Deep Erosion Research Articles

Simple model, complex strata: 2-D numerical forward model analysis of heterogeneity and controls in submarine fan systems

ABSTRACT Turbidite strata stacking patterns are interpreted as products of either allogenic forcing, autogenic processes, or a combination of both. However, the relative influence of each remains difficult to constrain. Here, a simple reduced-complexity 2-D numerical forward model (Lobyte2D) simulates gravity flows passing down a slope, running out, and depositing across a flat basin floor. Flows can erode, bypass, or deposit, cumulatively producing a variety of entirely autogenic retrograding, aggrading, and prograding strata with stratigraphic completeness values ranging from less than 1% to around 40%. Complexity of modeled strata is measured with a spatial entropy metric, and sensitivity analysis indicates that grain-size and flow-acceleration parameters are the key controls on stratal complexity: larger grain sizes are associated with deeper erosion, which makes more rugged topography, and higher values of flow acceleration make flow speeds more sensitive to topography, which triggers localized deposition and/or erosion. Such complexity produced by a simple two-dimensional numerical forward model suggests that even more complex behavior is likely in natural systems, and this should be reflected in outcrop and subsurface interpretations. However, comparison of geometries in chronostratigraphic and cross-section plots of modeled strata shows that, due to a variety of cryptic bypass and erosion surfaces, stacking trends visible in chronostratigraphic plots are much more difficult to detect in outcrop and subsurface cross sections and vertical sections. These insights suggest that many outcrop and subsurface interpretations of submarine-fan strata, particularly sequence stratigraphic interpretations, may be missing substantial complexity, and underestimating the uncertainty inherent in limited data.

The Erosion Pattern and Hidden Momentum in Debris‐Flow Surges Revealed by Simple Hydraulic Jump Equations

AbstractThe erosion‐deposition propagation of granular avalanches is prevalent and may increase their destructiveness. However, this process has rarely been reported for debris flows on gentle slopes, and the contribution of momentum hidden under the surge front to debris‐flow destructiveness is ambiguous. Therefore, the momentum carried by the apparent surge front is often used to indicate debris‐flow destructiveness. In this study, the erosion‐deposition propagation is confirmed by surge‐depth hydrographs measured at the Jiangjia Ravine (Yunnan Province, China). Based on simple hydraulic jump equations, the eroded deposition depth of surge flow is quantified, and the erosion pattern can be divided into two patterns (shallow and deep erosion). For surge flows with erosion‐deposition propagation, significant downward erosion potential is confirmed, and debris‐flow surge erosion is considered the deep erosion. The total momentum carried by surge flow is further quantified by two Froude numbers (surge‐front and rearward Froude numbers) and verified through the field observation of surge flows. The total momentum of surge flow not only originates from the apparent surge front, but also includes the momentum within the eroded deposition layer. This study provides a theoretical approach for quantifying the upper limit of erosion depth and revealing the destructiveness of debris‐flow surges. A perspective on the importance of substrate deposition for debris‐flow erosion on gentle slopes is emphasized, as this approach can improve the reliability of debris‐flow risk assessment.

Time-lapse surveys reveal patterns and processes of erosion by exceptionally powerful turbidity currents that flush submarine canyons: A case study of the Congo Canyon

