Facies and sequence stratigraphy of an estuarine incised-valley fill: Lower Aptian Bouzergoun Formation, Agadir Basin, Morocco

Abstract

Lower Aptian strata exposed in the Agadir Basin of the Western High Atlas represent the fill of a fluvial valley incised during the Early Aptian (Bedoulian) sea-level fall. The valley fill comprises a diverse assemblage of lithofacies that can be grouped into lowstand, transgressive, and highstand systems tracts. Fluvial conglomerates and pebbly sandstones, referred to the lowstand systems tract, incised into the underlying Late Barremian marginal-marine deposits to form a basal sequence boundary. As sea level began to rise, fluvial deposits were reworked into alternating couplets of moderately bioturbated sandstones and mudstones that display tidally-influenced, inclined, heterolithic strata. The transgressive systems tract comprises the bulk of the estuarine fill and consists of a seaward and landward thinning wedge of tidally-influenced fluvial, tidal flat, estuarine point-bar and bay-fill deposits. Highstand infilling of the valley was characterised by estuarine mouth bars and shoal progradation.