The Middle Jurassic fluvial record of the Central High Atlas (Guettioua Formation, Morocco): seasonal rivers in a dynamic palaeogeography

This paper addresses the need for a regional stratigraphic revision of the Bathonian-Callovian Guettioua Formation, widely exposed across the Central High Atlas (CHA, Morocco). Despite numerous studies, the stratigraphy of this formation, its relationship with tectonic activity, and fluvial dynamics are still not fully understood. This study employs a comprehensive approach integrating detailed geological mapping, facies analysis, paleocurrent measurements, and identification of multi-order unconformity surfaces to define the Guettouia Unit (GU), which records an articulated drainage network related to a source-to-sink system strongly controlled by active crustal deformation. From the depositional perspective, the GU is associated with seasonal rivers, whose sedimentological features conform to the distributive fluvial system (DFS) facies model. The syntectonic control on depositional processes during the deposition of the GU is evidenced by: (1) angular unconformities that bound and occur within the GU strata, and (2) regional paleocurrent trends, which indicate the presence of Middle Jurassic paleohighs and structural thresholds. Through our integrated stratigraphic and sedimentological analyses, we reveal the development of a regional fluvial drainage recorded by the GU strata, which positively supports the hypothesis of an incipient and diffuse uplift of the CHA, predating the relief caused by the Cenozoic plates’ convergence. As a generalizable conclusion, this study demonstrates that ancient fluvial systems not only provide insights into depositional processes and systems but also serve as valuable proxies for reconstructing the evolution of complex geodynamic settings. • The Bathonian Guettouia Unit is a prominent fluvial succession in the Late Mesozoic record of the Central High Atlas • This succession incudes conglomerates, sandstone and mudstones recording the development of a regional drainage network • Facies analysis suggests a marked seasonal character of the deposition in distributive fluvial systems • Evidence of syndepositional deformation of the Guettouia strata indicate that these fluvial systems adapted to an actively uplifting relief • The distribution of the Guettouia Unit, its facies associations and the regional paleocurrent pattern point to a dynamic palaeogeography possibly resulting from a complex geodynamic setting of the NW Africa margin and surrounding areas during the Middle Jurassic