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1.
Svetlana S. Kostrova Hanno Meyer Hannah L. Bailey Anna V. Ludikova Raphael Gromig Gerhard Kuhn Yuri A. Shibaev Anna V. Kozachek Alexey A. Ekaykin Bernhard Chapligin 《Boreas: An International Journal of Quaternary Research》2019,48(2):361-376
This article presents a new comprehensive assessment of the Holocene hydrological variability of Lake Ladoga, northwest Russia. The reconstruction is based on oxygen isotopes of lacustrine diatom silica (δ18Odiatom) preserved in sediment core Co 1309, and is complemented by a diatom assemblage analysis and a survey of modern isotope hydrology. The data indicate that Lake Ladoga has existed as a freshwater reservoir since at least 10.8 cal. ka BP. The δ18Odiatom values range from +29.8 to +35.0‰, and relatively higher δ18Odiatom values around +34.7‰ between c. 7.1 and 5.7 cal. ka BP are considered to reflect the Holocene Thermal Maximum. A continuous depletion in δ18Odiatom since c. 6.1 cal. ka BP accelerates after c. 4 cal. ka BP, indicating Middle to Late Holocene cooling that culminates during the interval 0.8–0.2 cal. ka BP, corresponding to the Little Ice Age. Lake‐level rises result in lower δ18Odiatom values, whereas lower lake levels cause higher δ18Odiatom values. The diatom isotope record gives an indication for a rather early opening of the Neva River outflow at c. 4.4–4.0 cal. ka BP. Generally, overall high δ18Odiatom values around +33.5‰ characterize a persistent evaporative lake system throughout the Holocene. As the Lake Ladoga δ18Odiatom record is roughly in line with the 60°N summer insolation, a linkage to broader‐scale climate change is likely. 相似文献
2.
Jana Just Bernhard Schulz Helga de Wall Fred Jourdan Manoj K. Pandit 《Gondwana Research》2011,19(2):402-412
The in-situ “chemical” Th–U–Pb dating of monazite with the electron microprobe is used to unravel the Neoproterozoic tectono-thermal history of the “Erinpura Granite” terrane in the foreland of the Delhi Fold Belt (DFB) in the NW Indian craton. These granitoids are variably deformed and show effects of shearing activity. Monazites from the Erinpura granitoids recorded two main events; (1) protolith crystallization at 863 ± 23 Ma and (2) recrystallization and formation of new Th-poor monazite at 775 ± 26 Ma during shear overprint. Some components of the Erinpura granitoids, such as the Siyawa Granite and granites exposed near Sirohi town, show evidence of migmatization. This migmatization event is documented by anatexis and associated monazite crystallization at 779 ± 16 Ma. The age data indicate an overlap in timing between anatectic event and ductile shear deformation. The end of the tectono-thermal event in the Sirohi area is constrained by a 736 ± 6 Ma Ar–Ar muscovite age data from the ductile shear zone. 相似文献
3.
The pre-Mesozoic, mainly Variscan metamorphic basement of the Col de Bérard area (Aiguilles Rouges Massif, External domain)
consists of paragneisses and micaschists together with various orthogneisses and metabasites. Monazite in metapelites was
analysed by the electron microprobe (EMPA-CHIME) age dating method. The monazites in garnet micaschists are dominantly of
Variscan age (330–300 Ma). Garnet in these rocks displays well developed growth zonations in Fe–Mg–Ca–Mn and crystallized
at maximal temperatures of 670°C/7 kbar to the west and 600°C/7–8 kbar to the east. In consequence the monazite is interpreted
to date a slightly pressure-dominated Variscan amphibolite-facies evolution. In mylonitic garnet gneisses, large metamorphic
monazite grains of Ordovician–Silurian (~440 Ma) age but also small monazite grains of Variscan (~300 Ma) age were discovered.
Garnets in the mylonitic garnet gneisses display high-temperature homogenized Mg-rich profiles in their cores and crystallized
near to ~800°C/6 kbar. The Ordovician–Silurian-age monazites can be assigned to a pre-Variscan high-temperature event recorded
by the homogenised garnets. These monazite age data confirm Ordovician–Silurian and Devonian–Carboniferous metamorphic cycles
which were already reported from other Alpine domains and further regions in the internal Variscides. 相似文献
4.
