The propagation of the deformation front in foreland systems is typically accompanied by the incorporation of parts of the basin into wedge‐top piggy‐back basins, this process is likely producing ...considerable changes to sedimentation rates (SR). Here we investigate the spatial‐temporal evolution of SR for the Tremp–Jaca Basin in the Southern Pyrenees during its evolution from a wedge‐top, foreredeep, forebulge configuration to a wedge‐top stage. SR were controlled by a series of tectonic structures that influenced subsidence distribution and modified the sediment dispersal patterns. We compare the decompacted SR calculated from 12 magnetostratigraphic sections located throughout the Tremp–Jaca Basin represent the full range of depositional environment and times. While the derived long‐term SR range between 9.0 and 84.5 cm/kyr, compiled data at the scale of magnetozones (0.1–2.5 Myr) yield SR that range from 3.0 to 170 cm/kyr. From this analysis, three main types of depocenter are recognized: a regional depocenter in the foredeep depozone; depocenters related to both regional subsidence and salt tectonics in the wedge‐top depozone; and a depocenter related to clastic shelf building showing transgressive and regressive trends with graded and non‐graded episodes. From the evolution of SR we distinguish two stages. The Lutetian Stage (from 49.1–41.2 Ma) portrays a compartmentalized basin characterized by variable SR in dominantly underfilled accommodation areas. The markedly different advance of the deformation front between the Central and Western Pyrenees resulted in a complex distribution of the foreland depozones during this stage. The Bartonian–Priabonian Stage (41.2–36.9 Ma) represents the integration of the whole basin into the wedge‐top, showing a generalized reduction of SR in a mostly overfilled relatively uniform basin. The stacking of basement units in the hinterland during the whole period produced unusually high SR in the wedge‐top depozone.
The study of 10 Myr evolution of sedimentation rates on a Foreland Basin Systemhas demonstrated the effect of tectonic evolution and overfilled versus underfilled accommodation zones in the basin.
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Die Landschaft im Jungmoränengebiet (Kreis Stormarn, Schleswig-Holstein) wurde maßgeblich während der Abschmelzphase der Weichsel-Gletscher geprägt. Der nördliche Bereich des Untersuchungsgebietes ...stellt eine Hohlform, vermutlich ein glazifluviatil oder durch Toteis überprägtes Gletscherschürfbecken dar. In diesem erfolgte eine organogene Sedimentation seit dem Spätglazial (Bölling /Alleröd), gefolgt von einer längeren limnischen Phase sowie dem Aufwachsen eines Niedermoores ab ca. 5.000 a BP (14C-Alter). Eine Hochmoorbildung fand nicht statt, vermutlich weil die zur Setzung neigenden Mudden im Untergrund das Aufwachsen eines Hochmoores über dem Grundwasser verhinderten. Typische Formen im Eiszerfallsbereich des zentralen Untersuchungsgebietes sind Kames und Esker, bzw. Esker-artige Vollformen. Ringförmige Glazifluviatil-Strukturen werden als Subzirkular-Esker interpretiert. Im Zentrum dieser Strukturen entwickelten sich spätestens ab ca. 5.000 a BP (Atlantikum/Subboreal) Kesselmoore. Der südliche, bzw. südöstliche Untersuchungsbereich stellt einen Hochflächen-artigen Moränenbereich, mit einem glazitektonisch gestauchten saalezeitlichen Kern dar. Die in diesen eingetieften, parallel verlaufenden Rinnen wurden überwiegend als subglaziale Schmelzwasser-Rinnen (Tunneltäler) gebildet. Räumlich begrenzte Becken sind mit glazilimnischen Beckentonen gefüllt. Die bei mehreren Rinnen zu beobachtende Asymmetrie im Querprofil geht vorwiegend auf einen periglaziären Hangabtrag zurück. Teilweise sehr blockreiche periglaziale Ablagerungen bilden heute die Talsohlen im Liegenden der holozänen Moore. Einige Rinnenabschnitte wurden vor der Vermoorung, spätestens ab dem Präboreal mit mächtigen See-Ablagerungen gefüllt. Strangförmige Moore entwickelten sich vielfach auf den glazilimnischen Beckentonen.
