a new scleritomous metazoan from the late ordovician georgian bay formation southern ontario a new genus and species of articulated scleritomous metazoan curviconophorus andersoni is described on the basis of a unique specimen from the late ordovician georgian bay formation of southern ontario the affinities of the organism remain obscure although the overall morphology of component sclerites suggests a possible relationship with the agmata an extinct phylum level group so far known with certainty only from the cambrian curved conical elements of the scleritome are preserved as internal moulds and yield no details of ultrastructure or primary composition precluding detailed comparisons with the aggultinated internally laminated sclerites of agmatans curviconophorus gen nov has a scleritome architecture similar to that of the early ordovician putative agmatan dimorphoconus granulatus though it has fewer elements that are strictly monomorphic

sub basin scale dust source geomorphology detected using modis 1 the spatial and temporal variability of dust emissions from different surfaces in the lake eyre basin australia is determined using modis data for 2003 6 the sources of 529 dust plumes were classified overall 37 of plumes originated in areas of aeolian deposits 30 from alluvial deposits and floodplains and 29 from ephemeral lakes or playas at this sub basin scale the relative importance of different dust source geomorphologies varied primarily in response to sediment supply and availability and was not related to aeolian transport capacity suggesting the lake eyre basin is a supply limited system

tectonic implications of 40ar 39ar muscovite dates from the mt haley stock and lussier river stock near fort steele british columbia the mt haley and lussier river stocks are located northeast of cranbrook b c near the south end of the western main ranges of the southern canadian rocky mountains both are multiphase potassium feldspar porphyritic monzonite plutons that intrude lower paleozoic miogeoclinal strata they crosscut and thermally overprint the lussier river fault and the thrust and fold structures in the east flank of the purcell anticlinorium and the west limb of the porcupine creek anticlinorial fan structure muscovite from the mt haley stock yielded a 40ar 39ar plateau age of 108 2 0 7 ma 2 and a single crystal step heating analysis of muscovite from a skarn in the metamorphic aureole adjacent to the lussier river stock gave a plateau date of 108 7 0 6 ma 2 these dates constrain the timing of thrusting and folding in this portion of the western rocky mountains and of the displacement along the lussier river st mary fault to pre middle albian

emplacement of the 18 may 1980 lateral blast deposit ene of mount st helens washington facies variations east northeast of mount st helens preserve a record of depositional processes in the 18 may 1980 lateral blast cloud this paper reports new field grain size and component data from the ene sector of the timber blowdown zone and presents a model for blast flow and sedimentation the first erupted ejecta was rich in juvenile components and extends to the distal blowdown limit the last erupted ejecta was rich in accidental lithics and reached no further than a few kilometres from the mountain due to waning discharge the blast cloud was a turbulent stratified flow which transported and deposited sediment in the manner of a high density turbidity current the possibility that the blast was emplaced as a giant shearing fluidised bed is not favoured by compositional zoning patterns depositional conditions were strongly influenced by the rate of suspended load fallout from the blast within about 8 km from vent rapid sedimentation caused deposition under moderate to high concentration conditions and formation of a basal hindered settling zone able to detach gravitationally and drain into local depressions the resulting proximal facies resembles a low aspect ratio ignimbrite fines depletion in the proximal facies is attributed to a combination of residual turbulence and rapid gas escape during particle settling and compaction through the hindered settling zone component data suggest that the blast head played no significant role in the generation of fines depletion in the blast deposit as suggested by previous workers with increasing distance from vent the rate of particle fallout declined and sedimentation took place under increasingly dilute and tractional conditions building up antidune like bedforms wavelengths of these bedforms range from 20 to 1 m and decrease away from vent there is a systematic relationship between antidune migration direction and depositional slope the transition from proximal ignimbrite like to distal surge like facies suggests a possible gradation in transport and deposition processes between conventional pyroclastic surges and high velocity pyroclastic flows

flash flood sediments and ichnofacies of the late pleistocene homeb silts kuiseb river namibia abstract the homeb silt formation consists of eroded remnants of fine grained alluvium that were deposited within the kuiseb river valley in southern namibia during the late pleistocene in holocene times the river deeply incised its valley fill leaving steep walled castles of relict alluvium the homeb silts this study is based on the 25 m thick type exposure of homeb silts at homeb and describes flash flood sediments that were colonised by successive generations of opportunistic arthropods the stacked flood units each comprise a massive tabular siltstone bed overlain by a narrower interval of rapidly alternating sandstone and siltstone with claystone veneers these flood units are interpreted as having accumulated under semi arid climatic conditions by episodic back flooding of the kuiseb river into embayments and tributary mouths soon after deposition as the floodwaters subsided the sediment was colonised by burrowing sediment ingesting organisms mostly arthropods that produced a taenidium ichnofacies after the floodwaters had drained the exposed sediment was colonised by grasses and burrowed by terrestrial arthropods probably ants and termites resulting in an overprint of termitichnus ichnofacies with associated pelletal chambers thirteen horizons of rhizocretions and root tubules occur toward the top of the succession and indicate a gradual reduction in the frequency of flooding these immature calcic palaeosols suggest that the climate in the central namib desert 20 000 years ago was semi arid being wetter and more seasonal than the hyperarid conditions that prevail today

iron solubility driven by speciation in dust sources to the ocean particulate aerosols are thought to be the primary source of iron to the oceans but the factors determining their solubility and thus bioavailability are unclear x ray absorption analysis reveals that speciation controls the solubility of iron in three large sources of aerosol iron

downstream hydraulic geometry and channel adjustment during a flood along an ephemeral arid region drainage in september 1997 a dissipating tropical storm caused a flood with an estimated maximum discharge of 240 m 3 s along yuma wash an ephemeral braided system draining 186 km 2 in southwest arizona older high water marks that record a flood peak of 1280 m 3 s provide a reasonable estimate for the probable maximum flood along the wash detailed channel crosssectional surveys during 1995 and again in 1998 6 months after the 1997 flood facilitated examination of downstream hydraulic geometry and channel adjustment during the flood channel width increased substantially downstream exponent of 0 78 presumably because of low bank resistance whereas hydraulic depth and velocity had modest downstream increases 0 15 and 0 14 respectively channel aggradation generally occurred along wider braided reaches moreover degradation occurred in narrow reaches with fewer channels aggradation and degradation also appeared to be governed by a threshold relationship between flow depth and vegetated bars degradation occurred where flow was confined within a channel or subchannel at discharges sufficiently high to overtop vegetated bars greater roughness facilitated sediment deposition and channels aggraded a discriminant function correctly classified nearly 90 of the cross sections as scoured or filled using a single hydraulic variable maximum depth of flow during the dissipating tropical storm d 2002 elsevier science b v all rights reserved

a paleohydrologic reinterpretation of the homeb silts kuiseb river central namib desert namibia and paleoclimatic implications abstract slack water deposits are usually fine grained fine sand and coarse silt flood sediments deposited in areas of the floodplain that are sheltered from high velocity flood flows slack water deposits have been recognized by many investigators in a wide variety of physiographic and climatic settings late quaternary slack water deposits have not been described from the extremely arid namib desert of southwestern africa fine grained flood sediments in the kuiseb valley near homeb accumulated between 23 000 and 19 000 14c years bp have been interpreted by previous workers as i sediments deposited behind dune dams ii river endpoint accumulations and iii flood deposits of an aggrading river controlled either by a base level change in the lower reaches or a change in the hydrological regime in the catchment area furthermore the so called homeb silts could document more arid climatic conditions in the kuiseb catchment area during the last glacial maximum lgm our research shows that the homeb silts are slack water deposits and that in many valleys of the namib desert slack water sediments are observed most commonly at the junctions of major rivers and minor tributaries in bedrock canyon settings here we present evidence that these slack water deposits accumulated as a result of more humid conditions and or more intense precipitation events in the upper reaches of the river they do not document climatic changes in the desert itself as postulated by many researchers

