Biomarker constraints on Mediterranean climate and ecosystem transitions during the Early-Middle Miocene.

Paleoenvironmental and paleoclimatic variations experienced by the Mediterranean region during the Miocene Burdigalian-Langhian interval have been investigated through analysis of biomarker signals (n -alkanes and glycerol dialkyl glycerol tetraethers, GDGTs) from slope mudstones of the northern Apennines (Marne di Vicchio Fm). Terrestrial signatures in marine sediments reflected by preserved long-chain n -alkanes with a identifiable odd-over-even carbon number predominance attest to the thermal immaturity of the sedimentary rock. Abundances of n -C 27 , n -C 29 and n -C 31 alkanes, coupled with the carbon isotopic signatures of the n -C 31 homologue suggest that Mediterranean vegetation crossed a transition phase adapting to arid conditions that may favored a shift from woodland to wooded grassland during the Middle Miocene. This ecosystem evolution could have been favored by the passage from warm humid conditions to a warm drier climate, as indicated by GDGT-based TEX 86 and BIT indexes. Strong similarities between these Mediterranean biomarker records and those from the Atlantic (DSDP Sites 94, 516, 608) imply a constant connection of the western Mediterranean to the Atlantic Ocean from ~19 Ma to ~14.5 Ma. • Mediterranean vegetation transition from woodland to grassland during Middle Miocene. • New hydrocarbon biomarker study for the Middle Miocene Mediterranean area. • Ecosystem evolution favored by the passage from warm humid to drier climate condition. • Similar biomarker values between Mediterranean and north Atlantic (IODP SITE 608). • Steady connection of western Mediterranean to Atlantic Ocean from19 Ma to 14.5 Ma. [ABSTRACT FROM AUTHOR]