Tunnel valleys are assumed to form near the margin of ice sheets. Hence, they can be used to reconstruct the dynamics of former ice margins. The detailed formation and infill of tunnel valleys, however, are still not well understood. Here, we present a dense grid of high-resolution 2D multi-channel reflection seismic data from the German sector of the southeastern North Sea imaging tunnel valleys in very great detail. Three tunnel valley systems were traced over distances ranging between 11 and 21 km. All tunnel valleys are completely filled and buried. They differ in incision depth, incision width and number of incisions. The tunnel valleys cut 130–380 m deep into Neogene, Palaeogene and Cretaceous sediments; they show a lower V-shaped and an upper U-shaped morphology. For individual tunnel valleys, the overall incision direction ranges from east–west to northeast–southwest. Two tunnel valleys intersect at an oblique angle without reuse of the thalweg. These valleys incise into a pre-existing glaciotectonic complex consisting of thrust sheets in the northwest of the study area. The analysis of the glaciotectonic complex and the tunnel valleys leads us to assume that we identified several marginal positions of (pre-)Elsterian ice lobes in the southeastern North Sea. 相似文献
Introduction Until the late 1980s, the mountainous regions of northern Thailand and northern Vietnam were largely cut off from the rapid economic develop- ment in the urban centers such as Bangkok, Chiang Mai and Hanoi, and from the dynamics of the ‘gree… 相似文献
Understanding the effects of microbiota on mineral alteration requires the ability to recognize evidence of bacteria-promoted dissolution on mineral surfaces. Although siderophores are known to promote mineral dissolution, their effects on mineral surfaces are not well known. We have utilized atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and Mirau vertical scanning interferometry (VSI) to investigate surfaces after incubation with the siderophore desferrioxamine-B mesylate (DFAM) and under colonies of bacteria. Iron-silicate glass planchets chemically similar to hornblende were incubated in buffered growth medium with siderophore-producing bacteria (Bacillus sp.) for 46 days with parallel abiotic experiments conducted with and without 240 μM DFAM, with and without 0.01 g l− 1 of microbially produced extracellular polysaccharides (EPS, alginate or xanthan gum). Some glass planchets were protected by dialysis tubing from direct contact with the EPS. Weekly sampling and analysis of all filtered sample solutions showed negligible Fe and Al release in the control experiments and significant release of Fe and Al in the presence of DFAM, with negligible changes in pH. Concentration of Fe in the filtered solutions after incubation with bacteria was below detection, consistent with uptake of Fe by cells. Release of Fe, Al, and Si in control, xanthan-only, and alginate-only experiments was negligible. Release of these elements was enhanced in all experiments containing DFAM, and greatest in alginate + DFAM experiments.
AFM and VSI analyses reveal widespread, small etch pits and greater root mean squared roughness on siderophore-exposed surfaces and fewer, localized, larger etch pits on bacteria-exposed surfaces. This is the first documented case of etch pit development during siderophore-promoted dissolution. Roughness was not affected by the growth medium, alginate, or xanthan gum alone. The roughness trends among samples correlate with trends in Fe depletion documented by XPS. Enhanced dissolution and roughness cannot be attributed to direct contact with EPS because no significant chemical or physical differences were observed between surfaces directly exposed to EPS and those protected by dialysis tubing. Acetate released from the EPS may have enhanced the siderophore-promoted dissolution. Siderophores produced by Bacillus sp. may be responsible for some of the ‘biopits.’ The difference in size and distribution of the biopits may be related to colonization. 相似文献
Volatile element, major and trace element compositions were measured in glass inclusions in olivine from samples across the
Kamchatka arc. Glasses were analyzed in reheated melt inclusions by electron microprobe for major elements, S and Cl, trace
elements and F were determined by SIMS. Volatile element–trace element ratios correlated with fluid-mobile elements (B, Li)
suggesting successive changes and three distinct fluid compositions with increasing slab depth. The Eastern Volcanic arc Front
(EVF) was dominated by fluid highly enriched in B, Cl and chalcophile elements and also LILE (U, Th, Ba, Pb), F, S and LREE
(La, Ce). This arc-front fluid contributed less to magmas from the central volcanic zone and was not involved in back arc
magmatism. The Central Kamchatka Depression (CKD) was dominated by a second fluid enriched in S and U, showing the highest
S/K2O and U/Th ratios. Additionally this fluid was unusually enriched in 87Sr and 18O. In the back arc Sredinny Ridge (SR) a third fluid was observed, highly enriched in F, Li, and Be as well as LILE and LREE.
