Geolunch seminar @ UiB

Matteo Demurtas
2022-04-27 00:00 - 13:00 (Europe/Oslo) | Kontinentalsokkelen (2G16e), Realfagbygget, Allégaten 41, Bergen, 5007, Norway
Fracturing and force distribution during shearing in bimaterial gouges
Fault gouges are amongst the main products of strain accommodation in the brittle upper crust. During shear, fracturing has a direct effect on grain size (and shape) evolution and ultimately grain-grain interactions. Such changes are believed to influence how stress is accommodated within the gouge and therefore control the mechanical and petrophysical properties of granular materials. Recent observations of both natural and experimental strain localisation features have highlighted the potential for compositional anisotropy within a deforming rock to play a key role in control fracturing processes. As a result, the occurrence of a polyphasic mineral assemblage in natural gouges may strongly influence the rheology of a fault during deformation. Numerical simulations using the Discrete Element Method (DEM) approach have proved, in recent years, to be a powerful tool in revealing grain scale processes associated with frictional sliding of granular fault gouges. Such an approach affords us unusual access inside a deforming material to precisely track the active grain processes and how they interact and evolve. We performed DEM simulations designed to investigate the influence of a bimaterial mineral assemblage on fracturing, grain size distribution evolution, force and stress distribution within a deforming gouge applied to the carbonate system, with a calcite-dolomite mixture. Our simulations show how even small amounts (c. 20%) of a more competent phase can results already in significant changes in the fracturing processes occurring during shearing, ultimately bearing the potential of controlling its slip behaviour.

Åse Hestnes
2022-03-30 12:00 - 13:00 | Kontinentalsokkelen (2G16e), Realfagbygget, Allégaten 41, Bergen, 5007, Norway
Preliminary results from apatite thermochronology and U-Pb calcite geochronology – insight into the topographic evolution of Western Norway

Hestnes, Å.1, Jacobs, J.1, Drost, K.2, Dunkl, I.3, Gasser, D.4,5, Ksienzyk, A.K.5, Scheiber, T.4, Sømme, T.1,6, Mayer-Ullmann, F.1, Chew, D.2
1 Department of Geoscience, University of Bergen
2 Department of Geology, Trinity College Dublin, The University of Dublin
3 Sedimentology and Environmental Geology, Geoscience Centre, University of Göttingen
4 Department of Environmental Sciences, Western Norway University of Applied Sciences, Campus Sogndal
5 Geological Survey of Norway
6 Equinor, Oslo

By using apatite in thermochronological studies, we can unravel the cooling history, and thus potentially the erosion history of the uppermost continental crust (<120°C). We have collected an extensive dataset for thermochronological studies from Western Norway, located between the Sognefjorden in the south and the Møre Margin in the north. During Geolunch, I will present new results from both Apatite Fission Track (AFT) and (U-Th)/He apatite thermochronology. These data are combined to make time-temperature models, both for single samples and as a multi-model of a vertical profile. Such a multi-model of a vertical profile has not been done before in Norway and I will illustrate how it can be used as a tool to understand the topographic evolution of a region. In addition, I will show the results from the first U-Pb Calcite analyses done in Norway.

Prof Cathy Hollis
2022-03-23 12:00 - 13:00 | Kontinentalsokkelen (2G16e), Realfagbygget, Allégaten 41, Bergen, 5007, Norway
Limestones: an essential user guide to sediments that dissolve, precipitate and grow
Carbonate sedimentary rocks form through the accumulation of organisms and chemically precipitated calcium carbonate, usually on the sea floor. They preserve fragments of marine organisms, which are sensitive to temperature, salinity and seawater chemistry during their growth, and they therefore provide an exceptional record of evolutionary and climatic change through Earth history. Carbonate sediments are also highly reactive, dissolving and precipitating in surface water. For these reasons, despite their simple mineralogy, they have a reputation for being difficult to understand and many clastic sedimentologists approach them with caution!
Nevertheless, carbonate sedimentary rocks are important for many reasons. They have been exploited for millenia for their minerals, water resources and, more recently, for cement, roadstone and hydrocarbon. Now, as we face the effects of climate change, we can use carbonate strata to understand how Earth responds to environmental stress and use this knowledge to better predict the effect of climate change on modern ecosystems. There is also growing interest in how carbonate sedimentary rocks can be used to good effect for carbon storage and geothermal heat production. This talk will provide an introduction to carbonate sedimentology and the principle processes that govern their formation and modification during lithification. It will illustrate their importance to our modern landscape and heritage and demonstrate how ancient carbonate systems can hold warnings, and solutions, to the effects of anthropogenic environmental impact.

