Radiolarite and spring in the Fribourger Prealps

A number of raw materials were used for the production of chipped stone artefacts at the site of Arconciel/La Souche, Kt. Fribourg, Switzerland. Some of you might already know that I am doing a use wear analysis of the finds from the Late and Final Mesolithic abri for my PhD.

Of course, I am curious to see these places and the sources of the raw material of the archaeological artefacts. And it is spring! Here on the Swiss plateau the snow is gone, and in the Alps much has already melted as well. So, with a trusted companion I set out on an expedition to go and find the radiolarite outcrops in the Fribourger Prealps on the Brendelspitz. As guides we had the article by Braillard etal 2003 and the great little book Geologischer Pfad Gastlosen by Braillard and Rebetez (2010) (thank you Luc!).  What these, sadly, did not tell us, was that we underestimated Lady Winter’s resilience and had to fight through leg-deep snow at times. And no, we did not bring snowshoes… By then, we were too foolhardy and just had to get up there!

various types of radiolarite, from Braillard etal 2003

The main raw materials used at the site during the Mesolithic are “Ölquartzite”, radiolarite and flint (Braillard, Menoud et al. 2003; Mauvilly 2005; Mauvilly, McCullough et al. 2008). Most of these raw materials are to be found at a not too great distance from the site of Arconciel/La Souche. The closest source would have been the Sarine riverbed. Radiolarite, “Ölquartzite” and some types of flint can be found there. In the Jura Mountains further flint sources are known. Sources of “Olquatzite” and radiolarite are known in the Fribourger Prealps, the range of middle high Alpine mountains in the southern parts of the canton, and in the neighbouring areas of the Bernese Oberland[1]. But I will focuss only on the radiolarite in this post.

Radiolarite outcrops near the Jaunpass

A number of outcrops of Radiolarite exist in the southern part of the Canton Fribourg, the Fribourger Prealps, and in the Simmental in the Bernese Oberland. We headed for the outcrop at the Brendelspitz near the Jaunpass (Braillard and Rebetez 2010). Others can, for example, be found near the Sattelspitz and near the Greuyre Pass (Braillard, Menoud et al. 2003).

As I mentioned in earlier posts, the region has been subject to much archaeological survey by the SAEF and now over 150 findspots dating to the Mesolithic are known in the Fribourger Prealps. Considering this and the fact that the region around the Jaunpass is not that far away from Arconciel/La Souche and relatively easily reachable by following the Sarine Valley and travelling up the Jaunpass, it is likely that the raw material used for the radiolarite artefacts found in Arconciel/La Souche originate from here and further outcrops in the region. The Jaunpass, by the way, still forms a mayor route between the Fribourg region and the Bernese Oberland, where – e.g. in the Simmental further (Late) Mesolithic and Late Upper Palaeolithic sites are known[2].

Radiolarite is the result of a compression of radiolarian ooze (L. Braillard, pers. comm.; Allaby and Allaby 1991). It thus consists mostly of the skeletal remains of radiolarians, which collected at the bottom of the Tethys Ocean during the Jurassic and Lower Cretaceous (Braillard and Rebetez 2010). Radiolarians are single celled organisms with siliceous skeletons (Allaby and Allaby 1991). Sometimes, when using a strong microscope, you can actually see these skeletons within the stone. Calcite is another of the stone’s component. Most of the calcite has disappeared over the ages, although some calcite can still be chemically detected, especially in the red varieties. It is also not uncommon to have cracks filled with calcite veins, (Braillard, Menoud et al. 2003). Further inclusions include the remains of organic matter and recrystalisations (both only microscopically visible).

Arconciel/La Souche Brendelspitz

As a sedimentary stone, Radiolarite is distinctly banded (~5-15cm, more rarely up to 30cm thick). These bands are often spectacularly folded (during the Upper Cretaceous) and this tectonic movement also caused the stone to be internally heavily fractured. This is, of course, of a disadvantage for knapping it. As is visible in the picture and in the slideshow, the colour varies from a rather opaque grey, via green to red. The majority is grey or green. The red only occurs in the top ca. 20% of the deposits (Braillard, Menoud et al. 2003).

The banded nature of the rock and the internal fractures must have had some influence on the production of chipped stone artefacts and thus, at least indirectly, also on the use wear traces (Braillard, Menoud et al. 2003; Braillard and Rebetez 2010). As the late Mesolithic artefacts found in Arconciel/La Souche are really small, it might be that the bandedness as well as the fissures did indeed have some influence on the chaîne opératoire, i.e. that theyare one of the reasons for the limitied size of the artefacts. on the other hand, other fators might have determined the relatively small size and the raw material was not an active cause of this. I expect that this will be one of the things I will be looking at when interpreting the use wear results.

The end

Naturally, I had to take a few lumps back with me to try out its knapping qualities and, besides, I need some material for the use wear analyses anyway, as control sample. I cannot wait trying my knapping skills on the radiolarite.

So, even though we should perhaps have waited a week or two, we survived the – rather more than anticipated – adventurous expedition. It was a fab first spring hike, though. And as an added bonus I now have a whole pile of radiolarite lying about. The round described in the booklet should take – with all the snow gone – about 4:00 hrs. (If you walk from the village of Jaun an extra hour up and ~30min down. There’s a little shop/bakery in Jaun.) I heard a lot about the beauty of the Fribourger Prealps, and it really is beautiful there. Have a look at the slides! As in life, not everything in the slideshow is about archaeology.

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Update June 2013:

@ferwen has written a very informative blogpost about the wonderfully beautiful radiolarians. It is really worth to have a look! You find it HERE.

Bilbiography

Allaby, M. and A. Allaby (1991). The consise oxford Dictionary of Earth Sciences. Oxford, Oxford University Press.

Andrist, D., W. Flückiger, et al. (1964). Das Simmental zur Steinzeit. Bern, Stämpfli & Cie.

Braillard, L., S. Menoud, et al. (2003). “Préalpes et chasseurs-cueilleurs en terres fribourgeoises, une vielli et longue histoire …” Cahiers d’Archéologie Fribourgeoise 5: 42-63.

Braillard, L. and D. Rebetez (2010). Geologischer Pfad Gastlosen. Fribourg, Itinéraires géologiques fribourgeois.

Crotti, P. (2002). Der Abri von Chateau-dOex; ein Siedlungsplatz in den Voralpen. Die ersten Menschen im Alpenraum von 50 000 bis 5000 vor Christus. P. Curdy and J.-C. Praz. Sitten, Walliser kantonsmuseen.

Mauvilly, M. (2005). “L’abri d’Arconciel-La Souche (FR), un site exceptionnel du Mésolithique récent et final ” Archäologie Schweiz 28(1): 40-41.

Mauvilly, M., F. McCullough, et al. (2008). Arconciel/La Souche 1998-2006: Rapport préliminaire

Press, F. and R. Sievers (1986). Earth. New York, W.H.Freeman and Company

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[1] For a more detailed description, see (Braillard, Menoud et al. 2003)

[2] Sites: e. g.Riedli Balm  (Andrist, Flückiger, et al. 1964) and Chateaux d’Œx (Crotti, 2002).