The Marmara region in the northwestern part of the country is situated on both continents, Europe and Asia. It is the most densely populated region in the country. Turkey's largest city Istanbul is located within the area. The Marmara region was home to the city of Troy. The Archaeological Site of Troyofficial website is a UNESCO World Heritage Site.
This regions has only a few carbonate rock patches with caves. The Thrace part has a region of Eocene limestone along the southern margin of the Istranca massif. In the Aegean part, Permian-Mesozoic limestones overlie the older metamorphic rocks. The Western Black Sea part has areas of Jurassic-Cretaceous flysch formations.