U24A-01 INVITED
Capturing Detailed Outcrop Geology Using Terrestrial Laser Scanning (Lidar) and Other Digital Technologies: Current Status and Future Directions
Geospatial data acquisition at global to regional scales has wide acceptance, and tools such as Google Earth have been instrumental in extending Earth visualisation far beyond specialist users of GIS and satellite imagery. At the outcrop scale, the number of industry and academic geoscientists adopting digital technologies to gather field data is steadily increasing. When integrated with traditional field skills, these technologies offer two fundamental advantages: firstly, outcrop geology can now be recorded with very high detail and precision; secondly, observations and data are precisely georeferenced, which is a prerequisite for 2D and 3D spatial analysis. Digital outcrop data are being used in a wide variety of ways, many of which can be characterised in terms of two end members. Firstly, using methods such as terrestrial laser scanning and digital photogrammetry, it is possible to create highly realistic virtual copies of the outcrop. These virtual outcrop models can be used to great effect to enhance teaching, to provide virtual field-trips (most effective in conjunction with a real visit to the outcrop), to promote group discussion and interpretation, or as part of Health & Safety briefing. Secondly, digital outcrop data is also being used to derive quantitative attribute measurements from specific geological features. Here the emphasis is not on capturing a photo-realistic copy of the outcrop, but rather on gathering the relevant types of data at the most appropriate resolution and geospatial precision for the type of analysis undertaken. In addition to laser scanning, useful technologies include dGPS, laser range-finding, and Total Station surveying. Examples of this kind of quantitative analysis include fault curvature, roughness, branch-line geometry, spatial variation in fault displacement, fracture spacing and 3D spatial clustering, fold curvature, sedimentary channel morphology, lateral and vertical facies variations, and geomorphological analysis of terrace offsets. These kinds of studies are giving new insights into geological processes, and provide real-world constraints for validation and calibration in geological modelling. Because of the versatility of terrestrial laser scanning, a raw lidar dataset can often be used both to generate realistic virtual outcrop models, and to carry out detailed quantitative analysis. The main difference lies in the way the raw data are processed. This is reflected in the challenges that we are now facing. To make it easier to generate and use photo-realistic virtual outcrop models we need more efficient methods to render very large datasets (hundreds of millions of points or polygons). This requires better ways to smooth and filter point data, more dynamic meshing of points to recreate the outcrop surface, improved texture mapping of higher quality photos onto the mesh, and more seamless "Level of Detail" functionality so that progressively more detail is shown as the user zooms in on the outcrop. To improve quantitative analysis of geological features from lidar data, we need better colour imagery, and better co-registration of images with the raw point cloud. This can help to improve methods for automatic picking of features and removal of vegetation. More relevant methods for 3D spatial analysis of geological data need to be developed and tested. Further work is needed to compare different types of laser scanning equipment and improve the quantification of errors. http://www.geospatial-research.com/
U24A-02
Virtual Geological Reality: Making Geospatial Models Applicable and Scientifically Memorable
Interpretation of geological data by using digital, geospatial models is a revolutionary breakthrough for analysis of high-resolution outcrop data as well as regional data sets. Like other major breakthroughs in geology and geophysics, this advance has been driven by access to new technology and data sets. CAVE visualization centers, high-resolution satellite imagery and digital photography, laser scanners/LIDAR and GPS/GIS technology have driven these new methods and ideas. This presentation summarizes major developments in collecting data and interpreting geospatial models over the last decade. A basic condition for making such models and data applicable is that visualization of the data is only a lead-in to advanced geological and geophysical analysis and not an aim in itself. Aiming for utilization of the visually attractive data leads to development of new geological methods which speed up, refine and alter existing classic methods and lead to interpretations on an entirely new level. Examples will be shown where highly complex fracture systems, fault systems and bed geometries can be understood in a much refined way compared to using classic techniques. In these and other cases, uncertainties, for instance for reservoir modeling, are reduced drastically. Thus, geospatial models become scientifically memorable and not merely visually attractive.
U24A-03
Capturing Geology in 3D – Essential Scaling of Geologic Features
A variety of techniques have been recently developed for capturing 3D data directly from outcrops, which has resulted in a myriad outcrops being ‘collected' for subsequent viewing and analysis. The essential factor that separates a 3D outcrop data set that is simply an aesthetic simulacrum of a rock face from a data set that can be effectively used to better understand geology in 3D is an understanding of the scale of feature that is to be captured, and whether a particular outcrop is suitable to capture data at that scale. It has been shown that tectonic faults tend to follow power-law scaling relationships that are consistent over a wide range of length scales, from the microscopic to the megascopic. So, when capturing 3D outcrop data for fault and fracture data, the essential scaling relationships can be derived from a 3D interpretation of an outcrop, almost regardless of the length scale of outcrop exposures being captured (within the limits of statistical population rules). However, the capture and analysis of 3D sedimentary features and bodies is much more complex, since these systems usually have a characteristic length scale. It is not be useful for 3D analysis to capture a tiny fraction of a large feature, nor to capture widely spaced single-dimensional outcrop faces to study a small-scale feature. Therefore, we propose a simple set of rules that specify what scale of feature will be captured from a specific outcrop exposure. Examples will be shown to illustrate this point and the proposed rules using both faulted/fractured outcrops and where an exemplary 3D outcrop exposure in shallow-marine/fluvial rocks captures few of the geometries of interest, both at the large and small scales.
