Field Guide for the NORDQUA Excursion to Sunnmøre, Western Norway, 22-25 September 2014
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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 1 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. 2 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. 3 Fig. 2. Overview map of the excursion area. 4 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. 5 Fig. 4. The depositional environments and sediment succession in Skjonghelleren, from Mangerud et al. (2010). 6 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). 7 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. 8 Fig. 7. The section in the innermost part of the cave, that we will see during the excursion. From Larsen et al. (1987). 9 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. 10 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). 11 Fig. 11. Correlation between the Ålesund and Greenland ice cores. From Mangerud et al. (2010). 12 Fig. 12. A glaciation curve for the entire Weichselian, where the events found in Sunnmøre are marked. From Mangerud et al. (2011). 13 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. 14 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) 15 Fig. 16. The distribution of the Vedde Ash – from Greenland to Italy. From Lane et al (2012). 16 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). 17 Fig. 19. Stratigraphy in Dimnamyra. From Koren et al. (2008). Fig. 20. Ashes in Dimnamyra (-bog). From Koren et al. (2008). 18 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). 19 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) 21 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). 23 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).