Academic literature on the topic 'Setting back dykes'

A sheeted dolerite dyke swarm has been discovered at Duniewick Fort, Ballantrae. It forms part of the Early Ordovician Ballantrae Complex of Ayrshire, southwest Scotland. Asymmetric chilled margins, parallel to sub-parallel dykes and multiple dykes (dykes within dykes) are found. Although the mineralogy has been altered by metamorphism, the geochemistry is comparable with modern day back-arc marginal basin basalt. Cross-cutting sills have the chemistry of within-plate basalt. The regional geological setting suggests that an ophiolite sequence has been dismembered and incorporated into a serpentinite mélange. This is the first description of a 100% sheeted dyke complex (senso stricto) from the Ballantrae ophiolite.

The volcanic and sedimentary rocks of the Passamaquoddy Bay (PB) area of southeastern New Brunswick are part of the Silurian–Devonian Coastal Volcanic Belt (CVB), an extensive belt of bimodal volcanic rocks. The PB sequence is 4 km thick, has four cycles of mafic and felsic volcanism, and is intruded by mafic dykes at all levels. There are two ages of dykes, those related to the Late Silurian PB volcanism (PB dykes) and Mesozoic dykes (the Minister Island Dyke) related to the opening of the North Atlantic. The PB mafic dykes are subalkalic basalt to basaltic andesite, within-plate tholeiites. The dykes are moderately to highly evolved (Mg# = 66.6 to 26.6), with trends of major and trace elements typical of the fractionation of olivine, pyroxene, plagioclase, and ilmenite. The PB mafic dyke swarm comprises over 155 dykes which represent a greater range of compositions than the associated flows, suggesting that they give a more complete representation of the Late Silurian PB mafic magmas. They exhibit incompatible element characteristics best accounted for by crustal contamination. The dykes plot on a linear array away from mantle mixing lines between depleted and enriched mantle sources and toward the composition of the PB felsic units, suggesting that these felsic units are representative of partial melts and fractionates of the source contaminate. The variable TiO2 contents (1.2–4.3 wt.%) and incompatible element ratio trends plotted against a fractionation index suggest that mantle metasomatism, either fluid or melt derived, may also have influenced the mantle source of the dykes. The dykes dip steeply and have a relatively consistent strike to the north. Most dykes range in thickness from 0.5 to 2 m, but range up to 9 m. The single orientation of the dykes, along with their chemical characteristics and volume, and association with a bimodal intraplate volcanic sequence, are consistent with an extensional tectonic setting. Constraints of the regional geology suggest that this extension was associated with convergence, perhaps in a back-arc setting.

Abstract In this paper, we present detailed field observations, chronological, geochemical and Sr–Nd isotopic data and discuss the petrogenetic aspects of two types of mafic dykes, of alkaline to subalkaline nature. The alkaline mafic dykes exhibit a cumulate to foliated texture and strike NW–SE, parallel to the main trend of the region. The 40Ar/39Ar amphibole age of 321.32 ± 0.55 Ma from an alkaline mafic dyke is interpreted as an indication of Carboniferous cooling through ca. 550 °C after intrusion of the dyke into the granitic Galeh-Doz orthogneiss and Amphibolite-Metagabbro units, the latter with Early Carboniferous amphibolite facies grade metamorphism and containing the Dare-Hedavand metagabbro with a similar Carboniferous age. The alkaline and subalkaline mafic dykes can be geochemically categorized into those with light REE-enriched patterns [(La/Yb)N = 8.32–9.28] and others with a rather flat REE pattern [(La/Yb)N = 1.16] and with a negative Nb anomaly. Together, the mafic dykes show oceanic island basalt to MORB geochemical signature, respectively. This is consistent, as well, with the (Tb/Yb)PM ratios. The alkaline mafic dykes were formed within an enriched mantle source at depths of ˃ 90 km, generating a suite of alkaline basalts. In comparison, the subalkaline mafic dykes were formed within more depleted mantle source at depths of ˂ 90 km. The subalkaline mafic dyke is characterized by 87Sr/86Sr ratio of 0.706 and positive ɛNd(t) value of + 0.77, whereas 87Sr/86Sr ratio of 0.708 and ɛNd(t) value of + 1.65 of the alkaline mafic dyke, consistent with the derivation from an enriched mantle source. There is no evidence that the mafic dykes were affected by significant crustal contamination during emplacement. Because of the similar age, the generation of magmas of alkaline mafic dykes and of the Dare-Hedavand metagabbro are assumed to reflect the same process of lithospheric or asthenospheric melting. Carboniferous back-arc rifting is the likely geodynamic setting of mafic dyke generation and emplacement. In contrast, the subalkaline mafic sill is likely related to the emplacement of the Jurassic Darijune gabbro.

