Recognising tectonic and climatic signals in the Paleogene stratigraphy offshore Norway

2020 ◽  
Author(s):  
Tor O. Sømme ◽  
Jakob Skogseid ◽  
Patricia Embry ◽  
Helge Løseth
Keyword(s):  
Seismic Data ◽  
Supply System ◽  
Sediment Supply ◽  
Sediment Flux ◽  
Similar Process ◽  
System Response ◽  
Seismic Reflection Data ◽  
Shelf Slope ◽  
Depositional System

<p>Landscapes and their sediment routing systems can be exposed to various tectonic and climatic perturbations that affect sediment production, transport and delivery to nearby sedimentary basins. Here we investigate a Paleogene depositional system offshore western Norway that was subjected to long-term (~10 Myr) tectonic perturbation and significant hinterland erosion. Superimposed on this long-term uplift, the system was also subjected to a short-lived climatic perturbation during the Paleocene-Eocene Thermal Maximum (PETM), which lasted ~200 kyr. Regional 3D seismic reflection data is integrated with high resolution well data to map the stratigraphic response to these different scales of perturbations on the depositional system. The initiation of the tectonic perturbation is marked by an angular unconformity in seismic data. A rapid increase in sediment flux followed, causing initial progradation of a shelf-slope wedge. Sediment supply estimates indicate that the tectonic uplift caused an order of magnitude increase in sediment flux to the basin, which peaked in the latest Paleocene. This period coincided with the PETM, which is documented by biostratigraphic data as a discrete event within the overall regressive system. Although the PETM often is characterised by increased continental runoff, no increase in sediment supply is evident from seismic data. This work shows that the system response to tectonic and climatic perturbations may vary along strike, depending on the size of the routing systems and the antecedent topography prior to hinterland uplift. A low supply system may produce a tectonically-linked shelf-slope wedge that is of similar thickness as a climatically-linked wedge in a high supply system. This study documents how the same routing system responded to perturbations operating at different spatial and temporal scales and may help recognise similar process-response relationships in other areas.</p>

scholarly journals Bedrock incision by bedload: insights from direct numerical simulations

2016 ◽  
Author(s):  
Guilhem Aubert ◽  
Vincent J. Langlois ◽  
Pascal Allemand
Keyword(s):  
Numerical Approach ◽  
Sediment Supply ◽  
Sediment Flux ◽  
Analytical Models ◽  
Water Stream ◽  
Direct Measurements ◽  
Bedload Sediment ◽  
Discrete Element Simulations ◽  
High Sediment

Abstract. Bedload sediment transport is one of the main processes that contribute to bedrock incision in a river and is therefore one of the key control parameters in the evolution of mountainous lanscapes. In recent years, many studies have addressed this issue through experimental setups, direct measurements in the field or various analytical models. In this article, we present a new direct numerical approach: using the classical methods of discrete element simulations applied to granular materials, we compute explicitely the trajectories of a number of pebbles entrained by a turbulent water stream over a rough solid surface. This method allows us to extract quantitatively the amount of energy that successive impacts of pebbles deliver to the bedrock, as a function of both the amount of sediment available and the Shields number. We show that we reproduce qualitatively the behaviour observed experimentally by Sklar and Dietrich (2001) and observe both a "tool-effect" and a "cover- effect". Converting the energy delivered to the bedrock into an average long-term incision rate of the river leads to predictions consistent with observations in the field. Finally, we reformulate the dependency of this incision rate with Shields number and sediment flux, and predict that the cover term should decay linearly at low sediment supply and exponentially at high sediment supply.

Revealing tectonic evolution across the Northeastern Flemish Cap-Goban Spur margin

2020 ◽  
Author(s):  
Pei Yang ◽  
J.Kim Welford
Keyword(s):  
Seismic Data ◽  
Potential Field ◽  
Field Data ◽  
Velocity Structure ◽  
Crustal Thickness ◽  
Borehole Data ◽  
Seismic Reflection Data ◽  
Potential Field Data ◽  
Shelf Slope ◽  
Goban Spur

