REE PATTERNS IN LATEST NEOPROTEROZOIC-EARLY CAMBRIAN PHOSPHATE CONCRETIONS AND ASSOCIATED ORGANIC MATTER

Abstract

Analyses of REE were conducted on phosphatic concretions and various types of associated organic matter in eight, key latest Neoproterozoic–earliest Cambrian, inner- to outer-shelf, marine phosphatic successions that are distributed worldwide. A pronounced REE fractionation during diagenetic degradation of the organic matter has been revealed. Selective MREE incorporation and bulk REE contents in some kerogens, organic megascopic fossils and humic acid are compatible with those recorded in associated phosphate. The similarity of REE patterns in apatite and organic matter suggests that early-diagenetic, microbial decomposition of organic matter does not only provide phosphorus and suitable sub-oxic, geochemical conditions, but it is also a likely source of REE enrichment in authigenic apatite formed at shallow depths below the marine water–sediment interface.