Late Triassic fluvial and marine shelf succession, Quebrada Doña Inés Chica, Atacama region, northern Chile

A 400-meter-thick volcanic and fine-grained clastic sedimentary succession in Quebrada Doña Ines Chica (26°07′S latitude; 69°20'W longitude) provides a record of Late Triassic deposition in the Atacama region of northern Chile. The strata are conformably overlain by fossiliferous marine limestones and sandstones of Late Triassic to Early Jurassic (Sinemurian) age which contain the oldest ichthyosaur remains known from Central and South America. The clastic succession is interpreted as coastal fluvial deposits, with the overlying limestones representing shelf deposits.     

Actualistic approaches to the systematics and facies relations of clastic karst deposits

Clastic karst deposits occur at different positions within karst areas, whereas surface karst deposits, sediments of the crack filling facies, the cave entrance facies and the inner cave facies have to be distinguished. The karstification itself is of minor importance for the formation of clastic deposits. Except for incasional debris and impure limestones or marls the contribution of carbonate rocks to clastic karst deposits is low. The majority of clastic material is allogenic and siliciclastic.

Regarding the depositional processes cave sediments can be divided into fluvial cave deposits, gravitative or percolative deposits, decomposition deposits and rock breakdown. An actualistic approach could be a useful tool for the identification of fluvial cave deposits. By means of the depositional features of recent cave sediments and classical sedimentological features cave deposits of unknown origin can be classified.     

A sedimentological and stable isotopic study of travertines and associated sediments within Upper Triassic lacustrine limestones, South Wales, UK

The Upper Triassic in South Wales is composed of up to 100 m of red, dolomitic mudstones of the Mercia Mudstone Group which overlie and are laterally equivalent to basin margin coarse clastic deposits. In the Sully Island and Dinas Powys areas, a series of carbonate deposits was laid down within small basins adjacent to the main Bristol Channel Basin. The rocks consist of dolomites containing replaced evaporites, overlain by perilittoral freshwater limestones. The limestones are fenestral intrasparites and contain abundant pedogenic and stromatolitic horizons, as well as locally developed travertines. Evidence for vadose diagenesis within the limestones is common. The travertines consist of sheets of fibrous calcite (flowstone) associated with pisoids and flöe calcite. Most of the travertines consist of single sheets several millimetres in thickness although ‘mounds’up to 1 m in height and 5 m in diameter are also present. The topmost metre of the limestones, which has been dolomitized, is deformed into tepee and megapolygonal structures. The carbon and oxygen stable isotopic composition of the limestones suggests that they were precipitated in low salinity waters. Successive samples from individual bands of flowstone show a covariance of δ¹⁸C and δ¹³C which is consistent with the mixing of resurgent groundwaters with pools of more evolved waters at the surface. The sedimentological and geochemical evidence suggests that the limestones were deposited in a small, enclosed basin fed by upwelling meteoric groundwaters in an environment distinct from that in which the laterally equivalent gypsiferous red mudstones were formed.     

山西交口县庞家庄铝土矿矿物学与地球化学研究

山西交口县庞家庄铝土矿属于典型的喀斯特型铝土矿,矿体赋存于上石炭统本溪组,其下部为中奥陶统灰岩。矿石以隐晶质结构为主,含少量碎屑结构与鲕粒结构;矿石的结构特征显示一些风化物质经过了一段距离的搬运,并且矿体在晚期遭受了构造变形作用。x射线衍射分析显示铝土矿石中的主要组成矿物为硬水铝石、高岭石、赤铁矿、针铁矿、方解石与少量...     

