precambrian medusoids the cyclomedusa plexus and cyclomedusa like pseudofossils abstract the medusoid fossils that were conventionally referred to cyclomedusa sprigg 1947 are among the commonest elements of the late precambrian ediacara metazoan assemblage in south australia specimens showing varying degrees of similarity have been reported worldwide from precambrian occurrences this study indicates that the fossils traditionally named cyclomedusa are a morphological plexus consisting of heterogeneous medusae the type species c davidi sprigg and c radiata sprigg are considered as a single species because of differences due to preservation c davidi can be compared with a living hydrozoan medusa aequorea in general configuration and an affinity with the family aequoreidae is suggested for the typical cyclomedusa spriggia southcott 1949 which was once regarded as a synonym of cyclomedusa is now re interpreted as a float bearing chondrophore hydrozoan colonial medusa the newly described s wadeae sp nov provides remarkable evidence for the amazingly conservative evolutionary history of the family porpitidae c plana glaessner and wade 1966 may be also chondrophoran in affinity but its configuration remains uncertain a critical review on the previously supposed cyclomedusa and other medusoids from the upper precambrian in southern liaoning china demonstrates that they are cyclomedusa like pseudofossils made by upwards escaping gas bubbles and water currents therefore they can not be used for stratigraphic correlation this example suggests the need for extreme caution in studies of various cyclomedusa like circular structures

moisture and temperature changes associated with the mid holocene tsuga decline in the northeastern united states abstract a decline of hemlock tsuga populations at ca 5 5 ka thousands of calibrated radiocarbon years before 1950 ad stands out as the most abrupt vegetation change of the holocene in north america but remains poorly understood after decades of study recent analyses of fossil pollen have revealed a concurrent abrupt oak quercus decline and increases in the abundance of beech fagus and pine pinus on cape cod in eastern massachusetts but the replacement of drought tolerant oaks by moisture sensitive beeches appears inconsistent with low lake levels in the region at the same time the oak and beech changes are also limited to coastal areas and the coastal inland differences require an explanation here we develop a new lake level reconstruction from deep pond cape cod by using a transect of sediment cores and ground penetrating radar gpr profiles to constrain the past elevations of the sandy littoral zone of the pond the reconstruction shows that a series of multi century episodes of low water coincide with the abrupt hemlock and oak declines and interrupt subsequent phases of hemlock recovery the lake level variations equal precipitation deficits of 100 mm superimposed on a holocene long moisture increase of 400 mm however because moisture deficits do not easily explain the oak and beech changes we also evaluate how the climate preferences of the regional vegetation changed over time by matching the fossil pollen assemblages from deep pond with their modern equivalents reconstructions of the precipitation requirements of the vegetation correlate well even in detail with the lake level record r 0 88 at deep pond and indicate close tracking of effective moisture precipitation minus evapotranspiration by the vegetation despite the abrupt species declines which could have decoupled climate and vegetation trends reconstructions of the temperature preferences of the vegetation indicate that coastal sites may have cooled by 0 5 2 5 c after ca 5 5 ka while inland sites warmed by 0 5 1 c the change in coastal temperature preferences agrees with sea surface cooling in the western atlantic ocean of 1 c consequently the persistence of low hemlock abundance after 5 5 ka in the northeast u s may have resulted from oceanic changes that produced multi century droughts and thus delayed the post decline recovery of hemlock populations