Dynamics of river mouth deposits Fagherazzi, Sergio; Edmonds, Douglas A.; Nardin, William ...
Reviews of geophysics,
September 2015, Volume:
53, Issue:
3
Journal Article
Peer reviewed
Open access
Bars and subaqueous levees often form at river mouths due to high sediment availability. Once these deposits emerge and develop into islands, they become important elements of the coastal landscape, ...hosting rich ecosystems. Sea level rise and sediment starvation are jeopardizing these landforms, motivating a thorough analysis of the mechanisms responsible for their formation and evolution. Here we present recent studies on the dynamics of mouth bars and subaqueous levees. The review encompasses both hydrodynamic and morphological results. We first analyze the hydrodynamics of the water jet exiting a river mouth. We then show how this dynamics coupled to sediment transport leads to the formation of mouth bars and levees. Specifically, we discuss the role of sediment eddy diffusivity and potential vorticity on sediment redistribution and related deposits. The effect of waves, tides, sediment characteristics, and vegetation on river mouth deposits is included in our analysis, thus accounting for the inherent complexity of the coastal environment where these landforms are common. Based on the results presented herein, we discuss in detail how river mouth deposits can be used to build new land or restore deltaic shorelines threatened by erosion.
Key Points
Bars and subaqueous levees form at river mouths
River mouth deposits can be used to build new land
Waves, tides, and vegetation affect river mouth deposits
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Rivers differ among themselves and through time. An individual river can vary significantly downstream, changing its dimensions and pattern dramatically over a short distance. If hydrology and ...hydraulics were the primary controls on the morphology and behaviour of large rivers, we would expect long reaches of rivers to maintain characteristic and relatively uniform morphologies. In fact, this is not the case - the variability of large rivers indicates that other important factors are involved. River Variability and Complexity presents an interesting approach to the understanding of river variability. It provides examples of river variability and explains the reasons for them, including fluvial response to human activities. Understanding the mechanisms of variability is important for geomorphologists, geologists, river engineers and sedimentologists as they attempt to interpret ancient fluvial deposits or anticipate river behaviour at different locations and through time. This book provides an excellent background for graduates, researchers and professionals.
The Yangtze Estuary in China has been intensively influenced by human activities including altered river and sediment discharges in its catchment and local engineering projects in the estuary over ...the past half century. River sediment discharge has significantly decreased since the 1980s because of upstream dam construction and water-soil conservation. We analyzed bathymetric data from the Yangtze Estuary between 1958 and 2010 and divided the entire estuary into two sections: inner estuary and mouth bar area. The deposition and erosion pattern exhibited strong temporal and spatial variations. The inner estuary and mouth bar area underwent different changes. The inner estuary was altered from sedimentation to erosion primarily at an intermediate depth (5–15m) along with river sediment decline. In contrast, the mouth bar area showed continued accretion throughout the study period. The frequent river floods during the 1990s and simultaneously decreasing river sediment probably induced the peak erosion of the inner estuary in 1986–1997. We conclude that both sediment discharge and river flood events played important roles in the decadal morphological evolution of the Yangtze Estuary. Regarding the dredged sediment, the highest net accretion rate occurred in the North Passage where jetties and groins were constructed to regulate the navigation channel in 1997–2010. In this period, the jetties induced enhanced deposition at the East Hengsha Mudflat and the high accretion rate within the mouth bar area was maintained. The impacts of estuarine engineering projects on morphological change extended beyond their sites.
•River sediment decline led to erosion in the inner estuary but not in the mouth bar.•River flooding played an important role in decadal morphological evolution.•The impacts of estuarine engineering projects extended beyond their given sites.