shallow marine sedimentary processes in the late devonian catskill sea new york state shallow marine strata of the upper devonian west falls group in south central new york comprise centimetre to decimetre thick sheetlike to lenticular beds of sandstone and siltstone interbedded with mudstone unidirectional current scour marks and tool marks occur on the basal erosion surfaces of the sandstones their internal structures are hummocky cross strata of various styles planar laminae and wave ripple cross laminae with characteristic vertical and lateral transitions among them vertical burrows of the skolithos ichnofacies dominate upper portions of sandstone beds whereas mudstones and silt stones contain mainly horizontal burrows of the cruziana ichnofacies transported and in situ shelly fossils occur throughout in places concentrated in coquinite lenses large scale 15 to 30 in bedding sequences are characterized by upward thickening and coarsening of sandstone beds increase in amalgamated hummocky cross strata coquinites plant debris and bivalves followed by abrupt fining and thinning of beds the depositional environment is interpreted as a shallow marine shelf episodically influenced by intense tropical storms hurricanes individual sandstone beds were deposited by spatially decelerating combined flows where an initially strong offshore directed flow component decreased in time relative to the oscillatory flow component large scale bedding sequences reflect changes in storm combined current intensity and deposition rate strong eustatic control is unlikely and there is no evidence of changing wave climate instead these sequences may be associated with delta lobe progradation and or offshore bar development

may 18 1980 mount st helens deposits in south coldwater creek washington beginning at 0832 pacific daylight time pdt mount st helens washington produced a rockslide debris avalanche and a lateral explosion blast that generated a laterally directed pyroclastic surge called here a blast surge the resulting deposits are thickest in the east west trending valley of north fork toutle river immediately north of the volcano but are almost as thick in south coldwater creek a small tributary of the toutle river in the lee of an east west trending ridge johnston ridge just north of the north fork toutle river the avalanche surmounted johnston ridge 300 m relief and flowed down the valley of south coldwater creek closely following the avalanche and in part contemporaneously with it the blast surge left thin up to 0 5 m deposits on johnston ridge and thick up to 15 m deposits in south coldwater creek these deposits have a lower layer layer a1 which is friable massive poorer in fines particles 1 16 mm and more poorly sorted than the upper layer layer a2 layer a2 is less friable because it contains more silt and clay sized material beneath layer a1 is a zone containing a small percentage of debris from the blast surge mixed with products eroded from the underlying surface this zone designated as layer a0 is a poorly mixed layer containing schlieren of soil shattered volcanic fragments and considerable quantities of organic material layer a1 is strongly sorted and fines depleted and is interpreted to have been deposited from just behind the turbulent head of the blast surge layer a2 is interpreted to have been deposited from the body of the blast surge which is believed to have been less turbulent than the head layer a0 is interpreted to have formed by shearing at the base of the head of the blast surge in the region between the front and the back of the head of the blast surge it is concluded that a strongly fines depleted basal layer of a pyroclastic flow or surge deposit underlain by a thin sheared zone is the signature of an extremely high velocity particulate density current

lithic breccia and ignimbrite erupted during the collapse of crater lake caldera oregon abstract the climactic eruption of mount mazama 6845 y b p vented a total of 50 km3 of compositionally zoned rhyodacitic to basaltic magma from a a single vent as a plinian pumice fall deposit and the overlying wineglass welded tuff and b ring vents as ignimbrite and coignimbrite lithic breccia accompanying the collapse of crater lake caldera new field and grain size data for the ring vent products are presented in this report the coarse grained poorly bedded clast supported lithic breccia extends as far as 18 km from the caldera center like the associated ignimbrite the breccia is compositionally zoned both radially and vertically and silicic mixed and mafic types can be recognized based on the proportion of rhyodacitic pumice matrix fractions in silicic breccias are depleted of fines and are lithic and crystal enriched relative to silicic ignimbrite due to vigorous gas sorting during emplacement ignimbrite occurs as a proximal veneer deposit overlying the breccia a medial 8 to 25 km from the caldera center compositionally zoned valley fill as much as 110 m thick and an unzoned distal 20 km facies which extends as far as 55 km from the caldera breccia within 9 km of the caldera center is interpreted as a coignimbrite lag breccia formed within the deflation zone of the collapsing ring vent eruption columns expanded pyroclastic flows of the deflation zone were probably vertically graded in both size and concentration of blocks as recently postulated for some turbidity currents an inflection in the rate of falloff of lithic clast size within the lithic breccia at 9 km may mark the outer edge of the deflation zone or may be an artifact of incomplete exposure the onset of ring vent activity at mt mazama was accompanied by a marked increase in eruptive discharge pyroclastic flows were emplaced as a semicontinuous stream as few ignimbrite flow unit boundaries are evident as eruption from the ring vents progressed flow runout distance and the extent of breccia deposition decreased due to a greater internal flow friction and b decreasing eruption column heights effect b probably resulted from a progressive decrease in magmatic gas content and discharge rate waning discharge may have been promoted by the tapping of more viscous crystal rich magma collapse of conduit walls and declining caldera collapse rate

mapping the iron oxide content of dune sands namib sand sea namibia using landsat thematic mapper data abstract a linear mixture model was applied to landsat thematic mapper data to map iron oxide content over the northern part of the namib sand sea namibia field samples were collected to calibrate the remotely sensed iron oxide proportions to dithionite extractable fe in mg g 1 the in situ proportions correlating strongly with the remotely sensed estimates r 0 91 the results reveal a region of high fe oxide concentration in the east an area of low fe oxide concentration in the west separated by a mixing zone we interpret this to indicate that there is more than one sand source contributing to the sand sea

widespread preservation of small carbonaceous fossils scfs in the early cambrian of north greenland the early cambrian ca 518 ma sirius passet lagerstatte of north greenland is one of the most celebrated sites bearing fossils of soft bodied organisms and provides key insights into the cambria

paleoecology and taphonomy of the early cambrian maotianshan shale biota chancelloriid allonnia junyuani adaptation to nonactualistic cambrian substrates article i nfo the cambrian radiation marks a period of extensive ecologic innovation within metazoan communities among these innovations were increasing levels of vertical bioturbation and a subsequent transition from proterozoic style firm unlithified substrates with very low levels of bioturbation to phanerozoic style soft substrates with a high water content and well developed mixed layer this transition termed the agronomic revolution had a significant impact on benthic organisms already adapted to firm unlithified substrates leading to evolutionary and ecological changes in these organisms known as the cambrian substrate revolution csr chancelloriids are morphologically unusual sessile suspension feeders restricted to the early and middle cambrian and as such are a likely candidate to have been affected by the csr examination of exceptionally preserved specimens of the species allonnia junyuani from the maotianshan shale of yunnan province china in addition to a study of the rocks in which they are preserved indicate that a junyuani was likely a shallow sediment sticker that used a tapered blunt basal end for insertion into firm unlithified substrates bioturbation levels in the maotianshan shale are very low ichnofabric index average ii1 suggesting that proterozoic style firm unlithified substrates dominated this environment consistent with the morphological adaptations of a junyuani these results suggest that a junyuani was adapted to nonactualistic environments and this may have partially contributed to its unusual morphology and extinction by the late cambrian complete well preserved specimens from the study group were very rare 3 7 of total whereas partly or completely disarticulated specimens dominated 77 5 of total suggesting that despite the burgess shale type preservation apparent in the maotianshan biota a junyuani typically underwent significant pre burial decay

pycnocrinus altilis a new late ordovician channel dwelling crinoid from southern ontario pycnocrinus altilis n sp is described from the upper ordovician georgian bay formation of ontario closely related to p dyeri meek 1872 the cup of p altilis is characterized by stellate ornamentation of plates comprising ridges bounded by deep subtriangular pits pycnocrinus altilis inhabited submarine channels in the prodeltaic regime of the queenston deltaic complex and is inferred to have been anchored to the substrate by a distally coiled column

mineralogy as a critical factor of dust iron solubility 1 to understand the impact of dust deposition on ocean primary productivity the evaluation of dust input is not sufficient and the soluble iron supply is also needed measurements of iron in aerosols suggest a much higher solubility than in soil implying substantial atmospheric processing of chemical or physical nature here we have investigated the effect of the mineralogy on iron solubility we have measured iron solubility from some minerals commonly found in dust clay feldspar and iron hydr oxides firstly we observe a greater solubility of iron resulting from clays 4 in comparison to iron hydr oxides 1 independently of specific surface of minerals secondly by considering amount of dissolved iron and the mineralogical composition of dust our results indicate that dissolved iron fraction mainly comes from clay dissolution in contrast to that assumed in some biogeochemical models in consequence it appears that iron solubility is closely linked to the mineralogical composition of aerosol

