排序方式： 共有41条查询结果，搜索用时 250 毫秒
11.
Acta Geotechnica - Offshore wind turbines founded on monopiles are highly dynamic structures in which the stiffness of the soil adjacent to the monopile controls the natural frequency of the... 相似文献
12.
Notwithstanding the great deal of attention that the Messinian evaporites of the Mediterranean region have received from an observational point of view, there is, to date, no consensus as to their mechanism of formation. We aim to contribute to the investigation through a quantitative analysis of the processes of desiccation and re-filling. These processes are thought to have played a role in particular during the deposition of the upper part of the evaporite sequence. We calculate the evolution of sea level and average salinity based on both the present-day geometry and a paleogeographic reconstruction and assess the sensitivity to variations in the freshwater budget. Our results support previous inferences that desiccation and re-filling are fast; desiccation occurs on a time scale of 3-8 kyr, re-filling probably even faster. Equilibrium sea levels imply that most water has gone from the western basin while a significant water column remains in the eastern basin. Whether or not the eastern basin reaches the level of halite saturation depends critically on, in particular, the freshwater budget. The fast rate of desiccation and re-filling imply that temporal differences in the onset of salt precipitation between western and eastern basin and between marginal basins and basin centres are below the resolution of (astronomical) dating. Also, when Atlantic sea level periodically varied from below to above the level of the intervening sill, the Mediterranean basin will have responded with repeated desiccation and re-filling. Fast re-filling is found to require only a small connection to the Atlantic Ocean. This, in combination with the previous results, suggests the Mediterranean is unlikely to attain stable intermediate water levels. 相似文献
13.
14.
LUO Junhu DAI Shuang DEKKERS Mark WANG Weiguo QIANG Xiaoke QIANG Lei TIAN Chao XI Haiyu KRIJISMAN Wout 《《地质学报》英文版》2019,93(Z1):132-134
正The natural remnant magnetization (NRM) of carbonate rocks in particular must be understood for the construction of a meaningful Paleozoic geomagnetic polarity time scale.This would enable evaluating geomagnetic features (e.g.reversal frequency) and would provide a paleomagnetic dating tool (Voo,1990).The Ordos block,central China,was reported at low latitudes inthe Southern Hemisphere during Ordovician times 相似文献
15.
Daniel Pastor-Galán Ícaro Fróis Dias da Silva Thomas Groenewegen Wout Krijgsman 《International Geology Review》2019,61(2):240-255
The amalgamation of Pangea during the Carboniferous produced a winding mountain belt: the Variscan orogen of West Europe. In the Iberian Peninsula, this tortuous geometry is dominated by two major structures: the Cantabrian Orocline, to the north, and the Central Iberian curve (CIC) to the south. Here, we perform a detailed structural analysis of an area within the core of the CIC. This core was intensively deformed resulting in a corrugated superimposed folding pattern. We have identified three different phases of deformation that can be linked to regional Variscan deformation phases. The main collisional event produced upright to moderately inclined cylindrical folds with an associated axial planar cleavage. These folds were subsequently folded during extensional collapse, in which a second fold system with subhorizontal axes and an intense subhorizontal cleavage formed. Finally, during the formation of the Cantabrian Orocline, a third folding event refolded the two previous fold systems. This later phase formed upright open folds with fold axis trending 100° to 130°, a crenulation cleavage and brittle–ductile transcurrent conjugated shearing. Our results show that the first and last deformation phases are close to coaxial, which does not allow the CIC to be formed as a product of vertical axis rotations, i.e. an orocline. The origin of the curvature in Central Iberia, if a single process, had to be coeval or previous to the first deformation phase. 相似文献
16.
The salinity crisis of the Mediterranean during Messinian time was one of the most dramatic episodes of oceanic change of the past 20 or so million years, resulting in the deposition of kilometer thick evaporitic sequences. A large and rapid drawdown of the Mediterranean water level caused erosion and deposition of non-marine sediments in a large ‘Lago Mare’ basin. Both the surface loading by the Lower Messinian evaporites, and the removal of the water load resulted in isostatic/flexural rebound that significantly affected river canyons and topographic slopes. We use flexure models to quantitatively predict possible signatures of these events, and verify these expectations at well-studied margins. The highly irregular shape of the reconstructed basin calls for a three-dimensional model. Near basin margins, plate-bending effects are most pronounced which is why flexure is particularly important for a relatively narrow basin like the Mediterranean. We focus on one specific sea level scenario for the Messinian Salinity Crisis, where most of the evaporite load was deposited during a sea level highstand, followed by a rapid desiccation. Evaporite loading at current sea level is expected to cause subsidence of the deep basins by hundreds of meters and simultaneous uplift of continental parts of the margins. Differential uplift may lead to significant slope angle changes and thus gravity flows. The relative scarcity of Lower Evaporite sequences along the margins may be a result of these phenomena. Normal faulting of Lower Evaporite and older sediments and rocks is expected on the margins. Desiccation enhances erosion of the freshly exposed continental shelf and slope. Subsidence and riverbed sedimentation occurs on the continental margins, and significant uplift towards the basin center. Reverse faulting is predicted at the margins. Finally, regional isostatic uplift following Zanclean flooding is predicted to destabilize margin slope deposits, and to cause marginal uplift, river down-cutting, and normal faulting. 相似文献
17.
