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1.
Attention has been paid for the levels, sources and health risks of atmospheric aliphatic and polycyclic aromatic hydrocarbons
(n-alkanes and PAHs) in remote areas, however, few studies have focused on those in the Tibetan Plateau. In this study, 18 pairs
of atmospheric samples were obtained during the period from August 2006 to July 2007 in Lhasa, the capital city of Tibet.
Both gas-phase and particulate-phase n-alkanes and PAHs were measured. Concentrations of n-alkanes (gas + particulate phase, 99.1–480.9 ng/m3) and PAHs (gas + particulate phase, 11.4–72.5 ng/m3) in Lhasa are lower than those in many cities. The sources of n-alkanes related to biological and petroleum sources were 67 and 33%, respectively. According to the results of diagnostic
ratios and principal component analysis, emission of traffic vehicles was one of the important PAH sources, and sources of
benzo(a)pyrene was likely attributed to incense burning. Good simulations were obtained by traffic soot-based model for fluoranthene,
pyrene and benzo(a)anthracene, while, wood soot-based model fitted the experimental results of benzo(a)pyrene better. This
meant atmospheric fate of PAHs was mainly influenced by the adsorptive partitioning that occurred during traffic and incense
burning procedures. In addition, the benzo[a]pyrene-equivalent carcinogenic power (BaPE) in the present study (0.1–1.6 ng/m3) is lower than those in other cities and also the air quality standard of China, suggesting that atmospheric PAHs caused
low health risks. 相似文献
2.
New insights into the origin of perylene in geological samples 总被引：1，自引：0，他引：1
Kliti Grice Hong Lu Pia Atahan Muhammad Asif Paul Greenwood Ercin Maslen Kenneth Williford 《Geochimica et cosmochimica acta》2009,73(21):6531-6543
The origin of the polycyclic aromatic hydrocarbon (PAH) perylene in sediments and petroleum has been a matter of continued debate. Reported to occur in Phanerozoic organic matter (OM), fossil crinoids and tropical termite mounds, its mechanism of formation remains unclear. While a combustion source can be excluded, structural similarities to perylene quinone-like components present in e.g. fungi, plants, crinoids and insects, potentially suggest a product-precursor relationship. Here, we report perylene concentrations, 13C/12C, and D/H ratios from a Holocene sediment profile from the Qingpu trench, Yangtze Delta region, China. Perylene concentrations differ from those of pyrogenic PAHs, and rise to prominence in a stratigraphic interval that was dominated by woody vegetation as determined by palynology including fungal spores. In this zone, perylene concentrations exhibit an inverse relationship to the lignin marker guaiacol, D/H ratios between −284‰ and −317‰, similar to the methoxy groups in lignin, as well as co-variation with spores from wood-degrading fungi. 13C/12C of perylene differs from that of land plant wax alkanes and falls in the fractionation range expected for saprophytic fungi that utilise lignin, which is isotopically lighter than cellulose and whole wood. During progressive lignin degradation, the relative carbon isotopic ratio of the perylene decreases. We therefore hypothesise a relationship of perylene to the activity of wood-degrading fungi. To support our hypothesis, we analysed a wide range of Phanerozoic sediments and oils, and found perylene to generally be present in subordinate amounts before the evolutionary rise of vascular plants, and to be generally absent from marine-sourced oils, few exceptions being attributed perhaps to a contribution of marine and/or terrestrial-derived fungi, anoxia (especially under marine conditions) and/or contamination of core material by fungi. A series of low-molecular-weight aromatic quinones bearing the perylene-backbone were detected in Devonian and Cretaceous sediments, potentially representing precursor components to perylene. 相似文献
3.
