湖北三峡地区埃迪卡拉系灯影组“蝌蚪状”遗迹化石*

遗迹化石是埃迪卡拉纪存在两侧对称动物最有力的证据。但多数埃迪卡拉纪遗迹化石为简单、水平的表面爬迹或潜穴。在湖北三峡地区灯影组石板滩段含典型埃迪卡拉软躯体化石的地层中新发现一类形态特别的化石,呈蝌蚪状,一端膨大,一端细管状。通过对化石形态、同位素分析以及沉积学特征的研究,说明该化石为遗迹化石,而不是实体化石。蝌蚪状化石为一种复合迹,垂向活动形成球状的膨大端,平行藻席层活动形成近于水平的潜穴,反映了造迹生物垂向切穿藻席层并沿藻席层进行觅食的行为。该发现说明了在埃迪卡拉纪晚期已有两侧对称动物开始形成较为复杂的潜穴。     

黔东北江口陡山沱组庙河生物群中的革辛娜藻Gesinella Steiner et al.,1992

贵州江口埃迪卡拉纪的江口庙河生物群是一个极为重要的早期后生生物群,不仅含有大量的宏观藻类化石,还发现了可靠的、重要的动物化石。宏观藻类化石数量丰富,保存完整,类型多样,提供了早期后生植物研究的极好材料。本文研究的江口庙河生物群中的大量碳质压模保存的湖南革辛娜藻Gesinella hunanensis,与产于湖南留茶坡组的模式标本相比,整体形态特征虽然一致,两者却存在一些差异,如江口的Gesinella hunanensis叶状体表面较光滑,碳膜厚度从基部向上逐渐变薄,边缘较中部厚,未见乳状突起及侧枝,但可见明显的碳膜压叠现象;叶状体周期性生长明显,一个生长周期形成的叶状体中部较宽,两端较窄;宽度从几个毫米至几十毫米,变化较大;固着结构分为须根状和盘状两种形态,固着器与叶状体之间为加厚的固着蒂,固着蒂之上的叶状体边缘呈波状。与带状棒形藻Baculiphyca taeniata明显不同,尽管整体均呈棒状,但度量相差一个数量级以上,且具独特的周期性生长方式,碳膜中部薄且时有叠压现象、而端部和边缘厚的特征显示其叶状体可能是中空的囊状,与Baculiphyca taeniata的叶状体碳膜极厚乃至保存为块状的特征明显不同。研究结果表明Gesinella hunanensis的形态趋于多样性,证实了Gesinella hunanensis与Baculiphyca taeniata是完全不同的另一类宏观藻类。     

北京十三陵地区前寒武纪雾迷山组叠层石和藻席中的藻类群落

北京十三陵地区位于燕山的中段,是华北晚前寒武纪地层发育良好的地区之一。本区雾迷山组厚两千余米,主要分布在萃花山,小宫门东山及卧虎山一带。数年前,笔者在本区萃花山雾迷山组一段采集到一批微小的柱状叠层石与层纹状藻席相互共生的标本,其中一些标本是由黑色燧石组成的。通过切片方法研究,我们发现在一些由黑色燧石组成的叠层石和藻席中保存有多种形态的微化石。作者扼要记述了这些微化石的形态特征,并将这一微化石群与世界其它地区的前寒武纪微生物组合进行比较,并探讨了这一微化石群的生态环境。     

高于庄古生物学(英)

