Mineral Magnetic Properties Research Articles

Confluence-based suspended sediment fingerprinting: an exploratory approach to determining source to sink sediment contributions in the Tsitsa River catchment, Eastern Cape, South Africa

ABSTRACT In the Tsitsa River catchment of the Eastern Cape Province, South Africa, concerns regarding the sedimentation of a proposed large, multipurpose, in-channel water storage scheme prompted investigations of sub-catchment suspended sediment loads and yields. Confluence-based fingerprinting and source apportionment was undertaken to explore whether this simple approach could identify relative sub-catchment contributions to downstream sediment loads, supplementing modelling and direct sampling. In November 2018, fine sediment sequestered in bed substrates was sampled above and below confluences, using a resuspension technique. The < 63 µm sample fraction underwent analysis of mineral magnetic properties, gamma emitting radionuclide activities and geochemistry to identify suitable tracers. Conservatism and range tests were used to select different combinations of composite fingerprints at seven confluences. Bivariate source apportionment using an unmixing model showed that the approach could be used as a preliminary means of determining relative sub-catchment sediment contributions. Catchment characteristics such as geology and land cover, as well as land tenure and management, were considered as explanatory factors for the difference in sediment contributions. The results for most sub-catchments were broadly similar to those from other studies. Shortcomings of this approach included the reliance on a single sampling effort, and uncertainty associated with sub-catchment sediment transport and residence times.

Mineral magnetic properties of urban forest soils tailored to soil quality indicator

Ecosystem surveys reveal the benefits to society, provided by the natural environment, which in turn is chiefly regulated by the geodiversity. Thus, physico-chemical processes regulating the solid rock/sediment response to environmental changes comprise an important part in the assessment of natural ecosystems. Environmental magnetism provides a wide set of field and laboratory data able to discover natural and anthropogenic processes affecting different environmental compartments. Despite this, geosciences and environmental magnetism in particular, are under-represented in ecosystem assessment tools due to the lack of unified and clearly articulated application template. In this study, we propose a new mineral magnetic indicator of soil’s quality, based on detailed appraisal of field- and laboratory mineral magnetic characteristics of a collection of 453 urban topsoil samples. Field magnetic susceptibility (Kfield) and laboratory measurements of magnetic parameters revealed that soil magnetism reflects sensitively soils affected by vehicle traffic and park’s alleys foot load from semi-natural soil. Geochemical analyses of the content of Potentially Toxic Elements (PTEs) on a sub-set of samples was used for magnetic data validation. Correlation analysis showed strong positive link between magnetic parameters and the main PTEs, the strongest being obtained between magnetic susceptibility and the complex pollution load index (PLI). Factor analysis suggested that three factors account for the 74% of data variability. They were assigned to: 1) traffic emissions, 2) pedogenic contribution and 3) lithogenic input plus anthropogenic organic waste additions. Novel mineral magnetic Indicator (MAG) was defined, combining information on composition, concentration and grain size of ferrimagnetic iron oxides, using scored contributions from five magnetic parameters and grain size sensitive ratios. Evaluation of the spatial MAG map showed its suitability as a complex indicator of soils’ contamination with PTEs. Kfield reflected sensitively overall anthropogenic load not necessarily related to PTEs contamination but also to foot trampling and application of fertilizers.

Mineral magnetic properties of surface soils from the Broknes and Grovnes Peninsula, Larsemann Hills, East Antarctica

