ABSTRACT:

Description of physical properties of sediments and polymetallic nodules has been an essential part of geotechnical studies postulated in phase 2 of the "Plan of work for exploration for polymetallic nodules of Interoceanmetal (IOM)". The relevant properties were determined in both shipboard and on-land laboratories. The shipboard analyses included sediment and nodule volumetric density (ρ) and water content (w), determined immediately after the samples had been retrieved. Other physical properties, such as dry unit weight (ρd), porosity (n), void ratio (e), and specific density (ρs) were calculated subsequently. Specific density (ρs) was also determined in on-land laboratories using the pycnometric technique.

INTRODUCTION

In 2009, sediment and polymetallic nodule samples were collected, using a box corer, from 50 stations visited during the Interoceanmetal Joint Organization (IOM) cruise to the IOM exploration area within the Clarion-Clipperton Fracture Zone (CCFZ) (approximate coordinates: 10.5°N, 120.2°W). Physical properties of sediments were determined on board (in the ship's laboratory) on samples collected at 2–3 depth intervals in a box corer; physical properties of nodules were determined on 3–4 nodules picked up from each box core sample containing them. Additional 30 nodule samples analyzed consisted nodule fragments collected with a dredge. Specific densities (ρs) of the sediment and nodules resulting from on board computations and produced by pycnometric analyses were compared.

Deep Seabed (Pelagic) Sediments in IOM area: Brief Characteristics

Kenneth (1982) suggested that pelagic sediments form via particle sedimentation down the water column and include biogenic material, terrigenous clays and silts, pyroclastic materials blown through the air to the oceans, ice-rafted debris, and extraterrestrial material. In terms of grain size, such sediments are fine-grained and are mostly classified as clay or silty clay. The IOM research showed 70–85 and 20–25% of the samples to represent the 8φ+ (clay) and 4–8φ (silty) fraction, respectively.

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