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1.
G. Keller P. K. Bhowmick H. Upadhyay A. Dave A. N. Reddy B. C. Jaiprakash T. Adatte 《Journal of the Geological Society of India》2011,78(5):399-428
A scientific challenge is to assess the role of Deccan volcanism in the Cretaceous-Tertiary boundary (KTB) mass extinction.
Here we report on the stratigraphy and biologic effects of Deccan volcanism in eleven deep wells from the Krishna-Godavari
(K-G) Basin, Andhra Pradesh, India. In these wells, two phases of Deccan volcanism record the world’s largest and longest
lava mega-flows interbedded in marine sediments in the K-G Basin about 1500 km from the main Deccan volcanic province. The
main phase-2 eruptions (∼80% of total Deccan Traps) began in C29r and ended at or near the KTB, an interval that spans planktic
foraminiferal zones CF1–CF2 and most of the nannofossil Micula prinsii zone, and is correlative with the rapid global warming and subsequent cooling near the end of the Maastrichtian. The mass
extinction began in phase-2 preceding the first of four mega-flows. Planktic foraminifera suffered a 50% drop in species richness.
Survivors suffered another 50% drop after the first mega-flow, leaving just 7 to 8 survivor species. No recovery occurred
between the next three mega-flows and the mass extinction was complete with the last phase-2 mega-flow at the KTB. The mass
extinction was likely the consequence of rapid and massive volcanic CO2 and SO2 gas emissions, leading to high continental weathering rates, global warming, cooling, acid rains, ocean acidification and
a carbon crisis in the marine environment. 相似文献
2.
Cretaceous climate, volcanism, impacts, and biotic effects 总被引：5，自引：0，他引：5
Cretaceous volcanic activities (LIPs and CFBPs) appear to have had relatively minor biotic effects, at least at the generic level. Major biotic stress during the Cretaceous was associated with OAEs and related to nutrient availability largely from weathering, greenhouse warming, drowning of platform areas, and volcanism. The biotic effects of OAEs were often dramatic at the species level, causing the extinction of larger specialized and heavily calcified planktonic foraminifera (rotaliporid extinction) and nannoconids (nannoconid crises), the temporary disappearances of other larger species, and the rapid increase in r-selected small and thin-walled species, such as the low oxygen tolerant heterohelicids and radially elongated taxa among planktic foraminifera and thin walled nannofossils. Biotic diversity increased during cool climates, particularly during the late Campanian and Maastrichtian, reaching maximum diversity during the middle Maastrichtian. High biotic stress conditions began during greenhouse warming and Deccan volcanism about 400 ky before the K-T boundary; it reduced abundances of large specialized tropical planktic foraminiferal species and endangered their survival. By K-T time, renewed Deccan volcanism combined with a large impact probably triggered the demise of this already extinction prone species group.Evidence from NE Mexico, Texas, and the Chicxulub crater itself indicates that this 170 km-diameter crater predates the K-T boundary by 300,000 years and caused no species extinctions. The Chicxulub impact, therefore, can no longer be considered a direct cause for the K-T mass extinction. However, the K-T mass extinction is closely associated with a global Ir anomaly, which is considered too large, too widespread, and too concentrated in a thin layer to have originated from volcanic activity, leaving another large impact as the most likely source. This suggests that a second still unknown larger impact may have triggered the K-T mass extinction. 相似文献
3.
Beecher's Trilobite Bed in the Upper Ordovician of New York State has yielded some of the most completely preserved trilobites. Abundant specimens of Triarthrus, and fewer of Cryptolithus, were buried in a single catastrophic influx of sediment, and the limbs and other features are preserved in pyrite. A recent re-excavation of the bed provided an opportunity to investigate the controls on the pyritization of soft tissues, an extremely rare phenomenon. Larval and juvenile specimens are common in the Trilobite Bed, allowing the life histories of the trilobites to be pieced together. The nature of the transition from larva to adult was significant in determining the trilobites' chances of surviving the mass extinction at the end of the Ordovician. 相似文献
4.
