Stratigraphy and sedimentology of Jurassic bedded chert overlying ophiolites in the North Apennines, Italy

In the North Apennines of Italy, Upper Jurassic bedded chert stratigraphically overlies ophiolitic rocks and is overlain by Lower to Middle Cretaceous pelagic limestone and shale, and Upper Cretaceous flysch. The bedded chert, best exposed in East Liguria and on Elba, is typically 30–80 m thick, but occasionally reaches 150–200 m thickness. It consists of two main alternating lithologïes: siliceous mudstone (SM) and radiolarite (R). Chert sections commonly show characteristic stratigraphic changes. Lower cherts display a striking rhythmic alternation of R and ferruginous SM beds. In middle cherts, SM beds are much less ferruginous and shalier intercalations are locally present. In upper cherts, R beds are less frequent and SM beds are essentially non-ferruginous. R beds are generally 1–4 cm thick, and consist of 80–90% quartz, 5–15% clays and usually < 1% hematite. They are commonly parallel-laminated, and rarely size-graded. In size-graded beds, large radiolaria are more abundant near the bed base (commonly together with ophiolitic or SM clasts) and small radiolaria more abundant near the bed top. Sorting is poor throughout most R beds. R beds are interpreted as turbidites (cf. Nisbet & Price, 1974). Model calculations suggest that typical settling velocities of radiolaria during redeposition are < 1 cm sec^?1, which is low and of restricted range relative to the 1–10 cm sec^?1 settling velocities of clastic grains of comparable size range. Radiolaria therefore should have only a limited tendency to grade and sort during deposition from a turbulent current. SM beds are commonly 1–7 cm thick, although much thicker ones occur near the base of sections, and consist mainly of 50–70% quartz, 15–35% clays and 0–15% hematite. Microscopic clay-silica aggregates and highly corroded remnants of radiolaria are common. SM beds are interpreted as mainly ambient pelagic sediment which accumulated slowly in topographic lows, and which was modified by near-surface dissolution of biogenic silica. In SM beds which contain two texturally different layers, the lower one is interpreted as the top of the underlying radiolarian turbidite. North Apennine cherts represent the first sediment deposited on oceanic crust formed during the opening of the North Apennine part of the Tethys. The ophiolitic basement had a rugged topography which favoured the redeposition of siliceous sediment. Hematite and local Mn enrichments in SM beds in the lower chert sections represent hydrothermal precipitates inferred to have originated at a spreading axis. During seafloor spreading, accumulation of siliceous sediments progressively reduced the topography. Deposition of ophiolitic detritus within the sediments phased out during early chert sedimentation, and the hydrothermal contribution during early-middle chert sedimentation. As local basins filled, during late chert sedimentation, radiolarian turbidites became less frequent. The first limestones at the top of chert sections are calcareous ooze turbidites derived from above the CCD and deposited slightly below it. Gradual descent of the CCD to ocean floor depths at the end of the Jurassic (Bosellini & Winterer, 1975) led to the replacement of siliceous by carbonate sedimentation.     

Effects of crude oil contamination on geotechnical properties of clayey and sandy soils

The southern coastal plain of Iran at the Persian Gulf encounters oil pollution due to the historical oil exploitation, related tanker navigations and accidents, and petrochemical industrial expansions in the recent years. Therefore, it is important to investigate the geochemical properties of oil-contaminated coastal soils and sediments for engineering and environmental purposes. Here, an extensive laboratory testing program was carried out to determine the effects of crude oil contamination on some of the geotechnical properties of clayey and sandy soils such as CL, SM and SP sampled from the coastal soils from this area. The testing included basic properties, Atterberg limits, compaction, direct shear, uniaxial compression and permeability tests on clean and contaminated soil samples at the same densities. The contaminated samples were prepared by mixing the soils with crude oil in the amount of 2%, 4%, 8%, 12%, and 16% by dry weight. The results indicated a decrease in strength, permeability, maximum dry density, optimum water content and Atterberg limits. Knowledge of these effects of oil contamination is important in coastal engineering and environmental remediation activities of the studied coastal plain.     

