Basement Features Research Articles

Experimental Study on the Anti-Scouring Characteristics of Bedrock in Engineering Reservoir Areas That Are Conducive to Sustainable Development

High-speed water flow conditions can cause erosion of the bedrock in engineering areas. Due to the lack of accurate evaluation of bedrock scour and erosion rates, there has been a consumption of manpower and resources without achieving satisfactory engineering outcomes. Therefore, studying the scouring and erosion effects of water flow on bedrock is of significant importance for maintaining the sustainable development and safety of engineering projects. Using the bedrock prototype from the Xiaonanhai site in the upper reaches of the Yangtze River, a model test device was developed to conduct anti-scour tests on the bedrock. The study quantitatively examined the basic physical properties, incipient erosion velocity, and erosion rates of different types of bedrock. The study found that the prototype bedrock under natural exposure, submerged immersion, and alternating wet and dry conditions showed a trend of decreased tensile strength, with the alternating wet and dry conditions being the most detrimental to maintaining the physical properties of the rock mass. The anti-scour velocity of silty claystone and clayey siltstone samples increased with the increase in tensile strength, and the erosion rate increased with the increase in shear stress. If the shear stress is kept constant, the erosion rate decreases with the increase in tensile strength. The erosion rate is inversely proportional to the ratio of the bedrock’s tensile strength to the riverbed shear stress, with the fitting relationship showing a piecewise linear distribution. The research results can provide guidance for the safe production of engineering involving bedrock erosion in engineering reservoir areas that are conducive to sustainable development.

Geophysical and geochemical characterization of Odogbo Dumpsite, Ijebu Ijesa, Southwestern Nigeria.

Due to incessant contamination of the groundwater system near the dumpsite in southwestern Nigeria Basement Complex, this study seeks to evaluate the impact of the Odogbo dumpsite on the local groundwater system by integrating geophysical and geochemical methodologies. Aeromagnetic data covering the study area was acquired, processed, and enhanced to delineate basement features that could potentially be passing plumes to the groundwater system. Concurrently, geoelectric methods using 2-D dipole-dipole imaging and vertical electrical sounding (VES) were utilized to characterize the vulnerability indices of the lithologies underlying the dumpsite. The resistivity data was collected with the UltraminiRES resistivity meter. Vulnerability assessment of the regolith was conducted through longitudinal conductance rating. Water samples from the vicinity of the dumpsite were analyzed using a spectra AA220 atomic absorption spectrophotometer (AAS). The results of magnetic derivatives and analytical signals filters revealed that the Odogbo dumpsite is directly situated atop lineaments trending mainly in an NE-SW direction. The 2-D resistivity model depicted the extent of the leachate plume percolation, characterized by resistivity values below 20 Ωm. The curve types identified from VES results were A, H, HK, and KQ while the geoelectric layers were identified as topsoil, weathered layer, lateritic layer, and fresh/fracture basement. The protective capacity varied across the area, from 0.02 to 0.473 mhos, signifying weak to moderate protective capacity of the overlying layer. Most elemental parameters tested fell below the World Health Organization (WHO) permissible values and some were within WHO standards except iron. All the water sampled were rated poor to unsuitable as their water quality index (WQI) ranged between 232.81357 and 1520.88776 due to high elemental iron content which could be from other sources. The study area is safe from contamination for now but there is a high tendency that the area may be contaminated in future; hence, the need to monitor the region periodically is highly recommended.

Comparison of the Dynamics of the Flowing Drainage Network and Water Chemistry for Four Headwater Catchments

ABSTRACTThe re‐emergence of water in dry stream reaches affects streamwater chemistry due to the flushing of sediment and nutrients from previously dry channels and the increased connectivity between hillslopes and streams. Although these processes have been studied at the reach scale, field data on stream network dynamics and hydrochemistry at the catchment scale are rare. We studied the temporal changes in the flowing drainage network (FDN) and hydrochemistry for two 5‐ha catchments in the Swiss pre‐Alps and two 25‐ to 32‐ha catchments on the Swiss Plateau. At each site, one catchment was relatively flat and had an extensive stream network augmented by artificial ditches, while the other catchment was relatively steep and had a shorter stream network where flow was maintained by springs. The dynamics of the FDN differed substantially for the geomorphologically different catchments in each region, despite their proximity, comparable size, soil and bedrock characteristics. Hydrochemistry and FDN were more dynamic in the flatter catchments with the extensive but shallow channels and ditches. For these catchments, nitrate mobilisation and a notable ‘first flush’ of solutes were observed during most rainfall events. Hydrochemistry and FDN remained relatively stable in the steeper catchments fed by perennial springs. These results highlight the notable spatial variations in stream chemistry responses to precipitation events and the insights that can be gained by joint observations of the FDN and hydrochemical dynamics.

