a middle cambrian trilobite faunule from the meguma group of nova scotia the meguma group of southern nova scotia is a thick succession of mostly deep water siliciclastic sedimentray rocks of uncertain age previous fossil finds have been in the halifax formation of the upper part of the sequence and have provided early ordovician ages a newly discovered trilobite bearing bed from the underlying goldenville formation yields middle cambrian taxa of acado baltic affinity specimens belonging to paradoxides s l agraulos dorypyge and ellipsocephalidae indicate that the meguma group is an exotic succession with faunal similarity to the adjacent avalon terrane and to middle cambrian successions in europe the middle east and west africa

cambrian ordovician acritarchs in the meguma terrane nova scotia canada resolution of early paleozoic stratigraphy and implications for paleogeography organic walled microfossils acritarchs provide age constraints for the previously poorly dated cambrian and lower ordovician turbiditic goldenville and halifax groups in the northern appalachian meguma terrane of nova scotia and address controversies about stratigraphy and provenance the oldest exposed formation of the 8 km thick goldenville group contains the trace fossil oldhamia which suggests an age of late early cambrian whereas the coticule bearing uppermost formation yielded an acritarch species consistent with middle cambrian epoch 3 age the conformably overlying 5 km thick halifax group includes basal pyritiferous units that yielded a late cambrian furongian assemblage of acritarch species providing further confirmation that the underlying manganese bearing formations are of cambrian epoch 3 age and not ordovician as recently claimed overlying nonpyritiferous formations contain the early ordovician graptolite rhabdinopora flabelliformis flabelliformis and acritarchs of similar age samples collected up section from the graptolite occurrence yielded acritarch species that are indicative of the later tremadocian and floian the new fossil data confirm a gap in age of 30 m y between the halifax group and the overlying silurian to lower devonian rockville notch group the new ages are consistent with stratigraphic units defined in regional mapping and support recent interpretation of fundamental differences in depositional and tectonic environments between the northwestern and southeastern parts of the meguma terrane they also provide new constraints on paleogeography of the terrane by confirming age similarities to stratigraphy in north wales with which correlation has been proposed previously based mainly on lithological similarities

the evolutionary significance of a lower cambrian trace fossil assemblage from the meguma terrane nova scotia we report a diverse assemblage of trace fossils from the lower cambrian high head member of the church point formation near yarmouth nova scotia based on the presence of sharp based beds load casts and flute casts along with other sedimentological criteria the strata are interpreted to have a turbidite origin other characteristics including wrinkle structures and high fidelity of trace fossil preservation suggest that the inter episode biotope was influenced by the presence of biomats the trace fossil assemblage includes in approximate order of abundance planolites helminthopsis oldhamia chondrites gordia cladichnus psammichnites gigas treptichnus phycodes lorenzinia palaeophycus and teichichnus trace fossils are increasingly abundant upwards in the section but they are ultimately mitigated by an increase in inferred sedimentation rates the trace fossil assemblage which bears many similarities to other lower cambrian locales e g puncoviscana formation of northwest argent

sequence stratigraphy and proveance on gondwana s margin the meguma zone cambrian to devonian of nova scotia canada the meguma zone is the second largest terrane in the canadian appalachians three thick sandstones cambrian upper ordovician and lower devonian alternate with two thick shales lower ordovician and silurian the succession is a marginal assemblage shoaling upward from deep sea fan complexes to coastal facies in terms of sequence stratigraphy the succession consists of a basal type 1 sequence the meguma supergroup and three overlying type 2 sequences collectively the annapolis supergroup interpretations of sedimentary environments and stratigraphic relations agree with those of classical systems tracts the meguma zone is a sedimentary sink for an enormous amount of well sorted fine grained sand and silt this quantity and its westward dispersal indicate a gondwanan derivation stratigraphic units of the west african craton mimic those of the meguma zone in lithology provenance dispersal succession and age during neoproterozoic time continental ice sheets rivers and wind moved sediment southeastward down a cratonic paleoslope from what is now morocco through mauritania and mali remnants of widespread sand sheets extend across southern mali this sand reservoir became the source rock for the meguma zone in the early cambrian the paleoslope reversed perhaps due to birth of iapetus these same agents eroded the malian sand sheets episodically during relative sea level lows in cambrian late ordovician and early devonian times remnants of the resulting northwestward moving cratonic sands and silts occur today as mesas and buttes in northern mali mauritania southern morocco and algeria the ultimate destination of this detritus was the continental margin of north gondwana this sediment now forms the meguma zone and other terranes of southern europe northern africa and the middle east

