Abstract

The Middle-Upper Jurassic boundary in western Europe is characterized by extensive condensed sections containing authigenic minerals together with abundant and varied fossils, both reworked and not reworked. We have analyzed ammonite shells and chronologically ordered taphonomic events in a taphonomic sequence extending from the time the dead organism settled on the seafloor to the time it became permanently incorporated in the sediment. Three types of taphonomic sequence are recognized; they are characteristic of (1) sedimentation in depositional environments having little and only occasional hydrodynamic activity (coinciding with periods of increasing accommodation), (2) sedimentation during maximum regional reductions in accommodation corresponding to third-order sequence boundaries at the scale of western Europe, or (3) sedimentation involving a sudden lithological change and an onset of a large-scale transgressive trend. In condensed sections, where little sediment is preserved, applying this classification is a useful new tool for sequence stratigraphy.

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