Outcrop Models Research Articles

Teaching with digital geology in the high Arctic: opportunities and challenges

Abstract. The Covid-19 pandemic occurred at a time of major revolution in the geosciences – the era of digital geology. Digital outcrop models (DOMs) acquired from consumer drones, processed using user-friendly photogrammetric software and shared with the wider audience through online platforms are a cornerstone of this digital geological revolution. Integration of DOMs with other geoscientific data, such as geological maps, satellite imagery, terrain models, geophysical data and field observations, strengthens their application in both research and education. Teaching geology with digital tools advances students' learning experience by providing access to high-quality outcrops, enhancing visualization of 3D geological structures and improving data integration. Similarly, active use of DOMs to integrate new field observations will facilitate more effective fieldwork and quantitative research. From a student's perspective, georeferenced and scaled DOMs allow for an improved appreciation of scale and of 3D architecture, which is a major threshold concept in geoscientific education. DOMs allow us to bring geoscientists to the outcrops digitally, which is particularly important in view of the Covid-19 pandemic that restricts travel and thus direct access to outcrops. At the University Centre in Svalbard (UNIS), located at 78∘ N in Longyearbyen in Arctic Norway, DOMs are actively used even in non-pandemic years, as the summer field season is short and not overlapping with the Bachelor “Arctic Geology” course package held from January to June each year. In 2017, we at UNIS developed a new course (AG222 “Integrated Geological Methods: From Outcrop To Geomodel”) to encourage the use of emerging techniques like DOMs and data integration to solve authentic geoscientific challenges. In parallel, we have established the open-access Svalbox geoscientific portal, which forms the backbone of the AG222 course activities and provides easy access to a growing number of DOMs, 360∘ imagery, subsurface data and published geoscientific data from Svalbard. Considering the rapid onset of the Covid-19 pandemic, the Svalbox portal and the pre-Covid work on digital techniques in AG222 allowed us to rapidly adapt and fulfil at least some of the students' learning objectives during the pandemic. In this contribution, we provide an overview of the course development and share experiences from running the AG222 course and the Svalbox platform, both before and during the Covid-19 pandemic.

Global investigation of martian sedimentary fan features: Using stratigraphic analysis to study depositional environment

Through the use of high-resolution orbital data, it is possible to study sedimentary fan features on the surface of Mars as archives of past hydrological and climate conditions. Previous studies have commonly interpreted the depositional environment of fan deposits using the geomorphology of the modern fan outcrop alone; however, billions of years of erosion has likely altered the morphology of fan outcrops significantly. Here, we examine the stratigraphy, or internal architecture, of 15 fan deposits across the surface of Mars using orbital outcrop models derived from high-resolution images overlain on digital elevation models. Specifically, we search for a slope break in exposed fan layers, characteristic of a delta deposit and in contrast with an alluvial/fluvial fan that is not expected to have such a slope break. A delta indicates the presence of a downstream standing body of water, providing constraints on the location and abundance of water reservoirs recorded in the sedimentary rock record on Mars. At least one fan outcrop in this study, located in Hargraves crater, shows previously undocumented evidence of a slope break and is thus classified as a delta. Other fan features show some, but not unequivocal evidence of a slope break, but the majority (11) show no evidence of a slope break in their exposed stratigraphy, indicating they cannot be robustly classified as a delta. Of the four fan outcrops with some evidence for deltaic deposition, three are interpreted to have been constructed subsequent to the valley network forming era, including the conclusive delta within Hargraves crater. We also find that all the fan features analyzed in this work have been significantly modified since lithification and have experienced a considerable amount of erosion since initial formation, an important consideration when interpreting the present-day morphology of these landforms on Mars.

