22 results on '"Pontén, Anna"'
Search Results
2. Holocene evolution and depositional model of a bayhead delta, Lake Illawarra, Australia.
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Hopley, Carl A., Jones, Brian G., and Pontén, Anna
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RELATIVE sea level change ,SEDIMENTARY facies (Geology) ,SEDIMENTARY structures ,HOLOCENE Epoch ,RIVER sediments ,ABSOLUTE sea level change - Abstract
Extensive research into the evolution of wave‐dominated estuaries has been documented since the 1960s. However, there has only been limited research on the prograding bay‐head deltas that are the primary drivers for the rate and stage of estuary evolution. This paper presents the findings of a high‐resolution spatial study into the evolution of the Macquarie Rivulet bayhead delta in the Lake Illawarra barrier estuary. The delta's evolution has been established based on sedimentological analysis of 74 cores, two 14C ages and 45 amino acid racemization ages. This study intersected two Pleistocene and 10 Holocene sedimentary facies associations representing both the retrogradational and progradational phases of delta development. The distribution of bayhead delta facies associations in shallow barrier estuaries is initially controlled by the antecedent morphology, but, in contrast to deeper estuaries, this influence decreases as sedimentation proceeds. Changing relative sea level also has a major control on facies distribution with transgressive facies deposited as relative sea‐level rises being replaced by prograding deltaic facies during the highstand and subsequent minor relative sea‐level fall. Fluvial sediment supply and river flood events affect the rate of delta progradation, and produce low and high flow sediment deposits within the overall deltaic sequence. The low tidal flux in barrier estuaries, the muddy cohesive nature of the sediments and the prevalence of bioturbation means that primary sedimentary structures are rarely preserved in these bayhead delta facies. The depositional model of bayhead delta evolution shown by the Macquarie Rivulet delta would be widely applicable to other similar barrier estuary settings. [ABSTRACT FROM AUTHOR]
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- 2022
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3. Middle Ordovician mass‐transport deposits from western Inner Mongolia, China: Mechanisms and implications for basin evolution.
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Li, Wenjie, Chen, Jitao, Hakim, Anne J., Myrow, Paul M., and Pontén, Anna
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INCRUSTATIONS ,SEDIMENT transport ,BRECCIA ,SILICICLASTIC rocks ,SOUND recordings ,FACIES - Abstract
Subaqueous mass‐transport processes are one of the mechanisms for transport of sediment into the deep sea. Internal structures and depositional processes of carbonate mass‐transport deposits are relatively poorly understood relative to siliciclastic facies due to their comparative paucity in the rock record. A variety of carbonate mass‐transport deposits, including slumps, debrites and deep‐channel‐confined density flow deposits, occur in Middle–Upper Ordovician slope deposits in western Inner Mongolia (Wuhai), China. These provide a rare opportunity to illustrate the emplacement history of carbonate mass‐transport deposits at the outcrop scale. The slumps and debrites host remarkable folds, chaotic beds and imbricated beds that reflect differences in both rheology and position on the slope. Individual slump sheets show gradations between undulating laminae, inclined and recumbent folds, highly deformed folds, and chaotic textures upslope from the toe region. Debrites are commonly interbedded with slump deposits, whereas imbricated beds are present in the middle and lower parts of the toes of slump sheets near the terminal wall. In the study area, thin‐bedded limestone with slump deposits of the Kelimoli Formation are overlain by fine‐grained, siliciclastic‐dominated, slope deposits of the Wulalike Formation. A thick breccia of the Wulalike Formation was deposited in a main feeder channel in south‐east Wuhai, but to the west‐north‐west the breccia was deposited in distributary channels possibly represented as a unique lower‐slope pattern of gullies. At the latter locality, the breccia was deposited solely within the channels on a steep west‐north‐west dipping slope under density‐driven flows. The mass‐transport deposits documented herein records passive to foreland basin tectonic transitions, and associated platform foundering and steepening of the slope. A slope facies model was constructed to demonstrate the spatial and temporal variations of mass‐transport deposits during basin evolution, and as such it provides a template for the interpretation of the deposits of ancient slopes that underwent passive to active tectonic transitions. [ABSTRACT FROM AUTHOR]
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- 2022
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4. Statistical characterization of a confined submarine fan system: The Pennsylvanian Lower Atoka Formation, Ouachita Mountains, USA.