a long flume study of the dynamic factors affecting the resistance of a loamy soil to concentrated flow erosion experiments were carried out in a 20 m long flume to assess the variation of the runoff erosion resistance of a loamy soil as a function of initial moisture content and compaction the results of seven experimental runs show that the runoff erosion resistance of a loamy material is extremely sensitive to variations in initial moisture content and to a somewhat lesser extent in bulk density the very low resistance to runoff erosion of initially dry material is explained by structural changes which take place at the time of wetting slaking and microfissuration cause a considerable decrease of the soil s shear strength and therefore of its resistance to runoff erosion a first analysis shows that during a given rainfall event initially dry soils may well show significantly more erosion than initially wet soils despite the increase of infiltration with decreasing initial moisture content

doomed pioneers gravity flow deposition and bioturbation in marine oxygen deficient environments isolated horizons of thalassinoides and gyrolithes burrows appear in exclusive association with gravity flow deposits within sequences of nonbioturbated hernipelagic sedimentary rocks of the miocene monterey formation of california and the oligocene miocene san gregorio formation of baja california these burrowed levels are not associated with other ichnogenera such as zoophycos and chondrites we infer a causal relation between gravity flow deposition and the presence of thalassinoides and gyrolithes and suggest that these gravity flows entrained thalassinidean crustacea upon deposition in oxygen deficient environments the surviving borrowers reworked substantial quantities of aminated commonly organic rich sediments in an environment from which they were previously excluded the persistence of or the ecologically rapid return to oxygen depleted conditions limited the survival time and ecological complexity of the transported infaunal dwellers and rendered them doomed pioneers ecological and physiological data support this hypothesis thalassinidean crustacea have the capability to endure turbulent transport and survive up to 5 7 days of anoxia without being severely limited in their biological activities the accurate recognition of doomed pioneer trace fossil assemblages as ephemeral ecological phenomena in otherwise laminated successions may contribute to a better understanding and interpretation of paleo oxygen levels and basin history

water and sediment yield from a small catchment in the hilly granitic region south china abstract shenchong experimental basin is located in subtropical deqing county in the hilly region of south china it has a catchment area of 0 73 km2 and is underlain by granitic rocks with a weathering mantle of about 30 m water and sediment yield were monitored at the basin outlet and at a location about 230 m upstream such that the section between the two stations coincides with the concentration of large gullies these gullies produce most of the sediment yield of the basin and the pattern of sediment discharge mirrors that of rainfall however gullies contribute comparatively little runoff to the basin outflow other surface types including bare slopes bare rills and the valley floor together yield considerable runoff because of their large areal coverage

events and sea level changes on gondwana s margin the meguma zone cambrian to devonian of nova scotia canada the meguma zone consists of thick siliciclastic and volcaniclastic strata and granitic plutons that underlie southern nova scotia and offshore areas the strata were deposited from late cambrian through early devonian time on the continental margin of gondwana grain size of the major stratigraphic units reflects the changing elevations of base level in the source region twelve major events in the zone can be related to changes in relative sea level and combined into four second order cycles each cycle consists of a fining then coarsening upward sequence that is capped by subaerial volcaniclastic material these subaerial events are assumed to represent significant hiati and so are bounding unconformities two unconformities are at system boundaries two at sequence boundaries third order cycles suggest idiosyncrasies of the source land ultimate cause of the meguma cycles may be mantle activity that affected continental base level relative sea level and direction of continental drift the meguma curve is similar to that of northwest africa

