North Atlantic deep-sea sedimentation of Late Quaternary tephra from the Iceland hotspot

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Piston cores recovered from the North Atlantic were used to study the sedimentation of Holocene and Pleistocene volcanic ash in the Irminger and Iceland Basins. Ash Zones 1 (≈ 11,100 yr B.P.), 2 (≈ 55,000 yr B.P.) and 3 (≈ 305,000 yr B.P.) were identified from their major element glass composition. The silicic and alkalic Ash Zones 1 and 2 originate from the Southeastern Volcanic Zone of Iceland, where they correlate with the Sólheimar ignimbrite from Katla volcano and the Thórsmörk ignimbrite from Tindfjallajökull volcano, respectively. The low-alkali composition of silicic Ash Zone 3 indicates a source from one of the silicic centers in the active rift system. Ash Zones 2 and 3 occur in the Irminger Basin as dispersed glass shards over a depth interval of several tens of centimeters. Their compositional and granulometric characteristics reflect an initial fallout on pack-ice north of Iceland, followed by ice-rafting sedimentation in the Denmark Strait, prior to bioturbation. δ18O stratigraphy of foraminifera in the cores indicates that the ash zones were deposited during a cold interval, at the time when seas north of Iceland were ice-covered. Sedimentary features indicate that turbidity currents were also involved in the dispersal of Ash Zones 1 and 2 south of Iceland. The initiation of these gravity currents from the shelf can be attributed to either glacier bursts (jökulhlaups) carrying tephra, or the entrance of pyroclastic flows into the ocean. © 1996 Elsevier Science B.V. All rights reserved.

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Marine Geology