Strontium isotope evolution of Late Permian and Triassic seawater

The ⁸⁷Sr/⁸⁶Sr values based on brachiopods and conodonts define a nearly continuous record for the Late Permian and Triassic intervals. Minor gaps in measurements exist only for the uppermost Brahmanian, lower part of the Upper Olenekian, and Middle Norian, and only sparse data are available for the Late Permian. These 219 measurements include 67 brachiopods and 114 conodont samples from the Tethyan realm as well as 37 brachiopods and one conodont sample from the mid-European Middle Triassic Muschelkalk Sea. The Late Permian/Lower Triassic interval is characterized by a steep 1.3 × 10⁻³ rise, from 0.7070 at the base of the Dzhulfian to 0.7082 in the late Olenekian, a rate of change comparable to that in the Cenozoic. In the mid-Triassic (Anisian and Ladinian), the isotope values fall to 0.7075, followed again by a rise to 0.7081 in the Middle/Late Norian. The ⁸⁷Sr/⁸⁶Sr values decline again in the Late Norian (Sevatian) and Rhaetian to 0.7076.The sharp rise in the ⁸⁷Sr/⁸⁶Sr values during the Late Permian/Early Triassic was coincident with widespread clastic sedimentation. Because of the paucity of tectonic uplifts, the enhanced erosion may have been due to intermittent humid phases, during mainly an arid interval, coupled with the absence of a dense protective land plant cover following the mass extinction during the latest Permian. The apex of the ⁸⁷Sr/⁸⁶Sr curve at the Olenekian/Anisian boundary coincides with cessation of the large-scale clastic sedimentation and also marks the final recovery of land vegetation, as indicated by the renewed onset of coal formation in the Middle Triassic. The rising ⁸⁷Sr/⁸⁶Sr values from the Middle Carnian to the Late Norian coincide with the uplift and erosion of the Cimmeride-Indosinian orogens marking the closure of the Palaeotethys. The subsequent Rhaetian decline that continues into Jurassic (Pliensbachian/Toarcian boundary), on the other hand, coincides with the opening of the Vardar Ocean and its eastern continuation in the Izmir-Ankara Ophiolitic Belt.Samples from the Upper Muschelkalk are more radiogenic than the global trend. This may reflect separation of the basin from the open ocean. Due to strong meteoric influx from a large land mass in the north, the Germanic Basin became increasing brackish up section in the north and east, but because of the high evaporation rates, the salt content was not much reduced in the southern and central basin where a rich, but increasingly endemic, marine fauna survived.     

Environmental impact assessment in the Moradabad industrial area (rivers Ramganga-Ganga interfluve), Ganga Plain,India

Sediment samples collected in the Moradabad area, lying in the interfluve of the Ganga and Ramganga Rivers, were analysed for heavy metals, after studying the geomorphology of the area. Geomorphologically, the area can be divided into three terraces - the T₀, T₁ and T₂ surfaces. The rivers on these three surfaces show varying amounts of pollution depending upon the input from industries and urban settlements. The Ramganga River on the T₀ surface shows the highest amount of pollution. However, the pollution levels in all these rivers show a downstream dilution effect. The characteristic feature of the vast interfluve area (T₂ surface) is the presence of several, independent basins which are closed and rarely interact with each other or with any river. The sediments are redistributed and redeposited within the basin itself, and thus these basins serve as sinks. The sediments of one such basin in the study area show significant concentrations of arsenic, chromium, copper, nickel, lead, zinc and organic carbon. The concentrations of heavy metals in such a basin will show exponential increases with time, because there is no activity to funnel out the sediments and dilute the effect of pollution. This increase will pose more threats, as ultimately it will make its way laterally and vertically through the sediments, thereby polluting groundwater.     