estimation of runoff critical shear stress for soil erosion from soil shear strength abstract critical shear stress is an important soil parameter governing detachment by runoff which appears in numerous erosion models soil shear strength has been often presented as the best soil property to predict critical shear stress however only a few studies have documented the relationship between soil shear strength and critical shear stress and the results obtained have sometimes seemed contradictory this is why we have put together all available data about the relationship between critical shear stress and soil shear strength in order to analyse and discuss its significance and its generality results showed that contradictions between different studies mainly arise because total shear stress is a poor predictor of detachment on rough soils when grain shear stress is used rather than total shear stress a significant relationship between saturated soil shear strength and critical shear stress does exist soil shear strength may thus be used to predict critical grain shear stress however it is recalled that in general only total shear stress is predicted by erosion models which makes detachment predictions difficult on rough natural soils

meguma terrane orocline u pb age and paleomagnetism of the silurian mavillette gabbro nova scotia canada

neoproterozoic substrate condition vis a vis microbial mat structure and its implications sonia sandstone rajasthan india dst fast track project young scientist scheme no sr ftp es 03 2011 cas phase v upe ii programme of jadavpur university national research foundation and university of pretoria south africa

discussion of the reply by r l romer and u kroner on geochemical signature of ordovician mn rich sedimentary rocks on the avalonian shelf in their article reply to the discussion by j w f waldron and c e white on geochemical signature of ordovician mn rich sedimentary rocks on the avalonian shelf r l romer and u kroner reinterpret geochronological data presented by j w f waldron d i schofield c e white and s m barr to imply an ordovician not a cambrian depositional age for the succession of the harlech dome north wales and meguma supergroup nova scotia however an extensive history of biostratigraphic and geological survey data refutes this interpretation and shows that the rocks are unequivocally cambrian waldron et al used the u pb zircon laser ablation multicollector inductively coupled plasma mass spectrometry technique primarily to provide information on sediment provenance and not depositional age investigation of anomalously young 206pb 238u ages showed evidence of pb loss these data provide little constraint on depositional age and cannot be used to infer that the harlech grits group is ordovician

the problems and potential of using animal fossils and trace fossils in terminal proterozoic biostratigraphy abstract despite the discovery of soft bodied megascopic fossils of late neoproterozoic age at numerous localities world wide there has been slow acceptance of their potential for intercontinental correlation the stratigraphic thickness of sediments separating individual occurrences of such fossils from the base of the cambrian is very varied basic questions have also been posed as to the classification of the organisms represented and hence their likely time significance recent geochronological studies support notions of a narrow time distribution well studied neoproterozoic sequences in eurasia eastern and western north america and southern australia show strikingly similar patterns of increase in the numbers and diversity of trace fossils and soft bodied megascopic remains up section though strata immediately preceding the cambrian are relatively barren other than for a sparse palynoflora and compressions of primitive plants trace fossils from australian sections relating to an early part of the ediacaran apparently overlap a time of abundance of large process bearing acritarchs and big leiosphaerids this overlap of early animal traces and distinctive acritarchs may prove to be of significant biostratigraphic importance rare discoveries of forms resembling rangea gurich in the flinders ranges of south australia precede the classical ediacara assemblage and may provide a possible correlation with occurrences of this genus in namibia the distinctive remains and trace fossils at this level constituting the rangeid hiemalora assemblage zone resemble a biota from the podolia region of the ukraine and show a similarity to finds in parts of the windermere supergroup of the northwest territories canada similarly the offshore frondose assemblage of newfoundland is comparable with the biota of charnwood forest england the type ediacara assemblage of the flinders ranges characterizing the dickinsonia costata assemblage zone is a climax biota with diverse taxa and large individual species as well as some 20 ichnogenera it closely correlates with a late redkinian or early kotlinian assemblage in the upper part of the section on the zimny gory coast of the white sea northern russia the trace fossils of these levels show that significant diversification began before the cambrian