AbstractDoleritic sills, lopoliths and dykes were emplaced into the Paleoproterozoic craton in central Sweden at 1271–1264, 1259–1256 and c. 1247 Ma, a complex temporal zonation occurring in a WSW–ENE direction. The dolerites are subalkaline to alkaline and show predominantly gabbroic, with a trend towards monzogabbroic and quartz monzodioritic, compositions. Positive ɛNd and ɛHf values suggest a significant depleted mantle component in the source volume of the parental magmas. Dyke orientations indicate extension, at least locally, in a northwesterly direction, consistent with a magma flow direction determined using the anisotropy of magnetic susceptibility values. Intracratonic rifting linked to the break-up of the supercontinent Columbia, back-arc extension above a subduction boundary in a westwards-retreating mode or a mantle plume tail above a continental hotspot have all been proposed for the tectonic setting. Renewed intracratonic rifting at c. 1.14 Ga in the coastal area in northeasternmost Sweden resulted in the emplacement of alkaline ultrabasic dykes, including carbonatites (beforsites), silico-carbonatites and lamprophyres, in a north–south direction along an older shear belt. The broader tectonic setting of this extensional event is not known.

A late Mesozoic belt of volcanic-intrusive complexes occurs in Southeast China. The Qianlishan granites are distributed in the northwest of the belt. The pluton is composed of porphyritic biotite granite (153 Ma) and equigranular biotite granite (151 Ma) and was intruded by granite-porphyry dykes (144 Ma) and mafic dykes such as lamprophyre and diabase (142 Ma). The granitic rocks, consisting mainly of K-feldspar, plagioclase, quartz and Fe-rich biotite, have SiO2 contents of 72.9–76.9%, and are enriched in alkalis, rare earth elements (REE), high field strength elements (HFSE) and Ga with high Ga/Al ratios, but depleted in Ba, Sr and transition metals. Trace-element geochemistry and Sr–Nd isotope systematics further imply that the Qianlishan granitic magmas were most probably derived by partial melting of Palaeo- to Mesoproterozoic metamorphic lower-crustal rocks that had been granulitized during an earlier thermal event. These features suggest an A-type affinity. The Qianlishan lamprophyre and neighbouring coeval mafic dykes (SiO2 = 47.9–53.8 wt%) have high MgO and compatible element contents. These rocks also have high K2O contents and are enriched in alkalis, light REE, large ion lithophile elements, and depleted in HFSE. They have low initial εNd values and relatively high initial 87Sr/86Sr ratios. We suggest a subduction-modified refractory lithospheric mantle (phlogopite-bearing harzburgite or lherzolite) for these high-Mg potassic magmas. The Qianlishan diabases (SiO2 = 48.4–48.7 wt%) are alkaline and have high TiO2 and total Fe2O3 contents, together with the positive initial εNd value, suggesting derivation from fertile asthenopheric mantle (phlogopite-bearing lherzolite). A back-arc extensional setting, related to subduction of the Palaeo-Pacific plate, is favoured to explain the petrogenesis of the Qianlishan granites and associated mafic dykes. Between 180 and 160 Ma, Southeast China was a continental arc, forming the 180–160 Ma plutons of the late Mesozoic volcanic-intrusive complex belt, and the lower-crust was granulitized. Since 160 Ma the northwestern belt has been in a back-arc extensional setting as a consequence of slab roll-back, resulting in the lithosphere thinning and an influx of asthenophere. The upwelling asthenosphere, on the one hand, induced the local lithospheric mantle to melt partially, forming high-Mg potassic magmas, and on the other hand it underwent decompression melting itself to form alkaline diabase magma. Pulsatory injection of such high-temperature magmas into the granulitized crustal source region induced them to partially melt and generate the A-type magmas of the Qianlishan granitic rocks.

