Geolunch seminar @ UiB

Isabel Edmundson
2017-10-25 00:15 - 13:00 (Europe/Oslo) | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Structural geometries associated with extension, inversion and strike slip deformation; insights from field observations along the northern Somerset coast, southwest UK.

Several kilometre long sections of the northern Somerset coastline showcase excellent exposures of faults and associated structures within the Triassic and Lower Jurassic. The combination of low tides uncovering cliffs and wave cut platforms, and a complex structural history documented by multiple outcrops ensure that this coastline is a popular destination for geologists. It was for these reasons that myself, David Peacock, Dave Sanderson, Vilde Dimmen and two master’s students arranged a three day field trip to this coastline. The trip provided an opportunity for the two students to carry out reconnaissance for their projects, and for myself and Vilde to see more field examples of fault structures that could complement our own PhD projects. It is hoped that this informal presentation will give an insight into how field observations can help to improve understanding of fault geometry and associated deformation as a result of extension and subsequent reactivation.
The area has a complicated tectonic history having been affected by several structural phases beginning with N-S orientated compression during the Variscan orogeny. This event established the dominant E-W trending structural grain along which periods of later extension and compression would follow. The first of three discrete rift events occurred in the Permian, the second in the early Jurassic and the third in the late Jurassic to early Cretaceous, each indicated by wedge thickening geometries. Following this protracted period of rifting, N-S compression associated with the Alpine orogeny in the late Cretaceous reversed the sense of motion along established E-W Mesozoic faults. Tightening of roll over anticlines previously established by extension and a Lower Cretaceous regional angular unconformity provides evidence for this event. Finally, strike-slip reactivation of NW-SE trending faults during the Miocene established several pull apart basins indicating a sinistral sense of displacement. Many of the observed outcrops document this restructuring but are generally below seismic resolution. However, recent research has shown that many fault systems and associated geometries are scale independent and so small scale examples can provide good analogues for larger scale structures observed on seismic. In addition to this, many features of faults and associated damage zones are not visible on seismic, reducing the fault to a simple feature. Consequently, the complexity of the fault and fault related deformation can be overlooked, yet these features have important implications for fluid flow and should be remembered during interpretation and modelling.

Photograph showing the hangingwall anticline formed by inversion of a south dripping extensional fault in the Lower Jurassic shales and limestones. Cliff is ~50m high.

Vivi Pedersen
2017-10-04 00:15 - 13:00 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Earth surface processes: interacting with the solid Earth, ice and sea level
Surface processes change the Earth surface dramatically and interact with the solid Earth, ice, and thereby also global sea level. For instance, changes in topography due to glacial erosion will influence ice-sheet configuration and dynamics. The deep glacial erosion in fjords will also cause erosional unloading and result in solid-Earth deformation. In addition, solid-Earth deformation will influence topography and therefore the first-order behaviour of surface processes.
In this seminar, I will exemplify these interactions, first with a strong focus on the formation and evolution of topography. In particular, I will target the outstanding question related to high topography at passive continental margins, where the importance of surface processes and solid-Earth deformation is still debated.
Secondly, I will elaborate on the importance of surface processes for sea level research, through their interaction with the solid Earth and ice sheets. Both a changed topography and solid-Earth deformation has the potential to influence the response of ice sheets to climate change, and thereby ice-sheet stability and sea level.

Kuvvet Atakan and other
2017-09-27 00:15 - 13:00
M 8.1 – 87km SW of Pijijiapan, Mexico
https://earthquake.usgs.gov/earthquakes/eventpage/us2000ahv0#executive
Opened discussion about this unusual major normal earthquake (MW8.1 – 70 km depth).
The September 8th, 2017, M 8.1 earthquake offshore Chiapas, Mexico, occurred as the result of normal faulting at an intermediate depth. Focal mechanism solutions for the earthquake indicate slip occurred on either a fault dipping very shallowly towards the southwest, or on steeply dipping fault striking NW-SE. At the location of this event, the Cocos plate converges with North America at a rate of approximately 76 mm/yr, in a northeast direction. The Cocos plate begins its subduction beneath Central America at the Middle America Trench, just over 100 km to the southwest of this earthquake. The location, depth, and normal-faulting mechanism of this earthquake indicate that it is likely an intraplate event, within the subducting Cocos slab, rather than on the shallower megathrust plate boundary interface.
While commonly plotted as points on maps, earthquakes of this size are more appropriately described as slip over a larger fault area. Normal-faulting events of the size of the September 8th, 2017 earthquake are typically about 200×50 km (length x width).
Over the preceding century, the region within 250 km of the hypocenter of the September 8th, 2017 earthquake has experienced 8 other M 7+ earthquakes. Most occurred in the subduction zone to the southeast of the September 8 event, near the Mexico-Guatemala border, and none were larger than M 7.5. The largest, a M 7.4 thrust faulting earthquake offshore Guatemala in November 2012, resulted in at least 48 fatalities and over 150 injuries, and significant damage near the coast.

Star: epicenter of the mainshock. Gray and white dots: historical seismicity epicenters.

Thilo Wrona
2017-09-13 00:15 - 13:00 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Seismic facies analysis using machine learning
Thilo Wrona1, Håkon Fossen1, Robert L. Gawthorpe1, Indranil Pan2
1Department of Earth Science, University of Bergen, Norway
2Department of Earth Science and Engineering, Imperial College London, UK
Seismic interpretations are, by definition, subjective and often require significant time and expertise from the interpreter. We demonstrate that machine learning techniques can help address these problems by performing seismic facies analyses in a rigorous, reproducible way. For this purpose, we use state-of-the-art 3D broadband seismic reflection data of the northern North Sea. Our workflow includes five basic steps. First, we extract seismic attributes to highlight features in the data. Second, we perform a manual seismic facies classification on 1000 examples. Third, we use some of these examples to train a range of models to predict seismic facies. Fourth, we analyze the performance of these models on the remaining examples. Fifth, we select the ‘best’ model (i.e. highest accuracy) and apply it to a seismic section. As such, we highlight that machine learning techniques can increase the efficiency and reproducibility of seismic facies analyses.

