Geochemistry of the Middle to Late Permian limestones from the marginal zone of an isolated platform (Laibin, South China)

Major, trace and rare earth elements were measured in 27 samples of the Middle to Late Permian limestones from the Tieqiao section located on the marginal zone of an isolated platform (Laibin, South China). Shale-normalized REE+Y patterns of all samples show notably negative Ce anomalies (0.21–0.66,...

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Bibliographic Details
Published in:Science China. Earth sciences 2013-10, Vol.56 (10), p.1688-1700
Main Authors: Qiu, Zhen, Wang, QingChen, Yan, DeTian
Format: Article
Language:English
Subjects:
Chemical analysis
Chert
Earth and Environmental Science
Earth science
Earth Sciences
Geochemistry
Limestone
Permian
Rare earth elements
Research Paper
Rocks
Seawater
Trace elements
Water analysis
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Summary:Major, trace and rare earth elements were measured in 27 samples of the Middle to Late Permian limestones from the Tieqiao section located on the marginal zone of an isolated platform (Laibin, South China). Shale-normalized REE+Y patterns of all samples show notably negative Ce anomalies (0.21–0.66, average 0.33), slightly positive Gd anomalies (1.08–1.30, average 1.20), and positive Y anomalies with superchondritic Y/Ho ratios (36–91, average 55), which are consistent with those of modern shallow seawater. Their relative LREEs enrichment with higher Nd SN /Yb SN ratios (0.58–1.80) than those of modern shallow seawater (0.21–0.50) suggests complicated sources of REEs for all samples. Compared with geochemical features of sediments influenced by terrigenous particles and hydrothermal fluids, it is concluded that ambient shallow seawater was the primary source of REEs in these limestones. Comparing the indicators of REE+Y elements (ΣREE, Nd SN /Yb SN , Ce/Ce*, Gd/Gd*, Eu/Eu* and Y/Ho) in limestones with those in bedded cherts from the Tieqiao section, we consider that limestone and bedded chert have similar sources of REE+Y elements: ambient shallow seawater with more or less hydrothermal fluids. In addition, there is a completely negative correlation between CaCO 3 and SiO 2 contents in limestones and bedded cherts. These results imply that precipitation of CaCO 3 was inhibited by that of SiO 2 which was derived mainly from hydrothermal fluid, especially in bedded cherts from the Tieqiao section.
ISSN:1674-7313
1869-1897
DOI:10.1007/s11430-013-4620-7