The effects of dolomite geobodies within carbonate clinoforms on fluid flow and connectivity: Insights from an outcrop analogue on Bonaire, The Netherlands (South Caribbean)

Carbonate clinoforms are often challenging to characterize and model due to their complex geometries and additional heterogeneity introduced by diagenetic processes. Dolomitization can influence petrophysical properties resulting in either an increase or reduction in porosity and permeability of the host rock and forms geobodies of varied shapes depending on pre-dolomitization permeability patterns and dolomitization mechanism. Therefore, in partially or fully dolomitized successions, the prediction of fluid flow behavior is not trivial. This study uses a well-studied outcrop analogue of Mio-Pliocene partially dolomitized clinoforms at Seru Grandi (Bonaire) to better understand fluid flow in different dolomitization scenarios. Clinothems consist of heterogeneous coralline algal facies overlying bioclastic facies, with dolomite geobodies truncated on their upper and lower bounds by clinoform surfaces. Digital outcrop models were used to characterize geometry and spatial relationship of facies and heterogeneity, such as clinoform dip, length, height, and spacing. Multiple realizations of clinoform and dolomite body geometries are modelled using a surface-based modelling (SBM) approach coupled with an unstructured mesh flow simulator (IC-FERST). Two scenarios are considered, in which dolomitization has resulted in either a decrease in porosity and permeability as observed in outcrop, or a relative increase of porosity and permeability values as a potential subsurface scenario. Flow simulation results reveal an exponential relationship between water breakthrough times and flow rates versus dolomite proportions. Additionally, the arrangement of the dolomite bodies (aligned vs. disjoined) exhibits very similar fluid flow behavior across a wide range of dolomite proportions. Sensitivity of flow behavior to the geological models is strongly dependent on dolomite permeability relative to precursor limestone. Dolomite body arrangement is more important for flow behavior at high dolomite proportions for low permeability dolomite, or at low dolomite proportions for high permeability dolomite. This study emphasizes the significance of having a good understanding of the dolomitization mechanism and dolomite body geometries, reducing uncertainty in dolomite distribution, petrophysical properties, and, therefore, fluid flow behavior.

Constraints upon fault zone properties by combined structural analysis of virtual outcrop models and discrete fracture network modelling

The permeability structure of a fault zone is strongly dependent on the occurrence of meso-scale fracture patterns within the damage zone. Here, structural analyses of Virtual Outcrop Models (VOM) integrated with Discrete Fracture Network (DFN) modelling are used to constrain the relationship between meso-scale fracture patterns and the bulk permeability of a regional-scale fault zone. The Goddo Fault Zone (GFZ, Bømlo – Norway) is a long-lived extensional fault zone cutting across a granodioritic body developed during the long-lasting rifting of the North Sea. Fracture geometrical characteristics and the spatial variation of fracture intensity derived from VOM structural analysis were adopted as input for stochastic DFN models representing selected portions of the GFZ to constrain the variability of the structural permeability tensor K related to the mesoscopic fracture pattern. The intensity of fault-related fracture set(s), and the associated structural permeability computed with DFN models, likely exhibits a decreasing power-law trend within the damage zone with increasing distance from the fault cores. The orientation of the maximum K tensor component is controlled by the intersection direction of the dominant fracture sets. These results highlight the fundamental role of mesoscopic fracture patterns in controlling the bulk petrophysical properties of large fault zones.

Identification of outcropping strata from UAV oblique photogrammetric data using a spatial case-based reasoning model

Due to the large scale and complex terrain of some outcrops, it is difficult to carry out comprehensive and detailed stratum identification using traditional geological methods. The emergence of oblique photogrammetry technology provides a new way to construct high-precision 3D models of outcrops, but the existing object extraction methods of 3D models cannot be applied to the differentiation of strata in an outcrop. Therefore, this paper proposes a novel identification method for outcropping strata from oblique photogrammetric data using a spatial case-based reasoning (SCBR) model. The method includes (a) constructing point cloud of the outcrop based on the photogrammetric data; (b) segmenting the point cloud into voxels; (c) creating an integrated expression of the spatial and attribute features of a stratum case; (d) creating an integrated similarity reasoning model of the spatial and attribute features; and (e) dividing the strata after reasoning. Furthermore, this study carried out stratum identification experiments on two cases of study in Fugu, Shaanxi, China. After Performing the SCBR model, the overall accuracies were found to reach 94%. After the stratum division after reasoning was carried out, the verification accuracies were found to exceed 99%. Based on the results of the manual stratum differentiation, the differentiation results of the proposed SCBR model were found to be much more consistent with the actual situation. The experiments show that the proposed method is very effective for differentiating outcropping strata and provides a new approach for the extraction of 3D objects generated with oblique photogrammetric data.

