depositional facies of a mud shoreface in suriname south america a mud analogue to sandy shallow marine deposits abstract immense volumes of argillaceous muds are being deposited along the world s longest continuous mud coastline which faces the open equatorial atlantic not only are these muds deposited in an environment normally associated with sand deposits but just as in sandstones sedimentary structures within these muds record the dynamic processes that deposited them this study investigates a 100 km long portion of the suriname coast utilizing cores bathymetric surveys and field observations from nearshore and innershelf environments using terminology borrowed from sand coastlines the innershelf nearshore of suriname is divided into transition zone shoreface foreshore and backshore the transition zone consists of a mix of offshore sands and shoreface muds shoreface and foreshore are subdivided into bank and interbank zones these zones are transitory because mud banks which make up the bank zones migrate westwardly mud banks are up to 5 m high 50 to 60 km long 10 to 20 km wide and oriented at oblique angles to the coastline these banks generally consist of fluid muds which are so fluid that they interact with surface waves causing them to be altered and damped banks are attached to the shoreline and commonly produce progradation of the coastline substrate within the interbank zone is more consolidat d than within the mud banks because of lack of wave dampening wave energies are relatively high within the interbank zone producing erosion of the shoreface and shoreline sand beaches are generally formed within the erosional interbank shoreline the vertical sedimentary sequence within the shoreface muds is a record of bank migration and other sedimentary processes present wave and current energies are recorded by scour and fill features discontinuity features micro cross laminations lenticular laminations and parallel to subparallel laminations laminations appear to be created by boundary layer shearing within fluid muds which are above wave base and made mobile by wave generated shore parallel currents large scale evidence for migration of the mud banks is westward dipping acoustical reflectors within the banks these reflectors which are over a kilometer apart mark the boundaries of annual migration events biogenic structures are generally absent within the fluid bank muds but are present within the more consolid ted interbank zone and associated with discontinuity features which are buried interbank surfaces migration and vertical stacking of mud banks are recorded by vertical sequences of massive and laminated muds which were deposited by mud banks and discontinuity features which were formed by interbank zones the coastal deposits of suriname are a mud analogue to nearshore and innershelf sand deposits transition zones of both mud and sand systems reflect a transition from offshore to shoreface processes and sediments both mud and sand shoreface foreshore systems reflect sediment input and wave current and tidal processes that act on them mud banks of suriname resemble linear sand ridges on the continental shelf of the eastern u s a in shape oblique orientation to the coastline and orientation with respect to dominant direction of transport processes the sequence of massive and laminated muds with discontinuity features resembles laminated to burrowed sequences found in ancient and recent nearshore and shallow marine sands

lenticular shale fabrics resulting from intermittent erosion of water rich muds interpreting the rock record in the light of recent flume experiments lenticular lamination is a fabric that is known from shales of all ages but its origin and paleoenvironmental significance is poorly understood we have successfully reproduced this fabric in flume experiments beds of water rich mud were eroded in a flume and yielded sub millimeter to centimeter size fragments that can be transported in bedload for distances of ten kilometers or more upon redeposition and compaction these deposits have the same textural qualities as lenticular laminated shales from the rock record although accumulation of fecal pellets or abundant burrow tubes in a shale may produce comparable fabrics upon compaction these can be distinguished from erosion produced lenticular lamination via petrographic criteria lenticular lamination in shales that is due to deposition of water rich mud fragments most likely records intermittent erosion and transport of surficial muds by currents

the characterisation of cohesive sediment properties abstract this paper describes apparatus techniques and methods used by participants in mast g6m project 4 cohesive sediments for determining cohesive sediment properties this comparison of methods aims to stimulate a more general discussion on standardisation of techniques which will lead to characterisation of muds in terms of physical parameters such characterisation would allow inter comparison of muds from different sources methods are given for sediment properties of grain size distribution settling velocity and rheological parameters and for water bed exchange properties of permeability effective stress and critical shear stress for erosion and deposition accuracy and repeatability are discussed a typical range of values is indicated for each of these parameters

