neoproterozoic snowball earth simulations with a coupled climate ice sheet model ice sheets may have reached the equator in the late proterozoic era 600 800 myr ago according to geological and palaeomagnetic studies possibly resulting in a snowball earth but this period was a critical time in the evolution of multicellular animals posing the question of how early life survived under such environmental stress here we present computer simulations of this unusual climate stage with a coupled climate ice sheet model to simulate a snowball earth we use only a reduction in the solar constant compared to present day conditions and we keep atmospheric co2 concentrations near present levels we find rapid transitions into and out of full glaciation that are consistent with the geological evidence when we combine these results with a general circulation model some of the simulations result in an equatorial belt of open water that may have provided a refugium for multicellular animals

fossils or sedimentary structures carbonaceous spheroids from the shale of the cryogenian nantuo formation in shengnongjia area south china abstract black shale of the cryogenian nantuo formation shennongjia area south china contains spheroids which co occur with fossils of macroalgae these three dimensional structures occur sparsely as isolated specimens or abundantly as clusters which show different types of boundaries between individuals they are generally circular on bedding surfaces and elliptical on transecting sections and range up to several millimeters in diameter both petrographic thin sections and scanning electron microscopy sem reveal that these spheroids are mostly organic carbon in composition and exhibit sharp well rounded external margins composed of microcrystalline clay minerals the carbonaceous nature of these spheroids and different elemental abundances between spheroids and matrix are also confirmed by raman spectroscopy and energy dispersive x ray spectroscopy eds organic carbon isotopic values of individual spheroids range from 28 55 to 28 83 with an average of 28 72 which show indistinguishable 13corg values with the surrounding sedimentary matrix but exhibit statistically significant difference to those of contemporaneous macroalgae a range of physical origins for these spheroids including concretions fluid escape structures raindrop impressions or bubble impressions are considered and cannot be entirely rejected alternatively biogenic origin is also a possible interpretation from observations of their morphological mineralogical geochemical and sedimentological characteristics although their nature remains unresolved the documentation of these new carbonaceous spheroids from the nantuo formation of shennongjia area adds to a growing list of fossil like structure records in the cryogenian period

marinoan aged red beds at shennongjia south china evidence against global scale glaciation during the cryogenian abstract the continuous existence of the marinoan ice age a late cryogenian panglaciation snowball earth is challenged by the occurrences of widespread glacial marine and nonglacial deposits consisting of stratified diamictite laminated siltstone and claystone and even carbonates which indicate an episode of partial deglaciation red beds that commonly accompany these glacial marine and nonglacial deposits have not received enough attention to date the middle nantuo formation of the cryogenian marinoan epoch in the sanshengtai section shennongjia area is composed of 6 lithofacies i e green massive diamictite green laminated lithic feldspar wacke green laminated siltstone and claystone red laminated lithic feldspar wacke red crudely stratified diamictite and red laminated siltstone among them the last three constitute the red beds and are interpreted as glacial lacustrine and nonglacial deposits which can be found and roughly correlated across several continents high fe2o3 and low ce ce values in the red beds suggest a probable association between the formation of red beds and the neoproterozoic oxygenation events coincidences between the occurrences of red beds and high values of al na ti na and chemical index of alteration cia indicate the favorability of warm intervals with high weathering intensities for the formation of red beds whose presence indicates partial deglaciation during the marinoan ice age and provides a new clue to contradict the worldwide snowball earth hypothesis

the age of the nantuo formation and nantuo glaciation in south china a u pb sensitive high resolution ion microprobe shrimp age of 654 5 3 8 ma from an ash bed immediately below the nantuo formation in south china provides the lowest age constraint for the nantuo glaciation which has been correlated with the global marinoan glaciation a u pb shrimp age of 636 3 4 9 ma from a fallout tuff within the basal layer of the nantuo formation along with the existing age of 635 2 0 6 ma from its overlying doushantuo cap carbonate suggests that the traditionally defined nantuo formation may have been deposited in a short time period at the end of the nantuo glaciation in combination with available ages globally the data support a relatively short duration and rapid termination of marinoan glaciations

the diagenetic and economic significance of composite grains of monazite and hydrocarbon in western australian arenites composite grains consisting of detrital monazite and solid hydrocarbon ranging up to 0 5 mm in diameter have been found in phanerozoic sedimentary rocks in three western australian basins the most common form is a monazite core surrounded by a hydrocarbon envelope the envelopes which have conchoidal fracture and radial cracks apparently congealed when hydrocarbons were polymerized and crosslinked by irradiation from the monazite some composite bodies contain fractured monazite grains within solid hydrocarbon and a few consist of a microbreccia of hydrocarbon and disseminated monazite fragments the breakup of the monazite was probably a diagenetic chemical process that began when crosslinked hydrocarbons within cracks and open cleavages swelled as they were infiltrated by fluid hydrocarbons of low molecular weight five microprobe analyses of the monazite reveal the following ranges in percent composition la 2 o 3 10 88 13 66 ce 2 o 3 25 58 28 78 pr 2 o 3 3 03 5 38 nd 2 o 3 9 15 12 11 tho 2 7 0 11 49 u 3 o 8 0 1 44 2v extends from 12 5 15 5 in the northern perth basin the composite bodies which contain cores of monazite derived from local gneissic basement rocks formed after the growth of siderite cement but before extensive silicification in the central perth basin the composite bodies seem to have formed after the growth of kaolinite and before silicification textures associated with the bodies allow them to be slotted into the diagenetic sequence and they therefore show when the oil was present analysis of the bodies has indicated a contribution of oil from the lower triassic kockatea shale but some may have grown from more than one generation of petroleum given the ubiquity of detrital monazite similar bodies are likely to be useful diagenetic and economic indicators elsewhere

