First finds of Eocene diatoms in the marine Paleogene reference section in the Il’pinskii Peninsula, northeastern Kamchatka

Diatom algae from the Eocene sediments of the marine Cenozoic section in the Il’pinskii Peninsula, northeastern Kamchatka, are studied. The taxonomic composition of the diatom assemblage is characterized, including rare representatives of oceanic plankton. Correlation with planktonic foraminifer associations found in the section indicates a Middle Eocene (Lutetian) age for the diatoms. These are the first records of Eocene diatoms from the northwestern Pacific rim for which such a correlation has been achieved.     

New data on diatoms from the marine Paleogene of Western Kamchatka

Diatom assemblages from the marine Paleogene of Western Kamchatka (the Kovachina, Viventek, and Kuluven formations) are studied. The shallow-water neritic assemblage from the Kovachina Formation of the Pyatibratskii Cape section is tentatively attributed to the middle Eocene, as it is lacking zonal index species. A high abundance and great taxonomic diversity are characteristic of diatoms from the upper part of the Viventek Formation in the Kovran River section. The zonal index species Cavitatus rectus identified here among the diatoms suggests that the respective assemblage is macerated from the synonymous diatom zone of the middle Oligocene (29.6?28.2 Ma). According to its taxonomic composition and structure, this assemblage is indicative of transgression environments and the presumable influence of the middle Oligocene climatic optimum. The Rocella gelida (upper part) and Thalassiosira praefraga diatom zones of the Oligocene-Miocene transition are established in the Kuluven Formation sediments of the Mt. Uvuch section in Kovachina Bay.     

湖光岩玛珥湖沉积物硅藻硅同位素环境示踪

硅是硅藻生长所必需的养分,硅藻在生长过程中从水体吸收主要以硅酸(H_4SiO_4)形式存在的溶解硅.硅藻δ~(30)Si_(distom)可反映硅藻吸收硅酸比例的变化,进一步可以反映湖区气候与环境变化.为探索湖泊沉积物硅藻δ~(30)Si_(distom)在指示湖泊古环境方面的潜力,我们测定了湖光岩玛珥湖沉积物硅藻硅同位素变化.研究结果表明,沉积物δ~(30)Si_(distom)变化与生物硅和有机碳含量变化呈显著相似性,可作为一种有效的古环境代用指标.同时,与已有温度记录的对比分析表明,两者具有很好一致性.较高的如δ~(30)Si_(distom)指示了温度较高的气候条件下硅藻对硅酸的利用率较高;当δ~(30)Si_(distom)较低时,对应着在温度较低的气候条件下硅藻对硅酸的利用率较低.目前,热带陆地区域古气候重建的方法中可用的温度代用指标很少,此项研究证明了δ~(30)Si_(distom)是一种很有潜力的古环境代用指标,有望在低纬度地区古温度重建中发挥重要作用,值得进一步深入研究.     

Diatoms as a source for 4-desmethyl-23,24-dimethyl steroids in sediments and petroleum

Analysis of the sterol composition of more than 100 diatom cultures, representing all major marine diatom orders, indicates that this group of algae may be an important source for 4-desmethyl-23,24-dimethyl steroids in sediments and petroleum, as their precursors, i.e. 4-desmethyl-23,24-dimethyl sterols, were present in 22 of the cultures. The phylogenetic positions of diatom species that produce 4-desmethyl-23,24-dimethyl sterols show that, within the centric diatoms, only a specific group of diatoms is able to produce these sterols, while within the pennate diatoms, a phylogenetic relationship between 4-desmethyl-23,24-dimethyl sterol-producing diatoms is less apparent. Based on the phylogenetic relationship, it is suggested that diatoms inherited the ability of producing these sterols from a single common ancestor, which originated between 150 and 100 Ma ago. Co-injection of an authentic 23R,24R-dimethyl-5α-cholestane standard with extracts confirmed its presence in sediments. We also tentatively identified three other 4-desmethyl-23,24-dimethyl sterane isomers having different side-chain stereo-configurations and observed that some of the isomers co-elute with other steranes including 24-ethyl-5α-cholestane.     

