The main geologic history locally had two stages. The first is the Miocene, determined by tectonic events that correlate with the closing of the Tethys Sea. The second is the Pleistocene noted for its glaciation cycles and the full run of the present Volga. During the first stage, the Tethys Sea had evolved into the Sarmatian Lake, that was created from the modern Black Sea and south Caspian, when the collision of the Arabian peninsula with West Asia pushed up the Kopet Dag and Caucasus Mountains, lasting south and west limits to the basin. This orogenic movement was continuous, while the Caspian was regularly disconnected from the Black Sea. In the late Pontian stage, a mountain arch rose across the south basin and divided it into the Khachmaz and Lankaran Lakes (or early Balaxani). The period of restriction to the south basin was reversed during the Akchagylian – the lake became more than three times its size today and took again the first of a series of contacts with the Black Sea and with Lake Aral. A recession of Lake Akchagyl completed stage one.