Fold Belt Research Articles

Distribution and Enrichment Mechanisms of Selenium in Stibnite from the Xujiashan Sb Deposit, Hubei Province, China

The Xujiashan Sb deposit located at the Mufushan fold thrust belt of the Yangtze block is one of the most important Sb deposits in this district. Stibnite in this deposit contains high and various contents of Se, but research on the distribution and enrichment of Se in stibnite remains limited. This paper conducts geochemical composition, C-H-O isotopic composition, and scanning electron microscopy morphology of the Xujiashan deposit to discuss the sources of ore-forming materials and fluid, as well as the distribution and enrichment mechanisms of selenium in stibnite. The results showed that the ores have trace element compositions comparable with the wall rocks, and Sb and Se contents are significantly higher than the average carbonate rocks. The δ13CPDB values of calcite and quartz range from −12.8‰ to 5.5‰, the δ18OSMOW values range from 20.4‰ to 24‰, and the δDV-SMOW values range from −57.8‰ to −86.9‰. Trace element and isotope compositions indicate that the ore-forming materials were mainly derived from the wall rocks (sedimentary–metamorphic rocks) that S, Se, and Sb dissolved during fluid–rock interactions. The ore-forming fluids were metamorphic water produced by metamorphism, which had experienced multistage mixing with meteoric water and organic-rich fluids. Selenium substitutes for sulfur in the stibnite crystal lattice, causing rhythmically distributed Se contents in stibnite, which resulted from multistage physicochemical changes in ore-forming fluids during crystallization. The varied patterns of Se contents are the result of different cross-sections of the stibnite.

Natural fractures and their attributes in organic-rich shales: Insights from the Paleozoic Wufeng-Longmaxi formation, southeastern Sichuan Basin

Fractures in organic-rich shale affect the evolution of permeability and control shale gas preservation. We characterize fracture attributes in the Qiyue-Huaying Fold-Thrust belt in the southeastern Sichuan Basin, revealing the distribution, origin and factors controlling fracture localization through investigation of cores, image logs, and thin section petrography. We found that the deformation intensity, organic matter content and lithology are the major factors for controlling fracture occurrence and location in the Wufeng-Longmaxi deep shale. The major fracture pattern in the Fuling Block is characterized by abundant inclined shear fractures, bed-parallel shear fractures, and bed-normal extension fractures, while bed-parallel veins prevail in the Luzhou Block. In general, fracture density and size in the Fuling Block are larger than those in the Luzhou Block. The competent layers (siliceous shale with high TOC) have the highest fracture density, and noticeably, organic matter content controls bed-parallel vein localization. Based on the distribution of fractures in two blocks, we suggest that the dominant origin of fractures in organic-rich shale gradually changes from tectonic events to fluid pressure changes due to organic maturation (organic events), from the Fuling Block to the Luzhou Block.

Geochemistry and petrogenesis of the mafic dyke swarm of the north eastern part of the Mesoproterozoic Irumide Fold Belt, North eastern Zambia

Geochemistry and petrogenesis of the mafic dyke swarm of the north eastern part of the Mesoproterozoic Irumide Fold Belt, North eastern Zambia

Geochronology and geochemistry of a Neoproterozoic syn-tectonic granitic pluton in the Gari-Gombo area, East Cameroun: Implications for petrogenesis and tectonic evolution

Granites are widespread in many Precambrian orogenic belts worldwide; therefore, they can provide insights into orogenic processes and associated magmatism. Zircon UPb age, monazite Th-U-total Pb age and whole-rock geochemical data for a granite pluton from the Gari-Gombo area in the Adamawa-Yade domain of the Central African Fold Belt (CAFB) in East Cameroon are presented. The granite is composed dominantly of perthitic K-feldspars, quartz, plagioclase and minor biotite with accessory monazite, apatite and zircon. LA-ICP-MS zircon UPb dating yielded an age at ca 631–620 Ma, which is interpreted as age of emplacement that coincides with the onset of D2 Pan-African deformation. Monazite grains in Gari-Gombo granite follow strictly the huttonite substitution trend in Th + U vs Si coordinates. Monazites give consistent Neoproterozoic ages of 630 ± 4 Ma and 602 ± 4 Ma, indicating that growth history and crystallization age of monazites also correlate well with the Pan-African plutonism and granulite facies metamorphism (ca 614–600 Ma) in the Gari-Gombo area. The Gari-Gombo pluton samples show high-K calc-alkaline magnesian, slightly peraluminous signature, high SiO2 (70.16–78.80 wt%), K2O (4.39–5.38 wt%), and Rb (165–248 ppm), and low P2O5 ≤ 0.01 wt% and Sr (146–222 ppm) contents. They have highly-fractionated REE pattern ((La/Yb)N = 6.17–148.18), moderately Eu negative anomalies (Eu/Eu* = 0.53–0.93) and the obviously Nb and Ti negative anomalies. These geochemical features suggest that the Gari-Gombo pluton is a highly fractionated I-type granite generated by partial melting of older meta-igneous materials at middle to lower crustal levels. The 2.9 and 0.95 Ga inherited zircon grains identified within the studied granites further confirm the existence of ancient crust in this region.

