The Harmancık Basin, in the north-easternmost Miocene graben in western Anatolia, hosts a 12.6-m-thick coal seam located in the Keles coalfield, in which coals are being exploited by open-cast mining methods. Syngenetic clinoptilolite/heulandite-type zeolite formation in the upper part of coal seam and carbonaceous clayey diatomite as a roof rock have been identified for the first time, and the palaeoenviromental reconstruction of the coal seam was conducted using a multidisciplinary approach. The coal facies and palynological data show that vegetation and depositional changes took place during the middle Miocene, which resulted in vertical variations in elemental and mineralogical compositions. During the initial stages of mire development woody vegetation (e.g. pollen with affinity to Cupressaceae) prevailed, telmatic conditions were common, and preservation of organic matter was high due to anoxic conditions. Thus, relatively low-ash yield was observed in the lower and middle parts of the coal seam. Furthermore, the presence of kaolinite and smectite-type clay mineral aggregates in these parts of the coal seam suggests that alteration of synchronous volcanic inputs took place under weak acidic to neutral conditions. In contrast, limnotelmatic conditions prevailed during the late stages of peat-accumulation, and macrophytes coinciding with herbaceous peat-forming vegetation (e.g. Osmundaceae, Polypodiaceae, and Nymphaeaceae) were dominant. The elevated Gelification Index (GI) values in the uppermost parts of the coal seam could be related to development of alkaline conditions in the palaeomires, which also caused formation of syngenetic clinoptilolite/heulandite-type zeolite from the alkaline activations of synchronous volcanic inputs. Even though palynological data points to the prevalence of freshwater conditions during peat-accumulation, B enrichments along Sr/Ba ratio higher than 1.0 could point to possible marine influence; however, no Neogene marine deposits have been identified in the Harmacik Basin. Nevertheless, the SEM-EDX data show the presence of traceable Ba and Sr in clinoptilolite/heulandite grains, and Sr-bearing barite around feldspar grains in the studied samples from the upper parts of the coal seam. This implies K-feldspars and K-rich alkali-feldspars, derived from synchronous volcanic ash fall, altered under alkaline conditions. Moreover, alginite proportions increased towards the upper parts of the seam, while relatively high Hydrogen Index (HI) values were reached in the uppermost part of coal seam and carbonaceous clayey diatomite roof-rock sample. Furthermore, palynolgical data imply that vegetation changes towards the roof of the coal seam reflect the progressive development of more humid conditions and nutrient-rich surface waters, which favoured increased algal activity.
|Journal||International Journal of Coal Geology|
|State||Published - Mar 15 2021|
Bibliographical noteFunding Information:
A part of this study is supported by Scientific Research Projects Coordination Unit of İstanbul University (Turkey) under project number 554. The authors would like to thank Prof. Dr. Y. Ersoy for his suggesting about regional volcanic activity data, Prof. Dr. A. Akbulut for his assistance in determining the diatom flora, Dr. Maria Mastalerz for her assistance on the interpretation of FT-IR data and Dr. E. Cicioğlu-Sütçü and Bülent Başara for their help during analyses. Finally, the authors thank Prof. Dr. Shifeng Dai, Editor-in-Chief of the Journal, Dr. T. Moore and anonymous reviewer are thanked for their comments and suggestions.
© 2021 Elsevier B.V.
Copyright 2021 Elsevier B.V., All rights reserved.
- Coal facies
ASJC Scopus subject areas
- Fuel Technology
- Economic Geology