The largest canyons on Earth occur on the seafloor, and seabed sediment flows called turbidity currents play a key role in carving these submarine canyons. However, the processes by which turbidity currents erode submarine canyons are very poorly documented and understood. Here we analyse the first detailed time-lapse bathymetric surveys of a large submarine canyon, and its continuation as a less-deeply incised channel. These are also the most comprehensive time-lapse surveys before and after a major canyon-channel flushing turbidity current. These unique field data come from the Congo Submarine Fan offshore West Africa, where canyon flushing turbidity currents between 2019 and 2020 eroded ~2.65 km3 of seabed sediment, as they travelled for over 1100 km at speeds of 5–8 m/s. This eroded sediment volume is equivalent to ~19–33 % of global sediment flux from all rivers to the oceans. The time-lapse surveys cover 40 % of the 1100 km long submarine canyon-channel. They show that erosion was predominantly (94 %) along the canyon-channel axis, with only 6 % from failures along canyon or channel flanks. However, erosion along the canyon-channel floor was very patchy; some areas were eroded to depths of 10–20 m, whilst intervening areas showed no significant change. Knickpoints with up-slope migrating headscarps account for 22 % of the total eroded volume. One knickpoint in the deep-sea channel migrated by 21 km in one year, making it the fastest moving submarine knickpoint yet documented. Most (62 %) eroded sediment was in zones extending across the canyon or channel floor, without distinct headscarps as is the case for knickpoints. Erosion restricted to outer bends only comprised 10 % of the total, suggesting processes of erosion differ significantly from meandering rivers in which outer bend erosion is more important. Patchy seabed erosion appears to be mainly due to flow-bed processes (e.g. knickpoints), but spatial variations in seabed sediment properties may also play a role. The irregular seabed erosion occurs despite near-uniform flow speeds observed between moorings and submarine cable breaks with spacing of tens to hundreds of kilometers. Patchy and localised erosion has important implications for assessing hazards to seabed telecommunication cables, which are more likely to break in areas of deep erosion, and for creating appropriate numerical models of seabed erosion and turbidity current behaviour, or how to interpretate ancient submarine canyons and channels in rock outcrops.

Assessing the level of river basin evolution, erosion susceptibility and its correlation with morphometric characteristics using Geoinformatics techniques

The application of Geoinformatics have become fastest and improved advanced tools to analyse and interpret the topography and hydrological characteristics. This study aimed to utilize the advantage of high resolution (30 m) remote sensing data of Shuttle Radar Topography Mission (SRTM) and the geoinformatic tools of Quantum Geographical Information System (QGIS) for extraction of detailed and accurate drainage morphometry and elevation information in preparation of hypsometric curves. Making use of QGIS, the SRTM data and topographic maps are georeferenced and pre-processed algorithm tools of stream burning and fill-DEM are applied for DEM preparation and extraction of accurate drainage network and its basin areas. From the DEM map, the details of elevation and area of basins are extracted for preparation of hypsometric curves. Hypsometric curves are analyzed to interpret and understand the heterogeneity in the levels of basin evolution/development and erosion at 4th order sub-basin level. The concave hypsometric curves of main basin and sub-basins indicate that total basin as well as sub-basins reached the old/monadnock stage due to the dominance of fluvial process. Based on the hypsometric area/integral (Ea) and Concavity of hypsometric curve values (Eh), five classes/stages of basin development and erosion levels are identified within the old/monadnock stage. The Ea values range from 0.10 to 0.35 and Eh range from 0.25 to 0.77 in this study area. Initial old/monadnock stage of basins have Ea values > 0.28 and Eh values < 0.4 indicating low levels of erosion among the sub-basins. Low hypsometric area/integral value (Ea) indicates the higher level of landmass removal by erosion and basin development. The oldest stage basins are identified with Ea values range from 0.10 to 0.15 and Eh values range from 0.61 to 0.77 indicating higher level of landmass removal/erosion. The lithological variation plays a significant role on hypsometry of the basins. The high hypsometric integral (Ea) values (i.e., 0.28 to 0.35) of 1,2 and 3 sub-basins indicating the early/ initial level of old stage in its’ basin development, since the resistant basalt formation is sandwiched between sandstones prevented deep erosion and depicting less dissected topography. The hypsometric integral has positive correlation with form factor and negative correlation with drainage morphometric characteristics. It indicates that the level of basin evolution increases as the form factor decreases but number of streams, length of streams, mean bifurcation ratio, relief, relief ratio and ruggedness ratio increases. This study is highly useful to understand the relation among morphometric characteristics, basin development and erosion levels through the analysis of hypsometric curves making use of Geoinformatic techniques.

