return of the coral reef hypothesis basin to shelf partitioning of caco3 and its effect on atmospheric co2 differences in the rate of coral reef carbonate deposition from the pleistocene to the holocene may account for the quaternary variation of atmospheric co sub 2 volumes of carbonate associated with holocene reefs require an average deposition rate of 2 0 times 10 sup 13 mol yr for the past 5 ka in light of combined riverine mid ocean ridge and ground water fluxes of calcium to the oceans of 2 3 times 10 sub 13 mol yr the current flux of calcium carbonate to pelagic sediments must be far below the pleistocene average of 1 2 times 10 sub 13 mol yr the authors suggest that sea level change shifts the locus of carbonate deposition from the deep sea to the shelves as the normal glacial interglacial pattern of deposition of quaternary global carbonates to assess the impact of these changes on atmospheric co sub 2 a simple numerical simulation of the global carbon cycle was developed atmospheric co sub 2 as well as calcite saturation depth and sediment responses to these carbonate deposition changes are examined atmospheric co sub 2 changes close to those observed in the vostok ice core approximately 80 ppm co sub 2 for the quaternary are observed as well as the approximate depth changes in percent carbonate of sediments measured in themore pacific ocean over the same time interval less

diatom derived ssts td ratio indicate warm seas off japan during the middle holocene 8 2 3 3 kyr bp abstract regression analysis was performed between the ratio of warm and cold water diatoms td ratio in 123 surface sediment samples in the northwest pacific ocean and the mean annual sea surface temperatures ssts c at the core sites in order to calibrate this proxy for paleo temperatures equations to derive annual sst c from diatom analysis were somewhat different for the tohoku area y 6 5711 0 273 r 0 89946 than for the japan sea y 5 4069 0 26841 r 0 89088 the annual paleo ssts c in the tohoku area were in general higher than in the japan sea despite lower td values because the warm water species fragilariopsis doliolus is abundant only in the tsushima warm current in the japan sea the reliability of the equations is supported by our understanding of the ecology of recent diatoms td derived annual paleo ssts c agree with alkenone derived summer paleo sst c at a site off central japan in the northwestern pacific in a south to north transect of cores around honshu and hokkaido paleo ssts c decreased when the kuroshio and tsushima warm currents weakened the middle holocene 8 2 3 3 cal kyr bp was warmer by 1 2 c than earlier and later parts of the holocene and mean annual paleo ssts c show rhythmic fluctuations with durations of 1000 years and 400 500 years these new data show that annual ssts were warm in the northwestern pacific at times that the northeastern pacific was cold in addition oceanic warm and cold water species defined by kanaya and koizumi kanaya t koizumi i 1966 interpretation of diatom thanatocoenoses from the north pacific applied to a study of core v20 130 studies of a deep sea core v20 130 part iv sci rep tohoku univ 2nd series geol 37 89 130 and koizumi et al koizumi i irino t oba t 2004 paleoceanography during the last 150 kyr off central japan based on diatom floras mar micropaleontol 53 293 365 are illustrated

orbital and millennial scale paleoceanographic changes in the north eastern japan basin east sea japan sea during the late quaternary two gravity sediment cores gh99 1239 and gh99 1246 obtained from the north eastern japan basin in the east sea japan sea were analyzed for the orbital and millennial scale paleoceanographic changes chronostrati graphically core gh99 1239 represents a continuous sedimentary record since 32 ka based on correlation of distinct lithological markers i e dark layer or tl layer with those in core gh98 1232 collected nearby for core gh99 1246 the age model is constructed through correlation of lightness l values and tephra aso 4 and toya layers with those in the well dated oki ridge core md01 2407 indicating about 134 ka of sedimentation since the latest marine isotope stage mis 6 new geochemical data from both cores corroborate orbital scale paleoceanographic variation such that surface water productivity represented by biogenic opal and total organic carbon toc contents increased during mis 1 and mis 5 caco3 contents do not show such distinct glacial interglacial cycles but were influenced by dissolution and preservation rather than foraminiferal production during the glacial periods when sea ice was prevalent surface water productivity was low and bottom water conditions became anoxic as indicated by high total sulfur ts contents and high mo concentrations the geochemical data further document millennial scale paleoceanographic variability corresponding to a series of thin tl layers in response to dansgaard oeschger cycles but irrespective of the glacial or interglacial periods in particular thin tl layers formed during mis 3 are characterized by less toc about 1 and ts about 0 4 contents and lower mo about 5 p p m concentration whereas those during mis 4 and mis 5 exhibit more toc up to 4 and ts up to 5 contents and higher mo up to 120 p p m concentration such a discrepancy is attributed to different degree of surface water productivity and of bottom water oxygenation which is closely related to the sea level position and extent of ventilation flux of the east china sea coastal water controlled by millennial scale paleoclimatic events is the most critical factor in deciding the properties of tl layers in the north eastern japan basin our results strongly confirm that tl layers in the japan basin also validate the unique feature of basin wide paleoceano graphic signals in the east sea japan sea copyright 2011 john wiley sons ltd

sedimentology and c isotope geochemistry of the sturtian cap carbonate south australia abstract a combined sedimentary and isotopic analysis of the sturtian aged tindelpina cap carbonate in south australia has revealed a strong relationship between sedimentary facies and 13 c carb depositional water depths for the cap carbonate are difficult to constrain however a lack of diagnostic shallow water structures and the inferred magnitude of post glacial transgression several 100 m indicates a relatively deep water environment for each key facies the shallowest facies peloidal dolomite has 13 c values ranging between 3 6 and 0 3 in comparison to deeper water laminated limestones which have lighter values ranging between 5 5 and 3 5 equivalent calcareous shales deposited at basinal depths show even more 13 c depletion with values ranging between 6 7 and 3 7 the average difference in 13 c between the shallowest and deepest cap facies is up to 3 6 and may be an approximation of the seawater 13 c depth gradient at the time of deposition we interpret this high 13 c depth gradient as the result of prolonged physical ocean stratification both during and after deglaciation variations in the rates of upwelling mixing under this stratified regime may have significantly influenced the climate as well as controlling the precipitation and isotopic composition of the cap carbonate

snowball earth ocean chemistry driven by extensive ridge volcanism during rodinia breakup the cryogenian snowball earth glaciations were followed by the deposition of massive cap carbonates geochemical modelling suggests that shallow ridge volcanism supplied much of the alkalinity and cations that fuelled this deposition

holocene relative sea level change and rate of sea level rise from coastal deposits in the toyooka basin western japan this study presents relative sea level rsl change from 11 200 to 500 cal bp in the toyooka basin western japan diatom assemblage and sedimentary sulfur analyses were performed for 32 sediment