This study presents the mineral magnetic, particle size, and organic content data of surface soils from Larsemann Hills, East Antarctica. The analysis of isothermal remanent magnetization and the high specific magnetic susceptibility values –mean (±S.D.) values of 117.7 (±175.0) × 10−8m3kg−1 for Broknes Peninsula and of 330.9 (±217.4) × 10−8m3kg−1 for Grovnes Peninsula– indicate high concentrations of low-coercivity magnetic minerals. The magnetic minerals are coarse-grained in the multidomain and pseudo-single domain range, and the significant correlation between some magnetic parameters suggests the dominant control of multidomain grains. The remanent acquisition coercivity H1/2 shows mean (±S.D.) values of 38.2 (±4.9) for Broknes and 38.3 (±3.7) mT for Grovnes soils suggesting magnetite dominance. The soils lie in the sand and loamy sand textural classes, and the concentration of organic matter is very low. Values of percentage frequency-dependent susceptibility indicate insignificant proportions of superparamagnetic grains, and therefore no significant evidence for pedogenic magnetic minerals was observed in these soils. The magnetic signal of Larsemann Hills soils was primarily terrigenous with no contributions from bacterial magnetite, authigenic greigite and anthropogenic magnetic minerals.

Mineral magnetic properties of ultisol profiles from tropical southern India

Mineral magnetic properties of ultisol profiles from tropical southern India

Holocene sedimentary history of South Danamandıra Lake: a peatland in west of İstanbul, Çatalca Peninsula, NW Turkey

This study investigates the sedimentological evolution of the South Danamandıra Lake (SDL) lake in Çatalca Peninsula, 70 km west of İstanbul, using Georadar data and multiproxy analyses of five sediment cores. The lake is a 1.3-m deep, endorheic freshwater peatland, heavily colonised by common reed (Phragmites sp.). The multiproxy core investigations include a lithological core description and environmental magnetism, physical properties (gamma density and magnetic susceptibility), geochemical elemental, pollen and radiocarbon dating analyses. The lithological sequence in the lake consists of an upper peat unit and a lower sand-silt-clay unit. The peat unit is characterized by lower magnetic susceptibility, density and lithophile elements (K, Fe, Ti, and Zr) concentrations than the sand-silt-clay unit. Overall interpretation of the multiproxy data and the age-depth model suggest that the SDL was formed in a shallow depression of a fluvial channel at ca 10.9 cal kyr BP, and became a eutrophic lake at 8.1 cal kyr BP during the early Holocene warm period. Redox-sensitive element (i.e. Mn) distribution and mineral magnetic properties indicate that the peat unit has accumulated under anoxic conditions below a thin oxic surficial layer. Increase in the Taraxacum, Asteraceae, and Poaceae pollen percentages, together with high siliciclastic inputs in the lake, indicate that anthropogenic influence in the area started at 5.4 cal kyr BP.

OSL-dating of the Pleistocene-Holocene climatic transition in loess from China, Europe and North America, and evidence for accretionary pedogenesis

Loess deposits intercalated by paleosols are detailed terrestrial archives of Quaternary climate variability providing information on the global dust cycle and landscape dynamics. Their paleoclimatic significance is often explored by quantifying their mineral magnetic properties due to their sensitivity to local/regional hydroclimate variability. Detailed chronological assessment of such regional proxy records around the climatic transitions allow a better understanding of how regional records react to major global climatic transitions such as the Pleistocene-Holocene climatic transition. Logs of high-resolution magnetic susceptibility and its frequency dependence were used as paleoclimatic proxies to define the environmental transition from the last glacial loess to the current interglacial soil as reflected in nine loess-paleosol sequences across the northern hemisphere, from the Chinese Loess Plateau, the southeastern European loess belt and the central Great Plains, USA. The onset of increase in magnetic susceptibility above typical loess values was used to assess the onset of, and developments during, the Pleistocene-Holocene climatic transition. High-resolution luminescence dating was applied on multiple grain-sizes (4–11 μm, 63–90 μm, 90–125 μm) of quartz extracts from the same sample in order to investigate the timing of Pleistocene-Holocene climatic transition in the investigated sites. The magnetic susceptibility signal shows a smooth and gradual increase for the majority of the sites from the typical low loess values to the interglacial ones. The initiation of this increase, interpreted as recording the initiation of the Pleistocene-Holocene climatic transition at each site, was dated to 14–17.5 ka or even earlier. Our chronological results highlight the need of combining paleoclimatic proxies (magnetic susceptibility) with absolute dating when investigating the Pleistocene-Holocene climatic transition as reflected by the evolution of this proxy in order to avoid chronostratigraphic misinterpretations in loess-paleosol records caused by simple pattern correlation. The detailed luminescence chronologies evidence the continuity of eolian mineral dust accumulation regardless of glacial or interglacial global climatic regimes. Coupled with magnetic susceptibility records this indicates that dust sedimentation and pedogenesis act simultaneously and result in a non-negligible accretional component in the formation of Holocene soils in loess regions across the Northern Hemisphere. The luminescence ages allowed the modeling of accumulation rates for the Holocene soil which are similar for European, Chinese and U.S.A. loess sites investigated and vary from 2 cm ka −1 to 9 cm ka −1 . While accretional pedogenesis has often been implicitly or explicitly assumed in paleoclimatic interpretation of loess-paleosol sequences, especially in the Chinese Loess Plateau, our luminescence data add direct evidence for ongoing sedimentation as interglacial soils formed. • High-resolution magnetic susceptibility record as paleoclimate proxy. • High-resolution luminescence dating applied on multiple quartz fractions. • Initiation of magnetic susceptibility enhancement dated prior to ~11.7 ka. • Continuous dust accumulation during Pleistocene-Holocene transition and in Holocene. • Accretional Holocene soils in European, Chinese Loess Plateau and US loess sites.