trace fossils in the ediacaran cambrian transition behavioral diversification ecological turnover and environmental shift abstract after taxonomic revision trace fossils show a similarly explosive diversification in the ediacaran cambrian transition as metazoan body fossils in shallow marine deposits of ediacaran age trace fossils are horizontal simple and rare and display feeding strategies related to exploitation of microbial matgrounds equally notable is the absence of arthropod tracks and sinusoidal nematode trails this situation changed in the early cambrian when a dramatic increase in the diversity of distinct ichnotaxa is associated was followed by the onset of vertical bioturbation and the disappearance of a matground based ecology agronomic revolution on deep sea bottoms animals have been present already in the ediacaran but ichnofaunas were poorly diverse and dominated by the horizontal burrows of undermat miners as shown by the ichnogenus oldhamia this life style continued to be predominant into the early and to a lesser extent middle cambrian nevertheless there was an explosive radiation of behavioral programs during the early cambrian when exactly the bioturbational revolution arrived in the deep sea is uncertain in any case the nereites ichnofacies was firmly established in the early ordovician the rich ichnofauna in the early cambrian guachos formation of northwest argentina probably marks a first step in this ecological onshore offshore shift

first evidence for locomotion in the ediacara biota from the 565 ma mistaken point formation newfoundland evidence for locomotion in the precambrian fossil record is scant reliable ediacaran trace fossils are all younger than 560 ma and consist of relatively simple horizontal burrows and trails from shallow water deposits here we describe an assemblage of macroscopic locomotory traces from deep water environments at mistaken point southeastern newfoundland canada dated to ca 565 ma these trails extend the record of complex trace fossils back into the earliest avalonian biota our new evidence for large motile organisms on the seafloor at this time suggests that at least some of these early ediacaran organisms whose biological affinities are widely debated could have been muscular and of metazoan grade

the changing face of the deep colonization of the early ordovician deep sea floor puna northwest argentina abstract an upper tremadocian deep sea ichnofauna from the chiquero formation of puna northwest argentina represents a link between ediacaran and cambrian microbial mat dominated ecosystems and younger ordovician deep marine trace fossil assemblages this ichnofauna is preserved at the base of thin bedded turbidites formed in the lobe fringe of a back arc deep sea fan while ediacaran cambrian deep marine trace fossils are typically linked to matground grazing and feeding microbial textures in the chiquero formation are rare and not associated with trace fossils morphologic patterns e g radial trace fossils and networks of the chiquero ichnofauna indicate the onset of novel trophic types recording trapping of microorganisms and bacterial farming however in comparison with younger ordovician deep sea ichnofaunas graphoglyptids are relatively rare poorly diverse and geometrically simpler this study indicates that the early ordovician was a pivotal point in the ecology of deep sea infaunal communities this upper tremadocian ichnofauna records the arrival of the agronomic revolution to the deep sea comparisons with slightly older and younger deep sea ichnofaunas demonstrate that the colonization of the deep sea was a protracted process spanning the early paleozoic lagging behind colonization of nearshore and offshore substrates

splash erosion of clay sand mixtures and its relationship with soil physical properties the effects of particle size distribution on soil structure abstract large quantities of disturbed soils and residues derived from engineering constructions have provided material resources for soil erosion and geological disasters which is becoming a serious problem in china to date studies on the erosion mechanism of these soils in a wide particle size distribution psd are limited and the relationships between soil psd and physical characteristics are not explicit here we analyzed the effects of psd on structural and mechanical parameters and attempted to quantify their relationships by blending silty clay soil and engineering sand as clay sand mixtures with various sand mass proportions ranging from 0 to 90 at a 10 increment in a wet and a dry mixing type mt in addition the effect of psd on splash erosion was measured under simulated rainfall changes of bulk density and porosity of soil mixtures for clay contents more than 13 with clay content displayed apparent differences separately in the wet and dry mixing types mainly due to the deformation and reorganization of soil grains internal friction angle and cohesion c of saturated soils showed a parabolic trend and an exponential increase with clay content respectively while cohesion c was better quantified by particle fractal dimension d than clay content shear strength indexes in the wet mixing type were generally larger than those in the dry mixing type when clay content was larger than 13 splash erosion temporal variation was significantly affected by psd mt rainfall duration rd and their interaction effects psd mt psd rd among which mt was the most prominent source of variation f 99 97 p

