Heavy-mineral Concentrates Research Articles

Geochemistry of sediments in three sectors of Trincomalee Bay, Sri Lanka: provenance, modifying factors and present environmental status

Purpose The geochemical compositions of sediments from three sectors in Trincomalee Bay (Koddiyar Bay, Thambalagam Bay and the Inner Harbour) in Sri Lanka were examined to determine fluvial and marine contributions and the effects of sorting and heavy mineral concentration. The present environmental status of the bay was also assessed.

Provenance, diagenesis and reservoir quality of the Upper Triassic Wolfville Formation, Bay of Fundy, Nova Scotia, Canada

Abstract The reservoir characterization and provenance of the Wolfville Formation were investigated using petrography, heavy minerals and microprobe analysis of tourmaline and garnet. Sandstone samples were taken from exposures at Rainy Cove and Cambridge Cove, and from the subsurface at Chinampas N-37 well beneath the Bay of Fundy. The surface and subsurface rocks have differences in their relative content and/or type of detritus, cement and heavy minerals (opaques, garnet, scheelite, tourmaline, rutile, apatite and others). These sandstones have continental block provenance in the subsurface rocks and recycled orogen provenance in the exposures. The main sources of the exposed Wolfville Formation sediments were the Palaeozoic rocks of the Meguma Supergroup, South Mountain Batholith, Horton and Windsor groups; meanwhile the subsurface sandstones might have been derived from the same sources or the Avalon Terrane and/or Gondwana. The sandstones were deposited during early stages of rifting post-dating earlier Palaeozoic collision orogenies that culminated with the Appalachian orogeny. The exposures of Wolfville Formation have low porosity ( c. 6%) that diminishes to negligible in the subsurface. The Wolfville Formation has a considerable thickness beneath the Bay of Fundy where it overlies the Horton Bluff Formation, Meguma and/or Avalon terranes. However, its reservoir potential is not encouraging.

Sediment geochemistry as a provenance indicator: Unravelling the cryptic signatures of polycyclic sources, climate change, tectonism and volcanism

AbstractInterpretation of bulk‐sediment geochemistry is one of several approaches for determining sediment provenance. This study investigates the value added by bulk‐sediment geochemical analysis in interpreting provenance in a passive margin clastic basin, the Upper Jurassic–Lower Cretaceous deltaic sediments of the Scotian Basin. Provenance studies in this basin are challenging because source tectonic terranes are parallel to the basin margin and polycyclic sediment sources are abundant. More than 400 samples of mudstone and sandstone representing the geographical and stratigraphic range of interest were analysed for 57 elements. Diagenetic processes added calcium to many samples and removed potassium in rocks buried below 3 km, thus impacting principal component analysis and published weathering indices. However, multiple geochemical approaches to assessing the degree of weathering showed climatically controlled changes in weathering in the Tithonian and Barremian, and changes in supply from major tectonic events, such as the top‐Aptian uplift in the Labrador rift. Covariance of elements in heavy minerals demonstrates the varying magnitude of polycyclic supply and stratigraphic changes in sources. Geochemical analyses revealed a previously unsuspected Tithonian alkali volcanic sediment source, characterized by high niobium and tantalum. The lack of highly contrasting sources means that geochemistry alone is inadequate to determine sediment provenance. Published discrimination diagrams are of limited value. Statistical analysis of geochemical data is strongly influenced by diagenetic processes, episodic volcanic inputs and polycyclic concentration of resistant heavy minerals in sandstones. Single indicator elements for particular sources are generally lacking. Nevertheless, careful consideration of geochemical variability on a case by case basis, integrated with detrital mineral studies, provides new insights into palaeoclimate, sediment provenance and, hence, regional tectonics. Although there is no simple template for such analysis, this study demonstrates an approach that can be used for other basins.

