Search Results (46)

Hydrologic assessment within the Southeast United States is challenging, particularly in upstream basins, necessitating improved approaches to drought forecasting and water management. Within the Tennessee Valley, dense populations intensify the need for robust hydrologic management and predictive capabilities. This study integrates dendrochronological proxy data, hindcast information, and future climate projections from the Oak Ridge National Laboratory (ORNL) to evaluate May–June–July drought regimes. Holistic hydrologic conditions were attained by integrating self-calibrating Palmer Drought Severity Index data from the North American Drought Atlas, basin-scale precipitation data from ORNL hindcasts and future predictions, and streamflow data from United States Geological Survey. Development of precipitation and streamflow reconstructions were completed using Stepwise Linear Regression, then bias-corrected and temporally smoothed using five- and ten-year moving windows. The reconstructions demonstrated strong statistical skill across all three basins (Little Tennessee River, Nantahala River, South Fork Holston River). When compared only to the hindcast, future drought is predicted to be the most severe on record, but within the context of the paleo record, while still severe, these future droughts remain inside the natural variability envelope. Findings highlight the importance of novel approaches to long-term drought monitoring, specifically integrating basins where instrumental periods are limited, and water management demands are high. Full article

The constituent elements of source-to-sink systems and their coupling relationships are key controls on the development of sedimentary systems and the spatial distribution of sand bodies. Taking the Paleogene strata in the southern Laizhouwan Sag of the Bohai Bay Basin as a case study, we integrate drilling, logging, core, thin-section, and high-resolution 3D seismic data to quantitatively characterize basement lithology and effective provenance area, drainage-unit subdivision, types and scales of sediment transport pathways, and geometric parameters of depositional fans, within a source-to-sink analytical framework. The results show that: (1) Two distinct provenance types are developed in the southern Laizhouwan Sag, including Proterozoic granitic–gneissic basement and Mesozoic volcanic–clastic basement. These provenance types exhibit pronounced differences in effective source area, vertical relief, and drainage-network configuration across different sequence stages. (2) Two main categories of sediment transport pathways are identified, namely paleo-valleys and fault-controlled troughs. V-shaped, U-shaped, and W-shaped paleo-valleys show systematic morphological transitions along topographic gradients. The width-to-depth ratio of transport channels exerts a significant control on depositional fan scale, with U-shaped valleys exhibiting the highest sediment transport efficiency. Finally, (3) the depositional domain is dominated by near-source fan-delta systems, whose scale shows a strong positive correlation with effective provenance area and transport-channel morphology. Overall, the southern Laizhouwan Sag is characterized by a typical fault-controlled, steep-slope source-to-sink system, in which sedimentary system distribution is jointly governed by effective provenance area, sediment transport pathway geometry, and fault-related slope-break zones. This study provides a quantitative example and methodological reference for source-to-sink system characterization and prediction of favorable sand body distribution in continental rift basins. Full article

Paleogeomorphology exerts first-order control on the distribution of structural hydrocarbon reservoirs across regional unconformities, whereas variations in pore-throat architecture and flow capacity among different geomorphic units further govern hydrocarbon migration pathways and accumulation sites. Therefore, high-resolution reconstruction of regional paleogeomorphology is essential for effective exploration. This study investigates the Yanwu area of the Ordos Basin, where pre-Jurassic paleogeomorphology was reconstructed based on detailed stratigraphic analyses of the Yan’an Formation and the Yan-10 oil-bearing interval, and its influence on reservoir formation was systematically evaluated. Paleogeomorphology was delineated using well-log-based compensated impression methods integrated with localized 3D seismic inversion. Reservoir samples from distinct geomorphic units were analyzed through thin-section petrography, FESEM imaging, high-pressure mercury intrusion, and visualized micro-scale hydrocarbon charging experiments to characterize pore-throat systems and flow behavior. Four geomorphic units—paleohighs, slope zones, terraces, and valleys—were identified. Seismic inversion across the Yanwu tributary valley and the Honghe paleovalley confirms the reliability of the reconstructed geomorphology. Reservoirs within slope zones and terraces exhibit superior pore-throat structures, dominated by intergranular and dissolution pores, and display grid-like displacement patterns with higher ultimate recovery in micro-charging tests. Portions of the paleohighs show comparable reservoir quality and flow capacity. Results indicate that slope zones and terraces represent the most favorable hydrocarbon accumulation domains. Where overlying strata provide effective sealing, hydrocarbons preferentially accumulate on structural highs within these geomorphic units; in contrast, insufficient sealing transforms them into efficient migration conduits. Certain paleohighs may also host structural-high accumulations when capped by effective traps. The clarified accumulation patterns across geomorphic units offer a robust framework for guiding hydrocarbon exploration and reserve growth in regions with similar tectono-sedimentary settings. Full article

