Lithological and hydrogeochemical role of the density convection in sedimentation basins with halogenous formations

This work treats lithofacies and hydrogeochemical features of the Late Paleozoic sedimentation on the eastern Russian Plate and the geochemistry of principal types of brines, which are spatially and genetically related to halogenous formations. It is shown that the density convection of primary magnesian chloride brines, which inflow into underlying Paleozoic and Proterozoic rocks from Permian evaporite paleobasins, plays the principal role in the formation of chlorocalcium brines that are predominant in the sedimentary cover of the Volga-Urals sedimentation basin. The problem of metamorpbization of brines by exchange-adsorption and hydrolytic processes in terrigenous rocks and the problem of metasomatic dolomitization of limestones are discussed.     

BASIN-RANGE TRANSITION AND GENETIC TYPES OF SEQUENCE BOUNDARY OF THE QIANGTANG BASIN IN NORTHERN TIBET

BASIN-RANGE TRANSITION AND GENETIC TYPES OF SEQUENCE BOUNDARY OF THE QIANGTANG BASIN IN NORTHERN TIBET     

辽宁省歪头山-北台地区太古代硅铁建造特征

歪头山-北台地区是太古代鞍山群火山-沉积岩系发育较完整地段.本文侧重于原岩建造和岩石类型讨论,并提出火山沉积岩系内沉积界面对铁矿的控制因素.     

The eastern flank of the Caspian Basin: Sedimentary complexes and sedimentation conditions in the Early-Middle Carboniferous

Carboniferous and Lower Permian Carbonate and terrigenous rocks with the total thickness of >4000 m serve as the productive units in the Paleozoic subsalt complex at the eastern flank of the basin surrounding the northern area of the present-day Caspian Sea (hereafter, Caspian Basin in the broad sense). In recent years, several large oil and gas-condensate fields were discovered in these rocks. The complexity of geological evolution of this region, which is situated at the junction between the East European Platform and the Ural orogen, as well as multiple changes of sedimentation conditions during the Middle and Late Paleozoic, are reflected in the diversity of types of terrigenous and carbonate sediments and their facies alterations. Reconstruction of these environments makes it possible to elucidate specific features of the location of reservoir rocks in vertical and horizontal sections, as well as regularities of variations in their filtration-capacitive properties.     

Permian marine sedimentation in northern Chile: new paleontological evidence from the Juan de Morales Formation,and regional paleogeographic implications

Permian marine sedimentary rocks that crop out in northern Chile are closely related to the development of a Late Paleozoic magmatic arc. A study of Upper Paleozoic units east of Iquique (20°S) identified three members within the Juan de Morales Formation, each of which were deposited in a different sedimentary environment. A coarse-grained terrigenous basal member represents alluvial sedimentation from a local volcanic source. A mixed carbonate-terrigenous middle member represents coastal and proximal shallow marine sedimentation during a relative sea-level rise related with a global transgression. Preliminary foraminifer biostratigraphy of this middle member identified a late Early Permian (late Artinskian–Kungurian) highly impoverished nodosarid–geinitzinid assemblage lacking fusulines and algae, which is characteristic of temperate cold waters and/or disphotic zone. The upper fine-grained terrigenous member represents shallow marine siliciclastic sedimentation under storm influence. The Juan de Morales Formation consists of continental, coastal and shallow marine sediments deposited at the active western margin of Gondwana at mid to low latitudes. A revised late Early Permian age and similar paleogeography and sedimentary environments are also proposed for the Huentelauquén Formation and related units of northern and central Chile, Arizaro Formation of northwestern Argentina, and equivalent units of southernmost Peru.     

新疆西准噶尔额敏前陆盆地的构造特征及其演化

西准噶尔吾尔喀什尔山与额敏盆地间的"盆"–"山"耦合关系清楚,盆地边界平行于造山带呈狭长带状展布。"山"区为志留系–石炭系海相陆源碎屑岩-火山岩沉积组合,"盆"区为二叠系陆相磨拉石与新近系红色砂砾岩及第四系河流阶地堆积,具有典型的海相-陆相双层结构。盆缘被巴尔雷克前陆冲断带围限,"山"区发育铲式逆冲断层与蛇头构造、叠瓦扇构造等逆冲推覆构造。表明该"盆"–"山"组合为一典型的前陆盆地系统。额敏前陆盆地形成于早二叠世,属后期冲断变形影响较弱、早期前陆盆地结构特征较明显的"早衰型"前陆盆地。这一成果为额敏盆地乃至西准噶尔盆地分析、构造演化、沉积作用、"盆"–"山"耦合等研究提供了重要信息。     

