Turonian concretionary phosphate-bearing bed near Srednya (NE Bulgaria): Paleontological, sedimentological and geochemical data

The Turonian concretionary phosphate-bearing bed outcropping NE of Srednya village consists of phosphate concretions and abundant phosphatized fauna, showing typical features of condensation and syn-sedimentary reworking. Key ammonite taxa indicate mixing of Collignoniceras woollgari and Subprionocyclus neptuni zones. The characteristics of burrows in the bed suggest an important role of biological activity for the formation of the concretions. The chemical composition of the phosphate-bearing bed is compared to the average phosphorite and non-phosphatized limestones and sandstones from the studied section. Authigenic and terrigenous chemical constituents are identified, and they correspond well to the authigenic and terrigenous fractions in the sediments. The PAAS-normalized patterns of the deposits reflect their high terrigenous content and imply possible post-depositional alteration of the primary seawater REY signal.