Sedimentological control on the reservoir and caprock properties of a bleached palaeoreservoir in the Entrada Formation at Salt Wash Graben, Green River, Utah

The stratigraphy and sedimentology of the Entrada Formation are central to understanding the origin of the bleached palaeoreservoir exposed at Salt Wash Graben. Aeolian sandstones of the Slick Rock Member formed high-permeability carrier beds which distributed reducing fluids laterally within the formation. The overlying Earthy Member is a massively-bedded succession of low permeability mudflat/sabkha deposits which acted as a caprock: albeit one that formed an imperfect seal and allowed the upward diffusion of reducing fluids for a distance of up to 4 m above the top of the reservoir. The Salt Wash Graben is located on the crest of the Green River Anticline and was filled by buoyant fluids that may have migrated updip along this north plunging fold; alternatively these fluids may have entered via the northern fault of the Salt Wash Graben. The role of this structure in forming an updip seal during the filling of the reservoir is uncertain. The reservoir was probably filled in the early Cretaceous at a depth of around 1 km or less, during the subsidence phase of the Paradox Basin. The fluids are likely to have been an admixture of H2S, CO2 and CH4. The reservoir was later breached by NNW-trending fractures related to extension across the crest of the Green River Anticline

Bromsgrove Aquifer Groundwater Modelling Study : results from Task 1.1 3D visualisation and geological framework of the Bromsgrove Aquifer

The Bromsgrove Sandstone aquifer is over-abstracted. This has resulted in a long-term fall in groundwater levels, the reduction or loss of baseflow and the derogation of surface water features. To support flows in Battlefield Brook (a BAP site and notable amenity feature in Bromsgrove), Bow Brook (BAP site) and water levels in Hewell Grange Lake (SSSI), four alleviation of low-flow (ALF) boreholes are operated (one by the Environment Agency and three by Severn Trent Water). These ALF boreholes were installed as short term measures, prior to the implementation of a long-term solution to reduce the impacts of groundwater abstraction on surface water features which is under discussion between the water company and the Environment Agency. In 2001 an existing groundwater model of the Bromsgrove Sandstone aquifer (developed by Birmingham University in 1990) was adopted and updated as part of the Environment Agency Midlands Region Groundwater Modelling Strategy. However, monitoring data collected since 2002 has shown that this groundwater model does not accurately simulate groundwater flows and levels in critical areas. The Bromsgrove aquifer groundwater modelling project aims to develop a new groundwater model that will be used to determine a more optimal groundwater abstraction regime which benefits the surface water environment, with the minimum of overall groundwater abstraction reduction and affordability. The British Geological Survey (BGS) was contracted to undertake Environment Agency Task 1.1 of the Bromsgrove aquifer groundwater modelling study, namely the production of a three dimensional geological model of the investigation area. The model was specified to cover the outcrop of the Bromsgrove Sandstone Formation, the outcrop of the Clent Formation to the north and the confined Sherwood Sandstone Group to the west. The geographical limits of the area are approximately Droitwich Spa and Astwood Bank in the south (Northing 261550) and Rubery in the north (Northing 279560), Elmley Lovett (Easting 387134) in the west and Redditch (Easting 405456) in the east. The outline of the project area is given in Figure 1. The 3D geological model will be used in a concurrent Task (Task 1.2) to develop the conceptual model of groundwater flow between the principal formations of the Bromsgrove Sandstone aquifer system, as well as providing the geometrical information for building the groundwater model (Task 2). This report outlines the methods used in the BGS 3D geological visualisation work and provides a brief summary of the stratigraphy, facies relationships and structure of the bedrock geology. Much of the information in the report has not been published before, and results from an extensive reinterpretation of existing borehole lithological descriptions and geophysical logs. The model integrates information from BGS 1:50000 geological sheets (E167 Dudley, E168 Birmingham, E182 Droitwich and E183 Redditch), borehole descriptions derived from core or cuttings, geophysical logs and NEXTMap digital terrain data. Published information on the regional geological framework was also incorporated into the model (e.g. Old et al., 1991, Old et al. 1987, Powell et al. 2000)