We argue from the decoupling of B and Li that dehydration of different water-rich minerals at different depths explains the
presence of different fluids across the Kamchatka arc. In the arc front, fluids were derived from amphibole and serpentine
dehydration and probably were water-rich, low in silica and high in B, LILE, sulfur and chlorine. Large amounts of water produced
high degrees of melting below the EVF and CKD. Fluids below the CKD were released at a depth between 100 and 200 km due to
dehydration of lawsonite and phengite and probably were poorer in water and richer in silica. Fluids released at high pressure
conditions below the back arc (SR) probably were much denser and dissolved significant amounts of silicate minerals, and potentially
carried high amounts of LILE and HFSE.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
Igneous garnets have the potential to strongly fractionate rare earth elements (REE). Yet informations on partition coefficients
are very scant, and criteria for distinguishing between hydrothermal and magmatic garnets are ambiguous. To fill this gap,
we present trace element and isotopic data for two types of Ca-rich garnets from phonolites (Mt. Somma-Vesuvius). Both Ca-garnet
populations are different in their style and dynamics of fractionation: one population is progressively strongly depleted
in HREE from core to rim, reflecting REE fractionation in the host phonolite via earlier-crystallized garnets. Such examples
for extreme changes in HREE in garnets are only known for hydrothermal grandites by REE-bearing fluids. The second garnet
population is homogeneous and formed in a closed system. Near-flat patterns between Sm and Lu confirm experimental data indicating
lower D(Sm)/D(Lu) for Ca-rich garnets than for e.g. pyrope-rich garnets. It follows: DGrt/PhMelt for La = 0.5, Sm = 48 and Yb = 110. 相似文献
Measurements of atmospheric turbulence made during the Surface Heat Budget of the Arctic Ocean Experiment (SHEBA) are used
to examine the profile stability functions of momentum, φm, and sensible heat, φh, in the stably stratified boundary layer over the Arctic pack ice. Turbulent fluxes and mean meteorological data that cover
different surface conditions and a wide range of stability conditions were continuously measured and reported hourly at five
levels on a 20-m main tower for 11 months. The comprehensive dataset collected during SHEBA allows studying φm and φh in detail and includes ample data for the very stable case. New parameterizations for φm (ζ) and φh (ζ) in stable conditions are proposed to describe the SHEBA data; these cover the entire range of the stability parameter
ζ = z/L from neutral to very stable conditions, where L is the Obukhov length and z is the measurement height. In the limit of very strong stability, φ m follows a ζ 1/3 dependence, whereas φh initially increases with increasing ζ, reaches a maximum at ζ ≈ 10, and then tends to level off with increasing ζ. The effects
of self-correlation, which occur in plots of φm and φh versus ζ, are reduced by using an independent bin-averaging method instead of conventional averaging. 相似文献
Multi-proxies of lacustrine sediments, such as total carbon (TC), total organic carbon (TOC), total inorganic carbon (TIC), total nitrogen (TN), total sulfur (TS), hydrogen index (HI), oxygen index (OI) and stable carbon isotopic composition of organic matter (δ 13Corg), were analyzed using a 7.3 m core from Zigê Tangco. The source of the organic matter in the sediment was mainly from autochthonous phytoplankton, therefore the significances of proxies can be interpreted as that high TOC, TOC/TS, HI and δ13Corg values, low TC, TIC values corresponded to warm and wet climatic condition, and vice versa. The process of climatic development in the Zigê Tangco region was hence recovered. During the early and Mid-Holocene, the climate was warm and wet and intensive cold events occurred during the periods of 8600 to 8400 cal a BP and 7400 to 7000 cal a BP. In the second half of Holocene, the climate became cold and dry gradually. The palaeoclimatic process during Holocene in Zigê Tangco region matched well with that in Co Ngoin region which is ca 40 km to the south-east. Therefore this palaeoclimatic process represents the Holocene climatic feature in the Central Tibetan Plateau which has the same pattern in the Northern Tibetan Plateau, but the time and duration of some climatic events might be different. We can conclude that in Holocene solar insolation controlled the climatic pattern on the central Tibetan Plateau. 相似文献
We formulate a method for determining the smallest time interval Tover which a turbulence time series can be averaged to decompose it intoinstantaneous mean and random components. From the random part the method defines the optimal interval (or averaging window) AW over which this part should be averaged to obtain the instantaneous spectrum. Both T and AW vary randomly with time and depend on physical properties of the turbulence. T also depends on the accuracy of the measurements and is thus independent of AW. Interesting features of the method are its real-time capability and the non-equality between AW and T. 相似文献