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Wan Zhifeng - One of the best experts on this subject based on the ideXlab platform.
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characteristics of Tertiary Sediments and main source rocks northern south china sea
Natural Gas Geoscience, 2008Co-Authors: Wan ZhifengAbstract:Basins in Northern South China Sea belong to passive margin basins,and they are located at the junction of the Eurasian,the Pacific and the Indian-Australian plates,and also at the Superposed areas of Palaeo-Tethyan structural regimes and Palaeo-Pacific structural regimes.So the geological settings of these basins are complex,their Tertiary Sediments developed well,and the phenomena of petroleum geology are rich and colorful.Based on the characteristics of framework and tectonics,the basins in Northern South China Sea can be classified into two types,strike-slip basins and rift basins.The source rocks of the former are mainly the well-developed,huge thickness of Neogene marine depression sedimentary rocks and Miocene marine sedimentary rocks;those of the latter are significantly the rift Sediments of Paleogene continental facies,and large-scale source rocks of medium-deep lacustrine facies and inshore paludal facies with coal measure strata well-developed.
H Thybo - One of the best experts on this subject based on the ideXlab platform.
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pre zechstein geology of the south east north sea offshore denmark a geophysical perspective
First Break, 1997Co-Authors: Shaohua Zhou, H ThyboAbstract:The aim of this paper is to present an integrated geophysical study of the pre-Zechstein geology in the south-eastern North Sea, offshore Denmark (Fig. 1). Main tectonic features of the area include the Central Graben in the west, the Horn Graben in the south-east, the East North Sea High in the middle, the Holmsland Block in the east, the southern part of the Norwegian-Danish Basin in the north, as well as the northern part of the North German Basin in the south (Fig. 2). The central part of the study area (i.e. East North Sea High) is commonly regarded as part of the Ringk˘bing-Fyn High, which is a major NWW±ESE trending positive structural element with a relatively thin cover of Mesozoic and Tertiary Sediments. This structural high divides the North German Basin from the Norwegian-Danish Basin. The main tectonic features in the area are clearly illustrated by the depth structure of the top pre-Zechstein (base Upper Permian) rock (Fig. 3a). In this study, geophysical evidence is presented to show the existence of substantial amounts of Palaeozoic Sediments in the area of the East North Sea High. The interpretation is based on a residual gravity anomaly map of the region, which outlines the potential area of Palaeozoic Sediments as indicated by relatively low residual gravity anomalies. Magnetic basement depths of a few selected areas are estimated using available aeromagnetic data. Interpretation of selected seismic sections is carried out to confirm the results derived from the potential field investigations. Finally, the implications of the finding of this study are discussed briefly in terms of the pre-Zechstein geology and the tectonic history of the region as well as its potential relevance to petroleum exploration in the area.
Zhifei Liu - One of the best experts on this subject based on the ideXlab platform.
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magnetostratigraphy of Tertiary Sediments from the hoh xil basin implications for the cenozoic tectonic history of the tibetan plateau
Geophysical Journal International, 2003Co-Authors: Zhifei Liu, Xixi Zhao, Chengshan Wang, Shun LiuAbstract:SUMMARY We conducted an integrated palaeomagnetic and stratigraphic study on a 5452.8 m thick sedimentary sequence of the Hoh Xil Basin in northern Qinghai-Tibet Plateau to obtain a chronostratigraphic framework for these Sediments. A total of 966 individual oriented palaeomagnetic samples (spaced at stratigraphic intervals) were collected from six measured sections in the Hoh Xil Basin. Magnetic directions in these samples were obtained by progressive thermal (mainly) and alternating-field demagnetization experiments. Most samples exhibit two components of magnetization. The lower unblocking temperature component is an overprint resembling the present-day geocentric axial dipole field direction at the sampling locality. The most stable, characteristic remanence (ChRM) appears to be an early chemical remanent magnetization residing mainly in haematite. The positive results of fold and reversal tests indicate that the ChRM is a record of the palaeomagnetic field close to the time of formation of these Sediments. Further evidence for the magnetization of these Sediments acquired close to their time of deposition is the fact that patterns of magnetic reversals can be matched with the established polarity timescale. On the basis of the distinct interval of magnetic reversal zones and biostratigraphic datums, 13 magnetozones can be recognized at the Hoh Xil Basin that range from chrons C11 to C23 (30.1‐51.0 Ma). The age of the Fenghuoshan Group is palaeomagnetically dated as 51‐31 Ma (Early Eocene‐Middle Early Oligocene), and the age of the Yaxicuo Group is between 31 and 30 Ma (Middle Early Oligocene‐Late Early Oligocene). The new palaeomagnetic data from the Fenghuoshan Group suggest that it has undergone no significant rotation since the Oligocene. In contrast, declination data from the Yaxicuo Group in Wudaoliang area imply a vertical-axis clockwise rotation (29.1 ◦ ± 8.5 ◦ ) since the Late Oligocene. The Tertiary palaeomagnetic pole position of the Hoh Xil Basin implies a significant northward convergence of the Hoh Xil Basin (∼1600 km) with respect to Eurasia (Siberia) since Early Eocene‐Late Oligocene time. Our results are consistent with the pattern of disturbingly low palaeolatitudes derived from a large number of high-quality palaeomagnetic studies of Tertiary rocks from sites that reach all the way from eastern China to Kyrgyzstan. Future work is needed to separate the influences of sedimentary inclination shallowing and tectonic shortening.