soil erosion by surface water flow on a stony semiarid hillslope soil erosion on hillslopes occurs by processes of soil splash from raindrop impacts and sediment entrainment by surface water flows this study investigates the process of soil erosion by surface water flow on a stony soil in a semiarid environment a field experimental method was developed whereby erosion by concentrated flow could be measured in predefined flow areas without disturbing the soil surface the method allowed for measurements in this study of flow erosion at a much wider range of slopes 2 6 to 30 1 per cent and unit discharge rates 0 0007 to 0 007 m2 s 1 than have been previously feasible flow velocities were correlated to discharge and hydraulic radius but not to slope the lack of correlation between velocity and slope might have been due to the greater rock cover on the steeper slopes which caused the surface to be hydraulically rougher and thus counteract the expected effect of slope on flow velocity the detachment data illustrated limitations in applying a linear hydraulic shear stress model over the entire range of the data collected flow detachment rates were better correlated to a power function of either shear stress r2 0 51 or stream power r2 0 59 published in 1999 by john wiley sons ltd

a candidate stratotype for the precambrian cambrian boundary fortune head burin peninsula southeastern newfoundland the burin peninsula exhibits an exceptionally thick and essentially continuous succession of marine strata through the precambrian cambrian transition fossils are abundant and include trace fossils small shelly fossils vendotaenid algae soft bodied megafossils and microfossils the burin peninsula is readily accessible and has long been considered a potential area for a precambrian cambrian boundary stratotype a continuous section through the upper part of member 1 and all of member 2 of the chapel island formation is exposed at fortune head and this section is herein proposed as a global stratotype for the precambrian cambrian boundary the boundary horizon is located 2 4 m above the base of member 2 of the chapel island formation this horizon marks the base of the basal cambrian phycodes pedum ichnofossil zone and immediately overlies the top of the late precambrian harlaniella podolica ichnofossil zone shelly fossils sabelliditids first appear a few metres below the proposed boundary sof

determination of finite strain in bedding surfaces using sedimentary structures and trace fossils a comparison of techniques abstract determination of the two dimensional finite strain in turbidite bedding surfaces is important in both structural and sedimentological investigations of deformed sediments the meguma group of nova scotia is one such sequence in which the directional distribution of paleocurrent markers has been modified by strain previous strain determinations have used sand volcanoes as strain markers which do not deform homogeneously with their matrix and hence may underestimate the true strain ratio intraclasts and concretions also suffer inhomogeneous deformation and are of limited use as strain markers hexagonal trace fossil networks can provide more reliable strain estimates but are rare widths of burrows exposed on bedding surfaces provide a new straightforward means of measuring strain each burrow is represented by a pair of parallel lines the separation of the lines is proportional to the burrow width and their direction represents burrow orientation the lines are tangential to the strain ellipse which can be discerned despite initial scatter in burrow widths

spatial heterogeneity of soil detachment capacity by overland flow at a hillslope with ephemeral gullies on the loess plateau abstract ephemeral gullies are typical erosional landforms and widespread on the chinese loess plateau to better understand the spatial variability in soil detachment capacity dc by overland flow and its influence at a hillslope with an ephemeral gully this study investigates a hillslope on the loess plateau using classical statistics geostatistical analysis and principal component analysis undisturbed soil samples were collected from 202 sites along nine 90 m transects in two completely developed ephemeral gullies and were scoured in a laboratory flume under consistent hydraulic conditions the results indicate that dc varied widely from 0 0004 to 1 25 kg m 2 s 1 with a mean of 0 22 kg m 2 s 1 the coefficient of variation also shows a high variability in dc the ephemeral gullies were divided into four sections uppermost upper middle and lower slopes and dc differed significantly among the four sections a semivariogram of dc indicated a moderate spatial dependence the sampling interval significantly affects the spatial pattern of dc when the sampling interval decreased from 10 to 2 m the nugget variance decreased whereas structured variance spatial dependence and range increased distribution maps of dc derived from kriging interpolation showed that samples in the lower slope position have greater dc than the other positions dc significantly correlates with clay content sand content median soil grain size bulk density cohesion water stable aggregate and litter mass density principal component analysis pca and a minimum data set mds method identified that the median soil grain size bulk density and litter mass density were the major factors affecting the spatial variability in dc

