Continental Margin (continental + margin)

Distribution by Scientific Domains
Distribution within Earth and Environmental Science

Kinds of Continental Margin

  • active continental margin
  • passive continental margin

  • Terms modified by Continental Margin

  • continental margin setting

  • Selected Abstracts

    3D seismic analysis of slope-confined canyons from the Plio,Pleistocene of the Ebro Continental Margin (Western Mediterranean)

    BASIN RESEARCH, Issue 1 2005
    Claudia Bertoni
    This paper documents the importance of three-dimensional (3D) seismic data for integrated stratigraphic,morphological analysis of slope systems. Furthermore, it contributes to the general understanding of the evolutionary mechanisms of slope-confined submarine canyons on continental margins and their significance in a sequence stratigraphic framework. Recently acquired 3D seismic data from the Ebro Continental Margin (Western Mediterranean) have been used to study a series of remarkably well-imaged submarine canyons in the Plio-Pleistocene succession. Detailed mapping shows that these canyons are restricted to the slope, and thus can be compared with slope-confined canyons observed on the present day seabed of many continental margins. The slope-confined canyons are typically 0.5,2 km wide, 10,15 km long, and incise more than 50 m into the slope units. Their most striking characteristic is an upslope branching geometry in the head region involving up to three orders of bifurcation, with downslope development of a single incisional axis. The submarine canyons are characterized by a nested stacking pattern, undergoing alternating phases of cutting and filling. Limited parts of the upper and middle slope remain outside the canyon system, confined in sharp depositional ridges. The canyons are observed on closely spaced surfaces and exhibit a geometry that allowed the construction and discussion of a local sequence stratigraphic model for their evolution. In general, active incision of the canyons is observed at times throughout almost the entire cycle of base-level change. However, erosional activity is more significant during the later stages of the relative sea level rise and the entire falling stage, with the timing of maximum erosion observed at the end of the cycle. The minimum erosional activity of the canyons is linked instead to the earliest part of the relative sea level rise. [source]

    Regional analysis of bedrock stream long profiles: evaluation of Hack's SL form, and formulation and assessment of an alternative (the DS form)

    Geoff Goldrick
    Abstract The equilibrium form of the fluvial long profile has been used to elucidate a wide range of aspects of landscape history including tectonic activity in tectonic collision zones, and in continental margin and other intraplate settings, as well as other base-level changes such as due to sealevel fluctuations. The Hack SL form of the long profile, which describes a straight line on a log,normal plot of elevation (normal) versus distance (logarithmic), is the equilibrium long profile form that has been most widely used in such studies; slope,area analysis has also been used in recent years. We show that the SL form is a special case of a more general form of the equilibrium long profile (here called the DS form) that can be derived from the power relationship between stream discharge and downstream distance, and the dependence of stream incision on stream power. The DS form provides a better fit than the SL form to river long profiles in an intraplate setting in southeastern Australia experiencing low rates of denudation and mild surface uplift. We conclude that, if an a priori form of the long profile is to be used for investigations of regional landscape history, the DS form is preferable. In particular, the DS form in principle enables equilibrium steepening due to an increase in channel substrate lithological resistance (parallel shift in the DS plot) to be distinguished from disequilibrium steepening due to long profile rejuvenation (disordered outliers on the DS plot). Slope,area analysis and the slope,distance (DS) approach outlined here are complementary approaches, reflecting the close relationship between downstream distance and downstream catchment area. Copyright © 2006 John Wiley & Sons, Ltd. [source]

    Quantification of microbial communities in near-surface and deeply buried marine sediments on the Peru continental margin using real-time PCR

    Axel Schippers
    Summary Deeply buried marine sediments harbour a large fraction of all prokaryotes on Earth but it is still unknown which phylogenetic and physiological microbial groups dominate the deep biosphere. In this study real-time PCR allowed a comparative quantitative microbial community analysis in near-surface and deeply buried marine sediments from the Peru continental margin. The 16S rRNA gene copy numbers of prokaryotes and Bacteria were almost identical with a maximum of 108,1010 copies cm,3 in the near-surface sediments. Archaea exhibited one to three orders of magnitude lower 16S rRNA gene copy numbers. The 18S rRNA gene of Eukarya was always at least three orders of magnitude less abundant than the 16S rRNA gene of prokaryotes. The 16S rRNA gene of the Fe(III)- and Mn(IV)-reducing bacterial family Geobacteraceae and the dissimilatory (bi)sulfite reductase gene (dsrA) of sulfate-reducing prokaryotes were abundant with 106,108 copies cm,3 in near-surface sediments but showed lower numbers and an irregular distribution in the deep sediments. The copy numbers of all genes decreased with sediment depth exponentially. The depth gradients were steeper for the gene copy numbers than for numbers of total prokaryotes (acridine orange direct counts), which reflects the ongoing degradation of the high-molecular-weight DNA with sediment age and depth. The occurrence of eukaryotic DNA also suggests DNA preservation in the deeply buried sediments. [source]

    Movement and behaviour of large southern bluefin tuna (Thunnus maccoyii) in the Australian region determined using pop-up satellite archival tags

    Abstract Pop-up satellite archival tags (PSATs) were deployed on 52 large (156,200 cm length to caudal fork) southern bluefin tuna (Thunnus maccoyii) in the western Tasman Sea during the austral winters of 2001,2005. Southern bluefin tuna (SBT) were resident in the Tasman Sea for up to 6 months with movements away from the tagging area occurring at highly variable rates. The data indicated a general tendency for SBT to move south from the tagging area in the Western Tasman Sea. Four individuals migrated west along the southern continental margin of Australia and into the Indian Ocean. Three individuals moved east into the central Tasman Sea, with one individual reaching New Zealand. We also describe the first observed migration of an SBT from the Tasman Sea to the Indian Ocean spawning grounds south of Indonesia. Individuals spent most of their time relatively close to the Australian coast, with an estimated 84% of time spent in the Australian Fishing Zone. SBT favored temperatures between 19 and 21°C, adjusting their depth to the vertical temperature distribution. Distinct diurnal diving patterns were observed and adjustment of depth to maintain constant ambient light levels over a 24-h period. The findings of this study are a significant advance toward greater understanding of the spatial dynamics of large SBT and understanding the connectivity between distant regions of their distribution. [source]

