The Akchagylian stage (late Pliocene-early Pleistocene) in the North Caspian region: Pollen evidence for vegetation and climate change in the Urals-Emba region

Abstract

Samples from 12 drillhole-cores from the Urals-Emba region to the north-east of the Caspian Sea were analysed for pollen and spores. The records reveal vegetation and climate changes for the late Pliocene to early Pleistocene within the time interval from ca. 3.6 to ca. 1.65 Ma. According to the results of the pollen analysis, at the beginning of the Akchagylian stage (3.6–3.4 Ma) there was a cooling and change in structure of the dendroflora, and steppe-dominated landscapes were present. At the end of the early Akchagylian, and continuing into the middle Akchagylian, a maximum variety of pollen from tree species occurred. The presence of mesophilic and thermophilic elements signifies a moderately warm and humid climate occurred at around 3.2 Ma, probably related to the ‘Mid-Pliocene Warm Period’. A second major cooling occurred at around 2.5 Ma coinciding with the onset of northern hemisphere glaciations. During this time, coniferous forests dominated by Picea, Pinus and Abies with lesser numbers of broad-leaved trees were established. At the end of the Akchagylian, at around 1.8 Ma, the climate became more arid and steppe landscapes were re-established. During the Akchagylian, alternations between forest- and steppe-dominated landscapes occurred at least three times in the Urals-Emba region. Results are compared with pollen spectra in surface samples, and with ostracods and foraminiferal assemblages in cores from the study region.