距今 14～ 16亿年的华北地区高于庄组黑色层状、结核状和透镜状燧石与叠层石的黑色硅质部分中保存着极丰富的原核和真核生物微化石。宏观藻类在该组的页岩中亦已发现。本组为评估中元古代生命状况、古环境和前显生宙生物地层提供了重要的生物信息。迄今为止在高于庄组地层中已有百余个化石种被人们认识。根据古植物和古环境的特征这些生物种类可分为三个不同的组合 ,即 :1.颤藻和色球藻组合 ,出现在高于庄组一段 ,代表浅水藻席建造者和居住者与一些可能的外来浮游生物的种类 ;2 .念珠藻组合 ,仅发生在该组的二段 ,还含一些底栖藻席建造者或居住者的种类 ;3.第四段的色球藻组合 ,它代表了潮间带至亚潮带的藻席建造者和外来的种类。元古代燧石中的微化石 ,尤其是蓝藻化石 ,尽管在元古代它们就已不断趋向于多样化 ,但由于它们形态上的保守性 ,对环境的指示比对地质时代的指示更有价值。高于庄组微化石的特点和大多数链状念珠藻垂直层理保存的事实表明 :1.高于庄组微化石的个体大小随时间趋向于增大 ;2 .高于庄组的沉积可能是处于一个淡水环境 ,且沉积率可能等于或少于微生物的生长率 ;3.高于庄组织沉积模式可能是从潮间带至亚潮带或深海 ,然后再至潮间带或潮上带 ;4 .当高于庄组沉积时真核生物亦已出现。     

高于庄古生物学

距今14～16亿年的华北地区高于庄组黑色层状、结核状和透镜状燧石与叠层石的黑色硅质部分中保存着极丰富的原核和真核生物微化石.宏观藻类在该组的页岩中亦已发现.本组为评估中元古代生命状况、古环境和前显生宙生物地层提供了重要的生物信息.迄今为止在高于庄组地层中已有百余个化石种被人们认识.根据古植物和古环境的特征这些生物种类可分为三个不同的组合,即:1.颤藻和色球藻组合,出现在高于庄组一段,代表浅水藻席建造者和居住者与一些可能的外来浮游生物的种类;2.念珠藻组合,仅发生在该组的二段,还含一些底栖藻席建造者或居住者的种类;3.第四段的色球藻组合,它代表了潮间带至亚潮带的藻席建造者和外来的种类.元古代燧石中的微化石,尤其是蓝藻化石,尽管在元古代它们就已不断趋向于多样化,但由于它们形态上的保守性,对环境的指示比对地质时代的指示更有价值.高于庄组微化石的特点和大多数链状念珠藻垂直层理保存的事实表明:1.高于庄组微化石的个体大小随时间趋向于增大;2.高于庄组的沉积可能是处于一个淡水环境,且沉积率可能等于或少于微生物的生长率;3. 高于庄组织沉积模式可能是从潮间带至亚潮带或深海,然后再至潮间带或潮上带;4.当高于庄组沉积时真核生物亦已出现.     

现生微生物群落形态研究及其对解释埃迪卡拉生物群化石属性的启示

通过对常见微生物种类进行纯培养获得多种微生物菌落形态,并将其与埃迪卡拉生物群化石形态进行对比研究,发现：1）盘状化石Aspidella与圆盘形菌落的轮廓和放射状分布的小脊具有相似性;2）“rangeomorphs”分支状化石与具有次级分支结构的菌落具有某些相似性;3）五边形似棘皮动物化石Arkaruaadami与五边形菌落较为相似;4）两侧对称类化石Kimberella与圆盘形边缘具放射状脊的菌落的表面形态非常相似;5）盘状化石Az—bumaresbrunsae与圆盘形表面具辐射状脊的菌落的轮廓和表面纹饰分布极为相似。以上对比结果表明部分埃迪卡拉生物群化石与微生物菌落形态具有一定的相似性。本研究为埃迪卡拉生物群化石生物属性的解译提供了新思路。     

高于庄古生物学

距今14～16亿年的华北地区高于庄组黑色层状、结核状和透镜状燧石与叠层石的黑色硅质部分中保存着极丰富的原核和真核生物微化石。宏观藻类在该组的页岩中亦已发现,本组为评估中元古代生命状况,古环境和显生宙生物地层提供了重要的生物信息。迄今为止在高于庄组地层中已有百余个化石种被人们认识,根据古植物和古环境的特征这些生物种类可分为三个不同的组合,即：1.颤藻和色球藻组合,出现在高于庄组一段,代表浅水藻席建造和居住与一些可能的外来浮游生物的种类;2.念珠藻组合,仅发生在该组的二段,还含一些底栖藻席建造或居住的种类;3.第四段的色球藻组合,它代表了潮间带至亚潮带的藻席建造和外来的种类。元古代燧石中的微化石,尤其是蓝藻化石,尽管在元古代它们就已不断趋向于多样化,但由于它们形态上的保守性,对环境的指示比对地质时代的指示更有价值。高于庄组微化石的特点和大多数链状念珠藻垂直层理保存的事实表明：1.高于庄组藻化石的个体大小随时间趋向于增大;2.高于庄组的沉积可能是处于一个淡水环境,且沉积率可能等于或少于微生物的生长率;3.高于庄组织沉积模式可能是多潮间带至亚潮带或深海,然后再至潮间带或潮上带;4.当高于庄组沉积时真核生物亦已出现。     

