A correlation between the Large Igneous Provinces and mass extinctions: constraint on the end-Guadalupian mass extinction and the Emeishan LIP in South China,eastern Tethys     

《International Geology Review》2012,54(10):1215-1233

ABSTRACT

Well-documented outcrops around the Emeishan Large Igneous Province (ELIP) in South China, eastern Tethys, encompassing the end-Guadalupian mass extinction have been investigated. Correlatable sections recording the event exhibit very similar lithological characters, positive-then-negative C isotope excursions and massive biotic demise. Detailed analyses of the fossil record and carbon isotopic variations were carried out on the Guadalupian–Wuchiapingian Boundary sections over the inner, middle, outer zones of the ELIP and its margin. Due to a pronounced decrease in marine habitat area and the environmental and ecological change over this part of the Tethys, the biota crisis records show the loss of numerous tropical invertebrate taxa, and exhibit fewer genera and smaller testing sizes and low productivity. The biota crisis was a sustainable and gradual reduction in diversity over the Capitanian. The associated carbon isotopic data reveal unusually high δ¹³C(carb) values before the late Capitanian, representing higher primary productivity (or buried rate) and more ¹³C-enriched CO₂ released by hydrothermal carbonate breakdown from the upper crust into the sediments at that time. Subsequently, an accelerated negative excursion across the boundary and the gradual excursion with low carbon isotope amplitude favours an increased influx of light ¹²C sourced by the volcanism around the eastern Tethys. The very similar time–space relation between the biota crisis and the Emeishan volcanism confirms that volcanic eruptions may have triggered the biota crisis event in South China. Intensive volcanism could result in detrimental environmental and ecological stresses, habitat loss, organic material splitting, or the emission of light carbon and thermal fluid (or aerosol), implying that the losses of the shallow-marine invertebrates either occurred geologically instantaneously or in a series of closely spaced crises coinciding with the initial phase of ELIP formation. These findings in South China may reveal the causal relation between mass extinctions and LIPs in a global context.  相似文献   

埃迪卡拉纪印痕化石是陡山沱期 宏体藻类的固着器吗？ ——Hiemalora与Gesinella的对比研究     

唐烽  金幸生  王约  丁明  赵元龙  高林志 《地质论评》2014,60(5):1009-1018

Hiemalora是一类广为分布的埃迪卡拉(Ediacaran)纪(震旦纪)圆盘状印痕化石,周围具流苏状或触须状突起,曾被解释为似水母动物,或某种叶状生物的固着器官,但以往罕见其与叶状生物体共同保存。本文报道了华南贵州震旦纪陡山沱组一类保存完好丰富的被确认为藻类的碳膜化石——革辛娜藻Gesinella,具有完整的须状固着构造。这一须状构造的形态和大小与Hiemalora非常相似,致密加厚的基部及其周围辐射状分布的丝状或须根状构造,可以分别和后者的中央盘以及周缘突起的"触须"相比较。陡山沱组的这一类碳膜化石同时保存有明显巨大的形同藻类的叶片和固着器,为研究埃迪卡拉生物群的底栖印痕化石提供了新的认识,即:盘状的Hiemalora可能是多细胞藻类的固着器官,而不一定是最初解释的似水母动物或其它叶状体生物的固着构造。不过,证实这一点尚需更进一步地研究埃迪卡拉纪生物的保存方式和埋藏环境。  相似文献   

关于《贵州关岭"6.28"特大滑坡特征和成因机理》一文的商榷     

张信宝 《山地学报》2011,29(2)

就滑坡组成和发生机制,与<贵州关岭"6.28"特大滑坡特征和成因机理>一文作者进行商榷.笔者认为"超压密岩土边坡失稳理论"可以较好的解释大寨滑坡-碎屑流灾害的突然发生."上硬下软"坡体结构,是大寨滑坡发生的地质基础;强降雨快速入渗,是导致岩层裂隙和大气突然贯通,负压立即消失,高陡坡体迅即失稳的诱因.  相似文献   

