长江口北支兴隆沙有孔虫组合与沉积环境分析

通过对长江口北支兴隆沙XL2孔25个沉积物样品的有孔虫定量分析,发现该孔自下而上有4个有孔虫组合带(含10个有孔虫组合亚带),有孔虫分异度偏低,丰度变化大,壳径偏小,含有壳径细小的浮游有孔虫,部分壳体有机械破坏现象,这些特点反映出埋葬群在形成过程中受潮流的搬运、机械分选和破坏作用.结合沉积物粒度分析和环境磁学分析,揭示了该孔沉积环境自下而上按潮流脊-潮汐水道-潮流脊-潮坪演变的模式,进而探讨了长江口北支沉积水动力和物源.     

香港底质沉积中的有孔虫埋葬群

本文通过对香港地区水底表层中有孔虫的分析,进行了有孔虫埋葬群组合特征分析,划分了4个有孔虫组合:Ammonia beccrii组合;Poroeponides cribrorepandus组合;Pseudorotalia schroeterians-Elphidium组合;Hanzawaia nipponica-Florilus japonicus组合。这些组合与四个地理小分区有密切的关系。文中还讨论了水流对港湾有孔虫埋葬群的影响;有孔虫壳体的来源及其沉积过程,对于河口相古地理与古环境的解释有一定的地质意义。     

舟山港表层沉积物中底栖有孔虫组合特征初步研究

作者对舟山港区43个表层沉积物样品进行定量分析,共鉴定出底栖有孔虫33属60种。研究海域各站位均发现浮游有孔虫壳体,个体细小、属种单一,未发现活体个体。研究海域底栖有孔虫组合以玻璃质壳为主,平均含量86.71%,有孔虫丰度均值为1 676枚/50克,总体有孔虫组合为Ammonia beccarii vars.-A.maruhasii-Epistominella naraensis。研究发现,表层沉积物中大个体有孔虫(Ammonia beccarii vars.等)与小个体有孔虫(Epistominella naraensis)分布与潮流搬运呈密切相关关系,提示可能存在不同的搬运机制。与前人研究相比,研究海域有孔虫组合呈现以下变化:(1)胶结质壳有孔虫含量增加,个别站位出现15.89%的高值;(2)出现耐污染属种;(3)环境敏感属种畸形比例增加。研究表明,沉积搬运作用和环境参数变化是影响研究区有孔虫组合的重要因素,为有孔虫作为环境指标的进一步研究提供了基础数据。     

苏北沿岸有孔虫壳体破损的一种半定量描述与统计方法

有孔虫壳体破损是一种常见现象,主要由环境的机械和化学破坏作用造成。本文尝试用两个适用于近岸浅海有孔虫的指标,暂称为破蚀度指数ＢＡＩ（Ｂｒｏｋｅｎｎｅｓｓ－ＡｂｒａｓｉｏｎＩｎｄｅｘ）和溶蚀度指数ＤＩ（ＤｉｓｓｏｌｕｔｉｏｎＩｎｄｅｘ）,定量描述和统计有孔虫壳体的破损和溶蚀现象。在江苏海岸带的应用实例表明该指数可为恢复古沉积环境提供一定的信息。     

海南岛鹿回头珊瑚礁区全新世有孔虫

对海南岛鹿回头小东海和三亚湾珊瑚区底质中的样品进行分析研究,共获得有孔虫４０属９０种,其中包括３新种４未定种。小东海有孔虫壳一般较坚固。大有孔虫占绝对优热;三亚湾有孔虫壳体易破碎,大有孔虫相对贫乏。水动力状况及盐度差异是造成两地有孔虫不同的主要原因。磨蚀试验表明,有孔虫壳孔形态结构与环境有密切的关系。     

连云港沿岸浅海底质中有孔虫分布及对沉积环境的指示

据２９个底质样中４４个主要有孔虫属种,运用Ｑ型聚类分析,连云港沿岸浅海海底表层沉积中有孔虫可划分为二个组合：Ａ．Ａｍｍｏｎｉａｂｅｃａｒｉｖａｒｓ．－Ｅｌｐｈｉｄｉｕｍｍａｇｅｌａｎｉｃｕｍ组合;Ｂ．Ａｍｍｏｎｉａｂｅｃｃａｒｉｖａｒｓ．－Ｔｅｘｔｕｌａｒｉａｆｏｌｉａｃｅａ组合。其分布主要受研究区水团控制,可分别代表苏北沿岸流起始段和黄海水团边缘水体的有孔虫组合。以有孔虫为指示,文中对研究海区某些沉积环境特征作了讨论,如废黄河口悬沙对本区的影响,灌河口潮流作用和搬运,以及海底环境等。研究区灌河口及附近海域底质中有浮游有孔虫壳体分布,属首次报道。     

