Neogene stratigraphy of the Eskişehir graben and the Investigation of coal deposition by seismic reflection method

The study area is located within the Eskişehir Graben, north of Ağapınar village in the Sevinç district and east of Eskişehir City. Miocene deposits unconformably overlie the basement of Paleozoic metamorphites and Mesozoic ophiolites. The m1 series constituted by gravel, sandstone and claystone is observed at the base of Miocene deposits. The overlying m2 series, from bottom to top, represents a sequence of partly conglomerate, green claystone, coal, gray sandstone, dark gray to green siltstone, bituminous marl, claystone, coal, green claystone, sandstone and fine grained conglomerate. The m3 series of limestone and conglomerate is patchy and Pliocene deposits consisting of loose gravel, claystone overly them. The stratigraphical succession in the region covered by Neogene deposits has been investigated during surveys and reservoir drilling in licence areas belonging to MTA. High resolution shallow seismic reflection data were collected on two lines crossing each other considering field conditions (vegetated areas, irrigation channels, Porsuk River, railway line, etc.) and locations of boreholes made in the basin. These collected data were assessed in the Data Processing Center of the Seismic Research Division of the Geophysical Research Department (MTA),to produce the final sections of the seismic reflection. The data were then correlated with borehole data on or adjacent to the lines. The surface of reflection (yellow colored level) which could be continuously traced through all sections was deduced as the Paleozoic basement corresponded to ophiolites in borehole data. Reflection surfaces which are observed in areas, where the seismic basement deepened by multi-staged discontinuity surfaces of the seismic basement and rely especially on slopes of seismic basement, were determined as coal-claycontactzone. It was also revealed that, data obtained from drilling works continuing in the region correlate with geophysical interpretations made on seismic profiles.