Provenance study on Eocene–Miocene sandstones of the Rakhine Coastal Belt, Indo-Burman Ranges of Myanmar: geodynamic implications

Abstract The Indo-Burman Ranges (IBR) represent an accretionary wedge, which is the result of subduction of the Indian plate beneath the Asian plate. In the Rakhine Coastal Belt it comprises a thick stack of Cretaceous to Neogene turbiditic sediments and localized thrust sheets of oceanic plate mafics and pelagic sediments. We investigate Eocene–Miocene sandstones, aiming to reveal the provenance of the detrital material using modal framework grain, heavy mineral and detrital zircon analysis (U–Pb laser ablation ICP-MS dating, Hf isotope geochemistry and typology). The results show a predominant derivation of the clastic material from: (i) Late Cretaceous to Oligocene igneous rocks, which are often bimodal with a low number of zircons spanning the Cretaceous–Palaeogene boundary, and (ii) recycled orogenic terrane sources comprising ophiolitic rocks. Age corrected Hf isotope ratios confirm subduction-related mixed mantle-crust sources. We also observe minor reworking of older magmatic zircons. By comparing our obtained petrographic parameters and zircon characteristics with potential Himalayan, Indian continent and Burman margin sources we conclude a Burman margin and arc origin provenance. With regard to hydrocarbon exploration in the IBR, a forearc and trench basin system model linked with the Burman arc appears more appropriate for evaluating the petroleum system. Supplementary material: sandstone modal composition, heavy mineral contents, detrital zircon U–Pb LA-ICPMS dating and hafnium results are available at http://www.geolsoc.org.uk/SUP18651 .

Surface dispersion of uranium in the Al-Hayt area, NE Arabian Shield

Al-Hayt area, although located on the Cenozoic basaltic plateau of Harrat Khaybar, is threatened by uranium contamination emanating mainly from the rhyolite hills of Asfar Thwelil just outside the eastern boundary of the lava field. This outcrop is an exhumed volcanic dome belonging to the Shammar Group of Late Proterozoic age. The rock units in this dome are porphyritic and flow rhyolites with some ignimbrites. The flow rhyolite is especially enriched in uranium and much of this is concentrated in thin vertical veins of uraninite and uranophane. Radiation measurements were carried out in the field using a portable gamma ray differential spectrometer that was capable of counting radiation at 5 spectral intervals representing uranium, thorium, potassium and total radiation (TC1 & TC2). Four traverses containing 67 points were made across the hills of Asfar Thwelil and nearby plains, and some measurements were also carried out in various parts of the Al-Hayt Town itself. Radiation measurements were also carried out in several parts of the eastern and northern shield for the sake of comparison. Soil samples for chemical analysis were also collected along the traverses and from the town and its main quarry. The samples were sieved to 3 sizes (coarse, medium and fine) and analyzed for 34 elements using the Neutron Activation technique. Results of the chemical analyses reveal the concentration of uranium and thorium in the fine soil fraction; although this may indicate adsorption onto clay minerals, a similar trend by immobile elements such as Zr, Hf, Ta, REE and Co rules out this possibility and points to heavy mineral concentration in the fine fraction as the main cause. Radiation was measured in 5 exploration trenches, and the upper layers (alluvium) were found to be the least radioactive, while layers containing salt and calcrete were highly enriched in radioactive elements. Correlation coefficients from soil samples are strongly in favor of the concentration of U & Th with other incompatible elements in heavy minerals such as zircon. Factor analysis of the same samples provides a number of underlying causes that control their chemistry; most important of all is the heavy mineral content followed by the influence of basaltic detritus form the Harrah.

Heavy-mineral analysis as a tool in tephrochronology, with an example from the La Sal Mountains, Utah, U.S.A.

Abstract An essentially pure tephra layer on a steep slope in the La Sal Mountains, Utah, U.S.A., is correlated with the 1.65 Ma old Guaje Tephra derived from the Jemez Mountains, New Mexico, U.S.A. The heavy-mineral contents and glass shards in sediments beneath the La Sal tephra layer indicate that tephra constituents are contained in deposits considerably older than the pure layer. This suggests that tephra material may become reworked while retaining its pure character, possibly due to laminar transport or to dislocation in a frozen condition. This raises the need to handle tephrochronological findings with great care.

