The Main Buntsandstein Subgroup in the Roer Valley Graben in the southern Dutch subsurface is a sand-prone sedimentary interval deposited in a fluvial-aeolian environment, and is currently investigated for its suitability as target for low-entalpy geothermal exploration. The current depositional models in the Roer Valley Graben do not fully address the facies heterogeneities within and between Buntsandstein sedimentary units and their impact on the prediction of reservoir architecture. A detailed analysis of the Main Buntsandstein sedimentary facies heterogeneities to de-risk future sustainable energy operations is therefore crucial. In the present study, the sedimentology and lithostratigraphy of the Buntsandstein are assessed in a multidisciplinary analysis by use of a subsurface dataset composed of well cores, gamma-ray logs, and thin section data. The deposition of the Main Buntsandstein sediments in the Roer Valley Graben is dominated by different fluvial processes, with minor aeolian reworking. River planform style evolved through geological time from highly mobile and ephemeral to more perennial in nature. These changes in river style seem to be dictated by a decrease in climatic aridity along with a decrease in tectonic activity. The depositional processes resulted in the development of six lithofacies associations, developing three different types of reservoir architectures with their own set of heterogeneities at different spatial scales. Amalgamated, stacked sandstones have the highest net-to-gross (N/G) with a high degree of lateral and vertical connectivity, and the highest average porosity and permeability. Compensational-stacked sandstone reservoirs have a lower N/G and are the most heterogeneous due to the frequent occurrence of cemented intervals as well as mud drapes in the sandstone bodies. Marginal isolated sandstones show a well preserved relationship between reservoir properties and depositional facies, while more data are needed to resolve the spatial connectivity and lateral continuity of these sandstone bodies. The results of this study enhance the understanding of Lower Triassic reservoir architecture and sedimentary heterogeneities in the Roer Valley Graben that can be applied well beyond the area and provide a solid basis for future investigation of the relationship between sedimentary facies, diagenesis, and reservoir quality.

An advection–diffusion model of fluvial processes was used to analyze the stratigraphic expression of avulsions in terminal river systems and understand their control on basin-fill architecture. The initial and boundary conditions of the model runs (i.e., catchment area, smoothed initial topographic surface, grain-size distribution and sediment supply rates) were extracted from the modern Rio Colorado dryland terminal river system in the Altiplano Basin (Bolivia). Water-discharge and sediment-load values were derived from global regression curves and the BQART equation, respectively. To evaluate the robustness of the simulations, the model was tested under increasing sediment-load scenarios ranging from 0.003 m³/s to 0.095 m³/s. Data-model comparison provided insights into the role of avulsions in the geomorphological evolution of terminal river systems. The observed stacking of sediments, as captured by geospatial and geochronological data from the Rio Colorado, is consistent with the high sediment-load scenarios, which start with a single-thread fluvial channel that in time radially expands over the floodplain by successive river avulsions on account of alluvial-ridge aggradation and channel-floor elevation above the surrounding floodplain. The model output shows a laterally extensive, convex-upwards lobate topography which is in agreement with the lateral and longitudinal geomorphology in the upper and lower coastal plain of the Rio Colorado. The simulated inter-avulsion period, which is the time period between two successive full (or stabilized) avulsions in the model, varies from 0.18 to 1.2 kyr and is consistent with the OSL-age determination in the Rio Colorado with inter-avulsion periods up to 1.28 ± 0.34 kyr.

Fluvial depositional architecture in an unconfined environment is governed by sediment dispersal across the alluvial plain through river-path switching by avulsion. Documented inter-avulsion periodicity from modern rivers ranges from tens to over a thousand years. In this study, a quantitative spatio-temporal reconstruction of avulsion history is presented of the non-vegetated and pristine modern Río Colorado dryland river system in the semi-arid Altiplano Basin (Bolivia), based on the integrated analysis of satellite imagery and absolute age dating using optically stimulated luminescence, complemented with sedimentological and geomorphological ground-truth data. This approach enables us to reconstruct the chronological order of channel belts of the Río Colorado, to determine avulsion recurrence time and inter-avulsion periodicity, to identify mechanisms for flow path changes, and to present a morphodynamic model for the spatio-temporal evolution of fluvial deposits in a semi-arid environment. In a maximum timespan of 12.71 ± 1.5 ka, successive avulsions of the Río Colorado created a sheet of interconnected fluvial deposits, consisting of diverging and juxtaposed alluvial ridges that formed by sediment aggradation in point bars, crevasse splays, levees, and on the channel floor. The ridges show lateral onlap and amalgamation as the result of repeated avulsion and compensational stacking, whereby the river avoided the positive alluvial-ridge relief of its precursors. The resultant morphology is fan-shaped, convex-up with a surface area of approximately 500 km ² and a maximum observed thickness of 3 m. The results show inter-avulsion periods of the river of up to 1.28 ± 0.34 ka. A paucity in fluvial activity around 2 ka BP, and at present, is interpreted as the result of low river discharge related to long-term dry periodicity in the El Niño Southern Oscillation circulation system. Each river path started as a low sinuous, single-thread channel in a narrow belt, and in time increased its width and sinuosity by point-bar expansion and rotation.