U24A-04
Tectonic Implications of a Crustal Scale 3D Model of the Eastern Mount Isa Inlier
A 3D model of the eastern part of the Proterozoic Mount Isa inlier has been constructed from surface geology, aeromagnetic and gravity data (including worms - multiscale wavelet edges of potential field data) and reinterpretation of seismic reflection data. The model was built from serial cross sections in GoCad, and has a volume of 200 km x 150 km x 50 km, to the base of the unusually thick crust. It shows major faults, lithostratigraphic units, and intrusions. The major feature of the model is a deepening of the cover sequence metasedimentary rocks in the center of the area, which coincides with an increase in stratigraphic thickness and is contained between two crust-penetrating faults that have reverse separations at surface. These features are interpreted as the result of positive inversion, in which major basin-bounding faults were reactivated as reverse faults, but preserve their original extensional geometry at the base of the cover sequences. The localization of contractional structures over the original extensional faults limits the amount of displacement that can have occurred on the reverse faults. Significant changes in model geometry occur from south to north along the strike of the inlier, and may be original variations in basin geometry. The model shows that dioritic - granitic composite batholiths, which postdate the major contractional Isan orogeny, are tabular features no more than a few km thick, and are spatially associated with the major faults. Batholith intrusion may have occurred by dike-like ascent along the major faults and sill-like emplacement. Estimates of the minimum volume of the intrusions can be made from the model, which need to be reconciled with isotopic constraints that suggest crustal sources for the batholiths. These observations and tectonic implications follow directly from constructing the geospatial model, and illustrate its major benefit: spatial relationships are revealed in 3D on a crustal scale. Quantitative data from these sorts of models are remarkably useful in tectonics. http://www.pmdcrc.com.au/final_reports_projectI2.html
U24A-05
An integrated geospatial model to investigate tectonics of the Caspian Sea region
The South Caspian Basin provides an outstanding example of a rifted marginal basin now undergoing 3D contractional deformation. It is a young, deep basin which contains a prolific hydrocarbon system and thus is an extremely valuable natural laboratory with extensive industry data coverage. Folds and mud volcanoes are notable features of the basin and both are actively growing in the Cenozoic sedimentary sequence. Here, we discuss ongoing work to understand the dominant controls on the origin and evolution of the South Caspian structures. Within the basin, a thick fluvio-deltaic sequence is being actively folded into trains of 10-20km wavelength, 5- 10km amplitude upright folds. Four main spatial domains are identified in regional 2D seismic interpretations with linear, closely spaced fold arrays near the western and northern basin margins. Towards the basin centre folds display short, bifurcating hinge traces that form polygonal patterns in places. Mud volcanoes are found on or near fold crests and where hinge traces meet or are segmented. Exposures of similar stratigraphy and structure are available in adjacent uplifted regions in onshore Azerbaijan and provide analogues for subsurface sedimentary and structural architectures. Current efforts are underway to integrate the surface and subsurface geology which means directly addressing issues of scale, resolution and multidisciplinary integration. We use a common platform (CoViz®) to covisualize, access, and interrogate a range of different datasets from the subsurface including seismic volumes, reservoir structure models, well data, image logs, structural sections and reservoir simulation models, reservoir cartoons (GDE maps) and horizon data. The onshore datasets comprise topographic data, remote sensed imagery, GIS layers, surface mapping data, outcrop photographs, stratigraphic logs and ground-based lidar data. Our work suggests that the interaction between plate movements, basement influence and mechanical stratigraphy produce effects that vary spatially across the basin and with scale of observation. These interactions have produced fold geometries that are not typical of those developed by buckling alone and the mud and fold systems are linked by feedback mechanisms.