Olatz Zuloaga Ailette Prieto Kawser Ahmed Santosh Kumar Sarkar Asokkumar Bhattacharya Mousumi Chatterjee Bhaskar Deb Bhattacharya Kamala Kanta Satpathy 《Environmental Earth Sciences》2013,68(2):355-367
The present work is the first attempt to compare the data of a comprehensive study of the origin and distribution of 16 priority pollutant polycyclic aromatic hydrocarbons (PAHs) in surface sediments (<63 μm) from 18 sampling stations, 9 from Sundarban of Bangladesh and 9 from Indian counterpart. Σ19PAHs concentration in sediments showed wide variations from 208.3 to 12,993.1 ng g?1 dry weight in Indian Sundarban, whereas 208.4 to 4,687.9 ng g?1 in the case of Bangladesh. Fluoranthene, pyrene, benzo(b)fluoranthene, benzo(a)pyrene and dibenzo(a,h)anthracene were predominant species for both the countries. The PAH diagnostic ratios indicated that the PAHs in sediments from both the countries were of mixed source of hydrocarbons of both petrogenic and pyrolytic origin. According to the numerical effect-based sediment quality guidelines, the levels of PAHs in the Sundarban wetland of Bangladesh and India should not exert adverse biological effects. The TEQ values calculated for samples from the Bangladesh and Indian Sundarban varied from 13.68 to 1,014.75 and 1.31 to 2,451 ng g?1 d.w. with an average of 221.02 and 358.63 ng g?1, respectively. The overall contamination status of PAH was higher in India than Bangladesh. 相似文献
4.
A. K. Inengite N. C. Oforka C. Osuji Leo 《International Journal of Environmental Science and Technology》2013,10(3):519-532
Sources of the sixteen polycyclic aromatic hydrocarbons (PAHs) in the United States Environmental Protection Agency priority pollutants list were determined in sediments of Kolo Creek using diagnostic ratios of parent PAHs[phenanthrene/phenanthrene + anthracene; fluoranthene/fluoranthene + pyrene; benz(a) anthracene/benz(a) anthracene + chrysene and indeno(1,2,3-d)pyrene/indeno(1,2,3-cd)pyrene + benzo(ghi)pyrelene]. The study was conducted over four seasons (dry, late dry, rainy and late rainy seasons). Applying cross plots of the diagnostic ratios revealed that PAHs in Kolo Creek sediment have pyrogenic origins except in the rainy season that had petrogenic origins. Comparison of diagnostic ratio values obtained from this study with literature values enabled the further classification into types of pyrogenic and/or petrogenic sources. While the pyrogenic sources of PAHs were mainly as a result of Grass/Wood combustion, the petrogenic PAHs were as result of drained diesel and lubricating oil. The predicted sources corresponded with the prevailing human activities in the vicinity, especially samples collected near a petrol station and an abattoir. This study further affirms the simplicity and accuracy of the use of diagnostic ratios for PAHs source prediction. 相似文献
5.
Birgit Nabbefeld Kliti Grice Roger E. Summons Lindsay E. Hays Changqun Cao 《Applied Geochemistry》2010
In this study the abundances of several polycyclic aromatic hydrocarbons (PAHs Table 1, I–XXI) have been measured throughout three Permian/Triassic (P/Tr) sections from Meishan (South China), Kap Stosch area (East Greenland) and Peace River Basin (Western Canada). Dibenzothiophene (I) and dibenzofuran (II) were found to decrease in abundance just before or shortly after the P/Tr transition in all three sections while perylene (III) was observed to increase in abundance at the onset of the main extinction horizon (bed 25) in Meishan. Perylene has been attributed to a wood degrading fungal source and, therefore, it seems possible these phenomena are related to the demise of land plants. Further, distinct patterns of various combustion-derived PAHs occurring in each section imply that forest fire events occurred within the Late Permian and Early Triassic. In the Meishan section high amounts of combustion-derived PAHs [pyrene (IV), fluoranthene (V), benzo[a]anthracene (VI), benzofluoranthenes (sum, i.e. VII), benzo[a]pyrene (VIII), benzo[e]pyrene (IX) and coronene (X)] occur within bed 25, also containing ash attributed to the fallout from massive volcanic eruptions in Siberia and/or China. 相似文献
6.
