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V. Cnudde | M. N. Boone
High-resolution X-ray Computed Tomography (HRXCT) or micro-CT (μCT) is a frequently used non-destructive 3D imaging and analysis technique for the investigation of internal structures of a large variety of objects, including geomaterials. Although the possibilities of X-ray micro-CT are becoming better appreciated in earth science research, the demands on this technique are also approaching certain physical limitations. As such, there remains a lot of research to be done in order to solve all the technical problems that occur when higher demands are put on the technique. In this paper, a review of the principle, the advantages and limitations of X-ray CT itself are presented, together with an overview of some current applications of micro-CT in geosciences. One of the main advantages of this technique is the fact that it is a non-destructive characterization technique which allows 4D monitoring of internal structural changes at resolutions down to a few hundred nanometres. Limitations of this technique are the operator dependency for the 3D image analysis from the reconstructed data, the discretization effects and possible imaging artefacts. Driven by the technological and computational progress, the technique is continuously growing as an analysis tool in geosciences and is becoming one of the standard techniques, as is shown by the large and still increasing number of publications in this research area. It is foreseen that this number will continue to rise, and micro-CT will become an indispensable technique in the field of geosciences. © 2013 Elsevier B.V.
Jun Deng | Qingfei Wang | Gongjian Li | M. Santosh
© 2014 Elsevier B.V. The Sanjiang region in SE Tibet Plateau, and the western Yunnan region in southwestern China constitute a collage of Gondwana-derived micro-continental blocks and arc terranes that were accreted together after the closure of the Paleotethys Oceans in Permo-Triassic. The lithospheric structure in Sanjiang prior to the Cenozoic was dominantly characterized by sub-parallel sutures, subduction-modified mantle and crust, Mesozoic basins between the sutures, and primary polymetallic accumulations. During the Cenozoic, intense deformation, episodic magmatism, and diverse mineralization occurred, jointly controlled by the underthrust of South China lithosphere and the subduction of Pacific plate to the east, the India-Eurasia continental collision and the subduction of Indian oceanic plate to the west. In this paper, we identify the following four main phases for the Cenozoic evolution in the Sanjiang region. (i) Subduction and rollback of Neotethyan oceanic plate before ca. 45-40. Ma caused lithosphere shortening, indicated by folding-thrusting in the shallow crust and horizontal shearing in middle crust, and multiple magmatic activities, with associated formation of Sn ore deposits in the Tengchong block, Cu polymetallic ore deposits within Mesozoic basins, and Mo and Pb-Zn ore deposits in the Cangyuan area nearby the Changning-Menglian suture. (ii) Breakoff of Neotethyan slab in 45-40. Ma in combination with the India-Eurasia continental hard collision caused the diachronous removal of the lower lithospheric mantle during 42-32. Ma, with the resultant potassic-ultrapotassic magmatism and formation of the related porphyry-skarn ore deposits along the Jinshajiang-Ailaoshan suture. (iii) Underthrusting of the South China plate resulting in the kinking of Sanjiang, expressed by block rotation, extrusion, and shearing in the southern Sanjiang during 32-10. Ma, with contemporary formation of the orogenic gold deposit along shear zones and the MVT Pb-Zn ore deposits within Mesozoic basins. (iv) Subduction of Indian oceanic plate possibly together with the Ninety East Ridge caused the local extension and volcanism in western Sanjiang, and the interplay between India-Eurasia collision and the Pacific plate subduction induced tensile stress and mantle perturbation in eastern Sanjiang from ca. 10. Ma to present. The Cenozoic tectonic process traces a continuum of lithosphere shortening, sub-lithosphere mantle removal, and lithosphere underthrusting. During the lithospheric mantle removal, the simultaneous melting of the metasomatized lithospheric mantle and juvenile lower crust with possible metal enrichment contributed to the formation of potassic-ultrapotassic intrusive rocks and related porphyry-skarn mineralization. It is proposed that the kinking in the Sanjiang region was controlled by the non-coaxial compressions of the South China block and India continent, which are much larger in size than the blocks in Sanjiang. The underthrust continental lithosphere of the South China block caused the formation of orogenic gold deposits due to the release of metamorphic fluids from the front of the underthrust zone and the development of MVT Pb-Zn deposits via fluid circulation in the farther metal-enriched Mesozoic basins. Our study reveals that the pre-Cenozoic lithospheric structure in Sanjiang played an important role in the styles of tectonic movement, the nature and spatial distribution of magmatism, and the large-scale metallogeny during the Cenozoic.
