A New Automated Technique for the Construction of More Accurate Composite Depth Scales and an Analysis of Core Deformation in Different Sediment Types

A composite depth section reconstructs a continuous record of the sediment at a drilling site by splicing together cores from different holes; its corresponding composite depth scale describes the correlation of the sediments between holes. Both are important tools for analyzing the sediment recovered from a drilling site. The standard splicing technique for creating composite depth sections does not correct for distortion within cores, so that a sedimentary feature may have a slightly different composite depth in each hole. Additionally, the splicing technique often results in composite depths which are ∼10% greater than recorded drill depths. A new automated compositing technique aligns features between holes and prevents the artificial increase in composite depth. The results of this technique are compared with the traditional composite depth scale. Additionally, the new technique allows for analysis of the deformation and extension that occurs in cores during the drilling and extraction process. This study describes typical core deformation and its effect on calculated sedimentation rates for the carbonate and siliceous sediments of ODP Leg 138 and the terrigenous-dominated pelagic sediments of ODP Leg 154. Preliminary results indicate that cores from Leg 138 are stretched by more than 5% and those from Leg 154 by nearly 3%. For both legs, extension is greatest in the top half of cores, but variability in deformation may increase toward either end of a core.