Age and conditions of formation of sedimentary cover of the Ulleung Plateau of the Sea of Japan according to micropaleontological data

The paper reports on the micropaleontologcal (diatoms, silicoflagellates, radiolarians, and pollen flora) data substantiating the age and conditions of sedimentary cover formation of the submarine Ulleung Plateau (Krishtofovich Rise) in the Sea of Japan. Five rock complexes with different age and origin were distinguished on the basis of micropaleontological and petrographic data. Complex 1 (tuffites, tuffogenous siltstones) with numerous freshwater diatoms and pollen flora that prove the lacustrine genesis and the Early Miocene age occurs at the base of the sedimentary cover. Complexes 2–5 are composed of marine tuffogenous sedimentary deposits of end of Early Miocene–Pleistocene age. Stratigraphic unconformity between continental and marine deposits involves a short-time interval in the end of the Early Miocene and points to rather fast tectonic submersion of the Ulleung Plateau. Marine sedimentation in bathyal conditions dominated from the end of the Early Miocene. In the Late Miocene, in the northern part of the plateau, the region of the large rise was characterized by shallow-water conditions, indicating supposed existence of an island territory in this place.     

新疆卡拉麦里蛇绿岩带中硅质岩的放射虫化石

新疆卡拉麦里构造带在奇台县南明水地区可划分为三个岩石一构造单元：①北带，由中泥盆世复理石组成；②南带，由中泥盆世—早石炭世沉积岩—火山质碎屑岩组成；③蛇绿岩带。三者之间均为断裂接触。蛇绿岩套上部单元的红色硅质岩中发现丰富的放射虫化石，经鉴定，其时代确定为晚泥盆世法门期一早石炭世杜内期，代表卡拉麦里蛇绿岩形成的晚期年龄。     

Sedimentation on the Ionian active margin (Hellenic arc) — Provenance of sediments and mechanisms of deposition

Lithological, sedimentological, mineralogical and faunal analyses of twenty cores from the western Peloponnesus margin and adjacent Matapan Trench permit the origin of the sediments and the processes of sedimentation to be defined in some detail.Except for the ash layers derived from the Ischian Province, the major part of the sediment is local in origin (Peloponnesus). Analyses of heavy, light and clay minerals enable three main provinces to be distinguished. Each of these provinces includes one or more slope basins and a portion of trench, without lateral connection between them and mixing of inputs.The diversity and complexity of sedimentary structures, the granulometric characters, the mixed fauna (molluscs and ostracods) and the variability of rates of sedimentation all testify to the prevalence of reworking phenomena and gravitative processes.These data confirm and elaborate on the model of sedimentation deduced from seismic studies in which sediments are successively trapped, released by the slope basins and transferred via channels and canyons towards the underlying trench basins. This “cascade feeding” appears characteristics of this subductive sedimentary environment.     

The rift origin of the Vilyui basin (East Siberia), from reconstructions of sedimentation and mechanical mathematical modeling

Results of modeling of the formation of the Vilyui sedimentary basin are presented. We combine backstripping reconstructions of sedimentation and thermal regime during the subsidence with a numerical simulation based on the deformable solid mechanics. Lithological data and stratigraphic sections were used to “strip” the sedimentary beds successively and calculate the depth of the stratigraphic units during the sedimentation. It is the first time that the evolution of sedimentation which is nonuniform over the basin area has been analyzed for the Vilyui basin. The rift origin of the basin is proven. We estimate the spatial distribution of the parameters of crustal and mantle-lithosphere extension as well as expansion due to dike intrusion. According to the reconstructions, the type of subsidence curves for the sedimentary rocks of the basin depends on the tectonic regime of sedimentation in individual basins. The backstripping analysis revealed two stages of extension (sediments 4–5 km thick) and a foreland stage (sediments > 2 km thick). With the two-layered lithosphere model, we conclude that the subcrustal layer underwent predominant extension (by a factor of 1.2–2.0 vs. 1.1–1.4 in the crust). The goal of numerical experiments is to demonstrate that deep troughs can form in the continental crust under its finite extension. Unlike the oceanic rifting models, this modeling shows no complete destruction or rupture of the continental crust during the extension. The 2D numerical simulation shows the possibility of considerable basement subsidence near the central axis and explains why mafic dikes are concentrated on the basin periphery.     

