sequence stratigraphy of the neoproterozoic infra krol formation and krol group lesser himalaya india a bstract a sequence stratigraphic study of terrigenous and carbonate rocks of the infra krol formation and krol group in the lesser himalaya fold and thrust belt of northern india was undertaken as part of a broader investigation of the significance of carbon isotope data in neoproterozoic successions eight regional stratigraphic discontinuities were traced over a distance of nearly 300 km and interpretations were anchored in a series of local studies involving the mapping of key beds and the measurement of closely spaced sections three of the regional surfaces are interpreted as sequence boundaries on the basis of 1 locally developed incised valleys 60 m deep 2 paleokarstic depressions with 50 m of mappable relief 3 subaerial dissolution and weathering products breccias and calcrete filling vertical fissures dikes cavities and shallow de pressions in underlying carbonate rocks and 4 small scale evidence for sub aerial exposure at an erosion surface the remaining five discontinuities are regional flooding surfaces identified on the basis of either facies changes with an abrupt upward deepening across the surface or transitions in facies stacking patterns typically from forestepping to backstepping a glacio eustatic origin is permitted although not required for the three sequence boundaries but no evidence has been found for marked lowering of sea level at other horizons a mismatch between the stratigraphic location of sequence boundaries and car bon isotope minima suggests that local diagenetic alteration or oceanographic phenomena unrelated to glaciation may be in part responsible for observed isotopic variation and that small ice sheets may have existed during apparently nonglacial times without producing either cap carbonates or negative carbon isotope excursions

anomalies in global carbon cycling and extinction at the triassic jurassic boundary evidence from a marine c isotope record this study investigates whether the end triassic biotic crisis was coupled with a perturbation of the marine c isotope budget the marine c isotope signature serves as a proxy of the marine carbon reservoir and ultimately of the global c cycle a continuous shallow water marine limestone succession from the western southern alps bergamasc alps northern italy provides information on the end triassic biotic crisis and on the evolution of the marine carbon reservoir across the triassic jurassic t j boundary the established carbonate c isotope curve is marked by a negative c isotope pulse coinciding with the disappearance of the end triassic benthic faunal assemblage and a widespread rhaetian carbonate platform drowning event the negative spike is followed by a positive c isotope excursion starting at the palynological t j transition the negative c isotope pulse may have resulted from the sudden release of gas hydrates the positive isotope excursion records a global change in organic carbon burial rates probably in response to elevated atmospheric co2 levels at a time of massive volcanic activity in the central atlantic magmatic province high co2 levels were responsible for the end triassic biocalcification crisis carbonate platform collapse and possibly the sudden release of methane from gas hydrate

c isotopic stratification in a neoproterozoic postglacial ocean we report c isotopic data from the cap carbonate overlying the terminal proterozoic nantuo diamictites in south china the c isotopic measurements reveal a large c isotopic gradient of 3 along paleoenvironmental transect from shelf to deep basinal sedimentary facies the c isotopic stratification may attribute to the effect of biological pumping in a postglacial ocean our results confirm that the sea level rise was rapid and that atmospheric co2 was significantly high immediately following deglaciation

cambrian ordovician depositional sequences in the middle east a perspective from turkey abstract in southern turkey taurus chain or taurides and southeastern turkey border folds of the arabian plate nearly complete cambrian to ordovician successions are preserved four major sedimentary sequences are defined according to the main transgressive events and the subsequent shelf progradations these sequences allow us to link the turkish mostly distal lower palaeozoic detritals to the more proximal arabian formations in spite of contrasting facies the lower palaeozoic development is outlined through four successive steps defined in southern turkey 1 initiation of a cratonic platform regime terreneuvian i e earliest cambrian depositional sequence 1 with fluviatile conglomerates and red bed sediments associated with volcanics 2 development of a stable marine platform late terreneuvian to early ordovician depositional sequences 2 and 3 including widespread but diachronous middle cambrian carbonates and subsequent storm dominated detritals 3 tectonic instability middle ordovician leading to a new palaeogeography on the gondwana platform with the differentiation of a sag basin bedinan qasim depocenter lower part of depositional sequence 4 and 4 glaciation latest ordovician upper part of depositional sequence 4 identified by glaciomarine deposits forming the hirnantian glacial record this thick 2000 m detrital succession records a first order long term subsidence driven cambrian to ordovician transgressive trend and includes second order sequences reflecting interactions between global eustasy and tectonic instability on a larger scale the identification of recurrent sequence stratigraphic features with similar trends in the cambrian ordovician successions on the arabian platform implies that a former location of the taurus domain cannot be situated in the present day eastern mediterranean area but should lie directly north of the arabian platform this location places southern turkey at the junction between the north african segment of the gondwana siliciclastic shelf to the west present day coordinates and the eastern arabian segment in good agreement with mixed faunal signatures from both areas primary control of the tectonostratigraphic development of southern turkey during the lower palaeozoic may be a forced evolution from arc platform to rift drift transitions cordilleran model that has migrated progressively eastwards from the avalonian domain along the northern gondwana margin to the arabian domain throughout the lower palaeozoic

modelling seismites with a digital shaking table abstract soft sediment deformation structures induced by seismically triggered liquefaction and or fluidization seismites have been reproduced with a digital shaking table we have used natural sediments with variable granulometric ranges clay silt and sand and an earthquake simulator that is able to reproduce real tridimensional seismograms acceleration and pore pressure recording allowed us to follow liquefaction and or fluidization processes in unconsolidated sediments during earthquakes different types of seismites were produced by variations in the tested sedimentary column

large isotopic variability at the micron scale in shuram excursion carbonates from south australia abstract ediacaran aged 635 541 million years ago marine sediments contain a large negative carbon isotope 13 c excursion in which carbonate 13 c values reach 12 vpdb known as the shuram excursion many workers have interpreted this 13 c record as an unprecedented perturbation to the global carbon cycle leading to speculation about a causal connection to the broadly contemporaneous rise of animal life others have interpreted the 13 c signal as a product of diagenesis thereby minimizing its relevance for understanding the evolution of metazoans here we present sem imaging and in situ 13 c and 18 o values measured by secondary ion mass spectrometry sims to assess these competing hypotheses in the wonoka formation of south australia our results from the minimum of the excursion show that rounded sedimentary grains of calcite have 13 c values between 12 8 to 10 6 and 18 o values between 17 8 to 15 5 vpdb euhedral dolomite that appears to have grown unimpeded in open sedimentary pore spaces also is present these early stage dolomites are interpreted as early authigenic in origin and have 13 c values that reach 5 requiring a formation fluid with a substantially different 13 c composition from basin waters or bulk sediment together these results provide little evidence for the hypothesis that a late diagenetic overprint has generated the shuram excursion in the wonoka instead they suggest the presence of a large carbon isotopic gradient in the surface environment with shallow waters capable of precipitating carbonates with very low 13 c down to 12 and deeper shelf and or marine pore waters generating carbonates with positive carbon isotope values up to 5 because negative isotope excursions of similar magnitude are found in widely dispersed ediacaran basins it is likely that this gradient was characteristic of shelf environments of this period and that a still unknown global process led to the shuram excursion in shallow water carbonates

facies stratigraphy and evolution of a middle ediacaran carbonate ramp khufai formation sultanate of oman the khufai formation is the oldest carbonate platform of the cryogenian to lowermost cambrian huqf supergroup a stratigraphic characterization of this unit includes detailed facies descriptions a sequence stratigraphic interpretation and evaluation of lateral heterogeneity and overall ramp evolution the khufai formation comprises one and one half depositional sequences with a maximum flooding interval near the base of the formation and a sequence boundary within the upper peritidal facies most of the deposition occurred during highstand progradation of a carbonate ramp facies tracts include outer ramp and midramp mudstones and wackestones ramp crest grainstone shoal deposits and extensive inner ramp microbially dominated peritidal deposits outcrops in the oman mountains are deep water deposits including turbiditic grainstone and wackestone interbedded with siliciclastic rich siltstone and crinkly laminite facies patterns and parasequence composition are variable both laterally across the outcrop area and vertically through time because of a combination of ramp morphology siliciclastic supply and possible syndepositional faulting the lithostratigraphic boundary between the khufai formation and the overlying shuram formation is gradational and represents significant flooding of the carbonate platform the stratigraphic characterization presented here along with the identification of key facies and diagenetic features will help further future exploration and production of hydrocarbons from the khufai formation

soft sediment deformation structures induced by cyclic stress of storm waves in tempestites miocene guadalquivir basin spain the identification of triggering agents for soft sedimentation structures is an enigmatic geological problem mainly seismic induced soft sediment structures have been recognized in ancient sediments rather than those resulting from storm waves we analyse soft sediment deformation structures in upper miocene calcarenitic tempestites of the guadalquivir basin southern spain the most common structures are load casts which vary in height and width from 10 centimetres to several metres the structures are always restricted to a small part of the stratigraphic sections in exclusive association with tempestites the analysed soft deformation structures are interpreted to be the result of liquidization processes chiefly from their inferred depositional environment and subordinately from the deformation style we have devised basic criteria to identify the trigger mechanism in these soft sediment deformation structures the liquefaction was triggered by pore pressure changes induced by cyclic and residual stress of storm waves

