Can sand dunes be used to study historic storm events?

Knowing the long‐term frequency of high magnitude storm events that cause coastal inundation is critical for present coastal management, especially in the context of rising sea levels and potentially increasing frequency and severity of storm events. Coastal sand dunes may provide a sedimentary archive of past storm events from which long‐term frequencies of large storms can be reconstructed. This study uses novel portable optically stimulated luminescence (POSL) profiles from coastal dunes to reconstruct the sedimentary archive of storm and surge activity for Norfolk, UK. Application of POSL profiling with supporting luminescence ages and particle size analysis to coastal dunes provides not only information of dunefield evolution but also on past coastal storms. In this study, seven storm events, two major, were identified from the dune archive spanning the last 140 years. These appear to correspond to historical reports of major storm surges. Dunes appear to be only recording (at least at the sampling resolution used here) the highest storm levels that were associated with significant flooding. As such the approach seems to hold promise to obtain a better understanding of the frequency of large storms by extending the dune archive records further back to times when documentation of storm surges was sparse. © 2017 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.     

Toxicopathic liver lesions in English sole and chemical contaminant exposure in Vancouver Harbour,Canada

The prevalence of toxicopathic liver lesions in English sole (Pleuronectes vetulus) was determined along a presumed gradient of chemical contamination in Vancouver Harbour, Canada. Fish were captured from five sites in or near Vancouver Harbour, British Columbia, Canada. No toxicopathic lesions were observed in fish examined at the reference site (Howe Sound outside Vancouver Harbour), or at the outer harbour site. In contrast, 20-23% of the fish from three sites located in the central harbour, Indian Arm and Port Moody Arm had one or more types of toxicopathic lesions. Likewise, aromatic hydrocarbon (AH) metabolites measured in bile exhibited a gradient in levels from lower concentrations at the reference site to significantly higher levels in fish from Indian Arm and Port Moody Arm harbour sites. The occurrence of toxicopathic liver lesions was statistically associated with concentrations of AHs measured in sediment and AH metabolite levels measured in bile.     

Gypsum as a monitor of the paleo-limnological–hydrological conditions in Lake Lisan and the Dead Sea

The isotopic composition and mass balances of sources and sinks of sulfur are used to constrain the limnological–hydrological evolution of the last glacial Lake Lisan (70–14 ka BP) and the Holocene Dead Sea. Lake Lisan deposited large amounts of primary gypsum during discrete episodes of lake level decline. This gypsum, which appears in massive or laminated forms, displays δ³⁴S values in the range of 14–28‰. In addition, Lake Lisan’s deposits (the Lisan Formation) contain thinly laminated and disseminated gypsum as well as native sulfur which display significantly lower δ³⁴S values (−26 to 1‰ and −20 to −10‰, respectively). The calculated bulk isotopic compositions of sulfur in the sources and sinks of Lake Lisan lacustrine system are similar (δ³⁴S ≈ 10‰), indicating that freshwater sulfate was the main source of sulfur to the lake. The large range in δ³⁴S found within the Lisan Formation (−26 to +28‰) is the result of bacterial sulfate reduction (BSR) within the anoxic lower water body (the monimolimnion) and bottom sediments of the lake.

Precipitation of primary gypsum from the Ca-chloride solution of Lake Lisan is limited by sulfate concentration, which could not exceed 3000 mg/l. The Upper Gypsum Unit, deposited before ca. 17–15 ka, is the thickest gypsum unit in the section and displays the highest δ³⁴S values (25–28‰). Yet, our calculations indicate that no more than a third of this Unit could have precipitated directly from the water column. This implies that during the lake level decline that instigated the precipitation of the Upper Gypsum Unit, significant amounts of dissolved sulfate had to reach the lake from external sources. We propose a mechanism that operated during cycles of high-low stands of the lakes that occupied the Dead Sea basin during the late Pleistocene. During high-stand intervals (i.e., Marine Isotopic Stages 2 and 4), lake brine underwent BSR and infiltrated the lake’s margins and adjacent strata. As lake level dropped, these brines, carrying ³⁴S-enriched sulfate, were flushed back to the shrinking lake and replenished the water column with sulfate, thereby promoting massive gypsum precipitation.

The Holocene Dead Sea precipitated relatively small amounts of primary gypsum, mainly in the form of thin laminae. δ³⁴S values of these laminae and disseminated gypsum are relatively constant (15 ± 0.7‰) and are close to present-day lake composition. This reflects the lower supply of freshwater to the lake and the limited BSR activity during the arid Holocene time and possibly during former arid interglacials in the Levant.     

