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1.
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
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《International Geology Review》2012,54(10):892-909
The Cretaceous-Paleocene (K-T) transition has been recorded in sedimentary carbonate rocks in northwestern Argentina and southern Chile. In the Yacoraite Basin, Argentina, this transition has been preserved in a 2 m thick marly layer, at the base of the Tunal Formation, which overlies lacustrine/marine carbonates of the Yacoraite Formation (Cabra Corral dam). The K-T transition is also preserved at Maimara, where Tertiary sandstones overlie a 50 m thick limestone bed of the Yacoraite Formation. In the Magellan Basin, Chile, glauconitic sandstones with calcitic cement and limestone concretions of the Maastrichtian Punta Rocallosa Formation are overlain by sandstones, claystones, and limestones of the Chorillo Chico Formation. The K-T transition is preserved in the lower portion of the Chorillo Chico Formation. Carbonates of the Yacoraite Formation display bulk-rock δ13C values from +1 to +2‰ PDB, with a negative incursion (?4‰ PDB) at the K-T transition. δ13C values in the Tunal Formation marls vary from ?3 to ?1‰ PDB. At Rocallosa Point, δ13C values in limestone strata, calcite cement, and limestone concretions vary from ?4 to ?33 ‰ PDB, and the lowest value in the Chorillo Chico Formation apparently marks the K-T transition. The δ18O fluctuations in the Yacoraite and Magellan carbonate rocks suggest a temperature drop at the K-T transition, followed by a temperature rise. High 87Sr/86Sr ratios (0.7140-0.7156) characterize the studied profiles of the Yacoraite Formation, documenting an important 87Sr-enriched source of Sr to the water from which these carbonates precipitated. At the Magellan basin, 87Sr/86Sr ratios are closer to the expected values for the global Late Cretaceous-Paleocene ocean. 相似文献
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A terrestrial scenario for the Cretaceous-Tertiary boundary collapse of the marine pelagic ecosystem
In this paper, we present an expansion of the model for marine ecosystem collapse at the Cretaceous-Tertiary boundary presented by Brinkhuis and Zachariasse (1988). A long-term sea-level drop at the end of the Cretaceous culminated in a short-term regressive pulse at K-T time. Deep-water production was curtailed, minimizing the vertical advection of nutrients and oxygen in the oceans. Consequently, a productivity crisis developed, which could only be survived by cosmopolitan shallow-dwellers, and the Oxygen Minimum Zone (OMZ) expanded. No sustained Oceanic Anoxic Event followed the K-T boundary event, since productivity had dropped to extremely low values. At K-T time, however, the short-term expansion of the OMZ, invoked by the combination of minimized oxygen advection and abrupt mass mortality, caused dysoxic conditions even to reach up to the shelves, as can be deduced from sedimentological, chemical and faunistic observations. 相似文献
6.
Alvarez W Smit J Lowrie W Asaro F Margolis SV Claeys P Kastner M Hildebrand AR 《Geology》1992,20(8):697-700
Restudy of Deep Sea Drilling Project Sites 536 and 540 in the southeast Gulf of Mexico gives evidence for a giant wave at Cretaceous-Tertiary boundary time. Five units are recognized: (1) Cenomanian limestone underlies a hiatus in which the five highest Cretaceous stages are missing, possibly because of catastrophic K-T erosion. (2) Pebbly mudstone, 45 m thick, represents a submarine landslide possibly of K-T age. (3) Current-bedded sandstone, more than 2.5 m thick, contains anomalous iridium, tektite glass, and shocked quartz; it is interpreted as ejecta from a nearby impact crater, reworked on the deep-sea floor by the resulting tsunami. (4) A 50-cm interval of calcareous mudstone containing small Cretaceous planktic foraminifera and the Ir peak is interpreted as the silt-size fraction of the Cretaceous material suspended by the impact-generated wave. (5) Calcareous mudstone with basal Tertiary forams and the uppermost tail of the Ir anomaly overlies the disturbed interval, dating the impact and wave event as K-T boundary age. Like Beloc in Haiti and Mimbral in Mexico, Sites 536 and 540 are consistent with a large K-T age impact at the nearby Chicxulub crater. 相似文献
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Mu Ramkumar Doris Stüben Zsolt Berner Jens Schneider 《Journal of Earth System Science》2010,119(1):1-17
The Ariyalur-Pondicherry sub-basin of the Cauvery basin comprises a near complete stratigraphic record of Upper Cretaceous-Lower
Tertiary periods. Earlier studies have documented variations of clay mineral assemblages, change in microtexture of siliciclasts
and many geochemical and stable isotopic anomalies far below the Cretaceous-Tertiary boundary (KTB) in these strata. This
paper documents the occurrences of two positive 87Sr/86Sr anomalies preceding K-T boundary in this basin and discusses plausible causes. Analysis of trace elemental and stable isotopic
profiles, sedimentation history, petrography and mineralogy of the rocks reveal that while both the anomalies may be due to
increased detrital influx caused by sea level and climatic changes, the second anomaly might have been influenced by Deccan
volcanism which in turn predated KTB. Record of such anomalies preceding K-T boundary supports the view of multi-causal step-wise
extinction of biota across KTB. 相似文献
9.
