Ancient underground mines in the Pontian (Middle Miocene) limestones in the Odessa area (locally called ‘catacombs’) intercept numerous karst caves and karstified fractures. This paper analyses their conditions of occurrence, structure and morphology, as well as features of cave sediments. It is shown that the origin of these caves fits well to the model of transverse hypogene speleogenesis in stratified artesian structures. Caves were formed by ascending waters under conditions of a leaky confined aquifer system, with increasing leakage during the period of breaching by erosional entrenchment. 

Caves and karstified fractures in the Pontian limestones of Odessa represent an unambiguous model example, the typological standard of hypogenic karstification in stratified platform sequences.  By virtue of some features, the caves of Odessa provide a key for regional interpretation of karst through the huge area of the south Ukraine and Moldova, as well as of the Plain and Piedmont regions of the Crimea Peninsula.

Research and genetic interpretation of caves in the Pontian limestones of Odessa is of great importance for an assessment of hydrogeological and engineering-geological conditions of the area. The scheme of evolution of karst caves developed in article in a regional paleogeographic context provides a new basis for solving of some disputable questions of paleogeography of the region and eliminates some misunderstanding in treatment of the cave palaeontologic sites of Paleocene fauna.