Deglaciation history of the southwestern Fennoscandian Ice Sheet between 15 and 13 14CkaBP ATLE NYGA˚ RD, HANS PETTER SEJRUP, HAFLIDI HAFLIDASON, MARCELLO CECCHI AND DAG OTTESEN Nyga˚rd, A., Sejrup, H. P., Haflidason, H., Cecchi, M. & Ottesen, D. 2004 (February): Deglaciation history of the southwestern Fennoscandian Ice Sheet between 15 and 13 14C ka BP. Boreas, Vol. 33, pp. 1–17. Oslo. ISSN 0300-9483. Analysis of 2D and 3D seismic records from the continental shelf off western Norway, in combination with chronological constraints from 14C dates, has led to a model for the glacial development in these shelf areas between c. 15 and 13 14C ka BP. On the shallow Ma˚løy Plateau adjacent to the Norwegian Channel, iceberg scours are preserved below a prominent moraine ridge, which by correlation to the Norwegian Channel indicate ice retreat at c.1514C ka BP. Subsequently, the ice advanced across the scoured surface and deposited a till sheet before stabilizing to deposit a prominent moraine, termed the Bremanger Moraine. Based on location on the shelf, seismic stratigraphy, morphology and 14C dates the Bremanger Moraine is correlated with a significant moraine on the continental shelf off Trøndelag. We suggest that these features are products of a regional glacial event, the Bremanger Event, dated to <15 – 13.3 14C ka BP. The Bremanger Event is probably a result of the deteriorating climatic conditions in the NE Atlantic during Heinrich event 1. Atle Nyga˚rd (e-mail: [email protected]), Hans Petter Sejrup, Haflidi Haflidason, Department of Earth Science, University of Bergen, Alle´gaten 41, NO-5007 Bergen, Norway; Marcello Cecchi, Enterprise Oil Norway, Stavanger. Present address: A/S Norske Shell, NO-4098 Tananger, Norway; Dag Ottesen, Geological Survey of Norway, NO-7491 Trondheim, Norway; received 8th January 2003, accepted 21st May 2003. Recent studies of the continental shelf and slope off suggesting ice advances around 15 and 13.5 14C ka BP. western Norway (Fig. 1) have concluded that the The present article is based on new acoustic and southwestern part of the Fennoscandian Ice Sheet bathymetric data from the Møre–Trøndelag Shelf (FIS) extended across the shelf during the last glacial combined with previously published material. The maximum, until c.1514C ka BP (Sejrup et al. 1994, main objective has been to improve the understanding 1995, 1996, 2000, 2003; King et al. 1996, 1998). Ice of the glacial history of the southwestern FIS, and to streams effectively draining ice through cross-shelf relate the temporal and spatial response of the ice on the troughs (Ottesen et al. 2001) have played an important Møre–Trøndelag Shelf to the changing physical envir- part in the dynamic behaviour of the ice sheet during the onment between c. 15 and 12.5 14C ka. glacial maximum (cf. the Norwegian Channel Ice Stream (NCIS), Sejrup et al. 2003). At c.1514Cka BP, a rapid shut down of the NCIS and subsequent Physiographic setting deglaciation of the outer Norwegian Channel (Fig. 1) are evidenced by 14C dates from the North Sea Fan and Water depths on the continental shelf adjacent to the Northern North Sea (Lehman et al. 1991; Haflidason western Norway range from 100 to 200 m in shallow et al. 1995; Sejrup et al. 1995; King et al. 1998). The bank areas, and from 200 to 450 m in distinct transverse deglaciation of the adjacent coastal areas, between troughs. The shelf off Møre (at 63°N) is particularly Bergen and Trondheim (Fig. 1), is also relatively well shallow, with large bank areas less than 100 m deep dated to around 12.5–12.7 14C ka BP (Mangerud 1977; (Fig. 1). The width of the shelf is more than 150 km off Mangerud et al. 1979, 1981; Rye et al. 1987; Svendsen Trøndelag, narrowing to less than 60 km at Møre, and & Mangerud 1987; Holtedahl 1993; Reite 1994; widening again southwards towards the Norwegian Andersen et al. 1995; Bondevik et al. 1999). The Channel (Fig. 1). The shelf edge is sharply defined at detailed information from the Norwegian Channel and the headwall of the Storegga Slide (Fig. 1B), a Holocene the coastal areas stands in contrast to the limited slide on the continental slope that removed parts of the information available on the deglaciation pattern of outer shelf moraines (Bugge 1983; Haflidason et al. the Møre–Trøndelag Shelf (c.62°–65°N; Fig. 1) in the 2001). The sedimentary succession on the shelf is period 15–12.5 14C ka BP. Andersen (1979) suggested a characterized by westward prograding sequences of gradual retreat from the shelf edge reaching the coastal Miocene/Pliocene age below an angular glacial areas around 13 14C ka BP. Other studies from the area, unconformity (e.g. Blystad et al. 1995; Rokoengen et however, have suggested fluctuations of the ice margin al. 1995; Martinsen et al. 1999; Brekke 2000). The in this period (e.g. Rokoengen 1979; Bugge 1980; angular unconformity represents the base of a several Holtedahl 1993), with Rokoengen & Frengstad (1999) hundred metres thick sequence of till and marine/ DOI 10.1080/03009480310006943 # 2004 Taylor & Francis 2 Atle Nyga˚rd et al. BOREAS 33 (2004) Fig. 1. A. Overview map of the continental shelf off western Norway, the northern North Sea and adjacent land and deep-water areas. Cores and localities discussed in the text are shown. References to cores: ENAM93-21 Rasmussen et al. (1996); MD95-2010 Dokken & Jansen (1999). See Table 1 for other core references. More onshore localities are given in Fig. 9. Bathymetry is in metres below sea level. Box indicates location of maps B and C. B. Detailed map of the local bathymetry on the Ma˚løy Plateau and on the central Møre Shelf. C. Same area as in (B), with location of the investigated 3D survey and the 2D seismic grid. BOREAS 33 (2004) Deglaciation of the SW Fennoscandian Ice Sheet 3 Table 1. Table of 14C dates from the Norwegian shelf and coastal areas discussed in the text and/or used in Fig. 11 to constrain the glacial development between c. 15 and 12.5 14C ka BP. 1GDF = Glacigenic Debris Flow. 2Holtedahl & Bjerkli (1982) and Bugge (1980) reported ages with 13C=0%, equivalent to a 410-year reservoir correction. In addition, 30 years have been subtracted in this study (cf. Mangerud & Gulliksen 1975). Reserv. age Marine sites Core no. Reference 14C age (yr) Dated material Setting correc. Lab. ref. Norwegian Channel Troll 3.1 Lehmann et al. 12410 Æ 110 N. labradorica Glacimarine unit 440 yr AA5382 (1991) above till Norwegian Channel Troll 3.1 Lehmann et al. 12590 Æ 150 N. labradorica Glacimarine unit 440 yr AA5383 (1991) above till Norwegian Channel Troll 8903 Haflidason et al. 12950 Æ 85 Yoldiella lenticula Glacimarine unit 440 yr TUa-283 (1995) above till Norwegian Channel Troll 8903 Haflidason et al. 13090 Æ 75 E. excavatum Glacimarine unit 440 yr TUa-755 (1995) above till Norwegian Channel Troll 8903 Haflidason et al. 13260 Æ 140 E. excavatum, Glacimarine unit 440 yr TUa-460 (1995) N. labradorica, above till C. lobatulus Norwegian Channel Troll 3.1 Lehmann et al. 13450 Æ 160 N. labradorica Glacimarine unit 440 yr AA5327 (1991) above till Norwegian Channel Troll 8903 Haflidason et al. 13720 Æ 95 N. labradorica Glacimarine unit 440 yr TUa-756 (1995) above till Norwegian Channel Troll 8903 Haflidason et al. 14065 Æ 170 N. labradorica, Glacimarine unit 440 yr TUa-147 (1995) E. asklundi above till Norwegian Channel Troll 3.1 Lehmann et al. 14690 Æ 120 N. labradorica Glacimarine unit 440 yr AA5329 (1991) above till Norwegian Channel Troll 8903 Sejrup et al. (1994) 15145 Æ 205 Mixed benthics Glacimarine unit 440 yr TUa-146 above till Trøndelag Shelf B77-121/1 Rokoengen & 13545 Æ 85 Astarte sp. Glacimarine unit 440 yr TUa-898 Frengstad (1999) above till Trøndelag Shelf B77-118/4 Rokoengen & 15320 Æ 115 Shell fragment In diamicton 440 yr TUa-1042 Frengstad (1999) interpreted as till Central Møre Shelf B77-139 Bugge (1980) 12900 Æ 240 H. arctica Glacitec. deformed 440 yr2 T-2647 gl.marine clay Central Møre Shelf B77-139 Bugge (1980) 13380 Æ 300 H. arctica Glacitec. deformed 440 yr2 T-2646 gl.marine clay Ma˚løy Plateau 74-AQ-07-14 Holtedahl & Bjerkli 13320 Æ 340 M. calcarea, Pebbely mud above 440 yr2 T-2708 (1982) Portl. arctica till (gl. marine) Mouth of Trænadjupet JM96-47/1 Laberg et al. (2002) 13150 Æ 70 N. pachyderma s Glacimarine unit 440 yr TUa-1767 trough above GDF1 North Sea Fan 83-06-56 King et al. (1998) 15825 Æ 130 N. pachyderma s Glacimarine unit 440 yr TUa-1246 above GDF North Sea Fan 79-08-224 King et al. (1998) 15870 Æ 105 N. pachyderma s Glacimarine unit 440 yr TUa-1251 above GDF North Sea Fan 79-20-90 King et al. (1998) 16250 Æ 120 N. pachyderma s Glacimarine unit 440 yr TUa-1245 above GDF Terrestrial sites (outer coast) Hitra Kjemperud (1986) 12680 Æ 230 Bulk date (gyttja) Lowest org. sed. dated T-4323 Lerstadvatn Lie et al. (1983) 12650 Æ 230 Bulk date Lake, date above T-3957A postgl. isolation contact Kulturmyra (Leinøy) Bondevik et al. 12725 Æ 55 M. calcarea Marine sequence 440 yr TUa-1902 (1999) Kulturmyra (Leinøy) Svendsen & 12530 Æ 240 Marine shells Marine sequence 440 yr T-5150 Mangerud (1990) Kra˚kenes Mangerud et al. 12320 Æ 120 Bulk date (silty Lake, date above T-2534 (1979) gyttja) deglac. silty/clayey beds Blomva˚g Mangerud (1977) 12670 Æ 350 M. edulis Within the Blomva˚g T-139 beds (below till) Blomva˚g Mangerud (1977) 12540 Æ 150 M.