Jökull


Jökull - 01.12.1987, Side 60

Jökull - 01.12.1987, Side 60
of Borgarfjördur are controversial, and that detailed studies on the stratigraphy, sedimentology and mor- phology of the deposits have been lacking. The Mela- bakkar-Ásbakkar cliffs are sensu strictu the type locality for Einarsson's (1961,1968) Álftanes Stadial, correlated with the Older Dryas of Scandinavia (Einarsson 1979) as the Álftanes glacial advance was radiocarbon dated by a mollusc sample from these cliffs (Einarsson 1971). I have studied the Melabakkar-Ásbakkar cliffs in or- der to identify glacial episodes, by investigating sedi- mentological and structural properties and stratigraph- ical relations of the sediments, to provide a depositional model for the sequence. Because of the long, almost continuous section, the geomorphic setting and the pre- served subfossil marine molluscs and barnacles in the sediments, the Melabakkar-Ásbakkar cliffs could give Fig. 2. Melabakkar-Ásbakkar coastal profile. Legend: (1) bedrock, (2) Ásbakkar diamicton, (3) Ás beds, (4) units of interbedded sands and diamictons, intrabedded in the Ásbakkar diamicton, (5) the Látrar beds cross stratified sand facies, (6) the Látrar beds interbedded silt and sand facies, (7) Melar diamicton, (8) boulders, (9) Landhólmi sands, (10) Ásgil gravels, (11) Melabakk- ar silts and sands, (12) Melagil gravels and sands, (13) important information on depositional environments in a glaciated fjord/bay setting, and also reflect changes in the proximity of the depositional basin to a glacier mar- gin. The present study discusses some recent models for glaciomarine sedimentation and for glaciotectonism. A preliminary report on the glacial stratigraphy and chro- nology was given by Ingólfsson (1985). The field work was carried out in 1980,1983 and 1984. The cliffs are actively eroded by the sea during high tides and westerly storms, which causes difficulties when mapping them, due to their nearly vertical stand and the risk of large scale slumping. The field mapping was thus partly conducted on photographs covering the cliffs in scale 1:200. This allows the recognition of major lithofa- cies, stratigraphic boundaries and deformational fea- tures. Accessible sections were described and measured location and no. of radiocarbon dated samples in Table III, (14) section covered, (15) major joints, (16) clastic wedges, (17) normal faults, (18) glaciotectonic deforma- tions, (19) major thrust faults, (20) direction of glacio- tectonic thrust, (21) paleocurrent direction, (22) direc- tion of glacial striae on bedrock substratum, (23) loca- tion of logs in Fig. 3. 2. mynd. Strandsnið Mela- og Ásbakka. 58
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