| Summary: | This paper presents the first biostratigraphic data obtained from nannofossils in combination with planktonic foraminifera from the lower part of the Escucha Formation. Samples have been obtained from offshore marly deposits. The occurrence of nannofossil Eprolithus floralis and the lack of Prediscosphaera columnata, allow to include the study succession in the Rhagodicus angustus Zone (Late Aptian). In the other hand, the occurrence of planktonic foraminifera Praehedbergella aptiana, Praehedbergella infracretacea, Praehedbergella convexa, Praehedbergella oculta, Hedbergella trocoidea, Globigerinelloides and Ticinella bejaouaensis allow to include the study succession in the Ticinella bejaouaensis Zone (late Upper Aptian). This planktonic foraminifera zone is correlated with the Nolani and part of Jacobi ammonite zones. Both biostratigraphic analysis suggest a late Upper Aptian age for the base of the Escucha Formation, an older age than that suggested by previous works
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