Abundance Of Heavy Minerals Research Articles

Discrimination between wave‐ravinement surfaces and bedset boundaries in Pliocene shallow‐marine deposits, Crotone Basin, southern Italy: An integrated sedimentological, micropalaeontological and mineralogical approach

AbstractThe lower Pliocene Belvedere Formation, cropping out in the Crotone Basin, southern Italy, exhibits a metre‐scale to decametre‐scale shallow‐marine cyclicity that shares features of both high‐frequency sequences linked to shoreline shifts and controlled by minor relative sea‐level and/or sediment supply changes, and sedimentological cycles unrelated to shoreline shifts. In order to better understand the high‐frequency sequence stratigraphic framework of this succession, an integration of sedimentological, micropalaeontological (micro‐foraminifera assemblages) and mineralogical (heavy mineral abundance) data is used. From a sedimentological/stratigraphic point of view, wave‐ravinement surfaces bounding high‐frequency sequences, and associated substrate‐controlled ichnofacies, are prominent in outcrop and document environmental and water‐depth changes, whereas bedset boundaries separating sedimentological cycles have a more subtle field appearance and are only associated with changes of environmental energy. Moreover, condensed deposits are present only above wave‐ravinement surfaces, and the high‐frequency sequences bounded by these surfaces have a thickness that is an order of magnitude greater than that of the bedsets. Micro‐foraminifera assemblages may change, and the content of heavy minerals usually increases, across wave‐ravinement surfaces, whereas both parameters do not change significantly across bedset boundaries. The abundance of heavy minerals is systematically higher, with respect to the underlying and overlying deposits, in the condensed shell beds that overlie wave‐ravinement surfaces. An integrated sedimentological, micropalaeontological and mineralogical approach represents a powerful tool to discriminate between wave‐ravinement surfaces bounding high‐frequency sequences and bedset boundaries, and in general to investigate at the intra high‐frequency sequence scale. This integrated approach is expected to be very useful in the study of potentially all shallow‐marine successions composed of small‐scale cycles, in order to delineate a detailed sequence stratigraphic framework and understand the factors that controlled the cyclicity.

Scenario of the 1996 volcanic tsunamis in Karymskoye Lake, Kamchatka, inferred from X-ray tomography of heavy minerals in tsunami deposits

The concentration and distribution of heavy minerals in tsunami deposits is not random and mostly source-dependent. Heavy minerals may thus be good indicators of sediment provenance and tsunami flow dynamics. The tsunamis generated by the 1996 phreato-magmatic eruption in Karymskoye Lake represent a relevant case-study because the provenance of the abundant heavy minerals found in the tsunami deposits is well constrained (the on-going basaltic eruption itself). X-ray computed tomography (X-CT) of cores of tsunami sediments is used to identify heavy minerals and characterise their source and spatial distribution in the tsunami deposit, and to propose a scenario of the coupled eruption and tsunamis. An original combination of methods including X-CT, SEM and XRF core scanner allows distinguishing subunits corresponding to pulses of sediments deposition and associated inputs of heavy minerals, together with erosive contacts, laminations, and rip-up clasts of the substratum. The structure of the tsunami deposits suggests that a major tsunami consisting of two main waves inundated the coastal terrace up to 100m inland on the eastern shore of the lake; a scenario that is consistent with waves generated by experimental explosions. This largest tsunami might have occurred when underwater explosions were at a critical water depth of 40m (corresponding to a two-third submerged explosion in the 60m deep lake). However, more investigations are needed to better understand the critical conditions leading to a tsunami during underwater eruptions.

Thunderbird heavy mineral sand deposit, Western Australia

The Thunderbird heavy mineral sand deposit is located in Canning Basin of Western Australia and is hosted by Jurassic-Cretaceous fine sands and silts. The large areal extent, width, grade, geological continuity and grainsize of the Thunderbird deposit are interpreted to have formed in an off-shore, sub-wave base depositional environment. The Thunderbird mineralisation is hosted within a well-sorted and rounded fine to very-fine-grained sand unit which is over 90 m thick and contains abundant heavy minerals (up to 40% HM). Mineralisation occurs as a thick, broad sheet-like body striking northwest, and dipping shallowly to the west and southwest, extending from surface to a maximum drilled depth of 155 m. The heavy minerals suite in the Thunderbird deposit is comprised of altered ilmenite, ilmenite, pseudorutile, haematite, goethite, leucoxene, zircon, rutile, anatase and monazite, with very minor amounts of tourmaline, spinel, staurolite and andalusite. The minerals are finer-grained than most deposits currently being mined.

