permian brachiopods from the baoshan and simao blocks in western yunnan china this paper describes and illustrates four permian brachiopod assemblages assemblages a d from western yunnan southwest china assemblage a occurs in the basal part of the yongde formation in the xiaoxinzhai section in the southern baoshan block and is assignable to the latest artinskian or earliest kungurian assemblage b occurs about 50 m stratigraphically above assemblage a in the same section and is of chihsian kungurian roadian age assemblage c was collected from the yongde formation in the anpaitian section in the southern baoshan block and is most likely roadian to wordian in age assemblage d came from the longtan formation in the simao block and is of late wuchiapingian in age the brachiopod faunas from the yongde formation of the baoshan block as a whole is dominated by species characteristic of the cathaysian province although some links with peri gondwanan faunas are also evident in contrast assemblage d from the simao block is characterised exclusively by taxa of the cathaysian province new taxa described and illustrated are neochonetes huangichonetes inflatus n sp costatumulus minor n sp and celebetus yunnanensis n sp

microfacies and carbon isotope records of mississippian carbonates from the isolated bama platform of youjiang basin south china possible responses to climate driven upwelling changes in mississippian global paleogeography derived from the reconfiguration of the continents have been suggested to result in a change in oceanic circulation carbon cycling as well as in global cooling here integrated 13ccarb chemostratigraphy and foraminiferal biostratigraphy across the mississippian late tournaisian visean early serpukhovian mfz6 mfz16 foraminiferal biozones of the gongchuan section located in the isolated bama platform in the youjiang basin south china are presented the 13ccarb trend shows an abrupt decline during late visean asbian early brigantian mfz13 14 this decline is also observed in subequatorial western euramerica whereas coeval sections in subequatorial eastern euramerica show consistently elevated 13c values across the entire visean the 13c decline in western euramerica and the south china block eastern paleo tethys coincides with a global regression with a suggested glacioeustatic origin the onset of high frequency climate and sea level oscillations and the closure of the rheic seaway between euramerica and gondwana we propose a model explaining the divergence of 13c records resulting from the closure of the rheic seaway and development of upwelling zones in the western margin of euramerica and the eastern paleo tethys realm quantitative microfacies analysis across the mississippian succession in the gongchuan section shows facies independent disappearance of corals and increased proportion of cortoids and filter feeding organisms at the onset of the asbian 13c decline which may support an increase in nutrient level that can be expected as a result of upwelling

palynological records of the permian ecca group south africa utilizing climatic icehouse greenhouse signals for cross basin correlations abstract the permian formations of the south african karoo basin play a crucial role in understanding gondwana s climate history during this time of major global changes in this paper we present two data sets one from the coal bearing vryheid formation witbank basin and one from the whitehill and upper prince albert formations of the dp 1 78 core ne karoo our main goal was to study the vegetation changes during this period of global warming and test if the climatic signals could be used to correlate the basinal ecca group facies with the fluvio deltaic coal bearing strata of the witbank basin the palynological record of the no 2 coal seam of the vryheid formation indicates a cold climate fern wetland community characteristic of lowland alluvial plains and an upland conifer community in the lower part of the coal seam up section these communities are replaced by a cool temperate cycad like lowland vegetation and gymnospermous upland flora the data set of the dp 1 78 core is interpreted to represent a cool to warm temperate climate represented by a high amount of gangamopteris and glossopteris elements both data sets are very different in their composition which can be explained by the differences in depositional environment however our findings reveal a different age of the studied assemblages and thus also suggest that both data sets represent different stages in the transition from icehouse to greenhouse during permian times as the stratigraphic correlation between the main karroo basin and the peripheral basins is still under discussion this paper provides new data to underpin the stratigraphic placement of the whitehill formation relative to the coal bearing vryheid formation

the pedo geochemistry of vertisols under tropical savanna climate abstract fourteen representative thai vertisols on lowland and upland areas under a tropical savanna climate were investigated to ascertain parent material and pedogenic influences on their geochemistry physico chemical mineralogical and geochemical properties were determined for 98 soil samples multivariate analysis was used to interpret the dataset and identify affinity groups of samples and properties silicon al fe and ca are the major constituents of the soils mean concentrations of elements are mostly within the range for worldwide normal soils the variations in concentration of elements between soils reflect differences in the abundance of the major mineral constituents beidellite calcite iron oxides and quartz factor analysis of geochemical data showed that most elements do not cluster into discrete affinity groups the composition of soils is mostly quite uniform throughout the profiles with no evidence for depositional layers beidellite is the dominant clay mineral and acts as a reservoir of many major and trace elements in these soils the accumulation of pedogenic calcium carbonate and fe mn nodules in distinct horizons has resulted in systematic variations in composition within and between soil profiles for those elements that are associated with these neoformed materials e g fe mn co v th ba and ge

permian phytogeographic patterns and climate data model comparisons abstract the most recent global icehouse hothouse climate transition in earth history began during the permian warmer polar conditions relative to today then persisted through the mesozoic and into the cenozoic we focus here on two permian stages the sakmarian 285 280 ma and the wordian 267 264 ma also known as the kazanian integrating floral with lithological data to determine their climates globally these stages postdate the permo carboniferous glaciation but retain a moderately steep equator to pole gradient judging by the level of floral and faunal differentiation floral data provide a particularly useful means of interpreting terrestrial paleoclimates often revealing information about climate gradations between dry and wet end member lithological indicators such as evaporites and coals we applied multivariate statistical analyses to the permian floral data to calibrate the nature of floral and geographical transitions as an aid to climate interpretation we then classified sakma

rapid onset of late paleozoic glaciation on gondwana evidence from upper mississippian strata of the midcontinent united states direct evidence of the late paleozoic glaciation of gondwana from glacial deposits suggests that geographically extensive continental glaciation began some time in the namurian late mississippian however the timing and characteristics of the onset of glaciation are poorly understood because of a lack of reliable paleontological control and reworking of initial glacial deposits by subsequent glacial advances indirect evidence of glaciation preserved in unconformity bounded low latitude ramp sequences in the illinois basin united states suggests that geographically extensive continental glaciation of gondwana actually began in the late visean an abrupt change from carbonate dominated sequences bounded by disconformities with little evidence of erosion to mixed carbonate siliciclastic sequences bounded by unconformities with deep incised valleys was likely produced by a three fold increase in the magnitude of eustatic sea level fluctuations the increase in the magnitude of sea level fluctuations was likely driven by an equally abrupt increase in ice volume and marks the onset of the geographically extensive late paleozoic glaciation of gondwana a possible explanation for the rapid onset of glaciation is the closing of the equatorial seaway between laurussia and gondwana closing of this seaway would have led to an abrupt change in oceanic and atmospheric circulation patterns that could have initiated major continental glaciation in the southern hemisphere

prevailing anoxia in the kungurian permian of south china possible response to divergent climate trends between the tropics and gondwana the kungurian ocean climate system has received little attention but a new compilation of geochemical and paleoclimatic proxies suggest more complex climate dynamics during the late paleozoic icehouse greenhouse transition than previously considered here integrated carbon isotope stratigraphical sedimentological and geochemical data across two early middle permian successions in the youjiang basin south china is presented these proxies indicate widespread anoxia below or near the water sediment interface in south china during the kungurian high primary productivity high sedimentation rate and a relative sea level rise are here proposed as being responsible for this process in the late kungurian but cannot account for the remaining anoxia at cycle boundaries we put forward a hypothesis that divergent climate trends between the tropics and gondwana might have played an important role in ocean stagnation and prevailing o2 deficient conditions in and probably outside south china during the kungurian the termination of anoxia in this region during the latest kungurian is attributed to an intensification of oceanic circulation a rise in atmospheric po2 concentrations a sea level drop depressed primary productivity and low sedimentation rates this study calls for further high resolution sedimentological and geochemical investigations on the paleotropics outside south china in order to elucidate the icehouse greenhouse transition at the global scale

enhanced productivity led to increased organic carbon burial in the euxinic north atlantic basin during the late cenomanian oceanic anoxic event 1 three cenomanian turonian c t 93 5 ma black shale sections along a northeast southwest transect in the southern part of the proto north atlantic ocean were correlated by stable carbon isotope stratigraphy using the characteristic excursion in 13c values of both bulk organic matter om and molecular fossils of algal chlorophyll and steroids all three sites show an increase in marine organic carbon oc accumulation rates during the c t oceanic anoxic event oae the occurrence of molecular fossils of anoxygenic photosynthetic green sulfur bacteria lack of bioturbation and high abundance of redox sensitive trace metals indicate sulfidic conditions periodically reaching up into the photic zone before as well as during the c t oae during the c t oae there was a significant rise of the chemocline as indicated by the increase in concentrations of molecular fossils of green sulfur bacteria and mo al ratios the presence of molecular fossils of the green strain of green sulfur bacteria indicates that euxinic conditions periodically even occurred at very shallow water depths of 15 m or less during the c t oae however bottom water conditions did not dramatically change as indicated by more or less constant v al and zn al ratios at site 367 this suggests that the increase in oc burial rates resulted from enhanced primary productivity rather than increased anoxia which is supported by stable carbon isotopic evidence and a large increase in ba al ratios during the c t oae the occurrence of the productivity event during a period of globally enhanced organic carbon burial rates i e the c t oae points to a common cause possibly related to the formation of a deep water connection between north and south atlantic basins