The magnetic effects of brecciation and shock in meteorites: I. The Ll-chondrites

The complex brecciation and shock history of amphoterite (LL-) chondrites is well reflected in their diverse natural magnetic remanence (NRM) behavior: Most LL-chondrites have a multicomponent, undemagnetizable NRM, analogous to that of lunar breccias. Only one meteorite among those studied, namely Dhurmsala (LL6), meets the criteria of NRM stability and directional coherence with progressive AF cleaning, indicative of a useful paleoremanence. Ancient field paleointensity determinations for Dhurmsala (LL6) of 0.03 and 0.1 Oe, agree well with our earlier estimates of 0.01 and 0.08 Oe for the LL6 Jelica and Vavilovka, respectively. In light of their petrographic structure, cooling rates, radiometric ages and shock indicators, it appears likely that the NRM may have been thermally imprinted, during cooling following shock-metamorphism. The closely similar saturation remanence (IRM_s) behavior for LL-chondrites, in contrast to the intragroup scatter in NRM characteristics, implies that - although formed by similar process from the same starting material, - the LL-chondrites have suffered widely different degrees of shock/metamorphic reheating.     

Clay minerals as an indicator of the accumulation of the Upper Quaternary deposits in the St. Anna Trough (Kara Sea)

This paper is devoted to the studies of clay minerals from two cores collected in the northern and central regions of the St. Anna Trough, the largest trough of the Kara Sea. The Upper Quaternary glacial, glaciomarine, and marine deposits are characterized by various contents of kaolinite, chlorite, illite, and smectite. It is established that, from older to younger deposits, the amounts of kaolinite and chlorite generally decrease, while those of illite and smectite, on the contrary, increase. A joint analysis of the distributions of clay and heavy minerals over the section allowed us to refine the position of the sources for the terrigenous matter and their temporal variability. It is shown the changes in the sources of supply were directly related to the climate changes that occurred when passing from the glacial to marine sedimentation environments.     

Grid adaptation for the Dirichlet–Neumann representation method and the multiscale mixed finite-element method

A Dirichlet–Neumann representation method was recently proposed for upscaling and simulating flow in reservoirs. The DNR method expresses coarse fluxes as linear functions of multiple pressure values along the boundary and at the center of each coarse block. The number of flux and pressure values at the boundary can be adjusted to improve the accuracy of simulation results and, in particular, to resolve important fine-scale details. Improvement over existing approaches is substantial especially for reservoirs that contain high-permeability streaks or channels. As an alternative, the multiscale mixed finite-element (MsMFE) method was designed to obtain fine-scale fluxes at the cost of solving a coarsened problem, but can also be used as upscaling methods that are flexible with respect to geometry and topology of the coarsened grid. Both methods can be expressed in mixed-hybrid form, with local stiffness matrices obtained as “inner products” of numerically computed basis functions with fine-scale sub-resolution. These basis functions are determined by solving local flow problems with piecewise linear Dirichlet boundary conditions for the DNR method and piecewise constant Neumann conditions for MsMFE. Adding discrete pressure points in the DNR method corresponds to subdividing faces in the coarse grid and hence increasing the number of basis functions in the MsMFE method. The methods show similar accuracy for 2D Cartesian cases, but the MsMFE method is more straightforward to formulate in 3D and implement for general grids.     

The magnetic effects of brecciation and shock in meteorites: III. The achondrites

We present results of a magnetic survey of achondritic meteorites, representing the aubrites (A), diogenites (D), Irowardites (H), and eucrites (E) groups and relate their magnetic behavior to respective class characteristics and models of origin.Magnetic susceptibility (x) values cluster well within each group and decrease systematically between groups (from 2 to 0.1×10^–3GOe^–1 cm^–3), with the average metal contents, (from 1 to <0.1 wt%) in the above order. The natural remanent magnetization (NRM) values range broadly within each group, but group averages decrease roughly as above. However, the considerable within-sample and intra-group variability in NRM level and its demagnetization characteristics attest to inhomogeneous and localized brecciation effects. Although petrological-chemical studies resolve a primary component of magmatic differentiation on the planetoid of origin, no clear magnetic record of such event has been preserved. The magnetization of achondrites is mainly the product of their complex, multi-stage impact brecciation and metamorphism history, in accord with other lines of evidence.The magnetic behavior of achondrites is remarkably similar to that characteristic of lunar breccias and impact-melt rocks and reinforces their analogous mode of genesis, as brought out by chemical and petrographic analyses.     

