The Middle Jurassic Sleipner Formation is sub-divided into three units in the Beryl Embayment area of the North Sea. The lowermost two units, the 'Interbedded Unit' and 'Lower Coal Marker', overlie Lower Jurassic marine silts and were probably deposited in progressively shallowing, coastal environments during a eustatic sea level fall. An estuarine deposit overlies the 'Lower Coal Marker', and was deposited following sea level rise or tectonic subsidence of the area. The 'Estuarine Succession' forms the bulk of the Formation, and is composed of seven facies, grouped into three facies associations representing sub-tidal, inter-tidal and salt marsh sub-environments.
The sub-tidal facies association is dominated by sandstones deposited in tidal channels and sand flats. The inter-tidal association is characterized by alternations of sandstone and siltstone on a scale of millimetres to several metres and consists of tidal channel sandstones, lenticular bedded siltstones and other tidally-influenced facies. The salt marsh association is dominated by coals and rooted siltstones, with minor amounts of creek-fill sandstones.
The estuary mouth probably lay towards the northern end of the Embayment, where a connection existed through the Viking Graben to the Boreal Ocean.