Relations between submarine fissures,internal breccias and mass flows during Triassic and earlier rifting periods

Deep fissures in shallow-water limestones filled with deep-water sediments are described from many places especially in the Triassic and Jurassic of the Tethys and in the Middle to Upper Devonian of the Variscian Mountains. Mass flows occur in the same formations and areas. On the island of Hydra (Greece) it was possible to show that both phenomena are linked by internal breccias of well-fitted limestone fragments. They are indicative of slope or near-slope positions and are very probably caused by flexure-like deformations of shallow-burial limestones. Seismic shocks producing overpressure may be instrumental in the disintegration of the semi-lithified limestones thus providing the material for mass flows. These events are associated with a tectonical subsidence as shown by deep-water matrix in the brecciated shallow-water limestones. They occur in areas and periods of submarine rifting, especially in late Devonian and Triassic time. At least four Triassic brecciation events can be traced from Greece to the Alps and correspond presumably to major transgressions in the cratonic basin of middle Europe.     

Mesoscale modeling of katabatic winds over Greenland and comparisons with AWS and aircraft data

Summary Simulations of the katabatic wind system over the Greenland ice sheet for the two months April and May 1997 were performed using the Norwegian Limited Area Model (NORLAM) with a horizontal resolution of 25 km. The model results are intercompared and validated against observational data from automatic weather stations (AWS), global atmospheric analyses and instrumented aircraft observations of individual cases during that period. The NORLAM is able to simulate the synoptic developments and daily cycle of the katabatic wind system realistically. For most of the cases covered by aircraft observations, the model results agree very well with the measured developments and structures of the katabatic wind system in the lowest 400 m. Despite NORLAM’s general ability of reproducing the four-dimensional structure of the katabatic wind, problems occur in cases, when the synoptic background is not well captured by the analyses used as initial and boundary conditions for the model runs or where NORLAM fails to correctly predict the synoptic development. The katabatic wind intensity in the stable boundary layer is underestimated by the model in cases when the simulated synoptic forcing is too weak. An additional problem becomes obvious in cases when the model simulates clouds in contrast to the observations or when the simulated clouds are too thick compared to the observed cloud cover. In these cases, the excessive cloud amount prevents development of the katabatic wind in the model. Received September 22, 2000/Revised March 16, 2001     

Synthesis of feldspar bicrystals by direct bonding

 We have produced synthetic feldspar bicrystals using a direct bonding technique. A gem-quality orthoclase crystal from Itrongay, Madagascar, was used for the bonding experiments. Microprobe analysis shows only minor concentrations of iron and sodium. Orthoclase single crystal plates oriented parallel (0 0 1) were cut and chemomechanically polished with silica slurry. From interferometry, final roughness of the square crystal plates was about 0.34 nm. Specimens were wet-chemically cleaned using deionised water. The bonding procedure produced an orthoclase bicrystal with an optically straight grain boundary-oriented parallel (0 0 1), which was investigated by HREM. Along the interface no amorphous layer was observed between lattice fringes of both crystals. We suggest that the bicrystals formed by initial hydrogen bonding and subsequent water loss and polymerisation of silanol and aluminol groups at elevated temperatures. Received: 19 February 2001 / Accepted: 16 May 2001     

Effects of weathering on organic matter in shales

The most drastic changes of the organic geochemical parameters examined (organic carbon, soluble organic matter content and composition, δC¹³ insoluble organic matter) occur over the near-surface 3 m intervals of two shallow core holes drilled into outcrops of the Upper Cretaceous Mancos Shale in Utah. This observation is believed to reflect the effects of weathering under the semi-arid climate of the study area. Therefore, organic geochemical data obtained from analysis of surface samples should be interpreted with caution.     

The KABEG’97 field experiment: An aircraft-based study of katabatic wind dynamics over the Greenland ice sheet

The aircraft-based experiment KABEG97 (Katabatic wind and boundary-layer front experiment around Greenland) was performed in April/May 1997. During the experiment, surface stations were installed at five positions on the ice sheet and in the tundra near Kangerlussuaq, West Greenland. A total of nine katabatic wind flights were performed during quite different synoptic situations and surface conditions, and low-level jets with wind speeds up to 25m s^-1 were measured under strong synoptic forcing of the katabatic wind system. The KABEG data represent a unique data set for the investigation of katabatic winds. For the first time, high-resolution and accurate aircraft measurements can be used to investigate the three-dimensional structure of the katabatic wind system for a variety of synoptic situations.Surface station data show that a pronounced daily cycle of the near-surface wind is present for almost all days due to the nighttime development of the katabatic wind. In a detailed case study the stably-stratified boundary layer over the ice and the complex boundary-layer structure in the transition zone ice/tundra are investigated. The katabatic wind system is found to extend about 10 km over the tundra area and is associated with strong wind convergence and gravity waves. The investigation of the boundary-layer dynamics using the concept of a two-layer katabatic wind model yields the results that the katabatic flow is always a shooting flow and that the pure katabatic force is the main driving mechanism for the flow regime, although a considerable influence of the large-scale synoptic forcing is found as well.     

