Abstract Landslides are common in aquatic settings worldwide, from lakes and coastal environments to the deep sea. Fast-moving, large-volume landslides can potentially trigger destructive tsunamis. Landslides damage and disrupt global communication links and other critical marine infrastructure. Landslide deposits act as foci for localized, but important, deep-seafloor biological communities. Under burial, landslide deposits play an important role in a successful petroleum system. While the broad importance of understanding subaqueous landslide processes is evident, a number of important scientific questions have yet to receive the needed attention. Collecting quantitative data is a critical step to addressing questions surrounding subaqueous landslides. Quantitative metrics of subaqueous landslides are routinely recorded, but which ones, and how they are defined, depends on the end-user focus. Differences in focus can inhibit communication of knowledge between communities, and complicate comparative analysis. This study outlines an approach specifically for consistent measurement of subaqueous landslide morphometrics to be used in the design of a broader, global open-source, peer-curated database. Examples from different settings illustrate how the approach can be applied, as well as the difficulties encountered when analysing different landslides and data types. Standardizing data collection for subaqueous landslides should result in more accurate geohazard predictions and resource estimation.

Abstract Eocene dykes extending over 50 km along the southern margin of the Ladakh batholith (NW India) fall into two main groups showing different orientations, as well as different isotope and trace element geochemistry. Both dyke families formed in the same tectonic setting over a time span of approximately 4 Ma. However, each family is far from monolithic, and therefore we tested several statistical approaches to identify geochemical subgroups from rare earth element (REE) data and relate them to magmatogenetic processes. Hierarchical clustering and multidimensional scaling calculate similarities/dissimilarities among individuals of a population. Both statistical tools, when applied to the Ladakh dykes, reflect the east–west dichotomy. However, detailed quantification of the resulting grouping varies according to input data. Normalization to chondrites yields slightly different groupings from unnormalized concentration data. Population internal REE normalization provides the most accurate grouping, as revealed by the fact that multiple samples from the same dyke are assigned the closest relatedness. Independently from normalization, east–west dichotomy is mirrored by marked differences in the degree of crustal assimilation and magma evolution, pointing to kilometre-scale geological heterogeneity. Finally, dykes intruding the Ladakh batholith 150 km SE of the present samples are geochemically similar, but cluster as a distinct group.

Abstract Microanalysis can provide rapid, quantitative characterization of mineral systems that complements the field- and core-scale observations traditionally made in ore deposits. We review recent innovations in microanalytical procedures and their application to studies of ore deposits. Case studies are presented examining how microanalysis can provide constraints on macroscopic processes within mineral systems. Synchrotron X-ray fluorescence shows centimetre-scale chemical variations associated with proximity to mineralization in samples from Sunrise Dam Gold Mine, Western Australia. Pseudomorphs of igneous plagioclase and chemically driven recrystallization interpreted from electron backscatter diffraction suggest that the system was dominated by fluid-driven brecciation with very little shearing. Both the fluid chemistry and fluid pressure evolved during a protracted sequence of vein formation and alteration accompanying gold mineralization. A second case study of sulphide mineralogy at the Mt Keith nickel sulphide deposit, Western Australia demonstrates how X-ray computed tomography combined with trace element mapping can constrain the chemistry and dynamics of magmatic systems. Large-scale interaction between silicate and sulphide melts, shown by homogenous palladium enrichment in pentlandite, leads to a large proportion of globular ores with a high nickel content. Increasing use of microanalysis in ore deposit geology is resulting in the constant reassessment of established models for ore genesis though a combination of micro- and macroscale datasets.

Abstract This study investigates the Late Aptian–earliest Albian platform carbonates of the Benicàssim area (Maestrat Basin, Spain) in order to assess the relationship between bed-parallel stylolites and the flow of diagenetic fluids during dolomitization and subsequent hydrothermal alteration. Dolostones and burial dolomite and calcite cements were studied by a combination of field geology and standard petrographic and isotope analysis. Field data indicate that dolostones are closely associated with seismic-scale synsedimentary faults, preferentially replace grain-dominated facies and typically show wavy dolomitizing fronts that mostly correspond to bed-parallel stylolites. The dolostones are corroded and contain bed-parallel pores that are filled with hydrothermal saddle dolomite and blocky calcite cements. This late calcite cement frequently engulfs clasts of the host dolostones, suggesting that hydraulic brecciation likely associated with overpressured fluid occurred. Results indicate that stylolites play a key role in the distribution of dolostones and subsequent hydrothermal mineralization. During the replacement stage, stylolites acted as baffles for the dolomitzing fluids controlling lateral fluid flow and resulting in the stratabound dolostone distribution. During the post-dolomitization stage, stylolites became preferred pathways for overpressured hydrothermal corrosive and mineralizing fluids that likely came from the underlying basement, and increased bed-parallel stylolitic porosity and probably also permeability.