pedogenic and diagenetic influences on void coating formation in lower cretaceous paleosols of the mill creek formation southwestern alberta canada abstract pedogenic and diagenetic influences on void coating formation were studied in two paleosols from the lower cretaceous albian mill creek formation in southwestern alberta canada using detailed micromorphological mineralogical and geochemical methods the paleosols consist of alternating decimetre scale beds of red grey green and variegated mudstone intermediate horizons red and grey green variegated mudstones contain associations of pale yellow clay coatings dark red clay coatings fe depletion hypo coatings and fe oxide quasi coatings sem edx ray analyses indicate that the dark reddish coatings are dominated by si al and fe with subordinate amounts of k na ca mg and ti pale yellow clay coatings have a higher si content and lower al k na ca and fe contents relative to reddish coatings within the paleosol profiles the distribution of clay minerals indicates 1 an increase in discrete clay minerals downward 2 a decrease in mixed layer illite smectite downward and 3 an increase in chlorite upward x ray diffraction indicates that the pale yellow and dark red clay void coatings are polymineralic pale yellow clay coatings have a higher proportion of mixed layer illite smectite and kaolinite less chlorite and are less crystalline than dark reddish coatings despite a diagenetic overprint including development of diffusion gleyans degradation of organic matter burial reddening and probably some smectite illitization both compositional and morphological gradients exist in the paleosol profiles and void coatings these gradients are most likely related to depositional variations and to pedogenic development in the original soils under variable eh ph conditions in the presence of organic matter therefore although the void coatings are altered diagenetic features their morphology mineralogy and perhaps even some of their microchemistry is attributable to the presence of pedogenic precursors initially formed in soils similar to modern temperate alfisols and glossic soils

comparison of the rainy ridge analcime phonolite sill and the crowsnest volcanics alberta canada a 5 7 m thick analcime phonolite sill occurs in the middle of the proterozoic gateway formation in southwest alberta the sill consists of sanidine aegirine augite magnesian hastingsite melanite with hydrogrossular rims titanite and minor biotite apatite and opaque minerals mineralogical and chemical similarities to the analcime rich phases of the cretaceous crowsnest formation found some 20 km to the north suggest a genetic relationship major differences are the presence of amphibole and hydrogrossular minerals not reported in the crowsnest formation the presence of amphibole as a primary hydrous phase in the rainy ridge sill indicates crystallization from a hydrous magma microprobe studies indicate a progressive enrichment of sodium in amphiboles and pyroxenes an apparent difference in chemical composition and alteration behavior of primary analcime phenocrysts and groundmass analcime is interpreted to reflect crystallization of analcime from a hydrous melt at depth followed by rapid trans

use of composite fingerprints to determine the provenance of the contemporary suspended sediment load transported by rivers sediment fingerprinting appears to offer a valuable alternative to direct monitoring for elucidating the provenance of suspended sediment and the relative importance of spatial zones or subcatchments comprising larger 500 km 2 drainage basins against this background a quantitative composite fingerprinting technique incorporating both statistically verified multicomponent signatures and a multivariate sediment mixing model has been employed to determine the spatial origin of contemporary suspended sediment transported from the upper and middle reaches of the river exe 601km 2 and river severn 4325 km 2 basins uk spatial origin is addressed in terms of the relative contribution from three distinct geological subareas constituting each study basin the consistency of the composite fingerprinting approach is examined using the estimates for mean and seasonal variations in source area contributions and also a comparison between the results obtained for individual flood events and alternative lines of evidence provided by flood travel times and the spatial distribution of precipitation it is argued that fingerprinting estimates for sediment provenance are consistent with existing information on suspended sediment yields from different subcatchments within the study basins although in the severn the role of storage and remobilization in producing signature averaging may complicate comparison of the fingerprinting data with typical floodwater routing times validation represents the greatest problem for the cost benefit of fingerprinting and scope still exists for further refinement of the procedures involved 1998 john wiley sons ltd

paleohydrology of extraordinary floods along the swakop river at the margin of the namib desert and their paleoclimate implications abstract the swakop river is a major ephemeral river drainage basin area about 30 000 km 2 crossing the western namib desert its hydrology and limited water resources depend on storms and floods therefore the hydrology and flow regime in the swakop river basin determines the availability of water for human use in this study we present a millennia long record of extreme floods using paleoflood hydrological methods and optically stimulated luminescence osl ages the record includes 44 large floods ranging in date from the late pleistocene to the present the oldest six to eight floods are dated from the late pleistocene to the mid holocene between 14 900 1700 and 5100 620 years ago with calculated peak discharges of 550 1280 m 3 s 1 eighteen floods eleven of which were between 1000 and 1600 m 3 s 1 occurred between 740 90 and 190 10 years ago additional 17 later floods occurred between about ad 1850 and 1963 with peak discharges between 100 and 1000 m 3 s 1 the historical record which partly parallels the latter period recorded 17 large floods during the period 1893 1963 flood frequency analysis ffa of the combined systematically gaged record 1963 2003 and the paleoflood record since ad 1270 740 90 years the most complete record was applied using the maximum likelihood method a two component extreme value distribution tcev estimates the 1 annual exceedance probability magnitude using only the systematic gaged record at 520 m 3 s 1 the combined paleoflood historical and gage records resulted in a much larger magnitudes for the 1 annual exceedance probability flood magnitude of 1320 1350 m 3 s 1 the 0 1 annual exceedance probability magnitude is estimated at 770 m 3 s 1 and 2100 2150 m 3 s 1 respectively the hydroclimatic interpretation of this paleoflood record is complex due to the discontinuity of the record during the late holocene our flood data show three intervals differing in their flood regime 1 1280 80 to 740 90 years bp with one extraordinary flood 200 m 3 s 1 about every 180 years 2 740 90 to 200 45 14 c years bp with one large flood per 80 years and 3 200 45 14 c years bp to ad1963 with one large flood per 7 years interval 2 represents large floods probably related to the transition from a drier climate to the colder and probably wetter climate of the little ice age lia the third period relates to the end of the lia and to a wetter period of the 19th and early 20th centuries in which more rainfall in the kalahari and namib deserts and many historical floods were documented the presence of three distinct calcretes rich in calcified rhizoliths at one of the sites two of which were dated by osl to 13 2 1 9 ka and 8 8 1 0 ka indicates at least locally higher moisture availability than in the current semiarid climate the presence of denser vegetation can be associated with increased groundwater seepage and wetter climatic conditions

lower cambrian anabaritids from south china anabaritids are a distinctive group of early skeletal fossils with tri radially symmetrical tubes they occur in the earliest cambrian deposits and seem to be especially characteristic of the tommotian strata and putative pre tommotian units e g manykay horizon a detailed redescription of anabarites rotundus qian from near kuanchuanpu shaanxi province emphasizes the degree of morphological variation new data on shell composition suggest a bilayered structure the outer unit composed of fibres parallel to growth lines overlying a distinctive inner lamella with a chevron ultrastructure tentative evidence for anabaritids possibly being operculate is presented the putative operculum being a simple convex disc more poorly preserved anabaritids from the yangtze gorges hubei province and meishucun yunnan province are referred to a trisulcatus all these chinese occurrences of anabaritids are consistent with a lower tommotian age of the associated faunas but reliable and precise correlations with other precambrian cambrian boundary sections remain inconclusive

evidence for pyroclastic emplacement of the crowsnest formation alberta the middle cretaceous crowsnest formation west of coleman alberta is composed of bedded alkaline volcanic deposits containing heterolithic volcanic rock fragments and crystal clasts comparison with modern examples of subaerial pyroclastic rocks suggests that pyroclastic flows surges fallout of material from vertical eruption columns and minor mud flows emplaced the deposits textural evidence in the form of plastically deformed volcanic fragments chilled deposit margins baked rock fragment margins recrystallization and the presence of charred wood and charred wood molds indicate emplacement at elevated temperature massive deposits containing a fine grained basal zone are interpreted as the product of pyroclastic flows whereas deposits characterized by a block rich base overlain by a thin layer of block depleted stratified material are interpreted as the product of density stratified surges deposits exhibiting pronounced stratification were emplaced by ash cloud surges thickly bedded breccias