flume experiments with fine grained suspensions with implications for the origin of mud laminites abstract the formation of mud laminites was studied in flume experiments with fine grained suspensions of varying sediment concentration and type a transition from lamina formation to uniform deposition was observed at a concentration of about 1 9 kg m 3 laminae formed during continuous deposition showed gradual contacts whereas breaks in deposition were marked by sharp contacts gradual contacts between laminae deposited from suspensions of concentration less than about 1 9 kg m 3 were more distinct than those separating laminae deposited from denser suspensions

ecologic interpretation of deep sea trace fossil communities abstract trace fossil types and their vertical arrangement tiering are closely related to the biotope and hence can provide information on ecological conditions especially on oxygenation benthic food content sedimentation rate and substrate consistency however to use the full potential of trace fossils for environmental analyses various ichnologic criteria are necessary in addition to trace fossil taxonomy based on a taxonomically oriented ichnologic evaluation of modern deep sea environments six ichnologic aspects to ecologic changes have been found to be of major importance 1 1 penetration depth of burrows is influenced by oxygenation benthic food availability and substrate consistency 2 2 the number and vertical extension of tiers varies due to environmental changes a decrease in the vertical extension of tiers telescoping indicates a decrease in oxygenation benthic food content and or sedimentation rate if shallow penetrating traces disappear oxygen may be depleted and if the deepest tiers disappear the benthic food content may be lowered 3 3 the size diameter of specific trace fossils can indicate oxygen and benthic food availability 4 4 degree of bioturbation is related to sedimentation rate and benthic food content and the diversity of the whole ichnocoenoses or within a specific tier is affected by oxygenation benthic food content sedimentation rate and substrate consistency 5 5 the type of burrow wall unlined mucus lined pellet lined mainly refers to substrate consistency and subordinately to pore water oxygenation 6 6 the type of sediment displacement by body appendages used for excavation ingestion sideward pressing or outside pumping is related to substrate consistency and grain size

sea surface temperature fronts in the midlatitude south atlantic revealed by using microwave satellite data 1 the subtropical convergence or frontal zone has been little studied in the central south atlantic ocean despite limited data some work has suggested that this feature exists continuously across the south atlantic here satellite microwave sensed sea surface temperature sst data available from june 2002 are analysed for the existence of frontal gradients in the subtropical to subpolar south atlantic with focus on the central to eastern region the frontal locations and sst gradients in the southwest south atlantic and in the agulhas current retroflection region obtained from this satellite data are consistent with those estimated previously from hydrographic observations evident in the satellite data is pronounced mesoscale variability in subtropical frontal features particularly south of africa and extending west from the agulhas current retroflection to at least the greenwich meridian and in the southwest south atlantic over the central to eastern part of the basin the analysis suggests that there is substantial interannual variability in the strength and latitudinal location of the northern and southern subtropical front as defined by belkin and gordon 1996 some of this variability may be related to shifts in the winds including that in the latitude of the strongest wind stress curl on seasonal scales this central to eastern region is also characterised by variations in the frontal intensity but shifts in the position of regions of strong gradients are less obvious thus the data indicate that there is no continuous subtropical frontal feature across the basin in terms of surface temperature

the possible role of benthic microbial mats during the formation of carbonaceous shales in shallow mid proterozoic basins a considerable portion of the upper member of the mid proterozoic newland formation meagher county montana consists of carbonaceous silty shales striped shale facies this type of shale facies is common in proterozoic basins and is host to several major base metal deposits the striped shales were deposited in a subtidal setting basinward of carbonates characterized by cryptalgal laminites mudcracks and flat pebble conglomerates the carbonaceous silty shales are considered remnants of benthic microbial mats irregular internal laminae patterns of particle trapping mechanical deformation during penecontemporaneous soft sediment deformation and filamentous microbiota provide evidence for this interpretation the dolomitic clayey shale contains graded silt clay couplets and these are interpreted as storm layers modern subtidal microbial mats can only survive under special conditions but in the proterozoic it is suggested that benthic microbial mats colonized the shallow seafloor during periods of low sediment input leading to the formation of carbonaceous shales

