Czech Academy of Sciences, Institute of Geology

The International Commission on Stratigraphy (ICS) has a long tradition of producing international charts that communicate higher-order divisions of geological time and actual knowledge on the absolute numerical ages of their boundaries. The primary objective of ICS is to define precisely a global standard set of time-correlative units (Systems, Series, and Stages) for stratigraphic successions worldwide. These units are, in turn, the basis for the Periods, Epochs and Ages of the Geological Time Scale. Setting an international global standard is fundamental for expressing geological knowledge. It is also of considerable pragmatic importance as it provides the framework through which regional-scale higher-resolution divisions can be linked, equated and collated. This is a status update on the International Chronostratigraphic Chart and the ICS website www.stratigraphy.org.

The Central Asian Orogenic Belt records the accretion and convergence of three collage systems that were finally rotated into two major oroclines. The Mongolia collage system was a long, N–S-oriented composite ribbon that was rotated to its current orientation when the Mongol-Okhotsk orocline was formed. The components of the Kazakhstan collage system were welded together into a long, single composite arc that was bent to form the Kazakhstan orocline. The cratons of Tarim and North China were united and sutured by the Beishan orogen, which terminated with formation of the Solonker suture in northern China. All components of the three collage systems were generated by the Neoproterozoic and were amalgamated in the Permo-Triassic. The Central Asian Orogenic Belt evolved by multiple convergence and accretion of many orogenic components during multiple phases of amalgamation, followed by two phases of orocline rotation.

Summary The various mechanisms which could cause oblique slip faulting are briefly reviewed. It is thought that such faulting may frequently arise from the existence of preferred planes of fracture within the rocks. The dynamics of this mechanism is studied in some detail and an expression is obtained for the first direction of slip within the plane under the influence of a general stress system of given orientation it is found that the initial slip may occur in any possible direction within the plane, the direction depending on the relative values of the three principle pressures. The theory suggests that when a pre-existing fault is subjected to a reorientated stress system (typical or rotated) the movement after fracture will usually be oblique. In conclusion, the general implications of the theory are discussed.

Two-dimensional electrical imaging surveys are now widely used in engineering and environmental surveys to map moderately complex structures. In order to adequately resolve such structures with arbitrary resistivity distributions, the regularised least-squares optimisation method with a cell-based model is frequently used in the inversion of the electrical imaging data. The L norm based least-squares optimisation method that attempts to minimise the sum of squares of the spatial changes in the model resistivity is often used. The resulting inversion model has a smooth variation in the resistivity values. In cases where the true subsurface resistivity consists of several regions that are approximately homogenous internally and separated by sharp boundaries, the result obtained by the smooth inversion method is not optimal. It tends to smear out the boundaries and give resistivity values that are too low or too high. The blocky or L norm optimisation method can be used for such situations. This method attempts to minimise the sum of the absolute values of the spatial changes in the model resistivity. It tends to produce models with regions that are piecewise constant and separated by sharp boundaries. Results from tests of the smooth and blocky inversion methods with several synthetic and field data sets highlight the strengths and weaknesses of both methods. The smooth inversion method gives better results for areas where the subsurface resistivity changes in a gradual manner, while the blocky inversion method gives significantly better results where there are sharp boundaries. While fast computers and software have made the task of interpreting data from electrical imaging surveys much easier, it remains the responsibility of the interpreter to choose the appropriate tool for the task based on the available geological information.

The taxonomic treatment of trace fossils needs a uniform approach, independent of the ethologic groups concerned. To this aim, trace fossils are rigorously defined with regard to biological taxa and physical sedimentary structures. Potential ichnotaxobases are evaluated, with morphology resulting as the most important criterion. For trace fossils related to bioerosion and herbivory, substrate plays a key role, as well as composition for coprolites. Size, producer, age, facies and preservation are rejected as ichnotaxobases. Separate names for undertracks and other poorly preserved material should gradually be replaced by ichnotaxa based on well-preserved specimens. Recent traces may be identified using established trace fossil taxa but new names can only be based on fossil material, even if the distinction between recent and fossil may frequently remain arbitrary. It is stressed that ichnotaxa must not be incorporated into biological taxa in systematics. Composite trace fossil structures (complex structures made by the combined activity of two or more species) have no ichnotaxonomic standing but compound traces (complex structures made by one individual tracemaker) may be named separately under certain provisions. The following emendations are proposed to the International Code of Zoological Nomenclature: The term ‘work of an animal’ should be deleted from the code, and ichnotaxa should be based solely on trace fossils as defined herein.

