Lower Famennian conodont-based stratigraphy of the Pripyat Trough

Three conodont assemblages characterizing the standard triangularis, crepida, and rhomboidea zones can be defined in lower Famennian sections of the Pripyat Trough. The defined local conodont units include the Icriodus iowaensis, Palmatolepis wolskae-Palmatolepis circularis, Palmatolepis klapperi-Polygnathus semicostatus, Icriodus divergentus, and Palmatolepis subperlobata helmsi beds. The defined conodont assemblages are correlated with their coeval standard counterparts of the East European Platform. New conodont species and subspecies are described: Palmatolepis klapperi biparapetus, Polygnathus barskovi, Po. chegodaevi, Po. semeni, Po. inaequilateralis, Polynodosus nodocostatus productus, Icriodus divergentus, I. pushkini.     

Middle Devonian salt-bearing deposits of the Pripyat basin

This first correlation of the data on the Middle Devonian salt-bearing deposits of the Pripyat basin considers the spatial location of the rock-salt stratum, its composition, and the nature of the insoluble components, fii paleogeographlc respects, salt deposition on the East European Platform coincided with the beginning of the Hercynian orogenic cycle. This process took place in two subbasins: the Pripyat and the Moscow. The Pyarnu-Narova “microcycle” is r e garded as a rudimentary phase of rift formation In the Pripyat basin—Authors.     

Rb-Sr and K-Ar isotopic systems of the Upper Devonian sediments in the Pripyat Trough,Belarus

The results of Rb-Sr and K-Ar isotope studies of the Famennian upper salt and suprasalt complexes sampled from the core material of exploratory boreholes drilled at the northwestern margin of the Pripyat Trough (Belarus) are presented. The suprasalt and saliferous portions of the sequence define an age of approximately 470 Ma. Despite multiple reworking of the material, we interpret this value as preservation of the provenance “memory.” Regardless of the Sr content in sample, the strontium isotope ratios obtained for low-Rb minerals (celestine, carbonate, and halite) varies throughout the section within 0.7083–0.7095, indicating the preservation of some primary features of the matter. The lowest isotope values obtained are slightly higher than those inferred for the upper Famennian. This fact confirms the concept that the studied complex was formed in a shallow-water setting. Data on sylvites show that the present-day isotopic characteristics of potassium salts were formed significantly later.     

Carbon and Oxygen Isotopes and Formation Conditions of the Upper Famennian Shale-Bearing Rocks in the Pripyat Trough,Southern Belarus

The behavior of stable carbon and oxygen isotopes in carbonates during the deposition and diagenesis of sediments in the bioproductive Upper Famennian Pripyat Trough (southern Belarus) is discussed. Limestones and clayey limestones (Corg 0.92 ± 0.11%) are characterized by very low δ13C values (–9.6 ± 0.3‰). Parental sediments of these rocks were deposited in the shallow-water zone during slow downwarping episodes of the seafloor. Lithification of the sediments took place in oxidative conditions of the diagenesis zone. Organic matter was actively oxidized by free oxygen. Carbon dioxide with isotopically light organic carbon formed in this process was used during the crystallization of diagenetic carbonates that are visually indiscernible from the sedimentational variety. Marls, clayey marls, and carbonate-bearing clays (Corg 6.02 ± 0.80%) are characterized by δ13C values as high as –3.5 ± 0.6‰. In combustible shales (Corg >10%), δ13C value is ‒1.2 ± 0.6‰). The clayey rocks mark the episodes of sedimentation in relatively deep-water conditions that appear during the uncompensated sagging of the basin floor. The diagenetic zone with free oxygen was significantly decreased or absent at all. Here, oxygen of marine sulfates was the main or single oxidizer of organic matter (sulfate reduction). The sulfate oxygen is a weaker oxidizing agent than free oxygen. Therefore, much more organic matter was retained and fossilized in clayey rocks than in carbonate rocks. Organic carbon released during the sulfate reduction and mobilized later for the diagenetic carbonate formation was insufficient for the significant decrease of δ13C values relative to the marine carbonate standard. Isotopic composition of carbonate oxygen in the studied rocks is invariable and does not depend on the content of clay and organic matter. In these rocks, δ18O values are at the level (approximately –5‰) shown for the Famennian in the Global Chemostratigraphic Chart. This fact is consistent with the supposition that oxygen isotope composition of atmospheric precipitates, which influenced the rock formation via continental flow, is close to that of sea water in low latitudes where the territory of Belarus was located in the Late Devonian.     