Provenance of sandstone on the western flank of Anambra Basin, Southwestern Nigeria

Petrographic and heavy mineral studies were carried out on clastic deposits that crop out in Ikpeshi, Auchi and Fugar localities in order to determine the provenance of the sediments and the tectonic setting of the source area. The localities are in the western flank of the Anambra basin, southwestern Nigeria. Petrographic study shows that the sandstone deposits are composed of variable amounts of quartz, feldspars and lithic fragments with minor occurrence of authigenic silica and chlorite cements. Quartz is the predominant detrital mineral in all the samples accounting for over 87 % of the total framework composition. The representative samples from all the localities contain 88-94 % quartz, 1-8 % lithic fragment, 1-4 % cement and 0-4 % matrix. Feldspar is present in small amount only in samples from Fugar locality. The sandstones each classify as quartz arenites and sublitharenites. Both opaque and transparent heavy minerals occur in the sandstones. The opaques are magnetite, ilmenite and leucoxene. Together, they account for 35 – 55 % of the total heavy mineral abundance. The transparent heavy minerals are zircon, tourmaline, rutile, staurolite, and apatite listed in order of decreasing abundance. The heavy mineral assemblages in the localities are similar except for the absence of rutile from the sediments of Ikpeshi locality. The heavy mineral grains are subangular to rounded. The zircon-tourmaline-rutile (ZTR) index for the sediments from the three localities are generally high and range from 90.5 to 100% indicating high degree of mineralogical maturity of the sandstones. The heavy mineral suites and the petrographic signatures of the sandstones suggest derivation mainly from acid igneous rocks, gneisses and older sandstones in both stable tectonic and recycled orogenic settings. However, the absence of rutile in sandstone from Ikpeshi may suggest derivation from lithologically more restricted provenance.

Heavy minerals in the late Eocene sandstone of Medicine Pole Hills, southwestern North Dakota

Late Eocene sandstone capping hills and small buttes in the Medicine Pole Hills in southwestern North Dakota has been correlated with the Chalky Buttes Member of the Chadron Formation. Heavy-mineral analysis was used to assess this correlation. Optical microscopy and chemical analysis using a scanning electron microscope/energy dispersive spectrometer (SEM/EDS) system were used to determine abundances and compositions of heavy minerals separated from 0.25–0.30 mm fractions of nine samples from seven depositional units (353–602 grains per sample). The 0.063–0.125 mm fraction was also studied for one of these samples. Samples ranged from coarse- to medium- to fine-grained poorly consolidated sandstone. Total heavy mineral recovery (0.4–14.1%) generally corresponded with the grain-size distribution of samples, with higher recoveries in coarser samples. Opaque grains (ferruginous aggregates, Fe-Ti oxides, and leucoxene) comprised 0.8–15.6 percent of heavy mineral grains. Non-opaque grains were dominated by amphibole (24.4–52.2%) and epidote-clinozoisite (10.6–38.1%), with variable diopside (0–51.1%). Generally less abundant minerals included garnet, apatite (bone fragments), biotite, and muscovite. One sample was biotite-rich (36.5%). Chemical compositions of heavy minerals showed no significant stratigraphic variations, suggesting the nature of the sources did not vary. Diopside, biotite, and approximately 1/3 of the amphibole grains were interpreted as derived from Tertiary volcanic sources. The majority of the amphibole grains (tremolite and blue-green hornblende), epidote, and garnet were derived from Precambrian metamorphic sources. The relative contribution of volcanic sources was variable (19–64%), being highest in those samples with more diopside and (with the exception of the biotite-rich sample) highest in those samples with higher overall heavy-mineral abundances. Individual heavy-mineral abundances also correlated fairly well with grain size. Overall, variations in heavy minerals were explained by variable volcanic source contributions and variations in grain-size distributions of the samples. Despite the variability found, cluster analysis showed that the samples from Medicine Pole Hills were consistently different than the generally much more stable heavy-mineral assemblages found in the Chalky Buttes Member. They were also consistently different when volcanic heavy minerals were ignored. The differences could not be explained by variable volcanic contributions, grain-size effects, and/or differences in heavy mineral stabilities alone. They require differences in provenance, suggesting that the sandstone of Medicine Pole Hills should not be correlated with the Chalky Buttes Member, or, at the very least, it should be considered a distinct facies of the Chalky Buttes Member.