ediacaran sulfur cycle insights from sulfur isotope measurements δ33s and δ34s on paired sulfate pyrite in the huqf supergroup of oman abstract the ediacaran period 635 541 ma was a time of dramatic environmental and ecological change sulfur isotopic records preserved in marine strata provide insights into these changes previous work using 34 s in pyrite and carbonate associated sulfate in the ediacaran aged huqf supergroup sultanate of oman suggested increases in marine sulfate concentrations changing microbial pathways and redox conditions and a long term increase in 34 s of sulfate delivery to the ocean however 34 s based analyses on their own were insufficient to uniquely reconstruct these environmental and ecological changes here we present new paired 34 s and 33 s data from carbonate associated sulfate and pyrite in these strata the results allow us to provide three new constraints on ediacaran sulfur cycling first a notable increase 34 s cas py previously attributed to possible disproportionation in upper buah strata is associated with 33 s evidence for an increase in sulfide reoxidation indicating a transition to more oxidizing conditions possibly associated with the onset of bioturbation secondly 33 s data indicate that a large positive shift in both sulfate and pyrite 34 s in ara group strata is mostly likely due to an increase in delivery of 34 s enriched sulfate to the basin finally paired 34 s 33 s data constrain possible changes in seawater sulfate concentrations suggesting an increase in sulfate supply related to enhanced evaporite weathering consistent with geological and geochemical observations that imply high so 4 17 mm during deposition of the ara group

some guidelines in reconstructing ancient sea conditions from wave ripplemarks abstract the collection of substantial field data on wave ripple mark spacing wavelength steepness grain size and symmetry index from the miocene burdigalian sandstones of western switzerland has allowed apparently close reconstruction of sea conditions results indicate however that ancient wave reconstructions must be restricted at present to data from relatively steep ripple marks vfi less than 7 5 i e vortex ripples data from the flatter ripple marks post vortex types formed at high oscillatory shear stresses do not provide reasonable estimates of wave conditions penecontemporaneous overwashing and or post depositional compaction ripple formation near the destruction condition rather than the threshold of sediment movement orbital diameters far exceeding ripple spacing and superimposed unidirectional currents are all factors which seriously affect wave reconstructions evaluation of ancient wave conditions provides insight into geologically important phenomena such as local water depth and basin size

extreme winds and waves in the aftermath of a neoproterozoic glaciation the most severe excursions in the earth s climatic history are thought to be associated with proterozoic glaciations according to the snowball earth hypothesis the marinoan glaciation which ended about 635 million years ago involved global or nearly global ice cover at the termination of this glacial period rapid melting of continental ice sheets must have caused a large rise in sea level here we show that sediments deposited during this sea level rise contain remarkable structures that we interpret as giant wave ripples these structures occur at homologous stratigraphic levels in australia brazil canada namibia and svalbard our hydrodynamic analysis of these structures suggests maximum wave periods of 21 to 30 seconds significantly longer than those typical for today s oceans the reconstructed wave conditions could only have been generated under sustained high wind velocities exceeding 20 metres per second in fetch unlimited ocean basins we propose that these extraordinary wind and wave conditions were characteristic of the climatic transit and provide observational targets for atmospheric circulation models

evolution of a terminal neoproterozoic carbonate ramp system buah formation sultanate of oman effects of basement paleotopography the buah formation is a carbonate unit of late neoproterozoic age exposed in the jabal akhdar of northern oman and the huqf region of central oman the buah formation is interpreted as a distally steepened storm dominated ramp containing inner ramp tidally influenced oolitic shoal and back shoal lagoon fades and storm dominated mid ramp facies a slope break separates mid ramp facies from outer ramp facies characterized by accumulation of redeposited carbonates on gently inclined slopes 1 2 degrees combined facies stacking patterns and outcrop correlation via 1 3 c profiles suggest that buah carbonates formed as a highstand systems tract characterized by a general upward shallowing of facies and strong lateral progradation on a regional scale buah facies distributions across oman were controlled by the presence of basement highs defining areas of reduced subsidence which promoted lateral progradation of the buah carbonate ramp for tens of kilometers while the faster subsiding areas became sites of deep water deposition

irreversible change of the oceanic carbon cycle in the earliest cambrian high resolution organic and inorganic carbon chemostratigraphy in the three gorges area south china the terminal neoproterozoic and its transition into the cambrian witnessed major evolutionary and geochemical changes large fluctuations in the carbon isotope ratio for inorganic carbon 13ccarb across the precambrian cambrian boundary pc c boundary indicate a significant change in the oceanic carbon cycle at that time this work presents the first high resolution 13corg chemostratigraphy of drill core samples across the pc c boundary in the three gorges area south china and discusses carbon cycles based on the relation between 13corg and 13ccarb we found that changes of 13corg and 13ccarb values were decoupled during the significant negative excursion of 13ccarb across the pc c boundary suggesting the presence of a huge organic carbon pool ocp previously the large ocp was inferred to have been established in the terminal proterozoic and to have disappeared at the end of the mid ediacaran shuram excursion in contrast our study suggests that the large ocp lasted until the early nemakit daldynian stage on the other hand in the middle nemakit daldynian to atdabanian the 13ccarb and 13corg changed in parallel as observed normally in the phanerozoic in order to evaluate these scenarios quantitatively we performed numerical simulations and calculated the time evolution of the 13ccarb masses of the inorganic and organic carbon pools and the fluxes between them as a result we show that the observed negative 13ccarb excursion with steady 13corg can be produced by enhanced primary productivity and remineralization of the large ocp if the rate constant for removal of organic carbon was considerably lower than that of today the end of the decoupled negative 13ccarb excursion is attributable to an increase in the removal rates of inorganic and organic carbon from the ocean the enhanced flux of organic carbon burials eliminated the large ocp so that the modern style carbon cycle was established by the early nemakit daldynian stage the inferred rapid increases of both organic and inorganic carbon burial rates in the middle nemakit daldynian stage were likely caused by the appearance of planktonic metazoans with guts making fecal pellets and by the first skeletal animals the biological innovations may have changed the oceanic carbon cycle irreversibly just after the pc c boundary

ultra high resolution multivariate record and multiscale causal analysis of pridoli late silurian implications for global stratigraphy turnover events and climate biota interactions abstract the upper silurian and especially pridoli epoch is a critical interval for the understanding the evolution of earth s biota since it witnessed series of powerful extinction events global reorganizations of paleocommunities and expansion of new clades which assumed dominance in the subsequent devonian period the stratigraphic record of the eastern part of the silurian baltic basin represents an excellent candidate for the fine scale analysis of paleoecological and paleoceanographic dynamics therefore we presenting here stratigraphic record of the milaiciai 103 core south western lithuania of conodonts brachiopods 13ccarb 18ocarb and a series of various geochemical and geophysical proxies most of which were sampled at a very high resolution 11 ka spanning uppermost ludlow pridoli and the lowermost devonian the analysis revealed that the pridoli was characterized by four distinct long term dynamic states here named i normal pridoli i ii silal negative carbon isotopic excursion and extinction event iii normal pridoli ii and iv klonk positive stable carbon isotopic event and excursion the most significant change in most variables is detected approximately in the middle of the pridoli at the beginning of the delotaxis detorta zone at the recovery after silal event of conodonts and at the onset of collapse of brachiopod communities the analysis of dynamic complexity revealed the strong evidence for the presence of 405 ka metronome milankovitch cycles in the record of 13ccarb which constrains the duration of the pridoli epoch to 4 3 0 2 ma the recurrence plot analyses revealed deterministic coordination between 13ccarband conodont paleocommunity dynamics at all scales finally lead lag analysis using conditional joint recurrence revealed that conodont dynamics as a rule were driven by perturbations in the carbon cycle although silal event interval shown opposite pattern thus confirming the unusual nature of this previously unrecognized coordinated climatic and biotic event

extinction of cloudina and namacalathus at the precambrian cambrian boundary in oman biostratigraphic carbon isotope and u pb zircon geochronological data from the ara group of oman indicate an abrupt last appearance of cloudina and namacalathus coincident with a large magnitude but short lived negative excursion in the carbon isotope composition of seawater that is globally coincident with the precambrian cambrian boundary u pb zircon age data from an intercalated ash bed directly define this negative excursion to be at 542 0 0 3 ma consistent with previous age constraints from siberia and namibia combined with the global biostratigraphic record these new data strengthen hypotheses invoking mass extinction within terminal proterozoic ecosystems at or near the precambrian cambrian boundary

