ALBERT

Description: In this paper the relationship between whole-core compressional wave velocities and gamma-ray attenuation porosities of sediments cored at CRP-2/2A is examined, and compared with results from CRP-1, CRP-2/2A core-plug samples, and global models for velocity/porosity relationships of marine sediments. The high degree of data scatter observed in the velocity/porosity relationship of CRP-1 core is even larger in CRP-2/2A core. The general pattern of the velocity/porosity relationship is similar in CRP-2/2A whole core and core plug measurements. Despite scatter, all data indicate a strong primary dependence of velocity on porosity. This relationship appears to be independent of lithology except for sections with zero porosity and porosity 〉0.6, which are attributed to large lonestones and lapillistones, respectively. Core velocity/porosity patterns of CRP-1 and CRP-2/2A are very similar for sediments from the same age interval (19-23 Ma), both characterized by relatively low velocities (mostly between 2 and 3 km s-1) compared to porosity (0.1 - 0.4). Within this range of porosity, core velocities increase significantly up to more than 4 km s-1 below ca 440 mbsf. The change in the velocity/porosity relationship as a function of core depth is attributed to down-core increase in intergrain coupling enhanced by carbonate cementation. This is confirmed by a positive correlation of carbonate content with velocities higher or lower than empirically predicted from porosity. After removing first-order compaction control from the whole-core porosity record, no significant control by clay content can be identified (R = 0.3). This is different to the results for core from CRP-1 (R = 0.6) which is not cemented.