We present the results of geological and palaeomagnetic mapping of several lava profiles in Southwestern Iceland, covering a transition from reverse to normal polarity about 2 M.y. ago. The transition was first described by SIGURGEIRSSON (1957). We confirm that the virtual-pole path of this transition is not confined in longitude. We also present and discuss instances of complex pole paths in older strata in Iceland, and we provide new evidence for the general reliability of palaeomagnetic directions from lava flows.
Abstract:The distribution and geochemistry of four rhyolitic tephra horizons from Iceland dated to the ad 700s-800s is assessed. These include the rhyolitic phase of the Landnám tephra (ad 870s), the ad 860 layer, a previously unrecorded tephra called the GA4-85 layer (c. ad 700-800) and the Tjïrnuv ‡k tephra (c. ad 800s). The ad 860 and GA4-85 layers were rst found in peat bogs in north Ireland. They are here correlated with equivalent horizons on Iceland which were found below the Landnám tephra (c. ad 870s). This time period is considered important in the North Atlantic region, because it coincides with a phase of human settlement in Iceland and the Faroe Islands. The establishment of a detailed tephrochronology may provide a tool for exact dating of sediment successions and sediments associated with archaeological excavations. Caution must be taken especially on Iceland where the Landnám tephra is often used for dating archaeological sites. This investigation show that several rhyolitic tephra horizons occur close in time to the Landnám tephra, and that mistakes can be made if detailed geochemical analyses are not carried out, especially in areas which are distal to the source of the Landnám tephra (the Veidivötn and Torfajökull volcanic systems, southern Iceland).
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