the contemporary physical and chemical flux of aeolian dust a synthesis of direct measurements of dust deposition abstract the deposition of aeolian or windblown dust is widely recognized as an important physical and chemical flux to ecosystems dust deposition adds exogenous mineral and organic material to terrestrial surfaces and can be important for the biogeochemical cycling of nutrients there have been many studies that characterize the physical and chemical composition of dust however few studies have synthesized these observations in order to examine patterns geochemical fluxes we have compiled observations of dust deposition rates particle size distributions psd mineralogy and bulk elemental and organic chemistry the rates of dust deposition observed across the globe vary from almost 0 to greater than 450 g m 2 yr 1 sites receiving dust deposition can be partitioned into broad categories based on there distance from dust source regions when compared to global dust models our results suggest some models may underestimate dust deposition rates at the regional and local scales the distance from the source region that dust is deposited also influences the particle size distributions mineralogy and chemical composition of dust however more consistent dust sampling and geochemical analyses are needed to better constrain these spatial patterns on average the concentrations of most major elements si al fe mg ca k in aeolian dust tend to be similar 20 to the composition of the upper continental crust ucc but there is substantial variability from sample to sample in contrast some elements tend to be depleted na or enriched ti in dust likely as a result of soil weathering processes prior to dust emissions trace elements especially heavy metals are consistently enriched in dust relative to the ucc ecologically important nutrients such as n and p are also present in dust deposition the geochemical flux attributable to dust deposition can be substantial in ecosystems located proximal to dust source regions we calculate estimates of elemental flux rates based on the average chemical composition of aeolian dust and varying rates of deposition these estimated flux rates are useful as a rough gauge of the degree to which dust deposition may influence biogeochemical cycling in terrestrial ecosystems and should be utilized to better constrain deposition estimates of global dust models

reinterpretation of middle cambrian stratigraphy of the rifted western laurentian margin burgess shale formation and contiguous units sauk ii megasequence rocky mountains canada abstract until recently research on the renowned fossil animals of the burgess shale has advanced to a greater degree than an understanding of the rocks in which they are found studies addressing lithostratigraphy and hydrothermal petrography of the so called inner carbonate belt and adjacent chancellor group however have begun to re evaluate long standing hypotheses on the middle cambrian of western canada tectonic activity along the kicking horse rim buried remnants of neoproterozoic rifting during the cambrian period had more influence on local sedimentation than previously thought notably large scale collapse of the cathedral carbonate platform margin at 509 ma bp is evidence of reactivated basement faults these failures produced listric megatruncation surfaces having near vertical escarpments 150 m in height where they terminate against the platform the majority of what have been interpreted as shed olistoliths from the cathedral platform margin is herein shown instead to be carbonate mud mounds these grew in situ along the face of the cathedral escarpment and are associated with fossiliferous intervals in overlying basinal mudstones at three distinct stratigraphic horizons two within the burgess shale during the delamaran and marjuman stages the mounds nucleated where deep seated normal faults intersected the seafloor building primarily during periods of relative sea level transgression mound growth is associated with syndepositional exhalative activity inferred from stratigraphic relations sedimentology and geochemistry the new name monarch formation is proposed for the initial post collapse beds and mounds deposited against the cathedral escarpment early glossopleura zone the variably defined term takakkaw tongue is thereby confined to pre collapse slope deposits coeval to and correlative with the cathedral formation

stratified flow in pyroclastic surges stratified flow theory is applied to pyroclatic surges in an effort to gain insight into transport dynamics during explosive eruptions particle transport is assumed to be by turbulent suspension and calculations contained herein show that this is likely for many cases including the 18 may 1980 blast at mount st helens the discussion centers on the rouse number pn which represents a ratio of particle settling velocity to scale of turbulence the brunt vaisala frequency n which is the maximum possible frequency of internal waves the froude number fr representing the ratio of inertial forces to gravitational forces and the richardson number ri a ratio of buoyant restoring forces to turbulent mixing forces the velocity or flow power dependence of bed form wavelength in surge deposits is related to a velocity dependence of wavelength of internal waves in the turbulent surge this produces a decrease in dune wavelength with increasing distance from vent migration direction of bed forms is related tofr as it is defined for a continuously stratified flow proximal to distal facies variations in surge deposits reflect increasingpn andri as the flows move away from their sources this produces the progression from sandwave to massive to planar facies with increasing distance from vent where the long axis of topography is at low angles to the flow direction massive facies in topographic lows may from concurrently with sandwave facies on highs due to the higher particle concentration in the lows where long axis of topography is at high angles to flow direction denser lower parts of the surge may be dammed or blocked blocked material tends to form massive flows that may move down slope independent of the overriding surge a model incorporating turbulent transport stratified flow and time evolution of pyroclastic surges is proposed for deposits which have been attributed to both pyroclastic flow and pyroclastic surge transport by various workers during the initial high energy waxing phase of the eruptive event pn is sufficiently low that only coarse but poorly sorted material is deposited to form relatively coarse bottom layers as the event wanes remaining finer material is deposited through a thin bed load to produce overlying bedded and cross bedded veneer deposits throughout most of the event blocking occurs to produce relatively thick and massive deposits in valley bottoms

distribution morphology and origin of sedimentary furrows in cohesive sediments southampton water patches of sedimentary furrows are developed at several locations in the cohesive estuarine sediments of southampton water water depth 1 12 m these furrows apparently result from short periods of erosion followed by long periods of deposition although all the furrows are similar regularly spaced parallel troughs 0 5 15 m wide aligned with the dominant current furrows in different patches have different characteristics in some areas furrow width is 1 5 1 15 of furrow spacing termed narrow whereas in other areas furrow width is about 1 2 of the spacing termed wide narrow furrows have developed where sediment accumulation rates are greater than 3 6 cm yr 1 wide furrows where accumulation rates are lower cockle shells and other coarse sediments concentrated on the furrow floors and on floors of smaller 2 10 cm wide minifurrows play an important role in furrow formation and evolution as they act to widen the furrows when mobilized during current episodes uniform sedimentation across the profile during slack periods tends to narrow the furrow some of the larger furrows have remained in the same position for 12 years while mini furrows have duration scales of a few months or less well developed furrows are also found in a recently dredged channel bedforms similar to those described here may be preserved in the sedimentary record while no analogues to the larger furrows are presently known minifurrows may be morphologically similar to the gutter casts described from ancient rocks

use of micromorphology for palaeoenvironmental interpretation of complex alluvial palaeosols an example from the mill creek formation albian southwestern alberta canada abstract field observations are often not sufficient for process based interpretations of palaeosols particularly where they form parts of thick aggradational pedocomplexes within alluvial successions under such conditions micromorphology provides genetic temporal and spatial information on soil forming processes that is critical to an understanding of past environmental conditions thick alluvial successions of the albian mill creek formation contain abundant evidence of pedogenesis but few well developed palaeosol profiles and therefore provide an ideal case study in which to demonstrate the usefulness of micromorphological data for palaeoenvironmental interpretation the micromorphological features of greatest interpretive value are types of clay coatings and ferruginous segregations structure and fabric papules evidence of bioactivity and ferruginous concretions provide information on geomorphic surface stability and assist in reconstructing temporal changes in drainage conditions while individual features can provide some palaeoenvironmental information the relationships of features to one another and assemblages of features provides additional information when analysed hierarchically to establish a sequence of sedimentologic and pedogenic events a common recurring sequence of palaeoenvironmental events subject to local variations can be recognized throughout the mill creek formation the presence of illuvial clay requires that water percolated through the soil and that the soil periodically dried out so that the translocated clay was retained dark reddish clay coatings indicate clay illuviation under freely drained conditions while pale yellow and silty clay coatings suggest that phases of free drainage alternated with phases of poorly drained or saturated soil conditions the presence of iron depletion coatings iron nodules and quasiferrans indicates that these units were at least periodically saturated and the occurrence of multiple overlapping phases within single thin sections demonstrates that redox conditions fluctuated strongly suggesting development in the vadose zone recent soils containing similar assemblages of features develop under warm temperate seasonal climates alternating phases of well drained and saturated conditions on the mill creek floodplains are attributed to changing sediment supply and local palaeogeomorphology rather than to any major regional climate change this type of process based micromorphological analysis should have broad application in other complex pedogenically modified alluvial successions and similar studies would lead to a more detailed understanding of ancient palaeoenvironments

ephemeral stream processes implications for studies of quaternary valley fills abstract three unstable ephemeral stream channels arroyos which drain source areas that have high sediment yields ranging from predominantly sand arroyo calabasas to a mixture of sand silt and clay sand creek to largely silt and clay sage creek were resurveyed to provide data on the rates and mechanics of erosion and sedimentation processes during periods ranging from 14 to 22 yr channel morphology changed significantly erosion occurred through nickpoint recession and bank collapse but erosional reaches are separated by aggrading or stable channel reaches in general sediment that is eroded as the nickpoint recedes upstream is trapped in the widened channel downstream in this manner sediment is transported episodically out of these basins during a series of cut and fill cycles the manner by which the channels aggrade and the morphology of the aggraded stable channels are controlled by the sediment type the wide and shallow channel of arroyo calabasas is filled by vertical accretion of sand size sediment the narrow and deep channels of sage creek and sand creek are created by the lateral accretion of cohesive fine grained sediment the channel modification and the cut and fill episodes are dependent on high sediment yields and therefore they are independent of subtle climatic shifts cut and fill deposits that have been created in this manner should not be equivalent in age from basin to basin and therefore channel trenching and filling in the semiarid western united states during the holocene need not be synchronous

