Limestone weathering in Eastern Australia. Part 2: Surface micromorphology study

Results from long term microerosion meter (MEM) studies indicate that microenvironments are characterized by different erosion rates. A complementary study, carried out on the same sites, examines the microscale morphology in each environment. Optical and scanning electron microscopy were used to identify a range of features thought to reflect different processes. Under subaerial conditions micromorphology is dominated by biological weathering features owing to the presence of microflora. Sites permanently covered by soil or stream water have only dissolution etch features, though stream sites may exhibit microfractures. Sites with periodic exposure exhibit both dissolution and biological etch features. The natural environment is more accurately reflected by allowing some microflora colonization of MEM sites rather than preventing colonization by artificial means.     

Southern Segment of the European Geotraverse — a wide-angle seismic refraction experiment in the Sardinia Channel

The Sardinia Channel dataset was collected as part of the European Geotraverse (EGT)—a 4000 km seismic refraction line running from Northern Norway to the Sahara, designed to investigate the structure of the lithosphere beneath Europe. Wideangle seismic data recorded by ocean bottom seismometers deployed in the Sardinia Channel as part of the Southern Segment of the EGT, together with gravity data, were used to constrain the final crustal model. In the centre of the Channel the crust is identified as thinned continental in nature, with a crystalline thickness of 10 km overlain by 4 km of sediments and 2.5 km of water in the most extended region. High velocities in the lower crust in the central region are thought to represent an area of underplating or intrusion by igneous material caused by extension related to the opening of the Tyrrhenian Sea. The crust overlies an anomalously low velocity upper mantle.     

Stratigraphy,structure and geochronology of ore leads in the Matsitama Schist belt of Northern Botswana

The Matsitama schist belt in northeastern Botswana comprises an area of metasediments, notably quartzites, limestones, shales and amphibolites that are bounded by granites and gneisses. The belt lies southwest of the Rhodesian cration and north of the Limpopo mobile belt.Stratigraphic, structural and lead isotopic evidence indicates that the Matsitama metasediments are equivalent to the Shashi metasediments in the Limpopo belt. There is strong evidence that the Matsitama and Shashi metasediments stratigraphically underlie volcanic rocks of the Tati belt which have been correlated with Archaean schist belts of about 2700 Ma of Rhodesia. Therefore, the Matsitama and Shashi rocks are at least as old as the schist belts of the Rhodesian craton and may represent a shallow-water facies that occurs only in the Limpopo area.There is no structural evidence that the Matsitama and Shashi metasediments were deposited unconformably on basement rocks, although the presence of gneiss, amphibolite and ironstone pebbles in a Matsitama conglomerate, as well as the presence of orthoquartzites, shows the existence of a basement source region. However, the surrounding granites intrude the Matsitama and Shashi metasediments and all underwent several deformation phases.The structural history of the Matsitama rocks can be described in terms of five phases of deformation. The main cleavage-producing deformation phase, F₂, folded the rocks into a major synform and intensely deformed them. Before this, however, the rocks had been folded and thrust so that part of the succession shows downward-facing F₂ structures and there are possibly repetitions of the stratigraphy due to imbrication. Structures of the F₃ and F₄ phases fold the main cleavage but locally are sufficiently intense to modify the shape of the finite strain ellipsoid. There is a major ductile shear zone of F₄ age, south of which F₄ folds are tight, while to the north, F₄ deformation is negligible. All of these structures can be correlated with deformation phases in the Tati schist belt to the east and in the northern part of the Limpopo mobile belt.Lead isotope evidence suggests that mineralization in the Matsitama metasediments occurred at least 2200 Ma ago, and that leads from Dihudi/Thakadu and Messina, in the centre of the Limpopo belt, underwent a two-stage history of events at 2600–2700 Ma and 2000–2100 Ma ago, agreeing with other geochronological evidence. The leads from Matsitama and Messina are isotopically distinct from leads from the Rhodesian schist belts, which show evidence of transfer to the crust some 3500 Ma ago. The absence of this 3500 Ma-old lead from the Matsitama and Messina environments may indicate different crustal conditions and possibly the absence of the Rhodesian-type early basement.     

First Data on Au–Sb Mineralization of the Ariadnoe Ultramafic Intrusion,Primor’e

Doklady Earth Sciences - A new promising source of mineral deposits is found in the southern part of the Far East of Russia: the Ti-bearing intrusions of ultramafic rocks of the Sikhote-Alin...     

Analytical and experimental investigation on vibrating rectangular plates with two opposite free edges and internal supports while the remaining are elastically restrained against rotation

This paper deals with the determination of an approximate fundamental frequency equation for a rectangular plate with two edges (y = 0, b) elastically restrained against rotation while the edges x=0, a are free but internal supports parallel to the free edges are present in the structural system. The algorithmic procedure can be easily implemented on a micro computer or even a hand, programmable calculator.Good engineering agreement with experimental results is shown to exist in the case of a plate with edges y=0,b rigidly clamped.     