广东深圳湾和海南新村港底质中的有孔虫

广东深圳湾和海南新村港均为非正常海相的潟湖型港湾,有孔虫十分贫乏,分异度很低,经初步坚定,计18属34种,其中包括3新种及3未定种。深圳湾以胶结壳有孔虫占优势,几乎不见瓷状壳,称Haplophragmoides shenzhenensis sp.nov.-Ammonia of.beccarii(Linne)组合;新村港则以瓷状壳占优势,未见胶结型壳,建立Triloculina trigonula(Lamaark)-Peneroplis planatus(Fichtel et Moll)组合。对两地各种不同类型的有孔虫壳体作成分分析及酸溶试验,表明水体的pH值是有孔虫分布差异的控制因子。     

南海东沙海域MIS 3期冷泉甲烷渗漏的钙质生物溶解证据

对南海东沙海域DH-CL5PC岩心开展了碳酸钙含量、钙质生物壳体保存状况,有孔虫群落结构组成及氧碳同位素分析,结果发现该岩心MIS 3期碳酸钙含量极低、5个层位钙质生物壳体出现显著溶解现象。发生溶解层位各门类钙质生物化石丰度显著降低,底栖有孔虫与浮游有孔虫丰度比例(底栖/浮游)大于1,有孔虫壳体化学溶蚀特征明显。分析其原因认为,陆源物质的稀释作用及潜在的钙质生物溶解作用共同导致了该岩心的碳酸钙含量极低,而甲烷的有氧氧化过程所形成的偏酸性环境可能是导致钙质生物壳体发生显著溶解的主要原因。根据有孔虫群落结构和钙质生物化石保存状况的差异性,推测DH-CL5PC岩心所在区域MIS 3期以来至少经历过5次甲烷渗漏至海底附近低氧或富氧区域的过程,而各期次甲烷渗漏的强度可能有所差异。钙质生物壳体溶解现象结合其他指标一定程度上可以作为反演地质历史时期甲烷渗漏过程和强度的有效指标。     

浙江舟山岛礁潮间带有孔虫种群季节性生态特征研究

作者选择位于舟山长峙岛西南淤泥质潮间浅滩,通过为期一年的采样(2014年7月—2015年6月),尝试探讨淤泥质岛礁潮间带有孔虫种群的季节性生态特征。共鉴定出有孔虫14属18种。有孔虫种群以玻璃质壳为主,占全群95%以上。优势种为Ammonia beccarii vars.,Elphidiella kiangsuensis,Cribrononion vitreum。研究结果显示:1)区域有孔虫总体平均丰度为850个/10cm~3,活体平均丰度为504个/10cm~3。丰度季节变化显著,秋冬季节总生物量仅为春夏季节的38%;2)活体与总体属种组成基本一致,以本地埋葬群为主,显示研究区潮流动力输送作用不强;3)区域潮间带有孔虫分带性不明显,国外研究中常见的属种Trochammina macrescens,Trochammina inflata和Miliammina fusca,在本区也有出现,但丰度显著减少;4)研究区有孔虫组合个体畸形率不超过5%,畸形个体以Ammonia beccarii vars.最为常见,可作为区域环境指示的敏感种。     

茅口期■类动物的灭绝过程——灭绝选择性与物种个体大小关系的验证

对茅口期类动物群灭绝过程的分析揭示 ,若将类物种按壳体大小分为两类 ,从动物群物种分异度、物种净增速率的变化来看 ,大个体 (壳长 >6mm)物种与小个体 (壳长≤ 6mm)物种的灭绝过程并无明显的区别。根据壳壁等特征 ,茅口期类可分为南京类、希瓦格类、费伯克类和新希瓦格类 4个主要类群 ,各主要类群及其壳体大小不同的物种灭绝过程有明显的差异。在灭绝事件早期 ,各类群及其壳体大小不同的两类物种所受的影响有所不同。在早期的灭绝中 ,南京类、新希瓦格类、希瓦格类中壳长 >6mm和费伯克类中壳长≤ 6mm的物种显著减少 ,而希瓦格类中壳长≤ 6mm以及费伯克类中壳长 >6mm的物种则未受明显的影响。在茅口期晚期 ,由于灭绝压力的增大 ,除南京类外 ,所有类群及其物种无论个体大小均受到重创 ,导致类动物群物种分异度陡然下降研究结果证明 ,在灭绝强度较小时 ,类动物的生物学特征 ,如壳体大小、壳壁特征对物种的存活率有一定影响 ,而在集群灭绝的高峰期间 ,这些特征则不能发挥有效的作用     

Changes in quaternary oceanographic bottom conditions as documented by foraminifera in sediment cores from the slope of the exmouth plateau (off Western Australia)

