An outline of the lithostratigraphy and depositional history of Quaternary deposits in the Sellafield district, west Cumbria
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SUMMARY A lithostratigraphical framework has been erected for Quaternary deposits of the Sellafield district in west Cumbria. It has enabled a sequence of glacial and deglacial events to be established that is one of the most detailed for the last glacial-inter-glacial cycle onshore in Britain and provides new constraints on models of the evolution of the Irish Sea basin during the last 120 000 years. The products of at least one major pre-Devensian (Oxygen Isotope Stage 6 or older) glaciation have been recorded in cored boreholes around Drigg and Nether Wasdale. Ice flowing from Wasdale terminated in proglacial lakes on two occasions during OIS 3 and 4 and an intervening cold-water marine incursion occurred that reached a height of at least 20 m below present sea level, probably during OIS 3. Glaciers emerged again from the Lake District during the build-up of the main Late Devensian ice sheet, which appears to have reached its maximum extent early in OIS 2, when the whole district was glaciated. Scottish ice flowing into the northern Irish Sea basin eventually deflected local ice southwards. The Irish Sea ice stream became dominant again during several readvances that followed a significant deglacial event. The first readvance (Gosforth Oscillation) over-rode most of the coastal plain. The last major one (Scottish Readvance) proglacially tectonized the glacigenic sequence along the coast, forming a push moraine at St Bees. Thick sequences of glaciolacustrine sediment accumulated within the major valleys of the district, both before and after the Gosforth Oscillation, when ice at the coast caused considerable ponding of meltwater inland.Keywords:
Lithostratigraphy
There is great difference in the sedimentary environment and depositional system of different formations of the Silurian in Tarim Basin.By combining the detailed observation and description of the cores with logging data,regional geological data and various laboratory analysis identification data,based on the analyses of the lithology and sedimentary structure,the sedimentary characteristics and sedimentary facies of Kepingtage Formation are thoroughly studied.It is held that deltaic,estuary and tidal flat depositional systems are mainly developed in Kepingtage Formation.Based on the study of the depositional systems,the corresponding sedimentary mode diagrams are established.
Lithology
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High-resolution lithostratigraphy has been attempted here to provide a detailed stratigraphic sequence of the Changhsingian Stage and the Lower Triassic in Meishan Section D. Previous stratigraphic data from Yin et al. (1996), Sheng et al. (1987) and Zhao et al. (1981) were compiled and revised with numerous errors in stratigraphic descriptions and thickness measurements corrected. Most importantly, the stratigraphic positions of the ash-beds and carbonatized tuff beds have been precisely measured. New microstratigraphic observation suggests that the Permian-Triassic transitional sequence at Meishan is a rather condensed or discontinuous at the uppermost part of Bed 24e and within Bed 27. Together with precise biostratigraphic data high-resolution lithostratigraphy will help us to improve our knowledge about the Permian-Triassic transition and the Permian-Triassic GSSP.
Lithostratigraphy
Chronostratigraphy
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Early Triassic
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All the units of waterlain, sorted gravel and sand repeatedly show suites of sedimentary structures that indicate deposition under broadly similar fluviatile conditions throughout the area. It is therefore possible, in general terms, to discuss the sedimentary sequences of deposits together.
Deposition
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Based on analyses of more than 600 surface sediment samples together with large amounts of previous sedimeutologic and hydrologic data, the characteristics of modern sedimentary environments and dynamic depositional systems in the southern Yellow Sea (SYS) are expounded, and the controversial formation mechanism of muddy sediments is also discussed. The southern Yellow Sea shelf can be divided into low-energy sedimentary environment and high-energy sedimentary environment; the lowenergy sedimentary environment can be further divided into cyclonic and anticyclonic ones, and the high-energy environment is subdivided into high-energy depositional and eroded environments. In the shelf low-energy environments,there developed muddy depositional system. In the central part of the southern Yellow Sea, there deposited the cold eddy sediments under the actions of a meso-scale cyclonic eddy (cold eddy), and in the southeast of the southern Yellow Sea, an anticyclonic eddy muddy depositional system (warm eddy sediment) was formed. These two types of sediments showed evident differences in grain size, sedimentation rate,sediment thickness and mineralogical characteristics. The high-energy environments were covered with sandy sediments on seabed; they appeared mainly in the west, south and northeast of the southern Yellow Sea. In the high-energy eroded environment, large amounts of sandstone gravels were distributed on seabed. In the high-energy depositional environment, the originally deposited fine materials (including clay and fine silt) were gradually re-suspended and then transported to a low-energy area to deposit again. In this paper, the sedimentation model of cyclonic and anticyclonic types of muddy sediments is established, and a systematic interpretation for the formation cause of muddy depositional systems in the southern Yellow Sea is given.