Z. T. Yao | X. S. Ji | P. K. Sarker | J. H. Tang | L. Q. Ge | M. S. Xia | Y. Q. Xi
© 2014 Elsevier B.V. Coal fly ash, an industrial by-product, is derived from coal combustion in thermal power plants. It is one of the most complex anthropogenic materials, and its improper disposal has become an environmental concern and resulted in a waste of recoverable resources. There is a pressing and ongoing need to develop new recycling methods for coal fly ash. The present review first describes the generation, physicochemical properties and hazards of coal fly ash at the global level, and then focuses on its current and potential applications, including use in the soil amelioration, construction industry, ceramic industry, catalysis, depth separation, zeolite synthesis, etc. Finally, the advantages and disadvantages of these applications, the mode of fly ash utilization worldwide and directions for future research are considered.
Sandra Arndt | B. B. Jørgensen | D. E. LaRowe | J. J. Middelburg | R. D. Pancost | P. Regnier
Quantifying the rates of biogeochemical processes in marine sediments is essential for understanding global element cycles and climate change. Because organic matter degradation is the engine behind benthic dynamics, deciphering the impact that various forces have on this process is central to determining the evolution of the Earth system. Therefore, recent developments in the quantitative modeling of organic matter degradation in marine sediments are critically reviewed. The first part of the review synthesizes the main chemical, biological and physical factors that control organic matter degradation in sediments while the second part provides a general review of the mathematical formulations used to model these processes and the third part evaluates their application over different spatial and temporal scales. Key transport mechanisms in sedimentary environments are summarized and the mathematical formulation of the organic matter degradation rate law is described in detail. The roles of enzyme kinetics, bioenergetics, temperature and biomass growth in particular are highlighted. Alternative model approaches that quantify the degradation rate constant are also critically compared. In the third part of the review, the capability of different model approaches to extrapolate organic matter degradation rates over a broad range of temporal and spatial scales is assessed. In addition, the structure, functions and parameterization of more than 250 published models of organic matter degradation in marine sediments are analyzed. The large range of published model parameters illustrates the complex nature of organic matter dynamics, and, thus, the limited transferability of these parameters from one site to another. Compiled model parameters do not reveal a statistically significant correlation with single environmental characteristics such as water depth, deposition rate or organic matter flux. The lack of a generic framework that allows for model parameters to be constrained in data-poor areas seriously limits the quantification of organic matter degradation on a global scale. Therefore, we explore regional patterns that emerge from the compiled more than 250 organic matter rate constants and critically discuss them in their environmental context. This review provides an interdisciplinary view on organic matter degradation in marine sediments. It contributes to an improved understanding of global patterns in benthic organic matter degradation, and helps identify outstanding questions and future directions in the modeling of organic matter degradation in marine sediments. © 2013 .