Professor Cathy Hollis
Chair of Carbonate Geoscience
The University of Manchester, UK

cathy.hollis@manchester.ac.uk
Cathy Hollis a geologist with a particular interest in low temperature fluid-rock reactions, geochemistry and petrophysics in sedimentary rocks. She is the research group lead for the Basins, Stratigraphy and Sedimentary Processes group in the Department of Earth and Environmental Science. She is also Adjunct Professor of Carbonate Geoscience at University of Bergen. Her work focuses on the origin, evolution and occlusion of porosity in carbonate strata utilising outcrop, subsurface core and geophysical data alongside geochemical proxies. She is particularly interested in how limestones react and transform to dolomite and how minerals precipitate and dissolve from fluids in sedimentary basins. Cathy is the principal investigator on a joint industry research consortium (PD3) with Universities of Bergen, Bristol and Liverpool, and collaborates with research groups in Canada, Qatar and France. She has extensive knowledge of the Lower Carboniferous Limestone of the UK, and she is leading a NERC funded project to assess the impact of hydrothermal karst on fluid flow. This work will be important to planning low-carbon, sustainable geothermal energy projects, which will be an essential part of our transition to net zero. Cathy has published over 45 papers in international, peer-reviewed journals in the last 10 years and graduated more than 15 PhD candidates in that time. She has a PhD from University of Aberdeen and prior to joining University of Manchester, in 2007, she worked for Badley Ashton and Associates Ltd in the UK and UAE (1995-2001) and Shell International Exploration and Production in The Netherlands (2001-2007).

Flávio Norberto de Almeida Junior
2022-02-23 12:00 - 13:00
Hyperpycnal flows: are they sediment-gravity flows?
Authors: Flávio N. de Almeida Júnior & Ronald Steel
Hyperpycnal flow is a process involving the underflow of denser material through sediment-laden river currents that enter lighter ambient water, e.g., lake or seawater. Relatively high suspended sediment concentration in the river flow is often the main cause of the high flow density forcing the river-discharge to plunge in the area of the river mouth. Sediment particles make hyperpycnal flows denser than the water they displace, otherwise fresh water would be lighter than seawater, so that many authors ubiquitously consider hyperpycnal flow as a type of sediment-gravity flow. Hyperpycnal flow models also idealize a hydraulic continuum between the fluvial current and the plunging of hyperpycnal flow, in the notion that hyperpycnal flow discharges beyond the river mouth into ambient water would have velocity profiles and duration approximate to the parental river currents.
However, recent studies show that : (i) the initiation of underflows may occur from extremely dilute river plumes so that any defined value of threshold sediment-concentration is not enough to explain the plunging of river discharges – thus, the notion of denser does not directly equate to excess of sediment-mass (volume x density) or sediment gravity transport in the flow; (ii) not all energy fluctuations in hyperpycnal flows are necessarily a function of river hydrography; and (iii) large-magnitude river floods do not necessarily imply high sediment concentration or hyperpycnal flows, and not all sediment-gravity currents generated during river-flood periods must necessarily be of hyperpycnal origin (e.g., slope collapse at Squamish Delta during river flood periods). All the above constraints are allusive: fluid mechanics of hyperpycnal flows are mired in controversy, and there has been a fuzzy use of the term ‘hyperpycnal flow’ since its early definition – in particular regarding the connection between river dynamics and hyperpycnal flows. Hence, there is still uncertainty on how to recognize the deposits of hyperpycnal flows in the sedimentary record.
This presentation aims to bridge between hydrodynamic processes and the deposits of riverine hyperpycnal flows by critically analyzing what is known-to-date from experiments, modern environments and the empirical evidence. We therefore propose a novel classification for hyperpycnal-flows based on the concept of discharge momentum, in which initial conditions of discharge momentum at river flow unconfinement and its subsequent dissipation into ambient water would primarily constrain hyperpycnal flow parameters. This approach allowed distinction of three hyperpycnal-flow types, which not all actually represent sediment-gravity flows. For the first time, we provide a simple resolution that links river-discharge hydrodynamics to hyperpycnal flows that can be used as diagnostic criterion for the identification of hyperpycnal-flow deposits (or hypepycnites) on strata. We support our arguments with published literature and new diagnostic field data from the Early-Middle Jurassic Lajas and Los Molles formations in the southernmost Neuquén Basin, Argentina.