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Hou, Pengfei, Jobe, Zane R., Wood, Lesli J., and Pontén, Anna
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SUBMARINE fans ,TIME series analysis ,MARKOV processes ,DISTRIBUTION (Probability theory) ,TURBIDITES - Abstract
Current knowledge of submarine fan deposits has historically relied heavily on qualitative field and subsurface observations and interpretations, but recent studies using statistical analyses have enhanced the understanding of submarine fan sub‐environments, including the degree of confinement, stratigraphic patterns and potential control factors. The purpose of this study is to improve the quantitative understanding of synorogenic submarine fan deposition at foreland basin settings with a statistical approach. A suite of statistical methods is integrated and developed (Hurst Statistics/rescaled range analysis, bed thickness frequency distribution analysis, Markov Chains and time‐series analysis), and applied to the well‐understood Pennsylvanian lower Atoka submarine fan system in the Ouachita Mountains, United States, for this purpose. The results of the Hurst Statistics and bed thickness analyses corroborate qualitative interpretations that: (i) the lower Atoka is lobe‐dominated; and (ii) the south‐eastern (wedge top) portion of the system is more strongly confined than the northern (foredeep) portion. The Markov Chains and time‐series analyses reveal the prevalence (56% of the measured sections) of stratigraphic orderliness and cyclicity; these results are used to discuss potential control signals, which are otherwise difficult to distinguish, on the turbidite sandstone recurrence cycles. The results of this study demonstrate that these integrated statistical methods can be utilized to quantify depositional interpretations and extract hidden information using outcrops with limited exposures. [ABSTRACT FROM AUTHOR]
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- 2022
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5. Relating seafloor geomorphology to subsurface architecture: How mass‐transport deposits and knickpoint‐zones build the stratigraphy of the deep‐water Hikurangi Channel.
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Tek, Daniel E., McArthur, Adam D., Poyatos‐Moré, Miquel, Colombera, Luca, Patacci, Marco, Craven, Benjamin, McCaffrey, William D., and Pontén, Anna
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IMAGING systems in seismology ,BATHYMETRY ,GEOMORPHOLOGY ,TERRACING ,FACIES - Abstract
Monitoring of modern deep‐water channels has revealed how migrating channel‐floor features generate and remove stratigraphy, improving understanding of how channel morphologies relate to their deposits. Here, seafloor and subsurface data are reconciled through an integrated study of high‐resolution bathymetry and three‐dimensional seismic data imaging a ca 150 km stretch of the trench‐axial Hikurangi Channel, offshore New Zealand. On the seafloor, terraced channel‐walls bound a flat, wide, channel‐floor, ornamented with three scales of features that increase then decrease in longitudinal gradient downstream, and widen downstream: cyclic‐steps, knickpoints and knickpoint‐zones (in increasing size). Mass‐transport deposits derived from channel‐wall collapse, are bordered by wide and flat reaches of channel‐floor upstream and by knickpoint‐zones (reaches containing multiple knickpoints) downstream. In the subsurface, recognition of ten seismofacies and five types of surface enables identification of four depositional elements: channel‐fill, sheet or terrace, levée, and mass‐transport deposits. Integration of subsurface and seafloor interpretations reveals that knickpoint‐zones initiate on the downstream margins of channel‐damming mass‐transport deposits; they migrate and incise through the mass‐transport deposits and weakly‐confined deposits formed upstream, as the channel tends towards equilibrium. Downstream of a knickpoint‐zone, a flat channel‐floor is bounded by newly‐formed terraces. Knickpoints migrate by eroding upstream and depositing downstream, generating filled concave‐up (cross‐sectional) surfaces in their wake. Within knickpoint‐zones, knickpoint‐generated surfaces are re‐incised by subsequently‐passing knickpoints to produce a composite bounding surface; this surface does not delineate the morphology of any palaeo‐conduit. The Hikurangi Channel's subsurface architecture records the localized erosional response to mass‐transport deposit emplacement via knickpoint‐zone migration, showcasing how transient seafloor features can build channelized stratigraphy. This model provides an additional mechanism to conventional models of channel deposit formation through 'cut‐and‐fill' over long stretches of channel. These findings may aid subsurface interpretation in systems lacking a contemporary self‐analogue or with poor data coverage. [ABSTRACT FROM AUTHOR]
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- 2021
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6. Sedimentary processes at the mouth of a tidally‐influenced delta: New insights from submarine observatory measurements, Fraser Delta, Canada.
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Hill, Philip R., Lintern, D. Gwyn, and Pontén, Anna
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SEDIMENTATION & deposition ,ACOUSTIC Doppler current profiler ,OBSERVATORIES ,SUSPENDED sediments ,SEDIMENT transport ,SILT - Abstract
This paper examines particle settling dynamics in a tidally‐influenced delta, including observations of convective settling, strongly modulated by seasonal discharge and tidal cycles. Long time series of Acoustic Doppler Current Profiler backscatter, a proxy for suspended sediment concentration in the water column, current and sediment accumulation measurements from the slope of the Fraser River delta show variability of sedimentary processes over timescales from semi‐diurnal to annual. Acoustic Doppler Current Profiler backscatter shows a lagged response to river discharge and strong diurnal/semi‐diurnal variability. Most of the tidal cycle is characterized by a buoyant effluent plume. During the ebbing phase of diurnal major tides, discrete settling events are observed extending through the entire water column. The pulse‐like nature of these events is the result of downward plunging fingers characteristic of convective settling, similar to those observed in laboratory flume experiments, and appear to be initiated at the interface between the surface buoyant plume and the underlying ambient water. Currents show strong variability in a three‐layer water column. The surface plume shows offshore and southward directed transport of sediments. The remaining water column is influenced by tidal flows, but near surface and intermediate water‐depth currents are out of phase by several hours, indicating a stratification of the basin water and decoupled propagation of surface and internal tides. This phase lag is unlikely to cause discernible facies changes, but may have implications for basin‐fill patterns in restricted basins with strong tidal range. The results of this work will help to better understand river mouth sedimentation processes and dispersal patterns in other modern deltas and in the geological record. [ABSTRACT FROM AUTHOR]
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- 2021
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7. Anatomy of a mixed bioclastic–siliciclastic regressive tidal sand ridge: Facies‐based case study from the lower Pleistocene Siderno Strait, southern Italy.