关于中国东海陆架沉积模式与第四纪海侵问题

世界上许多沿海国家为了开发和利用海底矿产资源,以及国防上的需要,都曾相继成立若干海洋研究机构,建造或改进海洋调查设备和海底钻探技术,使海徉第四纪地质学的研究,以前所未有的速度向前迈进。迄今,几乎所有的陆架海都程度不同地得到了研究,取得了相当丰富的地质资料,扩大了研究领域,推动了陆架海第四纪地质学的发展,使人们对该海域的研究进人到崭新的阶段。     

青海湖沉积物支链和环烷烃组分中C20，C25和C30高度支链类异戊二烯烯烃

在青海湖不同盐度的四孔近代沉积物岩芯（Ｑ－１６Ａ，ＱＨ，ＱＥ和ＱＧ）（图１）抽提物支链和环烷烃组分中检出了非常丰富的Ｃ₂₀，Ｃ₂₅和Ｃ₃₀高度支链类异戊二烯烯烃（ｈｉｇｈｌｙｂｒａｎｃｈｅｄｉｓｏｐｒｅｎｏｉｄａｌｋｅｎｅｓ），简称ＨＢＩ烯烃。这是在我国近代湖泊沉积物发现这类化合物的首次详细报导。由于Ｃ₂₀，Ｃ₂₅和Ｃ₃₀ＨＢＩ烯烃比正构烷烃具有较强的抵抗生物降解的能力（ＲｏｂｓｏｎａｎｄＲｏｗｌａｎｄ，１９８８ｂ），因此，它们广泛分布于各种近代环境中，如湖泊、海洋和高盐环境的近代沉积物中（ＲｏｗｌａｎｄａｎｄＲｏｂｓｏｎ，１９９０）。并且，具有１～６个双键的Ｃ₂₀，Ｃ₂₅和Ｃ₃₀烯烃经常是现代沉积物中丰富的烃类。最近在印度洋现代沉积物中又发现了一个新的具有７个双键的Ｃ₃₅ＨＢＩ烯烃（Ｈｏｅｆｓｅｔａｌ，１９９５）。全饱和的Ｃ₂₀（Ｉ，附图）、Ｃ₂₅（Ⅱ，附图）和Ｃ₃₀（Ⅲ，附图）ＨＢＩ烷烃已通过标样的合成确切地确定了它们的结构。在青海湖ＱＧ孔（尕海，咸水）和ＱＥ孔（耳海，淡水）抽提物中发现了Ｃ₂₀单烯（１号峰，图２ａ）。Ｃ₂₅烯烃（２号峰，图２ａ、２ｂ）和Ｃ₃₀烯烃（主要是３号和８号峰，图２ａ、２ｂ）存在于所有四孔沉积物中。     

武汉东湖现代沉积物磁组构特征及意义

采自武汉东湖现代沉积物的0．86m长的样品被用于研究湖泊现代沉积物的磁性各向异性，研究发现，东湖的现代沉积可划分为3个阶段，不同阶段的沉积特征与磁学性质反映了不同的沉积环境物源差异，通过分析样品沉积特征，磁化率K值特征并结合磁性矿物在各层面间的差别，从而分析得出磁化率K值可作为地层划分的有效辅助手段，磁铁矿广泛存在于所有砂质及泥质沉积物中，是引起东湖现代沉积物磁化率变化的主导性物质。     

Issue of the genesis of recent sediments on the Barents Sea shelf

This paper is a reply to the comment on our two previous publications (Krapivner, 2009a, 2009b) devoted to the genesis of recent sediments on the Barents Sea shelf in (Epshtein et al., 2011a, 2011b). It is substantiated that the physical nature of the reflection of recent sediments in seismoacoustic records, a very important point for the lithofacies analysis, is incorrectly interpreted by the above opponents. The paper presents geochronological and paleomagnetic data confirming invalidity of the popular concepts about the link between the cover of poorly consolidated sediments and the epoch of the last deglaciation. We show incorrectness of the statement of the opponents about the redeposited character of Pliocene-Quaternary marine biota of diamictons and the glacial processing of coarse-clastic material therein. Diverse properties of recent sediments and their topography artificially united into a complex of indicators of the glacial paragenesis are either simply explained in terms of the natural (for the Barents Sea) icemarine sedimentation or attributed to postsedimentary processes during intense neotectonic activity of the Barents Sea shelf.     

