biostratigraphic significance of stromatolites in upward shallowing sequences of the early proterozoic duck creek dolomite western australia abstract the branching columnar stromatolite pilbaria perplexa walter 1972 and the microdigitate asperia ashburtonia grey 1985 occur together in upward shallowing sedimentary sequences in the 2 ga duck creek dolomite the distribution of stromatolite taxa is controlled principally by sedimentary environment p perplexa grew in shallow lagoons with the larger p cf perplexa extending into the low intertidal zone a ashburtonia occupied a high intertidal or supratidal setting probably in laterally restricted pools throughout the world pilbariform and asperiform stromatolites occur in stratigraphic units of different ages within each group the taxa are not identical although morphologies are broadly similar the taxonomic variations may be due to evolutionary development rather than environmental factors

stable isotope and radiocarbon balances of two tibetan lakes sumxi co longmu co from 13 000 bp hydrologic and climatic changes in western tibet since 13 000 bp are inferred from mineralogical and isotopic analyses of lacustrine sediments from the sumxi longmu co basin the interpretation is based on isotope data from the modern system carbon isotope chemistry is complex because of the presence of old limestones on the watershed sediments contain detrital and authigenic calcites the proportions of which are quantitatively estimated by x ray diffractometry stable isotope contents of the authigenic calcite are reconstructed from mass balance equations the high 13c contents up to 6 are attributed to an enhancement of calcite precipitation from water surface during freezing periods the 18o content is related to residence time and evaporation the validity of 14c dates obtained from different types of material is discussed our record in good agreement with paleobiological data from the same material shows the sudden establishment of wet warm conditions at 10 000 bp which culminated at 7500 6000 bp after a brief reversal event at 7900 bp maximum aridity for the whole holocene is recorded at 4300 bp

drastic desalination of small lakes in east siberia russia in the early twentieth century inferred from sedimentological geochemical and palynological composition of small lakes reconstruction of temporal and spatial climate development on a seasonal basis during the last few centuries may help us better understand modern day interplay between natural and anthropogenic climate variability the objective of this paper is to reconstruct hydrology and landscape changes of east siberia during the termination of the little ice age and the subsequent recent warming we analysed sediment samples from the saltwater sulfatnoe lake bolshoye alginskoe and freshwater shuchie lake using high resolution x ray fluorescence spectroscopy at 1 mm scan resolution fourier transform infrared techniques and pollen analyses the depth age models of the cores were constructed by 210pb activity using the constant rate of supply model the lake sediment cover of these lakes began to form from ca 1870 three significant periods 1870 1895 1895 1925 and from 1925 to the present were defined in hydrology and chemical regime of these lakes for the past 140 years lake levels were extremely low and high saturated with salts during the final period of the little ice age lake levels began to slowly rise from 1870 to 1895 and vegetation was poor at that period intensive desalination of the lakes occurred in 1895 1925 and environment conditions were temperate and favourable for the majority of the taxa of the regional vegetation regional precipitation significantly increased and water saturation of the catchments was high from 1925 to the present the chemical precipitation of carbonate stopped completely in lake shichie and reduced considerably in lake sulfatnoe and b alginskoe strong increasing trend of weathering of the lake catchments began in 1970 and still continues

holocene palaeoenvironmental records from the high altitude wular lake western himalayas we present a comprehensive record of holocene 11 590 628 cal yr bp climate and hydrographic changes around the wular lake located in kashmir valley india based on the multi proxy investigation