Vincent Wicker
2022-02-16 12:00 - 13:00 | Kontinentalsokkelen (2G16e), Realfagbygget, Allégaten 41, Bergen, 5007, Norway
Transition from Aegean back-arc extension to Corinth rifting. Miocene to Pleistocene interacting extensional regimes of the Northern Peloponnese.
Vincent Wicker1, Mary Ford1, Robert Gawthorpe2, Haralambos Kranis3, Emmanuel Skourtsos3, Pierre Bouilhol1, Martin Muravchik2, Natacha Fabregas2, Kévin Beaufumé4, Hugo Beldame5
1 – University of Lorraine, CRPG-CNRS, Nancy, France; 2 – University of Bergen, Norway; 3 – National and Kapodistrian University of Athens, Greece; 4 – Perenco, UK; 5 – ENSG Nancy, University of Lorraine, France
Continental extension is characterized by two end members: rifting and highly extended terrains. These two modes of extension usually develop under very different conditions and are rarely observed together. However, in the northern Peloponnese, metamorphic windows recording Miocene late orogenic to back arc extension of the Southern Hellenides on low angle detachments, lie directly south of the younger Pliocene-Pleistocene Corinth rift and appear to interact with its southern margin fault system. This work integrates data from a recent structural and stratigraphic field campaign from the Central Peloponnese to the Corinth rift southern margin with regional cross-sections to document the style of regional Miocene to Pliocene extensional tectonics and the transition from the wide extensional regime to the narrow Corinth rifting. It shows that the pre-rift Hellenides nappe stack was stretched by about 15-25 km by low angle extensional faults that root into the Cretan detachment that forms the main decoupling level in this area. These low-angle extensional faults contribute to the exhumation of the Quartzite-Phyllite metamorphic nappe and contribute to the continental unroofing of the Southern Hellenides. New field data in the northern Peloponnese indicate that continental sedimentation controlled by these low angle normal faults underlies in apparent continuity the Corinth syn-rift succession, which is itself controlled by later high angle rift faults. We integrate in a regional structural model the transition from the pre-rift Aegean extensional tectonic regime to early-stage Corinth rifting recorded in newly mapped depocenters located in the south-eastern Corinth basin between Stymfalia and Nemea.

Gang Lu
2021-12-01 12:00 - 13:00 | Kontinentalsokkelen (2G16e), Realfagbygget, Allégaten 41, Bergen, 5007, Norway
Magmatism at Atlantic volcanic rifted margins: When do we need mantle plumes?
Breakup volcanism along rifted passive margins is highly variable in time and space. The factors controlling magmatic activity during continental rifting and breakup are not resolved and controversial. Here we use numerical models to investigate melt generation at rifted margins with contrasting rifting styles corresponding to those observed in natural systems. Our results demonstrate a surprising correlation of enhanced magmatism with margin width. This relationship is explained by depth-dependent extension, during which the lithospheric mantle ruptures earlier than the crust, and is confirmed by a semi-analytical prediction of melt volume over margin width. The results presented here show that the effect of increased mantle temperature at wide volcanic margins is likely over-estimated, and demonstrate that the large volumes of magmatism at volcanic rifted margin can be explained by depth- dependent extension and very moderate excess mantle potential temperature in the order of 50–80 °C, significantly smaller than previously suggested.

Enry Horas Sihombing
2021-11-17 12:00 - 13:00 | Kontinentalsokkelen (2G16e), Realfagbygget, Allégaten 41, Bergen, 5007, Norway
Form And Fill of A Transtensional Lacustrine Rift Basin: Lower Talangakar Formation, Jatibarang Subbasin, Offshore NW Java, Indonesia

Felix Halpaap
2021-11-10 12:00 - 13:00 | Geomorphology room 3F14, allegaten 41, Bergen, 5020, Norway
Tracing tectonically active faults with the smallest earthquakes:​ sensitive detection of the 2021 Bitdalsvatnet earthquake swarm​

Thomas Theunissen
2021-11-03 12:00 - 13:00 | Kontinentalsokkelen (2G16e), Realfagbygget, Allégaten 41, Bergen, 5007, Norway
Topography during Pangea Breakup – Case of the South Atlantic Central Segment – 2-D thermo-mechanical modelling and implications for salt basin formation

In this study we use observations from the central South Atlantic conjugate margins to constrain
the structural style of rifting and its relation with sedimentary basin evolution during
the syn and early post-rift. Three synthetics transects from North (Gabon-Brazil) to South
(Angola-Brazil) are used to constrain fault distribution, margin width, crustal thickness,
distribution of magmatism, syn-rift sedimentary section thickness and paleo-environment
from the start of rifting in the Berriasian (145 Ma) until the early post rift in the Aptian (114 Ma).
This integrated study aims to understand variations in along strike structural style,
magmatic output, and sedimentary basin evolution to assess the contribution of
mantle processes on topography using forward 2-D thermo-mechanical modelling.
We design a model setup that reproduces South Atlantic central segment main characteristics
before rifting. We then explore the effect of sedimentation rate on subsidence and the effect of
mantle temperature on topography. The model accounts for decompression melting with feedbacks
on temperature, viscosity and density of the mantle. The subsidence in the thermo-mechanical
models is calibrated with a reference mid-ocean ridge elevation, where a 6 km thick oceanic crust
is predicted, and explained by the different contributions on buoyancy of rifted passive
margin during rifting. We discuss conditions to get magma-poor margins and conditions
to reach a small topographic gradient and shallow water environment between the proximal
and distal domains over more than 200 km of the wide margin during most of the syn-rift.

