sedimentary challenge to snowball earth evidence from the magnetic field fossilized in sedimentary rocks suggests that more than 600 million years ago ice occupied tropical latitudes a popular explanation for these findings the snowball earth concept envisages a fully frozen earth for millions of years caused by a runaway ice albedo feedback a rapid catastrophic meltback at very high levels of atmospheric carbon dioxide is thought to have ended this extreme climatic state however sedimentary rocks deposited during these cold intervals indicate that dynamic glaciers and ice streams continued to deliver large amounts of sediment to open oceans throughout the glacial cycle the sedimentary evidence therefore indicates that despite the severity of glaciation some oceans must have remained ice free significant areas of open ocean have important implications for the survival and diversification of life and for the workings of the global carbon cycle the snowball earth concept envisages a fully frozen earth for millions of years several times during the neoproterzoic era between 1 000 and 542 million years ago however the sedimentary evidence suggests that despite the severity of glaciation some oceans must have remained ice free

ediacaran radiation of organic walled microbiota recorded in the ura formation patom uplift east siberia a new assemblage of morphologically complex ornamented and large organic walled microfossils acritarchs from the ura formation in the patom uplift east siberia is identified and taxonomically

conditions of formation and diagenetic evolution of upper proterozoic phosphate nodules from southern sweden evidence from petrology mineral chemistry and isotopes abstract dark gray to black cryptocrystalline francolite occurs as nodules 2 8 cm in diameter which are embedded in organic matter rich mudstones of the visingso group upper proterozoic southern sweden the 13cpdb values 18 4 to 0 98 of structural co2 complemented by studies of the petrographic character and strontium isotopic composition of francolite indicate precipitation in the suboxic and sulfate reduction zones francolite is intergrown with berthierine that has formed in the suboxic fe reduction zone calcite enriched in mn and to a lesser extent fe occurs as fracture and void fillings and as replacement of francolite mn and mg rich calcian siderites have precipitated as pseudomorphs after bacteria in the zone of microbial methanogenesis the carbon 13 c pdb 0 75 to 7 04 and oxygen 18 o pdb 14 21 to 10 58 isotopes of calcite suggest derivation of carbonate ions from microbial methanogenesis and from thermal decarboxylation of organic matter at temperatures of 60 to 80 c some of the void and fracture filling calcites 13 c 20 8 to 18 63 18 o 5 46 to 5 21 have however precipitated at lower temperatures 25 30 c in the sulfate reduction zone

a whiff of oxygen before the great oxidation event high resolution chemostratigraphy reveals an episode of enrichment of the redox sensitive transition metals molybdenum and rhenium in the late archean mount mcrae shale in western australia correlations with organic carbon indicate that these metals were derived from contemporaneous seawater rhenium osmium geochronology demonstrates that the enrichment is a primary sedimentary feature dating to 2501 8 million years ago ma molybdenum and rhenium were probably supplied to archean oceans by oxidative weathering of crustal sulfide minerals these findings point to the presence of small amounts of o 2 in the environment more than 50 million years before the start of the great oxidation event

organic walled microfossil assemblages from glacial and interglacial neoproterozoic units of australia and svalbard before the onset of the neoproterozoic snowball earth glaciations eukaryotes had begun diversifying and in their aftermath macroscopic life including both animals and macroalgae became abundant and widespread although glacially driven mass extinctions have been hypothesized little is known about the biosphere during and between these glaciations here we present new data from organic walled microfossil assemblages from five successions in australia and svalbard that collectively span the first sturtian glaciation and interglacial interval and integrate them with data derived from a critical evaluation of the literature to produce a new estimate of eukaryotic diversity from 850 to 650 ma these new glacial and interglacial assemblages consist of only smooth walled spheroids leiosphaerids aggregates of cells and filaments in contrast to the much more diverse organic walled microfossil assemblages found in early neoproterozoic rocks this contrast is not attributed to biases in deposition or preservation but is instead interpreted as reflecting an interval of lowered eukaryotic diversity that spanned the glaciations and that may have begun millions of years prior to their onset

protists of the upper mesoproterozoic ruyang group in shanxi province china abstract organic walled microfossils described in this paper have been obtained from the beidajian formation of the mesoproterozoic ruyang group ca 1300 ma in southern shanxi province china they are characterized by many eukaryotic organisms such as acanthomorphic acritarchs sphaeromorphic acritarchs with a distinct circular excystment acritarchs with multilayered walls and ornamentation and multicellular filaments and algal thallose recently more eukaryotic microfossils have been found and the triaromatic dinosteroid biomarker was extracted from the whole rock sample containing abundant acritarch specimens of dictyosphaera delicata and shuiyousphaeridium one acritarch form spiromorpha segmentata shows morphological similarities to the extant green alga spirotaenia it means that sexual reproduction by conjugation probably arose in the late mesoproterozoic a new genus spiromorpha is proposed here in combination with known mesoproterozoic microfossil assemblages from the roper group of australia and the bahraich group of ganga basin india we infer that marine protests had a rapid development during the mesoproterozoic era

a tonian age for the visingso group in sweden constrained by detrital zircon dating and biochronology implications for evolutionary events detrital zircon u pb ages from samples of the neoproterozoic visingso group sweden yield a maximum depositional age of 886 9 ma 2 a minimum depositional age is established biochronologically using organic walled and vase shaped microfossils present in the upper formation of the visingso group the upper formation correlates with the kwagunt formation of the 780 740 ma chuar group in arizona usa and the lower mount harper group yukon canada that is older than 740 ma mineralized scale microfossils of the type recorded from the upper fifteenmile group yukon canada where they occur in a narrow stratigraphic range and are younger than 788 ma are recognized for the first time outside laurentia the mineralized scale microfossils in the upper formation of the visingso group seem to have a wider stratigraphic range and are older than c 740 ma the inferred age range of mineralized scale microfossils is 788 740 ma this time interval coincides with the vase shaped microfossil range because both microfossil groups co occur the combined isotopic and biochronologic ages constrain the visingso group to between 886 and 740 ma thus tonian in age this is the first robust age determination for the visingso group which preserves a rich microfossil assemblage of worldwide distribution the organic and mineralized microorganisms preserved in the visingso group and coeval successions elsewhere document global evolutionary events of auto and heterotrophic protist radiations that are crucial to the reconstruction of eukaryotic phylogeny based on the fossil record and are useful for the neoproterozoic chronostratigraphic subdivision