三峡地区埃迪卡拉纪石板滩生物群定量古生物学和生态空间分析

埃迪卡拉化石组成了全球埃迪卡拉纪地层中最具代表性的大型软躯体生物群落。根据其时代、化石种类以及岩性等,埃迪卡拉化石被划分为阿瓦隆、白海、纳玛三个不同组合。产自我国三峡地区埃迪卡拉纪晚期的石板滩生物群是为数不多保存在海相碳酸盐岩中的埃迪卡拉化石生物群。本文利用多元统计分析和网络分析等定量古生物方法划分出四个化石组合,检验并探讨了石板滩生物群所属的组合类型,以及初步探讨了石板滩生物群的生态空间利用情况。聚类分析和网络分析的结果,均倾向于将石板滩生物群划归于纳玛组合。然而在非度量性多维标度变换(NMDS)分析中,石板滩生物群因其化石属种组成的独特性和复杂性,离其他典型的纳玛组合化石产地的点位相距较远。石板滩生物群的生活方式以底栖固着和底栖移动类型为主,其独有的实体化石和丰富、复杂的遗迹化石属种,拓展了人们关于该时期生物对生态空间利用的认识。从生态空间利用的角度来看,石板滩生物群要远高于阿瓦隆组合,接近甚至略高于典型的纳玛组合和白海组合。     

河北唐山寒武系芙蓉统江山阶的Barbitositheca ansatus Qian et Jiang,1980

本文描述了河北省唐山市丰润区寒武系芙蓉统江山阶长山组的锥石化石,鉴定为有柄琴状锥石(Barbitositheca ansatus Qian et Jiang, 1980)。化石保存为印模,轮廓及横肋特征清晰。其中一块标本保存有触手,是对该种特征的补充。目前的化石资料表明,寒武纪早期琴状锥石属主要分布在华南,寒武纪晚期分布范围扩大到华北,形态随时空发生一些变化,主要表现为华北标本角脊数量多于华南标本,并且前者每个角脊上都有一条触手。另外,研究发现寒武纪之后的锥石保存状态与寒武纪有所区别,可能反映了这类生物在不同时期内面临不同的生存压力。本文研究的寒武纪锥石为华北地区的首次发现,扩大了此类生物的时空分布。     

吉林汪清早白垩世似卷柏化石*

文中描述了发现于吉林汪清下白垩统大拉子组似卷柏化石:纤细草本,侧叶和中叶呈四行排列。侧叶互生,卵形,全缘,顶端尖锐,叶片前端略向内侧弯曲,叶背呈龙骨状,基部无柄,略呈鞘状;中叶生于两侧叶之间,形态与侧叶相似,在茎上密集贴生。该化石与报道自我国辽西下白垩统义县组下部尖山沟层的多产似卷柏Selaginellites fausta(Wu)Sun and Zheng特征相似,但由于未保存生殖器官结构,无法进一步详细对比,因此将其定为Selaginellites cf.fausta(Wu)Sun and Zheng。这是我国目前为止发现的距今最近的似卷柏化石,丰富了中国似卷柏的化石记录。     

