VOLCANOGENIC SEDIMENTATION IN THE ICELAND BASIN - INFLUENCE OF SUBAERIAL AND SUBGLACIAL ERUPTIONS

Cores recovered from the Iceland Basin show evidence of transport and deposition of volcaniclastic sediment from the Eastern Volcanic Zone o f Iceland during the Holocene and last glacial period. Three types of deposits have been identified: tephra fall, sediment gravity flows, an d bottom-current-controlled deposits. Tephra fall layers contain basal tic glass of composition that suggests Katla volcano as the major sour ce. A chronology of the volcano activity is reconstructed, back to iso topic stage 5d (120,000 yr). Glass chemistry of tephra in sediment gra vity flows deposited south of Myrdalsjokull Canyon indicates a source in the Grimsvotn-Lakagigar volcanic system. These volcaniclastic gravi ty flows were most Likely derived from jokulhlaups or large glacial fl oods, at a time of a more extensive ice cover over the volcanic zone. Deposition of the sediment gravity flows has created a deep-sea fan so uth of the canyon. Basalt glass composition, age, and depositional env ironment suggest that one early Holocene turbidite sequence was derive d from a large jokulhlaup of the Grimsvotn area. The volcanogenic sedi ment gravity flows were influenced by a strong contour current, moving across the Katla sediment ridges. The contour current has winnowed th e silt fraction and transported it downstream as suspended load. The r ecovery of numerous silty volcaniclastic layers, enriched in detrital crystals, indicates that they contributed to the sedimentation of cont ourite drifts. (C) 1998 Elsevier Science B.V. All rights reserved.