Petrographic study of the Miocene Mizunami Group, Central Japan: Detection of unrecognized volcanic activity in the Setouchi Province

A petrographic study of sandstones from the Miocene Mizunami Group in Central Japan has been performed on core samples from a single borehole, in order to evaluate the provenance of the sedimentary rock. Evaluation of the provenance is based on bulk mineral, heavy mineral and plagioclase contents and on whole rock chemical compositions. The sandstones studied are divisible into three types; the first type is characterized by the occurrence of biotite and plagioclase ranging from albite to oligoclase, the second type is characterized by the dominance of amphibole and labradorite with pyroxene (clinopyroxene > orthopyroxene), and the third type is characterized by the dominance of pyroxene (orthopyroxene > clinopyroxene) and andesine with lesser labradorite, bytownite and anorthite. The first type is interpreted to be derived from the basement granite, whereas the others were derived mostly from volcanic ash, judging from their mineral compositions. The volcanic activity that supplied the volcanic ash to the Mizunami Basin occurred in two phases, distinguishable by variations in their mineralogical and geochemical compositions, an indication of change in character of the volcanic activity. This petrographic study of the sandstones in the Mizunami Group suggests that unrecognized volcanic activity occurred around the Mizunami Basin, even though potential provenance of the volcanic ash has not yet been identified.

Morphological, drainage and eolian controls on the microtidal Patara Beach sediments (eastern Mediterranean): Textural, geochemical and mineralogical investigations

The effects of dominant hydrodynamic, morphological, fluvial and hinterland geological source conditions on the texture and composition of the microtidal and dissipative Patara Beach (Mediterranean coast of SW Turkey) sediments were investigated at 47 locations. Patara Beach sediments are composed entirely of sand. Fine sand (5–94%) was more abundant in the northwestern section, while medium sand contents (2–94%) increased in the central and southeastern sections. Moderately-to well sorted (mostly 0.3–0.7 Ø) sediments tend to show overall better sorting towards the southeast, in the net longshore current direction. Terrigenous carbonate grains derived from the hinterland constituted 6–50% (as CaCO3) with varying tendencies to increase or decrease within sections alongshore. Total heavy mineral concentrations in bulk sediments (1–17%, mostly <5%) were highest in localities of offshore sandy spit formation and with intense aeolian processes. The heavy mineral concentration comprises magnetite, hematite, amphiboles, pyroxene, epidote, garnet, and chromite, a mineral assemblage reflecting mafic/ultramafic/ophiolitic and metamorphic sources and mineral deposits. The concentrations of major elements (Si, Al, Ca, K, Na, P, Fe, Ti) and others (Co, Ba) are comparable with the average composition of Earth's crust rocks, and variations can be related to the varying texture and lithologies of the sediments. Higher abundances of Mg (3.3–7.7%), Cr (0.2–6.7%) and Ni (195–588 ppm) must be contributed by particular ophiolite sources. Mn (3385–4585 ppm) indicates presently-mined mineral deposits on the coast. Wind, wave, current and fluvial drainage regimes and corresponding morphological changes together with distribution of geological source rocks have great influences on the texture and composition of Patara Beach sediments.

Provenance of Paleozoic very low- to low-grade metasedimentary rocks of South Tisia (Slavonian Mountains, Radlovac Complex, Croatia)

Abstract Monazite age dating, detrital heavy mineral content and whole-rock geochemistry provided insight into the provenance, depositional history and paleogeological setting of the Radlovac Complex very low- to low-grade metasedimentary rocks (South Tisia, Slavonian Mountains, Croatia). Electron microprobe based Th-U-Pb dating of detrital monazite indicates a Variscan age of the protolith (330 ± 10 Ma). The detrital heavy mineral assemblages of representative metasedimentary rocks are dominated by apatite, zircon, tourmaline and rutile accompanied by minor quantity of epidote/zoisite, monazite and titanite. Judging from the heavy mineral assemblage, felsic igneous rocks served as the source material. This is consistent with the major and trace element spectrum of studied metasedimentary rocks characterized by high concentration of Th, high L + MREEs and high ratios of La/Sc, Th/Sc, La/Co, Th/Co and Th/Cr. The occurrence of magmatic monazite, zircon and xenotime and the absence of metamorphic heavy minerals suggest that granitoids, migmatites and migmatitic gneisses served as one major source for the metapsammites. Such rock types are commonly exposed in the Papuk Complex of the older surrounding complexes, while the Psunj Complex also contains metamorphic rocks. This is in good correlation with the monazite ages presented here which fits better with ages of Papuk Complex representative rocks than with those of the Psunj Complex known from the literature. Overall, data show that the Radlovac Complex represents the detritus of the local Variscan crust characterized by granitoid bodies, migmatites and migmatitic gneisses typical for the Papuk Complex.