Mineral magnetic properties of loess–paleosol couplets of northern Serbia over the last 1.0 Ma

AbstractWe conducted the first detailed mineral magnetic investigation of more than nine loess–paleosol couplets of the composite Titel-Stari Slankamen loess section in Serbia, which provides one of the longest and most complete terrestrial record of paleoclimatic changes in Europe since ~1.0 Ma. The results show that the ferrimagnetic mineral assemblage of the loess units is dominated by partially oxidized multidomain (MD) and pseudo-single domain (PSD) magnetite; however, with an increasing degree of pedogenesis, the eolian contribution is gradually masked by pedogenic superparamagnetic(SP) and single-domain (SD) ferrimagnets (mainly maghemite). The overall consistency of ferrimagnetic grain-size parameters indicates an absence of dissolution of the fine-grained ferrimagnetic fraction despite changes in climate regime over the past 1.0 Ma. The variations of normalized dJ/dT@120Kand normalized χheating@530°Creflect a long-term stepwise increase in aridity during glacials with a major step at ~0.6–0.5 Ma, over the last 1.0 Ma. Overall, the results provide an improved basis for the future use of the magnetic properties of Serbian loess deposits for paleoclimatic reconstruction.

Assessing anthropogenic contribution in highly magnetic forest soils developed on basalts using magnetic susceptibility and concentration of elements

Mineral magnetic properties are sensitive indicators for evaluating environmental changes, including environmental pressure caused by atmospherically deposited anthropogenic magnetic particles. The most commonly and easily measured magnetic parameter of soils is magnetic susceptibility, which reflects the combined ferromagnetic minerals of lithogenic, pedogenic, and anthropogenic origins. In volcanic soils rich in ferrimagnetic minerals, unfortunately, contributions of pedogenic and anthropogenic origins are masked by the lithogenic contribution. More study is therefore needed of soils developed on highly magnetic lithologies. This work aimed to determine links between magnetic susceptibility and concentration of potentially toxic elements derived from anthropogenic activities in soil (Aluandic Andosols) developed from highly magnetic parent material in a locality where contamination is not expected. The approach is based on relationships between magnetic properties and geochemical signatures of the investigated soils. Magnetic properties are represented by mass-specific magnetic susceptibility (χ) and frequency-dependent magnetic susceptibility (χFD%). Geochemical signatures are represented by concentrations of the elements Fe, Si, Ti, Zr, Sr, Al, Nb, Mn, Ca, Rb, K, P, Zn, S, Pb, Cr, V, Ni, Cu, and As; pH in H2O; soil organic carbon content; and granulometry. Soil contamination was evaluated using two indexes: enrichment factor and geo-accumulation index. Our findings show that χFD% correlates with presence of the toxic elements S and Pb, derived from human activities, while χ exhibits strong correlation with elements Al, Ti, V, and Fe, reflecting natural origin of parent material. In case of soils with well-developed humus horizon, χFD% can be used as a proxy parameter for identifying anthropogenic influence. Our findings are beneficial also for archaeologists using magnetic susceptibility of soils as a link to chemical signatures of past settlement activities.