Meandering-river geomorphology, forming abandoned channels/lakes with organic carbon-burial and microbial reductive dissolution, play many crucial roles in controlling arsenic (As) fluxes in sinks such as contaminated aquifers of riverine alluvial plains across the world. Suhiya oxbow-lake in the middle alluvial plain of the River Ganga, was selected as the natural laboratory. A top-down multidisciplinary approach was chosen employing satellite imagery to analyse the annual oxbow-lake surface vegetation dynamics (Eichhornia and Hydrilla). Side-scan sonar profiles across two oxbow lakes along with River Ganga core data and vintage topographical maps, estimated the lake-sedimentation rate of 9.6 cm/yr. Organic carbon [amino acids, aromatics, lingo-phenols and lipids hydrocarbons] infiltration-based on hydrophobicity and molecular-mass was detected at different depths along the water and sedimentary column. Elemental analysis showed lake surface to groundwater the As conc. varied from (0.37 to 185 μg/l). A microbial diversity based study showed that large sized photoautotrophs Nostoc, Anabaena are replaced by Fe-oxido-reducing As-metabolizing bacteria e.g. Acidovorax, Dechloromonas and enteric organisms e.g. Enterobacter, Salmonella at bottom of water column. Based on these inferences, a conceptual organic carbon transport model was constructed to understand the preferential preservation and microbial diagenesis resulting in mobilization of As and other geogenic elements.

The Rotliegend feather-edge area in the central part of the endorheic Southern Permian Basin in the Dutch offshore is characterized by a predominance of mud-prone, evaporite-bearing playa and lake deposits with a subordinate amount of interbedded, thin, fluvial sheet sandstones. The distribution and lateral facies changes of the sandstone bodies have been analyzed by generating a long-range, high-resolution chronostratigraphic correlation framework. The correlation technique of pattern matching of GR logs was applied, supported by calculating spectral trend curves. Flooding events are the primary near-synchronous correlation surfaces, which can be traced up to and over 100 km. The basin setting of the Southern Permian Basin, the studied sandstone depositional architecture (logs) and sedimentary characteristics (core) are analogous to the depositional setting of laterally-amalgamated terminal lobes of dryland-river systems in an endorheic basin, such as the Holocene Altiplano Basin in Bolivia, present-day Lake Eyre (Australia) and the Miocene Ebro Basin (Spain). The integrated approach has yielded a stratigraphic reservoir-architecture framework in which the reservoir sandstones, with net sand up to 10 m, have been identified as amalgamated terminal-splay sandstone sheets formed at the end of dryland-river pathways, alternating with lacustrine mudstone layers deposited during short-duration, high-magnitude flooding in intermittent wet climate periods.

Sandy braided dryland rivers, deposited under arid to semi-arid conditions, constitute important clastic reservoirs worldwide whose reservoir quality reflects the effect of primary sediment properties on near-surface diagenetic processes. A literature review is presented of existing facies models, based on geomorphological analysis of modern perennial braided rivers, further illustrated with own outcrop and subsurface examples of dryland river deposits in: (a) Argana Basin (Triassic, Morocco), (b) Iberian Meseta (Triassic, Central SE Spain), (c) Huesca Fluvial Fan (Miocene, Spain) and (d) Rotliegend hydrocarbon reservoir in the Southern Permian Basin (The Netherlands). The facies models, combined with the analyses of the rock record, provides a comprehensive depositional framework where the influence of depositional characteristics, such as grain-size and sorting variations, interstitial clay distribution and composition and amount of intrabasinal components, on the extent and pathway of near-surface mechanical and chemical processes can be investigated. The particular dryland setting is characterized by prolonged periods of inactivity and short, episodic periods of peak discharge, which lead to the transport and deposition of poorly-sorted, clay-rich extra- and intraformational conglomeratic sediments upstream. Downstream, channels, mid-channel and bank-attached bars develop with conspicuous anisotropic trough and tabular cross-stratified sandstones. The most common near-surface diagenetic processes that alter the textural properties of these deposits are the rapid decrease of porosity and permeability due to grain-rearrangements and mechanical compaction of mud intraclasts along with pervasive early carbonate cementation. The results of this study will help to better configure the boundary conditions (e.g., external versus local supply for carbonates cements) in state-of-the-art reservoir quality forward models for ancient dryland river sandstones, which are especially prominent in Devonian, Permian, Triassic and Jurassic reservoir settings.

In the past 10 years the mature hydrocarbon province the West Netherlands Basin has hosted rapidly expanding geothermal development. Upper Jurassic to Lower Cretaceous strata from which gas and oil had been produced since the 1950s became targets for geothermal exploitation. The extensive publicly available subsurface data including seismic surveys, several cores and logs from hundreds of hydrocarbon wells, combined with understanding of the geology after decades of hydrocarbon exploitation, facilitated the offtake of geothermal exploitation. Whilst the first geothermal projects proved the suitability of the permeable Upper Jurassic to Lower Cretaceous sandstones for geothermal heat production, they also made clear that much detail of the aquifer geology is not yet fully understood. The aquifer architecture varies significantly across the basin because of the syn-tectonic sedimentation. The graben fault blocks that contain the geothermal targets experienced a different tectonic history compared to the horst and pop-up structures that host the hydrocarbon fields from which most subsurface data are derived. Accurate prediction of the continuity and thickness of aquifers is a prerequisite for efficient geothermal well deployment that aims at increasing heat recovery while avoiding the risk of early cold-water breakthrough. The potential recoverable heat and the current challenges to enhance further expansion of heat exploitation from this basin are evident. This paper presents an overview of the current understanding and uncertainties of the aquifer geology of the Upper Jurassic to Lower Cretaceous strata and discusses new sequence-stratigraphic updates of the regional sedimentary aquifer architecture.