41 research outputs found
Modeling of a mixed?load fluvio?deltaic system
No full textPresent?day observations and classical classification schemes of alluvial deltas address feeder channel dynamics and multiple sediment fractions. However, high?resolution physics?based mathematical models have not been applied to address formation of both fluvio?deltaic links (channels) and nodes (diffluences and confluences), and their stratigraphy. Here, we present a simulated delta system under riverine forcing that shows striking similarity to its counterparts recognized in field and laboratory studies. These findings include distinct shifts in river planimetrical mode and altimetry, deltaic mouth bar and distributary formation, lateral fining in migrating?meander bend axes and fining?upward patterns in passive delta?plain distributaries.GeotechnologyCivil Engineering and Geoscience
The impact of changes in sediment supply and sea-level on fluvio-deltaic stratigraphy
No full textStudies in stratigraphy are often driven by the predicted climate change and possible gains for the oil and gas industry. Because, at present predictions of the development of future deltaic architecture are insufficient. This thesis addresses the problem of qualitative and quantitative understanding of sedimentary systems in two stages. In the first stage the stratigraphy of Holocene delta deposits of the Kura and Mahakam deltas (respectively in Azerbaijan en Indonesia) are studied. Results from these studies provide insights as an analogue to ancient systems and serve as an example for expected future conditions. The results form the Kura delta show a prominent role for the rapid sea-level change of the Caspian Sea, while the results of Mahakam delta suggest an important role for the eustatic Holocene sea-level curve and the absence of floods of the Mahakam River. Information obtained from studies in a similar context have the potential to reduce uncertainties and increase confidence in models. The second stage of this thesis covers the development of a process-response simulation model to assess the impact of changes in sediment supply and sea-level on fluvio-deltaic stratigraphy. Anticipating on the dominant role of sediment supply on fluvial dominated deltas, a choice is made for a detailed investigation in how to incorporate good estimates of sediment supply in the numerical model, that enable to explore the possibilities of using a probabilistic approach instead of a deterministic output or geostatistical analysis.Civil Engineering and Geoscience
Process-response simulation of fluvio-deltaic stratigraphy
No full textCivil Engineering and Geoscience
Alignment of fluvio-tidal point bars in the middle McMurray Formation: implications for structural architecture of the Lower Cretaceous Athabasca Oil Sands Deposit, northern Alberta
No full textThe northern Athabasca Oil Sands Deposit accumulated on sub-Cretaceous structure partially configured by multi-stage pre-Cretaceous salt dissolutions in Prairie Evaporite (Middle Devonian) substrate that continued concurrent with deposition of McMurray Formation (Aptian) strata. Dissolution fronts only 250 m below advanced along NW- and NE-oriented fracture-fault lineaments that coalesced into larger salt removal areas. This structural grain was transmitted to the overlying dissected Upper Devonian karst topography draped by lower McMurray braided rivers along a lattice-like channel network. The dominant NW structural grain continued during middle McMurray deposition with fluvial-estuarine point bars aligned along subparallel tidal channels. Regional salt removal fronts concurrent with middle McMurray deposition migrated north of the Bitumount Trough, resulting in the 200 km² central collapse. The northern Athabasca Deposit area was configured as a funnel-shaped lower estuary structure consisting of aligned Upper Devonian-lower McMurray fault block terraces that stepped down northward into the central collapse. Sinuous river channels of the upper estuary, constrained along stable substrate of the main paleovalley, flowed northward onto the unstable floor of this funnel-form lower estuary. The main paleovalley fairway branched into multiple 10s of km long sub-parallel fluvio-estuarine tidal channels aligned parallel to the NW structural grain. Sand transport fairways cascaded over the step down terraces and permitted aggradations of overlying fluvio-tidal point bars to accumulate into giant commercially attractive sand complexes. The internal architecture of these 10s of meters thick sand deposits included deposit-wide erosion surfaces resulting from cycles of collapse-subsidence, stabilized substrate and erosion, and renewed subsidence and aggradation.The presentation of the authors' names and (or) special characters in the title of the pdf file of the accepted manuscript may differ slightly from what is displayed on the item page. The information in the pdf file of the accepted manuscript reflects the original submission by the author
Changjiang Delta in the Anthropocene: Multi-scale hydro-morphodynamics and management challenges
No full textThe Changjiang Delta (CD) is one of well-studied large deltas of critical socio-economical and ecological importance regionally and global representativeness. Cumulated field data and numerical modeling has facilitated scientific understanding of its hydro-morphodynamics at multiple spatial and time scales, but the changing boundary forcing conditions and increasing anthropogenic influences pose management challenges requiring integrated knowledge. Here we provide a comprehensive synthesis of the multi-scale deltaic hydro-morphodynamics, discuss their relevance and management perspectives in a global context, and identify knowledge gaps for future study. The CD is classified as a river-tide mixed-energy, muddy and highly turbid, fluvio-deltaic composite system involving large-scale land-ocean interacted processes. Its hydro-morphodynamic evolution exhibits profound temporal variations at the fortnightly, seasonal, and inter-annual time scales, and strong spatial variability between tidal river and tidal estuary, and between different distributary channels. As the river-borne sediment has declined >70%, the deltaic morphodynamic adaptation lags behind sediment decline because sediment redistribution within the delta emerges to play a role in sustaining tidal flat accretion. However, the deltaic channels have become narrower, deepened and growingly constrained under cumulated human activities, e.g., extensive embankment and construction of jetties and groins, possibly initiating a decrease in morphodynamic activities and sediment trapping efficiency. Overall, the CD undergoes transitions from net sedimentation and naturally slow morphodynamic adaptation to erosion and human-driven radical adjustment. A shift in management priority from delta development to ecosystem conservation provides an opportunity for restoring the resilience to flooding and erosion hazards. The lessons and identified knowledge gaps inform study and management of worldwide estuaries and deltas undergoing intensified human interferences.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Coastal Engineerin