palynological biozones and radiometric data at the carboniferous permian boundary in western gondwana absolute radiometric data obtained recently in upper paleozoic basins of south america and southern africa are available to constrain the age of some palynological biozones defined in the western gondwana some dates obtained from argentina coincide with southern africa s and are useful to constrain the palynological associations in this way the permian argentinian lueckisporites weylandites lw biozone is compared with the lueckisporites virkkiae biozone of brazil and zone 3 of south africa on the other hand the palynofloras from dwyka south africa are comparable with argentinian and brazilian associations recovered near the carboniferous permian boundary tuffaceous intervals of the dwyka group in south africa suggest the beginning of that sequence at 307 ma reaching the 290 ma at the top the available palynological paleoenvironmental and radiometric data from these three western gondwanan areas are analyzed and compared 2006 international association for gondwana research published by elsevier b v all rights reserved

the trace metal content of recent organic carbon rich sediments implications for cretaceous black shale formation organic carbon rich sediments are enriched in several redox sensitive and stable sulfide forming trace metals tm and form an important sink in global tm cycles in today s ocean such sediments are deposited in coastal upwelling areas like those in the gulf of california off peru or off the namibian coast and euxinic basins like the black sea in an attempt to distinguish both environments by their specific tm patterns some important conclusions may be drawn 1 the tm enrichment seen in both environments broadly is rather similar 2 upwelling sediments are often enriched in cd and p and depleted in co and mn 3 sapropels have a tendency towards higher enrichments in ba and mo s re as cu ni sb and fe reflecting the strong sulfidation in an anoxic water column 4 upwelling systems cover a broad range of environmental settings where the steepness of the slope the proximity of h2s to the sediment seawater interface and the intensity of bio accumulation and regeneration play an important role for tm accumulation 5 the tm content of anoxic basins is mainly controlled by tm availability in the water column and sedimentation rate 6 enhanced bio productivity is the main switch turning an oxygenated into an anoxic environment cretaceous black shales oae 2 exhibit tm signatures of both coastal upwelling areas and sapropels the strong enrichments in cd mo tl v cu ni bi and sb demonstrate that bio accumulation and presence of h2s in the water column and associated sulfidation processes persisted during this time interval in large parts of the proto atlantic the usefulness of ba as a paleoproductivity proxy is obscured by diagenesis the extreme accumulation in ag and zn requires either an additional tm source for instance hydrothermal input or a different tm seawater composition during the cretaceous the geochemical data suggest that the major driving force for the widespread occurrence of c t black shales seems to be the increase in volcanic activity and associated co2 input throughout the cretaceous the ocean atmosphere system operated in a mode different from today during this time interval after conversion of the nutrient co2 into organic matter the system switched back into the normal operational mode

organic carbon accumulation and preservation in surface sediments on the peru margin concentrations and characteristics of organic matter in surface sediments deposited under an intense oxygen minimum zone on the peru margin were studied in samples from deck deployed box cores and push cores acquired by submersible on two transects spanning depths of 75 to 1000 m at 12 and 13 5 s the source of organic matter to the seafloor in these areas is almost entirely marine material as confirmed by the narrow range of of organic carbon obtained in the present study 20 3 to 21 6 pdb and the lack of any relationship between pyrolysis hydrogen index and carbon isotope composition organic carbon contents are highest up to 16 on the slope at depths between 75 and 350 m in sediments deposited under intermediate water masses with low dissolved oxygen concentrations 5 mol kg even at these low concentrations of dissolved oxygen however the surface sediments that were recovered from these depths are dominantly unlaminated strong currents up to 30 cm s associated with the poleward flowing peru undercurrent were measured at depths between 160 and 300 m on both transects the seafloor in this range of water depths is characterized by bedforms stabilized by bacterial mats extensive authigenic mineral crusts and or thick organic flocs constant advection of dissolved oxygen although in low concentrations active resuspension of surficial organic matter activity of organisms and transport of fine grained sediment to and from more oxygenated zones all contribute to greater degradation and poorer initial preservation of organic matter than might be expected under oxygen deficient conditions dissolved oxygen concentrations ultimately may be the dominant affect on organic matter characteristics but reworking of fine grained sediment and organic matter by strong bottom currents and redeposition on the seafloor in areas of lower energy also exert important controls on organic carbon concentration and degree of oxidation in this region

sedimentary corg p ratios paleocean ventilation and phanerozoic atmospheric po2 the corg p ratios of organic rich facies tocn1 exhibit considerable variation through the phanerozoic from b10 1 in the permian phosphoria formation to n1000 1 in some devonian black shales relative to the composition of phytoplankton c p 106 1 which provide the bulk of organic c and p to organic rich marine sediments the range of phanerozoic sedimentary corg p ratios largely reflects the influence of benthic redox conditions on diagenetic pathways of c and p remobilization enhanced preservationoforganiccatlowerredoxpotentials combinedwithenhancedsedimentaryretentionofremineralizedorganicpathigher redox potentials results in a strong relationship between benthic redox conditions and sedimentary corg p ratios the strong secular coherence of the phanerozoic corg p record i e limited variation within narrow time slices suggests that these ratios are controlled primarily by factors influencing benthic redox conditions on a global scale such as atmospheric po2 inversion and scaling of the phanerozoic corg p record yields a new atmospheric po2 model that has strong similarities to existing models based on elemental and isotopic mass balances yet differs in some potentially significant respects in particular the new model suggests that atmospheric po2 wasmarkedlylowerduringtheearlytomiddlepaleozoicthanpreviouslyinferred duringmostofthedevonian atmospherico2levels mayhavebeensufficientlylow b13 astopreventthesustainedcombustionofplantmaterial thisfeatureofthemodelmayaccount for ananomalous gapinthefossilcharcoalrecordduringthedevonian theredox dependentburialofpintheoceanresults inpositive and negative feedback mechanisms that tend to stabilize atmospheric oxygen concentrations on geologic timescales temporal variations in the burial of p relative to c suggest that the strength of these feedback mechanisms varied over the phanerozoic 2007 elsevier b v all rights reserved

development and origin of the microgranular structure in latosols of the brazilian central plateau significance of texture mineralogy and biological activity brazilian latosols are characterized by low activity clay little horizon differentiation a weak macrostructure and a strong microgranular structure the development of the latter that was reported as being possibly related to the fine material mineralogy location in the landscape parental material and biological activity is still under discussion the aim of this study is to discuss the origin of the microgranular structure of latosols located in the brazilian central plateau ten latosols l developed in different parent materials were selected along an approximately 350 km long regional toposequence across the south american surface sas l1 to l4 and velhas surface vs l5 to l10 the structure of the latosols was studied in the field and samples of the diagnostic bw horizons were collected for laboratory analyses basic soil characterization was performed on the 2 mm material according to the brazilian standard procedures the sio2 al2o3 fe2o3 and tio2 content was determined after dissolution with 1 1 h2so4 the microstructure was studied in optical microscopy and electron scanning electron microscopy in thin sections the results showed a varying compound strong microgranular structure and weak to moderate medium sub angular blocky structure independently of the landscape position as well as the parental material except for the latosol developed on a quartzite the latosols were classified as gibbsitic sexquioxic kaolinitic non sesquioxid or kaolinitic sesquioxid latosols but there was no relationship between their composition and the development of the microgranular structure in the bw horizon the analyses showed indeed several types of microgranular structure with different proportions but without any relationship with their texture and mineralogy actually the types of microgranular structure appeared to be mainly related to soil bioturbation by termites and eventually secondarily by ants thus the weak macrostructure and strong microgranular structure of the latosols studied the little vertical differentiation of the horizons and the lack of a clear relationship between their landscape position and parent material characteristics would result from long term biotic action with high probability

a new u pb zircon age dating and palynological data from a lower permian section of the southernmost parana basin brazil biochronostratigraphical and geochronological implications for gondwanan correlations abstract index species useful for correlations with the international stratigraphical column are rare or absent in the pennsylvanian permian strata of the parana basin in brazil preventing accuracy in geochronologic assignments besides absolute datings are very scarce in comparison with other gondwana basins this paper presents palynological data from an outcrop on the surroundings of the candiota coal mine southmost brazil from several levels of the rio bonito and palermo formations the presence of certain index species of spore pollen allowed the recognition of two permian palynozones the vittatina costabilis and the lueckisporites virkkiae zones furthermore u pb in zircons from a volcaniclastic level interbedded in the coal strata of the former unit was analyzed through la mc icp ms method providing a new absolute age dating of 281 4 3 4 ma cisuralian early permian this dating is assumed as the oldest occurrence of the l virkkiae zone in parana basin which contains index species that are widespread in other gondwana basins a well distributed surface boundary occurs in this section also allowing local and regional correlations these new biostratigraphical and geochronological data are integrated in order to offer a deep analysis on the stratigraphical significance for correlations across the occidental gondwana

raman study of olivines in 37 heavily and moderately shocked ordinary chondrites raman spectra generally in the delta wavelength range of 500 1200 cm 1 were taken from olivines in 37 ordinary chondrites to test whether the prominent laboratory produced high shock feature of olivine near 1100 cm 1 occurs in the olivines of the heavily shocked black chondrites in addition to the lines of olivine lines from the abundant orthopyroxene were also detected it was found that the 1100 cm 1 feature was absent from all of the spectra and that all spectra except that taken from the chondrite ramsdorf which showed line broadening and strong luminescence were essentially indistinguishable and very similar to spectra taken from the unshocked mineral the absence of the 1100 cm 1 feature and of strong luminescence from the chondritic raman spectra even in meteorites whose olivines are nearly x ray amorphous is thought to be due to thermal annealing during the comparatively slow cooling from peak shock temperatures