From the results of 747 experiments on dry basic and ultrabasic magmas and related synthetic systems equations have been derived which predict the olivine/liquid cation partition coefficients for Mg (correlation coefficient r = 0·996), Fe2+ (r = 0·993), Ca (r = 0·79) and Mn (r = 0·70) as a function of temperature, pressure and liquid composition. The ratio of the partition coefficients for Mg and Fe2+ (KD) varies from 0·25 to 0·38. For any given magma composition liquidus olivines are slightly more iron-rich at high pressures than they would be at low pressures. The Mg and Fe2+ partition coefficient equations may be used as geothermometers which are accurate to better than ±1 per cent if pressures can be estimated by independent methods. Minor element partition thermometers (Ca and Mn) are too sensitive to analytical errors, or to departures from equilibrium, to prove reliable. Temperatures may also be obtained from a geothermometer based on the concept of olivine saturation. This is independent of olivine composition and can be used where these is evidence of disequilibrium between olivine and host liquid. In such a situation the errors indicated by the Mg and Fe2+ partition thermometers are asymmetric about the true temperature except when the equilibrium olivine composition is Fo50. These geothermometers are sufficiently sensitive to demonstrate magma mixing. The partition coefficient equations may be used to model equilibrium crystallization of olivine even though the partition coefficients, and the ratio of the partition coefficients (KD). are continuously changing. Fractional crystallization of olivine may be approximated by sequential removal of small amounts of olivine formed by equilibrium crystallization.

Pressure on natural resources from growing populations, with growing demands for water supply, infrastructure and housing, has increased in the past decades and can be expected to continue to rise. Further stress on the environment due to pollution will increase the need for detailed geological knowledge, for geotechnical, hydrogeological, and environmental protection purposes.

Many hydrogeochemical models have appeared in recent years for simulating subsurface solute transport. The hydrological transport of solutes can be described by a set of linear partial differential equations, and the chemical equilibria are described by a set of nonlinear algebraic equations. Three approaches are currently used to formulate the problem: (1) the mixed differential and algebraic equation (DAE) approach, (2) the direct substitution approach (DSA), and (3) the sequential iteration approach (SIA). An extremely important consideration in any approach is the choice of primary dependent variables (PDVs). Six types of PDVs have been employed in the existing models: (1) concentrations of all species, (2) concentrations of all component species and precipitated species, (3) total analytical concentrations of aqueous components, (4) total dissolved concentrations of aqueous components, (5) concentrations of aqueous component species, and (6) hybrid concentrations. Because of many possible combinations of PDVs and approaches, many hydrogeochemical transport models for multicomponent systems have been developed. This paper critically evaluates and discusses these models. The discussion and evaluation are conducted in terms of (1) how severe can the constraints be that a model imposes on computer resources, (2) which equilibrium geochemical processes can a model include, and (3) how easily can a model be modified to deal with mixed kinetic and equilibrium reactions. The use of SIA models leads to the fewest constraints on computer resources in terms of central processing unit (CPU) memory and CPU time; both DAE and DSA models require excessive CPU memory and CPU time for realistic two‐ and three‐dimensional problems. Only those models that use the first three types of PDVs can treat the full complement of equilibrium reactions simultaneously. DAE and SIA models can be modified with reasonable ease to handle mixed chemical kinetics and equilibria. DSA models require strenuous efforts to modify for treating mixed chemical kinetics and equilibria. Therefore SIA models using the third type of PDVs are recommended for their practicality and flexibility. DSA and DAE models should remain research tools for one‐dimensional investigations.

This paper presents the development and demonstration of a two‐dimensional finite‐element hydrogeochemical transport model, HYDROGEOCHEM, for simulating transport of reactive multispecies solutes. The model is designed for application to heterogeneous, anisotropic, saturated‐unsaturated media under transient or steady state flow conditions. It simulates the chemical processes of complexation, dissolution‐precipitation, adsorption‐desorption, ion exchange, redox, and acid‐base reaction, simultaneously. A set of four example problems are presented. The examples illustrate the model's ability to simulate a variety of reactive transport problems. Important results presented include a depiction of the propagation of multiple precipitation‐dissolution fronts, a display of the large errors in model response if the number of iterations between the hydrologic transport and chemical equilibrium modules is limited to one, an illustration of the development of greater concentration of contaminants In groundwater away from a waste site than near the source, and a demonstration of the variation in distribution coefficients of more than 6 orders of magnitude.

Abstract In this study, a new finite-difference technique is designed to reduce the number of grid points needed in frequency-space domain modeling. The new algorithm uses optimal nine-point operators for the approximation of the Laplacian and the mass acceleration terms. The coefficients can be found by using the steepest descent method so that the best normalized phase curves can be obtained. This method reduces the number of grid points per wavelength to 4 or less, with consequent reductions of computer memory and CPU time that are factors of tens less than those involved in the conventional second-order approximation formula when a band type solver is used on a scalar machine.

