Vegetation succession and climate change across the Plio-Pleistocene transition in eastern Azerbaijan, central Eurasia (2.77-2.45 Ma)

The Plio-Pleistocene transition marked a key moment in global climate history, characterised by the onset of major glaciations in the Northern Hemisphere. The palaeoenvironmental history of the Plio-Pleistocene transition is not well known for the Caspian Sea region, despite its importance for global climate dynamics. Here we present an independently 40Ar/39Ar dated, high-resolution terrestrial palynological record spanning the Plio-Pleistocene boundary based on a lacustrine-marine sedimentary sequence from eastern Azerbaijan. Despite complex pollen transport pathways and the proximity of closely stacked mountain vegetation belts in the Greater and Lesser Caucasus, the record shows that regional vegetation responded to Milankovitch forced glacial-interglacial cycles, tentatively correlated with global climatic records spanning MIS G8 to 98 (~2.75-2.5 Ma). The persistence of mesophilous forests during glacial times indicates that some settings in the south Caspian basin acted as glacial refugia, and that vegetation response to glaciations was muted by increased moisture availability, linked to Caspian transgression. The palynological record shows a relationship with global δ18O stacks and specifically to the obliquity record, and we anticipate that precise correlation with this global climatostratigraphic timescale will allow better understanding of the nature and timing of important transgressive events in the Caspian Sea and their relevance on a global scale.