Tristan Salles (USyd)
2017-06-27 12:15 - 13:00 | Auditorium 5, 3rd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Adding stratigraphy to landscape evolution model: basin architecture on passive margins & peneplain preservation
First, I will present new results on the influence of dynamic topography on passive continental margin stratigraphy. Quantifying the interaction between surface processes and tectonics/deep Earth processes has been one important aspect of landscape evolution modelling in recent decades. Both observations and results from numerical modelling indicate that dynamic topography plays a significant role in shaping landscape through geological time. Recent research suggests that dynamic topography also has non-negligible effects on stratigraphic architecture by modifying accommodation space available for sedimentation. Using Badlands I will investigate the evolution of a continental scale landscape in response to transient dynamic uplift or subsidence, and model the stratigraphic development (looking at stratal stacking pattern, vertical cross-sections and wheeler diagram) on passive continental margins in response to sea-level change, thermal subsidence and dynamic topography.
Then, I will discuss using newly implemented erosion laws the role of bedload fluxes on the preservation of low-relief summit surfaces. Low relief upland areas form summit surfaces in many dissected mountain ranges. They are often distinguished by their conspicuous flatness compared to the surrounding dissected terrain. Such relict landscape generate two questions: 1, is preservation a random process, or is there a process that helps such surfaces to resist dissection, and 2, how come relict landscapes are generally exclusively composed of subdued terrain? Dissection of the landscape by renewed wave of incision is controlled by river erosive power. River incision is achieved by various processes, but one of the main contributors is bedrock abrasion by bedload. Here I will show how this process can explain the persistence of subdued topographies.

Rosa Polanco-Ferrer
2017-06-07 12:15 - 13:00
Title: TBA

Jeff Prancevic
2017-05-31 12:15 - 13:30 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
The influence of hillslope angle on landslide initiation and the occurrence of threshold hillslopes
The concept of threshold hillslopes has been widely applied to both soil-mantled and bedrock landscapes, postulating that once hillslopes achieve the critical topographic gradient where landslides dominate erosion they cannot steepen further. This process transition has been used to explain observations of ubiquitous modal hillslopes that cluster around values of 35° to 40° in steep landscapes globally, despite wide variability of climate, erosion rate, and soil characteristics. However, there is no clear explanation for why ~35° is the special slope towards which landscapes adjust. Landslides start occurring at slopes that are much lower (~20°), and the angle of repose of weathered bedrock is generally much steeper (45°+). In this study we use a series of laboratory landslide experiments and observations of landslide scars to examine how hillslope gradient affects the occurrence of landslides. Surprisingly, we find that similar runoff rates are required to initiate landslides at all hillslope gradients between 25° and 45°. The ubiquitous modal hillslope gradient of 35° sits in the middle of this range of gradients that are similarly susceptible to landslide initiation. Because hillslope gradients tend to be normally distributed, a modal hillslope gradient of 35° places the greatest portion of the landscape within the landslide regime. If landslides, specifically those caused by large rainfall events, are the most efficient mode of erosion, then a distribution of hillslope gradients that sits in the middle of this process regime should generate the fastest possible erosion rates.

Timm John
2017-05-24 12:15 - 13:30 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Ultra high pressure rocks – a window into metamorphic processes occurring in subduction zones

Anneleen Guerts
2017-04-05 12:15 - 13:00
TBA

Sebastian Wolf
2017-03-29 12:00 - 13:00 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Why do back-arcs open and the Andes form?
The crustal structures of overriding plates in subduction settings around the world can vary between a wide range of deformation styles, ranging from extensional structures and back arc opening induced by slab roll back as in the Tonga or Hellenic subduction zone to large, plateau-like orogens such as the central Andes. Both end member types have been intensively studied over the last decades and a range of hypotheses has been proposed to explain their characteristics.
To investigate the behavior of overriding plates in subduction zones we use high resolution, upper mantle scale plane-strain thermo-mechanical models, which also account for phase changes of rocks that enter the eclogite stability field and the phase transition at the 660 km mantle discontinuity. We consider varying plate velocities and back-arc lithospheric strength as the main variables affecting the strain regime of the overriding plate in subduction zones and conducted a sensibility study with those parameters. Our results show that the back arc lithospheric strength plays a pivotal role in determining whether and when the overriding plate will deform, and the combination of subduction and overriding plate velocity determines the type of strain regime in the overriding plate. Additionally, the interface strength of the subduction zone has an important impact. To verify our results we will have a closer look at the central Andes.