The Micangshan lead–zinc deposits, located in the northern margin of the Sichuan Basin, are classified as the Mississippi Valley-type (MVT) deposits. This study investigates the genetic linkage between Pb–Zn mineralization and paleo-oil reservoirs in the region, which is distinct from separate investigations on lead–zinc deposits or paleo-oil reservoirs. Through mineralogy, isotope, and fluid inclusion analyses, it is revealed that the direction of ore-forming fluid migration and the ore-forming process are closely related to the thermal cracking of paleo-oil reservoirs. The deposits show a characteristic clustered distribution along the southern part of the Micangshan area, with high-grade mineralization concentrated in the Nanmushu and Kongxigou Pb–Zn deposits. Rb–Sr isotopic dating indicates that mineralization occurred during the Late Cambrian to Early Ordovician (Nanmushu deposit 486.7 ± 3.1 Ma; Kongxigou deposit 472 ± 6.1 Ma), coinciding with the formation of the first-stage paleo-oil reservoirs. The study concludes that the MVT Pb–Zn mineralization in the Micangshan area is genetically linked to the first-stage paleo-oil reservoirs’ hydrocarbon generation and migration events. The organic-rich hydrothermal fluids facilitated the migration and precipitation of Pb–Zn minerals. Full article

As a strategic replacement area for hydrocarbon exploration in the Tarim Basin, the Kuqa Depression has been the subject of relatively limited research on the sedimentary characteristics of the Triassic strata within its western Wushi Sag, which constrains exploration deployment in this region. This study focuses on the Wushi Sag, systematically analyzing the sedimentary facies types, the evolution of sedimentary systems, and the distribution patterns of the Triassic Kelamayi and Huangshanjie formations. This analysis integrates field outcrops, drilling cores, wireline logs, and 2D seismic data, employing methodologies grounded in foreland basin theory and clastic sedimentary petrology. The paleo-geomorphology preceding sedimentation was reconstructed through balanced section restoration to investigate the controlling influence of foreland tectonic movements on the distribution of sedimentary systems. By interpreting key seismic profiles and analyzing vertical facies successions, the study classifies and evaluates the petroleum accumulation elements and favorable source–reservoir-seal assemblages, culminating in the prediction of prospective exploration areas. The research shows that: (1) The Triassic in the Wushi Sag mainly develops fan-delta, braided-river-delta, and lacustrine–shallow lacustrine sedimentary systems, with strong planar distribution regularity. The exposed strata in the northern part are predominantly fan-delta and lacustrine systems, while the southern part is dominated by braided-river-delta and lacustrine systems. (2) The spatial distribution of sedimentary systems was demonstrably influenced by tectonic activity. Paleogeomorphological reconstructions indicate that fan-delta and braided-river-delta sedimentary bodies preferentially developed within zones encompassing fault-superposition belts, fault-transfer zones, and paleovalleys. Furthermore, Triassic foreland tectonic movements during its deposition significantly altered basin configuration, thereby driving lacustrine expansion. (3) The Wushi Sag exhibits favorable hydrocarbon accumulation configurations, featuring two principal source–reservoir assemblages: self-sourced structural-lithologic gas reservoirs with vertical migration pathways, and lower-source-upper-reservoir structural-lithologic gas reservoirs with lateral migration. This demonstrates substantial petroleum exploration potential. The results provide insights for identifying favorable exploration targets within the Triassic sequences of the Wushi Sag and western Kuqa Depression. Full article

