Sediment history mirrors Pleistocene aridification in the Gobi Desert (Ejina Basin, NW China)

Central Asia is a large-scale source of dust transport, but it also held a prominent changing hydrological system during the Quaternary. A 223 m long sediment core (GN200) was recovered from the Ejina Basin (synonymously Gaxun Nur Basin) in NW China to reconstruct the main modes of water availability in the area during the Quaternary. The core was drilled from the Heihe alluvial fan, one of the world's largest alluvial fans, which covers a part of the Gobi Desert. Grain-size distributions supported by endmember modelling analyses, geochemical-mineralogical compositions (based on XRF and XRD measurements), and bioindicator data (ostracods, gastropods, pollen and non-pollen palynomorphs, and n-alkanes with leaf-wax delta D) are used to infer the main transport processes and related environmental changes during the Pleistocene. Magnetostratigraphy supported by radionuclide dating provides the age model. Grain- size endmembers indicate that lake, playa (sheetflood), fluvial, and aeolian dynamics are the major factors influencing sedimentation in the Ejina Basin. Core GN200 reached the pre-Quatemary quartz- and plagioclase-rich "Red Clay" formation and reworked material derived from it in the core bottom. This part is overlain by silt-dominated sediments between 217 and 110 m core depth, which represent a period of lacustrine and playa-lacustrine sedimentation that presumably formed within an endorheic basin. The upper core half between 110 and 0 m is composed of mainly silty to sandy sediments derived from the Heihe that have accumulated in a giant sediment fan until modem time. Apart from the transition from a siltier to a sandier environment with frequent switches between sediment types upcore, the clay mineral fraction is indicative of different environments. Mixed-layer clay minerals (chlorite/smectite) are increased in the basal Red Clay and reworked sediments, smectite is indicative of lacustrine-playa deposits, and increased chlorite content is characteristic of the Heihe river deposits. The sediment succession in core GN200 based on the detrital proxy interpretation demonstrates that lake-playa sedimentation in the Ejina Basin has been disrupted likely due to tectonic events in the southern part of the catchment around 1 Ma. At this time Heihe broke through from the Hexi Corridor through the Heli Shan ridge into the northern Ejina Basin. This initiated the alluvial fan progradation into the Ejina Basin. Presently the sediment bulge repels the diminishing lacustrine environment further north. In this sense, the uplift of the hinterland served as a tipping element that triggered landscape transformation in the northern Tibetan foreland (i.e. the Hexi Corridor) and further on in the adjacent northern intracontinental Ejina Basin. The onset of alluvial fan formation coincides with increased sedimentation rates on the Chinese Loess Plateau, suggesting that the Heihe alluvial fan may have served as a prominent upwind sediment source for it

Polycyclische aromatische Kohlenwasserstoffe (PAK) in feinkoernigen Sedimenten: Adsorption und mikrobieller Abbau

Das Adsorptionsvermoegen Polycyclischer Aromatischer Kohlenwasserstoffe (PAK) an Tonen und Tonmineralien wurde in Schuettelversuchen anhand der Verbindungen Naphthalin, Fluoren, Phenanthren und Fluoranthen untersucht. Mit zunehmender Wasserloeslichkeit des Kohlenwasserstoffes wurde eine abnehmende Bindungsstaerke der Sorption festgestellt. Bei Anwesenheit anderer PAK kann die Sorption einer gegebenen Verbindung durch Konkurrenzadsorption beeinflusst werden. Die Gegenwart des nichtionischen Tensids Brij 35 fuehrt zwar zu einer verstaerkten Loesung der unpolaren PAK, gleichzeitig jedoch durch die Sorption des Tensides zu einer verstaerkten Anlagerung, so dass die Anwendung von Tensiden bei der Reinigung eines PAK-kontaminierten tonigen Bodens kritisch betrachtet werden muss. In Perkolations- und Ruehrversuchen wurde ausserdem der Einfluss verschiedener Bodenmaterialien auf die mikrobielle Abbaubarkeit der Modellsubstanz Phenanthren untersucht, wobei in einem inhomogenen Sand/Kies-Gemisch ein langsamerer Abbau als in einem homogenen Feinsand festgestellt wurde. Als limitierender Faktor fuer den Phenanthren-Abbau wurden nicht die Tonmineralien an sich, sondern die Gefuegestruktur des Untergrundes ermittelt. (EF)The adsorption capacity of polycyclic aromatic hydrocarbons to clays and clay minerals was investigated in shake tests with the compounds naphthaline, fluorines, phenantrine and fluoranthene. With increasing solubility of the hydrocarbon the sorption loses its adhesive capacities. In the presence of other PAK, however, the sorption of a given compound can be influenced by competitive absorption. Presence of the non-ionic tenside Brij 35 causes a higher solution of the non-polar PAK, at the same time, however, sorption of the tenside leads to higher addition so that the use of tensides for the cleaning of a PAK-contaminated clay soil has to been critically viewed. In percolation- and shake tests the influence of different soil materials on the microbial decomposition capacity of the model substance phenanthrene was studied. Decomposition was found to be slower in an inhomogeneous sand/clay mixture than in homogeneous fine sand. The limiting factor for phenanthren decomposition was not clay minerals as such but the structure of the underground. (EF)SIGLEAvailable from TIB Hannover: RO 6603(31) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

In-situ-Sanierung kohlenwasserstoffbelasteter Boeden. Bd. 3 Limitierende geologische Parameter beim mikrobiellen KW-Abbau in klastischen Sedimenten. Abschlussbericht

In clays and clayey soil of different composition, the capacity for absorbing gas-works-specific and environmentally relevant hydrocarbons and associated microstructure changes were investigated by means of column and batch experiments. Striking differences were observed both as to the absorption capacity and absorption behaviour of the clays and the investigated hydrocarbons, which testifies to the complexity of the subject. Contact of water-saturated clays with non-polar hydrocarbons entailed marked shrinking with increasing contamination of the soil samples. The sensitivity of clays increases as the cation exchange capacity of the dominant clay mineral decreases. Owing to the contraction of the contact water film of the clay. (orig./EF)An verschieden zusammengesetzten Tonen und tonigen Boeden wurde unter Verwendung von Saeulen- und Batchversuchen das Adsorptionsvermoegen gegenueber gaswerksspezifischen und umweltrelevanten Kohlenwasserstoffen und die damit verbundenen Mikrogefuegeaenderungen untersucht. Dabei zeigten sich deutliche Unterschiede, sowohl in der Adsorptionskapazitaet, wie auch in dem Adsorptionsverhalten der Tone bzw. der untersuchten Kohlenwasserstoffe und belegt die Komplexitaet des Themenbereiches. Der Kontakt wassergesaettigter Tone mit unpolaren Kohlenwasserstoffen fuehrte zu einer deutlichen Schrumpfung mit steigender Kontamination der Bodenproben. Die Empfindlichkeit der Tone steigt mit abnehmender Kationenaustauschkapazitaet des dominierenden Tonmineralgehaltes. Durch die Kontraktion des Haftwasserfilmes der Tonminerale werden bevorzugte Wegigkeiten in Form von Schrumpfrissen und Makroporen geoeffnet. Die Durchlaessigkeit steigt sprunghaft auf sehr hohe Werte an, die Konvektion dominiert den Prozess. (orig./EF)SIGLEAvailable from TIB Hannover: F94B0523+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Forschung und Technologie (BMFT), Bonn (Germany)DEGerman