广西南部晚长兴期小型有孔虫及二叠系-三叠系界线讨论

广西南部板董和柳桥地区晚长兴期台地及台地坳陷区沉积地层中发育两个不同的小型有孔虫动物群,它们与放射虫相伴生,呈实体化石形式保存,展示出该时期有孔虫外部和部分内部构造特征。晚古生代以实体状态保存的有孔虫比较少见,长兴期有孔虫的研究更是主要基于薄片鉴定。本文系统描述了两个实体有孔虫动物群,它们主要由Nodosarioidea和Cornuspiroidea组成,多数是长兴期的常见分子,但同时也出现了中生代较繁盛的类型。与伴生的放射虫研究成果一致,这些中生代型有孔虫的发现指示了在古生代末一些分子穿过了二叠系-三叠系界线而没有受到大灭绝的影响。     

浙江煤山剖面二叠纪末的小有孔虫动物群

通过对浙江长兴煤山剖面长兴阶上部和二叠系三叠系界线地层进行系统切片和研究,共鉴别出小有孔虫化石18属50种。这一丰富的有孔虫动物群,不仅进一步完善了长兴阶标准剖面的化石资料,而且也为研究二叠纪末的生物灭绝形式提供了新的依据。     

贵州西部长兴期有孔虫化石

本文描述的有孔虫化石计12属、13种,其中包括7新种。多数化石是根据分离出来的完整壳体和做定向切片的观察和研究的。讨论了Angulodiscus 和Multidiscus 两个属的归属,并讨论了含有孔虫化石的地层时代应属晚二叠世。     

四川广安谢家槽剖面早―中三叠世有孔虫

四川海相三叠系地层分布广泛,发育富含有孔虫化石的碳酸盐岩,是我国研究三叠纪有孔虫生物地层的理想地区之一。四川广安谢家槽剖面早—中三叠世地层中产丰富的有孔虫化石,共识别出12属34种(包括未定种)。根据有孔虫化石群在地层中的分布特点,自下而上划分出4个组合带,即Rectocornuspira kalhori-Cornuspira mahajeri,Glomospirella vulgaris-Arenovidalina chialingchiangensis,Meandrospira pusilla-Glomospirella irregulariformis和Glomospira sinensis-Arenovidalina amylovoluta组合带。有孔虫化石带的建立为该地区海相三叠系地层的时代确定和划分对比提供了重要的化石依据。     

从有孔虫的特征探讨中新生代西塔里木古海湾的演变

塔里木盆地位于天山和昆仑山两个古生代褶皱带之间,是在塔里木地台的基础上发展起来的中新生代断陷盆地。塔里木盆地蕴藏有丰富的油气和盐类矿产资源。本区中新生代海相地层与这些矿产的关系尤为密切。进行这段地层层序及其沉积环境的研究,对于弄清晚白垩世到第三纪塔里木西部的基础地质问题和沉积矿产的生贮规律与远景评价都具有重要意义。本文根据近年来野外和室内工作中积累的材料,主要运用有孔虫化石在各层段地层中的分布规律及其生态特征对西塔里木中新生代海湾的发生、发展和终结     

珠江口盆地西部古近系与新近系生物地层界线研究

古近系与新近系的界线在浮游生物地层分带中的具体位置长期存在争议,笔者依据珠江口盆地西部50余口钻井微体古生物资料中的浮游有孔虫和钙质超微化石记录,辅以沟鞭藻和主要孢粉事件对研究区古近系与新近系的生物地层界线展开研究,探讨了浮游有孔虫Globigerina ciperoensis,Globoquadrina dehiscens,Globigeri-noidestrilobus以及钙质超微浮游生物Sphenolithus ciperoensis,Zygrhablithus bijugatus和Reticulofenestra bisec-ta等标志性化石的地层意义,并重新厘定了珠江口盆地西部古近系与新近系的生物地层界线标准。     

基于两级分段式算法的卷积神经网络的浮游有孔虫自动鉴定*

有孔虫个体微小、数量众多、地理分布广、演化迅速, 是记录海洋沉积环境的重要载体, 在海相生物地层划分和对比中具有十分重要的作用。因有孔虫属种众多, 传统的属种鉴定需要经验丰富的专业人员进行人工鉴定且耗时较长, 此外人工鉴定古生物面临人才匮乏和工作量大等问题。卷积神经网络在计算机视觉领域的应用可较好的解决上述问题。利用古生物专家对中新世浮游有孔虫化石标注为指导, 根据有孔虫化石不同方向的视角分类, 结合卷积神经网络算法, 开发了有孔虫化石图像识别系统。研究发现, 通过有孔虫化石腹视、缘视和背视角度分类, 采取两级分段式鉴定算法对中新世浮游有孔虫属一级进行识别, 属一级鉴定准确率达到82%左右。     

