Palaeoenvironmental reconstruction of the eastern part of the Karapınar-Ayrancı coal deposit (Central Turkey)

Abstract

Regional tectonic movements during the Neogene period resulted in the development of several fault-controlled basins in Central Anatolia; many of these basins host economic coal deposits. The recently discovered Karapınar-Ayrancı coal deposit is the most important one due to its large reserves (c. 1.8Gt) and location in the vicinity of important urban areas. The paper aims to reconstruct the palaeoenvironmental conditions before, during and after coal formation in the eastern part of Karapınar-Ayrancı deposit by means of coal-petrography and mineralogical data combined with sedimentological and palaeontological data. The basinal infilling consists of mainly lacustrine, fluvial and alluvial sediments. The coal seams comprise several beds intercalating with claystone, mudstone and marl. The coal being lignite in rank, displays high ash yield (36.4wt.%, on dry basis) and high total sulphur content (avg. 7.7wt.%, on dry, ash-free basis). Facies diagrams and lithological features of the coal seams suggest that peat was accumulating under pure telmatic to limnotelmatic conditions; however, peat accumulation ceased several times due to a rise in water level. Therefore, clastic (e.g. quartz, clay minerals) and authigenic (e.g. pyrite) mineral contents are variable along the seam profile. Gastropod and ostracod fauna points to freshwater conditions in the palaeomire. High total sulphur and evaporite mineral (e.g. halite) contents usually point to brackish-saline conditions during peat accumulation; however, in case of the Karapınar-Ayrancı deposit, high sulphur contents can be related to sulphate-rich karstic aquifer, which contributed to the palaeomire water supply.