Out-of-sequence thrusts and paleogeography of the Rhenodanubian Flysch Belt (Eastern Alps) revisited

The Oberstdorf nappe of the Western and the Laab nappe of the Eastern Rhenodanubian Flysch (ERF) were independently identified as out-of-sequence thrust units by facies studies (Mattern 1999) and zircon analyses (Trautwein et al. 2001a, b, c), respectively. A new look at both areas reveals mutual similarities and new evidence for the out-of-sequence concept. Paleocurrent and heavy mineral data make it possible to reconstruct the sediment influx directions. From the Barremian to the mid-Campanian, the western and eastern basin segments were fed with south-derived garnet and north-derived zircon/”ZTR” (i.e., zircon, tourmaline, and rutile). Because both out-of-sequence units are relatively rich in zircon/ZTR they must have occupied the northernmost basin position. In the Western Rhenodanubian Flysch segment, the Sigiswang nappe occupied the central and the Üntschen nappe the southernmost basin position. In the ERF segment the central basin is represented by the Greifenstein nappe and the southernmost basin by the Kahlenberg nappe. Both out-of-sequence units do not occur in the northernmost and tectonically lowest position in their respective nappe piles as they were thrust over the other nappes. The reconstructed basin positions of the thrust units are suggested by the observation of a gradient in heavy mineral content in the thrust units. This paleogeographic arrangement is least problematic and renders models with differently positioned thrust units, requiring debris-shedding intrabasinal ridges, as unnecessarily complicated. Instead, we suggest that gradual changes in heavy mineral composition existed in across-basin direction. Garnet may stem from the Central Gneiss Complex of the Tauern window and formerly exposed lateral equivalents, all representing the southern Mid-Penninic zone. We assign the Falknis/Tasna nappe and formerly exposed lateral equivalents to the northern Mid-Penninic zone which served as the zircon/ZTR source. Interpreting Ebbing’s (Ph.D. thesis, Freie Universität Berlin, pp 1-143, 2002; Fig. 6.10) density section, we suggest that Mid-Penninic crust exists beneath the Central Gneiss Complex. During the latest Cretaceous much garnet was also N-derived. This may reflect processes related to the consumption of the North Penninic basin.     

Sedimentology of the continental end‐Permian extinction event in the Sydney Basin,eastern Australia

Upper Permian to Lower Triassic coastal plain successions of the Sydney Basin in eastern Australia have been investigated in outcrop and continuous drillcores. The purpose of the investigation is to provide an assessment of palaeoenvironmental change at high southern palaeolatitudes in a continental margin context for the late Permian (Lopingian), across the end‐Permian Extinction interval, and into the Early Triassic. These basins were affected by explosive volcanic eruptions during the late Permian and, to a much lesser extent, during the Early Triassic, allowing high‐resolution age determination on the numerous tuff horizons. Palaeobotanical and radiogenic isotope data indicate that the end‐Permian Extinction occurs at the top of the uppermost coal bed, and the Permo‐Triassic boundary either within an immediately overlying mudrock succession or within a succeeding channel sandstone body, depending on locality due to lateral variation. Late Permian depositional environments were initially (during the Wuchiapingian) shallow marine and deltaic, but coastal plain fluvial environments with extensive coal‐forming mires became progressively established during the early late Permian, reflected in numerous preserved coal seams. The fluvial style of coastal plain channel deposits varies geographically. However, apart from the loss of peat‐forming mires, no significant long‐term change in depositional style (grain size, sediment‐body architecture, or sediment dispersal direction) was noted across the end‐Permian Extinction (pinpointed by turnover of the palaeoflora). There is no evidence for immediate aridification across the boundary despite a loss of coal from these successions. Rather, the end‐Permian Extinction marks the base of a long‐term, progressive trend towards better‐drained alluvial conditions into the Early Triassic. Indeed, the floral turnover was immediately followed by a flooding event in basinal depocentres, following which fluvial systems similar to those active prior to the end‐Permian Extinction were re‐established. The age of the floral extinction is constrained to 252.54 ± 0.08 to 252.10 ± 0.06 Ma by a suite of new Chemical Abrasion Isotope Dilution Thermal Ionization Mass Spectrometry U‐Pb ages on zircon grains. Another new age indicates that the return to fluvial sedimentation similar to that before the end‐Permian Extinction occurred in the basal Triassic (prior to 251.51 ± 0.14 Ma). The character of the surface separating coal‐bearing pre‐end‐Permian Extinction from coal‐barren post‐end‐Permian Extinction strata varies across the basins. In basin‐central locations, the contact varies from disconformable, where a fluvial channel body has cut down to the level of the top coal, to conformable where the top coal is overlain by mudrocks and interbedded sandstone–siltstone facies. In basin‐marginal locations, however, the contact is a pronounced erosional disconformity with coarse‐grained alluvial facies overlying older Permian rocks. There is no evidence that the contact is everywhere a disconformity or unconformity.     