基于决策树模型的上海城市湿地遥感提取与分类 总被引：5，自引：0，他引：5
城市湿地是上海重要的生态基础并具有复杂多变的自然特性。研究采用决策树分类方法,以TM影像多光谱波段特征为主要分类变量,采用经K-T变换、IHS变换等光谱增强后的数据以及利用灰度共生矩阵分析影像第一主成分的纹理统计量作为辅助分类变量,结合城市湿地几何特征信息,构建上海城市湿地决策树分类模型,进行上海市湿地信息的遥感提取和分类。结果表明：（1）上海城市湿地总面积为1 277.40 km2;其中水田面积最大,占总面积的65.30%;其次为河流、库塘、湖泊和芦苇。（2）决策树模型的分类方法在一定程度上提高了城市湿地提取和分类的精度,使其达到89.05%;与传统的最大似然法相比,总精度提高了约10%。 相似文献
10.
A fluvial sequence near Cave Stream (north of Castle Hill Village, central Canterbury), New Zealand, contains organically-preserved plant macrofossils (cuticles). The almost ubiquitous presence of Araucariaceae macrofossils in the lower part of the section and their stratigraphic disappearance roughly coincident with the appearance of the angiosperm leaf Dryandra comptoniaefolia and conifer taxa only known elsewhere from sediments of Paleogene age, indicates that the section spans the Cretaceous-Paleogene (K-T) boundary. This was subsequently confirmed by a palynological study that demonstrated the disappearance of Late Cretaceous index species within the investigated exposure. The sequence supports the pattern recognized elsewhere in New Zealand where Araucariaceae macrofossils either disappear or become very rare in end-Cretaceous and the leaf Dryandra comptoniaefolia is an important component in the early Cenozoic. The Cave Stream K-T boundary is one of the very few in the world with organically-preserved plant macrofossils and confirms the dramatic turnover in macroflora, which is known from North America. 相似文献
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Spherule deposits, commonly interpreted as ejecta from the Chicxulub impact at Yucatán, Mexico, are present in many K-T (Cretaceous-Tertiary) sections. Geological mapping of the northern La Sierrita area, NE Mexico, revealed the presence of (1) multiple spherule deposits embedded in late Maastrichtian marls, which are folded or disaggregated (breccia-like). They are up to 6 m thick, locally present in two outcrop areas, and show limited lateral continuity. These deposits consist of mm-cm sized spherical to drop-shaped vesiculated spherules, angular to filamentous (ejecta-) fragments and abundant carbonate. They are interpreted as primary ejecta fallout deposits that have been affected by subsequent local slumps-slides, liquefaction, and debris flows; welded components suggest an initial ground surge-like ejecta-dispersion mode. (2) A spherule deposit, 10-60 cm thick that constitutes the base of a channelized sand-siltstone deposit at, or close to, the K-T boundary and is characterized by wide lateral continuity. It is of similar petrologic composition to deposit (1), though slightly enriched in terrigeneous detritus, thus reflecting influx from proximal shelf areas. It is interpreted to result from debris flows and turbidite currents, though no size sorting and abrasion of ejecta has been observed. Petrological, mineralogical, and geochemical criteria suggest that ejecta components from both types of spherule deposits are similar and originated from the Chicxulub impact, with multiple deposits produced by subsequent remolding, reworking, and redeposition. Spherules and fragments have an Fe- (25-30 wt%), Al-, Mg-rich and Si-poor (<25 wt% SiO2) composition, and are altered to chlorite and iron-oxides, though rare K-rich mafic glass (~50 wt% SiO2; 5-8 wt% K) is also present. They contain Ti-, Fe-, K-rich schlieren, Fe-, Mg-rich globules, and rare µm-sized metallic and sulfidic Ni-, Co-rich inclusions. Carbonate as clasts and within spherules and fragments shows textures indicative of quenching and/or liquid immiscibility. Although potential ejecta fractionation and alteration make accurate evaluation difficult, this composition suggests an ejecta origin mainly from mafic lithologies and carbonaceous sediments, in addition to a contribution from intermediate felsic rocks and the possibility of meteoritic contamination. 相似文献
12.
