Downhole Resistivity log for HSDP-2-A

The GFZ Potsdam started a log interpretation study in cooperation with the Technical University of Aachen. As a first result, the logged profile allows for a subdivision of the lithological profile into at least two major zones: (1) a subaerial zone (1900-3600ft) and (2) a submarine zone (3600-6100ft). In addition, the geophysical measurements indicate a further subdivision into the Log Units 1-4 , each unit distinguished by different geophyshical log responses: (Fig.2) (Fig.4) The basaltic lava flows of the first unit (Log Unit1), consisting of Aa-and Pahoehoe-Lavas, show high total GR and low resistivity values in general. These flows do not only reveal large variations in resistivity and gamma ray activity between different flow types but also within single lava flows. This internal variation seems to be controled by vesicularity and alteration of the single lava flows. High total GR values appear in rocks with low olivine content and sparse vesicularity.