Petrogeochemical features of metaterrigenous rocks of the Kan Block of the Eastern Sayan: Reconstructions of provenances and sedimentation conditions

Chemical and isotopic compositions of Proterozoic metaterrigenous rocks of the Kan Block (Central and Idar terranes) of the Eastern Sayan are studied. The results of the reconstruction of their provenances and sedimentation conditions are presented. The rocks under investigation correspond by their petrogeochemical composition to graywackes of island arcs. The combination of geochemical and isotope data shows that sediments of the Central terrane had a local provenance represented by Early Proterozoic subduction magmatic complexes, whereas sediments of the Idar terrane formed probably as the result of mixing of terrigenous material related to the destruction of rocks of Meso-Neoproterozoic oceanic and more ancient continental crust.     

辽河西部凹陷雷家地区古近系沙四段混合沉积特征研究

雷家地区古近系沙四段广泛发育湖相碳酸盐与陆源碎屑混合沉积。通过对研究区混合沉积的区域地质背景、岩石学特征、沉积环境等分析,认为该区混合沉积特征为结构混合和互层混合,其中结构混合（狭义的混积岩）在不同构造部位混积岩岩石成分不同,西部以内源型混合沉积为主,中东部以陆源型混合沉积为主,局部为火山岩型混积岩。混合沉积作用类型包括渐变式混合沉积和复合式混合沉积Ⅰ类,局部发育突变式混合沉积。最后,分析本区白云岩的成因,进而探讨形成混合沉积的地质条件和沉积环境。     

二叠纪海平面变化研究

在研究全球不同地区二叠纪沉积、层序及生物资料基础上,通过全球诸大陆典型剖面层序划分和对比表明,二叠纪至少有６次海平面升降事件具全球对比意义。二叠纪全球海平面旋回曲线,在不同板块不同成因盆地,其形态及结构不同,但总体可分为两种类型或分支：一是以海相→陆相沉积序列为主的反映主体海平面下降的经典型或欧美型;二是以海相碳酸盐岩→碳酸盐－硅质岩沉积序列为特征的揭示主体海平面上升的特拉斯型或华南型。这与二叠纪特定的全球构造－古地理密切相关。     

内蒙古苏尼特左旗下二叠统大石寨组作用相与环境相序列演化

内蒙古苏尼特左旗地区下二叠统大石寨组火山沉积岩系的作用相类型主要包括爆发相、溢流相、爆发进流相、爆发沉积相、火山碎屑、陆屑风暴岩相、震积岩相；环境相类型主要包括滨海海滩、潮坪、浅海及近岸陆相。本文对它们的特征及识别标志进行了简述，并以达尔罕敖包东剖面为例，讨论了作用相与环境相序列演化的规律及其构造意义。     

Permian continental basins in the Southern Alps (Italy) and peri-mediterranean correlations

The Late Carboniferous to Permian continental successions of the Southern Alps can be subdivided into two main tectono-sedimentary Cycles, separated by a marked unconformity sealing a Middle Permian time gap, generally estimated at over 10 Ma. The lower cycle (1), between the Variscan crystalline basement and the Early Permian, is mainly characterised by fluvio-lacustrine and volcanic deposits of calc-alkaline acidic-to-intermediate composition, which range up to a maximum thickness of more than 2,000 m. The upper cycle (2), which is devoid of volcanics, is mostly dominated through the Mid?–Late Permian by alluvial sedimentation which covered the previous basins and the surrounding highs, giving rise to the subaerial Verrucano Lombardo-Val Gardena (Gröden) red-beds, up to about 800 m thick. The palaeontological record from the terrigenous deposits of both the above cycles consists mainly of macro- and microfloras and tetrapod footprints. The age of the continental deposits is widely discussed because of the poor chronological significance of a large number of fossils which do not allow reliable datings; however, some sections are also controlled by radiometric calibrations. The comparison with some selected continental successions in southern Europe allows to determine their evolution and set up correlations. A marked stratigraphic gap shows everywhere between the above-mentioned Cycles 1 and 2. As in the Southern Alps, the gap reaches the greatest extent during the Mid-Permian, near the Illawarra Reversal geomagnetic event (265 Ma). In western Europe, however, such as in Provence and Sardinia, the discussed gap persists upwardly to Late Permian and Early Triassic or slightly younger times, i.e. to the onset of the “Alpine sedimentary Cycle”, even though in northeastern Spain (Iberian Ranges, Balearic Islands) this gap results clearly interrupted by late Guadalupian–Lopingian deposits. The above two major tectonosedimentary cycles reflect, in our view, two main geodynamic events that affected the southern Europe after the Variscan orogenesis: the Late Carboniferous–Early Permian transformation of the Gondwana–Eurasia collisional margin into a diffuse dextral transform margin and the Middle–Late Permian opening of the Neotethys Ocean, with the onset of a generalised extensional tectonic regime and the progressive westward marine ingression.     