enhanced chemical weathering triggered an expansion of euxinic seawater in the aftermath of the sturtian glaciation abstract the cryogenian period comprised two episodes of global glaciation sturtian and marinoan glaciations separated by a non glacial interval which was characterized by early radiations of eukaryotic algae and putative metazoans geochemical data indicate that the non glacial interval might be marked by a transient marine oxygenation nevertheless oceanic redox conditions varied both in time and space further the links between non glacial climate and marine redox variations are not well constrained here we present high resolution lithium isotope 7 li fe speciation and trace element mo and u data for clastic sedimentary rocks from the cryogenian interglacial datangpo formation south china in order to track the evolution of continental chemical silicate weathering and driving factors behind marine redox variability during the cryogenian non glacial interval a significantly negative 7 li excursion of 5 is observed in the basal datangpo formation suggesting a dramatic increase in chemical silicate weathering intensity in the aftermath of the sturtian glaciation expansion and contraction of anoxic sulfidic conditions as demonstrated by fe speciation and trace element mo and u data mirror changes in silicate weathering intensity our study provides evidence that greater nutrient and sulfate availability due to high silicate weathering intensity associated with increased exposure of fresh rocks and a warm climate facilitated the spread of euxinic waters over the continental margins of the otherwise ferruginous cryogenian ocean

earthquake rupture at focal depth part i structure and rupture of the pretorius fault tautona mine south africa we analyze the structure of the archaean pretorius fault in tautona mine south africa as well as the rupture zone that recently reactivated it the analysis is part of the natural earthquake laboratory in south african mines nelsam project that utilizes the access to 3 6 km depth provided by the mining operations the pretorius fault is a 10 km long oblique strike slip fault with displacement of up to 200 m that crosscuts fine to very coarse grain quartzitic rocks in tautona mine we identify here three structural zones within the fault zone 1 an outer damage zone 100 m wide of brittle deformation manifested by multiple widely spaced fractures and faults with slip up to 3 m 2 an inner damage zone 25 30 m wide with high density of anastomosing conjugate sets of fault segments and fractures many of which carry cataclasite zones and 3 a dominant segment with a cataclasite zone up to 50 cm thick that accommodated most of the archaean slip of the pretorius fault and is regarded as the principal slip zone psz this fault zone structure indicates that during its archaean activity the pretorius fault entered the mature fault stage in which many slip events were localized along a single psz the mining operations continuously induce earthquakes including the 2004 m2 2 event that rejuvenated the pretorius fault in the nelsam project area our analysis of the m2 2 rupture zone shows that 1 slip occurred exclusively along four pre existing large quasi planer segments of the ancient fault zone 2 the slipping segments contain brittle cataclasite zones up to 0 5 m thick 3 these segments are not parallel to each other 4 gouge zones 1 5 mm thick composed of white rock flour formed almost exclusively along the cataclasite host rock contacts of the slipping segments 5 locally new fresh fractures branched from the slipping segments and propagated in mixed shear tensile mode 6 the maximum observed shear displacement is 25 mm in oblique normal slip the mechanical analysis of this rupture zone is presented in part ii heesakkers et al earthquake rupture at focal depth part ii mechanics of the 2004 m2 2 earthquake along the pretorius fault tautona mine south africa 2011 this volume

constraints on the nature of the marinoan glaciation cyclic sedimentary records from the nantuo formation south china abstract detailed sedimentological investigations of the cryogenian glacial deposits are critical for constraining the true nature of the sturtian and marinoan glaciations the entire succession of the nantuo formation which corresponds to the marinoan glaciation is well developed in south china here a detailed lithological and sedimentological analysis of two cores of the nantuo formation in guizhou south china is presented in which two continuous ice advance retreat cycles are identified the base consists of a massive diamictite lithofacies that is representative of glacier dominated subaqueous debris flow deposits these proximal glaciomarine deposits are overlain by a gravel free sandy mudstone lithofacies that is lacking in diamictites which implies distal glaciomarine deposits this ice advance retreat sedimentary cycle is overlain by a weakly laminated diamictite lithofacies which represents subaqueous debris flow deposits that formed during the second episode of ice advance these proximal glaciomarine deposits are overlain by an interbedded sandstone mudstone lithofacies which is indicative of distal glaciomarine deposits that formed during another episode of ice retreat these sedimentary cycles imply that the climate switched twice from relatively warm to extremely cold and back during the marinoan glaciation the global sea level and sedimentary environments fluctuated in response to these climate changes this co evolution of the climate sea level and sedimentary environments which is represented by the lithofacies and sedimentary sequence of the nantuo formation as well as the corresponding strata of other sections worldwide suggests that the marinoan glaciation is characterized by a progressive and dynamic course

