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Jökull - 01.12.1984, Qupperneq 125

Jökull - 01.12.1984, Qupperneq 125
vertical section of the Melasveit and Leirársveit strata (Fig. 4). Sea level changes and chronology Based on the works of Thoroddsen (1901, 1906) and Bárdarson (1923) a marine limit at 80— 100 m above present sea level is often postulated for the northern part of the Borgarfjördur region, and at 60—70 m a. s. 1. for its southern part (Áskelsson 1934, Thorkelsson 1935, Th. Einars- son 1961, 1963, 1964, 1968). Recent surveys by Sœmundsson and Einarsson (1980) and Ing- ólfsson (1981) have confirmed raised beaches at 60-70 m a. s. 1. in the area south of Hafnarf- jall-Skardsheidi. Surveys by Ashwell (1967, 1975) and Torfason (1974) suggest the existence of marine terraces and outwash plains at 65—70 m a. s. 1. in the Andakíll-Skorradalur area. Conspi- cuous raised beaches at 40—50 m a. s. 1., first described by Bárdarson (1923), have also been recognized by later workers (Áskelsson 1942, Thorarinsson et al. 1959, Torfason 1974, Ashwell 1975, Ingólfsson 1981). E.H. De Geer (1928) was first to recognize the Borgarfjördur area as an optimal area for geochronological studies in Iceland. She sug- gested that the laminated clays described by Bárdarson (1923) could possibly be dated by teleconnections with Swedish varve curves. She drew attention to the possibility of thus estab- lishing a chronological frame for the formation of the terminal moraines Bárdarson described in the tributary valleys of Borgarfjördur. E.H. De Geer also proposed that the different stages of land upheaval could be dated in this way. But the question of chronology remained unsolved for the years to come. Bárdarson (1923) postulated that the transgres- sion of the sea to the marine limit in the Borgar- fjördur region had occurred after the glaciers had retreated from the region. He was supported in this view by Áskelsson (1934) who rather favoured Postglacial age for the maximum trans- gression. Kjartansson (1940, 1943) suggested that his Búdi-stage occurred after or during the max- imum transgression in South Iceland, and thus established a Late Weichselian age for this event. The Búdi-stage in Iceland has been correlated with the Salpaussellká moraines in Finland, the Ra moraines in Norway and the Middle Swedish moraines (Kjartansson 1943). Th. Einarsson (1967, 1968, 1973, 1979) correlated the Búdi- stage with the Younger Dryas in Scandinavia. Table 1. Radiocarbon dates of marine molluscs collected from the lower part of the Borgarfjördur region. Tafla 1. Geislakolsaldur fornskelja úr neðri hluta Borgarfjarðarhéraðs. Location No. (Fig- 1) 1 2 3 4 5 6 Site name Staður Stóri- Sandhóll Andakílsár- virkjun Hreppur Árdalur Grjóteyri Melar Height of shell strata above sea level, m Hœð yfir sjó 114-135 16-24 18-23 25-30 15-21 5 14C date, Years B.P. Geislakolsaldur 12.270±150 12.240±200 12.100±250 12.100±150 12.800±220 12.290±160 Reference no of date 1-1824 1-1825 S-289 S-290 S-291 U-641 Samples no. 1—5 from Ashwell (1975). Sample no. 6 from Th. Einarsson in Olsson et al. (1969). All samples are referred to 0.95 NBS oxalic acid standard, using the value of 5570 years for the half life of C14. The base year is 1950. C13/C12 ratios have not been determined, and no corrections have been made for apparent age of living marine organisms. JÖKULL 34. ÁR 123
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