Uncovering a Seismogenic Fault in Southern Iran through Co-Seismic Deformation of the Mw 6.1 Doublet Earthquake of 14 November 2021

On 14 November 2021, a doublet earthquake, each event of which had an Mw of 6.1, struck near Fin in the Simply Folded Belt (SFB) in southern Iran. The first quake occurred at 12:07:04 UTC, followed by a second one just a minute and a half later. The SFB is known for its blind thrust faults, typically not associated with surface ruptures. These earthquakes are usually linked to the middle and lower layers of the sedimentary cover. Identifying the faults that trigger earthquakes in the region remains a significant challenge and is subject to high uncertainty. This study aims to identify and determine the fault(s) that may have caused the doublet earthquake. To achieve this goal, we utilized the DInSAR method using Sentinel-1 to detect deformation, followed by finite-fault inversion and magnetic interpretation to determine the location, geometry, and slip distribution of the fault(s). Bayesian probabilistic joint inversion was used to model the earthquake sources and derive the geometric parameters of potential fault planes. The study presents two potential fault solutions—one dipping to the north and the other to the south. Both solutions showed no significant difference in strike and fault location, suggesting a single fault. Based on the results of the seismic inversion, it appears that a north-dipping fault with a strike, dip, and rake of 257°, 74°, and 77°, respectively, is more consistent with the geological setting of the area. The fault plane has a width of roughly 3.6 km, a length of 13.4 km, and a depth of 5.6 km. Our results revealed maximum displacements along the radar line of sight reaching values of up to −360 mm in the ascending orbit, indicating an unknown fault with horizontal displacements at the surface ranging from −144 to 170 mm and maximum vertical displacements between −204 and 415 mm. Aeromagnetic data for Iran were utilized with an average flight-line spacing of 7.5 km. The middle of the data observation period was considered to apply the RTP filter, and the DRTP method was used. We calculated the gradient of the residual anomaly in the N-S direction due to the direction of the existing faults and folds. The gradient map identified the fault and potential extension of the observed anomalies related to a fault with an ENE-WSW strike, which could extend to the ~ E-W. We suggest that earthquakes occur in the sedimentary cover of the SFB where subsurface faulting is involved, with Hormuz salt acting as an important barrier to rupture. The multidisciplinary approach used in this study, including InSAR and magnetic data, underscores the importance of accurate fault characterization. These findings provide valuable insights into the seismic hazard of the area.

Seismo-stratigraphic and morpho-bathymetric analysis revealing recent fluid-rising phenomena on the Adventure Plateau (northwestern Sicily Channel)

The northwestern region of the Sicily Channel hosts a great number of morphological highs, the widest of which is the Adventure Plateau that is part of the Sicilian Maghrebian Fold and Thrust Belt system, formed since the Neogene. The Adventure Plateau was shaped in the Early Pliocene by an extensional phase that produced high-angle normal faults mostly WNW-ESE to N-S oriented. Through these faults, magmatic fluids ascended and produced widespread volcanic manifestations often associated to fluid flow processes. The interpretation of multibeam echosounder, seismic reflection (sparker, airgun) and well-log data allow us to identify several features related to the presence of fluids in the study area. The morpho-structural analysis showed a NW–SE oriented fault system and a string of pockmarks that follow the same trend. A detailed well-log analysis confirmed the presence of oil traces, at a depth of ~ 250 m, and gas (i.e., CO2) at a depth of ~ 450 m. The seismo-stratigraphic analysis highlighted seismic signals located below the pockmarks, (e.g. seismic chimneys, bright spots) which suggest the presence of fluids that would rise to a few meters’ depth. Based on the observations, two sources and two corresponding rising mechanisms have been identified. Morphometric analysis of pockmarks has been performed to delineate their possible interaction with the bottom currents. A fluids pathway model has been reconstructed, revealing the source of fluids emissions at depth in the Adventure Plateau, and providing new insights into the identification of fluid leakage pathways.

