Physical characteristics of tephra layers in the deep sea realm: the Campanian Ignimbrite eruption
S. L. Engwell, R. S. J. Sparks, S. Carey, 2014. "Physical characteristics of tephra layers in the deep sea realm: the Campanian Ignimbrite eruption", Marine Tephrochronology, W. E. N. Austin, P. M. Abbott, S. M. Davies, N. J. G. Pearce, S. Wastegård
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Tephra deposits in the deep sea can survive undisturbed for long periods of time and, on regional scales, tend to be much better preserved than their subaerial counterparts. In this study, grain size distributions and thicknesses of tephra deposits from the Campanian Ignimbrite (CI) eruption (39 000 yr BP; magnitude c. 7.7) preserved in thirty-three deep sea cores are analysed to infer key eruption parameters. Distal deep sea tephra thickness data show an exponential decrease with distance from source. Such trends are difficult to identify in distal subaerial data owing to reworking and limited exposure. We find that tephra grain size distributions are much less affected by depositional environment than thickness, with trends that are consistent across distal subaerial, lacustrine and deep sea environments. The CI layer exhibits bimodal grain size distributions to distances of c. 1000 km, after which it becomes unimodal. Such trends can be related to different mechanisms of tephra transport in the atmosphere, whereby at proximal to medial distances the Plinian and co-ignimbrite phases produce distinct plumes. Within 150 and 900 km from source, Plinian tephra constitutes 40±5% of the deposit volume. Beyond this region where coarse particles are deposited, the plumes merge and fines derived largely from co-ignimbrite elutriation are spread in the atmosphere at velocities greater than the settling velocities of the particles.
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This Special Publication includes articles presenting recent advances in marine tephrochronological studies and outlines innovative techniques in geochemical fingerprinting, stratigraphy and the understanding of depositional processes.
It represents a significant resource for the palaeoceanographic community at a time when marine tephrochronology is being more widely recognized. It will also serve as a valuable reference to a much wider community of Earth scientists, climate scientists and archaeologists, particularly in highlighting the role of tephra studies in stratigraphy and regional/extra-regional correlations, as well as in tracing the long-term history of regional and global volcanism in the deep-sea archive.