Ordovician rocky shoreline deposits–the basal Trenton Group around Quebec City,Canada

Around Quebec City the lowest Trenton Group sediments rest directly upon a highly irregular Precambrian surface and represent the deposits of a high-energy, irregular, rocky shoreline which developed as the Ordovician sea onlapped a major positive topographic feature known as Montmorency Promontory. The complicated lithofacies mosaic developed along this shoreline consists of: (1) Arkosic sandstones, representing reworked regolith and marginal marine elastics; (2) Solenopora gravels, which comprise partly reworked colonies from the bare rock substrate and partly reworked algal maerls; (3) Fine-grained limestones, which were deposited in low energy environments between and in the lee of numerous islands and shoals; (4) Skeletal limestones, representing island fringing shoals and ephemeral beaches, with extensive thickets of the ramose bryozoan Hallopora; (5) Bryozoan liméstones, which represent low-energy, subtidal deposits with abundant delicate bryozoans; and (6) Coquina limestone lenticles, which accumulated in channels cut into the subtidal Bryozoan limestones. The absence of older Ordovician and Cambrian sediments in the vicinity of Quebec City indicates that Montmorency Promontory at the time of deposition of these Trenton deposits was probably manifested as a rugged archipelago. This represented the remnant of large-scale topographic highlands which had developed at the continental margin during the late Precambrian in association with extensional rifting, transform faulting, and the inception of the Iapetus Ocean. Gradual subsidence of this topographic high and the development of the rocky shoreline relates to the subsequent development of a compressional system and initiation of ocean closure in the early Middle Ordovician.     

黑龙江多宝山、铜山大型斑岩铜(钼)矿床中辉钼矿的铼-锇同位素年龄

黑龙江多宝山、铜山大型斑岩铜（钼）矿床的成岩成矿年龄以往确定主要为华力西中晚期至印支期（３１１－２１９Ｍａ），本次研究测得辉钼矿ＲｅＯｓ等时线年龄为５０６±１４Ｍａ。它和用其他方法测定的同位素年龄有较大差别，从而为进一步讨论矿床的成矿作用提供了新的线索，推断此数据可能反映辉钼矿源岩下奥陶统酸性火山碎屑岩的年龄。研究还发现辉钼矿中１８７Ｏｓ的含量特高，且估算储量很大，具有巨大的潜在经济价值。     

Interplay between shoreline migration paths, architecture and pinchout distance for siliciclastic shoreline tongues: evidence from the rock record

Facies, geometry and key internal stratigraphic surfaces from eight Cretaceous and Eocene clastic shoreline tongues have been documented. The regressive parts of all the studied tongues represent storm‐wave influenced strandplains, deltas or fan‐deltas, and the regressive shoreline trajectories varied from descending to ascending. The transgressive parts of the tongues are dominated by either estuarine or coastal‐plain deposits. The distance from the coeval, up‐dip non‐marine deposits to the basinward pinchout of amalgamated shoreface sandstones, measured along depositional dip, is here termed the sand pinchout distance. The study shows that the angle of regressive‐to‐transgressive turnaround (defined by the angle between the regressive and subsequent transgressive shoreline trajectories) and the process regime during turnaround largely control the sand‐pinchout distance. The amount of transgressive erosion can also partly control the pinchout distance, but this parameter was comparable for the different examples presented here. If the type of depositional system at turnaround and the depth of transgressive erosion are constant, small angles of turnaround are associated with large pinchout distances, whereas larger angles of turnaround result in smaller pinchout distances. The model developed allows sand‐pinchout distance to be predicted, using data for the landward parts of shoreline tongues. The dataset also shows that steeply rising (aggrading) shoreline trajectories tend to produce more heterolithic sandstone tongues than those formed by lower‐angle trajectories.     

豫西太原组、山西组中潮道沉积的类型和特征

豫西太原组中的潮道为陆表海滨岸潮道类型,其特点为:向上变细的层序,冲刷切割下伏的灰岩层,具大型板状、槽状交错层理和双向交错层理,潮道曲流砂坝发育。山西组下段的潮道为障壁后潮道,位于障壁砂坝后的潮坪区;潮道砂岩泥质杂基较高,正粒序,砂体自海向陆分叉尖灭;潮坪、潮道等亚环境组合影响了其上发育的煤层的厚度变化。山西组上段的潮道为下三角洲平原潮道类型,多位于分流河口,砂岩为正粒序,双(单)粘土层和潮汐周期层序发育。     