What controls structural variations along the Zagros Collision Zone? Insights from geophysical observations and thermo-mechanical modelling

The Zagros Collision Zone is a complex tectonic region formed as a consequence of the collision between Arabia and Eurasia after the subduction of the Neo-Tethys ocean. The NW-SE striking Zagros orogen consists of the following parallel tectonic units (from SW to NE): Zagros Fold and Thrust Belt (ZFTB), Sanandaj–Sirjan Metamorphic Zone (SSZ), and Urumieh–Dokhtar Magmatic Arc (UDMA). In this study, we perform a combined analysis of recent geophysical data, revealing pronounced differences in the crustal and lithospheric structure along the Zagros Mountains. The northwestern sector shows a fairly uniform crustal thickening across the broad symmetric orogen from the ZFTB to the UDMA. In contrast, in the central Zagros, the transition from a relatively narrow zone of high elevations and high-frequency relief in the ZFTB to a smoother surface topography of the SSZ and UDMA occurs with an abrupt increase in Moho depth below the SSZ. The last observation has recently been interpreted as a result of “relamination” process, where the felsic upper crust of the Arabian plate underthrust the mafic crust of the Iranian plate. We present geodynamic numerical models of crustal relamination during continental collision and compute static gravity field of the resulting structures. We show that oblique closure of the Neo-Tethys affects lateral variations in the style and extent of crustal relamination, which control the observed along-strike changes in crustal configuration and orogen altitude. In particular, a narrow and higher orogen (as in the central Zagros) develops in the experiments with a young and wide oceanic plate, whereas an old and narrow subducting plate tends to form a broad and lower topography (as in the northwestern Zagros). This is geometrically consistent with the progressive closure of the Neo-Tethys from NW to SE during the oblique continental collision between Arabia and Eurasia.

Ramps first – Interpreting thrust nucleation in multilayers

Models are key for geoscientists working in subsurface fold thrust belts, who want to interpret complex geometries. However, models based on a few landmark outcrop studies dominate interpretation. In these models thrust faults form first as flats along weaker beds and propagate upwards, producing a “hard linked”, fully connected thrust fault structure. The Eisenstadt and De Paor (1987) model challenges the conventional thrust flat-first, reflecting field observations which show that fold thrust outcrops vary remarkably from each other, with a variety of geometric, linkage, and stratigraphic behaviours.Here we investigate an outcrop of thrusted sediments at St Brides Haven, Pembrokeshire. Structural observations of the outcrop show an imbricated stack, where isolated thrusts have developed within and localised along sandstone layers. The outcrop provides an example of the alternative Eisenstadt and De Paor model of ramps first. But here deformation in the encasing ‘soft’ mudstone layers is accommodate by homogeneous shortening.We suggest that the prevalence of “hard linked” thrust models is a bias towards conventional models and that promotion of a greater variety of fold thrust structures, geometries and evolution styles is needed to ensure a broader range of interpretations and evolutionary understanding that better reflects reality.

Structural inheritances, fault segmentation and seismogenic potential at the front of the eastern Southern Alps (central Carnic Prealps, NE Italy)

