The stratigraphical framework for the Palaeogene successions of the London Basin, UK

This document is the formal statement of the lithostratigraphy of Palaeogene1 The unit descriptions will also appear in the BGS Lexicon of Rock Unit Names ( deposits of the London Basin, in south-east England, as adopted by the British Geological Survey. It contains a review of the nomenclature used in BGS publications, including maps, and sets out the currently preferred scheme. This review draws heavily on the work of BGS staff, including that published outside BGS, as well as publications and some unpublished work from outside BGS. http://www.bgs.ac.uk/Lexicon/home.html) (Section 1.5), although as time passes the content of the Lexicon may be revised or expanded

Possible Late Pleistocene pingo development within the Lea Valley: evidence from Temple Mills, Stratford, East London

This report describes and discusses a borehole drilled at the Olympic Park development site at Temple Mills, in the Lea Valley near Stratford in East London. The original borehole number is MBHCZ6A-159. It has been registered as TQ38NE 1366 in the BGS Single Onshore Borehole Index. The borehole penetrates a 70 metre-thick sequence which, from the top downwards, passes through made ground and Quaternary fluvial deposits before revealing a 43 metre-thick zone of bedrock mélange. This mélange includes material from the lower part of the Lambeth Group, the Thanet Formation, and the Chalk. It is interpreted as being the product of pervasive soft-sediment deformation formed during a series of short-lived elevated pore water events, based upon the presence of diagnostic geological structures characteristic of ductile deformation, probably during rapid ejection of groundwater under artesian pressure. During these events, fragments of chalk were carried to within 17 metres of the surface, some 20 metres above where the top of the Chalk was encountered in nearby undisturbed sequences. Conversely, the presence of glauconitic sand apparently derived from the adjacent Palaeogene bedrock at 69 m depth, more than 30 m below the top of the Chalk nearby, implies that there was also some downwards movement during mélange formation. The presence of such a thick disturbed sequence beneath superficial deposits is extremely unusual although not unique. A model is proposed where this structure and internal deformation is explained by processes of pingo formation and decay in a part of the Lea Valley where the bedrock aquifer is confined by an aquitard as little as 3 m thick. Alternatively, it is possible that the structure formed during release of artesian groundwater pressure following fluvial scour. In either case, it is very likely that the structure lies above a fault zone including fractured, possibly karstic chalk, with high groundwater conductivity. The structure is most likely to have formed during Late Devensian times, during the deposition of the Shepperton Gravel, but it might be older, possibly pre-dating part or all of the Devensian Kempton Park Gravel

Benefits of a 3D geological model for major tunnelling works : an example from Farringdon, east-central London, UK

In the design of major construction works, the better the ground conditions are known, the more control there is on the assessment of risks for construction, contract and personnel, and ultimately on final costs. Understanding of the ground conditions is usually expressed as a conceptual ground model that is informed by the results of desk study and of dedicated ground investigation. Using the GSI3D software, a 3D geological model (a model composed of attributed solid volumes, rather than of surfaces) can be constructed that exactly honours geologists’ interpretations of the data. The data are used in their true 3D position. The 3D model of faulted Lambeth Group (Palaeogene) strata in the area of the proposed new Crossrail Farringdon underground station, in central London, has several types of benefit. These include allowing optimum use of available ground investigation data, including third party data, with confidence. The model provides an understanding of the local geological structure that had not been possible using other commonly used methods: in particular, it shows the likely distribution of numerous water-bearing coarse deposits and their faulted offsets, which has potentially significant effects on groundwater control. The model can help to focus ground investigation, constrain design and control ris

Under-representation of faults on geological maps of the London region: reasons, consequences and solutions

London lies mainly within an area of long-term tectonic stability known as the London Platform. This is characterised by relatively thin Cretaceous and Palaeogene sequences overlying Palaeozoic basement at shallow depths, less seismic activity than surrounding areas and, according to published geological maps, little faulting. However, observations of temporary exposures and borehole records, and other studies, show that in reality faults are numerous and widespread in the London region. Their relative absence on the geological maps is a consequence of past mapping methods, coupled with the relative uniformity of extensive bedrock units such as the London Clay Formation and the Chalk Group, and the widespread presence of Quaternary and anthropogenic deposits, and of urban development. However, complementary approaches to geological surveying, including the use of geophysical data and satellite-based radar interferometry, together with geological modelling in three dimensions using subsurface information, provide the means to accurately survey fault systems even in the most densely urbanised areas. Such work shows that earth movements in the London area, apparently including near-surface fault displacements, have taken place during the late Quaternary and continue at the present. These findings are important to civil engineering projects and hydrogeological studies in the London area and to understanding local tectonic development

