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1.
KLAUS FELIX KAISER UELI EICHER 《Boreas: An International Journal of Quaternary Research》1987,16(3):293-303
Pollen and mollusc deposits in a sedimentation series laid down in the Dattnau valley during the Late Glacial and early Post-glacial were studied. For the first time δ13 C and δ18 O in land-snail shells were measured. It was possible to reconstruct vegetational and climatic developments from the Bölling ( c . 12,500 B.P.) until well into the early Boreal ( c . 9,000 B.P.). The two sets of findings agree well. The Late Glacial is seen to comprise two intervals: the continuous, locally rather moist, warm Bölling/Alleröd period, and the subsequent dry . cold Younger Dryas. The profile ceases after the changeover from the Late Glacial to the Post-glacial. The transitions from the Alleröd to the Younger Dryas and hence to the Preboreal and Boreal are both clearly identifiable in the pollen diagram; the mollusc record, however, ceases to be interpretable shortly before the climatic change to the Post-glacial. The δ18 O curve shows a clear distinction between the AllerÖd and the Younger Dryas. The Gerzensee fluctuation, immediately before this transition. is evident as a negative deviation. 相似文献
2.
KARIN AHLBERG ELISABETH ALMGREN H. E. WRIGHT JR. EMI ITO SARAH HOBBIE 《Boreas: An International Journal of Quaternary Research》1996,25(4):257-267
Oxygen-isotope profiles for the Late-Glacial carbonate sediments from Red Bog and adjacent Lough Gur in County Limerick in western Ireland are readily correlated with the classical hiozones delineated on pollen diagrams for the same cores. The estimated summer temperatures of the Bølling/Allerød were as high as those in the early Holocene and are correlated with increasing Milankovitch summer insolation. This warm phase was abruptly terminated in the Younger Dryas cold episode by a depletion of 4% in δ18 O, suggesting a summer atmospheric temperature decrease of about 12°C, comparable to that inferred from fossil beetle data. The Younger Dryas phase is attributed to a major cooling of the sea-surface temperature by a postulated discharge of icebergs similar to that of the Heinrich events, for the icebergs were much more effective than simple meltwater in cooling the sea surface and thus the climate over Europe. Shorter-term cool phases (Older Dryas. Gerzensee. Preboreal oscillation) are also recognized. 相似文献
3.
Oxygen-isotope and pollen analyses were carried out on late- and postglacial (Late Weichselian and Holo-cene) sediment samples of the raised bog. The 18 O/16 O-ratio results provide the first unequivocal proof for the Eastern Alps of the climatic deterioration of the Younger Dryas period. High NAP-values in the pollen diagram and a strong negative deviation in the oxygen-isotope curve characterize this period. The earlier Gerzensee fluctuation is also indicated by small changes in the oxygen-isotope curve. During the postglacial the Frosnitz climatic deterioration (6,000–6,500 B.P.) is evidenced as a fluctuation in the lake-level. The oxygen-isotope values indicate that the air temperature conditions remained unchanged at that time. 相似文献
4.
DAN HAMMARLUND BJØRN BUCHARDT 《Boreas: An International Journal of Quaternary Research》1996,25(1):8-22
Stable oxygen and carbon isotope data from a lacustrine sequence at Grænge, southeast Denmark, revealed distinct cnvironmental changes related to Late Weichselian climatic development in the region. Comparison of isotopic records obtained from sedimentary carbonates and freshwater molluscs enabled reconstruction of changes in the lacustrine environment. The degree of thermal and chemical stratification of the lake was evaluated and supported by pollen data from an earlier study of the site. During the Allerød interstadial, dimictic and stagnant conditions characterized the lake, whereas the stratification was disturbed during thc Younger Dryas stadial probably as a result of deforestation and increased wind impact. The origin of sedimentary carbonates was examined by mineralogic and morphologic studies. A considerable input of clastics and detrital carbonates, associated with pronounced enrichment of 18 O and 13 C. wds recorded in the Younger Dryas sediments indicating soil degradation and increased erosion. A climatic warming preceding the Pleis-tocene/Holocene boundary is clearly reflected in the different stable isotope records and in the lithostratigraphy. 相似文献
5.