chemical fractionation of brine in the mcmurdo ice shelf antarctica abstract during the austral summers of 1976 77 and 1978 79 several ice cores were taken from the mcmurdo ice shelf brine zone to investigate its thermal physical and chemical properties this brine zone consists of a series of superimposed brine layers waves that originate at the seaward edge of the ice shelf and migrate at various rates depending upon their age and position in the ice shelf the brine in these layers becomes increasingly concentrated as the waves migrate inland through the permeable ice shelf firn chemical analyses of brine samples from the youngest uppermost brine wave show that it contains sea salts in normal seawater proportions further inland deeper and older brine layers though slightly highly saline s200 are severely depleted in s04 2 na ratio being an order of magnitude less than that of normal seawater analyses of na k ca2 mg2 so4 2 and c1 together with solubility and temperature considerations show that the sulfate depletion is due to selective precipitation of mirabilite na2s041oh2o the location of the inland boundry of brine penetration is closely related to the depth at which the brine encounters the firn ice transition however a small but measurable migration of brine is still occurring in otherwise impermeable ice this is attributed to eutectic dissolution of the ice by concentrated brine as it moves into deeper and warmer parts of the mcmurdo ice shelf

organic walled microfossils from the tonian gouhou formation huaibei region north china craton and their biostratigraphic implications abstract the meso and neoproterozoic huaibei group in the huaibei region north china craton ncc is emerging as a target for geobiological and tectonic studies due to its thick unmetamorphosed sediments with well preserved organic walled fossils however the lack of accurate age constraints for this sedimentary sequence dramatically hampers our ability to take full advantage of the rich geological and paleontological history recorded in the huaibei group particularly the depositional age of the uppermost unit of the huaibei group the gouhou formation is a controversial issue although it is widely accepted that there is an unconformity between the gouhou formation and the overlying early cambrian houjiashan formation the magnitude of this unconformity and hence the scale of the underlying tectonic event are unconstrained due to the uncertainty of the sedimentary age for the gouhou formation which has been variously interpreted as cambrian cryogenian ediacaran 720 ma to 541 ma and tonian 1000 ma to 720 ma to improve our knowledge about this sedimentary gap we carried out a biostratigraphic study of the gouhou formation our investigation using a low manipulation maceration technique revealed a diverse organic walled microfossil assemblage a total of 22 taxa have been revealed including a new species dictyosphaera tacita n sp importantly the co occurrence of trachyhystrichosphaera valeria and dictyosphaera in the gouhou formation suggests a likely tonian age the biostratigraphic data indicate an infra cambrian depositional gap of 200 myr between the tonian gouhou formation and cambrian houjiashan formation perhaps driven by a major tectonostratigraphic event

organic walled microfossils from earliest cambrian or latest proterozoic tindir group rocks northwest canada abstract uppermost tindir group limestones exposed in the headwaters of tindir creek yukon territory canada contain a diverse and abundant microbiota of mineralized and organic walled microfossils preserved primarily in chert modules and chert beds the organic walled forms include mat building cyanobacterial filaments and coccoids accompanied by less common bacteria fungi and forms of uncertain affinity as well as planktonic coccoidal cyanobacteria and acritarchs several lines of evidence support interpretation of an early cambrian age whereas others suggest a late proterozoic age of the 54 organic walled taxa recognized 12 are newly described yukonosphaeridion interior awramik n gen n sp microagglomeratus borealis awramik n gen n sp phacelogeminus lineatus awramik n gen n sp palaeoanacystis magna awramik n sp cephalophytarion majesticum allison n sp heliconema bulbosa allison n sp trachyhystrichosphaera magna allison n sp fusilabellum brevistriatum awramik n gen n sp sphaeranasillos irregularis allison n gen n sp hyalocyrillium clardyi allison n gen n sp eophycomyces herkoides allison n gen n sp and archeomyces dimakeloides allison n gen n sp

new record of organic walled morphologically distinct microfossils from the late paleoproterozoic changcheng group in the yanshan range north china abstract eukaryotic life has likely existed since the late paleoproterozoic yet little is known about its early diversity and phylogenetic relationships organic walled microfossils owms with conspicuous morphology provide a unique material to investigate the deep evolution of eukaryotic and prokaryotic microbial clades here we report a diverse assemblage of owms from the lower changcheng group c 1673 1638 ma changzhougou and chuanlinggou formations in the yanshan range north china which consists of 15 species including 2 that are newly described the fossil assemblage is dominated by spheromorphs with less numerous process bearing vesicles as are colonial and filamentous forms among these 6 morphologically complex taxa dictyosphaera 2 species of germinosphaera pterospermopsimorpha simia and valeria are identified as unambiguous unicellular eukaryotes four species cucumiforma navifusa schizofusa and large leiosphaeridia with relatively simple morphology but having large size thick wall and some showing median split excystment structures are of probable eukaryotic affinity however various colonial microfossils could be either eukaryotes or prokaryotes the new record of morphologically disparate owms represents one of the earliest occurrences of eukaryotes in both china and the world and indicates that the eukaryotic life was already well established in the late paleoproterozoic and was of moderate diversity similar to that of the mesoproterozoic