cyclostratigraphic constraints on the duration of the datangpo formation and the onset age of the nantuo marinoan glaciation in south china abstract constructing an accurate timeline is critical for reconstructing the earth systems through critical transitions in climate geochemistry and life existing dates constrain synchronous initiation ca 717 ma and termination ca 660 ma of the sturtian glaciation from multiple continents the termination of the younger marinoan glaciation is also well dated at ca 635 ma but the onset of this glaciation is only roughly constrained as ca 654 ma south china and ca 639 ma namibia to test if the marinoan glaciation started close to ca 654 ma or ca 639 ma we have conducted a cyclostratigraphic study on the cryogenian non glacial datangpo formation that conformably overlies and underlies sturtian and marinoan glacial diamictites respectively in a deep water basin section in south china a total of 28 765 magnetic susceptibility ms measurements from a drillcore of the 292 m thick muddy siltstone and shale dominated datangpo formation are used for cyclostratigraphic analysis the results reveal significant decameter to meter scale sedimentary cycles of 16 12 m 3 6 3 0 m 1 0 0 8 m and 0 6 0 4 m the ratios of these cycle wavelengths match well with those of the milankovitch cycles calibrated for the cryogenian period the established astrochronologic time scale suggests that the duration of the datangpo formation is about 9 8 million years together with the radiometric age of ca 660 ma for the termination of the sturtian glaciation the cyclostratigraphic data suggest that the nantuo marinoan glaciation in south china initiated at ca 650 ma which is slightly younger than but consistent with the ca 654 ma u pb age from the top of the datangpo formation in shelf sections this age however is significantly older than the ages obtained from marinoan age glacial diamictites in south china ca 636 ma and namibia ca 639 ma given that most of the shelf sections may have suffered from glacial erosion obtaining the onset age of the marinoan glaciation should focus on relatively complete deep water successions

condensation origin for neoproterozoic cap carbonates during deglaciation neoproterozoic deglacial stratigraphy is commonly characterized by a sharp contact separating glacial sediments from laminated capping carbonates this stratigraphic relation is generally assumed to have time significance and to reflect an abrupt shift from icehouse to greenhouse conditions in contrast to this sequence stratigraphic field studies of an ediacaran ca 635 ma glacial to postglacial transition in the amadeus basin of central australia reveal a complex deglacial stratigraphy in which more than 175 m of conglomerate sandstone marl and carbonate at the basin margin and portions of four unconformity bounded sequences pass basinward into no more than 3 m of laminated dolomicrite of typical cap carbonate facies the unconformities which are characterized by as much as several tens of meters of erosional relief oblique sections of incised valleys separate intervals of contrasting sediment provenance and are confidently mapped on the basis of both criteria comparable unconformities are absent in the overlying neoproterozoic succession which is 2 km thick and encompasses many tens of millions of years the amadeus basin cap carbonate was thus deposited during a protracted interval of multiphase cyclical transgression more similar to phanerozoic cyclical sea level rise than to the single catastrophic deglaciation and instantaneous precipitation invoked by popular current models to explain the classic cap carbonate the superposition of carbonate on glacial facies in distal sections evidently records condensation in the absence of siliciclastic sediment rather than abrupt shifts between glacial and tropical conditions facies lithologically similar to cap carbonates may be less obvious in phanerozoic successions because of a secular change in carbonate composition to reefal and deep sea pelagic deposits

high primary productivity during the ediacaran period revealed by the covariation of paired c isotopic records from south china abstract remarkable carbonate carbon isotope 13ccarb excursions accompanied by invariant organic carbon isotope 13corg values have been observed in many late neoproterozoic successions this decoupled relationship between 13ccarb and 13corg in the precambrian differs from most phanerozoic records which have been substantially imprinted by aqueous photosynthesis and it has been tentatively interpreted as resulting from exotic organic matter inputs or diagenesis in this study we present high resolution 13corg records in combination with previously published 13ccarb data from a continuous drill core from the yangtze platform of south china the studied interval spans the cryogenian nantuo formation the ediacaran doushantuo and dengying formations and the base of the cambrian yanjiahe formation the 13ccarb profile of this drill core can be reliably correlated with contemporaneous sequences and it reveals multiple negative 13ccarb excursions associated with phosphorite deposits intriguingly the 13corg profile exhibits a co varying trend with the 13ccarb profile and the coupled relationship between 13ccarb and 13corg is rare in geological records of the precambrian the 13corg values of the drill core vary from 22 13 to 34 12 and the overall isotopic difference 13ccarb org between 13ccarb and 13corg ranges between 19 61 and 34 58 most of the 13corg and 13ccarb org data can be interpreted in terms of oxygenic photosynthesis probably mainly by eukaryotic algae however it is possible that exotic organic matter most likely doc from the deep ocean may also have contributed to the sedimentary organic matter composition of specific intervals studied herein moreover high primary productivity in shallow water may have been sustained for a long period in phosphate rich conditions and the organic matter generated by photosynthesis may have been quantitatively sufficient to overwhelm the doc buffering effect in the total 13corg signal throughout the ediacaran period the enhanced burial of organic matter in sediments would gradually result in the accumulation of oxygen both in the ocean and atmosphere which would likely have paved the way for macroscopic animal evolution