Fracture density variations within a reservoir-scale normal fault zone: A case study from shallow-water carbonates of southern Italy

Fault zones can often display a complex internal structure associated with antithetic faults, branch and tip points, bed rotations, bed-parallel slip surfaces, and subordinate synthetic faults. We explore how these structural complexities may affect the development of fault-related fractures as displacement accumulates. We analysed in detail an incipient fault zone within well-bedded, shallow-water carbonates of the southern Apennines thrust belt (Italy). The fault zone crops out with quasi-complete exposure at a reservoir scale on an inaccessible sub-vertical cliff face, and fault and fracture mapping were carried out on a 3D virtual outcrop model of the exposure built for this study using photogrammetry. Comparing the structure of the fault zone and the density of 9444 mapped fractures allowed us to unravel their spatial relationships. Our results show that the areas of denser fractures coincide with: (i) rock volumes bounded by antithetic faults developed within the fault zone, (ii) branch points between these antithetic faults and fault zone-bounding fault segments, (iii) fault zone-bounding fault segments associated with significant displacement gradients, and (iv) relay zones between subordinate synthetic faults. These findings may aid locating sub-seismic resolution volumes of dense fracturing and associated enhanced permeability within faulted reservoirs.

Low‐Angle Shear Within the Exposed Mânzălești Diapir, Romania: Salt Decapitation in the Eastern Carpathians Fold‐and‐Thrust Belt

AbstractIn salt‐detached fold‐and‐thrust belts, contractional modification of salt structures may include decapitation by thrusting, but examples are not well known in the subsurface and undocumented in outcrop. Here we present a surface exposure of an intrasalt, sub‐horizontal shear zone at the boundary between the Tarcău and Subcarpathian nappes in the Romanian Eastern Carpathians. The Mânzălești diapir forms the largest rock salt outcrop in Europe, with unique salt‐karst geomorphology. Numerous wells show that the outcrop is above deep‐seated salt of a precursor salt‐cored anticline or passive diapir whose base is at >3,500 m. Multiscale observations using UAV‐based digital outcrop models, fieldwork, and microstructure analysis show that the outcrop is characterized by sub‐horizontal foliation with isoclinal folds, unlike the subvertical fabric of most Romanian diapirs. The halite is rich in clastic inclusions, with a power‐law size distribution caused by tectonic reworking of originally impure salt. Microstructures show that the halite matrix is strongly deformed by dislocation creep, forming subgrains and dynamically recrystallized grains around large porphyroclasts with piezometry indicating relatively high differential stress of around 4 MPa, at pressures sufficient to suppress dilatancy. The observations are best explained by sub‐horizontal shear generated by an overriding nappe, overprinting an original coarse‐grained salt fabric during decapitation of the salt body.

Digital outcrop models of a low-angle shear within the exposed Mânzălești diapir, Romania

Digital outcrop models of a low-angle shear within the exposed Mânzălești diapir, Romania

Multi-scale, multi-sensor data integration for automated 3-D geological mapping

Enhanced digital outcrop models attributed with hyperspectral reflectance data, or hyperclouds, provide a flexible, three-dimensional medium for data-driven mapping of geological exposures, mine faces or cliffs. This approach facilitates the collection of spatially contiguous information on exposed mineralogy, and so helps to quantify mineralising processes, interpret 1-D drillhole data, and optimise mineral extraction. In this contribution we present an open-source python workflow, hylite, for creating hyperclouds by seamlessly fusing geometric information with data from a variety of hyperspectral imaging sensors and applying necessary atmospheric and illumination corrections. These rich datasets can be analysed using a variety of techniques, including minimum wavelength mapping and spectral indices, to accurately map geological objects from a distance. Reference spectra from spectral libraries, ground or laboratory measurements can also be included to derive supervised classifications using machine learning techniques. We demonstrate the potential of the hypercloud approach by integrating hyperspectral data from laboratory, tripod and unmanned aerial vehicle acquisitions to automatically map relevant lithologies and alterations associated with volcanic hosted massive sulphide (VHMS) mineralisation in the Corta Atalaya open-pit, Spain. These analyses allow quantitative and objective mineral mapping at the outcrop and open-pit scale, facilitating quantitative research and smart-mining approaches. Our results highlight the seamless sensor integration made possible with hylite and the power of data-driven mapping methods applied to hyperclouds. Significantly, we also show that random forests (RF) trained only on laboratory data from labelled hand-samples can be used to map appropriately corrected outcrop scale data.

