湖北兴山寒武系覃家庙群底部三叶虫化石的地层学意义

三峡地区覃家庙群以一套缺乏化石的薄层白云岩沉积为特征。新近在湖北兴山古洞口剖面覃家庙群底部发现Kaotaia gedongensis Yuan & Zhao,Kunmingaspis yunnanensis Chang,Chittidilla sp.等三叶虫。依据三叶虫生物地层学对比结果,结合研究剖面与覃家庙群标准剖面和参考剖面岩石地层学对比,认为三峡地区覃家庙群为跨传统下、中寒武统的地层单元。     

北美西部陆相白垩系-古近系界线孢粉学特征简介——兼评中国东部白垩系-古近系界线研究

已经报道的北美西部陆相白垩系-古近系界线剖面已达近百处,这些剖面分布在阿拉斯加南部向南经加拿大直到美国南部的新墨西哥州北部的广大北美西部内陆地区,其中很多属迄今所知全球很好的陆相白垩系-古近系界线剖面。这些剖面常有标志性的界线黏土,并伴有其他地球化学、生物地层学特征。因为这些剖面所在地当时都在湿润或半干旱地区内,有利于生物化石,特别是孢粉化石的保存,易于开展孢粉学研究。经过近四十年不懈努力,孢粉学已经成为北美精确确定陆相白垩系-古近系界线最重要的、也是迄今为止所知最为有效的古生物学工具。孢粉植物群在界线上下特征差别显著,容易区分。界线之下含有大量主要繁盛于白垩纪的被子植物花粉,而在临近界线时则突然消失或仅零星出现,界线附近则以一层孢子异常丰富层为古近系底部特征。进入古近纪之后,虽然被子植物花粉有所恢复,但是繁盛于白垩纪的成分却很少出现。北美和新西兰、日本白垩系-古近系界线附近在沉积岩和孢粉学方面的相似性表明这一事件可能是全球性事件。简要回顾和讨论了我国与孢粉学相关的几个热点地区陆相白垩系-古近系界线的研究概况,我国东北及江苏北部和北美西部大部分地区白垩系-古近系界线附近的孢粉植物群及其沉积环境比较类似,在苏北到东北地区范围内首次发现陆相白垩系-古近系界线地层的可能性比其他地区大。     

全球维宪阶与谢尔普霍夫阶界线层的生物地层研究进展及展望

牙形刺、有孔虫和菊石是全球维宪阶与谢尔普霍夫阶界线层生物地层研究的重要化石门类。该界线定义及其候选层型剖面目前均未正式确立。详细介绍并讨论以牙形刺或有孔虫作为界线定义的可能方案 ,指出潜在的候选层型剖面存在于南乌拉尔的 Verkhnyaya Kardailovka、北美犹太州中西部的 Chainm an组等 ,我国具有潜在研究价值的剖面有广西忻城里苗剖面、贵州水城滥坝老街水库剖面和罗甸纳水剖面     

东海陆架盆地台北坳陷月桂峰组生物地层及古环境

月桂峰组分布于台北坳陷西带,上覆灵峰组、下伏石门潭组,由灰黑色泥岩、砂岩组成。在微体古生物和地球化学微量元素详细分析的基础上,确立它属古近纪古新世沉积,推测可能为古新世早期,该地层相当于苏北盆地阜宁组一段。月桂峰组所含孢粉、藻类化石组合及地球化学微量元素特征表明月桂峰组当时的沉积环境以淡水湖相为主,局部时期(晚期)可能演变成海陆交互相,或者受到海水的影响。     

High-resolution magnetostratigraphy and micropalaeontology across the J/K boundary strata at Brodno near ilina, western Slovakia: summary of results

This study summarizes the final results of magnetostratigraphic and micropalaeontological investigations of the Tithonian/Berriasian boundary (J/K) limestones at the locality of Brodno near ilina, Western Carpathians, West Slovakia. The aim is to prepare the background for correlation of a Late Tithonian and Early Berriasian biostratigraphic zonation with global magnetoevents (manifested in detailed magnetostratigraphic profiles) between the Tethyan realm and other regions, particularly the Boreal and Pacific realms. Suitable physical properties of the limestones studied, a favourable geological setting and rich microfossil assemblages (calpionellids) at Brodno (magnetozones M21r to M18r) allowed a systematic collection of new data on the original synoptic section, which now has the character of a high-resolution profile across the J/K boundary. Two reverse subzones detected within magnetozones M20n and M19n are named ‘Kysuca Subzone’ and ‘Brodno Subzone’, respectively. Both can be correlated with analogous subzones in the M-sequence of marine anomalies. Their existence can also be confirmed in the Bosso Valley section in Umbria, central Italy. A detailed study of the interval between magnetozones M20n and M17r in the Bosso Valley profile is presently in its final stage. Both magnetostratigraphic profiles, from the Brodno and Bosso Valley localities, were thoroughly investigated in the intervals close to the J/K boundary and are still unique among continent-based profiles in the detection and precise definition of both reverse subzones within M20n and M19n. Samples collected from the boundary strata of the reverse Kysuca Subzone at Brodno indicated a transition from N (R) to R (N) polarity of the Earth's palaeomagnetic field within a time interval of c. ±5 ka. Limestone samples (total number N=368) were subjected to progressive thermal demagnetization in 10–12 thermal fields and to subsequent multi-component analysis of remanence. The C-component, as the carrier of palaeomagnetic directions, was determined in the temperature interval of 300° to 540°, or possibly 580°C. Magnetomineralogical analyses of pilot samples and unblocking temperatures determined for all samples showed that magnetite is the carrier of remanent magnetization. The positions of the individual events of calpionellid stratigraphy relative to the global magnetic polarity timescale are precisely defined. The base of the Calpionella Standard Zone, which is considered a provisional J/K boundary indicator in ammonite-free sections in the Tethyan realm, lies within magnetozone M19n at the level of 35% of its local thickness. None of the boundaries in the calpionellid zonation coincides precisely with any of those in the palaeomagnetic zonation, but the first appearance ofCalpionella grandalpina , indicating the base of the Intermedia Subzone, lies in close proximity to the base of magnetozone M19r.     

