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1.
Mayla A. Ramos-Vázquez John S. Armstrong-Altrin Leticia Rosales-Hoz María L. Machain-Castillo Arturo Carranza-Edwards 《Arabian Journal of Geosciences》2017,10(6):148
Coastal margins, especially the river-influenced coastal areas, are considered as active interfaces between the continental and oceanic environments, which have huge dispersal of detrital materials and heavy metal input. It is well determined that the fine-grained sediments are important reservoir for the accumulation of heavy metals. In this study, we analyzed the radiocarbon age, texture, organic matter, carbonate content, and geochemical compositions of two sediment cores (GM42 and GM44) retrieved in front of the Coatzacoalcos River mouth basin, southwestern Gulf of Mexico (～864 and 845 m water depth, respectively). Our objective was to infer the sedimentation rate, intensity of weathering, provenance, and influence of anthropogenic activities on heavy metal contamination in sediments. The radiocarbon-age measurements of mixed planktonic foraminifera for core GM44 reveals an age of 21,289 ± 136 cal. years B.P., which fall within the Late Glacial Maximum (LGM; 21000 ± 2000 years B.P). The calculated sedimentation rate for core GM42 (~0.013 cm/year) is lower than in core GM44 (0.022 cm/year), which is probably due to the variations in detrital sediment input and/or seafloor topography. The weathering indices such as chemical index of alteration (CIA), chemical index of weathering (CIW), and plagioclase index of alteration (PIA) suggested that the source area experienced low to moderate intensity of chemical weathering under warm to humid climatic conditions. The SiO2/Al2O3, Al2O3/Na2O, and K2O/Al2O3 ratio values indicated moderate to high compositional maturity. The major and trace element concentrations suggested that the sediments were likely derived from intermediate source rocks. The heavy metal contents indicated that the sediments were not contaminated by the industrial waste disposals supplied by the Coatzacoalcos River. The redox proxy sensitive elements such as V, Cr, Cu, and Zn indicated an oxic depositional environment for the deep-sea sediment cores. The application of discrimination diagrams for the geochemistry data revealed a passive margin setting for the sediment cores. The compositional variations observed at the upper sections (<30 cm) between the two sediment cores revealed that the type of detrital sediments supplied by the Coatzacoalcos River to the deep sea area is not uniform, which is also revealed by the variation in sedimentation rate. 相似文献
2.
《Applied Geochemistry》2004,19(5):769-786
Heavy metal (Zn, Cd, Cu and Pb) mass balances in the Lot-Garonne fluvial system have been established for 1999 and 2000. The mean annual discharges of these years are close to the mean discharge of the previous decade. The estimated annual dissolved and particulate fluxes in this model watershed integrate daily input from diffuse and point sources, diffusive fluxes at the water/sediment interface, changes in the dissolved-particulate partition and changes in sediment stock. Cadmium, Zn, Cu and Pb entering the Gironde estuary via the Garonne River (11–14 t a−1 of Cd; 1330–1450 t a−1 of Zn; 126–214 t a−1 of Cu and 127–155 t a−1 of Pb) are mainly transported in the particulate phase and the major part (i.e. ∼74 to 96% for Cd, ∼60% for Zn, ∼50 to 60% for Cu and ∼80% for Pb) is transported by the Lot River. The main anthropogenic heavy metal point source is located in a small upstream watershed (Riou-Mort River) accounting for at least 47% (Cd), ∼20% (Zn), ∼4% (Cu) and ∼7 to 9% (Pb) of the total heavy metal inputs into the Garonne River, although it contributes only 1% of the discharge. Mass balances for 1999 suggest that under mean annual hydrologic conditions on the basin scale, the heavy metal budget of the Lot-Garonne fluvial system is balanced and that the stocks of Cd [200 t; Environ. Tech. 16 (1995) 1145] and Zn in the Lot River sediment are constant under mean discharge conditions. Heavy metal input by molecular diffusion at the sediment surface represents an important component of dissolved metal inputs into the system (e.g. 30% for Cu). Except for Cu, these dissolved inputs are totally removed from solution by SPM. Based on the generally constant Zn/Cd (∼50) concentration ratio in sediment cores from the polluted Lot River reaches and the sediment stock of Cd [200 t; Environ. Tech. 16 (1995) 1145], the present day Zn stock in the Lot River sediments has been estimated at about 10,000 t. In addition to the mobilization of river-bed sediment and associated heavy metals by intense floods, local human activities, including river-bed dredging, may strongly modify the heavy metal budget of the river system. In 2000, the dredging-related remobilization of polluted Lot River sediment released 2–6 t Cd. This additional Cd point source was estimated to account for 15–43% of the gross inputs into the Gironde Estuary. 相似文献
3.