Gang Lu
2021-10-29 12:00 - 13:00 | Geomorphology room 3F14, allegaten 41, Bergen, 5020, Norway
Potential temperature and depth-dependent extension control melt volume at Atlantic volcanic margins
Breakup volcanism along rifted passive margins is highly variable in time and space. The
factors controlling magmatic activity during continental rifting and breakup are not resolved
and controversial. Here we use numerical models to investigate melt generation at rifted
margins with contrasting rifting styles corresponding to those observed in natural systems.
Our results demonstrate a surprising correlation of enhanced magmatism with margin width.
This relationship is explained by depth-dependent extension, during which the lithospheric
mantle ruptures earlier than the crust, and is confirmed by a semi-analytical prediction of
melt volume over margin width. The results presented here show that the effect of increased
mantle temperature at wide volcanic margins is likely over-estimated, and demonstrate that
the large volumes of magmatism at volcanic rifted margin can be explained by depthdependent
extension and very moderate excess mantle potential temperature in the order of
50–80 °C, significantly smaller than previously suggested.

Ritske Huismans
2021-10-27 12:00 - 13:00 | Kontinentalsokkelen (2G16e), Realfagbygget, Allégaten 41, Bergen, 5007, Norway
Preliminary results from IODP Expedition 396 – Mid Norwegian Continental Margin Magmatism

Irfan Baig
2021-10-20 12:00 - 13:00 | Kontinentalsokkelen (2G16e), Realfagbygget, Allégaten 41, Bergen, 5007, Norway
Quaternary basin fill and evolution of the North Sea Basin: A synthesis of sequence stratigraphy and basin modeling techniques
by Baig, Irfan; Faleide, Jan Inge; Aagaard, Per; Chuahan, Teena; Hjelstuen, Berit Oline Blihovde & Sejrup, Hans Petter

Lucas Valore
2021-10-06 12:00 - 13:00 | Kontinentalsokkelen (2G16e), Realfagbygget, Allégaten 41, Bergen, 5007, Norway
Large Igneous Provinces, hydrovolcanism and paleoenvironments/paleohydrology: lessons from the Paraná Basin in South Brazil
In many continental flood basalt provinces (CFBPs), primary mafic volcaniclastic deposits have been shown to be significant counterparts of better-known effusive (lava flow) facies, a notion that challenged traditional views of CFB stratigraphy some decades ago. Many of such deposits have been linked to hydrovolcanic phenomena, which are basically all sorts of magma – water interaction that induce magma fragmentation and create specific types of volcaniclastic deposits. At the time, some studies linked this to how LIPs have been able to induce massive extinctions in the geological record. Until the early 2000s, one of the only exceptions to this was the Paraná Igneous Province in South America, where the enormous amounts of lavas from the so-called Serra Geral Group were emplaced above a seemingly completely arid paleoerg (Botucatu). However, this was later shown to not be entirely true, as during syn-volcanic times multiple types of humid environments have been recorded – many have been responsible for the repeated formation of peperites, a volcanic breccia with sedimentary matrix that in this case is formed as lava flows invade bodies of humid sediment. Further studies have shown that other hydrovolcanic deposits also exist in Paraná, although this has stirred a lot of controversy. These include pillow lavas, hydrothermal injectites and pyroclastic rocks – the latter, which were my main focus during my master’s, will be the main subject of the talk. Ultimately, detailed mapping of these facies show that they are far from being the exception, and that perhaps the volcanic activity is somehow linked to this change in paleoenvironmental conditions.

Leonardo Pichel
2021-09-17 12:00 - 13:00 | Kvartsitten, 3rd floor, Realfalbygget, Bergen, 5020, Norway
Coupling crustal-scale rift architecture with rifted margin salt tectonics: a geodynamic modelling approach
Many rifted passive margins are associated with widespread and thick evaporite (i.e., salt) deposits, and pronounced syn-and post-rift salt tectonics. The majority and largest salt basins known-to-date formed during the latest stages of rifting, immediately prior to continental breakup. We use 2D thermo-mechanically coupled finite-element modelling of lithospheric extension to investigate the interplay between variable styles of rifted margin, syn-rift architecture, and consequences for distribution of late syn-rift salt, and post-rift salt tectonics. We simulate the formation of salt basins in different types of continental margins: narrow, intermediate, wide, and ultra-wide margins. For each of these we evaluate: 1) the interplay between rifting, post rift sediment progradation, base-salt topography and margin scale salt tectonics, 2) the spatial and temporal distribution of salt-related structural domains, and 3) the contrasting styles of salt tectonics for different margin types. We show that narrow and intermediate margins form partially isolated salt basins in their proximal domain with limited translation and significant vertical diapirism. Their distal portions are associated with significant translation, development of updip listric normal faults and rollovers passing downdip to squeezed diapirs. Wide and ultra-wide margins form wide salt basins with a more subtle base-salt topography which result in significant salt expulsion and overburden translation towards their distal domains. These margins are characterized by updip extensional and/or expulsion rollovers and downdip salt inflation, diapirism and shortening in the form of diapir squeezing, buckle-folding and development of allochthonous salt sheets. All margins present a distal salt nappe that forms by a combination early rift-related stretching and post-rift thrusting. The nappes vary in width and magnitude of deformation according to each each margin type. These models are the first to integrate lithospheric extension with long-lived post-rift salt tectonics using a geodynamically self-consistent modelling approach where the geometries of the lithosphere and salt basins are not prescribed, allowing a natural evolution of syn and post-rift deformation. They also incorporate a more realistic style of post-rift progradation using a dynamically evolving profile and present unprecedent detail for salt, syn- and post-rift stratigraphy. The results can be directly compared to examples from various salt-bearing continental margins and provide an improved understanding on the kinematics and relative timing of rift and salt deformation, and on the controls and variability of salt tectonics for different margin types.