in situ u pb dating of monazite xenotime and zircon from the lantian black shales time constraints on provenances deposition and fluid flow events abstract the lantian formation located in eastern south china block scb forms the lower sequence of the ediacaran period at the transition from proterozoic to paleozoic the fossils of lantian formation have been proposed to predate the avalon biota about 579 565 ma the earliest known fossil assemblages with complex morphologies based largely on stratigraphy mineral chemistry and in situ u pb dating of monazites xenotimes and zircons from the black shale in fossil rich zone are studied for the first time to provide critical age constraints for provenance early diagenesis and fluid flow events detrital zircons and monazites give age populations similar to that of the doushantuo formation indicative of the same provenances for ediacaran basins throughout the scb the low y monazites formed during early diagenesis yield a weighted mean age of 612 29 ma n 9 mswd 3 1 age spectrum of analyzed monazites demonstrated that the sedimentation started from at least around 645 ma subsequently the overprinting events could be recorded by xenotimes and zircons precipitated from fluids during late diagenesis age results from xenotimes ranging from 441 ma and 585 ma were contemporaneous with the timing of collision of scb with gondwanaland and a weighted mean age of 394 8 3 7 ma n 23 mswd 2 8 obtained from diagenetic zircons could be correlated to the post tectonic granites widespread on the scb the pre existing monazites generally remain pristine and the multi staged fluids were locally interacted with the samples to form th rich domains in monazites

duration and nature of the end cryogenian marinoan glaciation the end cryogenian glaciation marinoan is portrayed commonly as the archetype of snowball earth yet its duration and character remain uncertain here we report u pb zircon ages for two ash beds from widely separated localities of the marinoan equivalent ghaub formation in namibia 639 29 0 26 ma and 635 21 0 59 ma these findings verify for the first time the key prediction of the snowball earth hypothesis for the marinoan glaciation i e longevity with a duration of 4 m y they also show that the nonglacial interlude of cryogenian time spanned 20 m y or less and that glacigenic erosion and sedimentation and at least intermittent open water conditions occurred 4 m y prior to termination of the marinoan glaciation

variation of chemical index of alteration cia in the ediacaran doushantuo formation and its environmental implications abstract the ediacaran period 635 541 ma witnessed rapid turnovers of marine organisms that eventually led to the early cambrian radiation the ediacaran doushantuo formation ca 635 551 ma serves as one of the most important and intensively studied stratigraphic units for understanding the co evolution of life and environment during this critical time interval to better understand the early middle ediacaran climate change we reconstruct a temporal variation curve of chemical index of alteration cia from a drill core and an outcrop of the doushantuo formation in combination with previously published cia data from segments of time equivalent strata the results show three distinct decreases in cia values that correlate well with the positive carbon isotope 13c excursion at the low doushantuo formation ep1 and the negative 13c excursion at the middle en2 and upper en3 doushantuo formation the decline of cia in ep1 is consistent with occurrence of glendonites at the same stratigraphic interval that suggests a cooling event the low cia values in en2 and en3 also suggest relatively colder periods that are consistent with evidence from strontium isotope 87sr 86sr and oxygen isotope 18o data with existing bio and chemostratigraphic constraints the cooling event associated with en2 might be synchronous with the gaskiers glaciation the other two cold periods associated with ep1 and en3 however have not been documented from other successions globally which needs to be tested in future studies

metal organic relationships from the irish carboniferous abstract a number of metal organic relationships have been observed in the carboniferous of ireland they include metal enrichments within black shales bitumen nodules bituminous solution seams woody material vein bitumens and reservoir bitumens and the association of hydrocarbon gases and bitumens with base metal deposits the source for the metals may have been in the strata on which the carboniferous rocks were deposited or in their carboniferous erosion products both syngenetic and epigenetic mineralisation have been observed with organic material associated with both types of mineralisation the solid bitumens are residues of migrated fluid hydrocarbon which may have been produced by 330 ma late visean

