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1.
R. Hetzel R. L. Romer O. Candan C. W. Passchier 《International Journal of Earth Sciences》1998,87(3):394-406
The Menderes massif consists of a Precambrian Core Series that preserves evidence for a polymetamorphic history and a Paleozoic/Mesozoic Cover Series that experienced only the Alpine tectonometamorphic evolution. Structural, petrographic, and geochronologic investigations in the central Menderes massif demonstrate that (a) part of the metamorphic and structural evolution of the Precambrian basement is older than the undeformed 551±1.4-Ma-old Birgi metagranite, and (b) inferred Alpine fabrics overprinting the Cover Series largely have the same attitudes as the old structures in the much older Core Series. The inferred Alpine fabrics include both contractional and extensional structures. Contraction under greenschist to amphibolite facies conditions resulted in the imbrication of the Core and Cover Series and generated an inverted metamorphic sequence by north-directed thrusting. During Alpine extension, most of the south-dipping thrust faults were reactivated as extensional shear zones under decreasing greenschist facies conditions. 相似文献
2.
We determined erosion rates on timescales of 101–104 years for two catchments in the northeastern Rhenish Massif, in order to unravel the Quaternary landscape evolution in a
Variscan mountain range typical of central Europe. Spatially averaged erosion rates derived from in situ produced 10Be concentrations in stream sediment of the Aabach and M?hne watersheds range from 47 ± 6 to 65 ± 14 mm/ka and integrate over
the last 9–13 ka. These erosion rates are similar to local rates of river incision and rock uplift in the Quaternary and to
average denudation rates since the Mesozoic derived from fission track data. This suggests that rock uplift is balanced by
denudation, i.e., the landscape is in a steady state. Short-term erosion rates were derived from suspended and dissolved river
loads subsequent to (1) correcting for atmospheric and anthropogenic inputs, (2) establishing calibration curves that relate
the amount of suspended load to discharge, and (3) estimating the amount of bedload. The resulting solid mass fluxes (suspended
and bedload) agree with those derived from the sediment volume trapped in three reservoirs. However, resulting geogenic short-term
erosion rates range from 9 to 25 mm/ka and are only about one-third of the rates derived from 10Be. Model simulations in combination with published sediment yield data suggest that this discrepancy is caused by at least
three factors: (1) phases with higher precipitation and/or lower evapotranspiration, (2) rare flood events not captured in
the short-term records, and (3) prolonged periods of climatic deterioration with increased erosion and sediment transport
on hillslopes. 相似文献
3.
Almut Hetzel Christian März Christoph VogtHans-Jürgen Brumsack 《Cretaceous Research》2011,32(4):480-494
Major- and minor- element determinations were carried out on a high-resolution sample set obtained from a sediment drill core at Wunstorf (N. Germany). This study interval includes the black shale-bearing Hesseltal Formation associated with the Oceanic Anoxic Event 2 (OAE 2), also referred to as Cenomanian-Turonian Boundary Event (CTBE). Seven black shale packages, each containing several black shale layers, were defined by elevated TOC values, with black shale packages 1-4 deposited during OAE 2. Packages 5-7 extend above the level of the positive carbon-isotope excursion defining OAE 2, indicating that conditions favouring organic carbon burial must have prevailed longer in the Wunstorf Basin than elsewhere. Geochemical analyses revealed no significant differences between black shale packages deposited during and after OAE 2. Enrichment patterns of sulphur, iron and redox-sensitive and sulphide-forming trace metals point to suboxic to anoxic conditions existing at the sediment-water interface during black shale deposition, whereas sulphidic conditions prevailed deeper in the sediment. Variations in element/Al ratios follow cyclic patterns which are interpreted to represent climatically-induced changes in sediment supply. Reduced vertical mixing led to water-column stratification and caused black shale deposition. 相似文献
4.
