TY - JOUR
T1 - Jianshuiite in oceanic manganese nodules at the Paleocene-Eocene boundary
AU - Post, Jeffrey E.
AU - Thomas, Ellen
AU - Heaney, Peter J.
N1 - Publisher Copyright:
© Walter de Gruyter Berlin/Boston 2016.
PY - 2016/1/1
Y1 - 2016/1/1
N2 - Synchrotron powder X-ray diffraction and scanning electron microscopy examinations of man-ganese oxide concretions/nodules (∼0.3-1.0 mm diameter) from ODP Site 1262 on Walvis Ridge in the Southeastern Atlantic Ocean revealed that they consist primarily of the layered Mn oxide phase jianshuiite [(Mg,Mn,Ca)Mn34+O7 3H2O]. The nodules are from an interval with severe carbonate dis-solution that represents the Paleocene/Eocene (P/E) thermal maximum (∼5 5.8 Ma). Most nodules from the middle of the carbonate dissolution interval contain internal open space, and consist almost entirely of euhedral plate-like jianshuiite crystals, 2-4 μm in diameter and ∼0.1-0.5 μm thick. Backscattered electron images and energy-dispersive X-ray analyses revealed stacks of interleaved Al-rich and Al-poor jianshuiite crystals in some nodules. The crystals in other nodules contain predominantly Mg (with trace K and Al) in addition to Mn and O, making them near "end-member" jianshuiite. Rietveld refinements in space group R3 confirmed the isostructural relationship between jianshuiite and chalcophanite, with Mg occupying the interlayer position above and below the vacant sites in the Mn/O octahedral sheet, and coordinated to 3 octahedral layer O atoms (1.94 Å) and 3 interlayer water O atoms (2.13 Å). Final refined occupancy factors suggest that small quantities of Ni and possibly Mn2+ are located on the Mg site. The transient appearance of the Mg-rich birnessite-like phase jianshuiite, probably abiotically produced, must indicate an exceptional transient change in the chemistry of the pore fluids within deep ocean sediments directly following the P/E boundary, possibly as a result of decreasing oxygen levels and pH, followed by a return to pre-event conditions.
AB - Synchrotron powder X-ray diffraction and scanning electron microscopy examinations of man-ganese oxide concretions/nodules (∼0.3-1.0 mm diameter) from ODP Site 1262 on Walvis Ridge in the Southeastern Atlantic Ocean revealed that they consist primarily of the layered Mn oxide phase jianshuiite [(Mg,Mn,Ca)Mn34+O7 3H2O]. The nodules are from an interval with severe carbonate dis-solution that represents the Paleocene/Eocene (P/E) thermal maximum (∼5 5.8 Ma). Most nodules from the middle of the carbonate dissolution interval contain internal open space, and consist almost entirely of euhedral plate-like jianshuiite crystals, 2-4 μm in diameter and ∼0.1-0.5 μm thick. Backscattered electron images and energy-dispersive X-ray analyses revealed stacks of interleaved Al-rich and Al-poor jianshuiite crystals in some nodules. The crystals in other nodules contain predominantly Mg (with trace K and Al) in addition to Mn and O, making them near "end-member" jianshuiite. Rietveld refinements in space group R3 confirmed the isostructural relationship between jianshuiite and chalcophanite, with Mg occupying the interlayer position above and below the vacant sites in the Mn/O octahedral sheet, and coordinated to 3 octahedral layer O atoms (1.94 Å) and 3 interlayer water O atoms (2.13 Å). Final refined occupancy factors suggest that small quantities of Ni and possibly Mn2+ are located on the Mg site. The transient appearance of the Mg-rich birnessite-like phase jianshuiite, probably abiotically produced, must indicate an exceptional transient change in the chemistry of the pore fluids within deep ocean sediments directly following the P/E boundary, possibly as a result of decreasing oxygen levels and pH, followed by a return to pre-event conditions.
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U2 - 10.2138/am-2016-5347
DO - 10.2138/am-2016-5347
M3 - Article
AN - SCOPUS:84958072773
VL - 101
SP - 407
EP - 414
JO - American Mineralogist
JF - American Mineralogist
SN - 0003-004X
IS - 2
ER -