Jökull

Eksemplar

Jökull - 01.12.1993, Side 38

Jökull - 01.12.1993, Side 38
Figure 3. The Þistilfjörður area with raised shoreline features and major sediment terraces. Contour interval is 100 m. —Fornfjörumörk, sethjallar og jökulgarð- ar við Þistilfjörð. Hœðarlínur eru á 100 m bili. initial state of a maximum glaciation when glaciers reached an unknown position on the Iceland shelf. Subsequently to a considerable glacial retreat the glaciers readvanced and an increased glacial overbur- den load caused a subsidence of the crust that exceeded the eustatic lowering of global sea-level generated by increased volume of ice masses around the world. Consequently, relative sea-level transgressed and a marine limit was formed when sea-level reached a tem- porary maximum position. Furthermore, the MAD- model accounts for a subsequent glacial retreat, re- duced crustal overburden load and a glacio-isostatic recovery exceeding the eustatic rise of global sea-level. Consequently, the isostatic uplift caused a regression ofrelative sea-level. During afollowing but less exten- sive glacial readvance and a concurrent transgression of relative sea-level a new set of shorelines was formed somewhat below the earlier marine limit. This rela- tionship between glacier extent and position of rela- tive sea-level has enabled us to recognize successively lower and younger shorelines within the study area. This paper follows the chronostratigraphical termi- nology of Mangerud et al. (1974), and the age of 14C- dated marine molluscs mentioned in the text has been corrected for reservoir effect according to Hákansson (1983). MARINE LEVELS THE APPARENT 65 m LEVEL The outermost identifiable Lateglacial position of a glacier margin in the study area is shown by a conspic- uous lateral moraine situated below the steep mountain slope above the Viðarvíkcove in the Þistilfjörðurarea (Figures 2 and 3). The moraine continues in a complex of kames and kettles south and east of the cove. A sed- imentary terrace, just outside the moraine (Figure 2) is made of semi-lithified sand overlain by a coarse grained, poorly sorted ablation till or gelifluction sed- iment. The formation of the terrace in this exposed position was probably controlled by sea-level, which at that time may have reached as high as 65 m a.s.l. SHORELINES BETWEEN 50 AND 40 m A 30-35 m thick sediment sequence was formed at or close to a glacier margin inside the above mentioned lateral moraine in Viðarvík (Figure 3), when relative sea-level stood at 40-45 m a.s.l. The delta sequence consists of at least two sedimentary units underlain by a compact sandy diamicton, probably a till. The lower unit - a few metres thick - comprises thinly bedded and laminated silt and fine sand, while the upper unit is made of coarser sand and gravel sediments. Near the middle of the upper unit, cross-bedded sediments have been slightly distorted by ice-push or melting of buried glacier ice. On the inside of the lateral moraine with its associated 65 m terrace we find shorelines at 50 and 40 m a.s.l. (Figures 2 and 3). A shoreline at about 50 m a.s.l. on the Digra- nes peninsula in the Bakkaflói area, just outside the Bakkafjörður village (Figure 4), was most likely formed close to a glacier margin, when the glaciers reached just beyond the present coastline and into the Bakkaflói bay. 36 JÖKULL,No. 43, 1993

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Jökull

Undirtitill:
Ársrit Jöklarannsóknarfélags Íslands og Jarðfræðafélags Íslands
Gerð af titli:
Flokkur:
Gegnir:
ISSN:
0449-0576
Tungumál:
Árgangar:
72
Fjöldi tölublaða/hefta:
73
Skráðar greinar:
Gefið út:
1951-í dag
Myndað til:
2023
Útgáfustaðir:
Ritstjóri:
Jón Eyþórsson (1952-1967)
Sigurður Þórarinsson (1957-1982)
Guðmundur Pálmason (1965-1976)
Sveinbjörn Björnsson (1967-1976)
Helgi Björnsson (1983-1985)
Leó Kristjánsson (1983-1985)
Ólafur G. Flóvenz (1986-1987)
Tómas Jóhannesson (1988-1989)
Helgi Björnsson (1990-1993)
Leó Kristjánsson (1990-1993)
Áslaug Geirsdóttir (1994-2007)
Tómas Jóhannesson (1998-1998)
Bryndís Brandsdóttir (1998-2007)
Halldór Gíslason (2002-2003)
Snævarr Guðmundsson (2006-2007)
Freysteinn Sigmundsson (2008-2008)
Leifur A. Símonarson (2008-2008)
Olgeir Sigmarsson (2008-2008)
Ívar Örn Benediktsson (2012-2012)
Helgi Björnsson (2012-2012)
Guðrún Larsen (2012-2012)
Olgeir Sigmarsson (2012-2012)
Bryndís Brandsdóttir (2013-2016)
Snævarr Guðmundsson (2013-2016)
Þorsteinn Þorsteinsson (2013-2016)
Efnisorð:
Lýsing:
Reykjavík Jöklarannsóknafélag Íslands Jarðfræðafélag Íslands 1951-.

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1. tölublað (01.12.1993)

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