Earth's free core nutation determined using C032 superconducting gravimeter at station Wuhan/China

The long series tidal gravity observations from 1997 to 2002 recorded with C032 superconducting gravimeter (SG) at station Wuhan/China are used in order to study the Earth's geodynamics. The tidal gravity parameters are determined precisely using Eterna software package after careful data pre-processing. The Earth's free core nutation (FCN) resonant parameters (eigenperiods, quality factors and resonant strengths) are determined accurately. The results show the determined eigenperiod to be 431.0 sidereal days with an accuracy of ±1.81%, the quality factor is a negative one as of −7002, and the resonance strength can be explained by the elastic property of the Earth's mantle. The discrepancy of the eigenperiods when using various ocean models can amount to ±1.8%. The 30 sidereal days difference between the determined eigenperiod in this paper and the one in theoretical computation given by Wahr and Bergen can be explained by the real dynamic ellipticity of the Earth's liquid core, i.e., it is about 5% larger than the one under the hydrostatic equilibrium assumption.     

Tests of phase center variations of various GPS antennas, and some results

Phase variations of GPS receiving antennas are a significant error component in precise GPS applications. A calibration procedure has been developed by Geo++ and the Institut für Erdmessung, which directly determines absolute phase center variations (PCVs) without any multipath influence by field measurements. The precision and resolution of the procedure allows the determination of reliable azimuthal variations. PCV may affect long-term static GPS differently than real-time GPS, depending on the applications. At the same time, different antenna types are involved. Less investigations have been done on absolute PCV of rover antennas than on geodetic antennas which, however, becomes more important due to the mixed antenna situation in GPS reference networks and RTK networks. The concepts of the absolute PCV field calibration are summarized and emphasis is placed on a variety of absolute PCV patterns of geodetic and rover antennas. Electronic Publication     

Sweden

Four invertebrate and one fish species (Cerastoderma edule, Mya arenaria, Arenicola marina, Crangon crangon, Solea solea) from a single area of the German Wadden sea were investigated for concentrations of ten organochlorine pollutants in 1976. PCB concentrations (wet tissue basis) were predominating with 10–200 ng g^?1, while p,p′-DDD, dieldrin, α-HCH, γ-HCH and p,p′-DDE generally ranged between 1 and 10 ng g^?1. Values of α-endosulfan were even lower; p,p′-DDT, endrin and heptachlor epoxide could not be detected. Residue levels in shrimps were close to the lower range of values which have been found in this species from other areas of the North Sea since 1974. The patterns of residue concentrations in the five aquatic species were remarkably different indicating species- and compound-specific bioaccumulation. Trophic level and lipid content were shown to be responsible for PCB concentrations increasing from bivalves to fish.     

Vergleich von marokkanischen Kreide-Küstenaufschlüssen und Tiefseebohrungen (DSDP): Stratigraphie,Paläoenvironment und Subsidenz an einem passiven Kontinentalrand

In comparison to other regions round the North Atlantic, good exposures in the Moroccan coastal basins offer an excellent opportunity to study the Mesozoic development of a passive continental margin including the relationship between oceanic and coastal sediments and datum levels of the pelagic fossils. From south to north, the Cretaceous sediments of the coastal basins of Tarfaya, Agadir, Essaouira and at the margin of the Meseta are described and compared with each other regarding macro- and microfauna, sedimentology, and paleoenvironment. For the mainly marine 2500 m resp. 1700 thick Cretaceous sequences of Agadir and Essaouira, a correlation of ammonite and foraminiferal zones is proposed. Probably both sections were formed in one basin, but certain facies differences were caused by different water depths since Middle Cretaceous times. Most of the early Cretaceous sediments of the Tarfaya region in the south and of the Meseta in the north are of continental origin. Late Cretaecous sediments of these regions reveal, however, principal differences, especially in view of the macrofauna. On the Meseta, the macrofauna is typical of the Mediterranean faunal province, whereas the Tarfaya fauna is characterized by north-boreal elements. This is explained by the influence of upwelling in connection with the initiation of an oceanic deep-sea circulation, which also can be traced into the Agadir section. As a result, already during Turonian times, here bituminous marls with chert layers are deposited. These are missing farther to the north, but later nannomarls, chalk, chert layers and, in addition, locally phosphates are formed there, too. Generally, during the Cretaceous period, a tendency towards decreasing sedimentation rates and a relative increase of the percentage of pelagic components such as planktonic foraminifera in the local sediment can be observed, indicating a sharp decrease of the terrigeneous influx and a landward transgression of the oceanic water mass. If the global eustatic curve for the Cretaceous oceans is compared to the local bathymetric curves of the Moroccan coastal basins, one can distinguish between local phenomena and global events (Turonian and Campanian transgressions). In comparing the Cretaceous sections of DSDP sites 370 and 137 with the Agadir sequence on the continent, an attempt is made to reveal the development of the marginal North Atlantic, related to an increase of the paleodepth and the influence of the CCD. At Cape Bojador, in a transect across the continental margin from inland wells to the upper rise (DSDP site 397), the subsidence history of the uniformly subsiding ?marginal basin“ is derived. In the Jurassic, the rates of subsidence as well as those of sedimentation reach the order of magnitude of about 100 m/million years. The early Cretaceous subsidence increases up to 140 m/million years. As a result, sedimentation soon cannot keep pace, the water depth at the outer margin increases, and the shelf edge and continental slope are formed. In the last 100 million years, the subsidence decreases more or less exponentially. For the well subdivided Cretaceous sequences of the coastal basins described above, the interrelationship between subsidence, paleowaterdepth, and sedimentation rate has been worked out in more detail.     

