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111.
Hilmar von Eynatten Thomas Voigt Angela Meier Hans-Joachim Franzke Reinhard Gaupp 《International Journal of Earth Sciences》2008,97(6):1315-1330
The Harz Mountains and the adjacent Subhercynian Cretaceous Basin figure as the most prominent surface representative for
Late Cretaceous inversion structures in Central Europe. Facies, depositional architecture and provenance of the basin fill
reflect mechanisms and timing of the exhumation of the Harz. From Hauterivian to Early Santonian there is no evidence for
detrital input from the nearby Harz area. Sediments are mature quartzarenites derived from Paleozoic basement rocks and/or
recycled Permian to Mesozoic sedimentary rocks. This situation changed drastically in Middle to Late Santonian when freshly
exhumed and eroded Mesozoic sedimentary cover rocks of the Harz were delivered into the basin. Feldspar and lithoclasts reflect
erosion of Triassic and, in places, Jurassic to Turonian strata. Apatite and garnet in heavy mineral spectra are derived from
largely unweathered Lower Triassic Buntsandstein as indicated by apatite and garnet chemistry. In Early Campanian, Paleozoic
lithoclasts indicate erosion cutting down into the basement of the Harz. Simultaneous strong decrease of feldspar, garnet
and apatite suggest an almost complete removal of the 2–3 km thick Mesozoic cover of the Harz within only 2–4 Myr. This translates
into an exhumation rate of approximately 1 mm/a consistent with apatite fission track data from granitoid rocks of the Harz
Mountains. 相似文献
112.
113.
An assessment of gully erosion along major armoured roads in south-eastern region of South Africa: a remote sensing and GIS approach 总被引:1,自引:0,他引:1
Khoboso Elizabeth Seutloali Heinz Reinhard Beckedahl Timothy Dube Mbulisi Sibanda 《国际地球制图》2016,31(2):225-239
An assessment of gully erosion along road drainage-release sites is critical for understanding the contribution of roads to soil loss and for informed land management practices. Considering that road-related gully erosion has traditionally been measured using field methods that are expensive, tedious and limited spatially as well as temporally, it is important to identify affordable, timely and robust methods that can be used to effectively map and estimate the volume of gullies along the road networks. In this study, gullies along major roads were identified from remotely sensed data sets and their volumes were estimated in a Geographic Information Systems environment. Also, the biophysical and climatic factors such as vegetation cover, the road contributing surface area, the gradient of the discharge hillslope and rainfall were derived from remotely sensed data sets using Geographic Information Systems techniques to find out whether they could explain the morphology of gullies that existed in this area. The results of this study indicate that hillslope gradient (R2?=?0.69, α = 0.00) and road contributing surface area (R2?=?0.63, α = 0.00) have a strong influence on the volume of gullies along the major roads in the south-eastern region of South Africa, as might have been expected. However, other factors such as vegetation cover (R2 = 0.52, α = 0.00) and rainfall (R2 = 0.41 and α = 0.58) have a moderately weaker influence on the overall volume of gullies. Overall, the findings of this study highlight the importance of using remote sensing and Geographic Information Systems technologies in investigating gully erosion occurrence along major roads where detailed field work remains a challenge. 相似文献
114.
Hervé Guyard Guillaume St-Onge Reinhard Pienitz Pierre Francus Bernd Zolitschka Garry K.C. Clarke Sonja Hausmann Veli-Pekka Salonen Patrick Lajeunesse Grégoire Ledoux Michel Lamothe 《Quaternary Science Reviews》2011,30(27-28):3892-3907
The Pingualuit Crater was formed by a meteoritic impact ca. 1.4 million years ago in northernmost Ungava (Canada). Due to its geographical position near the center of successive North American ice sheets and its favorable morphometry, the Pingualuit Crater Lake (water depth = 246 m) promises to yield a unique continuous sedimentary sequence covering several glacial/interglacial cycles in the terrestrial Canadian Arctic. In this paper, we suggest the existence of a subglacial lake at least during the Last Glacial Maximum (LGM) by hydraulic potential modeling using LGM ice-surface elevation and bed topography derived from a digital elevation model. These results support the hypothesis that the bottom sediments of the Crater Lake escaped glacial erosion and may contain a long-term continental sedimentary sequence. We also present the stratigraphy of a 9 m-long core retrieved from the deep basin of the lake as well as a multiproxy reconstruction of its deglacial and postglacial history. The base of the core is formed by very dense diamicton reflecting basal melt-out environments marking the end of subglacial conditions at the coring site. The overlying finely laminated silt are related to the onset of proglacial conditions characterized by extremely low lacustrine productivity. Infra Red Stimulated Luminescence and AMS 14C dating, as well as biostratigraphic data indicate sediment mixing between recent (e.g. Holocene) and much older (pre- to mid-Wisconsinan) material reworked by glacier activity. This process prevents the precise dating of these sediments that we interpret as being deposited just before the final deglaciation of the lake. Two finer grained and organic-rich intervals reflect the inception of lacustrine productivity resulting from the cessation of glacial meltwater inputs and ice-free periods. The lower organic interval corresponds to the early postglacial period (6850–5750 cal BP) and marks the transition between proglacial and postglacial conditions during the Holocene Thermal Maximum, while the uppermost organic-rich core section represents late Holocene sediments (~4200–600 cal BP). The organic intervals are separated by a basin-scale erosive slide occurring around 4200 cal BP and likely related to 1) a seismic event due to the glacio-isostatic rebound following the last deglaciation or 2) slope instabilities associated with rapid discharge events of the lake. 相似文献
115.
