Eustatic control on synchronous stratigraphic development: cretaceous and eocene coastal basins along an active margin

Abstract

Field studies document an apparent eustatic control on facies patterns along a tectonically active margin. In the San Diego Embayment and northern Baja California, progradational-retrogradational shoreline sequences characterize Late Cretaceous and Eocene forearc stratigraphy. Extensive benthonic foraminifera and nannoplankton data provide control on the age and distribution of facies changes along these depositionally compact, bathymetrically steep-gradient margins. The complete stratigraphic package is arranged into three scales and patterns of depositional sequences. Timing and geometry of the two largest sequences provide relative sea-level curves that correlate exceptionally well with worldwide sea-level curves. The major depositional cycle is asymmetric, hundreds of meters thick, characterized by a thin basal retrogradational sequence overlain by a thick progradational sequence; each cycle correlates to a coastal-onlap “supercycle”. Smaller scale stratigraphic rhythms, controlled by global “cycles” and “paracycles”, compose depositional cycles. Local depostional pulses overprint these two larger order sequences of sedimentation. Coeval cycles and depositional rhythms in isolated coastal basins from Oregon to Baja California further indicate a primary eustatic control on sedimentation. Field-based facies analysis thus supports the use of the “Vail curve” or other coastal-onlap and global sea-level curves as a predictive tool in basin analysis.