    Ophiolite-bearing mélanges in southern Italy

    GEOLOGICAL JOURNAL, Issue 2 2009
    Luigi Tortorici
    Abstract In southern Italy two ophiolite-bearing belts, respectively involved in the Adria-verging southern Apennines and in the Europe-verging thrust belt of the northern Calabrian Arc, represent the southward extension of the northern Apennines and of ,Alpine Corsica' ophiolitic units, respectively. They form two distinct suture zones, which are characterized by different age of emplacement and opposite sense of tectonic transport. The ophiolite-bearing units of the southern Apennines are represented by broken formation and tectonic mélange associated with remnants of a well-developed accretionary wedge emplaced on top of the Adria continental margin, with an overall NE direction of tectonic transport. These units consist of a Cretaceous-Oligocene matrix, which includes blocks of continental-type rocks and ophiolites with remnants of their original Upper Jurassic to Lower Cretaceous pelagic cover. The innermost portion of the accretionary wedge is represented by a polymetamorphosed and polydeformed tectonic units that underwent a Late Oligocene high pressure/low temperature (HP/LT) metamorphism. The northern Calabria ophiolitic-belt is indeed composed of west-verging tectonic slices of oceanic rocks which, embedded between platform carbonate units of a western continental margin at the bottom and the basement crystalline nappes of the Calabrian Arc at the top, are affected by a Late Eocene-Early Oligocene HP/LT metamorphism. The main tectonic features of these two suture zones suggest that they can be interpreted as the result of the closure of two branches of the western Neotethys separated by a continental block that includes the crystalline basement rocks of the Calabrian Arc. We thus suggest that the north-east verging southern Apennine suture constituted by a well-developed accretionary wedge is the result of the closure of a large Late Jurassic-Early Cretaceous oceanic domain (the Ligurian Ocean) located between the African (the Adria Block) and European continental margins. The northern Calabria suture derives indeed from the deformation of a very narrow oceanic-floored basin developed during the Mesozoic rifting stages within the European margin separating a small continental ribbon (Calabrian Block) from the main continent. Copyright © 2008 John Wiley & Sons, Ltd. [source]

    Duplex architecture and late-orogenic backthrusting in Foredeep Units of the Northern Apennines (Italy)

    GEOLOGICAL JOURNAL, Issue 4 2008
    Andrea Cerrina Feroni
    Abstract The Northern Apennines of Italy is a fold and thrust belt that resulted from the NE-ward progressive overthrusting of a Mesoalpine stacking (the ocean-derived Ligurian Units) onto the detached sedimentary cover of the Adria plate continental margin (Foredeep Units). The Futa Pass area represents a key sector for the reconstruction of the deformation history of two Foredeep Units (Acquerino and Carigiola Units). The tectonic evolution of this sector is characterized by the superposition of three main deformation stages, with a constant NNE,SSW compression direction. The oldest structure is represented by the NNE-verging Acquerino Unit duplex structure, the roof thrust of which is represented by the Ligurian stacking basal thrust. The interpretation of this structure as a large-scale duplex is supported by the presence in the outer sectors of the Northern Apennines belt of Ligurian Units directly overthrust on younger Foredeep Units. In the second deformation stage the NNE-verging Tavaiano Thrust developed. This regionally significant tectonic surface juxtaposes the Acquerino Unit (already developed as a duplex) and the overlying Ligurian Units, onto the Carigiola Unit. During this stage the fault pattern of the Carigiola Unit was also developed, characterized by two conjugate fault systems, coherent with a NNE,SSW maximum compression direction. During the last deformation stage, a backthrusting with a top-to-the SSW sense of movement (the Marcoiano Backthrust) brings the Carigiola Unit and its tectonic cover over the Acquerino and Ligurian Units, with the development of a large footwall syncline. The deformation history presented here differs from previous studies, and so provides a contribution to the debate on Northern Apennines tectonic evolution. Copyright © 2008 John Wiley & Sons, Ltd. [source]

    Controls of mantle plumes and lithospheric folding on modes of intraplate continental tectonics: differences and similarities

    Evgueni Burov
    SUMMARY Mantle plume activity and lithospheric folding by far-field stresses exerted from plate boundaries are two important end-members as mechanisms for continental intraplate deformation. The topographic expression of mantle plume impingement on continental lithosphere and lithospheric folding has some striking similarities. Observations from a number of areas in Europe's intraplate lithosphere demonstrate that these mechanisms commonly interact in space and time. We present the results of thermomechanical modelling addressing the role of factors such as the presence of a hot upper mantle, the spatial dimensions of the plume and the time constants involved in the temporal succession of plume activity and lithospheric folding by stress accumulation in intraplate continental lithosphere. The results demonstrate that both the processes, plume,lithosphere interactions and folding may interact resulting either in strong amplification, attenuation or modification of their surface expression. These inferences are compatible with a number of key observations on the nature and the temporal succession of topography evolution in the Alpine foreland, the Pannonian Basin, the Scandinavian continental margin and the Iberian Peninsula. [source]

    Crustal structure of the Newfoundland rifted continental margin from constrained 3-D gravity inversion

    J. Kim Welford
    ABSTRACT The rifting history of the Atlantic continental margin of Newfoundland is very complex and so far has been investigated at the crustal scale primarily with the use of 2-D seismic surveys. While informative, the results generated from these surveys cannot easily be interpreted in a regional sense due to their sparse sampling of the margin. A 3-D gravity inversion of the free air data over the Newfoundland margin allows us to generate a 3-D density anomaly model that can be compared with the seismic results and used to gain insight into regions lacking seismic coverage. Results of the gravity inversion show good correspondence with Moho depths from seismic results. A shallowing of the Moho to 12 km depth is resolved on the shelf at the northern edge of the Grand Banks, in a region poorly sampled by other methods. Comparisons between sediment thickness and crustal thickness show deviations from local isostatic compensation in locations which correlate with faults and rifting trends. Such insights must act as constraints for future palaeoreconstructions of North Atlantic rifting. [source]

    Geomorphic constraints on the active tectonics of southern Taiwan

    Lucy A. Ramsey
    SUMMARY Taiwan is a region of rapid active tectonics, yet the study of the tectonic processes that shape the interior of the island is difficult due to the high rates of erosion and dense vegetation. We use digital topography to look for indications of active deformation preserved in the local geomorphology. In particular, anomalies in the regional pattern of drainage are used to infer zones of enhanced tectonic activity. The apparent anticlockwise rotation of major river systems in plan view indicates the presence of a diffuse zone of left-lateral shear running down the southeastern side of Taiwan. Asymmetries in the catchments of individual drainage basins show the influence of varying rates of uplift across southern Taiwan, with the most rapid uplift close to Taitung at the indentation point of the Luzon arc with the Chinese continental margin. Our interpretations, though based predominantly on remote-sensing observations, are consistent with the available field evidence. This study demonstrates the usefulness of drainage basins as tectonic markers in the quantification of regional strain and uplift, which may have wider applicability in other deforming parts of the world. [source]