environmental interpretation and a sequence stratigraphic framework for the terminal proterozoic ediacara member within the rawnsley quartzite south australia abstract fossils of the ediacara biota are confined to preservational windows in the ediacara member of the rawnsley quartzite pound subgroup from the flinders ranges south australia the base of the ediacara member is a type 1 sequence boundary incised into the partly lithified chace quartzite member of the rawnsley quartzite the ediacara member and the upper half of the rawnsley quartzite comprise the rawnsley depositional sequence bounded above by the early cambrian uratanna depositional sequence the rawnsley sequence developed over an erosional surface cut into the chace quartzite member with some 250 m of relief southeasterly directed palaeovalleys are filled with a sequence of massive sandstone and laminated siltstone passing up into well bedded sandstone at lowstand local channels were filled by massive sand the highstand systems tract consists of several parasequence sets of laminated siltstone and channelized amalgamated massive sandstone overlain by interbedded siltstone and sandstone grading up into well bedded clean sandstone impressions of soft bodied ediacaran organisms are preserved above the valley fill facies on sandstone partings within upward shoaling delta front environments between storm and fairweather wavebase the ediacara member is in places conformably overlain by up to 500 m of sandstone of the same lithofacies as those underlying the member distinctive microbial mat bound sand laminae described as petee structures are characteristic of the rawnsley quartzite above and below the ediacara member during deposition of the ediacara member colonization of the deeper substrates by microbial mat communities enabled preservation of the ediacara biota the erosional surface at the base of the ediacara member is one of at least four incision events recorded in the terminal proterozoic and early cambrian succession of the adelaide geosyncline the similarity of incision filling lithofacies of the rawnsley and uratanna sequences has in condensed sections led to confusion between the depositional sequences characteristic trace and body fossil assemblages provide the only clear distinction between depositional cycles spanning the proterozoic cambrian boundary

ediacaran remains from intertillite beds in northwestern canada a turbidite sequence within the twitya formation windermere supergroup in the ackenzie mountains northwestern canada has yielded an assemblage composed of simple centimetric annuli and discs which are interpreted as biogenic and referred to nimbia occlusa fedonkin vendetta sp and irridinitus sp they occur below a glaciomarine diamictite about 2 5 km below the base of the cambrian and they may represent the oldest ediacaran fossils now known the find has implications for models that relate the evolution of the ediacara fauna to the waning of the varanger glaciation

textured organic surfaces associated with the ediacara biota in south australia abstract the ediacaran period takes its name from the fossils of the ediacara biota which represent the first appearance of large and diverse assemblages of organisms in the fossil record although the global record of these distinctive body fossils is now well known a previously unrecognized megascopic organic record of textured organic surfaces tos occurs in the ediacara biota however tos is also a feature over a wider range of paleoenvironmental settings where body fossils are unknown in ediacaran siliciclastic successions that have been studied in australia namibia and western north america paleoecological analysis of successive bedding planes of strata from the late ediacaran rawnsley quartzite in the flinders ranges of south australia reveals that tos represent the most common organic features in bedding surface assemblages of the ediacara biota the tos consist of preserved patterned assemblages of textured organic mats fibers and simple tubular body fossils complex ediacara body fossils while striking for their distinctive body plans and dominating some of the beds are relatively minor components of combined overall surface area many elements of tos have previously been miss diagnosed as trace fossils which are in practice limited to two or at most three morphotypes that indicate the presence of bilateria although tos represent a simpler grade of organismic construction than discrete and more complex ediacara body fossils they were preserved in a similar manner marked variability in all components of the biota between successive surfaces suggests that ediacara ecologies fluctuated at short intervals despite an apparently consistent sedimentary regime

microbial origin of early animal trace fossils abstract elongate surface trails that abound in late ediacaran and early paleozoic sandstone and siltstone are often attributed to early animals these trails commonly exist on the same beds as wrinkle structures millimeter to centimeter size ridges and pits that are interpreted as evidence of the former presence of microbial mats here we show that interactions between oscillatory flow and centimetric microbial aggregates produce elongate trails on the surface of a sediment bed trails left by moving microbial aggregates share a number of characteristics with some presumed trace fossils of the earliest animals elevated edges zig zag patterns smooth curves reversals intersections with other trails series of pits and paths that terminate abruptly and restart nearby under the same flow conditions millimetric microbial aggregates generate wrinkle structures thus the interaction between flow and microbial aggregates on a sediment bed can produce a number of structures that are commonly interpreted as evidence of early animal locomotion

evolutionary relationships within the avalonian ediacara biota new insights from laser analysis abstract we report new high resolution laser scanning of the type material for the earliest complex ediacaran genera charnia bradgatia charniodiscus and ivesheadia from charnwood uk and compare these with beothukis mistakensis gen et sp nov and the recently described taxa charnia wardi charnia antecedens and fractofusus spp from broadly coeval strata in newfoundland we use the laser and other techniques to map the similarities and differences in morphology between these ediacaran rangeomorphs key features are suggested to include the number of growth axes the number and placement of growth tips the presence of radiating or subparallel axes for the first and higher order branches the extent of displayed or undisplayed leaf like rangeomorph9 architecture and the extent of furling of the margins of these leaf like elements these features are then used to propose suggested homologies between these taxa leading to a preliminary phylogenetic hypothesis for the evolution of the avalonian ediacara biota

