元古代光球疑源类Valerialophostriata（Jank.）的全球分布

Valeria lophostriata是一种具明显纹饰有机壁的球状疑源类微体化石 ,对它的近 30个已知化石记录进行了评论。发现其产地集中在北纬 30°以北 ;并在近 7亿年的时间间隔 ,以双峰态时间分布。因此 ,将它作为重要的生物地层标志是不适宜的。其表面特征的韵律式样可能是Belousov- Zhabotinsky反应的一种显微实例。作者提出该属种的纹饰特征和壳壁的化学成分应是今后深入研究的课题。     

鲁西上元古界佟家庄组的微体植物化石

鲁西安丘地区停家庄组含保存很好的微体植物化石。经研究计有14属11种(含1新种),1相似种和6个未定种。这一微体植物化石组合以球形疑源类最多,另有少数Micrhystridium,?Ceratophyton conicum以及丝状微体化石的标本。根据佟家庄组微体植物化石组合与国内外已知组合的比较,并参考从上覆浮莱山组获得的同位素年龄资料,笔者认为鲁西佟家庄组与安徽淮南地区的刘老碑组是同时的,皆为800—700Ma前沉积形成。     

前寒武纪沉积碎屑岩中有机质壁微体化石的分析处理及观察方法

前寒武纪是地球演化历史上的重要时期,随着早期生命起源、构造演化、油气勘探等研究的不断深入,前寒武纪越来越受到关注。微体化石是研究前寒武纪生命演化和地层对比的重要窗口,尤其是在新元古代大冰期之前的地层中,主要保存的是体型较小、类型多样的微体化石,而宏体化石则凤毛麟角,仅有为数不多的类型。在许多前寒武纪碎屑岩地层中,以布尔吉斯页岩型方式保存的有机质壁微体化石,是其中保存的唯一的化石类型。但因这些有机质壁微体化石在围岩中遭受了长时间地成岩、变质、风化和剥蚀等作用,在化石处理过程中非常容易破碎,导致获取保存完整的微体化石较为困难,给属种鉴定、生物多样性评估和生物地层对比等研究带来诸多不便。本文主要介绍一种从粉砂岩-泥岩中获取有机质壁微体化石的处理方法,包括样品的碎样、酸处理、富集、挑选、制片和拍照等各流程的详细步骤,以及在分析处理中存在的问题和注意事项。     

国际古生代微体植物学会2010年会(CIMP,2010)简介

国际古生代微体植物学会2010年会(CI MP,2010)于2010年9月13—16日在波兰首都华沙举行。参加会议的有来自20个国家40余名代表,与会代表主要来自欧洲、北美和亚洲,我国有3名代表参加本次大     

论山西中元古代晚期汝阳群微体化石组合

我国北方18-19亿年前的串岭沟组中获得的大球形疑源类,迄今,被认为是可信的最古老真核化石记录。自上世纪80年代以来,东秦岭北坡的中元古代晚期汝阳群陆续发现了丰富的球形光面疑源类,具刺疑源类,丝状微体化石和一些有疑问的动物遗迹。很显然,在中元古代晚期真核生物曾有重大辐射。     

华南贵州寒武系(2-3统)凯里组有机质壁微体化石的新材料

凯里生物群既是中国华南寒武系重要的布尔吉斯页岩型生物群之一,同时也是国内外已知少数微体布尔吉斯页岩型特异埋藏化石库之一,化石以二维的有机质壁形式保存。本文改进孢粉学处理方法,对来自中国贵州寒武系凯里组苗板坡、丹寨、竹坪和屯州等几个剖面以及相邻地层的共22个样品进行酸泡处理,获得微体化石新材料。结果显示,苗板坡剖面保存的化石多样性明显较高,其中发现的疑源类和丝状藻类最多,占统计总数(N=1549)的90%以上;同时还发现少量的后生动物残片,如威瓦西虫的骨板、腕足动物壳体残块以及蠕形动物表皮等,这些后生动物化石残片为研究某些后生动物的细微结构提供了重要补充信息,有助于对这些动物化石进行分类鉴定,并可能具有一定生物地层学意义。     

贵州瓮安陡山沱组磷块岩中疑源类化石壳壁超微结构

未经化学处理的原始岩石样品的扫描电镜观察,确定了瓮安陡山沱组型刺饰疑源类Meghystri chospaeridium chadianensis的微结构特征。磷酸盐化疑源类化石由表面棘刺和球体组成,球体分为壳壁和腔体二部分。球体壳壁具黑色外层和白色内层的多层结构。棘刺具有与球体相似的多层状的壳壁和腔体。首次发现了发育于球体表面和体壳壁内部的网格超微结构。球体的腔体内存在的残余有机质。     