The Rhodope Zone as a primary sediment source of the southern Thrace basin (NE Greece and NW Turkey): evidence from detrital heavy minerals and implications for central-eastern Mediterranean palaeogeography

Detrital heavy mineral analysis coupled with a regional geological review provide key elements to re-evaluate the distribution of the Rhodope metamorphic zone (SE Europe) in the region and its role in determining the evolution of the Thrace basin. We focus on the Eocene–Oligocene sedimentary successions exposed in the southern Thrace basin margin to determine the dispersal pathways of eroded crustal elements, of both oceanic and continental origins, as well as their different contributions through time. Lithological aspects and tectonic data coupled with geochemistry and geochronology of metamorphic terranes exposed in the area point to a common origin of tectonic units exposed in NW Turkey (Biga Peninsula) with those of NE Greece and SE Bulgaria (Rhodope region). The entire region displays (1) common extensional signatures, consisting of comparable granitoid intrusion ages, and a NE-SW sense of shear (2) matching zircon age populations between the metapelitic and metamafic rocks of the Circum-Rhodope Belt (NE Greece) and those of the Camlica–Kemer complex and Cetmi melange exposed in NW Turkey. Detrital heavy mineral abundances from Eocene–Oligocene sandstones of the southern Thrace basin demonstrate the influence of two main sediment sources mostly of ultramafic/ophiolitic and low- to medium-grade metamorphic lithologies, plus a third, volcanic source limited to the late Eocene–Oligocene. Detrital Cr-spinel chemistry is used to understand the origin of the ultramafic material and to discriminate the numerous ultramafic sources exposed in the region. Compositional and stratigraphic data indicate a major influence of the metapelitic source in the eastern part (Gallipoli Peninsula) during the initial stages of sedimentation with increasing contributions from metamafic sources through time. On the other hand, the western and more external part of the southern Thrace margin (Gokceada, Samothraki and Limnos) displays compositional signatures according to a mixed provenance from the metapelitic and metamafic sources of the Circum-Rhodope Belt (Camlica–Kemer complex and Cetmi melange). Tectonic restoration and compositional signatures provide constraints on the Palaeogene palaeogeography of this sector of the central-eastern Mediterranean region.

Análisis de proveniencia de las arenas del complejo de dunas parabólicas El Socorro, Baja California, México, mediante una caracterización mineralógica y granulométrica

In this study, fourteen superficial sandy sediment samples and fifteen core samples, taken at 2 to 30 m in depth, were analyzed in order to determine the granulometry and mineralogical features of the dune system named duna costera El Socorro (DCES), San Quintin, Baja California, Mexico. In addition, we investigated the sediment provenance by analyzing twelve samples collected from three nearby arroyos and sand bars. The main components of the DCES are plagioclase and quartz (35 - 39 % and 36 - 58 % plagioclase, and 50 - 56 % and 38 - 60 % monocrystalline quartz for core samples and superficial samples, respectively). The remaining components include scarce lithic fragments and abundant heavy minerals, mostly hornblende and traces of pyroxene, but also small amounts of magnetite and ilmenite (> 1 % in volume). The samples from arroyo El Socorro (south of the DCES) and arroyo Santo Domingo (~45 km north of the DCES) contain 69 and 52 % monocrystalline quartz, respectively, while arroyo San Simon, located north of the DCES,

Sedimentary characteristics and source of loess in Baranja (Eastern Croatia)

