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

• 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
• ISSN: 1674-7313; 1869-1897
• DOI: 10.1007/s11430-013-4620-7

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.