Abstract
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.