滇西昌宁—孟连带西区两个地层问题——兼论昌宁—孟连带的闭合造山过程

对昌宁—孟连带西区的两个地层问题进行了讨论。根据牙形刺和放射虫的发现将原定为拉巴组的塔拉弄—南雅条带的时代厘定为晚泥盆世至早石炭世 ,时代大致与南皮河群的弄巴组或“中区”的“上泥盆统”相当 ,它们之间的确切关系仍有待进一步研究。怕拍组实际上主体属晚二叠世晚期 ,仅顶部可能包含有少量下三叠统印度阶最底部的沉积。对怕拍组的研究证实了澜沧运动的存在 ,昌宁—孟连带自此开始了由海洋盆地向造山带的演变进程 ,这一过程持续达七千万年之久。     

鲕粒粒度特征及其指示意义

沉积物的粒度资料是确定沉积环境的重要依据,一直以来多应用在碎屑岩方面,较少用于碳酸盐岩的分析。以北京西山寒武系张夏组鲕粒石灰岩为研究对象,在野外实测、室内薄片粒度统计的基础上,通过分析鲕粒粒度参数、粒度频率曲线及概率累积曲线特征,明确了鲕粒粒度在分析鲕粒灰岩沉积环境上的重要作用,并建立了下苇甸鲕粒粒度特征与鲕粒滩在空间上的耦合关系。研究结果表明:鲕粒粒径大小、分选系数、峰度及概率累积曲线组分截点可以很好地反映鲕粒沉积水动力环境;一般情况下,水动力环境较稳定的间歇高能滩沉积的灰泥鲕粒石灰岩鲕粒粒径较小,分选好,峰度尖锐,频率曲线主要为单峰态,鲕粒以悬浮搬运为主;水动力较为动荡的高能滩沉积的亮晶鲕粒石灰岩鲕粒粒径较大,分选较差,峰度多为平坦、中等,频率曲线主要为多峰态,概率累积曲线多为一跳一悬两段式;鲕粒的粒径与鲕粒圈层类型密切相关,粒径较大的鲕粒多以同心鲕、同心放射鲕为主,粒径较小的鲕粒多为放射鲕。研究结果为分析颗粒石灰岩的沉积环境提供了理论和依据。     

Structural and physiographic control on the Holocene marine sedimentation in the bay of Cadiz (SW Spain)

The Quaternary tectonic activity in the Gulf of Cadiz has considerably influenced the depositional regime and distribution of Holocene marine deposits. The aim of this work is to determine the nature of the recent sedimentary filling in the Bay of Cadiz sea bottom and adjacent continental shelf and to establish the main controlling factors on the Holocene marine sedimentation.

The sedimentary record indicates siliciclastic sedimentation supplied from the continent, with alternating episodes of high and low sedimentation rates. The recent sedimentary evolution of this marine area was controlled by the Late Quaternary eustatic fluctuations. Bathymetric, geophysical and drilling data have been employed to prepare a detailed isopach map of the non-consolidated recent sedimentary cover. Thickness distribution shows significant variations related to the infilling of former fluvial palaeochannels incised during the Late Pleistocene lowstand, and highly controlled by the structural neotectonic trends of faults and joints: NNW-SSE, NNE-SSW and ENE-WSW. The general distribution of isopachs in this area is clearly influenced by these morphostructural lines, which controlled the sedimentary processes during the Holocene. These results are coherent with the main regional neotectonic structures previously described in the nearby continental area, and confirm their prolongation towards the marine domain.     

Petrochemistry of Sandstones from the Siberian Hypostratotype of the Riphean in the Uchur–Maya Region

Based on 148 analyses, we report the petrochemical characteristics of Riphean and Vendian coarse-grained sedimentary rocks of the Uchur–Maya region in eastern Siberia, which is referred to the Proterozoic continental-margin domain. Various methods of petrochemical study applied to Precambrian sandstones are examined. Normative mineral compositions of specific groups of arenites, particularly basal potassic arkoses, are considered. Differences in sandstone compositions at certain stratigraphic levels are shown, and the evolution of chemical composition of rocks is traced through sections of sedimentary cover (Maya Plate) and margin region (Yudoma–Maya Trough). The work presents results of the application of data on mineralogical and chemical compositions of arenites for the restoration of paleodynamic environments in Late Proterozoic sedimentation basins at the southeastern margin of the Siberian Platform.     