facies and origin of shales from the mid proterozoic newland formation belt basin montana usa shales constitute more than 60 of the world s sediments yet while facies models for sandstones and carbonates are at a high level of sophistication the study of shales has clearly lagged behind in the mid proterozoic newland formation six major shale facies types deposited in nearshore to basinal environments are distinguished on the basis of bedding characteristics textural features and the proportions of silt clay and carbonate textural features of these shale types are related to sedimentary environments as deduced from associated lithologies the shales are undisturbed by bioturbation and their textural and sedimentary characteristics reflect subaqueous growth of microbial mats erosion and deposition by storms deposition of flocculated vs dispersed clays continuous slow background sedimentation winnowing by waves or currents and subaerial exposure

a role for organic petrology in integrated studies of mudrocks examples from devonian black shales of the eastern us abstract over the years the study of mudrocks has lagged far behind that of other lithologies a circumstance that is in part due to their fine grained nature and in part due to economic realities yet within petroleum systems mudstones are usually the main source of hydrocarbons and typically are also important as hydrocarbon seals recent work on late devonian mudstones from the eastern us shows that much progress can be made through an integration of outcrop study macro and micropaleontology ichnofossils gamma ray spectroscopy microscopic examination of thin sections in transmitted and reflected light electron microscopy sem bse electron microprobe carbon and sulfur isotopes and organic geochemistry erosion surfaces within this black shale succession have been traced over large distances and provide the foundation for a sequence stratigraphic re interpretation of these rocks evidence of storm wave reworking of the seabed as well as the realization that benthic colonization was much more widespread than previously believed suggest that anoxic conditions in the water column were not a controlling factor in the accumulation of the large quantities of organic matter found in these shales these distal devonian shales accumulated slowly and allowed accumulation of large proportions of organic matter in modern settings of abundant organic matter accumulation the original material is broken down by bacteria within a matter of months into a mass of largely unidentifiable organic particles and extracellular bacterial slime although one can still find identifiable material within this mass slime and amorphous material strongly dominate after burial and maturation this material turns into the various organic macerals that organic petrologists are accustomed to describe one might wonder in this context how much information about the origin of a given mudstone unit can we hope to extract through organic petrology in order to illustrate how organic petrology of mudrocks can contribute to their better understanding late devonian black shales of the eastern us will be examined from a sedimentological perspective combining sedimentologic and geochemical data with basic observations on organic petrology illustrates how the latter can contribute to more realistic scenarios of black shale genesis

cohesive sediment transport processes abstract the general aim of the project cohesive sediment of the mast programme g6 coastal morphodynamics is to advance the knowledge and modelling of physical processes related to cohesive sediment in coastal environments better insights are given into deposition modelling consolidation theories and associated constitutive relationships laboratory experiments of liquefaction by waves only or combined waves and currents modelling of flow sediment interaction and turbulence in the water column and the conduct of laboratory erosion experiments short term recordings of deposition events wave effects consolidation and bottom turbulence in muddy environments emphasise the distance which remains to be covered in order to understand and predict the processes in the field

the chemistry and mineralogy of haloed burrows in pelagic sediment at domes site a the equatorial north pacific the chemical and mineralogical composition of burrowed sediment recovered in 66 box cores at latitude 9 25 n and longitude 151 15 w in the equatorial pacific demonstrates the important role of infauna in determining the geochemistry of pelagic sediment haloed burrows approximately 3 cm across were present in many of the cores within early tertiary sediment that was covered by less than 5 cm of surface quaternary sediment in several cores the burrows in cross section consist of three units 1 a dark yellowish brown central zone of quaternary sediment surrounded by 2 a pale yellowish orange zone the halo of tertiary sediment which is surrounded by 3 a metal oxide precipitate the enclosing tertiary sediment is dusky brown several elements mn ni cu co zn sb and ce have been leached from the light colored halo whereas cr cs hf rb sc ta th u the rare earth elements exclusive of ce and the major oxides have not been leached the metal oxide zone 1 5 mm thick contains as much as 16 mno2 as the mineral todorokite the composition of the todorokite exclusive of the admixed tertiary sediment resembles the composition of the metal deficit of the halo and also the composition of surface ferromanganese nodules that have been interpreted as having a predominantly diagenetic origin thus bioturbation contributes not only to the redistribution of metals within pelagic sediment but also to the accretion of ferromanganese nodules on the sea floor

