trace fossils from interdune deposits an example from the lower triassic aeolian tumlin sandstone central poland abstract the tumlin sandstone up to 105 m thick is the deposit of a midcontinent extensive at least 1500 km2 dune field it consists of dune deposits and of subordinate intercalations of interdune deposits the latter are represented by horizontally bedded sandstone accumulated in frequently changing conditions on dry damp and wet surface dry surface deposits predominate subordinate but relatively common are damp surface deposits with characteristic adhesion structures and wet surface deposits represented by very thin mudstone layers and horizons of wave ripples which originated in ephemeral ponds the interdune deposits contain numerous trace fossils whose occurrence is almost entirely connected with wet surface and damp surface deposits the dune deposits are devoid of trace fossils the following forms have been recognized arenicolites isp cruziana problematica diplocraterion isp gordia marina planolites montanus planolites isp palaeophycus tubularis tetrapod footprints radial structures shallow double furrows and various oval depressions in places intensive but shallow bioturbation of sediment is observable the trace fossil assemblage is similar to the scoyenia ichnofacies but lacks scoyenia and ancorichnus the assemblage is more comparable to the mixed arenicolites cruziana ichnofacies sensu bromley and asgaard 1979 the invertebrate burrows show an r selected strategy in sediment colonization around the palaeozoic mesozoic transition the highly diversified ichnofauna compared to that of the permian interdune deposits shows increased colonisation of interdunes by an invertebrate mainly arthropod fauna

trace fossils and substrates of the terminal proterozoic cambrian transition implications for the record of early bilaterians and sediment mixing the trace fossil record is important in determining the timing of the appearance of bilaterian animals a conservative estimate puts this time at 555 million years ago the preservational potential of traces made close to the sediment water interface is crucial to detecting early benthic activity our studies on earliest cambrian sediments suggest that shallow tiers were preserved to a greater extent than typical for most of the phanerozoic which can be attributed both directly and indirectly to the low levels of sediment mixing the low levels of sediment mixing meant that thin event beds were preserved the shallow depth of sediment mixing also meant that muddy sediments were firm close to the sediment water interface increasing the likelihood of recording shallow tier trace fossils in muddy sediments overall trace fossils can provide a sound record of the onset of bilaterian benthic activity

paleotectonic significance of the quartzite of the sauratown mountains window north carolina recent mapping within the metamorphic core of the southern appalachians has led to the identification of several internal basement massifs interpreted to be windows that expose parautochthonous basement beneath the main thrust sheet one such internal massif is exposed within the inner piedmont of north carolina by the sauratown mountain window and is overlain by a cover sequence of arkose schist and quartzite detailed examination of the primary cross stratification types preserved within the quartzite at pilot mountain indicates that deposition took place in several marine environments ranging from foreshore to inner shelf deposits of similar origin within the early cambrian north american passive margin sediments appear to thin west to east from 80 m at the chilhowee group type locality at chilhowee mountain 300 km west southwest of pilot mountain to 40 m within the unaka belt 150 km west of pilot mountain the quartzite at pilot mountain is more than 45 m thick and therefore does not appear to represent a distal part of this passive margin sequence alternatively two paleotectonic interpretations seem plausible 1 quartzites of the sauratown mountains window north carolina represent late proterozoic tallulah falls ashe formation equivalent deposition along a sea floor high associated with the rifted basement terrane during the rift phase prior to the opening of iapetus or 2 quartzites of the sauratown mountains window north carolina represent latest proterozoic to early cambrian chilhowee group time equivalent deposition on an isolated rifted continental fragment during the drift phase of the north american iapetus margin evolution

depositional history and sequence stratigraphy of the precambrian cambrian boundary stratotype section chapel island formation southeast newfoundland abstract facies relationshps in the vendian to lower cambrian chapel island formation of southeast newfoundland are used to establish a sequence stratigraphic framework for this important boundary stratotype section the formation consists of five members of sandstone mudstone and minor limestone deposited in a variety of shoreline to shelf environments peritidal sandstone and shale units in member 1 are overlain by sandstone and silstone deltaic and shelf deposits of member 2 these make up a transgressive system tract in which small scale changes in relative sea level are superimposed on autocyclic deltaic processes the thickness 400 m of nearshore and inner shelf sediments resulted from high sediment accumulation rates which for member 2 nearly kept pace with subsidence upper member 3 and member 4 consist of inner shelf mudstone and peritidal limestone that were deposited in a low energy oxygen stratified basin these deposits are arranged in three large scale shoaling cycles representing three foresteping parasequences of one highstand systems tract an extensive limestone bed at the tope of member 4 contains a sequence boundary associated with or shortly postdating development of this surface is a significant epeirogenic event that resulted in basin reorganization increased subsidence and progradation of a thick clastic sequence represented by member 5 the deposits of this upper member consist of an upward coarsening storm dominated shelf to shoreface succession of sandstone and silstone deposits of nearly identical character are also found in new brunswick and suggest that these sediments and the underlying sequence boundary could be significant for interregional correlation global correlation of the paleobathymetric curve developed for the chapel island formation is considered unfeasible given the long history of epeirogenic movements during the vendian and early cambrian in this region

ichnology of a paleopolar river dominated shallow marine deltaic succession in the mackellar sea the mackellar formation lower permian central transantarctic mountains antarctica abstract the lower permian mackellar formation in the beardmore glacier area of the central transantarctic mountains antarctica was deposited between 80 and 85 s paleolatitude previous studies suggest that mackellar formation strata were deposited in either a large glacial lake or inland sea our study identified 30 ichnogenera from turnabout ridge and buckley island of which 1 none are exclusively freshwater forms 2 20 ichnogenera are found in freshwater brackish and marine settings and 3 10 ichnogenera are exclusively found in marine settings combining ichnologic evidence with sedimentologic observations suggests that the mackellar formation was deposited in a river dominated delta in a fully marine to brackish marine setting trace fossil associations are grouped into the arenicolites phycodes lingulichnus arenicolites planolites kouphichnium phycodes teichichnus arenicolites and planolites teichichnus phycodes ichnocoenoses of a mixed skolithos cruziana ichnofacies these associations are characteristic of epi and endobenthic worms arthropods and mollusks with the vast majority of the traces being diminutive in diameter and length and exhibit shallow 10 mm penetration depths these ichnocoenoses occur in paleoenvironments that include the prodelta distal to proximal delta front including mouth bars and subaqueous terminal distributary channels the diminutive morphology shallow penetration depth low bed ichnodiversity high overall ichnodiversity and sedimentologic characteristics are indicative of benthic organisms in a marine deltaic environment with short lived communities composed of small bodied organisms stressed by high freshwater input and high sedimentation rates