Effect of bedrock permeability on runoff and soil loss in soil-mantled karst slopes under successive rainfall conditions

Soil-mantled karst slopes exhibit rapid surface-belowground hydrological responses to rainfall because thin soil layers cover the bedrock. Bedrock features may play important roles in surface-belowground hydrological processes; however, the underlying mechanisms remain unclear. Herein, the effects of impermeable (no fissures) and permeable (3 % fissure rate) bedrock (BS1 and BS2, respectively) on the surface and belowground runoff and soil loss processes were investigated during three successive rainfall events. During each event, the surface runoff (SR), subsurface runoff (SBR), soil–rock interface flow (SRIF) and bedrock fissure permeation flow (BFPF) were recorded. The results showed that the SR and SBR rates for the BS1 slope were significantly greater than those for the BS2 slope (P < 0.05) under all rainfall events. During rainfall, the SR and SBR accounted for ∼ 19 % and 8 %-12 % of the rainwater on the BS1 slope, respectively, and both were less than 5 % of the rainwater on the BS2 slope. Approximately 40 %-55 % of the rainwater was partitioned into SRIF on BS1 slope, and 54 %-74 % of the rainwater was partitioned into the BFPF on the BS2 slope. Furthermore, the BFPF on the BS2 slope was 33 % greater than the SRIF on the BS1 slope at the 1st rainfall and it increased to 50 % at the 3rd rainfall, suggesting that the successive rainfall increased the difference in rainwater loss from the bedrock surfaces between the slopes with different permeabilities. The surface soil loss rate was very low (< 0.01 g·m2·s−1) due to the low SR, and a significant positive correlation was found between the SR rate and surface soil loss rate (P < 0.01) for both slopes. Compared with that on the BS2 slope, the soil loss on the BS1 slope was greater because of the higher SR rate. The belowground soil loss curves were discontinuous, indicating that the belowground soil loss process was very different from the surface soil loss. Therefore, bedrock permeability has a strong influence on runoff and soil loss in soil-mantled karst slopes, and this effect further increases with successive rainfall events.

Early Paleozoic tectonic affinity of the Lesser Xing'an–Zhangguangcai Range, NE China: A continental arc along the western margin of the Jiamusi Block

The Lesser Xing'an–Zhangguangcai Range (LXZGCR) in NE China was traditionally interpreted to be the eastern part of the Songliao–Xilinhot Accretionary Terrane, separated from the Jiamusi–Khanka Block to the east by the Heilongjiang Complex. However, recent studies have shown that the Heilongjiang Complex formed in the late Paleozoic–early Mesozoic. Therefore, the tectonic affinity of the LXZGCR during the early Paleozoic remains unclear. To constrain this key issue, we present new zircon UPb ages, Hf isotopic compositions, and whole-rock geochemical data for early Paleozoic igneous rocks in the LXZGCR. The new ages, along with previously published data, suggest that the early Paleozoic magmatism in the LXZGCR can be divided into four stages: Middle–Late Cambrian (523–486 Ma), Early Ordovician (485–469 Ma), Late Ordovician (464–443 Ma), and Late Silurian (433–423 Ma). Middle–Late Cambrian igneous rocks are dominated by calc-alkaline I-type granitoids and high-Mg andesite–dacite–rhyolite association. Early Ordovician igneous rocks consist of a suite of calc-alkaline diorites, granodiorites, monzogranites, alkali-feldspar granites, and rhyolites, with I-type affinities. Late Ordovician igneous rocks consist mainly of I-type granitoids with minor A-type granitoids and rhyolites. Late Silurian igneous rocks are composed of calc-alkaline I-type granitoids with minor dacites. The early Paleozoic granitoids and felsic volcanic rocks originated from partial melting of dominantly Paleoproterozoic–Mesoproterozoic lower crust, whereas the Late Cambrian high-Mg andesite–dacite–rhyolite association was probably derived from partial melting of a depleted mantle wedge metasomatized by subduction-related fluids. The rock associations and geochemical characteristics suggest that these early Paleozoic igneous rocks formed in active continental margin and back-arc extension settings. Comparing the early Paleozoic magmatism, zircon Hf isotopic compositions, Nd model ages, and Precambrian basement features of the LXZGCR and the Jiamusi Block suggest that the LXZGCR was part of the same tectonic unit as the Jiamusi Block during the early Paleozoic. We argue that the formation of the early Paleozoic igneous rocks in the LXZGCR was related to the eastward subduction of a branch ocean of the Paleo-Asian Ocean beneath the Jiamusi–Khanka Block.

