"Sivas and its surroundings is the most important gypsum karst terrain in Turkey with a massive Lower Miocene gypsum formation 750 m thick. The region east of Hafik has a wide variety of well developed karstic features such as karrens, dissolution dolines, collapse dolines, blind valleys, karstic springs, swallow holes, caves, unroofed caves, natural bridges, gorges and poljes. The karstification started in the Early Pliocene. The piezometric level to the east of Hafik has lowered at least 200 m since the Early Pliocene and 90–100 m since the Early Pleistocene. There is a youthful karst (doline karst) on the Higher Plateau (1520–1600 m) and a mature karst on Lower Plateau (1315–1420 m). The mature karst evolved in two stages, first stage where excessively karstic paleovalleys, uvalas and collapse dolines appear and the second stage where poljes, collapse dolines and degraded collapse dolines dominated. "
Abstract on ScienceDirect: Click here
Karst region around Sivas, Hafik and Zara
"Tertiary Era limestone extends underground between Sivas in the west and the regional center of Imranli in the east and a karst landscape dominates the upper Kizilirmak for a distance of 100km/62mi, extending 10-20km/6-12mi on both sides. The river has cut its way through the layers of gypsum to create this wide valley and for over 100km/62mi it flows mainly through red sandstone, gypsum and marl. There are many tributaries which give the water a permanently dull red color, hence the name Kizilirmak ("red river"). The high levels of sodium and potassium compounds also give the water a bitter taste. The higher gypsum plateaux at about 1,550-1,650m/5,000-5,500ft are riddled with a dense network of dolines. The slopes close to the river abound with 50-100m/165ft-325ft wide and 30m/100ft deep funnels and craters with swallow holes (ponors). Uvalas and tiny poljes with shallow lakes and marshes have been created from larger dolines merging together." Text from: PlanetWare