New geological and morphotectonic surface data coupled with the revision of the ENI-Exploration & Production seismic lines, made it possible to review the tectonic structure of the Pliocene-Quaternary front of the eastern Southern Alps in the area between the Cellina River and the Tagliamento River (central Carnic Prealps, NE Italy). The eastern Southern Alps are a SE-verging fold and thrust belt in activity from the middle Miocene to the Present. The presence of Paleogene structural inheritances influenced the current structural arrangement of the thrust-belt and the potential seismogenesis, supporting segmentation of the Neoalpine external front. In particular, the presence of the NW-SE trending Mt.Ciaurlec – Palmanova – Pozzuolo structural high, inherited from the W-ward propagation of the External Dinarides during Paleogene, generated lateral lithological facies change and influenced not only the undulation between the Neogene-Quaternary Maniago-Meduno and Toppo-Forgaria Thrusts, but also the segmentation of the outermost portion of the Neoalpine external front consisting into two segments with different geometric and structural characteristics: 1) the ENE-WSW striking Arba-Sequals segment that runs buried under the upper Pleistocene sequences of the piedmont Friuli plain; 2) the W-E Ragogna segment that shows widespread evidence of surface deformation of the Last Glacial Maximum (LGM) alluvial plain. In particular, the long-lasting activity of the Ragogna segment is testified by the late Miocene-Middle Pleistocene angular unconformities, forced drainage anomalies and tilted and uplifted Quaternary palaeosurfaces. A discussion on the seismogenic potential of the investigated structures is proposed.

Genesis of the Jiada pegmatite lithium deposit in the Ke’eryin ore field, western Sichuan, China: Evidence from whole-rock trace element and Li isotope

The origin and petrogenesis of pegmatite-type lithium deposits within the Songpan-Garze Fold Belt (SGFB) of western China remain subjects of debate. To provide further insight on this subject, this study investigated the whole-rock trace elements and whole-rock Li isotopic compositions of the two-mica monzogranite (TMG) from the Ke’eryin composite pluton, the Jiada albite pegmatite (AP) and albite-spodumene pegmatite (ASP) and their metasedimentary wall rocks within the Ke’eryin ore field in the eastern SGFB. Modeling of muscovite-dehydration melting based on the whole-rock trace elements (e.g., Li, Rb, and Sr) and Rayleigh dehydration modeling related to the whole-rock Li isotopes suggest that the Jiada pegmatites are unlikely to have originated from the low-degree partial melting of metasandstone (MS) of the Zhuwo Formation. Variations in the whole-rock trace elements and Li isotope between the TMG and the Jiada pegmatites are consistent with the evolution trend of magmatic fractionation. However, the whole-rock Li isotopic compositions of the AP and ASP display inverse variation characteristics with the muscovite Li isotopic compositions, with the AP exhibiting lower Li concentrations and higher whole-rock δ7Li values than ASP. Furthermore, the variation patterns of whole-rock trace elements do not align perfectly with the Rayleigh-type fractional crystallization processes, implying other geological processes would be also involved in the formation of the Jiada pegmatites. Collectively considering the Li isotope behavior during various geological processes, the observed variations in whole-rock Li isotopic compositions between AP and ASP can be explained by aqueous fluid enrichment during the pegmatitic melt evolution. This suggests that fractional crystallization and fluid exsolution jointly contributed to pegmatite formation and Li mineralization in the Jiada deposit. Moreover, the whole-rock δ7Li values of the wall rock of ASP (MS2) are lower than those of MS and the wall rock of ASP (MS1), primarily due to metasomatism by 6Li-enriched fluids expelled from ASP and the kinetic diffusion of Li isotopes. The high concentrations of highly mobile elements, especially Li and Cs, combined with the low whole-rock δ7Li value of the metasandstone, could serve as effective tracers for locating concealed orebodies and evaluating the metallogenic potential of Li mineralization.

Stress evolution of fault-and-thrust belts in 2D numerical mechanical models

We employed numerical models to examine the dynamics of fold-and-thrust belts (FTBs), particularly focusing on the spatial and temporal interplay between stress variations and fault development. Our study explores the effects of variables such as layer thickness, basal friction, and surface diffusivity on the FTBs’ structural development, emphasizing the conditions under which frontal thrusts form. We found that fault activities within FTBs exhibit a cyclic behavior characterized by phases of initiation, quiescence, and reactivation. For over 95% of the total cycle duration, the frontal thrusts are the only active structures, and the stress within the FTB predominantly remains in a critical state. During the remaining 5%, the stress becomes over-critical, leading to the formation of a proto-thrust zone and the reactivation of pre-existing thrusts within the FTB. The lateral growth rate of FTBs is directly related to the thickness of the deforming layer, with the progression of the deformation front maintaining a steady pace across the study period. Additionally, our analysis on the progression of FTBs highlights the critical role of zonal failure spacing in determining the structural styles within FTBs. Our results indicate that narrowly spaced zonal failures, which promote the emergence of low-angle forethrusts, are more likely to occur at increased distances from the backstop. This explains the sequential frontal failure in the FTB; however, the stress accumulating at the rear weak zones also play an important role in the evolutionary patterns of the FTB. Our study offers new insights into the complex processes governing the mountain formation.

