Phosphatic hardgrounds and stromatolites from the limestone/shale boundary section at Prossilion (Maastrichtian-Paleocene) in the Parnassus-Ghiona Zone, Central Greece

Sedimentological analysis of the limestone/shale boundary section (Upper Maastrichtian-Upper Paleocene) at Prossilion, Parnassus-Ghiona Zone, revealed that the Upper Maastrichtian sediments represent a shallowing pelagic sequence. Towards the top the sequence becomes highly condensed and owing to interruption of deposition at the Cretaceous/Tertiary boundary, culminates in a hardground through early lithification, boring and mineralization of the substratum by phosphates and iron-oxides. Several sedimentological features led us to assume that cementation-lithification of the sediments took place in a shallow submergent to periodically emergent setting.

Stratiform and columnar laminated phosphatic stromatolitic crusts have developed on the bored pavements, during the late Early Paleocene, trapping the pelagic sediments deposited. Phosphate is considered to be supplied to the sediment by a bacterially controlled precipitation from interstitially circulated solutions.

Both the uppermost Maastrichtian layers and stromatolitic crusts, are cross-cut by a system of thin slightly sinuous sheaths or tubular structures, interpreted as calcified filaments or rhizolitic structures. This fact suggests prolonged subaerial exposure, as a result of which pedogenic alteration of the already lithified sediments began. By progressive reorganization of the substrata by soil-forming processes, crusts of cryptocrystalline phosphate formed corresponding to phoscrete formations.