The “North American shale composite”: Its compilation,major and trace element characteristics 总被引：6，自引：0，他引：6
L.Peter Gromet Larry A. Haskin Randy L. Korotev Robert F. Dymek 《Geochimica et cosmochimica acta》1984,48(12):2469-2482
The compilation and major element composition of the “North American shale composite” (NASC) are reported for the first time, along with redeterminations for the REE and selected other elements by modern, high precision analytical methods. The NASC is not strictly of North American origin; 5 of the constituent samples are from Africa and Antarctica, and 15 are from unspecified locations. The major element composition of the NASC compares quite closely with other average shale compositions. New analyses of the NASC document that significant portions of the REE and some other trace elements are contained in minor phases (zircon and possibly other minerals) and that their uneven distribution in the NASC powder appears to have resulted in heterogeneity among analyzed aliquants. The results of this study show that the REE distributions of detrital sediments can be dependent to some extent on their minor mineral assemblages and the sedimentological factors that control these assemblages. Consequently, caution should be exercised in the interpretation of the REE distributions of sediment samples as they may be variable and biased relative to average REE distribution of the crustal rocks supplying detritus. These effects appear to be largely averaged out in sediment composites, with the result that their REE distributions are more likely to be representative of their provenances. 相似文献
4.
《Applied Geochemistry》2004,19(3):261-271
The distribution of Rare Earth Elements (REE) was investigated in the acidic waters (lake and groundwater) of a lignite mining district (Germany). The Fe- and SO4-rich lake water (pH 2.7) displays high REE contents (e.g. La∼70 μg/l, Ce∼160 μg/l) and an enrichment of light REE (LREE) in the NASC normalised pattern. Considering the hydrodynamic model and geochemical data, the lake water composition may be calculated as a mixture of inflowing Quaternary and mining dump groundwaters. The groundwater of the dump aquifer is LREE enriched. Nevertheless, the leachates of dump sediments generally have low REE contents and display flat NASC normalised patterns. However, geochemical differences and REE pattern in undisturbed lignite (LREE enriched pattern and low water soluble REE contents) and the weathered lignite of the dumps (flat REE pattern and high water soluble REE contents) suggest that lignite is probably the main REE source rock for the lake water. 相似文献
5.
A systematic study of the granulometric properties and the occurrence and distribution of rare earth elements (REE) within
surface sediments from ten bays situated along the coast of Southeast China has facilitated a more rigorous understanding
of constraints on sediment provenance in the area. The results show that REE concentrations are similar within a single bay,
but vary considerably (133.58–251.77 mg/kg) among the bays. The chondrite-normalized distribution patterns show the typical
enrichment of light REEs (LREEs: La–Eu) relative to heavy REEs (HREEs: Gd–Lu), and an apparent depletion of Eu, which is diagnostic
of a terrigenous sediment source. Obvious enrichments of the middle REEs (MREEs: Sm–Ho) in the PAAS-normalized (Post-Archean
Australian Shale) distribution patterns of these bay sediments are similar to results reported from large rivers in China.
Comparing the REE composition of the bay sediments with those of adjoining fluvial sediments and with the bedrock of the surrounding
drainage basins, the latter are indicated as the dominant sediment source. The uniform REE distribution patterns, and MREE
enrichments, prove that the sediments are derived from the material transported by the streams and rivers that discharge into
the bays. 相似文献
6.
Geochemical study of the Holocene sediments of the Meghna River Delta, Chandpur, Bangladesh was conducted to investigate the distribution of arsenic and related trace and major elements. The work carried out includes analyses of core sediments and provenance study by rare earth element (REE) analysis. Results showed that the cores pass downward from silty clays and clays into fine to medium sands. The uppermost 3 m of the core sediments are oxidized [average oxidation reduction potential (ORP) + 230 mV], and the ORP values gradually become negative with depths (−45 to −170 mV), indicating anoxic conditions prevail in the Meghna sediments. The REE patterns of all lithotypes in the study areas are similar and are comparable to the average upper continental crust. Arsenic and other trace elements (Pb, Zn, Cu, Ni, and Cr) have greater concentrations in the silts and clays compared to those in the sands. Positive correlation between As and Fe was found in the sediments, indicating As may be adsorbed on Fe oxides in aquifer sediments. 相似文献
7.
