Ammonite faunal turnover tracing sea-level changes during the Jurassic (Betic Cordillera, southern Spain)

Abstract

Ammonite faunal turnover has been used to trace changes in sea level during the Jurassic in the Betic Cordillera, southern Spain (i.e. westernmost Tethys). Major turnovers recorded in the Jurassic succession are interpreted as extinction phenomena, and as appearance, diversification and radiation bioevents of the various ammonite associations. They are explained as being due to falls and rises in sea level, respectively. The ten most abrupt diversification and radiation bioevents have been detected in the ammonite associations associated with pelagic Jurassic sedimentary rocks. All of these bioevents can be linked with sea-level rises, most coinciding with the eustatic increases of the same age expressed in the eustatic curves of Hallam and Haq et al . The relative sea-level falls, including eustatic ones coinciding with extinctions, are recorded as stratigraphic breaks and stratigraphic condensation phenomena in the Betic Jurassic succession. The seven most significant extinction events recognized in the Betic Jurassic are also largely attributable to eustatic falls. We conclude that the proposed faunal turnover curve is predominantly the expression of global changes in sea-level and it can be considered as a basis for plotting a Jurassic eustatic curve.