Guillaume Duclaux
2017-03-08 12:15 - 13:00 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Three-dimensional thermo-mechanical modelling unravels the complex deformation history of oblique rifts, transtensional margins, and gneiss domes
Throughout the Wilson cycle the obliquity between lithospheric plate motion direction and nascent or existing plate boundaries prompts the development of intricate three-dimensional (3-D) tectonic systems. Where oblique divergence dominates, as in the vast majority of continental rift and incipient oceanic domains, deformation is typically transtensional and strongly partitioned. Large stretching in the brittle upper crust is primarily achieved by the accumulation of displacement on fault networks of various complexities, while viscous flow and anastomosed shear zones dominate in the ductile lower crust. The occurrence of contrasting and superimposed structures and fabrics in these regions has fuelled countless debates about driving forces and tectonic interpretations, including timing of deformation.
But, there is a silver lining. Over the past three decades thermo-mechanical numerical modelling has transformed the way we look at deformation in the lithosphere. Thanks to the recent progress of computational methods, numerical models have evolved from 2-D to 3-D, and reached sufficiently high resolution that their predictions can be compared with analogue experiments and natural systems. More than just generating aesthetically pleasing pictures, outputs from numerical models contain a rich source of quantitative information that can be used to measure deformation quantities in 2- and 3-D. Post-processing adds value to the modelling and aims to produce visual information that will resonate to seasoned structural geologists, and assist with comparing experimental and observational data in order to unravel the deformation history of past and present tectonic regions.
Here, I will present a set of high-resolution 3-D thermo-mechanical finite element models of a simplified layered lithosphere, which combine non-linear viscous and strain-weakening frictional-plastic rheologies, undergoing oblique extension. These models explore the relative importance of varying initial inherited structures geometry, and crustal rheologies during oblique rifting and transdome formation. To analyse these models we apply newly developed methods to measure and visualise (1) the spatiotemporal evolution of active faults distribution and local stress orientation at the surface, and (2) the progressive development of finite strain patterns in the lower crust.
The analysis of the relative timing and distribution of structures and fabrics in the continental crust allows us to propose a deformation sequence for the models, and discuss the underlying controls governing deformation style in the obliquely extending continental crust. We found that in transtension and thanks to local stress rotations, extension-orthogonal fault arrays preferentially form at the surface during the early segmentation stage of the lithosphere to accommodate the thinning of the upper crust. The progressive rotation and overprinting of active structures at the surface after segmentation of the rift, along with the narrowing of the active deformation zone, suggests an increasing mechanical coupling between the brittle upper crust and the rising viscous sub-lithospheric mantle, that ultimately ends up with oblique breakup. In decoupled models with a weak viscous crustal rheology, strain partitioning promotes the development of oblique gneiss domes in the lower crust, while anastomosed fault networks form at the surface.
Conclusions drawn from our 3D thermo-mechanical numerical models are consistent with observations from oblique continental rift and transtensional margins in East Africa, and gneiss domes in the French Massif Central. This work confirms the importance of the rheological layering of the lithosphere and the geometry of inherited structures for controlling the characteristic orientation and spatiotemporal distribution of deformation in transtensional systems.

Benjamin Bellwald
2017-02-22 12:15 - 13:00
Modeling potential paleoearthquakes based on results from subaquatic mass movements in Western Norway
During my PhD as a Quaternary geologist, I did quite some work on turbidite paleoseimology in west- and mid-Norway, with some very interesting outcomings. I was further involved in a study in the Alps where we have been modeling the magnitudes and epicenters of potential paleoearthquakes in the last 10000 years. In the upcoming seminar, I would like to introduce my results and discuss the potential for modeling paleoearthquake magnitudes and epicenters offshore Norway and along the western Norwegian coast.
Benjamin Bellwald
Please find attached the abstract covering part of the seminar (AGU 2016).
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Holocene Mass Transport Deposits in Western Norwegian fjords and lakes revealing prehistoric earthquake history of Scandinavia
Bellwald, B.1, Hjelstuen, B.O.1, Sejrup, H.P.1, Stokowy, T.2, Kuvås, J.1
1Department of Earth Science, University of Bergen, Norway
2Department of Clinical Science, University of Bergen, Norway

The sensitivity of fjord sediments to seismic shaking makes fjord systems appropriate study sites when extending regional earthquake catalogs back in time and when estimating recurrence rates of prehistoric earthquakes in intraplate settings. In this study we compiled evidence of 140 postglacial mass movement events and their associated mass transport deposits (MTDs) from previously analyzed and new sediment cores and high-resolution seismic profiles from 22 fjord systems and six lakes in Western Norway. Evaluation of trigger mechanisms make us infer that most of these mass movement events were initiated by regional earthquakes, and that both climate-related processes and tsunamis most likely can be excluded as trigger mechanism for most of the events. A total of 33 individual earthquakes has been identified, which most likely outbalance the historically recorded events in magnitude, thus indicating magnitudes >6. Frequency plots of MTDs suggest high seismic activity in the early Holocene (11000-9700 cal. yrs BP), followed by seismic quiescence in the mid-Holocene before a seismic reactivation took place at ~4000 cal. yrs BP. Coevally-triggered MTDs at ~8100 cal. yrs BP are identified in all the archives, and are correlating with the age of the offshore Storegga slide. We estimate earthquake recurrence rates of 1/80 years directly after the last deglaciation of Western Norway (12800-11600 ca. yrs BP), 1/200 years for the early Holocene and 1/300 years for the last 4000 years. Our compilation suggests that the mid-Holocene is characterized by low seismic activity, suggesting recurrence rates of 1/1300 years. Comparisons of the Western Norwegian dataset with paleoseimologic studies of other previously glaciated intraplate settings indicate that both Scandinavia and the Alps show similar trends as Western Norway, whereas Eastern Canada is not correlating with the paleoseismologic trend of this study, which could be explained by different deglaciation histories.

Hongliang Wang
2017-02-08 12:15 - 13:00 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Water migration in the subduction mantle wedge: a two-phase flow approach
Hongliang Wang, Ritske S. Huismans, and Stéphane Rondenay

Subduction zones are the main entry points of water into earth’s mantle and play an important role in the global water cycle. The progressive release of water by metamorphic dehydration induces important physical-chemical process and may play an important role in the generation of subduction zone earth-quakes. Yet, how water migrates in subduction zones is not well understood. We investigate this problem by explicitly modeling a two-phase flow during subduction, in which the fluid migrates through compaction and decompaction of the solid matrix. Our results show that fluid migration may occur preferentially along the subduction interface from where it feeds into the mantle wedge. This process is strongly affected by the dynamics of the subduction process in our model, which includes in three characteristic phases: (1) an early stage of subduction initiation; (2) an intermediate stage of gravity-driven steepening of the slab; and (3) a late stage where the slab becomes supported from the bottom. With a background porosity of ϕ0= 2×10-4, water is able to migrate horizontally up to ~300 km from the subduction trench: the deeper the water releases from the subducting slab, the further it can migrate horizontally. The models suggest the mantle wedge may be characterized by a lower permeability zone surrounding by two high porosity pathways, which is consistent with Vp/Vs ratio anomalies observed in tomographic models of some subduction zones (e.g., western Greece). An explanation for the lower water zone in the mantle wedge is provided based on the two phase flow point of view. The porosity contrast in the mantle wedge caused by water migration depends on the bulk viscosity. We further find that (de)compaction enhances fluid migration significantly and water can still migrate into the mantle wedge even under very low background porosity and permeability (e.g. ϕ0= 2×10-5 and k0=10-25). The feedback of fluid migration on the solid dynamics, which is not included here, will be subject of further study and is anticipated to play an important role in the subduction dynamics.