<p>In past years, a good understanding of the structure and tectonics of the Flemish Cap and the Goban Spur margin has been obtained based on seismic data, potential field data, and borehole data. However, due to limited data coverage and quality, the rift-related domains along the margin pair have remained poorly defined and their architecture has been primarily delineated on the basis of a small number of co-located 2-D seismic profiles. In addition, according to previous studies, the geophysical characteristics (e.g. velocity structure, crustal thickness, seismic patterns, etc.) across both the margins are strikingly different. Furthermore, from restored models of the southern North Atlantic, some scholars argue against the linkage of the Goban Spur and the Flemish Cap, questioning the widely-accepted “conjugate” relationship of the two margins. However, these restored models are mainly dependent on potential field data analysis, lacking seismic constraints, particularly for the Irish Atlantic Margin.</p><p>In this study, new long offset 2D multichannel seismic data, acquired in 2013 and 2014 by Eni Ireland for the Department of Communications, Climate Action & Environment of Ireland, cover the shelf, slope, and deepwater regions of the offshore Irish Altlantic margin. Combining these with seismic reflection data at the NE Flemish Cap, seismic refraction data, DSDP drilling sites, gravity and magnetic maps, crustal thickness maps, and oceanic isochrones, we integrate all constraints together to characterize the structure and evolution of both margins. These geophysical data reveal significant along-strike structural variations along both margins, and aid to delimit five distinct crustal zones related to different rifting stages and their regional extents. The geometries of each crustal domain are variable along the margin strike, probably suggestive of different extension rates during the evolution of the margin and/or inherited variations in crustal composition and rheology. Particularly, the along-strike exhumed serpentinized mantle domain of the Goban Spur margin spans a much wider (~ 42 - 60 km) area while it is much narrower (~25 km) at the NE Flemish Cap margin. In the exhumed domain, only peridotite ridges are observed at the Flemish Cap, while both peridotite ridges and a wide region of exhumed mantle with deeper basement are observed at the Goban Spur, indicative of a more complex evolutionary model than previously thought for both margins. Plate reconstruction of the Goban Spur and the Flemish Cap using GPlates reveals asymmetry in their crustal architectures, likely due to rift evolution involving more 3-D complexity than can be explained by simple 2-D extensional kinematics. In spite of uncertainties, the crustal architecture comparison between the two margins provides 3D seismic evidence related to the temporal and spatial rifting evolution on both sides.</p>

scholarly journals Bedrock incision by bedload: insights from direct numerical simulations

2016 ◽  
Vol 4 (2) ◽  
pp. 327-342 ◽  
Author(s):  
Guilhem Aubert ◽  
Vincent J. Langlois ◽  
Pascal Allemand
Keyword(s):  
Numerical Approach ◽  
Sediment Supply ◽  
Sediment Flux ◽  
Analytical Models ◽  
Water Stream ◽  
Direct Measurements ◽  
Mountainous Landscapes ◽  
Bedload Sediment ◽  
Discrete Element Simulations

Abstract. Bedload sediment transport is one of the main processes that contribute to bedrock incision in a river and is therefore one of the key control parameters in the evolution of mountainous landscapes. In recent years, many studies have addressed this issue through experimental setups, direct measurements in the field, or various analytical models. In this article, we present a new direct numerical approach: using the classical methods of discrete-element simulations applied to granular materials, we explicitly compute the trajectories of a number of pebbles entrained by a turbulent water stream over a rough solid surface. This method allows us to extract quantitatively the amount of energy that successive impacts of pebbles deliver to the bedrock, as a function of both the amount of sediment available and the Shields number. We show that we reproduce qualitatively the behaviour observed experimentally by Sklar and Dietrich (2001) and observe both a "tool effect" and a "cover effect". Converting the energy delivered to the bedrock into an average long-term incision rate of the river leads to predictions consistent with observations in the field. Finally, we reformulate the dependency of this incision rate with Shields number and sediment flux, and predict that the cover term should decay linearly at low sediment supply and exponentially at high sediment supply.

scholarly journals Did the Construction of the Bhumibol Dam Cause a Dramatic Reduction in Sediment Supply to the Chao Phraya River?