permian palaeogeographic evolution of the jiangnan basin south china abstract the most striking geographic feature of the permian of south china is the jiangnan basin which intimately reflects the interplay between the yangtze and cathaysia blocks geographic and sedimentological evolution suggests that the jiangnan basin superposed on a precambrian collisonial megasuture and a folded early paleozoic deep basin was an extensional intracratonic basin it opened in the longlinian and became more passive and restricted in the latest maokouan the remarkably similar geographic patterns of the jiangnan basin in the early and late palaeozoic suggest that the yangtze and cathaysia blocks were coherent during the paleozoic

the geochemistry of soils on a catena on basalt at khon buri northeast thailand abstract a geochemistry study was carried out on a catenary sequence of soils formed on basalt under a tropical climate four soil profiles developed on crest backslope footslope and valley floor positions on an undulating basaltic lava corrosion plain were sampled and analyzed by optical microscopy xrd xrf icp ms and sem eds analytical techniques aluminum si fe and ti are the major elements in all soils across the catena the crest soil profile contains uniform quantities of al si fe and ti in each horizon and very low amounts of ca mg and k this reflects the dominance of kaolin iron oxide minerals anatase and quartz backslope and footslope soils also consist mostly of al si fe and ti but they contain higher amounts of mn as a result of a redox accumulation process other than quartz ilmenite is the only sand sized mineral in the valley floor soil redox reactions occurring in stagnant water do not support crystalline iron oxide minerals the high iron content of this soil is mostly present in authigenic smectite this soil has higher amounts of mg ca and k than upslope soils reflecting its accumulating position in the landscape and the in situ crystallization of carbonates and smectite factor analysis of chemical data shows quite different associations of elements in whole soils fine sand silt and clay fractions the element compositions of the whole soil and in all size fractions show that the crest soil is most uniform the backslope soil is quite uniform the footslope soil is quite diverse and resembles the backslope soil and the valley floor soil is highly diverse and quite different from the upslope soils three main elemental behavior groups exist for the whole soil the different concentrations of elements in the al group al ti li cs zr mo and the ca group ca si k mg result in the soils on crest and valley floor being distinctly different the fe group fe mn p ga cr pb rb v cu zn ni co k as causes the backslope and footslope soils to overlap differences in concentration of the mn group mn mg pb co pb k and fe group fe rb ni p u zn ga v al cu as ti cs li mo result in the soils on the backslope and footslope being different from the other two soils no soils on the catena have elemental compositions that overlap for silt or clay fractions element concentrations in each size fraction and each landscape position can be attributed to differences in parent rock and differential weathering

assessing response of local moisture conditions in central brazil to variability in regional monsoon intensity using speleothem 87 sr 86 sr values abstract delineating the controls on hydroclimate throughout brazil is essential to assessing potential impact of global climate change on water resources and biogeography an increasing number of monsoon reconstructions from 18 o records provide insight into variations in regional monsoon intensity over the last millennium the strength however of 18 o as a proxy of regional climate limits its ability to reflect local conditions highlighting the need for comparable reconstructions of local moisture conditions here speleothem 87 sr 86 sr values are developed as a paleo moisture proxy in central brazil to complement existing 18 o based reconstructions of regional monsoon intensity speleothem 87 sr 86 sr values are resolved using laser ablation and conventional solution mass spectrometry at high resolution relative to existing non 18 o based paleo moisture reconstructions to allow comparisons of centennial variability in paleo monsoon intensity and paleo moisture conditions variations in speleothem 87 sr 86 sr values from tamboril cave are interpreted to reflect varying extents of water interaction with the carbonate host rock with more interaction resulting in greater evolution of water isotope values from those initially acquired from the soil to those of the carbonate bedrock increasing speleothem 87 sr 86 sr values over the last millennium suggest progressively less interaction with the carbonate host rock likely resulting from higher infiltration rates expected under wetter conditions increasingly wetter conditions over the last millennium are consistent with an overall trend of increasing monsoon intensity decreasing 18 o values preserved in many existing 18 o records from the region such a trend however is absent in 18 o records from our site central brazil and cristal cave southeast brazil suggesting the existence of divergent relevant to 18 o precip shifts in the climate patterns within and outside the core monsoon region

global continental weathering trends across the early permian glacial to postglacial transition correlating high and low paleolatitude sedimentary records time equivalent early permian sedimentary successions from high latitude gondwana basins and from equatorial accumulations in north china covering the glacial to postglacial transition display correlatable trends in continental weathering intensity based on chemical index of alteration cia values the successions display a pattern of cia values that varies with latitude similar to modern estuarine suspended sediments based on the modern day cia temperature correlation the glacial early permian low to high latitude land surface temperature gradient is estimated as 20 c slightly higher than the calculated values for the contemporaneous sea surface temperature gradient

short lived u and th isotope distribution in a tropical laterite derived from granite pitinga river basin amazonia brazil application to assessment of weathering rate we have analyzed samples of a 15 m thick profile weathered from the madeira granite located in the pitinga basin river north of manaus in the state of amazonia brazil this profile consists essentially of a yellow red saprolite covered by a soil u and th concentrations are particularly high in the granite 20 and 80 g g respectively normalized element to th concentrations indicate that th is most resistant to chemical weathering except to some extent in the top soil higher concentrations in the saprolite compared to the granite comprise a relative enrichment resulting from a loss of mass the saprolites are initially generated by a descending weathering front which alters the granite to a yellow red saprolite a second front close to the top turns the saprolite into a soil weathering has led to leaching of u the 234u 238u and 230th 238u isotopic ratios are in radioactive disequilibrium numerous nodules are present and apparently started to form at the base of the saprolite these nodules achieve more developed form during their relative ascent until they are reached by the descending top front where they undergo dissolution the th and pb are concentrated in the nodules close to the top front the u being more mobile is strongly leached by the first front and most of the remainder freed by the second engages in a descending flux which supplies the underlying saprolite using the data an attempt is made to model the isotopic distribution in the profile we conclude that the first front has descended at a rate of 5 cm 1000 yt and that the time needed to create the saprolite must have been around 300 000 yr

co2 forced climate and vegetation instability during late paleozoic deglaciation the late paleozoic deglaciation is the vegetated earth9s only recorded icehouse to greenhouse transition yet the climate dynamics remain enigmatic by using the stable isotopic compositions of soil formed minerals fossil plant matter and shallow water brachiopods we estimated atmospheric partial pressure of carbon dioxide pco2 and tropical marine surface temperatures during this climate transition comparison to southern gondwanan glacial records documents covariance between inferred shifts in pco2 temperature and ice volume consistent with greenhouse gas forcing of climate major restructuring of paleotropical flora in western euramerica occurred in step with climate and pco2 shifts illustrating the biotic impact associated with past co2 forced turnover to a permanent ice free world

problems of a late palaeozoic glaciation in australia and subsequent climate in the permian the most recent information suggests two periods of glaciation separated by a considerable time interval the first is found in the namurian early carboniferous and may extend into the beginning of the late carboniferous evidence for the carboniferous glaciation is largely or entirely redeposited striated clasts known only from the new england area of northeastern new south wales these are considered to represent montane type glaciation associated with a developing alpine chain after a long interval glacial deposits are then found in many parts of australia in the asselian the lowest stage of the permian and the glaciation may extend into the beginning of the sakmarian the following stage in western australia a number of major fluctuations are recorded in the asselian the end of the glaciation seems to be associated with a worldwide eustatic rise in sea level in the tastubian the lower stage of the sakmarian after the tastubian no direct verifiable evidence indicates glaciation in the permian in australia or any other part of the world in australia there is no clear evidence on the climate in the interval between the two glacial periods but in south america and other parts of the world a warm interval is reported at this time most of the glacial debris is now found in sedimentary basins which were developing contemporaneously with the glaciation and is of a wet based type glaciers were active on steep hinterland carrying debris in adjacent water covered basins but how far the ice may have spread over lower lying land areas in not clear there is no real evidence of a thick dry based ice sheet like that of present antarctica after the tastubian there are a number of major fluctuations in climate during the rest of the permian at times seasonal ice and or perhaps icebergs may have been active but fluctuations which were cool or warm temperate or in some places in australia even subtropical or tropical are found in the sterlitamakian upper sakmarian beginning and end of the baighenzhinian upper artinskian kungurian kazanian and dzhulfian all separated probably by colder and in some cases considerably colder periods comparison of the marine faunas of the carboniferous and permian suggests that the levipustula fauna may not represent as cold sea water as the eurydesma fauna

pitfalls of normalization of marine geochemical data using a common divisor abstract normalization of trace element contents of sediment through division by the content of an immobile element usually aluminum is common practice in marine geochemical studies this might appear to be a simple way of correcting for dilution by sedimentary phases barren of a particular trace element for instance carbonates or silica and for comparison with its content in a standard clay or shale the purpose of this paper is to revive the awareness of the pitfalls of this practice by giving numerical examples of the often unexpected results of normalization taking a statistical perspective it is first shown that uncorrelated variables acquire spurious correlations when normalized but normalization can also increase decrease change sign of or even blur the correlations between unmodified variables next a number of realistic scenarios are worked out to show that the correlations between normalized element contents still suffer from the closure effect only in a few simple cases it is possible to extract from the normalized data realistic estimates of trace element contents in distinct sedimentary phases such as organic matter this is ascertained from data on copper contents in sediment from the black sea and arabian sea when the coefficient of variation i e standard deviation divided by the mean of the aluminum data is relatively low and much lower than for the original values of the trace elements comparisons of correlations can equally well or even better be made on the basis of the unmodified values then the comparison of trace element data with their values for standard shales is discussed the inherent problem is that the composition of the commonly used standard shale and consequently the reference values of normalized elements are not necessarily representative of the local or regional sediments in the study area also this method falls short of identifying the processes responsible for enrichment or diminution in trace element contents finally consideration is given to some aspects of a proper use of al normalization

