Provenance of Triassic sandstones in the basins of Northern Ireland—Implications for NW European Triassic palaeodrainage
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Palaeodrainage models for the mixed fluvial‐aeolian systems, which supplied detritus to Triassic basins on and offshore Britain and Ireland are well established. Basins such as those across Northern Ireland are not as well understood. Provenance studies of Triassic sandstones in the Slyne Basin offshore western Ireland and in basins west of Shetland have indicated that sediment supply was through a southward flowing fluvial system. Similar work on Triassic sandstones in the Wessex and East Irish Sea basins on and offshore Britain identified source rocks to the south supporting models, which evoke the northward flowing “Budleighensis” river system. The basins across Northern Ireland are potentially situated along the drainage divide between these two large‐scale drainage systems. K‐feldspar Pb‐isotopic analysis, apatite U–Pb geochronology and trace element geochemistry identify the Hebridean Platform, and the Scottish and Irish massifs to the north and west, respectively, and the remnant Variscan Uplands to the far south of the basins as source areas. The proportion of the northern‐ and southern‐derived detritus fluctuates several times over the sampled intervals, suggesting the dominance of drainage systems supplying sand to the basins “switched” intermittently over time. This may be due to abnormally heavy rains periodically powering the Budleighensis river system farther north or perhaps localised subsidence temporarily disconnecting Triassic basins on and offshore Britain and Ireland. The Triassic basins in Northern Ireland acted as either a major drainage divide between southern and northern river systems or as a regional sink for sediment preventing further expansion of either system.Keywords:
Tectonic subsidence
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Abstract Field investigations into the sedimentary evolution of the Mulargia–Escalaplano late- to post-Variscan basin in Sardinia have been carried out. This basin is the only Variscan molassic basin in the Southern Variscan Realm where relationships between all the Late Pennsylvanian to Middle Triassic sedimentary cycles have been detailed for the first time. Here the interplay between tectonics and sedimentation can also be inferred. The investigations evidence that the sedimentary response recorded in the basin matches the progress and final collapse of the southern Variscan chain branch. The basin preserves continental deposits of decreasing energy organized in cycles, separated by weak unconformities related to abrupt volcano-tectonic climaxes and influenced by progressively drying climates. The sedimentary facies and stratigraphy suggest a progressive widening of the basin and decreasing depositional energy to the southeast as well as the migration of the basin depocentre in the same direction. Stratigraphic, environmental and evolutionary correlations between the presently separated NW and SE parts of the basin are reconstructed by considering the role of tectonics. As a result, a detailed lithostratigraphic framework for the Mulargia–Escalaplano basin is proposed. The findings in the sedimentary evolution match the evolution of similar coeval basins of France and Germany, following a pull-apart to extensional model. Based on comparisons with the other Sardinian and SW Europe coeval basins, relationships between ‘limnic’ and red bed successions in SW Europe during the collapse of the Variscan chain are discussed. The renaming of the European tectonomagmatic ‘Mid-Permian Episode’ to the ‘Lower Permian Episode’ is proposed.
Red beds
Back-stripping
Extensional tectonics
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The Upper Jurassic in the Yanshan belt consists of the Tiaojishan and Tuchengzi formations. Analysis of the radiometric age data of the volcanic rocks indicates that the main parts of the two formations formed synchronously, rather than show a simple overlapping stratigraphic relation. Based on an analysis of the lithofacies, facies association, direction of paleocurrents and provenance, the Late Jurassic sedimentary environment in the Chengde area has been reconstructed, and it is thought that the sediments in the basins in the early stage of its development mainly came from north of the basin. However, even so, the authors do not think that the basin development was controlled by a south-vergent thrust fault in the north. The Shangyi-Pingquan fault has pronounced strike-slip features and controlled volcanic eruption. The paper proposes a new model for the basin evolution in the Chengde area, which may well explain the development of volcano-sedimentary sequences, changes in direction of paleocurrents and provenance and tectonic-sedimentary process of basins in the Chengde area.