Urban expansion in coastal areas involves infrastructure development, industrial growth, and mining activities. These coastal environments face various environmental and geological hazards that require geo-engineers to devise solutions. An integrated geophysical approach aims to address such complex challenges as sea level rise, sea water intrusion, shoreline erosion, landslides and previous anthropogenic activity in coastal settings. In this study, the proposed methodology involves the systematic application of geophysical methods (FDEM, 3D GPR, 3D ERT, seismic), starting with a broad-scale survey and then proceeding to a localized exploration, in order to identify lithostratigraphy, bedrock depth, sea water intrusion and detect anthropogenic buried features. The critical aspect is to leverage the unique strengths and limitations of each method within the coastal environment, so as to derive valuable insights for survey design (extension and orientation of measurements) and data interpretation. The coastal zone of Throrikos valley, Attica, Greece, serves as the test site of our geophysical investigation methodology. The planning of the geophysical survey included three phases: The application of frequency-domain electromagnetic (FDEM) and 3D ground penetrating radar (GPR) methods followed by a 3D electrical resistivity tomography (ERT) survey and finally, using the seismic refraction tomography (SRT) and multichannel analysis of surface waves (MASW). The FDEM method confirmed the geomorphological study findings by revealing the paleo-coastline, superficial layers of coarse material deposits and sea water preferential flow due to the presence of anthropogenic buried features. Subsequently, the 3D GPR survey was able to offer greater detail in detecting the remains of an old marble pier inland and top layer relief of coarse material deposits. The 3D ERT measurements, deployed in a U-shaped grid, successfully identified the anthropogenic feature, mapped sea water intrusion, and revealed possible impermeable formation connected to the bedrock. ERT results cannot clearly discriminate between limestone or deposits, as sea water intrusion lowers resistivity values in both formations. Finally, SRT, in combination with MASW, clearly resolves this dilemma identifying the lithostratigraphy and bedrock top relief. The findings provide critical input for engineering decisions related to foundation planning, construction feasibility, and preservation of coastal infrastructure. The methodology supports risk-informed design and sustainable development in areas with both natural and cultural heritage sensitivity. The applied approach aims to provide a complete information package to the modern engineer when faced with specific challenges in coastal settings. Full article

Unmanned systems provide significant prospects for improving the efficiency of electromagnetic geophysical exploration in mineral prospecting and geological mapping, as they can significantly increase the productivity of field surveys by accelerating the movement of the measuring system along the site, as well as minimizing problems in cases where the pedestrian walkability of the site is a challenge. Lightweight and cheap UAV systems with a take-off weight in the low tens of kilograms are unable to carry a powerful current source; therefore, semi-airborne systems with a ground transmitter (an ungrounded loop or grounded at the ends of the line) and a measuring system towed on a UAV are becoming more and more widespread. This paper presents the results for a new generation of semi-airborne technology SibGIS UAV-TEMs belonging to the “line-loop” type and capable of realizing the transient/time-domain (TEM) electromagnetics method used for studying a uranium object of the paleovalley type. Objects of this type are characterized by a low resistivity of the ore zone located in relatively high-resistivity host rocks and, from the position of the geoelectric structure, can be considered a good benchmark for assessing the capabilities of different electrical exploration technologies in general. The aeromobile part of the geophysical system created is implemented on the basis of a hexacopter carrying a measuring system with an inductive sensor, an analog of a 50 × 50 m loop, an 18-bit ADC with satellite synchronization, and a transmitter. The ground part consists of a galvanically grounded supply line and a current source with a transmitter creating multipolar pulses of quasi-DC current in the line. The survey is carried out with a terrain drape based on a satellite digital terrain model. The article presents the results obtained from the electromagnetic soundings in comparison with the reference (drilled) profile, convincingly proving the high efficiency of UAV-TEM. This approach to pre-processing UAV–electrospecting data is described with the aim of improving data quality by taking into account the movement and swaying of the measuring system’s sensor. On the basis of the real data obtained, the sensitivity of the created semi-airborne system was modeled by solving a direct problem in the class of 3D models, which allowed us to evaluate the effectiveness of the method in relation to other geological cases. Full article