ca and mg isotope constraints on the origin of earth s deepest δ13c excursion abstract understanding the extreme carbon isotope excursions found in carbonate rocks of the ediacaran period 635 541 ma where 13 c of marine carbonates 13 c carb reach their minimum 12 for earth history is one of the most vexing problems in precambrian geology known colloquially as the shuram excursion the event has been interpreted by many as a product of a profoundly different ediacaran carbon cycle more recently diagenetic processes have been invoked with the very negative 13 c values of ediacaran carbonates explained via meteoric alteration late stage burial diagenesis or growth of authigenic carbonates in the sediment column thus challenging models which rely upon a dramatically changing redox state of the ediacaran oceans here we present 257 44 40 ca and 131 26 mg measurements along with mg mn and sr data from carbonates of the ediacaran aged wonoka formation fm of south australia to bring new isotope systems to bear on understanding the shuram excursion data from four measured sections spanning the basin reveal stratigraphically coherent trends with variability of 1 5 in 26 mg and 1 2 in 44 40 ca this ca isotope variability dwarfs the 0 2 0 3 change seen coeval with the permian triassic mass extinction the largest recorded in the rock record and is on par with putative changes in the 44 40 ca value of seawater seen over the phanerozoic eon changes in both isotopic systems are too large to explain with changes in the isotopic composition of ca and mg in global seawater given modern budgets and residence times and thus must be products of alternative processes relationships between 44 40 ca and sr and 26 mg and mg are consistent with mineralogical control e g aragonite vs calcite limestone vs dolostone on calcium and magnesium isotope variability the most pristine samples in the wonoka dataset preserving sr concentrations in the 1000s of ppm range and 44 40 ca values inherited from an originally aragonitic polymorph have 13 c carb of 8 to 7 thereby providing strong geochemical evidence that extremely negative 13 c carb values are primary products of the ediacaran surface environment

veracity of neoproterozoic negative c isotope values the termination of the shuram negative excursion abstract there is widespread interest in the neoproterozoic period of the earth s history 1000 to 542 ma because of unprecedented 13 c fluctuations to 1000 m succession of stratigraphically complex sedimentary rocks deposited during tens of millions of years in contrast phanerozoic large negative c isotope excursions have been interpreted as the result of diagenetic fluid mixing during carbonate stabilization and burial and are less enigmatic due to the excellent biostratigraphic control on their timing and duration the ediacaran nafun group of oman part of the huqf supergroup spanning the cryogenian early cambrian contains a large 13 c negative excursion the shuram excursion reaching values as negative as 12 at the base of the shuram formation a steady recovery to positive values occurs over the entire shuram and half through the overlying buah formation suggesting a duration on the order of tens of my based on trace metal chemostratigraphic and sedimentological analyses the carbon isotope record obtained from the buah formation of northern oman indicates a systematic and reproducible shift of 13 c values from 6 to 1 in 1 a demonstrably diagenetic altered carbonate cemented siliciclastic facies and 2 a least diagenetically altered stromatolitic facies the identical reproducible isotopic pattern in these time equivalent sections combined to the presence of exceptionally preserved 18 o values around 2 to 1 associated with the most negative 13 c values rules out isotopic resetting by diagenetic fluids as a mechanism to explain these values it is concluded that it is possible to retain depositional 13 c values in demonstrably diagenetically altered carbonates this raises the issue of the ability to recognize diagenetic alteration of c isotopic values in neoproterozoic rocks where a robust time frame to support reproducibility is not available the results of this study provide strong support to a non diagenetic origin of the negative shuram c isotope excursion believed to be the most profound in terms of amplitude and duration in the earth s history

erratum to chemostratigraphic and sedimentological framework of the largest negative carbon isotopic excursion in earth history the neoproterozoic shuram formation nafun group oman j precam res 146 2006 68 92

insights from isotope stratigraphy a symposium on precambrian isotope stratigraphy was heldwithintheframeofthe33rdigcheldatoslo norway august2008 this symposium spawned the idea for a special issue on this themeand ultimately to the ten papers assembled here this special issueprovides the results of some of the latest cutting edge research ontraditional c sr s isotopechemostratigraphyandintroducesomenewer isotope systems ree ca and hg chemostratigraphy as apotential tracer for glacial events and estimate of the buildup ofvolcanicgases includingco

understanding carbonate ramp dynamics using δ13c profiles examples from the neoproterozoic buah formation of oman the late neoproterozoic buah formation nafun group oman is a carbonate unit outcropping in the jabal akhdar and huqf areas it is composed mostly of shallow water carbonates deposited on a distally steepened carbonate ramp correlation of two 13c isotope shifts shows that in the jabal akhdar ramp differentiation into fast and slow subsiding areas was followed by lateral progradation in the huqf area however a uniform scenario of upward shallowing of the facies and lateral progradation is demonstrated by chemostratigraphic timelines cross cutting the facies belts the chemostratigraphic profiles show that the buah formation was deposited during sea level highstand conditions and that ramp differentiation was due to synsedimentary tectonics high resolution correlation of 13c profiles from the same lithostratigraphic unit whether precambrian or phanerozoic in age lacking biostratigraphic data can shed light on carbonate systems dynamics tectonic vs eustatic controls on depositional sequences and basin subsidence

a pronounced negative δ13c excursion in an ediacaran succession of western yangtze platform a possible equivalent to the shuram event and its implication for chemostratigraphic correlation in south china abstract a pronounced negative 13 c shift that can be potentially correlated with the shuram excursion has been reported from middle ediacaran strata in the yangtze gorges area of south china whether it represents a perturbation to the ocean carbon cycle or a record of post depositional alteration is still open to debate resolving this controversy will help clarify if 13 c variations can be used for chemostratigraphic correlation of ediacaran successions to further understand the regional pattern of ediacaran carbon isotopic excursions in the yangtze platform we carried out a detailed 13 c analysis of the lianghong section in the western part of the yangtze platform the ediacaran system at lianghong is overlain by the maidiping formation yielding early cambrian small shelly fossils and underlain by the cryogenian lieguliu formation diamictite and tuffaceous siltstones it comprises the guanyinya and hongchunping formations which have been traditionally correlated with the doushantuo and dengying formations respectively in the yangtze gorges area two negative 13 c excursions occur in the lianghong section the lower one at the uppermost guanyinya formation with a nadir at 8 6 may be correlated with the pronounced negative 13 c shift en3 in the uppermost doushantuo formation in the yangtze gorges area and possibly with the well known shuram event in oman the upper negative 13 c excursion occurs in the upper hongchunping formation and may be correlated with negative excursions en4 near the ediacaran cambrian boundary other negative 13 c excursions e g en1 and en2 are not expressed in the lianghong section because the lower guanyinya formation is dominated by siliciclastic rocks combined with previously published ediacaran 13 c profiles our results indicate that the en3 excursion likely a shuram equivalent may occur widely in south china and can be a useful chemostratigraphic feature for regional and global stratigraphic correlation

analysis of soft sediment deformation structures in neogene fluvio lacustrine deposits of caybagi formation eastern turkey during the neogene both strike slip and extensional regimes coexisted in eastern turkey and a number of fault bounded basins associated with the east anatolian fault system developed the caybagi formation late miocene early pliocene deposited in one of these basins consists of fluvio lacustrine deposits numerous soft sediment deformation structures are encountered in this formation particularly in conglomerates medium to coarse grained tuffaceous sandstones and claystones folded structures slumps convolute laminations and simple recumbent folds water escape structures intruded sands internal cusps interpenetrative cusps and sand volcanoes and load structures load casts pseudonodules flame structures and pillow structures these structures are produced by liquefaction and or fluidization of the unconsolidated sediments during a seismic shock consequently the existence of seismically induced deformation structures in the caybagi formation and the association with a neogene intraformational unconformity growth faults and reverse faults in the caybagi basin attest to the tectonic activity in this area during the late miocene and early pliocene the east anatolian fault system in particular the uluova fault zone is the most probable seismogenic source earthquakes with a magnitude of over 5 in the richter scale can be postulated

reconstructing paleoceanographic conditions during the middle ediacaran evidence from giant ooids in south china abstract the ediacaran was a period of intense environmental change in earth history transient pulses of oxygenation and shifts in ocean chemistry have been interpreted from a range of geochemical proxies including rare earth elements and yttrium rey but it is still a challenge to reconstruct paleoceanographic conditions due to the scarcity of reliable recorder in this study we explore the possibility that a newly discovered deposit of giant ooids in the nanshanping outcrop in south china contains a relatively intact record of the ree composition of ediacaran seawater providing an important window into the redox state of the surface ocean at this time these ooids are relatively large in size 1 6 mm and exhibit densely banded laminae a regional chemostratigraphic correlation shows that the giant ooid bearing succession in south china is in the upper part of the second ediacaran positive carbon isotopic shift ep2 and thus its occurrence was not associated with the shuram excursion additionally the occurrences of giant ooid bearing oolites in different blocks were not synchronous during the middle ediacaran in situ laser ablation analysis of giant ooid cortices reveals that the shale normalized rey patterns are similar to those of modern seawater including depleted light rees superchondritic y ho ratios and positive la anomalies yet no ce anomalies 1 0 0 15 in numerous ooid cortices seems to indicate a suboxidized condition of surface ocean in south china at that time the petrographic and geochemical evidence support the weak diagenetic alteration of the pure giant ooids during burial they formed in open ocean settings with energetic hydrodynamic environments and were affected by early dolomitization that might preserve mostly original petrographic fabrics and rey signatures from further diagenetic overprinting the characteristics of ce anomalies and rey compositions acquired from the giant ooids indicate that the surface ocean was suboxidized in south china during the late stage of ep2 implying the very low atmospheric o2 level at that time our results suggest that giant ooids may be a reliable analytical target that provide a snapshot into palaeoceanographic conditions during this crucial period of dynamic changes in early earth history