precambrian cambrian boundary candidate meishucun jinning yunnan china in the particular area there occur monofacial transitional carbonate deposits of marine origin yielding in great abundance both small shelly fossils and trace fossils which are present in the close association and in some cases on the same bedding surface the sequence of biotic assemblages is clearly evident and can be used for wide intercontinental correlation in the lower part of the qiongzhusi stage stratigraphically higher there appear the oldest trilobites archaeostracods and baltisphaeridium characteristics of the early cambrian during the last six years great progress has been made in the study of the particular section through lithostratigraphic biostratigraphic geochronological magnetostratigraphic and seismostratigraphic approaches thus making the meischucun stage and the sinian cambrian boundary stratotype section in the meishucun area a chinese candidate for global stratotype section and point for the precambrian cambrian boundary modified journal abstract

trace fossils after the k t boundary event from the agost section se spain palaeogene trace fossils penetrate the uppermost cretaceous sediments in the agost section betic cordillera se spain chondrites targionii zoophycos isp planolites isp a planolites isp b thalassinoides isp a thalassinoides isp b thalassinoides isp c alcyonidiopsis longobardiae and diplocraterion parallelum have been identified a well developed endobenthic tiering pattern is interpreted the uppermost tier a represents major benthic activity in the shallowest sediments at or just below the seafloor recorded as bioturbated background only discrete rare planolites the next upper tier b displays the highest trace fossil diversity with planolites in the shallow levels and thalassinoides and alcyonidiopsis at slightly deeper ones the intermediate tier c contains randomly distributed thalassinoides and alcyonidiopsis cross cut by zoophycos and large and medium sized chondrites the deepest tier d contains zoophycos cross cut by medium and mainly small sized chondrites two interpretations are proposed 1 vertical partitioning of a singled multi tiered community under steady stable conditions in well oxygenated water bottom reflecting gradual changes deep into the sediment with decreasing oxygen pore water and benthic food and increasing substrate consistency and 2 sequential colonization and community replacement reflecting the work of two successive communities the first community mainly represented by planolites alcyonidiopsis and thalassinoides was produced in a shallow oxygenated soft substrate probably related to decreasing oxygen content and benthic food availability this community was replaced by deeply burrowing organisms that produced zoophycos and chondrites this sequential colonization can be determined by changes in environmental parameters related to the cretaceous palaeogene k t event or may have resulted from normal ecological and early diagenetic processes

ground movements due to shallow tunnels in soft ground i analytical solutions this paper presents simplified closed form analytical solutions that can be used to interpret and predict ground movements caused by shallow tunneling in soft ground conditions these solutions offer a more comprehensive framework for understanding the distribution of ground movements than widely used empirical functions analytical solutions for the displacement field within the ground mass are obtained for two basic modes of deformation corresponding to uniform convergence and ovalization at the wall of a circular tunnel cavity based on the assumption of linear elastic soil behavior deformation fields based on the superposition of fundamental singularity solutions are shown to differ only slightly from analyses that consider the physical dimensions of the tunnel cavity except in the case of very shallow tunnels this work demonstrates a simplified method to account for soil plasticity in the analyses and illustrate closed form solutions for a three dimensional 3d tunnel heading a companion paper describes applications of these analyses to interpret field measurements of ground response to tunneling

trace fossils and biofabrics at the precambrian cambrian boundary interval in western mongolia a small suite of trace fossils from the zavkhan basin govi altay includes many of the ichnotaxa typical of the nemakit daldynian tommotian and younger cambrian stages and other indeterminate forms the traces are almost entirely from the sandstone intervals of the large scale alternations of carbonate and siliciclastic sediments thus emphasizing the facies and taphonomic controls on trace fossil distribution and hence the inherent difficulties in using trace fossils in detailed global correlation especially in using first appearances the assemblage of traces and biofabrics is seen as resulting from the partly non uniformitarian non actualistic sedimentary environments that pertained over the boundary interval rather than as evolutionary failures and subsequently vacated environments

complex trace fossils from the terminal proterozoic of namibia we document for the first time the occurrence of the complex trace fossil treptichnus from the terminal proterozoic nama group namibia these traces differ in detail from the cambrian index fossil treptichnus pedum but document precursors with the same basic behavior the producer of the trace is not known in its complexity however this trace fossil provides strong evidence for advanced latest proterozoic bilaterians

pyrite framboids interpreted as microbial colonies within the permian zoophycos spreiten from southeastern australia two types of pyrite framboids pf probably sulphate reducing bacteria have been found within the zoophycos spreiten hosted in the guadalupian middle permian glaciomarine greywacke of the westley park sandstone member within the broughton formation from the southern sydney basin of southeastern australia they are composed of non sheathed pf1 and sheathed pf2 sub micron balls respectively chemically the sub micron balls consist of iron sulphur carbon and oxygen both pf1 and pf2 occur in rhythmic alternation within the thick light grey and thin dark grey minor lamellae of zoophycos spreiten the framboids from the minor lamellae are highly abundant and occur in an orderly arrangement of equal density and in a good state of preservation within zoophycos spreiten no homogeneous filling fecal pellets or any sign of re exploitation of the minor lamellae have been recognized no similar framboids have been observed outside zoophycos spreiten therefore the framboids are interpreted as the pyritized remains of microbial colonies within zoophycos spreiten the trace zoophycos would be a multifunctional garden that may have been carefully constructed by the zoophycos maker where different microbial colonies were orderly and carefully planted and cultured within different minor lamellae further it is proposed that the zoophycos maker had a symbiotic relationship with microbial colonies on the mutual basis of food supply and redox conditions the fact that the overlying spreiten cut the underlying ones indicates that the zoophycos from the study area is of an upward construction the rhythmic alternation of both the thick light grey and thin dark grey minor lamellae within zoophycos spreiten may be suggestive of a gardening manner of the zoophycos maker responding to the warm and cold changes food supply in pulses and variations of sedimentation rate for planting and culturing microbial colonies under the conditions of a glaciomarine environment at the high latitudes

