Analysis of Mn-nodules from Leg 51

• Main Authors: Borella, Peter E, Adelseck, C
• Format: Dataset
• Language: English
• Published: PANGAEA 1980
• Subjects: 51-417A; Deep Sea Drilling Project; DRILL; Drilling/drill rig; DSDP; Glomar Challenger; Leg51; NOAA and MMS Marine Minerals Geochemical Database; NOAA-MMS; North Atlantic/CONT RISE; North Atlantic
• Online Access: https://doi.pangaea.de/10.1594/PANGAEA.872489; https://doi.org/10.1594/PANGAEA.872489

Rhodochrosite crystals and manganese oxide micronodules which have formed in situ are found in abundance at depth (76.5 to 106.5 m) in Hole 417A. A gradual transformation of the rhodochrosite to manganese oxide micronodules is observed in many grains throughout the interval. The transformation process initially attacks the edge of the rhodochrosite crystal and proceeds inward, first forming a pseudomorph of the crystal. Some grains exhibit varying degrees of departure from the crystal shape of a true pseudomorph, suggesting either an overgrowth of manganese oxide or late-stage destruction of the pseudomorph. No significant differences were observed in the relative per cent of minor and trace metals when comparing the pure rhodochrosite with the manganese oxide pseudomorphs. This suggests that the manganese and other trace elements were not transported into the system but were incorporated directly from the rhodochrosite as the manganese oxide formed. Grains which did not exhibit pseudomorphic form showed enrichment in some trace elements. We postulate that the diagenetic environment changed from reducing to oxidizing. How and when this change occurred in the sedimentary column remains an enigma.