TATJANA BÖTTGER ACHlM HILLER FRANK WOLFGANG JUNGE THOMAS LITT DIETRICH MANIA NORBERT SCHEELE 《Boreas: An International Journal of Quaternary Research》1998,27(2):88-100
Combined investigations of isotopes, pollen, and molliisc shells were carried out on a Latc Glacial limnic high-resolution sediment sequence from the Geiseltal open-cast mine in Central Gcrmany. The dala confirm thc division of the Late Glacial biozones into two colder (Older and Younger Dryas) and two warmer periods (Bølling, Allcrød), which have already bccn cstablishcd lor the Central and Northern German area. Radiocarbon data, mainly based on wood material, cover a time span between c , 10 800 BP and 12 760 BP, indicating a mean sedimentation rate of c . 2 mm/yr. The stable isotope data (δ18 O, δ13 C) reflect the transition periods between the climatic phases as changes in relative air humidity (transition from dry, cold to warmer. more humid conditions). The dominance of evaporation effects, however, is superimposed on any ternpcratiirc aignal throughout the profile. Repeated conversions of the hydrologic regime (silting-up phases. lake-level variations) characterize the specific history of the lake development. 相似文献
6.
MEINRAD KÜTTEL 《Boreas: An International Journal of Quaternary Research》1977,6(3):259-274
New pollen-analytical investigations and two 14 C series indicate that, at the Bedrina on Mount Piottino (Tessin, Switzerland), the post-Allerød NAP phase (Piottino oscillation) represents the well-marked Younger Dryas at least for the most part. The late-glacial part of the profile is re-classified, and the term Piottino oscillation is rejected, as it is largely identical with the Younger Dryas. Individual 14 C dates from the transition between the Younger Dryas and the Preboreal should be considered critically. Considerable fluctuations in the 14 C level are supposed for this period. 相似文献
7.
Seasonal and interannual variability of Siberian river discharge in the Laptev Sea inferred from stable isotopes in modern bivalves 总被引:2,自引:0,他引:2
THOMAS MUELLER-LUPP HELMUT ERLENKEUSER HENNING A. BAUCH 《Boreas: An International Journal of Quaternary Research》2003,32(2):292-303
Stable oxygen and carbon isotope profiles from modern bivalve shells were investigated in order to reconstruct short-term hydrographical changes in the river-shelf system of the Laptev Sea. Oxygen isotopic profiles obtained from the aragonitic species Astarte borealis exhibit amplitude cycles interpreted as annual hydrographical cycles. These records reflect the strong contrast between summer and winter bottom water conditions in the Laptev Sea. The seasonal variations in δ18 O are mainly controlled by the riverine freshwater discharge during summer with 0.5‰ per salinity unit. Corrected for a defined species-dependent fractionation offset of -0.37‰, time-dependent salinity records were reconstructed from these δ18 O profiles. They indicate a good correspondence to seasonal hydrographic changes and synoptical data. Persistent trends with shell growth towards more negative δ13 C values are observed in all specimens and appear to be related to metabolic changes of the bivalves during ontogeny. In contrast, short-term fluctuations are likely linked to seasonal variabilities of the river water outflow patterns and enhanced phytoplankton productivity during summer. This is corroborated by a clear watermass-related distinction of the various δ13 C records made on the basis of water depth and distance from the riverine source. 相似文献
8.
Geochemical Process of Gas Hydrate Formation in the Nankai Trough Based on Chloride and Isotopic Anomalies in Interstitial Water 总被引:2,自引:0,他引:2
Abstract: Interstitial water expelled from gas hydrate-bearing and -free sediments in the Nankai Trough are analyzed in terms of Cl-, SO4 2 -, δ18 O and δD. The baselines for the Cl- concentration and δ18 O value are close to seawater values (530 mM and 0%), indicating that the interstitial water is of seawater origin. The δD values decrease with depth, implying isotopic exchange of hydrogen between upwelling biogenic methane depleted in D and interstitial water. The Cl- concentrations in gas hydrate-bearing sediments are anomalously low, while the δ18 O and δD values are both high, suggesting that the water forming these gas hydrates was poor in Cl- and enriched in 18 O and D during gas hydrate formation. Calculation of the gas hydrate saturations using Cl "and δ18 O anomalies gives results of up to 80 % in sand, and shows that the δ18 O baseline is not consistent with the Cl" baseline. The δ18 O baseline increases by +1% in gas hydrate-free clay and silt. This is considered to be caused by clustering of water molecules after gas hydrate dissociation in response to the upward migration of the base of gas hydrate stability, as indicated by the presence of a double bottom-simulating reflector at this site. The water clusters enriched in 18 O are responsible for the increase in the δ18 O baseline with normal Cl". The abrupt shallowing of the base of gas hydrate stability may induce the dissociation of gas hydrates and the accumulation of gases in the new stability zone, representing a geological process that increases gas hydrate saturation. 相似文献
9.
