Sequence Stratigraphy of Mixed Carbonate-Siliciclastic Platforms Developed in A Tectonically Active Setting, Upper Cretaceous, Betic Continental Margin (Spain)

Abstract

ABSTRACT The Late Cretaceous platforms in the Betic Continental Margin record a prolonged interval (30 m.y.) in which eustasy and tectonics operated simultaneously but with well-differentiated frequencies. This resulted in development of two types of unconformity-bounded units: sequence sets, which are tectonically controlled, and depositional sequences, which are the result of variations in relative sea level. Unconformities bounding sequence sets are the result of tectonic episodes that induced great changes in basin geometry and basin subsidence. They operated without apparent rhythmicity at intervals ranging from I to 12 m.y. Regional tectonics was related to variations in the intraplate stress regime associated with (1) the mid-Atlantic spreading, (2) the tectonic regime in the Africa-Iberia boundary, still poorly documented, (3) the opening of the Bay of Biscay between the Aptian and the early Campanian, and (4) the oblique convergence between Iberia and Europe in the Pyrenees, which started in the early Campanian. During periods of relative tectonic quiescence eustasy and subsidence controlled development of depositional sequences. These resulted from relative sea-level oscillations, most of them interpreted as third-order eustatic cycles. However, the correlation between our depositional sequences and the global cycles of the Exxon chart is not always easy, mainly because subsidence can mask or enhance the eustatic signal.