Jökull

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Jökull - 01.12.1985, Qupperneq 22

Jökull - 01.12.1985, Qupperneq 22
distal part of an alluvial cone or elevated sandur below one of these cirques (Grasadalur) on the south side of Rekavíkurvatn, and a similar altitude of the upper surface of a much dissected glaciofluvial deposit at the southern end of Rekavíkurvatn, indicate the approxi- mate base level at the time of deglaciation. It could not be ascertained whether the Rekavíkurvatn basin con- tained inactive ice when these sediments were depo- sited. However, an inactive ice body must have been left in the small basin (Hálsavatn) east of Rekavíkur- vatn, or the sediment pile between the two lake basins could not have been deposited. There are also remnants of a terminal moraine on the north shore of easternmost Rekavíkurvatn, deposited by a glacier coming from the east. On the watershed between the Rekavík valley and the Látrar lowlands an interlobate drainage pattern illustrates the separation of the two ice bodies. We re-examined Thoroddsen’s (1892a) evidence of an ancient strandline at 63 m above present sea level inside Rekavík and came to the conclusion that the featuere in question is a bedrock structure, without any relevance to ancient sea levels. No clear indications on the marine limit around northern Adalvík were found, but the above mentioned data and the rather diffuse border between abraded and non-abraded glacial features inland from Látrar places it somewhere between 15 m and 25 m above present sea level. Summary and correlation of the late glacial events The most complete late glacial sequence is probably found in Haelavík. Morphological and stratigraphical features there reveal the following sequence of events: (1) An initial glacial retreat was followed by (2) the deposition of marine silt to at least 8 m above present sea level and (3) by a glacial readvance, whereafter (4) the final deglaciation took place, when the sea stood 26-27 m higher than today. Deglaciation was (5) fol- lowed by regression of the sea to or below the present sea level. Another fairly complete glacial geological sequence is revealed in the Stadarvatn valley of southern Adalvík, where two glacial advances are probably documented. One interpretation of the geology there suggests a development similar to that in Haelavík. But the final deglaciation at Stadarvatn took place when the sea stood only 15 m higher than today, which indicates a later deglaciation than in Haelavík, perhaps contempor- aneously with that of Hlöduvík. We correlate the lateral terrace at Látrar with the short lower lateral terrace north of Stadarvatn (zone C in Fig. 6). The stratigraphy of the Látrar terrace may suggest a transgression from < 10 m up to 20—25 m above present sea level, i.e. to a level similar to the marine limit in Haelavík. The ELA during some part of the late glacial has been around or lower than 150 m above present sea level. This is inferred from the altitude of the low level cirques which were glaciated at that time. Such are found in Hornvík, Hlöduvík (Fig. 7) and at southeast- ern Adalvík, but also at places along the outer coast, near Ritur and Straumnes. A good example is shown in Fig. 11. Dating the full glacial to late glacial sequence No shell bearing sediments from the full glacial or late glacial periods were found on Hornstrandir. Probably most fine grained sediments from that time lie below present sea level, with the exception of the shell- and foraminifera-free silt in section 1 at Haelavík. Nor have we found any other material which could be absolutely dated, as the gyttja silt in sections 2 and 3 at Haelavík contains too little organic matter and too few pollen. Thus the age of the glacial deposits can only be sug- gested by analogy with other areas. New interpretations of data from Northeast Green- land (Funder 1982, 1984, Hjort and Björck 1984) sug- gest the nonexistence of any extensive Early or Middle Weichselian glaciation there and tentatively place the Weichselian maximum around 20.000—18.000 years BP. Data from Svalbard (Miller 1982) may be inter- preted in the same way. Norddahl (1983) suggested that the glacial maximum in central North Iceland dated from before 18.000- 24.000 BP, but his oldest glacial stages are not neces- sarily of Weichselian age. In fact, the Weichselian maxi- mum has never been properly defined or absolutely dated anywhere in Iceland, so there seems to be no reason to, initially, suggest any other age for it on Hornstrandir than the classical 20.000—18.000 BP one, as proposed for Iceland in general by Tr. Einarsson (1966) and Th. Einarsson (1973). The best clue to the age of the final deglaciation, of at least northern Hornstrandir, is the deposition at or near present sea level of lacustrine/fluvial sediments which, although with an erosional discontinuity, follow directly upon the till in section 3 at Haelavík. These mirror the regression after the final deglaciation, from the 26 m level (section 1 at Haelavík) down to present sea level. From other parts of Iceland we know that already around 9000 BP the relative sea level had come down to or below its present level (Thórarinsson 1956, 1964, Th. Einarsson 1956, 1964, 1968). If applied on Hornstrandir 20 JÖKULL 35. ÁR
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