paleoproterozoic accretionary orogenesis in the north china craton a shrimp zircon study abstract the inner mongolia suture zone imsz and the trans north china orogen tnco incorporate the major paleoproterozoic accretionary orogens in the north china craton ncc with the jiao liao ji belt jljb representing the third one here we investigate the paleoproterozoic tectonics of the imsz and tnco through zircon shrimp geochronology on a representative suite of rocks comprising metasediments and arc magmatic rocks shrimp analysis of zircons with textures indicating extreme recrystallization under ultrahigh temperature uht conditions from the metapelites at heling er in the southern domain of the imsz reveals a single population with a weighted mean 207 pb 206 pb age of 1913 17 ma the zircons in another uht granulite from this locality yield a weighted mean 207 pb 206 pb age of 1910 18 ma these data correlate with the ca 1 92 ga age reported from zircons in sapphirine bearing uht granulites further north and confirm the regional extent of the paleoproterozoic uht metamorphism within the imsz zircons in a charnockite from the southern margin of the khondalite belt fringing the uht granulites in the imsz show two distinct age groups an older population with a magmatic paragenesis and a weighted mean 207 pb 206 pb age of 1932 24 ma and a younger group of metamorphic zircons with an age of 1858 26 ma we also report zircon ages from charnockites in two localities around xing he in the huangtuyao belt belonging to the huai an complex within the westernmost domain of the tnco at the junction with the imsz the charnockite from first locality carries two distinct zircon populations with the older group yielding a weighted mean 207 pb 206 pb age of 2477 2 ma and the younger population showing an age of 1807 38 ma the internal structure as revealed from cl images and the overall high th u values up to 2 42 of the older zircons suggest their magmatic affinity whereas the younger group with extremely low th u 0 02 0 09 is of metamorphic origin zircons from the charnockite in the second locality also define two distinct age clusters with a dominant older magmatic group having a weighted mean 207 pb 206 pb age of 2147 11 ma and a minor younger group with an age of 1958 25 ma the range of ages from 2477 to 2147 ma from magmatic zircons in the charnockites from the eastern periphery of the imsz within the western margin of the tnco in combination with similar ages reported in recent studies from zircons in magmatic complexes within the imsz suggest a prolonged history of subduction related arc magmatism and accretionary tectonics analogous to those in some of the phanerozoic belts such as the central asian orogenic belt and the western pacific subsequent progressive collision and suturing of the continental blocks were accompanied by the exhumation of high pressure hp and uht metamorphic rocks the available data from the imsz and tnco suggest long lived convergent margins associated with the southward subduction of the yinshan block and westward subduction of the eastern block in a double sided subduction realm prior to the final amalgamation of the ncc and its incorporation within the columbia supercontinent in the late paleoproterozoic

tappania bearing association of the siberian platform biodiversity stratigraphic position and geochronological constraints abstract a new fossil microbiota yielding eukaryotic tappania is described from the mesoproterozoic kamo group of the central angara basin siberian craton the assemblage also includes valeria satka lophosphaeridium pulvinosphaeridium miroedichia osculosphaera tasmanites obruchevella glomovertella as well as branching and anastomosing filamentous microfossils of putative fungal affinities and peculiar short trichomes that together substantially increase the biodiversity of the tappania association stratigraphic position and geochronological constraints indicate a relatively young late mesoproterozoic age of the tappania bearing sediments there appears to be a continuity between the tappania association and the neoproterozoic microbiota the latter being firmly rooted in the late mesoproterozoic

biostratigraphic and chemostratigraphic constraints on the age of early neoproterozoic carbonate successions in north china abstract thick carbonate successions of proterozoic age were deposited in the huaibei and huainan regions along the southern margin of the north china block these successions including the huaibei group in the huaibei region and the huainan and feishui groups in the huainan region have been correlated with the qingbaikou group which outcrops in the jixian area of north china and is the eponymous succession of the qingbaikouan system traditionally regarded as 1000 800 ma recently it has been shown that lower qingbaikouan strata in the jixian area may be as old as 1300 1400 ma by correlation the huaibei huainan and feishui groups may include mesoproterozoic strata but these units have also been interpreted as tonian or cryogenian ediacaran cambrian in age these contradictory age interpretations hamper our ability to explore the rich paleontological and sedimentary records preserved in these rocks and to assess paleogeographic reconstructions in this report we describe new microfossils and stable isotope data 13ccarb 18ocarb 34scas from the huaibei huainan and feishui groups possible vase shaped microfossils from the jiayuan formation of the lower huaibei group and characteristic early neoproterozoic acritarchs particularly trachyhystrichosphaera aimika from the gouhou and liulaobei formations are consistent with a tonian age for the huaibei and huainan groups similarly carbon isotope trends in the huaibei huainan and feishui groups are comparable with tonian 13ccarb patterns in south australia and laurentia with a plateau of moderately positive 1 5 values followed by pronounced negative 13ccarb excursion in the gouhou formation which may be equivalent to the bitter springs anomaly in south australia 34scas values of the huaibei group are mostly 25 40 similar to values from the stratigraphically equivalent jingeryu formation in the jixian area overall the combination of biostratigraphic chemostratigraphic and available radiometric data suggests that the huaibei huainan and feishui groups are early neoproterozoic tonian in age

740 ma vase shaped microfossils from yukon canada implications for neoproterozoic chronology and biostratigraphy biostratigraphy underpins the phanerozoic time scale but its application to pre ediacaran strata has remained limited because proterozoic taxa commonly have long or unknown stratigraphic ranges poorly understood taphonomic constraints and or inadequate geochronological context here we report the discovery of abundant vase shaped microfossils from the callison lake dolostone of the coal creek inlier yukon canada that highlight the potential for biostratigraphic correlation of neoproterozoic successions using species level assemblage zones of limited duration the fossiliferous horizon dated here by re os geochronology at 739 9 6 1 ma shares multiple species level taxa with a well characterized assemblage from the chuar group of the grand canyon arizona usa dated by u pb on zircon from an interbedded tuff at 742 6 ma the overlapping age and species assemblages from these two deposits suggest biostratigraphic utility at least within neoproterozoic basins of laurentia and perhaps globally the new re os age also confirms the timing of the islay 13ccarbonate anomaly in northwestern canada which predates the onset of the sturtian glaciation by 15 m y together these data provide global calibration of sedimentary paleontological and geochemical records on the eve of profound environmental and evolutionary change

possible early foraminiferans in post sturtian 716 635 ma cap carbonates foraminifera are an ecologically important group of modern heterotrophic amoeboid eukaryotes whose naked and testate ancestors are thought to have evolved 1 ga ago however the single chambered agglutinated tests of these protists appear in the fossil record only after ca 580 ma coinciding with the appearance of macroscopic and mineralized animals here we report the discovery of small slender tubular microfossils in the sturtian ca 716 635 ma cap carbonate of the rasthof formation in namibia the tubes are 200 1300 m long and 20 70 m wide and preserve apertures and variably wide lumens folds constrictions and ridges their sometimes flexible walls are composed of carbonaceous material and detrital minerals this combination of morphologic and compositional characters is also present in some species of modern single chambered agglutinated tubular foraminiferans and is not found in other agglutinated eukaryotes the preservation of possible early foraminifera in the carbonate rocks deposited in the immediate aftermath of sturtian low latitude glaciation indicates that various morphologically modern protists thrived in microbially dominated ecosystems and contributed to the cycling of carbon in neoproterozoic oceans much before the rise of complex animals