The geology of the Falkland Islands

This report is complementary to the 1:250 000 scale geological map of the Falkland Islands compiled in 1998. The report and map are products of the Falkland Islands Geological Mapping Project (1996-1998). Geological observation and research in the Islands date from 1764. The Islands were visited during two pioneering scientific cruises in the 19th century. Subsequently, many scientists visited en route to the Antarctic or Patagonia. Geological affinities to other parts of the southern continents, especially South Africa, were noted early in the 20th century. There have been two previous attempts to create a geological map of the Islands, both motivated primarily by the search for economic mineral deposits onshore. In the last few decades much effort has been directed to understanding the Falklands’ place in Gondwana, the processes by which the Islands have moved to their present position by continental drift and the concomitant development of offshore sedimentary basins. Considerable progress in describing the superficial deposits was made in the 1970’s, and during the last ten years. The stratigraphic subdivisions of the geological sequence shown on the previous geological maps have been substantiated and defined more rigorously than before. In addition, several new stratigraphic units have been recognised. Each unit is described with an introductory summary of composition and distribution, followed by comments on nomenclature and stratigraphic relationships, associated landforms, distinguishing characters, and the criteria used to locate and survey the stratigraphic base. Detailed descriptions of composition, sedimentary structures and fossil content then lead to brief comments on the environment of deposition, age and correlation. The bedrock geological formations (‘solid geology’) can be divided into four age groups. The Proterozoic granites and amphibolite facies gneisses of the Cape Meredith Complex (about 1150 to 1000 million years old) are overlain in turn by sedimentary sequences of the ?Silurian to Devonian West Falkland Group and the Carboniferous to Permian Lafonia Group. Jurassic igneous rocks are widespread but only locally abundant. The West Falkland Group is dominated by sandstones, with some siltstones and mudstones. The oldest of four formations, the Port Stephens Formation, is divided into seven members, representing marine to fluvial environments. The basal member on East Falkland is probably the oldest part of the sedimentary sequence and might be latest Ordovician in age, but is more probably Silurian. The overlying Albemarle Member is notable for abundant trace fossils, mainly Skolithos, but also contains a new ichnospecies of Heimdallia. The succeeding marine Fox Bay Formation contains the Early to Middle Devonian Malvinokaffric invertebrate fossil fauna. One proximal facies member is recognised in the west. The Port Philomel Formation represents deltaic facies. It is notable for abundant fossil plant debris, most conspicuously lycophyte stems. The Late Devonian Port Stanley Formation, which includes the Stanley Quartzite, marks a return to marine conditions. The sandstones in the West Falkland Group are mostly quartz arenites and subarkoses, consistent with derivation from an area of stable continent crust. The West Falkland Group can be correlated with parts of the Cape Supergroup of South Africa

Absolute fixing of tide gauge benchmarks and land levels : the BGS contribution to a report on a study of the London and Thames estuary region

This report comprises material submitted as the British Geological Survey (BGS) contribution to the final report of a project measuring changes in land and sea levels using high precision global positioning system (GPS) surveying, absolute gravimetry (AG), persistent scatterer interferometry (PSI) and tide gauge records. Data was collected during the period 1997 to 2005 for a National study of changes around the coast of Great Britain, and a Regional study of changes along parts of the Thames Estuary and the River Thames at London. Since 2003, the national study has been funded by the Joint DEFRA/EA Flood and Coastal Erosion Risk Management R&D Programme, and a regional study, funded by the Environment Agency Thames Estuary 2100 project. The national study was carried out jointly by the Proudman Oceanographic Laboratory (POL) and the University of Nottingham’s Institute of Engineering Surveying and Space Geodesy (IESSG). The regional study was led by IESSG and carried out jointly by IESSG, POL, Nigel Press Associates Ltd. (NPA) and the British Geological Survey (BGS). The item in the project research plan relevant the main BGS input is Objective 08: ‘The estimates of changes in absolute ground level for the regional network of 13 GPS stations and a few thousand PSI points (output from 07) will be analysed, and geological interpretations presented using the geological database and other available information’. The final project report includes a condensed version of this material, with only a few of the figures. That is due to be published as Environment Agency R&D Technical Report FD2319/TR. The geological setting of the London region is described in a report for the EA/NERC CONNECT B project (Bingley et al., 1999), and by Ellison et al. (2004)