华南上泥盆统法门阶哲杜斯贝动物群的埋藏学和居群动力学特征*

哲杜斯贝是一种以高丰度和低物种分异度为显著特征、在全球广泛独立分布的小嘴贝类。笔者对华南台地相和台间盆地相5个含哲杜斯贝类上泥盆统剖面进行沉积环境和埋藏特征研究,确定华南哲杜斯贝类的原生沉积环境为台地的正常浅水,这与美国和摩洛哥生长在冷泉环境中的哲杜斯贝不同,表明其既可在浅海环境中生长,也可以在冷泉环境中生长,具有较强的生态可塑性。台地相(原地埋藏)的3个哲杜斯贝种群具有以下特征:(1)均呈现出壳体呈层状紧密堆积、集群生长特点,丰度极高,并且有相当数量的个体呈现出由于拥挤生长而导致的壳体生长畸形现象;(2)缺乏其他底栖后生生物,显示了极低的生物多样性;(3)壳体大小—频率分布和生存曲线揭示了3个哲杜斯贝种群都具有非常低的幼年期死亡率特点,同时同一介壳层内哲杜斯贝个体大小均一,表明绝大多数的个体能够达到或接近自然寿命后死亡。上述证据表明,哲杜斯贝具有密集群居生活的习性,其生活在一个独特的、不适合其他后生底栖生物生存的环境。     

Carbon, oxygen, and sulfur isotope compositions of carbonate and sulfate rocks from the Famennian potassium-bearing subformation of the Pripyat trough

Peculiar features of evaporitic process at the stage of potassium accumulation are considered on the basis of carbon and oxygen isotope data on carbonate rocks and sulfur isotope data on anhydrite from the Famennian potassium-bearing subformation of the Starobin potassic salt deposit in the Pripyat trough. It was found that potassium accumulation was accompanied by the influx of continental waters and highly concentrated brines, while the formation of thick salt-free units was related to the replenishment of fresh seawater to the basin.     

Isotope-geochemical systematics of kimberlites and related rocks from the Siberian Platform

Using the ICP-MS method we have studied the isotope systematics of Sr and Nd as well as trace element composition of a representative collection of kimberlites and related rocks from the Siberian Platform. The summarized literature and our own data suggest that the kimberlites developed within the platform can be divided into several petrochemical and geochemical types, whose origin is related to different mantle sources. The petrochemical classification of kimberlites is based on persistent differences of their composition in mg# and in contents of indicator oxides such as FeO_tot, TiO₂, and K₂O. The recognized geochemical types of kimberlites differ from one another in the level of concentration of incompatible elements as well as in their ratios.Most of isotope characteristics of kimberlites and related rocks of the Siberian Platform correspond to the earlier studied Type 1 basaltoid kimberlites from different provinces of the world: Points of isotopic compositions are in the field of primitive and weakly depleted mantle. An exception is one sample of the rocks from veins of the Ingashi field (Sayan area), which is characterized by the Sr and Nd isotopic composition corresponding to Type 2 micaceous kimberlites (orangeites).The most important feature of distribution of isotopic and trace-element compositions (incompatible elements) is their independence of the chemical rock composition. It is shown that the kimberlite formation is connected with, at least, two independent sources, fluid and melt, responsible for the trace-element and chemical compositions of the rock. It is supposed that, when rising through the heterogeneous lithosphere of the mantle, a powerful flow of an asthenosphere-derived fluid provoked the formation of local kimberlite chambers there. Thus, the partial melting of the lithosphere mantle led to the formation of contrasting petrochemical types of kimberlites, while the geochemical specialization of kimberlites is due to the mantle fluid of asthenosphere origin, which drastically dominated in the rare-metal balance of a hybrid magma of the chamber.     

Correlation of Devonian rocks

The Mount Black lead‐zinc deposit at Cooleman Plains, southern New South Wales, occurs in the uppermost part of the moderately folded, weakly metamorphosed, Upper Silurian Cooleman Limestone. A joint‐controlled collapse‐breccia zone interpreted as a palaeokarst structure has been partly replaced by quartz, sphalerite, galena, and a little chalcopyrite, pyrite, marcasite, tetrahedrite, arseno‐pyrite, and mackinawite. These minerals show evidence of having encrusted and replaced limestone fragments in the breccia. Oxidic Zn, Pb, Cu, and Fe minerals have formed by the near‐surface oxidation of the sulphides.

