ABSTRACT

Partitioning of Al, Fe, Mn, Zn, Pb, Cu and Tl in pelagic carbonate rocks (29 samples) has been determined by sequential chemical leaching, performed with 1 M NH₄OAc (easily extractable fraction), 0.8 M HOAc (carbonate component), 1 M NH₂OH HCl and dilute HOAc (hydrous oxides) and HF-HClO₄ (residual phases). The analytical results show great homogeneity among the samples, even though they cover a 20m.y. time-span. Mn, Zn, Pb and Cu are associated with the carbonate fraction in high percentages. Hydrous oxides, very likely because they are almost Mn-free, do not carry any significant amount of metals. Fe exhibits high percentage in residual fraction, probably because well-crystallized Fe oxides are not dissolved by NH₂OH·HCl/HOAc treatment. Tl is totally contained in residual phases, and as it shows a good, positive correlation with K, it is inferred to be carried by K-bearing silicates. The distribution pattern of elements is interpreted as the result of the redox conditions to which the sediments were submitted during the sedimentation as well as early diagenesis.