Channelized and hillslope sediment transport and the geomorphology of mountain belts

This paper uses the results of landscape evolution models and morphometric data from the Andes of northern Peru and the eastern Swiss Alps to illustrate how the ratio between sediment transport on hillslopes and in channels influences landscape and channel network morphologies and dynamics. The headwaters of fluvial- and debris-flow-dominated systems (channelized processes) are characterized by rough, high-relief, highly incised surfaces which contain a dense and hence a closely spaced channel network. Also, these systems tend to respond rapidly to modifications in external forcing (e.g., rock uplift and/or precipitation). This is the case because the high channel density results in a high bulk diffusivity. In contrast, headwaters where landsliding is an important sediment source are characterized by a low channel density and by rather straight and unstable channels. In addition, the topographies are generally smooth. The low channel density then results in a relatively low bulk diffusivity. As a consequence, response times are greater in headwaters of landslide-dominated systems than in highly dissected drainages. The Peruvian and Swiss case studies show how regional differences in climate and the litho-tectonic architecture potentially exert contrasting controls on the relative importance of channelized versus hillslope processes and thus on the overall geomorphometry. Specifically, the Peruvian example illustrates to what extent the storminess of climate has influenced production and transport of sediment on hillslopes and in channels, and how these differences are seen in the morphometry of the landscape. The Swiss example shows how the bedding orientation of the bedrock drives channelized and hillslope processes to contrasting extents, and how these differences are mirrored in the landscape. An erratum to this article can be found at     

Complex formation in the ternary system Mg(II)-CO2-H2O

The carbonato and hydrogencarbonato complexes of Mg²⁺ were investigated at 25 and 50° in solutions of the constant ClO₄^? molality (3 M) consisting preponderantly of NaClO₄. The experimental data could be explained assuming the following equilibria: Mg²⁺ + CO_2B + H₂O ag MgHCO⁺₃ + H⁺, $\text{log}{}^1\text{β}{}_1\text{= ?7.64}{}_4\text{± 0.01}{}_7\text{(25°), ?7.46}{}_2\text{± 0.01}{}_1\text{(50°)}$, Mg²⁺ + 2 CO_2g + 2 H₂Oag Mg(HCO₃)⁰₂ ± 2 H⁺, $\text{log}{}^1\text{β}{}_2\text{= ?15.00 ± 0.14 (25°)}$, ?15.37 ± 0.39 (50°), Mg²⁺ + CO_2g + H₂Oag MgCO⁰₃ + 2 H⁺, $\text{log}{}^1\text{k}{}_1\text{= ?15.64 ± 0.06 (25°)}$,?15.23 ± 0.02 (50°), with the assumption γ_MgCO3⁰ = γ_Mg(HCO3)⁰2, ΔG⁰(I = 0) for the reaction MgCO⁰₃ + CO_2g + H₂O = Mg(HCO₃)⁰₂ was estimated to be ?3.9₁ ± 0.8₆ and 0.6 ± 2.4 kJ/mol at 25 and 50°C, respectively. The abundance of carbonate linked Mg(II) species in fresh water systems is discussed.     

Characterization of ultrafine aerosol particles in Mt. Etna emissions

Particulate emissions from Mt. Etna in the fine-size range below 100 nm were studied in June and September 1989. The aerosol particles were characterized by size, concentration and photoelectric activity. These quantities are sensitive to the physical and chemical properties of the magma. Concentrations varied from 10⁴ to 10⁷ cm^-3. The size distributions peak below 20 nm (radius) and are very narrow. The particles are generated mainly by nucleation and condensation of magmatic volatiles in a strong temperature gradient. The photoelectric activity of these particles can indicate high magma levels and increased exsolution of volatiles. It is therefore related to the observed activity of the respective crater and may be helpful as a prediction tool when used in conjunction with other volcano-monitoring techniques.     

