Depositional sequences and ammonoid assemblages in the upper Cenomanian-lower Santonian of the Iberian Peninsula (Spain and Portugal)

Authors

  • M. SEGURA Grupo de Investigación IBERCRETA, Universidad de Alcalá de Henares 28871 Alcalá de Henares, España – Spain.
  • F. BARROSO-BARCENILLA Departamento de Paleontología, Universidad Complutense de Madrid 28040 Madrid, España – Spain.
  • P. CALLAPEZ Departamento de Ciências da Terra, Universidade de Coimbra 3000-272 Coimbra, Portugal. Centro de Geofísica, Universidade de Coimbra 3000-134 Coimbra, Portugal.
  • J.F. GARCÍA-HIDALGO Grupo de Investigación IBERCRETA, Universidad de Alcalá de Henares 28871 Alcalá de Henares, España – Spain.
  • J. GIL-GIL Grupo de Investigación IBERCRETA, Universidad de Alcalá de Henares 28871 Alcalá de Henares, España – Spain.

Keywords:

Depositional sequences, Ammonoid assemblages, Upper Cenomanian-Lower Santonian, Spain, Portugal

Abstract

A clear relationship exists between eustatic sea-level rises and falls recorded as cyclical depositional sequences and ammonite faunas during the Cenomanian-Santonian in the Iberian and West Portuguese basins. Most of the faunal turnovers correlate with stratigraphic intervals related to marine transgressions, maximum flooding of the shelf (locally associated to anoxic events), and marine regressions. Specifically, within each depositional sequence, three distinct and identical events of morphological change occur, involving ammonoids belonging to different groups. Transgressive sediments are characterized by moderately ornamented, inflated and evolute morphologies, which are replaced by smooth, involute and compressed oxycones (the most hydrodynamic shells) during maximum flooding (and to a lesser extent at the early highstand) of the sequences. The latter morphologies in turn are replaced by coarsely ornamented and evolute shells during late highstands. We conclude that ammonoid faunal analysis can be used to trace sea-level changes and provides an additional tool for sequence stratigraphy.

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