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The major features of many sedimentary basins can be understood in terms either of lithospheric stretching or of tectonic loading of the lithosphere. These models allow broad predictions to be made concerning the thermal evolution and the hydrocarbon-maturation histories of the basins in question. In any particular basin, however, the conductive temperature structure is liable to be modified significantly by the convective transport of heat by circulating pore fluids. Even very slow flows that are too small to be detected during drilling or by conventional hydrologic techniques may have a significant influence if they persist over long periods. Such flows have been demonstrated in the North Sea and the Alberta basin and may operate over a depth of several kilometers and have horizontal dimensions of tens of kilometers. Much remains to be learned about the causes and behavior of circulations of this kind. By disturbing the conductive distribution of temperature, they delay the maturation of hydrocarbons in some areas and accelerate it in others. They may influence the migration of hydrocarbons, both directly and indirectly, through modification of the permeability structure by solution and precipitation. It is not possible to interpret the fine structure of sedimentary basins and the distribution of hydrocarbons within them without an understanding of these processes. End_of_Article - Last_Page 797------------
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Progradation
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The sedimentary infill of a small continental basin and the processes involved in its transformation into an erosional basin have been studied. The Otinar basin is a fluvio-lacustrine basin developed during the Quaternary (?) on the Subbetic rocks at the south of Jaen city. Its sedimentary infill is made up of three stratigraphic units representing different stages as exorheic and endorheic basin. The destruction of the basin took place when the axial fluvial system base level occupied a relatively lower position and the fluvial system entrenched in the sedimentary infill leaving at least three terraces levels. Climatic and tectonic factors are discussed as controls of the sedimentary and erosional evolution of the Otinar basin.
Infill
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With introduction and discussion of the dynamics of sedimentary basins and basin reservoir(ore) forming systems to be a main line,this paper generalizes and summarizes author's thoughts and viewpoints in this area. Sedimentary basins are significant in three aspects(scientific research,material needs and living environment) of earth science research and application,especially those large and medium-sized basins having a large distribution area and long development history(e.g.,oil-gas basins). A sedimentary basin is a negative tectonic unit formed in a depression of crust or lithosphere,in which sediments continuously infill in geologic history.The author defines dynamics of sedimentary basin as: A coupling dynamic system and evolution process of earth internal and external dynamics directly controlling and obviously impacting on basin subsidence and sediments infilling,and it is an important component of geodynamic systems.According to different driven force of basin depression,the origin of basin can be divided into thermal,stress,gravity and composite four types.From redefinition and revealing distribution position,evolution and relationships of basin subsidence centre,depocenter and accumulation centre,ruling out the sedimentary effects generated by non-subsidence processes,it is possible to characterize the role of subsidence and its temporal-spatial correlation and reasons with deposit and accumulation centers. The Chinese sedimentary basins are characterized by their strong tectonic activities,deep processes and intensive late reforming.All these are attributed to tectonic features of China continent.Based on the main geological processes of reforming and reforming fashions,the reformed basins can be divided into eight types.Eliminating impacts of late reforming and recovering original basin can build up a firm basis for recognition of basin evolution-reforming processes and oil-gas reservoir forming,positioning and distribution. According to the geological facts of reformed basin and the research practice of the author,ideas and regulations of study on reformed basin and oil-gas evaluation are explored and proposed;The time limit of oil-gas late-extra late reservoir forming-positioning in Chinese basins is redefined in terms of Absolute time and relative time.And also,the influences of deep processes on oil-gas accumulation,oil-gas escape and geologic effects are discussed. The research for dynamics of petroliferous basins can be divided into three major systems of basin forming,reservoir forming and assessment.In the study of basin evolution and reforming,a close correlation and interaction exist between the major systems