Tracing uplift and erosion in orogenic settings using quartz luminescence sensitivity: Insights from the Northern Andes uplift

The optically stimulated luminescence (OSL) sensitivity of the fast component in quartz has been increasingly used in provenance analysis of Quaternary sediments. Quartz OSL natural sensitization is thought to be mainly controlled by the formation conditions of the source bedrock and surface processes occurring mainly in sediment source areas. Thus, quartz OSL sensitivity can be linked to distinct sediment source regions, based on their tectonic setting and erosion conditions. In this way, changes in quartz OSL sensitivity within siliciclastic successions would track variations in sediment provenance. So far, few works evaluated how the OSL sensitivity of quartz sand grains varies in sedimentary successions that experienced long-term cycles of deep burial, exhumation, and erosion. Therefore, this work aims to characterize the sensitivity of the fast OSL component of quartz sand grains retrieved from the Cenozoic sedimentary rocks of the Northern Andes basins and assess its spatiotemporal changes. We found that quartz grains with the lowest OSL sensitivity are sourced by crystalline and volcanic rocks related to the Andean Continental Arc emplaced in the Colombian Central Cordillera, reflecting the onset of denudation in orogenic sources during the Paleocene. Subsequently, increasing trends in OSL sensitivity are related to the sedimentary recycling during the Andean orogeny, reaching maximum values as a result of the progressive unroofing of Cretaceous rocks in the Colombian Eastern Cordillera, originally sourced from the low-relief Amazon Craton. Changes in quartz OSL sensitivity measured in the Cenozoic sedimentary basin-fill sequences of the Northern Andes vary according to the shifts in sediment provenance related to the orogenic construction and sediment recycling of the Andean range.

Climate-regulation of organic carbon export in erosive mountain settings: A case study from Taiwan since the last glacial maximum

The balance between the burial of biospheric organic carbon (OCbio) in the ocean and the oxidation of rock-derived organic carbon across landscapes (OCpetro) helps to regulate atmospheric CO2 and O2 over geological time. However, we lack reconstructions of these processes over the timescales necessary to properly understand the drivers and feedbacks operating. Here we use a sediment core from the Zhuoshui River delta in Taiwan, which receives sediments from a rapidly uplifting and eroding catchment, to reconstruct the variations in OC content and radiocarbon composition since the Last Glacial Maximum (LGM). We find that the export of OCbio and the oxidation of OCpetro are both modulated by climate-driven changes in physical erosion and temperature. During cold and dry periods, such as the LGM and the Younger Dryas (YD), shallow erosion and low temperature enhanced the preservation of OCbio in the biosphere in catchment, while deep erosion and high temperature during warm and wet periods, such as the Holocene, favored the dilution and degradation of OCbio. The weathering intensity of OCpetro (ω) was inversely related to physical erosion, suggesting a lower intensity of oxidation during the Holocene period while the overall oxidation flux was enhanced. This suggests that the degree of weathering was primarily controlled by physical erosion. We propose a proxy to estimate the ratio of fluxes of OCbio export and OCpetro oxidation, and show that the net balance between these two processes shifted from a carbon sink during the late deglacial period to a carbon source during the mid-late Holocene. Our study reveals that with CO2 rise, a warmer and wetter climate would promote the exposure and oxidation of OCpetro by erosion in this mountain range, leading the organic carbon balance towards a CO2 source to the atmosphere.

Analysis of bed changes in the segment of the Tien river flowing through Tan Chau

The segment of the Tien River flowing through Tan Chau town is a meandering section with complex flow patterns, influenced by the flow dynamics and the lack of upstream sediment supply. This has resulted in the formation of deep erosional channels that affect the bank stability. This study focuses on evaluating the bed change of the Tien River within Tan Chau town through the analysis of measurement data and some scenarios from numerical modeling. The findings reveal that the Tan Chau - Hong Ngu curved section experiences severe channel erosion, particularly concentrated in the topographic channel and inclined towards the concave bank of Tan Chau (the inner bank). An analysis of causative factors indicates that reduced sediment supply due to dam construction and sand mining activities have led to changes in the riverbed, deeper erosion, and bank erosion near the sand mining area. The results quantifies the sediment deficit in the area at 0.86%, while the impact of sand mining in this area is 0.26%. The findings from this research provide a database to support local planning for bank protection projects and disaster mitigation measures due to bank erosion.