Merche B. Bodí | Deborah A. Martin | Victoria N. Balfour | Cristina Santín | Stefan H. Doerr | Paulo Pereira | Artemi Cerdà | Jorge Mataix-Solera
Fire transforms fuels (i.e. biomass, necromass, soil organic matter) into materials with different chemical and physical properties. One of these materials is ash, which is the particulate residue remaining or deposited on the ground that consists of mineral materials and charred organic components. The quantity and characteristics of ash produced during a wildland fire depend mainly on (1) the total burned fuel (i.e. fuel load), (2) fuel type and (3) its combustion completeness. For a given fuel load and type, a higher combustion completeness will reduce the ash organic carbon content, increasing the relative mineral content, and hence reducing total mass of ash produced. The homogeneity and thickness of the ash layer can vary substantially in space and time and reported average thicknesses range from close to 0 to 50. mm. Ash is a highly mobile material that, after its deposition, may be incorporated into the soil profile, redistributed or removed from a burned site within days or weeks by wind and water erosion to surface depressions, footslopes, streams, lakes, reservoirs and, potentially, into marine deposits.Research on the composition, properties and effects of ash on the burned ecosystem has been conducted on material collected in the field after w ildland and prescribed fires as well as on material produced in the laboratory. At low combustion completeness (typically T < 450°C), ash is organic-rich, with organic carbon as the main component. At high combustion completeness (T > 450°C), most organic carbon is volatized and the remaining mineral ash has elevated pH when in solution. It is composed mainly of calcium, magnesium, sodium, potassium, silicon and phosphorous in the form of inorganic carbonates, whereas at T > 580°C the most common forms are oxides. Ash produced under lower combustion completeness is usually darker, coarser, and less dense and has a higher saturated hydraulic conductivity than ash with higher combustion completeness, although physical reactions with CO 2 and when moistened produce further changes in ash characteristics.As a new material present after a wildland fire, ash can have profound effects on ecosystems. It affects biogeochemical cycles, including the C cycle, not only within the burned area, but also globally. Ash incorporated into the soil increases temporarily soil pH and nutrient pools and changes physical properties such as albedo, soil texture and hydraulic properties including water repellency. Ash modifies soil hydrologic behavior by creating a two-layer system: the soil and the ash layer, which can function in different ways depending on (1) ash depth and type, (2) soil type and (3) rainfall characteristics. Key parameters are the ash's water holding capacity, hydraulic conductivity and its potential to clog soil pores. Runoff from burned areas carries soluble nutrients contained in ash, which can lead to problems for potable water supplies. Ash deposition also stimulates soil microbial activity and vegetation growth.Further work is needed to (1) standardize methods for investigating ash and its effects on the ecosystem, (2) characterize ash properties for specific ecosystems and wildland fire types, (3) determine the effects of ash on human and ecosystem health, especially when transported by wind or water, (4) investigate ash's controls on water and soil losses at slope and catchment scales, (5) examine its role in the C cycle, and (6) study its redistribution and fate in the environment. © 2014 Elsevier B.V.
John A. Moody | Richard A. Shakesby | Peter R. Robichaud | Susan H. Cannon | Deborah A. Martin
Research into post-wildfire effects began in the United States more than 70. years ago and only later extended to other parts of the world. Post-wildfire responses are typically transient, episodic, variable in space and time, dependent on thresholds, and involve multiple processes measured by different methods. These characteristics tend to hinder research progress, but the large empirical knowledge base amassed in different regions of the world suggests that it should now be possible to synthesize the data and make a substantial improvement in the understanding of post-wildfire runoff and erosion response. Thus, it is important to identify and prioritize the research issues related to post-wildfire runoff and erosion. Priority research issues are the need to: (1) organize and synthesize similarities and differences in post-wildfire responses between different fire-prone regions of the world in order to determine common patterns and generalities that can explain cause and effect relations; (2) identify and quantify functional relations between metrics of fire effects and soil hydraulic properties that will better represent the dynamic and transient conditions after a wildfire; (3) determine the interaction between burned landscapes and temporally and spatially variable meso-scale precipitation, which is often the primary driver of post-wildfire runoff and erosion responses; (4) determine functional relations between precipitation, basin morphology, runoff connectivity, contributing area, surface roughness, depression storage, and soil characteristics required to predict the timing, magnitudes, and duration of floods and debris flows from ungaged burned basins; and (5) develop standard measurement methods that will ensure the collection of uniform and comparable runoff and erosion data. Resolution of these issues will help to improve conceptual and computer models of post-wildfire runoff and erosion processes. © 2013.
F. Gutiérrez | M. Parise | J. De Waele | H. Jourde
© 2014 Elsevier B.V. Karst environments are characterized by distinctive landforms related to dissolution and a dominant subsurface drainage. The direct connection between the surface and the underlying high permeability aquifers makes karst aquifers extremely vulnerable to pollution. A high percentage of the world population depends on these water resources. Moreover, karst terrains, frequently underlain by cavernous carbonate and/or evaporite rocks, may be affected by severe ground instability problems. Impacts and hazards associated with karst are rapidly increasing as development expands upon these areas without proper planning taking into account the peculiarities of these environments. This has led to an escalation of karst-related environmental and engineering problems such as sinkholes, floods involving highly transmissive aquifers, and landslides developed on rocks weakened by karstification. The environmental fragility of karst settings, together with their endemic hazardous processes, have received an increasing attention from the scientific community in the last decades. Concurrently, the interest of planners and decision-makers on a safe and sustainable management of karst lands is also growing. This work reviews the main natural and human-induced hazards characteristic of karst environments, with specific focus on sinkholes, floods and slope movements, and summarizes the main outcomes reached by karst scientists regarding the assessment of environmental impacts and their mitigation.
