贵州寒武纪杷榔组古蠕虫类埋藏特征及意义*

贵州剑河寒武纪杷榔组辣子寨剖面含有丰度较高的古蠕虫类化石。化石鉴定为Wronascolex geyiensis, 主要保存在三个层位。在对三个层位的岩石、沉积特征、化石成因及埋藏特征探讨分析后, 证实W. geyiensis化石保存于快速的沉积事件导致的浊流沉积层内, 而化石埋藏的完美程度受到成岩过程中埋藏位置、沉积物中矿物结晶和充填方式的影响, 这些后期的成岩、成矿作用对先期形成的化石精细结构产生了直接和间接的破坏作用。本文通过对W. geyiensis化石体上黏土矿物、草莓状黄铁矿、自形–半自形黄铁矿的成因分析后, 获得最适合保存软躯体化石的环境应该为缺氧且生物体与孔隙水中的硫酸盐无接触的原地和近原地埋藏条件。     

华南埃迪卡拉纪化石保存方式及其时空分布

埃迪卡拉纪化石保存方式具有多样性,包括:磷酸盐化、有机碳质压膜、黄铁矿化、硅化、以及粘土矿物交代。文中综述了以上各种化石保存方式在地层中的时代分布规律、埋藏特征和形成机理,并分析了这些类型的化石库在我国埃迪卡拉纪地层中的地理分布规律和埋藏学意义。分析结果表明:华南埃迪卡拉纪化石库的保存方式主要以有机碳质压膜为主;磷酸盐化和硅化保存方式分布较广;黄铁矿化和粘土矿物交代方式在中国埃迪卡拉纪地层保存较少。有机碳质压膜、黄铁矿化多见于粉砂岩、泥岩中;磷酸盐化、硅化多出现于磷块岩、燧石层或碳酸盐岩的磷质、硅质结核中,化石多为微体化石。另外,多种化石保存方式常常同时出现在同一化石库中,形成复合式的保存模式。     

豫西寒武系苗岭统张夏组Talassinoides bacae 中莓状黄铁矿的成因及其生态学意义

豫西寒武系苗岭统张夏组薄层微晶灰岩中发育了大量的Thalassinoides bacae遗迹化石,利用微区X射线荧光光谱仪和扫描电镜观察,并结合能谱分析,对Thalassinoides bacae遗迹化石的元素分布及微观特征进行分析。结果表明:衬壁与围岩的元素特征相似,晕圈的Fe、Mg富集;在填充物与衬壁的边界处Fe的含量高,且有大量的莓状黄铁矿(微晶呈八面体、五角十二面体、立方体、球体和不规则形)、黄铁矿的自形单晶及其铁的氧化物。认为晕圈构造是受到铁白云石流体的影响而形成的成岩晕;莓状黄铁矿的特征表明其为生物成因,为Thalassinoides bacae的耕作行为习性提供了重要依据,表明造迹生物在潜穴衬壁的边缘培植微生物以提供食物来应对食物贫乏,这是早期生物行为习性进化及后生动物向不同环境辐射的重要标志。     

黑龙江下城子组类三角蚌的复合模化石及其形态和沉积学意义

复合模化石是贝壳被溶蚀后,由于早期成岩压缩作用的影响,原贝壳的内模和外模互相叠加压印而成的化石,其正、负模上均印有原壳的内面和外表的特征。这种石具有形态和沉积学意义。     

东营凹陷沙河街组介形虫化石保存特征研究及应用

本文对山东东营凹陷沙河街组介形虫化石壳体的保存特征进行了研究。研究结果表明：沙河街组介形虫化石壳体颜色可分为浅色、中色和深色三种类型;按有无充填物,可分为未充填壳和充填壳两种,其中充填壳充填物的成分有方解石、白云石、黄铁矿和泥质四种;按完整程度有双瓣壳、单瓣壳和碎壳。文中对这些保存特征形成的原因进行了讨论,最后以一口井的研究结果为例,探讨了介形虫保存特征在古湖泊学及石油地质方面的应用。     