ÁRNÝ E. SVEINBJÖRNSOTTIR JÓN EIRÍKSSON ÁSLAUG GEIRSDÓTTIR JAN HEINEMEIER NIELS RUD 《Boreas: An International Journal of Quaternary Research》1993,22(2):147-157
An exhaustive 14 C dating programme of molluscs from the Fossvogur sediments in Reykjavik. Iceland is presented. For the first time all the fossiliferous units of the sediments are dated. The results confirm earlier conclusions of a widespread occurrence of marine sediments of Allerød age in Reykjavik. The set of dates from the Fossvogur sediments shows a narrow 14 C age distribution (standard deviation of ±235 years) of molluscs from all localities and from successive marine units in vertical sections. The weighted mean conventional 14 C age is 11,400 BP. Assuming a reservoir effect of 400 years. this corresponds to a reservoir-corrected age of I1,000 BP. i.e. the Allerød- Younger Dryas transition for the sampled units, These new 14 C dates from Fossvogur confirm the need for a revision of the Upper Pleistocene chronology of the Reykjavik region. They also have a bearing on the Late Weichselian record of glacier readvances and sea-level changes in the area. The dates suggest that the marine units in Fossvogur accumulated within a restricted time-span of a few hundred years. The sediments in Fossvogur are of volcaniclastic origin and are extremely lithified, indicating local geothermal activity soon after their deposition. This may explain anomalously high D/L amino acid ratios measured in molluscs from the Fossvogur sediments. δ13 C and δ18 O results suggest that temperatures may have ranged up to 60°C. 相似文献
10.
Climate variability in the SE Alps of Italy over the past 17 000 years reconstructed from a stalagmite record 总被引:1,自引:0,他引:1
SILVIA FRISIA REA BORSATO CHRISTOPH SPÖTL IGOR M. VILLA FRANCO CUCCHI 《Boreas: An International Journal of Quaternary Research》2005,34(4):445-455
Stalagmite SV1 from Grotta Savi, located at the SE margin of the European Alps (Italy), is the first Alpine speleothem that continuously spans the past c . 17kyr. Extension rate and δ18 Oc record for the Lateglacial probably reflect a combination of temperature and rainfall, with rainfall exerting the dominant effect. Low speleothem calcite δ18 Oc values were recorded from c . 14.5 and 12.35 kyr, during GI-1 (Bølling— Allerød) interstadial, which in our interpretation, was warm and wet. The GS-1 (Younger Dryas) was characterized by a shift to heavier δ18 Oc , coinciding with δ13 Cc enrichment and extremely low extension rate (<8 μm/year). These characteristics indicate that GS-1 climate was cool and dry in the SE Alps. Calibration using historical data revealed that there is a positive δ18 Oc /dT relationship. A 1°C rise in mean annual temperature should correspond to c . 2.85% increase of SV-1 δc18 Oc . We reconstructed a slow and steady temperature rise of c . 0.5°C since 10 kyr BP, in broad agreement with reconstructions from pollen data for SE Europe. Stalagmite SV1 indicates that climate variability in the SE Alps has been influenced by the Mediterranean Sea for the past c . 17 kyr. 相似文献
11.
JAAN-MATI PUNNING TÖNU MARTMA HELGI KESSEL REIN VAIKMÄE 《Boreas: An International Journal of Quaternary Research》1988,17(1):27-31
The carbon (δ13 C) and oxygen (δ18 O) isotopic composistion in mollusc shells in mainly determined by the isotopic composition of water and dissolved bicarbonate. The δ18 O values of water show a good correlation with the salinity of the Baltic. This correlation served as a basis for reconstructing palaeosalinity and for stratifying the marine sediments according to the δ18 O values of the carbonate skeletons of subfossil shells. The δ13 C values in shells are mainly determined by the isotopic composition of land-originating bicarbonate, especially in the carbonate skeleton of Lymnaea balthica , which inhabits the immediate coastal zone. According to the δ18 O data, salinity in the investigated area (the coastal area of W and NW Estonia) was highest (about 9–11%) during the Littorina stage. The Limnae a stage had, in general, a salinity similar to the contemporary one, but during some phases possibly exceeding it by 2–3%. 相似文献
12.