a complex trace fossil from the spitskop member terminal ediacaran lower cambrian of southern namibia streptichnus narbonnei igen et isp nov a new trace fossil from the upper part of the spitskop member of the urusis formation southern namibia consists of clusters of unidirectionally curved radial elements in which individual elements typically are composed of imbricated sickle shaped segments somewhat comparable to those of treptichnus pedum such complex trace fossils generally are found only in cambrian or younger strata this opens to question the position of the ediacaran cambrian boundary in the nama group suggesting that it may locally be within the uppermost part of the urusis formation rather than at the base of the nomtsas formation

the lower middle cambrian stages and stratotypes from the iberian peninsula a revision lower middle cambrian regional stages of the iberian peninsula cordubian ovetian marianian bilbilian acadoparadoxides and solenopleuropsidae stages are now reconsidered in the light of new stratigraphic and palaeontological trace fossils trilobites and archaeocyaths studies these stages are re described with selected stratotypes and chronostratigraphic boundaries the names leonian and caesaraugustian are formally proposed to replace the provisional stages of acadoparadoxides and solenopleuropsidae respectively a correlation chart of the lower middle cambrian lithostratigraphic units from the iberian peninsula is also presented two regessive transgressive cycles are proposed to explain the lithological and palaeontological peculiarities through the lower middle cambrian sequence in the iberian peninsula

seismic tomography to obtain velocity gradients and three dimensional structure and its application to reflection data on vancouver island a seismic reflection survey was carried out on vancouver island as part of lithoprobe phase i to study the crustal structure and tectonics of this convergent margin four seismic profiles which

ethology of the trace fossil chondrites form function and environment abstract the behaviour of the iconic ichnogenus chondrites is re evaluated based on review of existing literature and analysis of novel data macroscopic thin section and esem edx observations ct scans and resin peels of modern analogues computer controlled serial grinding morphometric analysis and theoretical morphology the bedding plane expression of chondrites is well constrained by morphometry 1 the angle of dichotomy formed by a pair of adjacent branches is typically between 30 and 56 interquartile range mean 47 2 branching order is between 1 and 9 3 branches are on average nine times longer than wide in the third dimension downward branching is dominant but bundled shafts and upward branching may be present the size of chondrites increased markedly from the late jurassic to the late cretaceous suggesting that the tracemakers became larger and larger microfabric analysis of chondrites shows active fill or alternatively passive fill of empty tunnels by currents or clay percolation a new mechanism proposed herein the tracemakers built chondrites to obtain food 1 vermiform deposit feeders produced chondrites for searching for food in the sediment fodinichnion 2 asymbiotic bivalves built chondrites for cultivating and directly ingesting bacteria agrichnion 3 chemosymbiotic bivalves produced chondrites to provide symbionts with chemical agents chondrites was modified through the life of the tracemaker or it represented a part of the producer s lifespan chondrites and its modern tracemaker s is associated with a range of marine settings including well oxygenated dysoxic and space limited nucleocave environments as such chondrites is regarded as an extremotolerant ichnotaxon

ediacara type fossils in cambrian sediments fossil assemblages that preserve soft bodied organisms are essential for our understanding of the composition and diversity of past life the worldwide terminal proterozoic ediacara type fossils from 600 544 myr bp are unique in consisting of soft bodied animals which are typically preserved as impressions in coarse grained sediments1 2 3 4 these lagerstatten are also special because they pre date the major burst of skeletonization which occurred near the start of the cambrian period3 most ediacara type fossils are interpreted to be cnidarians but higher metazoans such as annelids and molluscs may also be represented1 2 3 4 however the unique style of preservation and difficulties in finding convincing morphological homologies with definite animals have led some specialists to prefer non metazoan interpretations such as vendobionta5 in addition the rarity of ediacara type fossils in younger sediments has led to suggestions of a terminal proterozoic mass extinction6 here we report typical ediarcara type frond shaped fossils that occur together with an assemblage of cambrian type trace fossils in unequivocally cambrian aged sediments of the uratanna formation south australia this occurrence bridges the apparent divide between the terminal proterozoic and cambrian fossil assemblages and also suggests that closure of a taphonomic window an interval of time with unique preservational conditions was as important as extinction in the disappearance of ediacara type organisms

chronology of early cambrian biomineralization data on the first appearances of major animal groups with mineralized skeletons on the siberian platform and worldwide are revised and summarized herein with references to an improved carbon isotope stratigraphy and radiometric dating in order to reconstruct the cambrian radiation popularly known as the cambrian explosion with a higher precision and provide a basis for the definition of cambrian stages 2 to 4 the lophotrochozoa and probably chaetognatha were first among protostomians to achieve biomineralization during the terreneuvian epoch mainly the fortunian age fast evolutionary radiation within the lophotrochozoa was followed by radiation of the sclerotized and biomineralized ecdysozoa during stage 3 the first mineralized skeletons of the deuterostomia represented by echinoderms appeared in the middle of cambrian stage 3 the fossil record of sponges and cnidarians suggests that they acquired biomineralized skeletons in the late neoproterozoic but diversification of both definite sponges and cnidarians was in parallel to that of bilaterians the distribution of calcium carbonate skeletal mineralogies from the upper ediacaran to lower cambrian reflects fluctuations in the global ocean chemistry and shows that the cambrian radiation occurred mainly during a time of aragonite and high magnesium calcite seas