u pb zircon ages and provenance of the white rock formation of the rockville notch group meguma terrane nova scotia canada evidence for the sardian gap and west african origin the white rock formation is the lowermost formation of the rockville notch group an assemblage of silurian devonian rocks preserved in five areas along the northwestern margin of the meguma terrane of nova scotia the formation consists mainly of mafic and felsic metavolcanic rocks interlayered with and overlain by marine metasedimentary rocks felsic metatuff has now been dated from four locations near both the bottom and top of the volcanic pile and yielded a narrow age range with errors of about 446 434 ma these dates confirm a 30 ma hiatus after deposition of the early ordovician hellgate formation in the underlying halifax group this hiatus is coeval with the sardian gap in the lower palaeozoic of peri gondwanan europe the metavolcanic metasedimentary assemblage is overlain by mainly metasiltstone with abundant quartzite and metaconglomerate lenses some of the latter were previously interpreted to be ordovician tillite an interpretation no longer viable new detrital zircon data from metas

how valid is cruziana stratigraphy the stratigraphic value of trilobite burrows has recently been questioned because of a seemingly ordovician form in the lower cambrian of canada closer examination shows however that the cambrian homeomorph cruziana pectinata n sp has a significantly different scratch pattern this raises the question whether the multiple scratches of the ordovician cruziana rugosa were also made by exopodites or by similarly shaped endopodites

effects of grass roots on the erodibility of topsoils during concentrated flow abstract traditional vegetative techniques to control gully development rely mainly on the effects of above ground biomass whereas little attention has been given to the role of below ground biomass yet in a context where above ground biomass may temporarily or spatially disappear e g due to fire or grazing roots can play an important role in protecting soil against erosion few studies have investigated the impacts of roots of natural vegetation such as grass on the resistance of topsoils in concentrated flow erosion zones although grasses grow in many environments therefore the objective of this study is to investigate the impact of root density and root length density of grass on the erodibility of root permeated saturated topsoils three plots were established on a sandy loam their treatments were 1 bare 2 low density drilled grass and 3 high density drilled grass simulating different root densities after one month topsoil samples were taken and subjected to concentrated flow using a hydraulic flume in the laboratory slope flow discharge mean velocity water temperature and sediment concentration were measured root density and root length density values were assessed relative soil detachment rates and mean flow shear stresses were calculated the results indicate a negative exponential relation between the relative soil detachment rate and root density as well as root length density independent of the applied flow shear stresses however the best relationship fitting the data is the hill curve indicating that relative soil detachment rates decrease to very low values 0 05 with an increase in root density from 0 to 4 kg m 3 or root length density from 0 to 400 km m 3 a comparison between the effects of vegetation cover on sheet and rill erosion rates and those of the root area ratio of grass roots on relative soil detachment rates reveals that grass roots are very effective in reducing soil detachment rates the equations obtained can be used to predict the effect of grass roots on soil erosion rates during concentrated runoff and to evaluate the ability of roots to increase topsoil resistance against erosion by concentrated flow calculations of relative erosion rates using the equations from the rusle and wepp models indicate that the observed trend is better predicted with the rusle model and the wepp model for croplands than with the wepp model for rangelands

changes in the trace fossil biota across the proterozoic phanerozoic boundary trace fossils became relatively diverse in shallow water clastic seas in the late proterozoic vendian with a further significant increase in abundance diversity and complexity in the tommotian and atdabanian little change followed in the remainder of the lower palaeozoic traces typical of deeper water facies evolved in shallow water during the vendian and early cambrian and may have slowly migrated into the deep ocean during the remainder of the lower palaeozoic there are a limited number of short ranging ichnogenera which may be useful for correlation but the first appearance of ichnogenera may be a more satisfactory method three trace fossil zones covering the ranges redkino and kotlin rovno and tommotian lower atdabanian are recognized and may be useful for world wide correlation

