下-中奥陶统之交陆架周期性缺氧：来自美国犹他州的遗迹沉积学证据?

美国犹他州中西部、北美下-中奥陶统之交重要剖面上的遗迹沉积学证据表明，在奥陶纪生物爆发的重要时期─早、中奥陶世之交和重要生态领域─陆架区，存在持续3.4 Ma、周期性的陆架缺氧事件。主要的遗迹沉积学证据包括：低的遗迹化石分异度，非常浅的生物扰动层厚度和潜穴深度（小于4 cm, 现代陆架区大于20 cm），稀少的居住滤食迹，遗迹化石和遗迹组构的分布与风暴事件层密切相关；细小的Chondrites 阶层占据较浅或最浅的生态阶层 （中生代以来，细小的Chondrites 阶层总是占据最深的生态阶层）；地层序列具轨道旋回地层结构，并且富含呈黄铁矿假象的褐铁矿结核。早古生代较低的大气氧水平，快速和高幅度的奥陶纪耗氧生物大辐射，早、中奥陶世之交陆架区快速和高幅度的海进和温暖的陆架环境可能是导致早、中奥陶世之交陆架环境周期性缺氧的主要原因。轨道旋回地层的研究表明，这次周期性缺氧事件始于473.27 Ma, 结束于 469.87 Ma，持续时间约3.4 Ma，如果早、中奥陶世之交的同位素年龄值为473.0 Ma。早、中奥陶世之交陆架环境周期性缺氧事件的发现，给正确认识奥陶纪生物辐射、古生代演化生物群起源环境和显生宙生物集群绝灭与缺氧关系增添了新资料。     

新疆和硕县红山地区中侏罗世地层研究新进展

根据孢粉和植物化石组合面貌 ,结合岩性及岩相特征 ,论述焉耆含油气盆地红山地区长期存有争议的侏罗纪地层的时代归属 ,认为该区仅发育了中侏罗世地层 ,包括西山窑组和头屯河组 ,为本盆地的石油勘探提供了地层划分与对比的时代依据     

辽西地区土城子组-义县组地层划分对比及时代讨论

本文介绍了辽西中生代土城组、张家口组、义县组地层特征、化石组合。通过岩石地层、生物地层、同位素年代学研究,并在宁城道虎沟地区的张家口组沉积层中采到的化石组合和同位素年龄多数反映时代为晚侏罗纪;义县组生物化石组合和同位素年龄反映时代为早白垩纪。故将侏罗纪与白垩纪界线置于张家口组与义县组之间,同国际年表年代界限（145.5 Ma）相一致。     

滇东震旦系—寒武系界线层遗迹化石新发现及对比意义

滇东震旦系—寒武系界线层含有丰富多样的遗迹化石,经对27条剖面系统地采集化石和研究,共鉴定有遗迹属45个,遗迹种87个。其中新属2个,新种7个,已知属在本区首次发现的有31个,已知种在本区首次发现的有38个。根据不同遗迹属在界线层中出现的顺序和组合特征,将本区震旦系—寒武系界线层遗迹化石由老到新划分为4个遗迹化石组合带,并与国外相当层位的遗迹化石进行了对比,对地质意义作了初步地探讨。     

Microbial fossilization in carbonate sediments: a result of the bacterial surface involvement in dolomite precipitation

ABSTRACT Recent dolomitic sediment samples from Lagoa Vermelha, Brazil, were examined microscopically to study the process of bacterial fossilization in carbonate sediments. Bacteria‐like bodies were intimately associated with carbonate mineral surfaces, and coatings on the former demonstrate the calcification of single bacterial cells. The bacterial fossilization process in Lagoa Vermelha sediments was simulated in the laboratory by cultivation of mixed and pure cultures of sulphate‐reducing bacteria, which were isolated from the Lagoa Vermelha sediments. These cultures produced carbonate minerals that were studied to provide insight into the initiation of the fossilization process. In mixed culture experiments, bacterial colonies became calcified, whereas in pure culture experiments, single bacterial cells were associated with dolomite surfaces. Dolomite nucleated exclusively in bacterial colonies, intimately associated with extracellular organic matter and bacterial cells. Electrophoretic mobility measurements of the bacterial cells in electrolyte solutions demonstrated the specific adsorption of Ca²⁺ and Mg²⁺ onto the cell surfaces, indicating the role of the bacterial surface in carbonate nucleation and bacterial fossilization. The affinity of the cells for Mg²⁺ was related to the capability of the strains to mediate dolomite formation. Combined with sulphate uptake, which dissociates the [MgSO₄]⁰ ion pair and increases the Mg²⁺ availability, the concentration of Mg²⁺ ions in the microenvironment around the cells, where the conditions are favourable for dolomite precipitation, may be the key to overcome the kinetic barrier to dolomite formation. These results demonstrate that bacterial fossilization is a consequence of the cell surface involvement in carbonate precipitation, implying that fossilized bacterial bodies can be used as a tool to recognize microbially mediated carbonates.     