Flávio Norberto de Almeida Junior, Felix Halpaap: Field trip reports
2021-09-03 00:00 - 13:00 | Kvartsitten, 3rd floor, Realfalbygget, Bergen, 5020, Norway
“Geology fieldwork in the High Arctic – some pictures taken during the 2021 Sequence Stratigraphy course on Svalbard”
By Flávio Norberto de Almeida Junior

“Picture report from new remote seismic stations on Svalbard – how we worked against fog, ice, and time to get the 1st station north of 80º in Norway up & running”
By Felix Halpaap

Matteo Demurtas
2021-06-02 12:15 - 13:00
Faulting at near-surface conditions: an example from unconsolidated deposits in the Central Apennines

Natacha Fabregas
2021-05-26 12:15 - 13:00
Deep-water syn-rift sedimentary response to alternating Late Quaternary palaeoenvironments in the Gulf of Corinth (Greece)
Relatively few detailed studies exist of rift axis depositional systems and the controls on their sedimentology and stratigraphy. Cores from the IODP Expedition 381 (Corinth Active Rift Development) provide a continuous high resolution stratigraphic record of depositional processes operating within this deep-water rift. During the Late Quaternary, the Gulf of Corinth alternated between marine and isolated/non-marine conditions due to intermittent connection with the open ocean across a sill driven by climate-related sea-level fluctuations. In this study we performed bed scale logging of the sedimentary deposits within the eastern Gulf of Corinth in order to understand key controls on sedimentation during the Late Quaternary. High resolution, mm-scale analysis was performed on the first 300 m of core from Site M0079 that records the last two glacial-interglacial cycles and the Holocene (Marine Isotope Stages 1 to 7). The succession is dominated by fine-grained gravity flows (event beds) and hemipelagic sediments. Event beds result from discrete events that interrupt/overprint ongoing low energy sedimentation. As such, these have been abstracted in order to define three main sedimentary unit types. Unit-scale logging was extended to the rest of the succession and to the other drill sites to build a stratigraphic and depositional model covering the last ca. 700 kyr of deposition. Our results show that during interglacial periods (i.e. marine conditions), the sediment record consists mainly of highly bioturbated mud with rarer occurrences of coarser grained sediment. Sedimentary structures and identifiable event beds have largely been lost due to the high degree of bioturbation. In contrast, during glacial periods (i.e. isolated/semi-isolated lake conditions) the deposits are well bedded with a low bioturbation index and background muds alternate with event beds. Transitional strata, between marine and non-marine units, show finely laminated beds rich in aragonite, often becoming more organic rich toward the top. The deepest parts of the core penetrate slumped units and thicker gravity flow deposits. This study allows us to recognise the response to high frequency climatic fluctuations recorded in the sedimentary succession of this deep-water rift.

Stéphane Rondenay
2021-05-12 12:15 - 13:00
What causes volcanic gaps in subduction zones? Insights from South central Alaska

Kristian Jensen
2021-05-05 12:15 - 13:00
Improving modelling of seismic images through Point-Spread Function-based convolution
Seismic images are generated when a source at the Earth’s surface initiates a pressure wave which travels through the Earth’s subsurface. As the wave hits layer boundaries in the Earth’s interior, energy is reflected back to the Earth’s surface where it is recorded, thus allowing us to obtain an image of the subsurface. The principle behind this approach is exactly the same as in medical ultrasound.
Due to the complexity of the Earth, and the intricate wave physics involved, the raw seismic images usually contain many distortions and artefacts. As such, extensive processing is often needed to obtain proper images of the subsurface. Yet, even after performing a processing workflow, features in the images may still be ambiguous and difficult to identify.
In order to study in greater detail exactly what seismic images will look like for a certain geological setting and survey geometry, seismic modelling may be performed. This involves using a computer to generate a model of the subsurface, and then simulating what the seismic images will look like for a given survey geometry over the model. Proper seismic modelling can be very helpful in identifying exactly why ambiguities occur, and what may be done to improve the quality of the images.
Seismic modelling approaches are, however, often computationally expensive. The aim of my PhD is therefore to further develop a method which may perform accurate seismic modelling at a low computational cost. The method estimates the local illumination and resolution at specified points in the model, referred to as point-spread functions (PSFs). The PSFs are computed by tracing the path of the wave through the Earth (a procedure referred to as ray tracing), and not through a full simulation of the wave equation. This allows for a very quick estimation of the PSFs. The PSFs may then be mathematically convolved with the Earth model in order to simulate a processed seismic image. Through this method we can quickly and efficiently study how survey geometry, seismic wave velocity, frequency bandwidth and amplitude effects influence the quality of the seismic image surrounding the point of interest. However, as the method does not solve the full wave equation, some simplifications and limitations exist. My PhD-project therefore aims to improve the quality of the modelled seismic images by attempting to overcome some of the inherent limitations while retaining the low computational cost.
Illustration of how changes in seismic modelling parameters yield different seismic images of the same target area. Foto/ill.: Kristian Jensen, UiB