    The sedimentary structure of the Lomonosov Ridge between 88°N and 80°N

    Wilfried Jokat
    SUMMARY While the origin of the 1800-km-long Lomonosov Ridge (LR) in the Central Arctic Ocean is believed to be well understood, details on the bathymetry and especially on the sediment and crustal structure of this unique feature are sparse. During two expeditions in 1991 and 1998 into the Central Arctic Ocean several high quality seismic lines were collected along the margin of the ridge and in the adjacent Makarov Basin (MB). The lines collected between 87°36,N and 80°N perpendicular to and along the LR show a sediment starved continental margin with a variety of geological structures. The different features may reflect the different geological histories of certain ridge segments and/or their different subsidence histories. The sediments in the deep MB have thicknesses up to 2.2 km (3 s TWT) close to the foot of the ridge. At least in part basement reflections characteristics suggest oceanic crust. The acoustically stratified layers are flat lying, except in areas close to the ridge. Seismic units on the LR can be divided into two units based on refraction velocity data and the internal geometry of the reflections. Velocities <3.0 km s,1 are considered to represent Cenozoic sediments deposited after the ridge subsided below sea level. Velocities >4.0 km s,1 are associated with faulted sediments at deeper levels and may represent acoustic basement, which was affected by the Late Cretaceous/Early Cenozoic rift events. Along large parts of the ridge the transition of the two units is associated with an erosional unconformity. Close to the Laptev Sea such an erosional surface may not be present, because of the initial great depths of the rocks. Here, the deeper strata are affected by tectonism, which suggests some relative motion between the LR and the Laptev Shelf. Stratigraphic correlation with the Laptev Sea Shelf suggests that the ridge has not moved as a separate plate over the past 10 Myr. The seismic and regional gravity data indicate that the ridge broadens towards the Laptev Shelf. Although the deeper structure may be heavily intruded and altered, the LR appears to extend eastwards as far as 155°E, a consequence of a long-lived Late Cretaceous rift event. The seismic data across LR support the existence of iceberg scours in the central region of the ridge as far south as 81°N. However, no evidence for a large erosional events due to a more than 1000-m-thick sea ice cover is visible from the data. South of 85°N the seismic data indicate the presence of a bottom simulating reflector along all lines. [source]

    Anomalous seaward dip of the lithosphere,asthenosphere boundary beneath northeastern USA detected using differential-array measurements of Rayleigh waves

    William Menke
    Summary Rayleigh wave phase velocities and azimuth anomalies in the period range of 30,100 s are measured for a set of four triangular arrays of broad-band seismometers in coastal northeastern USA. This is a region in which a strong upper mantle slow shear velocity anomaly (a ,New England Anomaly'), crosses the continental margin. Earthquakes from a wide range of directions are used to detect the variation of parameters with azimuth, ,, of propagation. No lateral heterogeneity in phase velocity is detected at these periods between stations at the centre and the edge of the Anomaly. However, large (10,20; per cent) azimuthal variations occur, and have a cos(1,) dependence, which is indicative of a dipping structure in the upper mantle. Corresponding azimuth variations, with a magnitude of ±5°, are also detected. This behaviour is consistent with a southeasterly (N150°E) dip of the lithosphere,asthenosphere boundary beneath New England. This dip is associated with the shoaling of the New England Anomaly beneath the Adirondack mountains, west of the array. It is opposite to the dip associated with lithospheric thickening toward the interior of the craton. [source]

    Olivine-spinifex basalt from the Tamba Belt, southwest Japan: Evidence for Fe- and high field strength element-rich ultramafic volcanism in Permian Ocean

    ISLAND ARC, Issue 3 2007
    Yuji Ichiyama
    Abstract Permian basalt showing typical spinifex texture with >10 cm-long olivine pseudomorphs was discovered from the Jurassic Tamba accretionary complex in southwest Japan. The spinifex basalt occurs as a river boulder accompanied by many ferropicritic boulders in a Permian chert-greenstone unit. Groundmass of this rock is holocrystalline, suggesting a thick lava or sill for its provenance. Minor kaersutite in the groundmass indicates a hydrous magma. The spinifex basalt, in common with the associated ferropicritic rocks, is characterized by high high field strength element (HFSE) contents (e.g. Nb = 62 ppm and Zr = 254 ppm) and high-HFSE ratios (Al2O3/TiO2 = 3.9, Nb/Zr = 0.24 and Zr/Y = 6.4) unlike typical komatiites. The spinifex basalt and ferropicrite might represent the upper fractionated melt and the lower olivine-rich cumulate, respectively, of a single ultramafic sill (or lava) as reported from the early Proterozoic Pechenga Series in Kola Peninsula. Their parental magma might have been produced by hydrous melting of a mantle plume that was dosed with Fe- and HFSE-rich garnet pyroxenite. The spinifex basalt is an evidence for the Pechenga-type ferropicritic volcanism taken place in a Permian oceanic plateau, which accreted to the Asian continental margin as greenstone slices in Jurassic time. [source]

    Zircon U,Pb ages and tectonic implications of ,Early Paleozoic' granitoids at Yanbian, Jilin Province, northeast China