evaluation of paired carbon isotopic signals from the ediacaran doushantuo phosphorites diagenetic or primary abstract this study reports high resolution c isotopic data of carbonate carbon 13ccarb and organic carbon 13corg from the ediacaran doushantuo carbonate and phosphorite as well as from the underlying tillite of the nantuo formation from the datang mine and chuanyuandong sections for the nantuo tillite in the datang section the striking negative 13ccarb values ranging mostly from 10 to 16 with negative 18o values down to 27 2 and clear covariance between 13ccarb and 18o suggest that nearly all of the primary c and o isotopic compositions have been reset by meteoric diagenesis the near complete modification of the primary isotopic signals may be due to frequent exposure to fresh water conditions during diagenesis and the lithification of porous tillite sediment the extremely negative 13ccarb values down to 16 8 suggest the contribution of 12c enriched dissolved inorganic carbonate which originated from the remineralization of organic carbon during burial diagenesis these observations suggest that caution is needed when using tillite samples for paleoenvironmental reconstruction the correlative lower phosphorite deposits from the datang and chuanyuandong sections show clear covariance between 13ccarb and 18o although the chuanyuandong phosphorites have more negative values of 13ccarb and 18o than the datang section although most of the 18o values of the lower phosphorites may have been altered by secondary diagenetic processes the 13ccarb values of 3 5 and the 13corg values of

quantifying temperature variation between neoproterozoic cryochron nonglacial interlude nanhua basin south china abstract three major late neoproterozoic global cryochrons mark the coldest climate state in earth history with glaciers covering most if not all continents however the terrestrial paleosurface temperature differential between cryochron and nonglacial interlude is unknown time equivalent cryogenian and ediacaran sedimentary successions from south china and oman show multiple negative excursions of the corrected values of their chemical index of alteration ciacorr these excursions reflect climate cooling and correlate with the sturtian marinoan and gaskiers cryochrons based on the na mat transfer function sodium chemical depletion index mean annual temperature we estimate the temperature differential between cryogenian cryochron and nonglacial interlude reached 20 5 4 at around 30 paleolatitude and 12 5 4 temperature difference between the ediacaran cryochron and nonglacial interlude near the equator the fluctuation of ciacorr and mat trends within individual cryochrons likely indicate cold warm climate cycling during the cryogenian cryochron

tracking the evolution of seawater mo isotopes through the ediacaran cambrian transition abstract the rapid increase in animal diversity and abundance over the ediacaran cambrian boundary has been attributed to among other parameters pronounced earth surface oxygenation at that time however whether atmospheric oxygen elevated to modern levels or whether the extent was smaller and oxygen remained relatively muted until the late paleozoic is currently debated here we present new mo isotope datasets of drill core material for two key black shale units the ediacaran doushantuo formation and the lower cambrian jiumenchong formation located on the yangtze block these data capture a 0 7 isotope fractionation between sediments experiencing quantitative and non quantitative mo removal by identifying this offset we provide integrated estimates for global seawater mo isotope compositions during the deposition of these two formations 1 2 1 4 and 1 8 2 respectively when paired with a mass balance model our results indicate that a large proportion of the early cambrian ocean was bathed under oxic waters we also discuss how recent discoveries have provided insights into the geochemical processes underpinning the oxygenation of the oceans

hydrocarbon rims on monazite in permian triassic arenites northern perth basin western australia pointers to the former presence of oil black opaque hydrocarbon rims about 0 05 mm thick are preserved around detrital monazite grains in permian triassic arenites of the norther perth basin western australia chromatographic analysis indicates derivation from oil chemically like that elsewhere in the sequence and the rims seem to be remnants of oil which was largely flushed away the hydrocarbon rims may have adhered to the monazite grains because of irradiation they are not found on other grains monazite rich heavy mineral bands are probably responsible for abnormally high radioactivity recorded locally by gamma ray logs in wells penetrating the sandstones a preliminary search has revealed similar rims around monazite in other western australian arenites ranging in age from silurian to cretaceous thin section examination of heavy mineral concentrations may therefore be a useful simple technique to indicate the former presence of hydrocarbons in dry arenites

stability of detrital heavy minerals on the norwegian continental shelf as a function of depth and temperature abstract petrographic analysis of 1931 thin sections from sandstones of pliocene to devonian age on the norwegian continental shelf indicate that the heavy minerals zircon tourmaline rutile apatite and spinel survive to depths exceeding 5000 m and to temperatures of around 200 c without showing signs of intrastratal dissolution on the other hand the maximum depth and temperature of occurrence for amphibole are 841 m and 40 c around 1500 m and 55 c for sphene when 0 5 km of probable uplift is taken into account 2231 m and 92 c for kyanite 2559 m and 95 c for epidote 2810 m and 109 c for staurolite and 4589 m and 175 c for garnet initial signs of garnet dissolution occur at around 2000 m depth and all garnets are partially dissolved at depths greater than 3500 m monazite is present down to 4858 m and 182 c and chloritoid to 3811 m and 149 c it is however uncertain whether this is due to the low number of samples deeper than 4858 m and to the rare occurrence of chloritoid or to intrastratal dissolution the same sequence of heavy mineral stability is found when volume of quartz cement is used as a proxy for time temperature exposure quartz cement is not found in samples containing amphibole or detrital sphene a maximum of a fraction of a percent quartz cement is found in samples containing kyanite up to 1 together with epidote up to 6 with staurolite up to 24 with chloritoid up to 25 with garnet whereas maximum values of 25 35 are present together with zircon tourmaline rutile patite spinel and monazite the sequence of persistence of heavy minerals versus depth found in this study is very similar to results from several previous studies although unstable heavy minerals survive to greater depths in very young and rapidly buried sandstones and there are some differences regarding the stability of sphene and epidote heavy mineral dissolution has created secondary pores and possibly has contributed to precipitation of kaolinite illite quartz and carbonates in the studied sandstones but these reactions are of very limited volumetric importance