西藏措勤盆地中侏罗世—早白垩世沉积充填特征

位于班公湖 怒江缝合带与雅鲁藏布江缝合带之间的措勤盆地,在中侏罗世—早白垩世期间具有以且坎古昌 阿索裂谷带为沉积、沉降中心向南北两侧展开的古地理格局:①中晚侏罗世时期,裂谷带内由深水浊积岩、放射虫硅质岩和浅水碳酸盐岩、碎屑岩岩片及基性—超基性岩等组成;裂谷带两侧由滨浅海相碎屑岩和碳酸盐岩组成。该期盆地古地理演化具有先变深后变浅的沉积序列。②早白垩世早中期,裂谷带内仍由基性—超基性岩、深水复理石碎屑岩及放射虫硅质岩和浅水碳酸盐岩及碎屑岩组成;裂谷带两侧的日松革吉它日错分区主要由浅海相碎屑岩和灰岩组成;盆地南北部的措勤 申扎分区和木嘎岗日分区主要由滨岸 三角洲相碎屑岩及火山岩组成。各相带在纵向上均具有向上变深沉积序列。③早白垩世晚期,盆地以台地相碳酸盐岩沉积为主,裂谷带附近以发育台地边缘礁滩相沉积;裂谷带两侧的日松 革吉 它日错分区主要由开阔台地相灰岩组成;盆地南北部的措勤 申扎分区和木嘎岗日分区由局限台地相灰岩和陆源进积碎屑岩组成。     

The genesis of calcite in carbonate rocks of the sedimentary basins: Evidence from the stable carbon and oxygen isotopes composition

The distributions of stable carbon and oxygen isotopes in modern and ancient limestones of various types were studied. Carbonate samples from modern sediments were collected in the Black and Barents Seas. Ancient carbonates were represented by Upper Jurassic (Kimmeridgian-Tithonian) limestones from the central part of the West Siberian basin. Carbonate samples include remains of modern and Upper Jurassic fauna, carbonate crust from sediments of the Black Sea, carbonate tube from sediments of the Barents Sea, and Upper Jurassic limestone from the carbonate layer found at top of Abalak, bottom of Bazhenov deposits in the central part of the West Siberian basin. According to the results of the isotope analysis and comparison with modern carbonates, Upper Jurassic limestones of the West Siberian basin belong to the group of methane-derived carbonates and precipitated as a result of anaerobic oxidation of methane (AOM). Fractures in limestones are filled with secondary calcite.     

Facies model of a mixed clastic–carbonate,wave‐dominated open‐coast tidal flat (Tithonian–Berriasian,north‐east Spain)

Detailed logging and analysis of the facies architecture of the upper Tithonian to middle Berriasian Aguilar del Alfambra Formation (Galve sub‐basin, north‐east Spain) have made it possible to characterize a wide variety of clastic, mixed clastic–carbonate and carbonate facies, which were deposited in coastal mudflats to shallow subtidal areas of an open‐coast tidal flat. The sedimentary model proposed improves what is known about mixed coastal systems, both concerning facies and sedimentary processes. This sedimentary system was located in an embayed, non‐protected area of a wide C‐shaped coast that was seasonally dominated by wave storms. Clastic and mixed clastic–carbonate muds accumulated in poorly drained to well‐drained, marine‐influenced coastal mudflat areas, with local fluvial sandstones (tide‐influenced fluvial channels and sheet‐flood deposits) and conglomerate tsunami deposits. Carbonate‐dominated tidal flat areas were the loci of deposition of fenestral‐laminated carbonate muds and grainy (peloidal) sediments with hummocky cross‐stratification. Laterally, the tidal flat was clastic‐dominated and characterized by heterolithic sediments with hummocky cross‐stratification and local tidal sandy bars. Peloidal and heterolithic sediments with hummocky cross‐stratification are the key facies for interpreting the wave (storm) dominance in the tidal flat. Subsidence and high rates of sedimentation controlled the rapid burial of the storm features and thus preserved them from reworking by fair‐weather waves and tides.     