On heavy metal concentrations and biogenic enrichment in microbial mat environments

Heavy metal concentrations of a recent salina on the shore of the Mediterranean Sea near Port Said (Egypt) were investigated. Samples for the heavy metal study were taken in different ponds of the salina. It was found that microbial mat dominated brine sediments concentrated and enriched heavy metal 2–3 times more than sediments lacking microbial mat developments, suggesting that cyanobacteria play a major role in this enrichment. Heavy metal enrichment by cyanobacteria was therefore also studied in the laboratory environment. This study is compared with a recent study of Solar Lake and Sabkha Gavish sediments (Sinai, Egypt). Our conclusion is that recent hypersaline environments with ambient microbial mat (potential stromatolite) developments are ideal examples of present-day environments of metal accumulations.     

Biogeochemical processes of carbon and sulfur cycles in sediments of the outer shelf of the Black Sea (Russian Sector)

Within the mass of recent (unit-I) and ancient Black Sea (unit-II) sediments on the outer shelf of the Russian sector of the Black Sea, the rates of anoxic processes participating in diagenetic transformations of carbon and sulfur compounds were first measured using ³⁵S and ¹⁴C radioactive tracers. The main energy source for biogeochemical processes in (unit-I) sediments is the organic matter (OM) supplied to the bottom from the water mass. In (unit-II) sediments, this is methane in a migratory form proved by the excess of its oxidation rate over that of its generation. In recent silt, the primary microbial process is sulfate reduction; in unit-II, this is methane anoxic oxidation by the consortium of archeides and sulfate reductants. The organic matter produced in methane oxidation, in turn, acts as an energy source for the community of anaerobic heterotrophic microorganisms in the bottom sediments, which are remote from the water-sediment interface.     

Geochemistry of continental margin sediments from northwest Africa

The geochemistry of the non-carbonate fraction of sediments from the continental shelf and slope off northwest Africa has been investigated using R-mode factor analysis. The geochemistry is governed by a small number of factors controlled quantiatively by glauconite, phosphorite, quartz, clay minerals and secondary iron oxides. The distributions of the factors and of their controls are governed by mineral provenance and by depositional processes. Clay mineral factors predominate in fine grained sediments. Phosphorite, glauconite and oxide factors and quartz predominate in sands. Provenance controls the relative abundances of the minerals of the sand fraction all of which, except a proportion of the glauconite which is clearly recent, are relict and detrital. The recent glauconite is concentrated in poorly oxidised sediments off the southern Sahara. Provenance differences are detected between Saharan and Moroccan clays, and also exist between the clays of north and south Morocco.     

Organic matter of the World Ocean

Available data on synthesis, input, and decomposition of organic matter (OM) in the water column and recent bottom sediments of the World Ocean are generalized. The most reliable values of OM production and masses in the ocean, the total supply of organic carbon, and the input of terrigenous OM with coastal erosion, river runoff, and eolian matter are estimated. Maps of fossilization coefficients, distribution, and accumulation of OM in recent bottom sediments of the World Ocean are presented. A numerical expression is proposed for the main circumcontinental pattern of OM accumulation in the ocean. The group and elemental compositions of living matter of the ocean, land, and the Earth as a whole and the organic composition of bottom sediments are briefly considered.     

Contamination des sédiments récents après leur prélèvement

The hydrocarbon content of recent sediments is often very low. Consequently, account must be taken of the numerous possibilities of contamination, which may completely obscure analytical results and, therefore, their interpretation. Two new contaminants are described and their causes determined: (1) hydrocarbons, essentially even-numbered $\text{n-}\text{alkanes}$, from the polyethylene core sleeves of Kullenberg corers, (2) $\text{n-}\text{heptadecane}$, biosynthesized during the storage of wet sediments at 4°C, in darkness.In order to avoid these contaminants, it is advisable to core without plastic core sleeves, and to store the freeze-dried sediments in metal or glassware, under an inert atmosphere. Some of the conclusions of previously published works about hydrocarbons in recent sediments should be re-evaluated.     

