Cycles Of Erosion Research Articles

Decadal and seasonal development of embryo dunes on an accreting macrotidal beach: North Lincolnshire, UK

ABSTRACTEmbryo dunes are often ephemeral, but can develop to become established coastal foredunes. In 2001 a patch of embryo dunes 13.11 m2 appeared on a beach in north Lincolnshire, UK and had expanded to over 3600 m2 by 2011. The rate of expansion is linked to storm occurrence, where expansion is slowed during years with a higher incidence of storm surges. From July 2009–October 2010 seasonal changes in dune field topography were determined using terrestrial laser scanning (TLS) data. Vegetation is important in the development of embryo dunes, but can cause errors in TLS data. Tests evaluating the impact of vegetation on the TLS data suggest the minimum elevation value from the TLS point cloud within a 0.05 m grid cell gives a good approximation of the ground surface. Digital elevation models (DEMs) of the dunes constructed using filtered data showed the embryo dunes underwent a classic seasonal cycle of erosion during the winter and accretion during the summer. For example from October 2009 to April 2010 over 375 m3 of sediment was eroded from the dunes whereas during spring and summer 2010 the dune field gained over 600 m3 of sand. The overall magnitude of change in dune height and volume from season to season exceeded the errors associated with the construction of the DEM from the TLS data and the vegetation filtering process, which suggests TLS can be useful for documenting topographic change in vegetated dunes. After 10 years, the patch of embryo dunes is still expanding but has not yet merged with more established foredunes to landward. Aeolian process measurements indicate that, at present, the embryo dunes do not prevent sand from reaching the foredunes, however the rate of foredune progradation has slowed concurrently with the expansion of the embryo dune field. Copyright © 2013 John Wiley & Sons, Ltd.

Characterization of weathering profile in granites and volcanosedimentary rocks in West Africa under humid tropical climate conditions. Case of the Dimbokro Catchment (Ivory Coast)

In granitic rocks, various models of weathering profile have been proposed, but never for the hard rocks of West Africa. Besides, in the literature there is no description of the weathering profile in volcanosedimentrary rocks. Therefore, we propose three models describing the weathering profiles in granites, metasediments, and volcanic rocks for hard rock formations located in West Africa. For each of these models proposed for granitic and volcanosedimentary rocks of the Dimbokro catchment, vertical layered weathering profiles are described, according to the various weathering and erosion cycles (specific to West Africa) that the geological formations of the Dimbokro catchment experienced from the Eocene to the recent Quaternary period. The characterization of weathering profiles is based on: i) bedrocks and weathering profile observations at outcrop, and ii) interpretation and synthesis of geophysical data and lithologs from different boreholes. For each of the geological formations (granites, metasediments, and volcanic rocks), their related weathering profile model depicted from top to bottom comprises four separate layers: alloterite, isalterite, fissured layer, and fractured fresh basement. These weathering profiles are systematically covered by a soil layer. Though granites, metasediments and volcanic rocks of the Dimbokro catchment experience the same weathering and erosion cycles during the palaeoclimatic fluctuations from Eocene to recent Quaternary period, they exhibit differences in thickness. In granites, the weathering profile is relatively thin due to the absence of iron crust which protects weathering products against dismantling. In metasediments and volcanic rocks iron crusts develop better than in granites; in these rocks the alterite are more resistant to dismantling.

Dinámica erosiva del "piping" : un ejemplo en la Depresión del Ebro

In the Bardenas regíon we recognize some hydric erosion processes, as follows: sheet-wash and runof/' rilling, badlanding and forming of gullies with Vand U section". This last type is relationed with certain piping forms, that indicate the importance of the subsurface eros ion at these points. We propose a classification for those forms, and an erosional cycle ofpiping. The anthropic inciden ce of this erosion type in the area is also considered.

KwaZulu-Natal coastal erosion events of 2006/2007 and 2011: A predictive tool?