Anna Ksienzyk
2017-02-01 12:15 - 13:00 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Digital field assistant – teaching structural geology by mobile device
Anna K. Ksienzyk, Christian Rønnevik, Joachim Jacobs & Hallgeir Sirevaag
University of Bergen, Department of Earth Science, P. O. Box 7803, 5020 Bergen, Norway; anna.ksienzyk@uib.no, cronnevik@gmail.com, joachim.jacobs@uib.no, hallgeir.sirevaag@uib.no
Rising student numbers present a challenge for field-based geology education. In the last years, participant numbers in our “Introduction to Structural Geology” field course have been around 70-80 students. Structural geology field courses involve a lot of individual student work, such as measuring the orientation of geological structures and plotting structures in the stereonet. Especially in an introductory course, students require a lot of help with these tasks and need to be tutored individually or in small groups. Even with several MSc students as teaching assistants, we have been struggling to provide the high-quality supervision that all students deserve. In order to improve this situation, we have started to develop an application for Android-based smartphones and tablets, to be used as a teaching support during structural geology field trips. The app guides the students through the different steps of outcrop description, rock description, structural measurements and fold classification. It includes short tutorial videos on how to measure planar and linear structures. For this early stage, we have selected suitable outcrops located in walking distance from the Department of Earth Science. The app guides the students to the outcrop and through all the tasks to be done on the outcrop during the field course. Structural measurements can be entered into the app, which will give the students direct feedback on their results. Thus students can visit these outcrops individually before or after the main field course to work at their own pace. Altogether, the app is not meant to replace traditional field education but to provide an additional source of help and information for students when the teacher is unavailable in a large group. Early tests with students this spring semester have been positively received. The overall feedback from students was very encouraging for future development and regular integration of this app in our field education.

Vivi Pedersen
2017-01-18 13:15 - 14:00 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Inverse modeling of Eocene to mid-Pliocene landscape evolution in Scandinavia using offshore sediment volumes
The origin of high topography in Scandinavia is highly debated, both in terms of its age and the underlying mechanism for its formation. Traditionally, the current high topography is assumed to have formed by several Cenozoic (mainly Neogene) phases of uplift and dissection of an old peneplain surface. These same uplift events are suggested to explain an increased deposition in adjacent offshore basins on the Norwegian shelf and in the North Sea. However, more recently it has been suggested that prolonged climate-dependent erosion and isostatic uplift of existing topography may also explains the recent evolution of topography in Scandinavia. For this latter view, an increased sedimentation towards the present has been assumed a consequence of a climate related increase in erosion.
In this study we explore whether inverse modeling of landscape evolution can give new insight into Eocene to mid-Pliocene (54-4 Ma) landscape evolution in the Scandinavian region. We do this by combining a highly efficient forward-in-time landscape evolution model (FastScape; Braun and Willett, 2012) with an optimization scheme suitable for non-linear inverse problems (the neighborhood algorithm – NA; Sambridge, 1999a,b). In order to limit our approach to the fluvial regime, we exclude the most recent mid-Pliocene to Quaternary time period where glacial erosion processes are expected to dominate landscape evolution.
The “goodness” of our forward-in-time landscape evolution models is evaluated using i) sediment fluxes based on decompacted offshore sediment volumes and ii) maximum elevation of topography from a mid-Pliocene landscape reconstructed using geophysical relief and offshore sediment volumes from the mid-Pliocene-Quaternary.
We find several scenarios consistent with the offshore sediment record and maximum elevation of our reconstructed mid-Pliocene landscape reconstruction: I) the combination of some (~0.9 km) initial topography at 54 Ma and minor continuous uplift until 4 Ma (<0.04 mm/yr), II) substantial (~ 2 km) initial topography at 54 Ma and no induced tectonic uplift until 4 Ma, and III) rapid tectonic uplift of initially low topography (~ 0.1 km) at ~54 Ma followed by tectonic quiescence until 4 Ma. However, out of these only scenario II (no tectonic uplift) matches large-scale characteristics of the estimated mid-Pliocene topography well.
Our preferred model for Eocene to mid-Pliocene landscape evolution in Scandinavia is therefore one where high topography (~ 2km) has existed throughout the time interval from 54-4 Ma. We do not find several phases of peneplain uplift necessary in order to explain offshore sediment volumes and large-scale topographic patterns. On the contrary, extensive peneplain dissection seems inconsistent with the low rates of erosion we infer based on the offshore sediment volumes.

Braun, J., Willett, S.D., 2012. Geomorphology 180-181, 170-179.
Sambridge, M., 1999a. Geophys. J. Int. 138, 479-494.
Sambridge, M., 1999b. Geophys. J. Int. 138, 727-746.