cap carbonate platform facies model noonday formation se california the neoproterozoic outcrop belt of the death valley region california preserves an oblique cross section of the noonday formation a mixed carbonate siliciclastic platform that hosts distinctive basal ediacaran cap carbonate affiliated sedimentary structures stromatolite textures and 13 c carb values the noonday platform encompasses two depositional sequences that reveal two cycles of relative sea level change within strata conventionally considered to record a single rapid postglacial sea level rise in updip localities facies of the first depositional sequence record the transition from a carbonate ramp to a stromatolite bearing tubestone textured reef rimmed platform downdip localities seaward of the reefal escarpment variably preserve a thin and condensed onlapping foreslope wedge base level fall exposed the reef crest to karstic dissolution and propagated submarine incised valleys into the seaward margin of the reef overlying strata record the backfilling of a submarine incised valley and reestablishment of a back stepping carbonate dominated ramp prior to a second subaerial exposure event that defines the contact between the noonday and johnnie formations we address the relative contributions of syndepositional tectonism and recovery from low latitude deglaciation in dictating noonday platform architecture and the intra noonday formation sequence boundary noonday formation deposition coincided with extension of the laurentian margin during disaggregation of the rodinian supercontinent within this framework previous work has suggested that the intra noonday formation sequence boundary records growth faulting that reinforced differential topography uplifting reef rimmed horsts exposing the reef crest to karstic dissolution and downdropping grabens however we trace the intra noonday formation sequence boundary seaward of the reef crest and demonstrate that for a time wave base was situated downdip of the reef escarpment on putatively downdropped fault blocks thus if the noonday margin were undergoing extension then the creation of the intra noonday formation sequence boundary required a concomitant decrease in accommodation due perhaps to postglacial isostatic uplift attendant with low latitude deglaciation we speculate that noonday formation sequence architecture records 1 immediate deglacial flooding 2 shoaling and exposure due to isostatic rebound induced by either a hiatus in meltwater flux or rapid ice sheet collapse against a background of global deglaciation and 3 resumed flooding following complete deglaciation as rift related tectonism could amplify or counter glacial isostasy inferences of the amplitude of local postglacial sea level change will require robust estimates of syndepositional extension across the noonday margin

palaeomagnetism and magnetic anisotropy of late neoproterozoic strata south australia implications for the palaeolatitude of late cryogenian glaciation cap carbonate and the ediacaran system abstract the ediacaran global stratotype section and point gssp is defined near the base of the nuccaleena formation the cap carbonate overlying the terminal cryogenian glaciogenic elatina formation at a basin wide sequence boundary in the adelaide geosyncline south australia previous palaeomagnetic data for 205 specimens from the elatina formation yielded a structurally corrected mean declination d 208 3 and inclination i 12 9 95 4 2 palaeolatitude 6 5 2 2 and pole position at latitude p 47 3 s longitude p 359 3 e dp 2 1 and dm 4 2 new palaeomagnetic data for 141 specimens from the nuccaleena formation yield a structurally corrected mean direction of d 208 3 i 34 9 95 3 4 19 2 2 3 2 2 and pole position at p 32 3 s p 350 8 e dp 2 2 and dm 3 9 there is a substantial difference in inclination between the elatina and nuccaleena formations despite their juxtaposition positive fold tests for both formations seem to rule out remagnetisation of one or both formations fold tests on tepee like structures in the nuccaleena formation accord with the magnetisation having been acquired at or near the time the structures formed during early diagenesis magnetisation therefore variably lags deposition causing the three identified magnetostratigraphic horizons to appear highly bedding transgressive whereas local correlations may seem satisfactory regional correlations are not nevertheless the number and duration of polarity chrons at various localities appear valid implying that the nuccaleena formation accumulated over an interval of 10 5 years the question of compaction related inclination shallowing was addressed by examining the anisotropy of remanence using a superconducting 12 t magnet the effective flattening factors f determined were nuccaleena dolostones n 4 f 0 98 0 02 elatina tidal rhythmites n 6 f 0 97 0 01 elatina arenites n 9 f 0 92 0 02 the mean elatina inclination is corrected to 14 0 palaeolatitude of 7 1 and the mean nuccaleena inclination to 35 4 palaeolatitude of 19 6 inclination shallowing also was investigated using the elongation inclination method the distributions of directions for the elatina were somewhat skewed with respect to bedding possibly invalidating use of this method nevertheless for the elatina the method yields an inclination of 19 palaeolatitude of 10 for the nuccaleena the corrected inclination is 41 9 palaeolatitude of 24 these corrections do not materially alter the near equatorial palaeolatitude for the elatina formation which is supported by data for other neoproterozoic strata in southern australia however the substantial increase in palaeolatitude between the late cryogenian and the early ediacaran is maintained the sequence boundary below the nuccaleena formation is a disconformity to low angle unconformity that in places cuts deeply into the 1500 m thick late cryogenian glaciogenic succession and may represent a significant time gap marked by rapid polar wander such a hiatus may be an important factor in the juxtaposition of glacial deposits and cap carbonates

sedimentary facies of the tide dominated paleo changjiang yangtze estuary during the last transgression abstract a large estuary was formed by marine inundation of the paleo changjiang yangtze incised valley during the transgression after the last glacial maximum this paper presents the sedimentary facies and architecture of the estuary fill based on the analysis of three sediment cores cm97 js98 and hq98 obtained from the present changjiang delta plain estuary fill deposits showing an upward fining succession were grouped into five depositional facies tidal river distributary channel muddy intertidal to subtidal flats transgressive lag and estuary front based on sedimentary textures lithology and physical sedimentary structures sand mud couplets are common in these deposits indicating that tides played a significant role in producing these sedimentary structures and that the estuary type was tide dominated some of the successive sand mud couplets probably recorded neap spring cycles as well as semidiurnal tidal cycles the nature of the estuary was very different from other representative tide dominated estuaries in sediment facies its distribution and sediment source for estuarine fill unlike the other estuaries that receive sediments mainly from the sea the paleo changjiang estuarine fill deposits were supplied largely from the river this difference would also have a great influence on the sedimentological and morphological component in the estuary the sediment distribution of the estuary showed fining seaward and estuary mouth sand bodies fed by marine source sand were absent the architecture model of tide dominated estuaries should be divided into two types by the degree of fluvial sediment supply the paleo changjiang estuary shows a good example for an estuary of large rivers

mid holocene forcing of the tsushima warm current to the coastal environments in southwestern japan with a view to foraminiferal faunas abstract we investigated fossil benthic and planktonic foraminifera in sediment cores fv10 05 and fv10 06 2 off fukuoka southwestern japan to evaluate the impact of the tsushima warm current on coastal environments around the strait between southeastern korea and southwestern japan during the early to middle holocene a cluster analysis of benthic foraminifera in these cores established four sample clusters a b c and d which are interpreted as indicators of relatively high energy condition due to wave current processes clusters a and c characterized by attached taxa became dominant at 6 6 ka such faunal changes are consistent with the current influenced sedimentation confirming that the tsushima warm current reached its present day distribution at that time a hiatus at 8 7 ka has been reported in cores from deeper water off fukuoka whereas our shallow core shows deposition under high energy conditions was continuous even at 8 7 ka near the coast off river mouth across the strait the maximum landward extent of benthic foraminifera occurred in the nakdong river delta southeastern korea in 8 7 ka and an outer bay fauna of benthic foraminifera with seagrass beds occurred transiently in the restricted bay of the san in district southwestern japan at that time the evolution of the tsushima warm current during the early to middle holocene thus appears to play an important role in coastal environments not only in the strait areas between southeastern korea and southwestern japan but also in the san in district

carbonate deposition climate stability and neoproterozoic ice ages the evolutionary success of planktic calcifiers during the phanerozoic stabilized the climate system by introducing a new mechanism that acts to buffer ocean carbonate ion concentration the saturation dependent preservation of carbonate in sea floor sediments before this buffering was primarily accomplished by adjustment of shallow water carbonate deposition to balance oceanic inputs from weathering on land neoproterozoic ice ages of near global extent and multimillion year duration and the formation of distinctive sedimentary cap carbonates can thus be understood in terms of the greater sensitivity of the precambrian carbon cycle to the loss of shallow water environments and co 2 climate feedback on ice sheet growth

