New data on the Turonian nodular phosphate-bearing bed in the Dobrindol Formation south of Kaspichan, NE Bulgaria

Abstract

The Turonian nodular phosphate-bearing bed outcropping near Kaspichan consists of early diagenetically mineralized (carbonate-fluorapatite – CFA, glauconite and goethite) limestone lithoclasts (nodules), mineralized macrofauna, and non-mineralized intraclasts, embedded in a glauconite-CFA cement. The characteristics of the nodular bed are consistent with a formation under extremely low net sedimentation rate with nodules demonstrating evidence for reworking. The identified ammonite association assigns late Turonian age of the bed. XRF and LA-ICPMS analyses reveal low P, U, and REE-Y concentrations, with correlations between REE and the other authigenic oxides indicating that glauconite and goethite could be main REE concentrators along with CFA. Fluctuations in the redox conditions are implied by the authigenic mineral association, mineralization stages, presence of diverse fauna and ichnofissils, and applied geochemical proxies.