mineral chemistry of igneous melanite garnets from analcite bearing volcanic rocks alberta canada the mineral chemistry of melanite garnets from the crowsnest volcanic rocks of sw alberta canada has been investigated by using electron microprobe scans quantitative analyses and multivariate statistical analysis the garnets occur with aegirine augite sanidine analcite and rare plagioclase as phenocrysts in trachyte and phonolite flows agglomerates and tuffs wavelength dispersive microprobe scans reveal complex zonation patterns both normal and oscillatory the results of fifty quantitative analyses were subjected to r mode factor analysis to delineate the chemical exchanges producing the zonation the chemical zonation of the garnets may be attributed to four independent binary exchanges al fe3 si ti ca mn and mg fe2 the stoichiometry of these garnets based on microprobe and wet chemical fe analyses combined with the strongly antithetic behavior of si and ti lead us to infer that the ti in these garnets is dominantly tetravalent it is clear from this study that quantitative modelling of the processes of crystal growth and zonation of melanite garnets in alkaline undersaturated igneous rocks should be aimed at simulating the four chemical exchanges listed above

storm influenced deltas and ice scouring in a late pleistocene glacial lake this paper identifies the sedimentary record of storms and bottom scouring ice masses that is preserved in upper pleistocene glaciolacustrine delta sediments deltaic sedimentation occurred on the margin of an enlarged ice dammed ancestral lake ontario with a surface elevation at least 80 m above the modern level beds of amalgamated hummocky and swaley cross strata separated by fairweather muds represent delta front storm deposits and overlie laminated prodelta clays the central and thickest part of a 5 km long outcrop exposes variably cross stratified sand in multiple channels inset within tabular sheets of rippled sand this complex represents a broad distributary channel system about 1 6 km wide and 20 m deep cut into delta front storm sequences a large scour and related deformation structures are attributed to bottom dragging ice masses possibly pressure ridged lake ice the depositional setting outlined in this paper emphasizes the importance of storm waves in large continental glacial lakes and provides a contrast with better known low energy conditions in small glacial lake basins

slow rates of rock surface erosion and sediment production across the namib desert and escarpment southern africa slow erosion has characterized the namib desert the namibian escarpment and the adjacent namibian highlands over the pleistocene paired analyses n 66 of in situ produced 10be and 26al in quartz bearing samples of bedrock primarily from inselbergs of sediment from dry river and stream channels and of clasts from desert surfaces reveal large inventories of these cosmogenic nuclides indicating significant landscape stability over at least the past million years bedrock samples n 47 collected in three transects from the coast across the escarpment and into the highlands show no spatial pattern in elevation normalized nuclide abundance despite a difference in mean annual precipitation map between sample sites at the coast map 400 mm yr 1 average model erosion rates inland of the escarpment 3 2 1 5 n 9 are indistinguishable from average rates seaward of the escarpment 3 6 1 9 n 38 indicating that rock on the pedimented coastal plain is eroding at the same rate as rock in the highlands sediment samples n 3 from small streams suggest that the landscape as a whole is eroding more rapidly than the bedrock outcrops and that a basin in the steep escarpment zone is eroding several times faster 16 m my 1 than either a basin in the highlands 5 m my 1 or a basin in the coastal plain 8 m my 1 data from large rivers n 4 constrain erosion rates averaged over 105 yrs and 104 to 105 km2 between 3 and 9 m my 1 small quartz clasts n 12 collected from four desert surfaces record extraordinarily long variable and in some cases complex exposure histories simple 10be model ages are as high as 1 8 my some minimum total histories considering both 10be and 26al and including both burial and exposure exceed 2 7 my as a group the namibian cosmogenic data do not support the model of significant and on going escarpment retreat the similarity of erosion rates calculated from 10be analysis of fluvial sediments and longer term 107 yr average mass removal rates estimated by others using fission track analysis of rock suggests that namibian erosion rates have reached a steady state and are changing little over time at outcrop scales the concordance of 10be and 26al in most bedrock samples suggests that the model of steady uniform bedrock erosion is valid there is no indication of intermittent burial shedding of thick rock slabs or stripping of previous cover at an intermediate scale a transect of bedrock samples north of gobabeb demonstrates that the northern boundary of the massive namib sand sea has been steady and unshifting similarly low cosmogenically estimated erosion rates across west and central namibia suggest that the landscape is in geomorphic steady state its overall appearance changing only slowly through time

storm deposited sandstones tempestites and related ichnofossils of the late ordovician georgian bay formation southern ontario canada the late ordovician geogian bay formation of southern ontario canada comprises up to 250 m of grey to blue grey shales interbedded with highly fossiliferous calcareous sandstones these strata were deposited in equatorial paleolatitudes after 448 ma in a shallow foreland basin created by overthrusting along the eastern margin of north america the taconic orogeny the georgian bay formation comprises the middle part of an upward shallowing progradational sequence from deep water transgressive shales of the underlying whitby formation to muddy tidal flat sequences of the overlying queenston formation exposures in brickyard and river cuts near toronto and northwards along a narrow outcrop belt along the foot of the niagara escarpment show laterally extensive 100 m sharp based sheets of sandstone up to 1 m thick with gutter casts and washed out hypichnial trace fossils dominantly planolites and paleophycus on their lower bedding surfaces detailed examination of sandstone beds in outcrop and i

is there evidence for geostrophic currents preserved in the sedimentary record of inner to middle shelf deposits abstract unidirectional oscillatory and combined flow paleocurrent data from many ancient wave dominated coastlines indicate that sediment transport was directed offshore at angles of 70 to 90 from the inferred local paleoshoreline solemarks and parting lineations from turbidite like storm beds and solemarks from hummocky beds indicate that flows transporting sediment offshore were orthogonal to the local shoreline the shore normal orientations of solemarks parting lineation and asymmetric ripples on hummocky cross stratification and their orthogonal relationship with respect to wave ripple crest orientation indicate that the dominant direction of wave approach at the sediment water interface was also orthogonal to the shoreline the formation of hummocky cross stratification by an al ng shore flow component superimposed on oscillatory wave motion is not supported by paleocurrent data rather much of the evidence from the ancient record suggests that hummocky cross stratification forms under high energy oscillatory flow with a weak shore normal combined flow component the orientation of wave ripple crests from the lower shoreface to offshore transitional zone of wave dominated coasts can be used to approximate the local paleoshoreline trend the paleocurrent data from the ancient examples suggest a strong predominance of offshore directed sediment transport as opposed to the nearly shore parallel orientation of currents observed in modern geostrophic flows

chondrites a trace fossil indicator of anoxia in sediments the trace fossil chondrites a highly branched burrow system of unknown endobenthic deposit feeders occurs in all types of sediment including those deposited under anaerobic conditions in some cases such as the jurassic posidonienschiefer formation of germany chondrites occurs in black laminated carbonaceous sediment that was deposited in chemically reducing conditions in other cases such as numerous oxic clastic and carbonate units throughout the geologic column chondrites typically represents the last trace fossil in a biotutbation sequence this indicates that the burrow system was produced deep within the sediment in the anaerobic zone below the surficial oxidized zone that was characterized by freely circulating and oxidizing pore waters