evolution of the coastal depositional systems of the changjiang yangtze river in response to late pleistocene holocene sea level changes abstract the paleo changjiang yangtze incised valley fills approximately 80 90 m thick provide an opportunity to document the evolution of coastal depositional systems with large sediment supply in response to late pleistocene holocene sea level fluctuations on time scales of 103 to 104 years the sedimentary facies of the incised valley fills record three main depositional systems fluvial tide dominated estuary and tide dominated delta radiocarbon ages for the incised valley fills suggest that these depositional systems developed before about 11 ka between 11 and 8 ka and after approximately 8 ka respectively by applying sequence stratigraphic concepts the evolution of the depositional systems can be divided into three systems tracts a lowstand systems tract lst a transgressive systems tract tst and a highstand systems tract hst sea level changes on a 104 year time scale controlled the basic architecture of the sequence of the incised valley fill on the other hand sea level changes on a millennial time scale affected the stacking pattern of the systems tracts in particular the continuous sea level rise with episodic rapid rises during the last deglaciation affected the stacking pattern of the tst which is characterized by a combination of aggradation and backstepping the aggradation of fluvial and estuarine systems was dominant and the shoreline migrated only gradually landward under the relatively slow rise in sea level and a very rapid sea level rise around 12 and 10 ka caused the system to migrate abruptly landward unlike the transgressive estuarine phase the stacking pattern of the regressive tide dominated delta hst which developed within the almost filled incised valley and on the surrounding interfluve zones was characterized by seaward progradation with clinoform architecture it was initiated with aggradational and progradational stacking about 8 ka during the last phase of decelerated sea level rise and was followed by a progradational phase after the highest sea level about 6 ka

variations of east asian summer monsoon since the last deglaciation based on mg ca and oxygen isotope of planktic foraminifera in the northern east china sea 1 variations in mg ca based sea surface temperature and oxygen isotope ratio 18o of the surface water in the northern east china sea ecs were reconstructed with high resolution during the last 18 kyr using planktic foraminifera millennial scale variations between warmer more saline surface water and cooler less saline surface water were recognized during the early deglacial period and the holocene suggesting changes in the mixing ratio between the kuroshio water and the changjiang diluted water stronger east asian summer monsoon easm precipitation events in south china are identified at 10 5 8 8 7 0 5 3 4 7 2 9 1 7 and 0 5 ka based on sea surface salinity sss records of the northern ecs weaker easm precipitation events are also detected at 9 3 8 3 7 3 6 0 3 3 2 3 0 7 and 0 4 ka during the holocene these events agree with the maxima in 18o records of stalagmites from various parts of the changjiang yangtze river drainage this agreement supports that our sss record properly captures the millennial scale dry less easm precipitation events over the drainage basin of the changjiang river during the holocene these dry events are also in good agreement with north atlantic ice rafted events suggesting a teleconnection between north atlantic climate and the easm during the holocene

low latitude and multiple geomagnetic reversals in the neoproterozoic puga cap carbonate amazon craton palaeomagnetic study of the carbonates that ubiquitously cap glacial deposits may constrain the latitudinal extent of neoproterozoic glaciations and the duration of the greenhouse recovery we present the first palaeomagnetic data on the neoproterozoic cap carbonates covering the amazon craton which are folded along the paraguay belt samples collected at deformed beds along the paraguay belt present a single polarity secondary magnetization acquired by the end of the brasiliano orogeny 540 520 ma in the cratonic area a dual polarity component was isolated in dolostones at the base of the sequence the presence of a stratabound reversal stratigraphy along with high unblocking temperatures strongly suggest that this magnetization is primary this result implies a low palaeolatitude 22 6 5 for the amazon block just after deposition of puga diamictites in addition the presence of multiple reversals across the first 20 m of the cap carbonate sequence suggests that their sedimentation must have spanned hundreds of thousands of years at least

condensation origin for neoproterozoic cap carbonates during deglaciation comment kennedy and christie blick 2011 1 describe sequence stratigraphic relations among a thick succession of ca 635 ma glacial to postglacial sediments in the amadeus basin of central australia which pass basinward into 3 m of laminated dolomicrite fig 1a 2 they conclude that the cap

the late palaeocene early eocene and toarcian early jurassic carbon isotope excursions a comparison of their time scales associated environmental changes causes and consequences although the earth9s environment is constantly changing there have been a few unusual episodes over the last c 200 ma when change was extreme in terms of its rapidity severity long lasting consequences and unpredictability the geochemical and biotic records for two of these episodes the palaeocene eocene thermal maximum and the toarcian oceanic anoxic event early jurassic possess many significant similarities each event was associated with a major carbon isotope excursion significant levels of biotic extinctions severe global warming an enhanced hydrological cycle and evidence for widespread seawater anoxia both carbon isotope excursions can be subdivided into distinct stages with broadly similar characteristics and durations based on a detailed comparison the palaeocene eocene thermal maximum may have been an incipient oceanic anoxic event the geochemical and biotic changes during these two events are most readily explained by the abrupt large scale dissociation of methane hydrate that followed a period of more gradual environmental change linked to the emplacement of a large igneous province carbon release rates at those times were of the same order of magnitude as the current anthropogenic release rate of carbon to the atmosphere indicating that ancient events such as these may usefully serve as analogues for present day environmental change

holocene benthic foraminiferal faunas in coastal deposits of the nakdong river delta korea and izumo plain japan abstract we documented the holocene benthic foraminifera in the coastal deposits based on drilled cores nd 01 nakdong river delta southeastern korea and hs02 izumo plain southwestern japan the rapid deepening and subsequent gradual shoaling during the holocene were recognized from the stratigraphic distribution of five clusters a to e and the ratio of planktonic foraminifera to the sum of benthic and planktonic foraminifera p t ratio in core nd 01 comparison of benthic foraminiferal faunas indicated that the faunal composition differs somewhat between the nakdong river delta and izumo plain or urauchi bay the east china sea the relationships between mds axis 1 and the rarefaction and between mds axis 1 and the rac kurtosis showed positive and negative linear like trends respectively in both the nakdong river delta and the izumo plain the biotic response of benthic foraminifera to taxonomic loss also seemed to be common in that both coastal deposits experienced shoaling or enclosing of the bay environments despite the different occurrence of benthic foraminifera between the nakdong river delta and izumo plain transient changes of benthic foraminifera in both areas at 8 ka might have been caused by the enhanced influence of the tsushima warm current

stratigraphy sedimentology and isotopic geochemistry of australian neoproterozoic postglacial cap dolostones deglaciation delta 13 c excursions and carbonate precipitation abstract thin d13c excursions in the geologic record they are interpreted to record a brief postglacial anomaly in ocean chemistry in australia the marinoan varanger equivalent 600 ma cap dolostone units exhibit many of the characteristics displayed by such deposits elsewhere around the globe including fine grained dolomitic mineralogy lateral persistenc at basinal scales thin laminae graded beds intervals with abundant marine cements crystal fans and a distinctive negative d13c isotopic signature of up to 5 pdb on the basis of these features the australian examples are interpreted here to be deeper water deposits below storm wave base resulting from an anomalous flux of inorganic carbonate to the sea floor during postglacial transgression detailed isotopic analysis of australian cap dolostones indicates d13c values ranging from 1 to 5 and gen rally becoming more depleted in 13c upsection trace element data indicate some diagenetic stabilization but textural evidence and the presence of similar profiles in different basins argue against a pervasive recrystallization event the range in d13c values between sections as well as more negative 13c values appear to correlate with greater paleobathymetry within basins this implies either 1 only partial preservation of the complete oceanic variation of d13c or 2 precipitation of this peculiar facies owes its genesis to basinal specific oceanographic processes such as proximi y of a given section to a postglacial upwelling zone in the later case d13c values would not represent whole ocean values stratigraphic constraints and paleoenvironmental interpretations suggest that much of this excursion lies within the geologically brief period of postglacial transgression this implies that the cause s of d13c variation likely operated on time scales significantly less than the residence time of carbon in the oceans 105 yr the continent wide and perhaps global nature of cap dolostones indicates that large volumes of carbonate were precipitated during the postglacial transgressive period such large scale carbonate precipitation over the hypothesized short time interval of postglacial transgression must have caused or have been the product of profound changes in the carbon cycle and global climate at tha time similar evidence for transgression and increased carbonate deposition in the holocene are attributed to the changing basin shape and ph of the oceans the coral reef hypothesis of berger 1982 cap dolostones may record a proterozoic equivalent of this process with the substitution of abiotic carbonate precipitation for skeletal precipitation by reef organisms