M. Blum | J. Martin | K. Milliken | M. Garvin
Ancient fluvial valley systems are long recognized as important features in the stratigraphic record, but emerged as a specific focus of attention with publication of first-generation sequence-stratigraphic concepts. This paper reviews current understanding of paleovalley systems from the perspective of Quaternary analogs and experimental studies.Paleovalley systems can include distinct mixed bedrock-alluvial, coastal-plain, and cross-shelf segments. Mixed bedrock-alluvial segments are long-lived, cut across bedrock of significantly older age, and have an overall degradational architecture. By contrast, coastal-plain and cross-shelf segments are non-equilibrium responses to high-frequency cycles of relative sea-level change: most coastal-plain and cross-shelf segments form as a geometric response to relative sea-level fall, as river systems cut through coastal-plain and inner shelf clinothems, and extend basinward to track the shoreline. After incision and cross-shelf extension, lateral channel migration and contemporaneous channel-belt deposition creates a valley-scale feature. Coastal-plain and cross-shelf paleovalley widths are set by the number of channel-belt sandbodies deposited during this time.Paleovalley systems play a key role in source-to-sink sediment routing. Early views included the model of incision and complete sediment bypass in response to relative sea-level fall. However, this model does not stand up to empirical, theoretical, or experimental scrutiny. Instead, there is a complex dynamic between incision, deposition, and sediment export from an evolving valley: periods of incision correspond with sediment export minima, whereas periods of lateral migration and channel-belt construction result in increased flux to the river mouth. Sediment export from evolving valleys, and merging of drainages during cross-shelf transit, play key roles in sediment transfer to the shelf-margin and genetically-linked slope to basin-floor systems. Connection between the river mouth and the shelf margin likely occurs for different periods of time depending on gradient of the river and shelf, as well as amplitude of high-frequency sea-level changes.Late Quaternary analogs and experimental studies provide an alternative sequence-stratigraphic interpretation for paleovalley systems. In coastal-plain paleovalleys, basal valley-fill surfaces meet criteria for an unconformity and a classically-defined sequence boundary: however, this surface is mostly everywhere of the same age as overlying fluvial deposits, and does not correspond to a long period of incision and sediment bypass. In cross-shelf paleovalleys, the basal contact between fluvial and deltaic or shoreface deposits is commonly interpreted as a sequence boundary, but is not an unconformity characterized by incision and sediment bypass. Instead, this surface is a facies contact that separates genetically-related fluvial and deltaic strata: the surface that correlates to the basal valley-fill surface within the coastal-plain paleovalley dips below cross-shelf prograding deltaic and/or shoreface strata, which are fed by deposition within the evolving valley itself, and should be the downlap surface.Many issues deserve attention in the future. We have stressed understanding the inherent scales and physical processes that operate during the formation and evolution of paleovalley systems. We also suggest the relative roles of allogenic forcing vs. autogenic dynamics, and the potential significance of high-frequency isostatic adjustments should be topics for future discussion. © 2012 Elsevier B.V.