广西南丹巴平石炭系中间界线地层的有孔虫

南丹巴平地区石炭系中间界线地层(相当于苏联上谢尔普霍夫亚阶)中含有丰富的有孔虫化石。本文自下而上建立了三个有孔虫化石组合。这些组合可与苏联、北美及日本等地区同期的有孔虫化石层(带)对比。 本文采用二分石炭系的方案,以有孔虫Globivalvulina moderata开始出现的层位作为上石炭统底界的标志。将石炭系中间界线划在有孔虫化石组合Ⅱ和组合Ⅲ之间。大部分具下石炭统面貌特征的有孔虫分子在这个界线附近消失。 在巴平剖面,有孔虫Globivalvulina moderata开始出现的层位较牙形刺Declinognathodus noduliferus开始出现的层位略低。分别以这两个种的开始出现来确定石炭系中间界线虽有差异,但相差不大。     

南海北部琼东南盆地BD-2井中新世有孔虫生物地层及沉积环境

南海北部琼东南盆地BD-2井中新世地层沉积连续,是琼东南盆地中新统较典型的钻井剖面之一。该井中新世地层中含丰富的有孔虫化石,共鉴定有孔虫62属98种,其中浮游有孔虫13属41种,底栖有孔虫49属57种。根据有孔虫标志种及螺旋浮游有孔虫旋向优势度的变化,对该井的有孔虫生物地层进行了详细划分,从早中新世至晚中新世共识别出11个有孔虫化石带或联合化石带。探讨了下中新统与中中新统,中中新统与上中新统界线的有孔虫划分标志。依据有孔虫丰度、分异度及组合特征,讨论了BD-2井从早中新世至晚中新世沉积环境演化特征。     

西藏札达晚白垩世-古新世浮游有孔虫及其时代意义

札达地处西藏最西部的阿里地区。本文对波林剖面、龙吉剖面和加纳崩剖面进行了研究,发现了丰富的浮游有孔虫动物群,属于Globotruncanita elevata 化石带、Globotruncana ventricosa 化石带、Globotruncanita stuarti 化石带和Globigerina eugubina 化石带,时代由晚白垩世至古新世早期。通过与岗巴、江孜和吉隆地区的地层对比,认为特提斯 喜马拉雅海区的海退可能是由东向西发展的。     

山东新汶煤田太原组小有孔虫动物群及石炭-二叠系界线的探讨

通过对山东新汶煤田太原组小有孔虫动物群的系统研究,共鉴定出小有孔虫化石24属66种,根据小有孔虫在太原组中的垂向分布和含量的变化,自下而上分为3个小有孔虫组合：1．Brad yina samarica- Palaeotextularia angusta elongata组合,2．Nodosaria sinensis- Tetrataxis组合,3．Geinitzina postacarbonica组合。通过与邻区及华北部分地区的对比,本区太原组小有孔虫动物群的地质时代应归属于早二叠世,其层位大致相当于华北各地太原组(ting)类的Pseudoschwagerina带。     

Decadal-scale changes in benthic foraminiferal assemblages off Key Largo,Florida

Assemblages of foraminiferal tests in sediments sampled off Key Largo, Florida, in 1982, 1991, and 1992 were significantly different from assemblages sampled along the same traverses in 1959–1961. Larger, algal symbiont-bearing taxa, primarily Soritidae, comprised 50–80% of the specimens in samples collected in 1959–1961, whereas Miliolidae and Rotaliidae comprised 65-90% of the specimens collected in 1991 and 1992. Test abundance in 1992 samples ranged from 1.0 × 10²/g to 8.1 × 104/g; tests were least abundant in coarse, well-sorted sediments. The lack of test-density data for the 1959-1961 samples prevented assessment of whether densities of smaller foraminifera have increased, symbiotic foraminifera have decreased, or both. Between 1982 and 1992, densities of smaller foraminifera appear to have increased. Although the causes of these changes in foraminiferal assemblages are not known, possible factors include nutrient loading inshore, winnowing and transport of tests by storm activity, and disease. The shift in dominance from long-lived, algal symbiont-bearing taxa in 1959--1961 to small, fast-growing, heterotrophic taxa in 1992 is consistent with predictions of community response to gradually increasing nutrient flux into south Florida's coastal waters. This study indicates that published accounts of foraminiferal assemblages from sediments collected 30 or more years ago can be valuable resources in efforts to determine if biotic changes have occurred in coastal ecosystems. This study also indicates that family-level identifications may be sufficient to detect decadal-scale changes in foraminiferal assemblages in reef-tract sediments.     

