Bench development along the regulated,lower River Dee,UK

Channel change to regulated flows along large lowland rivers with cohesive bank materials has been investigated on the lower Welsh Dee, including the tidally influenced reach. Reduction of channel width has involved the formation of a 5–40m wide discontinuous bench, often linking ‘point’ and ‘concave’ locations. Map evidence shows that wide benches occur where historically the channel had migrated laterally; narrow benches were found at stable channel locations. Auger cores of the bench deposits clearly differentiated the two contrasting depositional environments within meandering rivers: ‘point bench’ and ‘concave bench’. Around an individual bend a morphologically continuous bench showed a gradient in sediment characteristics from coarser sediments (point locations) to finer organic deposits (concave locations); it also showed a topographic gradient, gaining 0.5m in elevation around the bend suggesting that bench accretion at concave locations is faster than at point locations in fluvially dominated reaches. Such patterns are suggested to have important implications for riparian ecosystems. Copyright © 1999 John Wiley & Sons, Ltd.     

Local-soil and source-mechanism effects in the 1986 kalamata (Greece) earthquake

An M_s ～ 6 earthquake, originating at a normal fault directly underneath the town of Kalamata, caused substantial structural damage to reinforced-concrete and masonry buildings, to contemporary as well as centuries-old churches, and to a major harbour quaywall. Two accelerograms were recorded on stiff alluvial deposits. The seismologic and engineering facts of the earthquake are presented in the first half of the paper. Particular attention is paid to the non-uniform pattern of damage distribution, at both regional and local scale. The second half of the paper investigates the possible role of the ‘local soil conditions’ and of the ‘mechanics of the source’ in the observed pattern of damage and in the amplitude and frequency composition of the two records. To this end, numerical modelling of site-specific motions is attempted using state-of-practice methods, and utilizing the results of an extensive geotechnical exploration programme. It is concluded that substantial evidence does exist indicating that both soil and source effects have contributed to the non-uniform spatial distribution of damage. The effect of through-soil ‘filtering’ of the seismic waves appears most evident in the coastal neighbourhoods of the town, where the underlying loose saturated silty sands in the over-50 m-deep soil deposit may have played a beneficial role in weakening the ground-surface shaking; the structural damage in these areas was insignificant. Qualitative arguments are also put forward for explaining some aspects of the observed pattern of damage in terms of fault orientation and ‘directivity’ effects.     

Gas-induced erosion features in the North Sea

Pockmarks are prominent features on the seafloor at two main regions of the North Sea, the South Fladen area and the Norwegian Trench. The pockmarks vary in size from 5 m across to about 150 m and in depth from 1 m to about 20 m. Some of the features consist of several very small ‘unit-pockmarks’. These are probably gas-induced erosion features and found only in soft, finegrained, marine and glaciomarine sediments. They are probably caused by shallow- or deep-seated gas (or fluid) release through the seabed, whereby the finest particles are thrown into suspension and redistributed by nearbottom currents. On the North Sea Plateau a small pockmarked area has recently been found. A close relationship exists here between mobile gas in the upper sediments, faulting in the soft sediments and the morphology of the seabed. Other morphological features in the North Sea such as ‘coast parallel depressions’ and ‘elongated depressions’ or terraces are also interpreted here as gas-induced erosion products. This applies, yet again, to the ‘mottled seabed’ features, which appear as patches of high reflectivity on side scan sonar records from the North Sea Plateau; they correspond to shallow seabed depressions on the deep towed boomer records. Judging from reported observations from several shallow seas world wide volatile transport through the seabed is probably quite common and several morphological features are undoubtably induced by this process. Several erosion features of similar origin are probably common, also, in deep ocean basins.     

The effect of cyclic variation of shear stress on non-cohesive sediment stabilization by microbial biofilms: the role of ‘biofilm precursors’