The analysis of sand distribution in a marine–continental rift basin is of practical value for hydrocarbon prediction. The primary objective of this study is to investigate the correlation between Paleoproterozoic sand development and paleomorphology in the Nanpu sag, and to focus on identifying the key factors controlling sand deposition in the marine–continental rift basin. Correspondence between the development of the Paleoproterozoic sand in the Nanpu sag and the paleogeomorphology shows that the gully limited the deposition of the sand into the lake. The differentiation and aggregation of the sand in the lake basin were influenced by two kinds of slope break zones (the syn-sedimentary fracture tectonic slope break zone and the paleo-topographic flexural depositional slope break zone). Due to tectonic movements in the marine–continental rift basin, as well as provenance supply and weather during chasmic stages, the impact of valley and syndeposit slope break zone on sand development varies. In areas where allocation is better as valley–syndeposit slope break zone, basal slope and its vicinity usually are favorable for delta (braided channel) and fan delta sand development, which extend basinward through hydraulic transport. Meanwhile, under the influence of syntectonic and gravitational disequilibrium, gravity flow sand can be seen sporadically distributed in the deep end of fan fronts. This study is of great significance for oil and gas exploration in the Bohai Bay Basin region and contributes to a better understanding of depositional processes in similar marine–continental rift basins around the globe. Full article

Mud depocenters are found across most siliciclastic continental shelves, occurring in various bathymetric ranges and typically dating to the Holocene. This study analyzes the sedimentary characteristics and formation processes of mud depocenters in the central sector of the inner continental shelf of the São Paulo Bight. A total of 1700 km of high-resolution seismic profiles, four gravity cores, and 1346 surface sediment samples were analyzed. The sedimentary analysis involved determining grain size parameters, organic matter content, carbonates content, and radiocarbon dating. Seafloor sedimentary mapping shows the predominance of very fine siliciclastic sand, together with three mud depocenters located shallower than the 30-m isobath. The northern depocenter comprises one sedimentary unit (SU-NZ-01), while the central depocenter consists of two sedimentary units (SU-CZ-01 and SU-CZ-02) and the southern depocenter is made up of two other sedimentary units (SU-SZ-01 and SU-SZ-02). Units SU-SZ-02, SU-CZ-02, and SU-NZ-01 were deposited on Precambrian rock surfaces during the Holocene transgression and include reworked sediments from nearby Upper Pleistocene coastal plains, characterized by a transparent seismic pattern. Above these, units SU-SZ-01 and SU-CZ-01 developed following the Holocene Transgression Maximum, associated with local mud input from the Peruíbe River mouth and the Santos Estuary, respectively. The paleorelief of Precambrian rocks favored the formation of these depocenters by creating wave shadow zones and trapping mud within the paleovalleys. Full article

The peridotite massifs of New Caledonia are characterised by complex hydrodynamics influenced by intense inherited fracturing, uplift, and erosion. Following the formation of the erosion surfaces and alteration processes, these processes drive chemical redistribution during weathering; particularly lateritisation and saprolitisation. Magnesium, silica, and trace elements such as nickel and cobalt—released as the dissolution front advances—are redistributed through the system. New observations and interpretations reveal how lateritic paleo-land surfaces evolved, and their temporal relationship with alteration processes since the Oligocene. Considering the geometry of discontinuity networks ranging from micro-fractures to faults, the transfers occur in dual-permeability environments. Olivine dissolution rates are heterogeneously due to differential solution renewal caused by erosion and valley deepening. Differential mass transfer occurs between mobile regions of highly transmissive faults, while immobile areas correspond to the rock matrix and the secondary fracture network. The progression of alteration fronts controls the formation of boulders and the distribution of nickel across multiple scales. In the saprolite, nickel reprecipitates mostly in talc-like phases, as well as minor nontronite and goethite with partial diffusion in inherited serpentine. The current nickel distribution results from a complex interplay of climatic, hydrological and structural factors integrated into a model across different scales and times. Full article