early cambrian teichichnus dominated ichnofabrics and palaeoenvironmental analysis of the caerfai group southwest wales uk abstract the early cambrian caerfai group of pembrokeshire in southwest wales yields an intensely bioturbated teichichnus dominated ichnofabric and provides evidence for the early evolution of infaunal organisms three units of the caerfai group comprise the focus of this study in sections exposed at caerfai bay in the st non s sandstone few primary sedimentary structures are observed bedding being predominantly massive with subordinate parallel and current ripple cross lamination the topmost st non s sandstone contains common soft sediment deformation phenomena and collectively deposition is believed to have taken place in the proximal subaqueous reaches of a steep fronted delta system teichichnus is the dominant trace with subordinate planolites palaeophycus and possible rhizocorallium the overlying caerfai bay shales were deposited from mass flows with evidence of downslope creep suggesting deposition on a steep delta front sandstone debrites are common as are tuffaceous beds with evidence of reworking by bottom currents sandstone and tuff event beds contain common skolithos and arenicolites with less frequent planolites interbedded mudstones contain infrequent teichichnus the caerfai bay shales coarsen and thicken upwards into the caerbwdy sandstone debrite sandstone beds dominate and bed thickening upsection indicates progradation of the delta system the dominant trace fossil within the unit is teichichnus which is constrained to the top few centimetres of individual sandstone beds less common are planolites and palaeophycus the size and abundance of teichichnus in the caerfai group are similar to or exceed those in contemporaneous sections in avalonia and baltica local environmental factors were probably the primary control on trace fossil distribution substrate and salinity are proposed as the main influences on ichnodiversity and size in the caerfai group teichichnus is most abundant in the st non s sandstone where the proximal reaches of the delta experienced reduced salinity and possibly higher oxygen levels burrow diameter progressively decreases upsection and bioturbation becomes less pervasive in subsequent units of the caerfai group this indicates that by the cambrian stage 2 significant advances into reduced salinity environments had occurred along with the dispersal of the teichichnus producer throughout the avalonia baltica seaway correlation within avalonia indicates that a transgression in the cambrian stage 2 initiated the deposition of the caerfai group marking the onset of the welsh basin

analysis of undrained soil deformation due to ground loss closed form solutions are presented for obtaining the strain field in an initially isotropic and homogeneous incompressible soil due to near surface ground loss this problem fits into a category of cases in which the imposed boundary conditions are only or mainly in terms of displacements strain controlled problems in these cases there is a possibility of eliminating the stresses and obtaining the strains by using only the incompressibility condition the presence of the top free surface is considered by means of a virtual image technique and some results for the elastic half space the results are simple especially for the movements of the soil surface the application to some typical problems such as soft ground tunnelling and pile driving or extraction shows that the calculated movements agree well with the experimental observations and compare favourably with commonly used numerical methods some hints are given for extending the method to other cases such as to compressible materials des sol

vendobionta and psammocorallia lost constructions of precambrian evolution the non availability of biomineralized skeletons and low levels of predation led vendian evolution along strange avenues the ediacara type vendobionta appear to represent a kingdom in which foliate shapes large sizes and the necessary compartmentalization were achieved by quilting of the skin rather than by multicellularity psammocorallia in contrast are interpreted as coelenterates that constructed an internal sand skeleton both were immobile soft bottom dwellers that had high population densities and both became preserved by obrutional accidents thus they render fossil snap shots in which the original distributional patterns age structures and standing biomasses of populations are accurately recorded

ediacaran fossils from the stirling range formation western australia abstract metazoan body fossils of ediacaran affinity in the stirling range formation of western australia represent the first discovery in western australia thereby extending the biogeographic range of the australian ediacaran fauna although small size and poor preservation limits accurate classification body fossils have been classified with varying degrees of confidence to genus cyclomedusa sprigg 1947 in addition to ediacaran body fossils a single float sample containing simple protuberances was discovered these discoids were assigned to the ichnogenus bergaueria prantl 1945 whilst previously considered to have been deposited and deformed along with basement gneiss during the mesoproterozoic the presence of ediacaran fossils indicates a significantly younger timing for deposition and hence for deformation of the stirling range formation

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

watsonella crosbyi from the lower cambrian terreneuvian stage 2 normanville group in south australia correlation of lower cambrian strata is often confounded by provincialism of key fauna the widespread occurrence of the micromollusc watsonella crosbyi grabau 1900 is therefore an important biostratigraphic signpost with potential for international correlation of lower cambrian successions previous correlations of w crosbyi from australia normanville group suggested an atdabanian to botoman equivalent age however in the upper part of the mount terrible formation stratigraphic ranges of w crosbyi and aldanella sp cf golubevi overlap prior to the incoming of vertically burrowed piperock which is indicative of an age no earlier than cambrian stage 2 the stratigraphic range of w crosbyi in the normanville group south australia correlates with the ranges of the taxon in china france mongolia and siberia though not newfoundland the new australian data add further support for considering the first occurrence of w crosbyi a good potential candidate for defining the base of cambrian stage 2 the stratigraphic range of w crosbyi through the lower cambrian normanville group has been determined based on collections from measured sections although rare w crosbyi is part of an assemblage of micromolluscs including bemella sp parailsanella sp cf murenica and a sinistral form of aldanella a sp cf a golubevi other fauna present include australohalkieria sp eremactis mawsoni chancelloriids and cupitheca sp

ichnofossils and their significance in the cambrian successions of the parahio valley in the spiti basin tethys himalaya india abstract the spiti basin exposes well preserved cambrian successions in the tethys himalaya the present ichnofossil assemblage is reported from the debsakhad member of the kunzum la formation the ichnofossils includes the ichnogenera bergaueria chondrites cruziana didymaulichnus dimorphichnus diplichnites helminthorhaphe merostomichnites monocraterion monomorphichnus nereites palaeopascichnus palaeophycus phycodes planolites rusophycus skolithos scolicia treptichnus etc along with annelid worm burrow and scratch marks these ichnogenera can be assigned to cubichnial repichnial pascichnial to fodinichnial behaviors the ichnofossils reported from this section provide evidence regarding the developmental patterns during the early phase of life in absence of trilobites the present assemblage of ichnofossils is very significant in assigning the age of the debsakhad member the abundance of ichnofossils in sandstone siltstone and in shale beds indicate that the ichnocenosis is dominated by a high behavioral diversity ranging from the suspension to deposit feeders three lithofacies were observed in this section they show a vertical disposition which further reflects general upward coarsening trend ichnofossils are mostly produced by arthropods along with crustacean polychaetes and polyphyletic vermiforms due to the paucity of body fossil as well as microbiota in the lowermost beds of the debsakhad member the precambrian cambrian boundary could not be demarcated however the presence of treptichnus and phycodes can be considered as a horizon marker for the beginning of lower cambrian in this section