Biofilm mediated intertidal sediments exhibit more complex erosional behaviour than abiotic systems. A major feature of intertidal systems is the exposure to repeated cycles of high and low shear created by tidal conditions and also less predictable episodic events, such as storms. There is very little information on how biofilm-forming communities respond to these conditions. In this study, the effects of both single and repeated-cycles of shear on the stability of newly developed bio-sedimentary beds was examined. Cleaned sand, without any potential biostabilization, was used as the control. For the single-cycle scenario, biofilms were incubated on a non-cohesive sandy bed under prolonged low shear periods varying between 5 and 22 days, after which erosional stress was applied. No significant biostabilization was observed for the youngest bio-sedimentary bed (after five days of low shear incubation). After 22 days, microbial communities were characterized by a firmly attached surface biofilm. To cause erosion, greater hydrodynamic stress (0.28 Pa) was required. The erosional behaviour of the underlying sand was also affected in that bedform ripples noted in the control system were no longer observed. Instead, a sudden ‘mass erosion’ took place (0.33 Pa). The one-cycle scenario indicated that significant biostabilization of sand only occurred after a relative long calm period. Under repeated cycles of stress (five days of low stress followed by high stress event and re-incubation, repeated for four cycles = 20 days), frequent cyclic disturbance did not degrade the system stability but enhanced biostabilization. The properties of the sub-surface sediments were also affected where erosion rates were further inhibited. We hypothesize that organic material eroded from the bed acted as a ‘biofilm precursor’ supporting the development of new biofilm growth. A conceptual framework is presented to highlight the dynamics of bio-sedimentary beds and the effects of growth history under repeated-cycles. © 2019 John Wiley & Sons, Ltd.     

Spatial and temporal variations in bank erosion on sand‐bed streams in the seasonally wet tropics of northern Australia

Bank erosion rates and processes across a range of spatial scales are poorly understood in most environments, especially in the seasonally wet tropics of northern Australia where sediment yields are among global minima. A total of 177 erosion pins was installed at 45 sites on four sand‐bed streams (Tributaries North and Central, East Tributary and Ngarradj) in the Ngarradj catchment in the Alligator Rivers Region. Bank erosion was measured for up to 3·5 years (start of 1998/99 wet season to end of 2001/02 wet season) at three spatial scales, namely a discontinuous gully (0·6 km²) that was initiated by erosion of a grass swale between 1975 and 1981, a small continuous channel (2·5 km²) on an alluvial fan that was formed by incision of a formerly discontinuous channel between 1964 and 1978, and three medium‐sized, continuous channels (8·5–43·6 km²) with riparian vegetation. The bank erosion measurements during a period of average to above‐average rainfall established that substantial bank erosion occurred during the wet season on the two smaller channels by rapid lateral migration (Tributary Central) and by erosion of gully sidewalls due to a combination of within‐gully flows and overland flow plunging over the sidewalls (Tributary North). Minor bank erosion also occurred during the dry season by faunal activity, by desiccation and loss of cohesion of the sandy bank sediments and by dry flow processes. The larger channels with riparian vegetation (East Tributary and Ngarradj) did not generate significant amounts of sediment by bank erosion. Deposition (i.e. negative pin values) was locally significant at all scales. Bank profile form and channel planform exert a strong control on erosion rates during the wet season but not during the dry season. Copyright © 2006 Commonwealth Government of Australia.     

Role of fluids in surface deformation caused by the 1999 Chi‐Chi earthquake in Taiwan

The 1999 Chi‐Chi earthquake significantly altered the landscape of central Taiwan. Surface deformation produced by the earthquake along the trace of the Chelungpu thrust can be classified into two styles: (1) uplift without significant surface rupture, and (2) uplift accompanied by surface rupture. Here we examine areas that exhibited the first style of deformation (e.g. Wufeng). Seismic stress at the time of the main shock may have been relieved by high pore‐fluid pressure in a 300‐m‐thick sand and gravel aquifer. Along the thrust fault, frictional heating of these sediments resulted in thermal expansion and an increase in pore‐fluid pressure. High pore‐fluid pressure damped seismic‐wave energy and enhanced intergranular slips of unconsolidated sandy and gravel sediments, which were possibly assisted by sulphuric acid corrosion, leading to a high sulphate content in the groundwater (c. 70 mg L^?1). These changes permitted surface folding and terrace‐style uplifting to occur without significant rupture. In contrast, other areas in which the second style of deformation is dominant (e.g. Fengyuen‐Shihkang) have thin (0–10 m) sand and gravel deposits and lower concentrations of sulphate (c. 30 mg L^?1) in groundwater. In these areas, sediments were heated but not sufficiently to produce significant thermal expansion and increase in pore‐fluid pressure; accumulation of stress in these locations led to rupture at the ground surface, with the formation of steep fault scarps. The areas exhibiting the first deformation style are characterized by the presence of high pore‐fluid pressure, frictional heat conduction, and possibly chemical corrosion related to sulphuric acid attack and formation of sulphate, in contrast to those involving significant uplift and surface rupture. The areal distribution of these two surface deformation styles suggests that the aforementioned fluid‐related subsurface processes may have altered the characteristics of sediments and caused diverse responses to the quake. Copyright © 2002 John Wiley & Sons, Ltd.     