G. R. T. JENKIN C. M. FARROW A. E. FALLICK D. HIGGINS 《Journal of Metamorphic Geology》1994,12(3):221-235
Retrograde exchange of oxygen isotopes between minerals in igneous and metamorphic rocks by means of diffusion is explored using a finite difference computer model, which predicts both the zonation profile of δ18 O within grains, and the bulk δ18 O value of each mineral in the rock. Apparent oxygen isotope equilibrium temperatures that would be observed in these rocks are calculated from the δ18 O values of each mineral pair within the rock. In systems which cool linearly from a sufficiently high temperature or at a low enough cooling rate, such that the final oxygen isotope values are not dependent upon the initial oxygen isotope values ('slow cooling'), the apparent oxygen isotope temperature derived for a rock composed of a single mineral pair can be shown to be simply related to the Dodson closure temperatures ( T c ) for the two phases and the mode of the rock. Adding a third phase into a system which undergoes 'slow' cooling will cause the apparent temperature derived for the two minerals already present to differ from the simple relationship for a two-phase system. In some systems oxygen isotope reversals can be developed. If cooling is not 'slow', then the mineral δ18 O values resulting from cooling will be partly dependent upon the initial temperature of the system concerned. The model successfully simulates the mineral δ18 O values that are often observed in granitic rocks. Application of the model will help in assessing the validity of oxygen isotope thermometry in different geological settings, and allows quantitative prediction of the oxygen isotope fractionations that are developed in cooling closed systems. 相似文献
13.
Stanislaw Halas Janina Szaran Maciej Czarnacki Ahmad Tanweer 《Geostandards and Geoanalytical Research》2007,31(1):61-68
Refinements have been made to achieve over 99% yield in the conversion of CO to CO2 in order to improve the reproducibility and accuracy of δ18 O measurements in sulfates. BaSO4 (10-15 mg) was mixed with an identical amount of spectrographic-grade graphite and loaded into a Pt boat. The mixture was gradually heated to 1100 °C to reduce sulfate to CO and CO2 ; the former gas was simultaneously converted to CO2 by a glow discharge between Pt electrodes immersed in a magnetic field (produced by a pair of external neodymium magnets). A small memory effect was noticed during the analysis (less than 0.3‰ per 10‰ difference in δ18 O between two subsequently analysed samples). The memory effect, however, was suppressed by repetitive preparation of the same specimen. CO2 produced in this way from sulfate reference samples was analysed on a dual inlet and triple collector mass spectrometer along with CO2 equilibrated with VSMOW, GISP and SLAP water reference samples. To avoid large departures of measured isotope ratios from 18 O/16 O of the working calibrator we used CO2 gas prepared from ocean water sulfate for this purpose. The calibrated δ18 O values (in ‰) obtained in this way for NBS-127, IAEA SO-5 and IAEA SO-6 reference materials were 8.73 ± 0.05, 12.20 ± 0.07 and -10.43 ± 0.12, respectively. 相似文献
14.
Large amounts of fluid, bound up in the hydrated upper layers of the ocean crust, are consumed at convergent margins and released in subduction zones through devolatilization. The liberated fluids may play an integral role in subduction zone processes, including the generation of arc-magmas. However, exhumed subduction zone rocks often record little evidence of large-scale fluid flow, especially at deeper levels within the subduction zone. Basaltic pillows from the high-pressure Corsican and Zermatt-Saas ophiolites show a range of δ18 O values that overall reflect seafloor alteration prior to subduction. However, comparison between the δ18 O values of the cores and rims of the pillows suggests that the δ18 O values of the pillow rims at least have been modified during subduction and high-pressure metamorphism. Pillows that have not undergone high-pressure metamorphism generally have rims with higher δ18 O values than their cores, whereas the converse is the case in pillows that have undergone high-pressure metamorphism. This reversal in the core to rim oxygen isotope relationship between unmetamorphosed and metamorphosed pillows is strong evidence for fluid–rock interaction occurring during subduction and high-pressure metamorphism. However, the preservation of different δ18 O values in the cores and rims of individual pillows and within and between different pillows suggests that fluid flow within the subduction zone was strongly channelled. Resetting of the δ18 O values in the pillow rims was probably due to fluid-hosted diffusion that occurred over relatively short time-scales (<1 Myr). 相似文献
15.
