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Subsurface datasets typically lack the resolution or coverage to adequately sample fracture networks in 3D, and fracture properties are typically extrapolated from available data (e.g. seismic data or wellbore image logs). Here we assess the applicability of extrapolating fracture properties (orientation, length, and intensity) across observation scales in deformed, mechanically layered carbonate rocks. Data derived from high-resolution field images, medium-resolution digital outcrop data, and relatively low-resolution satellite imagery at Swift Reservoir anticline, NW Montana are leveraged to (i) assess interacting structural and stratigraphic controls on fracture development, and (ii) compare estimated fracture properties derived from multiple observation scales. We show that hinge-parallel and hinge-perpendicular fractures (i) make up the majority of fractures at the site; (ii) are consistently oriented with respect to the fold hinge, despite along-strike variability in the fold hinge orientation; and (iii) exhibit systematic increases in intensity towards the anticline hinge. These fractures are interpreted as having formed during folding. Other fractures recorded at the site exhibit inconsistent orientations, show no systematic trends in fracture intensity, and are interpreted as being unrelated to fold formation. Fracture orientation data exhibit the greatest agreement across observation scales at hinge and forelimb positions, where hinge-parallel and hinge-perpendicular fracture sets are well developed, and little agreement on the anticline backlimb, where fracture orientations are less predictable and more dispersed. This indicates that the scaling of fracture properties at Swift Reservoir anticline is spatially variable and partly dependent on structural position. Our results suggest that accurate prediction and extrapolation of natural fracture properties in contractional settings requires the assessment of structural position, lithologic variability, and spatially variable fracture scaling relationships, as well as consideration of the deformation history before and after folding. [ABSTRACT FROM AUTHOR]

Natural fracture patterns have long been associated with fold formation. Conceptual models of fold associated fractures are used to predict fracture networks and hence subsurface properties such as fracture connectivity, intensity and fluid flow. Subsurface datasets typically lack the resolution or coverage to adequately sample fracture networks in 3D, however, and geometric properties are typically extrapolated from available data (e.g., seismic data or wellbore image logs). Here we assess the applicability of extrapolating fracture properties (orientation, length and intensity) from one observation scale to another in a structurally complex setting and assess the interplay of fracture scaling with geological controls on fracture development. Fracture patterns are investigated at an outcrop exposure of layered carbonate rocks at Swift anticline, NW Montana. Data derived from high-resolution field images, medium resolution digital outcrop data, and relatively low resolution satellite imagery are leveraged to (i) assess interacting structural and stratigraphic controls on fracture development, and (ii) compare estimated fracture properties derived from multiple observation scales. We show that hinge-parallel and hingeperpendicular fractures (i) make up the majority of fractures at the site, (ii) are consistently oriented with respect to the fold hinge and, (iii) exhibit systematic increases in intensity towards the anticline hinge. These fractures are interpreted as having formed during folding. Other fractures recorded at the site exhibit inconsistent orientations, show no systematic trends in fracture intensity, and are interpreted as unrelated to fold formation. Fracture orientation data exhibit greatest agreement across observation scales at hinge and forelimb positions where hinge-parallel and hinge-perpendicular fracture sets are well developed, and little agreement on the anticline backlimb, where fracture orientations are less predictable and more dispersed. This indicates that the scaling of fracture properties at Swift anticline is spatially variable and partly dependent on structural position. Our results suggest that accurate prediction and extrapolation of natural fracture properties in contractional settings requires assessment of structural position, lithologic variability, and spatially variable fracture scaling relationships, as well as consideration of deformation history before and after folding. [ABSTRACT FROM AUTHOR]