experimental deposition of carbonate mud from moving suspensions importance of flocculation and implications for modern and ancient carbonate mud deposition abstract flume experiments with fine grained carbonate particles 62 5 m show that they form floccules that travel in bedload form current ripples and deposit laminated sediments in order to compare our flume experiments to work on sand transport we ran flume experiments with medium sand and observed that the velocities at which sand grains started to move and form ripples were in the same range as those where floccules move and form ripples these ripples are in essence identical to those formed by clay mineral floccules or sand grains under similar conditions in light of previous experiments with clay minerals these results indicate that of the key controls on mud deposition flocculation and suspended sediment concentration are more important than particle mineralogy or water chemistry and are about as important as bottom shear stress for deposition suspensions of carbonate mud show the same pattern of flocculation ripple formation and bed accretion as observed previously in experiments with clay mineral suspensions the resulting carbonate mud deposits show internal low angle 2 5 degrees laminae and in plan view a pattern of ripple foresets that is identical to rib and furrow structure in sandstones just as previously assumed for terrigenous muds there has been a long standing notion that accumulation of abundant carbonate mud reflects quiescent conditions of offshore and deeper water environments these experiments demonstrate unequivocally that carbonate muds can also accumulate in energetic settings in the sedimentary record of carbonate rocks interbedded grainstones and lime mudstones may thus not necessarily reflect shifts in depositional energy or water depth but alternatively may imply a shift in supplied sediment type the observations we report suggest that published interpretations of ancient lime muds and derived paleoceanographic conditions may need to be reevaluated

lithofacies summary of the mississippian barnett shale mitchell 2 t p sims well wise county texas the mississippian barnett shale is an important hydrocarbon source rock and has recently developed into a very active gas shale play commonly viewed as a homogeneous black shale the barnett actually consists of a variety of organic rich lithofacies of siliceous calcareous or phosphatic composition recognition of the different lithofacies is an important step in the evaluation of gas in place flow capacity and mechanical properties of the barnett petrographic study of conventional core samples from the lower part of the barnett has led to the recognition of the following rock types organic rich black shale fossiliferous shale dolomite rhomb shale dolomitic shale phosphatic shale and concretionary carbonate measured total organic carbon values averaged by rock type range by a factor of nearly two with the organic rich shale and phosphatic shale having the highest values the development of these lithofacies is a result of suspension fallout and sediment gravity flows combined with the extensive early microbial alteration of abundant organic matter the lithofacies vary in petrophysical and mechanical properties as well as organic content

origin of amazon mudbanks along the northeastern coast of south america abstract seismic profiles sediment cores and water column measurements were collected along the northeastern coast of brazil to examine the origin of mudbanks in the amazon coastal mud belt these 10 60 km long shore attached features previously had been observed to migrate along the 1200 km coast of the guianas in response to wave forcing chirp 3 5 khz seismic profiles of the shoreface and inner shelf located two mudbanks updrift of the previous eastern limit in french guiana 210 pb geochronology shows that these two banks are migrating to the northwest over a relict mud surface in 5 20 m water depth the mudbanks are 3 4 m thick and are translating over a modern shoreface mud wedge deposited by previous mudbank passage in