Severe coastal erosion occurred along the KwaZulu-Natal coastline between mid-May and November 2011. Analysis of this erosion event and comparison with previous coastal erosion events in 2006/2007 offered the opportunity to extend the understanding of the time and place of coastal erosion strikes. The swells that drove the erosion hotspots of the 2011 erosion season were relatively low (significant wave heights were between 2 m and 4.5 m) but of long duration. Although swell height was important, swell-propagation direction and particularly swell duration played a dominant role in driving the 2011 erosion event. Two erosion hotspot types were noted: sandy beaches underlain by shallow bedrock and thick sandy beaches. The former are triggered by high swells (as in March 2007) and austral winter erosion events (such as in 2006, 2007 and 2011). The latter become evident later in the austral winter erosion cycle. Both types were associated with subtidal shore-normal channels seaward of megacusps, themselves linked to megarip current heads. This 2011 coastal erosion event occurred during a year in which the lunar perigee sub-harmonic cycle (a ±4.4-year cycle) peaked, a pattern which appears to have recurred on the KwaZulu-Natal coast. If this pattern proves true, severe coastal erosion may be expected in 2015. Evidence indicates that coastal erosion is driven by the lunar nodal cycle peak but that adjacent lunar perigee sub-harmonic peaks can also cause severe coastal erosion. Knowing where and when coastal erosion may occur is vital for coastal managers and planners.

Geographical information system-based morphometric analysis of Bharathapuzha river basin, Kerala, India

A morphometric analysis of Bharathapuzha river basin has been carried out using geoprocessing techniques in GIS. This technique is found relevant for the extraction of river basin and its drainage networks. The extracted drainage network was classified according to Strahler’s system of classification and it reveals that the terrain exhibits dendritic to sub-dendritic drainage pattern. The Bharathapuzha drainage basin is sprawled over an area of 5,988.56 km2. The study area was designated as seventh-order basin and lower order streams mostly dominate the basin with the drainage density value of 1.07 km/km2. The slope of basin varied from 0° to 70° and the slope variation is chiefly controlled by the local geology and erosion cycles. The elongation ratio of the basin is 0.57 indicating that the study area is elongated with moderate relief and steep slopes. The drainage texture of the basin is 7.78 which indicates an intermediate texture that exists over the region. Hence, from the study, it can be concluded that remote sensing data (SRTM–DEM) coupled with geoprocessing techniques prove to be a competent tool in morphometric analysis and the data can be used for basin management and other hydrological studies in future.

Relief inversion in the geomorphological evolution of sub-Saharan West Africa

The geomorphology of much of sub-Saharan West Africa is dominated by the presence of plateaux and plains with ferruginous and, locally, aluminous (bauxitic) duricrusts. The plateaux occur at different elevations and have been correlated as two or more palaeosurfaces across much of the region. The duricrusts have generally been considered to be residual, formed by conformable erosion and chemical wasting of immediately underlying bedrock. This concept has been central to interpretations as diverse as the formation and evolution of the landscape and the development of geochemical exploration models. Recent regolith landform mapping, field observations and experience from mineral exploration in southern Mali and Burkina Faso, however, demonstrate that the duricrusts are mainly ferricretes, i.e., Fe oxide-cemented sediments. These observations require a re-interpretation of the geomorphological evolution of the region during the Cenozoic. The landscape has evolved by several cycles of weathering and erosion–deposition, triggered by climatic, tectonic or other environmental changes. It is proposed that an initial bauxitic/lateritic regolith was partly eroded following uplift and/or a change to a more arid climate, and that the detritus, rather than being removed, was deposited on slopes and valleys. During a subsequent humid period of lateritic weathering, Fe oxide cementation of this detritus formed ferricrete. Dehydration and hardening of the ferricrete after further uplift or aridity increased its resistance to erosion, resulting in relief inversion, with the detritus, in turn, being deposited downslope. This too has been weathered and cemented, to form a younger ferricrete. The occurrence of ferricrete landforms in adjacent countries, noted by field observation and inferred from satellite imagery, demonstrates that relief inversion is a very widespread and important phenomenon in southern Mali, Burkina Faso and adjacent countries in semi-arid West Africa.