    ISLAND ARC, Issue 4 2004
    Yanbin Zhang
    Abstract The Yanbian area is located in the eastern part of the Central Asian Orogenic Belt (CAOB) of China and is characterized by widespread Phanerozoic granitic intrusions. It was previously thought that the Yanbian granitoids were mainly emplaced in the Early Paleozoic (so-called ,Caledonian' granitoids), extending east,west along the northern margin of the North China craton. However, few of them have been precisely dated; therefore, five typical ,Caledonian' granitic intrusions (the Huangniling, Dakai, Mengshan, Gaoling and Bailiping batholiths) were selected for U,Pb zircon isotopic study. New-age data show that emplacement of these granitoids extended from the Late Paleozoic to Late Mesozoic (285,116 Ma). This indicates that no ,Caledonian' granitic belt exists along the northern margin of the North China craton. The granitoids can be subdivided into four episodes based on our new data: Early Permian (285 ± 9 Ma), Early Triassic (249,245 Ma), Jurassic (192,168 Ma) and Cretaceous (119,116 Ma). The 285 ± 9 Ma tonalite was most likely related to subduction of the Paleo-Asian Oceanic Plate beneath the North China craton, followed by Triassic (249,245 Ma) syn-collisional monzogranites, representing the collision of the CAOB orogenic collage with the North China craton and final closure of the Paleo-Asian Ocean. The Jurassic granitoids resulted from subduction of the Paleo-Pacific plate and subsequent collision of the Jiamusi,Khanka Massif with the existing continent, assembled in the Triassic. The Early Cretaceous granitoids formed in an extensional setting along the eastern Asian continental margin. [source]

    Provenance of sandstones from the Wakino Subgroup of the Lower Cretaceous Kanmon Group, northern Kyushu, Japan

    ISLAND ARC, Issue 1 2000
    Daniel K. Asiedu
    Abstract The Wakino Subgroup is a lower stratigraphic unit of the Lower Cretaceous Kanmon Group. Previous studies on provenance of Wakino sediments have mainly concentrated on either petrography of major framework grains or bulk rock geochemistry of shales. This study addresses the provenance of the Wakino sandstones by integrating the petrographic, bulk rock geochemistry, and mineral chemistry approaches. The proportions of framework grains of the Wakino sandstones suggest derivation from either a single geologically heterogeneous source terrane or multiple source areas. Major source lithologies are granitic rocks and high-grade metamorphic rocks but notable amounts of detritus were also derived from felsic, intermediate and mafic volcanic rocks, older sedimentary rocks, and ophiolitic rocks. The heavy mineral assemblage include, in order of decreasing abundance: opaque minerals (ilmenite and magnetite with minor rutile), zircon, garnet, chromian spinel, aluminum silicate mineral (probably andalusite), rutile, epidote, tourmaline and pyroxene. Zircon morphology suggests its derivation from granitic rocks. Chemistry of chromian spinel indicates that the chromian spinel grains were derived from the ultramafic cumulate member of an ophiolite suite. Garnet and ilmenite chemistry suggests their derivation from metamorphic rocks of the epidote-amphibolite to upper amphibolite facies though other source rocks cannot be discounted entirely. Major and trace element data for the Wakino sediments suggest their derivation from igneous and/or metamorphic rocks of felsic composition. The major element compositions suggest that the type of tectonic environment was of an active continental margin. The trace element data indicate that the sediments were derived from crustal rocks with a minor contribution from mantle-derived rocks. The trace element data further suggest that recycled sedimentary rocks are not major contributors of detritus. It appears that the granitic and metamorphic rocks of the Precambrian Ryongnam Massif in South Korea were the major contributors of detritus to the Wakino basin. A minor but significant amount of detritus was derived from the basement rocks of the Akiyoshi and Sangun Terrane. The chromian spinel appears to have been derived from a missing terrane though the ultramafic rocks in the Ogcheon Belt cannot be discounted. [source]

    Analysis of plant species diversity with respect to island characteristics on the Channel Islands, California

    Aaron Moody
    Abstract Aim Species richness of native, endemic, and exotic plant groups is examined relative to island area, disturbance history, geological history, and other physical characteristics. Of particular interest are the biogeographic factors that underlie (a) differences in species-area and species-isolation relationships between plant groups; and (b) adherence or departure of individual islands and/or plant groups from expected patterns. Location The eight Channel Islands lie along the continental margin between the U.S./Mexico border and Point Conception, CA. They range in size from 2.6 to 249 km2, and are located from 20 to 100 km off the coast. The islands are known for their high degree of plant endemism, and they have undergone a long history of human occupation by indigenous peoples, followed by over a century of intensive grazing and other biotic disturbances. Methods The study is based on linear regression and residual analysis. Cases where individual islands and/or specific plant groups do not adhere to patterns expected under species-area and species-isolation paradigms, are evaluated with respect to other island characteristics that are not captured by considering only island size and isolation. Results All three plant groups exhibit strong, positive relationships between species richness and island size. For native species, the variance that remains after consideration of island size is largely explained by island isolation. For exotic species, residuals from the species-area relationship are unrelated to isolation. For endemic species, residuals from the species-area relationship are negatively related to isolation. Several islands are outliers for endemic and exotic species, for which richness values are not explained by either island area or isolation. Main,conclusions Species-area and species-isolation relationships for native, endemic, and exotic plant groups differ in accordance with hypothesized differences in the biogeographic factors that govern species diversity for these three groups. Most notably, endemic richness increases with isolation, suggesting the influence of this variable on processes of speciation and relictualism. These general relationships persist despite a long and varied history of human activity on the islands. Analysis of residuals suggests that deviations from expected patterns correspond to island-specific biogeographic factors. It is hypothesized that primary among these factors are land-use history, island environmental characteristics, and community-type richness. [source]

    Microfabric characteristics and rheological significance of ultra-high-pressure metamorphosed jadeite-quartzite and eclogite from Shuanghe, Dabie Mountains, China