bedload transport of mud across a wide storm influenced ramp cenomanian turonian kaskapau formation western canada foreland basin abstract mudstone dominated shallow marine rocks of the kaskapau formation were deposited on a low gradient ramp that spanned the foredeep of the western canada foreland basin during the late cenomanian to middle turonian organic clay rich and silt rich mudstone accumulated on the flank of the forebulge 200 km from the western shoreline within this mudstone a large proportion of the clay minerals are organized into silt and very fine sand size aggregate grains these aggregates were produced both in the water column as marine snow and phytodetritus and also through reworking of previously deposited cohesive mud to form intraclasts the latter along with siliceous silt grains form wave and combined flow ripples graded beds scour fills and ripple tail lamination where sand size sediment comprising detrital siliceous calcareous bioclastic or phosphatic grains is present it is molded into combined flow ripples hcs gutter casts and lags thus all sediment grades indicate storm wave and current reworking of the sea floor at a distance of 200 km offshore the common occurrence of clay minerals in the form of aggregate grains organized into combined flow ripples and parallel lamination implies advective transport of clay minerals as bedload driven by combined flows across a very low gradient ramp on the distal part of this ramp latest cenomanian rocks include thin tongues of sw prograding quartz rich sandstone that was derived from an emergent forebulge this source was drowned during the early turonian eustatic rise when the sediment abruptly changed to organic rich mudstone dominated by clay mineral aggregates this compositional change was mainly a response to a sudden increase in distance to detrital sources in the west rather than a dramatic increase in water depth throughout much of early to middle turonian time the sea floor in the forebulge region lay above effective storm wave base for silt estimated at 70 m at sea level lowstands wave winnowing and erosion of the sea floor concentrated bioclastic lags at the top of siltier upward sequences lags are interpreted to correspond to falling stage lowstand and early transgressive systems tract deposits on the western margin of the basin previous studies may have substantially overestimated water depth for organic and clay rich calcareous mudstones in the western interior seaway

dryland continental mudstones deciphering environmental changes in problematic mudstones from the upper triassic carnian to norian mercia mudstone group south west britain

environmental reconstruction of a late burdigalian miocene patch reef in deltaic deposits east kalimantan indonesia abstract most studies of cenozoic shallow water mixed carbonate siliciclastic depositional systems have focused on their sedimentology to date however comprehensive analyses of biotas and biofacies of indo west pacific reefs that developed in mixed carbonate siliciclastic systems are lacking this study describes the palaeoenvironment and biodiversity of a late burdigalian patch reef that developed in a mixed carbonate siliciclastic depositional system the studied exposure is located at the northeast margin of the kutai basin near bontang indonesia and is approximately 80 m wide and 25 m thick multi taxon analysis of the most abundant fossil groups including larger benthic foraminifera corals coralline algae and bryozoans aims to provide a model for environmental interpretation that will allow comparison with similar deposits of indo west pacific region based on fossil content and lithology five different facies types have been distinguished foraminiferal packstone fp bioclastic packstone with foralgal communities bp thin platy coral sheetstone cs platy tabular coral platestone cp and shales s among larger benthic foraminifera smaller and more robust forms dominate in the fp and bp facies while larger and flatter forms are the most abundant in the cs and cp facies thin platy corals are dominant in the cs facies and gradually change into thicker platy tabular forms in the cp facies assemblages and growth forms of coralline algae show no major differences between the facies types and are dominated by melobesioids and sporolithon the majority of bryozoan species are encrusting and were found only in the cs facies light dependent organisms occurring in the reef indicate low light conditions typical for mesophotic reefs the relatively small size of this reef complex and quite distinct vertical changes in the facies types combined with the high siliciclastic content in most of the units points to strong terrigenous input affecting water transparency as the main factor controlling the reef growth

working with natural cohesive sediments summary of stabilizing and destabilizing biotic in uenceson natural cohesive sediment stabilizing destabilizingeps secretion extracellularpolymeric substances bybacteria and microphytobenthosenhances cohesion promotes occulation and hence deposition blistering trapping ofoxygen bubbles in bio lmsincreases buoyancy of thebio lm to such an extentthat it pulls away fromthe sediment sediment compaction burrowingmacrofauna increasesediment densityand hence stability pelletization theformationof faeces and psuedo faeces can enhanceerodibility increased drainage burrowand channel formationpromotes dewatering grazing organismsfeedingon intertidal ats causesphysical disturbance andresuspensionof the sediment andreduces the stabilizingin uence ofmicrophytobenthos network effects filamentous biotaramify through the sediment matrixbinding sediment particles together burrow cleaning somebenthic fauna cleantubes they inhabit inthe sediment giving riseto a localizedbenthic ux flow effects