Thomas Theunissen
2016-11-30 12:00 - 13:00 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Long-term coupling and feedbacks between surface processes and tectonics during rifting

Whereas significant efforts have been made to understand the feedback between mountain building and surfaces processes, limited research has been done on the relationship between surface processes and extensional tectonics.
Here we present high-resolution 2-D coupled tectonic-surface processes modeling of extensional basin formation. The main aim is to find out how erosion and deposition affect the deformation in extensional systems. We test the combined effects of crustal rheology and varying surface process efficiency (erodibility, sea level) on structural style of rift and passive margin formation.
The results show that both erosion of rift flank areas and basin deposition enhance localization of crustal deformation. Frictional-plastic extensional shear zones accumulate more deformation during a longer period of time, and loading of offshore basins can generate crustal ductile flow. In extreme cases, sediment deposition delays lithospheric rupture. These mechanisms are enhanced when fluvial erosion, transport and deposition are efficient.
We show that removal of mass from rift flanks and sediment loading in the basin area provide a first order feedback on tectonic deformation and control on rifted margin tectonic-morphology. However, surface processes do not change the first order mode of rifting, which is largely controlled by crustal rheology. Rift escarpment morphology is a function of paleo-topography and sea level. Variation of strain localization in natural rift systems correlates with the observed behavior and suggests similar feedbacks as demonstrated by the forward numerical models.

Thilo Wrona
2016-11-23 12:00 - 13:00 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Silica diagenesis and physical properties of Cenozoic rocks in the North Viking Graben, northern North Sea
by Thilo Wrona, Christopher A-L. Jackson, Mads Huuse and Kevin G. Taylor
As an introduction, I thought it would be nice to present some of the work that I’ve done in my PhD. This covers quite a range of disciplines, so I hope there’s something in there for everyone.
Silica diagenesis describes two dissolution-precipitation reactions that can drastically change the physical and fluid flow properties of its host strata. To study the effect of silica diagenesis, we combine mineralogical-, well- and 3-D seismic data of the North Viking Graben, northern North Sea. We use optical microscopy, scanning electron microscopy and X-ray diffraction to identify the opal-A/CT transformation in the Cenozoic succession. We determine the effect of the opal-A/CT transformation on the host rock properties by combining quantitative mineralogical data obtained by X-ray diffraction with wireline data of sixteen exploration wells using multiple linear regression analysis. The analysis shows that: (1) opal-A content explains host rock porosity to a large extent and (2) opal-CT and pyrite content explain host rock porosity to a lesser degree. The overall decline in opal-A content with depth is interpreted to reflect increasing biogenic silica production between the Eocene and Miocene. Focused reductions in opal-A content that coincide with increased opal-CT contents are probably the result of opal-A/CT transformation. Because the observed opal-A/CT transformation does not coincide with major lithology variations, it is assumed that the transformation is primarily a function of time and temperature. This assumption allows us to model the spatial and temporal evolution of the opal-A/CT transformation. Modelling results indicate that the opal-A/CT transformation started in the Balder Formation in the Middle-to-Late Eocene, migrated upwards through the lower Hordaland Group, and fossilised as a result of Middle-Miocene sea-level fall and erosion. Moreover, we use these basin modelling results and a detailed fault analysis to study the impact of silica diagenesis on the formation of polygonal faults. Polygonal fault systems comprise large numbers of layer-bound, low-displacement normal faults, which in plan-view have a polygonal arrangement. Based on our results, we are able to demonstrate that the majority of the polygonal faults nucleated in the silica-rich strata. In summary, this study highlights that silica diagenesis is a complex process that can significantly change compaction and deformation of siliceous sedimentary rocks.

Anna Ksienzyk
2016-11-09 12:00 - 13:00 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Post-Caledonian fault activity in W-Norway: onshore and offshore don’t match – or do they?
by Ksienzyk, A.K., Wemmer, K., Rotevatn, A., Fazlikhani, H., Jacobs, J., Fossen, H.
K-Ar or Ar-Ar analyses of fault gouge fine fractions are becoming well-established methods to investigate the timing of fault activity. They rely on the synkinematic growth of illite, a K-bearing clay mineral, to date periods of fault movement. These methods come with a number of challenges, including contamination with host rock illite/muscovite and other K-bearing minerals, potential Ar-loss from the very fine-grained illite and/or convoluted histories of polyphase faulting. However, our understanding of fault systems and the behaviour of illite in fault gouges, while still far from complete, has improved to allow increasingly complex structural histories to be disentangled.
Isotopic dating of fault rocks can provide valuable information on the timing of fault activity, particularly in areas where stratigraphic evidence of faulting is absent or not preserved. In Norway, a number of recent studies (Davids et al., 2013; Torgersen et al., 2014; 2015; Ksienzyk et al., in press; Viola et al., in press) gradually reveal a distinct pattern of onshore fault activity: (1) The oldest illite ages associated with post-Caledonian fault movement are Middle Devonian-Carboniferous, depending on the study area. (2) An early Permian period of fault activity is recognised over large parts of onshore Norway and correlates well with rifting in the northern North Sea and Oslo Graben. (3) In the Mesozoic, onshore and offshore tectonics appear to be diachronous. Offshore, the Early Triassic-Middle Jurassic is generally considered to be an inter-rift period of tectonic quiescence. Onshore, on the other hand, illite ages document significant Late Triassic-Early Jurassic fault activity in southern and western Norway. Additionally, a younger period of onshore fault reactivation in the Mid-Cretaceous post-dates Late Jurassic-Early Cretaceous rifting in the northern North Sea.
Fault reactivation during Late-Jurassic-Early Cretaceous North Sea rifting appears to have migrated outwards from the rift centre. Faults in the Viking Graben were active during the early stages of this rift phase, in the Middle-Late Jurassic, while faults on the Horda Platform towards the east were reactivated later, in the Late Jurassic-Early Cretaceous (Bell et al., 2014). The Mid-Cretaceous reactivation of onshore faults, even further to the east, might thus be a continuation of this trend. The Late Triassic-Early Jurassic inter-rift fault activity observed onshore, on the other hand, cannot easily be linked to offshore rifting. However, recent studies as part of the MultiRift project have revealed significant inter-rift fault movement also in the northern North Sea, offshore western Norway (Refvem, 2016; Deng et al., in review). A closer look at offshore fault activity through time might thus reveal that onshore and offshore tectonics are not diachronous after all.
References:
Bell, R.E., Jackson, C.A.-L., Whipp, P.S. & Clements, B. (2014) Strain migration during multiphase extension: observations from the northern North Sea. Tectonics 33, 1936-1963.
Davids, C., Wemmer, K., Zwingmann, H., Kohlmann, F., Jacobs, J. & Bergh, S.G. (2013) K–Ar illite and apatite fission track constraints on brittle faulting and the evolution of the northern Norwegian passive margin. Tectonophysics 608, 196-211.
Deng, C., Fossen, H., Gawthorpe, R.L., Rotevatn, A., Jackson, C.A.-L. & Fazli Khani, H. (in review) Structural evolution during multiphase rifting: Oseberg area, northern North Sea.
Ksienzyk, A.K., Wemmer, K., Jacobs, J., Fossen, H., Schomberg, A.C., Süssenberger, A., Lünsdorf, N.K. & Bastesen, E. (in press) Post-Caledonian brittle deformation in the Bergen area, West Norway: results from K-Ar illite fault gouge dating. Norwegian Journal of Geology.
Refvem, M.A. (2016) Spatial and temporal evolution of fault arrays on the northren Utsira High, northern North Sea. MSc thesis, University of Bergen, 75 pp.
Torgersen, E., Viola, G., Zwingmann, H. & Harris, C. (2014) Structural and temporal evolution of a reactivated brittle–ductile fault – Part II: Timing of fault initiation and reactivation by K–Ar dating of synkinematic illite/muscovite. Earth and Planetary Science Letters 407, 221-233.
Torgersen, E., Viola, G., Zwingmann, H. & Henderson, I.H.C. (2015) Inclined K–Ar illite age spectra in brittle fault gouges: effects of fault reativation and wall-rock contamination. Terra Nova 27, 106-113.
Viola, G., Scheiber, T., Fredin, O., Zwingmann, H., Margreth, A. & Knies, J. (in press) Deconvoluting complex structural histories archived in brittle fault zones. Nature Communications.

