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Structure of the Wyville-Thomson Ridge (preparing for EAGE 2018 in Copenhagen)

Bennett Haworth (ARK-CLS) and I have been putting the finishing touches to our talk on the structure of the Wyville-Thomson Ridge, which Bennett will be presenting at the EAGE conference in Copenhagen. The talk will be on Thursday morning (14th June), but we’ll both be present for the whole conference.

If you’d like to find out more about the project, or chat to me about integrating and interpreting different geological and geophysical datasets to achieve a more robust and defensible Earth Model, please get in touch.

In the meantime, here’s a little taster of what we’ve been up to…

The Wyville-Thomson Ridge is one of the largest Cenozoic structures on the UK Atlantic Margin. The ridge has been the subject of several studies, but its structure and the nature of its development remain uncertain due to the poor seismic imaging of deeper structures in the region.

We have addressed the seismic imaging problem by combining interpretations of multiple different geophysical datasets together. 2D broadband seismic and well data (released by the OGA in 2016) are used to interpret the shallow geology. This is then combined with gravity and magnetic data (public domain and released by the OGA), which record variations in the density and susceptibility of the entire crust, making it possible to account for the effect of the volcanic succession, so that the deeper structure can be determined.

Integrated interpretation of the combined datasets was undertaken in two stages. First, a qualitative interpretation of 18 2D seismic profiles was completed. Well tops were marked on to the seismic to provide a starting point for seismic interpretation. The principal horizons, unconformities and faults were interpreted on the seismic down to Top Basalt (which is shown in the image below).

3D horizon for Top Basalt interpreted from the 2016 OGA 2D seismic lines, and used as a constraint in subsequent gravity and magnetic modelling

Various corrections, transforms and filters of the gravity and magnetic data were calculated to enhance different parts of the signal, to help isolate the location and depth of gravity and magnetic sources. These map-view grids were interpreted at the same time as the seismic data, so that the two data-types could be used to produce a consistent interpretation. The map-view data were particularly useful for validating the placement of major structures and interpolating them away from seismic control.

XField was used to forward model the gravity and magnetic data along the seismic profiles. The seismic interpretation was used to build initial density and susceptibility models and density and susceptibility values derived from nearby wells and literature were used to populate the model. Additional constraints on the geology and crustal thickness were taken from recent publications. Incremental changes were made to the parts of the model that were unconstrained by other data, to produce an interpretation that tied across all the profiles and that satisfies all the data. The result is a robust geological model of the Wyville-Thomson Ridge.

We have shown that:

1) The Wyville-Thomson Ridge comprises an inverted pre-Cretaceous sedimentary basin, with folding caused by the reactivation of the pre-existing normal faults;

2) The eastern termination of the Wyville-Thomson Ridge is a horsetail splay, with a geometry indicative of left-lateral transpression in the Cenozoic.

Hope to see you in Copenhagen!

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