The Middle and Upper Devonian in southeastern flank of the Siberian platform (Southern Verkhoyansk Region,Sette-Daban Mountain Range)

Data on Middle and Upper Devonian deposits studied in southeastern flank of the Siberian platform are considered. A scheme of stratigraphic zoning in the study region is presented. Nineteen sedimentological and biotic events, which are recorded in the studied sections, are of the regional, interregional and global ranks. Their connection with eustatic sea-level fluctuations is established. Sections of the formation and regional horizon stratotypes and parastratotypes are described. The revision of species Mucrospirifer novosibiricus (Toll) is carried out.     

Chronology of landscape evolution and soil development in the upper Flinders River area,Queensland, based on isotopic dating of Cainozoic basalts

Victorian granites containing more than 750 ppm Ba are almost entirely confined to the region between a line from Geelong to Swan Hill and the Wonnangatta Fault Zone. Granite Ba contents normalised to 70% SiO₂ range from 620 to 733 ppm in western Victoria, 719 to 1560 ppm in central Victoria and 493 to 689 ppm in eastern Victoria. Melting of Ba-rich (meta)sedimentary rocks in the lower – middle crust is implicated in the petrogenesis of central Victorian S types, at least. Thus, granite geochemistry supports the concept of some sort of (largely concealed) Ba-rich Selwyn Block beneath central Victoria, although the boundaries that have been proposed for the block are modified here. There is a strong possibility that the Selwyn Block is an exotic terrane emplaced by northwest-directed strike-slip movement during the Bindian Orogeny. Such movement appears to have been controlled by the previously postulated Baragwanath Transform and another fundamental fault here called the Ulrich Transform. Asthenospheric upwelling related to movement on the Ulrich and Baragwanath Transforms may be the explanation for the twin belts of 400 Ma plutonism occurring to the west of the former and to the east of the latter. The southern extension of the Ulrich Transform may be the Tamar – Tiers structure in Tasmania. Plate-tectonic models suggesting Ordovician – Silurian subduction in Victoria need to be carefully revisited given the possibility of Siluro-Devonian exotic terrane emplacement.     

Le magmatisme basique calcoalcalin d'âge dévono-dinantien du nord du Massif Central,témoin d'une marge active hercynienne: arguments géochimiques et isotopiques Sr/Nd

Abstract

Samples of volcanic rocks from the main outcrops of Devono-Dinantian series in northern Massif-Central have been studied for Sr and Nd isotopes and immobile incompatible trace elements. In addition, two intrusive bodies of dioritic composition have been dated at 365 ± 3 Ma (Aydat) and 360 ± 1 Ma (Beaumont-Huriel), using the U/Pb zircon method. Together with geochemical data, these ages show that all the studied rocks belong to the same igneous episode. Based on trace element and radiogenic isotopes (⁸⁷Sr/⁸⁶Sr_i from 0,7041 to 0,7057; εNd_i from +1.5 to +5.0), the Late Devonian and Early Carboniferous igneous rocks bear distinct similarities with magmas produced in modern active margin settings. Combined with independent evidence for the occurrence of Devonian oceanic lithosphere in the northern branch of the Variscides, these geochemical affinities suggest that southward subduction of oceanic crust prevailed during the Late Devonian in northern Massif-Central. As a corollary, it appears that true continent-continent collision did not occur before Early Carboniferous times. © 2002 Éditions scientifiques et médicales Elsevier SAS. All rights reserved.     

Palaeosols and palaeokarst beneath subaerial unconformities in an Upper Devonian isolated reef complex (Judy Creek), Swan Hills Formation,west‐central Alberta,Canada