Frédéric Bouchard Reinhard Pienitz Joseph D. Ortiz Pierre Francus Isabelle Laurion 《Boreas: An International Journal of Quaternary Research》2013,42(3):575-595
Thermokarst ponds are widespread in arctic and subarctic regions, but little is known about their temporal evolution prior to human observations. This paper presents a pioneer biostratigraphic study conducted at a subarctic site with limnologically contrasted ponds located on the eastern shore of Hudson Bay, Canada. Fossil diatom and visible near infrared (VNIR) derivative spectral analyses were performed on short sediment cores, confirming the occurrence of three distinct stratigraphic facies as already inferred from an anterior sedimentological study: a lacustrine upper facies (UF) and a marine lower facies (LF), separated by an organic‐rich/peat transitional zone (TZ). Diatoms were almost absent from LF, but increased significantly in both TZ and UF. Identified diatom taxa were mainly benthic species (e.g. genera Fragilaria, Pinnularia), and their down‐core distribution appeared to be related to dissolved organic carbon (DOC) and possibly pH conditions. Diatom‐inferred DOC showed a decreasing trend towards the surface (potentially associated with an increase in pH), inverse to the general trend in this region, suggesting the action of other mechanisms on DOC, such as exhaustion of external inputs from limited catchments and the role of discontinuous peat layers (former surfaces of permafrost mounds) during the initial stages of pond formation. These bryophilous substrates in aerophilic habitats probably controlled diatom community composition. The combination of diatom and VNIR data revealed similar trends between (i) opal (amorphous silica) and diatom abundances; (ii) eukaryotic/prokaryotic algae ratio and anoxia or hypoxia in bottom waters; and (iii) limonite (iron oxide) and redox conditions in surface sediments. These findings indicate that diatom community changes and pond limnological evolution in the recent past were controlled mainly by autogenic processes (e.g. local vegetation/soil development, peat accumulation and erosion), rather than by allogenic forcing mechanisms (e.g. precipitation and temperature, geochemical leaching of the surrounding glaciomarine sediments). 相似文献
116.
Pavle Tan?i? Predrag Vuli? Reinhard Kaindl Bernhard Sartory Radovan Dimitrijevi? 《《地质学报》英文版》2012,86(2):394-405
The macroscopically-zoned grandite from the garnetite skarn of Meka Presedla (Kopaonik Mountain, Serbia) was studied with optical microscopy, electron microprobe analysis (EMPA), Fourier transform infra-red (FT–IR), and Raman methods. The EMPA results indicate that the main core–rim compositional variations (Ca2.93–2.97Mn0.05–0.06Mg0.00–0.01Al1.14–1.26Fe3+0.72–0.83Ti0.00–0.02Si2.97–3.02O12) slightly differ along the zones, showing evidence for a quasi-cyclic alternation of the oscillatory zoning nature. Among this, considerable variation is observed only by the Al–Fe3+ substitutions in the octahedral site. The EMPA also indicate that the grandite zones compositionally vary, mostly within ±1 and ±2 mol% of the homogeneity level range, that is, Grs64±1Adr36±1Sps2 (A), Grs62±1Adr38±1Sps2 (B), Grs59±2Adr40±2Sps2 (C), Grs58±2Adr41±2Sps2 (D), and Grs58±1Adr41±1Sps2 (E). Therefore, the investigated garnet can be considered as relatively highly homogeneous. The majority of compositions lie within the narrow miscibility region of 0.58±2相似文献
117.
Dieter Pudlo Viktor Reitenbach Daniel Albrecht Leonhard Ganzer Ulrich Gernert Joachim Wienand Bernd Kohlhepp Reinhard Gaupp 《Environmental Earth Sciences》2012,67(2):369-384
In the framework of the German R&D joint project CLEAN (CO2 large-scale enhanced gas recovery in the Altmark natural gas field), Rotliegend reservoir sandstones of the Altensalzwedel block in the Altmark area (Saxony-Anhalt, central Germany) have been studied to characterise litho- and diagenetic facies, mineral content, geochemical composition, and petrophysical properties. These sands have been deposited in a playa environment dominated by aeolian dunes, dry to wet sand flats and fluvial channel fills. The sediments exhibit distinct mineralogical, geochemical, and petrophysical features related to litho- and diagenetic facies types. In sandstones of the damp to wet sandflats, their pristine red colours are preserved and porosity and permeability are only low. Rocks of the aeolian environment and most of the channel fill deposits are preferentially bleached and exhibit moderate to high porosity and permeability. Although geochemical element whole rock content in these rocks is very similar, element correlations are different. Variations in porosity and permeability are mainly due to calcite and anhydrite dissolution and differences in clay coatings with Fe-bearing illitic-chloritic composition exposed to the pore space. Moreover, mineral dissolution patterns as well as compositions (of clays and carbonate) and morphotypes of authigenic minerals (chlorite, illite) are different in red and bleached rocks. Comparison of the geochemical composition and mineralogical features of diagenetically altered sandstones and samples exposed to CO2-bearing fluids in laboratory batch experiments exhibit similar character. Experiments prove an increase in wettability and water binding capacity during CO2 impact. 相似文献
118.