V. F. Bense | T. Gleeson | S. E. Loveless | O. Bour | J. Scibek
Deformation along faults in the shallow crust ( < . 1. km) introduces permeability heterogeneity and anisotropy, which has an important impact on processes such as regional groundwater flow, hydrocarbon migration, and hydrothermal fluid circulation. Fault zones have the capacity to be hydraulic conduits connecting shallow and deep geological environments, but simultaneously the fault cores of many faults often form effective barriers to flow. The direct evaluation of the impact of faults to fluid flow patterns remains a challenge and requires a multidisciplinary research effort of structural geologists and hydrogeologists. However, we find that these disciplines often use different methods with little interaction between them. In this review, we document the current multi-disciplinary understanding of fault zone hydrogeology. We discuss surface- and subsurface observations from diverse rock types from unlithified and lithified clastic sediments through to carbonate, crystalline, and volcanic rocks. For each rock type, we evaluate geological deformation mechanisms, hydrogeologic observations and conceptual models of fault zone hydrogeology. Outcrop observations indicate that fault zones commonly have a permeability structure suggesting they should act as complex conduit-barrier systems in which along-fault flow is encouraged and across-fault flow is impeded. Hydrogeological observations of fault zones reported in the literature show a broad qualitative agreement with outcrop-based conceptual models of fault zone hydrogeology. Nevertheless, the specific impact of a particular fault permeability structure on fault zone hydrogeology can only be assessed when the hydrogeological context of the fault zone is considered and not from outcrop observations alone. To gain a more integrated, comprehensive understanding of fault zone hydrogeology, we foresee numerous synergistic opportunities and challenges for the discipline of structural geology and hydrogeology to co-evolve and address remaining challenges by co-locating study areas, sharing approaches and fusing data, developing conceptual models from hydrogeologic data, numerical modeling, and training interdisciplinary scientists. © 2013 .
L. J. Bracken | J. Wainwright | G. A. Ali | D. Tetzlaff | M. W. Smith | S. M. Reaney | A. G. Roy
For effective catchment management and intervention in hydrological systems a process-based understanding of hydrological connectivity is required so that: i) conceptual rather than solely empirical understanding drives how systems are interpreted; and ii) there is an understanding of how continuous flow fields develop under different sets of environmental conditions to enable managers to know when, where and how to intervene in catchment processes successfully. In order to direct future research into process-based hydrological connectivity this paper: i) evaluates the extent to which different concepts of hydrological connectivity have emerged from different approaches to measure and predict flow in different environments; ii) discusses the extent to which these different concepts are mutually compatible; and iii) assesses further research to contribute to a unified understanding of hydrological processes. Existing research is categorised into five different approaches to investigating hydrological connectivity: i) evaluating soil-moisture patterns (soil-moisture connectivity); ii) understanding runoff patterns and processes on hillslopes (flow-process connectivity); iii) investigating topographic controls (terrain-connectivity) including the impact of road networks on hydrological connectivity and catchment runoff; iv) developing models to explore and predict hydrological connectivity; and v) developing indices of hydrological connectivity. Analysis of published research suggests a relationship between research group, approach, geographic setting and the interpretation of hydrological connectivity. For further understanding of hydrological connectivity our knowledge needs to be developed using a range of techniques and approaches, there should be common understandings between researchers approaching the concept from different perspectives, and these meanings need to be communicated effectively with those responsible for land management. © 2013.
Jianhua Li | Yueqiao Zhang | Shuwen Dong | Stephen T. Johnston
The Cretaceous tectonic evolution of South China is characterized by widespread extensional basin and dome generation, voluminous magma intrusion/eruption and associated polymetallic mineralization, all of which are of world-wide interests that have stimulated the attention of geologists for more than half a century. Due to the lack of a comprehensive understanding of regional tectonic evolution and geodynamics of South China, many controversies regarding the nature and origin of these features remain. This paper attempts to make a review by synthesizing existing structural, petrological, geochronological and geochemical data of the Cretaceous structures and magmas, which guides us to propose a three-stage tectono-thermal evolutionary history of South China during the Cretaceous period. The earliest Cretaceous (145-137. Ma) tectonic stage was characterized by syn-orogenic shortening deformation and metamorphism under a NW-SE compressional setting, which generated voluminous porphyry Cu-Au ore-bearing adakitic rocks in the Lower Yangtze River Belt and gneissic granites in the coastal area. Its geodynamic origin was interpreted as combined effects of the Pacific-Izanagi ridge subduction beneath the Lower Yangtze River Belt and the Pacific subduction beneath the Cathaysia Block. This syn-orogenic shortening stage was followed by a post orogenic stage (136-86. Ma) comprising two episodes of alternate extensional and shortening events. The extension (136-118. Ma) in the earlier episode was dominated by a NW-SE extensional regime, it led to significant taphrogenesis manifested by large-scale extensional basins and voluminous magma intrusion/eruption; this extensional event was associated with a combination of the slab window opening during the ridge subduction and the rollback of the subducted Pacific slab. The subsequent NW-SE transpressional event led to cessation of active marginal magmatism and resulted in tectonic inversion of previous rift basins; this transpression lasted from 117. Ma to 108. Ma, and its driving mechanism was attributed to the collision between the eastern Asian margin and the West Philippine Block. The extension (107-86. Ma) in the later episode was dominated by a WNW-ESE extensional regime, which led to a second phase of basin subsidence and produced numerous A- and I-type granites and bimodal volcanoes. The tectonic regime then changed at ca. 85. Ma to WNW-ESE-oriented transpression, causing inversion of the Late Cretaceous rift basins and cessation of extension-related magmatism. The change of stress field from WNW-ESE extension to WNW-ESE transpression was related to the variations of the subducted slab dynamics, i.e., the transition from either the ESE-ward retreat to WNW-ward subduction of the Pacific slab, or the alternate stress during slab break-off. During the latest Cretaceous, a drastic change of regional tectonic stress orientation from WNW-ESE to N-S occurred in South China, the third stage predominated by N-S extension was developed, which caused a new phase of regional crustal subsidence along the youngest E-W trending extensional structures. © 2014 Elsevier B.V.