河北兴隆中元古代古海底黑烟囱中微生物化石的发现及其意义

采用显微镜以及扫描电镜对冀东中元古代块状硫化物黑烟囱样品进行研究,首次发现了矿化微生物化石。它们为丝状体,均已黄铁矿化,经过激光拉曼光谱测试发现还保留少量有机质,可以与现代海底黑烟囱周围矿化微生物对比。这些化石微生物的鉴别基于大小、形状和群落聚集等物理标志。     

早奥陶世疑源类埋藏后的形体及纹饰变化

赖以鉴定的疑源类化石仅保留下褶皱的囊壁而原生质已流失,由于成岩过程中围岩挤压或有机质壳壁干水收缩而使化石轮廓,纹饰发生变化应普遍可见,本文以作者在贵州三都地区阿化尼克期地层发现的Striatotheca principalis保存形态连续变化系列为基础,论述埋藏作用对疑源类保存形态的影响,这是利用埋藏学资料防止属种误订的一个典型示例,对疑源类属种的正确鉴定有重要的意义。     

临夏盆地晚中新世鸵鸟化石的特异保存（英文）

报道了来自西北地区中新世晚期临夏盆地的一件鸵鸟化石,该标本包括鸵鸟的部分颈椎以及气管,由于缺乏物种级别的鉴定特征,被暂定为鸵鸟(Struthiosp.)。新标本还保留了平齿三趾马(Hipparionplatyodus)的部分头骨。利用多种分析测试方法,对该鸵鸟骨骼的微观特征进行了详细研究,以探讨临夏鸵鸟的埋藏条件和古气候背景。在鸵鸟化石的一个脱矿化的骨碎片中发现了软组织(内源性血管和红细胞的化石残留)。同时光学显微镜和扫描电镜成像显示,化石组织切片中存在显著的细菌改变(骨侵蚀现象)。这是中新世临夏盆地脊椎动物遗体中软组织的首次报道。通过相关的地质和沉积学证据与新的古生物数据相结合,认为季风气候可能是造成鸟类化石早期埋葬期间微生物侵蚀的原因,接下来延续了8Ma左右的盆地剧烈的干旱化作用,导致了微生物活动的停止,并进一步导致了成岩作用后期孔隙方解石的沉淀。这项工作显示出跨学科(包括形态学、沉积学、地球化学和软组织分析)研究可以更好地揭示中国西北临夏盆地柳树组的中新世晚期的动物群更替、气候和分子保存。     

湖南桑植早三叠世放射虫化石

上二叠统深海相地层中放射虫化石十分常见,浅海相灰岩中也时有发现。然而,格里斯巴赫阶至今未找到放射虫化石,迪纳尔期和史密斯期的放射虫化石仅有土耳其西北部,泰国南部、湖南桑植和美国俄勒冈州中部四个化石点。这些放射虫化石普遍产自灰岩中,并以极低的分层度为特征,仅由1到4个种组成,均为古生代型分子。根据牙形石化石,湖南桑植放射虫化石产物迪尔阶和史密斯阶的结核状灰岩中,鉴定有两个种,即Entactinia nikorni和？Polyentactinia phatthalungesnsis。它们与泰国南部迪纳尔期的放射虫可以对比,但与土耳其西北部迪纳尔斯至史密斯期的放射虫动物群略有不同。     