the low temperature geochemical cycle of iron from continental fluxes to marine sediment deposition suspended sediments from 34 major rivers geographically wide spread and 36 glacial meltwater streams have been examined for their variations in different operationally defined iron fractions fehr iron oxides soluble in dithionite fepr iron soluble in boiling hcl but not in dithionite and feu total iron less that soluble in boiling hcl river particulates show a close association between fehr and total iron fet reflecting the effects of chemical weathering which derive oxide iron from and retain it in close association with total iron consistent with this continental scale average fehr fet ratios vary with runoff ratios average river runoff per unit area average precipitation per unit area by contrast the diminished effects of chemical weathering produce no recognizable association of fehr with fet in glacial particulates and instead both fepr and feu are closely correlated with fet reflecting essentially pristine mineralogy a comparison of the globally averaged compositions of riverine particulates and marine sediments reveals that the latter are depleted in fehr fepr and fet but enriched in feu the river and glacial particulate data are combined with estimates of authigenic hydrothermal atmospheric and coastal erosive iron fluxes from the literature to produce a global budget for fehr f e pr f e u and fet this budget suggests that the differences between riverine particulates and marine sediments can be explained by i preferentially removing fehr from the riverine particulate flux by deposition into inner shore reservoirs such as floodplains salt marshes and estuaries and ii mixing the resulting riverine particulates with fehr depleted glacial particulates preliminary measurements of inner shore sediments are consistent with i above phanerozoic and modern normal marine sediments have similar iron speciation characteristics which implies the existence of a long term steady state for the iron cycle this steady state could be maintained by a glacioeustatic feedback where fehr enriched riverine particulates are either more effectively trapped when sealevel is high small ice masses diminished glacial erosion or are mixed with greater masses of fehr depleted glacial particulates when sealevel is low large ice masses enhanced glacial erosion further important controls on the steady state for fehr operate through the formation of euxinic sediments and ironstones which also provide sealevel dependent sinks for fehr enriched sediment

the 1982 eruptions of el chichon volcano mexico 3 physical properties of pyroclastic surges two major pyroclastic surges generated during the 4 april 1982 eruption of el chichon devastated an area of 153 km2 with a quasi radial distribution around the volcano the hot surge clouds carbonized wood throughout their extent and were too hot to allow accretionary lapilli formation by vapor condensation field evidence indicates voidage fraction of 0 99 in the surge cloud with extensive entrainment of air thermal calculations indicate that heat content of pyroclasts can heat entrained air and maintain high temperatures in the surge cloud the dominant bed form of the surge deposits are sand waves shaped in dune forms with vertical form index of 10 20 characterized by stoss side erosion and lee side deposition of 1 10 cm reversely graded laminae a systematic decrease in maximum lithic diameter with distance from source is accompanied by decrease in wavelength and amplitude modal analysis indicates fractionation of glass and pumice from the surge cloud relative to crystals resulting in loss of at least 10 25 of the cloud mass due to winnowing out of fines during surge emplacement greatest fractionation from the 1 0 0 0 grain sizes reflects relatively lower pumice particle density in this range and segregation in the formative stages of the surge cloud extensive pumice rounding indicates abrasion during bed load transport flow of pyroclastic debris in the turbulent surge cloud was by combination of bed load and suspended load transport the surges are viewed as expanding pyroclastic gravity flows which entrain and mix with air during transport the balance between sedimentation at the base of the surge cloud and expansion due to entrainment of air contributed to low cloud density and internal turbulence which persisted to the distal edge of the surge zone

two decades of research on the proterozoic phanerozoic transition 1972 1991 the most radical global change involving the biology chemistry and physics of life occurred near and at the stratigraphical level of the boundary between the neoproterozoic system precambrian and the cambrian system this stratigraphical level is held by consensus to be the proterozoic eonothem phanerozoic eonothem boundary and is regarded as being of fundamental importance research has involved not only archaeocyathans shelly small problematica earliest trilobites stromatolites and algae trace fossils soft bodied metazoans microphytolites and acritarchs but also physical and chemical aspects radio isotope dating carbon strontium and oxygen isotope stratigraphy polar wandering relating to palaeogeography and magnetostratigraphy a selected bibliography 1985 1990 is appended to enable further reading of the extensive research contributions

a burgess shale like fauna from the lower cambrian of north greenland the cambrian explosion refers to the major adaptive radiation of the metazoans during the earliest phanerozoic an event that is best known by the abrupt appearance of hard parts near to the precambrian cambrian boundary 550 myr bp 1 deciphering this important evolutionary episode depends largely on the study of these skeletal remains2 3 together with trace fossils that include burrows and trackways4 5 many of these latter fossils evidently represent the activities of soft bodied organisms such as worms and lightly sclerotized arthropods whose exact identity is seldom known not least because they can be fossilized only in exceptional circumstances6 however documenting the soft bodied representatives of early metazoan communities cannot be neglected if they accounted for a substantial fraction of these early biotas7 here we report a new soft bodied fauna from the lower cambrian of north greenland this assemblage has highly significant similarities with the younger burgess shale and provides additional evidence for the geological longevity of this faunal type and its widespread distribution in deeper waters of cambrian oceans

burgess shale type faunas in the context of the cambrian explosion a review burgess shale type faunas are now known from almost 40 lower and middle cambrian localities although those from british columbia canada yunnan china and peary land greenland are of paramount significance the diverse faunas are dominated by animals with an otherwise negligible fossilization potential and their stratigraphical position makes them of unique importance in documenting the major adaptive radiations at this time cambrian explosion important features of these faunas include the presence of taxa surviving from the late precambrian ediacaran faunas the discovery of articulated material that throws new light on scleritome organization in various cambrian skeletal taxa and the significance of the degree of anatomical disparity among cambrian animals in addition these soft bodied faunas offer some hope of reconciling soft part data with trace fossil occurrences new discoveries of burgess shale type faunas are inevitable and such finds will continue to enhance our under standing of early animal evolution

the scleritome of eccentrotheca from the lower cambrian of south australia lophophorate affinities and implications for tommotiid phylogeny the first partially articulated scleritome of a tommotiid eccentrotheca sp is described from the lower cambrian of south australia the eccentrotheca scleritome consists of individual sclerites fused in a spiral arrangement forming a tapering tube shaped skeleton with an inclined apical aperture and a circular to subcircular cross section traditionally tommotiid sclerites have been assumed to form a dorsal armor of imbricating phosphatic plates in slug like bilaterians analogous to the calcareous sclerites of halkieriids the structure of the eceentrotheca scleritome is here reinterpreted as a tube composed of independent irregularly shaped sclerites growing by basal marginal accretion that were successively fused to form a rigid protective tubular structure the asymmetrical shape and sometimes acute inclination of the apical aperture suggests that the apical part of the scleritome was cemented to a hard surface via a basal disc from which it projected vertically rather than being a vagrant member of the benthos eccentrotheca most likely represented a sessile vermiform filter feeder the new data suggest that the affinities of eccentrotheca and possibly some other problematic tommotiids lie with the lophophorates i e the phoronids and brachiopods a clade that also possesses a phosphatic shell chemistry and a sessile life habit

the last millennium largest floods in the hyperarid kuiseb river basin namib desert the largest kuiseb river floods initiate at the basin s semi arid headwater downstream along the hyperarid namib desert these floodwaters are feeding shallow alluvial aquifers the only available water for human activity and for the natural ecology here we characterize the largest floods and their changing frequency and magnitudes using palaeohydrological methods along 120 km of the rivers canyon 35 palaeoflood deposit sites were identified at five of these sites we conducted stratigraphic and geochronological analyses and flood discharge estimations the upper bound of the largest flood over the late holocene is 1475 m 3 s 1 over the last 1300 years more than ten floods have exceeded 1250 m 3 s 1 an additional 33 floods exceeded 400 m 3 s 1 the last millennium was characterized by one large flood every 30 40 years during the periods 1250 1335 1355 1565 and 1715 ad to the present a slight increase in flood frequency not magnitude occurred during 1565 1715 ad one large flood in 20 years and during two short episodes 1185 1205 and 1335 1355 ad seven and four floods in 20 years respectively these episodes of increased flood frequency are associated with other proxy records of higher water availability in the namib copyright 2013 john wiley sons ltd

deep sea fan deposits in the macigno formation middle upper oligocene of the gordana valley northern apennines italy abstract facies characteristics are described for a 2300 m thick turbidite succession of the macigno formation middle upper oligocene which crops out as a continuously exposed section in the gordana valley northern apennines in the study area the macigno formation consists of two sandy members separated by a shaly member the sandy members contain lithic associations characteristic of submarine fan deposits and form distinct fan complexes the middle shaly member represents a period of basin starvation three main facies associations are recognized in the macigno fan deposits fan fringe outer fan lobe and braided midfan facies associations the fan fringe deposits consist of monotonous or small scale cyclically arranged thin bedded turbidites the outer fan lobe deposits are composed of medium to very thick bedded classical turbidites internally organized in thickening upward cycles with minor intercalations of thin bedded sandstone beds two distinct types of outer fan lobe deposits distal and proximal are recognized on the basis of rock type internal organization and vertical facies relationships the midfan deposits consist of amalgamated massive sandstone and pebbly sandstone which display repeated thinning upward cycles the three main facies associations are superposed t define major thickening and coarsening upward cycles reflecting distinct episodes of fan progradation the relationships between the facies associations of the macigno deposits and the existing models of submarine fan sedimentation are discussed after the deposition of the fan complexes fan sedimentation in this part of the basin was replaced by movements of allochthonous units heralded by large olistostromes