the survival of benthic macroscopic phototrophs on a neoproterozoic snowball earth the greatest ice ages in earth s history occurred during the 654 635 ma marinoan glaciation when glaciers reached tropical oceans and our planet approached a snowball earth condition paleontological and genomic data suggest that several eukaryotic groups must have survived the marinoan glaciation but their fossil record is scarce and limited to microbes whose ecological and physiological ranges are poorly constrained thus hampering a full understanding of how and where eukaryotic life particularly macroscopic phototrophs survived this snowball earth here we report carbonaceous compression fossils from the marinoan age nantuo formation in south china these fossils are preserved in thin black shales sandwiched between glacial diamictites deposited in inner shelf environments of the mid latitudinal yangtze block some of these fossils are interpreted as benthic macroalgae thus the marinoan glaciation must have been punctuated by episodes of open waters where habitable benthic substrates were available in the photic zone and along the coast of mid latitudinal continents such open waters may have been the refugia where macroscopic phototrophs survived the marinoan glaciation and subsequently diversified in the early ediacaran period

extremely low oxygen concentration in mid proterozoic shallow seawaters abstract the mid proterozoic 1 8 0 8 ga witnessed the first appearance but unusually low diversification of eukaryotes the stagnant biotic evolution during this billion year long period commonly referred to as the boring billion was arguably ascribed to low oxygen levels in atmosphere and ocean however evidence supporting low oxygen in shallow marine environments where early eukaryotes first evolved is generally lacking or insufficient here we report rare earth element and yttrium ree y data particularly cerium ce anomalies from a suite of mid proterozoic sedimentary rocks of the north china platform the new data from north china in combination with available ce anomaly data from other proterozoic successions demonstrate that during mid proterozoic negative ce anomalies did not occur until 1 54 ga and after 1 54 ga only episodic negative ce anomalies were present in shallow water carbonates trace element enrichments u ef v ef and mo ef remained at the average continental crust level before 1 54 ga but showed a sudden increase at 1 54 ga the data suggest that oxygen concentration in shallow marine environments of the mid proterozoic ocean was extremely low probably

biotic turnover driven by eutrophication before the sturtian low latitude glaciation a dramatic oceanic biotic shift from eukaryotic phytoplankton to bacteria occurred about 740 million years ago microfossil and geochemical data from the chuar group in the southwestern united states link this biotic turnover to widespread eutrophication of surface waters reconstructions of the diversity of precambrian microorganisms suggest a pronounced biotic turnover coinciding with the onset of neoproterozoic low latitude glaciation in which diverse assemblages of organic walled microfossils known as acritarchs were replaced by assemblages of simple smooth walled forms called leiosphaerids and the remnants of bacterial blooms1 2 3 4 this turnover has been interpreted as the mass extinction of eukaryotic phytoplankton1 2 3 4 and the subsequent proliferation of bacteria5 however the causes of this mass extinction and its exact temporal relationship to the glaciations remain unclear1 2 3 4 here we present palaeontological data from the 742 6 myr old chuar group from arizona which indicate that the biotic turnover occurred before the first low latitude sturtian glaciation constrained to be between 726 and 660 myr in age6 in our record the turnover is associated with the appearance of abundant and diverse protozoan fossils and a shift to rising total organic carbon suggestive of increased primary productivity spurred by the influx of nutrients this is followed by an increase in the ratio of highly reactive iron to total iron which we interpret as persistent water column anoxia we therefore conclude that the biotic turnover recorded in the chuar group was driven by widespread eutrophication of surface waters rather than low latitude glaciation

modification of a rare earth element deposit by low temperature partial melting during metamorphic overprinting norra karr alkaline complex southern sweden abstract rare earth elements play a crucial role in modern technologies and are necessary for a transition to a green economy potentially economic deposits of these elements are typically hosted in minerals such as monazite bastnasite and eudialyte a complex na ca fe zr silicate mineral with cl making these prime targets for geological research globally rare earth mineral deposits commonly show evidence of polyphase development and mineralisation processes which need to be better understood to improve exploration strategies the norra karr alkaline complex sweden contains a globally significant deposit of rare earth elements hosted in the mineral eudialyte in this study we focussed on eudialyte crystals in undeformed cross cutting pegmatoid veins from norra karr in order to determine their age we refined an established micromilling method to enable sampling of minerals rich in rare earth elements for precise analysis of major and trace elements nd isotope ratios and sm nd geochronology down to a scale of

variations in the abundance of photosynthetic oxygen through precambrian and paleozoic time in relation to biotic evolution and mass extinctions evidence from mn fe ratios abstract this paper reports new information about variations in the abundance of photosynthetic oxygen through precambrian and paleozoic time non detrital marine sediments cherts limestones and dolomite were analysed for nh2oh hcl acetic acid extractable mn and fe and the mn fe ratio a proxy for the oxidation reduction potential of the sediment at the time of deposition was plotted against geologic age the method has never before been applied to ancient sediments but previously published data produced independently by other methods confirmed its applicability and underlying assumptions the mn fe ratio was unexpectedly high ca 3 416 ga implying localised oxidation due to oxygen production by cyanobacteria but fell dramatically over the interval 3 416 3 298 ga suggesting mass mortality or mass extinction of early archaean cyanobacteria owing to asteroid impacts however the ratio increased continuously though at episodically varying rates from a minimum at 1 8783 ga to a maximum at 0 680 ga signifying accumulation of oxygen in the atmosphere and hydrosphere the rate of increase was relatively high at first but dropped abruptly at some point during the interval 1 8783 1 6 ga possibly signalling the appearance of eukaryotic herbivores the ratio increased exponentially from 1 6 to 0 8 ga and then rose more rapidly from 0 8 to 0 680 ga indicating a late proterozoic upsurge of oxygen production whereupon it fell catastrophically to a minimum in the cambrian reflecting widespread anoxia due to mass extinction of ediacaran organisms the crisis at the precambrian cambrian boundary was followed by a logarithmic increase from the cambrian to the permian indicating a resurgence of photosynthetic activity

high order line elements in modeling two dimensional groundwater flow this paper presents a new analytic element formulation for high order line elements in modeling two dimensional groundwater flow these elements are line doublets line dipoles and line sinks the jump functions for line elements are expressed as chebyshev series the unknown coefficients are computed by applying the principle of overspecification to the boundary conditions the use of the high order elements and the principle of overspecification have resulted in high precision and significant improvements in computational efficiency compared to the existing collocation based formulation the new formulation is currently being used in the development of the metropolitan area groundwater model for twin cities minnesota usa and for enhancements of the next release of national groundwater model for the netherlands

