Phillip Clegg

Unlocking the spatial dimension: digital technologies and the future of geoscience fieldwork

The development of affordable digital technologies that allow the collection and analysis of georeferenced field data represents one of the most significant changes in field-based geoscientific study since the invention of the geological map. Digital methods make it easier to re-use pre-existing data (e.g. previous field data, geophysical survey, satellite images) during renewed phases of fieldwork. Increased spatial accuracy from satellite and laser positioning systems provides access to geostatistical and geospatial analyses that can inform hypothesis testing during fieldwork. High-resolution geomatic surveys, including laser scanning methods, allow 3D photorealistic outcrop images to be captured and interpreted using novel visualization and analysis methods. In addition, better data management on projects is possible using geospatially referenced databases that match agreed international data standards. Collectively, the new techniques allow 3D models of geological architectures to be constructed directly from field data in ways that are more robust compared with the abstract models constructed traditionally by geoscientists. This development will permit explicit information on uncertainty to be carried forward from field data to the final product. Current work is focused upon the development and implementation of a more streamlined digital workflow from the initial data acquisition stage to the final project output.

Domainal deformation patterns and strain partitioning during transpression: an example from the Southern Uplands terrane, Scotland

The partitioning of deformation into wrench- and contraction-dominated deformation domains is a widely reported but poorly described phenomenon in ancient transpression zones. This paper documents spectacularly exposed examples of such partitioning from the Southern Uplands terrane in SE Scotland (Berwickshire), which was deformed during late Llandovery to Wenlock time. A well-exposed coastal section from Eyemouth to Burnmouth preserves a broadly homoclinal sequence in which a highly heterogeneous array of contemporaneous structures formed during regional triclinic transpression. The deformation involved components of NW–SE contraction with subvertical extension, top-to-the-SE thrusting and top-to-the-SW sinistral shear. In the northern third of the section studied these components are partitioned into a series of fault-bounded, metre- to kilometre-scale structural domains that contain geometrically and kinematically distinct assemblages of variably curvilinear folds, strike-slip detachments and locally transecting cleavages. The structures are all broadly contemporaneous and, in individual domains, record either non-coaxial contractional- or sinistral wrench-dominated strains. Similar highly heterogeneous, domainal structural patterns are likely to be found in other regions of oblique convergence in both ancient and modern settings.

Complex deformation as a result of strain partitioning in transpression zones: an example from the Leinster Terrane, SE Ireland

Coastal exposures of Lower Palaeozoic rocks in SE Ireland provide an excellent opportunity to study structures formed during the sinistrally oblique Early Devonian Acadian orogeny. A highly heterogeneous assemblage of broadly contemporaneous Acadian structures is preserved and includes complex curvilinear folds, a regional, slightly clockwise transecting pressure solution cleavage, and networks of regional and smaller-scale sinistral shear zones and faults. The geometric and kinematic characteristics of these structures suggest components of NW–SE shortening, top-to-the-SW sinistral shear and a small component of top-to-the-SE thrusting. The structures are arranged into geometrically and kinematically different assemblages that define three fault-bounded structural domains, of hundreds of metres to kilometre scale. These are interpreted to result from the kinematic partitioning of the bulk triclinic sinistral transpressional strain into end-member monoclinic contraction- and wrench-dominated deformations. In this case, the nature and distribution of strain may be controlled by the presence of a pre-existing basin-bounding structure, the Courtown–Tramore Fault. The present study once again illustrates well how structural facing patterns can be used to unravel the structural complexities of kinematically partitioned transpression zones.

Calibration and validation of reservoir models: the importance of high resolution, quantitative outcrop analogues

Abstract Rapidly developing methods of digital acquisition, visualization and analysis allow highly detailed outcrop models to be constructed, and used as analogues to provide quantitative information about sedimentological and structural architectures from reservoir to subseismic scales of observation. Terrestrial laser-scanning (lidar) and high precision Real-Time Kinematic GPS are key survey technologies for data acquisition. 3D visualization facilities are used when analysing the outcrop data. Analysis of laser-scan data involves picking of the point-cloud to derive interpolated stratigraphic and structural surfaces. The resultant data can be used as input for object-based models, or can be cellularized and upscaled for use in grid-based reservoir modelling. Outcrop data can also be used to calibrate numerical models of geological processes such as the development and growth of folds, and the initiation and propagation of fractures.

The nature and regional significance of structures in the Gala Group of the Southern Uplands terrane, Berwickshire coast, southeastern Scotland

Structures deforming Llandovery turbidites of the Gala Group in the Southern Uplands terrane are spectacularly exposed in the Berwickshire coastal section, southeastern Scotland. The upward-facing, upright to NW-vergent folds and associated structures appear to record a single regional phase of subhorizontal NW-SE contractional deformation, with a steeply dipping direction of bulk finite extension. These structures are markedly different from those developed in rocks corre- lated with the Upper Llandovery Hawick Group exposed some 5 km to the south in the Eyemouth-Burnmouth coastal section. Here a highly domainal system of sinistral transpressional strain occurs, with zones of steeply plunging curvilinear folds, clockwise cleavage transection and bedding-parallel sinistral detachment faults. The markedly different bulk strain patterns in the Berwickshire coastal sections are thought to reflect the regionally diachronous nature of transpres- sional deformation in the Southern Uplands terrane. There are striking similarities in the structures recognized in the Berwickshire coastal sections and those developed in stratigraphically equivalent units along strike in southwestern Scotland and Northern Ireland. This confirms the lateral structural continuity and correlation of tracts and tract boundaries along the entire length of the Southern Uplands terrane. The regional structure suggests that a phase of top-to-the-NW backthrusting and backfolding associated with the southern margin of the Gala Group outcrop marks the transition from orthogonal contraction to sinistral transpression in the Southern Upland thrust wedge during late Llandovery times.

Putting the geology back into Earth models

New digital methods for data capture can now provide photorealistic, spatially precise, and geometrically accurate three-dimensional (3-D) models of rocks exposed at the Earths surface [Xu et al., 2000; Pringle et al., 2001; Clegg et al., 2005]. These “virtual outcrops” have the potential to create a new form of laboratory-based teaching aids for geoscience students, to help address accessibility issues in fieldwork, and generally to improve public awareness of the spectacular nature of geologic exposures from remote locations worldwide. This article addresses how virtual outcrops can provide calibration, or a quantitative “reality check,” for a new generation of high-resolution predictive models for the Earths subsurface.