综合考虑碳酸盐岩储层孔隙度、孔隙类型对储层物性参数的影响,对常规的Xu-White模型等效介质理论进行了改进,采用K-T理论增加多种不同类型的孔隙(如粒间孔隙、刚性孔隙、裂隙等),得到了一种新的改进的Xu-White模型等效介质理论,并提出了一套新的适用于碳酸盐岩储层的地震数值模拟方法。该方法首先采用改进的Xu-White模型等效介质理论,来计算碳酸盐岩储层的等效参数,将各向异性的储层转换为均匀介质;然后再采用声学波动方程进行地震数值模拟。模型试验的结果表明,该方法不仅计算效率高,而且可以得到高信噪比的模拟记录,其主要地层的反射波场特征与弹性波方程数值模拟完全一致,是一种简单高效的适用于碳酸盐岩储层的地震数值模拟方法。 相似文献
13.
藏南拉轨岗日变质核杂岩带的TM影像特征 总被引：5，自引：0，他引：5
通过对拉轨岗日地区TM图像进行主成分变换、缨帽变换、比值运算等数字处理, 其成果图像进一步印证了拉轨岗日变质核杂岩带具有典型三层结构这一野外区调成果.通过对系列成果图像的分析对比, 总结了变质核、接触带和盖层的影像特征, 分析了拉轨岗日构造带各变质核杂岩之间的变化规律. 相似文献
14.
横波速度对于地震模拟、AVO分析以及流体识别具有重要意义,实际测井数据中横波速度信息缺乏,因此横波速度预测已经成为岩石物理研究的一个焦点。综合Xu-White模型以及Pride模型,提出了一种新的用于计算干岩石模量的岩石物理模型。该模型综合考虑了孔隙形状和成岩作用对干岩石体积模量、剪切模量的影响,因此该模型更加合理并具有更高的精度。同时联合Gassmann理论,建立了饱和流体岩石的纵波、横波速度计算模型。将该模型成功地应用于实验室测量数据和实际测井数据的横波速度预测中,预测结果表明,基于本文提出的岩石物理模型的横波速度预测方法是行之有效的。 相似文献
15.
The Rajahmundry Traps, Andhra Pradesh: Evaluation of their petrogenesis relative to the Deccan Traps
Ajoy K. Baksi 《Journal of Earth System Science》2001,110(4):397-407
Geochemical and geochronological data for rocks from the Rajahmundry Traps, are evaluated for possible correlation with the
main Deccan province. Lava flows are found on both banks of the Godavari River and contain an intertrappean sedimentary layer.