ocean stagnation and end permian anoxia ocean stagnation has been invoked to explain the widespread occurrence of organic carbon rich laminated sediments interpreted to have been deposited under anoxic bottom waters at the time of the end permian mass extinction however to a first approximation stagnation would severely reduce the upwelling supply of nutrients to the photic zone reducing productivity moreover it is not obvious that ocean stagnation can be achieved numerical experiments performed with a three dimensional global ocean model linked to a biogeochemical model of phosphate and oxygen cycling indicate that a low equator to pole temperature gradient could have produced weak oceanic circulation and widespread anoxia in the late permian ocean we find that polar warming and tropical cooling of sea surface temperatures cause anoxia throughout the deep ocean as a result of both lower dissolved oxygen in bottom source waters and increased nutrient utilization buildup of quantities of h2s and co2 in the late permian ocean sufficient to directly cause a mass extinction however would have required large increases in the oceanic nutrient inventory

oxygen minimum zones in the eastern tropical atlantic and pacific oceans within the eastern tropical oceans of the atlantic and pacific basin vast oxygen minimum zones omz exist in the depth range between 100 and 900 m minimum oxygen values are reached at 300 500 m depth which in the eastern pacific become suboxic dissolved oxygen content 4 5 mol kg 1 with dissolved oxygen concentration of less than 1 mol kg 1 the omz of the eastern atlantic is not suboxic and has relatively high oxygen minimum values of about 17 mol kg 1 in the south atlantic and more than 40 mol kg 1 in the north atlantic about 20 40 of the north pacific volume is occupied by an omz when using 45 mol kg 1 or 90 mol kg 1 respectively as an upper bound for omz oxygen concentration for ocean densities lighter than 27 2 kg m 3 the relative volumes reduce to less than half for the south pacific 7 and 13 respectively the abundance of omzs are considerably smaller 1 and 7 for the south atlantic and only 0 and 5 for the north atlantic thermal domes characterized by upward displacements of isotherms located in the northeastern pacific and atlantic and in the southeastern atlantic are co located with the centres of the omzs they seem not to be directly involved in the generation of the omzs omzs are a consequence of a combination of weak ocean ventilation which supplies oxygen and respiration which consumes oxygen oxygen consumption can be approximated by the apparent oxygen utilization aou however aou scaled with an appropriate consumption rate aour gives a time the oxygen age here we derive oxygen ages using climatological aou data and an empirical estimate of aour averaging oxygen ages for main thermocline isopycnals of the atlantic and pacific ocean exhibit an exponential increase with density without an obvious signature of the omzs oxygen supply originates from a surface outcrop area and can also be approximated by the turn over time the ratio of ocean volume to ventilating flux the turn over time corresponds well to the average oxygen ages for the well ventilated waters however in the density ranges of the suboxic omzs the turn over time substantially increases this indicates that reduced ventilation in the outcrop is directly related to the existence of suboxic omzs but they are not obviously related to enhanced consumption indicated by the oxygen ages the turn over time suggests that the lower thermocline of the north atlantic would be suboxic but at present this is compensated by the import of water from the well ventilated south atlantic the turn over time approach itself is independent of details of ocean transport pathways instead the geographical location of the omz is to first order determined by i the patterns of upwelling either through ekman or equatorial divergence ii the regions of general sluggish horizontal transport at the eastern boundaries and iii to a lesser extent to regions with high productivity as indicated through ocean colour data

the phosphorus cycle phosphogenesis and marine phosphate rich deposits abstract phosphorus in the form of phosphate is an essential nutrient and energy carrier on many different levels of life and a key element in mediating between living and lifeless parts of the biosphere one of the most important aspects of the phosphorus cycle is its vital role in governing productivity thereby interacting with the exogenic part of the carbon cycle which in turn is important in regulating earth s climate phosphorus is a prime element to be traced in earth s history because it allows for the reconstruction of long term feedback mechanisms between climate environment and ecology and of global change as such marine sedimentary phosphate deposits are particularly suited to study aspects of the phosphorus cycle because in the case of ubiquity their origin may result from a general acceleration of the global phosphorus cycle sources of sedimentary phosphate are microbial breakdown of buried organic matter and redox driven phosphate desorption from iron and manganese oxyhydroxides dissolved sea water phosphate represents an additional source which may become important in the formation of phosphatic hardgrounds the main locus of phosphogenesis is near the sediment water interface but phosphogenesis also occurs at greater sediment depths current induced winnowing and transport processes along the sea floor concentrate phosphate precipitates into deposits which exhibit internal stratification patterns typical for the prevailing hydraulic energy regime in a sequence stratigraphic context phosphate deposits preferentially occur along marine or maximum flooding surfaces consequent sedimentary reworking may result in the transfer of phosphates to highstand or lowstand deposits bio chemical weathering on continents represents the most significant source of bioavailable phosphorus this implies that long term changes in marine phosphorus levels and with these changes in marine ecology productivity rates and ratios of exported carbonate carbon and organic carbon are a response to changes in continental weathering rates a compilation of marine sedimentary phosphorus burial rates for the last 160 myr suggests that natural variations have occurred that span one order of magnitude for the late jurassic cretaceous and most of the paleogene the phosphorus cycle appears to have been accelerated in times of climate warming which was most likely due to the spreading of zones of humid climate and more intense continental weathering in the neogene the phosphorus cycle appears to have responded to changes in glacially induced weathering this suggests that uniform interpretations with respect to the emplacement of major phosphorite deposits should be treated with caution integrated analyses of the sedimentary and biogeochemical context of phosphorite occurrences may help to identify paleoenvironmental conditions as well as to improve our understanding of periods of enhanced phosphate accumulation periods which were usually characterized by steep gradients in the development of climate and environment with regard to the complexity of feedback mechanisms between the phosphorus cycle and the biosphere the present day input rates of phosphate into the world s oceans should be of great concern they are more than doubled by anthropogenic means and affect ecological systems on a rapidly increasing scale

late paleozoic middle latitude gondwana environment stable isotope records from western australia abstract one hundred and twelve permian fossil brachiopod samples from two western australian basins carnarvon and canning basins have been analyzed for oxygen and carbon isotopes to study the middle paleolatitude environment in the permian all samples were thin sectioned and examined using petrography and cathodoluminescence microscopy for evaluating shell preservation a total of 249 isotopic analyses from the best preserved portion non luminescent nl of shells were found useful for inferring paleoenvironments for the carnarvon basin average 13 c values of nl shells were between 4 2 and 4 5 for the callytharra formation n 123 late sakmarian early artinskian jimba jimba calcarenite n 7 early artinskian coyrie madeline formations n 71 both late artinskian early kungurian and wandagee formation n 18 late kungurian average 13 c values of nl shells were 5 0 0 4 n 9 for the quinnanie shale cundlego formations both kungurian for the canning basin mean 13 c values of nl shells were 5 1 1 1 n 11 5 3 0 2 n 4 and 4 8 0 5 n 6 for the noonkanbah formation artinskian kungurian lightjack formation roadian capitanian and hardman formation wuchiapingian respectively within the uncertainty of the stratigraphical correlation the carbon isotope values spanning late sakmarian to kungurian in middle latitude western australia are comparable to those of coeval low latitude urals average 18 o values of nl shells were about 0 0 1 to 0 1 for the callytharra formation jimba jimba calcarenite coyrie madeline formations quinnanie shale cundlego formations noonkanbah formation and hardman formation and were 0 5 0 7 and 0 3 0 7 for the wandagee formation and lightjack formation respectively these oxygen isotope values are overall higher than the coeval values reported for low latitude regions and for eastern australia the positive oxygen isotope values are here interpreted to indicate a cool temperature and or a possibly moderately high salinity condition for the two studied basins in western australia during the permian

sedimentological record of the late paleozoic glaciation in queensland australia although much is known of the timing geographical extent and character of the late paleozoic gondwanan glaciation its rec ord in eastern australia is poorly resolved some previous investigations have asserted that large parts of australia were covered by a cold based continental ice sheet during the pennsylvanian late carboniferous new data from queensland in northeast australia reported herein however suggest that the glaciation there was restricted to discrete short lived periods in the namurian 315 ma westphalian 311 ma and sakmarian 289 293 ma thick successions in three widely separated areas indicate that the glaciation was confined in each case to local valley or mountain glaciers and that the mainly proglacial sediments were enclosed in every case by substantial intervals of fluvial lacustrine and shallow marine strata deposited under nonglacial conditions accordingly we submit that the cessation of glacial sediment deposition elsewhere in gondwana during the pennsylvanian to earliest permian was due to the decay of glaciers rather than to a transition to a cold based ice sheet or sheets as has been previously suggested the interpretations presented herein make a significant contribution toward constraining the size and extent of glaciation in gondwana which has major implications for late paleozoic world climate and sea level fluctuations

