Diagenesis of early Permian high‐latitude limestones,Lower Parmeener Supergroup,Tasmania

The Darlington (Sakmarian) and Berriedale (Artinskian) Limestones are neritic deposits that accumulated in high‐latitude environments along the south‐eastern margin of Pangea in what is now Tasmania. These rocks underwent a series of diagenetic processes that began in the marine palaeoenvironment, continued during rapid burial and were profoundly modified by alteration associated with the intrusion of Mesozoic igneous rocks. Marine diagenesis was important but contradictory; although dissolution took place, there was also coeval precipitation of fibrous calcite cement, phosphate and glauconite, as well as calcitization of aragonite shells. These processes are interpreted as having been promoted by mixing of shelf and upwelling deep ocean waters and enabled by microbial degradation of organic matter. In contrast to warm‐water carbonates where meteoric diagenesis is important, the Darlington and Berriedale Limestones were largely unaffected by meteoric diagenesis. Only minor dissolution and local cementation took place in this diagenetic environment, although mechanical compaction was ubiquitous. Correlation with burial history curves indicates that chemical compaction became important as burial depths exceeded 150 m, promoting precipitation of extensive ferroan calcite. This effect resulted from burial by rapidly deposited, overlying, thick, late Permian and Triassic terrestrial sediments. This diagenetic pathway was, however, complicated by the subsequent intrusion of massive Mesozoic diabases and associated silicifying diagenetic fluids. Finally, fractures most probably connected with Cretaceous uplift were filled with late‐stage non‐ferroan calcite cement. This study suggests that both carbonate dissolution and precipitation occur in high‐latitude marine palaeoenvironments and, therefore, the cold‐water diagenetic realm is not always destructive in terms of diagenesis. Furthermore, it appears that for the early Permian of southern Pangea at least, there was no real difference in the diagenetic pathways taken by cool‐water and cold‐water carbonates.     

Fusulinid biostratigraphy of the Lower Permian Zweikofel Formation (Rattendorf Group; Carnic Alps,Austria) and Lower Permian Tethyan chronostratigraphy

The Zweikofel Formation of the Rattendorf Group in the Carnic Alps (Austria) is 95–102 m thick and consists of a cyclic succession of thin‐ to thick‐bedded fossiliferous limestone and intercalated thin intervals of siliciclastic sediment. The siliciclastic intervals were deposited in a shallow marine nearshore environment. The variety of carbonate facies indicates deposition in a shallow neritic, normal‐saline, low‐ to high‐energy environment. The Zweikofel Formation is characterized by a paracyclic vertical arrangement of facies and represents sedimentary sequences that are not well understood elsewhere in the Tethys. Fusulinids and conodonts from the upper Grenzland and Zweikofel formations in the Carnic Alps clearly suggest that what has been called ‘Sakmarian’ in the Tethys includes both the Sakmarian and Artinskian stages of the Global Time scale. Fusulinids from the lower part of the Zweikofel Formation at Zweikofel closely resemble those of the Grenzland Formation and approximately correlate with the upper part of the Sakmarian and lower part of the Artinskian of the Global Time scale. The upper part of the Zweikofel Formation correlates approximately with the lower‐middle (?) parts of the Artinskian Stage of the Global Time scale. A new regional Hermagorian Stage of the Tethyan scale is proposed between the Asselian and Yakhtashian. The lower boundary of the Hermagorian Stage is proposed to be located at the base of bed 81 in the 1015 section of Darvaz (Tadzhikistan). The boundary between the Hermagorian and Yakhtashian stages is placed at the base of bed 73 in the Zweikofel section at Zweikofel, Carnic Alps. In the Darvaz region, Tadzhikistan, the type area for the Yakhtashian Stage, this boundary has never been precisely defined. The entire fusulinid assemblage of the upper part of the Grenzland and Zweikofel formations reported herein includes 62 species of 18 genera, of which one subgenus and 12 species and subspecies are new. Copyright © 2012 John Wiley & Sons, Ltd.     

