Geochemical behavior of rare earth elements in pore fluids of turbidite sediments from South Taiwan

Major and rare earth elements (REEs) concentrations in sediment pore fluids are crucial for tracking biogeochemical processes during early diagenesis. However, the low concentrations and volumes typically sampled, particularly from long sedimentary sequences, limit our understanding of the REE behaviors in pore fluids. Here, major and trace elements have been analyzed on pore fluids from nine cores collected along the Penghu and Gaoping submarine canyons (SE Taiwan), in order to constrain diagenesis processes in sediments characterized by turbidite deposits and to determine their potential influence on the REE behavior in pore fluids. The ΣREE decrease from 600 to 200 pM in the upper 500 cm, with the maximum value attributed to the dissolution of Mn oxides in the redox transition zone. A decrease with depth of Ca and Mg concentrations are most probably associated with the formation of authigenic carbonate during the sulfate reduction process. This process absorbs REE from pore fluids without the REE fractionations. At deeper depth, an HREE enriched pattern is observed in core along the Penghu Canyon and might be linked to the degradation of organic matter in the methanogenesis zone. For cores located along the Gaoping Canyon, super-chondritic Y/Ho ratios comparable to seawater suggest a pronounced mixing of pore fluids with seawater and stronger scavenging of detrital sediments in the turbidity system. Overall, our results indicate that the REE concentrations in the pore fluids are relatively low and partitioning at deep depth in South Taiwan, REE distributions of pore fluids from turbidites sequences show a non-steady state variations in the high energy depositional setting.