    L. WANG
    Abstract Quantitative analysis of the structural evolution of jadeite-quartzite, a rare ultra-high pressure (UHP) rock type from the Dabie Mountains of eastern China, sheds light on the formation and evolution of UHP orogenic belts worldwide. Geological mapping of the Shuanghe area, where jadeite-quartzites crop out, was carried out to determine the spatial relationships between different UHP rocks within this orogen. The deformation mechanisms of jadeite-quartzite, geodynamical parameters (stress, strain, strain rate), and microstructure including lattice preferred orientation (LPO) were determined from six jadeite-quartzite samples from the Shuanghe area. LPOs of clinopyroxene (jadeite and omphacite), garnet, rutile and quartz from these jadeite-quartzite samples are compared with those of three eclogites preserving different degrees of deformation from the Shuanghe area. Microstructural LPOs of jadeite, omphacite, garnet, rutile and quartz were determined using electron backscattered diffraction (EBSD) analysis. Quartz fabrics were largely recrystallized during late, low-grade stages of deformation, whereas garnet shows no strong LPO patterns. Rutile fabrics show a weak LS fabric along [001]. Jadeite and omphacite show the strongest eclogite facies LPO patterns, suggesting that they may provide important information about mantle deformation patterns and control the rheology of deeply subducted continental crust. Microstructural data show that the jadeite LPO patterns are similar to those of omphacite and vary between L- and S-types, which correlate with prolate and oblate grain shape fabrics (SPO); quartz LPOs are monoclinic. Microstructural analysis using TEM shows that the dominant slip systems of jadeite in one sample are (100)[001], (110)[001] and (1 1 0)1/2[110], while in another sample, no dislocations are observed. Abundant dislocations in quartz were accommodated by the dominant slip system (0001)[110], indicating basal glide and represents regional shearing during the exhumation process. This suggests that dislocation creep is the dominant fundamental deformation mechanism in jadeite under UHP conditions. The protoliths of jadeite-quartzite, metasedimentary rocks from the northern passive continental margin of the Yangtze craton, experienced the same deep subduction and were deformed under similar rheological conditions as other UHP eclogite, marble and paragneiss. Experimental UHP deformation of quartzo-feldspathic gneiss with a chemical composition similar to the bulk continental crust has shown that the formation of a jadeite,stishovite rock is associated with a density increase of the host rock similar to the eclogite conversion from basaltic protoliths. The resulting rock can be denser than the surrounding mantle pyrolite up to depths of 660 km (24 GPa). Thus, processes of deep continental subduction may be better-understood through understanding the rheology and mechanical behaviour of jadeite. Jadeite-quartzites such as those from the Shuanghe may be exhumed remnants of deeply-subducted slabs of continental crust, other parts of which subducted past the ,depth of no return', and remain in the deep mantle. [source]


    L. Tortorici
    Imbricate units in the western Sicilian fold-and-thrust belt originated on the southern continental margin of Neotethys, and were deformed during the Neogene-Recent in response to convergence between the African and European Plates. Neogene-Pleistocene synorogenic sediments, deposited in flexural foredeeps and satellite piggy-back basins, contain a record of the belt's evolution. Progressive migration of the thrust front southwards into the foreland has been documented, beginning in the Tortonian and continuing to the present-day particularly in western parts of the belt. In the eastern part, activity on Quaternary strike-slip fault zones has produced asymmetric flower structures and other interference structures. In this paper, we present two regional sections across the western Sicilian foreland-thrust belt system. These structural cross-sections extend down as far as the top of the Hercynian basement and integrate our field observations with previously-acquired well log, magnetic and seismic data. We show that complex interactions between the foreland-migrating thrust belt, which developed between the Late Miocene and the Pleistocene, and Pleistocene strike-slip faults led to the development of structural traps which constitute potential targets for hydrocarbon exploration. [source]

    Variability in temperature and geometry of the Norwegian Current over the past 600,yr; stable isotope and grain size evidence from the Norwegian margin

    Ida Malene Berstad
    Abstract Core P1-003MC was retrieved from 851,m water depth on the southern Norwegian continental margin, close to the boundary between the Norwegian Current (NC) and the underlying cold Norwegian Sea Deep Water. The core chronology was established by using 210Pb measurements and 14C dates, suggesting a sampling resolution of between 2 and 9,yr. Sea-surface temperature (SST) variations in the NC are reconstructed from stable oxygen isotope measurements in two planktonic Foraminifera species, Neogloboquadrina pachyderma (d.) and Globigerina bulloides. The high temporal resolution of the SST proxy records allows direct comparison with instrumental ocean temperature measurements from Ocean Weather Ship (OWS) Mike in the Norwegian Sea and an air temperature record from the coastal island Ona, western Norway. The comparison of the instrumental and the proxy SST data suggests that N. pachyderma (d.) calcify during summer, whereas G. bulloides calcify during spring. The ,18O records of both species suggest that the past 70,yr have been the warmest throughout the past 600,yr. The spring and summer proxy temperature data suggest differences in the duration of the cold period of the Little Ice Age. The spring temperature was 1,3°C colder throughout most of the period between ca. AD 1400 and 1700, and the summer temperature was 1,2°C colder throughout most of the period between ca. AD 1400 and 1920. Fluctuations in the depth of the lower boundary of the NC have been investigated by examining grain size data and benthic foraminiferal assemblages. The data show that the transition depth of the lower boundary of the NC was deeper between ca. AD 1400 and 1650 than after ca. AD 1750 until present. Copyright © 2003 John Wiley & Sons, Ltd. [source]

    Genetic structure of the deep-sea coral Lophelia pertusa in the northeast Atlantic revealed by microsatellites and internal transcribed spacer sequences

    MOLECULAR ECOLOGY, Issue 3 2004
    M. C. Le Goff-Vitry
    Abstract The azooxanthellate scleractinian coral Lophelia pertusa has a near-cosmopolitan distribution, with a main depth distribution between 200 and 1000 m. In the northeast Atlantic it is the main framework-building species, forming deep-sea reefs in the bathyal zone on the continental margin, offshore banks and in Scandinavian fjords. Recent studies have shown that deep-sea reefs are associated with a highly diverse fauna. Such deep-sea communities are subject to increasing impact from deep-water fisheries, against a background of poor knowledge concerning these ecosystems, including the biology and population structure of L. pertusa. To resolve the population structure and to assess the dispersal potential of this deep-sea coral, specific microsatellites markers and ribosomal internal transcribed spacer (ITS) sequences ITS1 and ITS2 were used to investigate 10 different sampling sites, distributed along the European margin and in Scandinavian fjords. Both microsatellite and gene sequence data showed that L. pertusa should not be considered as one panmictic population in the northeast Atlantic but instead forms distinct, offshore and fjord populations. Results also suggest that, if some gene flow is occurring along the continental slope, the recruitment of sexually produced larvae is likely to be strongly local. The microsatellites showed significant levels of inbreeding and revealed that the level of genetic diversity and the contribution of asexual reproduction to the maintenance of the subpopulations were highly variable from site to site. These results are of major importance in the generation of a sustainable management strategy for these diversity-rich deep-sea ecosystems. [source]

    Mid,Cretaceous Episodic Magmatism and Tin Mineralization in Khingan-Okhotsk Volcano,Plutonic Belt, Far East Russia