Six graywackes from the Archean greenstone belt in the Wind River of Wyoming and 11 graywackes and three shales from the Archean Fig Tree Group, South Africa, were analyzed for the rare earth elements (REE). There are real deviations beyond analytical uncertainty among sediments from the same formation. The absolute abundance of the REE (∑REE) is somewhat lower than that of the North American shale composite (NASC) which is representative of younger sedimentary rocks. Still, the results confirm previous suggestions that the RE pattern in Precambrian sediments is the same as the NASC but that, relative to the heavy REE, graywackes are slightly enriched in the light REE, shales are depleted, and there is a slight enrichment in Eu relative to the NASC. The average abundance of Eu relative to the other REE for all the Precambrian sediments is the same as that in chondritic meteorites. Attesting to the complexity of graywacke genesis, there is no correlation between the variations in the REE parameters and the variations in major or minor element concentrations. In particular, there is no obvious correlation between the excess Eu and Sr abundance. The total amount of REE, the ratio, and the Eu enrichment factor, however, all increase in the graywackes with the amount granite-gneiss detritus in the rocks. In general, the REE distributions in Archean graywackes and shales appear to be related to the relative amounts of clastic feldspar, mica, and minor phases which concentrate the REE. 相似文献
8.
9.
《Applied Geochemistry》1998,13(3):293-304
Distributions of 15 elements with depth in two sediment cores from Puck Bay in the Gulf of Gdansk show that Ag, Cd, Pb, Zn and possibly Cu and Ni are anthropogenically enriched in the sediments there. The concentrations of these elements decrease sharply with depth in the sediment column and the elements are preferentially enriched in the <2 μm size fraction of the sediment. The sequence of element enrichment depends on whether the enrichment factor (EF) and the anthropogenic factor (AF) are used to calculate the element enrichment. By contrast, the anthropogenic elements show no systematic decrease in concentration with depth in a sediment core taken from near the mouth of the Vistula River. This reflects the higher sedimentation rate there such that the entire upper 20 cm of the core was deposited during the major, post-war period of industrialization in Poland. In addition, these elements are enriched in the 2–63 μm fraction compared to the <2 μm fraction in these sediments. This suggests that the heavy metals are mainly adsorbed on Fe oxyhydroxide particles with diameters greater than 2 μm at the hydrological front where Vistula river water mixes with brackish Baltic water. It appears that heavy-metal pollution of sediments in parts of Puck Bay may be greater than that near the mouth of the Vistula River which may reflect, in part, the higher sedimentation rate near the mouth of the Vistula River. The mode of incorporation of heavy-metals into the sediments in the two areas may also be different. 相似文献
10.
《Chemie der Erde / Geochemistry》2014,74(4):557-570
The Matomb region constitutes an important deposit of detrital rutile. The rutile grains are essentially coarse (> 3 mm), tabular and elongated, due to the short sorting of highly weathered detritus. This study reports the major, trace, and rare-earth element distribution in the bulk and rutile concentrated fractions. The bulk sediments contain minor TiO2 concentrations (1–2 wt%), high SiO2 contents (∼77–95 wt%) and variable contents in Al2O3, Fe2O3, Zr, Y, Ba, Nb, Cr, V, and Zn. The total REE content is low to moderate (86–372 ppm) marked by high LREE-enrichment (LREE/HREE ∼5–25.72) and negative Eu anomalies (Eu/Eu* ∼0.51–0.69). The chemical index of alteration (CIA) shows that the source rocks are highly weathered, characteristic of humid tropical zone with the development of ferrallitic soils. In the concentrated fractions, TiO2 abundances exceed 94 wt%. Trace elements with high contents include V, Nb, Cr, Sn, and W. These data associated with several binary diagrams show that rutile is the main carrier of Ti, V, Nb, Cr, Sn, and W in the alluvia. The REE content is very low (1–9 ppm) in spite of the LREE-abundance (LREE/HREE ∼4–40). The rutile concentrated fractions exhibit anomalies in Ce (Ce/Ce* ∼0.58 to 0.83; ∼1.41–2.50) and Eu (Eu/Eu* ∼0.42; 1.20–1.64). The high (La/Sm)N, (La/Yb)N and (Gd/Yb)N ratios indicate high REE fractionation. 相似文献
11.