A geological model of the chalk of East Kent

This report describes the geological modelling of the Chalk in the North Downs of East Kent, within the catchment of River Great Stour and eastwards to the coast, including the Isle of Thanet. This work was funded by the Environment Agency to support investigations of the local hydrogeology and thereby to enhance catchment management. The whole area is underlain by the Upper Cretaceous Chalk Group, with the Palaeogene succession of the Thanet Sand Formation, the Lambeth Group and the Thames Group overlying it in the northern and central eastern parts. The project included a desk study revision of the Chalk of the North Downs, using the new Chalk lithostratigraphy. The revisions to the geology are shown on the 1:50 000 scale geological map which accompanies this report. Together with evidence from boreholes and from seismic surveys, the new outcrop patterns have been incorporated into a geological model, using both computer software (EarthVision) and manual methods. The introduction describes the background to the project. The second chapter describes the sources for the data used in the model: published and unpublished geological maps, borehole records (both lithological and geophysical), seismic surveys, biostratigraphic records, digital topographic information, and the published literature. Each Chalk formation present in the area is then briefly described in the third chapter, noting its relationship to the older lithostratigraphic divisions, and to biostratigraphic zones. The local Chalk succession extends from the base of the Chalk Group to the Newhaven Chalk Formation, here represented by the Margate Chalk Member. Evidence for the thickness of each formation is reviewed. The early Palaeogene formations (the Thanet Sand, Upnor, Harwich and London Clay formations) are also briefly described (Chapter 4) and the local superficial deposits mentioned, with references to detailed descriptions (Chapter 5). Apart from minor adjustments to the outcrop of the basal Palaeogene surface, no revision of these formations was done for this study

Uncertainty in mapped geological boundaries held by a national geological survey: eliciting the geologists' tacit error model

It is generally accepted that geological line work, such as mapped boundaries, are uncertain for various reasons. It is difficult to quantify this uncertainty directly, because the investigation of error in a boundary at a single location may be costly and time consuming, and many such observations are needed to estimate an uncertainty model with confidence. However, it is recognized across many disciplines that experts generally have a tacit model of the uncertainty of information that they produce (interpretations, diagnoses, etc.) and formal methods exist to extract this model in usable form by elicitation. In this paper we report a trial in which uncertainty models for geological boundaries mapped by geologists of the British Geological Survey (BGS) in six geological scenarios were elicited from a group of five experienced BGS geologists. In five cases a consensus distribution was obtained, which reflected both the initial individually elicited distribution and a structured process of group discussion in which individuals revised their opinions. In a sixth case a consensus was not reached. This concerned a boundary between superficial deposits where the geometry of the contact is hard to visualize. The trial showed that the geologists' tacit model of uncertainty in mapped boundaries reflects factors in addition to the cartographic error usually treated by buffering line work or in written guidance on its application. It suggests that further application of elicitation, to scenarios at an appropriate level of generalization, could be useful to provide working error models for the application and interpretation of line work

National geological screening : the Wealden district

This report is the published product of one of a series of studies covering England, Wales and Northern Ireland commissioned by Radioactive Waste Management (RWM) Ltd. The report provides geological information about the Wealden district region to underpin the process of national geological screening set out in the UK’s government White Paper Implementing geological disposal: a framework for the long-term management of higher activity radioactive waste (DECC, 2014). The report describes geological features relevant to the safety requirements of a geological disposal facility (GDF) for radioactive waste emplaced onshore and up to 20 km offshore at depths between 200 and 1000 m from surface. It is written for a technical audience but is intended to inform RWM in its discussions with communities interested in finding out about the potential for their area to host a GDF

National geological screening : London and the Thames Valley

This report is the published product of one of a series of studies covering England, Wales and Northern Ireland commissioned by Radioactive Waste Management (RWM) Ltd. The report provides geological information about the London and the Thames Valley region to underpin the process of national geological screening set out in the UK Government’s White Paper Implementing geological disposal: a framework for the long-term management of higher activity radioactive waste (DECC, 2014). The report describes geological features relevant to the safety requirements of a geological disposal facility (GDF) for radioactive waste emplaced onshore and up to 20 km offshore at depths between 200 and 1000 m from surface. It is written for a technical audience but is intended to inform RWM in its discussions with communities interested in finding out about the potential for their area to host a GDF