GIS model-based morphometric evaluation of Tamiraparani subbasin, Tirunelveli district, Tamil Nadu, India

A morphometric evaluation of Tamiraparani subbasin was carried out to determine the drainage characteristics using GIS model technique. Extraction of the subbasin and stream network model has been developed to quantify the drainage parameters in the study area. The input parameters required to run this model are: a pour point, a minimum upstream area in hectares, and a digital elevation model. After execution, the model provides a drainage basin with Strahler’s classified stream network supported by thematic layers like aspect, slope, relief, and drainage density. The developed model reveals that the drainage area of this subbasin is 2,055 km2 and shows subdendritic to dendritic drainage pattern. The basin includes seventh order stream and mostly dominated by lower stream order. The slope of the study area varies from 0° in the east to 61° towards west. The presence of Western Ghats is the chief controlling factor for slope variation. Moreover, the slope variation is controlled by the local lithology and erosion cycles. The bifurcation ratio indicates that the geological structures have little influence on the drainage networks and the drainage density reveals that the nature of subsurface strata is permeable.

Biostratigraphy of the Upper Pleistocene (Upper Neopleistocene) of the Southern Urals

This paper is a synthesis of the previously published and unpublished materials dealing with the stratigraphy of the Upper Pleistocene (Upper Neopleistocene according to the Russian stratigraphic scheme) of the Southern Urals. It is the second review about the characteristics of the Pleistocene deposits of the easternmost part of Europe. It follows a previous paper concerning the biostratigraphy of the Late Middle Pleistocene of this region. The deposits which constitue the regional stratigraphic units are characterized. The results of the mammalian, malacological and palynological investigations as well as the radiocarbon data provide the basis for the stratigraphical subdivision and the reconstruction of the palaeoenvironments. The main geological and biotical events of the Southern Urals region which took place during Late Pleistocene are characterized in the paper. Erosional processes became active at the beginning of Kushnarenkovo time when uplift took place in the Urals and when the Late Chosarian regression began on the Caspian Sea basin territory. Fluvial deposits can be observed at the base of the second terrace which developed above the floodplain. A soil was formed on the subhorizontal surfaces. Forest-steppe and steppe landscapes characterized this interval. The climate was warm and humid. The Saigatka horizon formed under cold conditions. Slope processes and solifluction were the main relief-forming processes and fluvial erosion processes became weaker. Floodplain sediments accumulated in the river valleys and formed the upper parts of the second terraces above the floodpain which were intensively eroded. The plains were covered by steppe and the mountainous areas were occupied by tundra and forest–tundra landscapes. The next erosional cycle began during the following Tabulda period, because of the lowering of base level of the erosion and increased uplift of the territory. The fluvial sediments now form the lower parts of the first terraces above the floodplain. A soil was formed on the watersheds. Sites contain Late Palaeolithic artifacts. The floral association was close to Southern Uralian flora of the present-day. The climate was moderately warm in the plains and drier and cooler in the mountains. The subsequent Kudashevo event can be correlated with the Late Glacial when the climate became colder. Loess-like sediments and floodplain deposits form the upper parts of the first terrace above the floodplain and cover the watersheds, where they contain cryogenic structures. The climate was moderately cold. Late Palaeolithic sites attributed to the Kudashevo time are known in the Southern Urals region. The stratigraphical positions of the main Upper Neopleistocene localities of the Southern Urals are discussed. The Southern Urals subdivisions are correlated with the Western European stratigraphical scheme (Eemian–Weichselian interval).

Stratigraphic paleobiology: understanding the distribution of fossil taxa in time and space by Mark E. Patzkowsky and Steven M. Holland. University of Chicago Press, Chicago, 2012. No. of pages: xi+259. Price: $35-00. ISBN 978-0-226-64938-2 (paperback).

