Integrated sedimentological and sequence stratigraphic framework of the Paleocene–Eocene Series at Kef Essnoun, Djebel Onk (Northeastern Algeria)

Abstract

The Paleocene–Eocene succession at jebel Onk, northeastern Algeria, remains poorly understood, despite its significance for reconstructing paleoenvironments during a critical period of global change. Unlike the well-studied equivalent series in the Metlaoui–Gafsa Basin, the Algerian counterpart lacks a robust stratigraphic and paleoenvironmental framework. This study addresses this gap by applying detailed sedimentological and petrographic analyses, integrated with sequence stratigraphic principles based on the model of Vail. Five erosional surfaces delineate five truncated depositional sequences, each containing only a transgressive and highstand systems tract, indicating repeated interruptions in sedimentation. Eight lithofacies were identified, reflecting deposition along a carbonate ramp system that ranges from outer ramp to restricted lagoonal and tidal flat settings. These facies transitions reveal shifts between transgressive and regressive phases, including a notable phosphatic-rich interval and an upper evaporitic horizon. The uppermost sequence is interpreted as an inner ramp deposit from the terminal Ypresian to early Lutetian. Stratigraphic correlation with distal, pelagic facies supports this age assignment. The integration of facies architecture with the influence of eustatic and tectonic controls allowed identification of two second-order tectono-eustatic cycles. This refined framework enhances regional correlation of Paleocene–Eocene deposits in North Africa and underscores the complex stratigraphic evolution of the Kef Essnoun section.