Qinling Faunal Region-The Third Ordovician Faunal Region: International Correlation

The Ordovician conodont faunal provinces were previously divided into the Midcontinent and Atlantic Faunal Regions situated respectively in low and high latitudes, where warm- and cold-water type conodont faunas flourished respectively. According to the international correlation this paper proposes the third Ordovician conodont faunal region-Qinling Faunal Region, in which cold-water conodont faunas were well developed in the Early to middle Middle Ordovician and warm-water conodont faunas were well developed in the late Middle and Late Ordovician, indicating that the Qinling Region was situated in high latitudes earlier and in low latitudes later. The origin was only due to plate movement In the Qinling Region the time interval of the change of the conodont fauna from the cold- to warm-water type was 4 Ma (from 474 to 470 Ma), during which the fauna geographically spanned 40° of latitudes, with a movement velocity of nearly 1.12 m/a, indicating that the high-latitude plates were divorced and reduced i     

The subsolidus segregation of layer-parallel quartz-feldspar veins in greenschist to upper amphibolite facies metasediments

Abstract Layer-parallel (i.e. parallel to foliation or bedding) vein formation in the graywackes and pelites of the Quetico Metasedimentary Belt occurred during synchronous prograde metamorphism and regional (D₂) compression. In a traverse across metasediments which change in metamorphic grade from greenschist to upper amphibolite (migmatite) facies, layer-parallel veins show the following trends: (1) an increase in thickness and internal complexity, the latter due to successive boudinage; (2) low-grade veins are parallel to planes of anisotropy due to the original sedimentary fabric of the host rocks, but at higher grades other sites are also used and (3) a systematic increase in plagioclase/quartz ratio in the veins towards higher grade, adjacent mafic selvedges first exhibit quartz depletion then, in the amphibolite facies, plagioclase depletion. Mineralogical zoning is often preserved in a single vein, older parts are more quartz-rich than younger. Mass balance calculations and whole-rock geochemistry based on veins, mafic selvedges and country rock are consistent with a closedsystem subsolidus segregation origin. The layerparallel veins are syntectonic, and migration of the mobile components required to form their mineralogy is a stress-induced mass transfer. The source of these components appears to be dominantly pressure solution of the same minerals in the host rocks, although metamorphic reactions may also have contributed. Veins nucleated first at those sites where initial sedimentary heterogeneites, such as fine-scale graded bedding, provided gradients of normal stress across grain boundaries, and hence of chemical potential, necessary to drive the subsolidus segregation process. The earliest veins are thus parallel to bedding. Later, nucleation of the veins could also occur along more randomly distributed sites within the metasediments, and these veins grew parallel to the schistosity rather than bedding, if the two were distinct. Once formed, the veins themselves, which are more competent than the surrounding rock, provide the stress heterogeneity required for their further growth. The increasing plagioclase/quartz ratio in the veins may be due to a temperature dependent increase in plagioclase component mobility relative to quartz. Alternatively, the increasing transfer distances for silica, resulting from prior quartz depletion in the inner parts of the mafic selvedge, may increase the relative mobility of plagioclase component.     

Bases Of the Chronological Classification with Special Reference to the Palaeozoic Stratigraphy of China

正 In conclusion, the chronological classification should base upon the followiag three bases:1. Cycle of Sedimentation2. Diastrophism3. Faunal AssemblageThe old classification mainly based upon palaeontological ground is not satisfactory, while the new classification of Grabau based on pulsation the     

Bottom water and benthonic foraminifera in the North Atlantic—Glacial-interglacial contrasts

Today, below 2500 m, benthonic foraminiferal faunas in the North Atlantic are dominated by a few species. Faunal composition changes slowly with increasing depth and decreasing temperature. Surface sediment and down-core counts of benthonic foraminifera reported by Phleger, Parker, and Peirson (1953) in the reports of the Swedish Deep-Sea Expedition have been supplemented by additional bottom sediment and piston core samples. Present-day benthonic foraminiferal assemblages from the deeper portions of the North Atlantic appear to be controlled more by the distribution of bottom water types than by bathymetry. In most piston cores, the assemblages vary greatly during the last 150,000 yr, suggesting depression and elevation of faunas at the core site through a depth range of several hundred meters. This would indicate that bottom water characteristics have shifted back and forth in this interval of time and, therefore, that bottom circulation partakes in the well-documented shifts recorded for surface waters of the North Atlantic. It appears that dense water, similar to present-day North Atlantic Deep Water, was produced over a wide area north of 45° N during cooler intervals and that it spread widely at depth.     