Joris De Vente | Jean Poesen | Gert Verstraeten | Gerard Govers | Matthias Vanmaercke | Anton Van Rompaey | Mahmood Arabkhedri | Carolina Boix-Fayos
Assessments of the implications of soil erosion require quantification of soil erosion rates (SE) and sediment yield (SSY) at regional scales under present and future climate and land use scenarios. A range of models is available to predict SE and SSY, but a critical evaluation of these models is lacking. Here, we evaluate 14 models based on 32 published studies and over 700 selected catchments. Evaluation criteria include: (1) prediction accuracy, (2) knowledge gain on dominant soil erosion processes, (3) data and calibration requirements, and (4) applicability in global change scenario studies. Results indicate that modelling of SE and SSY strongly depends on the spatial and temporal scales considered. In large catchments ( > 10,000km 2 ), most accurate predictions of suspended sediment yield are obtained by nonlinear regression models like BQART, WBMsed, or Pelletier's model. For medium-sized catchments, best results are obtained by factorial scoring models like PSIAC, FSM and SSY Index, which also support identification of dominant erosion processes. Most other models (e.g., WATEM-SEDEM, AGNPS, LISEM, PESERA, and SWAT) represent only a selection of erosion and sediment transport processes. Consequently, these models only provide reliable results where the considered processes are indeed dominant. Identification of sediment sources and sinks requires spatially distributed models, which, on average, have lower model accuracy and require more input data and calibration efforts than spatially lumped models. Of these models, most accurate predictions with least data requirements were provided by SPADS and WATEM-SEDEM. Priorities for model development include: (1) simulation of point sources of sediment, (2) balancing model complexity and the quality of input data, (3) simulation of the impact of soil and water conservation measures, and (4) incorporation of dynamic land use and climate scenarios. Prediction of the impact of global change on SE and SSY in medium sized catchments is one of the main challenges in future model development. No single model fulfils all modelling objectives; a further integration of field observations and different model concepts is needed to obtain better contemporary and future predictions of SE and SSY. © 2013 Elsevier B.V.
Dirk Scheuvens | Lothar Schütz | Konrad Kandler | Martin Ebert | Stephan Weinbruch
This paper presents a review of bulk compositional data of northern African dust and its potential source sediments and includes elemental, isotope and mineralogical data. Northern African dust represents about one half of the total global atmospheric mineral dust burden, and its uplift, transport and deposition have strong impacts on climate and various terrestrial and marine ecosystems. The chemical data set shows, that an 'average northern African dust' exhibits comparable Si, Fe and Mn contents with respect to the average composition of the upper continental crust, is slightly depleted in the alkali metals K and Na, and enriched in Ti and P. However, the complete data set yields clear evidence that northern African dust and its source sediments are compositionally heterogeneous on a regional scale and that this heterogeneity can be used to differentiate between major potential source areas on the basis of so-called source markers. An evaluation of these compositional fingerprints shows that the following parameters and especially their combination are effective in the discrimination of the most active source areas in northern Africa: ratio of (Ca+Mg)/Fe [wt.%], calcite (or carbonate) content, palygorskite occurrence and abundance, illite/kaolinite ratio, E Nd (0) value, and 87 Sr/ 86 Sr ratio. For example, the data set corroborates previous ideas, which assign carbonate-, illite- and palygorskite-rich mineral dusts to north(west)ern source regions. Because most of the above listed source markers do not change substantially during transport, even far-traveled dusts may be assigned to specific potential source areas in northern Africa. Some limitations of the presented data set are also discussed. Our compilation reveals some substantial gaps in the knowledge of the composition of source sediments and mineral dusts from important potential source areas that should be filled in the future.The here compiled data set can be used as a reference frame, when incorporating the composition of source sediments (e.g., mineralogy) into global or regional dust transport models and can be compared with source analysis by remote sensing or back-trajectory analysis. However, source apportionment studies supported by our data set will not only be useful for actual dust samples, but will also be helpful for the understanding of paleo-wind direct ions and hence paleo-climatological conditions through the investigation of Quaternary eolian sediments deposited in and around northern Africa. © 2012 Elsevier B.V.