Abstract Loess is a type of terrestrial clastic sediment formed by the accumulation of wind-blown dust, composed dominantly of silt-sized particles. It is usually inter-bedded with soil horizons forming loess–palaeosol successions (LPS). The thickest LPS in Croatia are found in Baranja, a region bounded by two large rivers, the Danube and the Drava. The results of grain-size and modal analysis provide information about source material and wind direction in different time periods during the Pleistocene. Grain-size distribution is in good accordance with other loess localities in the Pannonian Basin. Garnet, epidote and amphibole are the most abundant heavy minerals in samples of Danube river sediment. The comparison of heavy mineral assemblages (HMF) from LPS with that of the Danube river, shows that the main source area for loess in Baranja was in the Danube flood plain sediments. Main transport direction was from North or Northwest. Nevertheless the higher concentration of amphiboles in LPS (mean 26.3% in HMF) than in the Danube plain suggests an additional source area. Although the Western Carpathians with Neogene calc-alkaline volcanic rocks are the major source for amphiboles in the Pannonian Basin, those minerals may partly originated also from locally exposed volcanic and metamorphic rocks of the southward Slavonian Mountains. Mount Krndija and Mount Papuk, which of all Slavonian Mts. are closest to Baranja, consist indeed of amphibolites. In that case, a small amount of silt material for Baranja loess would be transported by WSW winds. Results obtained from sedimentological and SEM analyses show fairly good congruence with results from other LPS in the Pannonian Basin, with some differences in mineral composition which imply diversity and shifting of source area for Baranja loess during the Late Pleistocene.

Provenance of Tertiary sandstone in the northern Qaidam basin, northeastern Tibetan Plateau: Integration of framework petrography, heavy mineral analysis and mineral chemistry

An exceptionally thick Cenozoic sedimentary succession has developed in the Qaidam basin of the northeastern Tibetan Plateau. The provenance remains enigmatic; thus, more precise investigations are needed. An integrated study of sandstone framework petrography, heavy mineral analysis and mineral chemistry was adopted to perform provenance analysis of the Tertiary sandstones in the northern Qaidam basin.No individual method exists that can provide comprehensive provenance interpretations on spatial and temporal variations. Based on three types of data, three depositional areas can be distinguished. Sandstones of Area A exhibit relatively high abundances of quartz, garnet and zircon, as well as relatively high textural maturity, implying long-distance sources. Multi-composition garnets and tourmalines reveal derivations of metasedimentary rocks and intermediate-acidic igneous rocks. Sandstones of Area B are rich in metamorphic lithic fragments, epidote and garnet. A dominance of Fe-rich garnets with low Mg, low Mn and variable Ca contents and dravites demonstrates predominant derivation of metasedimentary rocks. Therefore, the North Qaidam and South Qilian terranes are potential source areas for these two depositional areas. Additionally, high metamorphic heavy mineral abundances in the upper formations imply increasing contributions of these two metamorphic belts during the Tertiary tectonic uplift. However, sandstones of Area C are characterized by relatively high abundances of feldspar, igneous heavy minerals and high-Fe+Mn garnet, which suggest a main source of igneous rocks. The Altun and Qilian Mountains are potential source regions. Furthermore, increasing amounts of feldspar and igneous heavy minerals in the upper formations indicate a significant presence of igneous parent rocks, which are most likely a response to the multi-stage uplift events in the Altun Mountains since the early Eocene.

Rare earth element compositions of core sediments from the shelf of the South Sea, Korea: Their controls and origins

Rare earth elements (REEs) of bulk sediments and heavy mineral samples of core sediments from the South Sea shelf, Korea, were analyzed to determine the constraints on REE concentrations and distribution patterns as well as to investigate their potential applicability for discriminating sediment provenance. Bulk sediment REEs showed large variation in concentrations and distribution patterns primarily due to grain size and carbonate dilution effects, as well as due to an abundance of heavy minerals. In the fine sandy sediments (cores EZ02-15 and 19), in particular, heavy minerals (primarily monazite and titanite/sphene) largely influenced REE compositions. Upper continental crust-normalized REE patterns of these sand-dominated sediments are characterized by enriched light REEs (LREEs), because of inclusion of heavy minerals with very high concentrations in LREEs. Notably, such a strong LREE enrichment is also observed in Korean river sediments. So, a great care must be taken when using the REE concentrations and distribution patterns of sandy and coarse silty shelf sediments as a proxy for discriminating sediment provenance. In the fine-grained muddy sediments with low heavy mineral abundance, in contrast, REE fractionation ratios and their UCC-normalized patterns seem to be reliable proxies for assessing sediment provenance. The resultant sediment origin suggested a long lateral transportation of some fine-grained Chinese river sediments (probably the Changjiang River) to the South Sea of Korea across the shelf of the northern East China Sea.