Mineralization at the Bralorne mesothermal gold vein deposit is closely related to a suite of early Late Cretaceous to early Tertiary dykes. Premineral albitite dykes (91.4 ± 1.4 Ma by U–Pb on zircons) and postmineral lamprophyre dykes (43.5 ± 1.5 Ma by K–Ar on biotite) set definite age limits on the mineralizing event. A late intra- to post-mineral green hornblende dyke set (85.7 ± 3.0 Ma by K–Ar on hornblende) that forms a transitional series to the albitites may further restrict the age. Thus, mineralization occurred long after emplacement of the host Bralorne intrusions, dated as Early Permian (minimum age of approximately 270 ± 5 Ma by U–Pb on zircons, 284 ± 20 Ma by K–Ar on hornblende, and 40Ar/39Ar plateau at 276 ± 31 Ma). Lithologically similar intrusions 20 km to the north near Gold Bridge are also Early Permian (287 ± 20 Ma by K–Ar on hornblende and 320 ± 80 Ma by a Rb–Sr whole-rock isochron). Geochronology, radiogenic and stable isotopes, and fluid-inclusion studies suggest that there were several pulses of mineralizing activity adjacent to and east of the Coast Plutonic Complex (CPC). Decreasing temperatures and younger age of mineralization with increasing distance from the CPC imply that plutons of the CPC were the main heat source responsible for mineralization. The main pulses were about 90 Ma for mesothermal Au–Ag–As ± W,Mo mineralization at Bralorne near the CPC, ranging outwards to 65 Ma for Ag–Au–Sb–As ± Hg mineralization at the Minto and Congress deposits, to 45 Ma for Ag–Au epithermal mineralization at Blackdome, 100 km east of the CPC.The Bralorne intrusions may have been emplaced below the sea floor in a spreading-ridge oceanic environment, as suggested by the petrology of the intrusive suite, which includes serpentinized ultramafite, hornblende diorite, and soda granite (trondhjemite), typical of an ophiolite association. The chemistry of volcanic rocks mapped as Cadwallader Group, which host these intrusive bodies, is transitional from mid-ocean-ridge basalts to island-arc tholeiite, suggesting a back-arc-basin setting. Gradational contact relations between the hornblende diorite and the volcanic rocks suggest that the diorite intruded its own volcanic products. Intrusive contacts of the diorite with adjacent elongate ultramafic bodies imply that the ultramafic rocks are of Permian or older age and had been structurally emplaced into crustal levels by the time of diorite intrusion. In the Bralorne fault block the Bralorne intrusions appear to cut the adjacent Cadwallader and Bridge River groups, implying an Early Permian or older age for at least parts of these groups. Thus, rocks mapped as Cadwallader Group in the Bralorne area could be distinct from and older than lithologic equivalents exposed elsewhere, although they are similar in terms of their petrology and major- and trace-element chemistry.

ABSTRACTCombined field and geophysical data show that plutons from the Bega Batholith are elongate, meridional, wedge-shaped bodies which intruded during a period of regional east–west extension in the Palaeozoic eastern Lachlan orogen, eastern Australia. Plutons within the core of the batholith have intruded coeval, syn-rift sediments and co-magmatic volcanics. The batholith is bound by high-temperature, dip-slip faults, and contains several major NE-trending transtensional faults which were active during batholith construction. In the central part of the batholith, the Kameruka pluton is an asymmetric, eastward-thickening, wedge-shaped body with the base exposed as the western contact, which is characterised by abundant, shallow-dipping schlieren migmatites which contain recumbent folds and extensional shear bands. A shallow (<30°), east-dipping, primary magmatic layering in the Kameruka pluton steepens progressively westward, where it becomes conformable to the east-dipping basal migmatites. The systematic steepening of the layering is comparable to sedimentary units formed during floor depression in syn-rift settings. The present authors suggest that the wedge-shaped plutons of the Bega Batholith are the deeper, plutonic expression of a hot, active rift. The batholith was fed and sustained by injection of magma through sub-vertical dykes. Displacement along syn-magmatic, NE-trending faults suggests up to 25 km of arc-perpendicular extension during batholith construction. The inferred tectonic setting for batholith emplacement is a continental back-arc, where modern half-extension rates of 20–40 mm yr−1 are not unusual, and are sufficient to emplace the entire batholith in ∼1 Ma. This structural model provides a mechanism for the emplacement of some wedge-shaped plutons and is one solution to the ‘room problem’ of batholith emplace