glacial sediments and erosional pavements near the cambrian precambrian boundary in western henan province china exceptionally well preserved glaciated pavements and a variety of glacigenic sediments comprising the luoquan formation in henan province central china are believed to have formed close to the cambrian precambrian boundary they may therefore be younger than the better known sinian tillites representing the changan and nantuo ice ages they perhaps belong to a distinct glacial epoch that is recorded elsewhere in china and in other continents but for which there is less evidence than for earlier late proterozoic glacial periods lithofacies represented in the luoquan formation are massive diamictite signifying deposition as lodgement or melt out till bedded diamictite waterlain till or glaciomarine glaciolacustrine sediments with dropstones rhythmites with dropstones glaciolacustrine or fjord deposits possibly varves tabular conglomerates and sandstones outwash deltaic or sub aqueous mass flow deposits lens shaped breccia deposits sub aqueous mass flow deposits and gravel sand wedges frost contraction crack infillings the glaciated pavements reveal well preserved striations grooves often intersecting 9plastically moulded9 forms crescentic gouges and steps on a regional scale the linear features are of variable orientation but they indicate a dominant ice flow direction towards the southeast all this evidence points to upland glaciation with erosion followed by deposition in a terrestrial glacial and glaciolacustrine environment

calibration of marine sediment core loggers for quantitative acoustic impedance studies abstract accurate density and p wave velocity measurements on marine sediment cores are needed for quantitative acoustic impedance studies an increasing number of international marine laboratories routinely measure p wave velocity and bulk density the product of which gives the acoustic impedance on marine sediment cores using automated core loggers mscls despite the progressive standardisation of mscls in recent years no standard calibration technique has been decided that will enable datasets from different marine laboratories to be validated and compared with confidence this problem is particularly acute for bulk density measurements because systematic mscl errors are typically much greater than 10 one solution is to use a calibration tube comprising a stepped aluminium insert inside a water filled core liner that mimics marine sediment porosities and velocities and that can be used during normal core logging the calibration tube enables a reliable gamma ray reference intensity to be measured and an apparent compton mass attenuation coefficient to be derived that is suitable for most marine sediments and that simplifies data processing the calibration tube results show that the mscl belonging to southampton oceanography centre soc used as part of the standard analysis procedure of the british ocean sediment core repository boscor gives measurement accuracies of better than 0 07 g cm 3 for bulk density and 0 3 for p wave velocity

microbenthic distribution of proterozoic tidal flats environmental and taphonomic considerations silicified carbonates of the late mesoproterozoic to early neoproterozoic society cliffs formation baffin island contain distinctive microfabrics and microbenthic assemblages whose paleo environmental distribution within the formation parallels the distribution of these elements through proterozoic time in the society cliffs formation restricted carbonates including microdigitate stromatolites laminated tufa and tufted microbial mats consist predominantly of synsedimentary cements these facies and the cyanobacterial fossils they contain are common in paleoproterozoic successions but rare in neoproterozoic and younger rocks less restricted tidal flat facies in the formation are composed of laminated microbialites dominated by micritic carbonate lithified early yet demonstrably after compaction these strata contain cyanobacteria that are characteristic in neoproterozoic rocks within the formation the facies dependent distribution of microbial populations reflects both the style and timing of carbonate deposition because of the strong substrate specificity of benthic cyanobacteria a reasonable conclusion is that secular changes in microbenthic assemblages through proterozoic time reflect a decrease in the overall representation of rapidly lithified carbonate substrates in younger peritidal environments as well as concomitant changes in the taphonomic window of silicification through which early life is observed

sinian ice ages and glacial sedimentary facies areas in china abstract glacial rocks of the sinian period are widespread in china on the bases of stratigraphy and geochronology three sinian ice ages can be discerned in ascending order these are the gucheng nantuo and luoquan ice ages the gucheng and nantuo ice ages are assigned to the lower sinian 740 700 ma and the luoquan ice age is tentatively placed between about 640 ma and 580 ma this paper is largely concerned with the distribution of glacial sedimentary facies areas a glacial sedimentary facies area is an area over which the same or similar facies are developed terrestrial transitional and marine glacial sedimentary facies areas have been differentiated nine glacial sedimentary facies have been recognized in the sinian of china