Abstract Discrete fracture and matrix (DFM) homogenization, simultaneously capturing reservoir layers and contained fractures, is an alternative to discrete fracture network (DFN) upscaling. Here, the DFM approach was applied to a fractured carbonate reservoir. Honouring geostatistical data from well logs, near-well multilayer reservoir models were constructed and analysed. Fracture aperture variations were modelled with a new semi-analytical model including a special treatment of layer-restricted fractures. Important results concern both pre-processing of stochastically generated DFMs for finite-element meshing, and the ensemble permeability values obtained by numerical homogenization of single v. multilayer models, respectively. Upscaling by volume averaging of vertically stacked single-layer DFMs results only in a fraction of the equivalent horizontal permeability that is obtained by homogenization of the multilayer models. Inspection of the flow patterns shows that this discrepancy arises because many fractures contact each other at layer boundaries fostering cross-flow. This effect is further enhanced where fractures intersect multiple layers. Compared to earlier DFN models for this reservoir, the DFM-derived fracture and matrix ensemble permeabilities are up to four times higher, highlighting how important it is to include the rock matrix into equivalent permeability calculations.

Abstract: Salt is mechanically weaker than other sedimentary rocks in rift basins. It commonly acts as a strain localizer, and decouples supra- and sub-salt deformation. In the rift basins discussed in this paper, sub-salt faults commonly form wide and deep ramp synclines controlled by the thickness and strength of the overlying salt section, as well as by the shapes of the extensional faults, and the magnitudes and slip rates along the faults. Upon inversion of these rift basins, the inherited extensional architectures, and particularly the continuity of the salt section, significantly controls the later contractional deformation. This paper utilizes scaled sandbox models to analyse the interplay between sub-salt structures and supra-salt units during both extension and inversion. Series 1 experiments involved baseline models run using isotropic sand packs for simple and ramp-flat listric faults, as well as for simple planar and kinked planar faults. Series 2 experiments involved the same fault geometries but also included a pre-extension polymer layer to simulate salt in the stratigraphy. In these experiments, the polymer layer decoupled the extensional and contractional strains, and inhibited the upwards propagation of sub-polymer faults. In all Series 2 experiments, the extension produced a synclinal hanging-wall basin above the polymer layer as a result of polymer migration during the deformation. During inversion, the supra-polymer synclinal basin was uplifted, folded and detached above the polymer layer. Changes in thickness of the polymer layer during the inversion produced primary welds and these permitted the sub-polymer deformation to propagate upwards into the supra-salt layers. The experimental results are compared with examples from the Parentis Basin (Bay of Biscay), the Broad Fourteens Basin (southern North Sea), the Feda Graben (central North Sea) and the Cameros Basin (Iberian Range, Spain).

Abstract: Fault-segment boundaries initiate, evolve and die as a result of the propagation, interaction and linkage of normal faults during crustal extension. However, little is known about the distribution, evolution and controls on the development of relay ramps, which are the key structures developed at synthetic segment boundaries. In this study, we use a series of scaled physical models (wet clay) to investigate the distribution and evolution of fault-segment boundaries within an evolving normal-fault population during orthogonal extension. From the models, we can establish a simple geometrical classification for segment boundaries, analyse their spatial and temporal evolution, and identify key factors that influence their variability. Development of overlapping fault tips is a prerequisite for fault growth via segment linkage. Synthetic segment boundaries are the most common segment boundary type developed in the models. The proportion of synthetic segment boundaries in the total fault population increases with increasing strain, whereas conjugate (antithetic) segment boundaries are very rare. Hanging-wall-breached relay ramps are the most common type (>70%) of breached-segment boundary, followed by footwall-breached relay ramps (<25%). Transfer faults are uncommon in our models. The type of breached segment boundary that develops cannot be predicted based on fault overlap to fault spacing aspect ratio alone. Instead, we show that fault linkage occurs in a range of styles across a wide range of fault overlap to fault spacing ratios (1:1–7:1). Furthermore, we show that fault spacing is constrained by stress-reduction shadows at the time of fault nucleation, whereas fault overlap changes during fault growth and interaction. Our study thus shows that scaled physical models are a powerful tool to assess the style, distribution and controls on the evolution of synthetic segment boundaries developing in rifts. Predictions from these models must now be assessed with data from natural examples exposed in the field or imaged in the subsurface.