New biostratigraphic data from Cretaceous planktic foraminifera in Sahlabad province, eastern Iran

The foraminiferal content of two stratigraphic sections, located in eastern Iran within the Sahlabad province, between the Lut and Afghan blocks and ranging in age from Turonian to Campanian is investigated. Previous studies were general and only indicated the presence of planktonic foraminifera in this province. This paper presents a detailed study of planktonic foraminifera of the Shirshotor unit and establishes for the first time a local biostratigraphy consisting of five biozones. Biozones from the upper Turonian to lower Campanian are recognized, but the upper lower Campanian to lower upper Campanian strata are missing, as demonstrated by the lack of the Globotruncana ventricosa biozone. Tectonic activity in this region during the late early Campanian and mid-Campanian resulted in the presence of an unconformity together with debrites (debris flow deposits) in the lower upper Campanian. About twenty-five planktonic foraminiferal species are reported and illustrated. The largest faunal diversity is encountered in the upper Santonian. The planktonic foraminiferal biozones are precisely defined in selected stratigraphic sections and allow age determinations for the deepest marine sediments (pelagic limestones and bedded cherts) before the collision of the Lut and Afghan blocks.     

Experimental dissolution of a fossil foraminiferal assemblage (Paleocene–Eocene Thermal Maximum,Dababiya, Egypt): Implications for paleoenvironmental reconstructions

Dissolution experiments were carried out on a foraminiferal assemblage from the Paleocene–Eocene Thermal Maximum (PETM) at Dababiya, Egypt, in order to: 1) reveal the effects of differential dissolution on the composition of the foraminiferal assemblage and 2) develop objective criteria for the evaluation of dissolution in foraminiferal assemblages used in early Paleogene paleoenvironmental reconstructions, particularly with respect to neritic Midway-type assemblages from the Paleocene/Eocene transition. Our results confirm two general observations on modern foraminifera: 1) planktic foraminifera are much more vulnerable to dissolution than benthic foraminifera, leading to depressed P/B ratios and 2) dissolution susceptibility differs between size fractions, with the smaller specimens dissolving more rapidly than the bigger ones, leading to a larger average size of the remaining assemblage. Within a size fraction, wall structure and thickness are considered to be the main factors controlling differential dissolution susceptibility. We propose a ranking scheme for taxa with respect to dissolution resistance. Among the benthic taxa, Lenticulina is most resistant, followed by the agglutinated Gaudryina cf. ellisorae and Alabamina midwayensis. Biserial and triserial hyaline taxa and the porcelaneous Spiroloculina sp. are most susceptible to dissolution, whereas rotaliines, such as Cibicidoides and Anomalinoides have an intermediate susceptibility. This implies that mild dissolution of a Midway-type benthic assemblage leads to a relative enrichment in Lenticulina, Gaudryina and rotaliines. Amongst planktic foraminifera, the muricate taxa Acarinina and Morozovella are most resistant, followed by the cancellate Subbotina. The smooth and generally small Globanomalina and Zeauvigerina are least resistant to dissolution. Our data enable to objectively evaluate various degrees of dissolution in benthic and planktic foraminiferal assemblages retrieved from the lower Paleogene Tethyan outcrops. In this way taphonomic artifacts can be readily distinguished from paleoenvironmental signals affecting the primary composition of the assemblages. More generally, we propose that the combined use of foraminiferal numbers, P/B ratio and relative abundances of non-calcareous agglutinated taxa and Lenticulina may provide a powerful proxy for assessing dissolution in hemipelagic assemblages from Cenozoic and upper Cretaceous continental margins. In order to achieve more robust pre-Quaternary paleoenvironmental reconstructions based on quantitative foraminiferal data, application of dissolution proxies, like proposed here, or in slightly modified form, should become a more widely used micropaleontologic procedure. Particularly continental margin studies dealing with major biotic events (e.g. PETM) or employing P/B ratios for sea-level reconstructions should benefit from such an approach.     

