Late Miocene stratigraphy, palaeoecology and palaeogeography of the Tabriz Basin (NW Iran, Eastern Paratethys)

The Tabriz Basin is located in NW Iran within the collision zone of the Arabian and Eurasian plates. Its Upper Miocene and ?Pliocene basin fill, termed Lignite Beds and Fish Beds, can provide detailed insights into the Neogene environments and processes during a time of intense tectonics and volcanism. However, a modern re-evaluation of the Lignite Beds and Fish Beds is lacking. Here we present fission track (FT) data from the northern hinterland of the Tabriz Basin (Upper Red Formation) and from the Fish Beds, which support previous age assumptions for the Upper Red Formation, but, together with the new biostratigraphic data, point to an older stratigraphic age for the Lignite and Fish Beds than previously thought (Lignite Beds: 11.6–10.0 Ma; Fish Beds: 10.0–7.5 Ma). Furthermore, we describe for the first time the fossil fish and ostracod fauna and the diatom assemblages from both the Lignite Beds and Fish Beds. All fossil groups are characterized by the occurrence of freshwater and brackish forms; additional marine–euryhaline taxa appear among the fishes and diatoms. It can be assumed that the Lignite and Fish Beds represent deposits of a lacustrine to euryhaline Late Miocene Lake Urmia during the initial state of the Tabriz Basin subsidence, and that the ancient lake was located farther to the east and in a higher altitude than the present-day Lake Urmia. The fossil assemblages indicate a new palaeogeography for the Late Miocene of the study area, with temporary connections between the Tabriz Basin and the southern Caspian Sea, perhaps via an ancient Araks River passage.