The Ordovician sedimentary rocks of the Oslo Rift

Guide: Morten Bergan, Bayerngas

After a fantastic field trip during the previous conferences, we are happy to announce a new little field trip for the upcoming conference. The leisure hike along the fjord will introduce the curious geologist to the stratigraphy of the Oslo Graben and make comparisons with the geology of the NCS, and make our own de-risking for what to see on the next trip stop in this very nice geotope along the shore.

Foto: Halfdan Carstens

Foto: Halfdan Carstens

On the afternoon of the first day we plan the short field-trip to the Lower Paleozoic sedimentary rocks of the Oslo Graben (Oslofeltet). Morten Bergan (Bayerngas Norge) who possesses detailed knowledge of this famous sequence, will again be our guide. The locations are right outside the hotel premises at Fornebu, along the coast of Oslofjorden.

Foto: Halfdan Carstens

Foto: Halfdan Carstens

The trip starts at 17:00 (Wednesday), and we meet at the main entrance of Hotel Scandic. The guiding starts at the circular stone building (“steinbadehuset”) just north of the light blue building of Sjøflyhavna kro which lies next to the fjord due east of the hotel.

Foto: Halfdan Carstens

Foto: Halfdan Carstens

In nice spring weather the tour will take roughly one and a half hour. It will not be a strenuous walk, but it is wise to bring shoes for outdoor activity. The return walk to the hotel is about 1 km, and we will be back in due time before dinner.

The Ordovician succession in the Oslofjord area totals about 475m thickness. The intermixed formations consist of grey shales and various kinds of whitish limestones that are well exposed and easily accessible along the coast of Fornebu. The Oslo-Asker district was the type area for the “etage” system established by Theodor Kierulf (1857) that was later modified by Waldemar Chr. Brøgger (1882 and 1887). Their mapping, including the work by the local Fornebu geologist Werner Werenskiold (1911), is still the most detailed mapping available, but the terminology was modernized to the use of formation names hundred years later (Owen at al., 1990).

Foto: Halfdan Carstens

Foto: Halfdan Carstens

We will compare our observations to the Norwegian continental shelves and encourage discussions as we trudge along the coastline.

The excursion will not display spectacular and breathtaking cliff faces, neither will there be many trilobites to see. However, we will pass through a very nice stratigraphic section with many of the Middle and Late Ordovician formations (“etage 4”) in a well exposed and beautiful coastline including several formation boundaries, unconformities, folds, faults, as well as sill and dyke intrusions. There will be stops for discussions on stratigraphy and depositional environments.

Overall, we believe you will all be surprised, and we will go to dinner with some new experiences. Although no “recent technological advances” are made here, we will learn geo-history from what the fathers of Norwegian geology once mapped out in the Oslo Graben.

Foto: Halfdan Carstens

Foto: Halfdan Carstens

 

More to read:

A rough guide to Oslofeltet (in Norwegian): Veien er målet
Biking through Oslofeltet (in Norwegian): Fra stein til stein

The Oslo Graben is part of a larger Palezoic graben system that originated in the Paleozoic.

The Oslo Graben is part of a larger Palezoic graben system that originated in the Paleozoic.

Cambo-Silurian sedimentary rocks (blue colour) are widespread around Oslo.

Cambo-Silurian sedimentary rocks (blue colour) are widespread around Oslo.

The conference and prospect fair is organised by the Geological Society of Norway, in cooperation with GeoPublishing

The conference and prospect fair is organised by the Geological Society of Norway, in cooperation with GeoPublishing