soil detachment by overland flow on hillslopes with permanent gullies in the granite area of southeast china abstract permanent gullies are often initiated from rill erosion followed by the formation of abrupt deep and wide gullies when topsoil and subsoil are carried away by fast flowing surface water few studies have been performed to evaluate soil detachment processes on hillslopes with permanent gullies which may significantly affect the further development of gully erosion soil detachment was investigated by using natural undisturbed soil samples collected in different spatial locations upper catchment middle slope lower slope and scour channel of hillslopes with permanent gullies the relationships of soil detachment capacity with soil property root system and hydraulic parameters were quantified selected samples were tested in a hydraulic flume 3 8 m length 0 2 m width under five different shear stresses 3 67 7 81 10 50 13 97 and 17 28 pa soil detachment capacity was found to be significantly greater in the scour channel than in the other three hillslope positions for the initial and stable gullies the soil detachment capacity was notably reduced in the middle slope relative to the upper catchment and lower slope while a different trend was observed in the active gully the variability of soil detachment capacity at different spatial locations showed a negative correlation to bulk density soil cohesion clay organic matter and root density p

the goldenville halifax transition mahone bay nova scotia relative sea level rise in the meguma source terrane in the meguma group of nova scotia the transition from sand rich turbidites of the goldenville formation to overlying mud rich turbidites of the halifax formation shows unusually rapid vertical facies variations the tancook member of the goldenville formation is divided into four laterally continuous units unit 1 consists of generally thinly bedded classical turbidites interpreted as lobe facies unit 2 comprises mottled bioturbated and laminated muds units 3 and 4 contain packets of thick amalgamated sandstone beds alternating with more thinly bedded muddy sections a unique bioclastic bed occurs near the top of unit 3 in unit 4 burrowed sandstone packets traced along strike across paleocurrent are not significantly incised into underlying muds laminated slates and siltstones of the overlying mosher s island member halifax formation are enriched in manganese and trace metals and contain diagenetic concretions of manganoan carbonate rimmed by metamorphic garnet the overlying cunard member c

precambrian cambrian trace fossils from the yangtze platform south china and the early evolution of bilaterian lifestyles abstract siliciclastic carbonaceous and phosphoritic shallow marine sediments from several neoproterozoic ediacaran and precambrian cambrian pc c boundary sections on the yangtze platform south china contain remarkable trace fossil assemblages the present paper provides a general overview on the distribution and the possible palaeobiological and palaeoenvironmental significance of these trace fossil assemblages from selected pc c boundary sections on the passive yangtze platform margins comparative investigations of the typology of neoproterozoic ediacaran ichnofaunas as well as of the related sedimentary environments accompanying the ichnoassemblages demonstrate in general correspondence with other studies worldwide that the neoproterozoic ichnofaunas are mainly composed of slightly curved to straight and unbranched horizontal traces which are usually related to the occurrence of shallow marine softgrounds sealed by microbial mats rare traces show ichnomorphological patterns that indicate developments toward a more effective horizontal exploitation of the feeding ground during the late neoproterozoic and earliest cambrian the majority of these traces appear to represent undermat miners with simple feeding strategies during the earliest phanerozoic early meishucunian stage equivalent to the nemakit daldynian stage of siberia the oxic shallow water environments along the ancient continental passive margins of the yangtze platform were populated by large as yet unknown arthropods which produced rusophycus type trace fossils the late precambrian to early phanerozoic sediments of the yangtze platform generally provide excellently preserved trace fossil records which together with the presence of index fossils ssf from the nemakit daldynian stage provide a more detailed insight into the development of pc c palaeoenvironments and the evolution of lifestyles among early bilaterian metazoans a preliminary comparison of the neoproterozic biotas occurring on the yangtze platform and in other time equivalent ediacaran habitats demonstrates general similarities but also some striking differences probably due to palaeoenvironmental variations the data presented here from south china are critically discussed in the light of current palichnological approaches and theories

burrowing below the basal cambrian gssp fortune head newfoundland the range of treptichnus pedum the index trace fossil for the treptichnus pedum zone extends some 4 m below the global standard stratotype section and point for the base of the cambrian period at fortune head on the burin peninsula in southeastern newfoundland the identification of zigzag traces of treptichnus isp even further below the gssp than t pedum in the fortune head section and in other terminal proterozoic successions around the globe supports the concept of a gradational onset of three dimensional burrowing across the proterozoic cambrian boundary although t pedum remains a reasonable indicator for the base of the cambrian period greater precision in the stratotype section can be achieved by a detailed re evaluation of the stratigraphic ranges and the morphological variation of ichnotaxa included in the t pedum zone