A wave‐dominated,tide‐modulated model for the Lower Ordovician of the Anti‐Atlas,Morocco

Hybrid depositional systems are created by the interaction of two or more hydrodynamic processes that control facies distribution and their characteristics in terms of sedimentary structures and depositional geometry. The interaction of wave and tide both in the geological sedimentary record and modern environments has been rarely described in the literature. Mixed coastal environments are identified by the evidence of wave and tidal structures and are well identified in nearshore environments, while their recognition in lower shoreface–offshore environments lacks direct information from modern settings. Detailed field analyses of 10 stratigraphic sections of the Lower Ordovician succession (Fezouata and Zini formations; Anti‐Atlas, Morocco) have allowed the definition of 14 facies, all grouped in four facies zones belonging to a storm‐dominated, wave‐dominated sedimentary siliciclastic system characterized by symmetrical ripples of various scales. Peculiar sedimentary organization and sedimentary structures are observed: (i) cyclical changes in size of sedimentary structures under fair‐weather or storm‐weather conditions; (ii) decimetre‐deep erosional surfaces in swaley cross‐stratifications; (iii) deep internal erosion within storm deposits; (iv) discontinuous sandstone layers in most depositional environments, and common deposition of sandstones with a limited lateral extension, interpreted to indicate that deposition at all scales (metric to kilometric) is discontinuous; (v) combined flow–oscillation ripples showing aggrading–prograding internal structures alternating with purely aggrading wave ripples; and (vi) foreshore environments characterized by alternating phases of deposition of parallel stratifications, small‐scale and large‐scale ripples and tens of metres‐wide reactivation surfaces. These characteristics of deposition suggest that wave intensity during storm‐weather or fair‐weather conditions was continuously modulated by another controlling factor of the sedimentation: the tide. However, tidal structures are not recognized, because they were probably not preserved due to dominant action of storms and waves. A model of deposition is provided for this wave‐dominated, tide‐modulated sedimentary system recording proximal offshore to intertidal–foreshore environments, but lacking diagnostic tidal structures.     

Soft-bedded subglacial meltwater channel from the Welzow-Süd opencast lignite mine, Lower Lusatia, eastern Germany

An excellent section in the Welzow-Süd open-cast lignite mine in Lower Lusatia, eastern Germany, provided a rare opportunity to study a small (5 m deep), buried subglacial meltwater channel of Saalian age. The channel is steep-sided and distinctly U-shaped. It is separated from undeformed outwash deposits in which it is incised by a sharp erosional contact and it is filled with meltwater sand and till. The till was possibly squeezed into the channel from the adjacent ice/bed interface. Directly beneath the channel, there is a partly truncated diapir of clayey silt, evidencing sediment intrusion into the channel from below. During channel formation, the pressure gradient was oriented from the surrounding sediments into the channel, so that the channel served as a drainage conduit for groundwater from the adjacent subglacial aquifer. The substratum consists largely of sandy aquifers with a total thickness of about 100 m, separated by two aquitards. Channel formation was initiated when hydraulic transmissivity of the bed did not suffice to evacuate all the subglacial meltwater as groundwater flow. As the Welzow-Süd channel belongs to a dense network of subglacial channels in eastern Germany, temporary ice-sheet instability in this region prior to channel formation seems possible.     

Tourist farms in Lower Silesia, Poland

In view of the small size of most Polish farms, attempts have been made to encourage diversification into rural tourism. The paper examines the progress made in Lower Silesia which has good resources for domestic and international tourism. Thanks to the promotional work of the Agricultural Consultative Centres over a hundred farms are now providing services. They do not generate a large share of the farm income but business is expanding and some areas are becoming very popular. Thus a base has been established for future expansion. Further development depends on easier access to credit and government support for ecological agriculture. Better promotion is also needed to increase interest in rural tourism in Poland and attract more visitors from abroad. This revised version was published online in July 2006 with corrections to the Cover Date.     