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Longhitano, Sergio G., Rossi, Valentina M., Chiarella, Domenico, Mellere, Donatella, Tropeano, Marcello, Dalrymple, Robert W., Steel, Ronald J., Nappi, Antonio, Olita, Fabio, and Pontén, Anna
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PLEISTOCENE Epoch ,SAND waves ,STRAITS ,TIDAL currents ,PLIOCENE Epoch ,SOUND recordings - Abstract
Sand ridges, a common feature of modern open shelves, reflect persistent currents and sediment availability under recent transgressive conditions. They represent the largest bedforms in the oceans and, as such, can yield information on long‐term oceanographic processes. However, there is a limited number of tidal sand ridges documented from the rock record, examples of regressive tidal sand ridges are scarce and studies describing ridges in straits are even more rare. This study analyses a Gelasian succession within a structurally controlled, tide‐dominated strait in the Siderno Basin, southern Italy. The strait connected two wider basins, and accumulated sediments reworked by amplified tidal (bi‐directional) currents. A series of tidal sand ridges with superimposed dunes developed close to the south‐eastern end of the strait, where bathymetry was deeper and flow expansion occurred. One of the best‐exposed tidal sand ridges, 65 m thick, crops out along a ca 2 km long cliff. Large‐scale, ESE‐prograding, seaward‐offlapping shingles contain sets of bioclastic–siliciclastic, coarse‐grained, cross‐stratified sandstones, erosionally overlying upper Pliocene shelf marls and fine‐grained sandstones. Cross‐strata show angular, tangential and sigmoidal foresets with compound architectures and a SSE migration, i.e. oblique to the main growth direction. Fossil content indicates open‐marine conditions. The succession changes abruptly across an erosion surface to non‐tidal, highly burrowed mixed siliciclastic–bioclastic fine‐grained sandstones, less than 15 m thick. Documented features reflect stages of nucleation, active accretion and abandonment of an individual sand ridge, during a complete cycle of relative sea‐level change. The ridge formed during a phase of normal regression, with accretion occurring during an initial highstand and the ensuing falling stage. During the lowstand the ridge was split into several minor bodies by enhanced tidal currents. The ensuing transgression draped the moribund ridge with tabular strata, whereas final highstand shelf sedimentation reworked the top of the underlying sand body with weak currents. [ABSTRACT FROM AUTHOR]
- Published
- 2021
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8. M86. CAN WEIGHT GAIN CAUSE METABOLIC SYNDROME A DECADE LATER IN PATIENTS WITH SCHIZOPHRENIA SPECTRUM DISORDER?
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Pontén Anna, Lars Helldin, Anna-Karin Olsson, and Moradi Hawar
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Pediatrics ,medicine.medical_specialty ,Poster Session II ,business.industry ,AcademicSubjects/MED00810 ,medicine.disease ,Psychiatry and Mental health ,medicine ,In patient ,medicine.symptom ,Metabolic syndrome ,business ,Weight gain ,Schizophrenia spectrum - Abstract
Background Patients with schizophrenia spectrum disorder have a reduced life time expectancy with up to 20 years. Obesity and metabolic syndrome is highly prevalent and cardio vascular disease, CVD, remain the most common cause of the excess mortality. Despite studies showing the reduced life time expectancy and its causes the patients with schizophrenia spectrum disorder yet remain to benefit of the development of the healthcare. In this study we aim to focus on how the weight changes in different age groups and when do the cluster of conditions of metabolic syndrome start to occur. Methods In this naturalistic study we follow 71 patients, 47 man and 24 women diagnosed with schizophrenia spectrum disorder. We divided the patients into 5 different groups based on age. Group 1 aged 20–30 years, Group 2 aged 31–40 years, Group 3 aged 41–50 years, group 4 aged 51–60 years and Group 5 aged 61 years and elder. The longest time of observation was 18 years. Data on weight (kg) and disorders such as diabetes, hypertension and dyslipidemia were collected at baseline and then yearly thereafter. Data from baseline and the last yearly follow up were included in this study. Weight and the presence of the cluster of conditions that make up metabolic syndrome in the above-mentioned groups were analyzed. Results Patients in group 1 make the highest gain of weight with 0, 9 kg per year and group 2 with the least gain of weight only 0, 01 kg per year. Patients in group 3 have a weight loss of 0, 2 kg per year. At endpoint 9 out 19 patients in group 3 and 11 out of 21 patients in group 4 were treated for one, two or three conditions of the metabolic syndrome. Discussion In our study we show that weight gain appears at least 10 years before the development of metabolic syndrome. Despite the loss of weight that appear in group 3 the negative effects of the weight gained a decade earlier may be a factor that make patients aged 41 years and older to be at risk of developing metabolic syndrome.