Key technologies for improving resilience of super-large diameter shield tunnel affected by large variable loads underneath the Yellow River

Environmental conditions may have a significant impact on the construction and operation of underground works, and sudden changes in environmental conditions may lead to underground engineering damage. Considering the Yellow River crossing tunnel on Huanggang Road in Jinan as an example, this paper analyzes the mechanical performance of the lining of the shield tunnel with an external diameter of 16.8 m, which faces the challenge of large variable loads in operation stage, such as deep riverbed erosion and deposition, large-scale heightening of river embankment, seasonal changes in groundwater level, and key technologies for improving the resilience of tunnel structure are proposed accordingly. The results can not only assist in the construction of the super-large-diameter shield tunnel project in Jinan City but also provide technical support for other shield tunnel projects crossing rivers, lakes, and seas.

Norwegian Sea Oceanic Basin and Prograded Margins Composite Tectono-Sedimentary Element

Abstract The Norwegian Sea oceanic basins and prograded margins have developed since NE Atlantic break-up in the earliest Eocene. Significant amounts of sediments were fed to the regionally subsiding and widening Norwegian Sea during the Cenozoic as a result of several phases of uplift and erosion of the bounding shelves and their hinterland. Despite an overall passive-margin evolution, the area experienced tectonic events and associated processes that interrupted the regional subsidence, causing contraction/inversion and tilting. The post-break-up depositional history of the mid-Norwegian margin comprises two main stages: (1) middle Eocene–Pliocene margin subsidence and relatively modest sedimentation during a period of climatic decline; and (2) latest Pliocene–Pleistocene full-scale northern hemisphere glaciations that resulted in deep erosion of shelves and hinterlands, and very high sedimentation rates and large-scale continental margin progradation. Slope failures within rapidly deposited glacial sediments affected both prograded margins, releasing large slides that travelled downslope into the oceanic Norway and Lofoten basins. Despite a long exploration history for hydrocarbon prospects in deeper waters and large amounts of data acquisition, no significant discovery has been made.

Cost accounting practices in SMEs: liability of age and other factors that hinder or burst its implementation in turbulent years

AbstractThis study aimed to investigate the level of cost accounting (CA) implementation in small- and medium-sized enterprises (SMEs). CA is a management accounting tool whose application in small companies has always been difficult. Nevertheless, academicians and practitioners recommend CA implementation in SMEs, especially because of the deep market instability, competitive pressure, and margin erosion that have occurred following the COVID-19 pandemic and 2022 European war scenario. Company size influences CA implementation; however, it is not the only influencing factor and perhaps not even the most important. To investigate the barriers to the adoption of CA and which conditions or actions can remove these barriers, leveraging from the contingency theory, a questionnaire was sent out in July 2022 to limited liability SMEs operating in the manufacturing, construction, and distribution macro-sectors in Verona and Vicenza provinces (Italy). Respondents answered a set of questions regarding CA implementation in their SMEs as of July 2022. Using a multivariate regression model to analyze data from the 120 questionnaires received, we found that lack of resources, limited training and skills, firm age, and the presence of the founder in the firm had a negative influence on CA implementation in SMEs. The low level of CA implementation was also associated with its supposed inefficiency, uselessness, and unsuitability for business. The effect of company size on CA implementation was not statistically significant. Despite this study’s limitations regarding the sample and period considered, we believe that it contributes to both academic debates and practice by illustrating the limiting factors and ways in which CA implementation can be fostered in SMEs in turbulent years.

БЛОКОВИЙ ХАРАКТЕР НОВІТНЬОЇ ТЕКТОНІКИ СЕРЕДНЬОГО ПРИДНІПРОВ'Я НА ОСНОВІ КАРТ РІЗНИЦЬ БАЗИСНИХ ПОВЕРХОНЬ

Background. The tectonic evolution of the Middle Dnipro region in modern times is particularly complex. The presented studies were conducted within the right-bank part of the Middle Dnipro, since the maximum activation of neotectonic activity zones is observed in this region, with significant gradients of the latest tectonic movements and their impact on the formation of the modern relief, that require a comprehensive assessment of the impact of geological and geomorphological factors on their formation. Methods. Structural and morphometric studies within the Middle Dnipro region, using remote sensing methods and spatial-analytical modeling, allowed us to determine morphometric parameters related to the terraced levels of the Dnipro River, the processes of deep erosion, denudation and accumulation, as well as the nature of recent and modern tectonic movements. Results. Detailed interpretation of multi-genetic and multi-order structural and morphometric maps, as well as in-depth geological analysis, allowed us to identify morphostructures and block structures of the crystalline basement (regional blocks and local microblocks), which are distinguished by differentiated tectonic movements and peculiarities of tectonic development. Сonclusions. The neotectonic conditions of formation and development of the paleorelief of the Right Bank of the Middle Dnieper are reconstructed. The peculiarities of the development of terraced levels in the Neogene and Quaternary periods are established. The obtained data can serve as a basis for analyzing the influence of tectonic movements on the activation of hazardous geological processes within the Middle Dnieper region and forecasting their development in the future.