early permian palaeoenvironment in damodar valley coalfields india an overview abstract in the damodar valley basin coalfields containing coal bearing barakar formation are raniganj jharia bokaro ramgarh and karanpura the barakar formation is composed of conglomerate sandstone siltstone shale fireclay and coal the lower part of barakar formation represents a braided channel deposit and also in few places glacio fluvial deposit which changes to meandering channel system with the formation of some ox bow lake and cut off channel in the middle part in a few places deltaic brackish water condition possibly existed along with this meandering channel system in the upper part of barakar formation marine signatures are more prominant marine signatures influences have been reported from barakar formation of ramgarh south karanpura and west bokaro coalfields on the basis of trace fossil assemblage sedimentation character and trace element content although definite marine signatures have not been observed from jharia and raniganj coalfields high concentration of boron vanadium and chromium and presence of skolithos and thalassinoides burrows possibly suggest a brackish water condition the upper part clearly suggest that the sediments were deposited in a geographic setting very close to the sea or at the edge of the sea possibly in a peritidal setting where storm activity played a vital role during sedimentation which in turn suggests the presence of a broad shallow sea epeiric epicontinental sea that develop during times of high sea level the sea water possibly entered from the northeastern side as vast seaways or as embayment through the damodar valley which acted as a channel

a chronology of paleozoic sea level changes sea levels have been determined for most of the paleozoic era 542 to 251 million years ago but an integrated history of sea levels has remained unrealized we reconstructed a history of sea level fluctuations for the entire paleozoic by using stratigraphic sections from pericratonic and cratonic basins evaluation of the timing and amplitude of individual sea level events reveals that the magnitude of change is the most problematic to estimate accurately the long term sea level shows a gradual rise through the cambrian reaching a zenith in the late ordovician then a short lived but prominent withdrawal in response to hirnantian glaciation subsequent but decreasingly substantial eustatic highs occurred in the mid silurian near the middle late devonian boundary and in the latest carboniferous eustatic lows are recorded in the early devonian near the mississippian pennsylvanian boundary and in the late permian one hundred and seventy two eustatic events are documented for the paleozoic varying in magnitude from a few tens of meters to 125 meters

interpreting carbon isotope excursions carbonates and organic matter abstract variations in the carbon isotopic compositions of marine carbonate and organic carbon provide a record of changes in the fraction of organic carbon buried through time and may provide clues to changes in rates of weathering and sources of organic carbon paired carbonate and organic carbon isotope determinations provide a possibility of interpreting not only changes in the global carbon cycle through time but changes in atmospheric pco2 as well interpretations of these types of data are typically rather qualitative a quantitative basis is required to develop a better understanding of changes in the carbon cycle for this purpose we employ a simple model of the global carbon cycle which is subjected to a number of different perturbations each lasting 500 ky i e much longer than the residence times of carbon and phosphorus in the ocean atmosphere system in addition to standard considerations of carbon mass and isotopic fluxes to the ocean atmosphere system from weathering and volcanism and fluxes of organic carbon and carbonate carbon to sediments the model incorporates sensitivity of the photosynthetic carbon isotope effect to changes in pco2 the inclusion of this parameter leads to unexpected carbon isotope responses to forcing that causes increased rates of organic carbon burial a series of simple to more complex simulations illustrates the significant effects of varying differences between the carbon isotopic composition of sedimented carbonate and organic carbon b with constant b a 50 increase in organic carbon burial produces a parallel increase in carbonate and organic carbon isotopic compositions however the same simulation with b responsive to pco2 changes produces an initial parallel 13 c increase but this is followed by an even greater 13 c enrichment in organic carbon because pco2 falls in response to increased organic carbon burial the counterintuitive overall result of the enhanced organic carbon burial event is that the carbonate carbon isotopic composition actually decreases because of the more substantial increase in 13 c org in addition we illustrate the effects on carbon isotopic compositions of the oceanic inorganic carbon reservoir and buried organic matter of a 50 increase in volcanic co2 outgassing a 50 increase in weathering rate with coupled phosphate and riverine carbon flux responses a 50 decrease in shale associated organic carbon weathering a 50 decrease in silicate weathering rate and the possible effects of the rise in abundance of c4 plants in the late miocene to recent we compare the model simulated carbon isotopic responses for some of these experiments to paired carbonate and organic carbon records to illustrate how these records might be interpreted in light of the model response

direct dating of weathering phenomena by 40ar39ar and k ar analysis of supergene k mn oxides abstract potassium bearing manganese oxides cryptomelane k1 2 mn3 mn4 8 o16 xh2oand hollandite k ba 1 2 mn3 mn4 8 o16 xh2o are often authigenically precipitated in weathering profiles the presence of structural potassium in manganese oxides makes these minerals datable by the k ar and 40 ar 39 ar methods dating of these phases allows us to time the progression of oxidation fronts during weathering and pedogenic processes detailed age resolution of the weathering history allows us to use deep weathering profiles as land based stratigraphic records of past climatic and geomorphic events complementing evidence from the marine sedimentary and paleontological record potential problems in manganese oxide dating such as ar and or k losses excess argon 39ar loss by recoil during neutron irradiation contamination by primary minerals resistant to weathering the presence of multiple generations of manganese oxides and proportionately low radiogenic ar yield due to adsorbed atmospheric gases are addressed the k ar and 40 ar 39 ar analytical results indicate that ar and or k losses excess 40ar and 39ar recoil seem not to pose problems in manganese oxide dating this investigation suggests that fine scale laser probe 40 ar 39 ar technique is most appropriate for dating of weathering phenomena because this technique permits us to identify contaminating phases and the presence of multiple generations of weathering minerals in the inherently complex mineral assemblage characteristic of weathering profiles k ar and 40 ar 39 ar dating of supergene k bearing manganese oxides formed during lateritization of archean and proterozoic bedrocks in the caraj s region amazonia brazil indicates that weathering started before 72 6 ma petrographic electron microscope and electron microprobe investigation reveal multiple generations of manganese oxide precipitation k ar and 40 ar 39 ar laser probe step heating results independently confirm the presence of these various generations of manganese oxides age clusters at 65 69 51 56 40 43 33 35 20 24 12 17 ma and zero age 0 2 0 2 ma suggest episodic precipitation of k mn oxides resulting from changing weathering conditions in the amazon throughout the cenozoic k ar and 40 ar 39 ar dating of supergene cryptomelane from weathering profiles in eastern minas gerais southeastern brazil suggests continuous weathering from 10 to 5 6 ma ago possibly reflecting local climatic conditions due to the proximity with the atlantic ocean

imprint of the late palaeozoic ice age on stratigraphic and carbon isotopic patterns in marine carbonates of the orogrande basin new mexico usa the permian records one of the most extreme climate transitions of the phanerozoic yet the climatic and environmental dynamics of this interval and their effects on neritic carbonate systems remain poorly constrained new stratigraphic and carbon isotope records from uppermost pennsylvanian to lower permian strata of the orogrande basin in south central new mexico usa provide fresh insights into the response of palaeotropical carbonate systems to the growth and demise of ice sheets on gondwana the earliest permian acme of glaciation is recorded in the orogrande basin as a series of subaerial exposure surfaces marked by highly variable 13c values that tend toward values as low as 6 these stratigraphic and isotopic patterns are interpreted to reflect the retreat of the sea from the basin during glacial expansion younger lower sakmarian to kungurian strata deposited during the long decline of the late paleozoic ice age are characterized overall by higher and more uniform 13c values 2 to 5 and show no evidence of long term subaerial exposure however these strata record two short lived excursions toward more negative 13c values these excursions occur through intervals that record shifts toward shallower and more restricted conditions in the orogrande basin the timing of these shifts corresponds to two periods of glacial expansion across eastern australia during late sakmarian to early artinskian and kungurian time these relationships suggest that pulses of glacial expansion in eastern gondwana were of sufficient magnitude to have caused relative sea level fall and possibly environmental change in the orogrande basin the results from this study suggest that marine chemistry depositional environments and sea level in the orogrande basin were profoundly influenced by epochs of gondwanan glaciation these inferences help improve the understanding of how palaeotropical carbonate systems responded to the effects of cryospheric changes during the acme and waning stages of the late palaeozoic ice age

evidence for an aeolian origin of the holocene lateritic surface cover of gabon central africa abstract field granulometric and geochemical data are reported for a set of twenty one samples collected at six sites spread over gabon in the extensive lateritic clayey to sandy layer cover horizon which constitutes the upper part of the profiles of surficial formations granulometric analyses show that this material of homogeneous aspect is a mixture of two fractions a clay fraction and a medium to coarse grained sandy fraction relative proportions of these two constituents show strong variations from one site to another but are almost constant from the bottom to the top of a given profile the coarse grained fraction includes lithic elements of local provenance irrespective of their underlying basement the samples display many common geochemical features including a lack of ca na and mg their major element compositions may be accounted by the combination of a discrete number of mineralogical phases namely quartz kaolinite gibbsite fe oxides hydroxides and subordinate k minerals micas the normative contents of aluminous and ferrous phases regularly increase with the weight percent of clays conversely the quartz regularly decreases this inverse relationship is consistent with mixing between an al and fe bearing clay fraction and a coarse grained fraction dominated by quartz correlations between most immobile trace elements and the weight percent of clays indicate a control of those elements by al and fe bearing phases the main exception is for zr and hf as those elements are probably associated with zircons in the coarse fraction because of the control of the trace element distribution by secondary phases the geochemical signatures of all samples are clearly distinct from those of the upper continental crust and any basement rocks thus the trace element characteristics of the cover horizon carry no sign of any source material being the sole consequence of mineralogical sorting prior to deposit from field granulometric and geochemical data an aeolian origin appears as the most probable for the cover horizon geochronological constraints including archaeological data and 14 c dating indicate that this aeolian event took place during the holocene and probably occurred in less than 3000 y additional works will be necessary to assess the global context which made possible this very fast and extended event over large areas of central africa

