Erosion Surface Research Articles

The “Lochkovian-Pragian Event” re-assessed: New data from the low latitude shelf of peri-Gondwana

In the late Lochkovian a regression is documented in several areas of the world, followed by a transgression in the early Pragian. Connected with the eustatic variation, a minor extinction event occurred (“Lochkovian-Pragian Event”), affecting several fossil groups, a strong reduction of carbonate production and sedimentary facies changes. The Carnic Alps are a key area for studying this event, because lower Devonian rocks are widely exposed, representing diverse sedimentary environments from shallow water to relatively deep shelf. Fourteen sections were measured along the Carnic Alps across the Lochkovian-Pragian boundary. In the shallower part of the basin, both the Polinik and the Seekopf formations span the boundary, but evident erosional surfaces are observable in the field at the Lochkovian-Pragian boundary. Above the unconformity, at places the so-called megaclast horizon is present in the Seekopf Formation. In intermediate settings the Rauchkofel Fm. Is unconfomably followed by the Kellerwand Fm., and different parts of the upper Lochkovian and lower Pragian are missing in the various sections. In the deeper parts of the basin the transition from the La Valute Fm. To the Findenig Fm. Is slightly diachronous from the latest Lochkovian to the earliest Pragian; however, conodonts and tentaculitids are rare in the marly boundary beds, preventing a precise chronostratigraphic calibration of these levels. At places, evidence of subaerial exposure at the formational boundary is documented. In general, the hiatus seems to be larger in the western part of the Carnic Alps, in correspondence with the shallower parts of the succession, suggesting a sea level drop in the late Lochkovian, followed by a transgression in the Pragian. Data from the Carnic Alps are compared with those of other regions of North Gondwana to demonstrate that the sea-level variation at the Lochkovian-Pragian boundary are of global importance

Peridotite Weathering and Ni Redistribution in New Caledonian Laterite Profiles: Influence of Climate, Hydrology, and Structure

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.

Palaeogeographical and eodiagenetic settings of host‐replacing phreatic calcrete intervals developed in mud deposits of the Famennian Kinnesswood Formation in the Pennyseorach Subbasin of south‐west Scotland

ABSTRACTIn the Pennyseorach Subbasin of south‐west Scotland, the Famennian Kinnesswood Formation of the Inverclyde Group includes several, ca 1 to 3 m thick erosional remnants of host‐replacing phreatic calcrete hardpans developed in mud deposits. The latter are most unusual hosts for such calcretes due to their relative impermeability, which would normally prevent them from sufficiently accommodating the circulation of an aquifer. In previously documented phreatic calcretes, mud deposits clearly acted as aquicludes that sharply constrained calcrete development. In the Kinnesswood Formation at Pennyseorach, tall desiccation fissures allowed groundwater to circulate in thick, semi‐consolidated mud deposits. Because of the inferred development of an adjacent evaporitic basin, the mixing of fresh and evaporitic groundwaters raised the pH enough for the replacement of phyllosilicates by calcite to occur along the fissure walls, forming ‘fissure calcretes’. The latter gradually expanded and eventually coalesced into mature, ‘columnar host‐replacing phreatic calcrete hardpans’ in which 90 to 100% of the muddy host material was replaced by calcrete. At Pennyseorach, host‐replacing phreatic calcrete hardpan formation not only affected the transition zone between the Doughend Sandstone and Foul Port Members of the Kinnesswood Formation (the Dunagoil Calcrete interval), as in other localities of south‐west Scotland, but also affected the uppermost part of the formation, which is marked by several erosion surfaces downcutting into columnar host‐replacing phreatic calcrete hardpan intervals in association with the episodic rise and fall of base‐level. These newly recorded host‐replacing phreatic calcrete hardpan intervals from the upper part of the Kinnesswood Formation have a tightly constrained stable isotopic signature that is distinct from that of both the Dunagoil Calcrete and the successive host‐replacing phreatic calcrete hardpans of the Visean Clyde Sandstone Formation within the same group, underlining their potential as stratigraphic markers and palaeoenvironmental indicators.