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- 2020
9. A numerical model of a 3-dimensional low-density turbidity current in the deep ocean: testing hypotheses on turbidity currents in deep detail
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Azpiroz Zabala, M., Storms, J.E.A., van der Vegt, H., Walstra, D.J.R., Obradors-Latre, Arnau, and Pontén, Anna
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- 2019
10. A stratigraphic example of the architecture and evolution of shallow water mouth bars.
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Cole, Grant, Jerrett, Rhodri, Watkinson, Matthew P., and Pontén, Anna
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WATER depth ,SEDIMENTATION & deposition ,WATER distribution ,JETS (Nuclear physics) ,CHANNEL flow - Abstract
Improved understanding of mouth bar morphodynamics, and the resulting stratigraphic architectures, is important for predicting the loci of deposition of different sediment fractions, coastal geomorphic change and heterogeneity in mouth bar reservoirs. Facies and architectural analysis of exceptionally well‐exposed shallow water (ca 5 m depth) mouth bars and associated distributaries, from the Xert Formation (Lower Cretaceous), of the Maestrat Basin (east‐central Spain), reveal that they grew via a succession of repeated autogenic cycles. An initial mouth bar accretion element forms after avulsion of a distributary into shallow standing water. Turbulent expansion of the fluvial jet and high bed friction results in rapid flow deceleration, and deposition of sediment in an aggradational to expansional bar‐form. Vertical bar growth causes flattening and acceleration of the jet. The accelerated flow scours channels on the bar top, which focuses further expansion of the mouth bar at individual loci where the channels break through the front of the mouth bar. Here, new mouth bar accretion elements form, downlapping and onlapping against a readily recognizable surface of mouth bar reorganization. Vertical growth of the new mouth bar accretion elements causes flattening and re‐acceleration of the jet, leading to channelization, and initiation of the next generation of mouth bar accretion elements. Thus the mouth bar grows, until bed‐friction effects cause backwater deceleration and super‐elevation of flow in the feeding distributary. Within‐channel sedimentation, choking and upstream avulsion of the feeding channel, results in mouth bar abandonment. In this study, mouth bars are formed of at least two to three accretion elements, before abandonment happened. The results of this study contrast with the notion that mouth bars form by simple vertical aggradation and radial expansion. However the architecture and facies distributions of shallow water mouth bars are a predictable product of intrinsic processes that operate to deposit them. [ABSTRACT FROM AUTHOR]
- Published
- 2021
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11. Storm‐flood‐dominated delta: A new type of delta in stormy oceans.
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Lin, Wen, Bhattacharya, Janok P., and Pontén, Anna
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SEDIMENTATION & deposition ,RIP currents ,REGIONS of freshwater influence ,SEDIMENT transport ,SEQUENCE stratigraphy - Abstract
Storms are increasingly identified as a key depositional process. Their deposits show unique sedimentary characteristics, distinct from deposits of fair‐weather wave processes, but are not currently separated in classic ternary deltaic classification schemes. The term 'storm‐flood‐dominated delta' is proposed for a new type of delta that more fully represents deltas dominated by storm‐flood processes. This study describes several outcrop cliffs of the Gallup Formation, deposited during the Late Turonian to Early Coniacian in north‐west New Mexico, that exemplify storm‐generated facies and provide examples that can be used to generate a facies model for storm‐flood‐dominated deltas. Key identification criteria include extensive sharp‐based planar to hummocky cross‐stratified sandstone beds, commonly presenting as large‐sized gutter casts. They are interbedded with mudstones that show low bioturbation intensity and normally and inversely graded beds, suggesting direct deposition from river plumes. Major types of gutter casts are classified based on geometry and dimension. The gutter casts are interpreted as storm channels of storm‐flood‐dominated deltas and formed by erosion and infill of submerged channels resulting from offshore‐oriented downwelling currents that may include localized rip currents. These amalgamated channels are likely linked to multiple feeding rivers and distributary channels that ensured high sediment supply rates and highly efficient offshore‐directed sediment transport through hyperpycnal flows. A four‐component pyramidal classification scheme of deltaic deposition is employed to emphasize storms as a distinct process in contrast to the traditional classification that lumps storm and fair‐weather processes in a single 'wave' end‐member. The four‐component depositional model can be readily applied to interpret storm‐dominated environments and provide new insights into depositional processes of the marine realm. Recognition of storm processes in deciphering depositional evolution will also help to better understand control mechanisms of sequence stratigraphy, such as relative sea‐level changes, and to analyze sedimentary processes governing sediment transport in 'source to sink' systems. [ABSTRACT FROM AUTHOR]
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- 2021
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12. Distribution of contourite drifts on convergent margins: Examples from the Hikurangi subduction margin of New Zealand.
