"An Historical Atlas of Central Asia" written by Yuri Bregel. This is stated on Page no 73 of this book.

The Turkmens are mentioned in Islamic historical sources as early as the 10th century, when this term did not yet have a clear ethnic meaning, but was rather used to designate Turks in some steppe areas bordering the Islamic world who had converted to Islam, irrespective of their tribal affiliations. With the Islamization of a part of the Oghuz and the beginning of the Seljuk movement at the end of the 10th and early 11th centuries, this name (whose etymology is not clear) became associated with the Islamized Oghuz, mostly the supporters of the Seljuk dynasty. Due to the role of the Turkmens in the rise of the Seljuk empire (see maps 13-15), information on them is found in many historical sources, beginning with the 11th century. During this period the Turkmens migrated westward as far as the Fertile Crescent and North Africa; but our maps deal only with the Turkmens who remained in Central Asia. Turkmen tribal genealogies traced their origin to the mythical Oghuz Khan, the progenitor of all the Oghuz. According to these genealogies, reflected in historical sources of the 11th and 13th centuries, there were 24 Oghuz tribes; many of their names are still the names of the modern-day Turkmen tribes or clans. Although general Turkmen migrations in the pre-Mongol period are sometimes well described in historical sources, the movements and location of individual tribes in Central Asia at that time remain unknown; only some of it can be tentatively reconstructed on the basis of Turkmen genealogical legends. More data are available from the early 16th century, primarily due to the two works written by the #Arabshahid Abu’l-Ghazi Khan, one on the history and genealogy of the Turkmens and another on the history of the #Arabshahids.

In the process of the Seljuk conquests most of the Turkmens went west, to Azerbaijan, Iran, Iraq, and Anatolia (where their descendants eventually founded the Ottoman empire); in Azerbaijan and Northern Iraq they formed two powerful tribal unions, the Qara-Qoyunlu and Aq-Qoyunlu, and many of them were included in the Qïzïlbash tribal union that founded the Safavid state in Iran. But from the beginning of the Seljuk conquests a part of the Turkmens did not move west with their fellow tribesmen, but remained in the steppes and deserts between the Aral Sea and Khorasan. Here, groups belonging to almost all Oghuz tribes could be found; some Turkmen groups that had moved westward later on, probably in the 13th14th centuries, returned east and joined those who had remained in Central Asia.

During the Mongol conquest battles and skirmishes between the Mongols and the Turkmens in Khorezm and Northern Khorasan are mentioned, but historians of the Mongol and Timurid periods are silent about these Turkmens. Only a few events of Turkmen history during these periods can be tentatively reconstructed on the basis of the Turkmen historical tradition and some circumstantial evidence. Apparently, during the Mongol conquest of Central Asia the Turkmens were driven away from the vicinity of the oases of Khorezm and Northern Khorasan, and during the next three centuries they nomadized mainly along the eastern coast of the Caspian Sea.
The Mongols were obviously little interested in this area, which was unfit for the Mongol type of horse-breeding economy, and for almost three centuries the Turkmens were left to their own devices, practicing relatively short-range nomadism based on camels (dromedaries) and sheep, and divided into independent tribes. As distinct from the nomads of the Dashi Qïpchaq, they were not incorporated into the Mongol tribal and imperial structure, and, as a result, they remained outside the Mongol imperial tradition: they did not have any Chinggis rulers, they did not have a “noble estate” comparable to the Qajaq “white bone” (cf. map 38), and they were not directly subjected to the Chinggis khans.