SUMMARY During the Permo-Triassic the Sellafield area formed part of the eastern margin to the East Irish Sea Basin. Basin-margin alluvial fan, shallow marine and coastal mudflat sedimentation created a locally thick Permian succession. Triassic sediments are represented by the Sherwood Sandstone Group, which comprises the St Bees, Calder and Ormskirk sandstone formations. The basal few metres of the St Bees Sandstone are characterized by sheetflood sandstones, interbedded with playa-mudflat deposits. These pass upwards into thick, multistorey fluvial sandbodies, formed on sandy braidplain. Rare aeolian units are interbedded with the channel facies. The top of the St Bees Sandstone is sharply defined and represents the regional abandonment of the fluvial system. The overlying Calder Sandstone Formation is coarser grained and dominated by aeolian sediments, with dune and interdune facies recognized. These sands were blown into the area from the east. Minor episodes of fluvial reworking punctuated aeolian deposition and the top of the Calder Sandstone is represented by a fluvially deposited unit. The lower part of the overlying Ormskirk Sandstone is of aeolian facies and can be distinguished from the Calder Sandstone by its finer grain size. The two formations can also be differentiated using geophysical logs, as aeolian and fluvial sandstones have diagnostic geophysical log characteristics allowing recognition of different sedimentary facies associations.

-Late Carboniferous red-beds, < 700 m thick, at outcrop and in the subsurface

The lower part of the post-Variscan succession around Exeter, south Devon, England, comprises some 800 m of breccias, with subordinate sandstones and mudstones, which rest upon Devonian and Carboniferous rocks folded during the Variscan Orogeny and are overlain, disconformably, by the Aylesbeare Mudstone Group (Early Triassic?). These deposits comprise the most westerly of the early post-Variscan successions preserved onshore in northwest Europe and lie to the south of the Variscan Deformation Front; they are assigned to the Exeter Group (new term). Geochronological and palaeontological studies, in conjunction with detailed geological mapping, show that the constituent formations comprise a lower (Late Carboniferous(?)-Early Permian) sequence separated from an upper (Late Permian) sequence by an unconformity which represents an hiatus with a duration of at least 20 m.y. The lower sequence contains volcanic rocks dated at between 291 and 282 Ma (Early Permian) and pre-dates intrusion of the nearby Dartmoor Granite (280 Ma). In the overlying, palynologically-dated, Late Permian sequence, older breccias contain clasts of the Dartmoor Granite aureole rocks, and younger ones contain clasts of that granite. The lower sequence occurs mainly within the Crediton Trough, an east-west trending, partly fault-bounded, sedimentary basin that probably formed by extensional reactivation of a Variscan thrust. Breccias in this sequence formed largely on alluvial fans; the common occurrence of debris flows and a down-fan passage from gravity flows into fluvially deposited sediments is typical of deposition on semi-arid fans. The upper (Late Permian) sequence is more widespread but includes similar deposits overlain, at the top of the Exeter Group, by aeolian dune and interdune deposits. Correlation within the laterally variable facies associations which comprise these sequences has been achieved using a combination of sedimentary facies analysis, sedimentary geochemistry, and petrographical and geochemical clast typing. The stratigraphy revealed within the Exeter Group is broadly comparable with that recognized in the early post-Variscan Rotliegend successions elsewhere in Europe. This similarity may, however, be deceptive; the upper part of the Exeter Group may be coeval with the Zechstein, and apparently correlatable major unconformities in the group and the Rotliegend may reflect different events in the Variscan fold-belt and Variscan Foreland areas, respectively.

Important coal deposits are present in Britain north of the Wales-Brabant High in the Pennine Basin, which was initiated by late Devonian to early Carboniferous extension. The formation of coals of sufficient thickness, quality and continuity to be commercially exploited was favoured during the latest Westphalian A (Langsettian) and much of the Westphalian B (Duckmantian), when deposition took place in an environment similar to an upper delta plain, with limited marine influence. During the early part of the Westphalian A, marine influence was important, with the consequence that the coals were thinner, less persistent and of inferior quality. By the late Westphalian, alluvial deposition became important, and coals of commercial quality are rare.Accurate determination of facies, lithological attributes and geometry is an important tool in exploration and mine planning. Sedimentary facies have thus been rationalized into those that may be consistently recognizable in boreholes and mine workings. However, facies may be further subdivided when conditions allow, and intermediate facies exist, reflecting the complexities of depositional environments. The characteristics of the following facies are described here: mire, palaeosol,/narine, lacustrine, lacustrine delta, major channel, minor channel, overbank and crevasse splay. Channel deposits have a number of adverse effects on mining and the range of channel-fill deposits reflects the operation of many different processes.A model of sedimentation is presented which emphasizes that local sedimentary and autocyclic processes, local tectonics, subsidence and compaction were important in controlling the distribution of facies at a mine scale.