Cenozoic forearc basin sediments in Southern Peru (15–18°S): Stratigraphic and heavy mineral constraints for Eocene to Miocene evolution of the Central Andes

A large sedimentary forearc basin developed in Cenozoic times between the present-day Coastal Cordillera and the Western Cordillera of the Central Andes, called Moquegua basin in southern Peru. The basin is filled by Moquegua Group deposits (~ 50 to 4 Ma) comprising mostly siliciclastic mudstones, sandstones and conglomerates as well as volcanic intercalations. Several facies changes both, along orogenic strike and through time, are described and have led to subdivision into four sedimentary units (Moquegua A, B, C and D). In this paper we present a refined stratigraphic scheme of the Moquegua Group combined with the first provenance analysis of the Moquegua basin based on (i) semi-quantitative analysis of heavy mineral abundance, (ii) electron microprobe (EMP) and laser ablation (LA) ICP-MS analyses of single detrital amphibole and Fe–Ti oxide grains, and (iii) comparative analysis of the different potential source rocks to clearly identify the most likely sources. Results allow us to reconstruct sediment provenance and to relate changes of the erosion-sedimentation system in the Moquegua basin to the evolution of the Andean orogen. At ~ 50 to ~ 40 Ma the Moquegua basin was close to sea level and fed by low energy rivers transporting mainly metamorphic basement and Jurassic-Cretaceous sedimentary detritus from local and distal sources. The latter might be as far as the present Eastern Cordillera. From ~ 35 Ma on the distal sediment sources were cut off by the uplift of the Altiplano and Eastern Cordillera leading to higher energy fluvial systems and increasing importance of local sources, especially the relevant volcanic arcs. From 25 Ma on volcanic arc rocks became the predominant sources for Moquegua Group sediments. The 10 Ma time lag observed between the onset of uplift-induced facies and provenance changes (at ~ 35 Ma) and the onset of intense magmatic activity (at ~ 25 Ma) suggests that magmatic addition was not the main driver for crustal thickening and uplift in the Central Andes during latest Eocene to Oligocene time.

Provenance study of early and middle bronze age pottery from Kaman-Kalehöyük, Turkey, by heavy mineral analysis and geochemical analysis of individual hornblende grains

The provenance of Early Bronze Age and early Middle Bronze Age pottery produced between 2100 and 1970 B.C. and excavated from Kaman-Kalehöyük, Turkey was studied using mineralogical methods, including heavy mineral analysis and geochemical study of individual hornblende grains. The relative abundances of heavy minerals in the fabrics of 20 Early Bronze Age (EBA) and early Middle Bronze Age (MBA) pottery sherds, together with 27 local sediments collected within a radius of 25 km of the site were studied. The heavy mineral distributions in the Kaman region were statistically analyzed for consistencies in their occurrence. Amphibole was found to be the most abundant heavy mineral in most of the analyzed samples, followed by titanite and epidote. The amounts of other minerals such as garnet, clinopyroxene, and zircon are subordinate. Different proportions of heavy minerals in the fabrics allow categorization of the EBA and early MBA potteries into 5 groups. Comparative study of heavy mineral assemblages of local sediments and pottery suggests that half of the EBA and most of the MBA potteries were produced from sediment near the excavation site, whereas the other half of the EBA potteries were produced from sediment occurring at 25 km east or more east of the site. The geochemistry of individual amphibole grains was studied by electron-microprobe analysis. Most of the studied amphibole grains are calcic and aluminous, corresponding to hornblende. They can be further characterized into four types based on their chemical composition. The combination of heavy mineral identity and hornblende geochemistry provides diagnostic evidence for the origins of Kaman-Kalehöyük pottery. These and analogous heavy mineral techniques are effective archaeometric tools for determining pottery provenance.

Geochemistry of the Lower Cretaceous Chaswood Formation, Nova Scotia, Canada: provenance and diagenesisGeological Survey of Canada Contribution 20080004.