Morphology and Quaternary geology of the Thames floodplain around Oxford

This report provides a summary of work undertaken on the geology and morphology of the River Thames floodplain around Oxford in the 13 km reach between Cassington in the northwest and Sandford-on-Thames in the southeast. The major part of the work was constructing 3D models and thickness maps of the valley gravels and alluvium using ArcGIS in conjunction with the 3D visualisation packages GSI3D and GOCAD. This work requires consideration of the available digital terrain models and how man-made features contribute toward the present-day floodplain topography. Surfaces were also constructed for areas of flooding based on their mapped extents from aerial photography. This allowed the interaction between terrain and flooding to be visualised in three dimensions

Mapping groundwater denitrification potential : methodology report

An understanding of the fate of nitrate in groundwater is vital for managing risks associated with nitrate pollution, and to safeguard groundwater supplies and groundwater-dependent surface waters. One of the main mechanisms to control nitrate is the designation of nitrate vulnerable zones (NVZs). Recent review of the designation process in England has highlighted that in some locations measured groundwater nitrate concentrations are not as high as might be expected from knowledge of the surface loads of nitrate applied at the ground surface. A possible reason for this is that the nitrate is being transformed through denitrification. The aim of this work was to develop a weight of evidence approach to allow the assessment of denitrification potential across groundwater in England using literature and existing groundwater and other relevant data

The Cretaceous Continental Intercalaire in central Algeria: subsurface evidence for a fluvial to aeolian transition and implications for the onset of aridity on the Saharan Platform.

The Lower Cretaceous Continental Intercalaire of North Africa is a terrestrial to shallow marine continental wedge deposited along the southern shoreline of the Neotethys Ocean. Today it has a wide distribution across the northern Sahara where it has enormous socio-economic importance as a major freshwater aquifer. During the Early Cretaceous major north-south trending basement structures were reactivated in response to renewed Atlantic rifting and in Algeria, faults along the El Biod-Hassi Messaourd Ridge appear to have been particularly important in controlling thickness patterns of the Lower Cretaceous Continental Intercalaire. Subsurface data from the Krechba gas field in Central Algeria shows that the Lower Cretaceous stratigraphy is subdivided into two clear parts. The lower part (here termed the In Salah Formation) is a 200 m thick succession of alluvial deposits with large meandering channels, clearly shown in 3D seismic, and waterlogged flood basins indicated by lignites and gleyed, pedogenic mudstones. The overlying Krechba Formation is a 500 m thick succession of quartz-dominated sands and sandstones whose microstructure indicates an aeolian origin, confirming earlier observations from outcrop. These interbed with brick red, highly oxidised mudstones representing deposition in temporary lakes or lagoons under an arid climate. The switch from fluvial to aeolian sedimentation at Krechba on the Saharan Platform occurred in the late Aptian and Albian and is thus synchronous to a comparable change observed by previous authors in Lower Cretaceous non-marine deposits of NE Spain. This was probably driven by a combination of sea-level fall and the northward shift of global arid belts into western Neotethys caused by oceanic rifting between Africa and South America

A physical property model of the Chalk of Southern England

This report describes the rationale and procedure for the construction of a new high-resolution stratigraphical and physical property model of the Chalk Group of southern England. The model integrates bedrock mapping data for the Chalk, with structural data and interpretations of formational and sub-formational (marker-bed) stratigraphy in boreholes (predominantly from geophysical logs and cored boreholes) and outcrops. A range of simple facies data (e.g. hard chalk, hardground, marl, marly chalk) are coded for the boreholes and outcrops using WellCadTM software, interpreted directly from geophysical logs, core logs, borehole video logs, or outcrop logs. The results of this work are modelled in SKUA-GOCAD 2013.2 software, using statistical algorithms to project the likely distribution of physical property data

Characterising variations in the salinity of deep groundwater systems: A case study from Great Britain (GB)