During the late Maastrichtian, DSDP Site 216 on Ninetyeast Ridge, Indian Ocean, passed over a mantle plume leading to volcanic eruptions, islands built to sea level, and catastrophic environmental conditions for planktic and benthic foraminifera. The biotic effects were severe, including dwarfing of all benthic and planktic species, a 90% reduction in species diversity, exclusion of all ecological specialists, near-absence of ecological generalists, and dominance of the disaster opportunist Guembelitria alternating with low O2-tolerant species. These faunal characteristics are identical to those of the K–T boundary mass extinction, except that the fauna recovered after Site 216 passed beyond the influence of mantle plume volcanism about 500 kyr before the K–T boundary. Similar biotic effects have been observed in Madagascar, Israel, and Egypt. The direct correlation between mantle plume volcanism and biotic effects on Ninetyeast Ridge and the similarity to the K–T mass extinction, which is generally attributed to a large impact, reveal that impacts and volcanism can cause similar environmental catastrophes. This raises the inevitable question: Are mass extinctions caused by impacts or mantle plume volcanism? The unequivocal correlation between intense volcanism and high-stress assemblages necessitates a review of current impact and mass extinction theories. 相似文献
5.
基于FY-3A遥感数据的冰岛火山灰云识别 总被引：1，自引：0，他引：1
2010年4月至5月期间冰岛艾雅法拉火山喷发造成了欧洲航空业史无前例的瘫痪以及巨大的经济损失,其严重影响再次显示,对火山灰云进行有效监测的重要性。火山灰云是由火山碎屑物及气体组成的混合物,火山碎屑物主要由直径小于2mm的岩石、矿物、火山玻璃碎片组成,火山灰云中的气体主要包括水汽、CO2、SO2、H2S、CH4、CO、HCL、HF、HBr、和NOx等。使用具有我国自主知识产权的FY-3A/VIRR数据,对此次艾雅法拉火山喷发的不同阶段选取具有典型风向变化的日期,采用分裂窗亮温差算法(SWTD)、RGB真彩色方法、中红外波段数据等进行火山灰云的识别,并将结果与冰岛地区的火山灰监测报告以及前人的研究结果进行对比研究,结果表明:火山喷发初期火山灰云中较高含量的水汽会补偿反面吸收的影响,妨碍分裂窗亮温差算法(SWTD)对火山灰云的识别,而中红外波段数据因对高温物体的敏感性,不受水汽的影响,对喷发初期较高温度的火山灰云识别效果较好;在喷发中期,火山灰云浓度较大时三种方法均表现良好,卫星图像中火山灰云的位置信息及漂移方向均非常清晰,且同气象条件相吻合,验证了识别方法的正确性。该项结果表明,具有我国自主知识产权的FY-3A数据能够达到监测火山灰云的目的,而如何更加清晰地界定火山灰云的边界位置以及更加准确的计算出火山灰云的浓度需要进一步的深入研究。 相似文献
6.
本文描述了石炭—二叠纪陆地维管植物在物种、生态和遗传方面的多样性。并根据古生代末这些植物在时空上的演化过程和数量统计数字,确认二叠—三叠纪集群绝灭事件同样在植物中存在。进而还探讨了植物集群绝灭事件发生的原因,笔者认为其直接外部原因,可能是局部地质事件(如:构造活动、火山爆发)引起热带雨林大面积消失,使气候变干旱所致。又根据当今对化石植物生殖生物学的研究结果,认为当时大部分植物(即古植代植物)的生殖方式较单一,胚在发育时无休眠期,成熟的胚缺少良好的保护结构,不适合在干旱环境下传种繁殖是这次植物集群绝灭事件发生的主要内部原因。 相似文献
7.
Christopher Stocker Mark Williams Tatsuo Oji Gengo Tanaka Toshifumi Komatsu Simon Wallis 《Geology Today》2019,35(1):15-19
‘We are such stuff as dreams are made on, and our little life is rounded with a sleep’. So sleep the trilobites of Yokokurayama, a sacred mountain hidden within the beautiful landscape of Japan’s Shikoku’s island. And though Prospero may have been speaking to his daughter and her fiancé (in William Shakespeare’s The Tempest), he might well have been contemplating the magnificent trilobite fossils of Yokokurayama. Japan may be better known for its sweeping volcanic landscapes, majestic castles, Shinto shrines and bullet trains, but it is also home to important collections of Silurian and Devonian trilobites. 相似文献
8.