Sedimentary facies, depositional environments and conceptual outcrop analogue (Dam Formation, early Miocene) Eastern Arabian Platform, Saudi Arabia: a new high-resolution approach

This paper presents the facies and depositional environment of the early Miocene Dam Formation, Eastern Arabian platform, Saudi Arabia. Deposition of Dam Formation (Fm.) was considered as a restricted shallow marine deposition. Few studies suggest the role of sea-level change in its deposition but were without decisive substantiation. Here, we describe the facies and high-resolution model of Dam Fm. under varying depositional conditions. The depositional conditions were subjected to changing relative sea level and tectonics. High-resolution outcrop photographs, sedimentological logs, and thin sections present that the mixed carbonate–siliciclastic sequence was affected by a regional tectonics. The lower part of Dam Fm. presents the development of carbonate ramp conditions that are represented by limestones and marl. The depositional conditions fluctuated with the fall of sea level, and uplift in the region pushed the siliciclastic down-dip and covered the whole platform. The subsequent rise in sea level was not as pronounced and thus allowed the deposition of microbial laminites and stromatolitic facies. The southeast outcrops, down-dip, are more carbonate prone as compared to the northwest outcrop, which allowed the deposition of siliciclastic-prone sedimentation up-dip. All facies, architecture, heterogeneity, and deposition were controlled by tectonic events including uplift, subsidence, tilting, and syn-sedimentary faulting, consequently affecting relative sea level. The resulting conceptual outcrop model would help to improve our understanding of mixed carbonate–siliciclastic systems and serve as an analogue for other stratigraphic units in the Arabian plate and region. Our results show that Dam Fm. can be a good target for exploration in the Northern Arabian Gulf.

A role for virtual outcrop models in blended learning – improved 3D thinking and positive perceptions of learning

Abstract. Virtual outcrop models are increasingly used in geoscience education to supplement field-based learning but their efficacy for teaching key 3D spatial thinking skills has been little tested. With the rapid increase in online digital learning resources and blended learning, most recently because of the global COVID-19 pandemic, understanding the role of virtual field environments in supporting and developing skills conventionally taught through field-based teaching has never been more critical. Here we show the efficacy of virtual outcrop models in improving 3D spatial thinking and provide evidence for positive perceptions amongst participants using virtual outcrops in teaching and learning. Our results show that, in a simple, multiple-choice scenario, participants were more likely to choose the 3D block diagram that best represents the structure when using a virtual outcrop (59 %) compared to more traditional representations, such as a geological map (50 %) or field photograph (40 %). We add depth to these results by capturing the perceptions of a cohort of students, within our full participant set, on the use of virtual outcrops for teaching and learning, after accessing a virtual field site and outcrops which they had previously visited during a day's field teaching. We also asked all participants if and how virtual outcrops could be used effectively for teaching and training, recording 87 % of positive responses. However, only 2 % of participants felt that virtual outcrops could potentially replace in-field teaching. We note that these positive findings signal significant potential for the effective use of virtual outcrops in a blended learning environment and for breaking barriers to increase the equality, diversity and inclusivity of geoscience field skills and teaching.

Integrating outcrop and subsurface data to improve the predictability of geobodies distribution using a 3D training image: A case study of a Triassic Channel – Crevasse-splay complex

Fluvial sandstones deposited by high-sinuosity fluvial systems are one of the most complex reservoirs to predict and model with confidence, a reflection of both the geometries and complex distribution of the component geobodies. By integrating both analogue outcrop data and associated subsurface data, as well as new technical advances in the reconstruction of the outcrop in 3D (Digital Outcrop Models, DOM), the geostatistical parameters, which condition the modelling of these reservoirs, can be better determined. In addition, DOMs also allow us to easily extract the necessary georeferenced input data (digitized outcrop interpretations, geometrical parameters, as well as key surfaces) and so create geocellular outcrop models (GOM); a useful tool with which to contrast the results obtained from geostatistical simulations, as well as to quantify the uncertainty associated with the results.In this study, classical field data, digital data derived from outcrop models and subsurface data were combined in order to carry out a geostatistical modelling of a Channel – Crevasse-splay complex outcrop analogue, located in the Triassic Red Beds of Iberian Meseta (TIBEM). Geostatistical modelling results were obtained by combining Object-based (OBM) and MultiPoint Statistics-based (MPS) modelling techniques.A critical element in this study was the design of appropriate modelling workflows with Petrel® which would best reproduce the distribution of heterogeneities at macroscale. The designed modelling workflow was used to construct a 3D Training Image (TI) of a fluvial reservoir comprising both a meandering channel system and its associated overbank sandstone deposits. The resulting TI represents all geobodies described in the studied outcrop example and is exportable to similar fluvial reservoirs. This TI was then used in MPS simulations, in order to establish how it could assist in the prediction of the reservoir geobodies, as well as confirming to what extent this prediction matched the outcrop.