Cell-cell and cell-surface interactions in an illuminated biofilm: implications for marine sediment stabilization

Most wetted surfaces that are illuminated support a population of phototrophs. The marine sediment is no exception and there the major component of the microphytobenthic population is diatoms. These organisms are credited with stabilizing the sediment against physical disturbance by virtue of the extracellular carbohydrate polymers that they elaborate. However, diatoms synthesize and secrete several carbohydrate polymers and it is not certain which of them is involved in the stabilization process. In order to investigate this, we have constructed small glass bead-filled flow through bioreactors to mimic marine sediments. The flow rate through the bioreactors was found to reflect the physical stability of the bead bed. Thus flow rate was measured as a function of diatom growth and the production of three operationally-defined polymers, i.e., those soluble in the medium, those soluble in 0.5 M NaHCO3 at 90 degrees C and those not soluble in either solvent (matrix polymer). Growth of the diatoms did not change the hydraulic conductivity of the bioreactors. For Amphora coffeaeformis, neither did the production of medium-soluble nor NaHCO3-soluble polymers. However, matrix polymer accumulation was directly correlated with a reduction in flow (regression coefficient R2 = 0.96) and stabilization against physical disturbance. Results with species of Navicula were not as clear. Both NaHCO3-soluble and matrix polymers were involved in producing the flow reduction. In the same manner we also measured the effect of Pseudoalteromonas haloplanktis growth on bead bed hydraulic conductivity and bead bed stability. Growing alone, no effect was found, but in co-culture with a single diatom species, the bacteria reduced the diatom effect on flow through the bioreactors seen earlier, however did not reduce the extent of their growth. Confocal scanning laser microscopy of beads colonized with diatoms alone, or diatoms in co-culture with bacteria, revealed that P. haloplanktis was able to inhibit diatom adhesion to the beads. When the bacteria were present there was less matrix polymer evident. We speculate that this interference with diatom metabolic activity was either the result of less matrix polymer synthesis, or its hydrolysis by the bacteria. The results are applicable to mixed species biofilms of this type on surfaces other than sediments.     

南海北部陆坡ODP 1144站位第四纪硅藻及其古环境演变

中国南海北部陆坡ODP 1144站位硅藻植物群的研究，建立了西太平洋边缘海一个新的中更新世晚期以来的硅藻生物地层图式，根据硅藻化石中具有指示意义的硅藻种的分布和生态变化（暖水种和冷水种），划分了8个硅藻组合带，其硅藻组合带分别在不同的高低海面环境下形成的，根据ODP1144站位氧同位素（OIS）测定结果，8个硅藻组合带与OIS 1－8期相对应。1、3、5、7硅藻组合带相当于OIS1、3、5、7期，间冰期是以热带和亚热带硅藻占优势，其中冷期出现大量的沿岸硅藻为特征，反映高海平面温暖的气候条件；2、4、6、8硅藻组合带相当于OIS2、4、6、8期，冰期是以亚热带，热带和出现较多冷水硅藻为特征，反映低海平面较冷气候条件，硅藻丰度值的变化与冰期和间冰期有关，可以证实间冰期时期高的海平面和较低的生物生产力以及冰期时低的海平面和高的生物生产力，而生物生产力的变化又与沉积时期沿岸流或上升流的强弱及水团活动有密切关系，进而揭示该区古海洋环境的演化与季风强弱之间的内在关系。     

Palaeoenvironmental Reconstruction of the Early to Middle Miocene Sequence in West Central Sinai,Egypt, as Revealed from Fossil Diatoms

A detailed analysis of the diatoms from the sedimentary sequence exposed in Abu Qada basin, west central Sinai, was used to determine the palaeoenvironmental changes during the Lower to Middle Miocene. A total of 85 diatom species and varieties belonging to 37 genera were identified from 154 samples collected throughout the stratigraphic succession. The lithological characters of the studied samples varied between sandstone, silty interbeds, sandy shales, shales, and terminated with anhydrite and limestones. These rock units are included in two lithostratigraphic formations (Rudies and Kareem), which are separated by a marked unconformity. The distribution and preservation of fossil diatoms in the sedimentary record are examined with the aim of outlining the temporal and spatial variation in the composition of the diatom assemblages, in order to estimate the changes in depositional environments during the Lower to Middle Miocene. The distributional pattern of the recorded diatom taxa distinguished four diatom eco-zones. The environment of each eco-zone is deduced and a proposed paleobathymetric change and depositional history of the Miocene sediments in the studied area are given.     

黄海晚更新世以来的硅藻组合及其沉积环境

黄海更新世晚期以来的硅藻化石,自下而上可划分为五个硅藻带。在Ⅰ带的上下层位,各含一个淡水藻类化石带,显示黄海在大理冰期时,由于气候变冷,海面下降,黄海陆架三次出露成陆。亚间冰期时,气候转暖,海面回升,复为海水淹没,海域中生长着Ⅰ带的各种海生硅藻。随着全新世气候转暖,沉积物中发现Ⅱ-Ⅴ带海生硅藻带,其中Ⅲ带硅藻外洋种比例较大,含亚热带暖海种多,表明此时水温较大,海域扩大,相当于大西洋期,其他各带与全新世各期相当。     

Quantitative relationship between surface sedimentary diatoms and water depth in North-Central Bohai Bay,China

To study the quantitative relationship between surface sedimentary diatoms and water depth, 67 surface samples were collected for diatom analysis on eight profiles with water depth variation from the muddy intertidal zone to the shallow sea area in North-Central Bohai Bay, China. The results showed that the distribution of diatoms changed significantly in response to the change in water depth. Furthermore, the quantitative relationship between the distribution of dominant diatom species, their a...     