neoproterozoic stratigraphy of the centralian superbasin australia abstract the basement of central australia includes the arunta block and the 1200 1100 ma musgrave block succeeded by 1075 1000 ma bimodal volcanic rifts and dolerite dykes a regional hiatus at 1000 800 ma interpreted as reflecting a central post volcanic underplated upland was followed at 800 ma by a second swarm of dykes in the musgrave block gawler craton and stuart shelf associated with the crustal sagging that initiated the centralian superbasin the centralian superbasin is defined here to encompass the neoproterozoic fill of the amadeus georgina ngalia officer and savory basins the intra cratonic superbasin was disrupted internally 540 600 ma ago petermann ranges orogeny by a central uplift and associated thrusts and by mid carboniferous 320 ma tectonism alice springs orogeny to form the structural basins listed above the stratigraphy and sedimentology of the relatively well known areas can be used as a basis for predicting those of the poorly known regions new results from acritarch biostratigraphy and isotope chemostratigraphy in conjunction with conventional lithostratigraphy and sequence analysis allow better stratigraphic resolution than previously possible field observations in the recently discovered savory basin in western australia provide a basis for correlations with the adjacent basins

integrated ediacaran chronostratigraphy wernecke mountains northwestern canada abstract terminal neoproterozoic ediacaran ca 600 543 ma strata of the upper part of the windermere supergroup are well exposed in the mackenzie mountains and the wernecke mountains of northwestern canada windermere strata in the mackenzie mountains contain an exceptional ediacaran biostratigraphic and isotopic c and sr record while the sequence stratigraphic record is subtle throughout this predominantly deep water succession coeval strata in the wernecke mountains can be correlated with the succession in the mackenzie mountains on a formational level in contrast to the deep water setting of the mackenzies succession the werneckes succession preserves a predominantly shallow water succession amenable to detailed sequence stratigraphy integrated lithostratigraphy chemostratigraphy biostratigraphy and sedimentology partitions the wernecke mountains succession into five depositional sequences and constrains correlation with strata in the mackenzie mountains the siliciclastic and carbonate sediments deposited along the margin of the proto pacific ocean record accumulation in continental slope neritic and terrestrial paleoenvironments distinctive temporal chemostratigraphic and biostratigraphic attributes allow these strata to be correlated with other ediacaran successions worldwide integrating sequence stratigraphy with these attributes is a robust yet under utilized correlation tool and is a step toward erecting a more detailed working neoproterozoic chronostratigraphy

early cambrian palaeogeography and the probable iberia siberia connection abstract the end of the proterozoic beginning of the cambrian is marked by some of the most dramatic events in the history of earth the fall of the ediacaran biota followed by the cambrian explosion of skeletonised bilaterians a pronounced shift in oceanic and atmospheric chemistry and rapid climatic change from snowball earth to greenhouse conditions all happened within a rather geologically short period of time these events took place against a background of the rearrangement of the prevailing supercontinent some authors view this as a sequence of individual supercontinents such as mesoproterozoic midgardia neoproterozoic rodinia and early cambrian pannotia assembled in the mesoproterozoic this supercontinent appears to have existed through the neoproterozoic into the early cambrian with periodic changes in configuration the final rearrangement took place during the precambrian cambrian transition with the cadomian and related phases of the pan african orogeny the distribution of early cambrian molluscs and other small shelly fossils ssf across all continents indicates a close geographic proximity of all major cratonic basins that is consistent with the continued existence of the supercontinent at that time subsequently rodinia experienced breakup that led to the amalgamation of gondwana separation of laurentia baltica siberia and some small terranes and the emergence of oceanic basins between them spreading oceanic basins caused a gradual geographic isolation of the faunal assemblages that were united during the vendian early cambrian

ediacarian fossils from the carolina slate belt stanly county north carolina discovery of metazoan fossils comparable to those of the late precambrian ediacarian fauna in the carolina slate belt stanly county north carolina extends the paleobiogeographic range of the ediacarian fauna into the southern piedmont of the southeastern united states these fossils provide paleontologic correlation with parts of the precambrian valdai series of the vendian system of the soviet union the nama group of south west africa and the pound quartzite of south australia in light of the recent discoveries north carolina fossil material previously described as the middle cambrian trilobite paradoxides carolinaensis st jean 1973 was re examined and identified as an element of the late precambrian ediacarian fauna