Crustal Imaging across the Princess Elizabeth Land, East Antarctica from 2D Gravity and Magnetic Inversions

The Princess Elizabeth Land landscape in East Antarctica was shaped by a complex process, involving the supercontinent’s breakup and convergence cycle. However, the lack of geological knowledge about the subglacial bedrock has made it challenging to understand this process. Our study aimed to investigate the structural characteristics of the subglacial bedrock in the Mount Brown region, utilizing airborne geophysical data collected from the China Antarctic Scientific Expedition in 2015–2017. We reconstructed bedrock density contrast and magnetic susceptibility models by leveraging Tikhonov regularized gravity and magnetic inversions. The deep bedrock in the inland direction exhibited different physical properties, indicating the presence of distinct basement sources. The east–west discontinuity of bedrock changed in the inland areas, suggesting the possibility of large fault structures or amalgamation belts. We also identified several normal faults in the western sedimentary basin, intersected by the southwest section of these survey lines. Furthermore, lithologic separators and sinistral strike-slip faults may exist in the northeast section, demarcating the boundary between Princess Elizabeth Land and Knox Valley. Our study provides new insights into the subglacial geological structure in this region, highlighting the violent impact of the I-A-A-S (Indo-Australo-Antarctic Suture) on the subglacial basement composition. Additionally, by identifying and describing different bedrock types, our study redefines the potential contribution of this region to the paleocontinent splicing process and East Antarctic basement remodeling.

Thematic mapping for sediment cascade analysis in small mountain catchments – The case of the Buscagna valley (Lepontine Alps)

The multi-scalarity of mountain systems primarily relates to their complex structural settings, which lead to the fragmentation of geological and geomorphological units. This may have strong implications for the hydrogeomorphological evolution of watersheds and the related sediment cascades. In the framework of this research, we selected the small Buscagna mountain catchment in the Lepontine Alps (Northwestern Italy), where the northern slope comprises very resistant gneissic rocks, while soluble rocks (i.e., marble) – in some case intensely foliated (i.e., calcschist) –crop out along the southern slope. The diversification of geomorphological processes and landforms (i.e., geomorphodiversity) is highly evident, and various techniques are applied to create thematic maps of geomorphological features (landforms; processes; erosion/deposition/deformation), sediment connectivity, and source/store/sink distribution in the Buscagna catchment. The obtained thematic maps were integrated and compared to depict the influence of bedrock features on geomorphological evolution. The geomorphological maps focussed on landforms and processes reveal that glacial and gravity-related processes and permafrost distribution are deeply influenced by the topographic and lithological dichotomy of the catchment. Permafrost distribution is again uneven in the basin, and its degradation allows relevant sediment sources to be delivered downstream. Lastly, debris flows represent the primary connectivity triggers between areas such as the hanging glacial basin slopes and the valley bottom (i.e., erosion/deposition/deformation and index of connectivity maps). What emerges is the importance of integrating and comparing different thematic maps for a correct interpretation of the past and present dynamics influencing the evolution of complex, albeit small, mountain catchments.

