Characterization of a fluvial aquifer at a range of depths and scales: the Triassic St Bees Sandstone Formation, Cumbria, UK

Fluvial sedimentary successions represent porous media that host groundwater and geothermal resources. Additionally, they overlie crystalline rocks hosting nuclear waste repositories in rift settings. The permeability characteristics of an arenaceous fluvial succession, the Triassic St Bees Sandstone Formation in England (UK), are described, from core-plug to well-test scale up to ~1 km depth. Within such lithified successions, dissolution associated with the circulation of meteoric water results in increased permeability (K~10−1–100 m/day) to depths of at least 150 m below ground level (BGL) in aquifer systems that are subject to rapid groundwater circulation. Thus, contaminant transport is likely to occur at relatively high rates. In a deeper investigation (> 150 m depth), where the aquifer has not been subjected to rapid groundwater circulation, well-test-scale hydraulic conductivity is lower, decreasing from K~10−2 m/day at 150–400 m BGL to 10−3 m/day down-dip at ~1 km BGL, where the pore fluid is hypersaline. Here, pore-scale permeability becomes progressively dominant with increasing lithostatic load. Notably, this work investigates a sandstone aquifer of fluvial origin at investigation depths consistent with highly enthalpy geothermal reservoirs (~0.7–1.1 km). At such depths, intergranular flow dominates in unfaulted areas with only minor contribution by bedding plane fractures. However, extensional faults represent preferential flow pathways, due to presence of high connective open fractures. Therefore, such faults may (1) drive nuclear waste contaminants towards the highly permeable shallow (< 150 m BGL) zone of the aquifer, and (2) influence fluid recovery in geothermal fields

Quantitative characterization of the sedimentary architecture of Gilbert-type deltas

Steep-fronted Gilbert-type deltas are common features of tectonically active settings, as well as of physiographic settings where accommodation is dictated by landforms with steeply inclined margins, such as incised valleys, fjords, and proglacial lakes. Existing facies models for Gilbert-type deltas are largely qualitative; this study presents a quantitative analysis of the variability in facies architectures of such deltas. A database approach is used to characterize the preserved sedimentary architecture of 62 Gilbert-type deltas of Cretaceous to Holocene ages developed in various basin settings worldwide. Data on 706 architectural elements and 12,872 facies units are used to develop quantitative facies models that describe the variability in architecture and facies of Gilbert-type deltas at multiple scales of observation, and to account for the possible controls exerted by allogenic and autogenic factors. The analysed data reveal high variability in the geometry and facies of Gilbert-type deltas. The thickness of the examined deltas varies from 2 to 650 m, yet positive scaling between delta thickness and length is consistently recognized across the studied examples, which is interpreted in terms of relationships between accommodation, sediment supply and delta lifespan. Based on their facies character, the deltas are classified into gravel- and sand-dominated types, with contrasting facies organizations of topset, forest and bottomset elements, and by different relationships between facies and dimensions; yet, both types exhibit significant spatial variability in the distribution of sediments linked to debris flows or turbidity currents, and in vertical stratal trends. Changes in allogenic (e.g., changes in base-level or, rate of sediment influx) and autogenic mechanisms (e.g., channel avulsion) are inferred as causes for significant differences in facies organization, both across distinct deltas and within individual deltaic edifices. The study highlights the marked variety of architectural and sedimentological (e.g., grain size, depositional processes) properties of Gilbert-type deltas. Findings allow the relation of outcrop observations to a general template and the quantitative determination of potential analogues with which to assist the prediction of the dimensions and facies of deltaic sedimentary bodies in the subsurface. Information on facies relationships and basinward variability of Gilbert-type deltas is valuable for the recognition and correlation of deltaic bodies in the subsurface

Hierarchical classifications of the sedimentary architecture of deep-marine depositional systems

Hierarchical classifications are used in the field of clastic deep-marine sedimentary geology to assign spatial and temporal order to the sedimentary architecture of preserved deep-marine deposits and to genetically related modern landforms. Although such classifications aim to simplify the description of complex systems, the wide range of developed approaches limits the ease with which deep-marine architectural data derived from different sources can be reconciled and compared. This work systematically reviews and compares a selection of the most significant published hierarchical schemes for the description of deep-marine sedimentary architecture. A detailed account of each scheme is provided, outlining its aims, environmental contexts and methods of data collection, together with the diagnostic criteria used to discern each hierarchical order from observational standpoints (e.g., via facies associations, geometry, scale and bounding-surface relationships) and also on interpretational grounds (e.g., processes and sub-environments of deposition). The inconsistencies and pitfalls in the application of each scheme are also considered. The immediate goal of this review is to assist sedimentologists in their attempts to apply hierarchical classifications, both in the contexts in which the classifications were originally developed and in alternative settings. An additional goal is to assess the causes of similarities and differences between schemes, which may arise, for example, in relation to their different aims, scales of interest or environmental focus (e.g., channelized or lobate units, or both). Similarities are found between the approaches that commonly underlie the hierarchical classifications. Hierarchies are largely erected on the basis of common types of observations, in particular relating to the lithology and geometries of deposits, in association with analysis of bounding-surface characteristics and relationships. These factors are commonly considered in parallel with their associated genetic interpretations in terms of processes or (sub-) environments of deposition. A final goal of the review is to assess whether a universal standard for the description of deep-marine sedimentary architecture can be devised. Despite the commonalities that exist between classification approaches, a confident reconciliation of the different hierarchical classification schemes does not appear to be achievable in the current state of knowledge