Neotectonic faulting and the Late Weichselian shoreline gradients in SW Norway

The Younger Dryas (YD) maximum highstand shoreline in SW Norway has traditionally been considered as being slightly concave, gradually steepening in the direction of uplift. This phenomenon is attributed to geoidal and isostatic effects near the former ice-sheet margin. On the basis of isolation basin data from the region, we have reconstructed this shoreline, and a Bølling-Allerød (B-A) lowstand shoreline, along three profiles in SW Norway. Along all profiles there are shore levels which, within the error limits estimated, cannot be captured by a single straight (or curved) shoreline. The anomalous shore levels occur near major fault zones and are interpreted to reflect differential uplift rates on opposite sides of faults, superimposed on the general glacio-isostatic tilting of the region. The inferred faulting is consistent with observations previously reported as neotectonic ‘claims’ in the region and shed new light on the deformational structures observed in seismic profiles of the fjord sediments. Excluding the anomalous shore levels, a straight shoreline with gradient ca. 1.1 m/km provides the best and most consistent representation of the YD shore levels along the three profiles. The B-A lowstand shoreline is constrained by fewer data points, but is approximately parallel-dipping the highstand shoreline. Our reconstructions imply a less steep YD maximum highstand shoreline compared to previous reconstructions, where gradients up to 1.4 m/km have been inferred. This may imply that the ice load effect on the lithosphere in SW Norway during the YD is less than previously assumed.     

Authigenic zeolites and their relation to silica diagenesis in ODP Site 661 sediments (Leg 108, Eastern Equatorial Atlantic)

At ODP Site 661 from the continental margin of Northwest Africa, authigenic clinoptilolites were investigated in detail. Based on chemical data, crystal size and shape and their intergrowth with associated mineral phases, two types of clinoptilolite (type A and B) occur representing different diagenetic conditions under which the formation of zeolites took place. Clinoptilolite type A was found in a sediment section comprises numerous hiatuses and stratigraphically condensed sediments and could have been formed during early diagenesis. In contrast, clinoptilolite type B was precipitated in Campanian sediments during later diagenesis, after the transformation from opal-A to opal-CT had taken place. At Site 661, the silica source for the authigenesis of both clinoptilolite types is biogenic opal. Volcanic ash material occurs, but in low amounts and thus is not a prerequisite for the formation of clinoptilolite at Site 661.

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Zusammenfassung In der ODP-Bohrung 661 (Leg 108) vom Kontinentalrand vor Nordwest-Afrika wurden authigene Klinoptilolith-Kristalle mit Hilfe der Rasterelektronenmikroskopie, Röntgendiffraktometrie und Mikrosonde im Detail untersucht. Anhand der Kristallgrößen und -formen, ihren Verwachsungen mit anderen Mineralphasen und ihren chemischen Zusammensetzungen wurden 2 Klinoptilolithtypen (Typ A und B) unterschieden. Typ A wurde in stratigraphisch kondensierten Sedimenten nachgewiesen und könnte im Zuge von frühdiagenetischen Porenwasserreaktionen entstanden sein. Klinoptilolithtyp B, welcher vorwiegend in den campanen Sedimenten der ODP-Bohrung 661 vorkommt, wurde während der späteren Silikatdiagenese nach der Transformation von Opal-A in Opal-CT gebildet. Als Silikatquelle für die Kristallisation beider Klinoptilolithtypen wurden überwiegend biogene Opalskelette benutzt. Vulkanisches Aschenmaterial, welches ebenfalls ein Potential für die Klinoptilolithentstehung bildet, wurde nur in einem Horizont nachgewiesen und hatte keinen wesentlichen Einfluß auf die Klinoptilolithentstehung.

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Résumé Des cristaux de clinoptilolite authigène, provenant du site ODP 661 (marge continentale nord-ouest-africaine), ont fait l'objet d'une étude détaillée par microscopie électronique, diffractométrie X et microsonde. Les données chimiques, la taille et la forme des cristaux ainsi que leur intercroissance avec d'autres phases minérales permettent de distinguer 2 types (A et B) de clinoptinolite, qui correspondent aux conditions diagénétiques différentes dans lesquelles les zéolites se sont formées. La clinoptilolite de type A a été rencontrée dans une succession de sédiments stratigraphiquement condensés; elle pourrait s'être formée au début de la diagenèse. La clinoptilolite de type B, par contre, rencontrée surtout dans les sédiments campaniens a précipité au cours des stades tardifs de la diagenèse, après la transformation de l'opale A en opale CT. Au site 661, la source de silice nécessaire à la formation authigène des deux types de clinoptilolite est constituée par l'opale biogénique. Les cendres volcaniques qui pourraient éventuellement être à l'origine de la formation de clinoptilolite, n'ont été rencontrées que dans un seul horizon et n'ont joué aucun rôle en l'occurence.

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大陆内的长余震序列和对地震危险性评估的意义

板块构造学说最强大的特点之一,是通过已知的板块运动可以了解板块边界未来大地震的地点和平均复发间隔。然而板块构造学却不能探知板块之内何时何处发生地震,因为理想的板块内部不发生形变。因此,在板块内部,进行地震危险性评估主要依靠的假设是,短期历史记录给出的小地震的位置反映出连续形变从而引发未来大地震（Shed—locketal,2000）。然而在此我们提出,最近的这些地震有许多可能是数百年前大地震的余震。我们提出一简单模型可预测：余震序列的长度和断层应力加载的速．率成反比。