Organized bacterial assemblies in manganese nodules: evidence for a role of S-layers in metal deposition

Polymetallic/ferro-manganese nodules (Mn-nodules) reach sizes of up to 10 cm in diameter and are abundantly found on the seabed. To date, the origin of Mn-nodules remains unclear, and both abiogenic and biogenic origins have been proposed. In search of evidence for a contribution of microbial processes to the formation of Mn-nodules, we analyzed those spherical nodules which contain a concentrically banded texture in their interior. The Mn-nodules were collected at a depth of 5,152 m from the Clarion-Clipperton Zone. Our high-resolution scanning electron microscopy analyses reveal first published evidence that endolithic microorganisms exist and are arranged in a highly organized manner on plane mineral surfaces within the nodules. These microorganisms are adorned on their surfaces with S-layers, which are indicative for bacteria. Moreover, the data suggest that these S-layers are the crystallization seeds for the mineralization process. We conclude that the mineral material of the Mn-nodule has a biogenic origin, and hope that these data will contribute to the development of biotechnological approaches to concentrate metals from seawater using bacteria in bioreactors.     

Remote sensing of substances in water

Remote sensing of water colour and its application to the mapping of pigments, suspended matter and other substances by means of airborne and spaceborne sensors is discussed. After an introduction to the physical process involved, the methods for a quantitative interpretation especially of CZCS data are indicated. Applications towards the monitoring of coastal pollution, of algae blooms and of dynamic processes are shown by means of selected examples. Multispectral scanner and imaging spectrometer technologies are discussed with special reference to NASA's Earth Observation System and ESA's Earth Observation Programme.     

Isothermal compression of low-cordierite to 30 kbar (25° C)

The compression of cordierite (Mg, Fe)₂Al₄Si₅O₁₈·n (H₂O, CO₂; Na⁺, K⁺) has been studied up to 30 kbar (25° C) by volumetric measurements with a piston cylinder apparatus and by X-ray measurements with a diamond-anvil cell. Natural cordierite of intermediate Mg-Fe composition and synthetic Mg-cordierite served as samples. Two discontinuities at 2.2±0.3 and 9.0±0.6 kbar which are correlated with very small volume changes (0.3?0.05%) have been found. The X-ray data indicate, however, no symmetry change of the crystal structure. The two discontinuities are interpreted as phase transitions. The two discontinuities establish three pressure dependent phases referred to as low-pressure (LP)-, first high-pressure (HP1)- and second high-pressure (HP2)-phase. The gross compressibility of cordierite decreases from 1.1 Mbar^?1 at low pressure to 0.7 Mbar^?1 at 30 kbar for the intermediate Mg-Fe cordierite, and to 0.4 Mbar^?1 for Mg-cordierite. Depending on the pressure transmitting medium used in the two different compression techniques, two kinds of compression behavior are observed for cordierite. The measurements with the piston cylinder apparatus where lead is used as quasihydrostatic pressure medium indicate normal compression properties. The X-ray data, however, obtained with the diamond anvil cell where a methanol-ethanol mixture provides hydrostatic pressure conditions yield, e.g. for the HP1-phase a dramatic decrease in compressibility to almost zero. IR-spectra from samples of augmenting experiments with methanol, deuteromethanol and D₂O as pressure media indicate that pressure media of which the molecule size is comparable with the dimensions of the cordierite channels may be incorporated in the structure. This suggests that under such hydrostatic conditions the compression of cordierite is modified by a structure internal component which is acting via the channel system.     

Characteristics of a planar rock slide: Hamersley range, Western Australia

A large planar rock slide in the Hamersley Range, Western Australia, is described and analysed for possible causes of failure. The general characteristics of the slide are determined by the major joint sets. The rock mass consists predominantly of alternating massive chert members and argillaceous horizons—giving the rock mass a distinctive flaggy appearance. The failure plane dips at 17° and is coincident with a shale horizon. Because of the low inclination of the failure plane factors of safety less than one cannot be obtained from limiting-equilibrium hindcast estimates, unless high joint-water pressures and/or seismic loading are invoked. But while the operation of these two factors cannot be totally ruled out, the field evidence suggests that the necessary conditions for failure were due to the weathering out of shale horizons which could have led to “adjustments” of the rock mass, giving rise to dynamic loading conditions along potential failure planes.