Major element geochemistry of recent sediments from the Fláje basin (Krus̆né hory–Erzgebirge,Czech Republic)

The weathering products of the granitic rocks (which are poor in base cations) and their sediments in the Fláje basin, in an environment that is strongly influenced by SO₂ and NO_x emissions have been studied. High deposition of SO₂ and consequent acidification of the environment causes further depletion of base cations, mobilisation of Al and modification of the weathering reactions resulting in changes of the geochemical features of recent sediments. Depletion of the bottom sediments of the Fláje basin in base cations and Al and their enrichment in Si, compared to the fresh stream sediments and eluvium, suggests a mineralogical modification of the weathering product due to prolonged contact with basin water. Depletion of the non-silicate phase of the sediment in base cations which are replaced with Al on the other hand appears to be more effective in eluvium and those sediments which are exposed directly to the effect of acid deposition, i.e. which are not below water level for the major part of the year. The water of the basin appears to be the main factor influencing the composition of the recent sediments of the basin in the acidified catchment.     

Early diagenesis of fatty acids in lacustrine sediments—II. A statistical approach to changes in fatty acid composition from recent sediments and some source materials

The percentage composition and total amounts of fatty acids from plankton, live and dead plants (waterweeds and higher plants) and a forest soil, considered as possible origins of autochthonous and allochthonous organic materials in lacustrine sediments, have been determined by gas-liquid chromatography. Statistical analyses were carried out by computing distance index of the fatty acid composition between these source materials and the uppermost sediment from Lake Suwa, and the composition diversity index (CDI) of fatty acids in the recent sediments from Lake Suwa.The distance index indicated that the fatty acid composition in the uppermost sediment is similar to those in diatoms, Zooplankton and forest soil, and the values for dead leaves were smaller than for live ones. It suggests that the autolysis and/or decomposition processes prior to deposition onto the top sediment makes the fatty acid composition of organic debris similar to the uppermost sediment. The CPI in recent sediments varied irregularly, whereas the CDI increased during early diagenesis to yield a value comparable to ancient sediments.     

布容-松山极性倒转事件的海陆地质记录及其不同步性探讨

布容-松山（B／M）极性倒转事件是第四纪发生的最近一次地磁极性倒转,研究地磁极性倒转的特征不仅对理解地磁场演化规律具有重要意义,同时极性倒转通常具有全球等时性,因此常被视为地层划分和全球气候对比的关键时间标记物。然而古地磁研究表明,布容-松山事件在海洋与中国黄土沉积物中的记录存在着“错位”现象,使得基于磁性地层年代框架...     

Hydrothermal metasomatic alteration of carbonate bottom sediments in the Ashadze-1 field (13° N Mid-Atlantic Ridge)

We have performed the first detailed study of hydrothermal alteration of the Holocene-upper Pleistocene sediments in the recent Ashadze-1 hydrothermal field sampled during the 26th cruise of R/V Professor Logachev in 2005. It has been established that alterations in mineralogy and geochemistry are caused by the dissolution of calcite shells in bottom sediments and their metasomatic replacement with sulfides and other hydrothermal minerals. A zone of sediments enriched in magnesian hydrothermal minerals has been revealed in the sediments of the MAR for the first time. It is suggested that metasomatism is related to diffuse percolation of hydrothermal fluids through sediments.     

细粒沉积物及其古地理研究进展与展望*

细粒沉积物特征及其古地理研究对含油气细粒沉积物的勘探开发、评价预测、工程技术设计等意义重大。近年来,细粒沉积物,尤其是含油气细粒沉积物研究的快速发展,带来了一系列新的研究领域。在讨论细粒沉积物的定义、分类与特征的基础上,通过分析细粒沉积的文献知识群,获取细粒沉积物、页岩研究等结构、热点与发展方向。国际上细粒沉积物研究主要关注微结构和成因机制,近年来主要在具有油气意义的特殊细粒沉积物--页岩研究方面取得关键进展,对页岩的研究过程可以分为以页岩表征为代表的主知识网络和以页岩气赋存、运移等构成的延伸知识网络。细粒沉积物古地理恢复方法丰富,适用性存在差异,但量化、多因素综合、数据集成与深度挖掘、人工智能化将是细粒沉积古地理恢复方法的方向。在含油气细粒沉积物的优选评价方面,需要对沉积物本身特征与控制影响因素展开精细研究,进而延伸出“更宏观”与“更微观”2个主要发展方向。     