Kord Ernstson Werner Mayer Andreas Neumair Dirk Sudhaus 《Central European Journal of Geosciences》2011,3(4):385-397
Sudden collapse of the Quaternary soil to form sinkholes on the order of meters and tens of meters has been a geologic phenomenon within living memory in a localized area north of Lake Chiemsee in Southeast Germany. Failing a satisfying explanation, a relation with an undefined glaciation process has always been proposed. Excavations and geophysical measurements at three newly affected sites show underground features such as prominent sandy-gravelly intrusions and extrusions typical of rock liquefaction processes well known to occur during strong earthquakes. Since strong earthquakes can reasonably be excluded to have affected the area under discussion, it has been suggested that the observed widespread liquefaction is related with the recently proposed Holocene Chiemgau meteorite impact event. Except for one earlier proposed but unassertive relation between impact and liquefaction, the obviously direct association of both processes in the Chiemgau area emphasizes that observed paleoliquefaction features need not necessarily have originated solely from paleoseismicity but can provide a recognizable regional impact signature. 相似文献
5.
Lateral fold growth and linkage in the Zagros fold and thrust belt (Kurdistan,NE Iraq) 总被引:1,自引:0,他引:1
The Zagros fold and thrust belt is a seismically active orogen that has accommodated the N–S shortening between the Arabian and Eurasian plates since the Miocene. Whereas the southeast parts of the belt have been studied in detail, the northwest extent has received considerably less attention, being part of the Republic of Iraq. In this study, we investigate fold growth in the area NE of Erbil (Kurdistan, Iraq). In particular, we focus on the interaction of the transient development of drainage patterns along growing antiforms, as this directly reflects the kinematics of progressive fold growth. Detailed geomorphological studies of the Bana Bawi‐, Permam‐ and Safeen‐fold trains show that these anticlines did not develop from a single embryonic fold but by lateral linkage of several different fold segments. These segments, with length between 5 and 25 km, have been detected by mapping ancient and modern river courses; these initially cut the nose of growing folds until eventually defeated, leaving curved wind gaps behind. Depending on the alignment of the initial embryonic folds, the segments can either record a linear‐ or an en‐echelon linkage. Comparison of natural examples from the Zagros fold and thrust belt in Iraq with published numerically modelled fold growth suggests that both linear‐linkage and en‐echelon linkage are mechanically feasible and are common processes during progressive shortening and fold growth. 相似文献
6.
7.
8.
Traditionally, the application of stable isotopes in Carbon Capture and Storage (CCS) projects has focused on δ13C values of CO2 to trace the migration of injected CO2 in the subsurface. More recently the use of δ18O values of both CO2 and reservoir fluids has been proposed as a method for quantifying in situ CO2 reservoir saturations due to O isotope exchange between CO2 and H2O and subsequent changes in δ18OH2O values in the presence of high concentrations of CO2. To verify that O isotope exchange between CO2 and H2O reaches equilibrium within days, and that δ18OH2O values indeed change predictably due to the presence of CO2, a laboratory study was conducted during which the isotope composition of H2O, CO2, and dissolved inorganic C (DIC) was determined at representative reservoir conditions (50 °C and up to 19 MPa) and varying CO2 pressures. Conditions typical for the Pembina Cardium CO2 Monitoring Pilot in Alberta (Canada) were chosen for the experiments. Results obtained showed that δ18O values of CO2 were on average 36.4 ± 2.2‰ (1σ, n = 15) higher than those of water at all pressures up to and including reservoir pressure (19 MPa), in excellent agreement with the theoretically predicted isotope enrichment factor of 35.5‰ for the experimental temperatures of 50 °C. By using 18O enriched water for the experiments it was demonstrated that changes in the δ18O values of water were predictably related to the fraction of O in the system sourced from CO2 in excellent agreement with theoretical predictions. Since the fraction of O sourced from CO2 is related to the total volumetric saturation of CO2 and water as a fraction of the total volume of the system, it is concluded that changes in δ18O values of reservoir fluids can be used to calculate reservoir saturations of CO2 in CCS settings given that the δ18O values of CO2 and water are sufficiently distinct. 相似文献
9.
