COMPOSITE DEPTHS

Introduction

We established composite depth based on the correlation between Cores 108-1109A-1H, 180-1109B-1H and 2H and 180-1109C-1H and 2H (Table T22). The correlation is based on key beds and magnetic susceptibility curves (Fig. F120).

Correlation

Sediments from 0 to 17 mbsf at Site 1109 have several key beds that enable visual correlation among the three holes. The magnetic susceptibility curves are similar to each other, and 53 peaks (29 positive peaks and 24 negative peaks) were used for correlation. Both key bed and magnetic susceptibility data sets provide consistent correlations (Fig. F120).

Composite Depths

Composite depths were calculated by the following procedure (Table T22):

1. To account for core length expansion in cores having recovery greater than 100%, depths were calculated by (distance from core top) × (cored length) ÷ (core length recovered).
2. The depth differences between correlative horizons in adjacent holes were calculated, and the average of these two or three differences were considered to be the differences in composite section.
3. The differences of composite section were cumulated for derivation of meters composite depth (mcd) for each horizon.

The gap between Cores 180-1109B-1H and 2H and between Cores 180-1109C-1H and 2H were estimated to be 0.14 and 0.24 m, respectively. The top of Cores 180-1109A-1H and 180-1109B-1H were evaluated to be 0.20 and 0.09 m deeper than the top of Core 180-1109C-1H.