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Bailey, William S., McArthur, Adam D., McCaffrey, William D., and Pontén, Anna
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SUBMARINE topography ,GLACIAL drift - Abstract
Contourite drift systems form a significant component of the marine clastic sedimentary record. Although contourites form in all tectonic settings, few studies have described their development along convergent margins; such characterization is needed to underpin oceanographic and palaeoenvironmental studies in active settings. This study is the first to document contourite drift development along the Hikurangi subduction margin of New Zealand. Integration of bathymetric, seismic and well data enables five classes of drift to be recognized around the subduction wedge, occurring in three principal associations: (i) an upper slope drift association of giant elongate mounded (ca 150 km long, 50 km wide and up to 1100 m thick) and plastered drifts (ca 300 km long, 8 km wide and <600 m thick), which occurs upon and inboard of a major intrabasinal thrust‐cored high, whose long axis parallels the coast; shallow bottom currents disperse sub‐parallel to this axis; (ii) a spatiotemporally discontinuous association of confined and mounded hybrid drifts (ca 500 m long, <2 km wide and up to 500 m thick) that occurs along the mid‐to‐outer slope domain of the wedge, recording the interaction of along‐slope and downslope currents within trench‐slope basins; and (iii) a trench fill assemblage that implies the passage of abyssal bottom currents across a 40 km reach of the trench‐axial Hikurangi Channel‐levée, with associated modification of the channel form and of overbank sediment waves. The fundamental presence of contourites along this margin appears to depend on the orientation and strength of oceanographic bottom currents. However, drift type and evolution vary depending on the slope gradient and the presence of irregular seafloor topography created by tectonic structures. The documented drifts are generally smaller, less continuous, and develop more intermittently than similar styles of drifts documented on passive margins; this mode of occurrence may be characteristic of contourite development on convergent margins. [ABSTRACT FROM AUTHOR]
- Published
- 2021
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13. Stratigraphic hierarchy and three‐dimensional evolution of an exhumed submarine slope channel system.
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Bell, Daniel, Hodgson, David M., Pontén, Anna S. M., Hansen, Larissa A. S., Flint, Stephen S., Kane, Ian A., and Baas, Jaco
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SEDIMENT transport ,CONTINENTAL margins ,HIERARCHIES ,FORECASTING ,EROSION - Abstract
Submarine slope channel systems have complicated three‐dimensional geometries and facies distributions, which are challenging to resolve using subsurface data. Outcrop analogues can provide sub‐seismic‐scale detail, although most exhumed systems only afford two‐dimensional constraints on the depositional architecture. A rare example of an accessible fine‐grained slope channel complex set situated in a tectonically quiescent basin that offers seismic‐scale, down‐dip and across‐strike exposures is the Klein Hangklip area, Tanqua‐Karoo Basin, South Africa. This study investigates the three‐dimensional architecture of this channel complex set to characterise the stratigraphic evolution of a submarine channel‐fill and the implications this has for both sediment transport to the deep‐oceans and reservoir quality distribution. Correlated sedimentary logs and mapping of key surfaces across a 3 km2 area reveal that: (i) the oldest channel elements in channel complexes infill relatively deep channel cuts and have low aspect‐ratios. Later channel elements are bound by comparatively flat erosion surfaces and have high aspect‐ratios; (ii) facies changes across depositional strike are consistent and predictable; conversely, facies change in successive down depositional dip positions indicating longitudinal variability in depositional processes; (iii) stratigraphic architecture is consistent and predictable at seismic‐scale both down‐dip and across‐strike in three‐dimensions; (iv) channel‐base‐deposits exhibit spatial heterogeneity on one to hundreds of metres length‐scales, which can inhibit accurate recognition and interpretations drawn from one‐dimensional or limited two‐dimensional datasets; and (v) channel‐base‐deposit character is linked to sediment bypass magnitude and longevity, which suggests that time‐partitioning is biased towards conduit excavation and maintenance rather than the fill‐phase. The data provide insights into the stratigraphic evolution and architecture of slope channel‐fills on fine‐grained continental margins and can be utilised to improve predictions derived from lower resolution and one‐dimensional well data. [ABSTRACT FROM AUTHOR]
- Published
- 2020
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14. Origin of mud in turbidites and hybrid event beds: Insight from ponded mudstone caps of the Castagnola turbidite system (north‐west Italy).