Rare earth element studies of surficial sediments from the southwestern Carlsberg Ridge,Indian Ocean
The rare earth element (REE) contents of sixteen surficial calcareous sediments from the southwestern Carlsberg Ridge, Indian
Ocean, have been determined. The total REE vary from 35 ppm to 126 ppm and are inversely related to the calcium carbonate
content. REEs show a strong positive correlation with Al + Fe + K + Mg + Na (r
2= 0.98) and Mn + Fe + Cu + Ni (r
2= 0.86) suggesting that the REE is associated with a combined phase of clays (mainly illite) and Mn-Fe oxyhydroxides. The
aeolian input into these sediments is suggested from the weak positive Eu/Eu* anomaly. Shale-normalized (NASC) pattern along
with La(n)/Yb(n) ratio suggest enrichment of heavy REE (HREE) relative to the light REE (LREE) with a negative Ce/Ce* anomaly implying retention
of a bottom water REE pattern.
An erratum to this article is available at . 相似文献
12.
煤系高岭岩的地球化学判别标志 总被引：7，自引：0，他引：7
本文主要研究了煤系高岭岩的微量、稀土、氧同位素地球化学特征。根据高岭岩产出层序、岩石学、矿物学、地球化学特征的研究，将煤系高岭岩分为两类：（１）铝土质高岭岩，微量元素含量、稀土总量，氧同位素值高，稀土配分模式与典型北美页岩相似，Ｅｕ负异常，反映其源岩为风化壳化学风化作用产物。（２）夹矸高岭岩，微量元素含量，稀土总量，氧同位素值低，稀土配分模式部分与典型北美页岩相似，反映其源岩与铝土质高岭岩类似；部 相似文献
13.
Kananathan Amalan Amila Sandaruwan Ratnayake Nalin Prasanna Ratnayake Shanaka Maduranga Weththasinghe Nimila Dushyantha Nalika Lakmali Ranjith Premasiri 《Environmental Earth Sciences》2018,77(21):737
Beach sediments in Sri Lanka contain industrial-grade heavy mineral occurrences. Samples of both offshore and onshore sediments were collected to examine the provenance, mineralogy and geochemical compositions of the heavy mineral occurrences. Coastal morphodynamic changes along the coastline of Sri Lanka were analyzed using the time-series satellite images. These coastal morphodynamic changes were used to identify the prominent directions of monsoon-influenced longshore currents, coastal sediment accretion and depositional trends and their relationships to the provenance of the heavy minerals. Results show the concentrations of detrital ilmenite, zircon, garnet, monazite, and rutile vary in the onshore and offshore sediments. The heavy mineral potential of the northeastern coast is high (average contents of about 45–50% in the Verugal deposit, 70–85% in the Pulmoddai deposit, and 3.5–5.0% in offshore samples stretching from Nilaveli to Kokkilai), compared to sediments in southwest (average content about 10% in onshore sediments and 2% in offshore sediments from the mouth of the Gin River). Therefore, no economic-grade heavy mineral placers were identified in the offshore environments. The high concentrations of heavy minerals in beach sediments and low concentrations in offshore sediments suggest operation of a panning system in the surf zone to form enriched placer deposits. Major and trace element compositions of beach sediments show marked enrichments of TiO2, Fe2O3, La, Ce, Zr, Cr, Nb, Th and V compared to average Upper Continental Crust (UCC) values. Analysis of prominent coastal longshore transport patterns identifies bidirectional sediment transport in the northeast coast of Sri Lanka. In the southwestern coast, two transport directions occur with anti-clockwise transport from Galle to Hambantota, and clockwise transport from Hikkaduwa to Wadduwa. The heavy minerals in the placers were mainly derived from Precambrian metamorphic rocks, and transported to the coast through the river systems of Sri Lanka. 相似文献
14.
北京平原沉积物稀土元素地球化学特征及物源意义 总被引：2，自引：0，他引：2
文中总结了北京平原永定河、潮白河流域钻孔沉积物中稀土元素分布特征,两流域沉积物稀土元素总量∑REE、轻重稀土比(LREE/HREE)及轻(La/Sm)N、重(Gd/Yb)N稀土分馏特征差异较为显著。粒度对沉积物稀土分布(总量、轻重稀土比及分馏特征)有一定影响;各流域沉积物均表现为轻稀土相对富集、弱Eu负异常的球粒陨石标准化曲线。细颗粒沉积物稀土分馏特征(La/Yb)N有较好的物源示踪意义。根据沉积物(La/Yb)N值对永定河、潮白河交互沉积区不同深度沉积物进行了物源示踪,不同深度上沉积物来源不同。此外,同一流域上、中、下游沉积物稀土分馏特征不同。常量元素Al2O3/Fe2O3与稀土元素(La/Yb)N划分结果相符,但精度低于稀土元素物源分析。 相似文献
15.