We present SHRIMP zircon dating, bulk-rock geochemical, and Sr-Nd-Pb isotopic results for Yeba volcanic rocks and a mafic dike from Southern Gangdese (SG), southern Tibet, in order to constrain their tectonic setting and origin. Yeba volcanic rocks span a continuous compositional range from basalt to dacite, although andesites are minor, and mafic and felsic rocks are volumetrically predominant. New SHRIMP zircon dating for a dacite coupled with previous SHRIMP zircon dating for a mafic dike and fossil constraints for the sedimentary sequence indicate that Yeba volcanic rocks were emplaced in the Early Jurassic (174-190 Ma). Yeba tholeiitic mafic rocks possess compositional diversity and are divided into three groups based on concentrations of MgO, Al2O3, and La. Mafic samples are all characterized by marked negative Nb, Ta, and Ti anomalies and positive ∊Nd(T) values (+ 2.4 to + 4.5). Yeba calc-alkaline felsic rocks are characterized by coherent, concave-upward MREE patterns and negative anomalies in Nb, Ta, P, and Ti, with positive ∊Nd(T) values (+ 0.3 to + 2.6). Sr-Nd-Pb isotopes overlap among the different groups of Yeba mafic rocks; Pb isotopic compositions in both mafic and felsic rocks are nearly identical. These features are consistent with a subduction-related origin, most likely in an arc built on thin, immature continental crust. Yeba volcanic rocks are interpreted as having been created by northward subduction of Neo-Tethyan oceanic crust in Early Jurassic time. Geochemical signatures and quantitative modeling indicate that fractional crystallization and crustal assimilation played insignificant roles in the generation of Yeba mafic magmas, and that their geochemical diversity was probably produced by variable degrees of partial melting from a common but heterogeneous mantle source, which had been metasomatized by variable contributions of sediments/fluids released from the subducted Neo-Tethyan oceanic crust. Yeba felsic rocks were probably generated by moderate degrees of partial melting of juvenile basaltic lower crust, which consists of dominant underplated magmas (similar to Yeba mafic rocks in composition) and variable contributions from ancient lower crust beneath the Gangdese Back-Arc fault uplift belt (GBAFUB).

The Quadrilatero Ferrifero is an area of some 7,000 square kilometers in central Minas Gerais, Brazil, centered about lat. 2015' S., long. 4330' W. For 250 years the region has poured forth a variety of mineral riches, now totaling more than $2 billion, and future production will undoubtedly be even greater. The main products are iron ore, manganese ore, and gold. To assist this development, the Brazilian and American Governments in 1946 jointly undertook the first detailed geologic study of the region; this report is a synthesis of the results of work and mapping by 17 Brazilian and American geologists under this program; other reports discussing the economic geology, the metamorphic geology, and the igneous geology of the region as a whole are being prepared.

A Zn-doped Ni₃S₂nanosheet array on Ni foam (Zn-Ni₃S₂/NF) acts as a high-performance and durable electrocatalyst for the oxygen evolution reaction in 1.0 M KOH, driving a catalytic current density of 100 mA cm⁻²at an overpotential of 330 mV, 90 mV less than that for Ni₃S₂/NF.

Ni₂P nanoflake arrays on carbon cloth act as an efficient and durable catalyst electrode for the urea oxidation reaction (UOR) and hydrogen evolution reaction (HER). Its two-electrode alkaline electrolyzer needs 1.35 V for 50 mA cm⁻², which is 0.58 V less than that required for pure water splitting.

ABSTRACT Four balanced cross sections, supported by longitudinal sections, structure contour maps, stratigraphic separation diagrams and hangingwall sequence diagrams are keys to this interpretation of the Moine thrust, which forms the western margin of the Caledonides in NW Scotland. New basement and cover correlations between foreland and thrust belt give new slip estimates for the Moine thrust (∼ 77 km), the Loch More klippe (≥ 43 km), Glencoul sheet (20–25 km), Ben More sheet (∼28 km), Achall and Dundonnell ‘sheet II’ (∼28 km). Like other major thrusts the Moine thrust moved in a smooth or rough fashion at different places and times, and many structures are a footwall response to its passage. Widely developed duplexes vary in thickness so that the roof thrust is folded and occasionally faulted; many late Caledonian folds in the Moine metasediments are of this origin. The presence of igneous bodies with contact aureoles increased the propensity to rough slip and this, by causing thickening in the footwall to the Moine thrust, is partly responsible for the Assynt culmination. The previously accepted sequence of thrusting from foreland to hinterland, which has been deduced from the concept of ‘overstep’ of the Moine thrust across lower thrusts, is considered to be a misconception of thrust geometry. Instead, a ‘piggy-back’ sequence of thrusts, from higher to lower, is proposed.