The fall and rise of metropolitan government in Copenhagen

In this paper it is argued that the re-establishment of a metropolitan government in the Greater Copenhagen Area in 2000 (Greater Copenhagen Authority) is not to be seen as a return to the kind of regional, coordinative authority (Greater Copenhagen Council) that was abolished in the Thatcherite climate of the 1980s. Throughout the 1980s and 1990s new forms of urban governance, entrepreneurialism and a higher national priority to the capital region were introduced, which changed the conditions under which the new metropolitan government is operating. This `contextualization' of the analysis of the two generations of metropolitan government points to the fact that typologies of metropolitan government, such as the one put forward by Sharpe (1995), often lacks analytical cogency. This revised version was published online in August 2006 with corrections to the Cover Date.     

Submarine hydrothermal activity and gold-rich mineralization at Brothers Volcano, Kermadec Arc, New Zealand

Brothers volcano, of the Kermadec intraoceanic arc, is host to a hydrothermal system unique among seafloor hydrothermal systems known anywhere in the world. It has two distinct vent fields, known as the NW Caldera and Cone sites, whose geology, permeability, vent fluid compositions, mineralogy, and ore-forming conditions are in stark contrast to each other. The NW Caldera site strikes for ??600?m in a SW?CNE direction with chimneys occurring over a ??145-m depth interval, between ??1,690 and 1,545?m. At least 100 dead and active sulfide chimney spires occur in this field and are typically 2?C3?m in height, with some reaching 6?C7?m. Their ages (at time of sampling) fall broadly into three groups: <4, 23, and 35?years old. The chimneys typically occur near the base of individual fault-controlled benches on the caldera wall, striking in lines orthogonal to the slopes. Rarer are massive sulfide crusts 2?C3?m thick. Two main types of chimney predominate: Cu-rich (up to 28.5?wt.% Cu) and, more commonly, Zn-rich (up to 43.8?wt.% Zn). Geochemical results show that Mo, Bi, Co, Se, Sn, and Au (up to 91?ppm) are correlated with the Cu mineralization, whereas Cd, Hg, Sb, Ag, and As are associated with the dominant Zn-rich mineralization. The Cone site comprises the Upper Cone site atop the summit of the recent (main) dacite cone and the Lower Cone site that straddles the summit of an older, smaller, more degraded dacite cone on the NE flank of the main cone. Huge volumes of diffuse venting are seen at the Lower Cone site, in contrast to venting at both the Upper Cone and NW Caldera sites. Individual vents are marked by low-relief (??0.5?m) mounds comprising predominately native sulfur with bacterial mats. Vent fluids of the NW Caldera field are focused, hot (??300°C), acidic (pH????2.8), metal-rich, and gas-poor. Calculated end-member fluids from NW Caldera vents indicate that phase separation has occurred, with Cl values ranging from 93% to 137% of seawater values. By contrast, vent fluids at the Cone site are diffuse, noticeably cooler (??122°C), more acidic (pH?1.9), metal-poor, and gas-rich. Higher-than-seawater values of SO₄ and Mg in the Cone vent fluids show that these ions are being added to the hydrothermal fluid and are not being depleted via normal water/rock interactions. Iron oxide crusts 3?years in age cover the main cone summit and appear to have formed from Fe-rich brines. Evidence for magmatic contributions to the hydrothermal system at Brothers includes: high concentrations of dissolved CO₂ (e.g., 206?mM/kg at the Cone site); high CO₂/³He; negative ??D and ??¹⁸O_H2O for vent fluids; negative ??³⁴S for sulfides (to ?4.6??), sulfur (to ?10.2??), and ??¹⁵N₂ (to ?3.5??); vent fluid pH values to 1.9; and mineral assemblages common to high-sulfidation systems. Changing physicochemical conditions at the Brothers hydrothermal system, and especially the Cone site, occur over periods of months to hundreds of years, as shown by interlayered Cu?+?Au- and Zn-rich zones in chimneys, variable fluid and isotopic compositions, similar shifts in ³He/⁴He values for both Cone and NW Caldera sites, and overprinting of ??magmatic?? mineral assemblages by water/rock-dominated assemblages. Metals, especially Cu and possibly Au, may be entering the hydrothermal system via the dissolution of metal-rich glasses. They are then transported rapidly up into the system via magmatic volatiles utilizing vertical (??2.5?km long), narrow (??300-m diameter) ??pipes,?? consistent with evidence of vent fluids forming at relatively shallow depths. The NW Caldera and Cone sites are considered to represent stages along a continuum between water/rock- and magmatic/hydrothermal-dominated end-members.     