mass and hyperconcentrated flow deposits record dune damming and catastrophic breakthrough of ephemeral rivers skeleton coast erg namibia channel shaped deposits of well sorted sand with only 2 4 fine grained material being either massive and structureless or upward fining with basal lag are found interbedded with aeolian sand in the skeleton coast erg namibia detailed analyses of the channel shaped deposits suggest that they are formed as hyperconcentrated flows within the erg grain size analysis and whole rock geochemical modeling revealed that some of the fluvial sediments contain up to 70 aeolian sand interpreted as a result of dune collapse into the fluvial system in certain cases this instantaneous supply of sand resulted in generation of sandy mass flows with laminar flow behaviour the presence of smectite as dominant clay mineral proved to be of crucial importance in formation of mass flow deposits these mass flows had no erosional capacity and drape the palaeotopography they are comparable to those generated by catastrophic collapse of dunes described in the literature this paper suggests that all these deposits should be termed intra erg mass flows as several of them carry little if any debris based on their origin intra erg mass flows can be divided into two groups

evidence of past climatic change in the namib desert abstract a preliminary survey of some areas of the central and northern namib desert was undertaken in order to identify geomorphic and sedimentary features that could potentially provide information on past climatic change in the region wherever possible samples were collected for radiocarbon dating the visits to the skeleton coast area were especially revealing practically every river valley in this tract shows a sequence of terraces and deposits that would warrant a detailed study in all about 120 new radiocarbon dates were obtained for the region these have supplied a wealth of individual results and collectively have enabled the construction of a tentative chronological sequence of the changes in climate for the past 40 000 yr three periods of increased aridity in the hinterland but with decreasing intensity are postulated during the last glacial maximum the early holocene and between a d 1200 and a d 1600 the inter pleniglacial up to 23 000 yr b p the late glacial and the period between about 4000 yr b p and 1200 yr b p on the other hand were more humid than today also with decreasing intensity other indicators of past climate were also identified but since they lie beyond the range of radiocarbon dating they cannot as yet be placed in a chronological context of significance is the fact that convincing evidence was obtained for climatic change within the last millennium and especially the rainfall is found to have been increasing since the 16th century

landsat identifies aeolian dust emission dynamics at the landform scale abstract the modelling of windblown mineral dust emissions remains a challenge this is in part due to the coarse spatial and temporal resolution of the data on which these models are based but also because the processes and mechanisms of aeolian dust emission are not well understood satellite imagery has been used extensively in the study of dust from the late 1990s with important contributions being made in terms of sources transport pathways and deposition areas using modis imagery the namib desert has been identified as one of the largest sources of dust in southern africa the opening of the landsat archive presents the opportunity to investigate these events at a higher spatial resolution up to 15 15 m than previously possible despite the low temporal resolution we used landsat imagery to identify 40 major dust episodes over the last 25 years that originated primarily from the ephemeral river valleys and pan complexes providing new insight into the spatial and temporal evolution of the dust sources from dryland surfaces examination of the imagery enabled the identification of local scale landform source points to direct ground based testing of the surfaces responsible for dust emission emissivity tests were undertaken using a pi swerl portable wind tunnel in three of the major dust producing river systems along the namib coast namely the kuiseb omaruru and huab rivers preliminary observations suggest that human impact on the hydrological systems in two of the river basins to cater for the increasing demand of water have dramatically altered the emission patterns of dust the source areas of greatest dust emission are found to be located on recently deposited fluvial surfaces which are not active in the contemporary environment

articulated halkieriids from the lower cambrian of north greenland metazoan skeletons appear abruptly in the fossil record near the base of the cambrian 540myrbp before present 1 2 in the initial stages of diversification familiar skeletal remains such as sponge spicules brachiopod valves and echinoderm ossicles are outnumbered by a remarkable array of skeletal types many of millimetric size3 9 particularly conspicuous in these early assemblages are various sclerites some of which are inferred to have formed cataphract coverings of slug like metazoans recognition of articula tory facets and fused sclerites contribute to partial scieritome reconstructions8 11 but discovery of articulated material is a vital ingredient in understanding the palaeobiology of these extinct groups here we report complete halkieriid scleritomes from the lower cambrian of north greenland this finding broadly confirms the predictions of an earlier hypothetical reconstruction11 but reveals entirely unexpected anterior and posterior shells it supports also the proposed phylogenetic link between the halkieriids and wiwoxia corrugata a metazoan with a cataphract scieritome best known from the middle cambrian burgess shale

dust emission from wet and dry playas in the mojave desert usa the interactions between playa hydrology and playa surface sediments are important factors that control the type and amount of dust emitted from playas as a result of wind erosion the production of evaporite minerals during evaporative loss of near surface ground water results in both the creation and maintenance of several centimeters or more of loose sediment on and near the surfaces of wet playas observations that characterize the texture mineralogic composition and hardness of playa surfaces at franklin lake soda lake and west cronese lake playas in the mojave desert california along with imaging of dust emission using automated digital photography indicate that these kinds of surface sediment are highly susceptible to dust emission the surfaces of wet playas are dynamic surface texture and sediment availability to wind erosion change rapidly primarily in response to fluctuations in water table depth rainfall and rates of evaporation in contrast dry playas are characterized by ground water at depth consequently dry playas commonly have hard surfaces that produce little or no dust if undisturbed except for transient silt and clay deposited on surfaces by wind and water although not the dominant type of global dust salt rich dusts from wet playas may be important with respect to radiative properties of dust plumes atmospheric chemistry windborne nutrients and human health published in 2007 by john wiley sons ltd

time sequence observations of wave formed sand ripples on an ocean shoreface analysis of an 18 day time lapse film record of shoreface ripple development with concurrent measurements of near bottom flow and surface waves provides new insight on equilibrium bedform conditions adjustment of ripple planform to variable hydrodynamics and ripple migration behaviour the study was conducted in approximately 10 m water depth 1 km off martinique beach on the atlantic coast of nova scotia canada under low energy summer wave conditions significant wave height and peak period during the study averaged 0 7 m and 8 s respectively with extremes up to 1 7 m and 11 s during passage of three weak weather disturbances six mutually exclusive ripple types have been defined 1 short wavelength regular ripples 2 variable bifurcated ripples 3 variable terminated ripples 4 short crested ripples 5 long wavelength regular ripples and 6 chaotic ripples ripple wavelength ranged from 0 07 m to 0 24 m and displayed a strong reynolds number dependence together with other published field data the results suggest a lower limit of 0 06 m for the wavelength of wave ripples in ocean shoreface environments ripple orientation ranged through 38 and responded rapidly to changes in wave approach direction but did not conform to the orientation of the adjacent shoreline ripples were observed to migrate both on and off shore with and against the wave advance direction at rates up to 0 1 m h 1 associated with net flows other than wave induced onshore asymmetry and mass transport migration mainly of ripple types 1 and 2 occurred during the peak of storm events but showed no obvious correlation with measured near bottom flow magnitude or direction ripple behaviour demonstrates equilibrium with prevailing dynamic conditions when straight crested rippie types 1 and 5 are present disequilibrium in orientation or dimensions is expressed by increasing sinuosity bifurcation and crest termination in types 2 3 4 and 6

holocene fluvial valley fill sources of atmospheric mineral dust in the skeleton coast namibia western namibia is a significant global source of atmospheric mineral dust we investigate the relationship between dust and source sediments assessing the sustainability of dust flux remote sensing studies vickery and eckhardt 2013 have highlighted specific ephemeral fluvial systems as important contributors to dust flux including highlighting sections of valleys that are the origins of dust plumes in the period 2005 8 little is known however about the specific within valley dust sediment sources particularly whether dust is derived from modern ephemeral channel floors or older valley fill sediments many of which have been reported in the region stone and thomas 2013 as part of a region wide analysis of aeolian dust flux we investigate the sediment properties of atmospheric dust samples and valley sediments from the huab valley one of the principal regional dust sources trapped dust samples contain up to 88 very fine sand and silt when collected samples are disaggregated prior to analysis valley fill surface samples comprise 80 very fine sand and silt and the surface of the modern ephemeral channel 30 valley fill sediments were sampled at depths up to 3 6m below the present surface and reveal holocene depositional ages from 0 6 0 03ka back to 9 79 0 73ka these sediments contain 30 to 6 very fine sand and silt with levels decreasing with depth and age aeolian bedforms in the valley system nebkhas on the fill surface and climbing dunes on valley margins indicate that aeolian processes under the influence of strong seasonal easterly winds likely result in dust being winnowed out of the valley fill surfaces with sandy bedforms being constructed from the coarser component of the fill sediments the volume of valley fill sediment suggests dust sourced from holocene sediments is likely to continue into the future regardless of flow conditions in the modern channel system