On the Age of the Ophiolitic Complexes in Northeastern Jiangxi:A Micropaleontological Analysis

The age assignment of cherts from ophiolitic/metamorphic complexes in northeastern Jiangxi is widely regarded as one of the crucial issues in the tectonic interpretation of South China. The ophiolitic and metamorphic complexes in northeastern Jiangxi have been traditionally regarded as part of the Proterozoic “Banxi (=Penhsi) Group” of the Jiangnan Uplift. However, recent reports of Late Paleozoic radiolarians from the rock complexes have caused some researchers to question the traditional interpretation of the tectonic and paleogeographic framework in the region; but other workers are suspicious about these findings. In order to test the validity of the putative radiolarians, we, an interdisciplinary study group including micropaleontologists, tectonic specialists and regional geologists, conducted field investigations and multiple re-samplings of the localities where the reported fossils were collected. Our comprehensive study shows that the chert of the ophiolitic complex and the associated low-grade metamorphic slate yield Mesoproterozoic and Neoproterozoic acritarchs, confirming the traditional view of their age assignment (Proterozoic); on the other hand, no recognizable radiolarian fossils have been discovered therein, thus raising questions about the recently published result of Paleozoic radiolarian findings. Probable causes for the putative radiolarian findings are thus discussed herein. Geochemical characteristics indicate that the chert sedimentation most probably occurred under a continental margin setting.     

The Cambrian to Aquitanian geological record of the Longi-Taormina Unit (Calabria-Peloritani Arc,southern Italy): geodynamic implications

The Longi-Taormina Unit forms the “Dorsale calcaire” of the Peloritani Alpine Belt (southern Calabria-Peloritani Arc). It is made by a thick sedimentary cover of Meso-Cenozoic age overlying a Variscan weakly metamorphosed Cambrian to Carboniferous succession.

The Palaeozoic series consists of pelitic to arenaceous sediments containing layers of acidic and basic volcanics. The acidic volcanics are affected by the “Caledonian” compressional deformations and are referred to Early Ordovician. The basic rocks belong to two different volcanic cycles; the first, not dated, is ascribed to the Caledonian cycle according to its geochemical signature; whereas the second, middle-late Devonian in age, is interpreted to have formed in the framework of pre-Variscan extensional tectonics. During the Variscan Orogeny (330 Ma), the area recorded metamorphism up to subgreenschist-to-greenschist facies and two main deformation phases, marked by syn-schistose early folds (Dv₁), overprinted by dominantly NW-SE trending late folds (Dv₂).

During the Aquitanian, deformation related to the Alpine Orogeny led to imbrication of the Palaeozoic and Meso-Cenozoic series. The sedimentary cover was affected by a series of N090° to N130° trending folds. Detailed stratigraphical and structural investigations on the tectonic contact between the Longi-Taormina Unit, and the overlying Fondachelli Unit indicate that this structure is part of a frontal thrust ramp which developed during the Aquitanian.

Our geological and structural studies on the Cambrian to Aquitanian rocks of the Longi-Taormina Unit of the Calabria-Peloritani Arc enable to unravel the complex geodynamic history of the central-western Mediterranean area.     

Comparative analysis of the mineral and chemical compositions of black smoker smoke at the TAG and Broken Spur hydrothermal fields,mid-Atlantic ridge

The paper presents newly obtained data on the fluxes of hydrothermal-sedimentary material collected with sedimentation traps within 3 m from the bottoms of black smokers at the TAG and Broken Spur hydrothermal fields and reports the results of comparative analysis of the mineralogical and chemical compositions of this material. The sedimentary material deposited near the vent was determined to account to approximately 3% of the overall mass of the orebody. The results demonstrate that, in both cases, the trap material is characterized by high contents of ore components and ore-forming chemical elements (Fe, Cu, Zn, and Co), and Se, As, Sb, Ba, and P compared to tholeiitic basalts from which these elements are leached. However, the material of a more “mature” (having an age of 40–50 ka) hydrothermal spring at the TAG field contains 40% Fe hydroxides, in contrast to the material of a spring at the Broken Spur field (age <1000 yr) whose material is dominated by sulfides (72%) and contains much pyrrhotite. These springs also show principal differences between the enrichment coefficients for Se (by a factor of 4.8), As (3), Ca (4.1), and Si (5.2). These differences are thought to reflect various evolutionary stages of the circulating hydrothermal systems.     