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Patacci, Marco, Marini, Mattia, Felletti, Fabrizio, Di Giulio, Andrea, Setti, Massimo, McCaffrey, William, and Pontén, Anna
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SUBMARINE fans ,BEDS ,TURBIDITES ,TURBIDITY currents ,MUD ,SANDSTONE - Abstract
The partitioning of different grain‐size classes in gravity flow deposits is one of the key characteristics used to infer depositional processes. Turbidites have relatively clean sandstones with most of their clay deposited as part of a mudstone cap or as a distal mudstone layer, whereas sand‐bearing debrites commonly comprise mixtures of sand grains and interstitial clay; hybrid event beds develop alternations of clean and dirty (clay‐rich) sandstones in varying proportions. Analysis of co‐genetic mudstone caps in terms of thickness and composition is a novel approach that can provide new insight into gravity flow depositional processes. Bed thickness data from the ponded Castagnola system show that turbidites contain more clay overall than do hybrid event beds. The Castagnola system is characterized by deposits of two very different petrographic types. Thanks to this duality, analyses of sandstone and mudstone composition allow inference of which proportion of the clay in each of the deposit types was acquired en route. In combination with standard sedimentological observations the new data allow insight into the likely characteristics of their parent flows. Clean turbidites were deposited by lower concentration, long duration, erosive, muddy turbidity currents which were more efficient at fractionating clay particles away from their basal layer. Hybrid event beds were deposited by shorter duration, higher‐concentration, less‐erosive sandier flows which were less efficient at clay fractionation. The results are consistent with data from other turbidite systems (for example, Marnoso‐arenacea). The approach represents a new method to infer the controls on the degree of clay partitioning in gravity flow deposits. [ABSTRACT FROM AUTHOR]
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- 2020
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15. Sand–mud couplets deposited by spontaneous remobilization of subaqueous transitional flows.
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Koo, Woong Mo, Mohrig, David, Buttles, James, Sturmer, Daniel, Pontén, Anna, Hess, Thomas, and Kane, Ian
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SEDIMENTATION & deposition ,TURBIDITY currents ,TURBULENT flow ,COMPOSITION of sediments ,SAND ,SANDSTONE - Abstract
Clean basal and capping argillaceous sandstone couplets in deep water settings have been previously interpreted as the result of spatially segregated turbidity currents and debris flows or spatio‐temporal transitioning of a turbulent flow to a transitional/laminar state. However, this paper presents three‐dimensional laboratory experiments demonstrating that a single sediment‐gravity flow can develop sand–mud couplets by autogenic remobilization of sediments that are still in the process of being deposited. This remobilization appears common to flows composed of mixtures of sand and mud with viscosities and strengths measurably greater than water, but not so high as to fully suppress the settling of sand through the depositional current. Dewatering in the early sand deposit acts to lubricate the basal portion of the increasingly muddy upper division of the flow, causing it to accelerate downslope, triggering a secondary flow with a sediment composition distinct from the original mixture. Sediment deposition and remobilization processes in a single sediment‐gravity flow and their resultant deposit were imaged acoustically and cored at representative locations within the deposit. The acoustic data and cores show sand–mud couplets that are qualitatively similar to interpreted turbidite–debrite‐like couplets in natural systems. [ABSTRACT FROM AUTHOR]
- Published
- 2020
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16. The stratigraphic record and processes of turbidity current transformation across deep-marine lobes.
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Kane, Ian A., Pontén, Anna S. M., Vangdal, Brita, Eggenhuisen, Joris T., Hodgson, David M., Spychala, Yvonne T., and Talling, Peter
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SEDIMENTARY facies (Geology) , *SEDIMENTARY structures , *TURBIDITES , *TURBULENCE , *SANDSTONE - Abstract
Sedimentary facies in the distal parts of deep-marine lobes can diverge significantly from those predicted by classical turbidite models, and sedimentological processes in these environments are poorly understood. This gap may be bridged using outcrop studies and theoretical models. In the Skoorsteenberg Formation (South Africa), a downstream transition from thickly bedded turbidite sandstones to argillaceous, internally layered hybrid beds, is observed. The hybrid beds have a characteristic stratigraphic and spatial distribution, being associated with bed successions which generally coarsen and thicken-upward reflecting deposition on the fringes of lobes in a dominantly progradational system. Using a detailed characterization of bed types, including grain size, grain-fabric and mineralogical analyses, a process-model for flow evolution is developed. This is explored using a numerical suspension capacity model for radially spreading and decelerating turbidity currents. The new model shows how decelerating sediment suspensions can reach a critical suspension capacity threshold beyond which grains are not supported by fluid turbulence. Sand and silt particles, settling together with flocculated clay, may form low yield strength cohesive flows; development of these higher concentration lower boundary layer flows inhibits transfer of turbulent kinetic energy into the upper parts of the flow ultimately resulting in catastrophic loss of turbulence and collapse of the upper part of the flow. Advection distances of the now transitional to laminar flow are relatively long (several kilometres) suggesting relatively slow dewatering (several hours) of the low yield strength flows. The catastrophic loss of turbulence accounts for the presence of such beds in other fine-grained systems without invoking external controls or large-scale flow partitioning and also explains the abrupt pinch-out of all divisions of these sandstones. Estimation of the point of flow transformation is a useful tool in the prediction of heterogeneity distribution in subsurface systems. [ABSTRACT FROM AUTHOR]
- Published
- 2017
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17. Submarine transitional flow deposits in the Paleogene Gulf of Mexico.
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Kane, Ian A. and Pontén, Anna S. M.
