3D architecture of Quaternary sediment along the NW Atlantic Moroccan Rharb continental shelf: A stratal pattern under the dual control of tectonics and climatic variations
Pascal Le RoyM. SahabiNissrine MaadMarina RabineauMarc‐André GutscherNathalie BabonneauBrigitte Van Vliet LanoëLahcen Aït BrahimNadia MhammdiAlain TrentesauxMohamed DakkiM. Hssain
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Passive margin
Neogene
Onlap
Continental Margin
SUMMARY During the Cambrian, two types of continental margins occurred around Gondwana. The eastern margin (Antarctica, Australia and southern South America) was characterized by a narrow continental shelf with a steep slope separating the shallow water environment from a deep‐oceanic one accompanied by mafidultramafic volcanics. The western margin was characterized by a wider continental shelf, probably passing gradually to an unknown outer basin. This comprised three main domains: the Asiatic shelf, composed of distinct cratonic blocks, presumably separated from each other by deeper‐water/ volcanic intracontinental basins; the European shelf, characterized by the development of shallow intracontinental siliciclastic basins; and the Americanc‐African shelf, morphologically and depositionally uniform. The distinction of these two Gondwana continental margins expresses their different geodynamic behaviour during Cambrian extensional tectonics. In fact, the sedimentary/palaeogeographic evolution, suggests the establishment of an active Pacific‐like margin in the eastern domain, and the tentative establishment of a divergent Atlantic‐like margin, in the westem one.
Continental Margin
Siliciclastic
Passive margin
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The continental slope and plateau off northern California are underlain by a well-defined and extensive acoustic reflector that crosses other reflectors and mimics the surface of the sea floor. This bottom-simulating reflector (BSR) lies at an average subsurface depth of 250 m and is laterally continuous beneath the Klamath Plateau (water depths of 800-1200 m) off northernmost California. Limited data show that it extends northward into offshore Oregon and seaward at least to the base of the slope (3000 m water depth). The BSR has been mapped along the continental margin for a distance of over 130 km and underlies an area of at least 3000 km/sup 2/. The water depths and sediment depths of the BSR, as well as its pervasiveness, all suggest that it represents the base of a natural-gas hydrate. Using standard phase-boundary diagrams for hydrate stability, the authors estimate that the geothermal gradient in this area is about 50/sup 0//km. Such a gradient is higher than found along most subduction margins, possibly because the subducting oceanic crust in this region is young. This acoustically inferred gas hydrate is the first mapped along the western US conterminous continental margin.
Continental Margin
Clathrate hydrate
Passive margin
Seabed
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Neogene
Continental Margin
Passive margin
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Marginal basins include those within the body of the continental terrace (shelf and slope basins) and those flanking the terrace where it is separated from the deep sea by intervening topographic highs. Geographically widespread investigations with continuous reflection profilers suggest that continental slope basins are more common than previously suspected, particularly in tectonically active regions. Because of well-known topography and surface-sediment distributions, selected California continental borderland basins can be used as natural laboratories to study details of internal structures of basin deposits. These are compared with records End_Page 351------------------------------ of normal open shelf and slope deposits from other regions. Early results suggest that basin plains are underlain predominantly by ponded turbidites with internal reflecting horizons of near horizontal initial attitude which conform to their flat featureless surface. Lateral continuity of these reflectors appears to be large compared to those within the gently sloping aprons and sea fans of the basins. Reflection profiles of the peripheral regions of the Tyrrhenian Sea show horizontally-bedded, probably ponded turbidites in closed slope-basins and hemipelagic sediments blanketing and conforming to underlying topography in open-slope areas. Similar features are recorded in profiles from the continental terrace and marginal basin of the East China Sea and other regions. Filled marginal asins are believed to be quantitatively important in retaining terrigenous sediments within the continental framework. End_of_Article - Last_Page 352------------
Sedimentation
Reflection