Enhancing aeolian sand stability using microbially induced calcite precipitation technology

This study investigates the effectiveness of Microbially Induced Calcite Precipitation (MICP) technology in enhancing the stability of aeolian sand. Applying MICP to desert sand samples from Kashi, Xinjiang, the results demonstrated significant structural stability and erosion resistance in treated soils during wind erosion tests. Particularly after 14 days of treatment, the soil samples exhibited optimal wind erosion resistance and surface crust strength. Additionally, the formation of calcite significantly improved the soil’s penetration strength and wind erosion resistance, with SEM analysis confirming that calcite “bridges” between soil particles enhanced inter-particle bonding. Environmental impact assessments indicated that MICP technology is not only environmentally friendly but also effectively reduces the risk of soil environmental pollution. These findings validate the potential application of MICP technology in enhancing the stability and environmental adaptability of aeolian sand.

Holocene paleoenvironment of the Nihewan Basin, China, inferred from high-resolution luminescence dating and a multiproxy analysis of gully sediments

As a pivotal region for studying early human occupation in East Asia, the Nihewan Basin has witnessed numerous studies on Paleolithic sites and associated paleoenvironmental records. However, little attention has been given to the Holocene period, despite the basin being a crossroads for the exchange of NE China Neolithic cultures. In the central part of the Nihewan Basin, we found a gully sediment section with a thickness of ∼9 m, which exhibits clear parallel bedding throughout. The section is composed of ten sediment layers (Layers 10–1 from bottom to top), from which three distinct dark-colored soil layers (Layers 8, 4 and 2) and two erosion surfaces (between Layers 10 and 9, and Layers 2 and 1) were identified. Forty-four sediment samples from the section were optically dated, and the obtained ages were refined using Bayesian statistical modeling. The age-depth relationship and sedimentary characteristics suggest that the sedimentation process of Layers 9–2 was continuous. To reconstruct the paleoenvironment, the grain-size distribution, magnetic susceptibility, and pollen content of the sediments were analyzed. The three soil layers exhibit high magnetic susceptibility values. Based on these climatic proxies, five climate stages were recognized. From ∼12.7 to ∼6.8 ka, the climate in the basin region was cold and dry. The period between ∼6.8 and ∼5.4 ka was marked by optimal climate conditions that led to soil formation. Subsequently, the climate was colder and drier during the period of ∼5.4 – ∼4.0 ka, and transitioned to warm and wet conditions again from ∼4.0 to ∼2.7 ka. Another stage of soil formation occurred between ∼2.7 and ∼1.7 ka, during which the climate was predominantly warm and humid, albeit punctuated by a brief interval of colder and drier conditions. These climate variations coincided with cultural evolution stages within the basin, highlighting a close relationship between environmental change and human adaptation.

The pre-Campi Flegrei caldera (>40 ka) explosive volcanic record in the Neapolitan Volcanic Area: New insights from a scientific drilling north of Naples, southern Italy

The oldest volcanism documented in near-vent sections around the Campi Flegrei (CF, southern Italy) caldera does not exceed ~78 ka, even though the mid- to ultra-distal tephrostratigraphic record would suggest that activity in this area started well before that. Reconstructing the activity preceding the large caldera-forming Campanian Ignimbrite (CI) eruption of ~40 ka, via surface geological surveys in proximal areas, is challenging because of the poor accessibility and paucity of sections recording the older chronostratigraphic interval. In order to fill the gap in knowledge of the activity preceding the CI eruption, a 113.2 m deep scientific drillhole was emplaced in the Ponti Rossi area, in the northern part of the city of Naples. The Ponti Rossi area was selected as representative of the stratigraphic setting prior to the CF caldera formation because it is close, although external, to any proposed caldera rim or downthrown area. The cored succession, consisting of pyroclastic deposits separated by paleosols, reworked humified deposits or subaerial erosional surfaces, has been logged and sampled for sedimentological, mineralogical, and geochronological analyses. Thirty-one Pyroclastic Units (PU) were identified. Based on the structural/textural features of the recovered sediments, the first relevant result is the possible absence of the CI, while the deposits of the ~15 ka Neapolitan Yellow Tuff eruption, the second largest caldera-forming event of CF, represent the shallowest sediments. 40Ar/39Ar age determinations on alkali feldspars, extracted from juvenile fragments collected at 45.8–45.9 (PU-29) and 99.5–99.6 (PU-1) metres of depth, yielded ages of 59.03 ± 0.50 ka and 110.00 ± 0.35 ka, respectively. The age obtained for the deepest cored unit, having sedimentological characteristics compatible with proximal deposition, represents the oldest age obtained for a pyroclastic deposit in the sequences near the CF caldera boundaries and extends by 30 ky the explosive history of this area. Furthermore, based on 40Ar/39Ar age constraints, at least 29 eruptions, spanning the ~59–110 ka interval, can be added to the volcanic history of the Neapolitan Volcanic Area. These eruptions can be largely attributed to the CF area, prior to the CI caldera formation, and testify to hitherto unknown, intense explosive activity.