The origin, conditions and mechanism for the formation of alpine-type hyperbasites of the Lesser Caucasus

The problem of hyperbasites origin is one of the widely discussed topics in geology. This is because they often appear when no expected. Their development does not correspond to the general regularities of the geological complexes’ development. Therefore, when problematic instances of hyperbasites appear, discussion is inevitable. This is due to the imperfections of existing concepts, which are not without flaws. The essence of this concept lies in the fact that during the rotation of the Earth around its axis, geodynamic forces are formed. The hyperbasites complex by its nature belongs to deep igneous formations formed at the initial stage of development of volcano-plutonic processes, where the composition of magmatic products was not subject to decomposition. In general, the origin of igneous rocks is associated with deep anomalous processes, which were formed under the influence of geodynamic forces, where decompression of mantle matter occurs, causing a catastrophic increase in the volume of mantle matter, as well as the associated development of volcanoplutonic processes. Hyperbasites are formed both in divergent and convergent zones of the Earth’s crust. The main factor for their formation is high pressure – deep thermodynamic conditions, where there are no favorable thermodynamic conditions for the complete separation of magmatic melts by composition. The emergence of hypermafic rocks on the surface is associated with geotectonic or denudation processes. Denudation processes can expose only those hypermafic formations that are located at the site of formation. These zones include ancient platforms, sheets, terranes, etc., which were cut by deep erosion processes. As for those hyperbasic formations that are classified as alpinotype hyperbasites, they were moved to the structure of the Alps-Himalayan folded zone from the basement with a collision with subsequent geotectonic processes, where they formed in the bed of the Paleotethys Ocean, both in the process of divergence and convergence. The noted pattern of formation and the mechanism of formation of alpine-type hyperbasites clearly corresponds to the patterns of development of geodynamic forces in the face of the Earth, also with natural laws, which are the main factors in the evolution of the Earth’s crust. From the standpoint of KDEZK, the origin, mechanism of formation, as well as the form of distribution of alpinotype hypermafic rocks of the Lesser Caucasus occurred in the Paleotethys bed, under different thermodynamic conditions and at depths. Further, as a result of the collision, it participated in the formation of folded zones of the Lesser Caucasus. Within the Lesser Caucasus, two genetic types of hypermafic rocks are exposed. Some of them correspond to the convergent zone of the Tethys paleocean, while others correspond to divergent zones. In terms of ore content, the most promising are those hypermafic rocks that are genetically related to convergent zones.

Mode and timing of the Early Cretaceous transgression in Iran: Insights from the stratigraphic evidence of sea-level changes and geodynamic events

The study of selected logs from the Central-Eastern Iran Microplate (CEIM; area of Arusan) and Sanandaj–Sirjan Zone (SSZ; areas of Esfahan east and Tiran) constrains timing and evolution of the Cretaceous successions, resting unconformably on older sediments or non-conformably on the metamorphic basement. The Cretaceous marine transgression occurred almost synchronously on a levelled topography, documenting a previous deep erosion. Above a basal siliciclastic unit, rudist- and orbitolinid-rich lower Aptian limestone (“Orbitolina Limestone”, Shak Kuh Formation, Taft Formation) were deposited. Later, the stratigraphic evolution of the three studied areas differentiates, documenting changes in the depositional environments, reflecting different subsidence rates. In the Tiran area, marls and cherty limestones covering shallow-water limestones record a deepening trend. A differentiation of depositional environment is observed at Arusan, where conglomerates to the west pass to basinal sandstone and marls to the east. Here, a Coniacian-Campanian reprise of the carbonate production (with skeletal limestones rich in rudists, ostreids, and abundant orbitoidids) is covered by cherty marls. In the Esfahan north area, glauconitic hardground marls covered by chert record important deepening during the early Cenomanian, followed by the reprise of shallow-water carbonate production (middle Cenomanian). The synchronous deposition of Aptian carbonate successions on large parts of the CEIM, SSZ and North-Iranian domains suggests a rapid regional transgression controlled by a sea-level rise. Stratigraphic differentiation occurring in late Aptian–Cenomanian times, recording the onset of tectonic events differently affecting the aforementioned domains, likely related to the opening of oceanic seaways in the CEIM and the SSZ.