Oleg Mandic Arjan de Leeuw Jeronim Buli? Klaudia F. Kuiper Wout Krijgsman Zlata Juri?i?-Pol?ak 《International Journal of Earth Sciences》2012,101(4):1033-1046
The Pannonian Basin, originating during the Early Miocene, is a large extensional basin incorporated between Alpine, Carpathian and Dinaride fold-thrust belts. Back-arc extensional tectonics triggered deposition of up to 500-m-thick continental fluvio-lacustrine deposits distributed in numerous sub-basins of the Southern Pannonian Basin. Extensive andesitic and dacitic volcanism accompanied the syn-rift deposition and caused a number of pyroclastic intercalations. Here, we analyze two volcanic ash layers located at the base and top of the continental series. The lowermost ash from Mt. Kalnik yielded an 40Ar/39Ar age of 18.07?±?0.07?Ma. This indicates that the marine-continental transition in the Slovenia-Zagorje Basin, coinciding with the onset of rifting tectonics in the Southern Pannonian Basin, occurs roughly at the Eggenburgian/Ottnangian boundary of the regional Paratethys time scale. This age proves the synchronicity of initial rifting in the Southern Pannonian Basin with the beginning of sedimentation in the Dinaride Lake System. Beside geodynamic evolution, the two regions also share a biotic evolutionary history: both belong to the same ecoregion, which we designate here as the Illyrian Bioprovince. The youngest volcanic ash level is sampled at the Glina and Karlovac sub-depressions, and both sites yield the same 40Ar/39Ar age of 15.91?±?0.06 and 16.03?±?0.06?Ma, respectively. This indicates that lacustrine sedimentation in the Southern Pannonian Basin continued at least until the earliest Badenian. The present results provide not only important bench marks on duration of initial synrift in the Pannonian Basin System, but also deliver substantial backbone data for paleogeographic reconstructions in Central and Southeastern Europe around the Early–Middle Miocene transition. 相似文献
18.
Karen A. Leever Liviu Matenco Traian Rabagia Sierd Cloetingh Wout Krijgsman Marius Stoica 《地学学报》2010,22(1):12-17
The signature of the Mediterranean Messinian Salinity Crisis (MSC) in the Paratethys has received wide attention because of the inferred changes in connectivity and base level. In this article, we present sequence stratigraphic interpretations on a seismic transect across the western part of the semi-isolated Late Miocene–Pliocene Dacic Basin (Eastern Paratethys, Romania), chronologically constrained by biostratigraphic field observations and well data. They reveal significant sea level changes during the middle Pontian that are coeval with the MSC. These changes were most likely transmitted to the western Dacic Basin from the downstream Black Sea and controlled by the sill height of the interconnecting gateway. During the middle Pontian lowstand of the western Dacian Basin, sedimentation continued in a remnant ∼300 m deep lake with a positive water balance. Our observations show that the evolution of semi-isolated sedimentary basins is strongly dependent on the communication with other depositional realms through its control on base level and sediment supply. 相似文献
19.
Cornelia M. Köhler Wout Krijgsman Douwe J. J. van Hinsbergen David Heslop Guillaume Dupont-Nivet 《地学学报》2010,22(1):52-63
The upper Tortonian Metochia marls on the island of Gavdos provide an ideal geological archive to trace variations in Aegean sediment supply as well as changes in the North African monsoon system. A fuzzy-cluster analysis on the multiproxy geochemical and rock magnetic dataset of the astronomically tuned sedimentary succession shows a dramatic shift in the dominance of 'Aegean tectonic' clusters to 'North African climate' clusters. The tectonic signature, traced by the starvation of the Cretan sediment, now enables to date the late Tortonian basin foundering on Crete, related to the tectonic break-up of the Aegean landmass, at c. 8.2 Ma. The synchronous decrease in the North African climate proxies is interpreted to indicate a change in the depositional conditions of the sink rather than a climatic change in the African source. This illustrates that interpretations of climate proxies require a multiproxy approach which also assesses possible contributions of regional tectonism. 相似文献
20.
A full understanding of the Mio-Pliocene palaeogeographical and palaeoenvironmental changes in the circum-Mediterranean region during the Messinian Salinity Crisis (MSC) is at present hampered by the lack of reliable chronostratigraphic correlations between the Mediterranean and Paratethys regions. Here, we present magnetostratigraphic ages for the Upper Miocene to Pliocene deposits of the southern Carpathian foredeep in Romania. These ages are in good agreement with those recently obtained from the eastern Carpathian foredeep and define a new chronology for the eastern Paratethys. The Meotian/Pontian boundary is not biostratigraphically constrained in our sections, but according to the geological map of the region arrives at ∼5.8 Ma. The Pontian/Dacian boundary is dated at c. 4.8 Ma and the Dacian/Romanian boundary at c. 4.1 Ma. The main part of the MSC (5.96–5.33 Ma) is thus represented by the Pontian Stage, but the observed palaeoenvironmental and biostratigraphic changes in our sections of the eastern Paratethys do not indicate any relation with the dramatic desiccation and reflooding events of the Mediterranean. 相似文献