Fold-thrust belt in the southern front of the central High Atlas (Morocco): Analysis and implications for the tectonic inversion of the atlas system

Thrust folds have developed significantly in the meso-Cenozoic rock units of the Errachidia-Boudnib basin. The study areas correspond to the north part of the Pre-African Trough, which is located between the Anti-Atlas and the Atlas systems. It is characterized by faulted anticlines that are indicative of a foreland orogenic context.The Atlas system's structural evolution underwent several stages, starting with a Triassic extensional event followed by a period of fault reactivation during the Atlas compression. This research focuses on examining the thrust and detachment folds associated with both reverse and strike-slip components. For this purpose, we performed detailed geological mapping and interpretation of folding and fault slip data.As a result of shortening, field observations reveal that the study area exhibited well-developed thrusting geometry. Preexisting blind faults and multiple decollement levels within favorable formations such as Cenomanian evaporitic marls, Cenomanian-Turonian marls rich in organic matter, and Senonian argillites influence the folding patterns, which are not uniform. The findings demonstrate two key points. First, the most significant folds have formed along major blind thrusts. Subsequently, between these major faults, detachment folds were developed within the Jurassic-Cretaceous strata. Currently, due to erosion, certain thrusts have become visible, including the Ta'bbast thrust fault, Ait Atman (from the first stage), and the Timazguit fault zone (from the second stage). The South Atlas fault largely remains a blind fault. Additionally, the study emphasizes the presence of strike-slip components and en-echelon folding, indicating a transpressional regime during the uplift of the Atlas system.

Lithofacies and deformation structure of the Bandarban Anticline, Chittagong–Tripura Fold Belt, Bangladesh – Depositional environments and tectonic implications

Lithofacies and deformation structure of the Bandarban Anticline, Chittagong–Tripura Fold Belt, Bangladesh – Depositional environments and tectonic implications

Subaerial to subaqueous volcaniclastics from the Bayana sub-basin, North Delhi Fold Belt (NDFB), India: Evidence for a Paleoproterozoic subduction margin

Subaerial to subaqueous volcaniclastics from the Bayana sub-basin, North Delhi Fold Belt (NDFB), India: Evidence for a Paleoproterozoic subduction margin

Heterogeneous deformation in fold and thrust belts induced by anisotropies in the ocean topography; the South Portuguese Variscan Zone example (SW Portugal)

The Variscan fold and thrust belt related with the South Portuguese Zone presents a SW forward propagation and the coeval development of synthetic folds and thrusts pervasive at all scales. Although several models have been proposed for their formation, the estimated strain pattern is more compatible with a push from the rear induced by the north-eastern subduction zone. Although there is a strong consistence concerning the kinematics of these Variscan structures, there is an important contrast of their geometries between the inner and the external sectors, where the very low dips prevails. Although, there are some previous models suggesting that the behaviour of the more external domains could be related with the interference between the undeformed sedimentary sequence of the upper plate with the active margin of the fold and thrust belt, independent evidence of this process is lacking. The realization of scaled analogue experiments concerning the Carboniferous evolution of SW Iberia Variscides, not only show that they could induced the flat lying major thrust of the external domains, but also emphasize their important role in the structural evolution of much of the fold and thrust belt.