To further our knowledge of the coupling between the hydraulic and mechanical behaviours of the swelling soils, this paper presents an experimental study on a bentonite/silt mixture using an osmotic odometer. A loading/unloading cycle was applied to samples with different initial dry densities (1.27, 1.48, and 1.55 Mg m− 3) at different constant suctions (0, 2, and 8 MPa). We noted that the initial state of the soils after compaction significantly influenced the values of the apparent preconsolidation stress p0(s), the virgin compression index λ(s), and the elastic compression index κ.These experimental results provided a sufficient database to interpret the mechanical behaviour of the swelling soil and define three yielding surfaces:
- – the suction limit between micro- and macrostructure (sm/M) and the suction limit between nano- and microstructure (sn/m), which depend completely on the soil fabrics and the diameter separating the nano-, micro-, and macrostructure,
- – the Loading Collapse (LC) curve, representing the preconsolidation stress variation as a function of suction,
- – the Saturation Curve (SC), representing the variation of the saturation stress (Psat) as a function of suction.
7.
Eighty-two palaeomagnetic samples of calcareous and jaspilitic grainstones (iron-formation or ‘taconite’) and chert carbonate were collected from the 1.88-Ga Gunflint Formation at 22 sites in the Thunder Bay area, Ontario. Twenty clasts of Gunflint taconite also were sampled from the basal conglomerate of the overlying Mesoproterozoic Sibley Group. Anisotropy of magnetic susceptibility measurements indicate the Gunflint Formation in the sampling area has not experienced regional dynamic metamorphism. Analyses by variable-field translation balance and X-ray diffraction show that the predominant magnetic mineral is hematite but a small amount of magnetite also is present in some samples. Altogether, 213 Gunflint specimens and 59 Sibley conglomerate specimens were subjected to stepwise thermal demagnetisation and 74 Gunflint specimens to stepwise alternating-frequency demagnetisation. The following components were isolated for the taconites:
- • Gunflint magnetite: normal declination D=293.4°, inclination I=30.8°, α95=7.2°, n=21; reverse D=86.7°, I=–54.6°, α95=5.8°, n=29.
- • Gunflint hematite: normal D=243.6°, I=23.6°, α95=6.0°, n=11; reverse D=70.3°, I=–51.4°, α95=3.2°, n=79.
- • Sibley clasts magnetite: normal D=282.7°, I=33.4°, α95=7.6°, n=20.
- • Sibley clasts hematite: normal D=254.5°, I=56.2°, α95=8.4°, n=13; reverse D=110.6°, I=–55.7°, α95=8.3°, n=11.
8.
多环芳烃(PAHs)是古环境、古野火以及古气候的重要地质记录,本文通过气相色谱质谱法(GC- MS)研究了柴达木盆地北缘中侏罗统石门沟组煤中多环芳烃分布特征,检测出一系列二环至七环芳烃化合物,包括高等植物衍生多环芳烃(卡达烯、6- 异丙基- 1- 异己基- 2- 甲基萘、惹烯、西蒙内利烯以及二氢惹烯)和燃烧衍生多环芳烃(荧蒽、芘、苯并\[a\]蒽、、苯并荧蒽、苯并\[e\]芘、苯并\[a\]芘、茚并\[cd\]芘、苯并\[ghi\]苝和晕苯)等。这些多环芳烃的检出表明石门沟组煤沉积于具有显著陆源高等植物输入的微咸水湖沼环境,成熟度较低(平均随机反射率为056%)。石门沟组煤中高等植物衍生多环芳烃以极高的惹烯含量为特征,且存在较高丰度的西蒙内利烯和二氢惹烯,卡达烯丰度极低,反映出成煤期陆地植被类型以松柏类植物的针叶林为主,气候温暖湿润。同时,煤中丰富的燃烧衍生多环芳烃证实了柴达木盆地北缘中侏罗世存在广泛的陆地古野火,较高的大气氧气浓度(256%)可能是该时期野火频发的一个重要诱因。本次研究为柴达木盆地中侏罗世古野火事件的研究提供了重要的分子化石证据,也是对中侏罗世古环境和古气候研究的有益补充。 相似文献
9.