Exposure age dating and Equilibrium Line Altitude reconstruction of an Egesen moraine in the Maritime Alps, Italy 总被引:1,自引:0,他引:1
PAOLO ROBERTO FEDERICI DARRYL E. GRANGER MARTA PAPPALARDO ADRIANO RIBOLINI MATTEO SPAGNOLO ANDREW J. CYR 《Boreas: An International Journal of Quaternary Research》2008,37(2):245-253
Four boulder samples from the Piano del Praiet frontal moraine in the Gesso della Barra Valley (Maritime Alps) have been 10 Be dated. The results give a weighted mean age of 11 340±370 (870) yr, constraining the frontal moraine to the Egesen glacial stadial, during the Younger Dryas cold phase. By applying the same 10 Be production rate to other Egesen moraines previously dated in the Alps, we obtain similar ages for all of them. This suggests a synchroneity of the Egesen deglaciation in the European Alps at the end of the Younger Dryas. From the palaeoshape of the Egesen glacier, reconstructed by means of geomorphological mapping, an Equilibrium Line Altitude depression (δELA) of −520 to −530 m, with respect to the present-day ELA, and of −260 to −320 m, with respect to the Little Ice Age ELA, has been calculated. Comparison with other Alpine sector δELAs indicates that the Maritime Alps experienced humid climatic conditions during the Younger Dryas. 相似文献
16.
Stable carbon and oxygen isotopic compositions of essentially unmetamorphosed Archean (> 2.6 Gyr old) cherts and carbonates of the Dharwar Sequence of southern India, from the northernmost part of the Dharwar-Shimoga supracrustal belt (Kalche and Nagargali), have been determined. The cherts from the Nagargali area, which preserve oolitic texture and cryptocrystalline silica, show highly enriched δ18 O values ranging from 28 to 31.4%o relative to SMOW. Such values are the highest yet reported from Archean nondetrital sediments, but are similar to those of modern marine cherts. On the assumption of a seawater δ18 O of 0%0 , calculation of temperature based on the maximum δ18 O value of 31.4%0 yields a value of 40°C. This is significantly less than 70–80°C reported for the Archean oceans based on cherts and chert-phosphate pairs. Diagenetically recrystallized microcrystalline chert-dolomite pairs of Kalche area exhibit a range of oxygen isotopic ratios similar to those reported for Archean cherts and carbonates from other parts of the world. The temperature of diagenesis is estimated to be about 68°C. 相似文献
17.
Abstract. Carboniferous-Permian limestones of the Akiyoshi Plateau, in the Inner Zone of southwestern Japan, are composed of essentially pure calcium carbonate containing only small amounts of other elements, and they are accompanied by marble and copper skarn deposits near the contact with late Cretaceous granitoids. The δ18 O values of the Akiyoshi limestones range widely from 7.6 to 28.3% and are mostly lower than those of other areas of the same age (23–29%), whereas the differences among the δ13 C values are small. The δ18 O values are negatively correlated with Mn and Fe contents. Samples with high δ18 O (>25%) and δ13 C (>2%) values do not contain Fe, Zn, or Pb, but those with low δ18 O values tend to be rich in these elements, indicating that these elements were introduced by interaction with H2 O dominant fluids, possibly of magmatic origin. Potential scores for evaluating the degree of interaction with hydro thermal fluids were calculated for δ18 O, δ13 C, Fe, Mn, Zn, Pb, and Sr. Higher scores implying much hydrothermal interaction were evident in the Mt. Hananoyama area, where there are many skarn deposits, and along faults oriented mainly NNW-SSE. Therefore, these are promising areas for exploring for blind deposits. It is likely that the hydrothermal fluid traveled through the limestones along fractures at the time of the granitic intrusions. However, the potential scores here are much smaller than those in the Pb-Zn mineralized area of the Kamioka mine, so more detailed petrological and mineralogical investigations are necessary. 相似文献
18.