扬子区晚震旦世动物化石新材料

扬子区晚震旦世地层中已有多种类型的动物及遗迹化石的报道。文中补充了不同地区和层位的骨骼及遗迹化石新材料,包括：江西上饶王家院陡山沱组顶部磷块岩中的磷酸盐化“十”字形骨针和云南晋宁王家湾灯影组上段隧石条带中的单轴双射硅质骨针,它们可能分属于钙质海绵和普通海绵类;贵州瓮安陡山沱组上段磷质白云岩中的可疑壳状化石;宜昌三斗坪金瓜墩陡山沱组下部（第二段）遗迹化石;瓮安陡山沱组上段及湖北南漳灯影组上段底部磷质硬底中的生物扰动构造。另外还报道了贵州清镇桃子冲剖面桃子冲组最底部的瓶状动物（Pro-tolagena limbata）化石,并认定桃子冲组与灯影组之间为假整合接触,其底界并无跨入震旦系的证据。     

新元古代陡山沱组具细胞裂殖结构的丝状蓝藻

新元古代陡山沱组丝状蓝藻化石Oscillatoriopsis sp.,具丝状蓝藻化石记录中罕见的细胞分裂结构;其胞壁内陷的二等分裂方式,可能的丝体断裂结构。是现生丝状蓝藻生长和繁殖的典型特征;不具异形胞结构的形态特征,可能与其当时生存的海底表面的缺氧环境有关;这种基底环境,可能有利于Oscillatoriopsis sp。等磷酸盐化化石细节构造的保存。     

Dickinsonia from the Ediacaran Dengying Formation in the Yangtze Gorges area,South China

Dickinsonia is an iconic fossil of the Ediacara biota (~575–539 Ma). It was previously known from siliciclastic successions of the White Sea assemblage in Australia, Baltica, and possibly India. Here we describe Dickinsonia sp. from the terminal Ediacaran Shibantan Member limestone (ca. 551–543 Ma) of the Dengying Formation in the Yangtze Gorges area of South China. The stratigraphic distribution of Ediacara-type fossils in the Shibantan Member indicates that this biota uniquely preserves both the White Sea and Nama assemblages in stratigraphic succession. The new data presented here suggests that Dickinsonia had wider paleogeographic and paleoenvironmental distributions, implying its strong dispersal capability and environmental tolerance.     

A New Stromatolitic Mat Builder Discovered from Late Precambrian in Northern China

Abundant and preserved chain algal microfossils have been discovered in cherty stromatolitic mats from the second member of Gaoyuzhuang Formation (about 1,500 Ma old), Ling-qiu county of Shanxi province, China. They are described as Veteronostocale moniliforme Xu et Gao sp. nov.. The small diametral trichomes resemble the Family Nostocaceae in possessing specilized cells resembling the classic heterocysts and akinetes. This paper gives emphasis to the following remark: (1) The Gaoyuzhuang stromatolitic mats were products of microbial (Veteronostocale moniliforme) activity and the plant Nostocaceae was one of the main stromatolitic builders as both modern and Precambrian stromatolite-forming microorganisms; (2) Based on the fact that the chain fossils are preserved perpendicularly to the laminations the rates of sedimentation and algal growth were probably equal and each small sedimentary rhythm could be completed in about one or two months; (3) According to the environment and habits of living Nostoc Precambrian hydrosphere might be of a fresh water type.     

陕西宁强早寒武世磷酸盐化具星状表饰胚胎化石研究

后生动物胚胎化石研究对了解寒武纪大爆发中生命的个体及系统发育具有十分重要的意义。陕南早寒武世灯影组宽川铺段发现大量磷酸盐化的球状化石标本,其中的一些为保存有十分精细的星状表饰的胚胎化石,目前发现至少3种具星状纹饰的胚胎化石:圆球状胚胎、具中央收缩带的球状胚胎和表面具“拉伸构造”的花生状胚胎,其中后者为新类型。研究表明,此新类型在演化序列上处于圆球状胚胎、具中央收缩带的球状胚胎发育阶段之后,是胚胎向成体演化的一个重要中间过渡环节,这一发现为研究早寒武世早期后生动物胚胎及个体发育提供了新线索。     

Suspected microbial-induced sedimentary structures (MISS) in Furongian (Upper Cambrian; Jiangshanian,Sunwaptan) strata of the Upper Mississippi Valley