Tide-dominated offshore sedimentation, Lower Cambrian, north Norway

The Duolbasgaissa Formation, Lower Cambrian, of northern Norway consists of 550 m of mineralogically and texturally mature sandstones with subordinate siltstones, mudstones and conglomerates. Four facies are defined on the basis of grain size, bed thickness and sedimentary structures. Facies 1–3 consist of a variety of erosively-based, cross-stratified and parallel-stratified sandstones interbedded with siltstone and mudstone. Many of these sandstones show evidence of deposition from waning currents. Facies 4 consists of trough cross-bedded sandstones with sets up to 4 m thick. Symmetrical ripples and bioturbation are ubiquitous. Bipolar palaeocurrent distributions are common to all facies and one mode is usually strongly dominant. Lateral facies variations and sedimentary structures suggest that deposition took place in a tide-dominated, offshore, shallow marine environment in which maximum sediment transport probably occurred when storm generated waves enhanced tidal currents. The four facies are thought to represent the deposits of various parts of tidal sediment transport paths such as exist in modern seas around Great Britain. Small scale coarsening upward sequences may represent the superposition of facies independently of changing water depth. Lack of information prevents a detailed palaeogeographic reconstruction. It is suggested that sand body shape is not accurately predictable.     

安徽巢北地区下石炭统岩石微相特征

通过对安徽巢北凤凰山剖面进行详细的野外测量和系统的岩石学、岩相学、沉积学的研究,尤其是进行岩石微相研究,分析其古地理特征及沉积环境.研究表明,巢北地区下石炭统整体为一套滨海相沉积,以石灰岩为主,含有少量的砂岩、泥岩,可识别出十种岩石微相类型.     

云南保山地区的下石炭统

<正> 云南保山地区下石炭统及其生物群曾引起许多学者的兴趣(Reed l927;王鸿桢,1945;段丽兰,1973,1985;宋学良,1982;金玉玕、方润森,1983;杨宗仁,1983;陈重泰,1984;陈根保,1984;金苏华,1992),其主要原因在于丰富而特殊的生物类群,悬而未决的地层问题以及独特的生物地理位置。本文以4条剖面(图1)为基础,依据多门类的生物化石对诸如本区杜内/维宪阶界线、Siphonophyllia-Keyserlingophyllum(Humboldtia)动物群的时代、冷水(凉水)珊瑚动物群、岩石地层单位等问题进行讨论。     

The role of shelf morphology on storm‐bed variability and stratigraphic architecture,Lower Cretaceous,Svalbard

The dominance of isotropic hummocky cross‐stratification, recording deposition solely by oscillatory flows, in many ancient storm‐dominated shoreface–shelf successions is enigmatic. Based on conventional sedimentological investigations, this study shows that storm deposits in three different and stratigraphically separated siliciclastic sediment wedges within the Lower Cretaceous succession in Svalbard record various depositional processes and principally contrasting sequence stratigraphic architectures. The lower wedge is characterized by low, but comparatively steeper, depositional dips than the middle and upper wedges, and records a change from storm‐dominated offshore transition – lower shoreface to storm‐dominated prodelta – distal delta front deposits. The occurrence of anisotropic hummocky cross‐stratification sandstone beds, scour‐and‐fill features of possible hyperpycnal‐flow origin, and wave‐modified turbidites within this part of the wedge suggests that the proximity to a fluvio‐deltaic system influenced the observed storm‐bed variability. The mudstone‐dominated part of the lower wedge records offshore shelf deposition below storm‐wave base. In the middle wedge, scours, gutter casts and anisotropic hummocky cross‐stratified storm beds occur in inferred distal settings in association with bathymetric steps situated across the platform break of retrogradationally stacked parasequences. These steps gave rise to localized, steeper‐gradient depositional dips which promoted the generation of basinward‐directed flows that occasionally scoured into the underlying seafloor. Storm‐wave and tidal current interaction promoted the development and migration of large‐scale, compound bedforms and smaller‐scale hummocky bedforms preserved as anisotropic hummocky cross‐stratification. The upper wedge consists of thick, seaward‐stepping successions of isotropic hummocky cross‐stratification‐bearing sandstone beds attributed to progradation across a shallow, gently dipping ramp‐type shelf. The associated distal facies are characterized by abundant lenticular, wave ripple cross‐laminated sandstone, suggesting that the basin floor was predominantly positioned above, but near, storm‐wave base. Consequently, shelf morphology and physiography, and the nature of the feeder system (for example, proximity to deltaic systems) are inferred to exert some control on storm‐bed variability and the resulting stratigraphic architecture.     