A series of hydropyrolysis (HyPy) experiments have been conducted on a small suite of authentic polycyclic aromatic hydrocarbons (PAHs: coronene, pyrene and perylene) to investigate the HyPy behaviour of these PAHs. This information may help in the interpretation of the structural significance of aromatic HyPy products, often detected in high abundance, from high maturity kerogens. The PAHs were separately treated by HyPy and were all susceptible to some extent of hydrogenation. Perylene also decomposed into low molecular weight aromatics (e.g. methylbiphenyls). Structurally, perylene is much less stable than the more condensed PAHs coronene and pyrene. The total product concentrations (wt% of starting PAH) from all HyPy experiments were consistently less than 100 wt%, probably due to either the condensation of semi-volatile products on walls of the transfer line prior to reaching the HyPy trap or the inefficient cold trapping of highly volatile products. Hydrogenation of PAHs was prevalent and was found to be significantly influenced by the addition of a Mo-S based catalyst and potentially the C/Mo ratio, but largely independent of the two final temperatures used (520 °C and 550 °C). The fully aromatised and hydrogenated products for any stable ring system may provide a general indication of the size distribution of aromatic units within the kerogen structure. 相似文献
10.
11.
W. Guo M. C. He Z. F. Yang H. Y. Zhang C. Y. Lin Z. J. Tian 《Environmental Earth Sciences》2013,68(7):2015-2024
The burial characteristics and toxicity risks associated with n-alkanes and polycyclic aromatic hydrocarbons (PAHs) in the riverine and estuarine sediments of the Daliao River watershed were investigated based on three sediment cores. The sum of the n-alkane and PAH concentrations, normalized to organic carbon (OC), ranged from 0.27 to 63.09 μg g?1OC?1 and 6.60 to 366.20 μg g?1OC?1, respectively. The features and the history of industrial activities, such as the oil and chemical industries and port activities near the river and estuary, resulted in different distributions and sources of hydrocarbons. The sources of pollution were identified based on n-alkane indexes and on diagnostic ratios of PAHs. The diagnostic ratios indicated that the n-alkanes were derived from both biogenic and petrogenic sources in different proportions and that the PAHs were derived primarily from petrogenic combustion sources. A hierarchical cluster analysis grouped the core samples into two clusters. The first cluster, river sediments, corresponded to industrial activities; the second cluster, estuarine sediments, corresponded to port shipping activities. The toxic potency of the PAHs in the cores was assessed in terms of toxic equivalents (TEQs) of dibenzo[a,h]anthracene and benzo[a]pyrene. The top layer of the sediment in the cores had a relatively high toxicity. The TEQ values for benzo(a)pyrene (TEQBaP) and dioxins (TEQTCDD) furnished a consistent assessment of the PAHs in the sediment cores. 相似文献
12.