seawater buffered diagenesis destruction of carbon isotope excursions and the composition of dic in neoproterozoic oceans carbonate sediments of nonglacial cryogenian 659 to 649 ma and early ediacaran 635 to 590 ma age exhibit large positive and negative 13ccarb excursions in a shallow water marine platform in northern namibia the same excursions are recorded in fringing deep sea fans and in carbonate platforms on other paleocontinents however coeval carbonates in the upper foreslope of the namibian platform and to a lesser extent in the outermost platform have relatively uniform 13ccarb compositions compatible with dissolved inorganic carbon dic in the modern ocean we attribute the uniform values to fluid buffered diagenesis that occurred where seawater invaded the sediment in response to geothermal porewater convection this attribution which is testable with paired ca and mg isotopes implies that large 13ccarb excursions observed in neoproterozoic platforms while sedimentary in origin do not reflect the composition of ancient open ocean dic

a rapid and synchronous initiation of the wide spread cryogenian glaciations abstract the neoproterozoic glaciations represent a remarkable milestone in earth evolution due to their major influence on atmosphere biosphere and hydrosphere the early cryogenian sturtian glaciations evidence for which has been recorded worldwide may have lasted for about 50 million years but the precise timing and synchroneity of these glaciations have been disputed jiangkou glacigenic strata in south china can be attributed to the sturtian glacial episode as they share sedimentological stratigraphic and lithological similarities with sturtian strata in south australia as such dating the onset of the jiangkou glaciation would contribute to testing the synchroneity of the worldwide sturtian glaciation in this paper we demonstrate by means of sims u pb zircon dating that the jiangkou glaciation in south china was initiated at 715 9 2 8 ma the new age is within uncertainty synchronous with dates obtained from the lower parts of glacigenic successions in laurentia and oman thereby indicating thereby indicating a synchroneity and global extent to the sturtian glaciation the synchronous occurrence of the sturtian glaciation in mid to low latitude regions implies rapid ice sheet advancement in response to ice albedo feedback as supported by numerical climatic modeling

wide but not ubiquitous distribution of glendonite in the doushantuo formation south china implications for ediacaran climate abstract glendonites are pseudomorphs of syndepositional or early authigenic ikaite caco3 6h2o that often forms at near freezing temperatures silicified glendonite has been reported from inner shelf deposits of the lower ediacaran doushantuo formation at a single stratigraphic section in south china where they are stratigraphically associated with the positive 13c excursion ep1 but predate the negative 13c excursion en3 shuram excursion indicating a period of cool climate somewhere between 609 ma and 551 ma this interpretation predicts a wider geographic distribution of ediacaran glendonites in equivalent strata in the yangtze block of south china to test this prediction we conducted a regional survey of doushantuo formation and found that although glendonites are not universally present they occur in expected stratigraphic intervals and in association with ep1 at two new sections representing inner shelf and intrashelf basin facies the wide but not ubiquitous distribution of doushantuo glendonites indicates that ikaite precipitation and glendonite formation was controlled by both regional climatic and local geochemical factors glendonites at the new localities are stellate clusters pseudomorphed by calcite spar and sometimes are rimmed with silica the calcite spar is characterized by highly variable and mostly negative 13c values as low as 37 indicating that diagenetic transformation of precursor ikaite to calcitic glendonite may be related to anaerobic oxidation of organic matter or methane in sediment the new data suggest an early ediacaran cold period prior to en3 or the shuram excursion and facilitation of glendonite ikaite formation by both climatic and local geochemical conditions such as redox conditions and phosphate concentrations