Water ◽  
2021 ◽  
Vol 13 (3) ◽  
pp. 386
Author(s):  
Matharit Namsai ◽  
Warit Charoenlerkthawin ◽  
Supakorn Sirapojanakul ◽  
William C. Burnett ◽  
Butsawan Bidorn
Keyword(s):  
Saltwater Intrusion ◽  
River System ◽  
Sediment Supply ◽  
Sediment Flux ◽  
Hydroelectric Power ◽  
Chao Phraya River ◽  
The Impact ◽  
Total Sediment ◽  
Hydroelectric Power Generation

The Bhumibol Dam on Ping River, Thailand, was constructed in 1964 to provide water for irrigation, hydroelectric power generation, flood mitigation, fisheries, and saltwater intrusion control to the Great Chao Phraya River basin. Many studies, carried out near the basin outlet, have suggested that the dam impounds significant sediment, resulting in shoreline retreat of the Chao Phraya Delta. In this study, the impact of damming on the sediment regime is analyzed through the sediment variation along the Ping River. The results show that the Ping River drains a mountainous region, with sediment mainly transported in suspension in the upper and middle reaches. By contrast, sediment is mostly transported as bedload in the lower basin. Variation of long-term total sediment flux data suggests that, while the Bhumibol Dam does effectively trap sediment, there was only a 5% reduction in sediment supply to the Chao Phraya River system because of sediment additions downstream.

scholarly journals Chemical stability of oil-infused polyethylene

2020 ◽  
pp. 088532822097735
Author(s):  
Fedra P Zaribaf ◽  
Harinderjit S Gill ◽  
Elise C Pegg
Keyword(s):  
Vitamin E ◽  
Chemical Stability ◽  
Antioxidant Properties ◽  
Oxidation Stability ◽  
Thermal Ageing ◽  
Similar Process ◽  
Mechanical Degradation ◽  
Suitable Material ◽  
Thermally Treated

Ultra-high molecular weight polyethylene (UHMWPE) can be made radiopaque for medical imaging applications through the diffusion of an iodised oil-based contrast agent (Lipiodol Ultra Fluid). A similar process is used for Vitamin E incorporated polyethylene which provides antioxidant properties. This study aimed to investigate the critical long-term properties of oil-infused medical polyethylene after 4 weeks of accelerated thermal ageing. Samples treated with an oil (Vitamin E or Lipiodol) had a higher oxidation stability than currently used medical grade polyethylene, indicated by a smaller increase in oxidation index after ageing (Vitamin E + 36%, Lipiodol +40%, Untreated +136%, Thermally treated +164%). The tensile properties of oil treated polyethylene after ageing were significantly higher than the Untreated and Thermally treated controls (p<0.05) indicating less mechanical degradation. There was also no alteration in the percentage crystallinity of oil treated samples after ageing, though the radiopacity of the Lipiodol treated samples reduced by 54% after ageing. The leaching of oil with time was also investigated; the leaching of Lipiodol and Vitamin E followed the same trend and reached a steady state by two weeks. Overall, it can be concluded that the diffusion of an oil-based fluid into polyethylene not only increases the oxidative and chemical stability of polyethylene but also adds additional functionality (e.g. radiopacity) providing a more suitable material for long–term medical applications.

Potentially Large Subsurface Gas Hydrate Bodies in the Mexican Ridges, Southwestern Gulf of Mexico

2021 ◽  
pp. 1-29
Author(s):  
Papia Nandi ◽  
Patrick Fulton ◽  
James Dale
Keyword(s):  
Gulf Of Mexico ◽  
Gas Hydrate ◽  
Seismic Data ◽  
Poor Quality ◽  
Reflection Point ◽  
Seismic Reflection Data ◽  
Reflection Data ◽  
High Impedance ◽  
Acoustic Velocities ◽  
Seismic Images

As rising ocean temperatures can destabilize gas hydrate, identifying and characterizing large shallow hydrate bodies is increasingly important in order to understand their hazard potential. In the southwestern Gulf of Mexico, reanalysis of 3D seismic reflection data reveals evidence for the presence of six potentially large gas hydrate bodies located at shallow depths below the seafloor. We originally interpreted these bodies as salt, as they share common visual characteristics on seismic data with shallow allochthonous salt bodies, including high-impedance boundaries and homogenous interiors with very little acoustic reflectivity. However, when seismic images are constructed using acoustic velocities associated with salt, the resulting images were of poor quality containing excessive moveout in common reflection point (CRP) offset image gathers. Further investigation reveals that using lower-valued acoustic velocities results in higher quality images with little or no moveout. We believe that these lower acoustic values are representative of gas hydrate and not of salt. Directly underneath these bodies lies a zone of poor reflectivity, which is both typical and expected under hydrate. Observations of gas in a nearby well, other indicators of hydrate in the vicinity, and regional geologic context, all support the interpretation that these large bodies are composed of hydrate. The total equivalent volume of gas within these bodies is estimated to potentially be as large as 1.5 gigatons or 10.5 TCF, considering uncertainty for estimates of porosity and saturation, comparable to the entire proven natural gas reserves of Trinidad and Tobago in 2019.