U24A-06
Chronotopographic Analysis To Detect Small, Seasonal Hillslope Change Based On Point Cloud Data, Black Mesa Escarpment, NE Arizona
TLS techniques have been introduced to an on-going investigations of semiarid landscapes, we are attempting to document the seasonal change related to hillslope processes that lead to pulses of erosion and sedimentation associated with weakly cemented sandstones along part of the Black Mesa escarpment of NE Arizona. Dendrochronology coupled with soil geomorphic analysis indicates that abundant sediment is being shed from weathered slopes at vertical denudation rates of 2-3 mm/year over 10-100 yr timescales, causing rapid localized valley floor aggradation. Employing the UNM LiDAR Laboratory Optech Ilris 3D terrestrial LiDAR scanner, we have devised a method for chronotopographic analysis where subsequent point-cloud data sets are compared directly to each other. Focusing on a single small (30x60m) area of a mostly non-vegetated, steep slope (>35°), we demonstrate that the devised method of comparative analysis of point cloud data sets can detect sub-centimeter change resulting from a single season of monsoon precipitation along the escarpment. Using repeat scans spanning the 2006 and 2007 monsoons has provided an empirical evaluation of single season erosion rates for the study site that ranges between 5-20mm/yr. Thi anomalously high value is consistent with previously work that suggests that large amounts of change occur during large rain events that follow periods of prolonged drought. The 2006 monsoon followed a well documented 7 year period of severe drought conditions and set regional records for summer rainfall throughout much of the southwest. This data set should also document the parts of the slopes that make the greatest contribution to local valley floor aggradation. In demonstrating the utility of this method, we expect that continued investigation of this site will provide insight to the key processes associated with soil- mantled vs. bedrock-dominated slopes during modern escarpment retreat and hillslope modification. Such insights may then elucidate the impacts of Holocene climate change on this rapidly evolving landscape.
U24A-07
Quantifying Fault Attributes at the Outcrop Scale: a Fault Network Model of Sub-Seismic Normal Faults in a Thinly-Bedded Reservoir Sequence
Three-dimensional (3D) seismic reflection data have revolutionized our knowledge of fault attributes in sedimentary basins. However, the resolution of such data is limited - faults with throws <30 m are not visible in typical 3D seismic profiles. Consequently, there are significant uncertainties in predicting the subsurface location, geometry, and connectivity of small-scale faults/fractures and hence the impact these structures have on reservoir performance. We can address this problem by capturing detailed (cm-resolution) 2.5D digital outcrop models (DOMs) of selected outcrops using terrestrial laser scanning (TLS) techniques. Here, we show an example of a DOM generated from a network of sub-seismic scale, post-sedimentary faults that cut a thinly bedded sandstone/shale sequence of Carboniferous age exposed at Lamberton, SE Scotland, and demonstrate how the DOM data may be used to quantify fault attributes to a remarkable level of detail. The faults are exposed in cross-section and plan view, respectively, in low cliffs and on a wave-cut platform defined by three sub- horizontal sandstone beds. The outcrop is characterized by small fault "scarps" (< 50 cm high) that formed due to erosion of the shale interbeds. We used TLS to capture the detailed surface topography of the three sandstone beds and adjacent cliffs and to build a cm-to m-scale fault network model of the outcrop. Attributes derived from the DOM include fault spacing, displacement-length profiles, 1- and 2-D strain, cumulative throw, fracture intensity, and fault connectivity. Analysis of the DOM shows that the faults are highly segmented and, in some cases, curvilinear in map view, with a mean trace spacing of ca. 30 cm and a mean throw of ca. 4 cm. The fault system is characterized by an abundance of relay ramps and rapid, along-strike changes in fault polarity consistent with a high degree of fault interaction. The relay zones themselves display a wide range of ramp dips and aspect ratios, consistent with the order of magnitude variation in horizontal displacement gradients measured at fault tips, between 0.026-0.26. The high spatial resolution of the Lamberton DOM gives hitherto unrecognised insights into fault and relay ramp geometry within a sub-seismic scale fault network, and has allowed us to evaluate and constrain fault system attributes to a level unachievable by field studies alone.
U24A-08 INVITED
Analysis of hyperspectral and lidar data: Remote optical mineralogy and fracture identification
Karst systems are widely recognized as highly complex and often extremely productive reservoirs of water as well as petroleum. They are also often associated with mineralization. The availability of a large (several tens of square kilometers), well-preserved paleokarst outcrop is rare; therefore, maximizing the information that we can extract from examples like the Franklin Mountains is critical to the study of karst-related fluid flow. The mapping process is confounded by the need to map very large areas to find relatively small and somewhat unpredictable zones of extreme deformation. Moreover, the brecciated regions interpreted to be of karst origin are often composed of the same lithology as the surrounding rock and thus make traditional remote sensing data such as multispectral satellite imagery or photographic data inadequate to delineate such systems. The Franklin Mountains in El Paso, Texas, expose lower Paleozoic carbonates deposited over a giant carbonate platform referred to as the Great Ordovician Bank. The limestone dominated bank was subsequently modified by surface karst and several large, vertically extensive caves that occupy up to 70,000 m2 of outcrop each. The breccia bodies are preferentially dolomitized within the limestone host rock. The size of these features is ideal for testing dolomite-calcite identification with high-elevation hyperspectral imagery at 20-m × 20-m pixel size. Terrestrial-based lidar (light detection and ranging) data were also utilized to identify collapse brecciation highlighted by hyperspectral image analysis. Results of this study delineate the distribution of dolomite and calcite in natural, passive light, well outside the visible spectrum, and combine active (lidar) and passive remote-sensing technologies to conduct remote mineralogical mapping linked to diagenetic alteration of carbonates. Through the combination of hyperspectral image processing and shape/texture analysis of terrestrial lidar data, a quantitative, multiscale facies map was generated in three dimensional, geographically rectified space.