Quantifying the uncertainty in the Eurasian ice-sheet geometry at the Penultimate Glacial Maximum (Marine Isotope Stage 6)

Abstract. The North Sea Last Interglacial sea level is sensitive to the fingerprint of mass loss from polar ice sheets. However, the signal is complicated by the influence of glacial isostatic adjustment driven by Penultimate Glacial Period ice-sheet changes, and yet these ice-sheet geometries remain significantly uncertain. Here, we produce new reconstructions of the Eurasian ice sheet during the Penultimate Glacial Maximum (PGM) by employing large ensemble experiments from a simple ice-sheet model that depends solely on basal shear stress, ice extent, and topography. To explore the range of uncertainty in possible ice geometries, we use a parameterised shear-stress map as input that has been developed to incorporate bedrock characteristics and the influence of ice-sheet basal processes. We perform Bayesian uncertainty quantification, utilising Gaussian process emulation, to calibrate against global ice-sheet reconstructions of the Last Deglaciation and rule out combinations of input parameters that produce unrealistic ice sheets. The refined parameter space is then applied to the PGM to create an ensemble of constrained 3D Eurasian ice-sheet geometries. Our reconstructed PGM Eurasian ice-sheet volume is 48±8 m sea-level equivalent (SLE). We find that the Barents–Kara Sea region displays both the largest mean volume and volume uncertainty of 24±8 m SLE while the British–Irish sector volume of 1.7±0.2 m SLE is the smallest. Our new workflow may be applied to other locations and periods where ice-sheet histories have limited empirical data.

Lateral flow in bedrock dominates baseflow and flood flow in a catchment underlain with permeable sedimentary rock in the high‐relief Chichibu Mountains

AbstractDetermining the mechanisms of runoff generation is essential to land and water resource conservation, but lateral flow processes in high‐relief mountain areas remain unclear due to the difficulty to observe and measure these processes. This study demonstrates that lateral flow in bedrock dominates both high and low flows in a catchment underlain with permeable sedimentary bedrock in the high‐relief Chichibu Mountains. Through measurement of precipitation, discharge, soil, and stream temperatures and tracers (SiO2 and δ18O) in the first‐order stream Bakemonozawa (0.51 km2) and comparison of its water balance with the nested Kawamata catchment (93.58 km2) i, we showed that 831–1012 mm/year or 47%–53% of annual precipitation leaked from Bakemonozawa. The streamflow was discharged from an average depth of 2.3 m or deeper, which were deeper than the measured deepest soil near the gauge. Furthermore, stream temperature decreased significantly during a large summer storm, demonstrating that the relative contribution of the deep bedrock flowpath increased. Large isotopic variation in precipitation was dampened in the stream, suggesting that most baseflow and some higher flows arose from groundwater storage with a constant isotopic ratio due to dispersion and mixing. The discharge–SiO2 relationship suggested at least two groundwater sources, namely, shallow and deep bedrock groundwater, with different runoff responses. Discharge increased dramatically when the catchment became wet, coinciding with the deep bedrock groundwater contribution. Further research is needed to clarify the hydrological characteristics of bedrock.

Dynamic responses and evolution characteristics of bedrock and overburden layer slope with space anchor cable anti-slide piles based on large-scale shaking table test

The study focuses on the anti-slide pile structure with space anchor cable, designing and conducting the large-scale shaking table test of bedrock and overburden layer slope with space anchor cable anti-slide pile system. The dynamic characteristics of bedrock and overburden layer slope with space anchor cable anti-slide piles are systematically explored from aspects of the overall acceleration field of the slope, the interface between overburden layer and bedrock, and the different depths of overburden layer. The results show that in the design of anti-slide pile with space anchor cable, the strength of the bedrock is utilized to resist the sliding force generated by the overburden layer in order to give full play to the role of the strength of bedrock in slope safety protection. The surface of the overburden layer appears a concentrated area of acceleration amplification and as the increase of ground motion intensity, and the concentrated area gradually shifts from the trailing edge of slope to the anchor head segment of anti-slide pile. Under accelerations in different peaks, the peak accelerations in the direction of free face and vertical direction have the asymptotic amplification effect, and the former is stronger. With the increase of ground motion intensity, the peak acceleration magnification decreases exponentially in direction of free face, while the peak acceleration magnification in the vertical direction presents a wavy distribution that first increases and then decreases.