neoproterozoic cap dolostone deposition in stratified glacial meltwater plume abstract neoproterozoic cap carbonates host distinctive geochemical and sedimentological features that reflect prevailing conditions in the aftermath of snowball earth interpretation of these features has remained contentious with hypotheses hinging upon timescale and synchronicity of deposition and whether or not geochemical signatures of cap carbonates represent those of a well mixed ocean here we present new high resolution sr and mg isotope results from basal ediacaran cap dolostones in south australia and mongolia least altered sr and mg isotope compositions of carbonates are identified through a novel incremental leaching technique that monitors the purity of a carbonate sample and the effects of diagenesis these data can be explained by the formation of these cap dolostones involving two chemically distinct solutions a glacial meltwater plume enriched in radiogenic sr and a saline ocean residue with relatively lower 87sr 86sr ratios model simulations suggest that these water bodies remained dynamically stratified during part of cap dolostone deposition most likely lasting for 8 thousand years our results can potentially reconcile previous conflicts between timescales estimated from physical mixing models and paleomagnetic constraints geochemical data from cap carbonates used to interpret the nature of snowball earth and its aftermath should be recast in terms of a chemically distinct meltwater plume

the possible synglaciogenic ediacaran hematitic banded iron salt formation bisf at hormuz island southern iran implications for a new style of exhalative hydrothermal iron salt system abstract the ediacaran bisf at hormuz island is a newly identified glaciogenic iron salt deposit in the tethyan margin of gondwana the bisf was formed by synchronous riftogenic a type submarine felsic volcanism and evaporate deposition the mineralization occurs in a proximal felsic tuff cone and jaspilitic distal zones and contains 1 million tonne of hematite rich ore with an average grade of 58 fe the ore structure shows cyclicity of macrobandings mesobandings and microbandings of anhydrite halite hematite and chert which marks a new record in bifs geohistory the alteration minerals in the proximal and distal zones are actinolite ripidolite epidote sericite tourmaline clinochlore anhydrite and clay minerals the occurrence of metamorphosed polygenetic bullet shape dropstones in bisf attests that there was probably a continuous process of ice melting episodic submarine volcanism and exhalative hydrothermal banded iron salt formation during the late ediacaran time the non metamorphosed neoproterozoic stratigraphy the presence of genus collenia u pb dating 558 7 ma and the marked negative 13c excursion in cap carbonates are representative of late ediacaran glaciation which has been identified worldwide the ree y display light ree enrichment unusually strong tb tm anomaly a weak positive y anomaly but no distinguished eu and ce anomalies reflecting the glaciogenic nature of the bisf the contents of zr hf nb ta th la ce and y in bisf dropstones halite and cap carbonates are similar to those of the neoproterozoic glaciogenic bifs also the ni fe p fe ratios and fe ti al al fe mn ca na k diagram suggest an exhalative hydrothermal ediacaran type bisf the absence of brecciated magnetite in the ore association and the low contents of copper 9 493 ppm and gold

paleoenvironmental changes and depositional history of the korea tsushima strait since the lgm abstract two deep cores ssdp 102 and ssdp 105 from the southeastern inner shelves of korea were examined in order to reconstruct the paleoenvironmental history of the korea strait during postglacial sea level fluctuations the results of the lithofaces organic geochemical components foraminiferal assemblages and stable isotopes show that the korea strait was influenced in different ways by river discharges and open ocean currents according to their temporal and spatial variability the results of core ssdp 105 indicate that the southeastern coast of korea was probably a shallow coastal environment such as a shoreface or beach by about 17 5 cal ka the area remained a coastal environment that was affected by high energy conditions and partly by freshwater input during the transgressive period of 17 5 8 1 cal ka the area has changed to a modern type shelf environment influenced by the inflow of the tsushima current and by the high supply of fine grained sediments derived from the nakdong river since 8 1 cal ka meanwhile the results of core ssdp 102 taken from the nakdong river mouth reveal that the river mouth area was most likely a terrestrial or fluvial environment at least before 13 9 cal ka it then changed to the estuarine deltaic environment that was directly affected by the nakdong river between 13 9 and 7 0 cal ka and established a modern type shelf prodeltaic environment which is similar in many respects to the southeastern coast of korea after temporarily undergoing erosion between 7 0 and 6 1 cal ka

centennial to millennial scale change of holocene shallow marine environments recorded in ostracode fauna northeast japan abstract using the record of shallow marine ostracode fauna and sediment grain size data from an 865 cm long piston core obtained from mutsu bay northeast japan paleoceanographic changes of the bay were determined at high resolution for the early to middle holocene changes in the relative frequencies of several species showed periodicities of 1300 1800 years similar to bond cycles at around 10 300 cal yr bp and again at 9500 9300 cal yr bp cold water strongly influenced the bay owing to cooling events since at least 10 200 cal yr bp the tsugaru warm current influenced the surface waters and since ca 7400 cal yr bp also the bottom waters of the bay since ca 8400 cal yr bp the water depth rapidly increased and peaked at 7000 5900 cal yr bp due to global sea level rise subsequently a drop of water temperature and sea level in the bay at 5900 and around 4000 cal yr bp influenced the composition of the ostracode assemblages these millennial scale oscillations in relative sea level and bay temperature during the holocene can be correlated to paleoclimate records elsewhere

two long and pronounced cold periods 3 000 5 000 and 6 600 8 400 years b p in east asia and the southward migration of the westerly jet abstract to reconstruct the variations in sea surface temperature sst during the holocene the alkenone unsaturation index of marine sediments from two deep drilled cores and 81 different core top surface sediments recovered from the heuksan mud belt located off the southwestern coast of the korean peninsula was measured first comparison of the alkenone temperature estimates of 81 core top sediments with in situ temperatures indicated that the alkenone temperatures corresponded to the average sst in april to october the spatial distribution pattern of the core top alkenone sst showed a north south temperature gradient which represented the in situ temperatures well this indicated that the effects of the resuspension and lateral transport of sediments on the past temperature estimation might be insignificant based on the two deep drilled cores variations in the alkenone sst during the holocene were reconstructed in general the alkenone sst decreased by less than 1 c from the early to late holocene an interesting feature was the presence of two long and pronounced cold approximately 2 c periods which occurred at 3 5 kyr and 6 6 8 4 kyr b p these cold periods were also observed in other mid latitude regions in east asia indicating that the cooling pattern was regional the cold periods appeared to be associated with the southward migration of the westerly jet at that time investigations into the effects of local sea level changes and resultant changes in the tidal regime on changes in the sst during the holocene period suggested that they were insignificant in the study area

song hong red river delta evolution related to millennium scale holocene sea level changes abstract the song hong red river delta occurs on the northwest coast of the south china sea its evolution in response to holocene sea level changes was clarified on the basis of sedimentary facies and 14 radiocarbon dates from the 40 m long duy tien core from the delta plain and using previously reported geological geomorphological and archaeological data the delta prograded into the drowned valley as a result of early holocene inundation from 9 to 6 cal kyr bp as sea level rise decelerated the sea level highstand at 2 3 m from 6 to 4 cal kyr bp allowed widespread mangrove development on the delta plain and the formation of marine notches in the ha long bay and ninh binh areas during sea level lowering after 4 cal kyr bp the former delta plain emerged as a marine terrace and the delta changed into the present tide and wave influenced delta with accompanying beach ridges delta morphology depositional pattern and sedimentary facies are closely related to holocene sea level changes in particular falling sea level at 4 cal kyr bp had a major impact on the evolution of the song hong delta and is considered to be linked to climate changes