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PALEOGENE , *SEDIMENT transport , *TURBIDITES , *LAMINAR flow , *RHEOLOGY - Abstract
Gravity-driven flows on the seafloor are the largest, yet least well understood, sediment transport agents on Earth. Recent exploration wells in ultradeep basins have revealed the presence of large sandy submarine fan systems of enigmatic facies types, many hundreds of kilometers from paleocoastlines. These sedimentary deposits often defy conventional turbidite or debrite interpretations, having a character suggestive of deposition from flows with transient turbulent-laminar rheologies. In the Wilcox Formation (Gulf of Mexico), inferred transitional flow deposits have distinctive stratigraphic stacking patterns, from fine-grained debrites to coarser grained turbidites. The vertical sequence of beds is here inferred to reflect the longitudinal bed distribution in response to lobe progradation, and demonstrates a transition from well-mixed turbulent flow, to progressively more rheologically stratified flow, and eventually to fully laminar flow. The progressive development of internal rheological boundaries resulted in a high-concentration but fluidal basal layer, and an upper quasi-laminar layer with an overriding sheared dilute turbidity current. The long runout of the flows is linked to their high silt and clay content; it is most likely flow expansion at the channel-lobe transition that drives flow transformation. This process-based model may be applicable to many deep-water settings and provides a framework within which to interpret the stratigraphic and spatial distribution of these complex deposits. [ABSTRACT FROM AUTHOR]
- Published
- 2012
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18. Depositional environments in an extensive tide-influenced delta plain, Middle Devonian Gauja Formation, Devonian Baltic Basin.
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PONTÉN, ANNA and PLINK-BJÖRKLUND, PIRET
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SEDIMENTATION & deposition , *EARTH movements , *MARINE sediments , *TIDAL currents , *LAKES - Abstract
The Middle Devonian Gauja Formation in the Devonian Baltic Basin preserves tide-influenced delta plain and delta front deposits associated with a large southward prograding delta complex. The outcrops extend over 250 km from southern Estonia to southern Lithuania. The succession can be divided into 10 facies associations recording distributary channel belts that became progressively more tide influenced when traced southwards towards the palaeo-shoreline, separated by muddy intra-channel areas where deposition was characterized by crevasse splays, delta plain lakes, abandoned channel deposits and tidal gullies. Tidal currents influenced deposition over the entire delta plain, extending up to 250 km from the contemporary shoreline. Tidal facies on the upper delta plain differ from those on the lower delta plain and delta front. In the former case, deposition from river currents was only occasionally interrupted by tidal currents, e.g. during spring tides, resulting in mica and mudstone drapes, and distinctive graded cross-stratification. The lower delta plain was dominated by tidal facies and tidal currents regularly influenced deposition. There was a change from progradation to aggradation from the lower to the upper part of the Gauja Formation coupled with a vertical decrease in tidal influence and a decrease in coarse-grained sediment input. The Gauja Formation contrasts with established models for tide-influenced deltas as the active delta plain was not restricted by topography. The shape of the delta plain, the predominant southward (basinward)-directed palaeocurrents, and the thick sandstone succession, show that although tidal currents strongly influenced deposition at bed scale, rivers still controlled the overall morphology of the delta and the larger-scale bedforms. In addition, there are no signs of wave influence, indicating very low wave energy in the basin. The widespread tidal influence in the Devonian Baltic Basin is explained by changes in the wider basin geometry and by local bathymetrical differences in the basin during progradation and aggradation of the delta plain, with changes in tidal efficiency accompanying the change in basin geometry produced by shoreline progradation. [ABSTRACT FROM AUTHOR]
- Published
- 2007
- Full Text
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19. INSIGHT VS COGNITION AND SYMPTOMATIC REMISSION AMONG PATIENTS WITH SCHIZOPHRENIA- THE INFLUENCE OF TRAIT VS STATE PHENOMENON?
- Author
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Helldin, Lars, Pontén, Anna, Hawar, Moradi, and Olsson, Anna-Karin
- Subjects
SCHIZOPHRENIA ,COGNITION ,CONFERENCES & conventions ,DISEASE remission - Abstract
Background: A high ability to understand symptoms and conceptualize illness, schizophrenia, may play a central role for long-term outcome. This based on the assumption that better insight will promote increased adherence. In this work insight is defined as patients´ ability to experience symptoms and furthermore understand what causes them. Cognitive performance and symptomatic remission are analyzed to explore in what way they are contributing to the level of insight. Methods: The study population is 294 patients with schizophrenia spectrum disorder. Two items with focus on insight, each 1 to 4 points, are used to decide level of insight. The first item “Experience of symptom” and the second item “Understanding the reason for symptoms”, where 1 point representing high and 4 point low level of insight and with a total of 8 points. Patients are then divided into three groups, Good (2 points), Moderate (3 – 5 points) and Poor (6 –8 points). Cognitive domains identified to be impaired in schizophrenia are analyzed related to the three groups of insight. Symptomatic remission is compared to the total score of insight with a Mann-Whitney test and then the different categories of insight in a cross-tabulation and Chi-square test. Results: Differences were found in insight between patients in symptomatic remission and those who are not. This in contrast to when patients were divided into the three insights groups and compared on cognitive performance. Only working memory and neurocognitive flexibility showed significant differences to insight. However, crystalized intelligence, as an expression of over-all cognitive ability, did not. Discussion: In conclusion, only symptomatic remission seems to be related to insight indicating more of a state than a trait phenomenon. Surprisingly could not different levels of insight be connected to differences in cognitive ability. As this is a cross-sectional study, further research are needed where insight and symptomatic remission are analyzed in longitudinal conditions. Such a study has to focus on if successful treatment promote insight or the other way around. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