Possible clay structures in frustules of living diatoms

Comparison of X-ray diffraction spectra of marine diatom frustules and suspended clay minerals suggests the presence of a distinctive smectite in diatoms. The frustules contained 1.5% Al₂O₃ and were partly covered with particles of 0.02 μm in diameter. The source of Al and the fate of diatoms in the sediment are briefly discussed.     

Stratigraphic evidence of human disturbance in an estuary

Prior to European settlement, oligohaline and mesohaline sections of Chesapeake Bay draining Piedmont saprolite supported diverse and abundant diatom and macrophyte populations. Compositional changes in diatoms and macrophytes in oligohaline sections correspond with 17th- and 19th-century deforestation and increased siltation, while effects on downstream populations were less notable. After deforestation, previously sparse diatom populations in a mesohaline estuary draining sandy Coastal Plain soils became more abundant. Fertilization of cultivated land was accompanied by increased production of both attached and free-floating diatoms. After the discharge of sewage, diatom populations increased enormously in the affected areas, followed by a dramatic decrease. The decrease suggests silica limitation after intense phosphorus enrichment. The loss of macrophytes and increase in planktonic diatoms in oligohaline areas in recent years resemble the historical sequences observed in lakes undergoing eutrophication. However, in the estuary, similar declines have also occurred in macrophyte populations in mesohaline areas where eutrophication is much less severe, but where chlorine and herbicide toxicity during the past 20 yr is similar to upstream areas.     

Surface chemistry and reactivity of biogenic silica

The surface chemistry of cultured diatoms was compared to that of biosiliceous material in Southern Ocean sediments, using potentiometric titrations and aluminum adsorption experiments. Aerosil 200, a well-studied synthetic amorphous silica, served as reference solid. Surface charge development and aluminum adsorption on cultured diatom shells were comparable to Aerosil. The surface chemical properties of biosiliceous material buried to depths of 15-25 cm in Southern Ocean sediments, however, deviated markedly from those of the cultured diatoms. In pH range 4-8.5, the surface charge density was systematically lower for biogenic silica from the sediments. In addition, the aluminum adsorption edge on the biosiliceous sediments was shifted to higher pHs by about 0.4 units. The results indicate that ionizable surface silanol groups on diagenetically altered diatom shells are less abundant and, possibly, less acidic than on freshly cultured diatoms. The observed differences in surface chemical structure are consistent with the progressive loss of reactivity, or aging, of biogenic silica which promotes its preservation in sediments.     

Review of the Analysis and Application of Diatoms in the Marine Sediments

With regard to the analysis and application of diatoms in the marine sediments, diatom purification method, data analysis method and diatom application in environmental reconstruction were summarized. The diatom purification is composed of four main processes (removing calcium carbonate, organic and minerogenic matter, and slide preparation). For each process, frequently used methods and improvements were introduced, while their pros and cons were compared. As to the data analysis, in order to ensure statistical reliability, the essential methods and principles were represented in detail with species identification and counting, data expression and error estimation involved to reduce errors as much as possible. On this basis, the numerical method application was explained for its advantage of improving the accuracy for analysis. The applications of diatom fossils in environmental reconstruction were studied more deeply abroad, including the investigation of relationship between diatom fossils and upper-water environment, the application of diatoms from deeper core sediment for reconstructing oceanic paleoenvironment, tracing salinity and reflecting eutrophication. As far as the deficiency of the domestic research was concerned, multidisciplinary technologies and observational data were suggested to be combined into the study in order to promote the quantitative research of diatom fossils and the accuracy of environmental reconstruction.     

A mechanism for emplacement and concentration of diatoms in glacigenic deposits

The occurrence of diatoms (both marine and freshwater) in sediments beneath the West Antarctic Ice Sheet (WAIS) is suggestive of past ice-sheet collapse. However, it is not the only model explaining such occurrences. We propose another mechanism for introducing diatoms beneath ice sheets by considering the fate of a diatom placed (by eolian processes) on top of an ice sheet. Mathematical modeling indicates that the route the diatom will take through the ice sheet is dictated by the basal melting rate. If no basal melting takes place, flowlines will crop out at the ice-sheet margin. However, if basal melting is as low as 0.01 m/yr the trajectories of all Howlines except for those nearest the margin will intersect the bed, with those diatoms deposited near the dome reaching the bed about halfway down the Howband. Larger values of basal melting lead to the diatoms reaching the bed even faster and closer to the point of origin. In light of these results, the presence of diatoms in sediments beneath the WAIS does not lead to a unique solution; it is not necessary to invoke past ice-sheet collapse to account for their presence.     