The Furongian (Upper Cambrian; Jiangshanian and Sunwaptan) Tunnel City Group (Lone Rock Formation and Mazomanie Formation), exposed in Wisconsin and Minnesota, represents a shallow-marine clastic environment during a time of exceptionally high sea level. Lithofacies from shoreface to transitional-offshore settings document deposition in a wave- and storm-dominated sea. Flooding of the cratonic interior was associated with formation of a condensed section and the extensive development of microbial mats. Biolamination, mat fragments, wrinkle structures, and syneresis cracks are preserved in various sandstone facies of the Lone Rock Formation, as is evidence for the cohesive behavior of sand. These microbial-induced sedimentary structures (MISS) provide unique signals of biological–physical processes that physical structures alone cannot mimic. The MISS are associated with a trilobite extinction event in the Steptoean–Sunwaptan boundary interval. This may support recent claims that Phanerozoic microbial mats were opportunistic disaster forms that flourished during periods of faunal turnover. Further investigation of stratigraphic, taphonomic, and other potential biases, however, is needed to fully test this hypothesis.     

Evidence for seafloor microbial mats and associated metazoan lifestyles in Lower Cambrian phosphorites of Southwest China

The increase in the depth and intensity of bioturbation through the Proterozoic-­Phanerozoic transition changed the substrates on which marine benthos lived from being relatively firm with a sharp sediment-water interface to having a high water content and blurry sediment-water interface. Additionally, microbial mats, once dominant on normal marine Proterozoic seafloors, were relegated to stressed settings lacking intense metazoan activity. This change in substrates has been termed the 'agronomic revolution', and its impact on benthic metazoans has been termed the 'Cambrian substrate revolution'. The shallow marine phosphorites of the Lower Cambrian Meishucun Formation of southwest China contain evidence suggestive of the presence of seafloor microbial mats. This evidence includes abundant and distinctive red-colored bedding planes enriched in heavy iron minerals and mica, interpreted as resulting from mat-decay mineralization and mica trapping by microbial mats. The radular grazing trace fossil Radulichnus is also found in this formation, indicating a firm, microbial mat-bound substrate. These radular scratches are always preserved with circular impressions around 10 cm in diameter, possibly the fossils of soft-bodied organisms. The first relatively intense bioturbation in this region is found in this formation and is dominated by horizontal Thalassinoides burrows, which could represent undermat mining behavior. The evidence for the presence of microbial mats in the Lower Cambrian Meishucun Formation, and for metazoan lifestyles associated with such mat-bound seafloors, reveals that normal marine environments dominated by typical Proterozoic-style soft substrates still existed during the Cambrian substrate revolution.     

Annual growth layers as proxies of past growth conditions for benthic microbial mats in a perennially ice-covered Antarctic lake

Perennial microbial mats can be the dominant autotrophic community in Antarctic lakes. Their seasonal growth results in clearly discernible annual growth layering. We examined features of live microbial mats from a range of depths in Lake Hoare, Antarctica, that are likely to be preserved in these layers to determine their potential as proxies of past growth performance. Cyanobacteria dominated the mat for all but the deepest depth sampled. Changes in areal concentrations of phycobilin pigments, organic matter and extracellular polysaccharide and in species composition did not correspond to changes in various water column properties, but showed a linear relationship with irradiance. Carbonate accumulation in the mats correlated with biomass markers and may be inferred as an index of mat performance. We examined the carbonate content of annual layers laid down from 1958–1959 to 1994–1995 in sediment cores from 12 m depth. The carbonate content in the layer showed a significant correlation with the mean summer air temperature. These data suggest a link between air temperature and microbial mat growth performance, and suggest that it is mediated via irradiance. Laminated microbial mats in Antarctic lakes have the potential to act as fine-resolution records of environmental conditions in the recent past, although interpretation is complex.     

广西南部二叠纪长兴期放射虫动物群

广西南宁南部柳桥区的长兴组上部硅质岩中存着精美的长兴期晚期放射虫动物群,共有24属39例,其中3个新种,其中以Latentifistularia最为常见,其次是Albaillllidae和Entactiniidae,属于二叠纪晚期的Neoalbaillella optima组合。半生生物有有孔虫、海绵骨针、腕足动物等。多数属在接近二叠纪－三叠世界线附近消失,但生物群中已出现少量三叠纪分子。