Origin of manganese carbonates in Jurassic red shale, central Japan
作者:
KOJI MINOURA,
SHU NAKAYA,
ATSUSHI TAKEMURA,
期刊:
Sedimentology
(WILEY Available online 1991)
卷期:
Volume 38,
issue 1
页码: 137-152
ISSN:0037-0746
年代: 1991
DOI:10.1111/j.1365-3091.1991.tb01859.x
出版商: Blackwell Publishing Ltd
数据来源: WILEY
摘要:
ABSTRACTManganese carbonate deposits in Japanese Jurassic sedimentary rocks were studied petrogeochemically. The deposits are characteristically composed of spheroidal micronodules, up to 1 mm in diameter, and always contain well‐preserved radiolarian shells. Chemical elemental composition and mineralogical characteristics indicate that the micronodules contain rhodochrosite in a mixed carbonate phase composition (Mn86.7−92.2Ca2.2−2.9Mg2.6−6.7Fe2.6−5.6)CO3Carbon and oxygen isotope values, which range from −7.99 to −4.78‰ and −4.05 to 0.28‰ relative to PDB, respectively, suggest that the manganese carbonate was precipitated in a suboxic zone. The micronodules closely resemble agglutinated benthic foraminifera in shape. We suggest that agglutinated foraminiferal tests composed of radiolarian shells accumulated selectively on the sediment surface during redeposition of bottom sediments and were replaced by manganese carbonate in suboxic diagenetic conditions of
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