The fossil record lies at the heart of understanding the history of life on Earth, but interpreting this history poses a major challenge. This is because fossils are preserved in a rock record that is structured by cycles of deposition and erosion, and is thus systematically biased. While major advances have been made in understanding the architecture of sedimentary successions and deposystems through the development of sequence stratigraphy, the effects this structuring has in shaping the fossil record has only recently begun to be recognised. The recurrent theme of this excellent little book is that if palaeontologists are to interpret the fossil record correctly then they need to understand the stratigraphical and geological context in which their fossils occur. Patzkowsky and Holland are pioneers in this field, and write with a clear and easy style. The book starts with a discussion of the resolution that can be achieved from the fossil record and provides a succinct summary of sequence stratigraphic principals that govern how the sedimentary record is built up. There then follows a section on how organisms (primarily marine invertebrates) are controlled by environmental gradients and how palaeontologists try to document these patterns in the fossil record. The next chapter adds a further level of complication by showing how environmental sampling is constrained by sequence stratigraphic and basin architecture so that the fossil record only ever captures a partial picture. The critical point here is that sequence stratigraphical architecture generates predictable biases to the fossil record, which can therefore be taken into account. The latter part of the book then deals with how best to approach the fossil record in the light of these problems, focusing on large-scale patterns of change through time in ecological community structure, morphological disparity and taxic diversity. This book presents a well-argued case for why all palaeontologists should have a wary eye on the geological context of their fossil collections before drawing conclusions about any sort of pattern that they observe. While the problems are many, the authors strive to show how these can be tackled successfully when the geological context of data is understood and appropriate methods are applied. Their focus throughout is on section- to basin-scale patterns, and so unfortunately they miss the opportunity to outline the really large-scale biases that afflict the geological record. These are certainly important when it comes to interpreting global diversity or making generalisations about community evolution in general. Nevertheless, this book is essential reading for all post-graduate and professional palaeobiologists, and makes an excellent introduction to the subject for advanced undergraduate courses.

Efficacy of the stannous ion and a biopolymer in toothpastes on enamel erosion/abrasion

ObjectivesSn2+ has promising erosion-inhibiting properties in solutions, but little is known about respective effects in toothpastes. In addition, biopolymers might have protecting potential. Aim of this study was to investigate the effects of Sn2+ in toothpastes and of a biopolymer (chitosan) added to a Sn2+ formulation on erosion/abrasion. MethodsEnamel samples were subjected to cyclic erosion procedures (10 days; 0.50% citric acid, pH 2.5; 6× 2min/day), and brushing (2× 15s/day, load 200g) during immersion in slurries (2min). The toothpastes were NaF formulations (NaF/1, NaF/2, NaF/3) and Sn2+ formulations (NaF/SnCl2, AmF/SnF2, AmF/NaF/SnCl2) and AmF/NaF/SnCl2+0.5% chitosan.Declared concentrations of active ingredients in toothpastes were 1400–1450μg/g F− and 3280–3500μg/g Sn2+. Negative controls were erosion only and placebo, positive control was a SnF2 gel. Tissue loss was quantified profilometrically, Sn on enamel surfaces was measured by energy dispersive X-ray spectroscopy. ResultsLoss values (μm) for erosion only and placebo were 14.4±4.5 and 20.2±3.8, respectively, and 4.6±1.9 for the positive control (p≤0.001 each compared to erosion only). The other loss values were: NaF/1 16.5±3.0, NaF/2 14.0±2.7, NaF/3 12.6±3.9, NaF/SnCl2 14.7±5.1, AmF/SnF2 13.5±4.8, AmF/NaF/SnCl2 12.4±4.2, AmF/NaF/SnCl2+chitosan 6.6±3.5 (except NaF/1 all p≤0.01 compared to placebo). AmF/NaF/SnCl2/chitosan was more effective than all other toothpastes (p≤0.01 each). Sn on the enamel surface ranged between 1.3±0.3 and 2.8±0.04wt.% with no obvious relationship with efficacy. ConclusionsThe NaF and Sn2+ toothpastes without chitosan exhibited similar anti-erosion and abrasion-prevention effects. The experimental Sn2+ formulation with chitosan revealed promising results similar to those of the positive control. Clinical significanceNaF toothpastes offer a degree of protection against erosion/abrasion, which is likely sufficient for most subjects with average acid exposures. For patients with initial erosive lesions, however, more effective toothpaste is desirable. The combination of Sn2+ and a biopolymer appears promising in this context.

