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The deposition and reworking of tsunami sediments in Agaete, Gran Canaria

Austin-Giddings, W.D.; (2012) The deposition and reworking of tsunami sediments in Agaete, Gran Canaria. Doctoral thesis, UCL (University College London).

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Abstract

Coarse-grained, polymict, deposits, draping hillslopes at high elevations on ocean island volcanoes, have been variously interpreted as sourced either from sea-level highstands or from tsunamis; their origin is thus controversial. A detailed facies analysis of coarse-grained, fossiliferous sediments located at Agaete, on the north-west coast of Gran Canaria, has been undertaken. Previously interpreted as the result of a sea-level highstand, these deposits have recently been re-interpreted as sourced from a tsunami; itself triggered by a volcano flank failure. The Agaete Fossiliferous Conglomerates occur at several locations in the Barranco de Agaete, up to 188m apsl. and 2 kilometres inland from the coast. They comprise seven facies, all of which are variably graded, matrix- and clast-supported, range from ~0.3 to 2 m thick, and contain a diverse assemblage of volcanic clasts, large beachrock boulders and a shallow marine fauna. All the facies have sharp, erosional bases. A facies at one site contains large palaeosol rip-up clasts up to 1.5 m across and at its base truncates plant roots. The upper facies of the conglomerates are all finer-grained, reverse-graded, clast-supported and better-sorted than the lower facies of the group. At one location the upper conglomerates comprise prograding beds that are interpreted as alluvial. The lower facies of the conglomerates are interpreted as primary tsunami deposits, whereas the upper facies are interpreted as tsunami deposits that have been reworked. The alternative, marine highstand, interpretation of the coarse-grained deposits is discounted on the basis of (i) an absence of supporting geomorphological features such as a marine terrace and/or a wave cut platform; (ii) the composition of the sediments; (iii) diagenetic features; (iv) distance from the coast; and (v) elevation of the deposits. Gran Canaria is in its erosional post-shield stage of development and the north-western coastline has experienced 40-50 m of tectonic uplift over the past 1.75Ma. Thus uplift of highstand deposits cannot account for the occurrence of the Agaete sediments at elevations of up to 188 m apsl. The Güimar lateral collapse event on the neighbouring island of Tenerife, dated at around 0.8Ma BP, is presented as the most likely tsunami source.

Type:Thesis (Doctoral)
Title:The deposition and reworking of tsunami sediments in Agaete, Gran Canaria
Language:English
UCL classification:UCL > School of BEAMS > Faculty of Maths and Physical Sciences > Earth Sciences

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