Vertical distribution of dissolved organic carbon (DOC) in the Western Mediterranean Sea in relation to the hydrological characteristics

Vertical profiles of dissolved organic carbon (DOC) from eight hydrological stations in the Tyrrhenian Sea, Sardinia Channel and Algerian Sea, are reported. DOC exhibits concentrations ranging from 58 to 88 μM in surface water, 43–57 μM in the intermediate layer and 49–63 μM in deep waters. The assessment of the hydrological characteristics allows different water masses in the study area to be identified; moreover, different hydrological processes are observed in the Tyrrhenian and Algerian basins. DOC exhibits different values in the different water masses. The lowest DOC concentrations (43–46 μM) were found in the Tyrrhenian Levantine Intermediate Water (LIW). Correlations between DOC and apparent oxygen utilization (AOU), investigated within each water mass, exhibit different behaviors in the intermediate and deep waters, suggesting the occurrence of different processes of oxygen consumption in the different water masses.     

Invertebrates in the trophic webs of the white sea near-shore ecosystem (using the example of Gryaznaya Inlet)

In the food clods of the mass species of macrobenthos of the Gryaznaya Inlet, nonstructured matter plays a great role. We identify this matter as derivates from plant tissues, which are the products of their external metabolism and degradation, with associated microorganisms. This way, the near-shore community considered is supported by a detrital trophic web. This feature distinguishes it from the similar community of the near-Atlantic waters that is based on a pasture web, at least as far as the bivalve mass species are concerned. The groups of the near-shore species of Gryaznaya Inlet separated by a cluster analysis are identified as consortia, combined by the biogeochemical conditions (edifice factor), which can hardly be analyzed at present.     

Thermal Stratification in Saldanha Bay (South Africa) and Subtidal, Density-driven Exchange with the Coastal Waters of the Benguela Upwelling System

A study was conducted to understand the mechanisms driving observed subtidal variability in the stratification of Saldanha Bay, located in the southern Benguela system. It was found that the 6–8 day period variability in bay stratification was caused by the inflow and outflow of cold upwelled water driven by changing baroclinic pressure gradients between the coastal and bay domains. The direction and magnitude of the pressure gradients were governed by coastal upwelling activity and a lag in the response of the bay to changes in density structure in the coastal ocean. When the pressure gradients were bayward and cold water was being driven into the bay the cycle was termed to be in an ‘ active phase ’ and the reverse was termed the ‘ relaxation phase ’. The upwelling-favourable equatorward wind stress impacted the bay stratification in two ways: on the regional scale, wind drives upwelling and governs the inflow–outflow of cold upwelled bottom water, which strengthens stratification; conversely, on the local bay scale, wind drives vertical mixing, which weakens stratification. A four-phase model is used to describe the observed variability in stratification in the bay. The associated density-driven exchange flows are capable of flushing the bay in 6–8 days, about one-third of the time for tidal exchange alone (c. 25 days). These inflows of cold bottom water are ecologically critical as they supply nutrients to the bay and thus impose a control on new production within the bay environment. Further ecological implications of this bay–ocean exchange include export of phytoplankton new production to the coast, limitation of the risk of harmful algal blooms (HABs) and the division of the system into two distinct ecosystems (bay and lagoon).     

Dynamic response of the leg of a tension leg platform subjected to an axial, suddenly applied load at one end

This paper deals with the solution of the problem of the dynamic response of the leg of a tension leg platform subjected to an axial, suddenly applied load at one end, considering a highly simplified model but taking into account several complicating factors. The problem is solved by means of a non-harmonic Fourier expansion in terms of eigenfunctions obtained from a non-regular Sturm-Liouville system.     

The mass ratio of Nova Muscae 1991

We report intermediate resolution H spectroscopy of the black hole candidate Nova Muscae 1991 during quiescence. We classify the companion star as a K3-K4V which contributes 85±6 percent to the total flux from the binary. The photospheric absorption lines are broadened by 106±13 kms⁻¹ with respect to template field stars, leading to a system mass ratio of q =M₁/M₂ = 7.8_−2.0^+3.4. Doppler imaging of the H line shows strong emission coming from the secondary star (EW=3.1±0.6Å) which we associate with chromospheric activity. However, the hot-spot is not detected and this may indicate a lower mass transfer rate than in other X-ray transients of comparable orbital periods. The surface brightness distribution of the accretion disk in H follows a relation I∝R^−1.1, less steep than typically observed in cataclysmic variables. Updated system parameters are also presented.