Bernhard Krautzer Wilhelm Graiss Giovanni Peratoner Christian Partl Sonia Venerus Brigitte Klug 《Natural Hazards》2011,56(2):547-557
Control of erosion, and all of its after effects, from increased surface drainage and erosion to the formation of karst, is
one of the essential problems when undertaking recultivation following necessary interventions in the sub-alpine and alpine
vegetation stage (high zones). Average slope inclinations of 30–45% in the vicinity of ski runs, and far above in areas of
natural erosion and avalanche zones, make restoration processes with sufficient erosion protection the prerequisite for success.
Only a sufficient vegetation development of more than 70% ground cover stabilises the topsoil in the long term and reduces
soil erosion to an acceptable degree. From 1999 to 2002, an international EU project with the participation of research groups
and private firms from Austria, Italy and Germany was carried out under the direction of the Agricultural Research and Education
Centre Raumberg-Gumpenstein (AREC) on five different Alpine sites at altitudes from 1,245 to 2,350 m above sea level. The
aim of the work was the formulation of practice-relevant requirements for recultivation following intervention in high zones,
especially following constructional measures in the vicinity of ski runs and lifts, torrent- and avalanche barriers. In a
statistical comparison, the relationship between restoration techniques, seed mixtures of differing ecological value and vegetation
cover was observed. The influence of application technique on erosion processes after restoration was obvious for the first
two vegetation periods. Only with the additional use of mulch covers could increase surface drainage and noticeable soil loss
be avoided. At high altitudes, the choice of seed mixture, irrespective of whether rapid or slow growing and independent of
the extent of accompanying fertilisation, had no significance in the first two vegetation periods following sowing. In the
following growing seasons, however, higher cover values were obtained with site-specific seed mixtures at three of the five
experimental sites. While few species of the commercial seed mixture showed satisfactory persistency, most of the grasses
and in particular the alpine leguminosae of site-specific seed mixtures increased their share during the observation period.
In the long-term, sufficient protection against erosion is only guaranteed by the use of stable, enduring and ecologically
adapted species. 相似文献
10.
Basin evolution and palaeoenvironmental variability of the thermokarst lake El'gene‐Kyuele,Arctic Siberia 下载免费PDF全文
Philipp Schleusner Boris K. Biskaborn Frank Kienast Juliane Wolter Dmitry Subetto Bernhard Diekmann 《Boreas: An International Journal of Quaternary Research》2015,44(1):216-229
Thermokarst lakes are a widespread feature of the Arctic tundra, in which highly dynamic processes are closely connected with current and past climate changes. We investigated late Quaternary sediment dynamics, basin and shoreline evolution, and environmental interrelations of Lake El'gene‐Kyuele in the NE Siberian Arctic (latitude 71°17′N, longitude 125°34′E). The water‐body displays thaw‐lake characteristics cutting into both Pleistocene Ice Complex and Holocene alas sediments. Our methods are based on grain size distribution, mineralogical composition, TOC/N ratio, stable carbon isotopes and the analysis of plant macrofossils from a 3.5‐m sediment profile at the modern eastern lake shore. Our results show two main sources for sediments in the lake basin: terrigenous diamicton supplied from thermokarst slopes and the lake shore, and lacustrine detritus that has mainly settled in the deep lake basin. The lake and its adjacent thermokarst basin rapidly expanded during the early Holocene. This climatically warmer than today period was characterized by forest or forest tundra vegetation composed of larches, birch trees and shrubs. Woodlands of both the HTM and the Late Pleistocene were affected by fire, which potentially triggered the initiation of thermokarst processes resulting later in lake formation and expansion. The maximum lake depth at the study site and the lowest limnic bioproductivity occurred during the longest time interval of ~7 ka starting in the Holocene Thermal Maximum and lasting throughout the progressively cooler Neoglacial, whereas partial drainage and an extensive shift of the lake shoreline occurred ~0.9 cal. ka BP. Correspondingly, this study discusses different climatic and environmental drivers for the dynamics of a thermokarst basin. 相似文献