ocean oxidation during the deposition of basal ediacaran doushantuo cap carbonates in the yangtze platform south china abstract precipitation of cap carbonate lithologies is a key feature of cryogenian global glaciations negative carbonate carbon isotopic compositions 13ccarb of these cap carbonates have been variably interpreted as massive drawdown of atmospheric co2 via extensive continental chemical weathering methane oxidation or postglacial upwelling each of these interpretations argues a non steady state of carbon cycle in the aftermath of marinoan global glaciation to further explore the postglacial marine carbon cycle we measured 13ccarb of cap carbonates from six localities in the yangtze platform south china the studied cap carbonates were deposited in a variety of sedimentary environments ranging from the open shelf slope to basin facies cap carbonates deposited in different environments show distinct stratigraphic trends of 13ccarb in the open shelf 13ccarb profile of the songlin section remains almost constant 3 to 4 while the 13ccarb of the jiulongwan section records a negative excursion decreasing from 3 5 to 7 13ccarb of cap carbonates deposited in the slope environment does not show stable stratigraphic trend in the basin environment 13ccarb demonstrates a sharp decline in the middle part of cap carbonates to the nadir value of 11 the negative 13ccarb excursion is best interpreted in terms of oxidation of dissolved organic carbon doc thus recording a pulse of ocean oxidation during cap carbonate precipitation clearly absence of negative 13ccarb excursion in all slope and most open shelf sections may imply that such oxidation event was not ubiquitous in the yangtze platform we speculate that the renewed thermohaline circulation during deglaciation brought oxic surface water into ocean interior which oxidized the basin environment of the yangtze platform however the deglacial thermohaline circulation was not strong enough to cause complete oxidation of the ocean the sporadic oxidation in the open shelf on the other hand might result from the terrestrial influx of oxidant from postglacial continental weathering our study suggests that ocean oxidation though sporadic might have occurred during cap carbonate precipitation and predated the first appearance of putative animal embryos

holocene influx of the tsushima current into the japan sea signalled by spatial and temporal changes in neogloboquadrina incompta distribution neogloboquadrina incompta is an optimal marker of the transitional water formed by mixing of the warm tsushima current with cold waters of the japan sea spatial and temporal changes in n incompta distribution have been analysed to reconstruct the timing and processes by which modern surface water conditions were established in the japan sea as a function of postglacial influx of the tsushima current resulting from rising sea levels the spatiotemporal distribution of n incompta suggests that transitional water formed in the eastern to southern marginal regions of the japan sea prior to the deposition of the k ah tephra 7 3 cal kyr bp and then expanded southwestward a northern cold water mass together with the cold liman current affected the southwestern part of the japan sea until 6 9 cal kyr bp which may have been a result of the weaker influence of the tsushima current during a time of lower sea level

carbon isotopic composition of neoproterozoic glacial carbonates as a test of paleoceanographic models for snowball earth phenomena consistently positive carbon isotopic values were obtained from in situ peloids ooids and stromatolitic carbonate within neoproterozoic glacial successions in northern namibia central australia and the north american cordillera because positive values continue upward into the immediately overlying postglacial cap carbonates the negative isotopic excursions widely observed in those carbonate rocks require an explanation that involves a short term perturbation of the global carbon cycle during deglaciation the data do not support the ecological consequences of complete coverage of the glacial ocean with sea ice as predicted in the 1998 snowball earth hypothesis of p f hoffman et al in the snowball earth hypothesis the postglacial cap carbonates and associated 5 negative carbon isotopic excursions represent the physical record of co2 transfer from the high p co2 snowball atmosphere 0 12 bar to the sedimentary reservoir via silicate weathering in the snowball aftermath stratigraphic timing constraints on cap carbonates imply weathering rates of 1000 times preglacial levels to be consistent with the hypothesis the absence of sr isotopic variation between glacial and postglacial deposits and calculations of maximum weathering rates do not support a post snowball weathering event as the origin for cap carbonates and associated isotopic excursions

correlation between faunal transitions of benthic foraminifera and ballasting of particulate organic carbon by siliceous plankton during the holocene off san in district southwestern japan we investigated the biotic response of benthic foraminifera rhizaria to holocene paleoceanographic changes in a upper bathyal environment by examining fossil benthic foraminifera younger than 13

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

aftermath of a snowball earth 1 using a simple 3 box model of the ocean atmosphere system we simulate the cycling of carbon and strontium in the aftermath of a global glaciation model simulations include the delivery of alkalinity to seawater from intense carbonate and silicate weathering under high pco2 conditions as well as ocean mixing air sea gas exchange and biological productivity the 13c of the first carbonate precipitated after the glaciation depends on the pco2 temperature the saturation state of the surface ocean and kinetic effects associated with mineral precipitation with no biological productivity the model produces 13c values between 1 and 3 consistent with observations this is in direct contradiction with arguments by kennedy et al 2001a who suggest that the 13c value of dissolved carbon in a snowball ocean and directly afterward must be 5 kennedy et al assume the carbon isotope cycle is in steady state which does not apply to a global glaciation and also neglect any effect of high pco2 on the carbonate chemistry of seawater a major difference between our findings and the qualitative predictions of hoffman et al 1998 is our interpretation of the cap dolostone as representing an interval dominated by carbonate weathering of exposed continental shelves as a result the 2 drop in the 13c observed in the cap dolostone is unlikely to be the product of rayleigh distillation of atmospheric co2 via silicate weathering instead we interpret the 2 drop in the 13c values as indicative of an increase in sea surface temperature which lowers the fractionation between co2 and carbonate kinetic isotope effects associated with rapid precipitation from a highly supersaturated surface ocean may also be important rayleigh distillation of atmospheric co2 via silicate weathering is a viable explanation for the continued drop in the 13c values in the limestone sequence above the cap dolostone with biological productivity and carbonate weathering driving a slow increase in 13c values once pco2 levels decline our study also simulates the cycling of strontium in seawater in contrast to the finding of jacobsen and kaufman 1999 and kennedy et al 2001a model simulations show a drop in 87sr 86sr of less than 0 001 during 5 million years of global glaciation and an increase of less than 0 001 over the entire episode of silicate weathering our calculations emphasize the importance of considering the changes in seawater chemistry due to high pco2 in evaluating the snowball earth hypothesis

