During several DSDP and ODP Legs in the NE Atlantic, basaltic lava flows of the early rifting and break-up phase in the Tertiary have been drilled and logged. The lava flows were deposited subaerially with characteristic variations in their physical and magnetic properties and it is possible to distinguish different intraflow zones (I-IV) by evaluating downhole and core measurements. The physical and magnetic properties are mainly influenced by the degree of vesicularity and alteration, especially in the top and bottom parts of the flows. The pattern of the magnetic properties susceptibility and remanence seems to be helpful in distinguishing different flow types (aa and pahoehoe) as well as intraflow structures.
These zonal characterizations of subaerial basaltic lava flows can be seen frequently in core as well as in downhole measurements. This holds true not only for one hole but also for holes at different locations in the NE Atlantic with an exceptional high correlation down to fine scale variations, pointing to comparable genetic mechanisms during the initial phase of rifting.
Reprinted with permission from The Geological Society of London.