Felix Halpaap
2021-04-16 14:00 - 15:00
Leveraging seismic data quality metrics for network supervision and sensitive earthquake detection

In earthquake seismology, the last decade has led to ever growing datasets of continuous seismograms being recorded, stored, and made openly available. These ever increasing datasets (e.g., about 50 M hours of seismograms or 17 TB for Norwegian networks alone) allow us to revisit the data with new methodologies, for example by template matching to detect previously uncataloged earthquakes. Template matching is based on correlatiing known earthquake waveforms against continous seismic data to detect similar and helps to obtain more complete catalogs of seismicity that are suited for further statistical analysis. One challenge in applying template matching to larger datasets is that one needs to be able to sysematically recognize problems in data quality that quickly lead to misdetections. What helps with this task are seismic data quality metrics – a set of up to 50 measures of specific data properties for each day and trace – for which two major systems now exist. In this talk, I will introduce how these data quality metrics help us to (a) keep better control of data quality in archived data, (b) monitor the state of the currently recording stations systematically, (c) apply sensitive template-matching without misdetections (with examples from the North Sea and a Norwegian reservoir), and (d) gain a new overview of seismic noise throughout the network operations.

Cheng-Cheng Wang
2021-04-07 12:15 - 13:00
Zircon Hf-O isotopic fingerprints in accretionary vs. collisional orogenesis
Zircon Hf isotopes are able to identify the relative proportion of mantle and crustal inputs to magma systems, and different Hf isotopic patterns can be expected in different tectonic settings. Coupled analysis of O with Hf isotopes has been proposed as an effective way to identify whether the magma was contaminated by sedimentary material. Combined zircon Hf-O isotopes have been widely used in the studies of magma petrogenesis and source composition. However, regional investigations of O isotopes in well-defined tectonic settings are scarce, so it is unclear if the O isotopic evolution can be linked with geodynamic settings.
We compiled Hf-O isotopic data of magmatic zircons from our current studies in four orogenic systems, including two accretionary orogens (the Gothian-Telemarkian orogen in western Fennoscandia and the Maud Belt in East Antarctica), and two orogens that formed related to continental collision (the East Africa-Antarctic Orogen and the Sveconorwegian belt). Their Hf-O isotopic patterns are compared with those of the arc magmas from the Paleo-Pacific margin and syn- and post-collisional magmas from the Himalaya-Tibet, which are considered as typical accretionary and collisional settings respectively. Zircon εHf(t) and δ18O values show a clearly negative correlation within subduction-related magmas. The most straightforward interpretation is the involvement of at least two sources, a mantle source with juvenile Hf and mantle-like O isotope values and an older crustal/sedimentary source with evolved Hf and elevated O values. In contrast, collision-related magmatic zircon shows a wide spread of Hf isotopic values, associated with relatively homogeneous O isotopic compositions. This probably reflects a mixed source, namely older lower crust and subordinate enriched mantle, which have similarly moderate O but significantly distinct Hf isotope values, while the sedimentary contribution is significantly less obvious than in arc magmas. This study indicates that the distinct zircon Hf and O isotopic evolution appears to provide a good potential to test accretionary vs. collisional orogenesis, although it remains to be explored further if the observation described here applies universally.

Åse Hestnes
2021-03-24 12:15 - 13:00
Structural framework and the timing of faulting in Western Norway
Geometric and temporal constraints on the brittle evolution are important to obtain a comprehensive picture of the post-Caledonian topographic evolution of Western Norway. In this study, we combine remote sensing, structural field measurements, paleo-stress analysis and isotopic dating to study the brittle evolution of a larger region of Western Norway. The region spans from the Sognefjord in the south to the Møre margin in the north. Lineament studies reveal important lineament sets trending N-S, NE-SW, E-W and NW-SE. Field observations show that these lineament sets correspond to both dip-slip and strike-slip faults, some of them parallel to ductile precursor structures and some cutting the ductile fabric. Epidote, chlorite, quartz and zeolite are the dominant mineralizations on fracture and fault surfaces. There is no clear correlation between the type of mineralization and fracture orientation in the region. Paleostress analysis on fault-slip data (n = 173), including faults reactivating older structures, show a good fit with a general E-W to NW-SE extensional regime. However, a considerable amount of faults (n = 115) formed under a strike-slip regime. We combine these findings with K-Ar fault gouge dating from six faults where five fractions (6-10 µm, 2-6 µm, 0.4-2 µm, 0.1-0.4 µm, <0.1µm) from each sample were analysed. The ages show a spread from the Triassic to the Cretaceous ages. Our results point to an important phase of Mesozoic strike-slip faulting in the region, with steep faults controlling the location of several major valleys.