Heavy mineral-based provenance analysis of Mesozoic continental-marine sediments at the western edge of the Bohemian Massif,SE Germany: with special reference to Fe–Ti minerals and the crystal morphology of heavy minerals

During the Mesozoic, the epicontinental Germanic Basin and the Regensburg Strait the latter being an embayment of the Tethys Ocean that had subsided into the Moldanubian Zone of the Central European Variscides were filled with terrigenous continental-marine sediments. Both sediments’ heavy mineral (HM) grains and aggregates have been studied in a drill section in the Wackersdorf area, SE Germany. The majority of them belong to the (semi)opaque group of Fe–Ti minerals. In Wackersdorf, the entire stratigraphy of the basin fill, which occurred between the Triassic and the Late Cretaceous, is well exposed. In addition to the chemical composition of HM, the morphology and texture of zircon, apatite and Fe–Ti compounds have been studied in a provenance-related mineral classification. Provenance analysis has yielded five discrete source rock lithologies: (1) Moldanubian H-T-metamorphics, (2) late Paleozoic (sub)volcanic rocks, (3) gneisses of the Tepla-Barrandian unit, (4) ophiolites of the Tepla-Barrandian unit, (5) silicified shear zones and quartz cores of pegmatites. The detrital minerals include zircon, tourmaline (dravite-schoerl), apatite, monazite (Ce–Th–La–Nd), xenotime, biotite, rutile, ilmenite, “nigrine” (ilmenite-rutile intergrowth), sphene, amphibole, staurolite, garnet and spinel (Cr–Mg–Al). Based on the allogenic Ti and Fe minerals, a magnetite-type source area (Eh > 0, near-surface felsic to intermediate (sub)volcanic rocks) was distinguished from an ilmenite-type source area (Eh < 0), deeply eroded crystalline basement rocks (gneiss, granite, shear zones). The latter may be subdivided into “nigrine –I” (deep) and “nigrine-II” (intermediate) subtypes, according to the level of erosion in the source area. At the Jurassic–Cretaceous transition, extrabasinal erosion provoked a noticeable variation of allogenic heavy minerals with the incisions of rivers into source rock lithologies (4) and (5). Uplift and erosion along the western edge of the Bohemian Massif took place contemporaneously with spreading and closure in the central parts of the adjacent Tethys Ocean.     

Vertical hydraulic exchange and the contribution of hyporheic community respiration to whole ecosystem respiration in the River Lahn (Germany)

To quantify the contribution of hyporheic community respiration to whole running-water ecosystem respiration in a cultural landscape setting, we studied the vertical hydraulic exchange in riffle–pool sequences of the River Lahn (Germany). We used flow through curves from four tracer experiments to estimate flow velocities in the surface and subsurface water. Generally, vertical exchange velocities were higher in riffle sections and a high temporal variability was observed (range of values 0.11–1.08 m day⁻¹). We then used (1) the exchange velocities and (2) time series of dissolved oxygen concentration in surface and subsurface water to calculate hyporheic respiration. Hyporheic respiration was estimated in a range of 10–50 mg O₂ m⁻³ day⁻¹ for the upper sediment layer (first 20 cm). It was much lower in the deeper sediment layer (20–40 cm), ranging from 0 to 10 mg O₂ m⁻³ day⁻¹ (volumes are volumes of interstitial water; the average porosity was 20%). We determined primary production and respiration of the biofilm growing on the sediment by modelling dissolved oxygen concentration time series for a 2,450 m long stream reach (dissolved oxygen concentrations with diurnal variations from 8 to 16 mg L⁻¹). Modelled respiration rates ranged from 2 to 21 g O₂ m² day⁻¹. All information was integrated in a system analysis with numerical simulations of respiration with and without sediments. Results indicated that hyporheic respiration accounted for 6 to 14% of whole ecosystem respiration. These values are much lower than in other whole system respiration studies on more oligotrophic river systems.     

Characterization of Water-Soluble Macromolecular Substances in Cloud Water

In this contribution we present to our knowledge the first investigations of macromolecular, often called humic-like substances (HULIS) in cloud water samples and compare them with water-soluble extracts from atmospheric PM_2.5, soils and waters to study its possible origin. Chemical analysis was done using high performance liquid chromatography (HPLC) coupled with UV and diode array detector, and HPLC coupled with ESI-MS (electrospray ionization mass spectrometer). The data have been treated by principle component analysis (PCA) and cluster analysis to state similarities and/or differences between different types of samples. Our results show that the content of organic and inorganic species is distinctly different in smaller and larger droplets suggesting varying origin. We conclude that smaller droplets are formed more from organic containing condensation nuclei (CCN) and larger droplets more from inorganic containing CCN organic compounds. Putting all experimental findings together we state that HULIS in cloud water—and consequently in particulate CCN precursors—are produced in an atmospheric polymerization process from low molecular weighted organics of different origin. Evidence is found that anthropogenic sources contribute to this pathway. Cloud drops may act as reactor in this HULIS formation process but more likely are gas-phase or gas-to-particle interactions.