Other fish in the sea dating
The northern Caspian, with an area of 38,380 square miles (99,404 square km), is the shallowest portion of the sea, with an average depth of 13 to 26 feet (4 to 8 metres), reaching a maximum of 66 feet (20 metres) along the boundary with the middle Caspian.
The bottom is formed of a monotonously rippling sedimentary plain, broken only by a line of southern bars and shoals—some of which constitute the foundations for Tyuleny and Kulaly islands and the Zhemchuzhny shoals—reflecting underlying structural rises.
The Mangyshlak Bank links the mountainous Tüpqaraghan Peninsula to the east with underlying western shore structures; those are the remnants of an outlying structural uplift of the Hercynian mountain-building movement, which occurred some 300 million years ago.
It has been suggested that the middle Caspian depression resulted from a sagging at the edge of those ancient structures that occurred in late Paleozoic times, before about 252 million years ago.
The Caspian is of exceptional scientific interest, because its history—particularly former fluctuations in both area and depth—offers clues to the complex geologic and climatic evolution of the region.
Human-made changes, notably those resulting from the construction of dams, reservoirs, and canals on the immense Volga River system (which drains into the Caspian from the north), have affected the contemporary hydrologic balance.
Beyond that belt, known as the Mangyshlak Bank, the middle Caspian, 53,250 square miles (137,917 square km) in area, forms an irregular depression with an abrupt western slope and a gentler eastern gradient.
The shallowest portion—a shelf with depths reaching 330 to 460 feet (100 to 140 metres)—extends along both shores, with the western slope furrowed by submerged landslides and canyons.
To the west the submarine shelf is part of the sagging edge of the Greater Caucasus Geosyncline (a downwarp of Earth’s crust), while the submerged Turan Platform in the east swells up in the feature known as the Kara-Bogaz (Garabogaz) Swell.Caspian shipping and fisheries play an important role in the region’s economy, as does the production of petroleum and natural gas in the Caspian basin.The sea’s splendid sandy beaches also serve as health and recreation resorts.The features of the Abşeron Peninsula region, along with the folded structures on the western side of the southern Caspian depression, derive from the Alpine mountain-building and folding processes (dating from some 26 to 10 million years ago) that created the Caucasus ranges.The border between the middle and southern Caspian is, in fact, still experiencing folding activity.
The sea is bordered in the northeast by The Caspian is the largest salt lake in the world, but that has not always been true.