Development of push moraines in deeply frozen sediment adjacent to a cold-based glacier in the McMurdo Dry Valleys,Antarctica

Previous studies of push moraines have concluded that structural architecture is controlled by a combination of stress exerted by flowing ice and the rheology of the deforming sediment. However, the relationship between deformation processes and the thermal/hydrologic conditions within the sediment remains ambiguous. Using a combination of surface mapping, logging exposures and ground penetrating radar we examine the relationships between surface morphology, material properties and development of deformation structures in deeply frozen sediment that has been deformed by Joyce Glacier, a cold-based glacier in the McMurdo Dry Valleys. The structural architecture of the push moraines is characterized by a combination of brittle and ductile deformation structures that have produced a structurally complex pattern of thrust faults, low angle listric thrusts and recumbent folds that extend 400 m beyond the glacier margin. Deformation is ductile where the ice concentration exceeds c. 65% volume and predominantly brittle where the ice concentration is less than c. 65%. The change in rheology reflects transition in behaviour from the material having a predominantly frictional character when the ice is limited to pore spaces to a non-frictional character in which strength is primarily determined by the cohesive strength of the ice. This work shows that glaciotectonic deformation can occur in deeply frozen permafrost where there is no liquid pore water. We conclude that the presence of liquid porewater is not a necessary condition for the development of glaciotectonic deformation or for the formation of push moraines. © 2019 John Wiley & Sons, Ltd.     

A re-examination of the evidence for a Plio-Pleistocene marine transgression on the Chiltern Hills. II. drainage patterns

The dry valley pattern of the Chiltern Hills is divided into 55 third order drainage basins which are grouped morphometrically into five groups. The character and distribution of the groups are determined mainly by the lithology of surface deposits and the structure of the underlying Chalk. No evidence has been found for different drainage patterns on the parts of the dipslope equivalent to the ‘Mio-Pliocene peneplain’ and ‘Plio-Pleistocene marine platform’ of Wooldridge and Linton (1955), nor for superimposition of drainage from covers of Plio-Pleistocene or Palaeogene sediments.     

The effects of kinetic sorting on sediment mobility on steep slopes

In poorly mobile static armour, sorting is usually considered the result of hiding/exposure effects. We called this effect ‘static sorting’ in opposition to very efficient grain‐to‐grain mechanisms produced by a mobile mixture, called ‘kinetic sorting’. We hypothesized that kinetic sorting can be an important contributor to the morphodynamics of mountain streams and attempted to demonstrate this with new flume experiments. Two long runs were produced with natural poorly sorted sediments, and with transport stages of the coarse fraction (defined by the ratio between the shear stress and the critical shear stress for transport), smaller and higher than 1, respectively. Both runs produced an efficient transfer downstream of the injected material, but with a major difference: the first run (no kinetic sorting) produced permanent armour figuring clusters, akin to what has already been observed in similar experiments; the second run (with kinetic sorting) also produced bed armouring, but this armour was periodically totally destroyed, leading to substantial bed erosion. This phenomenon was explained by kinetic sorting, the effects of which are to produce an efficient downward migration of fine materials and bed surface armouring. The consequence is that fine materials are hidden to the flow during aggradation, allowing the slope to attain values much steeper than would have been expected at equilibrium for the mixture. However, whereas the surface armouring tends to stabilize the bed, construction of a layer of fine sediments at the subsurface also contributes to making it very unstable. These two contradictory effects explain the complex bed behaviours and the existence of very large bedload and slope fluctuations. Copyright © 2014 John Wiley & Sons, Ltd.     

活动断裂带内第四纪松散沉积物的变形类型

选择了一些典型活断层地质剖面 ,对经受了构造变动的第四纪松散沉积物进行了定向原状样品采集。通过室内样品固结、显微薄片制作和显微构造现象观察 ,从显微域里找到了第四纪松散沉积物变形的一些特点 ,并进行了分类。第四纪松散沉积物的变形类型有两种 :一种是破裂变形 ,主要表现为平行滑动条带、平直滑动界面、碎屑颗粒的破碎等 ;另一种是流动变形 ,主要表现为 :流动构造、碎砾旋转、粘土矿物的拖曳滑动等     

