Tectonic transition from the Songpan-Garzê Fold Belt to the Sichuan Basin, south-western China

The formation of the Songpan-Garzê Fold Belt and the initiation of the terrestrial Sichuan Basin are related to closing of the Palaeo-Tethys during the Late Triassic Indosinian orogeny. The Songpan-Garzê Fold Belt is composed of Triassic (T₁-_-T²₃) turbiditic deposits and Palaeozoic greywacke-shale, whereas the Sichuan Basin consists of Sinian to middle Upper Triassic (T²₃) platform carbonates and Upper Triassic (T_3X to Quaternary terrestrial elastics. Three principal deformation episodes during the Late Triassic (Norian to Rhaetian) were progressively localized towards the south-eastern margin of the fold belt. D₁ was a SW-directed shortening event, related to continuous subduction of the Palaeo-Tethys, and produced NW-trending structures. Differential strain between the fold belt and the Sichuan Basin was accommodated by sinistral shearing along a NE-trending transitional zone during D₂^. D₃ SE-directed compression was the result of collision between the Cimmerian and Eurasian Continents and initiated the Longmen Mountains Thrust-Nappe Belt and terrestrial Sichuan Basin. Post-D₃ deformation, related to SE-directed thrusting in the Longmen Mountains, then propagated from hinterland to foreland. The Indosinian orogeny closed the Palaeo-Tethys and terminated the marine conditions that dominated the early evolution of the intracratonic Sichuan Basin. Tectonic loading from the exhumed fold belt and Thrust-Nappe Belt induced substantial subsidence in the Sichuan Basin, especially in the Western Sichuan Foreland Basin, resulting in the deposition of a terrestrial clastic sequence during Late Triassic (T_3X to Quaternary times. The foreland basin history comprises an early stage during the Late Triassic (T_3x^1–2), an over-fill stage during the latest Triassic to Early Cretaceous (T_3X³- K_1J), and a shrinking stage from the Late Cretaceous to the Quaternary (K_2J-Q). These can be correlated with tectonic events in the Thrust-Nappe Belt.     

Explosive volcanic eruptions—VIII. The role of magma recycling in controlling the behaviour of Hawaiian-style lava fountains

Explosive eruptions of mafic magmas produce lava fountains whose heights are a function of the exsolved volatile content of the magma, its erupted mass flux, and the geometry of the vent (which may be an elongate fissure or a localized, near-circular conduit). The geometry of the initial vent (and the eruptive behaviour) can be distinctly modified by lava drainback and accumulating ejecta. Hot pyroclasts landing near the vent may coalesce to form rootless flows, some of which may drain back into the vent to be recycled into the eruption products. Rootless flows may be at least partially confined by pre-existing topographic features, or by spatter or cinder ramparts being built up by the eruption itself, so that they accumulate into a lava pond over and around the vent. The erupting jet of magmatic gas and pyroclasts must force its way through such a pond and will entrain some of the pond lava as it does so. The energy expended in entraining and accelerating previously erupted materials will reduce the eruption velocity and the lava fountain height by an amount which can be calculated as a function of the eruption conditions and the lava pond depth (or lava drainback rate). The results of such calculations are presented, and are used to assess the influence of this process on attempts to infer magma volatile contents from field observations of lava fountain heights.     

On the choice of a windbreak porosity profile

Measurements of mean windspeed and turbulence were carried out behind two sections of 50% porous fence differing only in the vertical distribution of their porosity. One section of the fence was uniformly porous, the other relatively dense near the ground and open aloft. Slightly greater mean speed reduction was observed near the ground in the near lee of the section which was dense at ground-level without any detrimental increase in turbulence. However, this advantage was offset by less effective protection in the far lee. These findings are consistent with earlier work by Gandemer (1979) and with the predictions of a numerical model of windbreak flow.     

Modelling atmospheric dispersal of the Chernobyl release across Europe

At the time of the Chernobyl accident little was known about the magnitude and time pattern of the release from the damaged reactor. This paper describes the detective work done in the weeks following the accident to assess the release and its dispersal across Europe; also calculations done since the USSR presentations in Vienna at the end of August 1986 and some estimates of longer term collective dose commitment. To conclude some general remarks are made about the implications of the Chernobyl accident for technical support in emergency procedures for any future nuclear accident.     

