Detailed description of manganese nodules and micronodules from the R/V Valdivia VA-13/2 campaign

An area 20 x 20 nautical miles, within the abyssal hill region of the northern Central Pacific, has been sampled intensively by R/V Valdivia . The sediments represent four facies characterized by variations in color, structure and composition. A marked unconformity between facies II and III was dated by radiolaria and coccoliths as early Miocene to late Pliocene and is explained by an intensification of AABW circulation. A maximum of reworking, dissolution of siliceous organisms and growth of authigenic minerals is noted above and below this unconformity. Dissolution of siliceous organisms seems to control the growth of minerals such as zeolites and Fe-Mn-oxides. Fe-Mn-oxides were precipitated both as micro and macro nodules. While the micro nodules remained in place, most of the macronodules were pushed upwards by benthic organisms and were kept at the sediment surface. Thus, the surface nodules appear to be 'foreigners' in the recent sediments and represent the conditions of a past environment. During the VA-13/2 campaign 79 cores were taken from 60 locations. Fine scale sedimentary structures were determined using radiography of 252 samples. Mn nodules either at the surface or inside the cores were described. 2.0 cm thick samples were taken for sedimentological and bio-stratigraphical studies. Smear slides were also examined for the determination of Mn micronodule components