facies and allostratigraphy of high latitude glacially influenced marine strata of the early permian southern sydney basin australia the sydney basin of new south wales australia is a foreland basin containing a thick up to 10 km permo triassic succession the southern margin of the basin exposes strata deposited during late palaeozoic glaciation of south eastern gondwana the early permian wasp head pebbley beach snapper point formations and wandrawandian siltstone were deposited between 277 and 258 ma on a polar glacially influenced continental margin adjacent to ice sheets located over east antarctica and eastern australia sedimentary facies together with related ichnofacies and fauna can be grouped into six facies associations that record marine sub environments ranging from high energy storm dominated inner shelf to turbidite dominated upper slope settings cold marine conditions with near freezing bottom water temperatures are recorded by glendonites ice rafted debris most likely deposited by icebergs occurs in almost all facies associations an allostratigraphic approach emphasizing the recognition of bounding discontinuities i e erosion surfaces and marine flooding surfaces is used to subdivide the early permian stratigraphy into facies successions three types of succession can be identified and record changes in the relative influence of allocyclic controls such as basin tectonics sediment supply and glacio eustatic sea level variation together sedimentological and allostratigraphic data allow reconstruction of the depositional history of the south western margin of the sydney basin initial marine sedimentation characterized by sediment gravity flows and storm deposited sandstones of the lower wasp head formation occurred adjacent to a faulted basin margin overlying successions within the upper wasp head pebbley beach and snapper point formations record aggradation in inner to outer shelf settings along a storm and glacially influenced continental margin tectonic subsidence and basin flooding is recorded by deeper water turbidites of the wandrawandian siltstone

late paleozoic faunal climatic and geographic changes in the baoshan block as a gondwana derived continental fragment in southwest china abstract the carboniferous and permian of the baoshan block consist of three major depositional sequences a lower carboniferous carbonate sequence a lower permian siliciclastic sequence and a middle permian carbonate sequence these three sequences were interrupted by two major regressive events first the namurian uplift ranging in age from serpukovian to gzhelian and second the post sakmarian regression occurring probably at artinskian time in the baoshan block although the precise time interval of the latter event is still unclear the baoshan block is characterized by warm water highly diverse and abundant faunas during the early carboniferous by cold water and low diversity faunas during the early permian and by possibly warm water but low diversity faunas during the middle permian the sweetognathus bucaramangus conodont fauna constrains the upper boundary of the diamictite bearing siliciclastic deposits dingjiazhai formation to the sakmarian to early artinskian as well as the eruption of the rifting basalts woniusi formation to at least the post early artinskian paleozoogeographically affiliation of the faunas in the baoshan block changed from eurasian in the early carboniferous to peri gondwanan in the early permian and to marginal cathaysian cimmerian in the middle permian cimmerian blocks have more or less comparable geohistory to one another in the carboniferous and permian during the middle permian the eastern cimmerian blocks such as sibumasu s s baoshan and tengchong are not far from the palaeoequator but apparently more distant than the western cimmerian blocks based on the presence or absence of some index taxa such as the fusulinaceans eopolydiexodina and neoschwagerina and the corals thomasiphyllum and wentzellophyllum persicum

carboniferous permian palynostratigraphy of west australian marine rift basins resolving tectonic and eustatic controls during gondwanan glaciations abstract the longest interval of cold climate in earth s phanerozoic history spanned some 55 million years from the namurian late carboniferous to the kungurian early permian when glaciation affected much of high latitude gondwana uncertainty surrounds the timing of glaciation s and the frequency of interglacial episodes ice volumes and the location of ice centres this is because the glacial record is preserved predominantly within marine strata deposited in intracontinental rift basins marginal to onshore ice centres on uplifted basement highs the direct stratigraphic record of glaciation is meagre on adjoining basement highs and extremely difficult to date many basins contain broadly similar threefold lithostratigraphic successions of lowermost glaciomarine diamictite facies middle shales and uppermost carbonate and sandstone rich commonly coal bearing deltaic strata in the absence of absolute age control and infrequent presence of macrofossils such deglaciation sequences are widely assumed to be correlative from basin to basin recording gondwanan deglaciation s and a world wide glacioeustatic sea level rise a newly compiled biostratigraphic database for west australia using first appearance datums of spore pollen types allows correlation of late palaeozoic siliciclastic successions between seven basins bonaparte canning carnarvon collie gunbarrel northern and southern perth basins these extend some 3800 km along australia s western continental margin adjacent to the west australian shield all but the gunbarrel basin contain tripartite glacially influenced successions diamictite shale sandstone biostratigraphic data reveal sharp differences in ages and stratigraphic distributions and marked variations in the thickness of coeval units diamictite shale sandstone successions accumulated diachronously from basin to basin recording a dominant tectonic control on subsidence and relative sea level middle shale units are not exact correlatives between basins and thus are unlikely to simply represent widespread climatically controlled glacioeustatic events instead they are argued to record high relative sea levels during times of maximum synrift subsidence this tectonostratigraphic model can be applied to other intracontinental rift basin successions across gondwana

major element geochemistry and geomorphic relationships in brazilian cerrado soils abstract a thorough understanding of major and trace element geochemistry is important in assessing the impacts of rapid agriculturalization and increased human occupation of the cerrado region of central brazil a region with some of the oldest soils on earth the objectives of this paper are to summarize the major element composition of cerrado soils in the context of their morphology and geomorphology to describe impacts of biogeochemical cycling on the chemical properties of cerrado soils and to use elemental data to provide insights on the possible origin of soil parent materials on the south american erosion surface and on the serra geral basalts we sampled three major subregions selected to be representative of the main areas of the cerrado namely i eastern goias ii northwestern minas gerais and iii the tri ngulo mineiro area of western minas gerais five soils were sampled in each subregion each represented by three pedons sampled at 0 0 2 and 0 8 1 0 m depths geomorphologically the soils were on the south american velhas i and velhas ii erosion surfaces all sites were carefully selected to minimize potential anthropogenic contamination general chemical characterization was by standard procedures and total major and trace elemental contents were quantified using wavelength dispersive x ray fluorescence spectroscopy the soils ranged from loamy sands to clays with si 142 947 g kg 1 sio 2 al 14 439 g kg 1 al 2 o 3 fe 10 331 g kg 1 fe 2 o 3 and ti 3 101 g kg 1 tio 2 contents closely following the clay contents organic c averaged 17 g kg 1 for the surface and 7 g kg 1 for the subsurface horizons the na ca mg and k contents were very low tended to be higher in surface than in subsurface horizons because of recycling by vegetation and addition due to atmospheric deposition and were higher in soils containing hard plinthite nodules the th zr ratios suggest that the parent materials of the clayey soils on the south american erosion surface have a common origin in sediments from rocks in the central plateau of brazil that were transported eastwards to cover the underlying sandstone trace element signatures indicate that basalt derived soils occurring at different elevations in the tri ngulo mineiro area formed from distinctly different magmas that may have been deposited in different basalt flow events

marine productivity changes during the end permian crisis and early triassic recovery abstract the latest permian mass extinction lpme coincided with major changes in the composition of marine plankton communities yet little is known about concurrent changes in primary productivity earlier studies have inferred both decreased and increased productivity in marine ecosystems immediately following the end permian crisis here we assess secular and regional patterns of productivity variation during the crisis through an analysis of the burial fluxes of three elemental proxies total organic carbon toc phosphorus p and biogenic barium babio primary productivity rates appear to have increased from the pre crisis late permian through the early triassic in many parts of the world although the south china craton is unusual in exhibiting a pronounced decline at that time most of the 14 permian triassic study sections show concurrent increases in sediment bulk accumulation rates suggesting two possible influences linked to subaerial weathering rate changes 1 intensified chemical weathering resulting in an increased riverine flux of nutrients that stimulated marine productivity and 2 intensified physical weathering leading to higher fluxes of particulate detrital sediment to continental shelves thus enhancing the preservation of organic matter in marine sediments an additional factor especially in the south china region may have been the intensified recycling of bacterioplankton derived organic matter in the ocean surface layer reducing the export flux rather than primary productivity per se the ecosystem stresses imposed by elevated fluxes of nutrients and particulate sediment as well as by locally reduced export fluxes of organic matter may have been important factors in the 2 to 5 million year long delay in the recovery of early triassic marine ecosystems

a paleoclimatic review of southern south america during the late paleozoic a record from icehouse to extreme greenhouse conditions abstract this paper provides a review of the late mississippian to permian paleoclimatic history for southern south america based on lithologic indicators biostratigraphic information and chronostratigraphic data the region is divided into three major types of basins 1 eastern intraplate basins e g parana basin 2 western retroarc basins e g paganzo basin and 3 western arc related basins e g rio blanco basin four major types of paleoclimatic stages are recognized in these basins 1 glacial late visean early bashkirian 2 terminal glacial bashkirian earliest cisuralian 3 postglacial cisuralian early guadalupian and 4 semiarid arid late guadalupian lopingian the glacial stage began in the late visean and continued until the latest serpukhovian or early bashkirian in almost all of the basins in southern south america during the bashkirian earliest cisuralian terminal glacial stage glacial deposits disappeared almost completely in the western retroarc basins e g paganzo basin but glaciation persisted in the eastern basins e g parana and sauce grande basins a gradual climatic amelioration postglacial stage began to occur during the earliest permian when glacial deposits completely disappeared across all of south america during this interval glacial diamictites were replaced by thick coal beds in the parana basin while north south climatic belts began to be delineated in the western basins which were likely controlled by the distribution of mountain belts along the panthalassan margin of south america towards the late permian climatic belts became less evident and semiarid or arid conditions dominated in the southern south america basins eolian dunes playa lake deposits and mixed eolian fluvial sequences occur in the parana basin and in the western retroarc basins volcanism and volcaniclastic sedimentation dominated along the western margin of south america at that time the stratigraphic record obtained in southern south america supports a long duration transition from icehouse to extreme greenhouse conditions

