Field Guide for the NORDQUA Excursion to Sunnmøre, Western Norway, 22-25 September 2014

Field guide for the NORDQUA excursion to Sunnmøre, western Norway, 22-25 September 2014.

Eiliv Larsen1, Jan Mangerud2, and John Inge Svendsen2.

1The Geological Survey of Norway. E-mail: [email protected] Mobile phone: +47 95 85 50 51.

2Department of Earth Science, University of Bergen. [email protected], Mobile phone: +47 90 94 49 46 [email protected], Mobile phone: +47 97 46 50 13

Foreword

This excursion guide was written before our pre-excursion planning trip. It will therefore probably be some minor changes in the program. Most of the older literature that we refer to in the guide can be down-loaded from Jan Mangeruds home page: http://www.folk.uib.no/ngljm/. If any of you have problems to obtain papers where one of us is author/co-author then do not hesitate to send us an e-mail with request.

Program Day 1. Arrival at Ålesund airport, Vigra. Site 1: Skjonghelleren Cave. Only some 8-10 people can creep into Skjonghelleren at a time, so we will try to find some parallel activity. Site 2: Dimna bog. Coring. Vedde and Dimna ash beds. Stay overnight in Quality Hotel, Ulsteinvik.

Day 2. Site 3: Mulevika on the westernmost shore of Nerlandsøy. Beach ridge at marine limit. Site 4. Frøystadmyra, Leinøy. Coring. Tsunami, sea-level changes. Site 4: Litlevatn, Gurskøy. Coring. Sea-level changes. Litlevatn was isolated during Late Allerød. Stay overnight in Best Western Hotel Baronen, Spjelkavik.

Day 3. Site 5. Riksheim, Sykkylven. Sections in Younger Dryas local moraine. Site 6. Hundeidvik. Gravel pit in Younger Dryas sandur-delta. Stay overnight in Best Western Hotel Baronen, Spjelkavik.

Day 4. We will see Younger Dryas moraines, blockfields in the mountains, in addition to the major geomorphology along the fjords on our way. Site 7. Skorgenes in Tresfjorden. Three superimposed ice marginal deltas. Departure from Ålesund or Vigra.

Fig. 1 An overview map. The red square shows the excursion area. The Last Glacial Maximum (LGM) ice limit is marked along the continental shelf edge. Note that the YD ice margin in Sunnmøre is located near the fjord heads in contrast to around Bergen where the YD margin almost reached the open ocean.

Fig. 2. Overview map of the excursion area.

Skjonghelleren and the Ålesund interstadial

Skjonghelleren is a cave located close to the Vigra (Ålesund) airport and will be the first locality we visit. The cave is the type locality for the Ålesund Interstadial (Larsen et al., 1987), the best dated pre-LGM interstadial in the Nordic countries. The cave is formed by sea waves during the Early Weichselian or before. Simplified there are two types of sediments (Fig. 4); 1) blocks deposited during ice-free periods and 2) laminated clay deposited when the opening was blocked by the Scandinavian Ice Sheet. Three pre-Holocene block layers are described (Fig. 6) (Larsen et al., 1987); here we will concentrate on the youngest, the Ålesund interstadial bed. The Laschamp paleomagnetic excursion is identified in the clay bed below Ålesund, and the Mono Lake excursion in the bed above Ålesund (Fig. 10) (Larsen et al., 1987; Løvlie and Sandnes, 1987). These excursions are correlated with increased fluxes of cosmic-radiation produced isotopes in Greenland ice cores (Mangerud et al., 2003). The Ålesund interstadial is dated by more than 40 AMS 14C dates (Figs 8 and 10) (Mangerud et al., 2010) from Skjonghelleren and Hamnsundhelleren – a cave east of Skjonghelleren.

Fig. 3. Map of Valderøya with Skjonghelleren marked with blue dot.

Fig. 4. The depositional environments and sediment succession in Skjonghelleren, from Mangerud et al. (2010).

Fig. 5. Upper panel: Longitudinal profile of Skjonghelleren. Note that the cave is >70 m long and that there is >20 m thick sediments in the cave. Lower panel: map of the cave. From (Larsen et al., 1987).

Fig. 6. The section and coring results from the outer part of the cave. From Larsen et al. (1987). During the excursion we will see Laminated clay F and the block on top.

Fig. 7. The section in the innermost part of the cave, that we will see during the excursion. From Larsen et al. (1987).

Fig. 8 .Table of bones identified at an early stage From Larsen et al (1987). Presently > 30 000 bones are picked from Ålesund interstadial beds in Skjongehelleren and 15 000 in Hamnsundhelleren.

Fig. 9. The radiocarbon ages from Skjonghelleren, Hamnsundhelleren and shellbearing tills. From Mangerud et al. (2010).

