Chemical composition of sediments at DSDP Site 72-516

Sediment samples (32) from DSDP Holes 516 and 516F, Leg 72 were subjected to INAA (instrumental neutron activation analysis). Thirty-two major, minor and trace elements were determined. Ce anomalies, Ce_a = Ce (obs.)/Ce* (interpolated between La and Nd and relative to the NASC (North American Shale Composite)) = Ce (obs.)/[1.44 La (obs.) + 0.66 Nd (obs.)], in the carbonate phase were obtained. Calculations indicate that the Ce anomaly changed from 0.80 (80 My), 0.68 (67 My) to 0.30 (56 My), 0.27 (39 My) and 0.12–0.43 (avg. 0.26) (15?0.3 My). The Ce anomaly change observed at ~55 My coincides with the Ce anomaly change at ~58 My in marine carbonates from the Walvis Ridge, Hole 525A. These changes are attributed to improved water circulation caused by either the widening of the north-south Atlantic passage, subsidence of the Rio Grande Rise or subsidence of the Romanche Fracture Zone. The ultimate driving force behind the Ce anomaly changes is related to the pH and pO2 of the seawater and also related to global circulation of bottom ocean water and transport of the external terrestrial input from riverine or/and aeolian sources.