Study region The study region is Great Britain (GB), a small non-continental island landmass in North West Europe Study focus Data for Total Dissolved Solids (TDS) from groundwater samples can be used to characterise regional-scale variations in the quality of deep groundwater systems. Combined with information about typical well-depths, TDS data can be used to identify the presence of currently undeveloped fresh or brackish groundwater at depth that may require protection. This study considers the distribution of TDS with depth relative to sea level in the main GB aquifers and selected other key hydrogeological units, and demonstrates how useful insights can be obtained from data-led analyses of depth variations in groundwater chemistry if the regional context of hydrogeological systems is taken into account. New hydrogeological insights In GB, TDS varies over about five orders of magnitude, up to about 330,000 mg/L, with a general increase in mineralisation with depth. Overall, there is a transition from fresh 10,000 mg/L groundwater at about 700 m. Given that the 95 %tile depth of water wells is about 200 m, it is evident that there is currently undeveloped fresh groundwater at depth across large parts of the study area that may require protection, although it is inferred that TDS is not the only factor limiting exploitation and use of these deeper resources. As in this study, previous data-led analyses of fresh groundwater at depth have typically analysed TDS as depth below surface. However, if TDS data is analysed relative to sea level and in the context of regional hydrogeological information or models, additional insights can be gained on the distribution and controls on fresh groundwater at depth. Projecting TDS data into a 3D hydrogeological model of the study area shows that fresh groundwater at depth exhibits spatial coherence and is generally associated with relatively dee

A 3D geological model of post Carboniferous strata in the south Fylde area of the West Lancashire Basin, Blackpool, UK

The British Geological Survey (BGS), together with a number of partners is undertaking an independent environmental monitoring programme to characterise baseline conditions in the south Fylde east of Blackpool in an area proposed for shale-gas exploration and production. The monitoring will include measurement of: water quality (groundwater and surface water), seismicity, ground motion, air quality including radon, and soil gas. The programme aims to establish the environmental baseline before any shale-gas explorations begin. This report presents the results of a desk study to develop an initial summary of the post- Carboniferous bedrock geology of the south Fylde. It is a component and specific deliverable of the environmental baseline project. The bedrock deposits form a number of shallow aquifers that are used locally for drinking water supply and agriculture. A separate report considers the superficial geology. The geological information in this report will form the basis for identifying aquifer dimensions and configurations, groundwater flow paths and potential contaminant migration pathways, as well as determining optimum locations for sampling and monitoring. It will also provide information to support the locating of new borehole infrastructure (suitable for groundwater sampling and seismometers) and will underpin the interpretation of acquired hydrogeochemical data

A preliminary 3D model of post-Permian bedrock geology in the Vale of Pickering, North Yorkshire, UK

The British Geological Survey (BGS), together with a number of partners is undertaking an independent environmental monitoring programme to characterise baseline conditions across the Vale of Pickering in North Yorkshire, in the vicinity of a site close to Kirby Misperton (Third Energy, KM8) proposed for shale-gas exploration and production. The monitoring will include measurement of: water quality (groundwater and surface water), seismicity, ground motion, air quality including radon, and soil gas. The programme aims to establish the environmental baseline before any shale-gas explorations begin. This report presents the results of a desk study to develop an initial summary of the post-Permian bedrock geology across the Vale of Pickering. It is a component and specific deliverable of the environmental baseline project. The bedrock deposits form a number of shallow aquifers that are used locally for drinking water supply and agriculture. A separate report considers the superficial geology. The geological information in this report will form the basis for identifying aquifer dimensions and configurations, groundwater flow paths and potential contaminant migration pathways, as well as determining optimum locations for sampling and monitoring. It will also provide information to support the locating of new borehole infrastructure (suitable for groundwater sampling and seismometers) and will underpin the interpretation of acquired hydrogeochemical data

UK Stratigraphical Framework Series : Lower Cretaceous (Aptian-Albian) of Southern and Eastern England, and the Southern North Sea

This report forms part of the UK Stratigraphical Framework Series (UKSFS) and provides an overview of the stratigraphy of the Aptian-Albian (Lower Cretaceous) of southern and eastern England (and adjacent offshore areas). This interval includes the Lower Greensand and the Selborne Groups, the latter comprising the Gault and Upper Greensand Formations and coeval strata of the East Midlands Shelf. This interval forms a coherent body of transgressive marine siliciclastic deposits between the terrestrial to marginal-marine Wealden Group and the carbonates of the Chalk Group. The study adopted a surface to subsurface approach and makes extensive use of borehole geophysical log data. Stratigraphical picks based on geophysical log correlations were used to construct thickness maps. These maps were used in conjunction with borehole correlation panels to understand regional trends in thickness and lithology and how these evolved during Aptian-Albian marine transgression