ANNE JENNINGS JAMES SYVITSKI LINDA GERSON KARL GRÖNVOLD ÁSLAUG GEIRSDÓTTIR JÓRUNN HARDARDÓTTIR JOHN ANDREWS SVEINUNG HAGEN 《Boreas: An International Journal of Quaternary Research》2000,29(3):163-183
Foraminifera, sedimentology, and tephra geochemistry in core 93030-006 LCF from the southwestern Iceland shelf were used to reconstruct paleoenvironments between 12.7 and 9.4 14 C ka BP. Seismic-reflection profiles place the core in glacial-marine and marine sediments within one meter of the underlying glacial till. Foraminifers in the earliest glacial-marine sediments provide a record of ice-distal conditions and immigration of slope species onto the shelf in association with warm Atlantic water. Meltwater increased during the Allerød under a weakened Atlantic water influence. Arctic conditions began by 11.14 14 C ka BP with an abrupt increase in meltwater and near exclusion of boreal fauna from the shelf. Meltwater diminished in the early Younger Dryas, coinciding with sea-surface cooling between 11.14 and 10.5 14 C ka BP. A slight warming recorded in the uppermost glacial-marine sediments was interrupted by an inferred jökulhlaup event emanating from glacier ice on the Western Volcanic Zone. Retreat of the ice margin from the sea sometime between c. 10.3 and 9.94 14 C ka BP coincided with this event. The onset of postglacial marine sedimentation occurred along with increasing evidence of Atlantic water c. 9.94 14 C ka BP and was interrupted by a short-lived Pre-boreal cooling of the Irminger Current c. 9.91 14 C ka BP. Conditions similar to those today were established by 9.7 14 C ka BP. 相似文献
19.
Stable isotopic signature of a palaeoaquifer, Mississippian Alamogordo Member limestones, Sacramento Mountains, New Mexico, USA 总被引:1,自引:0,他引:1
Nine stratigraphic sections, each ≈5 m thick, were sampled from the Alamogordo Member limestones of the Lake Valley Formation, Sacramento Mountains, New Mexico, USA. Four stratigraphic sections consist entirely of lime mudstone and wackestone, whereas the other five sections have a prominent layer of crinoidal packstone about 1 m thick at their base. Stable isotopic analyses reveal that the lime muds in the sections with basal packstone layers show a downward decrease in δ18 O and constant δ13 C values, whereas those in the sections solely composed of lime mudstone and wackestone have, in general, relatively uniform δ18 O and δ13 C values. The diagenesis of the Alamogordo Member limestones was previously believed to have been governed by the downward percolation of meteoric water from a regional pre-Pennsylvanian exposure surface ≈100 m above this unit. However, the uniform δ13 C and downward decrease in δ18 O values in the lime muds in the sections with basal packstones indicate that the meteoric water ascended within the Alamogordo Member, rather than descended from the overlying exposure surface. This indicates that the basal packstones were probably a conduit for meteoric water. This is further supported indirectly by the relatively uniform δ18 O and δ13 C values of the lime mud in the sections without basal packstones. The implications are that the oxygen isotopic gradients may be used to identify palaeoaquifers, flow directions within these aquifers and that meteoric diagenesis below an exposure surface could be governed by flow through a palaeoaquifer. 相似文献
20.
Oxygen Isotopic Characteristics of Granitic Intrusions Related to Haobugao Zn-Pb-Cu-Sn Skarn Deposit, East Inner Mongolia, China 总被引:2,自引:0,他引:2
Jingbin Wang Lijuan Wang Yuwang Wang Tiejun Li Hidehiko Shimazaki 《Resource Geology》2004,54(2):205-208
Abstract. Granitic rocks related to the formation of Haobugao Zn-Pb-Cu-Sn skarn deposit, Inner Mongolia, China, show unusual low whole-rock δ18 O values down to -8.8 % (V-SMOW), whereas separated quartz crystals from those rocks give positive δ18 O values of+4.1 to +9.9 %. Chemical analyses and microscopic observation of those granitic rocks confirm that they suffered hydrothermal alteration. Some skarn specimens and quartz from the Haobugao deposit also show negative δ18 O values. The isotopic evidence indicates that intensive meteoric water circulation occurred at the time of granitic intrusion, and caused the pervasive hydrothermal alteration of granitic rocks and the precipitation of skarn deposit in this area. 相似文献