岷江上游堰塞湖沉积中软沉积物变形构造成因讨论

对在岷江上游及其支流河谷中的晚第四纪古堰塞湖地层中发现的大量软沉积物变形构造的类型、特征和成因进行了分析,发现这些软沉积物变形构造分为两类:一类是小型的层内变形构造,如液化卷曲变形、泄水构造、负荷构造、阶梯状微断裂等,其形成与软沉积物的塑性变形、液化和流动作用相关;另一类是崩(滑)塌体对软沉积物的扰动形成的大型褶曲构造.通过与其它成因的软沉积物变形构造的对比以及对区域构造环境的分析,得出地震、崩塌和滑坡等灾害性地质事件是造成河谷区古堰塞湖地层中软沉积物变形构造发育的最可能的驱动机制.     

Miocene hydrovolcanism in NW Colorado,USA, fuelled by explosive mixing of basic magma and wet unconsolidated sediment

The Yampa and Elkhead Mountains volcanic fields were erupted into sediment-filled fault basins during Miocene crustal extension in NW Colorado. Post-Miocene uplift and erosion has exposed alkali basalt lavas, pyroclastic deposits, volcanic necks and dykes which record hydrovolcanic and strombolian phenomena at different erosion depths. The occurrence of these different phenomena was related to the degree of lithification of the rocks through which the magmas rose. Hydrovolcanic interactions only occurred where rising basaltic magma encountered wet, porous, non-lithified sediments of the 600 m thick Miocene Brown's Park Formation. The interactions were fuelled by groundwater in these sediments: there was probably no standing surface water. Dykes intruded into the sediments have pillowed sides, and local swirled inclusions of sediment that were injected while fluidized in steam from heated pore water. Volcanic necks in the sediments consist of basaltic tuff, sediment blocks and separated grains derived from the sediments, lithic blocks (mostly derived from a conglomerate forming the local base of the Brown's Park Formation), and dykes composed of disaggregated sediment. The necks are cut by contemporaneous basalt dykes. Hydrovolcanic pyroclastic deposits formed tuff cones up to 100 m thick consisting of bedded air-fall, pyroclastic surge, and massive, poorly sorted deposits (MPSDs). All these contain sub-equal volumes of basaltic tuff and disaggregated sediment grains from the Brown's Park Formation. Possible explosive and effusive modes of formation for the MPSDs are discussed. Contemporaneous strombolian scoria deposits overlie lithified Cretaceous sedimentary rocks or thick basalt lavas. Volcanic necks intruded into the Cretaceous rocks consist of basalt clasts (some with spindle-shape), lithic clasts, and megacrysts derived from the magma, and are cut by basalt dykes. Rarely, strombolian deposits are interbedded with hydrovolcanic pyroclastic deposits, recording changes in eruption behaviour during one eruption. The hydrovolcanic eruptions occurred by interaction of magma with groundwater in the Brown's Park sediments. The explosive interactions disaggregated the sediment. Such direct digestion of sediment by the magma in the vents would probably not have released enough water to maintain a water/magma mass ratio sufficient for hydrovolcanic explosions to produce the tuff cones. Probably, additional water (perhaps 76% of the total) was derived by flow through the permeable sediments (especially the basal conglomerate to the formation), and into the vents.     

Earthquake-controlled event deposits and its tectonic significance from the Middle Permian Wandrawandian Siltstone in the Sydney Basin,Australia

Earthquake is a disaster event resulting from rapid and intensive crustal vibration caused by fault activity, volcanic eruption, or block dilapidation. Heezen and Ewing[1] and Heezen and Dyke[2] were the first to note earthquake-related mass movement and associated deposits in connection to the turbidity currents and submarine slumps triggered by the Grand Bank Earthquake in 1929. Seilacher[3] defined redeposited sedimentary beds, disturbed and modified by earth- quakes, as seismite. Since t…     

Using OSL to assess hypotheses related to the impacts of land use change with the early nineteenth century arrival of Europeans in south‐eastern Australia: an exploratory case study from Grabben Gullen Creek,New South Wales