Hierarchical classifications of the sedimentary architecture of deep-marine depositional systems

Hierarchical classifications are used in the field of clastic deep-marine sedimentary geology to assign spatial and temporal order to the sedimentary architecture of preserved deep-marine deposits and to genetically related modern landforms. Although such classifications aim to simplify the description of complex systems, the wide range of developed approaches limits the ease with which deep-marine architectural data derived from different sources can be reconciled and compared. This work systematically reviews and compares a selection of the most significant published hierarchical schemes for the description of deep-marine sedimentary architecture. A detailed account of each scheme is provided, outlining its aims, environmental contexts and methods of data collection, together with the diagnostic criteria used to discern each hierarchical order from observational standpoints (e.g., via facies associations, geometry, scale and bounding-surface relationships) and also on interpretational grounds (e.g., processes and sub-environments of deposition). The inconsistencies and pitfalls in the application of each scheme are also considered. The immediate goal of this review is to assist sedimentologists in their attempts to apply hierarchical classifications, both in the contexts in which the classifications were originally developed and in alternative settings. An additional goal is to assess the causes of similarities and differences between schemes, which may arise, for example, in relation to their different aims, scales of interest or environmental focus (e.g., channelized or lobate units, or both). Similarities are found between the approaches that commonly underlie the hierarchical classifications. Hierarchies are largely erected on the basis of common types of observations, in particular relating to the lithology and geometries of deposits, in association with analysis of bounding-surface characteristics and relationships. These factors are commonly considered in parallel with their associated genetic interpretations in terms of processes or (sub-) environments of deposition. A final goal of the review is to assess whether a universal standard for the description of deep-marine sedimentary architecture can be devised. Despite the commonalities that exist between classification approaches, a confident reconciliation of the different hierarchical classification schemes does not appear to be achievable in the current state of knowledge

Multi-storey shear type buildings under earthquake loading: Adversarial learning-based prediction of the transient dynamics and damage classification

In this paper, the transient dynamic response of shear type multi-storey buildings subjected to earthquake ground motion is generated via adversarial learning technique under different damage conditions, starting from the relevant undamaged responses. A Representation Generative Adversarial Network (RepGAN) is trained on a database of synthetic accelerograms to obtain the responses of the buildings in their undamaged state and in case of plausible damage patterns. Each structural response, represented by a set of time histories to catch the lateral storey displacements/accelerations, is encoded to learn its hidden features and infer the associated damage class. By re-sampling the encoded latent space, it is shown how to switch from the undamaged to the damaged class and to decode the damaged response. The proposed methodology enables damage classification in shear-type multi-storey buildings proving that it can successfully detect damage and assess two different damage severity levels whenever the time-history of a sufficient number of floors is monitored. To outline the generalization capability of the proposed approach, the signal reconstruction is quantitatively assessed for all damage conditions and even in case of a damage condition different from the one corresponding to the encoded signal

A novel method for estimating sandbody compaction in fluvial successions

Clastic sedimentary successions are subject to variable amounts of compaction, which causes a decrease in both the thickness and porosity of sand-rich depositional units. Methods for estimating the degree of sediment compaction are needed for characterizing changes in the geometry and petrophysical properties of depositional elements in relation to their burial history. Conventional methods for estimating compaction of rock successions through the application of several empirical equations return estimations whose uncertainties can be significant, and integrative approaches that can produce reliable estimations are therefore desirable. To this end, a new method is proposed here for the estimation of the degree of compaction of sandbodies in ancient channelized fluvial successions. For outcropping fluvial successions, the compacted geometry of channel-fill margins cut into non-cohesive deposits can be measured, whereas the decompacted angle of repose of the material originally forming the channel banks can be estimated experimentally. Sediment compaction can therefore be estimated by comparing the observed geometry of the uppermost part of a channel-fill margin with the angle of repose of the non-cohesive bank material. The proposed method has been applied to three different sand-prone fluvial successions seen in outcrop, for the purposes of (i) illustrating the approach, and (ii) testing it through a comparison of its estimations against results produced by a conventional method based on thin-section observations. The comparison demonstrates that the two methods yield similar results, highlighting how the proposed approach can be readily applied to the assessment of compaction in clastic successions, for scopes of both pure and applied geological research