Mineral Magnetic Characterization of High‐Latitude Sediments From Lake Levinson‐Lessing, Siberia

AbstractLevinson‐Lessing Lake in northern Central Siberia is a sedimentary archive characterized by continuous, widely constant sedimentation at high rates (0.7 m ka−1 for &gt;32 ka). This study provides the first evidence of the suitability of the lake′s sediments for paleomagnetic analyses using the 46‐m‐long core Co1401. Although the lowermost 8 m are disturbed, the upper 38 m of Co1401 provide the preconditions for an exceptional, high‐resolution paleomagnetic record located within the tangent cylinder of the inner core. High‐resolution analyses of magnetic susceptibility, anhysteretic remanent magnetization, isothermal remanent magnetization, and hysteresis parameters show largely uniform mineral magnetic properties. First‐order reversal curves indicate magnetite particles in pseudo‐single domain state are the main remanence carrier, supplemented by single‐domain particles, originating likely from magnetotactic bacteria. Above 6.7 m, the bulk magnetic mineralogy is slightly harder than below and initial greigite formation occurs. However, the main remanence carriers are still of detrital origin.

A 43-ka mineral magnetic record of environmental variations from lacustrine sediments of Schirmacher Oasis, East Antarctica

Glacial-interglacial climatic and environmental variations recorded in lake-bed sediments of Schirmacher Oasis (SO), East Antarctica, are rare; limited data exist on the past behavior of the East Antarctic Ice Sheet (EAIS). In this work, we present the mineral magnetic properties of a radiocarbon-dated sediment core, spanning the past 43,000 years, from a land-locked lake L-49 in SO. We also performed Scanning Electron Microscopic-Energy Dispersive X-ray Spectroscopic (SEM-EDS) studies on magnetic extracts to confirm the magnetic mineralogy. The values of magnetic susceptibility (χlf) and saturation isothermal remanent magnetization (SIRM) are relatively low during the Holocene but high during the last glacial period. Sediments of the last glacial period are composed mainly of coarse-grained (multi-domain - MD) magnetite/titanomagnetite (high values of S20 – an MD proxy, low susceptibility of anhysteretic remanent magnetism (χARM)/SIRM ratio values and high S-ratio values) indicating a stronger intensity of physical weathering in the Lake L-49 catchment. The mineralogy is confirmed by SEM-EDS data for magnetic extracts. Principal Component Analysis (PCA) of the data suggests three processes affecting magnetic properties of the lake sediments, i.e., ferrimagnetic input, biogenic processes and aeolian input. During deglaciation, a shift in the magnetic properties is documented: a decrease in χlf values from 18.6 cal ka BP onwards suggests melting of the snow and ice in the catchment thus leading to a significant production of fine-grained iron oxide minerals. At ~12.77 cal ka BP, high values of χlf and S20 ratio indicates cooling which is related to the Antarctic Cold Reversal (ACR). The Early Holocene Climate Optimum is distinctly imprinted in our record as a sudden decrease in χlf values and an increase in magnetic grain size ratio values (indicating finer iron oxide grains), suggesting a rapid thawing of the ice-sheet in response to a warm climate. The Mid-Holocene Hypsithermal (from 5.8 to 3.5 cal ka BP) and Neoglaciation (3.6 cal ka BP onwards) that are evident in this study correspond with reconstructions from lake and marine sediment, and ice-core records from Antarctica.