petrography and geochemistry of the magnesites and dolostones of the ediacaran ibor group 635 to 542 ma western spain evidences of their hydrothermal origin the ediacaran deposits between 635 and 542 ma of the central zone of the iberian massif consist of alternating siliciclastic and carbonate beds these carbonates are dolostones and magnesites which are interpreted to have been formed by the replacement of primary peritidal limestones through petrographic and geochemical analyses we recognize different types of dolomites d1 to d4 and magnesites m1 and m2 despite distinct petrographic features of the four types of dolomite their oxygen and carbon isotopes overlap with 18o values ranging from 15 45 to 17 51 smow and 13c from 0 13 to 3 21 pdb sr isotope values for d1 and d2 range from 0 7028 to 0 7091 magnesites m1 and m2 show oxygen values higher than 17 87 0 and 13c values show the same variability as for the dolomites d3 and d4 oxygen isotope values are between 18 91 and 19 61 and the carbon isotope values range are similar to the other diagenetic phases sr isotope values for the magnesites and late dolomites d3 and d4 are 0 7095 to 0 7104 being higher than those of the d1 and d2 dolomites d1 is a relatively early dolomite phase formed by the replacement of fine grained peritidal limestones the coarser crystal size of d2 which shows similar geochemical features as d1 suggests formation by dolomitization of coarser grained limestones the replacement of d1 and d2 by m1 and m2 advanced along stylolites fractures and bedding planes this replacement is interpreted to have occurred by hydrothermal fluids which is suggested by the presence of talc and forsterite d3 a coarse dolomite completely destroyed any previous texture and d4 dolomite cement post dates magnesite formation interactions of hydrothermal fluids with the prior carbonates reset the oxygen isotopes of the earlier dolomite the study of these magnesites and related dolostones may offer new insights into the model of formation of sparry magnesites hosted by mixed siliciclastic carbonate platform deposits the establishment of the factors and mechanism that control the diagenetic evolution of these carbonates has a great importance in order to understand and predicts porosity and permeability variations of rocks formed under similar geological conditions

50 myr recovery from the largest negative δ13c excursion in the ediacaran ocean sedimentary rocks deposited during the ediacaran period 630 542 ma contain carbonates whose carbon isotopic ratios show a marked negative excursion consisting of a precipitous drop from 5 to 12 followed by a sub linear recovery to positive 13c values isotopic ages u pb and thermal subsidence modelling are combined to constrain the excursion in time and indicate an onset at 600 ma and duration of recovery of approximately 50 myr the excursion is widely recognized in oman and has potential correlatives in ediacaran strata elsewhere and may thus represent a characteristic feature of the ediacaran period the amplitude of this carbon isotope excursion far exceeds those of other neoproterozoic anomalies the isotopic trend of negative excursion and long term recovery spanned at least one short lived glacial episode at 580 ma but appears unrelated to glaciation which indicates that negative anomalies in the neoproterozoic marine carbon isotope record are not directly or uniquely linked to ice ages

reconstruction of ancient sea conditions with an example from the swiss molasse ancient sea conditions can be estimated from the grain size spacing and steepness of preserved ripple marks the element of greatest uncertainty in such reconstructions is the relationship between near bed orbital diameter of water particles and the ripple spacing this relationship is simple for vortex ripples of high steepness but is problematical for the low steepness forms known as post vortex rolling grain or anorbital ripples the existence field for wave ripples is between the threshold velocity for sediment movement and the onset of sheet flow most low steepness forms occurring close to the bed planation threshold a range of maximum period of formative waves can be obtained using combinations of orbital diameter and orbital velocity assuming linear wave theory to be a reasonable approximation probable wave heights wave lengths and water depths can be investigated using the transformation of wave parameters in shallowing waters and the constraints on wave dimensions provided by the wave breaking condition given reasonable estimates of wave height crude estimates of wave power allow a comparison of ancient wave influenced sequences with modern counterparts wave ripple marks preserved in the upper marine molasse of western switzerland have been investigated results which are in agreement with regional geology suggest deposition in a seaway of approximately 100 km width where moderate period waves t 3 6 s were generated the depositional facies belts were adjusted to the prevailing waves tides and fluvial outflows

calibrating the coevolution of ediacaran life and environment the rise of animals occurred during an interval of earth history that witnessed dynamic marine redox conditions potentially rapid plate motions and uniquely large perturbations to global biogeochemical cycles the largest of these perturbations the shuram carbon isotope excursion has been invoked as a driving mechanism for ediacaran environmental change possibly linked with evolutionary innovation or extinction however there are a number of controversies surrounding the shuram including its timing duration and role in the concomitant biological and biogeochemical upheavals here we present radioisotopic dates bracketing the shuram on two separate paleocontinents our results are consistent with a global and synchronous event between 574 0 4 7 and 567 3 3 0 ma these dates support the interpretation that the shuram is a primary and synchronous event postdating the gaskiers glaciation in addition our re os ages suggest that the appearance of ediacaran macrofossils in northwestern canada is identical within uncertainty to similar macrofossils from the conception group of newfoundland highlighting the coeval appearance of macroscopic metazoans across two paleocontinents our temporal framework for the terminal proterozoic is a critical step for testing hypotheses related to extreme carbon isotope excursions and their role in the evolution of complex life

mapping of neoproterozoic source rocks of the huqf supergroup in the sultanate of oman using remote sensing abstract in recent years the neoproterozoic huqf supergroup formations of the oman salt basins have been the target for oil exploration the present study maps the surficial exposure of the huqf supergroup in and around khufai dome of the huqf area in the sultanate of oman using low cost multi spectral remotely sensed satellite data and image processing methods such as decorrelation stretching principal component analysis pca and spectral angle mapper sam as alternative to expensive and time consuming tools which have the capability and potential to be used by geoscientists for oil exploration in this research the study of advanced spaceborne thermal emission and reflection radiometer aster spectral bands 8 3 and 1 by decorrelation stretching well discriminated the masirah bay the khufai the shuram and the buah formations of the nafun group the source rocks of huqf supergroup with the quaternary deposits the analysis of visible and near infrared shortwave infrared spectral bands of aster by pca clearly showed the occurrence and spatial distribution of such formations in the rgb principal component images r pc1 g pc2 b pc3 the spatial distributions of such formations are assessed by confusion matrix after using maximum likelihood ml spectral angle mapper sam and spectral information divergence sid algorithms the matrix of ml algorithm has provided the best overall accuracy of 92 93 and kappa coefficient of 0 92 the minerals of the formations were detected by sam further the detection of such mineral groups was confirmed through the aster thermal infrared tir spectral indices image developed using the carbonate index ci quartz index qi and mafic index mi all results of image analyses are evaluated in the field and laboratory studies the study also evaluates the satellite data and image processing methods for the formations of jabal akhdar the equivalent formations of the khufai dome to show the sensor capability and the use of the image processing methods to study the source rocks the results of the study provided similar discriminations comparable to the khufai dome therefore the data and the techniques are recommended to the exploration geologists for use in similar regions of the world

soft sediment deformation in a tectonically active area the plio pleistocene zarzal formation in the cauca valley western colombia abstract the plio pleistocene zarzal formation corresponds to fluvio lacustrine sediments deposited in an intramontane depression within the colombian andes associated with the cauca romeral fault system it crops out mainly in the cauca valley where numerous field sections have permitted the mapping of the vertical and lateral lithological variations lacustrine deposits of sands silts clays and diatomites are interbedded with fluvial sand and gravel beds and fluvio volcanic mass flows derived from the volcanic central cordillera numerous soft sediment deformation structures are encountered in this formation particularly in fine to medium grained sands silts and clays load structures load casts flame structures pseudonodules water escape structures water escape cusps dish and pillar and pocket and pillar structures soft sediment intrusions clastic sills and dykes disturbed laminites convolute laminations slumps and synsedimentary faulting deformation mechanisms and driving forces are related essentially to gravitational instabilities dewatering liquidization and brittle deformations field and regional geological data show that most of these deformations are related to seismicity and can be interpreted as seismites this area has a geological and recent seismic history and outcrops show both syn and post depositional faulting related to the transpressional regime of this part of the colombian andes which generates strike slip faults and associated local normal faults the drainage pattern within the zarzal formation shows the signature of neotectonics moreover the fine to coarse grained sands of the zarzal formation are lithologies prone to liquefaction when affected by seismic waves the intercalation of the deformed intervals within undisturbed strata confirms the catastrophic nature of the events finally the large areal extent of the deformations and the type of structures are compatible with seismites consequently the existence of seismites in the zarzal formation represents corroboration of tectonic activity in this area during the pleistocene earthquakes with a magnitude higher than 5 can be postulated based upon the proximity of active faults and the types of deformations