Palaeosols and sequence stratigraphy of the Lower Permian Abo Member,south‐central New Mexico,USA

The relationship between palaeosols and sequence stratigraphy is tested in the Lower Permian Abo Member, south‐central New Mexico, by comparing interfluve and fluvial‐terrace palaeosols with palaeosols that developed within lowstand‐fluvial deposits. Interfluve and fluvial‐terrace palaeosols consist of primary pedogenic features, including vertical root traces, vertic structures, Stage II and III pedogenic calcite and translocated clay (argillans), which are cross‐cut or replaced by low‐aluminium goethite, gley colour mottling, sparry calcite veins and ankerite. The polygenetic character of the palaeosols is consistent with initial development for several thousand to tens of thousands of years on well‐drained interfluves or fluvial terraces, followed by waterlogging due to invasion by a rising water table that locally may have been brackish. In contrast, lowstand‐fluvial sediment that filled incised valleys contains only rooted and vertic palaeosols, whose immaturity resulted from high aggradation rates. Palaeosols similar to those in the Abo Member have been recognized in other ancient strata and, when combined with high‐resolution correlation, provide evidence for interpretation of sequence‐stratigraphic surfaces and systems tracts.     

Modelled palaeo-temperature on Vøring, offshore mid-Norway — The effect of the Lower Crustal Body

The Vøring area, offshore mid-Norway has a complex geological history, has experienced several extensional phases and was significantly influenced by the break-up of the North Atlantic. We have modelled a cross-section over the Vøring Basin aiming to 1) reconstruct the basin evolution in a realistic way, and 2) to investigate the heat flow and temperature history in the basin.For the modelling we used the following tectonic events: the opening of the basin during the Permo-Triassic, an event during the Middle to Late Cretaceous and an event in the Late Cretaceous/Paleocene. The theoretical effects of the lithospheric stretching are depending on the palaeo-water depths of the area. We present a prediction of the palaeo-water depth, and a sensitivity analysis of the influence of the palaeo-water depth on the estimated beta-factors in the area.A lower crustal high-velocity body found in the area is often interpreted as magmatic underplating related to the break-up of the Norwegian Sea. We show the temperature history calculated by models that were run with and without assumption of underplating by a magmatic body emplaced during the Early Tertiary. The observed vitrinite reflectance in the Vøring area is best explained by numerical calculations of the vitrinite reflectance without a magmatic underplating. Our conclusion is that the Lower Crustal Body is not related to magmatic underplating or to significant sill intrusions. The body may consist of older mafic rocks, or a mixture of old continental crust and mafic intrusions.     

Glauberite–halite association of the Zaragoza Gypsum Formation (Lower Miocene, Ebro Basin, NE Spain)

Glauberite is the most common mineral in the ancient sodium sulphate deposits in the Mediterranean region, although its origin, primary or diagenetic, continues to be a matter of debate. A number of glauberite deposits of Oligocene–Miocene age in Spain display facies characteristics of sedimentologic significance, in particular those in which a glauberite–halite association is predominant. In this context, a log study of four boreholes in the Zaragoza Gypsum Formation (Lower Miocene, Ebro Basin, NE Spain) was carried out. Two glauberite–halite lithofacies associations, A and B, are distinguished: association (A) is composed of bedded cloudy halite and minor amounts of massive and clastic glauberite; association (B) is made up of laminated to thin‐bedded, clear macrocrystalline, massive, clastic and contorted lithofacies of glauberite, and small amounts of bedded cloudy halite. Transparent glauberite cemented by clear halite as well as normal‐graded and reverse‐graded glauberite textures are common. This type of transparent glauberite is interpreted as a primary, subaqueous precipitate. Gypsum, thenardite or mirabilite are absent in the two associations. The depositional environment is interpreted as a shallow perennial saline lake system, in which chloride brines (association A) and sulphate–(chloride) brines (association B) are developed. The geochemical study of halite crystals (bromine contents and fluid inclusion compositions) demonstrates that conditions for co‐precipitation of halite and glauberite, or for precipitation of Na‐sulphates (mirabilite, thenardite) were never fulfilled in the saline lake system.     

