A short-term cooling event, 4.205 million years ago, in the Ptolemais Basin, northern Greece

A distinct clay-rich layer in the otherwise regular succession of alternating lignites and marls of the early Pliocene Ptolemais Formation reveals an equally distinct palynomorph assemblage; only in this layer (fresh water) dinoflagellate cysts, Spiniferites cruciformis and Gonyaulax apiculata, are encountered. These co-occurring dinoflagellate species may be taken to indicate that surface water temperatures must have been remarkably low for early Pliocene mid-latitudes, contrasting other indications that overall warm humid climates prevailed at this time. A multi-component study of this so-called ‘dinolayer’ with an astrochronologically derived age of 4.205±0.01 Ma was undertaken to further investigate the apparently contrasting climatic signals. Integrated sedimentological, micropaleontological, palynological and geochemical data indicate that the dinolayer was deposited in a shallow fresh water lake. The pollen record points to slightly cooler conditions during deposition of the dinolayer in comparison with conditions just below and above. An anomalously low winter temperature is proposed as a possible cause for the recorded phenomena.