The coexistence of numerous Mississippi-Valley-type (MVT) Zn–Pb deposits and (paleo) oil/gas reservoirs in the world suggests a close genetic relationship between mineralization and hydrocarbon accumulation. Xuequ–Shandouya middle MVT Zn–Pb deposits are mainly hosted in the Lower Cambrian Maidiping Member siliceous dolostone on the southwestern margin of the Yangtze Block, accompanied by large amount of bitumen in the orebodies. Therefore, this type of Zn–Pb deposit is a natural laboratory for studying the relationship between the mineralization and the accumulation of paleo-oil/gas reservoirs. The deposit is characterized by spheroidal and concentric banded sphalerite. In situ sulfur isotope studies are carried out to determine the sulfur sources, sulfate reduction mechanisms, and role of hydrocarbons in the zinc–lead mineralization process. According to the mineral paragenesis and relative temporal relationship, two mineralization stages (1 and 2) are identified. An in situ sulfur isotope analysis of spheroidal and concentric banded sphalerite particles from Stage 2 shows that there are the two following types of sulfur isotopes in the sphalerite: one with relatively invariable δ³⁴S values in the core (+8.31 to +9.30‰), and the other with a gradual increase from the core margin (core) to the rim (+0.39 to +16.18‰). These two types reflect that they may have formed in different times, with first type forming in the early period of Stage 2, while the second type was formed in the late period of Stage 2. The sulfur isotopic data suggest the sulfur source of evaporated sulfate minerals and multiple formation mechanisms for reduced sulfur (H₂S). In the early period of Stage 2 mineralization, the sulfate reduction mechanism is mainly a mixture of bacterial sulfate reduction (BSR) and/or thermochemical sulfate reduction (TSR), while a very small amount may come from the thermal decomposition of organic compounds (DOCs). In the late period of Stage 2, TSR is dominant, and the gradual increase in the δ³⁴S value may be related to Rayleigh fractionation. The oil/gasreservoir not only acts as a reducing agent to provide the required hydrogen sulfide for zinc–lead mineralization through TSR or BSR, but also provides reduced sulfur for mineralization through the thermal decomposition of organic compounds directly. Full article

Since 2013, 34 surveys of surface and ground waters within and outside the former Hg-mine of Abbadia San Salvatore (Italy), which is currently under remediation, were performed for determining Hg, As, Sb, and main and minor solutes. The water quality is rather poor since most waters show relatively high Hg concentrations (up to 695 µg/L). Differently, As and Sb only overcome the Italian law thresholds in a few sites. A high geochemical variability was observed for most groundwaters without any clear relationship between wet and dry periods. The main source of chalcophile elements is likely related to: (i) the interaction between meteoric waters and soils contaminated by the previous production of mercury; or (ii) the interaction between meteoric waters and the anthropic filling material of a former paleo-valley near the furnaces edifices. While the remediation is expected to be concluded in 2025, the aquifer contamination still remains a problem. Our investigation, including geochemical/hydrogeological modeling, is prodromal to future activities aimed at reducing the Hg content. Currently, the construction of a hydraulic barrier is apparently the most suitable solution to minimize the interaction processes between water–rock and man-made material, which are responsible for the 10-year concentration variability. Full article

A paleokarst system developed in the Upper Jurassic–Lower Cretaceous carbonate complex has been recognized in the Carpathian Foreland area. Well logs testing and core data as well as an acoustic imager, a microresistivity scanner and six-arm dipmeter images were used to identify and analyze the character of the paleokarst features. A detailed interpretation of microresistivity and acoustic image logs allowed for the identification of different types of karst forms, such as caverns; multidirectional fractures, including fractures widened by dissolution; and the type of sediments filling them. The analysis of the seismic survey was conducted by linking the paleokarst characteristic features recognized in the seismic image to the karst intervals determined from borehole data. The set of seismic attributes calculated from the analyzed 3D seismic data, including the RMS amplitude, instantaneous frequency, consistent dip, variance, sweetness and relative acoustic impedance, helped to delineate the zones of the paleokarst distribution. Within the interpreted paleokarst surface developed in the carbonate formations in the study area, there are sinkholes, limestone pavements and valleys. Furthermore, in the northwestern part of the analyzed area, the development of paleokarst forms is related to the presence of a relatively deep branch of a paleovalley formed in the Paleogene, as well as to numerous discontinuities developed in carbonate formations. The development of this type of larger karst form was probably controlled primarily by tectonic faults. The research conducted by the authors of this paper showed the widespread presence of paleokarst features in Upper Jurassic–Lower Cretaceous carbonate formations in the study area. A good spatial identification of the paleokarst surface can be important in a regional context, since the highest part of the profile of carbonate formations is the most important reservoir for geothermal or hydrocarbon resources in this region. Full article