Development of progressive failure in sensitive clay slopes

The development of progressive failure in sensitive clay slopes is analysed using principles from fracture mechanics, where failure stress depends on a material property (toughness) and length of an existing weakness, unlike traditional soil mechanics where failure stress is generally assumed to be only a function of material strength. An existing weakness, or partially developed failure surface, can propagate due to sudden loads, as might be induced by seasonal erosion cycles, small local landslides at a river bank or earthquake shaking. The paper examines the growth of the failure surface over time due to such loads. The analysis shows that a large landslide in sensitive clay can occur after a number of seasonal erosion cycles with no obvious trigger. It also shows that a larger load due to either a small landslide or earthquake can cause a developing failure surface to propagate freely toward general collapse. Large landslides in sensitive clay are often preceded by a smaller landslide at the river bank, but can be triggered by large earthquakes or may occur for no obvious reason. The agreement between predictions and real behaviour suggests that the model for progressive failure of large landslides in sensitive clay deserves further consideration.

Climatic and Tectonic Controls On Pedogenesis and Landscape Evolution In A Quaternary Intramontane Basin (Val D'agri Basin, Southern Apennines, Italy)

Abstract Paleopedological studies of alluvial systems in intramontane valley settings provide useful tools for understanding the interaction of tectonics, climate, and local base-level changes in controlling alluvial dynamics. An example is reported from the Quaternary alluvial deposits of the Val d’Agri Basin in Southern Italy, which were accreted in response to cycles of deposition, pedogenesis, and erosion. Several buried weathering profiles, representative of the main stratigraphic unconformities, were characterized by field description and micromorphological analyses. The profiles appear to be truncated at the top by intense erosion. The main pedological features and their formative processes occurred polycyclically, attesting to different and relict pedogenetic phases that are not in equilibrium with present-day environmental conditions. We interpret the weathering profiles as paleosols that developed mainly during Pleistocene interglacial periods. The (peri-) glacial phases mainly caused erosion of devegetated slopes and soil truncation processes. All of the paleosols in the Val d’Agri basin offer useful information on the chronological reconstruction of climatic phases and the associated sequence of pedogenetic events during the Quaternary in the Mediterranean region.

High‐resolution comparison of sediment dynamics under different forcing conditions in the bottom boundary layer of a shallow, micro‐tidal estuary

Data for high‐resolution profiles of current velocity and suspended sediment concentration (SSC) were collected in bottom boundary layer (BBL) of Mobile Bay, Alabama. The data were used to study the vertical and temporal variability in SSC under various forcing conditions of tide, wind and freshwater discharge. During the winter stormy season, the background SSC was low (0.015–0.03 g l−1). An episodic storm‐induced erosion/resuspension was responsible for the short‐lasting high SSC in BBL. During the spring flooding period, the background SSC was relatively high (0.04–0.07 g l−1) likely due to the large amount of suspended sediment from the fluvial input and bed softening, and the contribution of wind forcing to sediment resuspension was somewhat enhanced by the destratification in BBL. When the freshwater discharge was extremely high (>5000 m3 s−1), the entire water column in shallow areas of the Bay was influenced by freshwater input. Therefore, the thermohaline anomaly's contribution to the stratification considerably weakened, while the SSC's contribution strengthened. When the freshwater discharge was relatively low (<5000 m3 s−1), a critical wind stress for sediment erosion (0.08–0.1 Pa) was observed to abruptly increase the SSC. Despite a micro‐tidal regime, Mobile Bay exhibited the cyclic erosion and deposition pattern induced by the tidal acceleration and deceleration.