Tectonic Evolution of the Palaeo——Tethys in Changning——Menglian Belt and Adjacent Regions,Western Yunnan

The Changning-Menglian belt,located between theBaoshan-Gengma massif and the Simao-Lincangmassif in Western Yunnan,preserves the complete recordof a suture zone and the most continuous record of deepwater sedimentation,representing the main branch of thePalaeo-Tethys polyisland ocean in the Hercynian-Indo-sinian stage.This belt could be further subdivided into threetectono-lithofacies zones.In the east zone,terrigenouselastics,argillaceous,marl-argillaceous and silicate sediments lie on the metamorphosed Early Palaeozoic basement in concealed unconformity,representing deep watersediments on a passive continental margin.The centralzone,although the basement rocks are absent fromoutcropping here,includes a contemporary complexof various sedimentary types,among them one type is ofdeep ocean sediments represented by radiolarian beddedchert,appearing from at least early Early Devonian tothe Middle Triassic.Another type includes purecarbonates of the Early Carboniferous to the LatePermian,a type of shallow wa     

准南前陆冲断带烃源岩地质地球化学特征

准南前陆冲断带具有丰富的油气资源,但与资源评价关系密切的烃源岩研究不足。本文应用地球化学分析方法,对准南前陆冲断带的上二叠统、中下侏罗统、下白垩统和古近系等4套烃源岩的有机质丰度、有机质类型、热演化程度进行了系统分析和综合对比。结果表明,上二叠统烃源岩和中下侏罗统烃源岩为良好的烃源岩,古近系安集海河组其次,下白垩统烃源岩相对较差。     

猫场式黄铁矿矿床地质特征及成因探讨

在川滇黔交界地区二叠系峨眉山玄武岩被边缘地带,广泛分布着猫场式黄铁矿矿床(图1)。这一类型矿床具有典型特征,其成矿与峨眉山期火山岩密切相关,展布稳定,厚度大,品位较高,为我国西南硫矿带中佼佼者,颇具经济意义和地质找矿意义。     

Palaeoenvironments and weathering regime of the Neoproterozoic Squantum ‘Tillite’, Boston Basin: no evidence of a snowball Earth

The snowball Earth hypothesis describes episodes of Neoproterozoic global glaciations, when ice sheets reached sea‐level, the ocean froze to great depth and biota were decimated, accompanied by a complete shutdown of the hydrological cycle. Recent studies of sedimentary successions and Earth systems modelling, however, have brought the hypothesis under considerable debate. The Squantum ‘Tillite’ (Boston Basin, USA), is one of the best constrained snowball Earth successions with respect to age and palaeogeography, and it is suitable to test the hypothesis for the Gaskiers glaciation. The approach used here was to assess the palaeoenvironmental conditions at the type locality of the Squantum Member through an analysis of sedimentary facies and weathering regime (chemical index of alteration). The stratigraphic succession with a total thickness of ca 330 m documents both glacial and non‐glacial depositional environments with a cool‐temperate glacial to temperate non‐glacial climate weathering regime. The base of the succession is composed of thin diamictites and mudstones that carry evidence of sedimentation from floating glacial ice, interbedded with inner shelf sandstones and mudstones. Thicker diamictites interbedded with thin sandstones mark the onset of gravity flow activity, followed by graded sandstones documenting channellized mass gravity flow events. An upward decrease in terrigenous supply is evident, culminating in deep‐water mudstones with a non‐glacial chemical weathering signal. Renewed terrigenous supply and iceberg sedimentation is evident at the top of the succession, beyond which exposure is lost. The glacially influenced sedimentary facies at Squantum Head are more consistent with meltwater dominated alpine glaciation or small local ice caps. The chemical index of alteration values of 61 to 75 for the non‐volcanic rocks requires significant exposure of land surfaces to allow chemical weathering. Therefore, extreme snowball Earth conditions with a complete shutdown of the hydrological cycle do not seem to apply to the Gaskiers glaciation.     