Benthonic foraminifera from 15 surface- and 70 core-sediment samples (three cores) from the Western Australian continental margin (Exmouth Plateau) were quantitatively investigated. As far as possible, the occurrences of the species were correlated with the recent oceanographic conditions especially as related to water depths. The sampled sites are separated from the Australian Shelf by the Montebello Trough so that the taphocoenoses cannot become adulterated by foraminifera from the shelf. Only 1% or less of the foraminifera are benthonic species. The benthonic foraminiferal faunas of the surface sediment samples from 3800 to 1700 m are composed of about the same deep-water species as described from southeastern Indian Ocean basins by Corliss (1979a). They differ from one another only because different species dominate the faunas dependent on different water depth and/or water mass. Above 1700 m the character of the benthonic foraminiferal fauna is slowly changing from abyssal to bathyal. Downcore the benthonic foraminifera show marked changes in abundance patterns, which partly parallel the changes which can be observed with the “cool” and “warm” indicating planktonic foraminifera, partly show regular phase displacement with these changes. The different abundances of the same species in a core from, for instance, 3000 m or from 2000 m water depth, respectively, prevent a direct correlation between the cores. It also proved impossible to correlate the changes in the frequency patterns of certain species to certain paleo-oceanographic conditions. Examples for this are given.     

Foraminiferal taphofacies in the Mississippian rocks of the Guadiato area, SW Spain

Summary Microfacies analysis of over 1800 standard thin-sections of upper Viséan and Pendleian-aged platform limestones from southwestern Spain (Guadiato area) shows that foraminiferal assemblages contain many allochthonous specimens. The analysis of the cementation, recrystallization, abrasion, bioerosion, encrustation, dissolution, taphonomic distortion, orientation and sorting allow the recognition of eight taphofacies. They are based on the taphonomic features observed within the foraminiferal assemblages, which reflect the environmental conditions in which foraminifera were sedimented as well as about early diagenesis. The environmental conditions may be ascertained from the analysis of the biostratinomic processes, which comprise the energy, waves, tides, redox conditions, etc. The mechanisms of taphonomic alteration may be quantified, and thus the appearance or absence of these alterations may be used to define taphofacies of shallow- and deep-water environments, such as those from tidal flat, shoal, outer platform, microbial mound or slope. Moreover, the relationship among these taphofacies also helps to define depositional mechanisms and products, such as debris flows or olistolites.     

Möglichkeiten und Grenzen einer Ökosystem-Rekonstruktion am Beispiel des spätpaläozoischen lakustrinen Paläo-Ökosystems. 1. Theoretische und methodische Grundlagen

In analogy to ecosystems, palaeoecosystems are defined here as the palaeocommunities of a given area and their relationships to the abiotic variables of their respective environments. They are characterized by (a) their species diversity, (b) the trophic structure of their palaeocommunities, based on their food webs, and (c), based on their detailed historical development, ecosystem functions such as stability, resilience, and succession. Due to numerous taphonomic biases, palaeocommunities can only be reconstructed from very few fossil horizons (taphocoenoses). Important conditions for such reconstructions are an uninterrupted vertical sequence of taphocoenoses with little time-averaging, excellent fossilization potential, a minimal percentage of allochthonous species in the taphocoenoses, and reliable evidence concerning the original trophic interactions between the species or trophic guilds of the palaeocommunities. The following topics are discussed in detail: Taphonomic assessment concerning fossilization potential; estimation of autochthonous vs. allochthonous components, and time-averaging; reconstruction of food webs and their interpretation in terms of extant food webs, such as web parameters; various ecosystem functions, especially successions and structuring processes, and the limited possibilities for their reconstruction.     

Diatom assemblages along a former intertidal gradient: A palaeoecological study of a subboreal clay layer (Western coastal plain,Belgium)

Lateral and vertical variations in diatom taphocoenoses were studied in a clayey intercalation in the upper peat bed at Booitshoeke (western coastal plain, Belgium). The palaeoecological evolution, linked to sedimentary facies changes along the ecotone from fen to tidal flat, apparently involved two successive periods of increased local tidal activity. This result could be inferred from a weakly developed salt-marsh horizon within the clay, traceable by diatom analysis over a distance of a few hundred meters. Although influenced by taphonomic processes, the composition of the fossil assemblages appeared to reflect the relative position of the palaeoenvironment along the tidal gradient fairly accurately. Taphonomic groups of taxa could be distinguished, characterizing respectively the transition from fen to salt-marsh, the high salt-marsh, the low salt-marsh and high mud-flat, and the more polyhaline mud-flat. Sediments of drier salt-marsh conditions showed a very poor taphocoenosis, of mainly allochthonous origin, dominated by marine tychoplanktonic species with durable frustules. Some possible causes for the slight increase in marine activity during the mid-Subboreal, which resulted in the formation of the deposits considered here, are discussed.     