GIS based morphometric evaluation of Chimmini and Mupily watersheds, parts of Western Ghats, Thrissur District, Kerala, India

GIS and Remote Sensing have proved to be an indispensible tool in morphometric analysis. The identification of morphometric properties based on a geographic information system (GIS) was carried out in two watersheds in the Thrissur district of Kerala, India. These watersheds are parts of Western Ghats, which is an ecologically sensitive area. Quantitative geomorphometric analysis was carried out for the Chimmini and Mupily watersheds independently by estimating their (a) linear aspects like stream number, stream order, stream length, mean stream length, stream length ratio, bifurcation ratio, length of overland flow, drainage pattern (b) aerial aspects like circulatory ratio, elongation ratio, drainage density and (c) relief aspects like basin relief, relief ratio, relative relief and ruggedness number. The drainage areas of Chimmini and Mupily watersheds are 140 and 122 km2 respectively and show patterns of dendritic to sub-dendritic drainage. The Chimmini watershed was classified as a sixth order drainage basin, whereas Mupily watershed was classified as a fifth order basin. The stream order of the basin was predominantly controlled by physiographic and structural conditions. The increase in the stream length ratio from lower to higher order suggests that the study area has reached a mature geomorphic stage. The development of stream segments is affected by rainfall and local lithology of the watersheds. The slope of both watersheds varied from 0° to 50° and 0° to 42° respectively and the slope variation is chiefly controlled by the local geology and erosion cycles. Moreover, these studies are useful for planning rain water harvesting and watershed management.

Timing of supergene enrichment of low-grade sedimentary manganese ores in the Kalahari Manganese Field, South Africa

Low-grade carbonate-rich manganese ore of sedimentary origin in the giant Kalahari Manganese Field, South Africa, is upgraded to high-grade todorokite–manganomelane manganese ore by supergene alteration below the unconformity at the base of the Cenozoic Kalahari Formation. Incremental laser-heating 40Ar/39Ar dating of samples from the supergene altered manganese ore suggest that chemical weathering processes below the Kalahari unconformity peaked at around 27.8Ma, 10.1Ma and 5.2Ma ago. Older ages are dominant in the upper part of the weathering profile, while younger ages are characteristic of the deeper part of the profile. Younger ages partially overprint older ages in the upper part of the weathering profile and demonstrate the downward progression of the weathering front by as little as 10cm per million years. The oldest age obtained in the weathering profile, namely 42Ma, is considered a minimum estimate for the onset of the post African I cycle of weathering and erosion that followed the break up of Gondwanaland and formation of the Cretaceous to early Cenozoic African land surface. The youngest ages, recorded at around 5Ma, in turn, correspond well to the Pliocene transition from humid to arid climatic conditions in Southern Africa.

Aggregate Structures: Material and Machine Computation of Designed Granular Substances

AbstractIn inanimate nature, large masses of granular substances are in constant processes of formation through perpetual cycles of erosion and accretion. What if architecture was to emulate this behaviour and allow for its own continuous reconfiguration? Karola Dierichs and Achim Menges establish the notion of an ‘aggregate architecture’. Composed of large numbers of unbound yet designed granules, aggregates are based on a fundamentally different logic of construction. In contrast to assembly systems, aggregates materially compute their overall constructional configuration and shape as spatiotemporal behavioural patterns, with an equal ability for both: the stable character of a solid material and the rapid reconfigurability of a fluid. Copyright © 2012 John Wiley & Sons, Ltd.

Beach Erosion and Recovery

AbstractOur capability for predicting beach and dune erosion has improved in the last three decades, but the recovery of an eroded beach above the mean sea level (MSL) cannot be predicted at present. The cycle of beach erosion and recovery will need to be predicted for the long-term maintenance of a sand beach with a dune for coastal flooding reduction. The cross-shore numerical model (CSHORE) is extended and evaluated using natural beach erosion and recovery data along 16 cross-shore lines spanning 5 km alongshore for the duration of 272 days. The CSHORE predicts beach and dune erosion fairly well, as has been shown in previous comparisons. The bed-load formula used in the CSHORE is adjusted to predict the accreted beach profile with a berm. The computed beach profile evolutions are shown to be affected little by the alongshore gradient of the longshore sediment transport rate along the straight beach. The extended CSHORE predicts both erosion and accretion above MSL within a factor of about 2.