A CONTRIBUTION TO THE GEOCHEMISTRY OF RESERVOIR FORMATIONS: THE LOWER FRASNIAN OF THE VOLGA-URALS (Part 1 of 3)

The hydrocarbon concentrations in rocks of Frasnian, Givetian, and Famennian age are considerably higher than the concentrations in other units in the Devonian section of the Volga-Ural province, U. S. S. R. The maximum hydrocarbon concentration occurs in the Domanik, which is the host for the largest accumulation of ancient organic material on the Russian platform.

The correlation of hydrocarbon A with oils and other hydrocarbons and with organic carbon is very low. Trace elements are distributed uniformly throughout clastic sediments and differentially in precipitates, including clays, marls, and limestones. Iron, manganese, phosphorus, copper, and strontium concentrations increase as the host rocks become more clastic; chromium, niobium, and cobalt decrease. This difference is an additional criterion for mapping ancient pelagic zones and shoreline. However, weathering may lead to artificial concentrations for the various elements.     

Allogenic and autogenic controls on facies and stratigraphic architecture of the Lower Jurassic Mashabba Formation,Gebel Al-Maghara,North Sinai,Egypt

The Lower Jurassic Mashabba Formation crops out in the core of the doubly plunging Al-Maghara anticline, North Sinai, Egypt. It represents a marine to terrestrial succession deposited within a rift basin associated with the opening of the Neotethys. Despite being one of the best and the only exposed Lower Jurassic strata in Egypt, its sedimentological and sequence stratigraphic framework has not been addressed yet. The formation is subdivided informally into a lower and upper member with different depositional settings and sequence stratigraphic framework. The sedimentary facies of the lower member include shallow-marine, fluvial, tidal flat and incised valley fill deposits. In contrast, the upper member consists of strata with limited lateral extension including fossiliferous lagoonal limestones alternating with burrowed deltaic sandstones. The lower member contains three incomplete sequences (SQ1-SQ3). The depositional framework shows transgressive middle shoreface to offshore transition deposits sharply overlain by forced regressive upper shoreface sandstones (SQ1), lowstand fluvial to transgressive tidal flat and shallow subtidal sandy limestones (SQ2), and lowstand to transgressive incised valley fills and shallow subtidal sandy limestones (SQ3). In contrast, the upper member consists of eight coarsening-up depositional cycles bounded by marine flooding surfaces. The cycles are classified as carbonate-dominated, siliciclastic-dominated, and mixed siliciclastic-carbonate. The strata record rapid changes in accommodation space. The unpredictable facies stacking pattern, the remarkable rapid facies changes, and chaotic stratigraphic architecture suggest an interplay between allogenic and autogenic processes. Particularly syndepositional tectonic pulses and occasional eustatic sea-level changes controlled the rate and trends of accommodation space, the shoreline morphology, the amount and direction of siliciclastic sediment input and rapid switching and abandonment of delta systems.     

New Evidence for Hydrothermal Sedimentary Genesis of the Ni‐Mo Deposits in Black Rock Series of the Basal Cambrian,Guizhou Province: Discovery of Coarse‐Grained Limestones and its Geochemical Characteristics

The molybdenum-nickel deposits in Shuidong District of Nayong County (Guizhou Province, Southwest China) are found mainly in black shale series of Lower Cambrian Niutitang Formation, which is another Mo-Ni-rich region besides Zunyi District (Guizhou province). Our systematic study on the Mo-Ni deposits in Tangjiaba of Nayong reveals that layered coarse-grained limestones, spherical beaded limestones concretions are hosted at the lower seam of the Mo-Ni deposits. Its strong negative carbon isotope anomaly (the carbon isotope value of the coarse-grained limestones varies from ?2.148‰ to 8.223‰) is similar to that in the modern submarine black smoker chimney. The carbon in the coarse-grained limestones from black rock series of Nayong County might be deep source inorganic carbon. The seams, coarse-grained limestones, ore-bearing coarse-grained limestones and the roof and floor of the deposits are characterized by co-variation on the trace element spider diagram, showing good homology. The extraordinary enrichment of Ag, As and Sb resembles hydrothermal sedimentation. Pro-Earth's core elements Se is strongly enriched in Ni-Mo ore-bearing coarse-grained limestones. The ore-bearing rock series has an extremely low Th/U value (0.012–0.19); in the logU-logTh Cartesian Coordinates, the samples of the roof and floor of the deposits and ore-bearing coarse-grained limestones are found in the East Pacific tise; and the samples of coarse-grained limestones are found between the paleo-hydrothermal dedimentary area and the East Pacific tise. The chondrite-normalized rare earth element patterns of the Ni-Mo deposits show LREE enrichment, Ce negative anomaly, and Eu negative anomaly (which is supposed to be influenced by the deep magmatic processes in an extensional environment) resembles the rare earth element distribution patterns of the fluid and its sediments in modern submarine hydrothermal system. It proves that coarse-grained limestones is characterized by typical hydrothermal limestones, being closely related with the genesis of Mo-Ni deposits in Nayong County, which provides new evidence for hydrothermal sedimentary genesis of Mo-Ni deposit and negative carbon anomaly in the basal Cambrian on a global scale.     