Stratigraphy and Basin Analysis of the West Rand Group, Witwatersrand Supergroup

Abstract The Mesoarchaean West Rand Group displays a layer-cake stratigraphy with lithostratigraphic units correlatable on a basin-wide scale. The ~5 km-thick succession consists of fluvial braidplain and shelf deposits, which range from shallow inner shelf marine orthoquartzites, outer shelf argillites to starved shelf iron-formations. Minor diamictites are of debris flow origin and are possibly related to glacial activity. Three major sequences are present: Sequence I (Hospital Hill Subgroup) is bounded by an angular unconformity at the base of the Orange Grove Formation and a low-angle unconformity at the base of the Promise diamictite. Sequence II (Government Subgroup) extends from the base of the Promise diamictite to a well-defined low-angle unconformity at the base of the Koedoeslaagte Formation. Sequence III (Jeppestown Subgroup) comprises the succession between the Koedoeslaagte Formation and the Maraisburg Formation, up to the low-angle unconformity at the base of the Main Reef. Sequence I was deposited during a period of highstand of sea-level, Sequence II during a period of relative lowstand, and Sequence III during a period of relative highstand coupled with high rates of sediment supply. Isopach, depofacies and palaeocurrent analyses indicate that strata in the western to northwestern parts of the basin were deposited under more proximal sedimentary conditions compared to those in the central or southeastern parts of the basin. There is little relationship between the present outline of the basin and the distribution of depofacies or isopachs of sequences, and it is therefore concluded that the original sedimentary basin was significantly larger in areal extent. Depofacies and thickness distribution, as well as synsedimentary deformation of strata, indicate that the basin was most probably of flexural tectonic origin. These findings strongly support deposition in a wide, shallow, and rather stationary foreland basin, with an axial zone towards the west/northwest and a low amplitude peripheral bulge to the east/southeast. Such shallow foreland basins, with abundant sediment bypassing, are thought to be associated with windward-facing orogenic fronts. High rates of erosion along such fold-thrust belts lead to ineffective loading and advancement of the orogenic front, as well as an oversupply of sediment.

Petrography and Diagenesis of Thin-Bed Reservoirs from the Eastern Folded Belt of Bangladesh

The main purpose of the study is to identify the thin-bed reservoirs of the Eastern Folded Belt (Sylhet and Bandarban) and characterize them with diligence. A detailed qualitative and quantitative analysis has been carried out. It is based on thin-section petrographic analyses of sandstone samples. These samples are from the reservoir horizons of the Sylhet region and Bandarban region fields. The purpose of this analysis is to characterize the textural and mineralogical properties. Additionally, it aims to evaluate the post-depositional diagenetic changes. The results obtained from the field and laboratory analysis are studied extensively to characterize the thin-bed reservoirs. Samples from the Sylhet area are medium-coarse-grained, fairly sorted, tight packing, submature-mature sublithic characteristics. Contrarily, samples from the Bandarban region are mature-submature sublithic arenites, which are fine-medium-grained, moderately well-sorted, and moderately loosely packed. Despite the similarity of the detrital elements (quartz, feldspar, lithic grains, mica, etc.) in the two areas, silica cementation is more frequent in Sylhet region samples than early carbonate cementation in Bandarban region samples. Comparatively speaking, the sediments in the Sylhet region are more compact than those in the Bandarban region. The most important outcome of this study is that the thin bed of the unconventional reservoir and the conventional reservoir are in close proximity. The Thin-bed reservoir units of the Eastern Folded Belt are found to be medium to fine-grained and well sorted, with frequent alteration of sand-shale with the prevalence of parallel bedded sandstone. Average porosity is 4% to 12%, and pore spaces are interconnected. So, the permeability rate is good enough to flow the hydrocarbon through these pore spaces. Most importantly, the thin bed and tight reservoir (average porosity 4% to 12%, but pore spaces are not interconnected) are not more prominent than 1 meter or 2 meters. Subsequently, though the vertical thickness is not so high, they keep up a momentous tirelessness of horizontal progression. On the contrary, at whatever point it comes to a conventional reservoir, the vertical thickness is higher than that of the unconventional reservoir. But their lateral persistence is not as long as unconventional ones.

U-Pb detrital zircon age determination and provenance of the lower Karoo succession from the Karoo Research Initiative (KARIN) borehole KWV-1, Eastern Cape Province, South Africa