The significance of trilobites described from six cores from the Kalladeina 1 drillhole from the Warburton Basin, northeastern South Australia is discussed. The oldest are from a dark grey shale of Core 16 from a depth of 3453.7–3455.8 m; they are of possible early Drumian (Cambrian Series 3, middle Cambrian) age. The youngest come from a dark grey shale of Core 4 at a depth of 2017.2–2022.04 m. This fauna contains the trilobites Asaphellus? sp., Yosimuraspis sp., Conophrys sp. and Protopliomerops? sp. thus indicating a Tremadoc (earliest Ordovician) age. These are the youngest known trilobites from the Warburton Basin and the youngest known in South Australia. 相似文献
9.
中国扬子海盆奥陶纪末期生物集群绝灭事件 总被引：2，自引：1，他引：2
<正> 近年来,奥陶纪末期生物集群绝灭事件的研究,越来越为人们所关注。Raup和Sepkoski(1982)认为,在晚奥陶世大约有22％科的生物绝灭,是显生宙生物集群绝灭5个最大幕之一。这次事件造成了所有海洋无脊椎动物的分异度和丰度的降低。Brenchley(1990)把晚奥陶世绝灭的若干类群的重要变化作了如下概述:阿什极尔中期的38科三叶虫,仅有14科存活到志留纪;在或接近奥陶-志留系界线,有13科腕足类绝灭,27科穿 相似文献
10.
Ömer Elitok Züheyr Kamaci M. Nuri Dolmaz Kamil Yılmaz Meltem Şener 《Journal of Earth System Science》2010,119(6):853-860
Potassium-rich volcanic rocks in the Isparta area (SW Turkey) consist mainly of older (Pliocene) volcanic rock suites (e.g.,
lamprophyre, basaltic trachyandesite, trachyandesite, trachyte) and younger (Quaternary) caldera forming lava dome/flows (e.g.,
tephriphonolite, trachyte) and pyroclastics (ash/pumice fall deposits and ignimbritic flows). The magnetic susceptibility
(K) was performed for both groups. The magnetic susceptibility value of the less evolved rocks characterized by SiO2 < 57 wt% (e.g., basaltic trachyandesite, tephriphonolite, lamprophyric rocks) and having mostly mafic phenocrysts such as
pyroxene, amphibole, and biotite-phlogopite is over 10 (10−3 [SI]). Fine to medium-grained and subhedral to anhedral opaque minerals are scattered especially in the matrix phase of the
less evolved volcanic rocks. However, the K value of the more evolved rocks (e.g., trachyte and trachyandesites) with SiO2 over 57 wt% vary between 0.1 and 28, but most of them below 10. SI values are negatively correlated with SiO2, Na2O, but positively correlated with Fe2O3, CaO, MnO, P2O5 and MgO contents, suggesting inverse variation of SI with fractionation of potassic magma. That is to say that less evolved
volcanic rocks have relatively higher magnetic susceptibility values in the volcanic suite. Fine to medium-grained and subhedral
to anhedral Fe-Ti oxides are scattered mainly in the matrix phase of the less evolved volcanics, presumably cause the pronounced
relatively higher magnetic susceptibility. 相似文献
11.
12.
Identifying the spatial extent of volcanic ash clouds in the atmosphere and forecasting their direction and speed of movement has important implications for the safety of the aviation industry, community preparedness and disaster response at ground level. Nine regional Volcanic Ash Advisory Centres were established worldwide to detect, track and forecast the movement of volcanic ash clouds and provide advice to en route aircraft and other aviation assets potentially exposed to the hazards of volcanic ash. In the absence of timely ground observations, an ability to promptly detect the presence and distribution of volcanic ash generated by an eruption and predict the spatial and temporal dispersion of the resulting volcanic cloud is critical. This process relies greatly on the heavily manual task of monitoring remotely sensed satellite imagery and estimating the eruption source parameters (e.g. mass loading and plume height) needed to run dispersion models. An approach for automating the quick and efficient processing of next generation satellite imagery (big data) as it is generated, for the presence of volcanic clouds, without any constraint on the meteorological conditions, (i.e. obscuration by meteorological cloud) would be an asset to efforts in this space. An automated statistics and physics-based algorithm, the Automated Probabilistic Eruption Surveillance algorithm is presented here for auto-detecting volcanic clouds in satellite imagery and distinguishing them from meteorological cloud in near real time. Coupled with a gravity current model of early cloud growth, which uses the area of the volcanic cloud as the basis for mass measurements, the mass flux of particles into the volcanic cloud is estimated as a function of time, thus quantitatively characterising the evolution of the eruption, and allowing for rapid estimation of source parameters used in volcanic ash transport and dispersion models.