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

cambrian biostratigraphy of the tal group lesser himalaya india and early tsanglangpuan late early cambrian trilobites from the nigali dhar syncline precise biostratigraphic constraints on the age of the tal group are restricted to 1 a basal level correlative with the anabarites trisulcatus protohertzina anabarica assemblage zone of southwest china 2 a level near the boundary of the lower and upper parts of the tal group correlative with the early tsanglangpuan stage drepanuroides zone and 3 an interval low in the upper part of the tal group correlative with later in the tsanglangpuan stage palaeolenus zone these correlations are based on small shelly fossil and trilobite taxa other chronostratigraphic constraints include the marked negative 13 c isotopic excursion coincident with the transition from the krol group to the tal group this excursion is used as a proxy for the precambrian cambrian boundary in several sections worldwide and if applied to the lesser himalaya indicates that the boundary is at or just above the base of the tal group the upper parts of the tal group may be of middle or late cambrian age and might form proximal equivalents of sections in the zanskar spiti region of the tethyan himalaya both faunal content and lithological succession are comparable to southwest china furthering recent arguments for close geographic proximity between the himalaya and the yangtze block during late neoproterozoic and early cambrian time trilobites from the uppermost parts of the sankholi formation from the nigali dhar syncline are described and referred to three taxa one of which drepanopyge gopeni is a new species they are the oldest trilobites yet described from the himalaya

trace fossils in the aftermath of mass extinction events abstract ichnology has great potential to advance our understanding of mass extinction events and yet is currently an underutilized resource in such studies here we review published ichnological studies for the ordovician silurian permian triassic and cretaceous tertiary extinction recovery intervals in addition new information regarding the triassic jurassic ichnological record from england austria and the western usa is presented trace fossils provide important information on the ecological response of the benthic community at such times in the immediate post extinction aftermath the ichnodiversity burrow size depth of bioturbation and ichnofabric index of the sediments are all much reduced there is an increase in all these parameters through the post extinction recovery period in some cases the stepwise reappearance of certain distinctive ichnotaxa e g diplocraterion rhizocorallium and thalassinoides may be of some stratigraphic use evidence from permian triassic studies indicates that recovery took longer at low tropical palaeolatitudes than mid high palaeolatitudes trace fossils also provide important information on palaeoenvironmental change through the extinction recovery interval the application of ichnology to mass extinction studies is in its infancy but should prove a valuable tool in future research

ediacaran fossils and dubiofossils miette group of mount fitzwilliam area british columbia shallow water clastic beds flanking stromatolitic carbonate mounds in the upper part of the vendian miette group windermere supergroup of the rocky mountains contain a poorly preserved soft bodied fauna that comprises morphologically very variable discoid remains these include the taxa beltanella sp cf b grandis charniodiscus sp irridinitus sp nimbia occlusa protodipleurosoma sp cf p rugulosum and zolotytsia sp and seven types of dubiofossils

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

the neoproterozoic of southwestern africa with emphasis on platform stratigraphy and paleontology abstract neoproterozoic sediments in southwestern africa occur in the pan african kaoko khomas gariep vanrhynsdorp and saldania belts they were deposited in response to rifting break up of a supercontinent formed at 1000 ma and subduction and collisions of the congo kalahari rio de la plata and malvinas plates these collisions led to the formation of a neoproterozoic cambrian supercontinent this paper deals with the geology of the platform successions of the kaoko khomas gariep and vanrhynsdorp belts deposition of the sediments occurring in these belts commenced 900 to 1000 ma ago and probably ended between 500 and 520 ma the sediments record wilson cycles that ended with the deposition of red beds palaeontological and carbon isotope studies on the damara sequence gariep complex nama group and vanrhynsdorp group make intra and inter basinal correlations possible prior to deposition of the nama group two or perhaps three glaciations took place over an extensive area in southwestern africa these being the kaigas chuos 725 700 ma numees 650 600 ma or 610 590 ma and possibly the varianto 745 725 ma glaciations the numees tillite is overlain by a stratigraphic unit containing pinkish dolomite during deposition of the nama group the minor vingerbreek 600 545 ma glaciation or cold water period occurred the major kaigas chuos and numees and minor vingerbreek glaciations correspond with low 13c isotope ratios and appear to have taken place at relatively low palaeolatitudes the riphean sediments were deposited predominantly during rifting and break up of a supercontinent during the late vendian to early cambrian deposition of the nama group in southern namibia and the penecontemporaneous vanrhynsdorp group in the republic of south africa took place in the nama foreland basin detrital micas indicate that deposition of the nama group took place between 635 and 530 ma the nama foreland basin which was connected to a major ocean to the south formed as a result of collisions between the congo kalahari and rio de la plata plates with the exception of the nama group little is known about the palaeontology of the neoproterozoic in southwestern africa the lower nama group is latest proterozoic in age it contains an ediacaran fauna a depauperate assemblage of organic walled microfossils and a relatively well diversified ichnofauna with brooksella diplocraterion and nereites which are atypical of vendian strata many trace fossils are exceptionally small the occurrence of the shelly fossil cloudina and probable calcified metaphytes in the lower nama group suggest that skeletalization in animals and metaphytes occurred almost simultaneously towards the end of the proterozoic the upper nama group is early cambrian in age as indicated by the occurrence of the trace fossil phycodes pedum the upper nama group dominated by red beds contains a low diversity ichnofauna with trace fossils of normal size bio and chemostratigraphy combined with sequence stratigraphy will probably establish how the prominent unconformities which occur in the neoproterozoic of southwestern africa are related to the periods of formation of the wonoka canyons in south australia

precambrian cambrian transition problem in western north america part i tommotian fauna in the southwestern great basin and its implications for the base of the cambrian system an assemblage of shelly fossils has been discovered in the lower member of the deep spring formation in esmeralda county nevada preliminary taxonomic analysis suggests that the fossils consist of a variety of hyoliths coleolids and other elements the fossils lie about 1 000 m down section from the first trilobites and appear to be slightly younger than or possibly coeval with wyattia the fossils show affinities to tommotian taxa from siberia and other continents thus partial stratigraphic equivalents to the tommotian stage whose base marks the precambrian cambrian boundary can be defined for the southern great basin

