Kalaitzidis, and 3 co-authors, reported in 2003 that 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 xyliterich 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 diagrams, peat accumulated under pure telmatic conditions in a relatively wet forest fen. Both herbaceous and arboreal vegetation contributed to peat formation.
The authors concluded that the Greece lignites that derived from Taxodiaceae occur in several Miocene coal basins. Due to the fact that xylite-rich lignites formed only during Miocene, it has been adopted (Riegel et al., 1995) that in Northern Greece during Pliocene the conditions that prevailed prevented the growth and contribution of arboreal vegetation to peat formation. However, in the upper part of the Ptolemais Lignite-bearing Sequence being of Pliocene age, a xylite-rich lignite layer, namely the Upper Xylite Layer, occurs that laterally expands in the open pits of Notio Field and Tomeas Eksi. This layer is up to 6 m thick and consists of xylite-rich and matrix lignite intercalated with clay and marl layers.
The ash contents reach 42.2% reflecting intense inorganic influx, and the gross calorific values are up to 13.4 MJ/kg on a moist, ash-free basis. The stratigraphic, sedimentological, coal-petrographic and mineralogical features suggest an autochthonous to hypo-autochthonous peat formation during the Early Pliocene. Peat-forming vegetation consisted of herbaceous and woody (G. europaeus) vegetation that grew under wet and warm climatic conditions. Peat accumulated in an open-forest swamp under telmatic to limnotelmatic conditions, and under conditions of increased inorganic influx, depending on local tectonic events, the intensity of streams and the influence of the neighboring lake. Although from Pliocene and up today Cyperaceae species constitute the main peat-forming helophytes in the Greek palaeomires, forest-swamp habitats were established for short time in Early/Middle Pliocene at some places of Ptolemais Basin due to local (?) climatic conditions.
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