云龙天池湖泊水深与硅藻生物多样性的关系

以云龙天池湖泊为研究对象, 通过分析不同深度表层硅藻样品的生物多样性以及100年来硅藻生物多样性的变化特征, 探讨硅藻生物多样性与水深变化之间的关系。虽然硅藻组合随水深发生了明显的变化, 浅水区底栖硅藻占优势, 深水区浮游硅藻占优势, 但是不同深度表层样品中硅藻的属种数(简单分异度)基本相同, 硅藻种群的生物多样性也没有发生显著的趋势性变化。这主要是由于硅藻各属种在不同深度的权重互补, 导致云龙天池硅藻的多样性在湖泊的不同深度变化不大。近百年来的湖泊沉积速率显示, 自1960年前后, 湖泊水位在波动中逐步升高, 但是硅藻种群的生物多样性并没有发生相应的变化。以上研究结果说明, 云龙天池硅藻种群的生物多样性, 不管是在时间上, 还是空间上, 与水深变化均无明显相关性。     

Anoxic events during sedimentation of a Palaeogene diatomite in Denmark

A diatomite, about 60 m thick, of late Palaeocene-early Eocene age crops out in northern Jutland, Denmark. The diatomite is locally termed ‘Moler’. Frustules of marine diatoms constitute c. 65% (by weight) of the diatomite, and clay minerals, chiefly montmorillonite, make up the remainder. Slight variations in the relative supply of diatom frustules and clay minerals are preserved undisturbed in laminated diatomite, while lamination is partly destroyed by burrowing organisms in weakly laminated diatomite and obliterated by total bioturbation in structureless diatomite; these three facies alternate throughout the sequence. The presence or absence of infaunal burrowing organisms is interpreted as a record of the content of dissolved oxygen in the water above the sediment-water interface and hence of the position of the redox potential discontinuity. Interspaced in the diatomite are 179 identifiable layers of volcanic ash. These ash layers provide a means of precise lateral correlation. They show that levels of laminated diatomite may be followed throughout the basin and therefore that changes between anoxic and oxic conditions occurred simultaneously across the area. The laminated diatomites may consequently be interpreted as representing short-term anoxic events, of which twelve have been recognized.     

Diatom biostratigraphy of tsunami deposits: Examples from the 1998 Papua New Guinea tsunami

Distinctive diatom assemblages may be associated with tsunami sediments and may often contrast with the assemblages found within sediments underlying the tsunami deposit as well as those associated with the modern coastal environment. Sediments associated with the 1998 tsunami that destroyed much of the Sissano lagoon area in northern Papua New Guinea have been investigated. Surface sediments from three transects across the sediment spit near Warapu have been examined for diatom content and preservation. The preservation is variable, and the data show an, often chaotic, assemblage that can be attributed to the tsunami waves incorporating and depositing diatoms from distinctive habitat zones during their runup and subsequent backwash. The diatoms identified within the Warapu sediments indicate an origin from within the inter-tidal and offshore area rather than from the beach–sand spit complex. The sand deposits disclose a high percentage, in excess of 75%, of broken diatom valves, and a predominance of centric (circular) species due to preferential preservation. The study demonstrates that the application of diatom biostratigraphy to modern tsunami deposits can be used in conjunction with other stratigraphical lines of evidence to interpret the source and provenance of historical and palaeo-tsunami deposits.     

用模糊数学聚类分析研究南极菲尔德斯岛西湖全新世硅藻

非常好的硅藻和金藻组合出现在南极乔冶王岛菲尔德斯半岛西湖全新世沉积物中，共计硅藻有21属，131种和变种。用模糊数学方法对西湖W5、W4、W3、W24个钻孔柱状剖面中硅藻群进行研究，可以划分出10个硅藻组合，显示出硅藻组合的演化趋势和变异特征。研究重点是硅藻群的生活环境特征及其变化，重建古地理环境，提示南极西湖环境与气候的演变规律。     

Paleocene–Lower Eocene paleontological record of the Ulyanovsk-Syzran facial district,Volga-Peri-Caspian region

The stratigraphic subdivisions of the Paleogene included in the updated regional stratigraphic scheme of the Ulyanovsk-Syzran facial district with a wide development of biosiliceous deposits, are described and paleontologically characterized. The biostratigraphic subdivision of the reference sections using diatoms and dinocysts is discussed. The recently recognized stratigraphic units, Smyshlyaevka and Karanino within the Kamyshin (Upper Paleocene) and Proleyka (Lower Eocene) regional stages are described.