Thrace Basin basement, comprises interbedded fine to coarse grained clastics from a variety of depositional environments, turbidite, muddy carbonates with local reef developments, river channels and tuffs. More than 400 wells were drilled till 2008; 14 gas and 3 oil fields were discovered and all of them are producing. Main gas productions zones are between Eocene- Oligocene deposits; Hamitabat (turbiditic sandstones), Ceylan (tuffs), Sogucak (reefal limestone), and Osmancik (deltaic sandstone) formations. Shales of Hamitabat and Mezardere formations have good source potentials. Thrace Basin The European side of Turkey is called the Thrace Basin. It is the largest and thickest Cenozoic sedimentary basin
Immigration to Turkey enter through the Eastern border, which generally included all Iranians and Afghans who entered illegally. In 1923, more than half a million ethnic Muslims of various nationalities arrived from Greece as part of the population transfer between Greece and Turkey (the population exchange was not based on ethnicity, but by religious affiliation; as Turkey was seen as a Muslim country while Greece was viewed as a Christian country). After 1925, Turkey continued to accept Turkic-speaking Muslims as immigrants and did not discourage the emigration of members of non-Turkic minorities. More than 90% of all immigrants arrived from the Balkan countries.