Eirik Wiese, Felix Halpaap, Ronny Tømmerbakke, Sebastian Wolf
2016-11-02 12:00 - 13:00 | Glassburet, Allegaten 41, Bergen, Norway
Raiders of the Lost Arc
by Eirik Wiese, Felix Halpaap, Ronny Tømmerbakke, Sebastian Wolf
Abstract: In this more or less scientific geolunch, we present geological and some sociocultural revelations from our field trip to the Brasilia belt in southern Minas Gerais state in Brazil in September. In the frame of an educational collaboration between the Universities of Bergen, Rio de Janeiro and Saõ Paulo, we (four students and Indiana Fossen) participated in this 5th summer school of the “Integrated Orogen – Sedimentary Basin Studies” series. We introduce you to the large-scale geodynamic setting of southeastern Brazil and show features and lessons that we learned along three transects in the field. The geological setting of old orogens like the Brasilia belt and the passive margin along Brazil’s east is similar to the setting we find in Norway. We can thus discuss similarities and differences related to e.g. exhumation of subducted rocks, topography evolution and many more. This talk will be full of images, so bring your lunch, enjoy the journey and help us answer the geological questions that we brought back together with several kilograms of coffee!

Gang Lu
2016-10-26 12:00 - 13:00 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Potential temperature and margin width control melt volume at rifted margins
Gang Lu and Ritske S. Huismans

Passive continental margins may have a wide variety of structural and magmatim styles, but the controlling factors of magmatism remain controversial. Common explanations attribute the variation of magmatism to the change of mantle temperature, and associate volcanic margins to high temperature mantle plumes. However, this interpretation has been challenged due to the lack of evidences of plume tracks at some volcanic margins. Furthermore, anomalously low mantle temperature is required for non-volcanic margins, which is too low to produce normal oceanic crust. Here we use numerical models to investigate melt generation for margins with realistic rifting styles. Our results demonstrate a surprising correlation of enhanced magmatism with wide margin. This relationship is explained by the dynamic process of differential rifting, in which the lithospheric mantle ruptures earlier than the crust. On the basis of differential rifting, we derive an analytical prediction of melt volume over margin width, which is in agreement with both numerical results and nature observations. The new mechanism proposed here provides an alternative interpretation for enhanced magmatism, and suggests that mantle temperature at wide volcanic margins was probably over-estimated.

Hamed Khani
2016-10-19 12:00 - 13:00 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Pre-Mesozoic structural configuration in the northern North Sea rift basin; as a result of Devonian orogenic collapse in the Scandinavian-Scottish Caledonides
The northern North Sea rift basin is a product of multiple rifting phases during the Mesozoic time, developed on the heterogeneous crust comprising preexisting structures inherited from the Caledonian Orogeny and the Devonian post orogenic collapse. Pre-Mesozoic structural configuration and the basement rock distribution in the northern North Sea area has been investigated by an integration of more than 200,000 km² two dimensional regional seismic reflection data and more than 75 basement wells. Four main seismic facies has been described below the top acoustic basement surface and has been utilized to consistently map the seismic reflection patterns in the study area. Thick (500-1000 ms) high amplitude dipping reflection packages interpreted as offshore extensional shear zones that has been linked to the northwest and west dipping (towards the hinterland) onshore shear zones in the southwestern Norway including the Nord-Sogn Detachment Zone (NSDZ), Bergen Arc, Hardangerfjord, Karmøy and Stavanger Shear Zones (BASZ, HSZ, KSZ and SSZ respectively). However, several east and west dipping structures has also been mapped in the Måløy Slope, East Shetland Basin, East Shetland Platform and around the Utsira High and Åsta Graben. These structures shows the development of both foreland and hinterland dipping shear zones in the northern North Sea area, while towards the margin of the orogenic belt in the SW Norway and NE offshore Scotland only hinterland dipping structures have been developed. These pre-rifting structures seem to exert a first order control on the geometry and the development of the northern North Sea rift basin.

