The Jura Quartzite, a formation of probably late Precambrian metasediments over 5 km thick from the Caledonian belt in Southwest Scotland, has been divided into a coarse and three fine facies. The former comprises cross‐bedded sands with some laminated sands and silt horizons, interpreted as the deposits of shallow marine tidal dunes and other bedforms together with some beach units. Deposition from suspension of silt and sand formed climbing dunes while largescale erosion produced flat or channelled surfaces. The fine facies comprise laterally persistent, parallel and cross‐laminated sand units from millimetres to decimetres thick, interbedded with muds. The coarse and fine facies can be finely interbedded, the former sometimes filling decimetre deep, straight channels, cut in the latter. The fine facies exhibit structures indicative of deposition from decelerating currents and are interpreted as shallow marine storm deposits. The facies are compared with a model developed from published observations on modern shelf areas. Zones of erosion, large and small dunes, flat bedded sand and mud are considered to be the end product of a wide spectrum of tidal and storm conditions. During severe storms the fair weather tidal dunes may be modified or washed out, new dunes may be initiated downcurrent of the normal dune field while storm‐sand layers are deposited in the distal zones. Hence, the nature of the preserved sediment blanket reflects the rare severe storm event rather than normal tidal conditions. The Jura Quartzite was deposited in a tidal gulf intimately connected with an ocean basin. The north‐northeast directed palaeocurrent modes are probably roughly parallel to the coastline.

Submarine fans of Late Palaeocene and Early Eocene age form important hydrocarbon reservoirs in the Bruce-Beryl Embayment, northern North Sea. The Early Eocene fans are the main reservoirs in the Forth-Gryphon oilfields and in the giant Frigg gasfield. Significant oil discoveries have also been made in Late Palaeocene fans. Forth and Gryphon lie on the flanks of the Crawford Anticline, a drape structure that developed during the Palaeocene above the crest of a Mesozoic tilted fault block. The Early Eocene fans pinchout against the flanks of the anticline implying continued growth of the structure throughout the Eocene. Growth was accompanied by the development of major gravity slides that detached in a sequence of altered, basaltic tephras at the base of the Eocene sequence. Seismic-scale, post-depositional deformation (sandstone diapirism and the intrusion of clastic sills and dykes) connected with this sliding dramatically modified the original depositional geometries of the fans. A detailed account of the deformation features, illustrated with core, wireline log and three-dimensional seismic data is presented together with a discussion of their exploration/appraisal significance.

Summary The term facies is used either descriptively, for a certain volume of sediment, or interpretatively for the inferred depositional environment of that sediment. Facies models are intellectual aids to the understanding of sedimentary environments and the origin of ancient sedimentary rocks. Many different models can be constructed to explain a given set of data, depending on which aspect of the facies requires the most illumination and on the types of techniques used in the analysis. When dealing with ancient rocks, facies modelling is the last stage in the process of facies analysis which consists of the detailed description of exposed or cored sediments, their classification into objectively defined facies, the compilation of the characteristics of each facies, the deduction of the processes of deposition of each facies, the examination of the spatial relationships between facies and the recognition of facies associations, the interpretation of the overall depositional environment of the association and the detailed interpretation and modelling of individual facies. Short cuts can lead to fallacious interpretations. Reliable facies models cannot be produced without careful facies analysis. A facies model may be plausible, yet totally inapplicable to the facies from which it was supposedly derived.

Synopsis Sedimentological research on the Scottish Dalradian has progressed from the recognition of sedimentary structures in the 1930s, via the identification of sedimentary facies from the 1950s onwards, to the integration, in the 1970s, of sedimentological data with that from studies of stratigraphy, tectonics and volcanism. This has now led to an understanding of the pre-orogenic evolution of the Dalradian terrane in terms of progressive lithospheric stretching associated with the break-up of the Proterozoic Supercontinent. The Appin and Argyll Groups were deposited on the NW side of a late Precambrian marine gulf which developed over a complex zone of crustal thinning between the Laurentian and Baltic parts of the Super-continent. As extension accelerated, subsidence rates increased and the Dalradian area of the gulf evolved from a relatively shallow shelf into a series of turbidite basins. Thinning of the lithosphere gave rise, in Argyll Group times, to locally intense igneous activity. Subsequently, complete continental rupture along the gulf axis led to the birth of the Iapetus Ocean. By Southern Highland Group times the Dalradian terrane had become part of the new, thermally-subsiding, Laurentian continental margin. One can envisage the geometry and facies variations of many horizons within the Dalradian in terms of a pattern of numerous fault blocks defined by listric normal faults, dipping SE towards the site of continental rupture, and NW–SE trending transfer faults, which divided the gulf and subsequent margin into a series of compartments. It was movements on these faults that largely controlled Dalradian stratigraphic evolution. For example, pulses of rapid stretching, and consequent fault activity, produced basin-deepening sequences which mark the base of the Easdale and Crinan Subgroups.

During the late Precambrian the Dalradian environment evolved from a relatively stable subsiding shelf into a series of fault-bounded blocks and basins. This increase in tectonic instability can be interpreted as a precursor to the continental rifting which led to the inception of the Iapetus Ocean at the end of the Precambrian, or base of the Cambrian, and was marked in the Dalradian terrain by the eruption of the Tayvallich Volcanics. A comparison of the late Precambrian history of the areas now adjacent to the Iapetus suture suggests that prior to this rifting the Greenland–northern Britain–NW Newfoundland area and Scandinavia formed part of the same plate with northern Norway lying close to northern Britain. As the evolution of all these areas was dominated by the opening of Iapetus during the Cambrian followed by closing initiated by subduction in the early Ordovician, many aspects of their history are similar. Southern Britain and SE Newfoundland, however, had a quite different late Precambrian history. They probably formed a microcontinental plate which originated at a considerable distance from northern Britain and which, until the closure of the Iapetus Ocean, was never in contact with the rest of the Caledonian belt.