A. J. Koiter | P. N. Owens | E. L. Petticrew | D. A. Lobb
Sediment fingerprinting is a technique that is increasingly being used to improve the understanding of sediment dynamics within river basins. At present, one of the main limitations of the technique is the ability to link sediment back to their sources due to the non-conservative nature of many of the sediment properties. The processes that occur between the sediment source locations and the point of collection downstream are not well understood or quantified and currently represent a black-box in the sediment fingerprinting approach. The literature on sediment fingerprinting tends to assume that there is a direct connection between sources and sinks, while much of the broader environmental sedimentology literature identifies that numerous chemical, biological and physical transformations and alterations can occur as sediment moves through the landscape. The focus of this paper is on the processes that drive particle size and organic matter selectivity and biological, geochemical and physical transformations and how understanding these processes can be used to guide sampling protocols, fingerprint selection and data interpretation. The application of statistical approaches without consideration of how unique sediment fingerprints have developed and how robust they are within the environment is a major limitation of many recent studies. This review summarises the current information, identifies areas that need further investigation and provides recommendations for sediment fingerprinting that should be considered for adoption in future studies if the full potential and utility of the approach are to be realised. © 2013 Elsevier B.V.
E. J. Rohling | G. Marino | K. M. Grant
© 2015 Elsevier B.V. Mediterranean sapropels are layers with elevated organic carbon concentrations that contrast with surrounding sediments, which are organic poor. Sapropels occur (quasi-) periodically in sedimentary sequences of the last 13.5 million years, and exist both in the eastern and western Mediterranean sub-basins. They have been the subject of extensive study, based on records from both short (conventional) and long (Ocean Drilling Program) sediment cores, and from a wide variety of uplifted marine sediment sequences on the basin margins and islands. Previous syntheses in the 1990s and 2000s have discussed how the formation of sapropels is commonly ascribed to deep-sea anoxia, enhanced export productivity, or a combination of these effects. However, a wealth of new evidence and insights has emerged during the past 1-2 decades, based on traditional and novel proxy data as well as modelling, which has revealed intriguing new aspects and nuances to the reconstructed conditions. Hence, it is timely to present a new synthesis of current understanding of the processes behind the formation of sapropels, which have over the past decade also become a matter of commercial interest in sub-salt hydrocarbon exploration. In this review, we present a context of modern Mediterranean climate and oceanography, followed by an integrated assessment of the growing understanding of climatological and ocean circulation changes that were associated with sapropel deposition. We find that sapropels predominantly formed during (astronomically timed) episodes when climatic and oceanographic conditions and ecological responses broadly preconditioned the basin for sapropel deposition. There is strong correspondence with times of monsoon intensification, fuelling runoff from North Africa into the Mediterranean Sea, while preconditioning due to sea-level rise, and regional precipitation and runoff may have contributed as well. Within these broad episodes of surface buoyancy gain and resultant decline in deep-water ventilation, specific deposition under dysoxic, anoxic, or even euxinic conditions occurred within a clearly dynamic system that was characterised by complex spatial and depth-dependent patterns/gradients, with distinct temporal variability on (at least) decadal to centennial-millennial timescales. In the final section, we evaluate the implications of different modes of deep-water removal from silled basins, to investigate why sapropels are more frequently and often more intensely developed in the eastern Mediterranean than in the western Mediterranean.