New insights for ancient foraminifera through 3D visuals of fusulinids

Fusulinids are larger benthic foraminifera of late Paleozoic and index fossils for Permo-Carboniferous strata. The traditional methods to examine their internal structures are through ground thin sections, which however caused lots of ambiguities regarding the morphological diagnostics and taxonomic identification.In recent years, new technique of high resolution X-ray computed tomography sheds light on the microfossil examination and we had fusulinid individuals successfully processed with this innovative approach. Here we present the results of 19 Pseudofusulina specimens, including high resolution images and rendered three-dimensional (3D) visuals of the important internal structures, to unwrap more details of fusulinid morphology. This is the first time the full 3D visuals of fusulinid interiors were constructed and exhibited. Previous understandings on fusulinid basic morphology, such as proloculus, chamber development, are precisely described with 3D illustration; cuniculi and phrenotheca are discovered regularly among the specimens and therefore are not suggested to be diagnostic features of taxonomic splitting; test and proloculus morphology divergences caused by section orientation are captured. With assistance of high resolution CT technique, fusulinid morphology, especially internal structures, is much easier to acquire, understand, and exhibit, despite the critical limitation that only the fusulinid samples buried with terrigenous clasts, such as those from calcareous mudstone or argillaceous limestone, could be successfully scanned.     

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.     

Laboratory observations of benthic foraminiferal cysts

Long-term observations on living benthic foraminifera in the laboratory were performed to investigate their behaviour and life style. We noticed that the formation of cysts or sedimentary envelopes is a common feature within many groups of foraminifera (organic walled, agglutinated and calcareous) in the laboratory. Several kinds of cyst were observed. In most cases, the entire foraminiferal shell was canopied with detritus or particles, but some specimens covered only parts of their body, such as the aperture region or pseudopods. Cysts were found attached to the glass walls of culture vessels or free in and on the sediment. Foraminifera stayed within cysts for hours to weeks. After leaving sedimentary envelopes, some specimens immediately started to build new ones, others not. The function of cyst formation observed in the present study was not clear, except one case where reproduction took place. Some monitored structures seemed not to be sedimentary cysts but unilocular agglutinated foraminifera with probably allogromiid-like organization. The formation of sedimentary envelopes seems to be a very basic character of foraminifera, suggesting a mechanism for the evolution of shells.     

Plastogamy in Foraminifera: Glabratella ornatissima (Cushman)

SYNOPSIS. The foraminiferan Glabratella ornatissima (Cushman) undergoes plastogamy during reproduction. In this process, 2 (or rarely more) individuals join together by their apertural sides to mutually exchange gametes. The apertural sides and internal septa are dissolved, forming a single large brood chamber. After the zygotes grow to a 2- or 3-chambered stage, the young foraminifera are liberated from the enclosing parent tests.
Scanning electron micrographs and histochemically stained thin sections indicate that the reproductively mature individuals are firmly united by an organic membrane during plastogamy. This membrane is monolamellar, less than 1 μ thick and has minute lumps on its surface. Biochemically it contains a nonsulfated acid mucopolysaccharide, which is unlike the membranes associated with CaCO₃ deposition lining the interior of foraminiferal tests. The young foraminifera liberate themselves by secretion of an enzyme which degrades the membrane. The mechanism of plastogamy is interpreted to be an adaptation to life in turbulent waters that would decrease the chance of gamete union or zygote survival were the gametes released and fertilized freely.     

Benthic foraminiferal population fluctuations related to anoxia: Santa Barbara Basin

The pore-water geochemistry and benthic foraminiferal assemblages of sediments from two slope sites and within the central portion of the Santa Barbara Basin were characterized between February 1988 and July 1989. The highest foraminiferal numerical densities (1197 cm^–3 as determined by an ATP assay) occurred at a slope site in June 1988 (550 m) in partially laminated sediments. In continuously laminated sediments from the central basin, foraminifera were found living (as determined by ATP assay) in October 1988 to depths of 4 cm, and specimens prepared for transmission electron microscopy were found with intact organelles to 3 cm, indicating their inhabitation of anoxic pore waters. Ultrastructural data from Nonionella stella is consistent with the hypothesis that this species can survive by anaerobic respiration. However, the benthic foraminifera appear unable to survive prolonged anoxia. The benthic foraminiferal population was completely dead in July 1989 when bottom water O₂ was undetectable.