Fig. 10. Comparison betwen Greenland ice cores and Sunnmøre. Note that black curves and ages refer to the Middle Weichselian, whereas red refer to the Late Weichselian. From Mangerud et al. (2010).

Fig. 11. Correlation between the Ålesund and Greenland ice cores. From Mangerud et al. (2010).

Fig. 12. A glaciation curve for the entire Weichselian, where the events found in Sunnmøre are marked. From Mangerud et al. (2011).

Shellbearing tills

The Ålesund interstadial was originally defined from radiocarbon dates from shell fragments in till (Mangerud et al., 1981; Mangerud et al., 1979). Such tills are only exposed in temporarily excavations for buildings, roads, etc. and we do yet not know if any exposure will be available. Later re-dating with AMS confirm that most of the sites are of Ålesund age (as defined in Skjonghelleren), whereas some sites pre-date the Laschamp and we therefore named that ice-free period for Austnes interstadial (Mangerud et al., 2010).

Fig. 13. The excavated caves (red dots and names) and sites with shell-bearing tills (numbers). 1 - Rogne, 2 - Longva, 3 - Ullaholmen, 4 - Austnes, 5 – Hildrestrand, 6 – Gjøsundet, Vigra, 7 – Synnes, Vigra, 8 – Vikebukt, Vigra, 9 – Dyb, Godøy, 10 – Liaaen, Ålesund (that was the first site discovered), 11 – Spjelkavik, Ålesund, 12 – Eidsvik.

The Vedde and Dimna ash beds

The discovery of the Vedde Ash and its correlation with Ash Zone 1 in the North Atlantic and ash beds in the Norwegian Sea (Kvamme et al., 1989; Mangerud et al., 1984) triggered a search for Vedde and other ashes in the north-west Europe, the surrounding seas and in Greenland ice cores. Vedde is presently found at a large number of sites (Lane et al., 2012) and is a key horizon for correlation between continental, marine and Greenland ice core sequences. We will see the Vedde Ash at several coring sites the first and second day. We searched for more ashes and discovered the Dimna Ash with identical composition as the rhyolitic component of the Vedde Ash (Koren et al., 2008; Lane et al., 2012). We will core the type locality, where the Vedde Ash also is much thicker than any other place in Norway - up to 48 cm thick.

Fig. 14. Vedde Ash in the Ålesund area. After Mangerud et al (1984)

Fig. 15. Stratigraphic position of the Vedde Ash in different settings and elevations above sea level. After Mangerud et al (1984)

Fig. 16. The distribution of the Vedde Ash – from Greenland to Italy. From Lane et al (2012).

Fig. 17. Maps showing of the location and coring sites at Dimnamyra (-bog). From Koren et al (2008).

Fig. 18. Cross section of Dimnamyra. From Koren et al. (2008).

Fig. 19. Stratigraphy in Dimnamyra. From Koren et al. (2008).

Fig. 20. Ashes in Dimnamyra (-bog). From Koren et al. (2008).

Fig. 21. Left figure: Geochemistry of ash beds. Right figure: Late glacial ashes in NW Europe. From Koren et al (2008).

Fig. 22. Trace element composition of the Vedde and Dimna ashes. From Lane et al (2012).

Fig. 23. Pollen diagram from Dimnamyra. From Krüger et al. (2011). 20

Relative sea-level fluctuations

Shore lines and sea-level fluctuations will be the main theme for the second day. We have used the classical Nordic method utilizing isolation basins. This might be familiar for most participants, but we include a first figure explaining the principle. We include then a number of illustrations from the sites we will core. In the next section include some figures from a syntheses paper for sea-level changes for the entire Late Glacial and the Holocene and across a larger area. Note that these “old” papers use only un-calibrated C-14 years.

Fig. 24. The principle of isolation basin method. From Svendsen and Mangerud (1987)

Fig. 25. Location map for the coring sites. From Svendsen and Mangerud (1990).

Fig. 26. Map of Frøystadmyra. From Svendsen and Mangerud (1990). 22

Fig. 27. The stratigraphy in the studied basins – as we described them before we discovered the Storegga tsunami. Note “Mixed sediments” in Skolemyra. A “tsunami version” is given in Fig. 34. Note the dashed line that connect the Vedde Ash between the columns. From Svendsen and Mangerud (1990).

Fig. 28. Cross section of Frøystadmyra I. From Svendsen and Mangerud (1990).