organic walled microfossils from the proterozoic thule supergroup northwest greenland abstract the proterozoic rocks of the intracratonic thule basin on the northern margin of the canadian greenlandic shield have recently been referred to as the thule supergroup the succession comprises unmetamorphosed unfolded sedimentary and magmatic rocks which are with few exceptions not deformed five groups have been defined and fine grained siliciclastic samples from the uppermost three baffin bay dundas and narss rssuk groups yielded moderately well preserved acanthomorphic and non acanthomorphic acritarchs prasinophytes and filamentous microfossils the age of the supergroup is quite poorly constrained at the base by a 1268 ma basaltic sill and at the top by a basic dyke swarm with a k ar age range between 630 and 725 ma that cuts the entire succession biostratigraphical studies further constrain the age of the thule supergroup and suggest that the succession is of a late mesoproterozoic earliest neoproterozoic age this age assignment is corroborated by independent stable isotope data and correlation with the bylot supergroup to the south this leads us to propose that the thule supergroup was deposited between c 1300 and c 1200 ma microfossil taxa previously interpreted as exclusively occurring in pre varangerian neoproterozoic rocks i e simia annulare jankauskas tasmanites rifejicus jankauskas and possibly vandalosphaeridium varangeri vidal are consequently re evaluated process bearing acritarchs herein attributed under open nomenclature to comasphaeridium sp trachyhystrichosphaera truncata and vandalosphaeridium sp are of special palaeobiological importance since acanthomorphic acritarchs have rarely been reported from pre neoproterozoic successions

microbiotas from the late proterozoic chuar group northern arizona and uinta mountain group utah and their chronostratigraphic implications abstract samples of shales from the dominantly clastic upper proterozoic chuar and uinta mountain groups in northern arizona and utah yielded relatively abundant assemblages of acritarchs these are taxonomically varied and are interpreted as consisting of openwater cosmopolitan eukaryotic plankton the assemblages are compared with late proterozoic late riphean and early vendian c 800 700 ma sequences in the southern urals of the ussr the russian platform northern and southern scandinavia svalbard and east and north west greenland in all instances both the assemblages and discrete form taxa predate the varangerian vendian glacial event of the north atlantic region and this is taken to indicate a comparable age for glaciogenic rock units in western north america one new acritarch species vandalosphaeridium walcottii is erected and the partly megascopic species chuaria circularis is emended

marine redox conditions in the middle proterozoic ocean and isotopic constraints on authigenic carbonate formation insights from the chuanlinggou formation yanshan basin north china abstract to improve our understanding of ocean chemistry and biogeochemical cycling following the termination of large scale paleoproterozoic iron formation if deposition 1 85 billion years ago ga we conducted a fe s c mo geochemical study of the 1 65 ga chuanlinggou formation yanshan basin north china despite the cessation of if deposition our results suggest the presence of anoxic but non euxinic ferruginous conditions persisted below the surface mixed layer for the deepest portion of the continental rifting basin and that this pattern is apparently independent of the local organic carbon content however our paired s isotope data of carbonate associated sulfate and pyrite suggest presence of sulfate in pore fluids which is not consistent with insufficient sulfate for bacterial sulfate reduction in the water column despite evidence for deposition under anoxic conditions sedimentary molybdenum mo concentrations are mostly not enriched relative to average continental crust this relationship is consistent with the notion that sulfide dominated conditions in the water column and or the sediments are required for mo enrichment and validates past assertions that mo enrichment patterns in ancient shales track both the local presence and global distribution of euxinia specifically in addition we identified extensive diagenetic carbonate precipitation in the upper chuanlinggou formation with only moderately negative 13 c values 3 4 1 4 we propose with support from a numerical model that these diagenetic carbon isotope values were most likely derived from precipitation of carbonates dominantly in the methanic zone within the sediments diagenetic carbonate precipitation in the methanic zone is likely to have been more extensive in the proterozoic than the phanerozoic due to porewater oxidant limitation

chemostratigraphy of the shaler supergroup victoria island nw canada a record of ocean composition prior to the cryogenian glaciations a b s t r a c t a new 13 ccarb curve combined with 13 corg values is presented for the upper shaler supergroup 900 to 720 ma amundsen basin northwestern canada the dataset fills gaps in the existing stratigraphic record and makes correlations with adjacent basins more robust there is a pronounced negative 13 c excursion in the wynniatt formation that can be correlated with a putative worldwide negative car bon isotope excursion namely the bitter springs stage however in the amundsen basin the 13 ccarb excursion drops to anomalously negative values 14 which we attribute to local overprints wherein isotopically light carbon in pore waters released by oxidation of methane and organic matter during sulphate and iron reduction was incorporated into authigenic carbonate cement we document basin euxinia and anoxia during the same time interval using a multi proxy approach specifically fe speciation and redox sensitive trace metal data patterns of pronounced enrichment in mo v and u concentrations in euxinic black shales suggest that the bitter springs stage was a transitional period in earth s redox evo lution from the more reduced global oceans during the mid proterozoic to the more oxygenated oceans during the phanerozoic 2015 elsevier b v all rights reserved

morphologically diverse vase shaped microfossils from the russoya member elbobreen formation in spitsbergen abstract vase shaped microfossils vsms constitute a distinct group of fossils characteristic of late tonian marine rocks they often occur in high densities and in relatively diverse assemblages that include several morphotypes all vsms may have shared a test wall of similar structure and composition as inferred from common patterns of preservation however little is known about the detailed morphology and structure of this wall here we examine the diversity preservation and wall morphology of a diverse assemblage of vsms from the russoya member of the elbobreen formation in northeastern spitsbergen sem imaging of exceptionally preserved specimens with their wall replicated in iron oxide reveals that these vsms shared a well defined smooth micrometre thick wall ornamented with complex structures including facets closed pores and intricate relief patterns on the internal surface of the aperture the observed similarities among different morphotypes suggest vsms assemblages reflect the diversification of a single clade likely related to the arcellinida amoebozoa an extant order to which they have been phylogenetically linked