Christian Haug Eide
2016-10-12 12:00 - 13:00 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Tana – a very old river: Linking an Early Triassic delta to antecedent topography

The Fennoscandian Barents Sea Margin has been subject to little tectonic activity since the Carboniferous, and large portions have eluded significant Quaternary glacial erosion. Published fission track data indicate little denudation since the late Permian-Early Triassic. It may therefore be one of the most geologically stable margins on Earth, and it is therefore likely that catchments in the region could contain elements inherited from ancient catchments.

The catchment of the Tana River has long been interpreted to show features indicating that it was developed prior to present-day topography (Fig. 1A). A large delta-system that prograded from the present-day mouth of the Tana River during the Early Triassic, is visible in seismic data from the Finnmark Platform. In this study, we demonstrate that the present day Tana River Catchment shows several geomorphic evidence of having survived since the Earliest Triassic, that the studied Triassic delta was sourced from the present-day mouth of the Tana catchment, and that the post-Triassic modification of this catchment has been relatively small. We thus make the case that the present-day Tana catchment was formed close to the Permian-Triassic boundary.

This is important for explorationists because it demonstrates that reservoir properties in the Triassic of the Barents Sea are strongly influenced by catchment properties and sediment transport networks. Source-to-sink techniques can thus be instrumental in predicting extent and quality of subsurface reservoirs. Triassic strata in the Barents Sea generally show more favorable reservoir properties close to the Fennoscandian shield. This is because the majority of the basin fill was supplied through a vast fluvial system from the Uralian Orogen, and these sediments make up the bulk of the Triassic sedimentary package. Smaller catchments along the Fennoscandian margin supplied more mature shield-derived sediment to the basin margins only. Understanding these ancient catchments will help inform and constrain the amount of high-quality sand supplied from the shield to the basin through time.

Wenlu Zhu (UMD)
2016-10-05 13:00 - 14:00
Title: Reaction-induced cracking during mineral carbonation: Evidence from time-resolved microtomography

Laurent Montési (UMD)
2016-10-05 12:00 - 13:00 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Title: Melt extraction processes and speed at mid-ocean ridges

Jhon Munoz-Barrera
2016-09-28 12:15 - 13:15 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Subsurface characterization of structural traps in the outer Nunchia foothills, Colombia.
The foothills have been focus of several researches because (1) in their sediments are recorded the uplift history of the mountain belts, (2) these areas accommodate the regional shortening, and (3) these zones are highly prospective for hydrocarbon exploration. Usually in these areas the structural models are generated based on surface geology, 2D seismic and exploratory wells. After a discovery, the models are updated using 3D seismic, development wells and production history.
The Eastern foothill of the Eastern Cordillera of Colombia is highly explored by its hydrocarbon potential. Based on some transverse zones and changes in structural styles it have been divided in three zones (Bayona et al., 2008; Cortés et al., 2006 and Cortés et al., 2009) Northern, Central and Southern Llanos Foothills (Figures 1 and 2). The Central Llanos Foothill is the most prospective zone with more than 3000MMOB of original reserves tested. Eight oil fields are situated in this zone; in the south: Cusiana, Cupiagua, Pauto Complex (Pauto, Floreña, Volcanera and Dele) and Huron oil fields and in the north the Capachos oil field. Between these two areas a region of 130km has been explored without success. Informally this region is composed by the Nunchia and Zamaricote foothills (figure 1). Two important geological features can be highlighted in this region, first the Eastern Cordillera changes its direction from N30E to N-S and second, the presence of new thrust salient that keeps the N30E direction and is composed by the Piedemonte fault system. The area have been interpreted as thin-skinned (Rochat et al. 2003) to thick-skinned (Teson et al, 2013) with some variations between them (Cediel et al; Munoz 2015). Rochat et al. (2003) divided the Nunchia foothills in two main regions, internal and external structure (Figure 2).
This work used 533.5Km2 of an exploratory 3D seismic acquired with sparse design, 511Km of 2D seismic, two exploratory wells and surficial geological information located in the Nunchia outer foothills (Figure 1) to (1) recognize the geometry of the structures, (2) identify the variability of the structures along strike, (3) identify which structures involve the reservoir rocks, and (4) define the structural style.
This research presents the first 3D exploratory structural model of the Nunchía outer Foothills. An integration of surface geology, 2D and 3D seismic and well information in ArcGis and Petrel software allowed the surface analysis, seismic interpretation and well correlation. Additionally, the interpretation was exported to Move software to build the structural model and generate the displacement analysis. This tool allowed the identification of interpretation problems. The model was created in time domain because the study area had only two exploratory well separated 3.4km in the dip direction.
The end-member of the Nunchia Foothills can be classified as active-roof duplex, characterized by a thin-skinned structural style. In this zone, the shortening is accommodated in a series of imbricate to duplex structures with different detachment levels. Therefore, this area can be divided in three zones: 1) basal structures, defined as structures that have the lower detachment in the Gachetá Formation; 2) intermediate structures, with detachment in both C-8 (Lower Carbonera Formation) and C-6 (Middle Carbonera Formation), and; 3) upper to surface structures with detachment level in C-2 (Upper Carbonera Formation). Along strike the Nunchía outer foothill become deeper to the north and the distance between the inner antiformal stack and outer imbricate region widens. The well correlation between the foreland and foothills sequence allowed interpreting that the Carbonera, León and Guayabo formations are syn-deformation deposits, with lateral thickness variation, increasing to the west and to the north.
Only the basal structures involve the reservoir rocks. Two structures were identified. The southern structure, Tangara, is a water bearing structure and the northern structure is untested with remain oil prospectivity.

