Náttúrufræðingurinn

Ukioqatigiit

Náttúrufræðingurinn - 1993, Qupperneq 27

Náttúrufræðingurinn - 1993, Qupperneq 27
constitute less than one percent by volume. The tephra is ntoderately sorted and consists of fine and mediurn ash. On the basis of texture analyses, it can be con- cluded that these tephra layers formed in hydromagmatic eruptions, when hol magma comes into contact with suriace water or ice. This conclusion is in agreement with the locations oi the most potential sources, i.e. Grfmsvötn or Kverkfjöll volcanic systems, which are mostly covered by ice of the Vatnajökull ice cap. No direct dating method has been applied on the tephra layers or the peat deposits in Sogamýri, but several criteria can be used to evaluate the age of the tephra layers. Firstly, the close strati- graphic proximity of the tephra layers to the underlying clay indicates that they must be from early postglacial time. The ice of the last glaciation (Weichselian) retreated from the Reykjavík area, approxi- mately 10000 years ago. Secondly, with the aid of pollen analyses and radiocarbon dating of the peats in the Reykjavtk area it can be concluded that these two tephra layers are about 9000 years old. Thirdly, the upper tephra layer in Sogamýri can possibly be correlated with a tephra layer found in a Late Weichselian-Early Holo- cene lake sediments in North Iceland. The age of this tephra layer is about 8900 years B.P., according to radiocarbon dating. The geochemical composition of this layer and the upper Sogamýri tephra are sufficiently congruous to support this correlation. Recently, a basaltic tephra layer has been identified in the Saksunarvatn lake sediments in the Faroe Islands (Mangerud et al. 1986). Radiocarbon dating indicates an age of 9000-9100 years BP. A com- parison of textural and geochemical data reveals that the upper tephra layer in Sogamýri, rather than the lower one, closely resembles the Saksunarvatn lephra layer (Table 1). On the basis of this comparison, it is reasonable to conclude that these two tephra layers were probably formed by the same eruption event in either the Grímsvötn or Kverkfjöll volcanic systems about 9000 years ago. The thickness and areal distribution of the tephra layers found in Sogamýri is not known yet, but present data indicates that il must be substantial if thcir sources are subglacial in the Vatnajökull ice cap, as postulated here. Plausible equivalents to these tephra layers have recently been identified in several scattered locations in Iceland (Fig. 3). 137
Qupperneq 1
Qupperneq 2
Qupperneq 3
Qupperneq 4
Qupperneq 5
Qupperneq 6
Qupperneq 7
Qupperneq 8
Qupperneq 9
Qupperneq 10
Qupperneq 11
Qupperneq 12
Qupperneq 13
Qupperneq 14
Qupperneq 15
Qupperneq 16
Qupperneq 17
Qupperneq 18
Qupperneq 19
Qupperneq 20
Qupperneq 21
Qupperneq 22
Qupperneq 23
Qupperneq 24
Qupperneq 25
Qupperneq 26
Qupperneq 27
Qupperneq 28
Qupperneq 29
Qupperneq 30
Qupperneq 31
Qupperneq 32
Qupperneq 33
Qupperneq 34
Qupperneq 35
Qupperneq 36
Qupperneq 37
Qupperneq 38
Qupperneq 39
Qupperneq 40
Qupperneq 41
Qupperneq 42
Qupperneq 43
Qupperneq 44
Qupperneq 45
Qupperneq 46
Qupperneq 47
Qupperneq 48
Qupperneq 49
Qupperneq 50
Qupperneq 51
Qupperneq 52
Qupperneq 53
Qupperneq 54
Qupperneq 55
Qupperneq 56
Qupperneq 57
Qupperneq 58
Qupperneq 59
Qupperneq 60
Qupperneq 61
Qupperneq 62
Qupperneq 63
Qupperneq 64
Qupperneq 65
Qupperneq 66
Qupperneq 67
Qupperneq 68
Qupperneq 69
Qupperneq 70
Qupperneq 71
Qupperneq 72
Qupperneq 73
Qupperneq 74
Qupperneq 75
Qupperneq 76
Qupperneq 77
Qupperneq 78
Qupperneq 79
Qupperneq 80
Qupperneq 81
Qupperneq 82
Qupperneq 83
Qupperneq 84
Qupperneq 85
Qupperneq 86
Qupperneq 87
Qupperneq 88
Qupperneq 89
Qupperneq 90
Qupperneq 91
Qupperneq 92
Qupperneq 93
Qupperneq 94
Qupperneq 95
Qupperneq 96
Qupperneq 97
Qupperneq 98
Qupperneq 99
Qupperneq 100
Qupperneq 101
Qupperneq 102
Qupperneq 103
Qupperneq 104
Qupperneq 105
Qupperneq 106
Qupperneq 107
Qupperneq 108
Qupperneq 109
Qupperneq 110
Qupperneq 111
Qupperneq 112
Qupperneq 113
Qupperneq 114
Qupperneq 115
Qupperneq 116
Qupperneq 117
Qupperneq 118
Qupperneq 119
Qupperneq 120
Qupperneq 121
Qupperneq 122
Qupperneq 123
Qupperneq 124
Qupperneq 125
Qupperneq 126
Qupperneq 127
Qupperneq 128
Qupperneq 129
Qupperneq 130
Qupperneq 131
Qupperneq 132

x

Náttúrufræðingurinn

Direct Links

Hvis du vil linke til denne avis/magasin, skal du bruge disse links:

Link til denne avis/magasin: Náttúrufræðingurinn
https://timarit.is/publication/337

Link til dette eksemplar:

Link til denne side:

Link til denne artikel:

Venligst ikke link direkte til billeder eller PDfs på Timarit.is, da sådanne webadresser kan ændres uden advarsel. Brug venligst de angivne webadresser for at linke til sitet.