Regional distribution of Heavy-mineral concentrations along the Curonian Spit coast of Lithuania

ABSTRACT Pupienis, D., Buynevich I.V., Jarmalavicius, D., Žilinskas, G., and Fedorovic, J., 2013. Regional distribution of Heavy-mineral concentrations along the Curonian Spit coast of Lithuania Heavy-mineral concentrations (HMCs) in coastal sands serve as important indicators of hydrometeorological and sedimentological conditions. Along the southeast Baltic Sea coast, quartz- and feldspar-rich sands contain variable amounts (1–8%) of heavy minerals, such as garnet, rutile, zircon, magnetite, ilmenite, hornblende, and other accessory minerals. Their concentrations are found along the Baltic Sea coast of the Curonian Spit, a 98-km-long barrier divided between the Russian Federation (47 km) in the south and the Republic of Lithuania (51 km) in the north. The open sea beach sites range from 25 to 80 m in width and are backed by 5–16 m height foredunes. To examine the patterns in HMC distribution, a total of 303 surface sand samples were collected from the middle of the beach, foredune toe, and stoss slope at...

Provenance Discrimination Studies on Sediments of the SW Kachchh Coast, Western India: Insights from Heavy Mineral and Mineral Magnetic Analysis

Studies of the SW Kachchh coast, along the western coast of India, including granulometry, heavy mineral content, and mineral magnetic properties for sediment characterization, were undertaken to fingerprint probable source attributes. Heavy mineral analysis showed that the westernmost location received its dominant contribution from Indus-derived sediments (61%), whereas in the easternmost locations, the hinterland/Kachchh mainland–derived sediments dominated, with 79% of the total heavy mineral concentration. Mineral magnetic properties also showed that sediments derived from the fluvial system of the Kachchh mainland were rich in low-coercivity magnetic minerals with distinct multidomain (MD) grain size and were dominantly ferrimagnetic mineral assemblages (S-ratio 5 0.92–1.0), whereas at the western end, the concentration of magnetic minerals was low, with a dominant stable single domain (SSD) size range and antiferromagnetic minerals dominating the magnetic mineral assemblages (S-ratio 5 0.57–0.9). The granulometry, heavy mineral content, and mineral magnetic properties characterize different segments and multiple end members contributing to the coastal setup of the Gulf of Kachchh, India.

Control in Beach and Dune Sands of the Gulf of Mexico and the Role of Nearby Rivers

A sedimentological, petrographic, and geochemical study of beach, dune, and river sands was carried out along the northwestern Gulf of Mexico. The main goal of this work is to show how beach and dune sands are controlled texturally, compositionally, and chemically by the nearby rivers for each beach location using a particle size analyser, a polarized microscope, a X-ray fluorescence and ICP mass spectrometer to obtain the following: grain-size values from one river (Carrizal River) are similar in range to their counterpart beach sands but not similar to the dune sands (Barra del Tordo). Rivers (Panuco and Carrizal) are compositionally controlling the quartz and feldspar contents of their counterpart beach and dune sands (i.e., Playa Miramar and Barra del Tordo). Rivers (Soto La Marina River) are directly influencing the composition of the beach sands (La Pesca) based upon the total quartz content, beach and dune sands. The concentration of magnetite grain fractions (Barra del Tordo beach and dune sands) is not under the influence of the nearby river (Carrizal River). In this case the compositional influence of beach and dune sands is related to sediment discharges by other fluvial systems, redistribution of the beach and dune sands along the coast and deflation/winnowing of light minerals. The Eu positive anomaly in the beach and dune sands from the three sites (i.e. Playa Miramar, Barra del Tordo, La Pesca) is linked to an increase in the P(plagioclase)/K(potash feldspar) ratio. The (La/Lu)cn highest ratio for river sands (Carrizal River) suggests quartz enrichment compared to their beach and dune sands counterparts. The (Gd/Yb)cn ratio for one river (i.e., Carrizal River) indicates that it is low in heavy rare earth elements. HREE compared to their beach and dune sands counterparts indicates less concentration of heavy minerals as potential carriers of HREE seawards.

