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1.
BAI Zhiqiang 《中国科学D辑(英文版)》2000,43(3):302-307
Microspherules are found in different facies at the Lower-Middle Devonian boundary, Guangxi, South China. There are more than 20 grains per kilogram rock sample. Composition and form of the microspherules are very similar to those of the microtektites from modern deposits of South Pacific Ocean and F-F boundary (Devonian). This may indicate that the microspherules from Guangxi are most likely the products of an extraterrestrial impact event that occurred at the end of Early Devonian Epoch. The event may be responsible for the biomass reduction and extinction of benthic organisms at the end of Early Devonian. The impact products (ejecta) can be used as a potential tool for stratigraphic correlation. 相似文献
2.
The Upper Devonian orbital cyclostratigraphy and numerical dating conodont zones from Guangxi,South China 总被引：5，自引：3，他引：5
GONG Yiming XU Ran TANG Zhongdao & LI Baohua Faculty of Earth Science China University of Geosciences Wuhan China Laboratory of Marine Geology Tongji University Shanghai China 《中国科学D辑(英文版)》2005,48(1):32-41
The hierarchically organized laminae, bundles, bundlesets and superbundlesets which correspond to a sub-Milankovitch, obliquity or precession, eccentricity and long eccentricity cyclothems, respectively, have been distinguished from the Upper Devonian Fras-nian-Famennian (F-F) transitional carbonate successions deposited in the carbonate-basin and slope facies of Guangxi, South China. The durations of cyclothems are 8000-10000a, 16667a or 33333a, 100000a and 400000a, respectively. The ratio of eccentricity to precession, eccentricity to obliquity, and long eccentricity to eccentricity is 1 : 6, 1 : 3 and 1 : 4 in the Devonian, respectively. Orbital cyclostratigraphical studies show that the durations of the conodont falsio-valis Zone, transitans Zone, punctate Zone, Lower hassi Zone, Upper hassi Zone, jamieae Zone, Lower rhenana Zone, Upper rhenana Zone, linguiformis Zone, Lower triangularis Zone, Middle triangularis Zone and Upper triangularis Zone are 0.4, 0.4, 0.4, 0.3, 0.4, 0.2, 0.8, 0.6, 0.8, 0.3, 0 相似文献
3.
Abstract The abundance of magnetic microspherules in a Triassic-Jurassic continuous sequence of alternating chert and shale beds in the Mino accretionary complex, central Japan, was measured systematically. Depending on time, the magnetic microspherules extracted from shale beds change in abundance considerably from the minimum 0.9ppm/cm3 at latest Triassic ( ca 208Ma) and the maximum 75ppm/cm3 at late Early Jurassic ( ca 187Ma); however, the abundance is always higher approximately 10–100 (average 70) times than those from adjacent chert bed at any stratigraphic horizon. Such systematic difference reveals the origin of radiolarian bedded chert as cyclic-rapid accumulation of biogenic SiO2 under extremely slow accumulative environments of shale with probable aeolian dust in origin. The accumulation data for individual shale and chert beds were obtained based on the microspherule abundance and radiolarian biostratigraphy, i.e., ca 0.018g/cm2 Ka for lower Jurassic shale beds and ca 1.9g/cm2 Ka for adjacent chert beds.
Duration time to make a chert-shale couplet corresponds to a dominantly 15–20Ka interval (average 23 Ka) in Upper Triassic bedded cherts with a low paleolatitude, whereas a 40–45 Ka interval (average 42 Ka) in Lower Jurassic ones which may been formed in higher latitude than Triassics before the final accretion to the Asian continental margin. Depending on paleolatitude, the cyclicity of 23 and 42 Ka may correspond to Milankovitch cycles which have been well documented in deep-sea sediments. 相似文献
Duration time to make a chert-shale couplet corresponds to a dominantly 15–20Ka interval (average 23 Ka) in Upper Triassic bedded cherts with a low paleolatitude, whereas a 40–45 Ka interval (average 42 Ka) in Lower Jurassic ones which may been formed in higher latitude than Triassics before the final accretion to the Asian continental margin. Depending on paleolatitude, the cyclicity of 23 and 42 Ka may correspond to Milankovitch cycles which have been well documented in deep-sea sediments. 相似文献
4.