Cross‐strata palaeocurrent analysis using virtual outcrops

AbstractAlthough virtual outcrops or digital outcrop model applications in geological studies are becoming increasingly common, virtually no attention has been given to acquisition of palaeocurrent data from cross‐strata. Palaeocurrent indicators are abundant in the sedimentary record, mainly as cross‐strata, and present compelling implications for basin analysis, plate tectonics and palaeoenvironmental reconstructions, as well as for sediment transport systems. Palaeocurrents from cross‐strata also comprise a quantifiable parameter in sedimentary successions that can be used in quantitative modelling of depositional architecture with implications for reservoir characterization through outcrop analogue studies. A common obstacle in obtaining large cross‐strata orientation datasets is the limited access to steep and high outcrop faces, as well as financial and time restrictions on field work. To overcome these issues, the simplest workflow for drone‐based acquisition, photogrammetric processing and analysis of virtual outcrops aiming at the attainment of palaeocurrent data from cross‐strata is appraised here. The results show that orientations of cross‐beds measured on virtual outcrops, with and without ground control points, and using two different levels of resolution downsampling, are comparable to field measurements using analogue and electronic devices. Time and financial resources can thus be saved by using the straightforward method presented here to supplement palaeocurrent mapping across wide areas and distinct stratigraphic intervals.

Development and application of UAV-SfM photogrammetry for quantitative characterization of rock mass discontinuities

Remote sensing techniques (e.g., terrestrial laser scanning and digital photogrammetry) have been developed and applied rapidly in recent years for identification and analysis of rock mass characteristics. A direct validation of these digital measurements against well-constrained datasets obtained from conventional survey methods is reported here. A high-resolution digital outcrop model (DOM) generation method for rock exposures based on unmanned aerial vehicle (UAV) photogrammetry integrated with a structure from-motion (SfM) technique was introduced. A digital procedure based on mathematical algorithms for discontinuity detection, trace mapping and quantitative discontinuity characterization was established. The proposed method was applied to two rock slopes (from Greece and China) and fundamental discontinuity parameters, i.e., the orientation, number of sets, trace length, set spacing, linear frequency, areal frequency and areal intensity were statistically extracted and calculated. Their values were compared with carefully planned manual measurements, i.e., individual discontinuity measurements, scanline method, and window sampling method on the same sites. The results of two sites showed that most deviations are less than 5° for dip direction and dip angle, 0.13 m for exposed discontinuity length, 0.37 m for set spacing, 0.09 m-1 for linear frequency, 0.06 m-2 for areal frequency, and 0.15 m-1 for areal intensity. These deviations are reasonable and acceptable, which confirmed the reliability and accuracy of the developed method. With improved efficiency and workability comparing to conventional methods especially in difficult surveying environments, the UAV-SfM Photogrammetry can potentially become a routine method for on-site rock mass characterization.

Evolution of foreland basin fluvial systems in the mid‐Cretaceous of Utah, USA (upper Cedar Mountain and Naturita formations)