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

one or three cambrian radiations the cambrian explosion was a time of great evolutionary change especially in the appearance of organisms with bilateral symmetry in their research commentary balavoine and adoutte discuss recent findings that may allow a reinterpretation of animal phylogeny and may have a profound bearing on understanding of the cambrian explosion

the potential of paleozoic nonmarine trace fossils for paleoecological interpretations abstract many late paleozoic environments have been interpreted as marine because of the co occurrence of supposedly exclusively marine trace fossils beginning in the late ordovician however nonmarine trace fossil diversity increased throughout the paleozoic this diversification of nonmarine organisms and nonmarine trace fossils was especially prevalent in devonian and later times diversification of freshwater organisms is indicated by the large number of freshwater fish arthropods annelids and molluscs that had developed by the carboniferous in addition to diverse freshwater assemblages entirely terrestrial vertebrate and invertebrate ecosystems had developed by the devonian this rapid diversification of freshwater and terrestrial organisms is inherently linked to development and diversification of land plants and subsequent shedding of large quantities of organic detritus in nonmarine and marginal marine areas nearshore marine organisms and their larvae that are able to tolerate relatively short periods of lowered salinities will follow salt water wedges inland during times of reduced freshwater discharge similarly amphidromous marine organisms will migrate periodically inland into nonmarine environments undoubtedly both of these processes were active in the paleozoic however both processes are restricted to stream distributary channels interdistributary bays or estuaries therefore the presence of diverse trace fossil assemblages in association with floodplain deposits is interpreted to reflect true nonmarine adaptation and diversity conversely diverse trace fossil assemblages in association with stream distributary channel deposits interdistributary bay deposits or estuarine deposits may reflect migration of salt water wedges inland or migration of marine organisms into freshwater environments amphidromy or both

lower cambrian acritarchs from northern spain the precambrian cambrian boundary and biostratigraphic implications acritarchs are reported from basal cambrian rock units inthe cantabrian region of northern spain that are known to contain archaeocyathan and trilobite faunas biostratigraphic correlation of the iberian sequences with other regions has been hampered by the strong provincialism of these faunas however this report of evidently cosmopolitan acritarch taxaestablishes the time equivalence of early cambrian trilobite faunas from iberia baltoscandia and the east european platform eep our data suggest that the detrital deposition of the lower cambrian herreria formation embraces at least three and possibly four lower cambrian acritarch zones previously identified in the eep eastern siberia baltoscandia scotland greenland svalbard and western north america the early cambrian transgression in northern spain was probably initiated in talsy times schmidtiellus mickwitzi trilobite zone in baltoscandia and the eep in part corresponding to the dokidocyathus regularis archaeocyathian zone of the middle tommotian in siberia

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

the early paleozoic development of bioturbation evolutionary and geobiological consequences abstract bioturbation the physical and chemical mixing of sediments by burrowing animals is a critical engineering process in modern seafloor environments and exerts an important control on not only benthic ecology and sediment properties but also ocean wide biogeochemical cycling well mixed sediments have long been assumed to appear at the precambrian cambrian boundary with the first occurrence of the index fossil and three dimensional burrow treptichnus pedum however field based analyses synthesizing ichnological stratigraphic sedimentological and taphonomic data collected from lower paleozoic successions worldwide indicate that sediment mixing in marine shelf environments remained limited until at least the late silurian 120 million years after the precambrian cambrian transition in spite of early advances in complex modes of infaunalization mixed layer development had a much more gradual trajectory and did not occur in step with the first appearance of three dimensional burrows the delayed appearance of modern style intensities of sediment reworking postdating both the cambrian explosion and the great ordovician biodiversification event may be due to the late stage radiation of mobile infaunal deposit feeders biological bulldozers the organisms which are in modern marine settings the most efficient bioturbators the protracted development of the sediment mixed layer holds important implications for contemporaneous biogeochemical cycling and oxygenation of the ocean atmosphere system the delayed development of intensive sediment mixing may have also mediated exceptional preservation of both fossilized soft tissues and shallow tier trace fossils and may therefore have contributed to the anomalous preponderance of konservat lagerstatten and exceptionally preserved shallow tier trace fossils and bioglyphs characteristic of the lower paleozoic stratigraphic record

ichnological constraints of palaeoenvironmental and palaeoclimatological features of the middle palaeozoic palaeo asian ocean evidence from the western junggar nw china abstract late devonian to early carboniferous deep sea deposits of the western junggar nw china contain 21 ichnotaxa arenituba verso chamberlain chondrites cf intricatus brongniart chondrites targionii brongniart chondrites isp gordia marina emmons halopoa imbricata torell helminthoidichnites isp helminthopsis cf hieroglyphica wetzel and bromley laevicyclus isp lophoctenium comosum richter multina isp nereites missouriensis weller phycodes cf bilix ksi zkiewicz phycosiphon incertum fischer ooster phycosiphon isp planolites isp cf taenidium thalassinoides isp zoophycos isp undetermined short ridges and undetermined tubular structures they form three typical ichnoassemblages i e the helminthopsis helminthoidichnites arenituba ichnoassemblage characteristic of upper bathyal probably hyperpycnal flow influenced deposits zoophycos nereites phycosiphon ichnoassemblage in typical slope deposits and the phycosiphon nereites ichnoassemblage featuring bottom current influenced lower slope or basin floor muddy deposits they can be ascribed to the cruziana zoophycos and the nereites ichnosubfacies respectively comparison with contemporaneous deep water facies foremost the kulm facies in western and central europe reveals significant loss in the western junggar of otherwise common element dictyodora liebeana geinitz combining the global palaeozoic tectonic evolution we propose that dictyodora was probably originated from peri gondwana terranes and the larvae juveniles of dictyodora producers hadn t migrated to the northern palaeolatitudes open ocean kazakhstan archipelago in the early carboniferous the relatively global distribution of the phycosiphon nereites association indicates efficient larval dispersal of their producers intensive bioturbation in deposits dominated by the phycosiphon nereites ichnoassemblage implies a high level of food supply at certain stratigraphic levels most likely related to surface blooms and enhanced plant detritus input the monsoonal palaeoclimatic model is integrated with the archipelagic palaeogeography to account for the deep sea ichnofauna in the western junggar during the late devonian to early carboniferous the most important factors include seasonal climatic perturbations such as monsoon derived upwelling events and enhanced primary production and efficient food nutrients transport in the dotted island scenario