Upper Carboniferous to Lower Permian transgressive–regressive sequences of central Spitsbergen,Arctic Norway

Investigation of the Upper Carboniferous to Lower Permian sedimentary strata of central Spitsbergen shows that this highly cyclic rock succession is composed of four long-term transgressive–regressive cycles. These long-term cycles are themselves composed of stacked higher order cycles. Transgressive phases are characterized by increasing accommodation space, and include a basal transgressive part of marked retrogradation of facies belts and thickening-upward component cycles. Regressive phases are characterized by decreasing accommodation space, displayed by progradation of facies belts, overall shallowing and increased restriction of the depositional environment, influx of coarse terrigenous sediments and increasing evidence of exposure and/or non-deposition. The oldest transgressive–regressive sequence identified, Sequence 1, is of Serpukhovian to Bashkirian age and represents a syn-rift sequence. Also composed of syn-rift sediments is the transgressive–regressive Moscovian to mid-Gzhelian-aged Sequence 2. The late Gzhelian to late Asselian Sequence 3 is mainly a post-rift sequence. The youngest sequence, Sequence 4, is of Sakmarian to possible Artinskian age, and is also composed of post-rift sediments. The individual transgressive–regressive cycles are defined as second-order cycles, based on lithological signatures, lateral extent of bounding unconformities, and the actual time period the cycles span. Local tectonic activity is believed to control to some extent the development of short-term cycles in the syn-rift succession. However, cyclicity within the long-term cycles is mainly controlled by eustatic sea-level fluctuations, and therefore enables them to be correlated to other Circum-Arctic regions. Copyright © 1999 John Wiley & Sons, Ltd.     

江苏无锡嵩山下三叠统层序地层研究

无锡嵩山下三叠统碳酸盐浅滩相剖面在中下扬子区具有特殊性和代表性。碳酸盐滨岸浅滩相剖面不仅最灵敏地记录了海平面变迁历史，而且具有独特的副层序结构和特殊的层序识别和研究方法，在层序地层研究中占有重要地位。借助于与微古地理相结合的副层序分析方法，在嵩山下三叠统露头剖面上共识别出３个２类三级层序，并分别讨论了各层序的发育特点和识别分析方法。     

Hydrothermal alteration and fluid inclusion study of the Lower Cretaceous porphyry Cu–Au deposit of Tiámaro, Michoacán, Mexico

The Tiámaro deposit in Michoacán state has been dated as Lower Cretaceous (Valanginian), though most of the porphyry deposits in central Mexico were dated or have an attributed Eocene–Oligocene age. The host rocks belong to a volcanoplutonic complex overlain by red conglomerates. These rocks were intruded by pre-Valanginian plutonic and hypabissal rocks. Propylitic, phyllic, and argillic alteration assemblages developed, and their superimposition draws the evolution of the deposit. Stage I is represented by propylitic assemblages, stage II contains the main ore forming stockworks and both phyllic and argillic assemblages, and stage III contains late carbonatization assemblages. The obtained temperatures and salinities from inclusion fluids are low for a porphyry-type deposit, but we interpret that the known part of the deposit represents the shallow portion of a bigger deposit. The evolution of mineralizing fluids draws a dilution trend of brines from “porphyry-like” to “epithermal-like” stages. The richest ore zone is roughly located between the 300 and 350 °C isotherms, though unnoticed resources may occur at depth.     

Geophysical down-hole recognition of the Lower Devonian ‘Psammosteus’ Limestone and Townsend Tuff Bed,South Wales

Geophysical down-hole logs from the Maesteg and Senghenydd boreholes permit the recognition of the Townsend Tuff Bed and ‘Psammosteus’ Limestone markers on the basis of distinctive log motifs. The thickness of the interval between these markers is greater than at basin-margin localities and may be an indication of rapid deposition in the centre of the Anglo-Welsh basin in Lower Devonian times.