    RESOURCE GEOLOGY, Issue 1 2002
    Kohei SATO
    Abstract: Age of magmatism and tin mineralization in the Khingan-Okhotsk volcano,plutonic belt, including the Khingan, Badzhal and Komsomolsk tin fields, were reviewed in terms of tectonic history of the continental margin of East Asia. This belt consists mainly of felsic volcanic rocks and granitoids of the reduced type, being free of remarkable geomagnetic anomaly, in contrast with the northern Sikhote-Alin volcano,plutonic belt dominated by oxidized-type rocks and gold mineralization. The northern end of the Khingan-Okhotsk belt near the Sea of Okhotsk, accompanied by positive geomagnetic anomalies, may have been overprinted by magmatism of the Sikhote-Alin belt. Tin,associated magmatism in the Khingan-Okhotsk belt extending over 400 km occurred episodically in a short period (9510 Ma) in the middle Cretaceous time, which is coeval with the accretion of the Kiselevka-Manoma complex, the youngest accretionary wedge in the eastern margin of the Khingan-Okhotsk accretionary terranes. The episodic magmatism is in contrast with the Cretaceous-Paleogene long,lasted magmatism in Sikhote,Alin, indicating the two belts are essentially different arcs, rather than juxtaposed arcs derived from a single arc. The tin-associated magmatism may have been caused by the subduction of a young and hot back-arc basin, which is inferred from oceanic plate stratigraphy of the coeval accre-tionary complex and its heavy mineral assemblage of immature volcanic arc provenance. The subduction of the young basin may have resulted in dominance of the reduced-type felsic magmas due to incorporation of carbonaceous sediments within the accretionary complex near the trench. Subsequently, the back-arc basin may have been closed by the oblique collision of the accretionary terranes in Sikhote,Alin, which was subjected to the Late Cretaceous to Paleogene magmatism related to another younger subduction system. These processes could have proceeded under transpressional tectonic regime due to oblique subduction of the paleo-Pacific plates under Eurasian continent. [source]

    Geological and Geochemical Characteristics of the Hydrothermal Clay Alteration in South Korea

    RESOURCE GEOLOGY, Issue 4 2000
    Sang-Mo KOH
    Abstract: Hydrothermally altered areas forming pyrophyllite-kaolin-sericite-alunite deposits are distributed in Chonnam and Kyongsang areas, Cretaceous volcanic field of the Yuchon Group. The Chonnam alteration area is located within depression zone which is composed of volcanic and granitic rocks of late Cretaceous age. The clay deposits of this area show the genetic relationship with silicic lava domes. The Kyongsang alteration area is mainly distributed within Kyongsang Basin comprising volcanic, sedimentary and granitic rocks of Cretaceous and Tertiary age. Most of the clay deposits of this area are closely related to cauldrons. Paleozoic clay deposit occurs in the contact zone between Precambrian Hongjesa granite gneiss and Paleozoic Jangsan quartzite of Choson Supergroup. Cretaceous igneous rocks of the both alteration areas belong to high K calc-alkaline series formed in the volcanic arc of continental margin by subduction-related magmatism. Chonnam igneous rocks show more enrichment of crustal components such as K, La, Ce, Sm, Nd and Ba, higher (La/Yb)cn ratio, and higher initial 87Sr/86Sr ratio (0. 708 to 0. 712) than those of Kyongsang igneous rocks. This might be due to the difference of degree of crustal contamination during Cretaceous magmatism. The most characteristic alteration minerals of Chonnam clay deposits are alunite, kaolin, quartz, pyrophyllite and diaspore which were formed by acidic solution. Those of Kyongsang clay deposits are sericite, quartz and pyrophyllite which were formed by weak acid and neutral solution. The formation ages of the clay deposits of two alteration areas range from 70. 1 to 81. 4 Ma and 39. 7 to 79. 4 Ma, respectively. The Daehyun clay deposit in Ponghwa area of Kyongsang province shows the alteration age range from 290 to 336 Ma. This result shows the different alteration episode from the hydrothermal alteration of Cretaceous to early Tertiary in the Kyongsang and Chonnam alteration areas. These data indicate, at least, three hydrothermal activities of Tertiary (middle to late Eocene), late Cretaceous (Santonian to Maastrichtian) and Paleozoic Carboniferous Periods in South Korea. [source]

    Present-day stresses in Brunei, NW Borneo: superposition of deltaic and active margin tectonics

    BASIN RESEARCH, Issue 2 2010
    R. C. King
    ABSTRACT The Baram Delta System, Brunei, NW Borneo, is a Tertiary delta system located on an active continental margin. Delta top regions in many Tertiary delta systems (e.g. Niger Delta) are thought to exhibit a normal-fault stress regime and margin-parallel maximum horizontal stress orientations. However, unlike in passive margin Tertiary delta systems, two present-day stress provinces have been previously identified across the Baram Delta System: an inner shelf inverted province with a margin-normal (NW,SE) maximum horizontal stress orientation and an outer shelf extension province with a margin-parallel (NE,SW) maximum horizontal stress orientation. Before this study, there were few data constraining the inverted province other than in the vicinity of the Champion Fields. New data from 12 petroleum wells in the western inner shelf and onshore west Brunei presented herein confirm the margin-normal maximum horizontal stress orientations of the inverted province. A total of 117 borehole breakouts, all documented in shale units, and one drilling-induced tensile fracture (in a sandstone interval) reveal a mean maximum horizontal stress orientation of 117 with a standard deviation of 19°. This orientation is consistent with contemporary margin-normal maximum horizontal stress orientations of the inverted province described previously in the vicinity of the Champion Fields that have been linked to basement tectonics of the Crocker,Rajang accretionary complex and associated active margin. However, stress magnitudes calculated using data from these 12 petroleum wells indicate a borderline strike,slip fault to normal fault stress regime for the present day; combined with the absence of seismicity, this suggests that the studied part of the NW Borneo continental margin is currently tectonically quiescent. [source]

    Detrital zircon geochronology and its provenance implications: responses to Jurassic through Neogene basin-range interactions along northern margin of the Tarim Basin, Northwest China