Tectonostratigraphy of the Mesozoic complexes of the northwestern part of the Koryak Highland,Ust’ Belaya Mountains

New data on the structure, age, and composition of the tectonostratigraphic complexes of the western part of the Koryak Highland are presented. The conclusions on the sedimentation conditions are drawn and primary relations are interpreted for most complexes. New Kimmeridgian–Tithonian and Berriasian assemblages of radiolarians are established. Campanian radiolarians are found for the first time in the region.     

河北省滦县地区大红峪组沉积特征分析

河北省滦县地区大红峪组为野鸡坨镇至响棠镇一带中元古界沉积盖层的最底部层位,这与滦县地区在元古宙地处山海关古陆边缘的地理构造格局有关。根据"岩相一层序一沉积环境"的研究思路与方法,将大红峪组地层划分为碎屑岩型和碳酸盐岩型两种相序,两个由TST-HST体系域构成的层序。沉积环境表现为东南侧为山海关古陆,北西侧为浅海台地,沉积作用初期以河流作用为主,进而发展为潮汐作用为主,偶为浅水风暴作用。     

Stratigraphic Hiatuses in the Sedimentary Cover of the Ninetyeast Ridge

The Ninetyeast Ridge is one of the longest structures in the World Ocean. Owing to the seismostratigraphic analysis, three seismic complexes are distinguished in the sedimentary cover of this ridge, lower subaerial—shallow-water (SC3), transition (SC2), and upper deep-water (SC1), and nine reflectors: 0, 0a, 1, 1a, 2, 3, 4, 5, and F. On the basis of the results of correlation of seismic sections with those of deepwater sites recording the entire period of formation of the sedimentary cover of the Ninetyeast Ridge (Late Cretaceous—Quaternary), several nondepositional hiatuses are distinguished. The following reasons for these hiatuses are proposed. The hiatus in the beginning of the Early Paleocene coincides in time with the general decrease in the World Ocean level and is recorded only within the northern part of the ridge. The first “soft” collision of the Indian and Eurasian plates, as well as Paleocene—Eocene Thermal Maximum (PETM), could have been a reason for the most long-lasting hiatus in the Early—Middle Eocene in the northern and central parts of the Ninetyeast Ridge. The hiatus in the Early Oligocene is also distinguished in these parts of the ridge and is likely associated with underwater erosion. The formation of the Antarctic Circumpolar Current (ACC) and the change in the hydrodynamic regime of the Indian Ocean could have been reasons for the hiatus in the Middle Miocene, which is traced in the sedimentary cover throughout the entire Ninetyeast Ridge.     

再论“建始人”时代

就施林峰同志对湖北建始龙骨洞“建始人”的时代提出的异议进行讨论。哺乳动物化石、古人类化石和沉积速率研究表明,龙骨洞古地磁柱的两个正极性事件应与奥都威亚时和留尼旺亚时对比。     

Sedimentary cover and late Cenozoic history of the Okushiri Ridge (Sea of Japan)

A complex (petrographic, micropaleontological, and X-ray diffraction) investigation of the sedimentary cover on the northwestern slope of the Okushiri Ridge in the Sea of Japan revealed that its basal layers are of Oligocene age and composed of terrigenous silty-clayey sediments, which were deposited in coastalmarine environments with calm hydrodynamics and low sedimentation rates. The relative sea-level rise combined with regional tectonic processes at the early-middle Miocene transition resulted in widening and deepening of sea basins and accumulation of a thick diatomaceous-clayey sequence of middle-upper Miocene sediments. Tectonic activation in the Pliocene was responsible for development of the ridge and exhumation of rocks formerly occurring at depth of 500–1000 m.     