Behavior of heavy metals in sulfide mine tailings and bottom sediment (Salair,Kemerovo region,Russia) 总被引：2，自引：1，他引：1
The given work focused on solving the problem of environmental geochemistry related to investigation of element speciation,
their mobility, and migration in polluted areas. The purpose was to describe quantitatively migration, distribution, and redistribution
of heavy metals by the example of the old tailings (Talmovaya sands) of the Lead Zinc Concentration Plant (Salair, Kemerovo
region, Russia) and technogenic bottom sediments of the Malaya Talmovaya river. Contents of elements in the sulfide tailings
range in the following limits: Zn: 1,100–27,000 ppm, Cd: 1.3–240 ppm, Pb: 0.01–0.81 ppm, Cu: 220–960 ppm, As: 15–970 ppm,
Fe: 19,000–76,000 ppm, and Ba: 80,000–1,00,000 ppm. Element concentrations in the river sediment are proportional to the element
contents in the sulfide tailings. Element speciations in the sulfide tailings and technogenic bottom sediments were investigated
by the modified sequential extraction procedure. Chemical forms of heavy metals in pore water and surface water were calculated
by WATEQ4F software. Principles of heavy metal migration in the sulfide tailings and technogenic bottom deposits were established.
The obtained results about element species in the sulfide tailings and sediment explain the main principles of element migration
and redeposition. In the mine waste and technogenic bottom deposits, there is vertical substance transformation with formation
of geochemical barriers. 相似文献
16.
《Chemie der Erde / Geochemistry》2015,75(3):375-387
Banded iron-formations (BIFs) form an important part of the Archaean to Proterozoic greenstone belts in the Southern Cameroon. In this study, major, trace and REE chemistry of the banded iron-formation are utilized to explore the source of metals and to constraint the origin and depositional environment of these BIFs. The studied BIF belongs to the oxide facies iron formations composed mainly of iron oxide (mainly magnetite) mesobands alternating with quartz mesobands. The mineralogy of the BIF sample consists of magnetite and quartz with lesser amount of secondary martite, goethite and trace of gibbsite and smectite. The major element chemistry of these iron-formations is remarkably simple with the main constituents being SiO2 and Fe2O3 which constitute 95.6–99.5% of the bulk rock. Low Al2O3, TiO2, and HFSE concentrations show that they are relatively detritus-free chemical sediments. The Pearson’s correlation matrix of major element reveals that there is a strong positive correlation (r = 0.99) of Al with Ti and no to weak negative correlation of Ti with Mn, Ca and weak positive correlation of Si with Ca, suggesting the null to very minor contribution of detrital material to chemical sediment. The trace elements with minor enrichments are transition metals such as Zn, Cr, Sr, V and Pb. This is an indicator of direct volcanogenic hydrothermal input in chemical precipitates. The studied BIF have a low ΣREE content, ranging between 0.41 and 3.22 ppm with an average of 0.87 ppm, similar to that of pure chemical sediments. The shale-normalized patterns show depletion in light REE, slightly enrichment in heavy REE and exhibit weak positive europium anomalies. These geochemical characteristics indicate that the source of Fe and Si was the result of deep ocean hydrothermal activity admixed with sea water. The absence of a large positive Eu anomaly in the studied BIF indicates an important role of low-temperature hydrothermal solutions. The chondrite-normalized REE patterns are characterized by LREE-enriched (Mean LaCN/YbCN = 8.01) and HREE depletion (Mean TbCN/YbCN = 1.61) patterns and show positive Ce anomalies. With the exception of one sample (LBR133), all of the BIF samples analyzed during this study have positive Ce anomalies on both chondrite- and PASS-normalized plots. This may indicate that the BIFs within the Elom area were formed within a redox stratified ocean. The positive Ce anomalies in the studied samples likely suggest that the basin in which Fe formations were deposited was reducing with respect to Ce, probably in the suboxic or anoxic seawaters. 相似文献
17.