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Published stable isotope data from deep-sea sediments clearly show that the earth's climatic cycles have oscillated through at least 10 major glacial and interglacial episodes during the last million years. These high-frequency, orbitally-forced events should have resulted in major glacioeustatic sea-level fluctuations on the continental margins with dramatic sedimentologic effects and stratigraphic responses. However, such high-frequency events have proven difficult to resolve. Are they too short-lived to be recorded, to complex to decipher, or have traditional stratigraphic tools not been adequate to recognize them in continental margin sequences A detailed, multidisciplinary study of various continental margins is necessary to test the sensitivity of sedimentologic systems and response in stratigraphic records. This study must utilize (1) high-resolution event stratigraphy to define the depositional and erosional sediment sequences; (2) sediment analyses to delineate depositional environments and characterize lithofacies of specific system tracts; and (3) biostratigraphic and geochronologic analyses to place the depositional sequences in time. Integration of these data sets will (4) determine the resolving power of sequence stratigraphy; (5) develop working stratal models for recognizing short-pulsed, glacioeustatic sea-level events within the stratigraphic record; and (6) define a chronostratigraphy of changing paleoclimatic and paleoceanographic events operating on continental margin systems during themore » late Quaternary.« less
Chronostratigraphy
Continental Margin
Passive margin
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Application of integrated stratigraphic modeling of sedimentary basins with the help of sequence and chemostratigraphic methods for improved understanding on the relative roles of depositional pattern and history of a Barremian-Danian stratigraphic record of the Cauvery Basin, India was attempted. Through enumeration of facies characteristics, tectonic structures and geochemical characteristics of the sedimentary rocks the use of geochemical signatures in distinguishing the relative roles of major factors has been evaluated. The results indicate that the geochemical signatures of the sedimentary rocks accurately record the prevalent geological processes and an ability to distinguish them through employing stratigraphic variations of compositional values and discrimination diagrams help in understanding the basinal history better. In addition, predomination of relative sea level fluctuations and active nature of tectonic movements during few time slices, which in turn was overwhelmed by sea level fluctuations are also inferred.
Sequence (biology)
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Neogene
Continental Margin
Margin (machine learning)
Passive margin
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During Caledonian,the plates were active in South China,and a complete basin evolution cycle from passive continental marginal basin to foreland basin was finished.However,the Yunan movement occurred in lately Cambrian-early Ordovician finished the basin character change, and in space,the basin evolution character was from southeast to northwest.The Caledonian orogenic movement occurred in late Silurian resulted in the combination of Yangtze Landmass and Cathaysia along the Jiangshan-Shaoxing fault zone,and the wide South China fold belt formed in this process.Hereby,the authors classify it as one Ⅰsequence,and then,according to different periods and the difference of evolution stage and basin type,the oneⅠsequence is divided into seven Ⅱ sequences.Among them,Ⅱ sequence SS1 reflects the initial developed stage of the passive continental margin basin in South China,Ⅱ sequence SS2~SS5 represent the passive continental margin basin from developing stage to mature stage,respectively,Ⅱ sequence SS6 reflects the transition process that South China evolved from passive continental margin basin to foreland basin,and Ⅱ sequence SS7 reflects the initial foreland basin stage of South China.
Sequence (biology)
Continental Margin
Passive margin
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Abstract A sedimentological investigation of the Neogene deposits of the Zagros foreland basin in SW Iran reveals a continuous and largely gradational passage from supratidal and sabkha sediments at the base (represented by the Gachsaran Formation) to carbonates and marine marls (Mishan Formation with basal Guri carbonate member) followed by coastal plain and meandering river deposits (Agha Jari Formation) and finally to braided river gravel sheets (Bakhtyari Formation). This vertical succession is interpreted to represent the southward migration of foreland basin depozones (from distal foredeep and foredeep to distal wedge-top and proximal wedge-top, respectively) as the Zagros fold–thrust belt migrated progressively southward towards the Arabian foreland. This vertical succession bears a striking similarity to modern depositional environments and sedimentary deposits observed in the Zagros region today, where one passes from mainly braided rivers in the Zagros Mountains to meandering rivers close to the coast, to shallow marine clastic sediments along the northern part of the Persian Gulf and finally to carbonate ramp and sabkha deposits along the southeastern coast of the Persian Gulf. This link between the Neogene succession and the modern-day depositional environments strongly suggests that the major Neogene formations of the Zagros foreland basin are strongly diachronous (as shown recently by others) and have active modern-day equivalents.
Sabkha
Neogene
Diachronous
Marl
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