相似文献13.
扬子地台内晚奥陶世末—早志留世初五峰—龙马溪组内沉积了多层钾质斑脱岩,但对于该时期扬子地台西缘钾质斑脱岩的研究报道相对较少。本文旨在通过对云南大关地区新地2井五峰—龙马溪组内沉积的钾质斑脱岩进行矿物学及地球化学分析,进一步确定扬子西缘该时期钾质斑脱岩原始岩浆类型及其所产生的构造环境。矿物学特征表明,钾质斑脱岩主要由黏土矿物和非黏土矿物组成,其中黏土矿物由伊利石和伊蒙混层组成,非黏土矿物以石英、长石、方解石、白云石和黄铁矿等为主。钾质斑脱岩主量元素以高K_2O,低TiO_2为特征,微量元素特征表现为富集Rb、Ba、Th、U等元素,Ti、P元素相对亏损,Ti/Th值指示了酸性火山灰的性质;ΣREE在(49.86～209.43)×10~(-6);与球粒陨石相比,轻稀土轻微富集、具Eu负异常,无Ce异常;在Nb/Y-Zr/TiO_2图解中,数据点主要落在安山岩和粗面英安岩之间,表明钾质斑脱岩源岩浆性质为中酸性岩浆;依据微量元素特征和构造环境判别结果,初步认为原始岩浆可能形成于岛弧环境,其火山灰来源可能与扬子北缘早古生代秦岭洋闭合过程中的板块碰撞有关。 相似文献
14.
Famennian microbial reef facies, Napier and Oscar Ranges, Canning Basin, western Australia 总被引：5，自引：0，他引：5
Following the Frasnian–Famennian mass extinction, which eliminated most skeletal reef-building fauna, the early Famennian reefs of the Canning Basin were constructed primarily by reef-framework microbial communities. In the Napier and Oscar Ranges, the Famennian reef complexes had high-energy, reef-flat depositional environments on a reef-rimmed platform that transitioned into low-energy, deep-water reefs growing in excess of 50 m below sea level. High-energy, reef-flat depositional environments contain doming fenestral stromatolites that grade into porous thrombolites and are associated with coarse-grained sandstones and grainstones. The reef-margin subfacies contains mounds of microdigitate thrombolites, which are more delicate than the reef-flat thrombolites and locally contain abundant red algae, Girvanella, renalcids and sediment-filled tubes. Within the thrombolites, the red algae are in upright growth positions, suggesting that the thrombolites are largely composed of carbonate that precipitated in situ. Reefal-slope environments are dominated by Wetheredella and Rothpletzella with locally abundant Girvanella, renalcids and Uralinella. In reefal-slope strata, delicate fans and microdigitate stromatolites of Wetheredella and Rothpletzella are often oriented horizontal or diagonal to bedding and are interpreted as syndepositionally toppled over. Most mesoscale microbial community structures contain several species of microbial fossils, and no single microbial species appears to have controlled the morphology of the community structure. Therefore, the depositional environment must have determined the distribution and morphology of the stromatolites, thrombolites and other microbial community structures. The adaptability of microbial communities to various reef environments allowed them to fill ecological niches opportunistically after the Frasnian–Famennian mass extinction. 相似文献
15.