Feasibility of sedimentation strategies for the Mekong delta to counterbalance relative sea-level rise

2021 ◽  
Author(s):  
Frances E. Dunn ◽  
Philip S. J. Minderhoud
Keyword(s):  
Land Use ◽  
Sea Level Rise ◽  
Sea Level ◽  
Mekong Delta ◽  
Sediment Deposition ◽  
Sediment Supply ◽  
Sediment Flux ◽  
Relative Sea Level ◽  
Fluvial Sediment ◽  
Relative Sea Level Rise

&lt;p&gt;As one of the largest deltas in the world, the Mekong delta is home to over 17 million people and supports internationally important agriculture. Recently deposited sediment compacts and causes subsidence in deltas, so they require regular sediment input to maintain elevation relative to sea level. These processes are complicated by human activities, which prevent sediment deposition indirectly through reducing fluvial sediment supply and directly through the construction of flood defence infrastructure on deltas, impeding floods which deliver sediment to the land. Additionally, anthropogenic activities increase the rate of subsidence through the extraction of groundwater and other land-use practices.&lt;/p&gt;&lt;p&gt;This research shows the potential for fluvial sediment delivery to compensate for sea-level rise and subsidence in the Mekong delta over the 21st century. We use detailed elevation data and subsidence scenarios in combination with regional sea-level rise and fluvial sediment flux projections to quantify the potential for maintaining elevation relative to sea level in the Mekong delta. We present four examples of localised sedimentation scenarios in specific areas, for which we quantified the potential effectiveness of fluvial sediment deposition for offsetting relative sea-level rise. The presented sediment-based adaptation strategies are complicated by existing land use, therefore a change in water and sediment management is required to effectively use natural resources and employ these adaptation methods. The presented approach could be an exemplar to assess sedimentation strategy feasibility in other delta systems worldwide that are under threat from sea-level rise.&lt;/p&gt;

Embedding compaction processes in long-term evolution modeling of tidal marshes

2021 ◽  
Author(s):  
Riccardo Xotta ◽  
Claudia Zoccarato ◽  
Philip S. J. Minderhoud ◽  
Pietro Teatini
Keyword(s):  
Numerical Model ◽  
Marsh Surface ◽  
Long Term Evolution ◽  
Sediment Supply ◽  
Tidal Marshes ◽  
High Porosity ◽  
Fe Method ◽  
Geomechanical Properties ◽  
Term Evolution

&lt;p&gt;Tidal marshes are vulnerable and dynamic ecosystems with essential roles from protection against marine storms to biodiversity preservation. However, the survival of these environments is threatened by external stressors such as increasing mean sea level, reduction in sediment supply, and erosion. Tidal marshes are formed by deposition over the last centuries to millennia of sediments transported by surface water and biodegradation of organic matter derived from halophytic vegetation. Therefore, the sediment at the surface is characterized by high porosity and their large consolidation potential plays an important role in the future elevation dynamics, which is often not fully recognized.&lt;/p&gt;&lt;p&gt;Here we propose a novel three-dimensional numerical model to simulate the long-term dynamics of tidal marshes. A 3D groundwater flow equation in saturated conditions is implemented to compute the over-pressure dissipation with the aid of the finite element (FE) method, whereas the sediment consolidation is computed according to Terzaghi's theory.&lt;/p&gt;&lt;p&gt;A Lagrangian approach is implemented in the FE numerical model to properly consider the large soil deformation arising from the deposition of highly compressible material. The hydro-geomechanical properties, that depend on the intergranular effective stress, are highly non-linear.&lt;/p&gt;&lt;p&gt;The model takes advantage of a dynamic mesh that simulates the evolution of the landform elevation by means of an accretion/compaction mechanism: the elements deform in time as the soil consolidates and increase in number as the new sediments deposit over the marsh surface. The deposition is treated as input to the consolidation model and can vary in space and time.&lt;/p&gt;&lt;p&gt;The model is applied to simulate the long-term evolution of realistic tidal marshes in terms of accretion and consolidation due to the coupled dynamics of surficial and subsurface processes.&lt;/p&gt;

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