The Frasnian-Famennian Boundary Event (Kellwasser Event) is one of the seven strongest Phanerozoic faunal turnovers. The importance of this first order of global bio-event was taken into consideration when the International Subcommission on Devonian Strat… 相似文献
5.
廖卫华 《中国科学D辑(英文版)》2002,45(4):380-384
The Frasnian-Famennian (F-F) mass extinction is one of the five great extinctions of marine life during the Phanerozoic. The
F-F event killed most of the Devonian reefs, the characteristic Devonian corals, stromatoporoids, bryozoans, nearly all tentaculites,
a few superfamilies of brachiopods, such as Atrypacea and Pentameracea and some important elements of goniatites, such as
Manticoceras.
The end-Frasnian was a phase of mass extinction. A large number of shelly benthos were killed by the F-F event. Early and
middle Famennian was the survival interval. The marine faunas were very rare at that time. The late Famennian was the recovery
interval. There appeared to have many new taxa in the Strunian stage. It lacked a radiation interval in Late Devonian Famennian
because another event (the D-C mass extinction) happened at the Devonian-Carboniferous boundary.
Several causes for the F-F mass extinction have been proposed by some geologists, which have been grouped into two broad types,
terrestrial and extraterrestrial. The former is related to sea level changes, climate changes and anoxic water event. The
latter is linked with some forms of meteorite impact.
A large-scale eustatic change of sea level and black shales representing an anoxic environment has been invoked to explain
one of the causes for the F-F mass extinction. 相似文献
6.
The method for measurement of the isotopic composition of oxygen in phosphates has been improved and adapted for analysis of small quantities of apatite, down to 10 mg. This extension enables one to analyze hand-picked conodont samples with an analytical reproducibility better than ±0.5‰ (1σ).46 samples of conodonts ranging from the Ordovician to the Pennsylvanian of North America were analysed. Some insoluble phosphatic residues, ichthyoliths and inarticulate brachiopods of the same time range were also measured. The range of the δ18O values of the analysed conodonts is between 15 and 19‰. It shows a general trend of decreasing d18O with increasing age, from an average value of about 19 in the Pennsylvanian to 17 in the Ordovician. This trend parallels that previously detected in marine phosphorites. For the time range between the Devonian and Pennsylvanian our data are in agreement with independent paleoclimatic information. Specifically, we detect maximum18O enrichment at the end of the Pennsylvanian, and minimum enrichment at the end of the Devonian. The difference between these two extremes is equivalent to about 10°C (from about 40° to 30°C), assuming constant isotopic composition of ocean water.The success of oxygen isotopic analysis of conodonts raises the possibility of their use in Paleozoic paleo-oceanography in a similar way to foraminifera in the Mesozoic-Cenozoic. 相似文献
7.
Size variation of the end Permian conodont Neogondolella at Meishan Section,Changxing,Zhejiang and its significance 总被引：5，自引：0，他引：5
Recent works reveal that the size reduction of or- ganisms during the Permian-Triassic transition is of great importance for research on biotic mass extinction and recovery in this period[1,2]. Initially, Urbanek (1993) observed a decrease in the size of Silurian graptolites during the biotic crisis, and used the term “Lilliput Effect” to define the size reduction in sur- viving animal taxa[3]. Subsequently, researchers re- ported a decrease in size of late Devonian conodonts[4], heart urc… 相似文献
8.