Field-induced anisotropy of magnetic susceptibility in rocks

Summary An induced anisotropy of magnetic susceptibility results from the domain alignment which is produced by treating stationary specimens in a strong alternating field. Appreciable domain re-orientation occurs in fields as low as 50 oersteds and the effect must therefore normally be an important part of the process of alternating field demagnetization. Induced anisotropy has been measured in a number of igneous rocks with a range of palaeomagnetic stabilities and in magnetite powders of controlled grain sizes, dispersed in plaster or kaolin specimens which were mechanically deformed to produce instrinsic magnetic anisotropy by grain alignment. The saturation magnitude of the induced anisotropy is not a function of grain size but the saturating field required increases with decreasing grain size. In the larger grains, induced anisotropy is a function of grain orientation.     

The Néel transition and magnetic properties of terrestrial,synthetic, and lunar ilmenites

The magnetic susceptibility of a terrestrial, synthetic and lunar ilmenite specimen has been measured from 4 to 300 K. All specimens had a single Néel temperature transition which ranged from 56 to 57.7 K. In one case the powdered specimen was partially aligned in the magnetic field prior to the susceptibility measurements and the Néel transition was observed to shift to 60 K indicating magnetic anisotropy. A study of several magnetic parameters calculated from the experimental data showed gross impurities in the terrestrial specimen, single-domain to multi-domain metallic iron in the synthetic specimen, and a small amount of superparamagnetic metallic iron in the lunar sample. No multidomain iron was observed in the lunar ilmenite. The results of electron spin resonance measurements were also in general agreement with these findings. Because of the absence of Fe³⁺ compared to most terrestrial samples it is suggested that the anisotropic magnetic parameters be determined on lunar ilmenite when a large enough single crystal becomes available.     

Responses to the 2011 floods in Central Thailand: Perpetuating the vulnerability of small and medium enterprises?

Natural Hazards - The 2011 flood was the worst in Thailand in decades. Many of the impacts occurred in the Bangkok Metropolitan Region. The floods negatively affected small and medium enterprises...     

A pronounced dry event recorded around 4.2 ka in brine sediments from the northern Red Sea

Partly laminated sediments were sampled from the brine-filled, anoxic Shaban Deep basin in the northern Red Sea. At about 4200 cal yr BP more than two millennia of anoxic sedimentation is replaced by a sub-oxic facies strongly suggesting the episodic absence of the brine. At the same time stable oxygen isotopes from surface dwelling foraminifera show a sharp increase (within less than 100 yr) pointing to a strong positive salinity anomaly at the sea surface. This major evaporation event significantly enhanced the renewal of deep water and the subsequent ventilation of the small Shaban Deep basin. The timing and strength of the reconstructed environmental changes around 4200 cal yr BP suggest that this event is the regional expression of a major drought event, which is widely observed in the neighboring regions, and which strongly affected Middle East agricultural civilizations.