Influencing mechanism of saline sediments on pore system formation and evolution in terrestrial shales

The majority of oil and gas resources in the world are related to saline sediments, which mainly occur in sedimentary strata in the form of cap rocks or salt-associated shales. A large number of shale oil resources have been discovered in the saline shale sediments of the Cenozoic terrestrial lake basin in China. The hydrocarbon generation ability and the reservoir capacity of shale control the oil and gas generation. The reservoir capacity is mainly characterized by pore type, structure and porosity. Most of China’s shale oil and gas resources belong to salt-bearing formations. The role of gypsum-salt rocks in the formation and evolution of organic matter (OM) in such formations has received extensive attention. However, systematic understanding is lacking. Research on the pore formation and evolution in shale under the action of gypsum-salt rock sediments is especially weak. Taking the shales in the third member of the Shahejie Formation (Es3) of the Bohai Bay Basin as an example, the influence of halite on the formation and evolution process of pores was studied in this paper. The results show that halite and gypsum minerals were associated with OM, which made them more likely to develop OM pores. The samples with a high halite mineral content (HC) are more developed regarding the pore volume and specific surface area than those with a low HC. The formation of thick salt rocks is influenced by factors of deep thermal brine upwelling, sea erosion and arid environments. The frequent alternation between humid and arid environments led to the outbreak and death of organisms and the precipitation of gypsum-salt rock, which formed the simultaneous deposition of OM and halite minerals. Finally, we have established a model of shale pore evolution under the participation of the gypsum-salt rock, and halite minerals contribute to pore development in both Stage II and Stage IV. This study provides strong microscopic evidence for the pore system formation and evolution in salt-bearing reservoirs.

New exposure of the Cretaceous–Paleogene unconformity and Paleocene–Eocene pebble bed in the Paleogene outlier at Collier's End, Hertfordshire, UK

The Paleogene outlier at Collier's End, Hertfordshire lies on the northern rim of the London Basin. This small outlier has archaeological and geological significance. Silica-cemented concretions of Hertfordshire Puddingstone lie within a regionally mappable pebble bed. The first discovery of a Roman quarry to recover puddingstone for manufacture of querns was made in the outlier. A rare complete section from the Chalk Group up through the Paleogene was temporarily exposed in 2021 and is recorded here. The Paleogene shows features that may be associated with the Paleocene–Eocene Thermal Maximum (PETM). The chalk in the new exposure is Late Coniacian. This age provides further evidence of relatively deep erosion of the chalk in this area, as erosion of chalk at the crest of a regional dome preceded advances and retreats of the western shore of the Paleogene North Sea. These events may be linked to the early development of the Icelandic mantle plume.

Intensive geological alteration and gas accumulation in Longmaxi Formation shales at moderate and great depths: A case study of the Luzhou area in the southern Sichuan fold zone, China

In recent years, significant efforts have been directed towards extracting deep shale gas (SG) in Luzhou. Understanding the factors influencing the accumulation and preservation of SG in the section extending from the Upper Ordovician Wufeng (WF) Formation (Fm) through the Lower Silurian Longmaxi (LMX) Fm is crucial for its large‐scale, profitable development. The shale layers in the LMX Fm located in the Luzhou‐Zigong area in the southern part of the Sichuan Basin have undergone unique geological processes, including deep deposition, intensive uplift, erosion and deformation. The Luzhou block, situated in the low‐fold zone in southern Sichuan between the southern slope of the paleo‐uplift in central Sichuan and the down‐warping fold zone in south‐eastern Sichuan, was studied using seismic, well‐log, drilling and core analysis and test data to understand its tectonic, sedimentary, reservoir and fracture characteristics and identify the principal factors controlling gas accumulation in this area. The study found that SG in the Luzhou block is primarily distributed in the WF Fm through the Longyi1sub‐member. Class I continuous reservoirs, 2.6–20.3 m in thickness, are mainly found in the Longyi11–13sublayers and those with large continuous thickness produced high yields during tests. Gentle anticlinal zones and wide, gentle tectonic structures with relatively high‐pressure coefficients have formed in this area. High‐angle fractures (HACs) in this area tend to accumulate free gas and, therefore, facilitate the accumulation and production of SG. The study concludes that the continuous thickness of Class I reservoirs and natural HACs controlled by the centre of the deep‐water continental shelf are the primary factors controlling SG accumulation in the Luzhou block.