Development of slaty cleavage in a mudstone unit from the Cantabrian Mountains, northern Spain

A 200 m thick mudstone unit in the Carboniferous of the Cantabrian Mountains, northern Spain, exhibits an increase in intensity of the slaty cleavage from top to bottom which appears to be correlated with a decrease in the mean grain size, average bed thickness and quartz: mica ratio. Anastomosing cleavage domains, formed by pressure solution and by kinking and rotation of the detrital micas, become closer spaced, wider and more continuous towards the finer-grained base of the unit. Growth of strongly oriented new micas within the cleavage domains also appears to be correlated with the intensity of the domain development and hence with the initial lithology. Clay minerals have been completely replaced throughout the mudstone by muscovite, paragonite and pyrophyllite during low-grade metamorphism. The growth of an oriented mica fabric, however, is restricted to samples with well-developed cleavage domains.     

Thermal structure of the crust and upper mantle of Romania

A synthesis of the heat-flow data for Romania enabled a study of the thermal regime of the crust and upper mantle to be made. This showed lateral thermal differences between various tectonic units. The thermal structure of the crust and upper mantle appears to be mainly the result of mantle convection and plate interaction in the studied area.     

Evolutionary history of hoofed mammals during the Oligocene–Miocene transition in Western Europe

The biostratigraphy and diversity patterns of terrestrial, hoofed mammals help to understand the transition between the Palaeogene and the Neogene in Western Europe. Three phases are highlighted: (1) the beginning of the Arvernian (Late Oligocene, MP25-27) was characterised by a “stable” faunal composition including the last occurrences of taxa inherited from the Grande Coupure and of newly emerged ones; (2) the latest Arvernian (Late Oligocene, MP28-30) and the Agenian (Early Miocene, MN1-2) saw gradual immigrations leading to progressive replacement of the Arvernian, hoofed mammals towards the establishment of the “classical” Agenian fauna; (3) the beginning of the Orleanian (Early Miocene, MN3-4) coincided with the African-Eurasian faunal interchanges of the Proboscidean Datum Events and led to complete renewal of the Agenian taxa and total disappearance of the last Oligocene survivors. Faunal balances, poly-cohorts and particularly cluster analyses emphasise these three periods and define a temporally well-framed Oligocene–Miocene transition between MP28 and MN2. This transition started in MP28 with a major immigration event, linked to the arrival in Europe of new ungulate taxa, notably a stem group of “Eupecora” and the small anthracothere Microbunodon. Due to its high significance in the reorganisation of European, hoofed-mammal communities, we propose to name it the Microbunodon Event. This first step was followed by a phase of extinctions (MP29-30) and later by a phase of regional speciation and diversification (MN1-2). The Oligocene–Miocene faunal transition ended right before the two-phased turnover linked to the Proboscidean Datum Events (MN3-4). Locomotion types of rhinocerotids and ruminants provide new data on the evolution of environments during the Oligocene–Miocene transition and help understand the factors controlling these different phases. Indeed, it appears that the faunal turnovers were primarily directed by migrations, whereas the Agenian transitional phase mainly witnessed speciations.     

Correlation of the Kimmeridgian succession of the Normandy coast,northern France with that of the Dorset-type area,southern England

The Kimmeridgian Stage is represented in the cliffs of the Dorset-type area and those in Normandy by richly fossiliferous marine mudstones and limestones. Taken together, these coastal exposures provide the only complete composite outcrop through this part of the Jurassic in the Sub-boreal Faunal Province. Detailed correlations between the two successions are presented here: these enable the Normandy-coast sections to be more accurately placed than previously within in their regional chronostratigraphical context. The Normandy succession is more completely exposed than that in Dorset, and is situated midway between Dorset and the Sub-Tethyan succession of the Berry region. It therefore offers a better prospect than any English section for inter-province correlation at this stratigraphical level. To cite this article: R. Gallois, C. R. Geoscience 337 (2005).     