P/NF. In addition, it also demonstrates excellent long-term electrochemical durability for at least 25 h. This work offers us a promising catalyst material for water-splitting devices for large-scale production of hydrogen fuels.

The Eastern Qinling region, located in the southern margin of the North China Craton, is characterised by widespread granitoid intrusions. Precise geochronological constraints on the age and timing of these intrusions are lacking. In this paper, we report SHRIMP zircon U–Pb ages of 12 representative granitoid plutons, together with one syenite stock, dolerite, diorite and granitic dykes in Eastern Qinling. The results revealed two main magmatic events, which occurred in the Late Jurassic–Early Cretaceous (158 ± 3 to 136 ± 2 Ma) and the Early Cretaceous (134 ± 1 to 108 ± 2 Ma), respectively. The granitoids formed in the early magmatic event are similar in composition and are characterised by a mantle source mixed with variable amounts of crustal components, whereas those resulting from the late-stage magmatism show characters of I-, S- and A-types granite and coexist with coeval dolerite dykes and syenite stocks. A similar magmatic age distribution is also recognised in other belts or regions in East China, and even in other parts of the East Eurasian continental margin. This suggests that the Jurassic–Early Cretaceous magmatism was associated with the subduction of the Izanagi plate at a shallow angle or flat-slab subduction beneath the eastern China continent, whereas the Early Cretaceous magmatism was related to lithospheric thinning, asthenospheric upwelling and partial melting of the lower crust, induced by a change in Izanagi plate motion parallel to the continent margin.

The Late Ordovician (Katian-Hirnantian) through earliest Silurian (Rhuddanian) interval was a time of varying climate and sea level, marked by a peak glacial episode in the early-mid Hirnantian. Synthesis of recently published data permits global correlation of at least two cycles of glacial advance and retreat with a distinct interglacial period that is recognizable in sequence stratigraphic and chemostratigraphic records worldwide. A period of warming and sea level rise during the late Katian is marked by the widespread occurrences of oceanic anoxia in paleotropical and subtropical localities, mostly confined to regions of inferred upwelling and semi-restricted marine basins. Nitrogen isotope data show that the regions of oceanic anoxia were marked by intense water column denitrification in which cyanobacteria were the principal source of fixed N. In the overlying peak glacial interval of the Hirnantian, sedimentary successions indicate that anoxia was much restricted. The shift to more positive N isotope values also suggests less intense water column denitrification. In the late Hirnantian and early Rhuddanian the black shales showing evidence of anoxia spread over all paleolatitudes and water depths indicating a Rhuddanian ocean anoxic event comparable to examples from the Mesozoic. It is accompanied by a return to intensely denitrifying conditions within the water column. The two phases of Hirnantian mass extinction coincide with rapid, climate-driven changes in oceanic anoxia. The first extinction occurs at the onset of glaciation and with the loss of anoxic conditions at the end of the Katian. The second extinction occurs at the demise of glaciation and coincides with the return of anoxic conditions during the late Hirnantian/early Rhuddanian. The N isotope data suggest that the extinctions may be traced to changes occurring at the base of the marine food web, i.e., redox driven changes in nutrient cycling and primary producer communities.

Synopsis Basaltic rocks have chemical compositions and behave under experimental conditions in a way which suggests that extrusive basalt magmas are, in the main, the residual liquids of well advanced crystal fractionation processes operating at relatively low pressures. Once this is admitted, there is no reason to deny that such magmas have undergone appreciable crystal fractionation at all depths during their movement to the surface. The compositions of extrusive basalts should, therefore, be regarded as the end products of a continuous series of evolutionary changes whose precise effects will depend upon the place where partial melting occurred, and the rate at which the liquids move towards the surface relative to the rate of cooling. An attempt is made to construct a petrogenetic scheme for the basic magmas based on this view of igneous activity.

Summary Based on a large amount of published data and stimulated by the papers and discussion at the International Workshop on Fine-Grained Sediments held in Halifax, Canada in August 1982, we have attempted a synthesis of deep-water fine-grained sediment facies. Three main facies groups related to depositional processes can be identified: turbidites, contourites and pelagites/hemipelagites. There is a continuum between the different processes and hence a continuum between facies. Nevertheless, it is possible to define several distinct facies models within each of these groups on the basis of sedimentary structures, texture and composition, and to provisionally interpret these in terms of depositional hydrodynamics. Patterns of horizontal and vertical facies distribution can be related to depositional subenvironments. There is much variability within and departure from the facies models we propose, and many interesting and problematic areas of research remain in the quest for better understanding of deep-water fine-grained sediments.