a complex microbiota from snowball earth times microfossils from the neoproterozoic kingston peak formation death valley usa a thin carbonate unit associated with a sturtian age 750 700 million years ago glaciogenic diamictite of the neoproterozoic kingston peak formation eastern california contains microfossil evidence of a once thriving prokaryotic and eukaryotic microbial community preserved in chert and carbonate stratiform stromatolites oncoids and rare columnar stromatolites also occur the microbial fossils which include putative autotrophic and heterotrophic eukaryotes are similar to those found in chert in the underlying preglacial units they indicate that microbial life adapted to shallow water carbonate environments did not suffer the significant extinction postulated for this phase of low latitude glaciation and that trophic complexity survived through snowball earth times

paleontology of proterozoic shales and mudstones examples from the belt supergroup chuar group and pahrump group western usa abstract proterozoic black shales and other fine grained siliciclastic rocks contain a variety of fossils these fossils are illustrated by examples from three proterozoic units in the western usa the belt supergroup middle proterozoic the chuar group late proterozoic and the upper pahrump group late proterozoic a variety of microfossils and megafossils occur in the belt supergroup western montana acritarchs and filamentous microfossils are moderately well preserved in sub greenschist facies black shale in the little belt mountains the biologic affinity of the acritarchs is uncertain they could represent the vegetative or encystment stage of eukaryotic algae or the outer envelope of colonial coccoid cyanobacteria most of the filaments in these shales are of a size and morphology that is consistent with prokaryotic affinities however rare 20 and 40 m wide filaments could be either prokaryotic or eukaryotic higher grade sub greenschist facies dark gray to black mudstones in glacier national park contain poorly preserved acritarchs and spheroidal and filamentous pseudomicrofossils they are of interest because they provide information useful for distinguishing authentic microfossils from pseudofossils in mudstones and shales that have undergone substantial burial metamorphism several authentic megafossils occur in lower belt shales in the little belt and big belt mountains montana one of these is the carbonaceous compression beltina danai which could represent either fragments of a microbial mat or fragments of a sheet like megascopic alga the megafossil grypania spiralis has the form of a coiled ribbon and tentatively is interpreted as a megascopic alga green to purple mudstones and muddy sandstones in the lower belt supergroup in glacier national park contain markings that resemble a string of beads they are interpreted as megafossils that may have eukaryotic algal affinities black shales in the late proterozoic kwagunt formation chuar group grand canyon arizona contain a variety of acritarchs and filamentous microfossils of special interest is the vase shaped microfossil melanocyrillium which is interpreted as the sporangium of a eukaryotic and probably megascopic alga melanocyrillium also occurs in black mudstone in the late proterozoic pahrump group southeastern california

thick sulfate evaporite accumulations marking a mid neoproterozoic oxygenation event ten stone formation northwest territories canada thick sulfate evaporite accumulations are absent from proterozoic strata between ca 2000 and ca 1000 ma and detailed sedimentologic stratigraphic and geochemical data for the oldest neoproterozoic thick marine sulfate evaporite successions are largely lacking the middle neoproterozoic ten stone formation little dal group northwest territories canada consists of 500 m of pelagic lagoonal gypsite and anhydritite rocks consisting of the minerals gypsum and anhydrite deposited shortly before the ca 811 ma bitter springs carbon isotope anomaly in an intracratonic basin that developed prior to breakup of rodinia the thickness of regional stratigraphic subdivisions of this formation defined by subtle silt and carbonate bearing intervals indicates a minor terrigenous source in the southeast and a silled connection to the open ocean in the northwest deposition of the ten stone formation began with abrupt tectonically triggered subsidence and restriction and ended equally abruptly as shown by stratigraphic contacts across which lithofacies corresponding to strikingly different paleoenvironments change sharply with no evidence for hiatus or erosion stratigraphic cyclicity in the evaporite succession is minimal owing to isolation of bottom hugging dense lagoonal brine from overlying waters deposition of the ten stone formation in a basin that experienced intermittent basin scale tectonic adjustments as recorded by details of its stratigraphy supports the interpretation that the mackenzie mountains supergroup accumulated in an extensional tectonically active intracratonic basin whose structure resembled a lower plate extensional system the absence of halite from the ten stone formation contrasts with its abundance in the stratigraphically lower gypsum free dodo creek formation suggesting that deposition of the lower to middle little dal group spanned a major oxygenation event during which the sequence of evaporite mineral precipitation from seawater changed from halite first to sulfate first in response to rapid accumulation of atmospheric oxygen and concomitant increase in the global marine sulfate reservoir the limited range of sulfur isotope values in a new data set spanning hundreds of meters of gypsite indicates a strongly and persistently oxidizing mid neoproterozoic atmosphere an abundance of sulfate in seawater and marine oxygenation extending below storm wave base the mineralogy sedimentology stratigraphy and geochemistry of the ten stone formation are virtually indistinguishable from those of thick phanerozoic deep water below wave base evaporite successions and indicate that the tectonic climatic and geochemical conditions required for deposition of thick successions of marine sulfate evaporites were well established prior to ca 811 ma thick sulfate evaporite successions in equivalent stratigraphic positions just below the bitter springs carbon isotope excursion elsewhere in laurentia as well as on the congo craton and in south australia attest to the global impact of the rapidly increased seawater sulfate reservoir prior to rodinia s breakup high relative burial rates of organic matter prevailed before the breakup of rodinia and led to oxygenation of the atmosphere ocean system growth of the seawater sulfate reservoir and in association with a warm and arid climate deposition for the first time in earth s history of thick sulfate evaporites in the middle neoproterozoic 100 m y before the first cryogenian glacial episode the neoproterozoic oxygenation event may have taken place in several steps the first of which preceded the bitter springs anomaly

macroscopic worm like body fossils from the upper precambrian 900 700 ma huainan district anhui china and their stratigraphic and evolutionary significance abstract abundant and varied macroscopic worm like body fossils from the late precambrian liulaobei formation huainan group and the jiuliqiao formation feishui group in the huainan district northern anhui province china are further investigated through this progress report after the initial discovery by zheng wenwu and a recent study by wang guixiang sinosabellidites zheng in the liulaobei formation is a worm like organism of questionable metazoan origin it has merely a superficial resemblance with the tubes of late vendian early cambrian true sabelliditida but has much in common with the accompanying macroscopic algal remains of tawuia hofmann both pararenicola wang and protoarenicola wang are representatives of primitive worm like animals in the jiuliqiao formation their macroscopic size elongate cylindrical body anterior aperture and apparatus prominent and elastic annulations are characteristic for their metazoan origin although they lack sufficient evidence for their definite relationship with any known kind of living worms the liulaobei formation and the jiuliqiao formation are dated at about 850 ma and 740 ma respectively regional geology and stratigraphic correlation and the occurrence of the distinctive chuaria tawuia assemblage suggest a time range between less than 900 ma and over 700 ma for the whole shallow water marine sedimentary sequence of the huainan and feishui groups this latter group is disconformably covered by the drop stone facies diamictites and tillites of the late precambrian luoquan glaciation apart from the enigmatic sinosabellidites both pararenicola and protoarenicola are claimed to be the oldest multicellular animals so far discovered in the world and the first reliable evidence for the pre ediacarian evolutionary history of manifest metazoan life

