深海二叠——三叠系界线研究现状   总被引：4，自引：0，他引：4  

叶玫  冯庆来 《地质科技情报》1997,16(3):47-51

综述了深海二叠（Ｐ）－－三叠系（Ｔ）界线研究现状，介绍了深海Ｐ－Ｔ界线附近岩石地层，生物地层、缺氧事件及生物绝灭和复苏的研究进展，指出了深海Ｐ－Ｔ界线，缺氧事件和生物绝灭研究的分歧、不足及其症结。  相似文献   

地史转折期的生态系   总被引：7，自引：2，他引：7  

殷鸿福  童金南 《地学前缘》1997,(Z2)

生态系的演变是地球各圈层系统耦合关系变化的直接标志。地史转折期的生态系具有复杂的生物内涵，在绝灭—残存—复苏过程中，各生物类别的演替遵循着一定的生存型式。大绝灭后生态系复苏的原动力是绝灭后迁入避难所的复活类型和大绝灭末期高压环境中产生的祖先类型的新生和辐射发展。全面了解绝灭后生态系的组成和结构，对于正确认识地史转折期，即圈层耦合结点处的地质作用型式和过程具有重要作用。  相似文献   

The impact of shade on establishment of shrubs adapted to the high light irradiation of semi-arid environments   总被引：1，自引：0，他引：1  

L.V. Jefferson  M. Pennacchio   《Journal of Arid Environments》2005,63(4):706-716

Light may be an important limiting resource that influences community structure of chenopod shrublands. As part of a larger study that aimed to determine the factors that influence chenopod community structure, the focus of this study was the influence of plant canopy on the growth and establishment of smaller plants. We therefore measured the height and cover of three chenopods (Enchylaena tomentosa, Maireana brevifolia and Maireana georgei) when growing within and outside of the canopy of Atriplex bunburyana under field conditions. All three chenopods had lower cover and E. tomentosa was taller when growing within the canopy of A. bunburyana in comparison to those growing outside of the canopy. The chenopods were then grown under three artificial shade regimes. Plant height, cover, biomass, relative leaf area and photosynthetic surface area measurements showed that each species responded differently to shade. E. tomentosa biomass was facilitated by shade. This was inferred by an increase in total plant biomass. M. brevifolia, in contrast, tolerated shade by increasing above-ground biomass allocation. M. georgei was adversely affected by the shade regimes: root biomass decreased in response to shade. Competition for light is, therefore, likely to influence chenopod community structure of semi-arid and arid environments.  相似文献   

Re‐evaluating the Late Quaternary fossil mammal assemblage of Seton Rockshelter,Kangaroo Island,South Australia,including the evidence for late‐surviving megafauna          下载免费PDF全文

MATTHEW C. MCDOWELL  GAVIN J. PRIDEAUX  KERYN WALSHE  FIONA BERTUCH  GERALDINE E. JACOBSEN 《第四纪科学杂志》2015,30(4):355-364

  相似文献   

Holocene survival of the wild horse in Europe: a matter of open landscape?     

Robert S. Sommer  Norbert Benecke  Lembi Lõugas  Oliver Nelle  Ulrich Schmölcke 《第四纪科学杂志》2011,26(8):805-812

The wild horse Equus ferus was one of the most frequent species of the Late Pleistocene large ungulate fauna in Eurasia and played an important role in the subsistence of human groups, especially at the end the Late Glacial. It is frequently assumed that E. ferus became extinct in Europe at the beginning of the Holocene because of the development of woodlands and loss of open habitats. Because of its preference for open habitats and in spite of its adaptability, the appearance or disappearance of the wild horse could therefore be a suitable palaeoecological indicator for the opening of the Holocene primeval woodlands. We revised the dating and reliability of the subfossil record and dated several bones by atomic mass spectrometry ¹⁴C dating. From the beginning of the Holocene (9600 cal a BC) to the end of the Atlantic Period (3750 cal a BC) there are 207 archaeological sites with wild horse records available in Europe. E. ferus survived the Pleistocene Holocene transition in Europe, but the spatiotemporal dynamics of populations fluctuated remarkably in the early and middle Holocene. Small and sparse populations increasingly became extinct during the early Holocene, until between 7100 and 5500 cal a BC the wild horse was almost absent in central parts of the European Lowlands. Particular conditions in natural open patches in the canopy forests, chalklands and floodplains may have maintained the local survival of the horse in some regions of the Lowlands, however. In the Late Atlantic, between 5500 and 3750 cal a BC the range of the wild horse was again extended. It re‐immigrated into central and western Europe, probably as a consequence of increasing landscape opening by Neolithic peoples. The data presented here may be a valuable part of the debate on the degree of openness of the early and middle Holocene landscape. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