Magnetic signature of sewage polluted river sediments

The present study was designed to characterize the magnetic proxy for sewage-related pollution from river sediments. A suite of mineral magnetic analyses including low-field magnetic susceptibility, isothermal remanent magnetization (IRM) acquisition and demagnetization, back-field IRM treatment, and thermal demagnetization of composite IRMs are carried out for topsoil samples collected from river sediments in Daejeon, South Korea. A 350-m long in situ profile of magnetic susceptibility shows a background mean magnetic susceptibility of 22.4 ± 5.6 × 10−5 SI. The coercivity spectra display dual peaks of lower- and higher-coercivity fractions. The predominance of magnetic signal with maximum unblocking temperatures of 580 °C points to magnetite as the sole magnetic mineral. Hence the lower- and higher-coercivity fractions correspond to coarse-grained and fine-grained magnetite, respectively. Extraordinarily high magnetic susceptibility was observed from BTC02, near to the sewage discharge point. However, its mineral magnetic properties and particle morphologies are not different to those of other soil samples. Then, it is apparent that a high magnetic susceptibility simply reflects the high concentration of magnetites in BTC02. It is likely that a continuous discharge of heavy metal enriched water at the discharging point concentrated significant amount of magnetic particles. It is fortunate that anomalously high magnetic susceptibility (by implication heavy metal concentrations) diminished only several meters away from the discharge point. Perhaps, influences of anthropogenic magnetite were diluted as the high magnetic phases were washed away from the water cycles along the river. In practice, it can be proposed that a periodic replacement of soils near the sewage discharge point is efficient to reduce the heavy metal concentrations.

Imprints of paleo-environmental conditions and human activities in mineral magnetic properties of fired clay remains from Neolithic houses

Fire as a global phenomenon plays crucial role in the Earth’s climate feedbacks and forcing. However, human’s influence is becoming increasingly important during the Anthropocene epoch. Burnt Neolithic houses are among the most impressive remains from fire-related ancient human activities. Mineral magnetic properties and firing temperature estimates using magnetic susceptibility method were carried out on a collection of burnt clay remains from house destructions originating from 18 Neolithic sites from Bulgaria. All of the sites/dwellings ended their existence after extensive fire. The general aim of the study was to explore the mineral magnetic properties of fired clay materials against the most important environmental factors. The main magnetic minerals identified in the burnt structures were magnetite, maghemite and hematite, as well as recently reported in several studies ε-Fe2O3. The latter evidences high intensity fire since this specific mineral can be synthesized at temperatures exceeding 900 °C. Magnetic susceptibility and percent frequency dependent magnetic susceptibility at site level were considered in relation to the climatic conditions, as defined in the published anthracological studies involving most of the sites. The major difference in lithology of the outcropping rock formations between North and South Bulgaria may influence variations in magnetic enhancement of the burnt clay across the sites at similar other conditions. Firing temperature estimates vary in wide range – between 580 °C and 1050 °C. Estimated average firing temperatures at site’s level showed higher values in Early Neolithic sites (Tfire average = 815 °C) as compared to Late Neolithic ones (Tfire average = 746 °C and 713 °C). We suggest that possible hypotheses for the trend observed could be: difference in climate regimes across the territory, leading to different “fire weather”; or difference in the vegetation fuel used in house construction; and intentional burning of Early Neolithic houses.