Trace metals (Cd,Pb, Cu,Zn and Ni) in sediment of the submarine pit Dragon ear (Soline Bay,Rogoznica, Croatia) 总被引：1，自引：0，他引：1
Vertical profiles of trace metal (Cd, Pb, Zn, Cu, Ni) concentrations, organic matter content, carbonate content and granulometric
composition were determined in two sediment cores from the submarine pit Dragon Ear (Middle Adriatic). Concentrations of the
analyzed metals (Cd: 0.06–0.12 mg kg−1, Pb: 28.5–67.3 mg kg−1, Zn: 17.0-65.4 mg kg−1, Cu: 21.1–51.9 mg kg−1, Ni: 27.8–40.2 mg kg−1) were in usual range for Adriatic carbonate marine sediments. Nevertheless, concentrations of Cu, Zn, and especially Pb in
the upper layer of sediments (top 12 cm) were higher than in bottom layer, while Cd and Ni concentration profiles were uniform.
Regression analysis and principal component analysis were used to interpret distribution of trace metals, organic matter and
carbonate content in sediment cores. Results of both analysis showed that concentrations of all trace metals in the core below
the entrance to the pit were significantly positively correlated with organic matter and negatively correlated with carbonate,
while in the core more distant from the entrance only Pb showed significant positive correlation with organic matter. Obtained
results indicated that, except for lead which was enriched in surface sediment, in the time of sampling (before the building
of the nautical marina) investigated area belonged to unpolluted areas. 相似文献
18.
The geochemical characteristics of an approximately 6‐m‐long sediment core collected from the Jeongokri archaeological site (Hantan River, Korea) were examined to determine the provenance of the sediments and to reconstruct the palaeoenvironment of the study area during the Late Pleistocene (200–127 ka). The core sediments were subdivided into two parts based on grain size: an upper (0–380 cm depth) and lower part (>380 cm depth). The lower part was deposited primarily by fluvial processes during an interglacial period [marine isotope stage (MIS) 7] with warm and humid conditions. Conversely, the upper part was mainly deposited by aeolian processes during a cold and dry glacial period (MIS 6). Geochemical characteristics, represented by major, trace and rare earth element (REE) compositions, and textures of the Jeongokri core sediments show distinct differences between the upper and lower parts. The mineralogy and major, trace and REE compositions indicate that the influence of felsic source rocks (e.g. granite) was dominant in the lower sediments, which were derived from the Hantan River. In contrast, increased quartz content and the very fine and homogeneous grain size in the upper sediments indicate an aeolian origin. REE ratios and distribution patterns, and geochemical signatures indicate that these sediments were derived predominantly from Chinese loess deposits and partially from local sediments from the Korean Peninsula; the possible source area of the upper sediments is the northern part of the Yellow Sea basin. The Yellow Sea basin, having mixed geochemical signatures between Chinese loess and Korean‐derived sediments, was exposed because of low sea levels during MIS 6. The exposed Yellow Sea basin was located in the path of winter‐monsoon winds, which may have carried a great deal of airborne sediments from the basin to the Jeongokri area. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
19.
Robert Cullers Sambhudas Chaudhuri Neil Kilbane Richard Koch 《Geochimica et cosmochimica acta》1979,43(8):1285-1301
The REE (rare-earth) contents of sixty-three <2 μ fractions of Pennsylvanian and Permian platform sediment from the mid-continent of the U.S.A. vary considerably (ΣREE = 46–439 ppm;La/ Lu = 5.2–15.7; correlation coefficient of REE with La/Lu = 0.89), but the Eu/Sm ratios are nearly constant even in reducing environments that concentrate U (0.16–0.22). There is no correlation of REE content to clay mineralogy.Lower Permian <2 μ fractions from continental to nearshore marine sediment in Oklahoma have higher REE content (244–261 ppm) than marine facies in Kansas (46–140ppm), but <2μ Upper Permian fractions in an evaporite basin have constant but high REE content (288–281 ppm; one = 153—ppm). All Pennsylvanian <2 μ fractions from Oklahoma have high REE content (209–439 ppm), and fractions from Kansas cyclothems have variable REE content (86–438 ppm). REE content in the <2 μ fractions is inherited from the provenance, but is modified by ion exchange during weathering, transportation, or deposition. Exchangable REE tend to be concentrated in clay minerals in basic environments, but removed in acid environments.Sand and gravel-size fractions consist mostly of quartz or chert so their REE content is low (7.9–40.6 ppm) although heavy minerals may contribute a large fraction of the REE content. Unexpectedly, silt-size fractions have REE contents (74–355 ppm) that are usually lower but similar to their <2 μ fractions, and the REE contents do not correlate to clay mineral/quartz ratios. The interpretation of REE content in sedimentary rocks needs to be done cautiously due to the above factors. 相似文献
20.
REE geochemistry of the recent playa sediments from the Thar Desert, India: An implication to playa sediment provenance 总被引：3，自引：0，他引：3
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. 相似文献