trace element geochemistry in brazilian cerrado soils the cerrado region on the central plateau of brazil contains some of the oldest soils on earth with some soils weathering in place since the late cretaceous the region is currently undergoing rapid agriculturalization and industrialization the objectives of this paper are 1 to inventory the native trace element contents of pristine cerrado soils and 2 to better understand which trace elements accumulate and which are depleted in well drained soils over extremely long periods of pedogenic weathering we sampled the 0 20 and 80 100 cm layers of 45 pedons located in three widely separated areas on three different geomorphic surfaces and determined total elemental contents by x ray fluorescence analysis in comparing the contents of cerrado soils to soils worldwide the contents of sc v cr ga zr nb ce and th are 1 2 times the world average y la and u are about the same and mn co ni cu zn rb sr ba and pb are 0 4 times the world average trace elements that accumulated during weathering are either pentavalent nb5 tetravalent ti4 zr4 u4 th4 or trivalent sc3 v3 cr3 ga3 y3 la3 ce3 at the acid ph of these soils while trace elements that were depleted are either divalent or monovalent rb mn2 co2 ni2 cu2 zn2 sr2 ba2 and pb2 at acid ph thus trace element geochemistry over long periods of pedogenic weathering at acid ph mirrors major element geochemistry in that mono and divalent cations are leached and depleted while tri tetra and pentavalent elements accumulate

microbial community from the lower permian artinskian kungurian paleoclimatic transition mid panthalassan akiyoshi atoll japan abstract large oncoids up to 14 cm and microbialites are abundant in the artinskian lower permian section of mid panthalassan akiyoshi atoll carbonates the oncoids and microbialites consist mainly of a tubular microproblematicum girvanellid cyanobacterial filaments microbial micrite crusts and pore filling sparry calcite cements they are surrounded by intraclastic bioclastic grainstone rudstone indicative of moderate to slightly high energy subtidal conditions the microbial community was the primary boundstone forming organisms on the akiyoshi atoll during this time it represents a transitional stage in a mid panthalassan reef succession between a cooler water autotrophic palaeoaplysina microencruster community in the gzhelian asselian and a warmer water heterotrophic calcareous sponge microencruster community in the middle permian the flourishing mid panthalassan microbial community during the late early permian is related to enhanced alkalinity increasing nutrient levels elevated sea surface temperatures and the absence of major reef building metazoans which resulted from gondwanan deglaciation climatic changes and a pulse of active volcanism

a review of permian stratigraphy palaeobiogeography and palaeogeography of the qinghai tibet plateau the permian marine lithostratigraphy biostratigraphy and faunal compositions among all the major tectonic blocks in the qinghai tibet plateau are synthesised based on published literature authors unpublished data and field observations palaeobiogeographically the permian marine faunas in the qinghai tibet plateau can be assigned to four biotic provinces cathaysian indoralian cimmerian and himalayan provinces as well as a broad south transitional zone for parts of the permian the qamdo block clearly belongs to the cathaysian province as it is characterised by a lack of glacial deposits and a dominance of warm water faunas during the whole permian the qiangtang block lhasa block and the himalaya tethys zone in southern tibet can be grouped into the south transitional zone during the cisuralian which is characterised by the combination of the bivalve eurydesma the brachiopods cimmeriella bandoproductus and the fusuline monodiexodina the south transitional zone gave birth to the cimmerian province as shown in the qiangtang and lhasa blocks from roadian to capitanian during which its faunas were characterised by an admixture of cold and warm water elements supplemented by a limited number of endemic taxa such as the fusuline eopolydiexodina the non fusuline foraminifer shanita hemigordiopsis assemblage and the coral thomasiphyllum the formation and development of the south transitional zone and the cimmerian province is interpreted to be closely linked to and driven by the northward drift of the cimmerian continent superimposed with a gradual global warming in the wake of gondwanan deglaciation the consequently combined effects of these events forced the climate of the drifting peri gondwana blocks to ameliorate and its marine faunas to transform from an essentially cold water gondwanan type in the early cisuralian through a transitional stage to a predominantly warm water cathaysian type by the lopingian the himayala tethys zone in southern tibet is assigned to the himalayan province from late guadalupian to lopingian and identified by persistent occurrences and dominance of cold water brachiopods and corals both the permian sedimentary sequences and faunal successions are strongly different between the qamdo block and the qiangtang block this is taken to suggest that the longmu co shuanghu lancangjiang suture between the two blocks most likely represents the main branch of the palaeotethys suture in tibet a comparison and correlation of permian sequences and faunas between tibetan blocks and adjacent blocks in western yunnan indicates that the qiangtang block should be aligned with the baoshan block whereas the lhasa block more closely related to the tengchong block further comparison and correlations of permian stratigraphy and faunas of all major peri gondwana blocks suggest that they probably constituted three different continental slices rather than one as perceived in some previous literature the first slice is composed of central pamir the qiangtang block and the baoshan block the second slice consists of south pamir karakorum south afghanistan central iran and turkey these two continental slices are both characterised by a continuously active rifting event from artinskian to guadalupian by contrast the third slice is interpreted to consist of the lhasa block the tengchong block and the sibumasu block none of which has late cisuralian rift related basalts the baoshan block and the lhasa block are thought to have initially early cisuralian intersected probably at a triple junction point close to western australia and were then rifted off from gondwana at different times during the permian

impact of cretaceous sea level rise and anoxic events on the mesozoic carbonate platform of yugoslavia the adriatic dinaric carbonate platform of yugoslavia was influenced by rapid sea level rise and an oceanic anoxic event during the cenomanian turonian open marine biota such as planktonic foraminifera radiolarians and locally even ammonites associated with and bracketed by successions of typical shallow water carbonates indicate partial drowning of substantial areas of the platform during this time suggestive furthermore that the rate of increase of water depth was locally great enough to outpace carbonate production the presence of carbon rich and fish bearing platy limestones commonly cherty as an associated coeval facies indicates the development of anoxic or euxinic environments and the stromatolitic laminations in such rocks are attributed to the action of bacterial mats it is suggested that an extensive column of deoxygenated water developed in the neighboring marche umbrian adriatic deep water basin and was carried on to the carbonate platform during the cenomanian turonian transgression

benthic phosphorus regeneration net primary production and ocean anoxia a model of the coupled marine biogeochemical cycles of carbon and phosphorus we examine the relationships between ocean ventilation primary production water column anoxia and benthic regeneration of phosphorus using a mass balance model of the coupled marine biogeochemical cycles of carbon c and phosphorus p the elemental cycles are coupled via the redfield c p ratio of marine phytoplankton and the c p ratio of organic matter preserved in marine sediments the model assumes that on geologic timescales net primary production in the oceans is limited by the upwelling of dissolved phosphorus to the photic zone the model incorporates the dependence on bottom water oxygenation of the regeneration of nutrient phosphorus from particulate matter deposited at the water sediment interface evidence from marine and lacustrine settings modern and ancient demonstrates that sedimentary burial of phosphorus associated with organic matter and ferric oxyhydroxides decreases when bottom water anoxia dysoxia expands steady state simulations show that a reduction in the rate of thermohaline circulation or a decrease of the oxygen content of downwelling water masses intensifies water column anoxia dysoxia and at the same time increases surface water productivity the first effect reflects the declining supply of oxygen to the deeper parts of the ocean the second effect is caused by the enhanced benthic regeneration of phosphorus from organic matter and ferric oxyhydroxides sedimentary burial of organic carbon and authigenic calcium phosphate mineral francolite on the other hand is promoted by reduced ocean ventilation according to the model global scale anoxia dysoxia leads to a more efficient recycling of reactive phosphorus within the ocean system consequently higher rates of primary production and organic carbon burial can be achieved even when the continental supply of reactive phosphorus to the oceans remains unchanged

spatial variation in sediment fluxes redox conditions and productivity in the permian triassic panthalassic ocean abstract two permian triassic boundary sections in central japan provide a rare window into environmental conditions within the panthalassic ocean which encompassed more than half the earth s surface at 252 ma integration of petrographic geochemical and time series data provides new insights regarding the fluxes of major and trace components to the sediment as well as environmental conditions in both the deep and intermediate water masses at each study site the ubara section was located in a high productivity peri equatorial location whereas the gujo hachiman section was located in a moderate productivity location at some distance from the paleoequator an upward transition from gray organic poor cherts to black siliceous mudstones at both sites occurred in conjunction with increased primary productivity intensified euxinia within the oxygen minimum zone omz and decimation of the radiolarian zooplankton community euxinia in the omz of the equatorial panthalassic ocean developed episodically for a 200 250 kyr interval during the late permian followed by an abrupt intensification and lateral expansion of the omz around the permian triassic boundary throughout the study interval bottom waters at both sites remained mostly suboxic a finding that counters hypotheses of development of a superanoxic permo triassic deep ocean as a consequence of stagnation of oceanic overturning circulation

