New finds of exhalative deposits on the East Pacific Rise

Several gentle hills close to the crest of the East Pacific Rise are covered with extensive Fe-Mn-rich deposists. The setting of the sediments precludes the possibility that turbidite flows, slumping or downhill winnowing of material can have been responsible for the accumulation of these sediments, as is also indicated by the lack of reworked faunas or crushed shells.Palaeontological dating and the magnetic anomalies of the crustal substratum show that the sediments must be very young, that is, the sedimentation rates are very high; thus, 8-10-m-thick sediments were formed in 600,000 yeas. The accumulation rates on these hills for several elements, such as Fe, Mn, Cu and Ba, are much higher than in ordinary pelagic regions. The element deposition is best described as an exhalative-sedimentary process. The areal extent of these sediments is considerably larger than that of any other currently forming analogous deposits. The results have far-reaching implications for the discussion of how sedimentary-exhalative iron-manganese ores originate.