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Deltas are important coastal sediment accumulation zones in both marine and lacustrine settings. However, currents derived from tides, waves or rivers can transfer that sediment into distal, deep ...environments, connecting terrestrial and deep marine depozones. The sediment transfer system of the Rhone River in Lake Geneva is composed of a sublacustrine delta, a deeply incised canyon and a distal lobe, which resembles, at a smaller scale, deep‐sea fan systems fed by high discharge rivers. From the comparison of two bathymetric datasets, collected in 1891 and 2014, a sediment budget was calculated for eastern Lake Geneva, based on which sediment distribution patterns were defined. During the past 125 years, sediment deposition occurred mostly in three high sedimentation rate areas: the proximal delta front, the canyon‐levée system and the distal lobe. Mean sedimentation rates in these areas vary from 0·0246 m year−1 (distal lobe) to 0·0737 m year−1 (delta front). Although the delta front–levées–distal lobe complex only comprises 17·0% of the analysed area, it stored 74·9% of the total deposited sediment. Results show that 52·5% of the total sediment stored in this complex was transported toward distal locations through the sublacustrine canyon. Namely, the canyon–levée complex stored 15·9% of the total sediment, while 36·6% was deposited in the distal lobe. The results thus show that in deltaic systems where density currents can occur regularly, a significant proportion of riverine sediment input may be transferred to the canyon‐lobe systems leading to important distal sediment accumulation zones.
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The onset and evolution of the middle to late Cenozoic “icehouse” world was influenced by the development of the global ocean circulation linking the Norwegian–Greenland Sea‐Arctic Ocean to the ...Atlantic Ocean. The evolution of the early Neogene to early Quaternary Bjørnøyrenna Drift, located at the SW Barents Sea continental margin, shed new light on this important hydrological event. By analyzing seismic data and exploration wellbores, it is found that the drift likely started to form in the early/middle Miocene, probably as a result of an ocean circulation reorganization following the opening of the Fram Strait gateway (c. 17 Ma) and subsidence of the Greenland–Scotland Ridge (c. 12 Ma). Thus, the onset of drift growth is considered to have happened close in time to the Mid Miocene Climatic Optimum at 16–14 Ma, and was part of a regional onset of large‐scale ocean circulation in the Norwegian–Greenland Sea that influenced the subsequent climate cooling. The drift continued to grow under the influence of early Quaternary glacimarine sedimentation, and later overtopping of the drift mound by downslope transfer of glacigenic sediments during full‐glacial conditions resulted in a submarine failure. For the first time, minimum average sedimentation rates of a Neogene to Quaternary drift in this area is calculated, giving rates of 0.020–0.031 m/Kyr. These values are comparable to average deep‐sea sedimentation rates from modern low‐latitude river systems such as the Amazon and Mississippi, but lower than the Quaternary glacial sedimentation rates from the Barents Sea and Fennoscandian continental margins.
Plain Language Summary
The ocean water masses are constantly moving through the thermohaline circulation, which both distribute heat from low to high latitudes, as well as cold water in the opposite direction. This is crucial for maintaining the global climate, and the start and evolution of ocean currents can be decrypted from marine sedimentary deposits known as contourite drifts. This study outlines the evolution of a drift that likely started building up in the SW Barents Sea when the Gulf Stream first extended into the Arctic Ocean. This likely happened as important ocean passages such as the Fram Strait gateway west of Svalbard opened up, which occurred during a global temperature highpoint in the mid Miocene (16–14 Ma). The global temperatures dropped following this, possibly partly because of the establishment of this ocean circulation, allowing for precipitation and growth of larger ice caps on the northern hemisphere. The drift accumulated by 0.020–0.031 m per 1,000 years, before it was later rapidly buried (at a rate of 0.18–0.64 m per 1,000 years) by glacigenic sediments during the last 2.7 Ma. The weight of these overlying sediments likely caused parts of the drift to fail, resulting in a large submarine slide.