Subaerial unconformities are used widely for palaeoenvironmental and palaeogeographic reconstructions, sequence stratigraphy and petroleum reservoir assessments. Recognition and interpretation of these unconformities, particularly those with associated palaeosols, may be problematic in Lower and Middle Palaeozoic carbonate successions because of the collective effect of limited land plant development, superficial similarities between some pedogenic and marine features, and overprinting by later diagenesis. The isolated Judy Creek reef complex in the Lower Frasnian Swan Hills Formation in west‐central Alberta, Canada, contains two subaerial unconformities, R0.5 and R4, which formed as a consequence of relative sea‐level falls of at least regional scale. Deposits beneath these unconformities have distinctive palaeosol and palaeokarst features. The lower unconformity, R0.5, occurs at the top of a progradational reefal phase of stromatoporoid rudstones–floatstones and peloidal packstones–grainstones and has been recognized in at least one other isolated Swan Hills reef complex (Snipe Lake). Palaeosol–palaeokarst profiles beneath this unconformity extend as deep as ca 2 m below the unconformity. These profiles are characterized by the presence of small rhizoliths, laminar calcretes, ferroan dolomite glaebules, desiccation cracks, breccias, green shale and solution vugs. The upper unconformity, R4, occurs at the top of a backstepping phase of reef growth and has been correlated widely between isolated reefs and carbonate banks on both the western and eastern shelves of the Central Alberta Basin. Palaeosol–palaeokarst profiles, extending as deep as ca 9·5 m beneath the R4 unconformity, are distinguished by abundant, sub‐horizontal desiccation cracks filled with green shale, occurring in peloidal wackestones–packstones. Comparison of the R0.5 and R4 profiles indicates that the major intrinsic controls on the development and modification of the profiles are parent‐material lithology, particularly the prior degree of induration and particle size; the low topographic relief at the top of the reef interior; and limited vegetation of the exposed reef top due to unfavourable growth conditions and geographic isolation. In addition to climate, the major extrinsic controls are the extent of relative sea‐level fall, estimated to be 2·5 to 3 m and 13 to 14 m associated with the R0.5 and R4 unconformities, respectively, and the degree of shoreface erosion during the ensuing marine transgression, estimated to be up to 3 m. This study highlights the complex interplay of mainly physical and chemical processes influencing the formation of subaerial unconformities in carbonate environments during the Devonian, before major evolutionary innovations among vascular land plants led to more intense pedogenesis.     

东昆仑三道湾流纹英安斑岩锆石U-Pb年龄及其地质意义

东昆仑格尔木河西三道湾流纹英安斑岩构成火山通道侵出相,侵入到纳赤台群哈拉巴依沟组碎屑岩系中,其形成时代对于造山带火山作用的研究和限定哈拉巴依沟组地层时代均具有重要的意义。采用激光烧蚀多接收器电感耦合等离子体质谱(LA-MC-ICP MS)方法,对三道湾流纹英安斑岩进行了锆石U-Pb定年,结果表明,流纹英安斑岩中25个岩浆锆石206Pb/238U加权平均年龄为425.9 ± 2.6 Ma,它被解释为流纹英安斑岩的结晶年龄,说明三道湾次火山岩所代表的火山通道为早古生代造山晚期牦牛山组火山岩形成时的火山喷发中心之一,而非晚侏罗世次火山岩。野外地质关系和次火山岩年龄可以限定哈拉巴依沟组形成于中志留世之前。      

Extrinsic and intrinsic forcing of fluvial development: understanding natural and anthropogenic influences

This paper introduces a special issue arising from the biennial meeting of the Fluvial Archives Group (FLAG) that took place in September 2008 in Budapest, Hungary. Combining a two-day conference and three-day field excursion, this meeting provided an excellent opportunity for presentation and discussion of recent advances in research on fluvial evolution from the Plio-Pleistocene to the historical period. This editorial seeks to place these advances within the contexts both of long-term geomorphological research and the achievements of FLAG. It thus highlights progress towards a better understanding of fluvial responses to internal and external (including anthropogenic) forcing. It also points out some of the main obstacles, which can be targeted as goals for further research. Typically these relate to observed discrepancies in fluvial system responses, such as in patterns of lateral erosion and the timing of terrace incision, despite apparently similar fluvial parameters. Possible explanations for these discrepancies are mentioned, and the potential of new methods (especially in geochronology and modelling) to clarify such discrepancies is underlined. Finally the editorial provides brief reviews of the ten papers in this special issue (many of them developed from presentations in Budapest), which cover various areas in Europe (Hungary, England, Germany, Portugal, Russia), Asia (India) and South America (Bolivian Andes), placing them, in turn, within the context of this wider review of fluvial research.     

西藏俄卡地银多金属异常区地球化学

异常形态、分布严格受推覆断裂控制,范围大、浓集中心明显,浓度变化及因子载荷表明。区内找Ag、Pb有利,而Sb又为其最佳指示元素。     

滇西潞西上芒岗卡林型金矿

上芒岗金矿赋存于二叠系沙子坡组碳酸岩和侏罗系勐戛组下段砂岩、灰岩中,明显受上芒岗断裂控制,与美国模式卡林型金矿极为相似,具有相同的物质来源和成因模式。上芒岗地区具有广阔的深部找矿前景。     

森林沼泽景观区中大比例尺化探找矿工作方法的研究--记大梁金矿的发现

大梁金矿是通过森林沼泽景观区开展1：50000和1：25000地球化学测量及综合地质工作而发现的,证明采用的森林沼泽景观中大比例尺化探方法是行之有效的.     

岩盐及芒硝中各种化合物质量分数的计算

本文以等物质的量的反应规则建立了岩盐、芒硝中各种化合物的质量分数的计算公式。这些公式既符合法定计量单位的要求，又方便计算。