Mechanisms of partly flooded loose sand deposits

Partly flooded loose sand deposits are left back from lignite mining, particularly in east Germany. After flooding, gas inclusions in macropores enhance the pore pressure increase by total stress cycles without drainage, and this can cause the transition into a kind of suspension. Thus, natural and technical changes of surface loads triggered flow slides in chain reactions of sometimes catastrophic extent. Such collapsible deposits were and are stabilized by blast-induced liquefaction and densification. Successive collapse fronts in flooded grain skeletons are seismogeneous, and this appears as wavering in the near-field and leads to power-law spectra in the far-field. Apart from this evidence of mild fractality, the wild fractality of chain reactions eludes mathematical treatment. Therefore, uncommon methods of geotechnical design, operations and monitoring are required.     

Granular solid dynamics with eutaraxy and hysteresis

Acta Geotechnica - The dynamics of grain fabrics is captured by means of a hidden state variable , named eutaraxy, which quantifies the propensity for a heat-like micro-seismicity due to disturbing...     

Thermal modeling of Carboniferous to Triassic sediments of the Karawanken Range (Southern Alps) as a tool for paleogeographic reconstructions in the Alpine–Dinaridic–Pannonian realm

Vitrinite reflectance was measured in Late Carboniferous to Triassic shales, siltstones and marls of the Karawanken Range. Thermal models of the central South-Karawanken Range were calibrated on the basis of these data. They suggest an eroded overburden of more than 3,200 m of Jurassic to Cretaceous sediments and a heat flow in the range of 42 to 60 mW m^?2 during the time of maximum subsidence. Because the reconstructed thermal history of the South-Karawanken Range is very similar to the thermal history of the Generoso basin (western Southern Alps), these data provide strong evidence for a deep basinal position of the Southern Karawanken Range during Jurassic to Cretaceous times. A vitrinite reflectance anomaly at the northern margin of the South-Karawanken Range is explained by advective heat transport during the Oligocene. The heat source for the anomalies at the western margin of the Seeberg Rise and in the area between the Periadriatic Lineament and the Donat Fault Zone is unknown. Vitrinite reflectance in Late Triassic sediments indicates the South-Karawanken Range and the South-Zala Unit of the Pannonian basement as exotic blocks in the Sava Composite Unit. This is explained by Miocene displacement of structural units, which were derived from different paleogeographical segments of the Permo-Mesozoic western Tethyan margin.     

Mineral distribution and feldspar weathering in a saprolite from northeastern Nigeria

Mineral composition was analysed within a saprolite profile from NE Nigeria. The determination of identifiable feldspar phases is only based on X-ray powder diffractograms. Representative K-feldspar fragments were selected for detailed SEM (scanning electron microscope) studies and EDX (energy-dispersive X-ray analysis) from the profile.

The analytical data indicate a significant contrast in weathering states between the lower and the upper profile section. This contrast reflects a different weathering history: the feldspars from the lower section exhibit weathering features that are characteristic for decomposition below the water table. When raised above the water table, another type of decomposition attacked only the feldspars within the upper section while those in the lower section still preserve the older weathering state.     

Direct measurements of volume transports through Fram Strait

Heat and freshwater transports through Fram Strait are understood to have a significant influence on the hydrographic conditions in the Arctic Ocean and on water mass modifications in the Nordic seas. To determine these transports and their variability reliable estimates of the volume transport through the strait are required. Current meter moorings were deployed in Fram Strait from September 1997 to September 1999 in the framework of the EU MAST III Variability of Exchanges in the Northern Seas programme. The monthly mean velocity fields reveal marked velocity variations over seasonal and annual time scales, and the spatial structure of the northward flowing West Spitsbergen Current and the southward East Greenland Current with a maximum in spring and a minimum in summer. The volume transport obtained by averaging the monthly means over two years amounts to 9.5 ± 1.4 Sv to the north and 11.1 ± 1.7 Sv to the south (1 Sv = 10⁶ m³s⁻¹). The West Spitsbergen Current has a strong barotropic and a weaker baroclinic component; in the East Greenland Current barotropic and baroclinic components are of similar magnitude. The net transport through the strait is 4.2 ± 2.3 Sv to the south. The obtained northward and southward transports are significantly larger than earlier estimates in the literature; however, within its range of uncertainty the balance obtained from a two year average is consistent with earlier estimates.     

