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Title: Tephra in lake sediments : an unambiguous geochronological marker?
Author: Boygle, Jane E.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1995
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This thesis has three aims: (1) to construct tephrochronologies on large and small scales at sites in Sweden and Iceland; (2) to assess the effects of erosional and depositional processes on the nature and distribution of tephra in the sedimentological record; (3) to use these case studies to propose a model of the deposition of tephra in lakes. The Swedish Timescale based on the annually laminated sediments (varves) has recently been linked to the present. To test the chronology, traces of volcanic glass (tephra) from five historical eruptions of Icelandic volcanoes were sought within relevant sections of the varve deposits. Difficulties in isolating and identifying tephra to define isochrones in distal deposits led to the adoption of an integrated catchment and lake basin sampling strategy to assess the processes which affect the temporal and spatial distribution of tephra in lakes. A detailed tephrochronology of Svínavatn, a lake in northern Iceland, was constructed by identifying and correlating 95 tephra deposits from five lake cores and twelve profiles situated in the lowland peats, hillslopes and delta areas of the catchment. The tephra record from each site was highly variable due to both uneven fallout of the tephra following the eruption, and later reworking of the deposits in the lake and the catchment. The environmental changes of Svínavatn and its catchment were reconstructed using tephra as a geomorphological tracer. The peats and soils of the catchment were stable throughout most of the Holocene until the deposition of Hekla 3 (2800 yBP). Repeating layers of reworked Hekla and Katla tephra after this period at several terrestrial and lacustrine sites reflect increasing episodic instability of the catchment and the effects of this disturbance on the lake record. Until the arrival of Norse settlers in the 9th century, much of this disturbance was linked to climate and vegetation changes around the catchment. Significant, but temporally discrete, secondary inputs of H3 and H4 (3800 yBP) into the lake occur several thousand years after the original airfall.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available