Lateral deformation and acoustic emission characteristics of dam bedrock under various river flow scouring rates

To investigate the lateral deformation characteristics of dam bedrock scoured by river flow environments, standard specimens were prepared using cored sandstone from the barrage bedrock at the Sanhekou Water Conservancy Dam. The mechanical parameters, microstructure, and mineral fractions of the sandstones were analyzed after water scouring at five different rates (0, 200, 400, 600, and 800 mm⋅s−1) for 49 days. Scanning electron microscopy (SEM), electron energy spectroscopy (EDS), and X-ray diffraction (XRD) techniques were employed to track the changes. Laboratory tests including uniaxial compression, acoustic emission (AE), and digital image correlation (DIC) were conducted to elucidate the deformation damage mechanism of the scoured sandstones. The results indicate the following: (1) During the crack closure and compaction stage, the deformation of the rock samples primarily involves axial compression with minimal lateral deformation. However, as the crack propagates unstably and expands after the peak load, the lateral strain of the specimens accelerates. The lateral-axial ratio of the samples remains relatively low during the initial scouring period but increases rapidly after the first drop in axial stress until the end of the test. Higher scouring rates and longer durations weaken the strength and exacerbate the deformation of the sandstone. Under a flow rate of 800 mm⋅s−1, the elastic modulus decreases by 45.67%, while Poisson's ratio increases by 73.67%. (2) The acoustic emission process exhibits distinct phases, including a calm phase, growth phase, and rapid rise phase. As the flow rate increases, the internal crack types in the sandstone transition from shear cracks to tensile cracks, corresponding to the shift from shear failure to cleavage failure. The sandstone's damage variables show progressive abrupt changes under flow rates of 0, 200, and 400 mm⋅s−1, while segmented growth is observed under flow rates of 600 and 800 mm⋅s−1. (3) After absorbing water in a dynamic water environment, the interparticle cementation capacity of the sandstone weakens due to softening, water-rock interactions, and swelling reactions of clay minerals. The overall structure becomes destabilized, ultimately leading to failure through deformation. These findings provide a basis for predicting destruction and analyzing the stability of rock masses during water absorption and expansion deformation under dynamic water conditions.

Geochemical behaviors of uranium and thorium during weathering and pedogenesis of carbonate rock: constraint from their speciation.

During weathering and pedogenesis of carbonate rock with poor-uranium (U) and thorium (Th), U and Th present the characteristics of strong leaching (especially U) and significant residual enrichment, the cause of which is still unclear. In this paper, a weathering profile developed by dolomite in karst area of Guizhou province in southwest China was selected, which showed zonation characteristics of bedrock (Y), powdery rock (Yf), and soil layer (T1 to T12) from the bottom to up. Through the determination of the occurrence speciation of U and Th in Y and weathering profile, combined with mineralogical, geochemical characteristics, and element mass balance calculation, the constraints of U and Th speciation on the geochemical behavior of U and Th during the weathering of carbonate rock were revealed. The results proved that U and Th in Y preferentially existed in acid insoluble phase, for example, the contents of U and Th in Y were 0.90 mg·kg-1 and 0.28 mg·kg-1, respectively, while those in acid insoluble matter were 2.34 mg·kg-1 and 2.57 mg·kg-1, respectively, but because the mass percentage of acid insoluble matter was extremely low (0.95%), the mass percentages of U and Th in the acid soluble phase in the whole rock were absolutely superior (96% of U and 86% Th). The U and Th in the acid soluble phase of Y were mainly adsorbed on the crystal surface of carbonate minerals or existed in the cement, and the U and Th in the carbonate lattice only accounted for a small proportion. From Y to Yf with the initial dissolution, U and Th released from the surface of carbonate minerals and cements were in carbonate-rich alkaline environment, and these portions of U and Th were leached out, resulting in strong loss of U and Th in the Yf (the loss rates are 83% of U and 65% of Th, respectively). From the Yf to the overlying soil layer T1, the carbonate components were completely dissolved, and the U and Th released from the carbonate lattice showed different behaviors, where U was completely leached and Th tended to stay in the weathered residue. Thus, in the soil layer T1 formed by Y or Yf , the residual U was the inheritance of the U in the acid insoluble phase of Y; For Th, it not only inherited the Th of acid insoluble phase of Y, but also superimposed the Th from carbonate lattice in Y. On the other hand, during the evolution process from Y to Yf and to soil layer T1, with the dissolution of carbonate, the acid insoluble phase also showed a significant tendency of chemical weathering. However, the U and Th in the Y acid insoluble phase were not leached with the decomposition of the acid insoluble phase but were redistributed among the residual phases. For the geochemical behaviors of U and Th in the evolution of soil profile (T1~T12), they were subjected to the occurrence speciation of U and Th in T1 and the change of U and Th occurrence speciation with the upward direction of soil profile. The U and Th released from the carrier minerals were mainly redistributed among the residual solid phases, which weakened the intensity of their further loss. This study deepens the understanding of the geochemical behavior of radionuclides in karst environment and provides reference for the treatment of radioactive pollution in karst areas.