Schwefel-, Kohlenstoff- und Sauerstoff-Isotopenuntersuchungen am Kupferschiefer als Beitrag zur genetischen Deutung

The isotopic composition of sulfur, carbon and oxygen was determined in 106 samples mainly from profiles of Kupferschiefer occurences in N.W. Germany and N. Holland. From the bulk samples pyrite, non-pyritic sulfides and gypsum have been concentrated for isotopical analysis. C¹³/C¹²-ratios were measured in carbonates and in organic carbon and O¹⁸/O¹⁶-ratios in carbonates and in sulfates. Analytical data on CO₂, C, S in all samples and on Fe, Cu, Zn and Pb in a part of the profile samples are presented.Primary sulfates can be distinguished from sulfates formed from oxydized sulfides by their sulfur and oxygen isotopic composition. The abundance of light carbon and sulfur as well as the correlation between the S- and C-values are strong indications for bacterial sulfate reduction. Highly S³²-enriched metal sulfides (S³⁴ averages –30 to –35) have fixed the H₂S from bacterial production at its starting conditions. A large variation of the sulfide-S-values (–4 to –44) and the occurence of S³⁴-enriched residue-sulfates from closed systems (+11 to +26) support the above mentioned theory. A systematic fractionation of sulfur between the sulfur minerals as observed in hydrothermal deposits (increasing S³⁴ in the sequence: pyrite>sphalerite>chalcopyrite>galena) has not been detected. In our case the regular difference in S³⁴ between the sulfides is consistent with the idea of a successive precipitation of the metals due to their different solubility with increasing bacterial H₂S production. In such a sequence the increase of S³⁴ is due to the consumption of light sulfate by bacterial reduction after the transition from an open to a closed system.It is alternately discussed, whether bacterial reduction and metal precipitation took place in bodies of stagnant sea water above or within the sediment. Presuming a precipitation of metals in a closed water-reservoir observations of other authors concerning the vertical sequence of metals and of the present author regarding the accumulation of S³⁴ in the sequence of precipitated sulfides can be easily explained.Evidence from isotope fractionation in sediment sequences favours the assumption of a precipitation of metals in the sediment: light carbon above the zone rich in carbonates (with a marine carbon composition) and metals. This characteristic change in the C¹³/C¹²-ratio is due to the increasing influence of light carbon dioxide of biogenic origin. Assuming the production of H₂S as restricted to the sediment, the transition from the open to the closed system as a result of growing thickness of the sediment (with lowered permeability for sulfate- and metalbearing water) controls the sequence of carbon composition. The restriction of metal precipitation in the sediment causes difficulties in interpreting regular zoning of metals and the metal supply. Especially the numerous exchanges of pore water required for the supply of sulfate and metals in the bituminous sediment with very low permeability cannot be explained.The assumption of a syngenetic sulfide precipitation is confirmed by the results of the carbon isotope analysis. The trend to heavy carbonates in the sequence of the profiles can be interpreted as due to rising marine influence with time in the early Zechstein basin. This trend is only interrupted several times in the Kupferschiefer-sediment by the occurence of light carbonates of biogenic origin above zones of sulfide accumulation. A model of epigenetic metal supply forming this regular pattern of correlated sulfur and carbon distribution and composition cannot be constructed. The evidence from our data favours the assumption of concurring processes of carbon fixation in carbonates and in organic substances and sulfur precipitation as sulfides during the formation of the sediment.

---

---

Herrn Prof. Dr. K. H. Wedepohl danke ich für die Stellung des Themas, Überlassung des Probenmaterials und für sein reges Interesse am Fortgang der Arbeit. Meinen Dank möchte ich auch allen Mitarbeitern der mineralogischen Anstalten und des Zentrallabors aussprechen, die mich durch vielerlei Anregungen und Diskussionsbereitschaft unterstützt haben. Die massenspektrometrischen Untersuchungen wurden von der Deutschen Forschungsgemeinschaft durch die Einrichtung des Zentrallabors für Geochemie der Isotope an der Universität Göttingen ermöglicht.