Response of submarine braided channels to varying inflow hydrographs: Geomorphic experiments and stratigraphic implications

AbstractSubmarine channels on the seafloor experience a range of turbidity current‐flood hydrographs. The characteristics of the flood hydrograph influence channel dimensions, the number of channel threads (i.e. braiding intensity) and the depositional properties of sandbars within the channels. However, the morphodynamic response of submarine braided channels to different hydrograph patterns is poorly understood. In this study, six geomorphic experiments are used to test how varied flood hydrographs affect the braiding intensity and sandbar geometry within submarine channels. Three experiments represent the control group with constant density‐current inflow, and three experiments use different time‐varying hydrograph patterns. The experiments show that, as the inflow‐to‐sediment discharge ratio increases, multiple small channels coalesce into a few main channels, causing a decrease in active braiding intensity defined by the channel threads with flow. When the flow returns to the initial low flow rate, active braiding intensity increases again. These observations show that the inflow‐to‐sediment discharge ratio determines the value of active braiding intensity. Additionally, active braiding intensity is directly proportional to dimensionless sediment‐stream power and dimensionless stream power, in agreement with previously established trends for both submarine and fluvial braided channels. In contrast to active braiding intensity changes, the measured sandbar aspect ratio and compactness ratio (i.e. ratio of planform area to perimeter) of submarine braided channels is insensitive to changes in the hydrograph. However, when inflows reach peak discharge, the higher transport capacity erodes pre‐existing deposits, forming noticeable erosional surfaces, and subsequently depositing thicker sandbars during that stage. These observations imply that sandbar planform morphology is largely insensitive to hydrograph, but hydrograph variability induces a greater variability in the resultant stratigraphic packages. The experimental results predict that field‐scale stratigraphy should be dominated by strata deposited during intervals of high flow, but that these strata will also exhibit reduced lateral continuity compared to formation scenarios with constant discharge.

The Psematismenos-Maroni Basin (South Cyprus): Cenozoic tectonic and sedimentary evolution

The Tertiary regressive sedimentary succession, which forms the sedimentary cover of the Troodos Ophiolitic Massif, was studied in the Psematismenos-Maroni Basin in Southern Cyprus. A series of unconformity surfaces were identified based on key surfaces, morphologies, and sedimentary facies. These observations are reinforced by numerous new biostratigraphic datings mainly based on calcareous nannofossil analysis. Unsuspected biostratigraphic hiatuses ranging from million to dozens of millions of years are illustrated. Some unconformity surfaces are tectonically enhanced leading to the emersion of this basin. In addition, our work highlights the importance of the Messinian Salinity Crisis in the shaping of an onshore erosion surface in Cyprus as it is the case in the Sorbas basin in the western Mediterranean. Constrained by new datings, this work finally proposes a tectono-stratigraphic calendar for the Psematismenos-Maroni Basin, starting from the Paleogene Lefkara Formation up to the first alluvial deposits at the end of the Neogene.