Martin Kjenes
2021-03-17 12:15 - 13:00
Modern Fieldwork during a Pandemic: From outcrops to computers.

Doctoral defence - Sebastian Wolf
2021-03-10 14:15 - 15:00
Orogenesis from bottom to top – Investigating the geodynamics of mountain building using coupled thermo-mechanical-surface-process models

The objective of this project is to advance our understanding of mountain building processes in different plate tectonic settings and with specific focus on the interaction between surface processes and tectonics. Three topics are investigated:
1. The factors controlling overriding plate extension or shortening in ocean-continent
subduction systems.
2. The evolution of continent-continent collision orogens from small to large, their
typical distribution of shortening, variable structural style, and associated controlling
factors.
3. The relation between surface processes and tectonics during orogenic growth and
decay and the factors controlling height, width, and longevity of collisional mountain
belts.
The three research aspects are investigated with the help of numerical models and comparison to natural examples. The newly developed models allow for the first time to efficiently model the coupling between tectonic deformation, erosion and deposition. Results are synthesized in published or submitted articles, provide new geodynamic relationships, ideas, and theory, and simplify understanding of mountain building on Earth.

Lorenz Michel
2021-01-27 12:15 - 13:00
Evolution of rift structures, topography and the sediment supply – A perspective from numerical modelling on the respective importance of tectonic and earth surface processes during continental rifting
Lorenz Michel
Continental rifting is the response of the continental lithosphere to extension, and the subsequent evolution of the elevated rift shoulders and subsided basins is complex, depending on the respective contributions from tectonic and earth surface processes. Here, we use a coupled, numerical model in order to see how tectonic and earth surface processes impact the evolution of rifts. We test the sensitivity of the models to different combinations of rheology, extension rate and erosional efficiencies, and investigate the structural and topographic evolution of the rifts, and the associated sediment flux and sediment volumes.
We observe, that the amount of strain localization is critical in driving the structural evolution of the modelled rifts: Systems with slow extension, a high crustal strength and efficient surface processes show a high degree of strain localization, resulting in less faults being active, and more offset on them. The amount of fault offset is also highly sensitive to the erosional efficiency, and more efficient erosion leads to more fault offset, suggesting a strong feedback effect between tectonic and earth surface processes. In terms of the temporal evolution, there is a characteristic sequence for the peaks in (1) uplift, (2) topography and (3) sediment flux, with lag times between the single peaks depending on the extension rate (being between 2 – 5 Myr). We also identify a characteristic pattern for the temporal evolution of the sediment flux with six phases, which are related to the geomorpho-tectonic evolution of the rift. The magnitude of the total sediment volume produced during rifting depends on the degree of strain localization, such that systems with strong crust, slow extension and efficient surface processes produce most sediment. Importantly, we observe that for slower extension more sediment is produced (despite the lower uplift rate), which is related to the stronger feedback effect. As a summary, our models point towards a complex interaction between tectonic and earth surface processes, which has a strong impact on the evolution of structures, topography and the sediment flux during rifting.

Leonardo Muniz Pichel
2020-11-18 12:15 - 13:00
Salt Tectonics in the Santos Basin, Brazil: the effects of translation, base-salt relief and the enigma of the Albian Gap
Salt-driven translation over variable base‐salt relief produces three‐dimensionally complex and multiphase deformation. Understanding how pre- and base-salt structures influence salt‐related deformation is important to constrain regional salt tectonic kinematics (i.e. direction, timing and magnitude of salt flow) and the distribution of salt tectonic domains. The São Paulo Plateau, Santos Basin, Brazil is characterized by a >2 km thick, Aptian salt deposited above prominent base‐salt relief. We use 3D seismic data, numerical and kinematic models to investigate how gravity‐driven translation above thick salt, underlain by variable base‐salt relief, generated a complex framework of salt structures and minibasins. We show that ramp‐syncline basins (RSBs) developed above and downdip of the main pre‐salt highs and record c. 30 km of post-Albian basinward translation. As salt and overburden moved downdip, salt flux variations over base‐salt relief resulted in the coeval development of extensional, contractional and load-driven salt structures in the São Paulo Plateau. This style of salt deformation and the magnitude of translation afforded an improved kinematic model for the enigmatic Albian Gap, located immediately updip of the São Paulo Plateau.
The Albian Gap is a uniquely large (up to 65 km wide and >450 km long) structure characterized by the near-complete absence of Albian strata above depleted Aptian salt, and a 8-9 km thick basinward-dipping post-Albian rollover. Owing to its unique geometry, size and counter-regional aspect, the origin and evolution of the Albian Gap has been the centre of debate for >25 years. This debate revolves around two competing models; that is, did it form as a result of thin-skinned (i.e. supra-salt) extension, or progradational loading and salt expulsion? We combine regional 2D PSDM seismic data and novel structural restoration workflows that incorporate flexural isostasy, in addition to a detailed, sequential reconstruction of the intra-gap rollover sequences. We show that the geometry and kinematics of the Albian Gap vary along-strike, and that both post-Albian extension and expulsion play a significant role in its evolution. Where the Albian Gap is relatively wide (>50 km), these processes alternate and operate at approximately equal proportions. Our results seemingly reconcile one of the longest-running debates in salt tectonics, having also more general implications for understanding the regional kinematics and dynamics of salt tectonics in other basins, in particular the controls on the development of large, counter-regional faults and the effects of translation and pre-salt relief.