Elevational changes in climate response of Pinus nigra pallasiana tree-rings on the Crimean Peninsula

Climate change is most evident on the periphery of species distribution ranges. Using four tree-ring chronologies, we identified the most important climatic factors influencing the radial growth of black pine growing along an elevational transect on the eastern slope of Mount Ai-Petri (Crimean Peninsula), at the northernmost part of its range. The relationship between tree-ring width and climate was determined using response function analysis. Results indicate an increase in correlation between radial growth and hydrothermal data along the transect: from a near absence of any correlation at the lowest elevation to r = 0.6 at the top. This change in response was not only caused by differences in climatic variables, but also related to topography, soil, and bedrock features. The currently ongoing aridization may lead to a decrease in the stability and persistence of black pine stands only in the upper parts of Mount Ai-Petri.

Outdoor River Activities: Relations with Geological Background and Extreme Events in the Perspective of Geoeducation

As for sport climbing, also for outdoor activities such as rafting and canyoning, a strong connection with geofeatures on a long and short time scale exists. For investigating this, three river segments were selected in the Sesia hydrographic basin (Sesia Val Grande UNESCO Global Geopark, Northwest Italy). Here, commercial rafting and canyoning activities are popular, and important geological features are present (Sesia Supervolcano, Insubric Line). The segments were investigated using partly IDRAIM (system for stream hydromorphological assessment, analysis, and monitoring). Bedrock features, confinement, sinuosity, bankfull bottom, morphological units, and steepness were characterized. The segments were hence divided in several reaches. Correlations on the long time scale were found mainly between the geology and bankfull bottom configuration, while sinuosity allowed us to highlight the possible structural control on the genesis of gorges. Moreover, the analysis of changes in a short time scale along the river segments after the extreme meteorological event occurred on 2–3 October 2020, highlighted a rapids difficulty variation, channels diversion, and woody–rocky debris accumulation in the bankfull, deeply influencing river activities. Through the proposed approach, new frontiers in the outreach of geosciences could be opened, especially in virtue of the several Sustainable Development Goals that could be achieved through river outdoor activities, among the others new employment opportunities for local operators.

The interplay of bedrock fractures and glacial erosion in defining the present‐day land surface topography in mesoscopically isotropic crystalline rocks

AbstractThis paper addresses the effect of fractures within crystalline bedrock on glacial erosion processes in fast flowing hard bed glacier environments. In particular, we examine (i) whether the fracture type is critical for the capability of a glacier to erode the bedrock through quarrying/plucking processes and (ii) whether we can recognize specific fracture‐controlled erosion signatures from bedrock surface morphologies. We conducted an investigation within the northern part of the Åland Islands, southern Finland, where the ice‐flow direction (N–S) has remained constant through Late Pleistocene glaciations and where the bedrock is characterized by a lack of any mesoscopic anisotropies (such as foliation) and hence provides an optimal target to recognize the relationships between fractures and erosional morphologies. We characterized the fracture systems within the bedrock using both UAV‐acquired orthophotographs and standard field approaches and extrapolated the results to larger scales using LiDAR‐based digital elevation models. Our findings indicate that individual joints or shear fractures are associated with the development of minor vertical breaks along the bedrock surface. However, they do not provide sufficient mechanical weakness zones in the bedrock to allow effective glacial quarrying, even though their lengths can be relatively large (&gt;50 m). By contrast, the linkage of several parallel shear fractures or the presence of larger faults with gouge‐bearing cores and well‐developed damage zones leads to localized disintegration of the rock material and the subsequent development of distinct topographic depressions along the bedrock surface. Consequently, the results allow predictions to be made about the bedrock features underlying the observed topographic signatures along the bedrock surface. Applied to the area of this investigation, abrasion associated with N–S‐directed glacial flows is responsible for the N–S‐oriented elongate but smooth fjord‐like megagrooves, whereas the more abrupt topographic breaks were generated by quarrying controlled by sub‐vertical, E–W‐trending zones of localized brittle deformation.