GONG Yiming XU Ran TANG Zhongdao SI Yuanlan & LI Baohua . Faculty of Earth Science State Key Laboratory of Geological Processes Mineral Resources China University of Geosciences Wuhan China . Institute of Resources & Environments Henan Polytechnic University Jiaozuo China . Department of Computer Science South-Central University for Nationalities Wuhan China . Laboratory of Marine Geology Tongji University Shanghai China 《中国科学D辑(英文版)》2005,48(10)
The five major mass extinctions which occurred in the transition of the Ordovician-Silurian (440 Ma), Late Devonian Frasnian-Famennian (F-F) (370 Ma), Permian-Triassic (250 Ma), Triassic-Jurassic (205 Ma) and Cretaceous-Paleogene (65 Ma) are significant phenomena in the Phanerozoic global environment and organic evolution. Their corresponding extinction rates of marine invertebrate at the level of genus and family are 60% (genus) and 26% (family), 57% and 22%, 82% and 51%, 53% and 22%, … 相似文献
9.
Cages and fertilizers were used at Glover's Atoll, Belize to test the relative importance of nitrogen (N) and phosphorus (P) to microbial euendolithic communities (bacteria, algae and fungi) and their bioerosion rates of Strombus gigas shells after 56-days of exposure. By the end of the experiment, the abundance of green algae was higher than cyanobacteria and fungi in N and N+P treatments, although green algae did not increase proportionally with increasing N concentrations, suggesting that green algae were co-limited by P and N. In contrast, cyanobacteria abundance increased with increasing P concentration, suggesting that cyanobacteria were P-limited. Fungi were not significantly affected by the addition of nutrients. Microbioerosion rates in the N and N+P treatments were 2-times greater than rates in the P treatment and 15-times greater than the control treatment. Results demonstrate that increased nutrient concentrations on coral reefs may increase microbioerosion rates, and variations in nutrient ratios can modify microborers community composition. 相似文献
10.
This study is based on both a generic and species level investigation of the individual size of the latest Permian conodont
Neogondolella Pa elements collected from Meishan Section A, Changxing, Zhejiang Province. In this study, an obvious size reduction of Neogondolella Pa elements within bed 24e of the upper Changxing Limestone is recognized. The size variation of the Neogondolella occurs simultaneously with some important events including the negative shift of δ
13C, change in the ratio of the abundance of cyanobacterial biomarkers versus that of other general bacterial biomarkers and
the shallowing of the sea water. Through the investigation of the paleoenvironmental changes and the analysis of the paleoecology
of the conodont genus Neogondolella, the authors propose that the major factors for the size reduction of species of the conodont genus Neogondolella are food shortages caused by the mass extinction, the shallowing of the sea water as well as the increase in opacity of the
sea water during the end Permian. The same phenomenon of Neogondolella size reduction is also observed in preliminary research from the same horizon at Shangsi Section, Sichuan Province. All the
evidence suggests that there was a mass extinction that occurred at the horizon of bed 24e, and the evidence supports the
viewpoint of a multi-phase mass extinction during the Permian and Triassic transition in South China. 相似文献
11.
微囊藻水华期间水体及藻体上细菌的动态 总被引：1，自引：1，他引：0
通过对水体中及附着在藻类上的细荫数量、代谢活性细菌、Chl.a浓度等的研究,探讨了藻类与细菌之间的代谢耦联关系,结果表明:1)水体中细菌的丰度随着Chl.a浓度的增加而逐渐增大(r2=0.466,P<0.05),但其峰值滞后于Chl.a;附在藻体表面上的细菌也呈现出相似的变化规律;2)水体中代谢活性细菌数量与总细菌数量显著相关(r2=0.678,P<0.05);附着在藻体上的代谢活性细菌虽然总数量低于水体中的代谢活性细菌,但二者之间亦存在显著的相关性(r2=0.836,P<0.05).3)藻类表面附着细菌的数量取决与藻类的生长状况,附着在藻类体上的代谢活性细菌的比率均高于水体中代谢活性细菌的比率,且在水华盛行期间呈逐渐增加的趋势. 相似文献
12.