High-resolution palaeomagnetic record from Sea of Marmara sediments for the last 70 ka

SUMMARYMagnetostratigraphic and geochemical analyses were performed on two sediment cores recovered from the Sea of Marmara to investigate geomagnetic field variations over the last 70 ka. A chronology for each of the two cores was developed from eight AMS 14C datings, tephrochronology, and tuning of Ca concentrations with stadials and interstadials observed in Greenland ice core oxygen isotope data. Based on the age models, cores MD01–2430 and MRS-CS19 reach back to 70 and 32 ka, respectively. High average sedimentation rates of 43 cm kyr–1 for core MD01–2430 and 68 cm kyr–1 for core MRS-CS19 allow high-resolution reconstruction of geomagnetic field variations for the Sea of Marmara. Mineral magnetic properties are sensitive to glacioeustatic sea level changes and palaeoclimate variations in this region, reflecting the variable palaeoenvironmental conditions of the Sea of Marmara during last 70 ka. Despite the impairment of the palaeomagnetic record in some stratigraphic intervals due to early diagenesis, relative palaeointensity variations in the Sea of Marmara sediments correlate well with similar records derived from other regions, such as the nearby Black Sea and the GLOPIS-75 stack. The directional record derived from the Sea of Marmara cores exhibits typical palaeosecular variation patterns, with directional anomalies at 41 and 18 ka, representing the Laschamps and postulated Hilina Pali excursions, respectively. Both directional anomalies are also associated with palaeointensity minima. A further palaeointensity minimum at 34.5 ka is likely related to the Mono Lake excursion, with no directional deviation documented in the Sea of Marmara palaeomagnetic record so far.

Rock magnetics of carbonate systems–investigating palaeodune archives on Fuerteventura (Canary Islands)

ABSTRACTThe mineral magnetic properties of Pleistocene aeolian dune sands from the island of Fuerteventura (Canary Islands, Spain) were studied in order to reconstruct the palaeoenvironmental evolution of Pleistocene climates during their formation. The palaeodunes on Fuerteventura mainly consist of carbonate sands admixed with dust and material of volcanic origin. Due to the low magnetic background caused by the diamagnetic character of carbonate sands, these archives offer a lot of potential for environmental magnetic studies to detect the imprint of dust, volcanic material and paedogenesis. Four sections of alternating palaeosurface–aeolianite sequences in palaeodune fields have been analysed by means of extensive rock magnetic measurements. These Quaternary archives consist of deposits originating from different sources. I. material blown from the shallow shelf, II. material of volcanic origin, and III. long‐range transported dust. The rock magnetic findings enable a more detailed interpretation of the palaeosurfaces within the sequences. We are able to differentiate semiquantitatively between the different source materials on one hand and to distinguish on the other hand those from soil‐forming processes. Soil formation is only weakly developed in the dust imprints in the palaeosol aeolianite sequences, linked to sparse vegetation cover during the Pleistocene on Fuerteventura.

Mineral Magnetic Characterization of Archeological Potsherds:An Example from the Deccan Province, Western Maharashtra, India

The ancient (archaeological) and modern potsherds sourced from Deccan basaltic soils and sediments at selected sites in the Bhima and Godavari river basins of the western Maharashtra, India, show characteris-tic mineral magnetic properties. High magnetic sus-ceptibilities (χ lf ) for the Deccan-sourced sherds enable their distinction from other sources in the region. The modern pottery sourced from Deccan soils shows sig-nificant lower χ lf than ancient pottery in the region, which further shows lower χ lf than the associated soils (/sediments) due to successive removal of detrital grains as a function of improvement in the pre-processing techniques. The ancient and modern pot-teries show higher superparamagnetic content that is otherwise absent in the source, suggesting its neo-formation during firing. High hematite content in modern pottery relative to ancient pottery further in-dicates higher oxidative firing in the former. Based on close examination of Isothermal Remanence Magneti-zation (IRM) acquisition rates, we suggest the ratios: IRM 1.8 mT /IRM 0.3–0.025 mT and HIRM/Soft IRM along with other routine mineral magnetic parameters to esti-mate the relative degree of oxidative heating, source discrimination and the levels of pre-processing of raw material amongst the Deccan-sourced pottery. The present approach being rapid and economic, a large quantitative database can be generated from the pot-sherds for detailed characterization of these archaeo-logical materials.