ediacaran growth of the marine sulfate reservoir abstract the sulfur isotope record as preserved in sedimentary sulfate and sulfide minerals reflects the progressive oxidation of earth s surface environment the latest proterozoic to early paleozoic marine sulfur isotope record is distinguished by unusually high 34 s values in marine sulfates and sulfides geological considerations and sulfur isotopic data indicate that the 34 s enrichment of the marine sulfate reservoir was the result of a rapid increase in the net fractionation between sedimentary sulfate and pyrite 34 s without a compensatory decline in the fractional burial rate of pyrite f pyr a simple one box model in which 34 s is linked non linearly to marine so 4 is used to explore the response in sedimentary sulfur isotope records 34 s sulf and 34 s pyr to an increasing marine sulfate reservoir the model results when compared with a compilation of existing 34 s sulf and 34 s pyr data suggest that the marine sulfate reservoir grew rapidly to roughly phanerozoic levels in the middle ediacaran period before the gaskiers glaciation and prior to the onset of the shuram wonoka negative 13 c anomaly it is further hypothesized that p o 2 levels rose prior to the onset of this extreme perturbation to the global carbon cycle permitting the oxidation of a previously euxinic deep ocean and appearance of the first ediacaran fauna by ca 575 ma despite the enormous demand on oxidants implied by this large magnitude and long duration carbon isotope anomaly

isotope stratigraphy of the ediacarian neoproterozoic iii of the adelaide rift complex australia and the overprint of water column stratification abstract this study establishes a high resolution 13c chemostratigraphic framework for the type ediacarian terminal proterozoic section in the adelaide rift complex a framework that contributes to the emerging global chronostratigraphic synthesis of a period that saw momentous changes in the earth s surface environment only 15 m of the 3 5 km thick type section consists of shallow water carbonates of the kind that have formed the basis of most previous studies of neoproterozoic chemostratigraphy however the organic 13corg record reveals a surprising richness of information and shows excellent utility in correlation between sections in the adelaide rift complex lateral variations in 13corg profiles correspond to expected diachronous patterns of basin fill with the addition of 87sr 86sr data correlation can also be made to the officer and amadeus basins consistent with known lithostratigraphic and sequence stratigraphic constraints sublittoral micritic carbonates of the upper nuccaleena formation cap dolostone and lower and middle wonoka formation show strong basinwide 13c depletion 13ccarb 3 to 10 despite compelling evidence for preservation of depositional 13ccarb such as good textural preservation evidence for sea floor lithification and in the wonoka formation pristine 87sr 86sr and low mn sr associated with the depleted carbonates are rare subaqueous evaporite relatively heavy 13corg and anomalously 13c depleted organic carbon of benthic microbial mat origin and a common cause salinity stratification of the water column is postulated the indicated palaeogeographic setting an evaporative mediterranean like basin tenuously connected to the world ocean is entirely consistent with previous suggestions of one or more messinian type desiccation events to explain very deep 1 km incised valleys or canyons in the adelaide rift complex and officer basin at horizons within the wonoka formation and correlates positive excursions in 13corg during basin stratification may in part be due to 12c depletion of surface waters by photosynthetic carbon fixation despite the proposed semi isolation of australian ediacarian basins from the world ocean major 13c excursions which can to some extent be differentiated by the monotonic rise in ediacarian marine 87sr 86sr appear to be correlatable to the upper windermere supergroup northwest canada

provenance of ediacaran sinian sediments in the helanshan area north china craton constraints from u pb geochronology and hf isotopes of detrital zircons abstract the tectonic relationship between the alxa block and the north china craton has long been controversial the helanshan area lies at the western margin of the ordos block and to the east of the alxa block and it contains eidacaran zhengmuguan formation and tuerkeng formation the zhengmuguan formation is made up of tillites limestone and dolomine and the tuerkeng formation consists of silty slate a parallel unconformity marks the boundary between the tuerkeng formation and the early cambrian suyukou formation which is composed mainly of phosphatic pebbly sandstone and sandstone u pb dating ages of detrital zircons in the zhengmuguan and suyukou formations reveal two neoproterozoic age peaks of 818 4 ma n 88 and 905 8 ma n 20 neoproterozoic magmatic events have yet been reported in the basement of the ordos block while some neoproterozoic igneous rocks have been found in the basement of the alxa block moreover the two neoproterozoic age peaks correspond well with the ages of neoproterozoic igneous rocks in alxa block the hf isotopic characteristics of a part of neoproterozoic zircons from the ediacaran zhengmuguan formation in the helanshan area ehf t 7 812 to 3 274 tdmc 2211 1578 ma n 10 are similar to those neoproterozoic igneous zircons from the langshan area ehf t 1 105 to 5 928 tdmc 1 75 1 38 ga n 23 and bayinnuoergong area in the alxa block the parental magmas had a long residency time in the crust it seems therefore that alxa block provenance provided neoproterozoic clastics for helanshan area in ediacaran and alxa block had already been a part of the north china craton by the late neoproterozoic even earlier

massive dissociation of gas hydrate during a jurassic oceanic anoxic event in the jurassic period the early toarcian oceanic anoxic event about 183 million years ago is associated with exceptionally high rates of organic carbon burial high palaeotemperatures and significant mass extinction heavy carbon isotope compositions in rocks and fossils of this age have been linked to the global burial of organic carbon which is isotopically light in contrast examples of light carbon isotope values from marine organic matter of early toarcian age have been explained principally in terms of localized upwelling of bottom water enriched in 12c versus 13c refs 1 2 5 6 here however we report carbon isotope analyses of fossil wood which demonstrate that isotopically light carbon dominated all the upper oceanic biospheric and atmospheric carbon reservoirs and that this occurred despite the enhanced burial of organic carbon we propose that as has been suggested for the late palaeocene thermal maximum some 55 million years ago the observed patterns were produced by voluminous and extremely rapid release of methane from gas hydrate contained in marine continental margin sediments

carbonate platform facies models various types of carbonate platforms are characterized by distinctive profiles facies and evolutionary sequences ramps may be homoclinal or distally steepened and may have fringing or barrier shoal water complexes of ooid pellet sands or skeletal banks homoclinal ramps pass seaward into deeper water without major break in slope and lack deep water breccias distally steepened ramps may be low energy and characterized by widespread shallow subwave base mud blankets or high energy with coastal beach dune complexes and widespread skeletal sand blankets slope facies may contain abundant breccias of slope derived clasts rimmed shelves have relatively flat tops and marked break in slopes at the high energy shallow shelf edge where they pass into deep water such shelves may be aggraded with peritidal facies extending over much of the shelf or incipiently drowned depending on magnitude of sea level fluctuations they may be accretionary or bypass types that include gullied slope escarpment and high relief erosional forms intrashelf basins occur on some shelves controlling distribution of reservoir and source beds isolated platforms are surrounded by deeper water and may be located on rifted continental margins or on submarine volcanoes most have high relief rimmed margins platforms that have been subjected to rapid sea level rise may be incipiently drowned and characterized by raised rims elevated patch or pinnacle reefs and widespread subwave base carbonate or fine clastic blankets completely drowned shelves develop where the shelf is submerged to subphotic depths terminating shallow water deposition and commonly resulting in blanketing of the shelf by deeper water facies some margins show extensive down to basin faulting that is contemporaneous with carbonate deposition or associated with thick prograding clastic sequences the various types of platforms change in response to variations in sedimentation subsidence or sea level rise and may form distinctive evolutionary sequences the relatively few models presented appear to accommodate most geological examples some of which contain major reservoir facies

experiments on oscillatory flow and combined flow bed forms implications for interpreting parts of the shallow marine sedimentary record abstract analog laboratory experiments were conducted to investigate subaqueous bed forms generated under storm like oscillatory and combined flow experiments were carried out in a large wave tunnel and used a range of sand sizes fine and very fine wave periods 10 5 and 8 s oscillatory velocities 0 to 125 cm s and unidirectional velocities 0 to 25 cm s at low unidirectional velocities 10 cm s addition of an increasing collinear oscillatory flow caused the bed to evolve from small scale wavelength 100 cm symmetric orbital ripples to plane bed at higher unidirectional velocities 10 cm s a similar trend was noted but ripples were more asymmetric three phase diagrams are presented to summarize the observed relationships of bed configurations to flow conditions these diagrams are intended to assist in the interpretation of shallow marine sedimentary environments where oscillatory and combined flow are thought to be omnipresent distinctive features of small scale asymmetric combined flow ripples generated are a 3d planform round crest and convex up sigmoidal profile with local pronounced scour at the toe of the stoss side giving the ripple profile a boxy appearance similarly large scale asymmetric combined flow ripples had broad and round crests convex up stoss sides and compressed profiles due to scouring at the toe of the stoss side hummocky bed forms were generated under moderate to high oscillatory velocities and low unidirectional velocities hummocks were not observed as a distinct bed state but rather appeared to mark transitions in bed form scale and symmetry hummocks were more prevalent at longer oscillatory periods and in finer grained sediment stratification produced by synthetically aggrading hummocky bed profiles closely resembles hummocky cross stratification with the introduction of only a small unidirectional flow component hummocks evolve into downstream migrating large scale asymmetric ripples and the resultant cross stratification becomes similar to that produced by unidirectional flow dunes accordingly these experiments suggest that much of the hummocky cross stratification observed in the stratigraphic record is produced by storm generated long period oscillatory dominant combined flows inasmuch as long period high energy waves require deep wide basins to form hummocky cross stratification may therefore serve as a useful indicator of deposition in unrestricted open water conditions