Basement morphology of the fold-and-thrust belt and foreland basin of the United Arab Emirates: Evidence for thick-skinned tectonics in the northern Oman-UAE Mountains

We determined the basement depths in the fold-and-thrust belt (FTB) and the associated Aruma and Pabdeh foreland basins of the United Arab Emirates. Additionally, we investigated the relationship between shallow sedimentary structures and deep basement features. The Late Cretaceous Aruma basin is associated with Semail ophiolite thrusting and loading, while the late Oligocene to Miocene Pabdeh basin is associated with the culmination of Musandam and early Zagros collision. In the northern portions of the study area, seismic reflection profiles and derivative maps of gravity and magnetic data show NNW–SSE striking thrusts, backthrusts, and folds. The southern region around Jabal Hafit is dominated by the Tarabat backthrust, which cuts across the Upper Cretaceous and Cenozoic successions. Moreover, the Mesozoic platform carbonates are dissected by thrust faults. These thrusts may have originated from Jurassic extensional faults that were reactivated during the Late Cretaceous ophiolite obduction, as well as the late Oligocene to the early Miocene culmination of Musandam resulting from the collision of the Arabian Plate and Central Iran along the Zagros Suture. Results of the 3D gravity inversion indicate that the basement depths range from 11.5 km along uplifted areas of the FTB to 18.8 km within the deeper parts of the foreland basin. Significant northward increases in both basement depth and the thickness of the late Oligocene-early Miocene successions indicate a northward increase in the severity of thrusting and crustal loading along the Khusub thrust. The basement uplifts are found to be correlated with shallower anticlinal features, indicating a direct relationship between basement uplifts and shallow sedimentary structures. Therefore, we suggest that the basement structures were reactivated during the Late Cretaceous ophiolite obduction and the late Oligocene-early Miocene Zagros collision.

New metrics reveal the evolutionary continuum behind the morphological diversity of subglacial bedforms

Understanding the formation of subglacial bedforms is primordial to constrain ice-meltwater-bed interactions and the dynamics of past and present ice sheets. However, the difficulty to observe active subglacial bedforms below present-day ice sheets implies that their formation and evolution are essentially deduced from the inversion of morphological and sedimentological data from palaeo-subglacial bedforms. In this study, the morphological characteristics of subglacial bedforms are explored with a new approach based on the combination of three dimensionless morphometric indices i.e., circularity index, sinuosity index and elongation component ratio. We measure the spatial distribution of these indices on an unpublished database composed of ~13,500 digitized bedforms taken from two selected portions of the Irish Ice Sheet and Laurentide Ice Sheet beds considering that (1) all subglacial bedforms in each region were formed under a single ice flow configuration and (2) the bedforms may have developed either orthogonal, parallel, or oblique to ice displacement directions. Our results reveal a morphometric and spatial continuum along which ribbed bedforms of various lengths and shapes – ranging from circular to elongated flow-transverse forms – are incipient bedforms that can evolve into transitional sinuous ribbed bedforms, then into predominantly flow-parallel sinuous bedforms that progressively realign to form streamlined bedforms. Assuming the glaciological contexts of selected study areas, this continuum may provide a new geomorphic criterion to constrain spatial variations in subglacial conditions (e.g. ice flow velocity, bedrock characteristics, meltwater pressure).