the origin of uraninite bitumen nodules and carbon seams in witwatersrand gold uranium pyrite ore deposits based on a permo triassic analogue permo triassic dongara sandstones from the perth basin of western australia contain solitary bitumen nodules that are analogous to uraniferous bitumen nodules or fly speck carbon in late archean witwatersrand gold uranium pyrite ore deposits nodules in both contain cores of radioactive minerals and occupy depositional sites where heavy minerals were concentrated solitary bitumen nodules in the dongara sandstone formed during burial by radiation induced polymerization of liquid hydrocarbons migrating through primary porosity around detrital monazite grains similar bitumen nodules in witwatersrand ore deposits are likewise interpreted to have formed during burial although the radiation emitting detrital grains were uraninite carbon seams in witwatersrand ore deposits are stratiform bodies of coalesced bitumen nodules by analogy with solitary nodules individual nodules in carbon seams formed during burial as liquid hydrocarbons migrated through primary porosity past detrital uraninite grains but they differ from solitary nodules in that many have been stretched perpendicular to bedding to form an ellipsoidal or columnar structure although a columnar structure is consistent with deformation by vertical extension that deformation clearly postdated nodule formation in some seams elongated nodules are associated spatially with framework hosted bedding parallel microfractures which are commonly filled with fibrous secondary minerals again bedding parallel microfracturing clearly postdated nodule formation columnar textured bitumen and bedding parallel fractures are interpreted to be postdiagenetic structural fabrics whereas carbon seams appear to have been a microfocus of a compressive deformation neither columnar textured bitumen nor bedding parallel fractures are present in the dongara sandstone and they are not present in every witwatersrand carbon seam either supporting the contention that columnar textured bitumen and bedding parallel fractures are focused structural fabrics that postdate nodule formation recognition that solitary bitumen nodules and carbon seam hosted bitumen nodules of witwatersrand ore deposits are analogous in origin to bitumen nodules in the dongara sandstone supports historical mineralogical observations that the witwatersrand basin contained uraninite placers indeed carbon seams are most likely the former sites of heavy mineral uraninite strands given the chemical instability of uraninite under oxidizing conditions detrital uraninite in witwatersrand strata supports the long held contention that the archean atmosphere contained significantly less oxygen than the modern atmosphere

germanium silica ratio and rare earth element composition of silica filling in sheet cracks of the doushantuo cap carbonates south china constraining hydrothermal activity during the marinoan snowball earth glaciation abstract the rapid diversification of eukaryotes within 3 million years after the marinoan global glaciation suggests the potential linkage between the snowball earth event and biological evolution to understand how the global glaciation and the biological evolution were linked it is necessary to reconstruct the sequence of events with high temporal resolution that occurred during the deglaciation in this study we focus on silica filling within sheet cracks sheet cracks abundantly occur in the basal part of the marinoan cap carbonate 635 ma and are characterized by the interconnected horizontal and vertical cracks that are sequentially cemented by dolospars silica and calcite as the second stage of crack filling the origin of silica filling remains controversial if the seawater origin is confirmed the silica filling might archive the signal of ocean chemistry in the aftermath of snowball earth event in this study we measured the germanium silica ratios ge si and rare earth elements ree compositions of silica filling from the doushantuo cap carbonate in the yangtze platform south china the silica filling has low ge si ratios 1 mol mol and displays a light ree lree depleted ree pattern normalized to paas with positive eu anomalies eu eu these results indicate the predominant seawater origin of silica with some contribution from hydrothermal fluid suggesting the penecontemporaneous precipitation of silica filling with respect to sheet crack formation in order to quantify the contribution from hydrothermal fluid we developed a binary mixing model by using ge si ratio and eu eu as two independent proxies the modeling results indicate mixing of 5 vol hydrothermal fluid with contemporaneous seawater or 20 wt of si in silica filling from hydrothermal fluid the modeling results also show that the synglacial hydrothermal flux might be one order of magnitude lower than the modern level suggesting extremely weak hydrothermal activities during the marinoan snowball glaciation

globally synchronous marinoan deglaciation indicated by u pb geochronology of the cottons breccia tasmania australia u pb zircon data from the uppermost cottons breccia representing the marinoan glacial postglacial transition on king island tasmania provide the first direct age constraint on the cryogenian ediacaran boundary in australia zircons in four samples from the topmost meter of the cottons breccia dated by sensitive high resolution ion microprobe exhibit two modes ca 660 ma and ca 635 ma the younger component predominates in the uppermost sample a possibly volcanolithic dolomitic sandstone apparently lacking glacially transported debris in the transition to cap carbonate chemical abrasion thermal ionization mass spectrometry ca tims u pb dating of euhedral zircons from that sample yields a weighted mean age of 636 41 0 45 ma equivalence to published tims ash bed dates from cryogenian ediacaran transitional strata in namibia 635 51 0 82 ma within glacial deposit and china 635 23 0 84 ma 2 m above glacial deposit supports correlation of those strata to the australian type sections and globally synchronous deglaciation at the end of the cryogenian period

oil preserved in fluid inclusions in archaean sandstones oil is generally thought to be geologically young as it is thermodynamically unstable when subjected to elevated temperatures over long periods in open systems1 2 indeed almost all petroleum production comes from rocks younger than 400 million years ref 3 although the oldest known oil occurs in rocks 1 650 myr old4 suitable source rocks were abundant in older geological successions5 and circumstantial evidence suggests that some of these generated hydrocarbons early in their history6 here we report the discovery of oil preserved in fluid inclusions in sandstones dating back 3 000 myr most inclusions lie within healed microfractures confined to individual detrital quartz grains indicating that their oil was emplaced before archaean or palaeoproterozoic metamorphism sealed all voids and thus came from older in some cases archaean sources the fluid inclusions apparently acted as inert pressure vessels that protected the oil from subsequent degradation by circulating fluids and mineral catalysts because of its great age this oil can potentially yield valuable information about the size and diversity of the early biosphere particularly if it contains molecular fossils biomarkers of the primordial organisms from which it was derived

