Fig. 1
From: VOLCORE, a global database of visible tephra layers sampled by ocean drilling
Spatial distribution of drill sites, example of the tephra record at one drill site and typical volcanic ash forms. (a) Map of the drill sites. The combined DSDP, ODP and IODP drill sites, each site may contain multiple drill holes within a small distance from one another (e.g. 50 m offset). Filled circles show locations with reported tephra, open circles are locations with no reported tephra. (b) Drill holes with tephra and volcanic ash forms. Each drill hole may have one or more tephra horizons, as shown by horizontal bars in the 1149A drill hole on the left of the diagram. If a series of tephra are dated, they form a time series of volcanic activity. The tephra horizons often take different forms, as shown by the volcanic ash occurrences on the right hand side of the diagram. The most common distinction is a layer versus a patch, however not all layers are the same. Type 1 layer has sharp upper and lower boundaries, Type 2 layer has a sharp lower, and bioturbated or gradational upper boundary, Type 3 layer has both upper and lower bioturbated/gradational boundaries, Type 4 is a patch or pod.
