Depositional evolution of Miocene coal successions in the Soma coalfield, western Turkey

Abstract

Miocene alluvial and fluvial-lacustrine deposits comprising three lignite successions (Lower, Middle, and Upper) are exposed in the Soma coalfield in Western Anatolia. The total thickness of the coal successions is about 900 m and they rest unconformably on Mesozoic carbonate and siliciclastic basement rocks. Several lithofacies are recognised and are arranged into 15 facies assemblages (FA1 to FA15) within coal successions. The Lower Coal succession (FA1 to FA3) has been interpreted as the deposits of alluvial fan to ephemeral lacustrine and forest lower mire system, resulting in a subbituminous coal, which averages thickness of 20 m. The freshwater carbonate-dominated Middle Coal succession (FA4 to FA7) has been interpreted as the deposits of an anastomosed river system including shallow carbonate mudflats to lake and ponds and frequently drying poor forest mires depositing lignitic coal. The volcanic-influenced Upper Coal (UC) succession (FA8 to FA15) has been interpreted as the fluvial channel, floodplain, and allochthonous peat mire deposits (FA8 to FA10) associated with a braided river system that was rapidly buried and eroded by volcaniclastic apron deposits (FA11 to FA14) and culminated in large carbonate-dominated shallow lake deposits (FA15). The Miocene coal successions were probably deposited in a slowly subsiding and fault-controlled karst-based paleovalley and lowlands of the intramontane paleomorphology that resulted from the Early Tertiary collision of the Eurasian and Anatolian plates.