An analysis of the cross-shore beach morphodynamics of a sandy and a composite gravel beach

In this paper, beach profile surveys acquired over more than a decade at a sandy beach (Narrabeen Beach, New South Wales, Australia) and a composite sand–gravel beach (Milford-on-Sea, Christchurch Bay, UK) are analysed to compare and contrast cross-shore morphodynamics of the two beach types. The different behavioural characteristics of the two beach types at decadal, inter-annual and intra-annual time scales are investigated. Comparisons of beach profiles with Dean's equilibrium profile and Vellinga's erosion profile show that the Dean's profile satisfactorily represents the time mean profiles of both beach types. Statistical and Empirical Orthogonal Function (EOF) analyses confirm the generally accepted model that the inter-tidal zone is the most morphodynamically active region on a sandy beach whereas the swash zone is the most dynamic region on a mixed sand–gravel beach. The results also imply that during storms composite sand–gravel beaches may become unstable due to cutback of the upper beach while sandy beaches are more likely to be unstable as a result of beach lowering due to sediment transport from the inter-tidal zone to the sub-tidal zone during storms. EOF results also show that Milford-on-Sea beach is in a state of steady recession while the Narrabeen Beach shows a cyclic erosion–accretion variability. A multivariate technique (Canonical Correlation Analysis, CCA) shows that on the composite beach a strong correlation exists between incident wave steepness and profile response, which could be attributed to the unsaturated surf zone, whereas on the sandy beach any correlation is much less evident.

Distinguishing East and West Antarctic sediment sources using the Pb isotope composition of detrital K-feldspar

New Pb analyses of K feldspars (Kfs) from Archaean–Mesozoic crystalline rocks from across the Weddell Sea region of Antarctica show Pb isotopic compositions that vary geographically. Five distinct basement provinces are defined, each with characteristic Kfs Pb compositions, and indicate that the comparison of the Pb isotopic composition of individual detrital Kfs can be used as a sedimentary provenance tool in this region. This tool is tested on Permian sandstones deposited in a retro-arc foreland basin because the potential source regions for these sandstones, the active Palaeopacific margin arc of West Antarctica and uplifted regions of now ice-covered East Antarctica, comprise rocks with markedly different Pb isotope compositions. Pb compositions of detrital Kfs from sandstone samples collected from Dronning Maud Land suggest that their provenance was entirely from within East Antarctica, while those collected from the Theron Mountains, Coats Land, were wholly derived from the active margin of West Antarctica. Kfs Pb composition of bedrock samples is largely dependent on age and because Kfs tends to only survive a single cycle of erosion, transport, deposition and diagenesis, its provenance when compared with that determined by detrital zircon geochronology, may qualify what proportion of the more robust mineral zircon has been recycled through several sedimentary cycles. Detrital zircon analyses from a Permian sandstone from the Theron Mountains suggest that 45% of its detrital zircon was recycled from pre-existing (meta)sedimentary rocks. The detrital feldspar data also indicate that Archaean and 2.1 Ga crust, with a very different Pb isotope composition to any exposed in the Weddell Sea region, is likely to exist beneath the East Antarctic Ice sheet.

Experimental Research on High Performance Concrete under Drying-Wetting Cycles in Saline-Lake Environment

Aiming at the corrosion problem of concrete structure of bridges in Chaerhan salt lake area, the paper puts forward a new method of using multi-defense lines against salt erosion, helpful to improve the durability of concrete structures. Single factor experiment of salt erosion and a dual-action experiment of salt erosion and drying-wetting cycles were conducted, using 3 kinds of concrete specimens, including simple high performance concrete (HPC), HPC coated with waterproof material outside and HPC mixed with waterproof material. Results of experiments show that high performance concrete prepared in the experiments has good anti-corrosion performance. Moreover, HPC with multi-defense lines application effectively delays salt erosion to concrete, and lengthens service life of concrete structures in saline-lake environment.