3D geological models and their hydrogeological applications : supporting urban development : a case study in Glasgow-Clyde, UK

Urban planners and developers in some parts of the United Kingdom can now access geodata in an easy-to-retrieve and understandable format. 3D attributed geological framework models and associated GIS outputs, developed by the British Geological Survey (BGS), provide a predictive tool for planning site investigations for some of the UK's largest regeneration projects in the Thames and Clyde River catchments. Using the 3D models, planners can get a 3D preview of properties of the subsurface using virtual cross-section and borehole tools in visualisation software, allowing critical decisions to be made before any expensive site investigation takes place, and potentially saving time and money. 3D models can integrate artificial and superficial deposits and bedrock geology, and can be used for recognition of major resources (such as water, thermal and sand and gravel), for example in buried valleys, groundwater modelling and assessing impacts of underground mining. A preliminary groundwater recharge and flow model for a pilot area in Glasgow has been developed using the 3D geological models as a framework. This paper focuses on the River Clyde and the Glasgow conurbation, and the BGS's Clyde Urban Super-Project (CUSP) in particular, which supports major regeneration projects in and around the City of Glasgow in the West of Scotland

Clay mineral dating of displacement on the Sronlairig Fault: implications for Mesozoic and Cenozoic tectonic evolution in northern Scotland

Temporary excavations during the construction of the Glendoe Hydro Scheme above Loch Ness in the Highlands of Scotland exposed a clay-rich fault gouge in Dalradian Supergroup psammite. The gouge coincides with the mapped trace of the subvertical Sronlairig Fault, a feature related in part to the Great Glen and Ericht–Laidon faults, which had been interpreted to result from brittle deformation during the Caledonian orogeny (c. 420–390 Ma). Exposure of this mica-rich gouge represented an exceptional opportunity to constrain the timing of the gouge-producing movement on the Sronlairig Fault using isotopic analysis to date the growth of authigenic (essentially synkinematic) clay mineralization. A series of fine-size separates was isolated prior to K–Ar analysis. Novel, capillary-encapsulated X-ray diffraction analysis was employed to ensure nearly perfect, random orientation and to facilitate the identification and quantification of mica polytypes. Coarser size fractions are composed of greater proportions of the 2M1 illite polytype. Finer size fractions show increasing proportions of the 1M illite polytype, with no evidence of 2M1 illite in the finest fractions. A series of Illite Age Analysis plots produced excellent R2 values with calculated mean ages of 296 ± 7 Ma (Late Carboniferous–Early Permian) for the oldest (2M1) illite and 145 ± 7 Ma (Late Jurassic–Early Cretaceous) for the youngest (1M) illite. The Late Carboniferous–Early Permian (Faulting event 1) age may represent resetting of earlier-formed micas or authigenesis during dextral displacement of the Great Glen Fault Zone (GGFZ). Contemporaneous WNW(NW)–ESE(SE) extension was important for basin development and hydrocarbon migration in the Pentland Firth and Moray Firth regions. The Late Jurassic–Early Cretaceous (Faulting event 2) age corresponds with Moray Firth Basin development and indicates that the GGFZ and related structures may have acted to partition the active extension in the Moray Firth region from relative inactivity in the Pentland Firth area at this time. These new age dates demonstrate the long-lived geological activity on the GGFZ, particularly so in post-Caledonian times where other isotopic evidence for younger tectonic overprints is lacking

Exposure dating ( 10 Be, 26 Al) of natural terrain landslides in Hong Kong, China

We successfully apply exposure dating using cosmogenic nuclides to natural terrain landslides in Hong Kong. Forty-five samples from eight landslide sites were exposure dated using 10Be, and a subset of six samples was also dated using 26Al. The sites comprised four large, deep-seated landslides featuring well-preserved rock scarps and associated debris lobes; two sites of rock and boulder fall; and two sites where scarps only are preserved. All of the deep-seated landslides gave ages within the last 50,000 yr, and the largest landslide gave an age of ̃32,000 yr. The youngest (̃2000 yr) and oldest (̃57,000 yr) landslide events dated came from the two sites of rock and boulder fall. Exposure ages from the deep-seated landslide scarps generally gave the most internally consistent ages for the landslides. However, only in rare cases did the landslide scarp ages overlap with those of boulders in the associated debris. Generally, boulders in the debris appeared to contain significant inheritance of cosmogenic nuclides from previous exposure and so yielded ages greater than those from the scarps. Surface exposure ages of ̃285,000 yr from boulders in the debris of two deep-seated landslides provide minimum ages considered to represent the original rock surfaces. This study has shown that it is possible to measure exposure ages of surfaces associated with large landslides from 70,000 yr down to a few thousand years old, despite low cosmogenic isotope production rates in Hong Kong due to low latitude and low altitude

Towards attributed, parameterised and fully integrated urban 3D geoscience models and related GIS datasets in the UK