Refinement of the age of the Middle Miocene Fort Ternan Beds,Western Kenya,and its implications for Old World biochronology

It has become increasingly obvious over the past two decades that the fossiliferous strata at Fort Ternan, Kenya, are probably somewhat younger than 14 Ma, an age which has long been attached to the deposits. This realisation flows from geological and biochronological observations. In order to test the hypothesis, resampling of all the lava flows in the region of Fort Ternan was undertaken in 2003, especially those underlying the Fort Ternan Beds in the Kipchorion Gorge where the sequence is the most complete. Samples obtained from lava flows underlying and overlying the fossil beds were analysed for anorthoclase K/Ar and ⁴⁰Ar/³⁹Ar and biotite ⁴⁰Ar/³⁹Ar age determinations. The results reveal that the age of the fossiliferous sediments is ca $13.7\pm 0.3\text{Ma}$. Since Fort Ternan yielded the ‘core fauna’ that defines Faunal Set IV of the East African biochronological sequence this refinement of its age will impact on age estimates of neighbouring Faunal Sets, as well as on other faunas correlated to Fort Ternan, including those in Europe belonging to MN Zones MN 5, MN 6 and MN 7/8. To cite this article: M. Pickford et al., C. R. Geoscience 338 (2006).     

古新世/始新世全球增温在西藏岗巴地区的表现

随着深海钻探计划(DSDP)和大洋钻探计划(ODP)的开展,在古海洋学领域取得了许多重大发现。古近纪古新世与始新世(P/E)界线间的地质事件的发现便是其重要成果之一。西藏南部岗巴地区发育有良好的海相界线地层。对生物群、碳、氧、锶稳定同位素以及磁化率的研究显示,全球界线事件在西藏南部岗巴地区具有明显的影响。古新统宗浦组顶部底栖有孔虫动物群阶段性绝灭,总灭绝率为69%。始新统遮普惹组底部有孔虫逐渐复苏,除12种为古新世的残存类型外,始新世生物组合全为新的属种,并呈现三个复苏阶段。碳稳定同位素表现为三期负向偏移,在界线处出现-4‰的异常。这一异常与全球碳稳定同位素事件表现一致。锶同位素在界线位置没有明显的变化,而明显的峰值出现在界线之上,并与全球53Ma出现的锶同位素变化相对应。磁化率在界线之上2m处出现一个很明显的波动,与第3期碳同位素异常吻合。所有研究结果表明,西藏南部(特提斯-喜马拉雅低纬度浅海环境)在古新世与始新世界线时期出现明显的气候变化,说明全球深海温度增高在浅海环境具有相同表现,只是影响时间较长。     

迁移条件下磷污染红土的宏微观特性研究

以云南红土为研究对象,以六偏磷酸钠为污染源,通过磷污染红土的土柱迁移试验,探讨了土柱不同位置深度磷污染红土的宏微观特性。试验结果表明:随着土柱位置深度的增加,磷污染红土的相对质量、黏粒含量减小,液限、塑限和塑性指数中上部存在最小值;新生成不稳定的-钠铁矿,红土中磷的含量在中上部出现最大值,土柱表层氧化亚铁的含量最大;其微结构图像由上部致密的鳞片状单元向中部松散的凝块状进而向下部紧密的蜂凝状单元变化,对应孔隙比在中上部存在最大值;浸泡液的铁铝离子浓度随迁移时间延长而增大,渗流液中存在痕量的铁铝离子。磷与红土的作用机理可以从磷土间所存在的水解、吸附络合、还原氧化、成盐等作用过程来解释。其综合作用的结果改变了磷污染红土的宏微观特性。     

Distribution of the Permian Monodiexodina in Karakorum and Kunlun and its Geological Significance

The Permian fusulinoidean genus Monodiexodina is widely distributed in east Tethys.The genus might be an important indicator for the northern margin of Gondwana in northwestern China, but this is disputed.Monodiexodina-bearing areas can be restored as in either northern or southern middle latitudes with a symmetrical distribution between a high latitudinal,cool/cold water climatic realm and a paleotropical,warm water realm.Permian strata bearing Monodiexodina in Karakorum, Muztag Pear,and Buka Daban Pear...     

The geochemistry of iron in puget sound

The distribution of dissolved iron, ferrous iron and acid-reducing agent soluble iron has been investigated in the main basin of Puget Sound and its tributaries. Essentially all measurable iron in Puget Sound can be removed by filtration through 0.8 μm membrane filters, thus dissolved iron must be less than about 20 nM (our limit of detection). We could also detect no ferrous iron in Puget Sound. This is due to the rapid kinetics of oxidation of Fe(II). Our measured rate constant for the kinetics of oxidation suggests that strong ferrous-organic matter complexes do not exist in Puget Sound pore waters.The distribution of acid-soluble iron is low at mid-depth and increases toward the air-water and sediment-water interface and appears to be controlled by inputs from the rivers and the sediments. Only a small fraction of the river load appears to make it through the estuaries because the magnitude of the surface concentrations is smaller than predicted based on the calculated river flux. The “dissolved” iron in the rivers appears to be actually fine colloidal particles that coagulate before the salinity exceeds 5%. The increase towards the sediments is probably due to resuspension of botton sediments perhaps augmented by iron diffusing out of the sediments to form new iron oxide particles.     