Revised timing of rapid exhumation in the West Qinling: Implications for geodynamics of Oligocene-Miocene Tibetan plateau outward expansion

Two contrasting age models for initial mountain building in the northeastern (NE) Tibetan Plateau (Paleocene-early Eocene versus late Oligocene-early Miocene) have led to the debate on how the deformed continental lithosphere absorbs plate convergence in general. The initial compressional deformation in the West Qinling (WQL) of the NE Tibetan Plateau figures prominently in this ongoing debate. Here, apatite (U-Th)/He (AHe) thermochronology combined with geomorphological analysis are used to refine the onset of compressional deformation in the WQL. New AHe ages from two vertical transects and an updated reconstruction of an obliquely-tilted erosion surface document the accelerated exhumation in the northern WQL at 23-22 Ma, interpreted as the onset of north-vergent thrusting. The AHe results, together with sedimentary records in the intermontane and foreland basins, suggest that the entire WQL began experiencing compressional deformation in the late Oligocene-early Miocene. When integrated with previous studies, our findings show that the northern plateau boundary has not remained stationary since the collision, but has instead experienced ∼750 km of outward expansion during the late Oligocene to middle Miocene. This phase of rapid plateau growth is coeval with the ∼30–50 % reduction of the India-Eurasia convergence rate, which suggests that the increased gravitational potential energy of orogenic belts played a key role in plate motion changes.

Structural inheritance, morphotectonics and Holocene activity of the Cucalón-Pancrudo extensional fault (Iberian Chain, Spain)

A large active extensional fault is characterized, which will contribute to improve seismic hazard assessment in an intraplate region of the Mediterranean domain whose seismic potential until today has been underestimated. The Cucalón-Pancrudo fault (CPF) is a NNW-SSE striking extensional fault that represents the negative (extensional) inversion of a previous, Late Variscan and Paleogene, transpressional fault. It is part of the Río Grío-Pancrudo fault zone, the largest active structure in the intraplate central-eastern Iberian Chain. This study focuses on characterizing the CPF structure, morphotectonics and paleoseismology. The fault offsets a well-known regional planation surface (lower level of the Fundamental Erosion Surface, FES3, 3.5 Ma), providing a basis for calculating the maximum fault throw (c. 280–300 m, including the contribution of a minor synthetic fault and a gentle accommodation monocline), and hence estimating the net slip (c. 305–325 m) and the long-term slip rate (0.09 mm/a). A trench dug in a Holocene fluvial terrace reveals an ensemble of listric, domino-style ruptures synthetic to the main fault. They were activated during at least two paleoseismic events (X, Z), 14.9 ± 1.4 ka and 6.9 ± 0.4 ka in age. An intermediate event (Y), dated to 11.0 ± 1.0 ka, as an uncertainty because the attribution of their ruptures to event Z cannot be ruled out. The total net slip accumulated during these events (1.15–1.25 m) provides an apparent short-term slip rate of 0.07–0.09 mm/a, very similar to the long-term slip rate. Nevertheless, it is very likely that the faults exposed in the surveyed trench do not represent a complete paleoseismic record. Therefore, the actual slip rate during Late Pleistocene-Holocene times could be significantly higher, approaching that reported for most of the recent extensional faults in the central Iberian Chain. The inclusion of CPF in the map of Active Faults of Iberia (QAFI database) will result in improving seismic hazard assessment in Spain.

Geomorphological Compartmentation of Pereiro Massif and its surroundings, in Northern Northeast of Brazil

The Pereiro Massif (PM), located between the states of Ceará, Rio Grande do Norte and Paraíba, is a granitoid body that occupies an area of ​​approximately 2,200 km2, and and has maximum altitudes of 861 meters. This work aimed to elaborate and discuss the geomorphological compartmentalization of the Pereiro Massif and its surroundings. To this end, the following procedures were followed: 1) bibliographic and cartographic review on the geology and relief of the study area; 2) creation of the geomorphological map in a GIS environment, through SRTM image processing; 3) field activities for mapping conference, obtaining information to characterize the shapes and photographic survey. Fifteen units were mapped and grouped into three dimensions that consider the resulting processes and forms: accumulation, flattening and erosion surfaces. The compartments are classified recognizing processes associated with continental denudation with erosion, transport and deposition of material, based on structural geomorphology. The mapping carried out enhances the scientific notoriety of the PM and is expected to serve for environmental planning actions, such as the creation of protected areas and environmental licensing procedures.