下扬子PTB界线深水相区粘土岩的火山成因研究及其对LPME的指示意义     

廖志伟  胡文瑄  王小林  曹剑  姚素平  万野 《地质学报》2016,90(4):785-800

全球,尤其是特提斯域二叠—三叠纪之交(PTB)剖面中普遍发育火山成因的粘土岩,对理解晚二叠世末生物大灭绝(LPME)的触发机制及相关基础地质问题具有重要意义。本文报道了在华南下扬子区新发现两条深水PTB剖面(皖南牛山和蔡村)的粘土岩工作,包括岩石学、矿物学和全岩地球化学等,填补了区域研究空白。研究结果发现,粘土岩主要由伊利石等粘土矿物,以及石英、岩浆锆石、长石等斑晶矿物组成。在地球化学上具有高K_2O、低Na_2O、相对富集大离子亲石元素(LILE)、相对亏损高场强元素(HFSE)等特征。据此,认为这些粘土岩为火山成因的钾质斑脱岩,其原岩可能为中酸性流纹英安岩,具有弧岩浆作用的源区背景。对比华南其他地区已发现的PTB界线粘土岩,发现它们成因类似,可能来源于古特提斯洋周缘陆陆碰撞,抑或是泛大洋俯冲潘吉亚大陆东缘(包括华南板块)所导致的长英质火山岩浆喷发,且具有多期多源性特点。PTB时期全球活跃的火山岩浆活动(包括镁铁质火山作用和华南地区火山灰所指征的长英质火山作用)可能是导致LPME的主要原因。  相似文献   

Retrieval of effective leaf area index (LAIe) and leaf area density (LAD) profile at individual tree level using high density multi-return airborne LiDAR     

《International Journal of Applied Earth Observation and Geoinformation》2016

As an important canopy structure indicator, leaf area index (LAI) proved to be of considerable implications for forest ecosystem and ecological studies, and efficient techniques for accurate LAI acquisitions have long been highlighted. Airborne light detection and ranging (LiDAR), often termed as airborne laser scanning (ALS), once was extensively investigated for this task but showed limited performance due to its low sampling density. Now, ALS systems exhibit more competing capacities such as high density and multi-return sampling, and hence, people began to ask the questions like—“can ALS now work better on the task of LAI prediction?” As a re-examination, this study investigated the feasibility of LAI retrievals at the individual tree level based on high density and multi-return ALS, by directly considering the vertical distributions of laser points lying within each tree crown instead of by proposing feature variables such as quantiles involving laser point distribution modes at the plot level. The examination was operated in the case of four tree species (i.e. Picea abies, Pinus sylvestris, Populus tremula and Quercus robur) in a mixed forest, with their LAI-related reference data collected by using static terrestrial laser scanning (TLS). In light of the differences between ALS- and TLS-based LAI characterizations, the methods of voxelization of 3D scattered laser points, effective LAI (LAIe) that does not distinguish branches from canopies and unified cumulative LAI (ucLAI) that is often used to characterize the vertical profiles of crown leaf area densities (LADs) was used; then, the relationships between the ALS- and TLS-derived LAIes were determined, and so did ucLAIs. Tests indicated that the tree-level LAIes for the four tree species can be estimated based on the used airborne LiDAR (R² = 0.07, 0.26, 0.43 and 0.21, respectively) and their ucLAIs can also be derived. Overall, this study has validated the usage of the contemporary high density multi-return airborne LiDARs for LAIe and LAD profile retrievals at the individual tree level, and the contribution are of high potential for advancing forest ecosystem modeling and ecological understanding.  相似文献   

