This study is concerned with the sedimentary architecture of a shallow-marine sandstone unit in the Lower Eocene Ametlla Formation, Ager Basin, Spanish Pyrenees. The sandstone unit was formed in a tide-dominated setting, and is continuously exposed in a 10.5 km long, mainly strike-parallel, cutcrop. Its base is a prominent unconformity (sequence boundary), and it consists of two sub-units separated by a tidal ravinement surface. Sub-unit 1 (lower sub-unit) formed in an estuarine setting that was created by flooding of an incised valley system. Outside the incised valleys, an oyster bed is present as a lateral equivalent to the estuarine deposits. The sequence bounding unconformity was generated during relative sea-level lowstand, whereas the overlying estuarine and bioclastic deposits of sub-unit 1 formed in the early stages of the transgressive systems tract. In sub-unit 2, above the tidal ravinement surface, estuary mouth-bar and tide-dominated delta deposits are the main facies associations, interfingering with offshore to inner shelf sediments westwards. These deposits formed in later stages of the transgressive systems tract. The large-scale model of the sandstone unit served as a framework within which the internal arrangement of architectural elements (AE) was recorded. Twelve AE were recognized. They mostly have a lensoid geometry, and their lateral transitions are abrupt or occur by interfingering over distances of 50–250 m. The AE distribution shows that the tide-influenced setting was characterized by a high degree of spatial and temporal variability with regard to sedimentary processes. This, together with the prominent thickness variation of the unit studied, makes correlation between vertical profiles difficult, even over distances of only a few hundred metres. Stratal surfaces such as the sequence-bounding unconformity, the tidal ravinement surface, and the flooding surfaces, represent the only reliable correlation markers in this kind of environment.