neoproterozoic carbon isotope stratigraphy of the amadeus basin central australia neoproterozoic shallow marine and carbonate rich strata of the northern amadeus basin central australia comprise a geochemical record of neoproterozoic seawater that facilitates correlation with other basins in australia and worldwide this study includes new carbon and oxygen isotope measurements of cryogenian and ediacaran carbonate in the northern amadeus basin that in combination with previous data from tonian strata of the bitter springs formation form a composite amadeus basin neoproterozoic c record key features of the cryogenian ediacaran portion of this record include 1 negative c excursions in cap carbonates overlying cryogenian glacigenic deposits of the areyonga and olympic formations i e the rasthof and maieberg excursions respectively 2 a mid cryogenian negative excursion in the ringwood member of the aralka formation seemingly correlative with the taishir excursion of sw mongolia 3 a subsequent mid cryogenian positive excursion the keele peak excursion in the limbla member of the aralka formation and 4 relatively low magnitude excursions in the ediacaran julie formation in comparison with other neoproterozoic stratigraphic successions key portions of the overall neoproterozoic c record that appear to be absent from the amadeus basin based on existing data include large magnitude negative excursions islay and trezona excursions that immediately preceded basaland terminal cryogenian i e sturtian and marinoan respectively glaciations these missing c excursions are associated with significant unconformities in the amadeus basin c and o from carbonate clasts in diamictite of the areyonga and olympic formations suggest that deposition of islay and trezona equivalent strata was limited or nonexistent in the amadeus basin as opposed to the possibility that these strata were deposited but subsequently removed by glacial erosion our new amadeus basin results refine cryogenian and early ediacaran correlations among the amadeus basin adelaide rift complex and namibia the lower part of the ringwood member which was deposited during early stages of the cryogenian nonglacial interlude includes two negative c excursions that are also evident in previous results from the tapley hill formation of the adelaide rift complex the upper part of the ringwood member contains abundant stromatolites and seems to correlate with cryogenian stromatolite reefs of the balcanoona formation in the adelaide rift complex the overlying limbla member in the amadeus basin correlates with the yankaninna etina amberoona and enorama formations of the adelaide rift complex as well as carbonate from other continents that record the keele peak excursion c from the early ediacaran olympic cap of the amadeus basin is 1 comparable to previous results from the maieberg and elandshoek formations in namibia and 2 consistent with diachronous deposition of marinoan cap dolostone in the amadeus basin additionally new c from the julie formation of the amadeus basin is similar to previous results from the late ediacaran kuibis subgroup in southern namibia these correlations underscore that ediacaran strata of namibia as well as the cryogenian nonglacial interlude strata of the adelaide rift complex are roughly an order of magnitude thicker than stratigraphic counterparts in the amadeus basin the wide disparity in sedimentation rates implied by this finding is likely attributable to fundamental differences in the neoproterozoic tectonic settings of the three locations

continental weathering intensity during the termination of the marinoan snowball earth mg isotope evidence from the basal doushantuo cap carbonate in south china abstract the neoproterozoic global glaciations 720 635 ma represent the most severe icehouse climatic conditions in earth s history collectively known as the snowball earth events the snowball earth hypothesis hoffman et al 1998 proposed that the termination of the global glaciation was driven by the extremely high atmospheric pco2 level 300 times of present atmospheric level pal that was accumulated during the global glaciation by volcanic degassing for tens of million years because of extremely high temperature the deglaciation might associate with intense continental weathering that brought abundant bicarbonate and alkaline earth metals mg ca to the ocean resulting in the rapid precipitation of cap carbonate all over the world thus cap carbonate precipitation marks the termination of global glaciation the deglacial intense continental weathering has been recently supported by mg isotopes however the mg isotope data also indicate that the deglaciation might have significantly predated the cap carbonate precipitation and limited data suggest that the weathering intensity was already low during the cap carbonate precipitation in order to further test whether the cap carbonate precipitation was associated with low weathering intensity here we analyzed mg isotopic composition of siliciclastic component 26mgsil of the doushantuo cap carbonate in the yangtze block south china four cap carbonate sections the tongle tl drill core the fanyang fy section the wuluo wl drill core and the jiulongwan jlw section spanning from shelf to basin environments were analyzed 26mgsil ranges from 0 43 to 0 39 n 10 from 0 31 to 0 48 n 9 from 0 06 to 0 10 n 7 and from 1 42 to 0 03 n 8 for the jlw fy wl and tl samples respectively there are negative correlations between mg al and 26mgsil in jlw wl and tl the geochemical data indicate that the variation of 26mgsil might be attributed to authigenic clay formation during the cap carbonate precipitation the binary mixing model indicates that the isotopic compositions of terrestrial clays range from 0 to 0 3 comparable to the values of modern soil clays but significantly lower than the values of the upper nantuo formation up to 0 90 suggesting the moderate to low weathering intensity during the cap carbonate deposition our study suggests low atmospheric pco2 level during cap carbonate precipitation probably due to the consumption by intense continental weathering

珪藻paralia sulcataの増減からみた大陸系混合水の消長 東シナ海北東部の最終氷期 後氷期海洋環境

preservation and grain size trends of holocene wave dominated facies successions in eastern japan implications for high resolution sequence stratigraphic analysis vertical grain size trends provide significant information for the sequence stratigraphic analysis of siliciclastic wave dominated facies successions this paper discusses the relationships between the preservation timing and the grain size trends of holocene wave dom inated successions in two contrasting coastal plains the kujukuri and sendai using high resolution ams 14 c dating depositional facies and grain size modal grain size is proposed as a good criterion for eval uating qualitative changes of depositional depth the kujukuri and sendai successions are both fining upward to coarsening upward wave dominated successions that have developed upon ravinement surfaces the fining upward part of the kujukuri succession formed in regressive deposits during a highstand period whereas that of the sendai formed during transgression a difference in the timing of the generation of upward fining is due to the varying preservation potential of transgressive shoreface deposits on the ravi nement surface in the sendai area the potential was much higher than in the kujukuri area because the sendai ravinement surface had re ceived greater sediment supply from the adjacent rivers during trans gression a differing rate of tectonic uplift between the areas was not critical to the preservation potential because of the short time scale the successions show bimodal grain size distributions in the basal parts and unimodal distributions elsewhere the bimodality is consid ered to be the result of mixing of a coarse transgressive lag with finer sediment derived from external sources the finer mode forms a con sistent trend with unimodal grain sizes in overlying deposits the trend is of a simple upward coarsening in the kujukuri and an upward fining to coarsening in the sendai showing distinctive correlation with chang es of depositional depth thus the vertical trend of the modal grain size and not mean or median is best for evaluating changes of de positional depth in ancient wave dominated facies successions

snowball earth termination by destabilization of equatorial permafrost methane clathrate the recovery from the marinoan snowball ice age of about 635 million years ago is one of the most severe climate change events known to have occurred on earth hypotheses accounting for the abruptness of deglaciation include ice albedo feedback deep ocean out gassing during post glacial oceanic overturn or methane hydrate destabilization martin kennedy and colleagues now report the broadest range of oxygen isotope values yet measured in marine sediments in methane seeps in marinoan deglacial sediments underlying a thin interval of carbonate these deposits are thought to record widespread oceanic carbonate precipitation during postglacial sea level rise the range of values is likely the result of mixing between ice sheet derived meteoric waters and clathrate derived fluids during the flushing and destabilization of a clathrate field by glacial meltwater their findings suggest that methane released from low latitude permafrost clathrates acted as a trigger and or strong positive feedback for deglaciation and warming this paper reports the broadest range of oxygen isotope values yet measured in marine sediments in methane seeps in marinoan deglacial sediments underlying a thin interval of carbonate these deposits are thought to record widespread oceanic carbonate precipitation during postglacial sea level rise the range of values is likely the result of mixing between ice sheet derived meteoric waters and clathrate derived fluids during the flushing and destabilization of a clathrate field by glacial meltwater the start of the ediacaran period is defined by one of the most severe climate change events recorded in earth history the recovery from the marinoan snowball ice age 635 myr ago ref 1 marinoan glacial marine deposits occur at equatorial palaeolatitudes2 and are sharply overlain by a thin interval of carbonate that preserves marine carbon and sulphur isotopic excursions of about 5 and 15 parts per thousand respectively3 4 5 these deposits are thought to record widespread oceanic carbonate precipitation during postglacial sea level rise1 3 4 this abrupt transition records a climate system in profound disequilibrium3 6 and contrasts sharply with the cyclical stratigraphic signal imparted by the balanced feedbacks modulating phanerozoic deglaciation hypotheses accounting for the abruptness of deglaciation include ice albedo feedback3 deep ocean out gassing during post glacial oceanic overturn7 or methane hydrate destabilization8 9 10 here we report the broadest range of oxygen isotope values yet measured in marine sediments 25 to 12 in methane seeps in marinoan deglacial sediments underlying the cap carbonate this range of values is likely to be the result of mixing between ice sheet derived meteoric waters and clathrate derived fluids during the flushing and destabilization of a clathrate field by glacial meltwater the equatorial palaeolatitude implies a highly volatile shelf permafrost pool that is an order of magnitude larger than that of the present day a pool of this size could have provided a massive biogeochemical feedback capable of triggering deglaciation and accounting for the global postglacial marine carbon and sulphur isotopic excursions abrupt unidirectional warming cap carbonate deposition and a marine oxygen crisis our findings suggest that methane released from low latitude permafrost clathrates therefore acted as a trigger and or strong positive feedback for deglaciation and warming methane hydrate destabilization is increasingly suspected as an important positive feedback to climate change11 12 13 that coincides with critical boundaries in the geological record14 15 and may represent one particularly important mechanism active during conditions of strong climate forcing