氮、磷等营养物质对低洼盐碱地鱼塘水质的影响 总被引：4，自引：0，他引：4
通过在实验围隔中添加不同浓度的氮、磷等营养物质,对黄淮海平原低洼盐碱地鱼塘中的水质变化情况进行了初步研究,结果表明：1）围隔水体中异养细菌数量的变动,与水体中氮、磷等营养物质的浓度及比例密切相关,尤其是水体中磷的浓度对异养细菌数量的影响更为显著。2）围隔水体中的氮、磷等营养浓度及比率,明显地影响着其中藻类的数量和生物量。在实验条件下,水体中磷对藻类生长的影响要大于氮对藻类生长的影响,水体中N：P比为10：1左右是比较适宜藻类生长的比例。3）围隔水体中氮、磷等营养盐的去除能力与其中藻类的生物量及水体中N：P的比率密切相关,当围隔水体中的N：P比为10：1左右时,围隔水体中的藻类生长最好,生物量增加最快,相应地其对TN、TP的去除率也是最高的。 相似文献
13.
Gunnar Bratbak Stéphan JacquetAud Larsen Lasse H. PetterssonAndrey F. Sazhin Runar Thyrhaug 《Continental Shelf Research》2011,31(14):1500-1514
The purpose of the present study was to explore the composition and variation of the pico-, nano- and micro-plankton communities in Norwegian coastal waters and Skagerrak, and the co-occurrence of bacteria and viruses. Samples were collected along three cruise transects from Jæren, Lista and Oksøy on the south coast of Norway and into the North Sea and Skagerrak. We also followed a drifting buoy for 55 h in Skagerrak in order to observe diel variations. Satellite ocean color images (SeaWiFS) of the chlorophyll a (chl a) distribution compared favorably to in situ measurements in open waters, while closer to the shore remote sensing chl a data was overestimated compared to the in situ data. Using light microscopy, we identified 49 micro- and 15 nanoplankton sized phototrophic forms as well as 40 micro- and 12 nanoplankton sized heterotrophic forms. The only picoeukaryote (0.2-2.0 μm) we identified was Resultor micron (Pedinophyceae). Along the transects a significant variation in the distribution and abundance of different plankton forms were observed, with Synechococcus spp and autotrophic picoeukaryotes as the most notable examples. There was no correlation between viruses and chl a, but between viruses and bacteria, and between viruses and some of the phytoplankton groups, especially the picoeukaryotes. Moreover, there was a negative correlation between nutrients and small viruses (Low Fluorescent Viruses) but a positive correlation between nutrients and large viruses (High Fluorescent Viruses). The abundance of autotrophic picoplankton, bacteria and viruses showed a diel variation in surface waters with higher values around noon and late at night and lower values in the evening. Synechococcus spp were found at 20 m depth 25-45 nautical miles from shore apparently forming a bloom that stretched out for more than 100 nautical miles from Skagerrak and up the south west coast of Norway. The different methods used for assessing abundance, distribution and diversity of microorganisms yielded complementary information about the plankton community. Flow cytometry enabled us to map the distribution of the smaller phytoplankton forms, bacteria and viruses in more detail than has been possible before but detection and quantification of specific forms (genus or species) still requires taxonomic skills, molecular analysis or both. 相似文献
14.
15.
End-Permian conodont fauna from Dongpan section: Correlation between the deep-and shallow-water facies 总被引：1，自引：1，他引：0
GenMing Luo XuLong Lai QingLai Feng HaiShui Jiang Paul Wignall KeXin Zhang YaDong Sun Jun Wu 《中国科学D辑(英文版)》2008,51(11):1611-1622
This paper systematically investigated the conodonts from the uppermost Permian to the Lower Triassic at the Dongpan Section, Southern Guangxi, South China, and obtained abundant Late Permian conodonts from the syndepositional limestone lenses of beds 3 and 5-2 at this section. One genus and eight species of conodont P1 element including one new species, Neogondolella dongpanensis sp. nov., have been identified. The feature of conodont fauna indicates that conodonts collected from beds 3 and 5 at the Dongpan Section belong to the Neogondolella yini conodont zone, and correspond to bed 24 at the Meishan Section. Based on these conodont data, we suggest that the Neoalbaillella optima radiolarian zone at the Dongpan Section at least extended to the upper part of the N. yini conodont zone. 相似文献
16.
