The fluvial sandstone beneath the Mill Coal in the Westphalian ‘A’ of Scotland erosively overlies a lake mudstone. Slightly erosive surfaces within the sandstone, traceable for over 200 m, are used to divide it into two types of major sedimentary units termed type A and type B. Type A sand units are approximately 200 m wide, up to 7 m thick, convex upward, and lenticular in all directions. The constituent cosets overlap to the ENE and dip mainly at 1–2° downcurrent (NNW), but locally at 10–15°. Where thickest, type A sand units display a vertical facies sequence commencing with trough cross‐bedded and massive sandstone, overlain by a thick zone of ripple cross‐lamination, a thin zone of trough cross‐beds, and a variably eroded silt drape up to 0.4 m thick. Attenuated lateral margins are dominated by flat bedded sandstone with primary current lineation. Type A sand units are interpreted as deposits which were accreted on to a large fluvial bar during successive flood events. The bar is thought to have had a similar topographic significance to sand waves described from the Brahmaputra and slip face bounded bars observed in the South Saskatchewan river. Palaeocurrents measured from trough cross‐bed sets 0.3–1.0 m thick within type B sand units indicate flow to the WSW, perpendicular to the palaeoflow direction measured from type A units. In sections perpendicular to the WSW flow direction type B units are lenticular, and in ENE‐WSW trending sections they can be traced for over 80 m at a constant thickness. Type B sand units are interpreted as the product of low stage channels which flowed across bar fronts and tops. The sandstone described herein is interpreted as a braided‐type river deposit but is atypical, because it is fine grained and has an internal structure dominated by ripple cross‐lamination and upper phase plane beds. The palaeoriver is thought to have been of low sinuosity, 7–10 m deep, with a high suspended load and large rapidly fluctuating discharge. At low stage a braided‐type flow pattern developed around submerged bars. The regime of the palaeoriver was probably controlled by the fine sediment grain size and humid tropical climate.

This paper discusses the lithostratigraphy, bio stratigraphy and depositional sequence stratigraphy of the sandstones within the late Aptian Sola Formation in the Central and Northern North Sea (UK sector). The genesis and age of these sandstones are discussed and three depositional models are proposed. These sandstones have reservoir potential, and an exploration strategy is discussed in part two of this paper (referred to hereafter as Crittenden et al., in press). We interpret these sandstones to be the product of mass‐flow sedimentary processes initiated by a tectonically‐induced major fall in relative sea‐level during the late Aptian. Sediments, including sands, which accumulated on the shelfal and shelf/slope break areas of the North Sea during the early Aptian relative sea‐level high were subsequently reworked and eroded; together with the products of erosion of the bedrock geology, they were transported down‐slope into deeper‐water basinal depocentres during the late Aptian.

Synopsis A NNW dipping listric normal fault affecting a 6 m stratigraphic interval and displaying evidence of syn-sedimentary activity is described from the Sanquhar Coalfield, and interpreted as a gravity slide.

Facies analysis suggests that Westphalian (Upper Carboniferous) Coal Measure sequences on the Isle of Arran, Scotland, were deposited in a proximal alluvial plain environment close to the basin margin. Detailed examination of well exposed coastal sections has revealed the existence of six laterally and vertically interrelated sedimentary facies. Facies 1 to 3 are interpreted as fluvial channel deposits. Low sinuosity multistorey (facies 1), low sinuosity vertically accreted (facies 2), and rare high sinuosity laterally accreted channel deposits (facies 3) are developed. Associated overbank sediments comprise the deposits of crevasse splays (facies 4), flood plains (facies 5) and shallow lakes (facies 6). In terms of the spatial distribution of facies, a relatively high proportion of fluvial channel and floodplain deposits (facies 2 and 5) occur in the more proximal sequence at Laggan compared with the more distally located sequence occurring at Corrie. Palaeocurrent measurements from fluvial channel sandstones indicate that sediment source areas and the Westphalian basin margin lay to the north and northwest. Down palaeoslope towards the southeast, normal coal-bearing Westphalian sediments formed penecontemporaneously on the Scottish mainland in Ayrshire.A sedimentological model is presented for the proximal non-coal-bearing Westphalian sequences of Arran. This model can explain the differences observed between the Arran sediments, and contemporaneous normal coal-bearing Westphalian sediments of the Scottish mainland.

In this paper, we discuss the distribution in the Central and Northern North Sea (UK sector) of the Late Aptian sandstones of reservoir potential which are assigned to members of the Sola Formation. An exploration strategy for these sandstones is proposed, based on sequence‐stratigraphic and palaeogeographic models derived from the examination of numerous wells. The sandstones were deposited by mass‐flow processes as a consequence of a major, tectonically‐induced or enhanced, Late Aptian fall in relative sea‐level. The distribution of these lowstand sandstones, and the facies developed, was controlled by the structure and palaeogeography that existed in the study area both before and after this sea‐level fall. The pattern of faulting in the study area during Sola Formation deposition is related to Jurassic and older tectonism, which is associated with the development of the proto‐North Atlantic and the thermal subsidence of the North Sea rift system. Faults controlled the areas of sandstone provenance, and also determined the routes by which reworked sediments were transported into depocentres. We have mapped the distribution of these sandstones using both well and seismic data. Maps of fault patterns, basinal and high areas, and facies distributions have been generated for the top‐ Valhall Formation level (i. e. immediately beneath the Sola Formation), and also for the Sola Formation itself. These maps were used to model the distribution of Aptian lowstand sandstones and prospects in the UK Central and Northern North Sea. This modelling exercise is of relevance for the identification of lowstand sandstones with reservoir potential elsewhere on the NE Atlantic margin.