Contrasting red bed diagenesis: the southern and northern margin of the Central European Basin

We compare the diagenetic evolution of deeply buried Rotliegend (Permian) red bed sandstones at the southern and northern margin of the Central European Basin (CEB) in Germany. Main target is to evaluate the influence of maturation products from hydrocarbon (HC) source rocks during red bed diagenesis. At the southern margin of the CEB, thick coal-bearing Carboniferous source rocks are omnipresent beneath the Rotliegend. They contain dominantly gas-prone terrigenous organic material and some oil source rocks. Hydrocarbons were generated from Late Carboniferous onwards throughout most of basin subsidence. At the northern margin of the CEB, source rocks are almost absent due to deep erosion of Carboniferous rocks and a low TOC of local Lower Carboniferous relics. Early diagenetic processes are comparable at both basin margins. Significant differences in burial diagenetic evolution are spatially correlated to the occurrence of hydrocarbon source rocks. Burial diagenesis at the southern margin of the CEB is characterized especially by bleaching of red beds, major dissolution events, pervasive illite formation, impregnation of pore surfaces with bitumen, and formation of late Fe-rich cements. Almost none of these features were detected at the northern basin margin. Instead, relatively early cements are preserved down to maximum burial depths. This suggests that major diagenetic mineral reactions in deeply buried red bed sandstones are controlled by the presence or absence of maturing hydrocarbon source rocks.     

准噶尔盆地二叠纪盆地属性的再认识及其构造意义

准噶尔盆地及其邻区野外剖面、钻井剖面的系统对比和地震剖面的精细解释表明,二叠系沉积演化、断裂控制沉积、箕状断-超反射特征及大地构造背景均显示,二叠纪准噶尔盆地是形成于张性背景下的断陷-裂陷盆地。准噶尔盆地及邻区火山岩地化特征、年代学数据及区域构造研究成果也证明,二叠纪是张性的大地构造背景。早二叠世—中二叠世早期以发育冲积扇沉积为特征,各构造部位的沉积环境差异较大,强烈断陷并逐渐形成坳隆相间的沉积格局,为断陷盆地的裂陷期;中二叠统中晚期由早二叠世隆坳分割的局面逐渐转化为统一的大型内陆湖盆,吐哈盆地与准噶尔盆地水体相通,形成统一的沉积体系,为断陷盆地扩张期;晚二叠世时期以出现冲积-河流相红色粗碎屑沉积为特征,准噶尔盆地和吐哈盆地分割自成沉积体系,是断陷盆地的萎缩期。因此,中生代盆地演化是建立在二叠纪张性背景的基础之上,二叠纪断陷-裂陷盆地的提出对重新认识中生代盆地演化历程将具有重要启示意义,也将对今后的油气勘探具有重要指导意义,值得进一步研究。     

断陷湖盆陡坡带油气成藏类型及其分布规律探讨

断陷湖盆陡坡带油气生、储、盖层的发育与陆相层序中的体系域具有一定的成因联系,不同的陆相层序样式可构成不同的生、储、盖层组合,综合考虑陆相层序储集体类型及其特征,将断陷湖盆陡坡带油气成藏类型归纳为三大类,八亚类,十种。它们分别是：岩性上倾尖灭,岩性下倾尖灭,岩性透镜体,岩性相变,地层不整合,地层削截,地层超覆,地层退覆,构造－岩性复合,构造－地层复合等油气成藏类型,这些油气成藏类型在断陷湖盆陡坡带陆相层序各个体系域中的分布具不均衡性,以水进体系域为最,其次为水退休系域和高水位体系域,低水位体系域较少,从陆相层序各体系域中成藏类型的空间展布规律来看,水进体系域是陆相断陷湖盆陡坡带油气勘探的重要目的层段。     

Volcanic rocks of the Khabarovsk accretionary complex,southern Far East Russia

The results of study of the volcanic rocks of the Khabarovsk accretionary complex, a fragment of the Jurassic accretionary prism of the Sikhote Alin orogenic belt (the southern part of the Russian Far East), are presented. The volcanic rocks are associated with the Lower Permian limestones in the mélange blocks and Triassic layered cherts. The petrography, petrochemistry, and geochemistry of the rocks are characterized and their geodynamic formation conditions are deduced. The volcanic rocks include oceanic plume basalts of two types: (i) OIB-like intraplate basalts formed on the oceanic islands and guyots in the Permian and Triassic and (ii) T(transitional)-MORBs (the least enriched basalts of the E-MORB type) formed on the midoceanic ridge in the Permian. In addition to basalts, the mélange hosts suprasubduction dacitic tuff lavas.     

云南砚山红舍克原生及堆积型铝土矿

红舍克铝土矿分为沉积和堆积型两类,受上二叠统(P2l)含矿层控制明显:沉积矿位于上段(P2l2)下部,堆积矿位于沉积铝土矿上覆层。