17.
Lars Ramberg 《Aquatic Sciences - Research Across Boundaries》1987,49(3):294-302
A dense bloom of a green algae was reduced by 97% within 5 days. This was probably caused by grazing by a colourless flagellate
that increased logarithmic to high number under these days and disappeared as quickly. After this the green algae increased
rapidly and mucilage lumps excreated by the flagellate was colonized by a specialistChlomydomonas.
The flagellate attack was probably enhanced by the high cell density and the physiological weakness of the green algae, due
to a very low growth caused by shortage of inorganic carbon. The grazing seems to have caused an increase of inorganic nutrients
that promoted the following growth of the green algae. 相似文献
18.
O. V. Babanazarova R. Kurmayer S. I. Sidelev E. M. Aleksandrina E. G. Sakharova 《Water Resources》2011,38(2):229-236
The results of observations of some abiotic (water transparency, light intensity, depth, biogenic element concentrations) and algological (chlorophyll concentration, phytoplankton abundance and biomass, the concentration of microcystines—toxins of blue-green algae) characteristics of Lake Nero are given for study periods of 1999–2004 and 2005–2007. Variations of these characteristics in the latter period are shown to be significant. The lake phytoplankton is found to pass in a «catastrophic” manner to monodomination of planktotrichaetic complex of blue-green algae. High-performance liquid chromatography was used for the first time to determine the concentration of microcystines MC-LR and MC-RR in Lake Nero seston. The presence of these types of microcystines in samples was confirmed by mass-spectrometry. A statistically significant correlation was found to exist between the total concentrations of microcystines and the biomass of species of Microcystis genus, suggesting the possible toxicity of representatives of this type of algae in Lake Nero. 相似文献
19.
本文于2008-2009年按照季节调查了西藏地区尼洋河着生藻类群落的组成、丰度和多样性,并运用多元统计方法定量分析了着生藻类的空间和季节变化特征及其与主要环境因子之间的关系.结果显示,尼洋河着生藻类共计6门30科49属,其中硅藻为优势着生藻类.着生藻类的Shannon-Wiener多样性指数在尼洋河中游最高,在中上游河段和中下游河段呈下降趋势,符合中间高度膨胀(mid-altitude bulge)假说.着生藻类的总丰度、物种丰富度以及Shannon-Wiener多样性指数在尼洋河沿程不存在显著差异,总丰度在各个季节之间不存在显著差异,但物种丰富度在秋季和冬季存在显著差异,夏、秋季着生藻类的Shannon-Wiener多样性指数显著高于冬、春季.主成分分析(PCA)表明,随着海拔的升高,着生藻类的物种丰富度和总丰度呈递减趋势;典范对应分析(CCA)表明,尼洋河部分硅藻与理化因子相关联,如:双壁藻(Diploneis)的丰度与总磷相关联,窗纹藻(Epithemia)的丰度与铵态氮相关联,双菱藻属(Surirella)的丰度与pH值相关联;部分绿藻与理化因子相关联,如:小球藻属(Chlorella)、栅藻属(Scenedesmus)、溪菜属(Prasiola)的丰度与水温相关联,小椿藻(Characium)的丰度与硬度相关联,转板藻(Mougeotia)的丰度与表层溶氧、矿化度相关联,新月藻属(Closterium)的丰度与碱度相关联;分类回归树(CART)模型预测了尼洋河着生藻类时空分布与主要环境因子之间的定量关系,即低海拔水域的着生藻类总丰度较高海拔高,高矿化度水域的着生藻类总丰度较低矿化度的高,不能用影响尼洋河着生藻类种类和数量的环境因子来解释着生藻类的Shannon-Wiener多样性指数.这些关键环境因子对尼洋河水域着生藻类的时空变化有着重要的指示作用,建议加强对着生藻类及这些环境因子的关注,保障尼洋河水域生态环境的可持续发展. 相似文献