01876nas a2200145   4500000000100000008004100001100001500042700001400057700001300071245010300084856006000187300001000247490000800257520146500265       2014                            d1 aS. Engwell1 aR. Sparks1 aS. Carey00aPhysical characteristics of tephra layers in the deep sea realm: the Campanian Ignimbrite eruption  uhttp://sp.lyellcollection.org/content/398/1/47.abstract  a47-640 v3983 a<p>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\textpm5\% 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.</p>