AbstractAn analysis of the sedimentary fill of a foreland basin can provide information on the relative effect of tectonics, base‐level fluctuations and climate during basin development. This study analyzes fluvial strata from the upper Cedar Mountain and Naturita formations of the mid‐Cretaceous foreland basin of Utah (USA) to determine the effects of spatial location within the foreland basin on fluvial planform and architecture. The study results document consistent planform and architecture across the distal foredeep and forebulge depozones during flooding of the Western Interior Seaway suggesting that fluvial planform and architecture did not change as a function of position within foreland basin depozone or as a result of base‐level rise. Outcrop data, virtual outcrop models and satellite imagery were used to perform facies and architectural analysis and to collect dimensional and geometric data. Fluvial channel deposits consist of coarse‐grained, laterally accreting bars deposited within narrow, low to moderate sinuosity channels, that were vertically stacked and encased in floodplain fines regardless of geographic location or stratigraphic position and may represent distal deposits of a distributive fluvial system. Bar elements increased in thickness over time indicating increasing channel depths and enhanced discharge. Palaeohydraulic calculations indicate an increase in discharge from between 315 and 1023 to between 1896 and 5270 m3/s, likely due to enhanced precipitation and/or drainage capture in the catchment and basin. Calculated drainage areas for the system increased from 104 to 105 km2 scale over time. The uppermost fluvial deposits were in close proximity (≤60 km) to contemporaneous shoreface systems as the Western Interior Seaway expanded; yet backwater effects are not observed, suggesting that rising base level had no significant effect on fluvial planform or architecture. These results show that fluvial planform and architecture remained constant despite rising base‐level, changing climate, increased discharge and position in different foreland basin depozones.

Digital re‐evaluation of down‐dip channel‐fill architecture in deep‐water slope deposits: Multi‐scale perspectives from UAV‐SfM

AbstractRecent advances in sea floor measurements and modelling have revealed new insight into submarine channel processes; however, understanding how these short‐term perspectives influence long‐term evolution of submarine channels has been limited by the difficulty in linking processes to products in the stratigraphic record. Outcrops present opportunities to characterise the detailed internal architecture of deep‐water channel fills over a wide range of timescales, but obtaining observations is compounded by challenges in outcrop accessibility and perspective along broad exposures. To demonstrate the potential value of modern remote sensing techniques in supplementing fieldwork, an extensive dip‐oriented outcrop exposure of Cretaceous deep‐water channel deposits was re‐evaluated using a 3D digital outcrop model generated from uninhabited/unmanned aerial vehicle photogrammetry. Results confirmed previous field‐based documentation of depositional element‐scale stratigraphic architecture, but also revealed nuanced internal detail that was not captured from field‐based perspectives alone. Subtle internal channel‐fill architecture, including discontinuous sandstone wedges and the interpreted stratigraphic products of upslope‐migrating bedforms, are also recognised. This study demonstrates the sedimentary detail that can be uncovered by integrating conventional field‐based approaches limited by viewable scale, perspective, and/or accessibility, with emerging remote sensing techniques. The unmanned aerial vehicle photogrammetry approach used here provides valuable supplemental data in the investigation of deep‐water channel system deposits and has the potential to overcome inherent challenges in outcrop mapping for numerous applications.

An Open-Source Algorithm for 3D ROck Slope Kinematic Analysis (ROKA)

The Markland test is one of the most diffused and adopted methods of kinematic analysis for the identification of critical intersections of rock discontinuities that could generate rock failures. Traditionally, the kinematic analysis is based on the use of a stereographic approach that is able to identify the critical combination between the orientations of discontinuities and the rock wall. The recent improvements in the use of Digital Outcrop Models (DOMs) created the conditions for the development of a new automatized approach. We present ROck Slope Kinematic Analysis (ROKA) which is an open-source algorithm aimed at performing the Kinematic Analysis using the discontinuity measures collected onto a 3D DOM. The presented algorithm is able to make a local identification of the possible critical combination between the identified discontinuities and the orientation of the slope. Using this approach, the algorithm is able to identify on the slope the presence of critical combinations according to the traditional kinematic analysis of planar failure, flexural toppling, wedge failure, and direct toppling modes of failures and then visualize them on DOMs. In this way, the traditional approach is more effective and can be adopted for a more detailed analysis of large and complex areas.