A continental-margin magmatic arc is inferred to have existed on the southeastern (present coordinates) margin of Laurentia from Labrador to Texas from ~1500-1230 Ma, with part of the arc subsequently being incorporated into the 1190-990 Ma collisional Grenville Orogen. Outside the Grenville Province, where the arc is known as the Granite-Rhyolite Belt, it is undeformed, whereas within the Grenville Province it is deformed and metamorphosed. The arc comprises two igneous suites, an inboard, principally quartz monzonitic to granodioritic suite, and an outboard tonalitic to granodioritic suite. The quartz monzonite-granodiorite suite was largely derived from continental crust, whereas the tonalitic-granodiorite suite is calc-alkaline and has a juvenile isotopic signature. Available evidence from the Grenville Province suggests that the arc oscillated between extensional and compressional settings several times during the Mesoproterozoic. Back-arc deposits of several ages, that formed during relatively brief periods of extension, include (1) mafic dyke swarms subparallel to the arc; (2) continental sediments, bimodal volcanics and plateau basalts; (3) marine sediments and volcanics formed on stretched continental crust; and (4) ocean crust in a marginal basin. Closure of the back-arc basins occurred during the accretionary Pinwarian (~1495-1445 Ma) and Elzevirian (~1250-1190 Ma) orogenies, as well as during three pulses of crustal shortening associated with the 1190-990 Ma collisional Grenvillian Orogeny. During the Elzevirian Orogeny, closure of the Central Metasedimentary Belt marginal basin in the southeastern Grenville Province was marked by subduction-related magmatism as well as by imbrication of back-arc deposits. The presence of a continental-margin magmatic arc on southeastern Laurentia during the Mesoproterozoic implies that other coeval magmatism inboard from the arc took place in a back-arc setting. Such magmatism was widespread and chemically diverse and included large volume "anorogenic" anorthosite-mangerite-charnockite-granite (AMCG) complexes as well as small volume alkaline, quartz-saturated and -undersaturated "within-plate" granitoids. Recognition of the ~300 million year duration of the Mesoproterozoic convergent margin of southeastern Laurentia suggests that there may be useful parallels with the evolution of the Andes, which has been a convergent margin since the early Paleozoic.

ABSTRACTFluid dynamic modelling of crystallising calc-alkalic magma bodies has predicted that differentiated liquids will ascend as boundary layers and that accumulation of these buoyant liquids near chamber roofs will result in compositionally stratified magma chambers. This paper reports physical features in La Gloria Pluton that can be interpreted as trapped ascending differentiated liquids. Leucogranitic layers decimetres thick, which are locally stratified, are trapped beneath overhanging wall contacts. The same felsic magmas were also preserved where they were injected into the wall rocks as dykes and as large sill complexes. These rocks do not represent differentiated magmas produced by crystallisation along the exposed walls because the felsic layers occur at the wall rock contact, not inboard of it. Rather, we speculate that evolved felsic liquids are generated by crystallisation all across the deep levels of chambers and that initial melt segregation occurs by flowage of melt into tension fractures. Melt bodies so formed may be large enough to have significant ascent velocities as diapirs and/or dykes. The other way in which the leucogranite occurrence is at variance with the convective fractionation model is that the ascending liquids did not feed a highly differentiated cap to the chamber, as the composition at the roof, although the most felsic in this vertically and concentrically zoned pluton, is considerably more mafic than the trapped leucogranitic liquids. This suggests that these evolved liquids were usually mixed back into the main body of the chamber. Backmixing may be general in continental-margin calc-alkalic magmatic systems, which, in contrast to those in intracontinental settings, rarely produce volcanic rocks more silicic than rhyodacite. That the highly differentiated liquids are preserved at all at La Gloria is a result of the unusual stepped nature of the contact and the entirely passive mode of emplacement of the pluton, which, in contrast to ballooning in place, does not result in wall zones being “scoured”.