two from donegal neoproterozoic glacial episodes on the northeast margin of laurentia two glacial episodes the sturtian ca 720 ma and marinoan varangerian ca 590 ma characterize many neoproterozoic successions worldwide in contrast northeast laurentia is typically considered as containing only the latter in scotland and ireland this is represented by the port askaig tillite here we present evidence ice rafted debris for a second younger neoproterozoic glacial event in the dalradian southern highland group of donegal ireland these deposits overlie strata correlative to ca 595 ma rocks in scotland making this heretofore unrecognized glacial episode a marinoan varangerian equivalent in that the port askaig occurs 3 5 km stratigraphically below the southern highland group rocks it is most likely sturtian not marinoan varangerian in age thus the dalradian succession in the irish caledonides contains strata representing both the sturtian and marinoan varanger glaciations

origin of petroleum in the neoproterozoic cambrian south oman salt basin abstract the south oman salt basin sosb is host to the world s oldest known commercial deposits most of the south oman oils have been proven to be associated with the source rocks of the neoproterozoic to cambrian huqf supergroup but the assignment of oils to specific huqf intervals or facies has been hampered by the geochemical similarity of the organic matter across the entire huqf sequence possibly as a consequence of limited change in the local palaeoenvironment and biota over the time of its deposition this study was conducted to establish improved correlations between organic rich rock units and reservoir fluids in the sosb through detailed molecular and isotopic analysis of the huqf supergroup with special emphasis directed towards understanding the ara carbonate stringer play unusual biomarkers tentatively identified as a norsteranes show distinctive patterns among carbonate stringer oils and rocks different from those observed in nafun sediments and ara rocks from the athel basin these putative a norsteranes form the basis for new oil source correlations in the sosb and provide for the first time geochemical evidence of a self charging mechanism for the carbonate stringer play the paucity of markers specific to the nafun group shuram buah and masirah bay formations confounds attempts to quantify their respective contributions to huqf oil accumulations nafun inputs can only be determined on the basis of subtle differences between nafun and ara biomarker ratios the most useful geochemical characteristics delineating nafun group organic matter from ara group intra salt source rocks included low relative abundance of mid chain monomethyl alkanes x compounds low relative abundance of gammacerane 28 30 dinorhopane 25 28 30 trinorhopane and 2 methylhopanes low c 22 t c 21 t and high c 23 t c 24 t cheilanthanes ratio values based on these parameters molecular evidence for major contributions of liquid hydrocarbons from nafun group sediments shuram buah and masirah bay formations is lacking our results suggest that the majority of sosb hydrocarbon accumulations originate from within the ara group either from the carbonate stringers or from the package of sediments that comprises the thuleilat athel silicilyte and u shale formations subtle aspects of the composition of some carbonate stringer and post salt huqf oils could suggest some degree of sourcing from the nafun rocks but stronger evidence is needed to confirm this

stratigraphic expression of earth s deepest δ13c excursion in the wonoka formation of south australia the most negative carbon isotope excursion in earth history is found in carbonate rocks of the ediacaran period 635 541 ma known colloquially as the shuram excursion workers have long noted its broad concordance with the rise of abundant macro scale fossils in the rock record collectively known as the ediacaran biota thus the shuram excursion has been interpreted by many in the context of a dramatically changing redox state of the ediacaran oceans for example a result of methane cycling in a low o2 atmosphere the final destruction of a large pool of recalcitrant dissolved organic carbon doc and the step wise oxidation of the ediacaran oceans more recently diagenetic interpretations of the shuram excursion have challenged the various redox models with the very negative 13c values of ediacaran carbonates explained via sedimentary in growth of very 13c depleted authigenic carbonates meteoric alteration or late stage burial diagenesis a stratigraphic and sedimentological context is required to discriminate between these explanatory models and to determine whether the shuram excursion can be used to evaluate oxygenation in terminal neoproterozoic oceans here we present chemo stratigraphic data 13c 18o and trace element abundances from 15 measured sections of the ediacaran aged wonoka formation fm of south australia in some locations the wonoka fm is 700 meters m of mixed shelf limestones and siliciclastics that record a 17 permil 13c excursion 12 to 5 further north in the basin the wonoka fm is host to deep 1 km paleocanyons which are partly filled by tabular clast carbonate breccias canyon filling ceased during ongoing sedimentation on the shelf interior the canyon shoulder as evidenced by upper canyon shoulder units that overlie and cap certain canyon fill sequences the unprecedented size of the chemostratigraphic dataset presented here 2671 13c 18o measurements from the canyon shoulder 1393 13c 18o measurements from canyon clasts and 11 different trace elements measured on 247 wonoka fm carbonate samples when coupled with the unique canyon shoulder to canyon fill depositional system of the wonoka fm allows for new insights into ediacaran carbon isotope systematics the excursion is preserved in a remarkably consistent fashion across 12 000 km2 of basin area fabric altering diagenesis where present occurs at the sub meter vertical scale results in

deposition and deformation of fluvial lacustrine sediments of the upper triassic lower jurassic whitmore point member moenave formation northern arizona abstract the stratigraphic section of the upper triassic lower jurassic whitmore point member of the moenave formation at potter canyon arizona comprises c 26 m of gray to black shales and red mudstones interbedded with mainly sheet like siltstones and sandstones these strata represent deposition from suspension and sheetflow processes in shallow perennial meromictic to ephemeral lakes and on dry mudflats of the terminal floodout of the northward flowing moenave stream system the lakes were small as indicated by the lack of shoreline features and limited evidence for deltas changes in base level likely forced by climate change drove the variations between mudflat and perennial lacustrine conditions lenticular sandstones that occur across the outcrop face in the same stratigraphic interval in the lower part of the sequence represent the bedload fill of channels incised into a coarsening upward lacustrine sequence following a fall in base level these sandstones are distinctive for the common presence of over steepened bedding dewatering structures and less commonly folding deformation of these sandstones is interpreted as aseismic due to the lack of features typically associated with seismicity such as fault graded bedding diapirs brecciated fabrics and clastic dikes rapid deposition of the sands on a fluid rich substrate produced a reverse density gradient that destabilized and potentially fluidized the underlying finer grained sediments this destabilization allowed synsedimentary subsidence of most of the channel sands accompanied by longitudinal rotation and or ductile deformation of the sand bodies

enigmatic nature of thick sedimentary carbonates depleted in 13c beyond the canonical mantle value the challenges to our understanding of the terrestrial carbon cycle carbon and oxygen isotope measurements of 66 samples from the 60 m thick variegated marble in the upper allochthon of the norwegian caledonides have a mean 13ccarb of 8 4 0 9 v pdb and a mean 18o of 20 2 2 2 v smow the variegated marble is overlain by 150 m thick pale grey marble characterised by mean 13ccarb of 6 5 0 8 n 25 and underlain by dark grey marbles with a mean 13ccarb of 4 8 1 1 n 61 this tripartite unit of an poorly constrained age but between neoproterozoic and early silurian discontinuously developed over a distance of 500 km is likely to represent one of the largest isotopically anomalous sedimentary carbonate formations yet reported the marbles depleted in 13c beyond the canonical mantle value of 6 show no obvious evidence of post sedimentary repartitioning of carbon isotopes several other carbonate formations deposited within approximately 680 540 ma time interval chenchinskaya nikolskaya and torginskay in siberia ingta in nw canada shuram in central oman trezona and wonoka in south australia are several hundred meters thick developed over a distance of hundreds of kilometres and all show a similar depletion in 13c beyond the mantle value for reasons that are not well understood the existence of these carbonates represents a challenging problem for our current understanding of global carbon geodynamics changes in the ratio of reduced oxidised carbon sequestered in sediments a methane hydrate release or zero biological productivity if applied separately cannot explain carbon isotope characteristics and formation of these carbonates we tentatively propose that several factors associated with unusual geodynamic and palaeoclimatic scenarios developed between 600 and 540 ma might have been involved in the extreme lowering of the isotopic composition of carbon entering the global earth surface environment this period was marked by the retreat of neoproterozoic glaciers and break up of the supercontinent rodinia the late postglacial warming might have induced a massive release of methane hydrates extremely enriched in 12c the death of rodinia was marked by unusually rapid approximately 20 cm year motion of newly formed continental plates suggesting vigorous mantle convection and an enhanced restructuring of the lowest compartments of the earth this could provide a flux of 12c rich material from the isotopically light asthenosphere mantle source 13c 25 to 15 to the surface considerable reconfiguration of the continental and sea areas of the earth might have triggered enhanced weathering of previously deposited 12c rich organic matter in presenting this working hypothesis we also question the completeness of our understanding of the terrestrial carbon cycle and the popular assumption that the isotopic composition of carbon entering the global earth surface environment was always around 6