heterogeneous seawater phosphorus concentrations during the sturtian glaciation evidence from p fe ratios of fulu formation ironstone in south china abstract phosphorus p is one of the key bio limiting elements in the modern ocean and controls marine primary productivity over the geological time scales it is proposed that the ediacaran atmosphere oxygenation and animal evolution might have been triggered by high seawater p concentration in cryogenian oceans seawater p concentration can be reconstructed by the ratio of phosphorus to iron expressed as p fe 100 in ironstones here we measured the p fe ratios of the banded iron formation bif from the cryogenian fulu formation in south china the p fe 100 ratios of the fulu bif vary between 0 08 and 1 81 mean 0 45 n 22 considerably lower than the values of coeval bif deposited in other continents mean 1 24 n 74 variation of p fe ratio of ironstones may suggest a large seawater p concentration gradient during the sturtian glaciation which is comparable to or even higher than that in the modern ocean 1 2 m in north atlantic and 2 6 m in north pacific though being explained in different ways the heterogeneous seawater p concentration requires active organic matter production in the surface ocean and or decomposition in the ocean interior as well as possible onset of thermohaline circulation during the sturtian glaciation finally our study suggests that precipitation of bif in the completely ice covered ocean was unlikely

a cryogenian chronology two long lasting synchronous neoproterozoic glaciations the snowball earth hypothesis predicts globally synchronous glaciations that persisted on a multimillion year time scale geochronological tests of this hypothesis have been limited by a dearth of reliable age constraints bracketing these events on multiple cratons here we present four new re os geochronology age constraints on sturtian 717 660 ma and marinoan 635 ma termination glacial deposits from three different paleocontinents a 752 7 5 5 ma age from the base of the callison lake formation in yukon canada confirms nonglacial sedimentation on the western margin of laurentia between ca 753 and 717 ma coupled with a new 727 3 4 9 ma age directly below the glacigenic deposits of the grand conglomerate on the congo craton africa these data refute the notion of a global ca 740 ma kaigas glaciation a 659 0 4 5 ma age directly above the maikhan uul diamictite in mongolia confirms previous constraints on a long duration for the 717 660 ma sturtian glacial epoch and a relatively short nonglacial interlude in addition we provide the first direct radiometric age constraint for the termination of the marinoan glaciation in laurentia with an age of 632 3 5 9 ma from the basal sheepbed formation of northwest canada which is identical within uncertainty to u pb zircon ages from china australia and namibia together these data unite re os and u pb geochronological constraints and provide a refined temporal framework for cryogenian earth history

sturtian glaciation in siberia evidence of glacial origin and u pb dating of the diamictites of the chivida formation in the north of the yenisei ridge abstract knowledge on the age and distribution of glacial deposits is essential in order to solve issues surrounding the geological periodization of the neoproterozoic and the large scale changes in the environment and biosphere that took place at that time the glacial origin of diamictites of the precambrian chivida formation on the yenisei ridge on the western periphery of the siberian platform was proposed almost a century ago but has since been disputed the present study confirms the glacial origin of the chivida diamictites based on the findings of striated and faceted clasts and other characteristic features of glacial deposits results from u pb dating of zircon grains from diamictites matrix with and without volcanogenic admixture tuffaceous sandstones and volcanic breccias interbedding the diamictites of the chivida formation are presented the youngest population of zircon grains revealed in the volcanogenic and tuffogenic rocks of the chivida formation is assumed to characterize syn depositional volcanic activity thus its mean average age 696 4 ma is considered to characterize the glacial sediments time of deposition these results prove for the first time the presence of an ice sheet on the siberian craton during the sturtian glaciation

iodine records from the ediacaran doushantuo cap carbonates of the yangtze block south china abstract late neoproterozoic cap carbonates formed following the cryogenian glaciations may record information about the significant climate change and ocean chemistry evolution immediately after the snowball earth events large negative carbon isotope anomalies and enigmatic sedimentary structures have been identified from the post marinoan cap carbonates across the globe but their formation mechanism remains debatable due to difficulties of distinguishing overlapped chemical signatures and diagenetic alterations in this study we present i ca mg profiles of four sections from a shallow to deep water transect of the basal doushantuo cap carbonates one of the most extensively studied ediacaran units in south china most samples have i ca mg values lower than 1 mol mol with a few exceptions in the shelf sections up to 2 5 mol mol all calcite samples with extremely low 13c have iodine signal below detection limit suggesting carbonate precipitation from anoxic seawater or diagenetic fluids among the four sections the slope section has the lowest i ca mg values suggesting that it may have experienced more extensive fluid buffered diagenesis and more severe loss of io3 in combination with available major trace rare earth element and isotope data the temporal i ca mg variations support freshwater mixing and deep water upwelling in proximal sites and transient oxidation during deposition of the doushantuo cap carbonates