SIDE-SCAN SONAR CHARACTERISTICS OF SEAFLOOR AND MANGANESE NODULE OCCURRENCE BETWEEN THE CLARION AND CLIPPERTON FRACTURE ZONES, NE EQUATORIAL PACIFIC

The area between the Clarion and Clipperton fracture zones (NE equatorial Pacific) is one of the highest manganese nodule abundance in the world oceans. A detailed analysis of MR1 sonar images and free-fall grab (FFG) data with subbottom profiles in the area reveals a close relationship between sonar characters of seafloor and manganese nodule occurrence. Eight sonar facies are identified on the basis of back-scattered intensity, distribution pattern and texture. These sonar facies can be interpreted as (1) volcanic seamounts (facies I-1), (2) faults bounding abyssal hills (facies I-2 and II-1), (3) lava flows or mass-flow deposits around volcanic seamounts (facies I-3 and II-2), (4) crests of abyssal hills (facies II-1), (5) troughs between abyssal hills (facies III-1) or flat area (facies III-2) with relatively thick sediments, and (6) flat area covered with thin sediments (facies II-3). In the area consisting dominantly of facies II-1 and II-3, manganese nodules occur abundantly. In contrast, zones consisting of facies I-1, I-2, I-3, II-2, III-1 and III-3 are characterized by low abundance of manganese nodules.