DEVELOPMENT OF THE MINIATURE ANALOGUE OF THE SCABLANDS OF THE WEST USA IN THE LOWER POOL OF ONE OF THE KARELIAN HYDROELECTRIC POWER STATIONS&lt;a href="#FN1"&gt;&lt;sup&gt;1&lt;/sup&gt;&lt;/a&gt;

Until the end of the Late Pleistocene, the modern river valleys of most of Scandinavia remained buried under the cover of continental ice. The rivers of the region, including the Karelian ones, are distinguished by their geological youth, having formed as fluvial complexes only in the Holocene. The young age, combined with the strength of the crystalline rocks of the Baltic Shield, has affected the fact that the rivers here are characterized by the lack of development of the longitudinal profile. At the base of the thresholds, at which the flow acquires the character of rapid, the processes of formation of miniature scaffolds develop in places. A similar hydraulic situation developed at the front of the degrading glacier. The lower reaches of dams of hydraulic stations are also favorable for a powerful impact on the rock bed. Numerous traces of violent deep erosion, accompanied by the phenomena of indiscriminate erosion and hydrodynamic cavitation, can be found on the kilometer-long sections of the exposed rock bed of semi-mountain streams drained during hydraulic development.A miniature scaffold developed by powerful natural and technogenically provoked floods in the lower part of the large rapid Matkozhnia on the Nizhny Vyg River, in the zone of the White Sea-Baltic Canal, is indicative. Almost the entire route of the canal, starting from Vygozero, is laid along the valley of the Lower Vyg. Only in some sections between the locks, the channel bed was dug away from the river. There, the old valley is preserved either almost dehydrated or with a small amount of water in the rock bed. The bedrock is exposed along the entire riverbed. Small boulders and pebbles of different sizes and grades of rolling can be found only in scattered pockets along the river channel. There numerous glass–like forms of microrelief – with a diameter and a depth of up to the first meters – “glasses” and “wells” are formed on Precambrian crystalline rocks. The contribution of evorsia to the denudation of crystalline slates in the bottom of the Vyga Valley on the rapid Matkozhnia is very significant, although the evorsion-cavitation effect itself is carried out rarely and for a limited time. Similar processes of natural origin operated before the creation of reservoirs on rapid-waterfall sites in the Vyga Valley and other large rivers of Karelia; they were caused by natural factors. Emergency descents of water through high spillway dams could increase the destructive effect of the stream on its root bed. So, in particular, the formation of evorsion microforms in the bed of the Lower Vyg at the rapid Matkozhnia is partially technogenically caused. Karelian cavitation-evorsion complexes of forms associated with hydrospheric catastrophes can be considered as miniature analogues of giant Late Pleistocene scablands of the northwestern USA.

Microfossils and Sedimentary Environments of the Zherba Basin: Upper Vendian of the Patom Highland of Siberia

In the Upper Vendian deposits of the Zherba Formation of the Siberian Patom Basin, an association of organic-walled microfossils was described for the first time. The microfossils differ markedly from each other in the type of preservation. One group of microfossils includes highly corroded filamentous and rare spheromorphic acritarchs. The other group is represented exclusively by spheromorphic and acanthomorphic acritarchs with well-preserved vesicles, which are identical to microfossils from the underlying Lower Vendian Ura Formation. The performed facies analysis showed the coastal-continental and shallow-water-shelf environments of the Zherba basin, which existed under low sea level conditions and deep continental erosion in adjacent uplifts. Under such conditions, the ancient Ura microfossils contained within fine-grained lithoclastics could enter the sedimentation zone inhabited by primitive shallow-water communities. The processes of large-scale recycling throughout almost the entire Zherba time led to the mixing of taphocenoses of different ages, represented by ecologically and taxonomically contrasting associations of microorganisms.