The fluvial Chaswood Formation records a complex history of tectonic reactivation of basement horsts and shedding of clastic sediment. Previous mineralogical studies indicate sources from both local and more distant basement rocks of the Appalachians. Because such mineralogical studies identify only particular source rocks, the geochemistry of 60 samples from a complete section through the Chaswood Formation in borehole RR-97-23 was investigated to determine the character of bulk sediment supply. The detrital signature is partially obscured by diagenetic processes that caused concentration of K, P, Sr, and U at three regional unconformities. The elements Ti (in ilmenite and its alteration products), Zr (in zircon), Th, and Y are largely controlled by the abundance of heavy minerals in the rocks. Ilmenite is the dominant first-cycle heavy mineral, whereas much of the zircon is of polycyclic origin; therefore, the Ti/Zr ratio is a guide to the proportion of first-cycle sediment supply from crystalline basement. High Cr, Sr, and Ni/Co ratio in mudstones appear related to supply from weathered mafic crystalline basement. Three cycles of sediment supply are recognized, each overlying a regional unconformity. These reflect uplift of horsts that resulted first in shedding of readily eroded Carboniferous sandstones, then rapid erosion of crystalline basement and, finally, greater supply of deeply weathered regolith. This study provides a template for interpreting more distal sediments in the Scotian Basin, where the direct effects of source-area tectonics are not recorded in the stratigraphic succession.

Evidence for an eolian origin for the silt-enriched soil mantles on the glaciated uplands of eastern Upper Michigan, USA

We provide textural, geochemical, and mineralogical data on a thin, silty deposit that unconformably mantles glaciated uplands in the eastern Upper Peninsula of Michigan. Previous research on this deposit, which we hypothesize to be loess, is nonexistent. The uplands were islands or narrow peninsulas within one or more glacial lakes. We compare the distribution, likely source and nature of the 20–60 cm thick silty mantle by using the loess formation model of Mason et al. [Mason, J.A., Nater, E.A., Zanner, C.W., Bell, J.C., 1999. A new model of topographic effects on the distribution of loess. Geomorphology 28, 223–236], which focuses on the generation of eolian silt by saltating sand across upwind, barren surfaces. Parabolic dunes, with arms open to the NW, are common on former lake floors upwind of the silt-mantled uplands, attesting to the strength and direction of paleowinds. The abrupt termination of the dunes at the footslopes of the uplands, associated with silt deposition on upland soil surfaces in downwind locations, are both consistent with the model of Mason et al. [Mason, J.A., Nater, E.A., Zanner, C.W., Bell, J.C., 1999. A new model of topographic effects on the distribution of loess. Geomorphology 28, 223−236]. Sediments on former lake floors contain abundant strata of fine/medium sand and silt, and thus are likely sources for the silt and dune sand. The cap, dune and lake sediments are similar along many different geochemical axes, whereas the substrate sediment, i.e., the drift below the cap, is unique. Cap sediments, normally containing roughly 30% silt, are enriched in quartz and depleted in Ti and Zr, relative to dune sediment. The dune sediment, a more residual eolian deposit, is enriched in Ti and Zr, relative to the cap, probably due to its greater abundance of heavy minerals. Therefore, we conclude that the silty cap is loess that was deflated from abandoned lake floors after nearby glacial lakes drained, probably contemporaneously with dune migration across the former lake floors.

REE geochemistry of the recent playa sediments from the Thar Desert, India: An implication to playa sediment provenance

The playas (saline lakes) situated in the Thar Desert, north-west India, provide prominent examples of alkaline brine and varying assemblages of detrital and evaporite mineralogy. The eastern margin of the desert is relatively semi-arid, whereas the central to western region is arid to hyper-arid in nature. Rare earth elements (REEs) systematics in the sediments of nine different playas of the Thar Desert were studied to understand the provenance of the sediments and the intensity of chemical weathering in the region. Based on the REE patterns, fractionation of light REE (LREE) (La/Sm) N and heavy REE (HREE) (Gd/Yb) N, and Eu anomaly (Eu/Eu*), the upper continental crust normalised playa sediments are divided into two different groups. The eastern margin playa sediments show homogeneous REE contents, relatively positive Eu anomaly and depleted HREE values, whereas the western arid core playa sediments have highly variable REE contents, relatively negative Eu anomaly and similarly fractioned LREE and HREE patterns. The dissimilarity in the degree of HREE fractionations both in the eastern and western playa sediments is attributed to the differential distribution of minerals, depending upon their resistance to chemical weathering. It is believed that the relatively higher abundance of REE bearing heavy minerals and the presence of higher amounts of evaporites influence the large variation of REE distribution and enriched HREE in the western playa sediments. Apart from the relatively higher abundance of heavy minerals, the presence of rock fragments of variable petrographic character and roundness mirror the lower rock–water interaction in the arid western region. The presence of well-rounded metamorphic rock fragments and minerals, sourced from the eastern margin Aravalli mountains, indicates that the playas of the entire desert get the detrital and dissolved material mainly from the Aravalli mountains. Additionally, the western playas receive sediments from their surrounding Proterozoic and Mesozoic formations. This interpretation is supported by the presence of angular rock fragments of basalt, rhyolite and limestone in the western playas.

