Palynology and micropalaeontology of the Pliocene - Pleistocene transition in outcrop from the western Caspian Sea, Azerbaijan: Potential links with the Mediterranean, Black Sea and the Arctic Ocean?

Abstract

New palynological, ostracod and foraminiferal data are presented from a long outcrop section in the Jeirankechmez river valley, Azerbaijan, near the western coast of the Caspian Sea. The interval studied includes the upper part of the Pliocene Productive Series and overlying Plio-Pleistocene Akchagylian (Akchagyl) and Apsheronian (Apsheron) regional stages. Productive Series sediments were deposited in a closed fluvio-lacustrine basin, isolated from any marine influence. The onset of Akchagyl deposition is marked by a lithological change associated with a significant flooding event that, at its maximum extent, reached the Sea of Azov and into present-day Iran, Kazakhstan, Turkmenistan and Russia. At the Jeirankechmez locality, the lowermost beds of the Akchagyl contain predominantly freshwater assemblages with very minimal marine or brackish content showing that the onset of Akchagyl deposition was not a marine induced event. Reworked Mesozoic palynomorphs occur frequently in this lowermost interval, including the reworked pollen taxa Aquilapollenites-Triprojectus that were eroded from the north or north-east. Significant marine influence is evident ca. 30 m above the base of the Akchagyl in the studied outcrop, marked by the ‘Cassidulina Beds’ which contain a distinct but low diversity assemblage of foraminifera that occurs widely and can be correlated in many parts of the greater Caspian region. Dinoflagellate cysts (dinocysts) in the marine interval include frequent specimens very similar to Algidasphaeridium capillatum (Matsuoka and Bujak), a species only previously recorded from the northern Bering Sea. The combined evidence from these dinocysts and foraminifera suggests that a marine (i.e. seaway) connection existed briefly between the Arctic Ocean and the Caspian Sea at the very end of the Pliocene. Re-examination of core material from the Adriatic Sea shows that Cassidulina reniforme (Nørvang) was present in the Mediterranean during and shortly after the Last Glacial Maximum. The possibility that the end Pliocene marine incursion came from the Mediterranean via the Black Sea region to the Caspian Sea cannot be entirely ruled out but is considered unlikely. Biometric analyses are applied to obtain a better understanding of the palaeoenvironmental significance of the assemblages dominated by cassidulinids. An interval >300 m thick is assigned to the Apsheron regional stage on the basis of predominantly brackish ostracod and dinocyst associations. The dinocysts are of ‘Peri-Paratethyan’ affinity and closely resemble species first described from Miocene and Pliocene sediments in the Pannonian and Dacic basins of Eastern Europe. Many similarities exist in the microplankton records (dinocysts and acritarchs) between the Caspian Sea, the Black Sea and Central Paratethys.