The Bridport Sand Formation is an intensely bioturbated sandstone that represents part of a mixed siliciclastic‐carbonate shallow‐marine depositional system. At outcrop and in subsurface cores, conventional facies analysis was combined with ichnofabric analysis to identify facies successions bounded by a hierarchy of key stratigraphic surfaces. The geometry of these surfaces and the lateral relationships between the facies successions that they bound have been constrained locally using 3D seismic data. Facies analysis suggests that the Bridport Sand Formation represents progradation of a low‐energy, siliciclastic shoreface dominated by storm‐event beds reworked by bioturbation. The shoreface sandstones form the upper part of a thick (up to 200 m), steep (2–3°), mud‐dominated slope that extends into the underlying Down Cliff Clay. Clinoform surfaces representing the shoreface‐slope system are grouped into progradational sets. Each set contains clinoform surfaces arranged in a downstepping, offlapping manner that indicates forced‐regressive progradation, which was punctuated by flooding surfaces that are expressed in core and well‐log data. In proximal locations, progradational shoreface sandstones (corresponding to a clinoform set) are truncated by conglomerate lags containing clasts of bored, reworked shoreface sandstones, which are interpreted as marking sequence boundaries. In medial locations, progradational clinoform sets are overlain across an erosion surface by thin (<5 m) bioclastic limestones that record siliciclastic‐sediment starvation during transgression. Near the basin margins, these limestones are locally thick (>10 m) and overlie conglomerate lags at sequence boundaries. Sequence boundaries are thus interpreted as being amalgamated with overlying transgressive surfaces, to form composite erosion surfaces. In distal locations, oolitic ironstones that formed under conditions of extended physical reworking overlie composite sequence boundaries and transgressive surfaces. Over most of the Wessex Basin, clinoform sets (corresponding to high‐frequency sequences) are laterally offset, thus defining a low‐frequency sequence architecture characterized by high net siliciclastic sediment input and low net accommodation. Aggradational stacking of high‐frequency sequences occurs in fault‐bounded depocentres which had higher rates of localized tectonic subsidence.

Detailed seismic stratigraphic analysis of 2D seismic data over the Faroe-Shetland Escarpment has identi¢ed 13 seismic re£ection units that record lava-fed delta deposition during discrete periods of volcanism. Deposition was dominated by progradation, during which the time shoreline migrated a maximum distance of $44 km in an ESE direction. Localised collapse of the delta front followed the end of progradation, as a decrease in volcanic activity left the delta unstable. Comparison with modern lavafed delta systems on Hawaii suggests that syn-volcanic subsidence is a potential mechanism for apparent relative sea level rise and creation of new accommodation space during lava-fed delta deposition. After the main phase of progradation, retrogradation of the delta occurred during a basinwide syn-volcanic relative sea level rise where the shoreline migrated a maximum distance of $75 km in a NNW direction. This rise in relative sea level was of the order of 175^200 m, and was followed by the progradation of smaller, perched lava-fed deltas into the newly created accommodation space. Active delta deposition and the emplacement of lava £ows feeding the delta front lasted $2600 years, although the total duration of the lava-fed delta system, including pauses between eruptions, may have been much longer.

The macrotidal Severn Estuary (southwestern UK) has received a broad range of industrial discharges since the beginning of the Industrial Revolution. A more recent anthropogenic input to the estuary has been technogenic tritium (specifically organically bound tritium, OBT). This was derived from a specialized industrial laboratory producing custom radiolabeled compounds for life science research and diagnostic testing from 1980 until 2008. While it was generally acknowledged that the radiological impact of the tritium discharges into the Estuary was small, public concern motivated the company and regulatory agencies to commission several research studies from 1998 to 2005 to better understand their environmental impact. This study examined OBT interaction with estuarine sediment by acquiring a broad range of geochemical and sedimentological data from a suite of sediment cores collected from the northern side of the Estuary. Two important observations are that the OBT compounds are strongly bound to the clay/silt fraction of sediment and that the down-core OBT profiles in intertidal and subtidal sediments are broadly similar to the discharge record. Geochemical and chronometric methods (Cu, Pb and Zn elemental profiles, (210)Pb, (137)Cs) provide important corroboration of the OBT record. A key additional piece of evidence that firmly authenticated the established chronology was the discovery of a previously unreported sedimentary marker layer that was generated by a major storm surge that occurred on December 13, 1981. Although this study has provided clear evidence of systematic accumulation of OBT in sedimentary sinks of the region, an estimation of its depositional inventory shows it represents only a small fraction of the total discharge. This modest retention in the principal sedimentary sinks of the Severn Estuary system reflects the particular dynamics of this highly macrotidal sediment starved estuary.

The Lower Jurassic Bridport Sand Formation records net deposition in the Wessex Basin, southern UK of a low-energy, siliciclastic shoreface that was dominated by storm-event beds reworked by bioturbation. Shoreface sandstones dip at 2-38 to define (subaerial?) clinoforms that pass distally into a near-horizontal platform, and then steepen again to form steep (2-38) subaqueous clinoforms in the underlying Down Cliff Clay Member. The overall morphology indicates mud-dominated clinoforms of compound geometry. Compound clinoforms are grouped into progradational sets whose stacking reflects tectonic subsidence and sediment dispersal patterns, and also controls basin-scale reservoir distribution and diachroneity of the formation.Each shoreface clinoform set consists of an upward-shallowing succession that is several tens of metres thick with a laterally continuous mudstone interval at its base. The successions are punctuated by calcite-cemented concretionary layers of varying lateral continuity, which formed along bioclastic lags at the base of storm-event beds. Concretionary layers thus represent short periods of rapid sediment accumulation, while their distribution likely results from variations in stormwave climate, relative sea-level, and/or sediment availability. The distribution of impermeable mudstone intervals that bound each clinoform set and concretionary layers along clinoform surfaces controls oil drainage in the Bridport Sand Formation reservoir.An understanding of time-stratigraphic relationships is important within hydrocarbon-bearing basins, because it facilitates prediction of the distribution of lithological units, including source rocks, reservoirs, and seals (e.g. Van Wagoner et al. 1990). Such understanding is most commonly developed via the application of sequence stratigraphic methods at either relatively large spatial scales (tens to hundreds of kilometres laterally) to define the constituent elements of hydrocarbon plays during exploration, or at smaller scales (hundreds of metres to tens of kilometres laterally) to define flow units within producing hydrocarbon reservoirs. These spatial scales typically translate into temporal scales of 10 5 -10 8 yr for hydrocarbon exploration applications and 10 2 -10 6 yr for hydrocarbon production applications, although there may be considerable uncertainty in these estimated time spans in the absence of appropriate biostratigraphic age control.In this paper, we present a case study of the hydrocarbon exploration and production applications of time-stratigraphic relationships to a shallow-marine siliciclastic sandstone, the Jurassic Bridport Sand Formation of the Wessex Basin, UK. At exploration scale, we focus on using time-stratigraphic relationships to constrain the spatial distribution of reservoir lithologies, particularly via the application of a revised depositional model that relates sedimentological facies to seismically resolved geomorphology (after Morris et al. 2006) (at time spans labeled for 'subaqueous clinoform set' in Fig. 1). These time-...