Katia Sanhueza-Pino Oliver Korup Ralf Hetzel Henry Munack Johannes T. Weidinger Stuart Dunning Cholponbek Ormukov Peter W. Kubik 《Quaternary Research》2011,76(3):295-304
Numerous large landslide deposits occur in the Tien Shan, a tectonically active intraplate orogen in Central Asia. Yet their significance in Quaternary landscape evolution and natural hazard assessment remains unresolved due to the lack of "absolute" age constraints. Here we present the first 10Be exposure ages for three prominent (> 107 m3) bedrock landslides that blocked major rivers and formed lakes, two of which subsequently breached, in the northern Kyrgyz Tien Shan. Three 10Be ages reveal that one landslide in the Alamyedin River occurred at 11–15 ka, which is consistent with two 14C ages of gastropod shells from reworked loess capping the landslide. One large landslide in Aksu River is among the oldest documented in semi-arid continental interiors, with a 10Be age of 63–67 ka. The Ukok River landslide deposit(s) yielded variable 10Be ages, which may result from multiple landslides, and inheritance of 10Be. Two 10Be ages of 8.2 and 5.9 ka suggest that one major landslide occurred in the early to mid-Holocene, followed by at least one other event between 1.5 and 0.4 ka. Judging from the regional glacial chronology, all three landslides have occurred between major regional glacial advances. Whereas Alamyedin and Ukok can be considered as postglacial in this context, Aksu is of interglacial age. None of the landslide deposits show traces of glacial erosion, hence their locations and 10Be ages mark maximum extents and minimum ages of glacial advances, respectively. Using toe-to-headwall altitude ratios of 0.4–0.5, we reconstruct minimum equilibrium-line altitudes that exceed previous estimates by as much as 400 m along the moister northern fringe of the Tien Shan. Our data show that deposits from large landslides can provide valuable spatio-temporal constraints for glacial advances in landscapes where moraines and glacial deposits have low preservation potential. 相似文献
5.
Roland Schmidt Christian Kamenik Christina Kaiblinger Markus Hetzel 《Journal of Paleolimnology》2004,32(2):177-196
Diatom abundances in the surface sediment samples of 41 mountain lakes in the central Austrian Alps (Niedere Tauern) were related to environmental variables using multi-variate techniques. Canonical correspondence analysis (CCA) revealed that the pH, date of autumn mixing (A
mix), mean August water temperature (T
Aug), dissolved organic carbon (DOC), and relative water depth (Z
rel) made significant contributions to explain the diatom assemblage variation in the lakes of the training set. A weighted averaging partial least square regression and calibration model was used to establish Di-pH (R
2
boot= 0.72, RMSEPboot= 0.131), and a thermistor measurements-based PLS model for A
mix (R
2
boot= 0.71, RMSEPboot= 0.006 log10 Julian days). The latter showed a better prediction than T
Aug, and was used in terms of climate change. These transfer functions, together with analyses of loss on ignition (LOI), the total carbon/nitrogen (C/N)-ratios, and selected pollen, were applied to an early to mid-Holocene (11.5–4 cal. ky BP) sediment core section from an Austrian Alpine treeline lake on crystalline bedrock. Additionally, passive sample scores in the CCA of the diatom training set were used to show trends in the variables DOC and Z
rel. During the early Holocene, diatoms indicative of increased pH, extended warm summers, and low water levels dominated. Between 10.2 and 7.6 cal. ky BP it was followed by diatom assemblages that indicated an increase in lake water depth and an earlier A
mix. The multi-proxy data suggest that the A
mix decline is the result of a series of snow-rich summer cool and wet climate fluctuations, which were divided by climate warming at ∼9 cal. ky BP. Increased A
mix, LOI and DOC, and the correspondent decline in the C/N-ratios, show subsequent climate warming between 7.3 and 6 cal. ky BP. The long-term trend in Di-pH indicates the impact of catchment-related processes during the early-Holocene, that were superimposed by climate. 相似文献
6.
The kinematic evolution of an orogen-parallel strike-slip fault in the Middle Urals demonstrates that orogen-parallel mass transfer was an important, previously underestimated process during the syncollisional evolution of the Middle Urals. The Kyshtym strike-slip fault extends NNE, parallel and adjacent to the Main Uralian fault, which is the main suture of the Uralide orogen. The Kyshtym fault is interpreted as one of two conjugate strike-slip fault zones that have accomodated the longitudinal transfer of material along the margins of a rigid indenter belonging to the East European craton. The dextral Kyshtym shear zone was active under retrograde lower amphibolite to middle/lower greenschist facies conditions. Four metagranitic, muscovite-bearing mylonites yielded Rb-Sr internal mineral isochron ages of 247.5DŽ.9, 244.5Lj.5, 240.0ǃ.4, and 240.4DŽ.3 Ma, whereas a biotite-rich sample, without muscovite, gave a mineral isochron age of 229.1Dž.2 Ma. The results indicate almost complete Sr-isotopic reequilibration on the hand specimen scale during mylonitization. The muscovite ages are interpreted as deformation ages and demonstrate a Late Permian/Early Triassic age for the Kyshtym shear zone. The shear zone transects a pre-orogenic syenite intrusion of Ordovician age. A maximum shear strain of %=7Dž is estimated from the shape of the ductily deformed syenite body in map view and from the length/width ratios of deformed amphibolite bodies in the country rock. This shear strain suggests a maximum displacement of 28ᆠ km for the ~4-km-thick Kyshtym shear zone. A younger brittle fault, oriented subparallel to the shear zone, accomplished an additional horizontal displacement of 15Dž km; thus, the total displacement along the fault system is 43ᆣ km. 相似文献
7.