Crustal structure in the Changbaishan volcanic area, China, determined by modeling receiver functions 总被引：5，自引：0，他引：5
During 1998–1999, we installed a temporary broadband seismic network in the Changbaishan volcanic region, NE China. We estimated crustal structure using teleseismic seismograms collected at the network. We detected a near surface region of strong anisotropy directly under the main volcanic edifice of the volcanic area. We modeled 109 receiver functions from 19 broadband stations using three techniques. First we used a “slant-stacking” method to model the principal crustal P reverberation phases to estimate crustal thickness and the average crustal P to S speed ratio (vp/vs), assuming an average P-wave velocity in the crust. We then estimated crustal S-wave velocity (vs) and vp/vs profiles by modeling stacked receiver functions using a direct search. Finally, we inverted several receiver functions recorded at stations closest to the main volcanic edifice using least squares to estimate vs velocity profiles, assuming a vp/vs value. The results from the three estimation techniques were consistent, and generally we found that the receiver functions constrained estimates of changes in wave speeds better than absolute values. We resolved that the crust is 30–39 km thick under the volcanic region and 28–32 km thick away from the volcanic region, with a midcrust velocity transition at about 10–15 km depth. We estimated that the average crust P-wave velocity is about 6.0–6.2 km/s surrounding the main volcanic region, while it is slightly lower in the vicinity of the main volcanic edifice. The estimates of vp/vs were more ambiguous, but we inferred that the bulk crustal Poisson's ratio (which is related to vp/vs) ranges between 0.20 and 0.30, with a suggestion that the Poisson's ratio is lower under the central volcanic region compared to the surrounding areas. We resolved low S-wave velocities (down to about 3 km/s) in the middle crust in the region of the main volcanic edifice. The low velocity anomaly extends from about 5–10 to 15–25 km below the surface, probably indicating a region of elevated temperatures. We were unable to determine if partial melt is present with the data we considered in this paper. 相似文献
16.
R. E. BEIERSDORFER 《Journal of Metamorphic Geology》1993,11(3):415-428
Abstract The metamorphic history of the Middle to Upper Jurassic volcanic and hypabyssal rocks exposed in the Klamath Mountains and Sierra Nevada of California is related, in part, to the rifting of a volcano-plutonic arc. The Callovian to Kimmeridgian rocks exposed in the region consist of, from north-west to south-east, a back-arc ophiolite, a rifted volcanic arc and a volcanic arc complex. All of these units have been metamorphosed and contain various combinations of the phases chlorite, amphibole, epidote, prehnite and pumpellyite. Projection of coexisting phases onto the composition plane MgO/(MgO + FeO) and Al2O3+ Fe2O3 - 0.75 CaO - Na2O through quartz, water, albite and epidote results in consistent mineralogical compatibilities within each region, but crossing tie-lines between regions. This suggests that the volcanic and hypabyssal rocks from each region have equilibrated under different intensive conditions. The back-arc ophiolite in the north has suffered subseafloor high-T/P hydrothermal metamorphism with geothermal gradients on the order of 100° C km?1. The rifted volcanic arc has undergone synchronous burial, hydrothermal and contact metamorphism. Metamorphic field gradients in the region pass through the prehnite-pumpellyite and greenschist facies suggesting geothermal gradients on the order of 30° C km?1. The southernmost volcanic arc complexes contain metavolcanics of the pumpellyiteactinolite and greenschist facies suggesting moderate- to high-P/T metamorphism and geothermal gradients on the order of 20° C km?1. The apparent increase in rifting and calculated geothermal gradients from south-east to north-west suggest that the observed very low- and low-grade metamorphism may be a response to enhanced thermal gradients during extension of the volcanic arc. This correlation between the extent of rifting and metamorphism is consistent with a model of diastathermal metamorphism of a propagating rift along the western margin of North America during the Late Jurassic. The plate tectonic setting may be analogous to the present-day Andaman Sea region. 相似文献
17.
《Gondwana Research》2006,9(4):579-584
A first report of discovery of spherules, glassy balls, highly magnetic fine dust and microbracciated matrix in the Fatehgarh Formation of Barmer Basin, Rajasthan, India is being presented in this paper. The Fatehgarh Formation is a mixed siliciclastic, carbonate and phosphorite formation of Cretaceous age in the Barmer Basin that comprises sediments of Middle Jurassic to Lower Eocene age. The phosphorite zone in the Fatehgarh Formation is ∼8 metre-thick zone that comprises phosphatic sandstone, bone bed, bedded phosphorite and phosphatic and non phosphatic gastropod beds. The spherules occur in a thin phosphatic-clay mud and silt band of bone bed, which also yielded a very rich and diverse microvertebrate assemblage with a dominant Late Cretaceous (Maastrichtian) form of Igdabatis along with forms comprising of Semionodontid, Lapisosteum and Enchodontid. The end Cretaceous is marked for a mass extinction of numerous species including dinosaurs. An extraterrestrial impact is interpreted as the reason for this mass extinction. Whether these spherules are related to the volcanic source or K/T Boundary impact ejecta found at Caribbean and Gulf of Mexico region needs detailed chemical and age characterization for which study is in progress. 相似文献
18.
