Jökull


Jökull - 01.12.1980, Side 10

Jökull - 01.12.1980, Side 10
Tjörnes sequence is divided into Series (Table 1). Old Quaternary age is assigned to the Breiðavík Series with reference to Askelsson’s work. Voice of a sceptic — early palaeomagnetic studies A tone of scepticism towards Pjetursson’s glacial history was struck by T. Einarsson (1940a, 1940b, 1946), who interpreted many of Pjetursson’s moraines (“grey conglomer- ates”) as being entirely of volcanic origin, being mudflow deposits either directly erupted by volcanic vents or formed as a secondary product of certain eruptions. Ear- lier, Hawkes (1938) had studied some of Pjetursson’s localities, including Tjörnes, and rejected a glacial origin of the conglomerates in question. T. Emarsson’s investigations on Tjörnes began in 1939 and continued until the early sixties. In the first instance he dealt mainly with the stratigraphy and structure of the peninsula, but the origin of the sediments and the palaeomagnetism of the lava flows were also investigated (71 Einarsson 1957a, 1957b, 1958). The study of palaeomagnetism on Tjörnes had been initiated by Hospers (1953, 1954). T. Einarsson (1957b) found that the youngest rocks on Tjörnes consisted of two groups of lava flows separeded by a “moraine-like” conglomerate, an upper nor- mally magnetized group, and a lower rever- sely magnetized one that rested conformably on the Breiðavík sediments (cf. Fig. 3). The upper part of these in turn consisted of an old Quaternary sequence (of presumed Villa- franchian age). In this paper T. Einarsson stated that the Tertiary/Quaternary boun- dary should be drawn at the base of R1 (the Quaternary thus spanning the two youngest polarity groups). T. Einarsson (1958) presented the first detailed survey of the interior of Tjörnes peninsula, and identified angular un- conformities within the sequence. He defined stratigraphical units for the Tjörnes sequence (Table 1). Tectonic aspects and age relation- ships were again discussed in later papers (Thorarinsson et al. 1959, T. Einarsson 1960). While eariier authors had generally assumed an unconformity beneath the “Lower sediments”, T. Einarsson (1958) c.oncluded that they were conformable with and partly of the same age as the “Basal Basalts” at Kaldakvísl. He visualized the early Pliocene Tjörnes as a subsiding area of low relief, the subsidence amounting to 700—800 m during the Pliocene. After an emergence (still within the Pliocene, at which time he suggested a regional uplift of some 300 m predating the Breiðavík sediments) the area was covered by lavas. T. Einarsson pointed out that Tjörnes is cut off from the area south of Húsavík village by a fault running from Húsavík to the southeast. To the north of the fault, the “Basal Basalts” have been uplifted to an altitude of 700 m, while they cannot be seen to the south of the fault. T. Einarsson suggested that the fault was of Pleistocene age. T. Einarsson collected pollen samples from lignite horizons and terrestrial sediments in the Tjörnes sequence. The palynological results were discussed along with the problem of provenance of rhyolitic pebbles in his work on Upper Tertiary and Pleistocene rocks in Iceland, and in later papers (71 Einarsson 1962, 1963a, 1963b, 1964). The results of his study of palaeomagnetism on Tjörnes were compiled on a map in a paper where 71 Einarsson (1965) also delt with lavas resting on fossiliferous shale to the south of Húsavík. The strati- graphy and sedimentological aspects of the Tjörnes sequence were briefly dealt with in 71 Einarsson’s (1972) textbook on geology. In a recent paper he emphasized a Pliocene age of the Breiðavík beds on Tjörnes and emphati- cally rejected the interpretation that interca- lated glacial signs were produced by Pleistocene ice caps. Instead, he suggested, they were in many cases formed in the vicinity of high ice capped volcanoes (71 Einarsson 1977). Climatic evidence examined In his study of the climatic history of Ice- land, Schwarzbach (1955) examined the climatic evidence of the Tjörnes beds and 8 JÖKULL 30. ÁR

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