有机壁藻类微体化石分析中的几个问题

藻类分析是藻类研究的前提。本文主要讨论以下几个问题：微体化石藻类分析与孢粉分析的异同、分析处理的时间掌握、超声波清洗机和筛选作用,重液浮选及药品用量等。     

中元古代中期神农架群台子组微体化石组合和热演化阶段*

扬子台地北缘神农架群发育一套中元古代中期和晚期的海相碳酸盐岩与碎屑岩地层,其中台子组是神农架群中部地层,也是该群古生物化石丰度最高的组。本文利用化学浸泡法对中元古代中期台子组细粒碎屑岩进行微体化石研究,结果显示:台子组化石总的特征是组合简单、化石个体较小,大部分标本直径介于20-50μm。本文共鉴定出微体化石7属11种,包括光面球形类Leiosphaeridiacrassa、L.minutissima、L.jacutica、L.bicrura和Leiosphaeridiasp.,细胞聚合体Synsphaeridium sp.、Eomicrocystismalgica和相对复杂的疑源类Navifusa sp.、Satka sp.、Germinosphaera sp.与Arctacellularia tetragonala。台子组微体化石组合中原核生物是主要的化石类型,真核生物丰度很低。其化石多样性和膜壳平均直径远小于邻近时期的生物化石群落,这可能与台子组沉积期的地表环境特征以及独特的生物群落特征有关。拉曼光谱分析表明台子组有机质处于较高的热演化阶段,埋藏温度约280℃,过高的埋藏温度也可能降低了台子组化石保存质量。     

新疆哈密地区晚泥盆世疑源类化石的发现及地质意义

从新疆哈密地区石城子北剖面7件样品获得分异度较高、有机质壁显著炭化保存的疑源类化石,根据其形态特征,共鉴定出14个形态属和15个形态种(其中8个未定种,3个比较种)。结合国内外古生代晚泥盆世已知疑源类组合进行比较,清楚表明当前获得的疑源类组合代表了晚泥盆世海洋微体浮游植物群面貌。我国涉及晚古生代疑源类生物地层的调查研究相对薄弱,而有关晚泥盆世疑源类化石的发现和报道更为匮乏,当前疑源类化石的发现,填补和丰富了新疆乃至国内晚泥盆世疑源类化石研究资料。该发现佐证了关于卡拉麦里洋在早石炭世闭合的认识;作为基础食物链的海洋微体浮游植物是重要成烃生物,晚泥盆世疑源类的保存预示研究区域具有石油、天然气勘察的前景。     

Petsamomyces, a new genus of organic-walled microfossils from the coal-bearing deposits of the Early Proterozoic, Kola Peninsula

A new genus of organic-walled microfossils of supposed fungal origin, Petsamomyces Belova gen. nov., is described from the black shales of the Pechenga complex of the Early Proterozoic (Kola Peninsula). The find testifies to the development of eukaryotic heterotrophic microorganisms as early as 2 Ga ago.     

The role of clay minerals in the preservation of Precambrian organic-walled microfossils

Precambrian organic-walled microfossils (OWMs) are primarily preserved in mudstones and shales that are low in total organic carbon (TOC). Recent work suggests that high TOC may hinder OWM preservation, perhaps because it interferes with chemical interactions involving certain clay minerals that inhibit the decay of microorganisms. To test if clay mineralogy controls OWM preservation, and if TOC moderates the effect of clay minerals, we compared OWM preservational quality (measured by pitting on fossil surfaces and the deterioration of wall margins) to TOC, total clay, and specific clay mineral concentrations in 78 shale samples from 11 lithologic units ranging in age from ca. 1650 to 650 million years ago. We found that the probability of finding well-preserved microfossils positively correlates with total clay concentrations and confirmed that it negatively correlates with TOC concentrations. However, we found no evidence that TOC influences the effect of clay mineral concentrations on OWM preservation, supporting an independent role of both factors on preservation. Within the total clay fraction, well-preserved microfossils are more likely to occur in shales with high illite concentrations and low berthierine/chamosite concentrations; however, the magnitude of their effect on preservation is small. Therefore, there is little evidence that bulk clay chemistry is important in OWM preservation. Instead, we propose that OWM preservation is largely regulated by physical properties that isolate organic remains from microbial degradation such as food scarcity (low TOC) and low sediment permeability (high total clay content): low TOC increases the diffusive distances between potential carbon sources and heterotrophic microbes (or their degradative enzymes), while high clay concentrations reduce sediment pore space, thereby limiting the diffusion of oxidants and degradative enzymes to the sites of decay.     

