The geochemical similarity of Oligocene and recent phosphorites from the Chiatura deposit (Georgia) and the Namibian shelf

Abstract

Detailed studies of the distribution of macro- and microelements in phosphorites associated with Oligocene manganese ores of the Chiatura deposit revealed their geochemical similarity to the Late Quaternary phosphorites on the recent shelf of Namibia in the Atlantic Ocean. This shows that the Chiatura nodular phosphorites were formed in the shallow-water bioproductive zone of the Oligocene basin by biogenic supply of phosphorus onto the bottom and its subsequent diagenetic concentrating similarly to the granular-nodular phosphorites on the shelf of the recent ocean. The Chiatura phosphorites were later subjected to the epigenetic impact of hydrogeological processes, which modified the initial composition of the contained rareearth elements.