iron and nutrient content of wind erodible sediment in the ephemeral river valleys of namibia abstract research concerning the global distribution of aeolian dust sources has principally focussed on salt clay pan and desiccated lacustrine emission areas in southern africa such sources are identified as etosha pan in northern namibia and makgadikgadi pans in northern botswana dust emitting from ephemeral river valleys however has been largely overlooked rivers are known nutrient transport pathways and the flooding regimes of ephemeral river valleys frequently replenish stores of fine sediment which on drying can become susceptible to aeolian erosion such airborne sediment may be nutrient rich and thus be significant for the fertilisation of marine waters once deposited this study investigates the dust source sediments from three ephemeral river valleys in namibia in terms of their particle size distribution and their concentrations of bioavailable n p and fe we compare the nutrient content of these sediments from the ephemeral river valleys to those collected from etosha and makgadikgadi pans and consider their relative ocean fertilising potential our results show that the ephemeral river valleys contain fine grained sediment similar in physical character to etosha and makgadikgadi pans yet they have up to 43 times greater concentrations of bioavailable iron and enriched n and p macronutrients that are each important for ocean fertilisation the known dust emitting river valleys of namibia may therefore be contributing a greater fertilisation role in the adjacent marine system than previously considered and not yet investigated given this finding a re assessment of the potential role of ephemeral river valleys in providing nutrient rich sediment into the aeolian and marine systems in other dryland areas is necessary

characterization of dust emission from alluvial sources using aircraft observations and high resolution modeling 1 we investigate mineral dust emission from alluvial sediments within the upland region in northern mauritania in the vicinity of a decaying nocturnal low level jet llj for the first time the impact of valleys that are embedded in a rather homogeneous surrounding is investigated with regard to their role as dust source measures for local atmospheric dust burden were retrieved from airborne observations satellite observations and model simulations and analyzed in order to provide complementary information at different horizontal scales observations by the leandre nouvelle generation backscatter lidar system flying aboard the french falcon 20 aircraft were taken along five parallel flight legs perpendicular to the orientation of the main valley system dominating the topography of the study area results from a comparison of lidar derived extinction coefficients with topography and aerial photographs confirm the relevance of 1 alluvial sediments at the valley bottoms as a dust source and 2 the break down of the nocturnal llj as a trigger for dust emission in this region an evaluation of the arome regional model forecasting dust at high resolution 5 km grid points toward an under representation of alluvial dust sources in this region this is also evident from simulations by the mesonh research model although mesonh simulations show higher dust loadings than arome which are more comparable to the observations both models underestimate the dust concentrations within the boundary layer compared to lidar observations a sensitivity study on the impact of horizontal grid spacing 5 km versus 1 km highlights the importance of spatial resolution on simulated dust loadings

microclimate and weathering in the central namib desert namibia data on rock surface microclimates at four sites kleinberg vogelfederberg gobabeb and ganab along a transect across the central namib desert over a 3 year period have been collected alongside some shorter term data sets rock surface temperature rst air temperature wind relative humidity and surface wetness data are presented here weathering of exposure blocks of local marble and granite has also been monitored over the 3 year period with change observed visually and with scanning electron microscopy complex temporal patterns of rock temperature fluctuations are observed over the 3 years although the four sites show very similar overall trends suggesting spatial homogeneity in the rock surface temperature regime relative humidity and surface wetness data show clear differences between the four sites related to the frequency of fogs granite blocks show no visible changes after 2 years of weathering whereas marble blocks especially those at ganab show sem evidence of structural weakening after 1 year

characteristics of dune bedded pyroclastic surge bedsets abstract the grainsize characteristics of dune bedded pyroclastic surge bedsets are surveyed the variance between coarsest and finest beds ranges from 1 to 6 phi in different surge bedsets and it increases as the grainsize of the coarsest bed increases reflecting an increasing velocity of emplacement deposits of wet surges identified as those which contain accretionary and ash coated lapilli tend to be finer and show less variance this partly because wet ash is cohesive but mainly because wet surges tend to be weaker dry surge bedsets are strongly fines depleted wet ones less so the lack of erosion of underlying ash layers shows that the environment is a strongly depositional one individual bedsets are demarcated by thin intervening fine ash fall layers which are the complementary ash cloud deposits settled or flushed out after the passage and decay of each turbulent surge surge deposits are generally less coarse than the coarsest associated airfall deposits which shows that they are formed by generally weaker events this study helps interpret the dune bedded parts of the landscape mantling may 18th 1980 blast deposit of mount st helens the blast was a very violent event but the variance and the grainsize of the coarsest bed are those of a relatively weak surge this suggests that the dune bedding was produced by a weak effect such as minor turbulence in a thin pyroclastic flow coming to rest in a mountainous terrain roughened by tree stumps and fallen logs

the role of aeolian dust in ecosystems abstract the recent upsurge in research attention to aeolian dust has shown that dust transport systems operate on very large spatial and temporal scales and involve much larger quantities of sediment than was previously realized an inevitable consequence of this is that researchers from a range of neighbouring disciplines including ecology are beginning to realize that this new knowledge has important implications for their study areas in the present paper we examine the ecological implications real and potential of this expanding knowledge of dust transport systems with a particular emphasis upon the australian dust transport system we track these ecological effects from source to sink at source wind erosion soil vegetation relationships are often dominated by temporal changes in rainfall nine years of measurements in the channel country of the lake eyre basin australia show that vegetation and soils in dune fields can recover from drought whereas on inter fluve grasslands uni directional and negative successional vegetation changes can result from wind erosion during drought on floodplains both wind erosion and vegetation responses are complicated by flood frequency up to 1999 flooding of saline claypans did not increase vegetation but did increase wind erosion through the supply of alluvial fines however after three floods within as many months vegetation became established and wind erosion rates were dramatically reduced wind erosion research attention is now gradually turning from the physical to the organic content of eroded dusts in australia organic matter content can reach 65 by mass but this cannot be explained by removal of soil organic matter alone biological soil crusts not only stabilize soils against wind erosion but contribute to some of the organic dusts the role of dust as a vector for pathogens is an area which deserves greater research attention in the future downwind from source we show that dust contributions to soils are more widespread and more variable in time and space than earlier work on dust derived loess soils has suggested recent studies also show positive dust impacts upon nutrient budgets within distant forest ecosystems and significant contributions to river nutrient loads especially in the arid sectors of internally draining river basins the number of studies of dust impacts upon marine ecosystems is increasing dramatically studies of dust within antarctic ice cores combined with dust modelling provide compelling evidence that increased soluble iron rich dust inputs to the southern ocean have stimulated phytoplankton populations modern process studies are however yet to clearly demonstrate these relationships finally we examine the potential for major dust impacts upon global climates using its positive and negative effects upon solar radiation and precipitation as examples of the complexity and importance of this new research area

dust emission and transport in mali west africa vertical dust fluxes were measured in the inland delta region of the niger river mali west africa during april june 1989 and 1990 measurements of dust flux represent for the most part non dust storm conditions or dust haze periods the observed concentration versus height relationships are similar to data presented by other investigators the relationship between wind shear velocity u m s 1 and vertical dust flux f g m 2 s 1 can be described by a relationship in which f is proportional to u 4 however there is considerable scatter within the data set which is attributable to textural controls and surface conditions the vertical dust fluxes measured in mali are compared to dust fluxes measured in texas usa and yukon territories canada the significantly different values for the constant of proportionality a in the f a u 4 relationship for these geographically diverse areas is a function of surficial controls on the release of sediments to the air stream dust concentrations measured in mali were found to be uniformly high and in general exceed who health standards for acceptable total suspended particulate loadings as a result background dust may be considered a long term stress on health for the people of this region of mali