varves in marine sediments a review the global compilation of reported marine varved sedimentary records throughout the quaternary contains 52 sites marine varve deposition and preservation typically depend on environmental and sedimentological conditions such as a sufficiently high sedimentation rate severe depletion of dissolved oxygen in bottom water to exclude bioturbation by macrobenthos and a seasonally varying sedimentary input to yield a recognizable rhythmic varve pattern additional oceanographic factors include the strength and depth range of the oxygen minimum zone omz and regional anthropogenic eutrophication from point sources such as large polluted rivers quaternary marine varves are not only found in those parts of the open ocean that comply with these conditions but also in fjords embayments and estuaries with thermohaline density stratification and nearshore marine lakes with strong hydrologic connections to ocean water this review critically describes settings and sedimentological characteristics of marine sites where varves have been reported broader applications of marine varve records are discussed for example in terms of radiocarbon calibration on high resolution time scales constraining paleoceanographic variability and global change teleconnections diagnosing factors affecting modern fish population dynamics based on past performance detailing biogeochemical cycles and deciphering complex factors influencing marine productivity varves in saline water bodies without hydrologic connection to the global ocean are not included in this review and instead pertain to the companion review on lacustrine varves where also general and fundamental principles of varve deposition classification and dating are covered zolitschka et al 2015 the postulated occurrence of varves in pre quaternary rocks is critically discussed in this review with representative examples in the case of non evaporitic laminations in fine grained ancient marine rocks such as banded iron formations and black shales laminations may not be varves but instead may have multiple alternative origins such as event beds or formation via bottom currents that transport and sort silt sized particles clay floccules and organic mineral aggregates in the form of migrating bedload ripples

sedimentary structures on the bengal shelf a multi scale approach to sedimentary fabric interpretation abstract sedimentary structures on the bengal shelf are examined using x radiographic thin section and scanning electron microscopic sem techniques which reveal contrasting depositional processes for the inner and middle shelf as well as for either side of a major submarine canyon indenting the western shelf margin the inner shelf is characterized by tidally produced interlaminated silts and muds that reveal a neap spring cyclicity the cyclicity is more pronounced for the winter season when high discharge monsoon conditions do not obscure the tidal signature on the middle shelf alternating beds of silts and muds probably represent high discharge and low discharge conditions respectively silty beds on the western margin of the submarine canyon are thinner than those found on the eastern margin the western margin receives predominantly fine grained ganges sediments in contrast to the eastern area which receives both ganges and coarser brahmaputra sediments these observations indicate that the submarine canyon presently intercepts westward along shelf sediment transport muddy beds and laminae that appear internally homogeneous in the x radiographs and exhibit faint bedding in thin sections often are composed of resistant protruding and less resistant recessed microlaminae as observed with the sem on the inner shelf resistant microlaminae are composed of fine grained polymineralic equant particles the less resistant microlaminae are composed of large platy illite grains rimmed by smaller platy or lath like illite particles resistant and less resistant microlaminae within middle shelf muddy sediments have the same textural characteristics observed on the inner shelf however both types essentially are monomineralic on the middle shelf the smallest particles within the less resistant microlaminae exhibit an open flocculated structure that may result from higher salinity and or decreased bottom shear stress associated with tidal currents biological structures predominantly occur on the western inner and middle shelf particularly in intervals of high smectite concentrations this relationship may exist because of a preferential organic affinity for expandable minerals providing a favorable substrate for benthic organisms