Relationship between mineral magnetic properties and soil textural parameters

The study analyzed the relationship between mineral magnetic properties and particle size in order to determine the suitability of magnetic measurements to serve as particle size proxy for urban top soils samples collected from Jalingo, NE Nigeria. Pearson correlation analyses between mineral magnetic parameters (χlf, χfd%, χARM, SIRM, Soft IRM, ARM/SIRM) and particle size properties (PM2.5, PM10, clay, silt and sand) are reported. Results indicate that each particle size class shows different strength of correlation with magnetic parameters, implying that each particle class contains a proportion of magnetic minerals. For the whole data set (n = 154), χfd%, χARM and ARM/SIRM show significant positive correlation with the fine size fractions (PM2.5, PM10, clay and silt) but negatively correlated with the sand proportion, while χlf, SIRM and Soft IRM exhibit contrasting relationship. Of all the magnetic parameters, the magnetic parameters indicating fine-grained ferrimagnetic minerals (ARM/SIRM and χARM) have the strongest and most significant correlations. The nature of the magneto-particle size relationship is different when examined in terms of land use. The fact that magnetic properties and textural parameters have strong relationship indicates that magnetic methods could be considered a potential particle size proxy in Jalingo. However, since the relationship does not follow predictable and consistent patterns of other studies in top soils and sedimentary settings, it brings to fore the non-universality of the method. Hence, the type of relationship existing between magnetic and particle size properties in an environmental setting must be determined before applying the magnetic method as particle size proxy.

Proxy mineral magnetic and elemental analyses for 2004 tsunami impact deposit along the Muttukadu backwater, East Coast of India: Scope of the palaeotsunami studies

Following the line of approach enumerated in the tsunami toolkit of Chagué-Goff et al. (2011), ‘Expanding the proxy toolkit to help identify past events - Lessons from the 2004 Indian Ocean Tsunami and the 2009 South Pacific Tsunami, Earth Sci. Rev. 107 (1–2), 107–122’, measurements of elemental and mineral magnetic properties coupled with textural parameters have been used to evaluate the 2004 Indian Ocean Tsunami (IOT) induced sediments on the Muttukadu backwaters, East Coast of India. To investigate the sediment provenance, specific Fe, Mn and Pb elemental concentrations were measured in surface sediments and compared with the previously published pre-tsunami database of backwater/inner continental shelf sediments. We found the enrichment of Fe and Pb, against depletion of Mn concentration in present tsunami sediments as compared with pre-tsunami Muttukadu sediments, reflecting the variation of the sediment source area. However, the present data of Fe and Pb enrichment and Mn depletion correlates well with continental shelf sediments hinting at sedimentary routes, processes of erosion and wave propagation. The studied tsunami deposits are characterized by dominant ∼40–85% coarse sand fractions and higher proportion of detrital low and high coercivity Fe-Ti oxides, such as magnetite, titanomagnetite and hematite, reflected by magnetic concentration (magnetic susceptibility (χ), anhysteretic remanent magnetization (ARM)) and coercivity-dependent parameters (soft isothermal remanent magnetization (Soft IRM), Hard IRM, magnetomineralogical S-Ratio and saturation IRM (SIRM)). So, it can be shown that the random spatial variability and the inverse relationship between magnetic concentration χ, ARM and SIRM parameters and grain-size ARM/χ, SIRM/χ and ARM/SIRM ratios as diagnostic criteria for the tsunami impacted the distribution of magnetic parameters in coastal backwater environments. Contrasting mineral magnetic and geochemical properties together with more sand (mean 65%) when compared with silt (mean 25%) content in tsunami sediments indicates that the area was affected by high-energy tsunami waves. The study validates environmental magnetism as a proxy, which is fast and robust for identifying the tsunami or palaeotsunami deposits.