Fig. 29. The original sea-level curve and the one revised after we discovered the Storegga tsunami. From Bondevik et al (1998). 24

The Storegga tsunami

The very last day of field work for his Master thesis in 1983 John Inge Svendsen discovered a bed of marine sand and shell above the Tapes transgression level. He proposed that it possibly could be a deposit from a tsunami that the Storegga Slide could have released. However, because Jan Mangerud now had started a major research project on Svalbard, where John Inge followed to do his Dr. thesis, the tsunami hypothesis was not tested until Stein Bondevik started with his Dr. thesis ten years later. We, and other scientists, had earlier interpreted the tsunami deposits as the result of the Tapes transgression (relative sea-level rise). This had led to construction of a too fast, and some places too high Tapes transgression (Bondevik et al., 1998). We subsequently found that the Tapes very rarely (never?) had eroded sediments in basins that are some few meter deep, whereas the tsunami most often had eroded. Deposits from the Storegga tsunami are now found around the entire North Sea and also on Greenland (Bondevik et al., 2005a; Bondevik et al., 2005b; Bondevik et al., 1997a; Bondevik et al., 1997b).

Fig. 30. The Storegga Slide and sites where Storegga tsunami deposits are described. From Bondevik et al (2005).

Fig. 31. How run-up for the tsunami is determined. From Bondevik et al (2005).

Fig. 32. Modeling of the tsunami. After Bondevik et al (2005).

Fig.,33. Tsunami facies. From Bondevik et al (1997a). 27

Fig. 34. The Storegga tsunami deposits in Frøystadmyra and neighbouring sites. From Bondevik et al. (1997a)

A synthesis of sea-level changes.

Fig. 35. An overview map showing the area we studued (Hatched) and the profile line for Fig. X. After Svendsen and Mangerud (1987).

Fig. 36. The isobases and projection planes used. After Svendsen and Mangerud (1987).

Fig. 37. Shoreline diagram for Sunnmøre-Trøndelag. Note that ages are in uncalibrated C-14 years. After Svendsen and Mangerud (1987).

Fig. 38. Sea-level curves deduced from the shore-line diagram. After Svendsen and Mangerud (1987).

Fig. 39. Profiles across Scandinavia, indicating how “shorelines” should bend over the landmass. After Svendsen and Mangerud (1987).

Younger Dryas cirque moraines

As seen from the map Fig. 1 the Younger Dryas ice sheet moraines are located near the head of the fjords. In the, often alpine type, mountains farther west there were numerous cirque glaciers during the Younger Dryas. Most of these local glaciers apparently survived the Allerød, although they probably were smaller than during the Younger Dryas (Larsen et al., 1998), whereas the well- studied Kråkenes glacier was formed soon after the onset of the Younger Dryas (Larsen et al., 1984; Lohne et al., 2014; Mangerud et al., 1979). On day 3 we will visit the site Riksheim with an exposure in such a moraine and also some other sites in the vicinity of Riksheim.

Fig. 40. The black lines are moraines, mainly cirque moraines. Note Ålesund in upper left corner. We will visit Sykkylvsfjorden, a tributary to Storfjorden in the right hand part of the map. From Follestad (1995) 33

Fig. 41. Maps of the cirque moraines at Riksheim and adjacent sites. From Larsen et al (1998).

Fig. 42. Profile from Riksheim. From Larsen et al (1998).

Fig. 43. Glaciation relative to sea level at Riksheim. From Larsen et al (1998).

Fig. 44. Reconstructions of the develoment at Riksheim. From Larsen et al (1998).

Skorgenes – two pre-LGM interstadials in superposition

Skorgenes is a rare, if not unique site in Norway because the late-glacial marine limit delta directly overlies two earlier deglacial sequences separated by two basal tills (Larsen and Ward, 1992).

Fig. 45. Location of Skorgenes. From Larsen and Ward (1992).

Fig. 46. Map of the Skorgens site. From Larsen and Ward (1992).

Fig. 47. Stratigraphy at Skorgenes. From Larsen and Ward (1992).

Fig. 48. Stratigraphy and fabric at Skorgenes. From Larsen and Ward (1992).

Fig. 49. Obtained OSL dates from Skorgenes and correlation with Skjonghelleren. From Larsen and Ward (1992).

In the lowest formation at Skorgenes there are some spectacular clastic dikes, interpreted as injection veins from the sole of the ice sheet into the underlying sediments (Larsen and Mangerud, 1992). They are some few cm in diameter and many meters long, mainly almost vertical, but sometimes horizontal for several meters. This part of the section is normally covered by sloped material, but we will attempt to find an operator with excavator to clean that part for our excursion.

Fig. 50. Detail of a clastic dike at Skorgenes – horizontal with a branch turning down. Note the small offset in the primary bedding. The scale is the top of a knife, so this vein is 2-3 cm thick.

Other topics

As we travel around and see the landscape the excursion guides and any of the participants can comment on, ask questions, or start a provocative discussion about the observations.  We will for example see the large, almost horizontal platform along the coast, named the Norwegian Strandflat, for which ages and processes are much discussed.  Fjords and fjord formation is probably easier, or ---?  We will from Vigra (see Gamlemsveten) and when crossing the mountains the last day, see extensive mountain block fields. Do they demonstrate ice free summits during glaciations?  If we are not too unlucky with the weather we will several places have nice view of the alpine topography of the mountains “Sunnmørsalpene”. Did these narrow peaks escape glaciation, or did they survive under cold-based ice?