Thomas Theunissen
2020-11-04 12:15 - 13:00
Relative continent/mid-ocean ridge elevation: a reference case for isostasy in geodynamics
The choice on crustal and mantle densities in numerical geodynamics model is usually based on common habits. However, lithospheric deformation involving regional or fault-related flexure or involving strong change in elevation as distal rifted margin formation or long-term erosion of mountain belt require good constrain on densities to provide a reasonable estimation of isostatic response. Accommodation space for sediments, absolute elevation (gravity potential and conditions for erosion and deposition) and long term survival of relief depends on isostasy.
We use 2-D incompressible plane strain finite element method for viscous-plastic creeping flows coupled with a melt prediction routine to solve for the dynamic evolution during extension from continental rifting to mid-ocean spreading. Two independent melting prediction procedure to compute density structure below the mid-ocean ridge are compared in order to evaluate sensitivity to phase changes on solution. The first approach considers the use of P-T density maps and melt prediction from thermodynamic solution. A simple conversion from batch to incremental melting is proposed in order to use only one thermodynamic solution. The second approach considers a simpler approach that uses approximate mantle solidus to compute melt fraction and degree of depletion.
Both approaches provide a solution to fit mid-ocean ridge elevation. Crustal and mantle densities and mid-ocean ridge elevation are calibrated based on observations. We use thermodynamic solution using characteristic bulk mantle compositions to estimate the average degree of depletion of the lithospheric mantle repectively -15 kg/m3, -28.5 kg/m3 and -35 kg/m3 respectively for 125 km, 180 km and 240 km thick lithospheres. The average crustal density is 2850 kg/m3 in this reference model in agreement with global and regional estimations. Finally the reference model fits the characteristic mid-ocean ridge elevation of -3000 m +/- 100 m and continental elevation of 300 m +/- 100 m obtained from a global analysis. This study provides a reference case for isostasy in geodynamics and we discuss the importance of such reference model to use geodynamic numerical models to calculate subsidence and melting histories which could be compared with observation.

Hasbi Ash Shiddiqi
2020-10-28 12:15 - 13:00
More details soon !

Christian Haug Eide
2020-10-21 00:15 - 13:00
Underneath the volcano: Trying to understand how igneous sills are emplaced using outcrops and seismic from East Greenland

Here I will tell you about our ongoing work to understand sill emplacement, using data from Jameson Land in East Greenland. It is a unique onshore basin, in many ways analogous to the Mid-Norwegian margin, where host-rocks and sills occur in both outcrops AND crustal-scale seismic data. This makes it possible to investigate how igneous intrusions are imaged in seismic data, how lithology influences sill emplacement, and possibly how large-scale tectonic stresses influence geometries of the igneous system.

Christopher Jackson
2020-10-14 12:15 - 13:00
Hot rocks under our feet; seismic reflection imaging of the processes and products of crustal magmatism
Volcanoes are hot, loud and scary, thus we know little of their internal structure or underlying ‘plumbing systems’. Magma intrusion in the Earth’s crust, and the extrusion of this material on its surface, represent a natural (geo)hazard; however, these processes can also result in the formation of economic quantities of hydrocarbons. In this talk I will show how 3D seismic reflection data can illuminate the structure and emplacement mechanics of these ‘hot rocks’. I will also demonstrate the key role igneous processes and products play in the development of petroleum systems on continental margins.

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Professor Christopher Aiden-Lee Jackson
Equinor Professor of Basin Analysis
Basins Research Group (BRG)
Department of Earth Science & Engineering
Imperial College
Prince Consort Road
LONDON
SW7 2BP
UK

Email: c.jackson@imperial.ac.uk
Web: www.imperial.ac.uk/c.jackson
Twitter: @seis_matters
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