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Progradational, wave‐dominated shoreface sandstones are typically reported to have thicknesses of less than 30 m. The shoreface sandstones of the Rannoch and Etive formations in the North Sea Brent Group, however, comprise far greater thicknesses (in places exceeding 100 m). The genesis of these successions have not been well understood, and the purpose of this study is to investigate within the framework of facies geometries in both modern and ancient depositional systems how the Rannoch‐Etive sandstones could have been formed, on a local‐regional scale. The facies analysis concludes that the Brent delta advance represents a single progradational event, not punctuated by transgressions. In such a scenario, the vertical sandstone thickness would be determined by: 1) shoreline trajectory angle, 2) the horizontal (dip‐directed) length of shoreface sand (typically 1–2 km in modern systems), and 3) shoreface sand pinch‐out depth (typically 5–12 m in modern systems). Within a framework of modern facies geometries, a 100 m thick vertical shoreface sandstone succession could result from a regression characterised by a shoreline trajectory of 2.6–5.4° (implying 80–95 m rise in relative sea level per 1–2 km of progradation), a 5–12 m deep shoreface sand pinch‐out depth, and a 1–2 km shoreface sand length. If, however, one applies such a model for the entire Brent delta progradation in the study area (200 km) this implies a rise in relative sea level of c. 5000 m, which clearly would be associated with large amounts of deposits accumulating behind and in front of the advancing shoreline. Such deposits are not present, which implies that modern facies geometries do not apply and that rising sea level was not of major importance in defining stratigraphic architecture. It is more likely that the regional overthickening of the Rannoch‐Etive sandstones resulted from progradation with a deep shoreface sand pinch‐out depth.

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