References. Bondevik, S., Løvholt, F., Harbitz, C., Mangerud, J., Dawson, A., Svendsen, J.I., 2005a. The Storegga Slide tsunami—comparing field observations with numerical simulations. Marine and Petroleum Geology 22, 195-208. Bondevik, S., Mangerud, J., Dawson, S., Dawson, A., Lohne, Ø., 2005b. Evidence for three North Sea tsunamis at the Shetland Islands between 8000 and 1500 years ago. Quaternary Science Reviews 24, 1757-1775. Bondevik, S., Svendsen, J.I., Johnsen, G., Mangerud, J., Kaland, P.E., 1997a. The Storegga tsunami along the Norwegian coast, its age and runup. Boreas 26, 29-53. Bondevik, S., Svendsen, J.I., Mangerud, J., 1997b. Tsunami sedimentary facies deposited by the Storegga tsunami in shallow marine basins and coastal lakes, western Norway. Sedimentology 44, 1115-1131. Bondevik, S., Svendsen, J.I., Mangerud, J., 1998. Distinction between the Storegga tsunami and the Holocene marine transgression in coastal basin deposits of western Norway. Journal of Quaternary Science 13, 529-537. Follestad, B.A., 1995. Møre og Romsdal Fylke - kvartærgeologisk kart 1 : 250 000. Norges geologiske undersøkelse. Koren, J.H., Svendsen, J.I., Mangerud, J., Furnes, H., 2008. The Dimna Ash -- a 12.8 14C ka-old volcanic ash in Western Norway. Quaternary Science Reviews 27, 85-94. Krüger, L.C., Paus, A., Svendsen, J.I., Bjune, A.E., 2011. Lateglacial vegetation and palaeoenvironment in W Norway, with new pollen data from the Sunnmøre region. Boreas 10, no-no. Kvamme, T., Mangerud, J., Furnes, H., Ruddiman, W., 1989. Geochemistry of Pleistocene ash zones in cores from the North Atlantic. Norsk Geologisk Tidsskrift 69, 251-272. Lane, C.S., Blockley, S.P.E., Mangerud, J., Smith, V.C., Lohne, Ø.S., Tomlinson, E.L., Matthews, I.P., Lotter, A.F., 2012. Was the 12.1 ka Icelandic Vedde Ash one of a kind? Quaternary Science Reviews 33, 87-99. Larsen, E., Attig, J.W., Rune Aa, A., Sønstegaard, E., 1998. Late-glacial cirque glaciation in parts of western Norway. Journal of Quaternary Science 13, 17-27. Larsen, E., Eide, F., Longva, O., Mangerud, J., 1984. Allerød - Younger Dryas climatic inferences from cirque glaciers and vegetational development in the Nordfjord area, western Norway. Arctic and Alpine Research 16, 137-160. Larsen, E., Gulliksen, S., Lauritzen, S.-E., Lie, R., Løvlie, R., Mangerud, J., 1987. Cave stratigraphy in western Norway; multiple Weichselian glaciations and interstadial vertebrate fauna. Boreas 16, 267-292. Larsen, E., Mangerud, J., 1992. Subglacially formed clastic dikes. Svergies Geologiska Undersøkning, Ser. Ca 81, 163-170. Larsen, E., Ward, B., 1992. Sedimentology and stratigraphy of two glacial-deglacial sequence of Skorgenes, western Norway. Norsk Geologisk Tidsskrift 72, 357-368. Lohne, Ø.S., Mangerud, J., Birks, H.H., 2014. IntCal13 calibrated ages of the Vedde and Saksunarvatn ashes and the Younger Dryas boundaries from Kråkenes, western Norway. Journal of Quaternary Science 29, 506-507. Løvlie, R., Sandnes, A., 1987. Paleomagnetic excursions recorded in mid-Weichselian cave sediments from Skjonghelleren, Valderøy, W. Norway. Physics of the Earth and Planetary Interior 45, 337-348. Mangerud, J., Gulliksen, S., Larsen, E., 2010. 14C-dated fluctuations of the western flank of the Scandinavian Ice Sheet 45-25 kyr BP compared with Bølling-Younger Dryas fluctuations and Dansgaard-Oeschger events in Greenland. Boreas 39, 328-342. Mangerud, J., Gulliksen, S., Larsen, E., Longva, O., Miller, G.H., Sejrup, H.-P., Sønstegaard, E., 1981. A Middle Weichselian ice-free period in Western Norway: the Ålesund Interstadial. Boreas 10, 447-462.

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