hydrodynamics and sedimentation in wave dominated coastal environmentsreconstruction of ancient sea conditions with an example from the swiss molasse ancient sea conditions can be estimated from the grain size spacing and steepness of preserved ripple marks the element of greatest uncertainty in such reconstructions is the relationship between near bed orbital diameter of water particles and the ripple spacing this relationship is simple for vortex ripples of high steepness but is problematical for the low steepness forms known as post vortex rolling grain or anorbital ripples the existence field for wave ripples is between the threshold velocity for sediment movement and the onset of sheet flow most low steepness forms occurring close to the bed planation threshold a range of maximum period of formative waves can be obtained using combinations of orbital diameter and orbital velocity assuming linear wave theory to be a reasonable approximation probable wave heights wave lengths and water depths can be investigated using the transformation of wave parameters in shallowing waters and the constraints on wave dimensions provided by the wave breaking condition given reasonable estimates of wave height crude estimates of wave power allow a comparison of ancient wave influenced sequences with modern counterparts wave ripple marks preserved in the upper marine molasse of western switzerland have been investigated results which are in agreement with regional geology suggest deposition in a seaway of approximately 100 km width where moderate period waves t 3 6 s were generated the depositional facies belts were adjusted to the prevailing waves tides and fluvial outflows

dynamic changes in sulfate sulfur isotopes preceding the ediacaran shuram excursion large excursions in 13 c and 34 s are found in sedimentary rocks from the ediacaran period that may provide detailed mechanistic information about oxidation of earth s surface however poor stratigraphic resolution and diagenetic concerns have thus far limited the interpretation of these records here we present a high resolution record of carbon and sulfur isotopes from the khufai formation leading up to and including the onset of the shuram carbon isotope excursion we document large coherent excursions in the sulfur isotope composition and concentration of carbonate associated sulfate cas that occur both independently and synchronously with the carbon isotope excursion isotopic changes appear decoupled from major stratigraphic surfaces and facies changes suggesting regional or global processes rather than local controls our data suggest that very low marine sulfate concentrations are maintained at least through the middle khufai formation and require that the burial fraction of pyrite and the fractionation factor between sulfate and pyrite necessarily change through deposition reconciliation of simultaneous up section increases in marine sulfate concentration and 34 s cas requires the introduction of strongly 34 s enriched sulfate possibly from weathering of cryogenian and earlier ediacaran 34 s enriched pyrite our analysis of the onset of the shuram carbon isotope excursion observed in stratigraphic and lithologic context is not consistent with diagenetic or authigenic formation mechanisms instead we observe a contemporaneous negative excursion in sulfate 34 s suggesting linked primary perturbations to the carbon and sulfur isotope systems this work further constrains the size isotopic composition and potential input fluxes of the ediacaran marine sulfate reservoir placing mechanistic constraints on possible drivers of extreme isotopic perturbations during this critical period in earth history

a 600 million year carbonate clumped isotope record from the sultanate of oman carbonate clumped isotope thermometry is a promising technique that has the potential to help decode the significance of the variability of both physical and geochemical compositions of ancient carbonate rocks this study utilizes a 600 million year record of marine carbonate rocks from the subsurface and surface of the sultanate of oman to explore how burial and exhumation affected the carbonate clumped isotope thermometer samples span 6 km of burial depth and include calcite and dolomite mineralogies and a range of carbonate rock textures we find evidence for two broad patterns in the physical and geochemical behavior of carbonate rocks during burial the first group of carbonates yield water 18 o vsmow compositions slightly enriched or equal to an expected ice free seawater composition of 1 2 and display good to fair textural preservation suggesting that cementation and lithification occurred within tens of meters of the sediment water interface temperatures from the second group sit on the present day geotherm yield highly enriched water 18 o vsmow compositions and display fair to poor textural preservation we find no evidence for solid state reordering in paired analyses of calcites and dolomites our results contribute to a growing body of work that indicates that the seawater 18 o vsmow composition has not changed significantly over 600 myr and was not 6 in the ediacaran

expressions for the formation of load casts in soft sediment abstract a simple equation predicting the dimensions of sediment load casts is obtained from the fluid mechanics literature the equation relates the density and viscosity of the upper and lower sedimentary materials to the size of the expected load cast these results are extended to predicting load cast size as a function of median grain size and sediment concentration which are of more utility in geological studies the results are based on the assumption of newtonian fluid behavior and predict load cast dimensions of less than 10 cm for a wide range of sediment conditions it is hypothesized that although the results are of the correct order of magnitude non newtonian rheologic properties are important to load cast formation given the common occurrence of load casts larger than those pr dicted

stratigraphic investigations of carbon isotope anomalies and neoproterozoic ice ages in death valley california an unusual richness of biogeochemical events is recorded in neoproterozoic cambrian strata of the death valley region california united states eight negative carbon isotope d13c excursions are found in carbonate units between 1 08 ga and the precambrian cambrian boundary four of these excursions occur in carbonates that contain textural features similar to those found globally in postglacial cap carbonates including one or more of the following laminite with rollup structures apparent tube rocks seafloor precipitates and sheet crack cements however only two of these units the sourdough limestone member of the kingston peak formation and the noonday dolomite rest directly upon glacial strata the basal beck spring dolomite and the rainstorm member of the johnnie formation each contain negative excursions and cap carbonate like lithofacies but do not rest on known glacial deposits if the negative d13c excursions are assumed to record depositional processes two equally interesting hypotheses are possible 1 the death valley succession records four glacial pulses in neoproterozoic time but glacial units are not preserved at two stratigraphic levels 2 alternatively other global oceanographic processes can cause negative excursions and cap carbonate like facies in addition to or independent of glaciation

palynology of the huqf supergroup oman extensive subsurface sampling of the huqf supergroup in the sultanate of oman has yielded microfossil assemblages of cryogenian ediacaran and early cambrian age microfossils have been recovered from most stratigraphic units in the huqf including marinoan equivalent horizons of the ghadir manqil formation cryogenian abu mahara group the masirah bay shuram and buah formations of the ediacaran nafun group and the a3 latest ediacaran and a6 early cambrian cycles of the ara group despite the extensive recovery of leiosphaerid acritarchs from the shuram formation there is no indication of the large acanthomorphs typical of other early middle ediacaran assemblages this absence suggests a relatively young post extinction depositional age for the shuram however the signal is complicated by local deep water conditions and the facies specific distribution of proterozoic microfossils a shallower water sequence of undivided nafun group sediments preserves sphaeromorphic acritarchs in association with filamentous microfossils fragmentary vendotaenids and possible vaucheriacean algae

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

facies dependent δ13c variation from a cryogenian platform margin south australia evidence for stratified neoproterozoic oceans abstract analysis of a cryogenian interglacial platform margin in the adelaide geosyncline reveals a strong carbonate 13 c facies relationship detailed chronostratigraphic correlation between sections ranging from shallow platform facies to deep basinal facies indicates the presence of a carbon isotopic gradient of between 8 and 11 in time equivalent strata shallow water back reef facies have 13 c values up to 8 2 while equivalent basinal sediments have 13 c values between 3 and 0 allochthonous blocks that have been transported from the platform margin into basinal environments retain their heavy 13 c values 4 9 and are surrounded by basinal calcareous shales with light 13 c values ave 0 8 the regional and stratigraphic consistency of these 13 c trends suggests a primary marine origin we interpret this 13 c facies correlation to be the result of ocean stratification stagnation that significantly reduced the rate of deep ocean ventilation and produced a large deep water organically derived carbon reservoir we suggest that stratification may have been a persistent feature of the global ocean throughout much of neoproterozoic time ocean stratification may explain many of the unusual features that characterise the sedimentary record of this era including large scale 13 c variation extreme climatic fluctuations and the presence of cap carbonates a highly variable climatic regime would be expected with the development of a large deep water carbon reservoir small changes in ocean circulation could rapidly transfer or remove large volumes of carbon to and from the surface ocean and atmospheric reservoirs leading to intense greenhouse or icehouse conditions respectively

late precambrian cambrian sediments of huqf group sultanate of oman the huqf group is the oldest known sedimentary sequence overlying crystalline basement in the sultanate of oman it crops out on a broad regional high the huqf axis which forms a dominating structural element on the southeastern edge of the arabian peninsula subsurface and outcrop evidence within and outside of oman suggests that the sediments of the huqf group lie within the age span of late precambrian to early middle cambrian the huqf group is subdivided into five formations corresponding to an alternation of clastics abu mahara and shuram formations and carbonates khufai and buah formations deposited in essentially shallow marine to supratidal or fluviatile conditions and terminated by an evaporitic sequence ara formation evaporites are absent on the huqf axis but they are thickly developed to the west over a large part of southern and central oman where they acted as the major structure former of most of oman s oil fields and even locally pierced up to the surface in the subsurface the huqf group has been reached by the drill mainly in southern oman where its lithostratigraphy resembles that defined in the type area in central oman the oldest sediments exposed in the core of the oman mountains may be correlative with the huqf group regional correlations suggest that the predominantly carbonate evaporitic facies of the huqf group was widely distributed in late precambrian early cambrian time the huqf basin is tentatively considered part of a belt of evaporitic basins and intervening carbonate platforms which stretched across the pangea landmass from the indian subcontinent salt range of pakistan through south yemen oman and saudi arabia into the gulf states and iran hormuz series and carbonate platform north of the zagros