Based on40Ar/39 Ar age data, rocks on the east bank are post K-T boundary, show normal magnetic polarity, and belong to chron 29N. Their
chemistry is identical to lavas in the Mahabaleshwar Formation in the Western Ghats, ∼1000km away. It was suggested earlier
that the genetic link between these geographically widely separated rocks resulted from lava flowing down freshly incised
river canyons at ∼ 64 Ma. For the west bank rocks, recent paleomagnetic work indicates lava flows below and above the intertrappean
(sedimentary) layer show reversed and normal magnetic polarity, respectively. The chemical composition of the west bank flow
above the intertrappean layer is identical to rocks on the east bank. The west bank lava lying below the sedimentary layer,
shows chemistry similar to Ambenali Formation lava flows in the western Deccan.40Ar/39 Ar dating and complete chemical characterization of this flow is required to elucidate its petrogenesis with respect to the
main Deccan Province. 相似文献
16.
J. Mallikharjuna Rao G. V. S. Poornachandra Rao K. P. Sarma 《Journal of the Geological Society of India》2009,73(1):143-152
The Archaean gneissic basement of Shillong plateau has been traversed by number of mafic dyke swarms. At least two suites
of dykes are identified in the region represented by Proterozoic Khasi greenstone related dolerites and younger Cretaceous
dolerite dykes in addition to mafic alkaline dykes. The older Khasi greenstone dolerites are altered and have undergone low-grade
metamorphism compared to fresh Cretaceous dykes, which are well exposed in the West Garo Hills region. All the Khasi greenstone
dolerites are tholeiite in composition and range from basalt to basaltic andesite in composition and show olivine or quartz
normative character. Most of the dykes show continental nature of emplacement with some overlapping oceanic tectonic setting
of origin. Petrochemical study suggests that they were derived from picrites that subsequently undergone low-pressure fractionation.
Palaeomagnetic study of the older Khasi greenstone related dolerites show a direction of magnetization of Dm=17, Im= +57 (α95= 23.34; K=31.5; N=24) with a palaeolatitude of 29.7°N to the Indian subcontinent that clearly support the Proterozoic dyke/dyke
swarm emplacement in the region. The magnetic carrier as inferred from K-T studies is in multi domain (MD) size and cation
deficient (CD) domain states. 相似文献
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《Geochimica et cosmochimica acta》1996,60(17):3187-3196
The flux of particulate extraterrestrial (ET) matter to the deep-sea has been calculated using a four-component mixing model based on osmium concentrations and isotope ratios in slowly accumulating pelagic sediments from the Pacific Ocean. Nineteen published bulk-leach osmium isotope data pairs that cover the last 80 million years have been used for the calculation. The calculated annual particulate flux, averaged over several 100 ka by slow accumulation and bioturbation, ranges from ∼18,000 to ∼67,000 tons, with a mean value of ∼37,000 ± 13,000 tons. The data indicate no significant variability in the flux with time, except at the K-T boundary and are thus compatible with results based on Ir accumulation in deep-sea sediments. The inferred constancy of the ET matter flux is in contrast to recent results based on the ET 3He flux that integrates only a small size fraction of the entire ET matter flux. 3He data indicate variability by a factor of 6 over the past 70 Ma and a fivefold increase in the ET flux between 3 Ma and 1 Ma that is not seen in the bulk ET matter flux based on osmium isotope data.The apparent constancy of the cosmic matter flux over the past 80 Ma stands in marked contrast to the dynamic nature of the marine osmium isotope record and indicates that dissolution of cosmic matter does not drive changes in this record, except at the K-T boundary. A comparison between osmium isotope and Ir data from two pelagic sediment cores from the Pacific (DSDP Site 596 and LL44-GPC3) indicates that the seawater-soluble fraction of ET Os cannot exceed ∼36 kg/a and most likely is significantly smaller. The maximum value of 36 kg/a can account for approximately one half of the seawater-soluble ET matter flux necessary to balance the radiogenic continental runoff of Os without any additional unradiogenic source. Simple mass balance calculations indicate that an additional unradiogenic source of Os to the oceans, most likely alteration of oceanic crust, is required to balance the present-day seawater osmium-isotopic composition. This source is probably more important in balancing radiogenic continental runoff than is dissolution of cosmic matter in seawater. 相似文献
18.
