Azerbaijan - The Oligocene & Lower Miocene.

In the early stages of the Oligocene, there was a turning point in the geotectonic development of the Caucasus. Many local troughs ceased to exist in the Greater and Lesser Caucasus. The elevation within their boundaries intensified sharply.

Conversely, in the Kura depression there was a sharp strengthening of submersions. Some interior elevations have disappeared.

The explored parts of the Shamakhy-Gobustan Basin and the nearby Absheron peninsula in the Lower Oligocene were surrounded by relatively low land. The south-eastern end of Caucasus island, bordering from the north, had low relief and is marked only by a low elevation. As a result, clays were deposited in the basin and inter-layers of sands were rare and of limited thickness.

The depth of the sea at that period was about 200 metres. Some extension of the area occurred from the beginning of the Middle Oligocene. This and the northern wing of the Shamakhy-Gobustan trough were occupied by sea.

The Oligocene/Lower Miocene, or Maykop series, is found in the south-eastern Caucasus and in the interfluve of the Kura and Iori rivers. It is lithologically represented by brownish, brownish-gray clays with jarosite tarnish and inter-layers of gray, fine-grained sandstones, and by marlaceous and sideritic concretions.

Most Maykopian outcrops are tied with phenomena of diapirism, which have caused the deposits to be in the surface or down along the kernels of numerous diapiric folds.

In Southern Gobustan and the Pre-Caspian region, the commercial flows of oil and gas of the Umbaki and Siazan monoclines are related to the Maykop series, with thickness of up to 1,800 metres.

The thickness of the Maykop in the Shamakhy-Gobustan trough is less than that in the basic part of the Kura depression, and its axial zone is slightly thicker than 1,500 metres.