boron and calcium isotope composition in neoproterozoic carbonate rocks from namibia evidence for extreme environmental change the level and evolution of atmospheric carbon dioxide throughout earth s history are key issues for palaeoclimate reconstructions especially during times of extreme climate change such as those that marked the neoproterozoic the carbon isotope ratios of marine carbonates are crucial in the correlation and identification of neoproterozoic glacial deposits and they are also used as a record for biogeochemical cycling and potential proxy for atmospheric pco2 likewise the boron and calcium isotope compositions of marine carbonates are potential proxies for palaeo seawater ph and the ratio of calcium fluxes into and out of seawater respectively and together they may be used to estimate atmospheric carbon dioxide here we use b and ca isotopes to estimate palaeoenvironmental conditions in the aftermath of a major neoproterozoic glaciation in namibia the validity of the b and ca isotope variation in the ancient marine carbonates is evaluated using the oxygen isotope composition of the carbonates and its correlation to the carbon isotope variation a negative 2 7 to 6 2 11b excursion occurs in the postglacial carbonates and is interpreted to reflect a temporary decrease in seawater ph associated variations in 44ca values ranging between 0 35 and 1 14 are linearly coupled with the carbon isotope ratios and imply enhanced postglacial weathering rates the reconstructed seawater ph and weathering profiles indicates that high atmospheric co2 concentrations were likely during the melt back of neoproterozoic glaciations and precipitation of cap carbonates however the b isotope trend suggests that these concentrations rapidly ameliorated and they do not co vary with 13c thus models attempting to link long lived negative 13c excursions to elevated pco2 need to be reconsidered

chemostratigraphic and sedimentological framework of the largest negative carbon isotopic excursion in earth history the neoproterozoic shuram formation nafun group oman abstract oman records in its neoproterozoic nafun group huqf supergroup an essentially complete carbonate rich ediacaran succession the nafun group overlies the presumed marinoan rift related fiq member ca 635 ma and ends just below the precambrian cambrian boundary 542 ma tectonic subsidence caused by thermal contraction following fiq aged rifting allowed the preservation of about 1 km of postrift stratigraphy with no major stratigraphic breaks the nafun group above the marinoan cap carbonate hadash formation represents two siliciclastic to carbonate grand cycles both initiated by significant transgressions these cycles comprise the masirah bay khufai formations and the shuram buah formations the khufai shuram boundary is associated with the start of a major carbon isotope perturbation the uppermost ramp carbonates of the khufai formation record a smooth decrease in 13c from about 4 to values around 0 followed by two descending steps across which values plunge to a nadir of 12 in the overlying red siltstones and shales interbedded with thin limestones of the shuram formation this fall in isotopic values is temporally rapid and coincident in both shallow and deep water sections in the time span of a single parasequence the 13c nadir is then followed by 50 million years of monotonic recovery the shuram shift represents the largest 13c inorganic carbon negative excursion in earth history although the snowball earth theory links periods of depleted carbon isotopic ratios with periods of global glaciation the non glaciated context of the shuram formation suggests that the causal relationship between global glaciation and negative carbon isotopic excursions is non unique although the precise mechanism driving this major perturbation of the carbon cycle remains enigmatic the long term remineralization of an isotopically depleted organic carbon reservoir in ocean water is a promising candidate

integrated stratigraphy of the upper neoproterozoic succession in yunnan province of south china re evaluation of global correlation and carbon cycle abstract this study provides a chemostratigraphic and sequence stratigraphic framework of a relatively unfossiliferous sub cambrian marine sedimentary succession in yunnan province of south china our results allow its global stratigraphic correlation and provide an improved understanding of marine carbon cycle during the late neoproterozoic the succession has a basal glacial diamictite nantuo formation and comprises two large scale depositional cycles towards the precambrian cambrian pc c boundary each of which changes from siliciclastic to carbonate sediments with environments ranging from shallow subtidal to evaporitic supratidal in the absence of biostratigraphic control attribution of the tillite has remained equivocal between the 710 ma sturtian and 635 ma marinoan glaciations a compilation of known paleomagnetic and other geochronologic constraints suggests that the nantuo glaciation in south china was at least diachronous in which the nantuo tillite in yunnan belongs to the older glaciation stratigraphic patterns of the diagenetically screened 13c variation and depositional sequences during the carbonate dominated interval show a striking similarity with those of the upper cryogenian and entire terminal proterozoic carbonates at widely separated other localities rather than the terminal proterozoic alone supporting the view that deposition of the nantuo tillite in yunnan reflects the sturtian rather than marinoan glaciation further considerations of the 13c results provide three important implications for the late neoproterozoic marine carbon cycle first comparison of different 13c profiles suggests considerable variability in the absolute values of carbonate on both intra and inter basinal scales which differs profoundly from their relative homogeneity in marine phanerozoic counterparts and may therefore reflect lateral isotopic heterogeneity in the oceanic carbonate reservoir during the late neoproterozoic second an empirical correlation between the 13c and relative sea level changes was applied to evaluate hypothesized explanations for 13c temporal variation in surface sea yielding short term inverse and long term positive relationships the short term trend marks periods of the negative 13c excursions and is compatible to most of the existing arguments for the 13c events on the other hand mechanisms causing the long term trend remain enigmatic in the absence of comparable data from other localities our observation however suggests that at least two different mechanisms operated marine carbon cycle during the late neoproterozoic third the negative 13c anomaly characterizing the period following the marinoan glaciation worldwide was not coincident between kerogen and carbonate but occurs as a lagged drop in yunnan where a 7 depletion in kerogen preceded an 3 depletion in carbonate their lagged trends likely reflect different sources as kerogen and carbonate signals are considered to monitor surface and deeper waters respectively the negative 13c event would therefore have occurred in surface water followed by a smaller 13c depletion through the entire water column due to vertical mixing between surface and deeper waters at the studied site this mechanism supports the proposed hypothesis that injection of the 13c depleted atmospheric co2 into the surface sea deriving ultimately from quantitative dissociation of methane hydrate in terrestrial permafrost during the post glacial warming contributed to the negative 13c anomaly

eruptive and emplacement mechanisms of widespread fine grained pyroclastic deposits on vulcano island italy tufi di grotte dei rossi inferiori are thick ash deposits representing the most voluminous stratigraphic unit on vulcano island the deposits are related to hydromagmatic eruption which occurred under shallow water inside a caldera depression grain size data and results of sem investigation allow the character of the transporting medium solid material concentration in the cloud during the lateral expansion and the nature and role of the fluids present at the time of deposition to be constrained we suggest that the eruption was characterized by closely timed hydromagmatic pulses giving rise to eruption clouds rich in water vapor and steam the coarser material was not significantly transported in the eruptive cloud and it probably deposited in the caldera depression area the finer material was extensively transported in the cloud creating turbulent flows which surmounted the caldera rim barrier and dispersed in a southward direction forming widespread deposits in the piano area lower concentrated flows produced laminated deposits of more limited dispersion whereas higher concentrated flows formed more dispersed thicker massive layers

the stratigraphic complexity of the middle ediacaran carbon isotopic record in the yangtze gorges area south china and its implications for the age and chemostratigraphic significance of the shuram excursion abstract the middle ediacaran shuram excursion represents the most pronounced negative carbon isotopic shift in earth history and has been considered as evidence for a profound disturbance to the global carbon cycle and proposed as a key chemostratigraphic marker for ediacaran stratigraphic subdivision and global correlation previous study has revealed a pronounced negative 13c shift en3 in the upper doushantuo formation of south china which has been interpreted as an equivalent of the shuram excursion detailed 13c investigation of multiple sections of the ediacaran doushantuo formation around the huangling anticline western hubei province south china indicates that the 13c variation in the upper doushantuo formation is more complex than previously reported in the western region of the huangling anticline a moderately positive 13c excursion here termed the diaoyapo positive excursion bisects two strongly negative 13c excursions here termed the jiuqunao negative excursion and the younger miaohe negative excursion with a 551 ma ash bed capping the miaohe negative excursion in the central region there is only one negative 13c excursion whereas in the eastern region the negative 13c excursion is absent the variable stratigraphic expression of these 13c excursions is most parsimoniously interpreted as reflecting local facies variation diagenesis and or a cryptic unconformity the more complete but more complex 13c chemostratigraphic record in the western region of huangling anticline implies that depending on how this record is correlated with the shuram excursion the latter may be significantly older than 551 ma if it does represent a global chemostratigraphic marker

precambrian cambrian transition death valley united states the death valley region contains one of the best exposed and often visited precambrian cambrian successions in the world but the chronostratigraphic framework necessary for understanding the critical biologic and geologic events recorded in these sections has been inadequate the recent discovery of treptichnus phycodes pedum within the uppermost parasequence of the lower member of the wood canyon formation allows correlation of the precambrian cambrian boundary to this region and provides a necessary global tie point for the death valley section new carbon isotope chemostratigraphic profiles bracket this biostratigraphic datum and record the classic negative carbon isotope excursion at the boundary for the first time biostratigraphic chemostratigraphic and lithostratigraphic information from pretrilobite strata in this region can be directly compared with similar data from other key sections that record the precursors of the cambrian explosion few precambrian cambrian boundary sections contain both the facies restricted boundary fossil t pedum and carbon isotope data as found in death valley thus the death valley succession provides a critical link toward our understanding of the correlation between siliciclastic dominated and carbonate dominated precambrian cambrian transition sections