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

trace fossil evidence for ediacaran bilaterian animals with complex behaviors abstract distinguishing ediacaran trace fossils from tubular body fossils can be a challenge and several ediacaran fossils previously interpreted as animal traces have been shown to be tubular body fossils nonetheless true ediacaran trace fossils are present but they are relatively few and morphologically simple dominated by horizontal trails and shallow burrows such simple morphologies have been taken as evidence for a modest behavioral complexity and limited geobiological impact of animal bioturbators before the cambrian explosion here we report three types of trace fossils horizontal tunnels surface tracks trails and vertical traces from the latest ediacaran dengying formation 551 541 ma in the yangtze gorges area of south china cross cutting tunnels and the presence of scratch marks indicate that these traces are unlikely tubular body fossils instead these three types of traces likely represent animal activities related to under mat feeding epibenthic locomotion and temporary dwelling respectively we show that these three types of traces were constructed by the same bilaterian animals that had moderately complex interactions with microbial mats to exploit nutrients and o 2 resources these animals heralded a new age in ecosystem engineering animal sediment interaction and biogeochemical cycling

sedimentary geology and evolution of an outcropping shelf margin delta late proterozoic wonoka formation south australia discrete sand units or accumulations crop out within the late proterozoic wonoka formation northern flinders ranges south australia these sand wedges are unique in their size contacts facies and associations to other sands in the formation and are interpreted as shelf margin deltas the wedges can be divided into a main body and a series of discrete feeder channels the main body consists of basal slump masses a sandstone dominated succession and an overlying shale dominated facies lithofacies grossly define a deepening upward succession from a lower shoreface to outer shelf setting the formation and deposition of the feeder channels and sand wedges was controlled largely by relative sea level changes initial exposure of the shelf and subaerial erosion produced a regional erosional surface and incised valleys across the paleoshelf prior to deposition of the wedges slope instabilities and minor uplift occurred sediment was then transported across the shelf and deposited near or at the shelf break and reworked in a shallow marine environment deposition of the shelf margin deltas continued during relative sea level rise but ended with shelf drowning

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

dispersion in tumbling flow steep mountain streams are often in the tumbling flow regime that is alternating sub and super critical flow with energy dissipation caused mainly by sudden changes in slope and cross section though longitudinal dispersion characteristics of tumbling flows are important in time of travel stream gauging and contaminant spread considerations very little pertinent information is available the results of a laboratory study intended to provide preliminary data on tumbling flow dispersion are discussed to simulate tumbling flow a 1 m wide flume was divided into 11 pools by placing identical triangular weirs at 3 m intervals slugs of fluorescent dye were injected at the first weir and the resulting concentration time variations measured downstream at every second weir test results are analyzed according to existing theoretical models and corresponding parameters evaluated it is concluded that conventional river dispersion models are possible means of describing tumbling flow dispersion but it is unclear at this time whether storage dispersion models are relistic

two late proterozoic glaciations mackenzie mountains northwestern canada glacial influence on deposition of the upper proterozoic sayunei and shezal formations rapitan group of northwestern canada is well established diamictites of the stelfox member of the ice brook formation 1 km higher in the section and resting on platformal carbonate and siliciclastic strata of the keele formation are here interpreted as glaciomarine the glacial interpretation is based on the presence of dropstones till pellets extremely angular quartz grains intercalations of laminated mudrocks and sandstone and rare striated stones the stelfox glacial deposits are unique in that they lie above the lowest occurrence of faunas of ediacaran type the establishment of two episodes of late proterozoic glaciation in northwestern canada as opposed to the previously recognized single episode enhances the possibility that these two glaciations correspond to the two recognized in parts of australia and africa