latest proterozoic stratigraphy and earth history the end of the proterozoic eon was a time of pronounced biological biogeochemical climatic and tectonic change new bio and chemostratigraphic data provide an improved framework for stratigraphic correlation making possible a deeper understanding of latest proterozoic earth history and providing tools for a chronostratigraphic division of late proterozoic time

the proterozoic cambrian transition within the charnian supergroup of central england and the antiquity of the ediacara fauna a revised interpretation for the charnian supergroup is suggested from ichnological and lithological comparisons with the cambrian of nuneaton and other parts of the avalonian superterrane late neoproterozoic volcaniclastic sediments contain an ediacara fauna in the maplewell group these are succeeded by one or more inferred erosional breaks and overlain by passive margin sediments quartzarenites glauconitic greywackes pelites of the brand group which yield cambrian trace fossils including abundant large teichichnus this transformation is compared with that between the neoproterozoic caldecote volcanic formation and the cambrian hartshill formation at nuneaton the hanging rocks formation of the brand group lies above a major erosional break but shares a volcanogenic island arc petrology with the underlying maplewell group conglomeratic sandstones at the base of the brand hills formation contain purple pelite clasts comparable with underlying lithologies plus clasts of weathered diorite showing granophyric textures identical to those seen in the enigmatic south charnwood diorites nd sm isotope studies confirm the geochemical similarity between these diorites and those that intruded the caldecote volcanics at nuneaton previously u pb zircon dated at 603 2 ma these strong similarities with the nuneaton succession suggest that deposition of the brand hills formation in the cambrian was preceded by the local unroofing of diorite and erosion of underlying mudrocks much as seen in other parts of avalonia a date of 603 2 ma for the south charnwood diorites provides a minimum age for the local ediacara fauna but this is in need of substantiation

surface settlements due to deformation of a tunnel in an elastic half plane deformations of a tunnel may result in settlementsof the ground surface in engineering practice thesesurface settlements are often described by empiri cal formulae based upon eld observations forinstance a normal gaussian distribution curve peck 1969 attewell woodman 1982 in thisnote an approximate analytical solution is presented considering the soil as a linear elastic material although it is realized that this is a very poorschematization of the real behaviour of soils anelastic solution may well serve to investigate someof the characteristics of the resulting elds of stressand strain and it may also serve as a reference formore re ned numerical computations two basic deformation mechanisms of thetunnel are considered a uniform radial displace ment representing in rst approximation theground loss that may occur during constructionof the tunnel and an ovalization of the tunnel see fig 1 even though in practice the tunnellingprocess may be executed very carefully andappropriate engineering techniques may be appliedto minimize the deformations for instance theinjection of grout into the soil surrounding thetunnel it remains of interest to study the defor mations and stresses caused by both ground lossand ovalization the method used is an extension of a methodsuggested by sagaseta 1987 for the case ofground loss in an incompressible soil the startingpoint is the solution for a singularity at a point ofan elastic half plane at the axis of the tunnel byadding the image solution for a singularity at apoint located symmetrically above the soil surface the shear stresses at the surface are made equal tozero in order to balance the normal stresses at thesurface a third solution is added by solving aboussinesq type problem the approximation inestablishing the solution is that in balancing thenormal and tangential stresses on the surface thepresence of the tunnel with its prescribed dis placements is disregarded although an exactsolution might well be obtainable by the methodsoutlined by mindlin 1939 using bipolar coordi nates such a solution is very complicated thepresent approximate solution will be seen to bevery simple and easy to apply the solution given in this technical note is ageneralization of sagaseta s solution in that it givesthe solution for the case of ground loss not onlyfor the incompressible case with poisson s ratioequal to 0 5 but for arbitrary values of poisson sratio and that it includes the effect of ovalization the process of ovalization has been studied beforefor a tunnel in an in nite elastic medium muirwood 1975 here the surface displacements for atunnel in a semi in nite medium are considered aswell as the displacements and stresses throughoutthe half space

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

engineering the cambrian explosion the earliest bioturbators as ecosystem engineers by applying modern biological criteria to trace fossil types and assessing burrow morphology complexity depth potential burrow function and the likelihood of bioirrigation we assign ecosystem engineering impact eei values to the key ichnotaxa in the lowermost cambrian fortunian surface traces such as monomorphichnus have minimal impact on sediment properties and have very low eei values quasi infaunal traces of organisms that were surficial modifiers or biodiffusors such as planolites have moderate eei values and deeper infaunal gallery biodiffusive or upward conveying downward conveying traces such as teichichnus and gyrolithes have the highest eei values the key cambrian ichnotaxon treptichnus pedum has a moderate to high eei value depending on its functional interpretation most of the major functional groups of modern bioturbators are found to have evolved during the earliest cambrian including burrow types that are highly likely to have been bioirrigated in fine grained or microbially bound sedimentary environments trace makers of bioirrigated burrows would have had a particularly significant impact generating advective fluid flow within the sediment for the first time in marked contrast with the otherwise diffusive porewater systems of the proterozoic this innovation is likely to have created significant ecospace and engineered fundamentally new infaunal environments for macrobiotic and microbiotic organisms alike

trace fossils from the precambrian cambrian boundary candidate at meishucun jinning yunnan china the precambrian cambrian boundary candidate section at meishucun china has yielded trace fossils which are abundant at some horizons the earliest occur in unit 3 of the zhongyicun member approximately 8 m above the lower selected stratotype reference point for the boundary and include arenicolites sp asteriacites sp neonereites biserialis n uniserialis and sellaulichnus meishacunensis the next trace fossil bearing horizon is in unit 6 of the zhongyicun member where cochlichnus sp monomorphichnus sp neonereites biserialis and n uniserialis occur immediately above in unit 7 are cruziana sp didymaulichnus miettensis monomorphichnus sp and rusophycus sp in the badaowan member at the top of the section there are didymaulichnus sp and taphrhelminthopsis circularis in unit 9 arenicolites sp diplocraterion sp gordia molassica skolithos sp and t circularis in unit 11 and gordia meandria plagiogmus sp skolithos sp and t circularis in unit 12 comparison of this trace fossil distribution with that in key precambrian cambrian boundary sections in other countries indicates that the ranges of a few trace fossils cross the boundary e g didymaulichnus neonereites planolites but most appear only in the cambrian different ichnogenera seem to appear at various levels above the boundary arenicolites and asteriacites are among the first while taphrhelminthopsis circularis is only encountered higher in all sequences some have only been recorded at much higher levels and relatively close to the first appearance of trilobites e g cruziana diplocraterion rusophycus this suggests that the first appearance of specific trace fossils or groups of trace fossils may be valuable for locating the boundary in some sections and for correlating late precambrian and early cambrian strata