A common explanation for intense soil erosion and gullying in SE Australia is the introduction by Europeans of new land use practices following their arrival in Australia in the late 18th century. Eucalyptus woodlands were cleared to introduce farming, and valley bottoms, characterized by chains of ponds with organic‐rich swampy meadow (SM) soils, were subsequently buried by thick deposits of ‘post‐settlement alluvium’ (PSA) generated by erosion in the catchment. In this study, optically stimulated luminescence (OSL) is used to evaluate the source(s) of the PSA in Grabben Gullen Creek (GGC), Australia. We use a portable OSL reader to measure total photon counts on bulk polymineral and polygrain‐size samples from nine profiles along the Creek. We use these luminescence signals as geotracers of sediment source(s) and transport pathways. We obtained higher luminescence signals in the PSA than in the SM sediments, suggesting different sources and fluvial transport conditions for these two widespread sedimentary units. Portable OSL reader data from soils in the GGC catchment that are potential sources for the SM sediments and PSA show that the high luminescence signals recorded in the PSA are similar to those from subsoil samples in granite soils, suggesting that the PSA was derived by gullying of granite subsoils. In the SM sediments, luminescence signals decrease upwards from the base of the profile, as expected in well‐reset fluvial deposits, but with one or more changes in gradient in the profile of photon counts with depth, most likely indicating changes in sediment deposition rates. To calculate deposition rates in the SM sediments, several samples were dated using OSL. The OSL ages produced low scatter in the equivalent doses, confirming the well‐reset nature of the grains composing the SM and indicating a process of sediment transport in dilute flows, as is interpreted from the portable OSL signals. Copyright © 2014 John Wiley & Sons, Ltd.     

呼伦湖地区扎赉诺尔晚第四纪湖泊沉积物的磁化率变化及其影响因素

呼伦湖盆地扎赉诺尔晚第四纪湖泊沉积物为砂,泥质碎屑沉,地东露天矿剖面沉积物样品进行了低,高频磁化率测量,粒度分析,磁性矿物成分鉴定和Al2O3 ,Fe2O3含量分析,分析表明,磁铁矿是沉积物磁化率的主要贡献者,全铁含量控制了磁化率值的变化,磁化率与沉积物粒度呈负相关,进一步讨论认为,磁性矿物主要为粉砂－粘土级碎屑,集中分布在细粒沉积物中,因此造成其率较高,砂质沉积物中频率磁化率较高,其原因可能是其中的磁性颗粒比粉砂一粘土级沉积物中的磁性颗粒更细一些。     

Chalk micropalaeontology and the provenancing of middle pleistocene lowestoft formation till in eastern England

The distribution and deposits of British and Scandinavian Middle Pleistocene ice sheets in eastern England remain problematic. A new till provenancing technique based on Chalk micropalaeontology is described, with the object of refining understanding of the ice sheet which deposited the Lowestoft Formation till (Anglian/Elsterian) and its relationship to Scandinavian ice sheets. The technique involves extracting foraminifera from Chalk erratics and till matrix obtained from stratigraphically controlled till sections and comparing their micropalaeontology with that of Upper Cretaceous Chalk bedrock. Application to the Lowestoft Formation till of eastern England suggests that current models of ice‐flow in this region require revision involving reinstatement of some earlier ideas. Chalk provenance data indicate an initial phase of glaciation, with ice streaming southwards across eastern England before fanning across East Anglia from the position of the Fen basin. This was followed by a later phase in which the main southward trajectory of ice‐flow was located further east in the North Sea Basin, but again with ice fanning out across East Anglia. These ice‐flow trajectories imply constraint of the British ice sheet by Scandinavian ice. Copyright © 2001 John Wiley & Sons, Ltd.     

Metallogenesis in the southeastern Pacific: A progress report on the IDOE Nazca Plate project

Under the auspices of the International Decade of Ocean Exploration, scientists from Oregon State University and the Hawaii Institute of Geophysics, along with representatives from the several South American countries which border the Nazca Plate, are intensively studying the origin and economic importance of metalliferous sediments which form extensive deposits on and near the East Pacific Rise. The sediments, enriched in iron, manganese, copper, nickel, zinc, silver, molybdenum, and lead are mineralogically and chemically similar to deposits cored by the “Glomar Challenger”, implying a common origin. The metalliferous sediments are especially abundant in an extensive basin, the Bauer Deep, which occurs about 800 km east of the East Pacific Rise. Elemental and isotopic data, supported by geologic information provided by cores and by geophysical instrumentation, suggest that the enriched elements in the sediments originate by the interplay of volcanism and sea water, by precipitation from sea water alone, and perhaps by the influence of deep-ocean physical processes acting on detritus transported from the continents or from the basaltic East Pacific Rise.An additional objective of the project is to define the possible relationship between marine metalliferous sediments of the plate to ore deposits of the Andean Cordillera. As pointed out by several writers, much of the earth's economic mineralization occurs along zones of convergence between subducted oceanic crust, including metalliferous sediments if present, and continental margins. Field and geochemical techniques are being applied to determine if sediments are in fact subducted beneath the Andean margin, and if they are remobilized into the continental ore deposits of the Andes. Isotopic tracers may prove most useful in testing this relation. Before the model can be tested rigorously, one must know not only the important chemical parameters of the ocean sediment that may be subducted, but also those of the pertinent rock and ore bodies of the South American Cordillera.     