Study on the Erosion Resistance of Different TiN Crystal Planes by Molecular Dynamics.

In this study, we innovatively combined the Fe-Ti-N potential function file to construct simulation models of different crystal facets of TiN/Fe ((001), (110), and (111)), which had not been previously explored. Employing molecular dynamics (MD) simulations, the research investigates the microscale differences in erosion resistance and surface properties of various TiN crystal planes under continuous impacts at varying velocities and angles. The results indicate that both surface wear and internal defects of the model increase with the impact velocity. Both TiN(110) and TiN(111) exhibit damage on their surfaces and interiors, with a larger wear range. In contrast, TiN(001), due to its superior elastic recovery capability, maintains a better surface condition, showing significantly less wear compared to TiN(110) and TiN(111). This disparity in performance among different crystal planes is attributed to variations in molecular gaps between planes, bonding points within the lattice, types of forces, and modes of action. Further research revealed that the wear volume increased with the rise in impact angle, reaching its peak at 90°. Regardless of the impact angle, TiN(001) consistently outperformed TiN(110) and TiN(111). The aim of the research is to compare the surface and internal defects of different crystal facets at the microscopic level, thereby selecting superior crystal facets and providing theoretical reference for the application of TiN materials in practical fracturing environments.

Structural and stratigraphic history of the southern domain of the Indian Mountain Deformed Zone, southeastern New Brunswick, Canada: Tournaisian (Lower Carboniferous) tectonic ‘pop-up’ and collapse

The southern domain of the Indian Mountain Deformed Zone (IMDZ) in southeastern New Brunswick marks a major right-lateral strike-slip fault belt active during late Tournaisian (Lower Carboniferous) sedimentation. The rocks of the Sussex Group, representing a depositional cycle from subsidence to basin inversion, occupy this zone and lie unconformable on crystalline basement, the latter representing a partially exhumed portion of the adjacent (to the south) buried Westmorland uplift. Deformation is related to early reverse faults/thrusts, later strike-slip faults. and latest normal faults. The Gorge Fault zone in the southern domain of the IMDZ demonstrates many essential features of the entire zone. The offset of The Gorge Fault zone increases to the east. In the west it forms a blind thrust and asymmetric anticline whereas in the east it expands into a reverse fault/thrust complex. A progressive evolution from reverse faults/thrusts to strike-slip fault movement resulted in a tectonic pop-up, culminating in gravitational collapse along normal faults with listric profiles that flatten out within 100–200 metres of the present erosion surface. Megabreccias formed during deposition of the Sussex Group are contemporary with reverse fault/thrusts. The geometry of the various faults is best explained by progressive deformation within an overall right-lateral strike-slip regime under general shear, with early formed features rotating both congruently and incongruently to the main IMDZ boundaries. Further complexity is a consequence of many reverse faults/thrusts and normal faults occurring close to a free surface and the latter a response to gravitational instability of the pop-up structure controlled by topography. A revised stratigraphy for the Sussex Group in the Indian Mountain Deformed Zone and its interpretation is integral to constructing the structural history. Two units, Stilesville Formation and Briggs Cross Formation, are formally defined here.

Large-scale variability in style and magnitude of footwall rift-related unconformities, Northern Carnarvon Basin, offshore NW Australia

Fault-scarp degradation complexes record rift-related erosion of normal fault scarps. At the scale of an individual fault segment, the magnitude and distribution of erosion are related to the total and along-strike variability in fault throw. However, previous studies on degradation complexes focused on one type of rift-related erosional unconformity, with the factors controlling the development, magnitude, and style of footwall erosion at a far larger scale (i.e., several fault blocks) being poorly constrained. This study uses high-resolution subsurface data to constrain the timing, magnitude, and style of footwall erosion across the NW Shelf of Australia. By doing so, we test conceptual and numerical model predictions for rift-related unconformities development. We show that footwall erosion complexes development is dependent on the occurrence and duration of footwall exposure and that fault throw and footwall uplift control the magnitude of erosion. Furthermore, the style of footwall erosion depends on the driving process(es), with gravitational instabilities resulting in cuspate footwall crest erosional surfaces, whereas peneplain-style surfaces develop in response to wave-driven erosion dictated by the base level. The results of this study can help refine rift-related faults evolution and the effects of sea level changes in tectono-stratigraphic models of rift basins.