Holocene Hydroclimate Variability in Central Scandinavia Inferred from Flood Layers in Contourite Drift Deposits in Lake Storsjön

Despite the societal importance of extreme hydroclimate events, few palaeoenvironmental studies of Scandinavian lake sediments have investigated flood occurrences. Here we present a flood history based on lithological, geochemical and mineral magnetic records of a Holocene sediment sequence collected from contourite drift deposits in Lake Storsjön (63.12° N, 14.37° E). After the last deglaciation, the lake began to form around 9800 cal yr BP, but glacial activity persisted in the catchment for ~250 years. Element concentrations and mineral magnetic properties of the sediments indicate relatively stable sedimentation conditions during the Holocene. However, human impact in the form of expanding agriculture is evident from about 1100 cal yr BP, and intensified in the 20th century. Black layers containing iron sulphide appear irregularly throughout the sequence. The increased influx of organic matter during flood events led to decomposition and oxygen consumption, and eventually to anoxic conditions in the interstitial water preserving these layers. Elevated frequencies of black layer occurrence between 3600 and 1800 cal yr BP reflect vegetation changes in the catchment as well as large-scale climatic change. Soil erosion during snowmelt flood events increased with a tree line descent since the onset of the neoglacial period (~4000 cal yr BP). The peak in black layer occurrence coincides with a prominent solar minimum ~2600 cal yr BP, which may have accentuated the observed pattern due to the prevalence of a negative NAO index, a longer snow accumulation period and consequently stronger snowmelt floods.

Low temperature magnetic properties of basalts containing near ~TM30 titanomagnetite

The paper is devoted to studying the mineral composition and magnetic properties, mainly at the cryogenic temperatures, of the Middle–Late Devonian basalts from North Timan. The magnetic minerals in these basalts are dominated by intermediate-composition titanomagnetites (TM25–TM30) which demonstrate unusual magnetic properties in a wide temperature range. At room temperature, a low coercive force coexists with relatively high Mrs/Ms ratios. At cryogenic temperatures, the dependences of magnetic susceptibility on the temperature and frequency of the applied field are characteristic of this titanomagnetite composition, whereas the remanent saturation magnetization acquired at 2 K is destroyed at significantly lower temperatures compared to the synthetic analogs. The obtained results again highlight the necessity of studying the low-temperature properties of titanomagnetite samples with a controlled composition and grain size.

Variability in the mineral magnetic properties of soils and sediments within a single field in the Cape Fold mountains, South Africa: Implications for sediment source tracing

When tracing the sources of sediment, reference to potential source groups is a necessity. However, the range of uncertainty present in source fingerprinting outputs has been shown to be increased by a high within-source group variability. The environmental factors controlling the magnetic properties of samples within a single field were examined on a particle size specific basis to continue building on the recent studies of the spatial variability associated with different tracer types. The study area was in the Eastern Cape of South Africa over a Quartzite geology and was covered by rough grassland.Topsoils and gully walls were intensively sampled within the study field. Further samples were collected from weathering bedrock exposures, burnt soil and wetland soil in order to explore potential controlling factors on source magnetism. Each sample was fractionated to 125–63μm, 63–32μm, 32–25μm, 25–10μm and <10μm.Topographic position was a major controlling factor on soil magnetism, with saturated lowland gully walls and wetland topsoils being less magnetic than dry topsoils, especially within the <25μm size fractions. The magnetism of the fields soils was primarily controlled by the concentrations of super paramagnetic and single domain grains formed through pedogenesis and combustion. The magnetism of samples increased with decreasing particle size. Dissolution of fine magnetic grains in the <25μm fractions provided a potential basis for surface – subsurface source discrimination but also increased within-source group variability. The 25–10μm fraction was a good compromise between good discrimination and a low within-source variability.Little difference was found between the low frequency magnetic susceptibility of quartzite topsoils and the shale and sandstone topsoils found elsewhere in the Eastern Cape. However, igneous sources such as dolerite are far more magnetic than the quartzite topsoils. Discrimination between sediment sources can be highly variable within the <63μm fraction. For example, the <10μm fraction of soils from the study site had a higher magnetic susceptibility than Karoo shales (sieved to <63μm), whilst the 63–32μm fraction had a lower susceptibility than the Karoo shales.