a re examination of the nama type vendian organism rangea schneiderhoehni the need to re examine rangea has been motivated by two factors first by the recent progress in the understanding of three dimensional mouldic preservation of vendian fossils and second by discoveries of this taxon outside gondwana albeit in the same sedimentary environment as seen in namibia several important features are revealed including the in situ posture in the sediment the double layered quilted structure the tripartite stemless body and the mucous supported sheath in the sediment it is suggested that rangea represents an infaunal organism and that the similarity with other members of the nama type biota reflects convergence in functional and fabricational constraints in relation to infaunal life habit

early cambrian continental reconstructions climatically related sedimentary facies and faunal distributions have been combined with palaeomagnetic data to make provisional reconstructions of the early cambrian world laurentia baltica and siberia appear to have formed a continental group which rifted apart from each other prior to 600 ma the consolidation of much of gondwana probably occurred in the pan african orogeny well before the cambrian though the assembly of several east asian terranes is still speculative the archaeocyathan reefs of siberia southern europe and morocco with their bigotinid trilobite fauna suggest that these areas were adjacent to each other and at low latitudes avalonia had close faunal links with western gondwana but lacked bigotinids and archaeocyathans and may have been situated off west africa and florida during the early cambrian there was a northward migration of laurentia towards the equator as its separation from baltica and siberia increased and a southward movement of gondwana

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

prokaryotic and eukaryotic microfossils from a proterozoic phanerozoic transition in china cherts of the doushantuo formation in the yangtze gorges south china contain a superbly preserved heterogeneous assemblage of bacteria cyanobacteria planktonic algae submillimetre sized burrows and problematica the microbiota has a bearing on defining the precambrian cambrian boundary baltisphaeridium and associated spinose microfossils in the chert suggest an early cambrian age whereas other acritarchs vendotaenids and pretrilobite small shelly fossils from the conformably overlying the dengying formation indicate a late proterozoic age for the doushantuo this mixed benthic planktonic assemblage preserved in silicified laminated microbial mat like fabrics provides a unique sample of diverse microbiotic elements existing at the dawn of the phanerozoic and records the earliest evidence of meiofauna

sequence stratigraphy and the interpretation of neoproterozoic earth history abstract the application of sequence stratigraphy to neoproterozoic successions is important for improving the resolution of time correlation within individual sedimentary basins and potentially at a global scale the methodology is illustrated in this paper by reference to two contrasting examples from the flinders ranges adelaide geosyncline of south australia where the younger part of the neoproterozoic to earliest cambrian succession 770 ma to 540 ma has been divided into thirteen unconformity bounded depositional sequences one of the most prominent sequence boundaries at or near the base of the wonoka formation is characterized by a series of buried canyons as much as 1 km deep high resolution sequence stratigraphic studies at umberatana syncline continue to support the view that the canyons were cut subaerially and filled by fluvial and shallow water sediments in contrast to the wonoka canyons sequence boundaries interpreted at the base of the nuccaleena formation seacliff sandstone and near the top of the abc range quartzite are relatively subtle with only limited evidence for erosion and valley incision four sequence boundaries at the level of the sturtian and marinoan varanger glacial deposits and in the vicinity of the precambrian cambrian boundary are thought to correlate with surfaces in the amadeus basin of central australia other prominent sequence boundaries including the wonoka canyons and surfaces within the upper part of the wonoka formation and at the base of the ediacara member of the rawnsley quartzite correspond with a relatively condensed section in the amadeus basin and their lateral persistence beyond the adelaide geosyncline is therefore difficult to evaluate given the lack of precision in biostratigraphy and isotope geochemistry in neoproterozoic rocks and in a marked departure from phanerozoic practice we recommend placement of a terminal proterozoic gssp at a sequence boundary a prime candidate in australia is the sequence boundary at the base of the nuccaleena formation seacliff sandstone immediately above the marinoan glacial rocks in the adelaide geosyncline and its likely correlative at or near the base of the gaylad sandstone in the amadeus basin

