents–Kara seas after the last interglacial: one during the Early Weichselian (about 90 ka) that dammed Lake Komi and one during the Middle Weichselian (about 60 ka). Normal fluvial drainage prevailed during the Late Weichselian, when the ice front was located offshore.     

Novel Analysis of Tadpole and Horseshoe Orbits

A simple analysis of tadpole and horseshoe orbits is performed using a new perturbation technique. The first-order results are presented explicitely, extension to any perturbation order is delineated. This revised version was published online in July 2006 with corrections to the Cover Date.     

Ductile deformation of garnet in mylonitic gneisses from the Münchberg Massif (Germany)

Mylonitic gneisses from the Münchberg Massif contain single grains (type I) and polycrystalline aggregates (type II) of garnet displaying a distinct elongation parallel to a macroscopic lineation which is interpreted as the result of ductile deformation. Lattice-preferred orientations of quartz (textures) symmetrical to the macroscopic foliation and lineation and the lack of rotational microfabrics indicate that the bulk deformation was pure shear at least during the latest strain increments. Garnet textures measured by EBSD together with microprobe analyses demonstrate that these two structural types of garnet can be related to two different processes of ductile deformation: (1) For the single grains stretching can be attributed to diffusion creep along grain boundary zones (Coble creep). The related mass transfer is indicated by the fact that primary growth zones are cut off at the long faces of the grains while the related strain shadow domains do not show comparable chemical zoning. Pressure solution and precipitation suitable to produce similar structures can be largely ruled out because retrogressive reactions pointing to the presence of free hydrous fluids are missing. (2) For the polycrystalline garnet aggregates consisting of cores grading into fine-grained mantles, dislocation creep and associated rotation recrystallization can be assumed. Continuous lattice rotation from the core to the outer polycrystalline rim allow a determination of the related dominant slip systems which are {100}<010> and equivalent systems according to the cubic lattice symmetry. The same holds for garnets which appear to be completely recrystallized. For this type of fine-grained aggregates an alternative nucleation model is discussed. Due to penetrative dislocation glide in connection with short range diffusion and the resulting lattice rotation, primary growth zones are strongly disturbed.Since for the considered rock unit of the Münchberg Massif peak metamorphic temperatures between 630 and 670 °C can be assumed, this study clearly demonstrates that the inferred processes of ductile garnet deformation can occur not only in HT regimes as often suggested in the literature even if embedded within a matrix of “low-strength” minerals like quartz, feldspars and micas.     

Reaction of soil enzymes and spring barley to copper chloride and copper sulphate

Study was carried out to compare the effect of the degree of contamination of soil with copper on the soil enzyme activity, depending on the type of chemical compound with which a metal reaches the soil and on the method of soil use. An effect of increasing doses of copper on growth and the development of spring barley has been studied. The study was carried out as a pot experiment on two types of soil: loamy sand and light loam. Copper was introduced to soil as copper(II) sulphate(VI) and copper(II) chloride at four doses: 150, 300, 450 and 600 mg Cu²⁺ kg^?1 d.m. of soil. Soil without copper was used as a control sample. The experiment showed that contamination of soil with copper applied as CuCl₂ and CuSO₄·5H₂O upset the homeostasis of soil. Dehydrogenases and urease were the most sensitive to contamination of soil with Cu²⁺, both as copper(II) chloride and as copper(II) sulphate(VI), and acid phosphatase and alkaline phosphatase were the least sensitive. Greater changes in enzymatic activity were observed in loamy sand than in light loam. The differences in the impact of copper(II) sulphate(VI) and copper(II) chloride on the soil microbiome were relatively small, because mean ED₅₀ for copper(II) chloride was 341 mg Cu²⁺ kg^?1 d.m. of soil, and for copper(II) sulphate(VI) it was 364 mg Cu²⁺ kg^?1 d.m. of soil. This inhibitory effect of copper persisted throughout the period of the experiment. The sensitivity of spring barley to copper compounds was lower than the enzymes under study.     