Geoscience educators and students often find field-based exercises the most effective medium for understanding complex geological concepts and visualizing relationships in 3D. Traditional barriers to field-based training, including physical disabilities, lack of financial resources, and geographical restrictions, mean that this method of training is not available to everyone, however. Recent advances in data acquisition and processing techniques mean that 3D reconstructions of outcrop and landscapes are increasingly used by the geoscience community as a research tool and, more recently, as an accessible means of communicating geoscience within industry and academia. In spite of these developments, little has been done to leverage this technology as a tool to circumvent barriers to physical site access or supplement traditional educational practice in the geosciences. Further, little evidence exists as to the efficacy of these tools for reinforcing and improving understanding of 3D geological structures; potential benefits of virtual outcrop-based teaching methods have, as yet, not been quantitatively assessed in the geoscience education community. In this study, aimed at participants from a range of educational and professional backgrounds, we assess whether virtual outcrops enhance 3D geological understanding. Through a series of classroom-based and online multiple choice exercises, we compare how effectively virtual outcrops impart 3D geological information, compared to traditional 2D materials such as geological maps and field images. We collect qualitative data on the perceived benefits and pitfalls of virtual outcrops as tools for geoscience education. Results show that virtual outcrops are more effective than traditional teaching materials at conveying geological information: structural geometries and 3D relationships are better understood via virtual outcrops than through the use of oriented field imagery or geological maps alone. Undergraduate respondents also reported an improvement in their perception of 3D landscapes and visualization of complex geological structures after revisiting, in virtual outcrop form, a site where they had previously received field-based training. Finally, we find that across participant cohorts, the use of virtual outcrops for teaching and learning is perceived favourably, with the majority of participants regarding the use of virtual outcrops as a positive, useful technique for communicating geological concepts. Based on these results, we suggest that digital realisations of outcrops can improve 3D understanding of complex geological structures, irrespective of user background or education level. Participant feedback, however, highlights the need for contextualisation of virtual outcrops if they are to be an effective tool for education. Supplementary materials should be provided so that students can understand the scale of the object they are looking at, its geological significance, and how it relates to the surrounding landscape and subsurface. eRock (www.e-rock.co.uk), our online repository of virtual outcrops and hand specimens in 3D, takes this approach: virtual outcrops are provided as part of a suite of educational materials, including geological maps, cross sections, field photographs, and text. Our results show that virtual outcrops can be effective teaching tools - eRock aims to provide the necessary context to make these a useful teaching tool for the geoscience education community. [ABSTRACT FROM AUTHOR]

Coastal exposures of Carboniferous-age strata in SW Wales are recognised for their excellent preservation of Variscan deformation. The classic fold-thrust outcrop at Broadhaven, Pembrokeshire, is a particularly well-known example, and an oft-cited 'type example' of fault-related folding, following work by Williams & Chapman (1983). The outcrop has been important for generating conceptual models of fault-fold interaction, and was one of the sites where distance-displacement data were first used to infer thrust slip/propagation ratios. Here we employ the virtual outcrop method to digitally map and measure this classic locality. 3D reconstruction of the outcrop by digital photogrammetry allows us to extract high-density structural measurements, reassess the existing model of structural development, and re-evaluate the link between faulting and folding at the site. We find that high-resolution digital measurements record greater variability in thrust displacement and bed thicknesses than previously documented at the site. Distance-displacement data record the influence of mechanical anisotropy on slip/propagation ratios through the deformed multilayer. Bed thickness changes are linked to this variability in thrust displacement, highlighting transitions in strain accommodation patterns. Fracture analysis shows that fracture intensity is closely linked to structural position and bed thickness changes, and that fracture orientations record the existence of discrete mechanical boundaries through the structure. These results record complex patterns of strain distribution and multi-phase deformation. Evidence for temporal and spatial variability in strain distribution suggests that multiple kinematic and non-kinematic models of deformation are required to faithfully describe even this apparently simple structure. We use this detailed field evidence to propose an alternative to and develop, for multi-layered stratigraphy, the ductile bead model of Elliot (1976), as exemplified at Broadhaven by Williams & Chapman (1983).ReferencesElliott, D., 1976. The motion of thrust sheets. Journal of Geophysical Research, 81(5), pp.949-963.Williams, G. and Chapman, T., 1983. Strains developed in the hangingwalls of thrusts due to their slip/propagation rate: a dislocation model. Journal of Structural Geology, 5(6), pp.563-571. [ABSTRACT FROM AUTHOR]