Equivocal carbonatite markers in the mantle xenoliths of the Patagonia backarc: the Gobernador Gregores case (Santa Cruz Province,Argentina)

Amphibole ± phlogopite ± apatite-bearing mantle xenoliths at Gobernador Gregores display modal, bulk-rock and phase geochemical characteristics held as indicators of carbonatitic metasomatism. However, part of these xenoliths has high TiO₂/Al₂O₃ and those displaying the most pronounced carbonatitic geochemical markers modally trend towards harzburgite. Bulk-rock, clinopyroxene and amphibole show Zr, Hf and Ti negative anomalies, which increase at decreasing Na₂O and high field strength elements (HFSE) concentrations. Steady variation trends between xenoliths which have and do not have carbonatitic characteristics suggest a control by reactive porous flow of only one agent, inferred to be initially a ne-normative hydrous basalt (because of the presence of wehrlites) evolving towards silica saturation. Variation trends exhibit cusps when amphibole appears in the mode. Appearance of amphibole may explain the Ti anomaly variations, but not those of Zr and Hf. Numerical modelling [Plate Model (Vernières et al. in J Geophys Res 102:24771–24784, 1997)] gives results consistent with the observed geochemical features by assuming the presence of loveringite. Modest HFSE anomalies in the infiltrating melt may be acquired during percolation in the garnet-facies.In memory of Carlo Rivalenti     

Attenuation in Southeastern Carpathians area: Result of upper mantle inhomogeneity

The systematic analysis of seismograms recorded on the Romanian territory using Vrancea intermediate-depth earthquakes shows a strong asymmetric pattern relative to the epicentral area: on one side, in the Transylvanian Basin and the Eastern Carpathians (approximately along the inner volcanic chain), the amplitudes are reduced by a factor of 20 on average and the high frequencies are attenuated, in contrast with the other side, in the foreland platform. This pattern is explained by a significant attenuation increase caused by a strong lateral variation of the structure in the upper mantle, immediately towards NW of the Vrancea seismic active volume. This region corresponds to the most recent volcanic activity in the Persani Mountains and with the low-velocity body adjacent toward NW to the high-velocity body subducted beneath Vrancea area as indicated by seismic tomography and heat flow results. The CALIXTO'99 tomography experiment, deployed for 6 months in 1999, provides the largest number of observations for Vrancea earthquakes ever recorded on the Romanian territory. We select data from 8 earthquakes generated in this time interval in the Vrancea nest, which were recorded with signal / noise ratio greater than 5 by at least 25 stations. All of them are small- to moderate-magnitude events (3.6 ≤ M_w ≤ 4.2). The attenuation is much more important in the high-frequency range (> 1 Hz), than at low frequencies. Since the large Vrancea earthquakes can radiate significant energy in the low-frequency range (< 1 Hz), our results show that the seismic hazard level is much more uniform all over the Romanian territory in the low-frequency range than in the high-frequency range.     

Crystallographic and chemical variations during pyritization in the upper Barremian and lower Aptian dark claystones from the Lower Saxonian Basin (NW Germany)