    BASIN RESEARCH, Issue 1 2010
    Zhong Li
    ABSTRACT Previously published research from the Kuqa Subbasin along northern margin of the Tarim Basin shows five tectonic-depositional phases from Triassic to Neogene time. In order to reveal additional detailed information on the nature of provenance terrains and tectonic attributes since late Mesozoic time, five typical sandstone samples from Jurassic,Neogene strata were collected for U,Pb dating of detrital zircons. Geochronological constitution of detrital zircons of the Middle Jurassic sample is essentially unimodal and indicates major contributions from the South Tian Shan even Yili,Central Tian Shan, wherein most 370,450 Ma zircons probably resulted from tectonic accretion events between the Yili,Central Tian Shan block and South Tian Shan Ocean during Silurian and Devonian time, with sandstone provenance tectonic attributes of passive continental margin. The Lower Cretaceous sample shows a complicated provenance detrital zircon signature, with new peak ages of 290,330 Ma as well as 370(or 350),450 Ma showing evident arc orogenic provenance tectonic attribute, probably reflecting a new provenance supply that resulted from denudation process whthin the South Tian Shan and South Tian Shan suture. There are no obvious changes within age probability spectra of detrital zircons between the Cretaceous and early Paleogene samples, which suggests that similar provenance types and basin-range framework continued from Cretaceous to Early Paleogene time. However, unlike the Cretaceous and early Paleogene samples, an age spectra of the Miocene sample is relatively unimodal and similar to that of the Pliocene sample, with peak ages ranging between ,392 and ,458 Ma older than the comparable provenance ages (peak ages about 370,450 Ma) of the Middle Jurassic and Lower Cretaceous samples. Therefore, we conclude that the South Tian Shan was rapidly exhumated and the southern South Tian Shan had become the main source of clastics for the Kuqa Subbasin since the Miocene epoch. [source]

    Jurassic synorogenic basin filling in western Korea: sedimentary response to inception of the western Circum-Pacific orogeny

    BASIN RESEARCH, Issue 4 2009
    Kosuke Egawa
    ABSTRACT This is the first sedimentologic and stratigraphic attempt to demonstrate Jurassic subduction-induced basin-filling processes in the early stage of the western Circum-Pacific orogeny. The Chungnam Basin in western Korea was filled with a Lower to Middle Jurassic nonmarine succession, the Nampo Group, whose deposition postdated the Triassic final assembly of Chinese continental blocks. The Nampo Group consists of two repeated, fining- to coarsening-upward alluvio-lacustrine sequences, separated by an interval of thick breccia,gravel progradation deposits and its related strong proximal unconformities. No temporal variation in the degree of chemical weathering, along with the predominance of coals and a tropic to subtropic paleoflora, reveals little or no climate fluctuations during deposition of the Nampo Group. The observed relationships provide a record of sedimentation most likely controlled by temporal variations of tectonically driven sediment flux. Such syntectonic sedimentation of the Chungnam Basin occurred at a convergent margin of continental-arc setting during the Daebo orogeny, synchronous with the early subduction of the western paleo-Pacific ocean that resulted in formation of an accretionary complex along the East Asian continental margin during Jurassic time. Hence, synorogenic deposition in the Chungnam Basin is interpreted as sedimentary response to subduction,accretion of the western paleo-Pacific plate. [source]

    A subsurface evacuation model for submarine slope failure

    BASIN RESEARCH, Issue 4 2009
    Suzanne Bull
    ABSTRACT Analysis of three-dimensional (3D) seismic reflection data from the Norwegian continental margin provides an insight into an unusual, buried submarine slope failure, which occurred adjacent to the later Holocene-age Storegga Slide. The identified failure, informally named the ,South Vøring Slide' (SVS), occurs in fine-grained hemipelagic and contourite sediments on a slope of 0.5°, and is characterised by a deformed seismic facies unit consisting of closely spaced pyramidal blocks and ridges bound by small normal faults striking perpendicular to the slope. The SVS contrasts with other previously described submarine slope failures in that it cannot be explained by a retrogressive model. The defining characteristic is the high relative volume loss. The area affected by sliding has thinned by some 40%, seen in combination with very modest extension in the translation direction, with line length balancing yielding an extension value of only 4.5%. The volume loss is explained by the mobilisation of an approximately 40 m thick interval at the lower part of the unit and its removal from beneath a thin overburden, which subsequently underwent extensional fragmentation. Evidence for the mobilisation of a thick fine-grained interval in the development of a submarine slope failure from a continental margin setting may have implications for the origins of other large-scale slope failures on the Norwegian margin and other glacially influenced margins worldwide. [source]

    Sedimentation record in the Konkan,Kerala Basin: implications for the evolution of the Western Ghats and the Western Indian passive margin

    BASIN RESEARCH, Issue 1 2008
    D. Campanile
    ABSTRACT The Konkan and Kerala Basins constitute a major depocentre for sediment from the onshore hinterland of Western India and as such provide a valuable record of the timing and magnitude of Cenozoic denudation along the continental margin. This paper presents an analysis of sedimentation in the Konkan,Kerala Basin, coupled with a mass balance study, and numerical modelling of flexural responses to onshore denudational unloading and offshore sediment loading in order to test competing conceptual models for the development of high-elevation passive margins. The Konkan,Kerala Basin contains an estimated 109 000 km3 of Cenozoic clastic sediment, a volume difficult to reconcile with the denudation of a downwarped rift flank onshore, and more consistent with denudation of an elevated rift flank. We infer from modelling of the isostatic response of the lithosphere to sediment loading offshore and denudation onshore infer that flexure is an important component in the development of the Western Indian Margin. There is evidence for two major pulses in sedimentation: an early phase in the Palaeocene, and a second beginning in the Pliocene. The Palaeocene increase in sedimentation can be interpreted in terms of a denudational response to the rifting between India and the Seychelles, whereas the mechanism responsible for the Pliocene pulse is more enigmatic. [source]

    Testing long-term patterns of basin sedimentation by detrital zircon geochronology, Centralian Superbasin, Australia