Relationship between watershed scale macroinvertebrate community and environmental factors in the Japanese archipelago     

《Limnologica》2021

The conservation and restoration of freshwater ecosystems require the understanding of potential biota of the target area. My ultimate study goal was to clarify the potential fauna of the watershed unit of the Japanese archipelago, a hotspot of biodiversity. Here, I attempted to classify the macroinvertebrate community of the major rivers within the Japanese archipelago, thereby elucidating its biogeography, and to investigate the extent to which environmental factors drive the watershed’s macroinvertebrate community. I classified the rivers located in the northern region of the Japanese archipelago geographically, but did not group the geographically adjacent rivers in the western region together. Differences in watershed size, geological history (including river conflict), and paleo-drainage systems seem to affect the classification results. Moreover, Indicator Species Analysis results suggest that river groups in the northern part of the Japanese archipelago had highly endemic species, whereas, the river groups in the western part of the Japanese archipelago had few highly endemic species. The result of the canonical correspondence analysis indicated that topographic factors, the flow regime, geology, water quality, and anthropogenic factors were significantly correlated with macroinvertebrate classification and distribution. The results of the decision tree model indicated that water temperature and maximum specific discharge were explanatory factors in the classification of the macroinvertebrate community. Further, my results also suggest that environmental factors at a smaller scale than that of the watershed were needed to explain further subdivisions in classification of the macroinvertebrate community.  相似文献   

The correlation between macroscopic algae and metazoans in the Ediacaran: a case study on the Wenghui biota in northeastern Guizhou,South China     

Y. Wang  Y. Wang  W. Du  X. Wang 《Australian Journal of Earth Sciences》2013,60(7):967-977

After the Marinoan glaciation, macroscopic organisms thrived in the Yangtze Sea, South China, during the Ediacaran period. The Wenghui biota, which is found from the upper Doushantuo Formation black shales (>551 Ma) in northeastern Guizhou, South China, includes macroscopic algae, metazoans and ichnofossils. Most macroalgae in the Wenghui biota bear a holdfast to secure them onto seafloor and have a thallus of various lengths extending into the water column. This biota can be divided into Globusphyton, Sectoralga–Longifuniculum, Cucullus, Beltanelliformis and Baculiphyca–Gesinella assemblages. A fossil-barren interval containing a thin layer of feldspathic sandstone separates the macroscopic organisms into two distinct parts. From the Globusphyton assemblage through the Sectoralga–Longifuniculum assemblage to the Cucullus assemblage, metazoans show a positive correlation with the abundance and diversity of branching macroalgae at both metre and millimetre scales. Nevertheless, both Beltanelliformis and Baculiphyca–Gesinella assemblages, in which the number and diversity of macroscopic algae and metazoans, especially the shorter branching macroalgae, are obviously decreasing or even lacking, might be related to a special environment and a fragile ecosystem. In addition, the ratios of Ni/Co, U/Th and V/(V + Ni) display zigzagged profiles at millimetre scales indicating frequent redox fluctuations. Variations in macrofossils and trace elements at both millimetre and metre scales indicate that the oxygen content in the northeast Guizhou Sea fluctuated frequently during the middle–late Ediacaran period and the Wenghui biota possibly lived in the redox buffering zone. Moreover, the abundance and diversity of macroalgae, especially the branching macroalgae, could have significantly influenced the redox conditions in water column. The increase in oxygen may have improved the environment for the growth and reproduction of macroalgae and metazoans.  相似文献   

Modelling wetland connectivity during overbank flooding in a tropical floodplain in north Queensland,Australia   总被引：2，自引：0，他引：2  

Fazlul Karim  Anne Kinsey‐Henderson  Jim Wallace  Angela H. Arthington  Richard G. Pearson 《水文研究》2012,26(18):2710-2723