Elevated marine deposits in Bermuda record a late Quaternary megatsunami

Deposits of coral-bearing, marine shell conglomerate exposed at elevations higher than 20 m above present-day mean sea level (MSL) in Bermuda and the Bahamas have previously been interpreted as relict intertidal deposits formed during marine isotope stage (MIS) 11, ca. 360–420 ka before present. On the strength of this evidence, a sea level highstand more than 20 m higher than present-day MSL was inferred for the MIS 11 interglacial, despite a lack of clear supporting evidence in the oxygen-isotope records of deep-sea sediment cores. We have critically re-examined the elevated marine deposits in Bermuda, and find their geological setting, sedimentary relations, and microfaunal assemblages to be inconsistent with intertidal deposition over an extended period. Rather, these deposits, which comprise a poorly sorted mixture of reef, lagoon and shoreline sediments, appear to have been carried tens of meters inside karst caves, presumably by large waves, at some time earlier than ca. 310–360 ka before present (MIS 9–11). We hypothesize that these deposits are the result of a large tsunami during the mid-Pleistocene, in which Bermuda was impacted by a wave set that carried sediments from the surrounding reef platform and nearshore waters over the eolianite atoll. Likely causes for such a megatsunami are the flank collapse of an Atlantic island volcano, such as the roughly synchronous Julan or Orotava submarine landslides in the Canary Islands, or a giant submarine landslide on the Atlantic continental margin.     

Electrical structure of the upper mantle beneath Central Europe: Results of the CEMES project

In the years 2001–2003, we accomplished the experimental phase of the project CEMES by collecting long-period magnetotelluric data at positions of eleven permanent geomagnetic observatories situated within few hundreds kilometers along the south-west margin of the East European Craton. Five teams were engaged in estimating independently the magnetotelluric responses by using different data processing procedures. The conductance distributions at the depths of the upper mantle have been derived individually beneath each observatory. By averaging the individual cross-sections, we have designed the final model of the geoelectrical structure of the upper mantle beneath the CEMES region. The results indicate systematic trends in the deep electrical structure of the two European tectonic plates and give evidence that the electrical structure of the upper mantle differs between the East European Craton and the Phanerozoic plate of west Europe, with a separating transition zone that generally coincides with the Trans-European Suture Zone.     

Reconstruction of paleocoastlines for the northwestern South China Sea since the Last Glacial Maximum

The range of relative sea level rise in the northwestern South China Sea since the Last Glacial Maximum was over 100 m. As a result, lowland regions including the Northeast Vietnam coast, Beibu Gulf, and South China coast experienced an evolution from land to sea. Based on the principle of reconstructing paleogeography and using recent digital elevation model, relative sea level curves, and sediment accumulation data, this paper presents a series of paleogeographic scenarios back to 20 cal. ka BP for the northwestern South China Sea. The scenarios demonstrate the entire process of coastline changes for the area of interest. During the late glacial period from 20 to 15 cal. ka BP, coastline slowly retreated, causing a land loss of only 1×10⁴ km², and thus the land-sea distribution remained nearly unchanged. Later in 15–10 cal. ka BP coastline rapidly retreated and area of land loss was up to 24×10⁴km², causing lowlands around Northeast Vietnam and South China soon to be underwater. Coastline retreat continued quite rapidly during the early Holocene. From 10 to 6 cal. ka BP land area had decreased by 9×10⁴km², and during that process the Qiongzhou Strait completely opened up. Since the mid Holocene, main controls on coastline change are from vertical crustal movements and sedimentation. Transgression was surpassed by regression, resulting in a land accretion of about 10×10⁴km². Supported by Key Laboratory of Marginal Sea Geology, Chinese Academy of Sciences (Grant No. MSGL0711), the Guangdong Natural Science Foundation (Grant No. 04001309) and Open Fund of the Key Laboratory of Marine Geology and Environment, Chinese Academy of Sciences (Grant No. MGE2007KG04)