Quantifying Downstream, Vertical and Lateral Variation in Fluvial Deposits: Implications From the Huesca Distributive Fluvial System

Quantifying sedimentary deposits is crucial to fully test generic trends cited within facies models. To date, few studies have quantified downstream trends alongside vertical and lateral variations within distributive fluvial systems (DFS), with most studies reporting qualitative trends. This study reports on the generation of a quantitative dataset on the Huesca DFS, Ebro Basin, Spain, in which downstream, vertical and lateral trends in channel characteristics are analyzed using a fusion of field data and virtual outcrop model derived data (VOM). Vertical trend analysis reveals that the exposed portion of the Huesca DFS does not show any systematic changes through time, which suggests autogenic-driven local variability. Proximal-to-distal trends from field data display a downstream decrease in average channel body thicknesses (13.1–0.7 m), channel deposit percentage (70–4%), and average storey thicknesses (5.2–0.7 m) and confirm trends observed on other DFS. The VOM dataset shows a similar downstream trend in all characteristics. The range in values are, however, larger due to the increase in amount of data that can be collected, and trends are thus less clear. This study therefore highlights that standard field techniques do not capture the variability that can be present in outcrops. Channel percentage was found to be most variable (37% variation) in the medial setting, whereas channel body thickness is most variable (∼15 m range) in the proximal setting. Storey thickness varied in both the proximal and medial settings (range of 9 and 11 m for field and VOM data respectively) becoming more consistent downstream. Downstream shifts in architecture are also noted from massive, highly amalgamated channel-body sandstones in proximal regions to isolated or offset-stacked channel-bodies dominating the distal region. Trends are explained by spatial variability in DFS processes and preservation potential. The overlap present indicates that no single value is representative of position within a DFS, which has important implications for interpreting the location that a data point sits within a DFS when using limited (i.e., single log) datasets. These comparative results contribute to improving the accuracy of system-scale downstream predictions for channel characteristic variability within subsurface deposits.

New Understanding of Bar Top Hollows in Dryland Sandy Braided Rivers from Outcrops with Unmanned Aerial Vehicle and Ground Penetrating Radar Surveys

Bar top hollows (BTHs) are morphological elements recognized in modern braided rivers; however, information regarding their depositional features and types of filling units in ancient strata is unclear. This is an important reason behind why it is difficult to identify BTH units in subsurface reservoirs. A Middle Jurassic dryland sandy braided river outcrop in northwestern China is characterized in this study through the application of an unmanned aerial vehicle (UAV) surveying and mapping, and ground penetrating radar (GPR). A workflow of UAV data processing has been established, and a 3D digital outcrop model has been built. By observation and measurement of the outcrop model and GPR profiles, two types of BTH filled units were found: (a) sandstone-filled, and (b) mudstone-filled hollows. Both of these units were located between two adjacent bar units in an area that is limited to a compound bar, and were developed in the upper part of a braided bar depositional sequence. The ellipse-shaped, sandstone-filled unit measures 10 m × 27 m in map view and reaches a maximum thickness of 5 m. The transversal cross-section across the BTHs displays a concave upward basal surface, while the angle of the inclined structures infilling the BTHs decreases up-section. The GPR data show that, in the longitudinal profile, the basal surface is relatively flat, and low-angle, inclined layers can be observed in the lower- and middle part of the sandstone-filled BTHs. In contrast, no obvious depositional structures were observed in the mudstone-filled BTH in outcrop. The new understanding of BTH has a wide application, including the optimization of CO2 storage sites, fresh water aquifers exploration, and oil and gas reservoir characterization.

InCorr: Interactive Data-Driven Correlation Panels for Digital Outcrop Analysis.

Geological analysis of 3D Digital Outcrop Models (DOMs) for reconstruction of ancient habitable environments is a key aspect of the upcoming ESA ExoMars 2022 Rosalind Franklin Rover and the NASA 2020 Rover Perseverance missions in seeking signs of past life on Mars. Geologists measure and interpret 3D DOMs, create sedimentary logs and combine them in 'correlation panels' to map the extents of key geological horizons, and build a stratigraphic model to understand their position in the ancient landscape. Currently, the creation of correlation panels is completely manual and therefore time-consuming, and inflexible. With InCorr we present a visualization solution that encompasses a 3D logging tool and an interactive data-driven correlation panel that evolves with the stratigraphic analysis. For the creation of InCorr we closely cooperated with leading planetary geologists in the form of a design study. We verify our results by recreating an existing correlation analysis with InCorr and validate our correlation panel against a manually created illustration. Further, we conducted a user-study with a wider circle of geologists. Our evaluation shows that InCorr efficiently supports the domain experts in tackling their research questions and that it has the potential to significantly impact how geologists work with digital outcrop representations in general.