In Situ Biorestoration as a Ground Water Remediation Technique

In situ biorestoration, where applicable, is indicated as a potentially very cost-effective and environmentally acceptable remediation technology. Many contaminants in solution in ground water as well as vapors in the unsaturated zone can be completely degraded or transformed into new compounds by naturally occurring indigenous microbial populations. Undoubtedly, thousands of contamination events are remediated naturally before the contamination reaches a point of detection. The need is for methodology to determine when natural biorestoration is occurring, the stage the restoration process is in, whether enhancement of the process is possible or desirable, and what will happen if natural processes are allowed to run their course.
In addition to the nature of the contaminant, several environmental factors are known to influence the capacity of indigenous microbial populations to degrade contaminants. These factors include dissolved oxygen, pH, temperature, oxidation-reduction potential, availability of mineral nutrients, salinity, soil moisture, the concentration of specific pollutants, and the nutritional quality of dissolved organic carbon in the ground water.
Most enhanced in situ bioreclamation techniques available today are variations of hydrocarbon degradation procedures pioneered and patented by Raymond and coworkers at Suntech during the period 1974 to 1978. Nutrients and oxygen are introduced through injection wells and circulated through the contaminated zone by pumping one or more producing wells.
The limiting factor in remediation technology is getting the contaminated subsurface material to the treatment unit or units, or in the case of in situ processes, getting the treatment process to the contaminated material. The key to successful remediation is a thorough understanding of the hydrogeologic and geochemical characteristics of the contaminated area.     

Metal accumulation rates in northwest Atlantic pelagic sediments

Measurements of ²³⁰Th, ${}^{87}\text{Sr}{}^{86}\text{Sr}$ and twenty-four metals were made on cores from the Nares Abyssal Plain. The sediment is characterized by slowly-accumulating (0.3–0.7 g/cm² 10³ yr) pelagic red clays and rapidly deposited grey clays transported by turbidity currents. Despite their colour differences and the enrichment of Mn, Fe, Cu, Co, Ni, Zn, V and, to a lesser degree, the rare earths in the red clays, Sr isotope evidence demonstrates that the clays have the same terrigenous origin. The excesses of metals in the red clays have been attributed to metal removal from the water column and a comparison with the grey clays has enabled the authigenic fluxes of metals to be estimated. The fluxes obtained are in the ranges 20–50 μmol/cm² 10³ yr for Mn and Fe, 0.1–0.4 μmol/cm² 10³ yr for Cu, Co, Ni, Zn, V, Sr and Ce, 10–20 nmol/cm² 10³ yr for La and Nd, and 0.5-3 nmol/cm² 10³ yr for Sm, Eu, Gd, Dy, Er and Yb. Authigenic fluxes of Y, Nb, Cr, Zr, Rb, U and Th were not resolvable. Fluxes appear to be near constant on the Plain but comparison with other areas shows that they are quite variable both between and within ocean basins. The chief factor controlling authigenic fluxes is the geochemical abundances of the elements but fractionation within both the transition element and rare earth series can be recognized from inter-element comparisons and from differences in fluxes between Atlantic and Pacific red clays corresponding to the oceanic reactivities of the elements.     

Non-steady state diagenetic record in eastern equatorial Atlantic sediments

The radiocarbon age profile of a sediment core from the eastern equatorial Atlantic shows a marked decrease in both clay and carbonate accumulation rates at the end of the last glacial period, with overall rates of 3.2 and 8.1 cm/kyr for the Holocene and late glacial respectively. The transition from glacial to postglacial conditions recorded in the sediments at 39 cm is above the visual Fe(II)/Fe(III) redox boundary at 48 cm which has been used in the past to identify the glacial section, and even further above the increase in preserved organic carbon content at 55 cm. It is concluded from the present organic carbon profile, and recent observations in this area and elsewhere, that organic diagenesis in these sediments is not steady state. Instead it is suggested that the uppermost glacial sediments lost carbon through oxic remineralisation at the change to postglacial conditions, and that this process is now continued with nitrate as the electron acceptor. These observations suggest that the double MnO_x solid phase peak which occurs in these and similar sediments is a direct consequence of an adjustment of the oxic layer depth following the decrease in carbon flux at the onset of the Holocene.     

A study on hydrogen peroxide in the atmosphere

Hydrogen peroxide (H2O2) concentrations were measured at two sites. One was on Lushan Mountain in May, 1987. The other was in Beijing in August, 1987 and in December, 1986. The automated fluorometric method was used for the determination of H2O2. The concentrations of H2O2 ranged from approximately 0.50 to 4.32 ppb on Lushan Mountain. The concentrations of H2O2 ranged from approximately 0.05 to 1.49 ppb in August in Beijing, and it was only 0.01 ppb in December in Beijing.     

In Situ Bioreclamation: A Cost-Effective Technology to Remediate Subsurface Organic Contamination

In situ bioreclamation is a proven technology that cost-effectively treats organic contamination in subsurface environments. As a remediation strategy, it reduces both the contamination dissolved in ground water, as well as residual soil-bound contamination.
To maximize biodegradation, the technology is applied after conducting laboratory studies. Application of the technology involves infiltrating necessary nutrients to the contaminated subsurface.
Results of a specific case study indicate excellent performance with rapid cleanup of petroleum hydrocarbon contamination from soils and ground water.
Costs associated with in situ bioreclamation technology showed a savings of approximately 50 percent over simple pump-and-treat technology. Time frame for cleanup was shown to be approximately 30 percent of the projected time frame of simple pump-and-treat technology.