experimental testing of the transport durability of shale lithics and its implications for interpreting the rock record abstract detailed petrographic studies of shales show that they consist of a wide range of components including a wide spectrum of composite particles that were contributed to the precursor muds in the form of high water content suspended floccules bedload floccules rip up intraclasts pedogenic aggregates and fully lithified shale clasts experimental studies show that shale clasts of sand to silt size shale lithics can survive hundreds to thousands of kilometers of bedload transport observations of modern river and shelf muds reveal the common presence of shale lithics in these sediments and suggest that a significant portion of ancient shale formations could potentially consist of reworked shale lithics and not as commonly assumed of primary composite particles such as clay floccules and organo minerallic aggregates identification of shale lithics in the rock record presents challenges but careful petrographic examination using sem and ion milled samples and case studies will help to develop robust criteria for recognition the presented observations have manifold implications for the interpretation of many aspects of shales mud transport and accumulation sediment compaction and basin fill modeling and geochemical proxies they emphasize the essential need for petrographic examination of shale samples before more advanced analyses are undertaken

erosion of soft cohesive sediment deposits erosion behavior of soft cohesive sediment deposits has been investigated in laboratory experiments such deposits are representative of the top active layer of estuarial beds an experimental procedure involving layer by layer erosion under a range of bed shear stresses b of successively increasing magnitude was utilized interpretation of the resulting concentrationtime data together with bed density profiles yielded a description of the variation of the bed shear strength s with depth as well as an expression for the rate of surface erosion in general s increased with depth and was also influenced by the type of sediment bed consolidation period and salinity the rate of erosion was found to vary exponentially with b s 1 2 in modeling estuarial bed erosion it is essential to take these characteristics of s and the rate of erosion into account

bedload transport of mud across a wide storm influenced ramp cenomanian turonian kaskapau formation western canada foreland basin discussion we would like to comment on a recent paper by plint et al 2012 that discusses mud transport across a cretaceous shelf the authors have taken to heart recent research that advocates looking for evidence of bedload transport of aggregated clays and we are comfortable that much of the clay component in the kaskapau formation did indeed arrive via bedload transport rather than simply settling out of the water column however whereas we are perfectly comfortable with the proposed mode of transport we do have several concerns and suggestions concerning one type of mud aggregate discussed by plint et al 2012 in the depositional model that the authors present their fig 16 they envision that cohesive mud is reworked by storms into intraclasts and that these then are carried across the seabed in bedload that in itself is no problem because it can be shown in experiments that surficial muds with as much as 85 water content can be transported as millimeter size aggregates for considerable distances schieber et al 2010 one class of aggregates however described as intraclastic aggregates ias for the remainder of this manuscript by the authors did capture our attention the authors state that storm wave reworking of the seafloor produced intraclastic aggregates because the mud had been rendered cohesive by the chemical compaction and biostabilization processes that operated shortly after deposition we are aware that surficial sediments can gain enhanced cohesion and improved erosion resistance due to mucus from benthic worms and endo sedimentary microbes but we are not quite sure what the authors mean by chemical compaction if they mean that cementation renders the muds firmer and more cohesive it would have been rather appropriate to document this critical factor in the aggregates in question by definition

repeated sedimentation and exposure of glacial lake missoula sediments a lake level history at garden gulch montana usa abstract glaciolacustrine sediments record lake transgression regression and subaerial modification of the silty lake bottom of glacial lake missoula in the clark fork river valley the sequence preserved at garden gulch mt documents lake level fluctuations at 65 of its full pool volume twelve sedimentary cycles fine upwards from 1 very fine grained sandy silt to 2 silt with climbing ripples to 3 rhythmically laminated silt and some clay the cycles are fine grained turbidites capped locally by thin layers of angular gravel derived from local bedrock outcrops the gravels appear to be the toes of mass wasting lobes carried onto the exposed lakebed surface during repeated lake level lowerings periglacial wedges small rotational faults involutions and clastic dikes deform the tops of eleven cycles the wedges are 10 30 cm wide penetrate 30 70 cm deep are spaced the lowest five cycles are thicker and display more periglacial modification at their tops than the upper seven cycles the garden gulch section may represent as few as seven and as many as twelve substantial fillings and partial to complete drainings of glacial lake missoula