3D electrical structure definition of aquifer systems in the Kalahari basin in Southern Angola based on legacy data reprocessing

The Kalahari-Ohangwena transboundary aquifer system, recently identified in Northern Namibia, comprises 3 major aquifers with very different characteristics. The shallowest is discontinuous and with limited reserves, but it has local importance in water supply for the population, since it is easy to reach, and often presents good hydrochemical quality. An intermediate deeper aquifer is characterized by high salinity while the deepest aquifer, also mostly saline, can present zones with fresh water. However, the latter is located at considerable depths and is shaped by the bottom of the basin basement. There hasn't been a systematic hydrogeological data acquisition for decades in this area of Angola, but legacy electrical resistivity data reprocessing from geophysical surveys conducted >50 years ago in the Cunene Province allowed the construction of a quasi-3D geoelectrical model for the Angolan side of KOH aquifer system in the Cuvelai-Etosha basin. This model is based on 482 vertical electrical soundings carried out in 1966–67, using the Schlumberger array, that contribute to confirming the presence of the Kalahari-Ohangwena aquifer system in Angola. The obtained quasi-3D model highlights the geoelectrical features of hard bedrock and is validated with other hydrogeological and geophysical information. The quasi-3D electrical resistivity data is interpreted using selected boreholes and two time-domain electromagnetics transects carried out in Namibia, in the 2000s. Although both geophysical data acquisitions were >40 years apart, the results show a very good correlation between the deeper aquifer and the aquitard separating the intermediate aquifer from the deeper aquifer either with the results from Namibia or the borehole data. This is a direct result of the lack of alteration in the hydraulic conditions over these decades, without significant anthropogenic activity and negligible extraction from deep wells. Based on this analysis, the original dataset was considered a reliable source and this quasi-3D model was validated. Furthermore, the model can be considered in the future as an important tool for groundwater resources management, as well as a good starting point for further hydrogeological research in the province of Cunene.

In Search of Basement Indicators from Street View Imagery Data: An Investigation of Data Sources and Analysis Strategies

Street view imagery databases such as Google Street View, Mapillary, and Karta View provide great spatial and temporal coverage for many cities globally. Those data, when coupled with appropriate computer vision algorithms, can provide an effective means to analyse aspects of the urban environment at scale. As an effort to enhance current practices in urban flood risk assessment, this project investigates a potential use of street view imagery data to identify building features that indicate buildings’ vulnerability to flooding (e.g., basements and semi-basements). In particular, this paper discusses (1) building features indicating the presence of basement structures, (2) available imagery data sources capturing those features, and (3) computer vision algorithms capable of automatically detecting the features of interest. The paper also reviews existing methods for reconstructing geometry representations of the extracted features from images and potential approaches to account for data quality issues. Preliminary experiments were conducted, which confirmed the usability of the freely available Mapillary images for detecting basement railings as an example type of basement features, as well as geolocating the features.

Предиктивное археологическое моделирование методом максимальной энтропии (на примере поселений позднеримского времени в бассейне Верхнего Дона)

The paper is devoted to an archaeological predictive modeling technique with GIS and machine learning based on maximal entropy algorithm (MaxEnt). Archaeological sites of the late roman time presented by settlements of Kashirka-Sedelok type (mid-3rd — early 4th century AD) in the Upper Don basin were the modeling objects. We found out that there are 169 known sites of such type in the study region, and collected all available information on their locations into a geodatabase including our own field survey data. The coordinates of these sites split into training and testing subsets served for developing a predictive model with MaxEnt. Environmental GIS-layers based on a digital elevation model and thematic maps were the model predictors. We made such predictors to reflect the paleogeography of the Upper Don basin in the study time period by choosing relatively stable landscape features of relief, bedrock, climate, hydrography and soils of the area. The trained model analyzed through more than 7 million cells of 90x90 m with overall area of 59 400 sq. km to identify potentially suitable areas for the Kashirka-Sedelok settlements and found 29 860 ha the most suitable areas (less than 1 % of the study area) as the result. The efficiency of the conducted modeling, evaluated on the testing sites, is high based on metrics of receiver operating characteristic (AUC = 0,915) and Kvamme’s Gain (KG = 0,97). The results of modeling serve as an agenda for the upcoming archaeological surveys in the region.