neoproterozoic marine dolomite hardgrounds and their relationship to cap dolomites abstract neoproterozoic cap dolomites are unusual and distinctive marker units that occur after large cryogenian glaciations several thin dolomite units that have features resembling cap dolomites occur within the cryogenian ediacaran succession of the adelaide geosyncline while each of these dolomite units has distinctive features they also share many similarities with cap dolomites including stratigraphic thickness ranging from several centimetres to several metres impure dolomicrite composition graded beds with a sharp top that become more dolomite rich upwards and evidence of volume expansion in the form of sheet cracks tepees or other soft sediment deformation structures the carbon isotopic compositions for these thin dolomite horizons have values ranging from 5 to 2 per mil vpdb which overlap those commonly found in both sturtian and marinoan cap dolomites the generally negative carbon isotope compositions of these dolomites and cap dolomites is most easily explained by mixing of marine and authigenic carbonate sedimentological evidence indicates the graded beds within cap dolomites and other dolomite units are a form of submarine hardground or firmground where dolomicrite is precipitated authigenically at or near the seafloor during periods of little or no sedimentation dolomite replacement of clay and other silicates is an important process in the formation of these dolomicrite firmgrounds volume expansion structures are a product of this near surface dolomicrite precipitation brought about by the high degrees of dolomite supersaturation with a consequent large force of crystallization and unlimited marine carbonate source for the precipitating dolomite we suggest that this deepwater authigenic dolomicrite precipitation is a result of the dominantly anoxic nature of cryogenian early ediacaran oceans and caused by alkalinity producing anoxic bacterial reactions when sedimentation rates slow sufficiently e g during transgressions thin dolomicrite horizons are produced in this hypothesis cap dolomites may largely be the result of sediment starvation combined with a possible increase in carbonate saturation during and following the post glacial transgressions associated with the sturtian and marinoan glacial events this scenario explains most of the sedimentological features of these unusual carbonates the widespread development of such authigenic carbonate would have profound implications for the interpretation of precambrian marine carbon isotopic compositions

late neoproterozoic cap carbonates mackenzie mountains northwestern canada precipitation and global glacial meltdown the 3 27 m thick cap carbonate overlying marinoan ice brook formation glacigene sediments and keele formation carbonate and terrigenous clastic rocks consists of two distinctive stratigraphic units a lower splintery buff weathering microcrystalline dolostone of extensive lateral uniformity comprises mm laminated peloidal sediment with local low angle hummocky like cross stratification micro ridges and synsedimentary tepees all elongated per pendicular to depositional strike this dolostone is unconformably overlain by an upper limestone that exhibits pro nounced facies variation from inboard peloidal lime grainstone and mudstone to shelf edge cementstone to outboard lime wackestone and mudstone calcite cementstones range from isolated crystal fans in laminated limestone to huge decimetre scale crystal arrays to hemispherical and elongate crystal stromatolites wholly composed of acicular crystals that form decametre scale reeflike structures crystal stromatolites are precipitates and replaced microbiolites that con structed biostromes and bioherms like those on many flat topped reef rimmed platforms the calcite crystals have all the physical and chemical attributes of neomorphosed aragonite this aragonite extensively replaced sediment and microbiolite just below the sea floor and grew upward into the overlying water column such interpreted massive synsedimentary replacement is rare in geological history and attests to the highly saturated state of the immediate postglacial ocean all sediment is interpreted to have been caco3 originally low and constant 18 o values reflect diagenetic modification of these carbonates although chemical attributes such as sr and c isotopes in some lithologies are near pristine lower dolostones virtually identical to most other coeval marinoan caps worldwide were part of a global precipitation event of remarkable similarity upper limestones are a more local phenomenon deposited during sea level rise in an aragonitic sea returning to equilibrium after global glaciation low 87 sr 86 sr ratios and varying 13 c values with carbonate sedimentary facies indicate that both units must have formed relatively rapidly prior to significant flu vioglacial runoff or that the influence of this runoff on the chemistry of seawater along continental shelves was mini mal the cap carbonate is thus interpreted to have formed in two steps 1 during initial marine ice melting accompanied by oceanic overturn and upwelling preceding continental margin rebound and 2 during initial stages of sea level rise accompanying continental deglaciation while confirming brief but extensive carbonate precipitation from an ocean highly perturbed by global glaciation the rocks also suggest that this event did not permanently affect either late neoproterozoic ocean chemistry or the contained marine biosphere 1262

low latitude glaciation in the neoproterozoic of oman although earth is widely believed to have undergone a series of extreme low latitude snowball glaciations during the neoproterozoic ca 1000 543 ma only one reliable paleomagnetic result from elatina south australia places glacial rocks close to the equator we report new paleomagnetic data from the neoproterozoic huqf supergroup of oman that pass fold and reversal tests and yield a paleopole at 52 3 s 074 4 e n 25 sites 95 7 3 this paleopole places the muscat region of oman at a latitude of 13 in the late neoproterozoic and provides the first direct evidence that both glacial and overlying cap carbonate units were deposited in the tropics the presence of glacial interglacial cyclicity within the huqf supergroup indicates that areas close to the equator may have been largely free of ice at the time of deposition a result that is inconsistent with the classic snowball earth model our result precludes the possibility that contrasting lithologies mark a phase of rapid plate motion and provides the first evidence for low latitude glaciation in arabia a series of magnetic reversals in the fiq tillite and the overlying hadash dolomite in northern and central oman correlates well with a similar sequence in the mirbat formation in southern oman and indicates that recovery from glacial conditions took place over long time scales possibly 105 106 yr

