The Late Oligocene flora of Aschudasty, Zaisan depression (East Kazakhstan)

Abstract

The Late Oligocene is the time of the flourishing of typical warm temperate Turgay vegetation in Kazakhstan and adjacent areas. The Aschudasty flora described here originates from the Oshagandy Formation which correlates with the early part of the Chattian. The palaeobotanical analysis reveals 38 plant taxa, identified by macro- and microfloral remains related to Lycopodiophyta (1), Pteridophyta (3), Gymnospermae (7), Gnetophyta (1), Magnoliophyta (25) and plantae incerta sedis (1). Macrofossils include mainly Cupressaceae (Metasequoia, Taxodium and Glyptostrobus), Betulaceae (Alnus, Corylus) and Ulmus, as well as large number of monocots and aquatic ferns. The palynospectrum is dominated by pollen of the genus Picea (about 30%) and Alnus (about 40%), with noticeable amounts of pollen from other birch genera (about 7% in total). Plant functional type (PFT) and Coexistence Approach were used for palaeoenviromental reconstructions. Vegetation reconstruction shown that the microflora has a very temperate aspect reflecting a mixed deciduous conifer forest with a diverse, mainly deciduous shrub layer. The macroflora also reflects deciduous forest vegetation with conifers and possibly a very minor evergreen component. The climatic analysis shows a seasonal temperate climate. The pollen data reflect the zonal regional vegetation, the macroflora most probably reflects the lakeside wetland vegetation which may have experienced a warmer microclimate, compared to the upland realm. In whole significant climatic changes was not documented since Early Oligocene Rupelian time.