深海沉积物中的稀土矿产资源研究进展

近年发现,太平洋和印度洋的深海盆地中存在大量富含稀土的深海沉积物。主要类型为多金属软泥、沸石黏土和远洋黏土,其中的全稀土含量(∑REY,∑REE+Y)为400×10-6~2000×10-6,最高可达6600×10-6,重稀土含量(HREE)已达到或超过中国南方离子吸附型矿床的重稀土品位两倍以上,是潜在的新型稀土资源,具有重要的经济价值。目前不少学者对富稀土的深海沉积物进行了大量地球化学及部分矿物学的工作,认为多金属软泥中的稀土元素多赋存于与海底热液作用有关的铁锰氧化物和氢氧化物中,而沸石黏土和远洋黏土中稀土元素的富集则与磷酸盐的混入密切相关,其稀土元素主要存在于与磷灰石成分相当的生物鱼骨屑中。深海黏土的北美页岩标准化稀土配分模式与海水相似,表明其中的稀土元素主要来自于海水,REY富集成矿可能主要受控于磷灰石早期成岩阶段,期间稀土元素未发生分异。尽管近些年对深海沉积物中的稀土元素研究取得了不少成果,但是,对于沉积物中的稀土富集机制及影响因素等问题仍然需要更加深入的研究。作为稀土资源大国,为了争取我国在国际海底稀土资源竞争中的话语权,维护中国的稀土利益,中国应加紧开展相关的稀土资源勘查和潜力评价。     

南海北部大陆架现代礁源碳酸盐与陆源碎屑的混合沉积作用

在南海北部大陆架陆源碎屑沉积占优势的背景上，在珊瑚岸礁和堡礁周围，广泛发育着礁源碳酸盐和陆源碎屑组成的混合沉积。它们以砂屑、砂砾屑结构为主并含有生物格架结构。混合沉积的形成条件是具备碳酸盐和硅质碎屑两类物源，活跃的水动力，干湿交替的气候，此外，海平面的相对波动，也会造成积极的影响。混合沉积方式有随机式、相变式和随机 - 相变式等三种。混合沉积体常是多种混合方式交替、叠加而成的沉积复合体。礁源与陆源混合沉积相模式是从岸礁 - 堡礁相模式基础上发展而来，按沉积相和沉积结构可以分为五种混合沉积：1)礁基混积岩和礁格架混积岩，2）礁坪砂砾屑混积岩，3）礁后海滩 - 沙堤砾砂屑混合沉积，4）礁后泻湖砂屑混合沉积和5）礁前（翼）浅海砂屑混合沉积。礁源与陆源混合沉积的鉴别标志是珊瑚骨屑和岩屑各占10 - 50 ％，其它生物碎屑不计。南海大陆架现代混合沉积是一个典型的实例，可为全面研究现代南海沉积学和比较沉积学提供依据。     

Structure,composition, and depositional environments of recent sediments in the Upper Don River basin inferred from the Korostelevo section

The complex study carried out in the Upper Don River basin yielded comprehensive lithogeochemical, paleopedological, and paleontological data on recent sediments of the Korostelevo stratotype section. They provided grounds for the facies-genetic discrimination, subdivision, and correlation of the defined horizons based on paleopedological and paleontological data with the Neopleistocene time scale. The results made it possible to reconstruct environmental paleogeography for the early Neopleistocene-Holocene period and provided rhythmoclimatic substantiation of the stratigraphic subdivision of recent sediments in the study region.     

Problems of phytostratigraphy and the correlation of the Lower Jurassic continental sediments in West Siberia and Kuznetsk and Kansk-Achinsk basins

Paleofloral and palynological records of Lower Jurassic sediments in West Siberia, Kuznetsk (Kuzbass), and Kansk-Achinsk basins and their correlation are discussed. In a number of recent papers dedicated to the Jurassic stratigraphy of Siberia this problem is ambiguously treated. The reference palynological scale has been developed for the Jurassic West Siberian sediments and an uninterrupted succession of floral assemblages associated with it and with regional stratigraphic units has been recognized. On this basis the scheme of the correlation between the Lower Jurassic sediments of the Kansk-Achinsk and Kuznetsk basins and West Siberia permitting a better age estimate of coal-bearing deposits, is proposed.