Durch die anthropogene Nutzung sind viele Auen in Mitteleuropa verändert worden, wobei insbesondere die Retentionsflächen stark verringert wurden. Während Auen seit längerem im Fokus der wissenschaftlichen Bearbeitung stehen, gibt es bisher große Wissensdefizite in der Frage der Auenreaktivierungen. Zum einen sind derartige Projekte bisher kaum verwirklicht und zum anderen ist ein langfristiges Monitoring notwendig, um die Anpassung von Biozönosen an die veränderten Standortbedingungen beobachten zu können. Um die Folgen derartiger Eingriffe zu analysieren, bieten sich computergestützte Modellierungen der Landschaftsentwicklung an, wie sie in der vorliegenden Arbeit verwirklicht wurden. Ziel der Arbeit war, mit Hilfe eines Geografischen Informationssystems (GIS) das Entwicklungspotenzial der Landschaft bei verschiedenen Rückdeichungsvarianten auf der Ebene der Biotoptypen darzustellen. Dabei ging es nicht um die Erstellung eines allgemein gültigen Auenmodells sondern um die Erarbeitung eines Modells für einen konkreten Anwendungsfall. Der erarbeitete Ansatz sollte zudem für die landschaftsplanerische Praxis geeignet sein. Als Beispielgebiete wurden Flächen an der Mittleren Elbe bei Rogätz und Sandau, beide im nördlichen Teil von Sachsen-Anhalt, ausgewählt.<br> Die vorliegende Arbeit gliedert sich in zwei Teile. Im ersten Teil werden Erhebungen und Auswertungen als Grundlage der Modellentwicklung dargestellt. Dazu wurden die Biotoptypen der Beispielgebiete flächendeckend erhoben und mit punktuellen Vegetationserhebungen ergänzt. Aus dem Forschungsprojekt "Rückgewinnung von Retentionsflächen und Altauenreaktivierung an der Mittleren Elbe in Sachsen-Anhalt" des Bundesministeriums für Bildung und Forschung (BMBF) standen standortökologische Daten der Hydrologie und Bodenkunde zur Verfügung. Ziel der Auswertung war, Schlüsselfaktoren für Hydrologie und Bodenbedingungen innerhalb der rezenten Aue zu identifizieren, die zur Ausprägung bestimmter Biotoptypen führen.<br> Im zweiten Teil der Arbeit wurde ein Modell für Biotoptypenpotenziale auf den geplanten Rück&ndash;deichungsflächen entwickelt. Das Modell bearbeitet die Datenbank der verwendeten GIS-Dateien, die auf Daten zum Bestand beruht und um solche der Prognose der Standortökologie (Hydrologie und Boden) im Rückdeichungsfalle aus dem BMBF-Projekt erweitert wurde. Weitere Voraussetzung für die Modellierung war die Erarbeitung von Leitbildern, in denen unterschiedliche Nutzungsszenarios für die Landschaft nach Deichrückverlegung hypothetisch festgelegt wurden. Insbesondere die Nutzungsintensität wurde variiert, von einer Variante intensiver land- und forstwirtschaftlicher Nutzung über sogenannte integrierte Entwicklungsziele aus dem BMBF-Projekt bis hin zu einer Variante der Naturschutznutzung. Zusätzlich wurde eine zukünftige Potentielle Natürliche Vegetation modelliert.<br> Eine Überprüfung des Modell fand für den Raum der rezenten Aue in der intensiven Nutzungsvariante statt, die der gegenwärtigen Nutzung am nächsten kommt. Werden Informationen des Bestandsbiotoptyps als Korrekturgröße in das Modell einbezogen, konnte für viele Biotoptypen eine Trefferquote von über 90 % erreicht werden. Bei flächenmäßig weniger bedeutenden Bio&ndash;toptypen lag dieser Wert aufgrund der schmaleren Datenbasis zwischen 20 und 40 %. Als Ergebnis liegt für unterschiedliche Deichvarianten und Leitbilder in den Beispielgebieten die Landschaftsentwicklung als Biotoppotenzial vor. Als eine vereinfachte Regionalisierung der punktuellen Vegetationsdaten wurde im Modell geprüft, inwieweit die modellierten Biotopflächen der Charakteristik der pflanzensoziologischen Aufnahmen aus der rezenten Aue entsprechen. In dem Falle wurde die Pflanzengesellschaft der jeweiligen ökologisch im Rahmen der Untersuchung einheitlichen Flächeneinheit zugeordnet. Anteilig lässt sich damit die Biotopprognosefläche pflanzensoziologisch konkretisieren. Die vorliegende Arbeit gehört zu den bisher wenigen Arbeiten, die sich mit den Folgen von Auenreaktivierung auf die Entwicklung der Landschaft auseinandersetzen. Sie zeigt eine Möglichkeit auf, Prognosemodelle für Biotoptypen und Vegetation anhand begrenzter Felduntersuchungen zu entwerfen. Derartige Modelle können zum Verständnis von Eingriffen in den Naturhaushalt, wie sie die Deichrückverlegungen darstellen, beitragen und eine Folgenabschätzung unterstützen.