    BASIN RESEARCH, Issue 3 2007
    D. W. Maidment
    ABSTRACT Detrital zircon geochronology of Neoproterozoic to Devonian sedimentary rocks from the Georgina and Amadeus basins has been used to track changes in provenance that reflect the development and inversion of the former Australian Superbasin. Through much of the Neoproterozoic, sediments appear to have been predominantly derived from local sources in the Arunta and Musgrave inliers. Close similarities between the detrital age signatures of late Neoproterozoic sedimentary rocks in the two basins suggests that they were contiguous at this time. A dominant population of 1.2,1.0 Ga zircon in Early Cambrian sediments of the Amadeus Basin reflects the uplift of the Musgrave Inlier during the Petermann Orogeny between 560 and 520 Ma, which shed a large volume of detritus northwards into the Amadeus Basin. Early Cambrian sedimentary rocks in the Georgina Basin have a much smaller proportion of 1.2,1.0 Ga detritus, possibly due to the formation of sub-basins along the northern margin of the Amadeus Basin which might have acted as a barrier to sediment transfer. An influx of 0.6,0.5 Ga zircon towards the end of the Cambrian coincides with the transgression of the Larapintine Sea across central Australia, possibly as a result of intracratonic rifting. Detrital zircon age spectra of sedimentary rocks deposited within this epicontinental sea are very similar to those of coeval sedimentary rocks from the Pacific Gondwana margin, implying that sediment was transported into central Australia from the eastern continental margin. The remarkably consistent ,Pacific Gondwana' signature of Cambro-Ordovician sediments in central and eastern Australia reflects a distal source, possibly from east Antarctica or the East African Orogen. The peak of the marine incursion into central Australia in the early to mid Ordovician coincides with granulite-facies metamorphism at mid-crustal depths between the Amadeus and Georgina basins (the Larapinta Event). The presence of the epicontinental sea, the relative lack of a local basement zircon component in Cambro-Ordovician sedimentary rocks and their maturity suggest that metamorphism was not accompanied by mountain building, consistent with an extensional or transtensional setting for this tectonism. Sediments deposited at ,435,405 and ,365 Ma during the Alice Springs Orogeny have detrital age signatures similar to those of Cambro-Ordovician sedimentary rocks, reflecting uplift and reworking of the older succession into narrow foreland basins adjacent to the orogen. [source]

    Dynamic modelling of passive margin salt tectonics: effects of water loading, sediment properties and sedimentation patterns

    BASIN RESEARCH, Issue 3 2005
    Lykke Gemmer
    We investigate the evolution of passive continental margin sedimentary basins that contain salt through two-dimensional (2D) analytical failure analysis and plane-strain finite-element modelling. We expand an earlier analytical failure analysis of a sedimentary basin/salt system at a passive continental margin to include the effects of submarine water loading and pore fluid pressure. Seaward thinning sediments above a weak salt layer produce a pressure gradient that induces Poiseuille flow in the viscous salt. We determine the circumstances under which failure at the head and toe of the frictional,plastic sediment wedge occurs, resulting in translation of the wedge, landward extension and seaward contraction, accompanied by Couette flow in the underlying salt. The effects of water: (i) increase solid and fluid pressures in the sediments; (ii) reduce the head to toe differential pressure in the salt and (iii) act as a buttress to oppose failure and translation of the sediment wedge. The magnitude of the translation velocity upon failure is reduced by the effects of water. The subsequent deformation is investigated using a 2D finite-element model that includes the effects of the submarine setting and hydrostatic pore pressures. The model quantitatively simulates a 2D approximation of the evolution of natural sedimentary basins on continental margins that are formed above salt. Sediment progradation above a viscous salt layer results in formation of landward extensional basins and listric normal growth faults as well as seaward contraction. At a later stage, an allochthonous salt nappe overthrusts the autochthonous limit of the salt. The nature and distribution of major structures depends on the sediment properties and the sedimentation pattern. Strain weakening of sediment favours landward listric growth faults with formation of asymmetric extensional depocentres. Episodes of low sediment influx, with partial infill of depocentres, produce local pressure gradients in the salt that result in diapirism. Diapirs grow passively during sediment aggradation. [source]

    Holocene denudation of the northwest sector of Iceland as determined from accumulation of sediments on the continental margin

    BOREAS, Issue 3 2007
    JOHN T. ANDREWSArticle first published online: 28 JUN 200
    Radiocarbon-dated marine cores, measurements of sediment density and seismic surveys were used to estimate the sediment and mass accumulation rates (m/kyr and kg/m2/kyr) in the troughs from the southwest to north-central Iceland shelf (i.e. northwest sector of Iceland). The 3.5-kHz seismic survey showed varying thicknesses of acoustically transparent sediment in the troughs, whereas the inter-trough banks were largely devoid of sediment. The survey showed a pervasive reflector 1 to , 60 m below the sea floor, which turned out to be Saksunarvatn tephra, dated at 10 180 ± 60 cal. yr BP. The 3.5-kHz analogue data were digitized at 1-min intervals and provided 1645 estimates of maximum sediment thickness and 979 estimates of sediment accumulation over the last 10200 cal. yr BP. Maximum sediment accumulation occurred in the mid-troughs and not, as expected, in the fjords. The median sediment accumulation rate (SAR) based on the core data was 0.23 m/kyr, but was 0.77 m/kyr based on the seismic data: the difference is attributed to coring limitations. Based on the volume of offshore sediment and the contributing terrestrial drainage area, the Holocene denudation of northern Iceland (c. 50 000 km2) is calculated to have been between 0.02 to 0.05 m/kyr, substantially lower that the 1,3 m/kyr derived from the suspended sediment load of rivers from southern Iceland but in agreement with the rate of accumulation of Holocene glacial lacustrine sediments in central Iceland. [source]

    Configuration, history and impact of the Norwegian Channel Ice Stream

    BOREAS, Issue 1 2003
    Hans Petter Sejrup
    The Norwegian Channel between Skagerrak, in the southeast, and the continental margin of the northern North Sea, in the northwest, is the result of processes related to repeated ice stream activity through the last 1.1 m yr. In such periods the Skagerrak Trough (700 m deep) has acted as a confluence area for glacial ice from southeastern Norway, southern Sweden and parts of the Baltic. Possibly related to the threshold in the Norwegian Channel off Jæren (250 m deep), the ice stream, on a number of occasions over the last 400 ka, inundated the coastal lowlands and left an imprint of NW-oriented ice directional features (drumlins, stone orientations in tills and striations). Marine interstadial sediments found up to 200 m a.s.l. on Jæren have been suggested to reflect glacial isostasy related to the Norwegian Channel Ice Stream (NCIS). In the channel itself, the ice stream activity is evidenced by mega-scale glacial lineations on till surfaces. As a result of subsidence, the most complete sedimentary records of early phases of the NCIS are preserved close to the continental margin in the North Sea Fan region. The strongest evidence for ice stream erosion during the last glacial phase is found in the Skagerrak. On the continental slope the ice stream activity is evidenced by the large North Sea Fan, which is mainly a result of deposition of glacial-fed debris flows. Northwards of the North Sea Fan, rapid deposition of meltwater plume deposits, possibly related to the NCIS, is detected as far north as the Vøring Plateau. The NCIS system offers a unique possibility to study ice stream related processes and the impact the ice stream development had on open ocean sedimentation and circulation. [source]