『Abstract
Two contrasting patterns of Mn distribution emerged from geochemical
examination of marine cores in several regions. Uniformly abundant
Mn is contained in sediments from pelagic open oceans, while in
hemipelagic regions, Mn is often concentrated in several specific
horizons and is associated with CO2. Mn carbonate
layers, designated as “manganese bands” in this paper, occur typically
in hemipelagic sediments; carbon isotopic data show that the possible
source of the carbonates is organic material supplied to hemipelagic
regions from nearby lands. Ancient analogs of the present-day
manganese bands were found to occur in shale and chert within
the Paleozoic-Mesozoic Mino terrane of central Japan. Manganese
bands, consisting largely of rhodochrosite, are characterized
by higher contents of P, Ba, and some heavy metals and a lower
ratio for Zn/Co, compared with the ambient rocks. This suggests
that manganese bands formed under suboxic conditions where organic
materials are oxidized to supply CO2 necessary
for the carbonate formation. Some manganese bands, particularly
those hosted by chert, are characterized by extremely light carbon
isotopes; this may result from methane-derived CO2.
Furthermore, manganiferous schists, such as piemontite-quartz
schist in the Sambagawa terrane, can be correlated to the chert
with manganese bands in the Mino terrane. On the basis of the
several lines of evidence obtained here, forearc and back arc
basins like the Sea of Japan and rifted continental margins with
narrow basins such as the Gulf of California are possible tectonic
settings that are modern analogs to the Paleozoic-Mesozoic complex
in the Japanese Islands.』
Introduction
Distribution patterns of Mn in marine sediments
Manganese bands on land
Kamiaso
Taniai
Yoro
Unuma
General characteristics of manganese
High phosphorus character of manganese bands
Trace element features
Genesis of manganese bands
Geological significance of manganese bands
Origin of chert
Depositional site of the Mino Terrane strata
Manganiferous schist vs. manganese band
Conclusion
Acknowledgments
Referenced cited