microfossils from the lower mesoproterozoic kaltasy formation east european platform abstract basinal shales of the lower mesoproterozoic kaltasy formation sampled from three boreholes drilled into the southeastern east european platform russia contain abundant and moderately well preserved microfossils 34 distinct entities have been identified most assigned to simple sphaeromorphic or small filamentous taxa found widely and characterized by long stratigraphic ranges ornamented microfossils found in coastal successions of other lower mesoproterozoic basins are absent but large filamentous microfossils interpreted as possible benthic photosynthetic eukaryotes are recorded drawing comparisons to relatively deep water shales in siberia in overall aspect the kaltasy microfossils are consistent with other broadly coeval assemblages but they highlight the importance of environment as well as age in determining the distributions of remains that record the early diversification of marine eukaryotes rectia magna is described as a new species

early neoproterozoic sequence stratigraphy and acritarch biostratigraphy eastern officer basin south australia abstract the early neoproterozoic torrensian latest tonian 800 750 ma succession in the central and eastern officer basin was deposited in an intra cratonic rift basin the outcropping pindyin sandstone consists of basal lowstand conglomerate and upward fining transgressive sandstone and is conformably overlain by marine highstand shale of the alinya formation in the giles 1 well the pindyin sandstone contains aeolian to fluvial deposits and is overlain by peritidal and sabkha sediments of the alinya formation seismic interpretation suggests that the succession is thin on the murnaroo platform and thickens toward the munyarai trough the two sedimentary provinces are separated by the ungoolya hinge which probably marks the southeastern margin of the fraser musgrave fold belt highstand organic rich shale in the alinya formation is probably an important petroleum source rock acritarchs occur in both chert and shale in the alinya formation and their distribution was probably controlled by sedimentary environments similar assemblages from outcrop and subsurface provide a reliable evidence for regional correlation the assemblages in giles 1 are dominated by benthic coccoids and contain many distinct spinose acritarchs which are particularly abundant in the subtidal grey shale whereas mainly phytoplankton is present in the chert the assemblage represented by trachyhystrichosphaera vidalii t aimica cymatiosphaeroides kullingii can be used for global correlation in the early neoproterozoic the abundant microfossils from the alinya formation and equivalent beds around the world probably indicate a microorganism explosion at 750 800 ma prior to the neoproterozoic glaciations thirty seven acritarchs spheroids and seven cyanobacterial filaments are briefly described in this study including 5 new species comasphaeridium tonium eoentophysalis gilesis goniosphaeridium alinyum gorgonisphaeridium pindyium and gorgonisphaeridium torrensium and a newly combined species archaeoellipsoides karatavicus comb nov

microbial fossils from the kheinjua formation middle proterozoic semri group lower vindhyan son valley area central india abstract abundant coccoid and filamentous microfossils are found in petrographic thin sections of stratiform stromatolitic cherts from the 1200 ma old fawn limestone of the kheinjua formation lower vindhyan supergroup central india the assemblages is dominated by coccoid forms of probable chroococcacean and entophysalidacean affinities most filaments closely resemble the oscillatoriacean gunflintia minuta unlike other middle to late proterozoic stromatolitic microbiotas the kheinjua is dominated by microfossils taxonomically the kheinjua microbiota most closely resembles proterozoic microbiotas described from the belcher islands kasegalik formation mcarthur group bitter springs formation and the yudoma suite the following taxa are formally described chroococcaceae myxococcoides minor schopf eosynechococcus isolatus n sp tetraphycus congregatus n sp kheinjuasphaera vulgaris n gen n sp glenobotrydion aenigmatis schopf melasmatosphaera media hofmann entophysalidaceae eoentophysalis belcherensis hofmann e magna n sp oscillatoriaceae cf gunflinta minuta barghoorn eomycetopsis siberiensis lo

early neoproterozoic scale microfossils in the lower tindir group of alaska and the yukon territory the tindir group is a 4 km thick neoproterozoic succession exposed in the tatonduk inlier of east central alaska and the western yukon territory the tindir group is informally divided into the lower tindir group which consists of 2 km of mixed carbonate and clastic rocks and the overlying upper tindir group which contains two cryogenian glacial deposits and an additional ediacaran succession of mixed carbonate and clastic strata unique mineralized scale microfossils have been recovered from sections previously correlated with the upper tindir group and interpreted variously as cryogenian to early cambrian in age our remapping of the area indicates that these sections are stratigraphically below an early cryogenian glacial diamictite unit 2 of the upper tindir group and are actually part of the lower tindir group carbon and strontium isotope correlations further suggest that the fossiliferous lower tindir group is correlative with early neoproterozoic strata of the northwestern canadian cordillera this new age model is consistent with the accompanying microfossil assemblage and indicates that the diverse microfossils in the lower tindir group can be added to the early neoproterozoic record of eukaryotic evolution

analytic elements for flow in harmonically heterogeneous aquifers 1 existing implementations of the analytic element method aem for simulating groundwater flow rely upon a zonal representation of hydraulic conductivity where the conductivity is piecewise constant within the modeled domain using a dependent variable transformation the analytic element method is extended to simulate two dimensional groundwater flow through smoothly heterogeneous media represented using pilot points that is the conductivity field is interpolated between a set of locations with specified conductivity this new implementation maintains the existing attributes of aem solutions the governing equation is met exactly within the domain and boundary continuity conditions are met with extremely high precision all without volumetric discretization a number of test cases are used to demonstrate and evaluate the efficacy of the new method

co evolution of eukaryotes and ocean oxygenation in the neoproterozoic era the oxygenation of the earth s deep oceans is often thought to have triggered the evolution of simple animals a review article proposes that instead the evolution of animal life set off a series of biogeochemical feedbacks that promoted the oxygenation of the deep sea