Calibration of the Albian/Cenomanian Boundary by Ammonite Biostratigraphy: U.S. Western Interior

Calibration of numerical ages to the geological time scale is a long scientific pursuit that requires the integration of multiple data sets. A case study of the Albian/Cenomanian stage boundary, also the Lower/Upper Cretaceous series boundary, illustrates the calibration process. The numerical age of this boundary has shifted from 96 Ma to 99 Ma over a time span of nearly fifty years. Re-calibration resulted first from improvements in radiometric dating, and later from inferences about ammonite phylogeny, and most recently from radiometric dates of newly discovered volcanic beds interbedded with diagnostic guide fossils. However, the calibration process continues with study of cosmopolitan dinoflagellates.     

贵州紫云四大寨早三叠世地层初步研究

贵州紫云四大寨剖面下三叠统发育较齐全,化石较丰富。在此剖面上发现了大量牙形石、双壳类、菊石等生物化石,其中牙形石在该剖面上为首次发现,并识别出了早三叠世Neospathodusdieneri带、Neospathoduscrista-galli带、Neospathoduswaageni带和Neospathodushomeri-Neospathodustriangularis带的重要牙形石分子或带化石,可与国际同期地层中相应的牙形石化石带进行较好的对比;同时还发现了Claraiagriesbachi-C.concentrica组合和Claraiastachei-Claraiaaurita组合带的双壳类代表性分子。通过对这些化石综合分析,大致拟定了本剖面下三叠统格里斯巴赫亚阶(Griesbachian)、亭纳尔亚阶(Dienerian)、斯密斯亚阶(Smithian)和斯派斯亚阶(Spathian)的年代地层单位界线。     

藏南吉隆地区二叠纪生物地层

藏南吉隆地区二叠系主要为一套中厚层状碳酸盐岩、石英砂岩夹泥质岩岩性组合,产丰富的腕足类、珊瑚、苔藓虫、菊石及海百合茎、遗迹化石等多门类化石,包括5个腕足动物组合、1个菊石带、2个珊瑚组合、1个海百合化石层、1个遗迹化石层。根据岩性二叠系划分为基龙组和曲布日嘎组。基龙组时代相当于早二叠世阿丁斯克期—萨克马尔期。曲布日嘎组时代以栖霞期—茅口期为主,顶部可能包括部分吴家坪期。     

中国白垩纪叶肢介生物地层学

叶肢介是一种淡水甲壳类动物,个体不大,一般在几毫米到两厘米之间,软体有点像虾,具有很多附肢,雌雄异体,外裹一对几丁质壳瓣,形似蚌壳,但不如后者的钙质壳那么厚实坚硬。叶肢介从泥盆纪开始出现,中生代时其演化中心从欧洲迁移到了东亚,白垩纪它们的分异和演化达到顶峰,到了新生代则进入衰亡阶段。叶肢介化石一般出现在陆相地层中,由于它数量多、演化快、分布广泛,近年来已成为中国和邻近地区中生代非海相生物地层划分和对比研究的重要手段之一。中国大陆白垩系主要是陆相沉积,按古地理和生物地理区系,早白垩世可以划分为西南湖群和东北、东南、西北两个大区,前者出现的是直线叶肢介(Orthestheria)动物群,后者则是东方叶肢介(Eosestheria)和延吉叶肢介(Yanjiestheria)动物群;晚白垩世在西南湖群出现的是华美叶肢介(Aglestheria)动物群,在东北松花湖水系出现的是真瘤模叶肢介(Euestherites)动物群,在华中和东南沿海云梦泽水系出现的是薄壳叶肢介(Tenuestheria)动物群。链叶肢介(Halysestheria)是联系它们相互对比的共同分子;晚白垩世早期的线叶肢介(Nemestheria)动物群则在上述3个区系都有分布,甚至在西北喀什地区的塞诺曼期海陆交互相沉积和美国德克萨斯州同期海相地层的陆相夹层中都有发现的记录,它是将中国陆相白垩系与国际海相标准划分联系起来的重要证据。关于中国白垩纪的叶肢介动物群和有关陆相地层的划分对比,产东方叶肢介的义县组以前放在上侏罗统顶部或做为侏罗系-白垩系过渡层处理,这次按全国地层表将东方叶肢介群归入早白垩世。     

安徽巢湖石炭系和州组地层学和沉积学研究新进展

石炭纪—二叠纪旋回层是由晚古生代冈瓦纳冰川的冰期与间冰期的交替而造成的海进—海退循环沉积的层序,出现在全球尤其是北半球的很多地区。根据岩石微相和沉积构造特征,安徽巢湖凤凰山石炭系和州组,可识别出5个海进—海退沉积序列;根据和州组中有孔虫的分布特征,自下而上可分为5个有孔虫带,确定其地质年代是从维宪期晚期到巴什基尔期早期。这5个海进—海退沉积旋回,与华南其他地区和欧美地区的同时代地层中出现的大的海进—海退事件基本一致。