化石Anabarites的发现及再论玉尔吐斯组的时代归属

本文根据在新疆阿克苏—乌什地区下寒武统玉尔吐斯组中发现的真正Anabarites化石,纠正了过去误定为Anabarites的几个化石,再次论证了玉尔吐斯组的时代归属.与梅树村阶可以对比.本文还阐述了玉尔吐斯组中,与小壳化石共生的高肌虫是一类较原始的最古老的甲壳类高肌虫,区别于筇竹寺阶的高肌虫.     

内蒙古查干敖包地区上石炭—下二叠统宝力高庙组特征及时代

提要：笔者在查干敖包地区开展1∶5万区域地质调查工作时,发现本区出露的宝力高庙组层序齐全、植物化石丰富、划分标志明显,通过路线调查、剖面测量对其进行了重新划分,即据岩性组合、生物面貌等特征划分为4个岩性段,一段为河湖相灰色、灰绿色碎屑岩夹少量中性火山岩,在粉砂岩中采到了大量安格拉植物化石;二段为中偏碱性-酸性砖红色、紫色火山岩夹砂（砾）岩,其中粗面岩获得锆石U-Pb同位素年龄为(297.0±1.2) Ma;三段为灰色、灰紫色安山质火山岩夹碎屑;四段以灰白色流纹质火山岩为特征,夹砂岩、泥灰岩等,在砂岩中采到了大量安格拉植物群化石。据植物化石鉴定结果、同位素年龄资料将其形成时代确定为晚石炭—早二叠世。     

Magnetochronology of Late Miocene Mammal Fauna in Xining Basin, NE Tibetan Plateau, China

The Xining basin is located in the northeastern margin of the Qinghai-Tibet Plateau. It is a rift basin formed in Mesozoic and Cenozoic and structurally belongs to the intersection of Kunlun and Qilian Mountains. Cenozoic fluvial and lacustrine sedimentary strata are continuous in the Xining basin, with a thickness of more than 800 m, completely recording the deformation uplifting, weathering and denudation history and climate change process of the northeastern plateau. Currently, early Miocene Xijia fauna, early Middle Miocene Danshuilu fauna and late Middle Miocene Diaogou fauna are discovered in the Xining basin, which provide an important basis for the stratigraphic correlation of the Cenozoic strata in the Xining basin. However, in the next few decades, there are no reports about the large mammal fossils in the Xining basin, especially about late Miocene fauna. The author discovered a large amount of mammal fossils in the Neogene sedimentary strata in Huzhu area, Xining basin. According to the identification results of the Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, these fossils mainly included Hipparion dongxiangense, Chilotherium sp., Parelasmotherium sp., Stephanocemas sp. and Kubanochoerus sp. and their age was early Late Miocene. Since the discovery of this set of fossils directly filled the blank that there were no large mammal fossils in the Xining basin in Late Miocene, it was very important for studying the magnetic stratigraphic chronology of fossil-forming strata and establishing the paleomagnetic chronology scale plate of mammal fossils. In this paper, the paleomagnetic data of the fossil-forming stratigraphic profile, Banyan profile, were measured and the paleomagnetic records were collected through high density sampling, and finally the paleomagnetic polarity column of the profile was established. The results showed that five positive and five negative polarity segments were recorded in Banyan profile, which corresponded well to the polarity between C3Br.1n-C4n.2n in the standard polarity column. The age of profile top was about 7.25 Ma and profile bottom was about 8.4 Ma, with an age range of 1.15 Ma. The mammal fossils discovered this time were exposed between positive and negative polarities N5 and R5 at the bottom of the profile, corresponding to C4r.1r at negative polarity and C4n.2n at positive polarity in the standard polarity column. The age of mammal fossils was about 8.3 Ma. The paleomagnetic chronology of the strata and paleontological fossils determined the absolute age of late Miocene mammal fossils and expanded the upper age of late Miocene Xianshuihe Formation (N1xn) in the Xining basin, which had provided new basic data for further studying the stratigraphic deposition and correlation of late Cenozoic strata and regional environmental evolution.     

内蒙古乌达早二叠世含植物化石凝灰岩及其地质意义

本文通过对乌达地区山西组下部含树干化石凝灰岩岩性的观察,结合区域构造背景及前入研究成果,与邻区同-火山事件层进行对比,推测凝灰岩层的火山物质可能来源于乌达以北地区,即古亚洲洋向华北板块俯冲引起的弧火山喷发。凝灰岩层中下部和上部所含植物化石差异明显,表明该期火山事件对研究区的地理环境影响显著。另外,古亚洲大洋向华北板块俯冲及其后碰撞作用,可能是贺兰拗拉槽再次活动接受沉积的重要的动力学条件,特别是在晚石炭世-早二叠世时期。     

大连贝壳博物馆

通过对大连贝壳博物馆的介绍,揭示贝壳博物馆的特点及发展趋势,总结贝壳博物馆设计和建设对我们的启发。