Multi-scale simulation of fluvio-deltaic and shallow marine stratigraphy
No full textSimClast is a basin-scale 3D stratigraphic model, which allows several interacting sedimentary environments. We developed it from 2004 to 2008 at Delft University of Technology and implemented part of the Meijer (2002) code for accounting, loading and storing algorithms. SimClast is a fully plan view 2D, depth-averaged model, allowing the complex interaction between fluvial and wave influences on deltaic and shoreface development to be studied. It focuses on theoretical experiments, as quantitative experiments are intrinsically difficult to recreate in real world settings. Yet there lies the great strength of numerical modelling, as we can improve upon the understanding of these systems by focussing on the process forming and removing the deposits. The modelling applications focus especially on the erosional and nondepositional events as these probably represent the greatest amount of “stratigraphic time”. Short-term, high-resolution processes are coupled with the long-term stratigraphic model by nesting a parameterised version of the high-resolution processes. We extrapolate physical and empirical relationships of the geomorphological development and implement these. A necessary constraint on these long-term models is a relatively large grid sizing (i.e. km scale), as the area to be modelled is on the scale of continental margins and the modelling time is on the scale of many millennia. Areas of special importance are modelled by implementing sub-grid scale processes into a large-scale basin-filling model; this refines the model dynamics and the resulting stratigraphy. Processes included are; fluvial channel dynamics and overbank deposition, river plume deposition, open marine currents, wave resuspension, nearshore wave induced longshore and crosshore transport. This combined modelling approach allows insight into the processes influencing the flux of energy and clastic material and the effect of external perturbations in all environments. Many governing processes work on relatively small scales, e.g. in fluvial settings an avulsion is a relatively localised phenomenon, yet they have a profound effect on fluvial architecture. This means that the model must mimic these processes, but at the same time maintain computational efficiency. Additionally, long-term models use relatively large grid sizing (km scale), as the area to be modelled is on the scale of continental margins. We solve this problem by implementing the governing processes as sub-grid scale routines into the large-scale basin-filling model. This parameterization greatly refines morphodynamic behaviour and the resulting stratigraphy. SimClast recreates realistic geomorphological and stratigraphic delta behaviour in river and wave-dominated settings.GeotechnologyCivil Engineering and Geoscience
Structures périglaciaires syngénétiques dans quelques terrasses fluviatiles du Nord de la France et en Belgique
No full textThe author presents a detailed description of pillar-channels characteristic for the sedimentary structure of some pleistocene terraces. He puts forward a genetic interpretation, stresses their value as an indicator for the fluvio-periglacial nature of the terrace deposit and questions their stratigraphic meaning. He presents a more accurate definition of some terrace-levels in the southern part of the pleistocene Scheldt basin
Three hundred eighty thousand year long stable isotope and faunal records from the Red Sea : influence of global sea level change on hydrography
No full textStable isotope and faunal records from the central Red Sea show high-amplitude oscillations for the past 380,000 years. Positive δ18O anomalies indicate periods of significant salt buildup during periods of lowered sea level when water mass exchange with the Arabian Sea was reduced due to a reduced geometry of the Bab el Mandeb Strait. Salinities as high as 53‰ and 55‰ are inferred from pteropod and benthic foraminifera δ18O, respectively, for the last glacial maximum. During this period all planktonic foraminifera vanished from this part of the Red Sea. Environmental conditions improved rapidly after 13 ka as salinities decreased due to rising sea level. The foraminiferal fauna started to reappear and was fully reestablished between 9 ka and 8 ka. Spectral analysis of the planktonic δ18O record documents highest variance in the orbital eccentricity, obliquity, and precession bands, indicating a dominant influence of climatically - driven sea level change on environmental conditions in the Red Sea. Variance in the precession band is enhanced compared to the global mean marine climate record (SPECMAP), suggesting an additional influence of the Indian monsoon system on Red Sea climates
Organic biogeochemical study of deeper southeastern Bengal Basin sediments in West Bengal, India
No full textThe Bengal Basin is a fluvio-deltaic basin spanning Bangladesh and part of east and northeast India. The evolution of the peripheral foreland basin has been studied, but published literature on depositional conditions, source and maturity of organic matter in the deeper sediments of the Indian section of the basin is rare, despite the fact that natural gas is often encountered during hydrocarbon exploration. Our research assesses the depositional environment and source of the organic matter (OM) in the Pleistocene-Miocene sediments from five wells drilled by Oil and Natural Gas Corporation Limited in the southeastern Bengal Basin, West Bengal, India and aims to understand its maturity and potential to yield natural gas. The total organic carbon/nitrogen ratio and stable isotope (δ13C and δ15N) signature indicate primarily aquatic and C3 terrestrial plant sources of the OM and deposition under tidal flat and marshy environments. The n-alkane and isoprenoid alkane distribution are consistent with an autochthonous source of OM and terrestrial oxic-suboxic shallow-water depositional setting. The Rock-Eval parameters, such as maximal pyrolysis temperature, hydrogen and oxygen indices, indicate the immature nature of Type III and Type IV kerogen. The presence of methanogenic archaea, as indicated by phylogenetic analysis, in two Miocene sediment samples from one well indicates an active microbial activity in Type III immature OM, derived from C3 marsh vegetation and deposited under oxic shallow-water conditions. Our research describes the presence of methanogenic archaea for the first time in Miocene Bengal Basin sediments and is one of the few reports of their presence in deep (> 4000 m) horizons.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Sanitary Engineerin