Melanie Siegburg (U. of Southampton)
2016-09-14 12:15 - 13:15 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Geological Evolution of Boset-Bericha Volcanic Complex, Ethiopia, northern East African Rift
Continental rifting and break up is accompanied by tectonism and magmatism that varies over time in the Main Ethiopian Rift (MER) at the northern part of the East African rift. The Boset-Bericha volcanic complex (BBVC) is one of the largest stratovolcano complex in the MER, but little is known about the eruptive history, despite the fact that 4 million people live within 100 km of the volcano. The BBVC consists of the Gudda Volcano and the younger Bericha Volcano, two silicic eruption centres along the rift axis. The main volcanic activity of the BBVC is estimated to have occurred over the last ~2 Ma. Here I present a detailed
relative eruption chronology for the BBVC from morphometric analyses and mapping using high resolution LiDAR data. Petrographical and whole rock analyses provide new constrains on magmatic evolution at the BBVC.
The formation of the BBVC can be differentiated into 5 main eruption stages, subdivided in at least 12 phases with in total 128 mapped lava flows. Cross-cutting relationships of lava flows and eruption phases provide a relative chronology of the eruption history of the BBVC, starting with pre-BBVC rift basalts, pre-caldera and caldera activity and two post-caldera phases at
the Gudda Volcano. The Bericha Volcano formed during two main phases, followed by another post-caldera phase at Gudda Volcano. At least four fissure eruption phases recurred on the rift axis temporally in between the main eruptions phases. Morphometric analyses indicate a total corrected volume of eruptive material at the BBVC of ~36 km3, of which 68 % is
felsic, in particular erupted by the pre- and first post-caldera phase of the Gudda Volcano, 25 % is basaltic and 7 % has an intermediate composition. The total area of the BBVC is ~870 km2, of which ~62 % are rift basalts. Magma evolution is spatially and temporally complex shown by a bimodal distribution of rift floor basalts as well as peralkaline trachytic and rhyolitic lavas for the Gudda and Bericha Volcano, respectively, with rare intermediate lavas from fissure eruptions. Main compositional correlations indicate that fractional crystallisation may have played a major role in the development of magmas at the BBVC. Different FeO, MnO and Al2O3 contents at the Gudda and Bericha lavas may suggest different parental magmas
and/or a separate feldspar crystallisation due to changed conditions in the magma chamber of the Gudda volcano. Detailed differentiation of processes for magmatic evolution will be investigated by trace element and isotopic analyses. The composition and morphometry of lava flows changed over relative time from mafic rift floor basalts covered a large area, to explosive large – volume activity at silicic centres, which demonstrates a complex development of the BBVC.

Johannes Wiest
2016-09-07 12:15 - 13:15 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Title: Constraints from the Lyderhorn Gneiss on the tectonomagmatic evolution of the Øygarden Complex, SW Norway

The Øygarden Complex and the Bergen Arc System are enigmatic large-scale structures in the SW Norwegian Caledonides. So far, the lack of published U-Pb zircon ages from the Øygarden Complex limits clear interpretations. Located in the poorly studied eastern part of the Øygarden Complex, the Lyderhorn Gneiss forms the core of the Bergen Arc System. Detailed field mapping was conducted and seven samples were dated by SIMS U-Pb zircon geochronology.
Igneous protoliths formed during the Gothian-Telemarkian (1504 Ma) and Sveconorwegian (1041 Ma; 1026 – 1022 Ma) orogenic periods. Metamict zircons were reset by an Early Ordovician (483 Ma) thermal event and sustained elevated temperatures annealed previous radiation damage. Caledonian regional metamorphism left no measurable effect on the U–Pb system.
The structure of the Lyderhorn Gneiss is characterized by lineation-parallel, recumbent folds that record constrictional strain. Consistently oriented, top-to-ENE shearing prevailed during deformation from amphibolite facies conditions to the brittle-plastic transition. Fluid-assisted strain weakening formed E-dipping, phyllonitic detachments.
Mesoproterozoic protolith ages correlate the Lyderhorn Gneiss (and Øygarden Complex) with the Telemarkia domain of the Baltican basement and show a relation with the Sirdal Magmatic Belt. Our results suggest a continuous NNW-trend of Sveconorwegian domain boundaries and contradict widespread Sveconorwegian high-T metamorphism.
The structure of the Lyderhorn Gneiss is inconsistent with the current tectonic model of the Bergen area, however, it is well explained by an alternative model that considers core complex exhumation of the Øygarden Complex. The discussed model reconciles the interpretation of basement culminations along the entire Norwegian margin and enhances onshore-offshore correlations.

Gino De Gelder (IPGP)
2016-08-31 12:15 - 13:15 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Title: Flexural normal faulting in Corinth and an uplifting Hellenic fore-arc (S-Greece): tectonic changes in the Plio-Quaternary

Michael Gazley (CSIRO)
2016-08-24 12:15 | 4C12a, CGB seminar room 4th floor
High resolution characterisation of gold mineralisation
Microcharacterisation techniques are becoming increasingly advanced, with speed of data collection and detection limits continually improving. As micro-scale variation can be key to understanding the large-scale variations in a mineral system, these developments are enhancing the geologist’s ability to resolve mineral systems complexity
This talk will summarise some of the research currently being undertaken in the Mineral Resources program of Australia’s Commonwealth Scientific Industrial Research Organisation (CSIRO). This talk will highlight applications of advanced resource characterisation to a variety of settings including samples from orogenic and epithermal systems. Techniques discussed will include scanning electron microscopy, electron back scatter diffraction, synchrotron X-ray fluorescence mapping, high-resolution X-ray computed tomography, and atom probe, as applied to understanding the elements and minerals that are associated with gold and the micro-nano-structure of the gold itself.

Joint seminar with GeoBio

Sarah Schröder (GFZ)
2016-08-23 12:15 - 13:15 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Title: Calibration of Surface Evolution Codes (SECs) Using a DEM as Initial Topography: A case Study for the Pamir
