Climate and vegetation changes in the southwestern Mediterranean during the Plio-Pleistocene

Palynological and climatostratigraphic record of the Gulf of Ham­mamet (NE Tu­­nisia)

Abstract

Because of the convergence of Africa and Eurasia and the opening of the Atlantic Ocean, the Gulf of Hammamet, which makes up the southwestern portion of the Mediterranean, experienced significant relative sea-level fluctuations and eustatic variations during the late Cenozoic.    
The sedimentary successions deposited between the Late Miocene and the earliest Pleistocene in the Gulf of Hammamet preserve precious environmental and climatic information. The present paper focuses on the latest Messinian to Gelasian deposits of the Jiriba-1 borehole, which is located off the coast of Tunisia. Here, previous datings obtained through planktonic foraminiferal biostratigraphy are calibrated chronologically on a high-resolution scale. Palynological analysis based on the spores and pollen content of the borehole allows for reconstructing the environmental and vegetational evolution, as well as establishing a precise climatostratigraphic framework for the study area. The latest Messinian to Gelasian palynological record is comprised of abundant continental (pollen and spores) and marine (dinoflagellate cysts) inputs. Distality markers (halophytes, D/S, Pinus, and dinoflagellate cysts) indicate that the Gulf of Hammamet was an epicontinental setting that evolved from a proximal to a distal neritic environment.    
The Lygeum, Artemisia, and S/T ratio curves enable climatostratigraphic correlations with northwestern Europe, the northwestern Mediterranean, and the Black Sea. Furthermore, the climatic evolution depicted by the steppe elements (Artemisia and Ephedra) from the Jiriba-1 borehole shows parallelisms with the δ¹⁸O isotope curve.    
The vegetation cover was open, dominated by herbaceous plants that inhabited the lower altitudes, and developed into mixed forest-plant formations at mid-altitudes. Between these two formations, a group of trees made up of Mediterranean species was present.    
Repetitive changes in vegetation as well as relative sea-level fluctuations in the Gulf of Hammamet suggest that these cyclical variations resulted from the influence of astronomical forcing.