The aim of this paper was to investigate the possible connections
between ammonite faunal turnover and the eustatic events recorded in
Tethyan sequences during the middle Toarcian/early Bajocian time
interval. For this we have analysed the biostratigraphic ranges, at the
subzone level, of approximately 600 ammonite species belonging to 160
genera from several selected sections of the western Tethys
(Mediterranean and Submediterranean provinces). The analysis of taxon
ranges enabled us to plot curves for ammonite faunal turnovers,
inter-subzonal distance, and diversity. Comparing the mentioned curves
with Tethyan sequences [Hardenbol et al., 19981, we find that
sea-level changes correlate well with origination and extinction events
and faunal diversity. Most of the faunal turnovers correlate with
stratigraphic events. Extinction events with their corresponding
decrease in diversity correlate with regressive intervals and with major
or minor sequence boundaries. Origination events and their corresponding
increase in diversity were clearly connected with transgressions in
Tethyan sequences. In several cases, the major sequence boundary and the
subsequent transgressive phase correlate with major ammonite faunal
turnover, whereas minor or medium sequence boundaries generally gave
rise to minor or medium turnovers.