Glaciers,rock avalanches and the ‘buzzsaw’ in cirque development: Why mountain cirques are of mainly glacial origin

It has been proposed that most cirques are source-area depressions of large, deep-seated rock-slope failures. Yet the close relation between cirques and climate is convincing evidence of the dominance of glacial erosion, rather than rock-slope failure, in mountain cirque development and distribution. Cirque floor altitudes have a lower limit that varies with snowfall by 1000 m or more between windward and leeward sides of mountain systems. Glaciation levels and equilibrium line altitudes implied by cirques vary in parallel with those for modern glaciers. Cirques are often found mainly on the poleward or leeward slopes of individual mountain ranges, as are modern small glaciers (because of solar radiation and wind effects on ablation and accumulation). Most rock-slope failures (RSFs: rock slides, rock avalanches and gravitational deformations) do not involve the deep-seated rotational movement that would produce a cirque form. Although some deep-seated RSFs with arcuate head scars may be confused with cirques, identification as a glacial cirque is more confident as the floor is longer, wider and more gently sloping. Some scars from major RSFs may resemble poor or moderately developed cirques, but tend to have steeper floors, to be more scattered and closely related to geology, whereas glacial cirques develop on all rock types. Deep-seated RSFs high on slopes can be associated with seismic shaking, but cirques develop without relation to seismicity. Degree of cirque development can be related to duration of exposure to glaciation. Often RSFs are found adjacent to cirques, or in glacial transfluences; only a proportion are well situated to develop into glacial cirques. Valley-head cirques are continued down-valley by glacial troughs. The ‘overdeepening’ (rock basins with reversed slopes) found in a large minority of cirques is not due to rock avalanching, fluvial or periglacial erosion. The RSF proposal should therefore be rejected in favour of the traditional glacial explanation, without any nivation stage being necessary. Rock-slope failure is one of several possible ways of initiating hollows for glacier accumulation, as well as an ancillary process of cirque extension or widening through collapse of glacially oversteepened slopes. Headward extension of adjacent cirques on a ridge leads to displacement of the divide, sometimes by 2 km or more, lowering ridge and summit altitudes and producing the ‘glacial buzzsaw’ effect. Where a relatively lower snowline has led to cirque erosion on all sides of a mountain, cirque intersection lowers summits further. The buzzsaw hypothesis is not applicable, however, where remnants of a preglacial summit surface survive. © 2020 John Wiley & Sons, Ltd.     

Erodibility of soft freshwater sediments in Markermeer: the role of bioturbation by meiobenthic fauna

The Markermeer is a large and shallow man-made freshwater lake in the Netherlands, characterized by its high turbidity. As part of a study aiming to mitigate this high turbidity, we studied the water–bed exchange processes of the lake’s muddy bed. The upper centimeter’s–decimeter’s of the lake bed sediments mainly consists of soft anoxic mud. Recent measurements have proved the existence of a thin oxic layer on top of this soft anoxic mud. This oxic layer, which is much easier to be eroded than the anoxic mud, is believed to be related with Markermeer’s high-turbidity levels. Our hypothesis is that the thin oxic layer develops from the anoxic mud, enhanced by bioturbation. Actually, we will demonstrate that it is the bioturbated state of the bed that increases its erodability, and not the oxidation state of the sediments. In particular, we will refer to bioturbation caused by meiobenthic fauna. The objective of this study is therefore to determine the influence of the development of the thin oxic layer on the water–bed exchange processes, as well as to establish the role of bioturbation on those processes. This is done by quantifying the erosion rate as a function of bed shear stresses, and at different stages of the development of the oxic layer. Our experiments show that bioturbation increases the rate at which Markermeer sediments are eroded by almost an order of magnitude. The short-term fine sediment dynamics in Markermeer are found to be driven by the complex and highly dynamic interactions between physics, chemistry, and biology. Finally, the long-term fine sediment dynamics are driven by the erosion of the historical deposits in the lake’s bed, which is only possible after bioturbation, and which leads to an increase of the stock of sediments in the lake’s muddy bed.