埃迪卡拉纪晚期疑难化石Shaanxilithes在云南会泽朱家箐剖面的首现及其意义

陕西迹(Shaanxilithes)见证了埃迪卡拉纪–寒武纪之交生物演化及生态环境的变化,是埃迪卡拉纪末期标志性的疑难化石,具有全球对比意义。本文首次报道了云南曲靖会泽县大海乡朱家箐剖面灯影组旧城段泥质灰岩中新发现的宁强陕西迹(Shaanxilithes ningqiangensis Xing, Yue and Zhang, 1984)。所采集的标本整体形态上呈条带状,边缘呈锯齿状参差不齐,可见环状体分布。通过镜下观察,可发现散落圆盘状单元。将大海乡朱家箐剖面与晋宁六街镇王家湾剖面渔户村组旧城段所产出的Shaanxilithes化石对比后发现,朱家箐剖面的标本宽度更窄,长度更长,碎片化更加明显。通过微区X射线荧光光谱仪(μ-XRF)将朱家箐剖面和王家湾剖面的标本进行对比分析后可知,前者形态在Si、Al、K的元素分布图中显示清晰,而后者的形态主要体现在Fe元素的分布图上;前者化石和围岩中Ca元素的含量远远高于后者;S元素仅在前者存在微量的分布,在后者中未有信号显示。新的化石证据表明Shaanxilithes并非只产出自碎屑岩中,还可以在灰岩中保存。化石μ-XRF的面扫描和半定量分析表明Shaanxilithes可能为伊利石矿物交代,并且说明在不同岩相背景下,风化作用程度的强弱造成两个产地化石的差异性保存。随着研究区域不断扩大, Shaanxilithes相继在华南板块滇东地区、印度西北缘、纳米比亚、华北板块西南缘等地区晚埃迪卡拉世地层中被发现。此次在滇东会泽地区发现的Shaanxilithes,进一步表明该化石分布的广泛性,可作为全球晚埃迪卡拉世地层对比的标准化石。本文结合形态学分析和微区X射线荧光光谱分析,讨论了Shaanxilithes的埋藏学信息与亲缘关系,为探索埃迪卡拉纪–寒武纪过渡时期的生物和生态特征提供了更多视角。     

陕西宁强胡家坝地区晚埃迪卡拉世高家山生物群岩相变化与化石保存关系

我国上扬子陕西宁强-勉县境内产出埃迪卡拉纪晚期高家山生物群,根据大量野外追踪、实地观察与室内岩相分析,对碎屑岩相黄铁矿化软躯体化石的出现与岩相横向变化之间的关系以及相应的埋藏相进行初步探讨,认为胡家坝露头带为相对远离风暴源的沉积序列,最利于化石的保存;高家山露头带则属于相对靠近风暴源的沉积序列,化石保存潜力不如胡家坝露头带的沉积序列。     

FOSSIL DIAGENESIS IN THE BURGESS SHALE

Abstract:  Current models for the exceptional preservation of Burgess Shale fossils have focused on either the HF-extractable carbonaceous compressions or the mineral films identified by elemental mapping. BSEM, EDX and microprobe analysis of two-dimensionally preserved Marpolia , Wiwaxia and Burgessia identifies the presence of both carbonaceous and aluminosilicate films for most features, irrespective of original lability. In the light of the deep burial and greenschist facies metamorphism documented for the Burgess Shale, the aluminosilicate films are identified as products of late-stage volatilization and coincident mineralization of pre-existing compression fossils, whereas the three-dimensionally preserved gut-caecal system of Burgessia is interpreted as an aluminosilicate replacement of a pre-existing carbonate phase. The case for late diagenetic emplacement of aluminosilicate minerals is supported by the extensive aluminosilicification of trilobite shell and (originally) calcareous veinlets in the Burgess Shale, as well as documentation of other secondarily aluminosilicified compression fossils. By distinguishing late diagenetic alteration from the early diagenetic processes responsible for exceptional preservation, it is possible to reconcile the range of preservational modes currently expressed in the Burgess Shale.     