Effect of organic carbon flux and dissolved oxygen on the benthic foraminiferal oxygen index (BFOI)

Variations in oceanic primary productivity, flux of organic carbon to the sediments, and dissolved-oxygen levels in the water column are thought to be important in the control of benthic foraminiferal test size, wall thickness, morphology, and species composition of assemblages by many foraminiferal paleontologists. Aspects of these processes should be reflected by the benthic foraminiferal oxygen index (BFOI) based on these foraminiferal characteristics. However, analyses indicate that the BFOI correlates most strongly with dissolved-oxygen levels in overlying water (R²=0.81), weakly with oceanic primary productivity (R²=0.55), and weakly with organic carbon flux to the sediments (R²=0.51). Although both dissolved oxygen and organic carbon flux are main controlling factors for benthic foraminiferal assemblages, the BFOI is a useful indicator extracted from benthic foraminiferal assemblages for estimating the condition of dissolved oxygen in Cretaceous and Cenozoic oceans.     

Benthic foraminiferal assemblages of the Middle and Upper Jurassic sediments from the northeastern Alborz and western Koppeh Dagh,Iran: Systematic palaeontology and palaeoecology

This research is focused on a poorly studied Jurassic sequence in the eastern part of Alborz and Western Koppeh Dagh basins. The foraminifera are reported from Callovian (Middle Jurassic) to Tithonian (Upper Jurassic) sediments of the Farsian and Chaman Bid formations. The benthic foraminiferal associations belong to the families Ammodiscidae, Epistominidae, Hauerinidae, Hormosinidae, Ichthyolariidae, Lagenidae, Nodosariidae, Nubeculariidae, Ophthalmidiidae, Polymorphinidae, Rhabdamminidae, Saccamminidae, Spirillinidae, Spirocyclinidae, Textulariidae, Trocholinidae, and Vaginulinidae. In the studied area, the foraminifera are dominated by the families Nodosariidae, Vaginulinidae and Epistominidae. Palaeoecological analysis of the foraminiferal assemblages from the Farsian Formation indicates that these sediments were deposited on the inner to mid shelf environment, with normal salinity (euhaline), and relatively well oxygenated waters, with eutrophic conditions in the Goznawwi area and oligotrophic conditions in the Chaman Bid area. The foraminiferal assemblages in this study are the first record from Jurassic sediments of the eastern part of the Alborz and Koppeh Dagh basins in northern Iran.     

崇明东滩DT孔有孔虫组合特征及其环境意义

通过对崇明东滩DT孔的微体古生物学研究,结合沉积物粒度特征、环境磁学特征及14C测年分析,详细阐述了崇明东滩13.0kaBP年来的有孔虫组合特征。自下而上将该孔有孔虫划分出5个组合带,探讨了DT孔5个有孔虫组合带潮流作用变化特点,自组合带1(13.0—8.0kaBP)至组合带4(1.0—0.36kaBP)潮流作用依次增强;组合带4(1.0—0.36kaBP)至组合带5(0.36—0kaBP)潮流作用呈减弱趋势变化;沉积速率自组合带1(13.0—8.0kaBP)至组合带5(0.36—0kaBP)变化特点为较低→高→较高→低→较低;自13.0kaBP年来,按浅海→浅海-河口湾→三角洲前缘-前三角洲→河口沙坝→潮汐水道-潮滩的规律演变。     

Heterosteginapapyracea Seguenza du Miocène du Corridor Sud-Rifain (Maroc) : biométrie et particularités paléoécologiques

Biometric study of the inner features of Heterostegina specimens preserved in tortonian sediments of the oued Yhoudi member allows to confirm the presence of species Heterostegina papyracea Seguenza, 1880. Analysis of both large and small components of the foraminiferal assemblage in all examined samples establishes the dominant character of species Heterostegina papyracea Seguenza (more than 60% of total benthic foraminifera). The assemblage of small benthic foraminifera associated with the Heterostegina is different from that described from Recent sediments, as well as from Miocene sediments of Calabria and Spain. In order to explain this result, two hypotheses can be put forward: (1) the Tortonian Heterostegina from Morocco proliferated abundantly in very shallow environments in association with small foraminifera (i.e. abundant Ammonia beccarii). (2) Because of powerful tidal currents in the South Rifian Corridor, Heterostegina tests were probably transferred after death. This transfer could possibly be due to the narrowness of the South Rifian Corridor in the Early Late Tortonian and its position between the Atlantic and the Mediterranean. Similar cases foraminiferal displacements are also known from modern basins. This study illustrates the difficulties in reconstructing the paleogeography of the studied area and the importance of considering all available components of the assemblage.