Pb-isotope evidence for the origin of lead in strata-bound Pb-Zn deposits in triassic carbonates of the Eastern and Southern Alps

A comparison of ore-lead isotope ratios of Pb-Zn deposits hosted in Triassic carbonates of the Eastern and Southern Alps with the isotopic composition of trace leads of their host rocks, of Triassic volcanics, and of the underlying clastic sediments shows that these rocks could have supplied only part of the ore lead. The isotopic signature of feldspar lead from crystalline basement rocks, however, reveals that they must have contributed a significant amount of metal to these deposits. The presence of barite and of thallium is also indicative that feldspars were the main source of lead. Arsenic is one of the few important trace elements in these deposits and is known to occur in some areas of Lower Paleozoic metasediments in unusually high concentrations. Any model explaining the origin of these deposits must consider the extensive leaching of the basement and to some extent of the overlying clastic sediments as well. How the metal-bearing solutions entered the lagoonal back-reef areas is still open to question as feeder channels have not yet been positively identified. The results further demonstrate that the basement also acted as a metal source for galena-bearing deposits hosted in Permian sediments, vein-type deposits in Permian volcanics, and probably the barite-fluorite polymetallic deposits along a Devonian erosional surface in the Carnic Alps as well.     

Stratigraphy and palaeoenvironmental development of Quaternary coarse clastic beach deposits at Plage de Mezpeurleuch,Brittany (France)

Quaternary deposits are described from well‐exposed sections in cliffs at Plage de Mezpeurleuch, Finistère, Brittany (France). The general lithostratigraphic sequence comprises Holocene perched dune sand, calcrete and palaeosol overlying Weichselian head and coarse clastic palaeobeach units attributed to the last interglacial (Eemian–isotope substage 5e). A lower and an upper palaeobeach, separated by a thin head deposit, are reported resting on an irregular palaeorock platform eroded in Hercynian granite. From a comparison with modern coastal environments a palaeoenvironmental interpretation of the palaeobeach deposits is made. Erosionally bounded facies of the lower palaeobeach, are considered to be a transgressive sequence preserved by drowning associated with a rapid rise in relative sea‐level. Its subsequent abandonment is attributed to a relative sea‐level fall, which allowed a terrestrial environment to develop briefly. Facies of the upper palaeobeach however indicate a prograding shoreline developed during a prolonged period of relatively stable sea‐level. These sea‐level observations are in good agreement with other evidence for a brief widespread intra‐Eemian cold event. Copyright © 2001 John Wiley & Sons, Ltd.     