Major and trace elements in pyrope–almandine garnets as sediment provenance indicators of the Lower Carboniferous Culm sediments, Drahany Uplands, Bohemian Massif

The Lower Carboniferous Culm Basin is part of the European Variscan foreland basin. Garnet is an abundant heavy mineral at all stratigraphic levels of the Culm sediments (the Protivanov, Rozstání and Myslejovice Formation from base to top). This paper compares the major element (electron microprobe) and trace element (LA-ICP-MS) compositions of garnet for the purpose of studying the provenance of the Culm sediments. The polymict garnet assemblages ranging from the Protivanov to lower part of the Myslejovice Formation (Goniatite zones Pe γ-Go α) pass into oligomict ones dominated by pyrope–almandine garnets (uppermost part of the Myslejovice Formation; Goniatite zones Go β-Go γ). As the predominant low-grossular pyrope–almandines from oligomict garnet assemblages are very uniform and homogeneous in major element composition, we studied their trace element composition and zoning. Pyrope–almandine garnets are poor in LREE and show enrichment in HREE; the chondrite-normalized patterns are almost flat from Dy to Lu and show a significant negative Eu anomaly, typical for granulite-grade garnets. Major element compositions of detrital low-grossular pyrope–almandines can only be matched with some granulites and garnetiferous felsic gneisses of the Bohemian Massif. Garnets from granulites cropping out at the present-day erosion level of the Bohemian Massif have usually higher Ca and/or lower Mg contents. The major and trace element compositions and zoning patterns of pyrope–almandine garnets from the upper part of the Myslejovice Formation compare well with garnets from the Miroslav granulites and small Moldanubian granulite bodies west of the Třebíč Massif. The Moldanubian granulites are commonly associated with mantle-derived peridotites and eclogites. The presence of detrital Cr-spinels with high Cr# and low Mg# (single grains of Cr-spinels and fine-grained kelyphitic intergrowths of Cr-spinel with chlorite) comparable with spinel types from Moldanubian peridotites could indicate the joint occurrence of peridotites, serpentinized peridotites, and granulites at the erosion level of the Bohemian Massif during the deposition of the uppermost Culm sediments (325 Ma). While the older Culm sediments (polymict garnet assemblages) represent the accumulation of clastic material from the northern and north-western areas (Moravo-Silesian and Lugian Zone), the uppermost Culm sediments (oligomict garnet assemblages) contain material from western and south-western areas (Moldanubian Zone and Moravian Nappe); the general influx of clastic material changed as a result of clockwise rotation of the eastern part of the Variscan belt during this time span (340–325 Ma).

Surface sediment chemistry in the Olympic Games 2004 Sailing Center (Saronikos Gulf)

Construction of the Olympic Games 2004 Sailing Center is planned in the Saronikos Gulf, in the area of Agios Kosmas. A multi-disciplinary base-line study was carried out to provide background levels of inorganic and organic pollutants before the construction. Two shallow reefs (water depth 2-3 m) are the predominant features in the area’s underwater topography. The reef consists of solid rock formations and pebbles, whereas sandy sediments cover predominantly the remaining seabed. Some pockets of fine-grained sand were identified within the existing marina. Sedimentary heavy metal contents were found to be low, showing only slight heavy metal enrichment, attributed mainly to heavy mineral abundance in the area. A small enrichment for lead could be related to anthropogenic sources. Patterns of low concentrations were observed for organic carbon and organic nitrogen. Conversely, the sediment petroleum hydrocarbon content was found to be relatively high, implying anthropogenic pollution related to ship effluents and increased marine traffic.

