BATHYMETRIC RECONSTRUCTIONS OF THE MIOCENE-AGE CALCARI A LUCINA (NORTHERN APENNINES, ITALY) FROM OXYGEN ISOTOPES AND BENTHIC FORAMINIFERA

Two independent methods of paleobathymetry, applicable to hydrocarbon-derived carbonates, are explored in this study. The oxygen isotope method exploits the temperature decline with depth that leaves a measurable imprint on the delta(18)O composition of pristine products of venting comprised of aragonites and dolomites. The other method makes use of the bathymetric preferences of benthic foraminiferal taxa entrapped in the carbonate buildups. These two methods were tested on the ''calcari a Lucina'' limestones hosted in turbidites and mudstones infilling the Miocene-age Marnoso-arenacea basin. The limestone blocks, rich in fossils of chemosymbiotic-like fauna, preserve a 10-Ma record of hydrocarbon venting from Langhian to lower Messinian times. Our results indicate that carbonate accretion and lithification occurred at upper bathyal depths in waters not shallower than 200-250 m. The delta(18)O of venting products contains the imprints of profound hydrographic changes that occurred in the ancient Mediterranean basin from the lower Serravallian to the lower Messinian.