A J Melfi - One of the best experts on this subject based on the ideXlab platform.
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from plinthic acrisols to plinthosols and gleysols iron and groundwater dynamics in the Tertiary Sediments of the upper amazon basin
European Journal of Soil Science, 2007Co-Authors: Emmanuel Fritsch, A J Herbillon, N Do R Nascimento, Michel Grimaldi, A J MelfiAbstract:Topography has been reported to be the major factor ruling the spatial distribution of Acrisols, Plinthosols and Gleysols on the seasonally flooded, low elevation plateaux of the upper Amazon basin occupied by Tertiary (Ica & Solimoes) Sediments. In this study, detailed morphological and mineralogical investigations conducted in a representative 25-ha site were combined with hydro-geochemical data to relate the vertical and lateral soil differentiations observed to the hydro-geological history of that part of the basin. As a result of the uplift of the Andes, several cuts in the extensive Tertiary marshlands have formed, at first, slightly incised plateaux of low elevation. There, weathering under hot and humid climates would have generated a reddish, freely drained and bioturbated topsoil layer and the vertical differentiation in subsoil Sediments of a plinthite over an iron-depleted mottled clay. The second episode of soil differentiation is linked to the replacement of the forest by a savannah under the drier climates of the late Pleistocene, which favours surface runoff and the infill of the incisions by fine particles. This infill, combined with the return to the present humid climate, has then enabled the local groundwater to rise on the plateaux and to generate episaturation at the topsoil/subsoil transition close to the depressions. Nowadays, ferrous iron is released from the partly iron-depleted topsoil weathering front at high water levels during the rainy seasons. It moves from footslope to low-lying positions and from top to bottom in the soil profile according to the groundwater dynamics. The present general trend is thus to the lateral export of iron at high water levels due to subsurface and overland flows, its vertical transfer during the recession of the groundwater and accumulation in a nodular plinthite. In the latter, ferrous iron is adsorbed onto its softest iron masses where it feeds the neoformation of ferrihydrite that rapidly dehydrates into haematite.
L P Sha - One of the best experts on this subject based on the ideXlab platform.
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the magnetic properties of quaternary and Tertiary Sediments in the southern north sea
Journal of Quaternary Science, 1992Co-Authors: R Thompson, T D J Cameron, C Schwarz, K A Jensen, V Van Maenhaut Lemberge, L P ShaAbstract:Cores from boreholes penetrating late Quaternary, glacial, interglacial and postglacial Sediments and the underlying late Cenozoic delta complex of the southern North Sea have been examined for their magnetic properties. A magnetic polarity stratigraphy has been established as an aid to biostratigraphic dating of the Sediments; the Kaena-Gauss and Gauss—Matuyama transitions and the base and top of the Olduvai subchron have been identified. The strength and stability of laboratory-induced isothermal remanent magnetisation display clear magneto-petrological variations, which match lithostratigraphic changes in the cores. Principal component analysis has picked out a basin-wide and palaeoenvironmental consistency in the magnetic data. Large, multi-domain magnetite grains predominate in the post-deltaic and fluvio-deltaic Sediments, whereas smaller greigite or titanomagnetite grains are concentrated in the intertidal and marine deltaic facies. Since heavy mineral analysis indicates that most of the deltaic detritus derived from common source areas, the differences in magnetic mineralogy have probably been caused by the sediment transport processes operating within the delta complex.