Heavy Mineral Distribution and Characterisation of Ilmenite of Kayamkulam - Thothapally Barrier Island, Southwest Coast of India

Abstract Mineral concentration and ilmenite characterization of the Thothapally - Kayamkulam Barrier Island of the southern Kerala has been studied. 96.86% concentrations of heavy minerals are recorded in the surficial and core samples (4 m) in the southern Kayamkulam and northern Thothapally areas. The total heavy mineral content decreases with depth. The primary heavy mineral suite of the surficial and core samples consists of ilmenite, sillimanite, zircon, garnets, rutile, monazite and magnetite. Longshore current and onshore- offshore movements of sediment during the southwest monsoon are primarily responsible in sorting of the heavy minerals. TiO2 content in ilmenite is significantly higher in the Kayamkulam core sediments than the surface samples. XRD analysis supports intensive weathering and alteration leading to the higher TiO2 concentration. Higher percentage of ferric iron than ferrous iron in the core samples reveals that considerable weathering occurred under burial condition. SEM examination of ilmenite grains reveal the presence of solution pit, chemical leaching, corrosion and replacement textures, supporting the intense epigenetic alteration and weathering under subaerial condition and post- depositional changes by water–table condition.

Planktonic foraminifer biostratigraphy as a tool in constraining the timing of flysch deposition: Gurnigel flysch, Voirons massif (Haute‐Savoie, France)

AbstractNew biostratigraphic, sedimentological and petrographic data and a thorough review of existing literature modify existing knowledge on the age, the sedimentology, the petrography and the palaeogeographic origin of the Gurnigel flysch from the Voirons massif (Haute Savoie, France). Planktonic foraminiferal biostratigraphy assigns the flysch to the upper Middle Eocene (zones P12 to P14) through to Lower Oligocene (zones P16 to P20) stages. This result contrasts with previous work, which assigned the unit to the Lower Palaeocene to upper Middle Eocene on the basis of calcareous nannofossil and dinoflagellate assemblages. The following findings suggest that the Voirons massif comprises several stacked flysch units that do not have exactly the same palaeogeographic origin: (i) the occurrence of flysch exposures in reverse stratigraphic order combined with the lack of evidence for bed overturning; (ii) the variability of palaeo‐depositional settings inferred from different flysch outcrops of similar age; (iii) the differences in the heavy mineral content; and (iv) the anomalous superimposition of distal turbidites and/or basinal contourites (Saxel Marls) over proximal turbidites (Vouan Conglomerates). The young age of these kilometre‐sized flysch slices precludes their hitherto postulated locus of deposition in the South‐Penninic Ocean, and rather indicates a provenance from the Ultrahelvetic and/or North‐Penninic (Valais) palaeogeographical domains. Finally, none of the nannofossil assemblages are contemporaneous with the observed planktonic foraminifera associations, suggesting that they have been reworked, dissolved, or just simply diluted and not found by earlier researchers. This study from the Voirons massif shows that planktonic foraminifera associations are a highly reliable biostratigraphic tool for obtaining accurate ages of flysch successions.

Forensic applications including mapping and classification of tsunami sand deposits and sand dunes with ground penetrating radar

The coastal region experiences erosional, transportational and depositional events during mega events such as tsunami. The onshore deposits are significant in determining the past events of high-energy events in the coastal region. The Optically Simulated Luminescence (OSL) dating of the sediments by combining Ground Penetrating Radar (GPR) records will reveal the past tsunami events. OSL dates obtained on the sediments, trenched manually will indicate the depositional events having a characteristic recurrence interval and also the presence of heavy mineral concentration (HMCs). These characteristic layers can be identified using the radar signatures. GPR is a high-resolution technique of imaging shallow soil and ground structures using electromagnetic waves in the frequency band of 100–400 MHz, with penetration depths of 30–40 m. This paper highlights the application of radar technique as a forensic tool combined with the analysis of soil samples for the study of tsunamis and sand dunes in India.