climatic implications from the sequential changes in diversity and biogeographic affinities for brachiopods and bivalves in the permian of eastern australia and new zealand abstract brachiopoda and bivalvia of successive macro invertebrate zones of eastern australia and new zealand are analysed to demonstrate a sequence of climatic change throughout the permian period reflecting glacial episodes separated by warmer intervals three such glacial intervals are indicated for the early cisuralian permian a long asselian episode a brief artinskian episode and a substantial kungurian interval followed by a cold roadian interval middle permian guadalupian and a very late permian lopingian episode markedly warmer intervals developed in the possibly late asselian baigendzinian and much of the lopingian in addition relatively long cool times allowed the flourishing and comparative diversification of eastern australian faunas at several stages

permian gondwanaland paleoenvironment inferred from carbon and oxygen isotope records of brachiopod fossils from sydney basin southeast australia abstract the 13 c and 18 o records of permian fossil brachiopods with biostratigraphical age control from southeastern australia have been constructed to investigate the high latitude paleoenvironment of gondwanaland all samples were thin sectioned and examined using petrographic and cathodoluminescence microscopy for evaluating shell preservation elemental compositions of select brachiopod shells were measured using electron probe microanalysis to further evaluate shell preservation within these intervals the average 13 c values of the best preserved non luminescent nl portion of the brachiopod shells are all greater than 5 1 with the highest value 7 0 at lower wandrawandian siltstone late kungurian these carbon isotope values are similar to those of contemporaneous tropical eastern pangea russian platform but heavier than those of western pangea north america the oxygen isotope difference between brachiopods of high southern latitudes and low latitudes fluctuated during early to middle permian the mean 18 o values of the high latitude nl brachiopod shells were more positive than those of the low latitudes in early sakmarian 0 3 early late artinskian 1 1 late kungurian 1 0 roadian 0 2 and wordian 0 7 comparable to those of tropical western pangea in early artinskian 2 1 and early kungurian 2 5 and more negative than those of tropical western pangea in late late artinskian 3 9 assuming the oxygen isotope value for permian seawater in southeast australia was 1 the calculated oxygen isotope temperatures were mostly between 12 c and 16 c reflecting southeast australia s cool high latitude temperature conditions higher apparent oxygen isotope temperatures for the upper pebbly beach formation 29 c late late artinskian berriedale limestone 21 c early artinskian and snapper point formation 22 c early kungurian may be attributed to a combination of warmer climate and lower seawater 18 o in this region

goethite calcite and organic matter from permian and triassic soils carbon isotopes and co2 concentrations abstract pedogenic goethites in each of two early permian paleosols appear to record mixing of two isotopically distinct co2 components atmospheric co2 and co2 from in situ oxidation of organic matter the 13c values measured for the fe co3 oh component in solid solution in these permian goethites are 13 5 for the lower leonardian 283 ma bp paleosol mcgoeth and 13 9 for the upper leonardian 270 ma bp paleosol sap these goethites contain the most 13c rich fe co3 oh measured to date for pedogenic goethites crystallized in soils exhibiting mixing of the two aforementioned co2 components 13c measured for 43 organic matter samples in the lower leonardian waggoner ranch fm has an average value of 20 3 1 1 1s the average value yields a calculated early permian atmospheric p co 2 value of about 1 pal but the scatter in the measured 13c values of organic matter permits a calculated maximum p co 2 of 11 pal pal present atmospheric level measured values of the mole fraction of fe co3 oh in mcgoeth and sap correspond to soil co2 concentrations in the early permian paleosol profiles of 54 000 and 50 000 ppmv respectively such high soil co2 concentrations are similar to modern soils in warm wet environments the average 13c values of pedogenic calcite from 9 paleosol profiles stratigraphically associated with mcgoeth waggoner ranch fm range from 6 5 to 4 4 with a mean 13c value for all profiles of 5 4 thus the value of 13c between the pedogenic calcite data set and mcgoeth is 8 1 0 9 which is in reasonable accord with the value of 7 7 expected if atmospheric p co 2 and organic matter 13c values were the same for both paleosol types furthermore the atmospheric p co 2 calculated for the early permian from the average measured carbon isotopic compositions of the paleosol calcite and organic matter is also analytically indistinguishable from 1 pal with a maximum calculated atmospheric p co 2 permitted by one standard deviation of the organic matter 13c value of 5 pal if however measured average 13c values of the plant organic matter are more positive than the original soil organic matter as a result of diagenetic loss of 13c depleted labile organic compounds calculated permian atmospheric p co 2 using these 13c enriched organic values would underestimate the actual atmospheric p co 2 using either goethite or calcite this is the first stratigraphically constrained intrabasinal study to compare ancient atmospheric co2 concentrations calculated from pedogenic goethite and calcite these results demonstrate that the two different proxies record the same information about atmospheric co2 the fe co3 oh component in pedogenic goethite from a triassic paleosol in utah is significantly enriched in 13c relative to fe co3 oh in goethites from soils in which there are mixtures of two isotopic co2 components field relationships and the 13c value 1 9 of the triassic goethite indicate that this ancient paleosol profile experienced mixing of three isotopically distinct co2 components at the time of goethite crystallization the three components were probably atmospheric co2 co2 from in situ oxidation of organic matter and co2 from in situ dissolution of preexisting calcite although mixing of three isotopically distinct co2 components as recorded by fe co3 oh in goethite has been described in modern soil this is the first example from a documented paleosol its preservation affirms the need for careful case by case assessment of ancient paleosols to establish that goethite in any particular soil is likely to be a valid proxy of atmospheric p co 2

shrimp u pb zircon dating and palynology of bentonitic layers from the permian irati formation parana basin brazil abstract this paper presents the first shrimp zircon age data from bentonitic ash fall layers intercalated with the irati sedimentary rocks as well as palynofossils retrieved from the petrobras six mine parana state southern brazil the permian irati formation is one the most important oil source horizons within the parana basin and consists mainly of siltstones gray claystones as well as organic rich claystones intercalated with limestones zircon morphology based on cathodoluminescence images includes two different populations a dominant population of euhedral prismatic elongate to acicular grains which are most likely related to an ash fall volcanism and a population of rounded to large prismatic grains that were interpreted as detrital grains shrimp analysis performed on the euhedral and prismatic grains revealed an age of ca 278 4 2 2 ma 7 points with 95 confidence interpreted as the crystallization age of the volcanic eruption based on this new dating the irati formation should be placed on the lower permian cisuralian artinskian in age modifying substantially the traditional ages previously attributed to this unit the palynofossils from this level include key species of the lueckisporites virkkiae zone such as l virkkiae l densicorpus l stenotaeniatus weylandites lucifer alisporites splendens typical species of this zone also occur in african and other south american argentina permian strata allowing stratigraphical correlations the origin of the ash falls is not clearly defined it may be related either to calc alkaline arc magmatism associated to the sanrafaelica orogeny 275 and 250 ma or to bimodal volcanic events associated to an early intracontinental rift developed within southwestern gondwana at ca 278 my the dating of this unit is significative to calibrate biostratigraphic schemes along the parana basin as well as equivalent zones in gondwana areas mainly in its occidental portion

search for evidence of impact at the permian triassic boundary in antarctica and australia life on earth was almost destroyed some 250 m y ago in the most profound of all known mass extinction events we investigated the possible role of impact by an extraterrestrial bolide through chemical and mineralogical characterization of boundary breccias search for shocked quartz and analysis for iridium in permian triassic boundary sections at graphite peak and mount crean antarctica and wybung head australia thin claystone breccias at the isotopically and paleobotanically defined boundary at all three locations are interpreted as redeposited soil rather than impact ejecta the breccias at all three locations also yielded shocked quartz but it is an order of magnitude less abundant 0 2 vol and smaller only as much as 176 micrometers m diameter than shocked quartz at some cretaceous tertiary boundary sites faint iridium anomalies were detected up to 134 pg g 1 these values are an order of magnitude less than iridium anomalies at some cretaceous tertiary boundary sites furthermore peak iridium values are as much as 1 m below the isotopically and paleobotanically defined boundary the idea that impact caused the extinctions thus remains to be demonstrated convincingly

evidence for enhanced phosphorus regeneration from marine sediments overlain by oxygen depleted waters phosphorus regeneration and burial fluxes determined from in situ benthic flux chamber and solid phase measurements at sites on the californian continental margin peruvian continental slope north carolina continental slope and from the santa monica basin california are reported comparison of these sites indicates that o2 depleted bottomwaters enhance p regeneration from sediments diminishing overall phosphorus burial efficiency based on these observations a positive feedback linking ocean anoxia enhanced benthic phosphorus regeneration and marine productivity is proposed on shorter timescales these results also suggest that o2 depletion in coastal regions caused by eutrophication may enhance p regeneration from sediments thereby providing additional p necessary for increased biological productivity

glendonites from an early jurassic methane seep climate or methane indicators abstract an early jurassic late pliensbachian section margaritatus to spinatum ammonite zone northeast of cremlingen germany revealed three horizons with abundant glendonites calcite pseudomorphs after ikaite caco3 6h2o as well as authigenic carbonates these pseudomorphs have previously been used as indicators for organic and phosphate rich paleoenvironments with near freezing bottom water temperatures stable isotope measurements clearly show that the ikaite glendonite was precipitated at a methane seep location with methanotrophic sulfate reduction as the triggering geochemical process for ikaite formation at the sulfate methane interface the termination of methane seepage probably led to the disintegration of the primary mineral ikaite and successive pseudomorph formation reconstructed paleo bottom water temperatures ca 10 c from belemnites and ostracods indicate temperatures well above the previously observed range of ikaite stability near freezing raising the question if methane seeps are distinct geochemical sites promoting ikaite formation at higher temperatures