Lower and middle Eocene ironstone sequences of the Naqb and Qazzun formations from the north‐east Bahariya Depression, Western Desert, Egypt, represent a proxy for early Palaeogene climate and sea‐level changes. These sequences represent the only Palaeogene economic ooidal ironstone record of the Southern Tethys. These ironstone sequences rest unconformably on three structurally controlled Cenomanian palaeohighs (for example, the Gedida, Harra and Ghorabi mines) and formed on the inner ramp of a carbonate platform. These palaeohighs were exposed and subjected to subaerial lateritic weathering from the Cenomanian to early Eocene. The lower and middle Eocene ironstone sequences consist of quiet water ironstone facies overlain by higher energy ironstone facies. The distribution of low‐energy ironstone facies is controlled by depositional relief. These deposits consist of lagoonal, burrow‐mottled mud‐ironstone and laterally equivalent tidal flat, stromatolitic ironstones. The agitated water ironstone facies consist of shallow subtidal–intertidal nummulitic–ooidal–oncoidal and back‐barrier storm‐generated fossiliferous ironstones. The formation of these marginal marine sequences was associated with major marine transgressive–regressive megacycles that separated by subaerial exposure and lateritic weathering. The formation of lateritic palaeosols with their characteristic dissolution and reprecipitation features, such as colloform texture and alveolar voids, implies periods of humid and warm climate followed major marine regressions. The formation of the lower to middle Eocene ironstone succession and the associated lateritic palaeosols can be linked to the early Palaeogene global warming and eustatic sea‐level changes. The reworking of the middle Eocene palaeosol and the deposition of the upper Eocene phosphate‐rich glauconitic sandstones of the overlying Hamra Formation may record the initial stages of the palaeoclimatic transition from greenhouse to icehouse conditions. 相似文献
119.
Udo Haefeker Reinhard Kaindl Peter Tropper Hannes Krüger Volker Kahlenberg Maria Orlova 《Mineralogy and Petrology》2014,108(4):469-478
The crystal structures of synthetic hexagonal and orthorhombic Fe-cordierite polymorphs with the space groups P6/mcc and Cccm were refined from single-crystal X-ray diffraction data to R 1, hex?=?3.14 % and R 1, ortho?=?4.48 %. The substitution of the larger Fe2+ for Mg leads to multiple structural changes and an increase of the unit cell volumes, with a, c (hex)?=?9.8801(16) Å, 9.2852(5) Å and a, b, c (ortho)?=?17.2306(2) Å, 9.8239(1) Å, 9.2892(1) Å in the end-members. Furthermore Fe incorporation results in an increase of the volumes of the octahedra, although the diameters of the octahedra in direction of the c-axis decrease in both polymorphs. X-ray powder diffraction analysis indicates a high degree of Al/Si ordering in the orthorhombic polymorph, the Miyashiro distortion index is ~0.24. Estimations of site occupancies based on the determined tetrahedral volumes result in the following values for hexagonal Fe-cordierite: ~73 % Al for T1 and ~28 % Al for T2. For the first time Raman spectroscopy was performed on the hexagonal Fe-cordierite polymorph. In the hexagonal Fe-cordierite polymorph most Raman peaks are shifted towards lower wavenumbers when compared with the Mg-end-member. 相似文献
120.
Natural electromagnetic radiation (EMR) and its application in structural geology and neotectonics 总被引:2,自引:0,他引:2
Reinhard O. Greiling Hennes Obermeyer 《Journal of the Geological Society of India》2010,75(1):278-288
Natural electromagnetic radiation (EMR) impulses are emitted from rocks under stress. Electromagnetic emission may start during
crystal deformation prior to and during the nucleation phase of nanocracks. The emission direction is either parallel with
or normal to the crack surfaces. The EMR magnetic component is measured by the sensor or aerial of an instrument, the Cerescope,
at frequencies from 5 to 50 kHz. Measurements at the surface show directions of recent stresses remarkably well. A calibration
of EMR intensity in terms of stress magnitude is possible in tunnels, where the overburden pressure can be calculated. Two
examples from the Upper Rhine Graben and NW India show EMR line measurements. In both cases, stress concentrations at fault
or bedding surfaces can be detected. These surfaces can be regarded as tectonically active. Two further examples of EMR determinations
in tunnels give more detailed information on the regional stress field. The example from the Swiss Jura fold-and-thrust belt
shows directional results, with different directions beneath and above the regional detachment horizon at the base of the
belt. The example from central Scandinavia shows a late Caledonian shear zone as a boundary between two recent stress domains,
and gives absolute values of stress. 相似文献