Geethanjali Krishnan Hema Achyuthan V. H. R. Siva 《Journal of the Geological Society of India》2017,90(1):20-24
This paper examines the difference in the geophysical and chemical characteristic of the volcanic ash and thermal fly ash to evaluate environmental pollution. Natural volcanic ash (VA) samples from Sagirelu, Cuddapah dist., Andhra Pradesh and thermal fly ash (FA) samples from the Thermal Power Station, Ennore, Chennai, were collected, analysed and compared. The particle sizes of the ash samples were determined using the laser particle size analyzer and the different surface morphological characters were studied using SEM analyses. The chemical components such as pH, major oxides, trace metals and mineral compositions were determined using pH metre, XRF and XRD methods. pH value of the volcanic ash varies from 8.5 to 8.9 indicating its alkalinity (8.5 to 9) in volcanic ash, while the thermal ash is neutral to mildly alkaline with pH varying from 6 to 7.5. Both the ash samples have higher concentration value in SiO2 (VA - 69.25%, FA - 46%) in major oxides and Cl (VA - 0.8%, FA - 0.1%) in trace elements. Quartz is the dominant mineral in both the types of ash, however, the volcanic ash has amorphous silica, while the fly ash contains crystalline quartz. 相似文献
19.
《International Geology Review》2012,54(17):2164-2183
ABSTRACTTephra fallout beds in marine sediments provide chronologically precise and highly resolved records of volcanism at time scales relevant to Quaternary climate cycles. While the record of discrete (visible) thin tephra beds is readily accessible, the significance of the dispersed (invisible) tephra record remains unclear. Here we evaluate the role of dispersed tephra for orbital-scale volcanic time variations in the Quaternary (<1.2 Ma) carbonate mud of IODP Hole U1437B (Northwest Pacific). The carbonate mud contains cyclic series of discrete fallout tephra beds from the oceanic Izu Bonin (~85% of tephra beds) and the continental Japan (~15%) volcanic arcs, respectively. Our results show the inorganic aluminosilicate (lithogenic) fraction is a mixture of dispersed Izu Bonin and Japan ash, and Asian dust. The time distribution of the Izu Bonin ash with its distinct composition appears to confirm and enhance the cyclic time variation of the discrete ash beds at Hole U1437B. Dispersed Japan ash resembles Asian dust in trace elements and is only distinguishable in Sr-Nd isotope space. Collectively, our results confirm the existence of periodic, orbital-scale fluctuations of arc volcanic frequency. Orbital-scale time variations of marine ash may be best established by series of discrete marine ash beds, yet the concomitant dispersed ash flux must also be recorded in order to understand the total flux of arc volcanic ash into the ocean basins and thus the role of the volcanism-climate link. 相似文献
20.
ZHONGKANG YANG NANYE LONG YUHONG WANG XIN ZHOU YI LIU LIGUANG SUN 《Journal of Earth System Science》2017,126(1):7
The contents of Ti, Al and Fe 2 O 3 in a lacustrine sediment core (DY6) collected from Dongdao Island, South China Sea (SCS), were determined to be much higher than those in the three major sediment end-members (coral sand, guano and plants), and their likely sources include terrigenous dust and volcanic ash. At 61 cm (～AD 1300), the contents of Ti, Al and Fe 2 O 3 have an abnormally high spike, which cannot be explained by terrigenous dust. The Sr and Nd isotope compositions at 61 cm are in excellent agreement with those in volcanic materials, but they are significantly different from those in terrigenous dust, implying a possible material input from historical volcanic eruptions in the lacustrine sediment DY6. The documented great Samalas volcanic eruption at AD 1257 in Indonesia is likely the candidate for this volcanic eruption. 相似文献