关于峨眉山大火成岩省一些问题的研究现状   总被引：4，自引：1，他引：3  

HE Binghui 《地球科学进展》2016,31(1):23-42

峨眉山大火成岩省(ELIP)位于扬子板块西缘,是我国唯一被国际学术界认可的大火成岩省,受到国内外学者的广泛关注。主要围绕峨眉山玄武岩喷发前的隆升剥蚀情况、喷发时限、地幔柱的轴部位置等争议性问题进行探讨,总结了前人的研究成果。由于地幔柱和岩石圈之间相互作用的复杂性,加之地幔柱模型的不完善,峨眉山地幔柱活动在地表的真实响应也许更复杂。在今后的研究中,应该加强不同学科间的相互合作,着重研究地球深部动力学过程以及地球系统各圈层的相互作用。  相似文献   

青岛冷水团的消亡机理研究   总被引：1，自引：0，他引：1  

张启龙  刘志亮  齐继峰  杨德周  郑冬梅 《海洋学报》2016,38(5):27-33

本文基于多年月平均水温资料,分析了青岛冷水团的长消过程,并利用气候态月平均大气数据和数值模拟结果,探讨了青岛冷水团的消亡机理。结果表明,青岛冷水团3月出现,4月成型,5月最盛,6月减弱,7月消失;南黄海6-7月间偏南风的增强和温跃层以下反气旋涡的减弱是青岛冷水团消亡的动力机制,而海面净热通量的下传和水平热量的输入则是青岛冷水团消亡的热力机制。  相似文献   

Sedimentology of the continental end‐Permian extinction event in the Sydney Basin,eastern Australia     

Christopher R. Fielding  Tracy D. Frank  Allen P. Tevyaw  Katarina Savatic  Vivi Vajda  Stephen McLoughlin  Chris Mays  Robert S. Nicoll  Malcolm Bocking  James L. Crowley 《Sedimentology》2021,68(1):30-62

Upper Permian to Lower Triassic coastal plain successions of the Sydney Basin in eastern Australia have been investigated in outcrop and continuous drillcores. The purpose of the investigation is to provide an assessment of palaeoenvironmental change at high southern palaeolatitudes in a continental margin context for the late Permian (Lopingian), across the end‐Permian Extinction interval, and into the Early Triassic. These basins were affected by explosive volcanic eruptions during the late Permian and, to a much lesser extent, during the Early Triassic, allowing high‐resolution age determination on the numerous tuff horizons. Palaeobotanical and radiogenic isotope data indicate that the end‐Permian Extinction occurs at the top of the uppermost coal bed, and the Permo‐Triassic boundary either within an immediately overlying mudrock succession or within a succeeding channel sandstone body, depending on locality due to lateral variation. Late Permian depositional environments were initially (during the Wuchiapingian) shallow marine and deltaic, but coastal plain fluvial environments with extensive coal‐forming mires became progressively established during the early late Permian, reflected in numerous preserved coal seams. The fluvial style of coastal plain channel deposits varies geographically. However, apart from the loss of peat‐forming mires, no significant long‐term change in depositional style (grain size, sediment‐body architecture, or sediment dispersal direction) was noted across the end‐Permian Extinction (pinpointed by turnover of the palaeoflora). There is no evidence for immediate aridification across the boundary despite a loss of coal from these successions. Rather, the end‐Permian Extinction marks the base of a long‐term, progressive trend towards better‐drained alluvial conditions into the Early Triassic. Indeed, the floral turnover was immediately followed by a flooding event in basinal depocentres, following which fluvial systems similar to those active prior to the end‐Permian Extinction were re‐established. The age of the floral extinction is constrained to 252.54 ± 0.08 to 252.10 ± 0.06 Ma by a suite of new Chemical Abrasion Isotope Dilution Thermal Ionization Mass Spectrometry U‐Pb ages on zircon grains. Another new age indicates that the return to fluvial sedimentation similar to that before the end‐Permian Extinction occurred in the basal Triassic (prior to 251.51 ± 0.14 Ma). The character of the surface separating coal‐bearing pre‐end‐Permian Extinction from coal‐barren post‐end‐Permian Extinction strata varies across the basins. In basin‐central locations, the contact varies from disconformable, where a fluvial channel body has cut down to the level of the top coal, to conformable where the top coal is overlain by mudrocks and interbedded sandstone–siltstone facies. In basin‐marginal locations, however, the contact is a pronounced erosional disconformity with coarse‐grained alluvial facies overlying older Permian rocks. There is no evidence that the contact is everywhere a disconformity or unconformity.  相似文献