Key Points
The Bjørnøyrenna Drift records the high north ocean circulation that influenced climate deterioration after the Mid Miocene Climatic Optimum
The drift accumulated on the slope until Quaternary glacigenic sediments buried it, resulting in a submarine failure
The drift sedimentation rates compare to deep‐sea input from the Amazon/Mississippi rivers, but are less than from continental ice caps
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Clinoforms are ubiquitous deltaic, shallow-marine and continental-margin depositional morphologies, occurring over a range of spatial scales (1–104m in height). Up to four types of progressively ...larger-scale clinoforms may prograde synchronously along shoreline-to-abyssal plain transects, albeit at very different rates. Paired subaerial and subaqueous delta clinoforms (or ‘delta-scale compound clinoforms’), in particular, constitute a hitherto overlooked depositional model for ancient shallow-marine sandbodies. The topset-to-foreset rollovers of subaqueous deltas are developed at up to 60m water depths, such that ancient delta-scale clinoforms should not be assumed to record the position of ancient shorelines, even if they are sandstone-rich.
This study analyses a large dataset of modern and ancient delta-scale, shelf-prism- and continental-margin-scale clinoforms, in order to characterise diagnostic features of different clinoform systems, and particularly of delta-scale subaqueous clinoforms. Such diagnostic criteria allow different clinoform types and their dominant grain-size characteristics to be interpreted in seismic reflection and/or sedimentological data, and prove that all clinoforms are subject to similar physical laws.
The examined dataset demonstrates that progressively larger scale clinoforms are deposited in increasingly deeper waters, over progressively larger time spans. Consequently, depositional flux, sedimentation and progradation rates of continental-margin clinoforms are up to 4–6 orders of magnitude lower than those of deltas. For all clinoform types, due to strong statistical correlations between these parameters, it is now possible to calculate clinoform paleobathymetries once clinoform heights, age spans or progradation rates have been constrained.
Muddy and sandy delta-scale subaqueous clinoforms show many different features, but all share four characteristics. (1) They are formed during relative sea-level stillstands (e.g., Late Holocene); (2) their stratigraphic architecture and facies character are dominated by basinal processes, and are quite uniform; (3) their plan-view morphology is shore-parallel and laterally extensive; (4) their sigmoidal cross-sectional geometry contrasts with the oblique profiles of most subaerial deltas. Holocene-age, delta-scale, sand-prone subaqueous clinoforms occur on steep (≥0.26°) and narrow (5–32km) shelves, at typical distances of 0.6–7.2km from the shoreline break. That contrasts with mud-prone subaqueous deltas, which form clinoforms on gently-sloping (0.01–0.38°), wide (23–376km) shelves, at usual distances of 7.5–125km from the shoreline. Delta-scale sand-prone subaqueous clinoforms have diagnostically steep foresets (0.7–23°). Similarly steep gradients were observed in much larger shelf-prism- and continental-margin-scale clinoforms. Gentler foreset gradients are shown by sand-prone subaerial deltas (0.1–2.7°), and mud-prone subaqueous and subaerial deltas (0.03–1.50°). Due to the lack of connections with river mouths, Holocene delta-scale sand-prone subaqueous clinoform deposits have progradation rates (1–5×102km/Myr) and unit-width depositional flux (1–15km2/Myr) that are up to 3–4 and 2–3 orders of magnitude lower, respectively, than age-equivalent input-dominated subaerial deltas and muddy subaqueous deltas. Lower progradation/aggradation ratios are reflected in a larger spread of clinoform trajectory angles (from −0.4° to +3.5°) than the very low values displayed by age-equivalent subaerial and muddy subaqueous deltas.
As slowly prograding, steep, sigmoidal clinoforms are strongly suggestive of sand-prone subaqueous deltas, the Sognefjord Formation and Bridport Sand are likely Jurassic examples of this clinoform type, and host hydrocarbon reservoirs. In contrast, the Campanian Blackhawk Formation is an outcrop example of delta-scale compound clinoforms with a muddy subaqueous component.
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