New insights on the stratigraphy of the Upper Cretaceous-lower Paleogene successions at Esh-ElMellaha half-graben, Gulf of Suez, Egypt

Detailed field and stratigraphic (lithostratigraphy & biostratigraphy) studies were carried out on the Upper Cretaceous–lower Paleogene successions at Esh-ElMellaha half-graben, Gulf of Suez, Egypt. Four stratigraphic sections were investigated and arranged in a geologic profile extends from south to north as follow: Gabal El-Mellaha, Wadi Abu Had, Wadi Dib and Gabal Tarbul. The field work led to recognize four lithostratigraphic units (formations): Sudr (upper part), Dib, Esna and Thebes (top). The distinctive Dababiya Quarry Member (DQM) which characterizes the Paleocene Eocene Thermal Maximum (PETM) was initially recorded at Esh-ElMellaha region. Sudr Formation is stratigraphically differentiated into two distinctive informal rock units, argillaceous bedded limestone unit and calcareous shale unit. The Dib Formation is here reviewed and correlates with the Dakhla Formation (upper part) in the different geographic neighborhoods of Egypt. It consists of glauconitic carbonate rocks (bioclastic limestone) embracing reworked gravelly and pebbly extra-clasts and broken exhumed mega-fossils (e.g. cephalopods, gastropods and bivalves, corals). Dib Formation is assigned to thelower Paleocene (Danian Stage) according to the occurrence of praemuricids taxa (e.g. Praemurica inconstans and P. uncinata) index fossils. Esna and Thebes formations are assigned to the Ypresian Stage. Dib Formation is bounded by two regional unconformity surfaces (erosional surfaces) as a result of two tectonic events (I and II) linked to Syrian Tectonic Event.

Changes in marine sedimentation patterns in the northeastern South China Sea in the past 35,000 years

In the continental margin of the northeastern South China Sea, the sea level fluctuations since the Last Glacial Maximum have profoundly impacted the sedimentary environment. Our sub-bottom profiler data show a sedimentation process change from deposition to erosion during the Last Glacial Maximum. After the widespread erosion, the sedimentation process returned depositional throughout the Holocene, probably due to the rise of the sea level. This sedimentary process results in a widespread sedimentary unconformity in the continental slope, providing a benchmark for the end of the Last Glacial Maximum. Analyzing the sediment cores, we affirm that the change in current intensity is the primary factor controlling the sedimentary environments. The current intensities strengthened during the eustatic lowstand and weakened during the highstand periods, leading to alternating erosional and depositional processes. The widespread distribution of the erosive surface represents a regional-scale change in the sedimentary environment instead of a local event.

The Desiccation and Catastrophic Refilling of the Mediterranean: 50 Years of Facts, Hypotheses, and Myths Around the Messinian Salinity Crisis.

According to some authors, the Messinian salinity crisis was ended by a giant waterfall or megaflood 5.33 million years ago, when the Atlantic Ocean reconnected in a catastrophic way with the desiccated Mediterranean, creating the Strait of Gibraltar. An erosional surface deeply cutting upper Miocene or older rocks and sealed by lower Pliocene sediments is the geological feature that inspired this fascinating hypothesis. The hypothesis, which recalls several ancient myths, is well established in the scientific community and often considered to be a fact. However, several studies are suggesting that the Atlantic-Mediterranean connection through the Strait of Gibraltar was probably active before and during the entire Messinian salinity crisis. This allows us to consider the possibility that long-lived, more gradual physical processes were responsible for the evolution of the strait, opening the idea of a nondesiccated Mediterranean Sea.