significance of styles of epicontinental shale sedimentation in the belt basin mid proterozoic of montana u s a abstract within the strongly shale dominated sediment fill of the mid proterozoic belt basin a large variety of shale types can be distinguished sedimentological investigations of several formations have yielded valuable data about lateral associations of shale types as well as about the principal mechanisms of shale deposition depositional environments of shales in the belt basin range from red bed mudstones of ancient flood plains to deep water mudstones in a turbidite setting graded silt mud couplets are ubiquitous in most shales of the belt basin however they differ in detail and can be related to a variety of depositional processes such as low density turbidity currents sheet floods storms and wave reworking in several formations there is evidence that microbial mats colonized the sediment surface and probably protected the sediment surface from erosion shales from comparable phanerozoic settings generally lack the silt mud couplets that are so commonly observed in shales from the belt basin and other proterozoic epicontinental basins this difference probably reflects the proliferation of bioturbating organisms in the phanerozoic the absence of benthic microbial mats in phanerozoic shales is probably due to the evolution of metazoan grazers towards the end of the proterozoic

reverse engineering mother nature shale sedimentology from an experimental perspective abstract experimental study of the sedimentology of shales can take a variety of forms at its simplest one can experiment with suspensions in a glass jar and try to understand their settling behavior or one can manipulate mud in a tank or bucket to gain insights into its rheology this approach was championed over a century ago by sorby and the insights gained can be quite profound more recently tank and settling tube experiments of animal sediment interactions compaction behavior and sediment unmixing via re suspension have proven to be highly informative in spite of their simplicity flumes can be used to obtain quantitative information about depositional and erosional parameters and to generate fundamental bedforms in flume experiments however it is of critical importance that the flume be designed in a way that flocculated materials move under shear stress conditions that would be reasonable in natural environments although much flume work on muds has been conducted by hydraulic engineers the transfer of that knowledge to sedimentology is hampered by the fact that engineers and sedimentologists are interested in different though not mutually exclusive products from such experiments engineers and hydrologists are commonly concerned with quantifying fluid flow properties whereas sedimentogists are particularly interested in the sedimentary products that result from a variety of flow conditions recent sedimentologically oriented flume studies have shown that muds can form deposits at flow velocities and shear stresses that would suffice to transport and deposit medium grained sand mud suspensions are prone to flocculation and the resulting floccules travel in bedload and form ripples that accrete into beds the latter finding suggests that many laminated shales were deposited from currents rather than by settling from slow moving or still water there are many other sedimentary features in shales that can potentially be reproduced in flume studies and in the future serve to provide a quantitative basis for shale sedimentology

critical bed shear stress for cohesive sediment deposition under steady flows results of two laboratory experiments on the cohesive sediment deposition behavior are presented data indicate that an annular flume either with or without the channel bed and the top ring rotating in opposite directions to minimize the secondary circulation can be used to study the deposition behavior of cohesive sediments direct observations on when and where the bed is formed suggest that deposition only occurs when the local bed shear stress b is less than a critical value secondary circulation in the flume which produced upward current near the inner corner and downward current near the outer corner did not prevent deposition near the inner corner because of the small b nor promote deposition near the outer corner because of the relatively large b

rotating circular flume a rotating flume installed at the national water research institute in burlington ontario canada to undertake basic research on cohesive sediment dynamics is described the flume is 5 0 m in mean diameter 0 30 m in width and 0 30 m in depth an annular cover plate ring which can be transversed in the vertical direction fits inside the flume with a radial clearance of 1 5 mm on either side and makes contact with the water surface the flume and the ring can be rotated independently at speeds ranging from 0 to 3 rpm the flume is equipped with a laser doppler anemometer a laser particle size analyzer and a preston tube a set of performance tests carried out in this flume indicate that generation of a nearly two dimensional flow field is possible if both the flume and the ring are rotated simultaneously in opposite directions flows generated by keeping the flume stationary and rotating only the ring were found to contain a strong secondary circulation cell and a large variation of bed shear stress