Alireza Riyahi Bakhtiari Mohamad Pauzi Zakaria Mohammad Ismail Yaziz Mohamad Nordin Hj Lajis Xinhui Bi Mohamad Che Abd Rahim 《Applied Geochemistry》2009,24(9):1777-1787
Four anoxic sediment cores were collected from Chini Lake, Malaysia in order to investigate the variability of polycyclic aromatic hydrocarbon (PAH) and perylene concentrations. The study also determined significant differences of perylene concentrations in different sediment layers. Total PAH concentrations ranged from 248 to 8098 ng g−1 in the samples. Diagnostic PAH ratios such as methylphenanthrenes/phenanthrene (MP/P), phenanthrene/anthracene (P/A) and fluoranthene/(fluoranthene + pyrene) (Fl/(Fl + Py) revealed a dominance of pyrogenic influences and partial petrogenic inputs to the top sediment layers. Perylene concentrations were high in the top layers (<12 cm) and increased with increasing depth. There is a significant positive correlation (r = 0.705, p = 0.01) between perylene concentrations and TOC. Analysis of variance (ANOVA) and LSD revealed significant differences (p < 0.05) in TOC-normalized perylene concentrations between the upper (<12 cm) and bottom layers (>12 cm). The average perylene concentrations accounted for 26–50% (0–12 cm) and 50–77% (12–36 cm) of pentacyclic-aromatic hydrocarbon isomers (PAI) present whereas it made up 10–34% (0–12 cm) and 46–66% (12–36 cm) of the total PAH. The average pyrene concentrations decreased with increasing depth and accounted for 62% (0–3 cm), 20–23% (3–12 cm) and 3–1.4% (12–36 cm) of perylene present. The results of hierarchical cluster analysis based on these ratios suggested different input sources for the top and bottom layers. It is concluded that the activity of termites on woody plants produced perylene which is supplied to the lake by run-off from the heavy and frequent rains in this Asian tropical climate. In addition, there was also in situ formation of perylene in the bottom layers due to diagenetic processes. 相似文献
13.
14.
The study area is located in the south-eastern part of the Crati valley (Northern Calabria, Italy), which is a graben bordered by N–S trending normal faults and crossed by NW–SE normal left-lateral faults. Numerous severe crustal earthquakes have affected the area in historical time. Present-day seismic activity is mainly related to the N–S faults located along the eastern border of the graben. In this area, much seismically induced deep-seated deformation has also been recognised.In the present paper, radon concentrations in soil gas have been measured and compared with (a) lithology, (b) Quaternary faults, (c) historical and instrumental seismicity, and (d) deep-seated deformation.The results highlight the following:
- (a) There is no evidence of a strong correlation between lithology and the radon anomalies.
- (b) A clear correlation between the N–S geometry of radon anomalies and the orientation of main fault systems has been recognised, except in the southernmost part of the area, where the radon concentrations are strongly affected by the superposition of the N–S and the NW–SE fault systems.
- (c) Epicentral zones of instrumental and historical earthquakes correspond to the highest values of radon concentrations, probably indicating recent activated fault segments. In particular, high radon values occur in the zones struck by earthquakes in 1835, 1854, and 1870.
- (d) Deep-seated gravitational deformation generally coincides with zones characterised by low radon concentrations.
15.
Imogen Poole Pim F. van Bergen Johan Kool Stefan Schouten David J. Cantrill 《Organic Geochemistry》2004,35(11-12):1261
The degree of isotopic variation in fossil organic matter renders bulk δ13C signatures strongly influenced by molecular isotopic heterogeneity. For example, in fossil wood the relative abundance of less depleted 13C moieties, i.e. preserved 13C enriched polysaccharides versus the relatively 13C depleted lignin moieties, can be seen to significantly bias δ13Cfossil wood values. Moreover the variation in δ13C values of specific compounds within fossil material are themselves highly variable and reflect the heterogeneity in isotopic values of different carbon atoms within individual compounds. For studies using δ13C values of fossil plant material as proxies (e.g., for δ13Cpalaeoatmosphere, δ13Cbiomass) it is recommended that the biases introduced through molecular heterogeneity, preservation type and taxonomic status of the fossil material are determined initially. Biases inherent in the bulk signature can then be reduced, rendering this value more robust. Alternatively, compound specific stable carbon isotope measurements of individual moieties preserved through geological time might prove to be an alternative proxy for monitoring changes in the bulk δ13C value of the plant and might reveal atmospherically induced trends. 相似文献
16.