20. OVERESTIMATING FUNCTION – A RISK FACTOR FOR SUBOPTIMAL COMMUNITY AID IN SCHIZOPHRENIA.
- Author
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Pontén, Anna, Helldin, Lars, Moradi, Hawar, and Olsson, Anna-Karin
- Subjects
CONFERENCES & conventions ,SENSORY perception ,SCHIZOPHRENIA ,SELF-perception ,SOCIAL support - Abstract
Background: Patients with schizophrenia have difficulties in judging their own performance. Patients with no or little practical experience of demands from active performance in society tends to overestimate their ability. Research has also found that patients who overestimate their function also runs a risk to be perceived as better functioning than what they actually are when judged by caregivers. The aim with this study is to examine if patients who overestimate their ability will receive less community support compared to patients who have an accurate perception of their ability? Methods: The study population was 184 patients with schizophrenia spectrum disorder. They were tested with the Swedish version of the UCSD Performance-based Skills Assessment–Brief Version (UPSA-B). Before the test they were asked how they thought their functioning were in four different domains covered in the UPSA-B. After the test they were divided into four groups: “Good functioning with realistic perception”, “Good functioning but underestimating their function”, “Impaired function with realistic perception” and “Impaired function but overestimating their performance”. The amount of received community support were investigated and related to patients´ actual performance and self-perception. Results: Analyzes showed that patients who had an impaired function and a realistic view of their ability had more support than those who were impaired but overestimated their ability. Also, patients with good functioning but underestimating their performance had more support than those who had a good ability and a realistic perception. Finally, there were no difference in community support to the patients in the two groups “Good function with realistic perception” and “Impaired function but overestimating their performance”. Discussion: Our results indicate that patients with impaired functioning who overestimate their ability risk an insufficient community support. This in combination with earlier findings, that staff-members in psychiatric outpatient settings are likely to base their judgement on patients´ report consequential leading to false positive conclusions, may have both short- and long-term implications. Not achieving symptomatic remission, as a consequence of inability to follow medical prescriptions, and sub-optimal social functioning with isolation are two possible implications. The findings once again raises the need for the testing of patients´ function instead of only conducting interviews. [ABSTRACT FROM AUTHOR]
- Published
- 2020
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21. A numerical model of a 3-dimensional low-density turbidity current in the deep ocean: testing hypotheses on turbidity currents in deep detail.
- Author
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Azpiroz-Zabala, Maria, Storms, Joep, van der Vegt, Helena, Walstra, Dirk-Jan, Obradors-Latre, Arnau, and Pontén, Anna
- Published
- 2019
22. Spatial variability in depositional reservoir quality of deep-water channel-fill and lobe deposits.
- Author
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Bell, Daniel, Kane, Ian A., Pontén, Anna S.M., Flint, Stephen S., Hodgson, David M., and Barrett, Bonita J.
- Subjects
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TURBIDITES , *SEDIMENTARY rocks , *LAND consolidation , *HYDROCARBONS , *ORGANIC compounds - Abstract
Abstract Initial porosity and permeability in deep-water systems are controlled by primary sedimentary texture and mineralogy. Therefore, understanding the sedimentary processes that control changes in primary texture is critical for improved reservoir quality predictions. A well-constrained, exhumed submarine lobe in the Jaca Basin, and a submarine channel-fill element in the Aínsa Basin, northern Spain, were studied to characterize the depositional reservoir quality in axial to marginal/fringe positions. Construction of architectural panels and strategic sampling enabled analysis of the spatial changes in textural properties, and their relationship to reservoir quality distribution. Samples were analyzed in thin-section to establish how depositional processes inferred from outcrop observations affect textural properties. Results show that high-density turbidites are concentrated in lobe- and channel-axis positions and exhibit good depositional reservoir quality. Lobe off-axis deposits contain high- and low-density turbidites and have moderate depositional reservoir quality. Conversely, low-density turbidites dominate lobe fringe and channel-margin positions and have relatively poor depositional reservoir quality. There is a sharp decrease in depositional reservoir quality between the lobe off-axis and lobe fringe due to: 1) an abrupt increase in matrix content; 2) an abrupt decrease in sandstone amalgamation; and 3) a decrease in grain-size. There is an abrupt increase in depositional reservoir quality from channel margin to channel axis corresponding to: 1) an increase in total sandstone thickness and amalgamation; 2) an increase in grain-size, 3) a decrease in matrix content. Rates of change of key properties are up to two orders of magnitude greater between channel-fill sub-environments compared to lobe sub-environments. Spatial variability in properties of discrete architectural elements, and rates of changes, provides input to reservoir models during exploration, appraisal, and development phases of hydrocarbon fields. Highlights • Bed- and grain-scale properties mapped in individual architectural elements. • Sediment gravity flow-type controls depositional reservoir quality. • Process-based approach to reservoir quality aids prediction. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
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