The evolution process of fluting damage on bearing outer races during rolling with a shaft current

This study focuses on the evolution of fluting damage in bearing outer races. Fluting damage first occurred at the loading position and then extended along outer races. This non-uniform distribution of fluting damage is related to the non-uniform load inside bearing. It is speculated that the alteration of bright and dark areas in fluting is related to the periodic destruction and reconstruction of lubricating film. The phase transition from α′-Fe to α-Fe is observed beneath erosion surface. At microscale, non-uniform damage of the fluting appears as the dark area exhibiting more severe erosion, lower oxidation, greater roughness, deeper depth, and lower hardness. The results can provide deeper understanding of the failure process and damage mechanism of bearings in electric fields.

Storm deposits and trace fossils of Xinji Formation (Cambrian Series 2) in the southern margin of North China Plate

The Xinji Formation (Cambrian Series 2) in the southern margin of the North China Plate developed typical siliciclastic storm deposits and abundant trace fossils. These deposits are characterized by essential indicators, such as erosional surfaces, lag deposits, blocky beddings, hummocky cross stratifications, horizontal or wavy beddings. Storm deposits in the study area are dominated by the development of hummocky cross stratifications, which is categorized into five storm deposit types based on the arrangement of different sedimentary units in the profile. These five types of storm deposits from I to V show the transition from proximal storm deposits to distal storm deposits, the gradual weakening of storm intensity, and the associated growth of quiescent intervals. The trace fossils are mainly developed in the sandstone-mudstone interbeds between storm events and include 14 ichnospecies in 11 ichnogenera: Didymaulichnus isp., Gordia marina, Helminthopsis tenuis, Oldhamia radiata, Palaeophycus striatus, Palaeophycus tubularis, Phycodes isp., Planolites beverleyensis, Planolites montanus, Planolites punctatus, Skolithos isp., Taenidium isp., Torrowangea rosei, Treptichnus pedum. By analyzing the ichnological index (burrow size, BPBI, ichnodiversity and ichnodisparity) from different storm deposits, it can be seen that from storm deposit type I to storm deposit type V, the ichnological index shows an increasing trend. Combined with the relationship between storm deposits and trace fossils, it is inferred that differences in storm intensity result in different colonization windows, and thus variations in ichnological index of preserved trace fossils. Based on the characteristics of storm deposits and distribution of trace fossils, the preservation forms of trace fossils under storm influence are explored.

The regressive surface of marine erosion generated by tides: A case study from a Pleistocene tidal sand ridge sequence, Calabria, Southern Italy

AbstractThe regressive surface of marine erosion is a key stratigraphic discontinuity used to identify episodes of forced regression in marine strata. Typically, it marks the base of shallow‐marine (e.g. shoreface and deltaic) deposits eroding over relatively deeper‐water (e.g. shelf and prodelta) lithofacies. While well‐documented in marginal‐marine areas, its occurrence in offshore or strait settings dominated by tidal currents is less understood. This study investigates lower Pleistocene outcrops in the Plio‐Quaternary Siderno Basin, Calabria, southern Italy, where tidal sand ridges developed in a Mediterranean strait. High‐resolution drone images reveal a basinward‐dipping basal surface marking the onset of tidally dominated sedimentation. This discontinuity separates underlying shelf fines from overlying cross‐stratified, tidal bioclastic/siliciclastic arenites, indicating a prolonged period of marine regression in a strait setting. The stratal architecture of the ridges shows cross‐strata aggradation in up‐dip sections, transitioning down‐dip into balanced aggrading/prograding strata, and further basinward into markedly prograding deposits. These features are interpreted to reflect an initial phase of normal regression, evolving into forced regression. This latter stage is characterised by a progressive deepening of the basal discontinuity, causing more erosional effects on the underlying beds, with a vertical basinward fall of about 60 m over 2 km. Internal foreset geometry (two‐dimensional vs. three‐dimensional cross strata) and their vertical and lateral repetition indicate stages of equilibrium and disequilibrium for tidal bedforms, reflecting varying current speeds and water depth changes. The regressive surface of marine erosion here is formed by tidal currents, rather than waves, suggesting a new type of sequence stratigraphic discontinuity associated with tide‐dominated settings.