oxygen and carbon isotope stratigraphy of early cambrian carbonates in southeastern newfoundland and england carbonate rocks have been sampled through predominantly siliciclastic sediments above the precambrian cambrian global stratotype level in southeastern newfoundland to assess their potential for oxygen and carbon isotope stratigraphy comparable successions were sampled at nuneaton and comley in england greatly depleted 18 o signals are attributed to widespread thermal alteration during deep burial and granitic intrusion including within the stratotype region carbon isotope ratios appear to have been less affected and these are described from nine sections a provisional composite 13 c curve is based on non ferroan pink nodular and bedded micrites several 13 c excursions occur in the fossiliferous bonavista group and allow the position of the tommotian atdabanian boundary to be identified chemostratigraphic correlation of the new precambrian cambrian boundary stratotype may however prove difficult because of the lack of suitable well preserved carbonates the search must begin for a comparable reference section allowing global correlation of the boundary level using chemostratigraphy as well as biostratigraphy

the record and stratigraphie implications of organic walled microfossils from the ediacaran terminal proterozoic of south australia two assemblages of organic walled microfossils have been recognized in drillcore samples from the late proterozoic rodda beds in the eastern officer basin south australia the fossils include tube like remains and large simple and sculptured acritarchs lithostratigraphic studies and seismic information in conjunction with previous albeit limited acritarch finds allow local correlation of the rodda beds with ediacaran or terminal proterozoic sequences in the northern adelaide fold belt site of the nominated ediacaran stratotype the new palynofloras are comparable with acritarch assemblages in the amadeus basin of central australia and suggest tentative correlations with sequences in china and the u s s r the presence of isotopically heavy marine carbonate in the lower fossiliferous horizons of the rodda beds pcpdb 3 to 6 0 is consistent with isotopic data from the equivalent interval in china in contrast the upper fossiliferous strata occur higher in the rodda beds where carbonate is significantly lighter 13 cpdb 1 to 3 o

silicified horodyskia and palaeopascichnus from upper ediacaran cherts in south china tentative phylogenetic interpretation and implications for evolutionary stasis horodyskia is one of the earliest known macroscopic life forms with a fossil record dating from c 1 4 ga palaeopascichnus represents a key ediacaran element with world wide distribution however their body constructions and affinities are poorly understood partly because previously described species are mostly preserved as casts and moulds in siliciclastic rocks silicified specimens from the upper ediacaran liuchapo formation in eastern guizhou south china are described as horodyskia minor sp nov and palaeopascichnus jiumenensis sp nov their taxonomic assignments are based on their uniserial arrangement of spheroidal or discoidal units which are connected by a filament and surrounded by a quartz halo they are unlikely to be brown algae animal traces faecal pellets colonial metazoans or giant sulphide oxidizing bacteria instead we propose that horodyskia and palaeopascichnus may be phylogenetically related and their collective morphologies allow tentative comparison with agglutinated foraminifers the segments can be compared with cytoplasm filled chambers connecting filament with small passage between chambers and quartz haloes with agglutinated tests however their ontogeny appears to be distinct from that of modern foraminifers the occurrences of horodyskia fossils in mesoproterozoic and ediacaran rocks indicate an extremely long range c 900 ma and echoes the proposition of extended evolutionary stasis in the proterozoic

latest proterozoic plankton from the amadeus basin in central australia the plankton of the proterozoic is preserved mainly as microfossils known as acritarchs most of which are considered to be cysts of eukaryotic algae in recent studies of the diversity of proterozoic and early palaeozoic acritarchs a gradual increase in diversity from the middle into the late proterozoic has been shown to be followed by a sharp decrease in diversity in the latest proterozoic ediacarian or vendian and then a rise again in the early cambrian1 2 these observations have been interpreted in terms of the evolutionary diversification of eukaryotic algae and the ecological effects of the pre ediacarian glaciation occasional discoveries of complex acritarchs in ediacarian rocks3 6 have raised some doubts about these interpretations but more recent work seems to have supported this view7 here we report the discovery of a diverse assemblage of large and morphologically complex acritarchs from the ediacarian age upper pertatataka formation in the amadeus basin of central australia this with a recent report of similar fossils from the upper sinian of china8 provides a significant new perspective on the history of the plankton it is now necessary to suggest an earlier radiation at least in off shore environments or to question the reality of the postulated decrease in diversity in addition there may well have been an extinction event late in the ediacarian neither of these phenomena has been recognized previously