This work focuses on the mechanisms that trigger internal erosion of the pervious foundation of flood protection dikes. The origin of these permeable layers is generally attributed to the presence of a paleo-valley and paleo-channels filled with gravelly-sandy sediments beneath the river bed and dikes. These layers may extend into the protected area. Visual observations of leaks, sand boils and sinkholes in the protected area testify to internal erosion processes in the underground soil. Local geological conditions are part of the information to be sought to explain these processes: presence of permeable soils and position of interfaces. Results obtained on Agly dikes (France), using two classical geophysical methods (EMI and ERT), were analyzed using cored soils and showed that it is not enough to simply conclude to the presence of backward erosion piping. The possibility of internal erosion, such as suffusion or contact erosion, must also be considered as the cause of leaks, sand boils and sinkholes. As the results obtained are explained by the presence of a paleo-valley and paleo-channels beneath the river bed and dikes—commonly encountered in this context—the methodology presented and the results obtained are likely to be relevant for many dikes. Full article

The formation of the Jinsha River drainage is a significant subject of concern in the geological and geomorphological fields. Among them, one key question is whether there was a regional paleo lake into which Lower Jinsha River drainage drained during the late Pliocene to early Pleistocene, due to massive fluvio-lacustrine sediments widely distributed in the Lower Jinsha River. Nevertheless, there has yet to be a consensus on the genesis of those fluvio-lacustrine sediments due to poor sedimentological and chronological data. In this study, to unravel the origin of those fluvio-lacustrine sediments and the formation model of the Lower Jinsha River, sedimentary characteristics, including spatial distribution, lithological composition, and stratigraphic contact relationship of those fluvio-lacustrine sediments were analyzed, and chronological determination of the fluvio-lacustrine sediments using Electron Spin Resonance and Optically stimulated luminescence method was conducted. The results show that in the Lower Jinsha River, the lacustrine sediments are mainly composed of silt and clay, with apparent horizontal bedding, stacked with fluvial cobble-gravel and sand, and are in unconformable contact with the underlying bedrock strata or paleo soil. The lacustrine sediments are spatially discontinuous and mainly distributed in the Shigu, Taoyuan, Panzhihua, and Longjie reaches. Downstream of these reaches are deeply incised gorges with an average slope >30°, and many landslide landforms and deposits can be identified here. In each reach, the lacustrine sediments were closely distributed along the trunk and tributary channels in the plane and were distributed at different altitudes, forming a sequence of lacustrine terraces. Chronological analysis shows that in different reaches, the deposition ages of lacustrine sediments are significantly different. In each reach, the deposition age of the lacustrine terraces of high altitude is older than that of low altitude. The above characteristics collectively indicate that the lacustrine sediments in the Lower Jinsha River were locally deposited by individual dammed lakes, probably induced by landslide rather than a regional paleo lake by tectonic activities. During the incision process of the river valley, landslides continuously block the river channel, forming dammed lakes, and then deposited lacustrine sediments at different elevations, forming lacustrine terraces. The lacustrine sediment of the topmost lacustrine terrace in Panzhihua reach was dated to be 1.78 Ma, combined with previous studies on the fluvial terraces, indicating the Lower Jinsha River existed and started to incise its valley before the early Pleistocene. The widespread dammed lake sediment indicates that the formation of the Jinsha River valley follows the pattern of “incision-landslide-damming-aggradation-incision”. Full article