云南华宁-峨山地区震旦系沉积岩铜矿床成因

云南震旦系沉积岩铜矿是产于红色碎屑岩系中的沉积叠加热液改造型铜矿床,矿床产在上震旦统陡山沱组灰白色砂岩,白云岩,泥灰质页岩中,具有明显层控特征。地球化学分析表明,震旦系碎屑岩中铜富集系数明显高于正常壳源沉积岩,因此加里东期后生改造矿化物质直接来自下部红色沉积岩层的淋滤迁移,最终在氧化还原过渡带与同生富集矿层叠加。     

Litho- and biostratigraphy,facies patterns and depositional sequences of the Cenomanian-Turonian deposits in the Ksour Mountains (Saharan Atlas,Algeria)

The Cenomanian-Turonian deposits exposed in the Ksour Mountains, western part of the Saharan Atlas (Algeria), document marine shelf environments that had been thriving on the North African passive margin, connected northwards to the Tethys Ocean, and fringed southwards by the Saharan craton. Their lithological, palaeontological, and sedimentological characteristics have been investigated to provide new insights into the biostratigraphy, palaeo-environmental evolution and sea-level changes in this western part of the Saharan Atlas. Three formations are recognized, from base to top of the studied succession: 1. The El Rhelida Formation comprising two informal units: the mixed siliciclastic-carbonate unit deposited under different flow regime conditions, from shoreline to backshore environments, and the limestone–claystone unit including coastal mudflat deposits prone to storm events. The early Cenomanian age of the El Rhelida Formation is supported by vertebrate assemblages. 2. The Mdaouer Formation comprising two units: the evaporitic unit dominated by claystone and evaporite alternations deposited on a flat coastal sabkha with occasional storms, and the marlstone–limestone unit formed in a peritidal-lagoonal environment. The Mdaouer Formation is of early-middle Cenomanian age. 3. The Rhoundjaïa Formation comprising three units: the lower limestone unit consisting of relatively homogeneous fossiliferous limestones; the middle marly unit composed of marlstone and bioclastic limestones, and the upper limestone unit consisting of carbonates showing vertical variations in faunal content and stratonomy. The Rhoundjaïa Formation was deposited in homoclinal ramp setting. Ammonite data indicate an early late Cenomanian to early Turonian age for this interval. Within an overall transgressive trend, the Cenomanian-Turonian deposits of the Ksour Mountains record three third-order depositional sequences bounded each by regional discontinuities.     

Geology and Genesis of Barite Deposits of Lasbela and Khuzdar Districts, Balochistan, Pakistan

Abstract: Geology and genesis of the sediment-hosted barite deposits in the Lasbela and Khuzdar districts of Balochistan, Pakistan have been studied and described. Hot solutions generated in rifting environments during the initial stage of separation of the continental crustal block related to the Gondwanaland fragmentation subsequently reposed in Jurassic rocks, most probably played an important role on barite formation.
Paragenetic relationships indicate that the period of barite mineralization was distinctly later than that of zinc-lead sulphide mineralization in the Lasbela and Khuzdar districts. The barite deposits occur on top and in peripheral to the zinc-lead sulphides. The earliest barite mineralization took place in the clastic rock sequence of the lower Spingwar Formation as cross cutting veins. Younger mineralization as stratabound-replacement type occurred within the platform limestones of Loralai Formation, just above the Spingwar Formation. The youngest mineralization as stratiform is hosted within black shales, mudstones and argillaceous limestones of Anjira Formation at the top of Loralai Formation. In the light of the evidences gathered from field and laboratory investigations a genetic model has been deduced.     

西准噶尔晚泥盆世新建岩石地层单位:塔克台组

西准噶尔塔克台高原周围一套碎屑岩地层曾被划为下石炭统和布克河组(洪古勒楞组的晚出异名),但其岩性组合、沉积环境与化石面貌均与和布克河组或洪古勒楞组的定义不符,也难以归纳到区域上其他已知地层单元中,故以此建立一个新的岩石地层单位:塔克台组,并分为上、下2段:下段为火山碎屑岩夹火山岩,上段为正常碎屑岩、火山碎屑岩、钙质碎屑岩夹少量灰岩、火山岩和薄煤层.该组与下伏文洛克统沙尔布尔组呈角度不整合接触,上未见顶,多门类动植物化石的发现限定了该组的时代为晚泥盆世,形成于水体逐渐变浅的滨、浅海至沼泽环境.塔克台组与邻区同期的朱鲁木特组、洪古勒楞组为同时异相关系,晚泥盆世研究区海水从西向东侵入并退出是造成这种同时异相关系的主要原因.