stable isotope geochemistry and palynology of the late precambrian to early cambrian sequence in newfoundland a sequence of clastic sediments in southeastern newfoundland straddling the precambrian cambrian boundary has been investigated for its stable isotope geochemistry of carbon and sulfur and acid resistant organic walled microfossils a detailed study of the chapel island formation which includes the boundary interval has revealed fluctuations in the isotopic composition of organic carbon these are largely interpreted as caused by differences in the depositional environments highly variable sulfur isotopic compositions indicate bacterial sulfate reduction as a pyrite forming process sometimes under sulfate limited conditions palynological results are quite limited with respect to diagnostic microfossils

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

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

stromatolitic and trace fossils community of the cerro victoria formation arroyo del soldado group lowermost cambrian uruguay abstract the cerro victoria formation of the arroyo del soldado group uruguay comprises 400 m of mainly stromatolitic micritic and oolitic limestones in this low diversity stromatolite paleocommunity moundlike and planar laminites dominate but columnar forms ooids and pisoids occur as well stromatolites played a major role in the construction of the carbonate ramp which developed onto a passive eastern margin of the rio de la plata craton a paleobiological reconstruction of the stomatolite community which includes subtidal intertidal and supratidal environments is presented a low diversity trace fossil association dessignated as thalassinoides gyrolithes palaeophycus assemblage is preserved in syngenetic concretions the stromatolite community ichnofossil assemblage and ichnofabrics are typical for the lowermost cambrian corroborating earlier age estimations the unit represents a shallowing upward sequence deposited under predominantly subtidal normal marine high energy conditions tropical climate prevailed as shown by thick carbonate deposits evaporitic minerals halite gypsum and abundance of ooids the cambrian of western gondwana is characterized by scarcity of carbonate ramps this was mainly determined by high siliciclastic input related to erosion of the pan african rio doce orogenic belts carbonate ramps developed in blocks located at tropical paleolatitudes and characterized by low clastic input such as the nico perez terrane and argentine precordillera

ichnological analysis the common ground between ichnofacies workers and ichnofabric analysts abstract this work compares the approaches taken by the two schools of applied ichnology ichnofacies and ichnofabric analysts and proposes an integrated approach for future improvement there are many similarities between the two approaches which mainly differ in the resolution at which ichnological analysis is undertaken ichnofabric work is by necessity performed on a bed by bed basis and interpreted at a scale consistent with that of the sedimentologist s facies ichnofacies studies in contrast seldom report bed by bed changes in ichnological content instead highlighting bedset to facies association scale changes in ichnology through comparison with summary models of ichnological trends this work highlights the fact that workers from both schools utilize the same tools with slightly different emphases to reach their ichnological conclusions contention between the two schools has in recent years centred upon which is the better method for studying trace fossils an artificial construct that detracts from the fact that both are extremely useful to sedimentological and palaeoenvironmental studies ichnofabric analysis is in addition a highly effective means of documenting bioturbated sedimentary fabrics as the basis for petrophysical studies ichnofacies and ichnofabric analysts use the same toolbox of ichnological methods to determine ancient palaeoenvironments the scale of observation is generally different but the results closely comparable the recognition of key stratal surfaces on ichnological grounds is also possible with both methodologies ichnofacies analysts look to recognise glossifungites ichnofacies firmgrounds in offshore mudstones ichnofabric studies would look to recognise overprinting of fabrics created by groups of organisms from different palaeoenvironments but associated with the same key surface it is proposed that the terms ichnofacies method and ichnofabric analysis are abandoned in favour of a neutral ichnological analysis method encompassing the approaches and terminology of both to produce a unified scientifically rigorous user friendly methodology

lowermost cambrian acritarchs from the yanjiahe formation south china implication for defining the base of the cambrian in the yangtze platform the asteridium heliosphaeridium comasphaeridium ahc acritarch assemblage is composed of common organic walled microfossils in the basal cambrian chert phosphorite units in south china indicating that the ahc assemblage can be a useful biostratigraphic tool for the ediacaran cambrian boundary successions in the yangtze platform to test the validity of the ahc acritarch assemblage as a biostratigraphic tool the stratigraphic range of the ahc acritarch assemblage was confirmed and its spatial and temporal relationships to other bio and chemostratigraphic tools were analysed in the yanjiahe formation yangtze gorges area south china the result shows that the ahc assemblage temporally correlates to the anabarites trisulcatus protohertzina anabarica assemblage zone and spatially correlates to the large negative carbon isotope anomaly of the lowermost cambrian bace in the yanjiahe formation this implies that the radiation of phytoplankton occurred slightly before the radiation of the small shelly fossils and the ahc acritarch assemblage can be another important chronological reference to the lowermost cambrian successions in south china and potentially to global correlations

taxis behaviour of burrowing organisms recorded in an ediacaran trace fossil from ukraine abstract the trace fossil archaeonassa cf fossulata fenton and fenton is a bilobate slightly undulating corrugated ridge on upper bedding plains in the ediacaran shallow marine siltstones of ukraine which are no younger than 557 ma it was produced partly under microbial mats this trace fossil shows strong orientation within a sector of 20o 40 which is approximately perpendicular to the expected shoreline the orientation points to ability of some ediacaran burrowing organisms to taxis during early evolutional stages of bilaterians in response to physical or chemical stimuli probably according to direction of tides undulations of a cf fossulata can be regarded as a record of the in and out burrowing in response to diurnal cycles of oxygen production within microbial mats probably this is one of the oldest examples of such behaviour in general archaeonassa is considered as a relatively common trace fossil in upper ediacaran deposits worldwide especially in shallow marine deposits in the time interval from 560 to 550 ma