Geologic structure and neotectonics of the North African Continental Margin south of Sicily

Marine geological and geophysical data together with drilling information indicate that the North African passive continental margin has been subjected to extension and wrenching after it collided with the northern part of Sicily. The area of the Tripolitania Basin, Jarrafa Trough, Melita and Medina Bank and the Ragusa-Malta Plateau has formed part of a sinking passive margin since the dispersal of Gondwanaland at about 180 My ago as observed from geohistory diagrams. A record of rifting in a NW-SE direction accompanied by dextral shear along the southern troughs is observed in seismic reflection data. The rifting started during the Neocomian and lasted until the Eocene when activity became minor. A pre-Middle Miocene period of northward subduction of oceanic crust is inferred from the geology in NE Sicily. Uplift of the northern part of the African margin after collision in the Middle Miocene is seen in wells in southern Sicily. After the Messinian a rift and dextral shear zone established itself across the African Margin from the Strait of Sicily to the Medina Ridge in the lonian Basin. The zone is marked by up to 1.7 km deep grabens, narrow active wrench faulted channels, volcanic fissures and local uplifted ‘Keilhorsts’ such as Malta. This zone, which varies in width from 100 to 35 km, forms the southern boundary of a microplate which includes Sicily. We speculate that the present motion of this microplate is partly due to the eastward movement of the Calabrian Arc with the Sicilian block over the last remaining oceanic lithosphere in the Eastern Mediterranean.     

The relation between the synodic and sidereal rotation period of the Sun

The relation between the synodic and sidereal rotation period of the Sun for an arbitrary date of observation is derived taking into account details of the Earth's motion. The transformation procedure between the synodic (apparent) and sidereal rotation period presented here can be performed without using the annual ephemerides.     

Sedimentology of the Upper Burdekin River of North Queensland, Australia—an example of a tropical, variable discharge river

The Burdekin River is an example of a class of tropical streams which experience two to four orders of magnitude variation in discharge, in response to seasonal but erratic monsoonal rainfall. Floods of the Burdekin rise abruptly, reaching peak discharges of up to 40,000 m³ s^-1 in less than 24 h; maintain peak flow for up to a few days, and recede exponentially. The geomorphology and deposits of these rivers reflect the extreme discharge fluctuations, and have not previously been described. A stretch of the upper Burdekin River comprising four bends and one straight reach was examined near the town of Charters Towers. The river bed is largely exposed for most of any year, with a small, misfit perennial channel carrying low stage flow. Major geomorphic elements of bends include point bars with ridge-and-swale topography, three distinct types of chute channels, avalanche slipfaces up to 5 m or more high around the downstream edges of bars, and on the outer part of one point bar an elevated, vegetated ridge. Straight reaches are flat or gently inclined, sand- and gravel-covered surfaces. Much of the river bed is covered by well sorted, in places gravelly, coarse to very coarse-grained sand with local accumulations of pebble to boulder gravel. Lower parts of the river bed are periodically draped by mud which is desiccated on exposure. Dunes and plane beds are the most commonly occurring bedforms, with local development of gravelly antidunes. Most bank tops and upper, vegetated bars are covered by silt and fine-grained sand. The river bed also hosts a low-diversity but locally high-abundance, flood-tolerant flora dominated by the paperbark tree Melaleuca argentea, which plays an important role in controlling the distribution of sediment. The gross geomorphology of the river bed and most of the sedimentary features are interpreted as having formed during major (bankfull or near bankfull) flows, which have a recurrence of about 18 years (based on 65 years hydrographic data). The initial rapid drop in discharge following flood peaks appears to preserve flood peak features on upper bars more or less intact, whereas lower areas are subjected to variable degrees of modification during falling stage and by more frequent, non-bankfull discharge events.     

Determination of surfactant activity and anionic detergents in seawater and sea surface microlayer in the Mediterranean

The study of the physico-chemical properties and the determination of different classes of organic substances in the sea are of substantial interest and importance for understanding biogeochemical processes in the sea. The preferable method should be sensitive enough for direct measurement without pretreatment procedures in order to avoid changes in the composition of organic substances initially present in the sample.Surfactant activity data are presented here as measured by electrochemical methods during 1979, 1980 and 1981 in samples from open waters of the Western Mediterranean, and in a few characteristic coastal areas of the Adriatic Sea with different biological activity and different influence of man's activities. Data on sea surface microlayer samples collected during 1977, 1978 and 1981 at different locations and seasons in the Rijeka Bay, which is an integral part of the Adriatic Sea, are presented and discussed in more detail.It was found that the type and concentration of natural surface active material vary within different Mediterranean regions and along the depth profile of the water column.Petroleum hydrocarbons and detergents were found to be prevalent pollutants responsible for high surfactant activity values. Pollution effects are most pronounced in the sea surface microlayer.Electrochemical methods are proposed for research and monitoring of surface-active substances in the sea.     

A determination of the parameters of the level surface of lunar gravity

The spectral coefficients of the selenoid have been obtained by inverting the potential series for lunar gravity. The reference value of the lunar level surface has been determined on the base of the mean radius of lunar topography. This enables to evaluate the parameters of the tri-axial reference ellipsoid best fitted to the lunar level surface.     

Determination of origin of NASA stratospheric particles

Paper presents a reanalysis of four stratospheric particles registered in the Cosmic Dust Catalogs (CDC). Two particles have been classifed in the NASA Johnson Space Centre (JSC) in Houston as natural, terrestrial contaminants and the origin of the other two particles was found questionable, probably cosmic. Present study has confirmed these conclusions; however some new additional features in the chemical analysis have been found which can finally determine the classification of the particles with unclear origin.     

Coronal index of solar activity VIII, years 1992–1994

The coronal index of solar activity over the period 1992–1994 is given. The data are a good tool to study solar activity, for the Sun as a star, in the solar corona over a solar cycle and its influence in the heliosphere.     

Primary and derived parameters of common relevance of Astronomy,Geodesy, and Geodynamics

Problem of selecting primary parameters has been discussed. Primaries should be defined uniquely, as well as, physically. Since no unique definition for semimajor axis exists, it should be replaced by the geoidal geopotential valueW ₀ or by the geopotential scale factorR ₀ =GM/W ₀, geocentric gravitational constantGM be also primary parameter. Current best estimates of some parameters are given numerically.     

Secular love and tidal numbers of synchronously orbiting satellites

The secular Love and the secular tidal numbers have been computed for eight synchronously orbiting satellites in the solar system for which the triaxiality parameters and satellite-centric gravitational constant are available. Excepting Deimos the total mass of which should be first refined, the secular Love and tidal numbers are rather close to unity, as a rule. That is why, the centrifugal and tidal distortions can be assumed responsible for the actual figures of the synchronously orbiting satellites resulting from the primordial spheres, as well as, their static equilibrium nearly satisfied. The hypothesis of the origin of synchronously orbiting satellites by accretion in orbits is supported by the results obtained.