Hydrological connectivity between floodplain wetlands and rivers is one of the principal driving mechanisms for the diversity, productivity and interactions of the major biota in river–floodplain systems. This article describes a method of quantifying flood‐induced overbank connectivity using a hydrodynamic model (MIKE 21) to calculate the timing, the duration and the spatial extent of the connections between several floodplain wetlands and rivers in the Tully–Murray catchment, north Queensland, Australia. Areal photogrammetry and field surveyed stream cross data were used to reproduce floodplain topography and rivers in the model. Laser altimetry (LiDAR)–derived fine resolution elevation data, for the central floodplain, were added to the topography model to improve the resolution of key features including wetlands, flow pathways and natural and artificial flow barriers. The hydrodynamic model was calibrated using a combination of in‐stream and floodplain gauge records. A range of off‐stream wetlands including natural and artificial, small and large were investigated for their connectivity with two main rivers (Tully and Murray) flowing over the floodplain for flood events of 1‐, 20‐ and 50‐year recurrence intervals. The duration of the connection of individual wetlands varied from 1 to 12 days, depending on flood magnitude and location in the floodplain, with some wetlands only connected during large floods. All of the wetlands studied were connected to the Tully River for shorter periods than they were to the Murray River because of the higher bank heights and levees on the Tully River and wetland proximity to the Murray River. Other than hydrology, land relief, riverbank elevation and levee banks along the river were found key factors controlling the degree of connectivity. These variations in wetland connectivity could have important implications for aquatic biota that move between rivers and off‐stream habitats during floods. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

云贵交界地区中上三叠统之交地球化学特征及其环境意义   总被引：1，自引：0，他引：1       下载免费PDF全文

曾雄伟  程龙  王建坡  危凯  杨梅 《古地理学报》2014,16(4):503-516

中国西南部云贵交界地区中上三叠统海相地层以拥有丰富的海生爬行动物化石为特色的古生物群落而闻名。近期,笔者在云贵交界地区发现了一个完整的中上三叠统竹杆坡组至上三叠统小凹组剖面,即云南罗平江底剖面。在该剖面中,分别在竹杆坡组纹层灰岩段顶部及小凹组上部发现了典型的兴义动物群及关岭生物群生物组合。为了研究中晚三叠世之交生物群落演化的环境背景,对采集的97件地球化学样品进行了常量、微量及稀土元素测试与分析。微量和稀土元素的分析结果表明,竹杆坡组纹层灰岩段及小凹组处于缺氧环境,产兴义动物群及关岭生物群的地层含氧量相对增加,而两生物群落之间的竹杆坡组瘤状灰岩段主要为贫氧环境。中晚三叠世之交的海水含氧量的变化规律与生物群落的演替较为吻合,说明该时期海水含氧量的变化对生物演替具有一定的控制作用。  相似文献   

美国滨海核电厂温排水混合区的设置及启示     

魏新渝  张琨  王韶伟  徐海峰  方圆  杨端节 《海洋科学》2017,41(8):53-63

系统调研美国温排水法规标准体系、混合区政策以及滨海核电厂混合区的设置,并与我国现状进行比较。可以看出,美国清洁水法和联邦法规给出温排水和水质标准的一般要求,各个州的水质标准给出水质准则、混合区政策以及对水生生物保护的要求。水质准则给出各种类型水体温度限值(包括温升限值和/或温度上限值);混合区政策给出混合区的位置、尺寸、形状以及混合区内水质要求;具体厂址应基于"一事一议"的方式确定混合区范围,并满足混合区最小化要求,大部分美国滨海核电厂混合区范围满足州的混合区政策要求;少数核电厂混合区范围超过了州混合区政策要求,这些电厂需进行厂址特性热影响研究,以证明当前的温排水限值能够确保受纳水体中结构稳定的土著贝类、鱼类和其他野生生物种群的生长和繁育。我国当前没有地区差异的水质准则,无温排水混合区政策、设置方法或导则。美国温排水混合区设置方法和实践有助于我国滨海核电厂温排水混合区的设置和优化,以减小对水生生物的影响。  相似文献   