benthic perspective on earth s oldest evidence for oxygenic photosynthesis the great oxidation event goe is currently viewed as a protracted process during which atmospheric oxygen increased above 10 5 times the present atmospheric level pal this threshold represents an estimated upper limit for sulfur isotope mass independent fractionation s mif an archean signature of atmospheric anoxia that begins to disappear from the rock record at 2 45 ga however an increasing number of papers have suggested that the timing for oxidative continental weathering and by conventional thinking the onset of atmospheric oxygenation was hundreds of million years earlier than previously thought despite the presence of s mif we suggest that this apparent discrepancy can be resolved by the earliest oxidative weathering reactions occurring in benthic and soil environments at profound redox disequilibrium with the atmosphere such as biological soil crusts and freshwater microbial mats covering riverbed lacustrine and estuarine sediments we calculate that oxygenic photosynthesis in these millimeter thick ecosystems provides sufficient oxidizing equivalents to mobilize sulfate and redox sensitive trace metals from land to the oceans while the atmosphere itself remained anoxic with its attendant s mif signature as continental freeboard increased significantly between 3 0 and 2 5 ga the chemical and isotopic signatures of benthic oxidative weathering would have become more globally significant from a mass balance perspective these observations help reconcile evidence for pre goe oxidative weathering with the history of atmospheric chemistry and support the plausible antiquity of a terrestrial biosphere populated by cyanobacteria well before the goe

analytic elements for multiaquifer flow abstract the objective of this paper is to present an analytic element formulation for groundwater flow in multiaquifer systems analytic element equations are presented for wells line sinks and circular infiltration areas each analytic element is a solution to the governing system of differential equations and thus simulates the leakage between aquifers exactly the head discharge and leakage may be computed analytically at any point in the aquifer superposition of these analytic elements allows for the simulation of regional multiaquifer flow a hypothetical example is presented of a system with three aquifers a river network and three pumping wells it is demonstrated that the leakage between aquifers may vary significantly over short distances and that each aquifer has its own water divide

thermohaline steps induced by melting of the erebus glacier tongue a vertically stable step like thermohaline structure is observed throughout a continuous 400 m conductivity temperature depth ctd profile taken near the erebus glacier tongue mcmurdo sound antarctica the pattern is best developed between the sea surface and 250 m depth the interval corresponding to that of the irregular underwater profile of the glacier tongue the steps average 17 m in thickness and typically display discontinuities of 0 1 c in temperature 0 04 in salinity and 3 5 10 4 g cm 3 in density the observations are compared with theory and laboratory experiments of cell development and lateral flow near ice melting into vertically stratified salt water at this location subsurface seawater is inferred to remain above the in situ freezing point year round and contains sufficient heat to account for much of the glacier tongue thinning by basal melting an adequate volume of meltwater would result to produce the measured salinity steps we discuss related observations and some implications of this process for ocean circulation and biological productivity in the antarctic

phosphate biomineralization in mid neoproterozoic protists the origin and expansion of biomineralization in eukaryotes played a critical role in earth history linking biological and geochemical processes however the onset of this phenomenon is poorly constrained due to a limited early fossil record of biomineralization although macroscopic evidence for biomineralization is not known until the late ediacaran we here report biologically controlled phosphatic biomineralization of scale microfossils from mid neoproterozoic pre sturtian strata of northwest canada primary biological control on mineralization is supported by the identification of apatite in both chert hosted and limestone hosted specimens the conspicuously rigid original morphology of the scale microfossils relative to co occurring organic walled cyanobacteria and acritarchs and the microstructure of the constituent phosphate cell enveloping mineralized scales occur in a wide range of extant protists but the apparent restriction of phosphate scales to one modern taxon of green algae suggests a possible affiliation for these fossils documentation of primary phosphate biomineralization in fifteenmile group yukon territory canada microfossils greatly extends the known record of biologically controlled mineralization and provides a unique window into the diversity of early eukaryotes

the effect of rising atmospheric oxygen on carbon and sulfur isotope anomalies in the neoproterozoic johnnie formation death valley usa abstract carbonates within the rainstorm member in the terminal neoproterozoic johnnie formation of death valley california record a remarkable negative carbon isotope anomaly to a nadir of near 11 that accompanies a dramatic rise in trace sulfate abundance and fall of carbonate associated sulfate 34 s values the carbonates including the laterally extensive johnnie oolite were deposited during marine flooding atop a sequence boundary best observed in cratonward sections the 12 c rich alkalinity delivered to the seawater pool was likely associated with a dramatic rise in atmospheric o 2 which resulted in 1 the oxidation of exposed continental shelf sediments rich in fossil organic matter and sulfides and 2 the ventilation of the oceans similar carbon isotope anomalies are recorded in broadly equivalent successions that post date known marinoan glacial deposits and pre date the precambrian cambrian boundary in oman india china australia and namibia supporting the view that the oxygenation event was global thus the biogeochemical anomaly post dates the last widely recognized neoproterozoic ice age but is nonetheless associated with sea level drawdown that is likely to be eustatic in origin the radiation of a high diversity microbiota and the first appearance of large metazoan fossils ediacaran animals follow this carbon isotope anomaly suggesting that a critical threshold with respect to atmospheric o 2 had been crossed by this time a negative excursion of similar magnitude occurs in overlying strata at the precambrian cambrian boundary which likely reflects similar processes

high resolution δ13c stratigraphy of the chuar group ca 770 742 ma grand canyon implications for mid neoproterozoic climate change a high resolution c isotope record based on 13 c org from organic rich shales and 13 c carb from dolomites in the ca 770 742 ma chuar group provides important new data for evaluating the signifi cance of large magnitude c isotope anomalies in neoproterozoic climate change three successive large magnitude isotopic excursions 8 15 are interpreted to represent primary seawater values based on a series of diagenetic tests and they are not associated with evidence of signifi cant long term 10 6 10 7 m y sea level change nor glaciomarine deposits intrabasinal correlation of 13 c org values suggests that most chuar shales record primary values and is consistent with previously reported h c ratios of 0 49 indicating that chuar shales experienced minimal thermal alteration although some chuar dolomites reveal early diagenetic alteration their 13 c dol values typically fall near those of coeval least altered dolomites or organic rich shales relative to dolomite values the chuar carbon record is interpreted to refl ect predominantly primary organic carbon 13 c values and contains suf