Procedure of Numerical Modelling and Estimation of Sieve Curve Changes as a Tool to Define Riverbed’s Erodibility

The numerical 1-D HEC-RAS modelling tool was supported by the estimation of the sieve curve changes procedure to measure the scale of predicted discharges along a stretch of stream in southern Poland on the Olkusz Upland. The procedure was calibrated in southern Poland on the mountain streams during high-stage events, using a radiotracer application in bedload transport. Particular terrain hypsometry, created by the dissolution of limestone, forced the deep erosion of the river valley bottom; it is here that the current shape of the riverbed of the Prądnik stream is placed. While numerical modelling is widely used in hydraulics, standards have been set for the estimation of flood risk zones; these estimations suggest that the densities of the measured cross-sections are less then optimal, and that the erosive processes are more frequent. This was proved by identifying a number of erosive sections. A new procedure proposed combining the prediction of grain size distribution with hydraulic modelling. Calculations using the estimation of sieve curves, based on the processes of creation and destruction in the armouring layer, have proven to be a challenge for the existing standards of hydraulic modelling. We believe that it is easy to expand the usefulness of the 1D model by utilising its results for this procedure. For the purpose of this type of analysis, dense cross-section measurements are involved, careful modelling is required and a wide range of additional in-field data has to be gathered. For the interpretation of the results, the relation between channel-forming discharge, bankfull discharge, present and critical shear stresses, as well as the mean diameter of the grain size and other estimated sieve curve parameters, were evaluated. Channel-forming discharge is smaller than the bankfull discharge in more than one third of the segment where the erosion process is more frequent and the stability of the riverbed is compromised. Channel-forming discharge was at least twice as high in the stable sections, compared to the erosive section. The presented method will help to find unstable riverbed sections, in order to mitigate the dimension of river training techniques and protect the natural state of the river. While we are in the period of development in this region of Europe, limiting the scope of interference in rivers and streams by applying this method may create an opportunity for the concept of river training close to nature.

Using a New Cenozoic Glacial History Paradigm to Explain Saline-Smoky Hill River Drainage Divide Area Topographic Map Evidence: Kansas, USA

A recently proposed glacial history paradigm (new paradigm) explains previously ignored Saline-Smoky Hill River drainage divide area topographic map drainage system and erosional landform evidence by headward erosion of the east-oriented Saline River valley across large and prolonged south-oriented meltwater floods which flowed in complexes of closely-spaced anastomosing channels. The eastward sloping drainage divide extends from the Saline River&amp;rsquo;s western Kansas headwaters between the Saline River (north) and the Smoky Hill River (south) until in central Kansas the Smoky Hill River turns in a southeast and then north direction to join the Saline River with their combined flow continuing as the Smoky Hill River in an east direction to join the Republican River with the combined flow then becoming the Kansas River. Evidence for closely-spaced south-oriented anastomosing channels consists of previously undescribed low points (divide crossings) which are found along the drainage divide and which link north-oriented Saline River tributaries with south-oriented Smoky Hill River tributaries. Evidence that Saline River valley headward erosion beheaded and reversed south-oriented anastomosing channels also consists of the numerous low points along the drainage divide and of barbed tributaries to the now north-oriented Saline River tributaries which suggest large south-oriented meltwater floods extended much further west than commonly accepted glacial history interpretations permit. The topographic map evidence is consistent with the new paradigm interpretation that a thick continental icesheet by its weight and by deep erosion created and occupied a deep &amp;ldquo;hole&amp;rdquo; as massive south-oriented meltwater floods flowed across the rising deep &amp;ldquo;hole&amp;rdquo; rim until the deep &amp;ldquo;hole&amp;rdquo; rim uplift diverted the floodwaters toward what became the deep &amp;ldquo;hole&amp;rsquo;s&amp;rdquo; only remaining southern outlet (the Mississippi River valley).