罗平生物群产出层位氧碳稳定同位素的初步研究   总被引：5，自引：1，他引：4  

孙媛媛 《地质学报》2009,83(8):1110-1117

为了解云南罗平地区新近发现的罗平生物群的古环境信息,我们对其产出层位－－中三叠统关岭组二段大凹子剖面的碳酸盐岩进行了全岩氧碳稳定同位素测试。测试结果显示,中三叠世安尼期Pelsonian亚期大凹子剖面δ13C值分布范围在-4.543‰～1.069‰之间,平均为-3.0298‰,δ18O值分布在-5.202～-0.971‰之间,平均为-3.3645‰。 同位素数据的相关性分析显示大凹子剖面的同位素值受后期大气水参与的成岩作用影响较小。结合沉积学和古生物学的证据,我们提出了一个假说：δ13C值明显偏负的层位主要是由硫酸菌的还原作用所导致。这种活动所释放的H2S也部分解释了罗平生物群大规模死亡的原因。 在排除掉成岩作用的影响之后,本剖面δ13C分布在-2.976～1.069‰之间,平均值为-1.4556‰,δ18O分布在-3.455～-2.516‰之间,平均值为-2.9258‰。尽管如此,与同时期其它有关剖面相比,大凹子剖面δ13C值仍然偏低,对此我们进行了探讨和解释,并利用高水位时期的δ18O数据作为基本资料对罗平地区的古海水温度进行了恢复。结果显示其温度值分布在27℃～32℃之间,平均为29℃左右,说明罗平地区当时气候比较温暖。  相似文献   

Phase contrast synchrotron X-ray microtomography of Ediacaran (Doushantuo) metazoan microfossils: Phylogenetic diversity and evolutionary implications   总被引：1，自引：0，他引：1  

Jun-Yuan Chen  David J. Bottjer  Eric H. Davidson  Gang Li  Feng Gao  R. Andrew Cameron  Michael G. Hadfield  Ding-Chang Xian  Paul Tafforeau  Quan-Jie Jia  H. Sugiyama  Rui Tang 《Precambrian Research》2009,173(1-4):191

Microfossils from the Ediacaran Weng’an Phosphate Member of the Doushantuo Formation (Guizhou Province, southern China) have received widespread attention. The Doushantuo, which overlies the glacial deposits of the Nantuo Formation, was deposited following the Marinoan glaciation, the last extensive glaciation of Snowball Earth. Radiometric age dating indicates that the Doushantuo is older than 580 my, and hence that these microfossils are older than the Ediacara Biota. However, the diversity represented by these fossils has yet to be fully documented. A recent technological approach that has increasingly been used to image fossils, propagation phase contrast synchrotron X-ray microtomography, has allowed non-destructive study of both exterior and interior features of a variety of Doushantuo microfossils from the gray facies of the Weng’an Phosphate Member, cropping out along the axis of the Mt. Beidou anticline. Studies of Doushantuo embryos demonstrate the existence of a large suite of modern embryonic features, including macromeres and micromeres, cell lineage, polar lobes, compacted epithelia, equal and unequal cleavage, blastulation and gastrulation, and chorionic protection. Because embryos such as those here studied provide only a limited amount of phylogenetic information, and because adult metazoans of the types that produced these embryos have yet to be discovered in Doushantuo-age rocks, these fossilized embryonic forms can at present be assigned only to the various superclades represented amongst living Metazoa. The diversity of the embryos here studied suggests that the metazoan fauna of the Doushantuo may well have included animals of poriferan, cnidarian, and both protostomial (representatives possibly of basal protostome lineages) and deuterostomial affinity. If this interpretation is correct, it would then follow that the last common ancestor of the bilaterian metazoan lineage, as well as the last common ancestor of sponges, cnidarians and bilaterians, pre-dated deposition of the Doushantuo strata.  相似文献