In the Lower Saxonian Basin, cores from three drill holes provide a cross-section from the basin centre towards the margin through the upper Barremian/lowermost Aptian pyritic claystones and marls. Microscopic analyses distinguish six types of pyrite (I: ‘cones and tubes’, II: ‘tubes’, III: ‘isometric crystal aggregates’, IV: ‘pseudomorphs of fossils’, V: ‘star-like concretions’, and VI: ‘filiform pyrite-marcasite intergrowths’) which are associated with subordinate amounts of Fe carbonate, chalcopyrite, sphalerite and wurtzite. The crystal morphology of these sulphides shows a clear-cut diagenetic sequence from pyrite crystals dominated by the octahedron to those dominated by the cube. Among these early to late diagenetic pyrites, the conversion of crystal habits is accompanied by a striking variation in trace element contents, some of which have extremely low values (e.g. Au, Se, Te, Tl, Co). In this context, classification of crystal habits and analyses of As and Ni establishes a sequence of pyritization which may help define a basin zonation for these argillaceous sedimentary rocks, categorized as ‘normal facies’—oxygenated bottom waters—interrupted by short episodes of bottom water oxygen depletion (‘bituminous facies’). Substitution of the cube for the octahedron in the Fe bisulphide aggregates led to a continuous removal of As and Ni from the pyrite, attesting to a steady decrease of those elements in the pore fluids with time. By contrast, within each type of pyrite, As and Ni contents increase from the margin towards the centre of the basin, owing to pre-concentration of both elements in the basinal sediments, which are more abundant in organic matter. Some other elements, however, such as Mn, Cu, Sb and Ag, do not follow this trend and are unrelated to the lattice transformation of the Fe bisulphides. Their sometimes anomalously high quantities in Fe bisulphides are controlled by the host rock chemistry (presence of volcaniclastic material) and accessory minerals intergrown with pyrite (e.g. chalcopyrite). Pyrite I through III formed in tubular hollows of burrowing organisms, and type IV in tests of fossils. Types V and VI did not result from replacement or void filling but were generated by diffusion of sulphate along inhomogeneties, such as bedding planes, shrinkage cracks or water escape structures.     

Distribution of the Permian Monodiexodina in Karakorum and Kunlun and its Geological Significance

The Permian fusulinoidean genus Monodiexodina is widely distributed in east Tethys. The genus might be an important indicator for the northern margin of Gondwana in northwestern China, but this is disputed. Monodiexodina-bearing areas can be restored as in either northern or southern middle latitudes with a symmetrical distribution between a high latitudinal, cool/cold water climatic realm and a paleotropical, warm water realm. Permian strata bearing Monodiexodina in Karakorum, Muztag Pear, and Buka Daban Pear of the east Kunlun Mountains can be correlated with each other. Faunal analyses and the stratigraphical position of Monodiexodina-bearing strata indicate that both Karakorum, east Kunlun, and the Pamirs were formed in a cool temperate sea area of the northern hemisphere in middle latitudes during the Permian, rather than at the Gondwana margin.     

The geology of the Llanuwchllyn to Llanymawddwy area,south gwynedd,north wales

A geological map of the Caradoc rocks of the Llanuwchllyn to Llanymawddwy area is presented and the geology of the area described in detail. Hitherto unrecorded outcrops provide important stratigraphical evidence which is used to redraw the Caradoc-Ashgill Series boundary and many of the formational boundaries within the Caradoc Series. The stratigraphy of the area is revised to conform with the standard classification of the Caradoc Series in the Bala region. The only modifications are as follows: the Llaethnant Siltstone is proposed as a formational name for a group of beds which are broadly equivalent to the Glyn Gower Formation but which represent a distinct facies. The greater part of the Nod Glas Formation north of Dinas Mawddwy is shown to be laterally equivalent to the upper part of the Gelli-grin Formation; it is also subdivided into two members, the Dyfi Mudstone and the Corris Shale, differentiated on lithological and faunal grounds. The stratigraphy of the Dinas Mawddwy area is also amended. Faunal elements (genera) new to the Caradoc Series of this area, and to Wales, are noted.     

Paleo-oceanography of the Norwegian Sea during the past 130,000 years: coccolithophorid and foraminferal data

Faunal, floral and sedimentological properties of Norwegian Sea core V27-86 were examined in order to reconstruct the paleo-oceanographic history of this region. Downcore variations in the relative abundance of three microfossil groups and several sediment properties exhibit three different climate response patterns (CRP). Each pattern is judged to represent the response of a different part of the climate system. The covariance patterns among coccoliths, henthic foraminifera, and other properties suggest that the Norwegian Sea has been ice-free and productive during the present interhlacial. the penultimate interglacial (isotopic-stage se) and at least partially ice-free during an intermediate climatic regime (stages sa-d). A maximum change in these measures occurs at the boundary between isotopic stage 5a (an intermediate climatic regime)and isotopic stage 4 (a glacial climatic regime). In contrast, planktic foraminiferal assemblages and oxygen isotope measurements on planktic foraminifera show a major change at the end of stage 5e (the penultimate interglacial). The contrasting behavior of these two sets of observations is explained by a model which postulates a low-salinity surface layer 115,000 to 75,000 years ago (stages 5a-d).