Environmental context for the terminal Ediacaran biomineralization of animals

In terminal Ediacaran strata of South China, the onset of calcareous biomineralization is preserved in the paleontological transition from Conotubus to Cloudina in repetitious limestone facies of the Dengying Formation. Both fossils have similar size, funnel‐in‐funnel construction, and epibenthic lifestyle, but Cloudina is biomineralized, whereas Conotubus is not. To provide environmental context for this evolutionary milestone, we conducted a high‐resolution elemental and stable isotope study of the richly fossiliferous Gaojiashan Member. Coincident with the first appearance of Cloudina is a significant positive carbonate carbon isotope excursion (up to +6‰) and an increase in the abundance and ³⁴S composition of pyrite. In contrast, δ³⁴S values of carbonate‐associated sulfate remain steady throughout the succession, resulting in anomalously large (>70‰) sulfur isotope fractionations in the lower half of the member. The fractionation trend likely relates to changes in microbial communities, with sulfur disproportionation involved in the lower interval, whereas microbial sulfate reduction was the principal metabolic pathway in the upper. We speculate that the coupled paleontological and biogeochemical anomalies may have coincided with an increase in terrestrial weathering fluxes of sulfate, alkalinity, and nutrients to the depositional basin, which stimulated primary productivity, the spread of an oxygen minimum zone, and the development of euxinic conditions in subtidal and basinal environments. Enhanced production and burial of organic matter is thus directly connected to the carbon isotope anomaly, and likely promoted pyritization as the main taphonomic pathway for Conotubus and other soft‐bodied Ediacara biotas. Our studies suggest that the Ediacaran confluence of ecological pressures from predation and environmental pressures from an increase in seawater alkalinity set the stage for an unprecedented geobiological response: the evolutionary novelty of animal biomineralization.     

Distinguishing geology from biology in the Ediacaran Doushantuo biota relaxes constraints on the timing of the origin of bilaterians

The Ediacaran Doushantuo biota has yielded fossils that include the oldest widely accepted record of the animal evolutionary lineage, as well as specimens with alleged bilaterian affinity. However, these systematic interpretations are contingent on the presence of key biological structures that have been reinterpreted by some workers as artefacts of diagenetic mineralization. On the basis of chemistry and crystallographic fabric, we characterize and discriminate phases of mineralization that reflect: (i) replication of original biological structure, and (ii) void-filling diagenetic mineralization. The results indicate that all fossils from the Doushantuo assemblage preserve a complex mélange of mineral phases, even where subcellular anatomy appears to be preserved. The findings allow these phases to be distinguished in more controversial fossils, facilitating a critical re-evaluation of the Doushantuo fossil assemblage and its implications as an archive of Ediacaran animal diversity. We find that putative subcellular structures exhibit fabrics consistent with preservation of original morphology. Cells in later developmental stages are not in original configuration and are therefore uninformative concerning gastrulation. Key structures used to identify Doushantuo bilaterians can be dismissed as late diagenetic artefacts. Therefore, when diagenetic mineralization is considered, there is no convincing evidence for bilaterians in the Doushantuo assemblage.     

Hipparion material from Gaojiashan locality in the Late Miocene of Linxia Basin,Gansu, China and associated mammalian fossil assemblage

Two Hipparion species, H. forstenae and H. hippidiodus from Gaojiashan locality in the Linxia Basin, Gansu, China are described in this paper, with the first presence of the former in the Linxia Basin. The lower cheek teeth of Hipparion from Gaojiashan bear deep ectoflexids, and after comparisons to other Chinese Hipparion fossils with deep ectoflexids, the mandibles with deep ectoflexids on the lower premolars suggest their attributions to H. forstenae. The presence of a deep ectoflexid on p2 may be interpretable as an intraspecifically variable feature in H. forstenae, and can also be found in H. dermatorhinum. Besides the Hipparion material, at least 8 species of large mammals occur at the Gaojiashan locality, including Adcrocuta eximia, Chilotherium wimani, Shansirhinus ringstroemi, Eucladoceros cf. proboulei, Palaeotragus cf. coelophrys, Giraffidae gen. et sp. indet., and the previously studied Promephitis hootoni and Eostyloceros hezhengensis. Although the sample from Gaojiashan shares five species with the Yangjiashan fauna, the Gaojiashan fossil assemblage may date to the Baodean because of the presence of H. forstenae. The overall taxonomic composition of the Gaojiashan assemblage at least suggests an approximate Baodean age, which would imply survival of C. wimani into the Baodean of the Linxia Basin.     