C.J. Clayton 《Organic Geochemistry》1991,17(6)
For modelling isotopic variations in oils it is convenient to differentiate the effects of oil generation ( 100–150°C) from the effects of oil to gas cracking ( 150–180°C). During generation, δ13C of kerogen may increase by up to 1% due to release of isotopically light oil and gas, although most kerogens show little or no chan δ13C of the generated oil increases by between 0 and 1% (av. 0.5%) due to mixing of isotopically heavy oil with an initial isotopically light unbound fraction, possibly of bacterial origin. The change occurs mostly over the first 20% of generation. During oil to gas cracking, kinetic isotope effects become important and the effect on δ13C of the remaining oil can be modelled as a Rayleigh process. δ13C increases by 1.5% by 50% cracking. Insufficient data are available to calibrate the effects at higher levels of cracking, and modelling these variations is hindered by a lack of understanding of the mechanism of pyrobitumen formation. However, increases greater than about 4% are unlikely to be observed. With increasing maturity, the low molecular weight fractions become isotopically heavy faster than the high molecular weight fractions. As a result, any separation of the low molecular weight fraction into a gas phase (“condensate formation”) will produce an isotopic difference between oil and condensate that depends on maturity. In the early stages of generation the condensate may be up to 1% lighter than the remaining oil. With increasing maturity, this difference at first decreases and then increases in the opposite sense. By half way through oil to gas cracking the condensate may be 1.5% heavier than the residual liquid. More subtle rearrangement reactions may result in small, but significant, changes to the shape of the isotope “type-curves” when different oil fractions are compared. 相似文献
17.
18.
Previously studied thermosequences of wood (chestnut) and grass (rice straw) biochar were subjected to hydrogen pyrolysis (hypy) to evaluate the efficacy of the technique for determining pyrogenic carbon (CP) abundance. As expected, biochar from both wood and grass produced at higher temperature had higher CP amount. However, the trend was not linear, but more sigmoidal. CP/CT ratio values (CT = total organic carbon) for the wood thermosequence were ⩽0.03 at biochar production temperature (TCHAR) ⩽ 300 °C. They increased dramatically until 600 °C and remained relatively constant and near unity at higher biochar production temperature. Grass biochar was similar in profile, but CP/CT values rose dramatically after 400 °C. The findings are consistent with the hypothesis that hypy residues contain polycyclic aromatic hydrocarbons (PAHs) with a degree of condensation above at least 7–14 fused rings, with labile organic matter and pyrogenic PAHs below this degree of condensation removed by hypy.Both wood and grass thermosequences displayed δ13CP values that decreased with increased TCHAR, indicating that recalcitrant carbon compounds (pyrogenic aromatic PAHs with a relatively high degree of condensation) were first formed from structural components with relatively high δ13C values (e.g. cellulose). Relatively constant δ13C values at TCHAR ⩾ 500 °C suggested the dominant pyrolysis reaction was condensation of PAHs with no additional fractionation. Comparison of hypy with benzene polycarboxylic acid (BPCA), ‘ring current’ NMR and pyrolysis gas chromatography–mass spectrometry (GC–MS) results from the same suite of samples indicated a consistent overview of the structure of CP, but provided unique and complimentary information. 相似文献
19.