Infrared video microscopy—an efficient-method for the routine investigation of opaque organic-walled microfossils

Summary Dark or even opaque organic-walled microfossils are frequently represented in palynological residues which are derived from sediments of high maturity. Such particles may be studied surficially by SEM or incident light, but internal details remain obscured. It has been known for some time that transparency may be achieved by applying infrared microscopy, but the method never became routine. We have now assembled an IR equipment which is based on a regular transmitted light microscope and tested our setup on various kinds of palyno-morphse.g. spores, acritarchs, chitinozoans, scolecodonts as well as phytoclasts and zooclasts. Our examples are from several localities of different stratigraphic and palaeogeographic position within the Palaeozoic. The studies revealed a high potential for IR video microscopy to become an important tool in the study of thermally altered organic particles in palynological slides.     

Thermally-induced structural and chemical alteration of organic-walled microfossils: an experimental approach to understanding fossil preservation in metasediments

The identification and confirmation of bona fide Archean–Paleoproterozoic microfossils can prove to be a challenging task, further compounded by diagenetic and metamorphic histories. While structures of likely biological origin are not uncommon in Precambrian rocks, the search for early fossil life has been disproportionately focused on lesser thermally altered rocks, typically greenschist or lower‐grade metamorphism. Recently, however, an increasing number of inferred micro‐ and macrofossils have been reported from higher‐grade metasediments, prompting us to experimentally test and quantify the preservability of organic‐walled microfossils over varying durations of controlled heating and under two differing redox conditions. Because of their relatively low‐intensity natural thermal alteration, acritarchs from the Mesoproterozoic Ruyang Group were chosen as subjects for experimental heating at approximately 500°C, with durations ranging from 1 to 250 days and in both oxic (normal present day conditions) and anoxic conditions. Upon extraction, the opacity, reflectivity, color, microchemistry, and microstructures of the heated acritarchs were characterized using optic microscopy, scanning electron microscopy, Raman spectroscopy, and X‐ray photoelectron spectroscopy. The results differ for acritarchs prepared under oxic vs. anoxic conditions, with the anoxic replicates surviving experimental heating longer and retaining biological morphologies better, despite an increasing degree of carbonization with continuous heating. Conversely, the oxic replicates show aggressive degradation. In conjunction with fossils from high‐grade metasediments, our data illustrate the preservational potential of organic‐walled microfossils subjected to metamorphism in reducing conditions, offer insights into the search for microfossils in metasediments, and help to elucidate the influence of time on the carbonization/graphitization processes during thermal alteration.     

Paleoenvironmental distribution of microfossils and stromatolites in the Upper Proterozoic Backlundtoppen Formation, Spitsbergen

The Upper Proterozoic (ca. 700-800 Ma old) Backlundtoppen Formation, northeastern Spitsbergen, preserves an abundant and varied record of ancient microbial life. Five distinctive microfossil assemblages occur in five equally distinct sedimentary settings; differences among the assemblages appear to reflect original ecological heterogeneity, although taphonomic circumstance may contribute to some distinctions. Microfossil assemblages occur in: oncolites, oolites, and pisolites; stratiform stromatolites and associated intraclastic rudites; partially silicified micrites; and siltites interbedded with quartz arenites. Individual assemblages contain one to eight differentiable taxa; a minimum of 17 distinct populations is present in the formation as a whole. Additional microbial community diversity an be inferred from the presence of domal, columnar, pseudocolumnar, and coniform stromatolites, none of which contains microfossils. On the basis of macrostructure, four stromatolite types appear to be present, but only three distinct mat-building communities can be inferred from microstructural features. Eohyella elongata n. sp., a euendolithic cyanobacterium found in silicified pisolites, is described as new.     

A biomechanical analysis of the early eukaryotic fossil Valeria and new occurrence of organic-walled microfossils from the Paleo-Mesoproterozoic Ruyang Group

The Paleo-Mesoproterozoic Ruyang Group of North China hosts early eukaryotic fossils such as Dictyosphaera, Shuiyousphaeridium, and Valeria, and thus offers valuable insights into the early evolution of single-celled eukaryotic life. In this paper, we report several additional forms of organic-walled microfossils from the Ruyang Group, including Plicatidium latum, Spiromorpha sp., and an unnamed form. V. lophostriata from the Ruyang Group is investigated using transmitted light microscopy, scanning electron microscopy, transmission electron microscopy, and biomechanical analysis. V. lophostriata is reconstructed as a spherical vesicle with two hemispherical halves bearing concentric striations resembling latitudinal circles. The formation of striations could be explained using the Belousov-Zhabotinsky reaction model or the Turing reaction-diffusion model. A biomechanical analysis using the thin-walled spherical pressure vessel model suggests that the concentric striations of V. lophostriata may have functioned as a mechanism to guide biologically programmed excystment through medial split. Our analysis provides essential paleontological data to better understand the functional biology and life cycles of early eukaryotes such as Valeria.     