<br>Most of the floodplains in Central Europe are highly altered by man. In particular, recent inundation areas have been dramatically reduced. Before the Elbe-flood-disaster of the year 2002 there had already been considerations about combining flood-protection and restoration of floodplains. While research has focused on floodplains for a considerable time, knowledge on the reactivation of floodplains is still significantly lacking. Until now, only a few projects have been realized, and there has not been enough long-term moni&ndash;toring of the adaption of habitats to changing conditions. Computerized models of landscape development, as utilized in the presented work, can help to address these questions. The aim of the study was to show the potential development of the landscape on the scale of biotopes under different scenarios of floodplain expansion by application of a geographic information system (GIS). It was not intended to create a general floodplain-model. The model aimed at a specific applied case and should also be applicable for questions of landscape planning. Two areas near the villages of Sandau and Rogätz at the Middle Elbe River in the north of the German federal state of Saxony-Anhalt were selected.<br> The presented work is divided into two parts. The first describes the sampling and evaluation of data as a basis for modeling. For this, the biotopes were mapped in total in the two study areas. Additionally, vegetation data were collected from selected sites mainly in the grassland and forest-biotopes. Hydrological and soil condition data were available through the project "Rückgewinnung von Retentionsflächen und Altauenreaktivierung an der Mittleren Elbe in Sachsen-Anhalt" of the German Ministry of Education and Science (BMBF). This part of the study aimed to identify the ecological key factors in the recent floodplain that lead to the development of the different biotopes.<br> In the second part of the presented work a model for the potential biotopes on the expanded floodplain after setting back the dikes was developed. The model alters the GIS database and adds a potential biotope. First this database must be expanded to integrate the hydrological and soil data of the BMBF-project for the expanded floodplain. Different hypo&ndash;thetical land use scenarios were assumed and applied to the model. The three different variants of land use adapted from the BMBF-project were intensive land use, land use under conditions of nature-conservation an integration of both extremes. In the case of intensive land &ndash;use arable fields were modeled in areas which are flooded on average only every ten years or less. As a fourth scenario the potential natural vegetation was modeled.<br> An evaluation of the model was made for the recent floodplain under intensive land use conditions, which are close to the current land use. By correcting the models results with information of the current biotope composition, many biotopes could be predicted correctly with 90 % accuracy. For biotopes which are rare in the study area the prediction rate lay between 20 and 40 %. The result of the second part of the presented work was the modeling of the potential biotopes for the different land use scenarios and the different variants of setting back the dikes.<br> Integrated in the model was a module of a simplified regionalization of the vegetation data. It was tested whether the characteristics of the processed unit of the GIS-database fit the results of the vegetation sampling of the first part of the study. Where this was the case, the whole unit was characterized as a phytosociologic vegetation-unit. Thus, for part of the modeling area the biotope-potentials could be expanded with information on the actual vegetation.<br> The present work is one of the few studies so far dealing with the consequences for the landscape of reactivating floodplains which are separated from rivers by dikes. It shows the possibility to use models to predict changes in biotopes and vegetation based on limited field data. Such models can help to understand the altering of nature caused by such impacts and to estimate the possible consequences.

The deltaic landscape of the Ganga-Brahmaputra delta has evolved through a complex interplay of geomorphic processes and tidal dynamics coupled with the anthropogenic modifications brought over in course of the reclamation of the islands since the late 18th century. The reclamation process was characterized by clearing lands for paddy farms and fish ponds by building a mesh of earthen embankments along creek banks to restrict saltwater intrusion. The length of the embankments in the Indian Sundarbans alone is 3638 km (World Bank, 2014) which altered the tidal inundation regimes, sediment accretion and geomorphic character of the deltaic inlets. The mean annual sedimentation rate (2.3 cm y−1) in the central Ganga-Brahmaputra delta is over two times higher than sedimentation within the natural intertidal setting of the Sundarbans (Rogers et al., 2017). The tidal range has also increased inland due to polder construc¬tion, with high water levels within the polder zone increasing as much as 1.7 cm y−1 (Pethick and Orford, 2013). Embankments have impacted on the biodiversity and physiological adaptations of mangroves within the sphere of tidal ingression, habitat fragmentation and seedling establishment. The chapter attempts to reappraise the impact of dykes on the geomorphology of the deltaic landscape and on the functionalities of mangrove forests.