Analysis of Mineral and Heavy Metal Content of Some Commercial Fruit Juices by Inductively Coupled Plasma Mass Spectrometry

The presence of potentially toxic elements and compounds in foodstuffs is of intense public interest and thus requires rapid and accurate methods to determine the levels of these contaminants. Inductively coupled plasma mass spectrometry is a powerful tool for the determination of metals and nonmetals in fruit juices. In this study, 21 commercial fruit juices (apple, peach, apricot, orange, kiwi, pear, pineapple, and multifruit) present on Romanian market were investigated from the heavy metals and mineral content point of view by ICP-MS. Our obtained results were compared with those reported in literature and also with the maximum admissible limit in drinking water by USEPA and WHO. For Mn the obtained values exceeded the limits imposed by these international organizations. Co, Cu, Zn, As, and Cd concentrations were below the acceptable limit for drinking water for all samples while the concentrations of Ni and Pb exceeded the limits imposed by USEPA and WHO for some fruit juices. The results obtained in this study are comparable to those found in the literature.

Geochemical characteristics of stream sediments, sediment fractions, soils, and basement rocks from the Mahaweli River and its catchment, Sri Lanka

Geochemical variations in stream sediments (n=54) from the Mahaweli River of Sri Lanka have been evaluated from the viewpoints of lithological control, sorting, heavy mineral concentration, influence of climatic zonation (wet, intermediate, and dry zones), weathering, and downstream transport. Compositions of soils (n=22) and basement rocks (n=38) of the catchment and those of <180μm and 180–2000μm fractions of the stream sediments were also examined. The sediments, fractions, soils and basement rocks were analyzed by X-ray fluorescence to determine their As, Pb, Zn, Cu, Ni, Cr, V, Sr, Y, Nb, Zr, Th, Sc, Fe2O3, TiO2, MnO, CaO, P2O5 and total sulfur contents. Abundances of high field strength and ferromagnesian elements in the sediments indicate concentration of durable heavy minerals including zircon, tourmaline, rutile, monazite, garnet, pyriboles, and titanite, especially in <180μm fractions. The sediments show strong correlation between Ti and Fe, further suggesting presence of heavy mineral phases containing both elements, such as ilmenite and magnetite. The basement rocks range from mafic through to felsic compositions, as do the soils. The river sediments lack ultrabasic components, and overall have intermediate to felsic compositions. Elemental spikes in the confluences of tributary rivers and high values in the <180μm fractions indicate sporadic inputs of mafic detritus and/or heavy minerals to the main channel. Al2O3/(K2O+Na2O) and K2O/Na2O ratios of the sediments and LOI values of the soils correlate well with the climatic zones, suggesting intense weathering in the wet zone, lesser weathering in the intermediate zone, and least weathering in the dry zone. Low Sr and CaO contents and Cr/V ratios in stream sediments in the wet zone also suggest climatic influence. Fe-normalized enrichment factors (EFs) for As, Pb, Zn, Cu, Ni and Cr in stream sediments in the main channel are nearly all <1.5, indicating there is no significant environmental contamination. The chemistry of the sediments, rocks and the soils in the Mahaweli River are thus mainly controlled by source lithotype, weathering, sorting, and heavy mineral accumulation.

