Phosphatized Punctatus with mouthparts and its embryo fossils from the Lower Cambrian of Ningqiang, south Shaanxi, China

The appearance of coelenterates marks the real beginning of metazoan evolution. It therefore has a prominent position in the origin and evolutionary history of organisms, and is also a pivotal question of evolutionary biology. Punctatus is an extinct, ancient marine animal from the early stage of the Cambrian explosion, occurring at the lowermost Cambrian of both Kuanchuanpu (Ningqiang, Shaanxi) and Maidiping (Emei, Sichuan) areas. Punctatus has been studied for many years since the discovery of its fragments. Systematic and phylogenetic analysis has long been limited because of the rarity of complete specimens. In order to improve research into Punctatus, more than ten thousand globular fossils were recovered by means of “Chemistry Retting”. On the basis of the study of these globular fossils, a series of Punctatus fossils with cone parts and finely preserved soft-tissue mouthparts and fossilized metazoan embryo were recovered. Through research on characteristics such as shape, modality and structure of these fossils symbiotic with Punctatus emeiensis, the author found many possible embryo fossils including the evidence of gastrula-stage animal fossils. The sequence of fetation might have appeared on the corolliform oral region of Punctatus emeiensis. A study of the soft tissues, functional morphology and the sequence of embryo fossils shows evidence that Punctatus resembles coelenterate polyps in systematic classification. Perhaps it also represents an ancestor of the coelenterate with an original tentacle. A comparison with the real “tentacle animal” found in the Chengjiang Fauna, shows that the original tentacle is very tiny and its function range is limited. This reveals the primitive nature of the animal. Although the original tentacle is so small, it does exist, representing the first big step towards the real flexible tentacle with a strong function from the early evolving tentacle. Translated from Journal of Acta Palaeontologica Sinica, 2006, 45(2): 182–194 [译自: 古生物学报]     

Dominance of lithogenic effect for nickel,cobalt, chromium and mercury as found in freshly deposited sediments of the river Subernarekha,India

The importance of study of heavy metal distribution in river sediments is a component in understanding the exogenic cycling as well as in assessing the effect of anthropogenic influences of the elements. In India, the river Subernarekha flows over Precambrian terrain of Singhbhum craton in the eastern India. The geological succession in this part of India is through (1) iron ore series, (2) ultrabasic igneous rocks, (3) diorite, (4) granite, (5) newer dolerites, (6) newer tertiary and (7) alluvium. The first four groups belong to the Archaean era, and the representative is the iron ore series consisting of iron ore, manganese and chromite which are abundantly present. The primary rock types are schist and quartzite layers. One main tributary, the Kharkhai flow through granite and schist and quartzite layers. Two important creeks are Gurma and Garra, respectively. The former after originating in basic igneous area travels through schist quartzite, while the later one originates in granite area where some functional but old gold mines are located. Freshly deposited sediments of river were collected upstream and downstream the industrial zone (East Singhbhum district). Samples were collected from four locations and analysed in <63 μm sediment fraction for heavy metals like Ni, Co and Cr by adsorption stripping voltammetry on hanging mercury drop electrode and Hg by anodic stripping voltammetry using polished rotating gold disk electrode. Enrichment of these metals over and above the local natural concentration level (NCL) has been calculated and applied to determine metal-pollution index (MPI) proposed by Goncalves et al. and also geo-accumulation index (I _geo) by Muller. Based on Muller’s classification, Ni, Cr and Hg have been classified from unpolluted to moderately polluted range in pre-monsoon period but for metals Ni and Cr, during the post-monsoon period the values have reached moderately polluted level while Hg has been classified under unpolluted to moderately polluted level except at the monitoring station situated upstream to Gurma Creek where it was found at unpolluted level. Presence of natural resources of the minerals is primarily the reason for their detection in river sediments (lithogenic) but some anthropogenic sources are also contributing for their presence at some sampling stations. Hg is considered to be chalcophilic in nature and is detected wherever known sulphidic ores of copper or nickel are present.     

