Ice-Contact Deposits in Fjords from Northern Norway
Total Page：16
File Type：pdf, Size：1020Kb
Ice-Contact Deposits in Fjords From Northern Norway Astrid Lysa and Tore O. Vorren Department of Geology, Institute of Biology and Geology, University ofTroms¢, Norway During the retreat of the Fennoscandian Ice Sheet broad ridge exceeding a height of 70 m on the ice Yorren, T.O., Lebesbye, E., Andreassen, K. and Larsen, several ice-contact systems were deposited on the proximal side. The internal architecture of this K.B., Glacigenic sediments on a passive continental shelf and in the fjords along the norwegian coast ridge shows a complex seismic pattern (Fig. 2). margin as exemplified by the Barents Sea. Marine (Fig. 1). The most conspicuous system was formed Inclined reflectors representing foreset bedding Geology, 85,251-272,1988. by the glacial readvance during the Younger Dryas dominate. This implies that ice-contact sediments chron (10,000-11,000 BP). This system is termed were deposited on sloping surfaces prograding Department of Geology, Institute of Biology and the Troms0-Lyngen moraine in northern Norway towards the west simultaneously with advance of Geology, University of Tromsjll, N-9037 Tromsjll, [Andersen 1968]. A less distinctive ice-contact the glacier which climbed up the ice-proximal Norway. system which often is found a few kilometres ice slope of the ridge. This suggests that the ridge was distal of the Troms0-Lyngen moraine, the Skarpnes formed during a period of progressively advancing moraine, is dated to 12,500-12,000 BP [Andersen glacier rather than a period of glacier stillstand. 1968, Vorren & Elvsborg 1979]. The submarine parts of these moraines have been mapped by Acknowledgement. The project has been financed by seismic investigations in fjords and sounds [Vorren the Univerity of TromSjll. We wish to thank the captain et al. 1988] and detailed investigation on emerged and crew on FIF "lohan Ruud" for good collaboration outcrop data from the Troms0-Lyngen moraine has and J.P. Holm and F. Strand for help with the figures. been done by L¢nne [1993]. A longitudinal sparker profile from Astafjorden REFERENCES (cf Fig. 1) illustrates the internal structures and the Andersen, B.G., Glacial Geology of western Troms, relation between the Skarpnes and the Troms0- North Norway. Norges Geologiske Unders¢kelse 256, Lyngen moraines, respectively (Fig. 2). The 160 pp, 1968. acoustic system used was a 800 J multi-electrode Comer, G., Preboreal deglaciation chronology and sparker with bandpass filter settings 100-1000 Hz. marine limits of the Lyngen-Storfjord area, Troms, The Skarpnes moraine is deposited on a bedrock North Norway. Boreas, 9, 239-249, 1980. threshold and occurs as a c. 400-600 m broad and L!/}nne, I., Physical signature of ice advance in a Younger 40-50 m high ridge. The larger Troms0-Lyngen Dryas ice-contact delta, Troms, northern Norway: moraine is deposited on a smooth subsurface in the implications for glacier terminus history. Boreas, 22, 59-70,1993. middle of the fjord. However, it is located on a Yorren, T.O. and Elvsborg, A., Late Weichselian areas buried threshold which narrows the fjord. The of Troms, North Norway -a review. Boreas, 8, 247- deposits occurs as an asymmetric, up to 1800 m 253,1979. 80 T. A. Davies et al. (eds.), Glaciated Continental Margins © Chapman & Hall 1997 A Profile 36-92 T·LiFP max B SiFP max SOOm , , 200ms " Figure 1. Location of the study area in northern Norway. The positions of the ice marginal moraines [after Andersen 1968 and Comer 1980] are for the Troms!!S Lyngen (younger Dryas chron, 11,000-10,000 BP) and Skarpnes events (12,500-12,000 BP), marked as black Figure 2. A. Seismic section from Astafjorden. The profile transects the Skarpnes and the Troms!!S-Lyngen moraines, and dotted features, respectively. Isobases for the respectively (cf. fig. 1). B. Interpretation of the section shown in A. Vertical scale is given in ms two-way travel time. Younger Dryas shore line are after Andersen [1968] and S IFPmax and T-L IFPmax are maximum ice-front positions for the Skarpnes and Troms!!S-Lyngen moraines, respectively. Comer [1980]. 81 .