Age and formation conditions of the Co-rich manganese crust on guyots of the Magellan seamounts

Based on the analysis of planktonic and benthic foraminiferal assemblages, geological dating of the major elements of the section (layers) in the Co-rich manganese crust of the Magellan seamounts has been accomplished. The ore crust layers were formed at the following age intervals: layer I-1 in the Late Paleocene-Early Eocene, layer I-2 in the Middle-first half of Late Eocene, layer II in the Middle-Late Miocene, and layer III in the Pleistocene. Relict layers of the older crust, which underlies the main section in some places, are dated at the Campanian-Maestrichtian and Late Paleocene(?). Data on foraminifers generally fit the results obtained previously based on the analysis of nannoplankton assemblages. Insignificant discrepancies in the datings require further refinement and explanation. Biostratigraphic investigations of the sedimentary cover made it possible to identify the Aptian-Turonian, Campanian-Maestrichtian, Late Paleocene-Eocene, and Miocene rock associations and the unlithified Pliocene-Quaternary sediments. Comparison of the structure and composition of ore crust layers with the coeval rocks of the sedimentary cover revealed that layers I-1 and I-2 were deposited at depths corresponding to the shelf-upper bathyal zone (shallower than 600 m). Relict layers could be formed at even shallower depths up to the photic zone. The upper layers II and III were formed under nearly present-day conditions.     

Sedimentationsabläufe im Atlas-Golf (Kreide Küstenbecken Marokko)

The Geological Institute of Bonn University since 1975 investigates in connection with DSDP/IPOD the Cretaceous of the Atlantic coastal basin in south-western Morocco. 30 main stratigraphic sections and numerous auxiliary ones were taken along several traverses, running along distances of 150 to 200 km in west-east direction. The recognized epicontinental facies-pattern along the traverse of the southern High Atlas mountain range depicts clearly, that we cut here the critical region of intertonguing marine, fine-clastic-carbonaceous sediments and continental detritic deposits. The littoral zone successively progrades with three major transgressions (Neocomian, Upper Aptian, Turonian) towards the African Continent. Sedimentation processes, stratigraphy, paleomagnetics, geochemistry, sedimentology and paleogeography are investigated, taking selected horizons on one hand and complete stratigraphic columns on the other. A new sedimentation model reflecting transgression and regression events in the Cretaceous “Atlas Gulf” show some probabilities of eustatic sea-level changes. There are similarities between the Atlas Gulf and other coastal basins on both sides of the Atlantic Ocean. There are certain relations between the sedimentary record of the proand regrading littoral zone on the continent and in the nearby deep sea deposits. There is an exciting coincidence between the stratigraphie succession of the downwarping Atlas Gulf and the sedimentary cover of the interior of Africa, especially the Mesozoic Sahara Basin.     

The use of lanthanides for the reconstruction of Phanerozoic and Proterozoic sedimentation environments exemplified by sections in the cover and basement of the East European platform

Criteria were established for the estimation of the lanthanide composition of sedimentary complexes for the reconstruction of sedimentation conditions. The distribution of lanthanides was investigated in phosphorites and sedimentary rocks from the cover of the East European platform, and published data on the geochemistry of phosphorites from Eurasia were analyzed. Indicator lanthanide ratios were established for the determination of the climate and depth of sedimentation, and the possibility of the use of rare earth elements for the facies settings and transgression-regression cycles of sedimentation was demonstrated. The sedimentation conditions of the iron formations of the Proterozoic Kursk and Krivoi Rog sedimentary groups were inferred from the distribution of lanthanides: the hematite and magnetite quartzites are the deepest water complexes of the sedimentation profile; the climatic conditions of sedimentation were estimated as humid for shale subformations and humid-semihumid for iron formations; the depths of sedimentation in the Kursk basin was 50−300 m; the sources of iron were the material of weathering profiles and endogenous influx.     

塔里木东南缘早二叠世牙形刺的发现及其意义

首次于塔里木盆地东南缘洛浦阿其克克孜里奇曼组发现牙形刺，其中重要的有Ｎｅｏｓｔｒｅｐ－ｔｏｇｎａｔｈｏｄｕｓｐｅｑｕｏｐｅｎｓｉｓ和Ｓｗｅｔｏｇｎａｔｈｕｓｉｎｏｒｎａｔｕｓ，根据化石组合面貌，属Ｎｅｏｓｔｒｅｐｔｏｇｎａｔｈｏｄｕｓｐｅｑｕｏｐｅｎｓｉｓ带，其时代为二叠纪亚丁斯克期（Ａｒｔｉｎｓｋｉａｎ），说明塔里木盆地东南缘洛浦阿其克克孜里奇曼组应属早二叠世，而不是晚石炭世。