Beitrag zur Tektonik archaischer Sedimente im Barberton-Bergland (Transvaal-Südafrika)

Zusammenfassung Die Serien des Swaziland-Systems im Gebiet der Montrose Farm (25 km südwestlich von Barberton) zeigen ähnliche Deformationen wie die wesentlich jüngeren Serien des Moodies-Systems. Strukturbestimmende Störungen mit Versetzungsbeträgen von mehr als 1000 m sind in wesentlich stärkerem Maße vorhanden als bisher angenommen. Das zu beobachtende spröde bis plastische Verhalten von gebändertem Hornstein wird auf unterschiedlichen SiO₂-Gel-Gehalt zur Zeit der Deformation zurückgeführt. Eine Gliederung der orogenetischen Ereignisse für einen Teil der Swaziland-Geosynklinale wird gegeben.

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In the Montrose Farm area (25 km SW of Barberton) Series of the Swaziland System show similar deformations as the essentially younger series of the Moodies System. Thrustfaults with desplacements of more than 1000 m are developed more often than formerly assumed. The brittle to plastic behaviour of banded cherts is due to a different content of gelic SiO₂ during deformation. A possible development of a part of the Swaziland geosyncline is given.

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Résumé Dans les séries du système Swaziland dans la région de Montrose Farm (à 25 km sud-ouest de Barberton) il y a des déformations analogues aux séries beaucoup plus jeunes du Système Moodie. Des Failles avec des déplacements de plus de 1000 m se trouvent plus souvent qu'on n'avait supposé jusqu'à présent. La conduite mobile à solide du silex zoné s'explique par le différent contenu de Gel de SiO₂ au movement de la déformation. Les événements de la période orogénétique seront exposés pour une partie du Swaziland géosynclinal.

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Swaziland Montroes (25 - ). , Moodies. Swaziland.

     

Thermal metamorphism of primitive meteorites—XL The enstatite meteorites: origin and evolution of a parent body

We report neutron activation data for Ag, As, Bi, Cd, Co, Cs, Cu, Ga, In, Rb, Se, Te, Tl and Zn in samples of Abee heated at temperatures of 1000–1400°C in a low-pressure environment (initially ~ 10^?5 atm H₂) and in 9 enstatite achondrites (aubrites) and the silicate portion of the unique stony-iron, Mt Egerton. Trace element losses in heated Abee progress with temperature, the lowest retention being 2.4 × 10^?6 of initial contents. These data indicate trace element loss above 1000°C via diffusion-controlled processes having apparent activation energies of 8–55 kcal/mol ; only Co exhibits a significantly higher energy. These trace element data and those for aubrites, Mt Egerton and E4–6 chondrites, and mineralogic and isotopic evidence link all enstatite meteorites to a common parent body. Volatile, mobile elements vary inversely with cobalt content in aubrites and Mt Egerton but directly in E4–6 chondrites; this is inconsistent with all genetic models positing fractionation of such elements during nebular condensation and accretion. However, the data are consistent with the idea that aubrites and Mt. Egerton reflect fractional crystallization of a magma produced from enstatite chondrite-like parent material (probably E6) and late introduction of chalcophiles and mobile elements transported by FeS-Fe eutectic from an E4–6 region experiencing open-system metamorphism. As suggested earlier, the only primary process that affected enstatite meteorites involved fractionation of non-volatile lithophiles from sulfides and metal during condensation and accretion of chondritic parent material from the nebula. If, as seems likely, volatile/mobile elements reflect secondary processes, they can only be used to establish alteration conditions within the enstatite parent body and not to estimate temperatures during primary nebular condensation and accretion.