the palaeobiology and geochemistry of precambrian hydrocarbon source rocks abstract organic carbon productivity and formation of hydrocarbon source rocks during the early precambrian was almost exclusively the product of the growth of microbial mats indirect evidence of microbial mats can be traced back to at least 2 6 2 7 ga neoarchaean with the earliest evidence of mat development in siliciclastic sediments coming from the 2 9 ga mesoarchaean predominantly marine sedimentary rocks of the mozaan group in south africa the earliest direct evidence for terrestrial microbial mats in siliciclastic sediments comes from the 2 75 ga palaeoproterozoic fluviolacustrine sediments of the hardey formation of the pilbara craton in western australia well preserved proterozoic hydrocarbons provide valuable information about the early evolution of the biosphere eukaryotic steranes biomarker for eukaryotic cells and therefore evolved forms of life are present in the geological record from about 2 7 ga but they are not abundant or diverse within archaean communities which tend to be dominated by archaea isoprenoids some hydrocarbons have been generated and migrated from archaean organic rich shales but they were probably not of sufficient volume to be of commercial interest the world s oldest significant hydrocarbon source rocks are palaeoproterozoic in age and include the shungite deposits 2 0 ga in the lake onega region of arctic russia there is strong evidence of a global biospheric oxygenation event at c 1300 1250 ma mesoproterozoic in conjunction with a first order positive shift in the marine carbon isotope record this is supported by the appearance of the oldest bedded marine gypsum deposits and of the earliest unambiguously multicellular eukaryotes at this time this oxygenation event probably played a significant role in supporting the more diverse eukaryotic communities preserved in the neoproterozoic molecular record and provided the volume of organic material required to generate commercial volumes of hydrocarbons hydrocarbon source rocks of late mesoproterozoic and early neoproterozoic age are widespread and include highly organic rich shales deposited in restricted basinal settings adjacent to stromatolitic carbonate banks by c 850 ma the neoproterozoic molecular record is dominated by hopanes from cyanobacteria with a significant abundance and diversity of eukaryotic steranes including those of multicellular eukaryotes red and green algae as well as molecular evidence for heterotrophic protists the most widespread hydrocarbon source rocks of mid to late neoproterozoic age are commonly transgressive organic rich black shales associated with inter glacial and post glacial phases of the neoproterozoic global scale glaciations the relative dominance of microbial mats in the contribution of organic matter as a source for hydrocarbon generation probably decreased significantly during the late neoproterozoic and earliest cambrian perhaps as a result of the rapid growth of grazing metazoan communities or possibly as a result of changes in seawater chemistry and or nutrient supply precambrian and infracambrian petroleum systems are relatively abundant and widespread the oldest live oil recovered to date is sourced from mesoproterozoic rocks within the velkerri formation roper group of the mcarthur basin of northern australia dated at 1361 21 ma and 1417 29 ma re os dates with at least the initial phase of oil generation and migration having taken place before 1280 ma however the geologically oldest commercial production is currently from the somewhat younger mid to late neoproterozoic cryogenian ediacaran petroleum systems of the lena tunguska province in east siberia and in southern china from the latest neoproterozoic to early cambrian huqf supergroup in oman and potentially in the near future from the age equivalent mawar supergroup in western india

late quaternary inner shelf deposits in response to late pleistocene holocene sea level changes nakdong river se korea abstract the high resolution seismic profiles from the inner shelf off the nakdong river in se korea can be directly correlated with the lithologic characteristics in the borehole data these correlations offer an opportunity to document the evolution of the inner shelf deposits with sediment supplies in response to the late quaternary sea level changes the inner shelf sequence in this area consists of four sedimentary units which comprise a set of lowstand transgressive and highstand systems tracts deposited since the last glacial maximum incised channel fill su1 estuary su2 sand veneer su3 and subaqueous delta su4 the lowermost unit su1 which overlies the sequence boundary is interpreted as fluvial deposits formed during the last glacial period and the early stage of transgression and belongs to the lowstand to transgressive systems tract the lower middle unit su2 lying below the ravinement surface represents a paralic component that consists of estuarine sandy mud or muddy sand developed between approximately 13 and 8 cal ka bp whereas the upper middle unit su3 above the ravinement surface corresponds to a marine component that consists of sand veneer produced by the shelf erosion during the ensuing sea level rise these two units su2 and su3 belong to the transgressive deposits the uppermost unit su4 regarded as the highstand systems tract formed the nakdong subaqueous delta including the proximal and distal systems developed after the highstand sea level at approximately 6 cal ka bp the lateral transition from the proximal to distal facies suggests a prograding delta system in the nakdong river

early to middle holocene development of the tsushima warm current based on benthic and planktonic foraminifera in the nakdong river delta southeast korea abstract fossil benthic and planktonic foraminifera from a part of core nd 02 and the published data of core nd 01 from the nakdong river delta southeast korea were analyzed to evaluate the impact of the tsushima warm current on coastal environments in the korea tsushima strait between korea and japan during the early to middle holocene based on cluster analysis four sample clusters a b c and d suggestive of a landward seaward gradient of environmental conditions can be defined according to the spatio temporal and cluster distributions of benthic foraminifera in faunal compositions the landward occurrence of benthic foraminifera was delimited in the inner part of the nakdong river delta at 8 7 ka the common occurrence of warm water planktonic foraminifera suggests that this maximum landward expansion of benthic foraminifera within the delta was caused by the intensification of the tsushima warm current in addition to sea level rise during the early to middle holocene changes in both marine biota and sedimentation were reported in the coastal areas of southwestern japan in that period they were also caused by a precursor of the enhanced tsushima warm current at 8 ka thus the evolution of the tsushima warm current during the early to middle holocene is important for understanding various phenomena in the coastal environments of the korea tsushima strait

microbialite recovery in the aftermath of the sturtian glaciation insights from the rasthof formation namibia abstract ice sheet meltback in the aftermath of the sturtian mid cryogenian glaciation was accompanied or followed by deposition of thick carbonate successions in northern namibia the rasthof formation is a 200 400 m thick cap carbonate sequence divided into 1 a basal cap dolostone 2 a microbial member and 3 an epiclastic member this subdivision applies for 100 km along strike at the southern and western edges of the owambo basin in this paper we focus essentially on macrofacies of the cap dolostone and the microbial member cap dolostones are commonly interpreted as subtidal to deep water deposits with delicate mm thick laminae we describe well preserved ungraded hummocky cross stratification in the cap dolostone expected to occur no deeper than the offshore transition zone the overlying microbial member contains thickly laminated microbialites with folded and contorted intervals interpreted as soft sediment deformation structures the thickly laminated microbialites are followed by more thinly laminated microbialites with roll up structures and more unusual individual vertical stromatolite morphologies we interpret the vertical growths in the microbial member as a direct response to the changing environment the new observations and interpretations presented in this paper contrast with previous work on the rasthof formation we recognise a relatively shallower setting associated with a trend in the geometries of the microbial member

empirical estimation of viscoelastic seismic parameters from petrophysical properties of sandstone viscoelastic seismic parameters are expressions of underlying petrophysical properties theoretical and empirically derived petrophysical seismic relations exist but each is limited in the number and the range of values of the variables used to provide a more comprehensive empirical model we combined lab measurements from 18 published data sets and well log data for sandstone samples and determined least squares coefficients across them all the dependent variables are the seismic parameters of bulk density compressional and shear wave velocities vp and vs and compressional and shear wave quality factors qp and qs the independent variables are effective pressure porosity clay content water saturation permeability and frequency as the derived expressions are empirical correlations no causal relations should be inferred prediction of is based on volumetric mixing of the constituents for vp and vs predictions separate sets of coefficients are fitted for three water saturation condi

sediment trapping in deltas of small mountainous rivers of southwestern taiwan and its influence on east china sea sedimentation abstract taiwan s setting of high mountains steep gradients frequent earthquakes erodible lithology and heavy rainfall represents an ideal site to focus on sedimentary processes of the deltas of small mountainous rivers smrs several smrs in southwestern taiwan have deposited a thick sedimentary succession in the composite southwest taiwan delta swtd since the middle holocene evidence from the swtd can help to determine its trapping efficiency and assess the role of smrs in sediment transport to the sea we used historical nautical charts bathymetric data satellite radar data and 14c dates to calculate the sediment volume of the swtd on millennial and decadal scales the 14c dates of core samples indicate deposition of thick deltaic sediment in subsiding areas since the time of the maximum flooding surface about 7 cal ka bp the paleo shoreline changes of the swtd suggest a steady westward progradation since 7 cal ka bp in contrast the nautical charts suggest minor volume reduction of the offshore part of the swtd with a deepening trend and retreating shorelines during the last seven decades the results show that at least 201 72 13 90 km3 3 23 105 mt of sediment has been trapped in the swtd since 7 cal ka bp and that the delta has shifted to a destructive phase during the past seven decades as human influences such as construction of reservoirs dams and weirs in the hills have reduced the sediment supply the birth of the taiwan warm current and following continuous sediment supply from the western rivers of taiwan to the east china sea since 7 3 cal ka bp have played a crucial role in the sedimentation of the east china sea particularly in the okinawa trough and the japan sea through the tsushima warm current