The Relationship between Fractures and Tectonic Stress Field in the Extra Low-Permeability Sandstone Reservoir at the South of Western Sichuan Depression

The formation and distribution of fractures are controlled by paleotectonic stress field,and their preservative status and effects on development are dominated by the modern stress field. Since Triassic,it has experienced four tectonic movements and developed four sets of tectonic fractures in the extra low-permeability sandstone reservoir at the south of western Sichuan depression. The strikes of fractures are in the S-N,NE-SW,E-W,and NW-SE directions respectively. At the end of Triassic,under the horizontal compression tectonic stress field,for which the maximum principal stress direction was NW-SE,the fractures were well developed near the S-N faults and at the end of NE-SW faults,because of their stress concentration. At the end of Cretaceous,in the horizontal compression stress fields of the NE-SW direction,the stress was obviously lower near the NE-SW faults,thus,fractures mainly developed near the S-N faults. At the end of Neogene-Early Pleistocene,under the horizontal compression tectonic stress fields of E-W direction,stress concentrated near the NE-SW faults and fractures developed at these places,especially at the end of the NE-SE faults,the cross positions of NE-SW,and S-N faults. Therefore,fractures developed mostly near S-N faults and NE-SW faults. At the cross positions of the above two sets of faults,the degree of development of the fractures was the highest. Under the modern stress field of the NW-SE direction,the NW-SE fractures were mainly the seepage ones with tensional state,the best connectivity,the widest aperture,the highest permeability,and the minimum opening pressure.     

Numerical Modeling of the Effect of Mantle Plume on Continental Drift: Revelation of the Rapid Drift of the Indian Tectonic Plate in Late CretaceousEI北大核心CSCD

Numerical modeling is used to investigate the interaction between mantle plume and continental lithosphere, especially the effect of the continental lithosphere structure, the scale and position of mantle plume on the rate of continental drift. Numerical results show that, under the effect of mantle plume, the existence of a thick root of the continental lithosphere affects the rate of continental drift. Moreover, under identical scale of mantle plume, the drift rate decreases with increasing thickness of the root. Besides, the velocity and distance of a continental plate drift are negatively correlated in scale of the continental lithosphere, but correlated with the scale of the mantle plume. For the model without lithospheric root, the mantle plume has a more appreciable impact on the plate drift rate when it comes closer to edge of the continental plate. Our models show that mantle plume can accelerate the continental drift by more than 10 cm/a. The modelling results can provide significant dynamical constraint and geological enlightenment. © 2018, Science Press. All right reserved.     

赣南南迳盆地加里东期火山岩锆石U-Pb年龄及其地质意义

赣南南迳盆地位于华南加里东褶皱带中西部,盆地内火山岩组合常因风化强烈,出露不好,长期被认为属于中生代火山岩系的一部分。该火山岩组合与下伏晚奥陶世地层呈整合接触,与上覆中泥盆世地层呈角度不整合,应为早古生代火山岩组合,但缺乏精确的年代学和岩石地球化学制约。对南迳盆地火山岩进行了锆石U-Pb年龄、Sr-Nd-O同位素及地球化学研究。安山岩和英安岩SHRIPM锆石U-Pb年龄分别为442.1±3.9Ma和439.9±3.7Ma,表明一次晚奥陶世末期—早志留世初期的岩浆事件。微量元素分析显示,Rb、K和轻稀土元素富集,Nb、Ta、Zr、Hf、Ti元素亏损,Nb/U、Nb/Th、Ti/Yb值较低,轻、重稀土元素分馏明显,负Eu异常,主量元素贫钛、富铝。研究认为,南迳盆地火山岩是早古生代时期,随着南华洋关闭、扬子地块与华夏地块发生碰撞,地壳加厚、岩石圈地幔拆沉、软流圈上涌,导致EMI型富集地幔与下地壳发生部分熔融的结果。     

Crustal structure and sedimentation history over the Alleppey platform,southwest continental margin of India:Constraints from multichannel seismic and gravity data

The Alleppey Platform is an important morphological feature located in the Kerala-Konkan basin off the southwest coast of India. In the present study, seismic reflection data available in the basin were used to understand the sedimentation history and also to carry out integrated gravity interpretation. Detailed seismic reflection data in the basin reveals that:(1) the Alleppey Platform is associated with a basement high in the west of its present-day geometry(as observed in the time-structure map of the Trap Top(K/T boundary)),(2) the platform subsequently started developing during the Eocene period and attained the present geometry by the Miocene and,(3) both the Alleppey platform and the Vishnu fracture zone have had significant impact on the sedimentation patterns(as shown by the time-structure and the isochron maps of the major sedimentary horizons in the region). The 3-D sediment gravity effect computed from the sedimentary layer geometry was used to construct the crustal Bouguer anomaly map of the region.The 3-D gravity inversion of crustal Bouguer anomaly exhibits a Moho depression below the western border of the platform and a minor rise towards the east which then deepens again below the Indian shield. The 2-D gravity modelling across the Alleppey platform reveals the geometry of crustal extension,in which there are patches of thin and thick crust. The Vishnu Fracture Zone appears as a crustal-scale feature at the western boundary of the Alleppey platform. Based on the gravity model and the seismic reflection data, we suggest that the basement high to the west of the present day Alleppey platform remained as a piece of continental block very close to the mainland with the intervening depression filling up with sediments during the rifting. In order to place the Alleppey platform in the overall perspective of tectonic evolution of the Kerala-Konkan basin, we propose its candidature as a continental fragment.     

