Hydrothermal activities and seawater acidification in the Late Devonian F-F transition:Evidence from geochemistry of rare earth elements

Rare-earth elements(REE) in limestones were measured by ICP-MS from the Yangdi section across the Frasnian-Famennian(F-F) transition in Guilin,Guangxi of South China.The averageΣREE contents of measured samples are 33.32 ppm.The average LREE/HREE ratio is 6.35.Data show LREE-enriched REE distribution pattern in the Yangdi section.Most of samples are characterized by positive Eu anomaly with average of 1.13,and there are two maxima of Eu anomaly just below the F-F boundary.Almost all analytical samples show obvious tetrad effects.Remarkable M-shaped tetrad effects are observed in these samples with positive Eu anomaly.The characters of REE and some relative elements(Fe,Mn,Al,etc.) indicate that hydrothermal activities occurred and resulted in seawater acidification in Upper and Lower Kellwasser horizons of the Late Devonian.The changes of marine environment caused by hydrothermal activities,such as seawater acidification,heavy metal pollution,and eutrophication,would destroy the neritic ecosystem and finally result in the F-F mass extinction.