The variation of the trace-element content of fossil biogenic apatite through eustatic sea-level cycles

Shark teeth from the Oligocene Boom Clay Formation (Belgium) have been analyzed for trace elements by neutron activation analysis to examine whether biogenic apatite might record changes in seawater trace-element chemistry throughout a eustatic sequence. An additional set of samples from a wide range of depositional environments has been studied to shed light on the nature of factors that govern the trace-element variation of fossil apatite. ic apatite samples from a given sedimentary basin exhibit rather specific and distinctive trace-element fingerprints, which shows that they reliably record geochemical parameters of the sedimentary environment. It appears that sea-level changes do not substantially affect geochemical processes in an epicontinental marine sedimentary basin. But minor chemical changes do coincide with sequence stratigraphic levels. Slightly higher La/Yb ratios correlate with periods of higher turbulence. Positive Ce anomalies indicate that a large fraction of the REE adsorbed by the shark teeth can be derived from the upward flux of reduced pore water. This process greatly diminishes the usefulness of the Ce anomaly as a palaeoredox probe. A factor analysis performed on trace-element data and sedimentary environment parameters suggests that REE contents, REE/Sc and Th/REE ratios are related to sediment input.