Náttúrufræðingurinn

Volume

Náttúrufræðingurinn - 1993, Page 26

Náttúrufræðingurinn - 1993, Page 26
adjacent regions (ritstj. D.R. Bowes & B.E. Leake). Geol. J. Spec. Iss. No. 10. 415-432. Kvamme, T., J. Mangerud, H. Furnes & W. Ruddiman 1989. Geochemistry of Pleistocene ash zones in cores from the North Atlantic. Norsk Geologisk Tids- skrift 69. 251-272. Magnús Á. Sigurgeirsson 1992a. Gjósku- myndanir á Reykjanesi. M.S.-ritgerð við Háskóla Islands. 114 bls. Magnús Á. Sigurgeirsson 1992b. Gjósku- gos við Reykjanes á 13. öld. Yfirlit og ágrip, veggspjaldaráðstefna. Jarðfrœða- félag íslands. Bls. 48-49. Mangerud, J., H. Furnes & J. Jóhansen 1986. A 9000-year-old Ash Bed on the Faroe Islands. Quaternary Research 26. 262-265. Sigurður Þórarinsson 1956. Mórinn í Seltjörn. Náttúrufrœðingurinn 26. 179- 193. Sveinn P. Jakobsson 1979. Petrology of Recent Basalts of the Eastern Volcanic Zone, Iceland. Acta Nat. Isl. 26. 1-103. Þorleifur Einarsson 1956. Frjógreining fiörumós úr Seltjörn. Náttúrufrœðingur- inn 26. 194-198. Þorleifur Einarsson 1961. Pollenanalyt- ische Untersuchungen zur spát- und postglazialen Klimageschichte Islands. Sonderv. Geol. Inst. Univ. Köln 6. 52 bls. Þorleifur Einarsson 1962. Vitnisburður frjógreiningar um gróður, veðurfar og landnám á íslandi. Saga 1961-63. Bls. 442-469. SUMMARY Two early holocene tephra layers in the Sogamýri peat deposit, Reykjavík , by Magnús Á. Sigurgeirsson National Energy Authority Grensásvegi 9 IS-108 REYKJAVÍK Iceland and Markús A. Leosson The University of Leeds Dep. of Earth Science LEEDS LS2 9JT England Tephrochronological investigation of the Sogamýri peat deposil in Reykjavík reveals that at least eleven tephra layers are preserved there (Fig. 1). The peat is between 2 and 3 meters thick and rests upon a blue-green clay, formed at the end of the Weichselian glaciation. With the aid of major element analyses, the sources for the tephra layers can be evaluated. According to the geochemical data, at least five possible sources may be involved: the Hekla, Katla, Torfajökull, Veiðivötn and Grímsvötn or Kverkfjöll volcanic systems. Two closely spaced tephra layers are found near the base of the peat deposit. In this study, special attention was paid to these two layers, which were clearly from early postglacial time and had not been described in previous studies of this area. The main objective of this paper is to present some results obtained from geo- chemical and textural analyses of these two layers. Chemical analyses indicate that the tephra layers are basaltic, of tholeiitic composition, and that their sources may either be in the Grímsvötn or Kverkfjöll volcanic systems (Fig. 2). Texture analyses indicate that the lephra layers are com- posed of brown-coloured, angular, sparsely vesiculated, glass shards with irregular concave and concex surfaces. Crystals u 136
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