First record of organic-walled microfossils from the Tonian Shiwangzhuang Formation of the Tumen Group in western Shandong,North China

Organic-walled microfossils offer important information on the biospheric evolution in pre-Cryogenian and provide biostratigraphic implications for many Proterozoic fossiliferous sequences that are poorly age constrained for the lack of reliable radiometric date. Recently, macroscopic carbonaceous compression fossils have been reported for the first time from the Tonian Shiwangzhuang Formation of the Tumen Group in western Shandong, North China. However, organic-walled microfossils have never been discovered from this formation up till now. To improve our knowledge about Proterozoic biodiversity in North China, we conducted a micropaleontological survey on the argillaceous limestone samples of the Shiwangzhuang Formation, which also contain macroscopic carbonaceous compression fossils, from the Baishicun section in Anqiu, western Shandong, North China. Our investigation shows that the Shiwangzhuang microfossil assemblage is dominated by smooth-walled sphaeromorphic acritarchs and cyanobacterium-like filaments and relatively low abundance of other acritarchs, including 16 taxa, such as Polysphaeroides filliformis, Ostiana microcystis, Simia annulare, ?Jacutianema sp., Arctacellularia tetragonala, Pellicularia tenera, Polythrichoides lineatus, and Navifusa actinomorpha. The Shiwangzhuang organic-walled microfossil assemblage, although consisting of long-ranging and not age diagnostic taxa, is consistent with a Tonian age suggested by macroscopic carbonaceous compression fossils, including the Chuaria-Tawuia and Sinosabellidites-Protoarenicola-Pararenicola assemblages, revealed from the same fossiliferous horizon of the Shiwangzhuang Formation and by organic-walled microfossil assemblage, including the late Mesoproterozoic to Tonian index fossil Trachyhystrichosphaera aimika, from the underlying Tongjiazhuang Formation. However, it is also worth noting that a Cryogenian or Ediacaran age cannot be completely excluded based just on the Shiwangzhuang microfossils because of their limited biostratigraphic utility.     

High-temperature, acid-hydrolyzed remains of Polytrichum (Musci, Polytrichaceae) resemble enigmatic Silurian-Devonian tubular microfossils

Gametophytes and sporophyte components of two species of the evolutionarily early-divergent moss Polytrichum were separately subjected to high-temperature acid hydrolysis, and remains were examined by fluorescence microscopy and scanning electron microscopy. Remains included fragments of capsule, seta, leaves, stems, and calyptra. Cell walls of all remains were autofluorescent in violet and UV excitation, suggesting occurrence of resistant polyphenolic compounds. Calyptras of both species dissociated into smooth- walled, acutely branched filamentous associations of tubular cells with distinctively thickened cell junctions. In these aspects and measurements of wall dimensions made from SEMs, the hydrolysis-resistant Polytrichum calyptra remains were similar to several tubular microfossils described from Silurian and Lower Devonian deposits, whose provenance is unknown or ascribed to fungi. Our data suggest the possibility that at least some ancient tubular microfossils might have originated from Polytrichum-like early mosses. They add to increasing evidence that bryophytes left microfossil evidence for their presence millions of years earlier than is indicated by their macrofossil record.     

Paleobiology of distinctive benthic microfossils from the upper Proterozoic Limestone-Dolomite "Series," central East Greenland

Populations of Polybessurus bipartitus Fairchild ex Green et al., a large morphologically distinctive microfossil, occur in silicified carbonates of the Upper Proterozoic (700-800 Ma) Limestone-Dolomite "Series," central East Greenland. Large populations of well-preserved individuals permit reconstruction of P. bipartitus as a coccoidal unicell that "jetted" upward from the sediment by the highly unidirectional secretion of extracellular mucopolysaccharide envelopes. Reproduction by baeocyte formation is inferred on the basis of clustered envelope stalks produced by small cells. Sedimentological evidence indicates that P. bipartitus formed surficial crusts locally within a shallow peritidal carbonate platform. Among living microorganisms a close morphological, reproductive, and behavioral counterpart to Polybessurus is provided by populations of an as yet underscribed cyanobacterium found in coastal Bahamian environments similar to those in which the Proterozoic fossils occur. In general morphology and "jetting" behavior, this population resembles species of the genus Cyanostylon, Geitler (1925), but reproduces via baeocyte formation. Polybessurus is but one of the more than two dozen taxa in the richly fossiliferous biota of the Limestone-Dolomite "Series." This distinctive population, along with co-occurring filamentous cyanobacteria and other microfossils, contributes to an increasingly refined picture of ecological heterogeneity in late Proterozoic oceans.