Abstract In recent years, the maximum age of sedimentation and possible sources of detritus to the sedimentary successions of the Karoo Supergroup has received a lot of interest, with various authors presenting age data from across the main Karoo Basin (MKB). Our paper aims to contribute to this ever-growing geochronological database as we report weighted mean ages for the youngest zircons as well as detrital zircon age distributions for the lower Karoo Supergroup succession sampled from the Centre of Excellence for Integrated Mineral and Energy Resource Analysis (CIMERA)-Karoo Research Initiative (KARIN) drill core KWV-1. A total of 880 near concordant zircon ages were determined using Laser Ablation Quadrupole Inductively Coupled Plasma Mass Spectrometry (LA-Q-ICP-MS) from fifteen samples representing the Dwyka Group, the Collingham-, Ripon-, Fort Brown- and Waterford formations of the Ecca Group and the Koonap Formation of the Beaufort Group as intersected by this ~2 352 m deep research borehole drilled in the southeastern sector of the basin. The weighted mean ages for the youngest zircons calculated for the formations of the Ecca- and Beaufort groups compares with findings reported by other authors and with the ages reported for tuffaceous layers associated with these units. The weighted mean ages for the youngest zircons of the Dwyka Group reflect the age of the youngest source area and do not aid in constraining the maximum age of deposition. A significant change in detrital zircon age distribution was noted between the Dwyka Group and the overlying formations of the Ecca and Beaufort groups, which we interpret as a change in provenance. The major Meso-to Neoproterozoic detrital zircon age fractions present in the Dwyka Group are attributed to source areas located towards the north and northeast of the MKB, in line with regional ice flow directions. A significant late Carboniferous to Permian detrital zircon age fraction is however observed throughout the formations of the Ecca- and Beaufort groups, with a lesser fraction of older zircon ages. The prevailing youngest age fraction reflects ages associated with magmatic source areas in the Gondwanide Orogeny located towards the south of the MKB at the time of deposition, while the recycling of deformed sedimentary strata of the Cape Supergroup contained in the Cape Fold Belt is considered the source of older detritus. The source of detritus to the MKB remained unchanged during the deposition of the respective formations of the Ecca- and Beaufort groups, despite changes in the depositional environment brough on by regional tectonics.

Potentially toxic metals contamination in stream sediments of Mbal area (Pan-African fold belt, Cameroon)

The Mbal area is situated within the Neoproterozoic Lom Basin in Cameroon. The objective of this paper was to determine the level of contamination and risk associated of potentially toxic metals (PTMs) in stream sediments of Mbal. Sampling was performed by panning and collected sediment were analysed using an inductively coupled plasma-mass spectrometer. The sediment samples showed significant enrichment in mercury, above 10000 ppb. The other transition metals including manganese, zinc, lead were also elevated, ranging from 825 to 1950, 50.80 to 97 and 9.80 to 87.20 ppm, respectively. Multivariate statistical analyses revealed that the enrichment of the PTMs were attributed both to geogenic and anthropogenic sources. Pollution indicators such as degree of contamination, modified degree of contamination and pollution load index yielding 10809.33–200005, 982.67–18182.33 and 0.59–1.18 respectively, suggest high degree of sediments contamination from natural and anthropogenic sources. Geo-accumulation index and enrichment factor revealed moderate to extreme levels of metallic pollution. Potential ecological risk indices show extreme ecological risk index of PTMs suggesting ecological effects to biota and humans in the ecosystem. Mercury, lithology, mining, domestic and agricultural activities were major sources of PTMs pollution. Toxic metals may cause chronic health problems such as cardiovascular diseases, nervous system disorder, kidney damage and gastrointestinal disorder. This study underlines the importance of continuous monitoring and adaptive management for the preservation of the biotic and non-biotic environment. The results may assist mining companies and local populations in setting realistic targets for monitoring and remediation programs.

Neotectonics on the Namuncurá (Burdwood) Bank: unveiling seafloor strike-slip processes along the North Scotia Ridge

The North Scotia Ridge is the offshore morphostructural expression of the left-lateral transcurrent South America–Scotia plate boundary. Several blocks make up the ridge, including the scarcely studied Namuncurá Bank (also known as the Burdwood Bank). We present the first detailed study of active structures on the seafloor of the western Namuncurá Bank from a database of 3D and 2D seismic data, multibeam bathymetry and sub-bottom profiles. This work assesses the architecture, style of deformation and Cenozoic evolution of Namuncurá Bank, where several groups of faults and en echelon folding affect the seabed and shallow sub-bottom. These features compound the northernmost structures associated with a releasing bend, fitting well with a left-lateral Riedel shear model oriented at N74°E, slightly rotated with respect to the present day plate boundary stress regime. The current tectonic scenario started with a main deformational phase in the Neogene, partially distributed by the Malvinas fold–thrust belt, while modern deformation continues to be conditioned by pre-existing structures. This study allows a better understanding of the tectonics of the North Scotia Ridge, a morphostructure that influences the circulation of the Antarctic Circumpolar Current, thus impacting the global climate.