Transport and Deposition of Cassiterite by a Malaysian Stream

ABSTRACT Low abundances of heavy minerals, such as cassiterite and gold, in natural sediments make it difficult to observe and monitor the sedimentological processes that lead to the development of their placer deposits in fluvial channels. We have overcome this problem by installation of a pit trap in a Malaysian stream that contains abnormally high concentrations of cassiterite. Rates of accumulation of cassiterite grains up to 500 µm and sediment up to 32 mm have been measured under changing discharges during a flood event. Transport-equivalent sizes of sediment and cassiterite are obtained, and the critical shear stresses to mobilize different sizes of sediment and cassiterite are estimated from their rating curves. Rates of accumulation of both cassiterite and sediment vary systematically with grain size and changing discharge. Mobilization of fine (< 180 µm) cassiterite requires higher shear stresses than like-sized sediment, and once mobilized this cassiterite is transported at velocities similar to those of sediment approximately three times coarser--roughly a 50% greater difference in size than would be expected on the basis of hydraulic equivalence. For larger grains the critical shear stresses required to mobilize sediments and cassiterite increase, but also converge, so that near the upper limit of grain hiding, both the critical shear stresses and transport-equivalent sizes of cassiterite and sediment are most similar. This convergence likely results from increased exposure to s ream flow facilitating grain entrainment and motion, regardless of grain density, as the grains become too large to hide in the bed. Results emphasize the importance of grain size and bed roughness, as well as differences in density, in developing fluvial concentrations of heavy minerals. In particular, repeated grain settling, entrainment, and motion is most effective in concentrating heavy minerals that are sufficiently fine to be fully hidden in the bed.

SHRIMP constraints on sediment provenance and transport history in the Mesozoic Statfjord Formation, North Sea

Detrital zircons in sandstones of the Statfjord Formation (late Triassic-early Jurassic) in the northern North Sea have been dated with the sensitive high resolution ion microprobe (SHRIMP). These sandstones lack detailed biostratigraphic control, but display distinct variations in heavy mineral assemblages which facilitate a three-fold subdivision of the sequence. The lower and middle zones (heavy mineral Zones A and B) have similar characteristics, both displaying a marked upward decline in garnet abundance which has proved difficult to attribute unambiguously to change in either provenance or sedimentation history. The base of the highest zone (heavy mineral Zone C) is marked by changes in several heavy mineral indicators attributable to a shift in ultimate provenance compared with the underlying zones. The detrital zircon ages are a direct fingerprint of the sediment source terrains, and so resolve ambiguities in interpreting provenance from heavy mineral abundances alone. The age spectra indicate that both low-garnet and high-garnet parts of Zone A have the same ultimate provenance. This strongly suggests that garnet removal was not a function of changing provenance, but took place during the sedimentation process, probably by weathering during periods of prolonged alluvial storage. The source of Zone A is not represented in any presently exposed landmass: the required combination of Caledonian granitoids intruding or in immediate proximity to high-grade Archaean-sourced metasediments is likely to have been either to the west, in the northern part of the Shetland Platform, or to the north, in what is now the Norwegian Sea. Zircons in Zone C have a distinctly different age spectrum consistent with a source in the Western Gneiss Region of southern Scandinavia, where there is the required combination of Proterozoic protoliths and Caledonian reworking.

Heavy Mineral and Geochemical Studies of Lower Bharathapuzha Sediments, Kerala

Abstract Size specific abundance of heavy minerals (HM) in sediments of lower Bharathapuzha indicates an increase towards finer sizes, with the average maxima at ASTM +170. HM content in the bulk sample is similar to that of ASTM +60. Opaques, hornblende and pyroxenes are responsible for more than 90% variability. Garnet, monazite, zircon and sillimanite are least abundant. Hornblende, pyroxene and garnet are enriched in ASTM +60 but depleted in ASTM +230, whereas opaques show a reverse trend. HM content of bulk is similar to that of ASTM +60 and +120. Heavy metal distribution has also been examined and the order of abundance is Fe&amp;gt;Mn&amp;gt;Ni&amp;gt;Cr&amp;gt;Zn&amp;gt;Pb&amp;gt;Cu&amp;gt;Cd. Bulk samples show the lowest content. Mud fraction is emiched in metals, i.e., more than five fold for Zn, Cu and around three fold for Ni, Cr, Mn and Fe. The difference of metal abundance between HM and mud fraction is only marginal for Ni and Pb. In HM, Cd, Cu and Zn content are very low whereas Cr, Mn and Fe are enriched. EF (Enrichment Factor) values of Cu, Zn, Cr and Mn are close to crustal abundance whereas Cd and to a small extent Pb show relatively high values possibly resulting from anthropogenic contributions.