and the sub-systems.The whole,dynamic,integrated principle for research of the basins is promoted to follow. More than 82 percent of proven sandstone-type uranium deposits on the earth coexist with oil-gas or coal fields in the same basins.Association and enrichment of the four main energy minerals within the same basin is common.But,the distribution of enrichment for different minerals is localized especially this is typical in central-east Asia.The characteristics of occurrence of multi-energy mineral deposits in all basins of mineralization domain in central-east Asia show a complex but orderly spatial distribution,close correlation of each(reservoir) ore-bearing stratum and region background,the same or similar timing of reservoir(ore) forming-positioning,related occurrence setting and reservoir(ore) forming.Also,the uranium main mineralization processes and mineralization period is in response to the regional dynamic changes,and basically consistent with the reservoir forming-positioning period of oil-gas in basins,indicating a close inherent relationships and unified geodynamic setting between them. The single sedimentary basin having multi-organic and inorganic,metallic and non-metallic minerals and water resources inside represents a basic unit and a giant complex system for multi-mineral accumulation and reservoir(ore) forming in the same basin.The system is called the reservoir(ore) forming system of sedimentary basin.In the system,the occurrence of various sedimentary minerals is not isolated.Their formation and distribution are closely related,interacting,mutually affecting,and intrinsic relationship exhibits in different forms.This system possesses its own characteristics of ore forming and reservoir(ore) forming setting.Thus,it should be treated as an independent mineralization system differing from and paralleling to other ore-forming systems. This paper discusses types of small-sized petroliferous basins and the conditions of oil-gas accumulation,the necessity and guidance for further study of mature basins.It is suitable for the system dynamics study of(stable continental) block-basin-belt(all types of tectonically active belts) in west China. The earth and basin all belong to the complex giant systems of different classes.It is an effective approach to use integrated and systematic academic thoughts to study complex science such as geosciences.In study of complex systems,the interaction of various sub-systems is the most important.In the mean while,the attention has to be drawn to the evolution of ideology and methodology,and to effort to disclose the individual characteristics of research objects.
Back-stripping
Tectonic subsidence
Thermal subsidence
Basin modelling
Pull apart basin
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Understanding how the sedimentary responses adapt to the structural styles of fault basins in the strike-slip fault systems is one of the key goals of basin analysis. Variability of volcanic and epiclastic provenance-depositional systems and tectonic controls of the Lower Cretaceous Hengtongshan Formation in the Tonghua Basin are crucial to determine the evolution of the fault basins and wrench tectonics in southern Jilin and eastern Liaoning provinces (SJELP), NE China. Study of volcanism-induced sedimentation, composition plot, and depositional systems elucidates the sequence stratigraphy and volcano-sedimentary responses to wrench tectonics based on cores, outcrop sections, and seismic profiles of the Tonghua Basin. Two types of provenance-depositional systems (volcanic and epiclastic) were reconstituted using eight lithofacies and seven lithofacies associations. Of the lithofacies, six pyroclastic lithofacies and two epiclastic lithofacies were identified based on compositions, textures, and sedimentary structures. The presence of these lithofacies in different vertical successions was described as different lithofacies associations to interpret depositional processes and sedimentary environments. Depositional-system maps of the three sequences in the Hengtongshan Formation and analysis of structural framework indicate that volcanism and sedimentation were controlled by wrench faulting. Statistical analysis of rock compositions reveals that the deposition of the Hengtongshan Formation shows mixed contribution from both the volcanic and granitic fragments. Triangular compositional plots of detrital composition suggest a diverse provenance by straddling the litho-feldspatho-quartzose (lFQ), feldspatho-litho-quartzose (fLQ), feldspatho-quartzo-lithic (fQL), and quartzo-feldspatho-lithic (qFL) fields, indicating that the sources were derived from uplifted basement blocks and volcanic eruptions in a rift basin related to strike-slip faulting. The Tonghua Basin developed as a wrench-fault basin on the east side of Dunhua–Mishan Fault systems (DMF). This model for the Tonghua Basin can be used to understand the Liuhe Basin in the DMF and other Early Cretaceous basins in adjacent areas.
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