Geochemical Characteristics of a Veinlet Kupferschiefer Profile from the Lubin Mine, Southwestern Poland 总被引：3，自引：0，他引：3
Previous studies have shown that the ascending, oxidizing brines play a very important role in Kupferschiefer mineralization. Fractures could be the pathway of the brines. In order to clarify the influences of the brines on bulk organic matter, aromatic hydrocarbons and Kupferschiefer mineralization, one veinlet Kupferschiefer profile from the Lubin mine, southwestern Poland was studied with the microscopic, geochemical and Rock-Eval methods. The microscopic results indicate that organic matter of the veinlet sample consists dominantly of bitumen. Its extract content is higher than in other samples. The dominant aromatic compounds are naphthalene and alkylated naphthalenes (Na-PAH), which have migrated into the veinlet sample from other sediments. The content of phenanthrene and its methylated derivatives (Ph-PAH) is much lower than in other samples. The reason may be due to their heavier mass than Na-PAH. It is more difficult for Ph-PAH to migrate. The Na-PAH was probably removed from the shale by dist 相似文献
19.
富勒烯（Fullerene）为除金刚石和石墨外碳元素的第三种同素异形体，自Kroto等1985年发现以来，对富勒烯的研究一直是世界性的热点话题，并在多个方面取得重要进展。它具有稳定的封闭笼状结构，被认为在星际空间广泛存在。富勒烯的形成条件特殊，普通的地球环境和地质过程不利于富勒烯的生成。1992年天然富勒烯在俄罗斯前寒武纪地层桑加岩（Shungite）中被发现，引起了人们对天然富勒烯研究的兴趣。随着富勒烯在陨石和撞击构造中的发现，人们更加关注事件地层中富勒烯存在的可能性以及它们的可能来源。二叠纪—三叠纪（P-T）之交发生了地质历史上规模最大的生物灭绝事件，因此，学者十分关注P-T界线地层中是否能检测到天然富勒烯的的存在。文章回顾了富勒烯在陨石、撞击构造、K-T界线地层和P T界线地层的研究进展，并重点对P-T界线富勒烯的存在问题进行讨论，指出从样品采集到样品测试，每一个环节都可能影响富勒烯的检出。P-T界线地层富勒烯可能源于陨石撞击、天然大火等极端地质事件，而包裹在富勒烯碳笼的稀有气体的同位素组成提供了进一步区分的重要证据。事件地层中普遍存在富勒烯，表明天然富勒烯可以作为地层中发生过重大灾变事件的重要的地球化学指标，而具有异常稀有气体同位素组成的富勒烯则是地外撞击事件的最直接证据。 相似文献
20.
In this study we report similar biotic response patterns in planktic foraminiferal assemblages, whether in association with volcanism, impacts or climate change at the end of the Cretaceous and early Tertiary. During and after each type of catastrophe two groups dominate high stress assemblages: (1) the small Guembelitria species, which are interpreted as having thrived in eutrophic surface waters where other species rarely survived; and (2) the low oxygen tolerant small Heterohelix species, which thrived at times of an expanding oxygen minimum zone associated with high nutrients and a stratified water column. The ecosystem collapse appears to be primarily the result of high macro- and micronutrient influx (from impacts, volcanism and erosion) leading to eutrophication and phytoplankton blooms (i.e., primary producers) that result in toxic conditions for foraminifera. Once nutrients decrease due to consumption by phytoplankton, the first opportunistic foraminifera, the Guembelitria, appear and graze on phytoplankton, rapidly reproduce (heterochronic acceleration) and increase populations exponentially. With nutrient depletion Guembelitria populations rapidly decrease leading to ecologic niches for other generalists and ecosystem recovery. Small low O2 tolerant heterohelicid populations mark this second stage, followed by small trochospiral and planispiral species. With further environmental recovery, increasing competition, niche development, and restoration of a well-stratified watermass, oligotrophic conditions are restored opening habitats for large, highly specialized species and a return to normal diverse assemblages. Such highly stressed ecological successions are observed in association with mantle plume volcanism in the Indian Ocean, Andean volcanism in Argentina and shallow inland seas in Egypt and Madagascar during the late Maastrichtian, the K-T impact, volcanism during the early Danian, and intense upwelling and climate extremes. We present a simple model to explain the ecological succession and recovery phases that follow major biotic perturbations. 相似文献