Abstract
The Greek peninsula is an area where vivid neotectonic activity takes place and many lignite deposits are located. During the period from the Neogene to the Quaternary were formed the most economically important lignite deposits in Greece, such as Florina, Ptolemais, Megalopolis and Drama. The study of the coal-forming conditions provides information useful in exploration and utilization of this economically important raw material. The aim of the present study is the specification of the palaeoenvironment type and its different vegetation zones that evolved during the formation and evolution of the Achlada lignite deposits (Florina), the subdivision of xylitic lithotype of lignite to independent sub-lithotypes, as well as the role of the intercalated inorganic seams that appear in the same lignite-bearing sequence. In addition, it was evaluated the industrial use of intercalated inorganic horizons in ceramic industry. For this purpose many palaeobotanical, coalpetrographical and minera ...
The Greek peninsula is an area where vivid neotectonic activity takes place and many lignite deposits are located. During the period from the Neogene to the Quaternary were formed the most economically important lignite deposits in Greece, such as Florina, Ptolemais, Megalopolis and Drama. The study of the coal-forming conditions provides information useful in exploration and utilization of this economically important raw material. The aim of the present study is the specification of the palaeoenvironment type and its different vegetation zones that evolved during the formation and evolution of the Achlada lignite deposits (Florina), the subdivision of xylitic lithotype of lignite to independent sub-lithotypes, as well as the role of the intercalated inorganic seams that appear in the same lignite-bearing sequence. In addition, it was evaluated the industrial use of intercalated inorganic horizons in ceramic industry. For this purpose many palaeobotanical, coalpetrographical and mineralogical results were combined and interpreted, while the field observations gave crucial data. A main characteristic of the Achlada lignite deposits is the high contribution of xylite lithotype in many deferent forms such as xylite mass and xylite horizons which present thickness from 2 cm to12 cm. The xylitic texture is accomplished by the presence of small xylite parts inside the lignite mass as well as roots, brenches and stems. There are also positions where in-situ huge endwise stems are present. The studied lignite-bearing sequence was formed in a forest swamp environment on the floodplain area of a meandering river system that was flowing the Achlada area. The macroscopic description of lignite horizons resulted in the classification of the organic mater into three main lithotypes: the xylite, the matrix and the mixed tissue/matrix lithotype. According to the macerals analysis the prevailing maceral group is huminite (60,7-98,2%). Liptinite contents range up to 38,3%, while inertinite content is very low (≤2,9%). These macerals contents imply that peat formation in the studied area took place under wet and anoxic conditions favorable to fine cell tissue preservation and gellification of the organic matter. The overall maceral composition of the studied lignite affected by many different factors such as the distance of the deposition site from the main channel of the meandering river system. The palaeobotanical data imply that peat-forming vegetation derives so from mixed forest palaeoenvironment as the reedmoor one. Moreover, during the evolution of the palaeomire these two palaeoenvironments were alternating one another, while the reedmoor was periodically toggled to open water one. The lignite seams derive from terrestrial higher plants mainly arboreal and herbaceous Gymnosperms and Angiosperms. In details, the Angiosperm arboreal vegetation is represented by the pollen grains of Quercus, Acer, Cyrillaceae, Carea, Ulmaceae, Ulmus, Juglans, Tilia, Alnus, Myrica, Castanea, Corylus, Carpinus, Ostrya, Salix, Betula, Betulaceae, Palmae, Pterocarya sp. and Fraxinus, as well as seeds and fruits of Meliosma pliocenica, M. wetteraviensis, and M. sp.,. Moreover, the Gymnosperm arboreal vegetation mainly consists of Taxodiaceae, Taxodium, Picea, Pinaceae, Pinus, Abies, Cedrus, Tsuga, Cupressaceae and Juniperus, as well as seeds and fruits of Glyptostrobus europaeus and G. sp.,. The herbaceous vegetation is represented by the pollen grains of Chenopodiaceae, Gramineae, Ericaceae, Compositae, Ephedra and Umbelliferae and the seeds and fruits of Batrachium sp., Sparganium sp., Decodon gibbosus, D. sp., Epipremnites ornatus, Actinidia sp., Rubus sp., Sambucus Pulchella, S. sp.1, S. sp.2, aff. Symplocos lusaticum and Vitis sp. The fern spores comprises Polypodiaceae and Osmundaceae, while the aquatic plants Nymphaceae, Nymphaea neogenicus neogenicus, Myriophyllum, Nuphar, Cyperaceae and Comaceae as well as Potamogeton sp., Potamogeton cf. piestanensis, Taddalia sp. and Nyssa sp., are present. In comparison to other lignite deposits the vegetation type from which the Achlada lignite horizons were formed is analogous to the prime vegetation that gave rise to the formation of Vevi (Florina) and Aliveri (Evia) lignite deposits. The plant communities that grew up in the studied area imply wet and warm climatic conditions with occasional dry periods; while the presence of the genera Nymphaea neogenicus neogenicus, indicates that the Achlada lignite deposits were formed during lower Pliocene. The mineralogical composition of both lignite and inorganic intercalated horizons of the lignite-bearing sequence was investigated by means of X-ray diffraction (XRD), fourier transform infra-Red (FT-IR) spectroscopy and thermo-gravimetric (TG/DTG) and differential thermal analysis (DTA). The mineral mater of lignite consists mainly of alumino-silicate minerals that were introduced occasionally into the palaeomire by surface waters during flooding events. The carbonate minerals are almost absent except from siderite, while for authigenic minerals; on the one hand the pyrite displays low content, on the other hand gypsum is present in the majority of the lignite horizons. In addition, the clay minerals prevail in all inorganic intercalated seams with illite being the dominant phase, kaolinite and chlorite to be the next. No smectite was found. The other mineral phases identified are mainly quartz and feldspars, while the presence of siderite is also remarkable. The evaluation of intercalated inorganic horizons of Achlada lignite-bearing sequence for industrial use in ceramic industry showed that these specific raw materials are appropriate for the production of red-stoneware products. In details, during the heating of these raw materials their vitrification begins from ~900 °C, while new mineral phases such as Al,Si-spinel and hematite (a-Fe₂O₃) are observed. At the temperature of ~1100°C the glaze mass prevail, enclosing both the new-formed mineral phases and rests of quartz and feldspars crystals. At the temperature of ~1200°C the formation of mullite is observed (3Al₂O₃*2SiO₂). As a whole: The Achlada lignite deposits can be divided into three different palaeoenvironments: the main river channel, the floodplain of the river system, and the oxbow lake. The floodplain model, in combination with the formation of the oxbow lake within the abandoned channel, represents a landscape with predominantly telmatic/limnotelmatic conditions and periodical flood episodes together with the deposition of fine sediments. Additionally, so the classification of inorganic raw materials on adaptable ternary diagrams as the results of their mineralogical analysis of the heated samples indicate that these particular materials are appropriate for the production of red-stoneware products in ceramic industry.
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