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Jökull - 01.12.1987, Qupperneq 63

Jökull - 01.12.1987, Qupperneq 63
descriptions give locations as the distance in m from the northernmost point of the cliffs, point 0 in Fig. 2. THE ÁSBAKKAR DIAMICTON: A GLACIOMARINE FACIES ASSOCIATION The lowermost stratigraphical unit in the sequence, rest- ing on striated bedrock, is composed of two major litho- facies of diamicton (Dms, Dmu) and a number of in- trabedded units of diamictons, sands and gravels (Logs A and H, Fig. 3). The Ásbakkar diamicton makes up the bulk of the cliffs over long stretches (Fig. 2). All its lithofacies can be seen in the Ásbakkar-part of the sec- tion. Facies Dms Description: The lowest lithofacies is a fossiliferous, matrix supported, vaguely to clearly stratified silty diamicton with occásional gran- ule and pebble clasts (Fig. 10A). The stratification is due to occasional laminae and thin interbeds of medium sorted to nonsorted sand (Sl, Ss). The diamicton is light gray to slightly bluish gray in color, compact to lithified. The grain size of the matrix (samples 1 and 2, Fig. 4) is silt with a minor content of sand. A thin section study of a third sample showed that 85% of the matrix was silt with interstitial altered volcanic glass frag- ments, and 15% sand grains and granules. Facies Dms is rich in subfossil marine molluscs and barnacles, which are not in situ, primarily due to postdepositional deformation of the sediments. Sand Fig. 4. Grain size distribution for selected samples from the sequence. Samples from (1) Ásbakkar diamicton, (2) Látrar beds, (3) Melabakkar silts and sands, (4) Ás beds, (5) Ásgil gravels, (6) Melagil gravels and sands. Samples described in the text refer to figures within the triangle. 4. mynd. Kornastcerðardreifing nokkurra sýna frá bökk- unum. The shells are evenly distributed in the sediments, except in the random beds of gravelly sand (sample 6, Fig. 4) where concen- trations of shells that have been subject to transport occur. The transport has probably only been slight as paired valves were found, and external ornamentation, siphon sheath, periostra- SPECIES GLACIOMARINE UNIT RECENT DISTRIBUTION Lusi- tanian Boreal Arctic * o -1 T3 i | High| |Low| Mid 1 High| 1 2 3 Natica (Tectonatica)affinis Trophon (Boreotrophon) truncatus Colus fusiformis Buccinum undatum Nucula (Leionucuia) tenuis Chlamys(Chlamys) islandica Tridonta (Tridonta)elliptica Tridonta (Nicania)montagui Macoma (Macoma) caicarea Hiatella (Hiatella) arctica Mya (Mya)truncata Balanus (Balanus) balanus Balanus sp. • • • • • •• • •• • ••• • • • • • • • • • • • • •• • •• —' • •• • • • • • • REGIONAL DIVISION OF THE EUROPEAN SEAS • Rare, fragments only; •• Present; • •• Common; •••• Very common TABLE II. Molluscs and barnacles collected from the Melabakkar-Ásbakkar glaciomarine sediments. Stratigraphical position and Recent geographical distribution. Glaciomarine units: 1: Ásbakkar diamiction, 2: Látrar beds, 3: Melabakkar silts and sands. Location of samples in the cliffs: see Fig 2. Regional division of the European seas from Feyling-Hansen (1955). Taxonomical nomenclature and recent geographical distribution of species from Simonar- son (1981). TAFLA II: Fornskeljar úr mela- og Ásbökkum: Tegund, staðsetning, landfræðileg dreifing í dag. 61
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