Petrographic and field evidence indicates that the quartz and sulphides were deposited mainly by encrustation and precipitation from saline solutions (possibly diagenetically expelled connate brines) in cavities, probably at low temperature at shallow depth. The deposit has many similarities to Mississippi Valley‐type lead‐zinc deposits.     

The geochemical features of terrigenous host rocks at massive sulfide deposits in the eastern Caucasus

Based on a great body of factual data, geochemical peculiarities in the distribution of rare, noble, radioactive, and other trace components in the Lower-Middle Jurassic terrigenous ore-enclosing (hereafter, host) rocks at massive sulfide deposits in the Vostochnyi (eastern) segment of the Greater Caucasus are high-lighted. Study of the Filizchai base metal massive sulfide deposit made it possible to define general regularities of element distribution in the ore body and altered wall rocks that reflect the general geochemical zonality. Concentrations of most components depend on the lithology and wall-rock alteration, distribution of rocks in the section, proximity of the contacting ore, and its mineral composition. Contents of typical elements in host rocks are closely associated with their concentrations in the ore bodies.     

Organic matter in Upper Devonian deposits of the Chernyshev Ridge

The study provides the first data on organic matter from Upper Devonian deposits of the Shar’yu River section (Chernyshev Ridge, Northern Urals). Oil shales from the Middle and Middle–Upper Domanik intervals and carbonaceous shales from the Upper Frasnian intervals were analyzed. The biomarker analysis revealed similar characteristics of organic matter from studied samples and Domanik-facies rocks of the Ukhta area. It was also shown that organic matter from the studied Domanik section is characterized by compositional heterogeneity. The biomarker and stable carbon isotope compositions of bitumen extracts, their fractions, and kerogen of the Middle and Middle–Upper Domanik shales are different from those of the Upper Frasnian shale, which may indicate the variation in depositional setting.     

冲绳海槽北、中段火山岩地球化学特征及其地质意义

为去除非火山物质对样品化学性质的影响，得到火山岩真实的地球化学及同位素组成数据，作者对采自冲绳海槽的酸性火山岩样品严格的前处理，其中海槽北段火山岩同位素数据以前还未见公开报道。根据所得U系同位素组成数据及其分布规律分辩混染物中俯冲板片的成分，结合Sr-Nd同位素组成，本文对海槽火山活动的岩石种类、物质来源和岩浆演化过程作了一些初步的讨论。结果表明，冲绳海槽酸性火山岩分布广泛，为钙碱性系列岩石，碱性弱（里特曼指数〈1．8）；海槽岩浆主要源于地幔，源区同位素组成类似PREMA地幔，结晶分异作用是演化过程中最主要的地质作用，但岩浆也受到了不同程度地受到上地壳与／或俯冲板片物质的混入；根据混合模拟结果将海槽火山岩大致分成以上地壳物质混染为主和上地壳-俯冲板片混染两类，且认为上地壳混染发生在岩浆演化的晚期，此时岩浆体系SiO2含量要高于混染物。     

Geochemical features of ore fluid for gold deposits related to alkaline rocks in China

Fluid inclusion studies of 5 gold deposits connected with alkaline rocks show that quartz separated from auriferous quartz veins contains abundant three-phase CO2-NaCl-H2O inclusions and two-phase CO2-dominated ones,measuring 5-20um in diameter,Homogenization temperatures of the fluid inclusions are mostly within the range of 150-300℃,and the salinities,mainly 0.2wt%-12 wt%(NaCl),Gold mineralizations occurred at depths of 1.4-2.8km,The most striking character of fluid composition is that among the cations,Na^ in dominant,followed by K^ ,Ca^2 ,among the anions,Cl^- is slightly higher than SO4^2-,In the evaporate,H2O is dominant,followed by CO2,The pH values are mainly within the range of 6.5-8.5,indicating that the ore-forming solutions are alkaline in nature.The hydrogen and oxygen isotopic ratios indicate that the ore fluid is composed mainly of magmatic water.With the dropping of temperature in the ore fluid,the contents of CO2 decreased while the salinity increased.The relations between Au and other components of the ore fluid are discussed in the paper,and it is concluded that in these deposits,Chlorides,H2S,SiO2,CO2,etc.in the fluid all are involved in the migration and concentration of Au.     

