Polygonal feeder tubes filled with hydroclasts: a new volcanic lithofacies marking shoreline subaerial-submarine transition

Abstract

This paper describes for the first time a new lithofacies that formed in the passage zone during the construction of pahoehoe lava-fed deltas in the north and NE coastal areas of Gran Canaria (Canary Islands, Atlantic Ocean). These lavafed deltas, which are Pliocene in age, present similar lithofacies associations to those previously described in the literature, except for two distinct features: low abundance of hyaloclastites and a new lithofacies in the passage zone. This new lithofacies, which we propose to name ‘polygonal feeder tubes filled with hydroclasts’, comprises metre-scale lava feeder tubes with decimetre-scale coherent poorly vesicular and aphanitic rinds of polygonal morphology, filled with closely packed hydroclasts generated in situ. It represents the first stage in the interaction between seawater and thick lava flows entering the sea under the influence of a tidal regime, thus marking sea level. This lithofacies should be easily recognizable in ancient successions, and thus represents a useful marker of palaeoshorelines.