A short-term establishment of forest fen habitat during Pliocene lignite formation in the Ptolemais Basin, NW Macedonia, Greece

The intermontane basin of Ptolemais is part of a major tectonic trench, located in NW Greece and includes around 65% of Greek coal reserves. The Upper Xylite Layer (UXL) is a distinct lignite layer, being 3–6 m thick and outcropping in the upper part of the Pliocene Lignite-bearing Sequence at the Notio Field and Tomeas Eksi Mines of Ptolemais. Compared with the xylite-rich lithotypes, the matrix lithotypes within UXL contain more ash. Micropetrographic studies suggest that the Upper Xylite Layer is rich in huminite (>90%). Textinite dominates in the xylite-rich lithotypes, while attrinite dominates in the matrix lithotypes. The liptinite content is <10%, while inertinite rarely occurs. Palaeobotanical determination revealed that the xylite-rich coal originated from Coniferous vegetation, specifically from Glyptostrobus europaeus. The occurrence of G. europaeus as a coal-forming element is significant because, though this kind of vegetation was common in many Greek coals of Miocene age, this is the first time it has been recorded from the Pliocene. This study suggests that the Upper Xylite Layer is autochthonous. According to coal-facies diagrammes, peat accumulated under pure telmatic conditions in a relatively wet forest fen. Both herbaceous and arboreal vegetation contributed to peat formation.