R. Hetzel 《International Journal of Earth Sciences》1999,87(4):577-588
The high-pressure/low-temperature Maksyutov Complex is situated in the southern Urals between the Silurian/Devonian Magnitogorsk island arc and the East European Platform. The elongated N-S-trending complex is made up of two contrasting tectono-metamorphic units. Unit 1 consists of a thick pile of Proterozoic clastic sediments suggested to represent the passive margin of the East European Platform. The overlying unit 2, composed of Paleozoic sediments, volcanic rocks, and a serpentinite mélange with rodingites, is interpreted as a remnant of the Uralian Paleo-ocean. Devonian eastward subduction of oceanic crust beneath the Magnitogorsk island arc resulted in an incipient blueschist-facies metamorphism of unit 2 indicated by lawsonite pseudomorphs in the rodingites. While unit 2 was accreted to the upper plate, subduction of the continental passive margin caused the high-pressure metamorphism of unit 1. Buoyancy-driven exhumation of unit 1 into the forearc region led to its juxtaposition with unit 2 along a retrograde top-to-the-ENE shear zone. Further exhumation of the Maksyutov Complex into its present tectonic position was accomplished by later shear zones that were active as normal faults and are exposed along the margins of the complex. At the western margin a top-to-the-west shear zone juxtaposed a low-grade remnant of a Paleozoic accretionary prism (Suvanyak Complex) above the Maksyutov Complex. Along the eastern margin a top-to-the-east shear zone and the brittle Main Uralian Normal Fault emplaced the Maksyutov Complex against the Magnitogorsk island arc in the hanging wall. 相似文献
8.
Wind gaps in actively growing mountain ranges are unique geomorphological features testifying to the competition between tectonics and fluvial incision. Although it is clear that these landforms reflect the defeat of rivers during sustained rock uplift, the role of climate changes in their formation has never been explored. Here, we use a coupled tectonics–landscape evolution model to show that temporal changes in precipitation rate exert an important control on wind gap formation. In models with a constant precipitation rate, rivers flowing across a growing range are either defeated at an early stage or they abandon their valleys very late, if at all. If precipitation varies, wind gaps form mostly c. 100–200 ka after a transition to drier conditions because of sediment aggradation upstream of the range. Our results suggest that the Pliocene–Quaternary aridification of Central Asia contributed to wind gap formation in active mountain ranges in the foreland of northeastern Tibet. 相似文献
9.
10.
The geochemistry of dissolved and suspended loads in river catchments of two low mountain ranges in Central Europe allows comparison of pertinent chemical weathering rates. Distinct differences in lithology, i.e. granites prevailing in the Black Forest compared to Palaeozoic sediments in the Rhenish Massif, provide the possibility to examine the influence of lithology on weathering. Here we determine the origin of river water using the stable isotope ratio δ18OH2O and we quantify the geogenic proportions of sulphate from stable isotope ratios δ34SSO4 and δ18OSO4. Particularly in catchments with abundant pyrite, determination of the geogenic amount of sulphate is important, since oxidation of pyrite leads to acidity, which increases weathering. Our results show that spatially averaged silicate weathering rates are higher for the river catchments Acher and Gutach in the Black Forest (10–12 t/km2/yr) compared to the river catchments of the Möhne dam and the Aabach dam in the Rhenish Massif (2–6 t/km2/yr). Correspondingly, the CO2 consumption by silicate weathering in the Black Forest (334–395 × 103 mol/km2/yr) is more than twice as high as in the Rhenish Massif (28–151 × 103 mol/km2/yr). These higher rates for watersheds of the Black Forest are likely due to steeper slopes leading to higher mechanical erosion with respective higher amounts of fresh unweathered rock particulates and due to the fact that the sediments in the Rhenish Massif have already passed through at least one erosion cycle. Carbonate weathering rates vary between 12 and 38 t/km2/yr in the catchments of the Rhenish Massif. The contribution of sulphuric acid to the silicate weathering is higher in the catchments of the Rhenish Massif (9–16%) than in the catchments of the Black Forest (5–7%) due to abundant pyrite in the sediments of the Rhenish Massif. Three times higher long-term erosion rates derived from cosmogenic nuclides compared to short-term erosion rates derived from river loads in Central Europe point to three times higher CO2 consumption during the past 103 to 104 years. 相似文献