Urban regeneration in the UK tackles deprivation stemming from industrial decline. These long-term projects (up to 25 years) are some of Europe’s largest. They implement land recycling, sustainable development and effective management of land and water resources. Those engaged in regeneration and large-scale construction (e.g. Olympic Games 2012 in London) need accessible and readily understood environmental geoscience information. The British Geological Survey (BGS) increasingly meets these needs with interactive, bespoke, 3D attributed geologic models, constructed with GSI3D and other software, and related GIS datasets. Close partnerships with decision-makers, including environmental regulators, help ensure effective data use. For example, in the Clyde Corridor, Scotland’s national regeneration priority, BGS works with Glasgow City Council, delivering 3D models of surficial deposits and bedrock in an urban area undermined for coal and ironstone, and masked by variably contaminated anthropogenic deposits. Comprehensive geochemical datasets are also produced. The models incorporate engineering data, and provide a platform for groundwater recharge and flow models, developed using ZOOM object-oriented software, which will be parameterized with data from a groundwater monitoring network under development. This will facilitate monitoring of groundwater quality and levels during regeneration, and aid assessment of: large-scale remediation of chromium waste; point-source groundwater recharge associated with sustainable urban drainage, a growing part of metropolitan drainage strategy; and the potential for and sustainability of ground source heat from extensive minewaters and aquifers beneath Glasgow

Modelling shallow urban geology using reservoir modelling techniques: voxel-based lithology and physical properties of the greater Glasgow area

Conventional 3D geological models of lithostratigraphy undertaken by BGS have facilitated a significant step forward in understanding of the 3D sedimentological and structural controls in the subsurface of the UK. However, when lithostratigraphic units are mapped or modelled in 3D, intra-unit variability is often not recognized, and may be substantial particularly in sedimentologically heterogeneous successions. Because of this BGS has been testing voxel grid-based approaches in urban areas with high borehole density. A city-scale lithology model of shallow, unconsolidated sediments in Glasgow, Scotland has been developed as a test of the applicability of these techniques to aid geological understanding and possible future applications. This is of particular significance in this location due to the complex fluvial and glacial history of the superficial geology which alternates between inter-fingering sedimentary packages and short-scale variability of subsurface materials. The model has been created by developing a stochastic model of clastic geology on a voxel support, based on upscaling of observed borehole lithology, independent of lithostratigraphy. Multiple realisations of lithology were generated, each honouring the borehole observations. Lithology information has therefore been used to both develop a model of the distribution of lithology throughout the grid, but also to develop an understanding of the associated uncertainty by providing estimates of the probability with which a particular lithology occurs at a given node. This lithological model compares well with ‘traditional’ deterministic lithostratigraphic 3D models created in the same area, and with field-based geological maps. This lithological voxel model has been used as a matrix through which physical property data can be attributed within the grid by stochastic modelling and simulation of the variability of properties within the lithological units. Several different property datasets have been populated across the grid, including geotechnical parameters, such as density, derived directly from site investigations, and properties derived from particle size distribution such as hydraulic conductivity. This can be augmented in deeper parts of the succession with geophysical log derived property data. This model may be applied to understanding of both the strength of the subsurface materials to aid development, and also hydrogeological properties to inform 4D process models, thus extending BGS’s capabilities to deliver scientific understanding of geological problems. For example, ongoing large-scale redevelopment of post-industrial sites across the Greater Glasgow area, these techniques have the potential to provide a clearer understanding of both the risks and opportunities of these sites. This project will act as an exemplar of the applicability of voxelated representations of lithology and physical property data to subsurface planning as a precursor to the wider rollout of the techniques to many UK cities

Volcanic-plutonic connections in a tilted nested caldera complex in Hong Kong

Exceptional exposures of four, precisely-dated, Middle Jurassic to Early Cretaceous,silicic volcanic centers and their plutonic equivalents in Hong Kong have provided an excellent opportunity to examine close connections in time and space between magma chambers and their overlying calderas. Here, we describe a ~14 km crustal section through a collapsed caldera in southeastern Hong Kong where the intracaldera fill suggests that the magmatic discharge was of supereruption scale. The main subvolcanic components that link a magma chamber with surface are revealed by well-established field relationships, supplemented by high precision geochronology, whole-rock geochemistry, and geophysical data. Exposures and outcrop reveal kilometer-scale caldera subsidence and evidence of the simultaneous evacuation of hundreds of cubic kilometers of high-silica rhyolite magma through dike-like conduits from a shallow subcrustal reservoir. The resultant volcanotectonic depression, within which is preserved a single cooling unit of massively columnar-jointed densely welded tuff (High Island tuff), is interpreted to form part of a larger tilted Early Cretaceous nested caldera complex. The High Island eruption signaled the end of a 24 Myr-Early Cretaceous silicic magmatism in the Hong Kong region characterized by four discrete ignimbrite ‘flare-ups’