Sedimentation
Anticyclone
Silt
Seabed
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Deposition
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Based on analyses of more than 600 surfacesediment samples together with large amounts of previoussedimentologic and hydrologic data, the characteristics ofmodern sedimentary environments and dynamic deposi-tional systems in the southern Yellow Sea (SYS) are ex-pounded, and the controversial formation mechanism ofmuddy sediments is also discussed. The southern Yellow Seashelf can be divided into low-energy sedimentary environ-ment and high-energy sedimentary environment; the low-energy sedimentary environment can he further divided intocyclonic and antieyclonic ones, and the high-energy envi-ronment is subdivided into high-energy depositional anderoded environments. In the shelf low-energy environments,there developed muddy depositional system. In the centralpart of the southern Yellow Sea, there deposited the coldeddy sediments under the actions of a meso-scale cycloniceddy (cold eddy), and in the southeast of the southern YellowSea, an anticyclonic eddy muddy depositional system (warmeddy sediment) was formed. These two types of sedimentsshowed evident differences in grain size, sedimentation rate,sediment thickness and mineralogical characteristics. Thehigh-energy environments were covered with sandy sedi-ments on seabed; they appeared mainly in the west, southand northeast of the southern Yellow Sea. In the high-energyeroded environment, large amounts of sandstone gravelswere distributed on seabed. In the high-energy depositionalenvironment, the originally deposited fine materials (includ-ing clay and fine silt) were gradually re-suspended and thentransported to a low-energy area to deposit again. In thispaper, the sedimentation model of cyclonic and anticyclonictypes of muddy sediments is established, and a systematicinterpretation for the formation cause of muddy depositionalsystems in the southern Yellow Sea is given.
Sedimentation
Seabed
Silt
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Sedimentation
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It was considered by predecessor study that Eh 3 in Shuanghe Oilfield was a Gilbert type fan delta. Study of its depositional background, sedimentary facies distribution, its deposit properties, sedimentary structure and its sedimentary sequence shows that in the studied area depositional slope is gentle, frontal subfacies is developed, deposit particles are relatively fine in the target zone, its sedimentary structure is mainly of drag flow sedimentary structure, gravity flow sedimentary structure is undeveloped. The characteristics of its sedimentary sequence is not a typical fluvial depositional one, or a obvious gravity flow depositional one, there are bigger differences among these 3 deltaic modes, the fan delta sedimentary mode is similar to that of continental fan delta formed under more gentle conditions on the basin bottom.
Mouth bar
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There is a complicated dynamic sedimentary environment in Yangtze River Estuary-Hangzhou Bay and its adjacent waters,which is affected by the material transport and eco-environment of waters.In this paper,grain size distributions,rate earth elements and platinum group elements were analyzed for surface sediments from the Yangtze River Estuary-Hangzhou Bay and its adjacent waters.The investigated area has been partitioned into eight dynamic sediment environment divisions with a triangular diagram advanced by Pejrup M:two estuarine modern depositional regions with intense hydrodynamics;two nearshore modern depositional regions with the interaction on different water masses;one frontal region in the continental shelf;two relict sedimentary regions influenced by modern material supply from the warm current and the coastal current;and one modern depositional region with cyclonic eddy.By comparing grain size distributions and hydrodynamic patterns in different dynamic sedimentary environment regions,sedimentary features were revealed under different hydrodynamic conditions and the provenance characteristics were recognized in a variety of depositional environment.
River mouth
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