Ediacaran microbial colonies

Enigmatic discoidal fossils are common in Neoproterozoic sedimentary sequences and in the stratigraphic record pre-date the first appearance of diverse Ediacaran fossil assemblages. Termed 'medusoids', these Neoproterozoic discoidal fossils have generally been interpreted as coelenterate-grade organisms implying a radially symmetrical body plan for ancestral eumetazoans. Analysis of exceptionally preserved discoidal fossils from the White Sea area, however, indicates that most of these discoidal forms represent colonial microbes. Localized pyritization, for example, reveals the presence of a conspicuous filamentous substructure in Ediacaria , whereas concentric rings, radial sectors and central structures in Cyclomedusa and Paliella compare directly with Recent microbial colonies growing in a nutritionally heterogeneous environment. At least some Ediacaran discoids can be compared with extant concentric ring-shaped microbial colonies that grow in hypersaline microbial mats. Insofar as most of the remaining record of Ediacaran discoids can be attributed to the holdfast structures of non-radiate modular organisms, there is no support from the fossil record for identifying a radiate ancestry for the Metazoa.     

Shell composition of Terreneuvian tubular fossils from north‐east Sichuan,China

Identification of the primary constituents of small shelly fossil (SSF) shells is important for explaining the evolution of SSF faunas. The characteristics and constituents of Terreneuvian tubular SSFs found in north‐east Sichuan, China, are revealed using light microscopy, scanning electron microscopy and energy dispersive X‐ray spectroscopy. Petrographic thin sections indicate that the chemical composition of the shells is mainly calcium carbonate with smaller amounts of phosphorus, silica and pyrite. Most of the tubular shells composed of calcium carbonate have a distinct layered structure. Evidence of replacement of the original shell by phosphatization, pyritization and silicification, and recrystallization of calcium carbonate have been found, all of which destroyed the shell's original layered structure. Most fossils treated with acetic acid are phosphatic casts or steinkerns, with some preserving organic textures of the shell as phosphatic casts. We conclude that the Terreneuvian tubular SSFs from north‐east Sichuan were originally composed mainly of calcium carbonate; indeed, most Terreneuvian small skeletal fossils appear to have had an originally calcareous composition. The fossil casts or internal core fossils are composed of phosphate, which is related to local taphonomic processes.     

陕西宁强埃迪卡拉系顶部管状化石Sinotubulites形态学与古生态学新知

陕西宁强选将坪地区埃迪卡拉系灯影组高家山段上部的碎屑白云岩中产出大量磷酸盐化三维立体保存的Sinotubulites化石,这为埃迪卡拉纪末期生物的演化及多样性研究提供了一个很好的窗口。文中通过对Si-notubulites的形态结构、纹饰特征、保存特征等方面的观察研究,认为Sinotubulites管体外壁上不规则的褶皱状纹饰是变形过程中展现出的各种形态,而不是管体固有的纹饰形态特征。并且根据管体内外层管壁的不同形态学特征以及在原始生态条件下弯曲生长的管体,将Sinotubulites解释为表栖平躺生物。Sinotubulites可能具有一定的蠕动能力,而不规则褶皱状外壁在变形过程中可以产生微弱的蠕动力,使得管体对自身的位置得以调整。     

寒武纪早期宽川铺生物群中圆管螺化石显微结构及显微谱学分析

陕南寒武系底部宽川铺组不仅保存了大量的小壳化石,还以磷酸盐化的方式立体保存了多种软躯体动物的胚胎和成体化石,为研究早期动物矿化模式、个体发育方式以及动物躯体构型的早期辐射过程提供了非常关键的信息。然而宽川铺生物群的研究大多聚焦于化石系统分类及亲缘关系探索,对生物群的沉积背景、埋藏过程和保存模式的分析甚少。本文以宽川铺生物群的核心产出层位——陕西省西乡县大河镇宽川铺组下部磷质碎屑灰岩为研究对象,对其中的一类管状化石圆管螺及其围岩进行了显微结构学和显微谱学综合分析,获得了化石显微结构和关键结构对应的元素、矿物成分等信息,讨论了管状化石圆管螺的埋藏过程和保存模式,并在此基础上对其生物学特征进行了初步探讨。该研究对理解宽川铺生物群的埋藏机制提供了新的线索。