environmental tolerance and range offset of treptichnus pedum implications for the recognition of the ediacaran cambrian boundary the ediacaran cambrian boundary arguably the most important in the stratigraphic column is based on the first appearance of the ichnospecies treptichnus pedum however most trace fossils have long temporal ranges and occur in a narrow range of facies and are typically of little use in biostratigraphic studies therefore understanding the environmental tolerance and range offset of t pedum is essential to evaluate the reliability of the ediacaran cambrian boundary our study in fortunian units in the vanrhynsdorp group of south africa shows a broad environmental tolerance for the t pedum producer in shallow marine clastic settings this ichnotaxon is not only present in low energy offshore wave dominated marine settings but it also occurs at considerably shallower water in intertidal and shallow subtidal zones of tide dominated systems t pedum seems to have high values of peak abundance in the upper offshore and lower intertidal sand flats in many sections the ediacaran cambrian transition occurs in successions containing a sequence boundary due to incision of valleys that were filled with coarse grained deposits of fluvial or estuarine origin both representing facies that are unsuitable for t pedum the range offset of this ichnotaxon is typically greater above sequence boundaries and within transgressive systems tracts providing some constrains on its use however the broad environmental tolerance of t pedum in shallow marine clastic settings supports evolutionary innovations rather than facies controls as the main mechanism underlying the observed vertical pattern of distribution of this ichnospecies in the relatively continuous succession of the ediacaran cambrian boundary global standard stratotype section and point

variability of the atlantic off equatorial eastward currents during 1993 2010 using a synthetic method 1 we have developed validated and applied a synthetic method to monitor the off equatorial eastward currents in the central tropical atlantic this method combines high density expendable bathythermograph xbt temperature data along the ax08 transect with altimetric sea level anomalies slas to estimate dynamic height fields from which the mean properties of the north equatorial countercurrent necc the north equatorial undercurrent neuc and the south equatorial undercurrent seuc and their variability can be estimated on seasonal to interannual timescales on seasonal to interannual timescales the synthetic method is well suited for reconstructions of the necc variability reproduces the variability of the neuc with considerable skill and less efficiently describes variations of the seuc which is located in a region of low sla variability a positive correlation is found between interannual variations of the necc transport and two indices based on an interhemispheric sea surface temperature sst gradient and southeasterly wind stress in the central tropical atlantic the neuc is correlated on interannual timescales with ssts and meridional wind stress in the gulf of guinea and zonal equatorial wind stress this study shows that both altimetry and xbt data can be effectively combined for near real time inference of the dynamic and thermodynamic properties of the tropical atlantic current system

40ar 39ar ages for detrital white mica in meguma terrane nova scotia canada implications for provenance of the goldenville and halifax groups single grain 40 ar 39 ar ages are reported for detrital white mica along with conventional step heating data for whole rocks from low grade metasandstone samples from the goldenville halifax and rockville notch groups in the meguma terrane of southern nova scotia the majority 166 of single grains from 11 samples yielded ages between ca 615 and 350 ma and the remaining 12 grains yielded ages between ca 1900 and 870 ma the late neoproterozoic paleozoic age distributions are consistent with derivation of sediments from the rapidly uplifted flanks of an active rift where partial to complete resetting of white mica ages occurred at ca 520 500 ma preceding sediment deposition the ca 615 ma ages may be relics of the original detrital white mica that existed in the source rocks prior to the rifting event ages from the upper silurian white rock formation appear to reflect this same ca 520 500 ma event suggesting that sediments in the white rock formation were recycled from the goldenville and halifax groups the older precambrian ages are inferred to represent white mica in the source region likely amazonia the whole rock age spectra are discordant with pronounced age gradients and no well defined age plateaus initial gas released from five of the samples at low laboratory extraction temperatures ca 450 500 c yielded ages of ca 260 300 ma not seen in the single grain data whereas gas released at the highest extraction temperatures yielded ages in the range ca 510 530 ma possibly reflecting the principal result obtained from the single grain data