“地质调查+”支撑服务脱贫攻坚模式探索与实践——以赣南苏区为例

2016年以来,自然资源部中国地质调查局开展的地质调查支撑服务脱贫攻坚工作围绕赣南矿业经济发展、特色农业发展、饮水安全、特色旅游业、绿色矿业等需求,开展了矿产地质调查、土地质量地球化学调查、水文地质调查、资源综合利用、地质遗迹调查等工作,支撑赣南革命老区脱贫攻坚工作已见实效,形成了行业特色明显的"地质调查+"扶贫模式,走出了一条独具特色的"地质调查+"扶贫新路。     

第四系科学钻探及地层对比方法探讨

随着社会经济发展的需要,地方经济可持续发展中部分环境、资源问题的基础——第四纪地质变得日益重要,第四系钻探作为第四系覆盖区填图的重要工作手段,钻探质量及编录资料的质量直接影响着第四系区域填图成果的表达。该文结合1∶5万辛安庄等五幅区调项目实践经验,对第四系科学钻探的工作流程进行了总结,并对第四纪钻孔多重地层划分与区域对比方法进行了初步的探讨。     

古岛弧地体的俯冲是南羌塘增生杂岩形成的重要机制:来自日湾茶卡洋岛的证据

洋内岛弧及微陆块的俯冲增生是形成增生杂岩的重要机制。本文通过对南羌塘地区日湾茶卡组进行野外实测地质剖面,开展沉积特征、古生物化石、碎屑组分模式、碎屑锆石测年等研究,发现:(1)日湾茶卡为近源沉积,最年轻碎屑锆石年龄峰值为325～375 Ma,但在龙木错-双湖古特提斯大洋周边陆块均未发现源区,其真正物源应为其下伏的望果山组火山岩;(2)日湾茶卡组内珊瑚化石丰度虽然高,但分异度非常低,其沉积位置应是一个相对突出的孤立位置。根据日湾茶卡组下伏望果山组火山岩所具有的洋内岛弧地球化学特征,并与同期SSZ型蛇绿岩组成的类似洋内俯冲的大地构造体系对比,本文认为日湾茶卡组与其下伏的望果山组火山岩共同组成了泥盆纪—石炭纪由洋内俯冲形成的古岛弧地体。根据碎屑锆石分布型式的相似性,本文进一步认为猫儿山地区部分南羌塘增生杂岩的源岩为日湾茶卡组。因此,日湾茶卡洋岛应曾经历过俯冲增生作用:浅部发生前端"刮削作用"形成冈玛错地区有变形但无变质的日湾茶卡组及望果山组,俯冲到深部的日湾茶卡组则发生高压变质作用并在后期折返至增生杂岩的浅部层次。因此,本文认为在南羌塘增生杂岩的形成过程中,日湾茶卡古岛弧地体的俯冲与增生也起到了重要的作用。     

西伯利亚高压南界东段季节及季节内变化特征及成因

利用NCEP/NCAR再分析资料和Hadley中心海冰密集度资料,对1951—2017年冬季西伯利亚高压南界东段(SHSBES)的变化特征及其与北极海冰的关系进行研究,并比较季内差异。结果表明:冬季SHSBES在20世纪60年代中期由偏南转偏北,70年代末偏南,自20世纪90年代进入正常略偏南状态。12月SHSBES年代际转折时间较早,1月和2月与冬季相似。冬季SHSBES与同期北极大西洋扇区海冰关系最好,海冰偏少有利于冬季贝加尔湖阻塞高压建立;9月北极大西洋扇区海冰与12月SHSBES关系最好,海冰偏少有利于12月西欧阻塞高压建立;3月北极西半球区海冰则可影响到次年1月和2月的SHSBES,3月海冰偏少使次年1月贝加尔湖西侧阻塞高压建立,2月形成三阻(西欧、贝加尔湖、勘察加半岛)。在动力作用上,阻塞高压环流使西伯利亚高压东南部及其以南处于脊前负涡度平流区,气流下沉,地面增压,促使SHSBES南伸,反之亦然。在热力作用上,9月大西洋扇区和3月西半球区海冰偏少(多)分别使12月、次年2月西伯利亚南界及其以南偏冷(暖),利于地面加压(减小),引导SHSBES南(北)移。