Petrographical and micro‐Raman analysis of Terra Sigillata shatters from a Vandalic settlement in North‐Eastern Hungary

Micro‐Raman spectroscopy is one of the most advanced analytical techniques used in the field of archaeometry investigations. Terra Sigillata is a frequently occurring find from the Roman period; thus, its detailed scientific analysis has a significant impact on archaeological research. Finds recovered from the ‘Barbaricum’ (beyond the area of the Roman Empire) have particular importance because their analysis can contribute to our knowledge about the circumstances and conventions of the trade and transit of such ornaments. The studied samples were found in North‐Eastern Hungary (Garadna, Vandalic settlement, 2nd–3rd century), and based on archaeological investigations of the terra sigillata ornaments, they are assumed to be made from manufactories in Rheinzabern, Pfaffenhofen and Westerndorf. Raman analysis indicates that the temper grains of samples from Pfaffenhofen and Westerndorf contain more calcic minerals, including plagioclases and heavy minerals (e.g. augite, diopside, actinolite, apatite and titanite). Conversely, the temper grains of samples from Rheinzabern do not contain plagioclases; their feldspars are almost completely potassium, and only anatase and rutile represent their heavy mineral content. The largest difference between the slip and body can be observed in samples from Westerndorf, while the largest heterogeneity of the slip and body material is observable in samples from Pfaffenhofen. The results indicate the remarkable ability of micro‐Raman spectroscopy to contribute to the discrimination of ancient light‐clay products. The data obtained from the analysed samples are usable for comparative studies of the pottery. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Heavy minerals in the 2011 Tohoku-oki tsunami deposits—insights into sediment sources and hydrodynamics

The 2011 Tohoku-oki tsunami left sand and mud deposits more than 4km inland on the coastal plain of Sendai, Japan. The tsunami deposits, pre-tsunami soils and beach sediments were analysed for grain size, and heavy mineral content and assemblages to test the applicability of heavy mineral analyses in the identification of tsunami deposits and interpretation of associated sedimentation processes. Heavy minerals comprised on average 35% of the tsunami deposit in the 0.125–0.25mm grain size fraction. The most common were orthopyroxenes, clinopyroxenes, amphiboles, limonites and opaque minerals. Heavy mineral concentrations and assemblages were similar in the tsunami deposits, beach and pre-tsunami soils and sediments and thus tsunami deposits could not simply be identified based on their heavy minerals. Sediment provenance analysis revealed that tsunami deposits left within 1.5km of the shoreline were mostly eroded from the beach, dune and local soils, while deposits farther inland (>1.5km) were mostly derived from local soil erosion. No evidence was found for a significant contribution of offshore sediments. Detailed analyses revealed that the lowermost portion of tsunami deposits was mostly of local origin, while the sediment source of the upper portion was variable. A comparison with a previous study of heavy minerals in 2004 IOT deposits confirms that heavy minerals in tsunami deposits are mostly source-dependent and may represent a useful supplementary tool in studies of tsunami deposits. However, the interpretation must always be placed in the local geological context and corroborated with other “tsunami proxies”.

Elevated radionuclide concentrations in heavy mineral-rich beach sands in the Cox's Bazar region, Bangladesh and related possible radiological effects

The study focuses on elevated levels of environmental radioactivity present in heavy mineral deposits located along a 120-km coastal section of Cox's Bazar on the eastern panhandle of Bangladesh. The deposits are situated in or at sand dunes located on the recent beach (foredune area) or in attached paleo-beach areas (backdune area). This study investigates activity concentrations in bulk beach sands (six representative samples) and in five mineral fractions separated from the beach sands in order to assess potential radio-ecological effects and the possible use of the mineral deposits as a source for uranium and thorium. The bulk beach sands and individual mineral fractions were analysed by gamma-ray spectroscopy. The activity concentrations of U-238, U-235, Th-232 and K-40 in the bulk beach sand samples were found to be considerably high and positively correlated to the concentration of heavy minerals in the sand. In the mineral fractions, the highest activity concentrations were found in the zircon fraction followed by garnet, rutile, ilmenite and magnetite. The determination of (i) the radium activity, (ii) several radiation hazard indices and (iii) adsorbed and effective gamma doses allowed to assess the related exposure of the environment and the local population to elevated radioactivity. It becomes evident from the present data that (1) if raw sands or mineral fractions mined in the study area are used for building purposes or industrial use, their activity concentrations have to be considered from a radio-ecological perspective and (2) if mining and processing of the minerals is being considered, uranium and thorium may become strategically significant by-products.