Distribution and possible sources of polycyclic aromatic hydrocarbons (PAHs) have been investigated in 23 late Eocene to early Pleistocene mudstones from the Sylhet succession of the northeastern Bengal Basin, Bangladesh. Paleoclimatic conditions in the southern Himalaya region throughout the Himalayan uplift were reconstructed, based on combustion derived PAHs and aromatic land plant derived biomarkers. Phenanthrene, fluoranthene (Fla), pyrene (Py), benz[a]anthracene (BaAn), chrysene/triphenylene (Chry + Tpn), benzofluoranthenes (Bflas), benzo[e]pyrene (BePy), benzo[a]pyrene (BaPy), perylene (Pery), indeno[1,2,3-cd]pyrene (InPy), benzo[ghi]perylene (BghiP), coronene (Cor) and retene (Ret) were the identified PAHs. Fla/(Fla + Py) ratios > 0.5 and InPy/(InPy + BghiP) > 0.2 from almost all Sylhet samples suggest occurrence of natural wildfires. Low contents of BaAn and BaPy indicate decomposition by long exposure to sunlight before sedimentation, or early diagenetic weathering. Increased Cor, InPy and BghiP contents suggest occurrence of larger, high temperature wildfires. Correlation coefficients of the PAHs and p-values for statistical hypothesis testing showed that the positive and negative correlations within the PAHs may be indicative of high or low temperatures in wildfires. Fungi derived Pery showed negative correlations with Py (r = −0.67, p = 4.6 × 10−4) and Fla (r = −0.56, p = 5.0 × 10−3), but not with Cor, Bflas, InPy and BghiP. Based on the correlation coefficients for all PAHs and their p-values, five statistical groups ([Py, Fla], [Cor, Bflas, InPy, BghiP], [BaAn, Chry + Tpn, BaPy], [Pery] and [Ret]) were recognized. These groups are probably correlated with origins and depositional processes. According to the results, the Sylhet succession was deposited in three differing paleoclimatic regimes: (1) First phase (late Eocene to early Miocene, early to middle stage of Himalayan uplift): High contents of combustion derived PAHs (Fla, Py and BePy), significant gymnosperm derived Ret, and low Pery abundances in the Jaintia and Barail groups indicate arid climatic conditions. Although wildfires could often occur, 5- or 6-ring combustion PAHs (Cor, InPy and BghiP) contents are low, suggesting that the wildfires were relatively low temperature. (2) Second phase (middle to late Miocene: middle to late stage of Himalayan uplift): Combustion derived PAHs and fungi derived Pery were dominant in the Surma Group. The climate was arid to humid and seasonal, with a dry season giving conditions suitable for combustion. Abundant Fla, Bflas, BePy, Cor, InPy and BghiP imply high temperatures in large wildfires. However, frequency of the wildfires decreased because of wet climate. (3) Third phase (late Miocene to Pleistocene: late stage of Himalayan uplift): Moderate to high Pery contents and low Fla, Py and BePy abundances in the Tipam and Dupitila groups indicate establishment of more humid climate. InPy, BghiP, Cor, Bflas and BaPy were predominant. Intensified humid and seasonal climate arising from the Himalayan monsoon decreased the incidence and frequency of general wildfires, but increased the ratio of large to small wildfires. 相似文献
20.
The middle Cenomanian–lower Turonian deposits of Ohaba-Ponor section (Southern Carpathians) were studied from biostratigraphic and isotopic points of view. Both the qualitative and semiquantitative nannofloral analyses, as well as the stable isotope (δ13C and δ18O) data support significant palaeoenvironmental changes in the investigated interval. Two δ13C positive excursions were recognized: (1) an excursion up to 1.8‰ (PDB) within the middle/late Cenomanian boundary; (2) an excursion up to 2.2‰ (PDB) in the Cenomanian/Turonian boundary interval. The oldest δ13C positive excursion recorded (placed within the Acanthoceras jukes-brownei/Eucalycoceras pentagonum Ammonite Zone boundary interval, and in the NC11 Calcareous Nannofossil Zone respectively) could be assigned to the middle Cenomanian Event II (MCEII). During the above-mentioned event, significant increase in abundance of Watznaueria barnesae, followed by successive blooms of Biscutum constans and Eprolithus floralis, were observed. The youngest δ13C positive excursion was identified in the Cenomanian/Turonian boundary interval (in the NC12 and lower part of the NC13 Calcareous Nannofossil Zones). Even the amplitude of this δ13C positive excursion is lower in the Ohaba-Ponor section, as generally reported, this may represent the regional record of the OAE2. The successive peaks of the nannofossils Biscutum constans, Zeugrhabdotus erectus and Eprolithus floralis indicate episodes of cooler surface water and high fertility, which preceded and lasted the Cenomanian/Turonian boundary event. Additionally, fluctuations of δ18O values between −2 and −6‰ suggest also cooler conditions within the Cenomanian/Turonian boundary interval. 相似文献