Isotopic Composition of Oxygen and Carbon and Formation Temperature of Accessory Minerals from Evaporitic Sediments in the Pripyat Trough

The isotopic composition of oxygen and carbon was studied in accessory carbonates and quartz separated from salts in Upper Devonian halogenous formations of the Pripyat Trough (Belorus). It is established that isotopic characteristics vary in a wide range. Values of ¹⁸O vary in the following range (SMOW): from 18.2 to 29.2 in calcites, from 15.7 to 32.5 in dolomites, and from 17.4 to 27.2 in quartz. Values of ¹³C range from –13.4 to 1.4 in calcites and from –11.1 to 1.7 in dolomites (PDB). Results obtained indicate highly variable isotope-geochemical conditions of sedimentation and early diagenesis during the formation of evaporitic sediments. Accessory minerals were repeatedly formed in a wide temperature range and probably at various stages of the lithogenesis.     

Upper lithospheric seismic velocity structure across the Pripyat Trough and the Ukrainian Shield along the EUROBRIDGE'97 profile

We present new results on the structure resulting from Palaeoproterozoic terrane accretion and later formation of one of the aulacogens in the East European Platform. Seismic data has been acquired along the 530-km-long, N–S-striking EUROBRIDGE'97 traverse across Sarmatia, a major crustal segment of the East European Craton. The profile extends across the Ukrainian Shield from the Devonian Pripyat Trough, across the Palaeoproterozoic Volyn Block and the Korosten Pluton, into the Archaean Podolian Block. Seismic waves from chemical explosions at 18 shot points at approximately 30-km intervals were recorded in two deployments by 120 mobile three-component seismographs at 3–4 km nominal station spacing. The data has been interpreted by use of two-dimensional tomographic travel time inversion and ray trace modelling. The high data quality allows modelling of the P- and S-wave velocity structure along the profile. There are pronounced differences in seismic velocity structure of the crust and uppermost mantle between the three main tectonic provinces traversed by the profile: (i) the Pripyat Trough is a ca. 4-km-deep sedimentary basin, fully located in the Osnitsk–Mikashevichi Igneous Belt in the northern part of the profile. The velocity structure is typical for a Precambrian craton, but is underlain by a ca. 5-km-thick lowest crustal layer of high velocity. The development of the Pripyat Trough appears to have only affected the upper crust without noticeable thinning of the whole crust; this may be explained by a rheologically strong lithosphere at the time of formation of the trough. (ii) Very high seismic velocity and Vp/Vs ratio characterise the Volyn Block and Korosten Pluton to a depth of 15 km and probably also the lowest crust. The values are consistent with an intrusive body of mafic composition in the upper crust that formed from bimodal melts derived from the mantle and the lower crust. (iii) The Podolian Block is close to a typical cratonic velocity structure, although it is characterised by relatively low seismic velocity and Vp/Vs ratio. A pronounced SW-dipping mantle reflector from Moho to at least 70 km depth may represent the Proterozoic suture between Sarmatia and Volgo–Uralia, the structure from terrane accretion, or a later shear zone in the upper mantle. The sub-Moho P-wave seismic velocity is high everywhere along the profile, with the exception of the area above the dipping reflector. This velocity change further supports a plate tectonic origin of the dipping mantle reflector. The profile demonstrates that structure from Palaeoproterozoic plate tectonic processes are still identifiable in the lithosphere, even where younger metamorphic equilibration of the crust has taken place.     

广西大厂法门期岩相古地理与锡多金属矿的关系

广西大厂法门期岩相古地理与锡多金属矿的关系李酉兴，雷元青（桂林冶金地质学院，广西桂林，５４１００４）广西大厂代化组（相当于法门阶）为一套条带状灰岩和扁豆状灰岩岩组，厚达２６５．７ｍ，含有竹节石、牙形刺和介形虫等化石。对１３个剖面中代化组的１６个特征变...     

Deformation and metamorphism of Devonian rocks in the outer Solund area, western Norway: implications for models of Devonian deformation

Many modern accounts of the Devonian rocks of western Norway, which emphasise the extensional processes by which the basins were formed, tend to ignore or gloss over the deformation and metamorphism which these rocks have suffered during contractional deformation. The present account describes extensive ductile folding, penetrative cleavage formation and low-grade regional metamorphism developed in the Devonian strata of the outer Solund region. Although the deformation in this area is more intense than in other Devonian basins, it belongs to the same movement plan. It will also be shown that the Devonian rocks of the Scandinavian Caledonides apparently share a common tectonothermal development. This regional contractional event, conceptually, may relate either to a Mid-Late Devonian arc-continent collision, or to a transpressional strain regime.