holocene environmental changes in bangong co basin western tibet part 4 discussion and conclusions abstract a 12 4 m core taken in lake bangong provides a continuous holocene climatic record we summarize information on changes in stable isotope and radiocarbon balances in the lake hydrobiology and vegetal cover in the catchment deduced from detailed analytical results given in the three preceding papers the bangong record is then compared with the environmental history of the neighbouring lake sumxi also constructed from multidisciplinary analyses the two records show a major environmental change at 10 9 5 ka b p attributed to a rapid strengthening of the summer monsoonal circulation which led to wet warm conditions this event was followed by a long term trend toward aridity which culminated around 4 3 ka b p in western tibet maximum monsoon rainfall seems to have occurred from 9 5 to 8 7 ka b p and from 7 2 to 6 3 ka b p as two wet pulses separated by a reversal event centered on 8 0 7 7 ka b p our results broadly agree with the records from lake seling in central tibet and lake qinghai at the plateau s northeastern margin and with palaeoclimatic studies in western china which document conditions wetter and warmer than those of today during the early middle holocene the environmental fluctuations recorded in western tibet appear in phase with climatic changes recognized in tropical north africa suggesting that the 8 0 7 7 ka b p and the 4 0 3 0 ka b p dry events were caused by abrupt disequilibrium in the climatic system

c isotope composition of carbonates from indravati basin india implications for regional stratigraphic correlation abstract the indravati basin represents an unmetamorphosed and unfossiliferous sequence and shows a broad similarity in lithological association with other purana basins of central india the carbonates belonging to indravati basin have on average moderately positive 13 c values up to 4 5 numerous successions reported from other parts of world show similar 13 c values and contain evidence to suggest that the latest mesoproterozoic to early neoproterozoic period may represent an isotopically recognizable interval globally the elevated 13 c values of indravati basin are also correlatable with other purana basins in india including upper vindhyan supergroup

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

1 3 billion years of acritarch history an empirical morphospace approach abstract acritarchs are a group of organic walled vesicular microfossils interpreted as protists and are among the first eukaryotes preserved in the fossil record taxonomic inconsistencies amongst acritarch workers have made it difficult to address the evolutionary history of this group through more traditional methods i e biodiversity through species counts we have constructed an empirical morphospace to examine the first 1 3 billion years of acritarch evolution we show that protist morphologic evolution is broadly correlated with major environmental and biologic revolutions in earth history such as late neoproterozoic global glaciations the first appearance of the ediacaran metazoans and the cambrian explosion our results also show that protist morphologic expansion precedes their taxonomic diversification this pattern similar to that seen in phanerozoic animal clades suggests that early morphospace saturation and convergence are common occurrences in eukaryote macroevolution in addition our data do not support a monotonic increase in maximum diameter of acritarch vesicles through the proterozoic instead maximum vesicle diameter appears to fluctuate in the proterozoic before decreasing significantly in the early cambrian

stratigraphic variations in carbon and oxygen isotopes in the dolostone of the carswell formation proterozoic of northern saskatchewan petrographic and stable isotopic analyses of stromatolitic sediments deposited in nearshore environments provides us with some of the best information available on ancient environments diamond dri

synsedimentary cements as paleoproterozoic platform building blocks pethei group northwestern canada peritidal and subtidal carbonates of the pethei group are a complex arrangement of fibrous and micritic synsedimentary precipitates carbonate grains and detrital micrite synsedimentary precipitates present largely as stromatolitic laminae constitute the bulk of the pethei platform providing about 75 of the total carbonate they occur as stromatolitic precipitates precipitates closely associated with stromatolitic laminae which constitute about 60 of the rock and encrusting precipitates precipitates outside stromatolites and between grains i e cement which constitute about 15 of the rock the most abundant precipitates are fibrous in the form of stromatolitic microdigitate stalks tufa and masses of radial fans as well as encrusting pore filling fans isopachous rinds and laminar crusts micrite precipitates occur as stromatolitic clotted micrite and encrusting isopachous rinds the ratio of fibrous to micritic precipitates is 2 1 stromatolitic precipitates are arranged in three distinct microfabrics 1 ubiquitous spar micrite couplets of fibrous and clotted micrite laminae 2 deep water vertical fibrous masses that precipitated over micritic precipitate cores and 3 supratidal microdigitate crusts of branching fibrous stalks micritic cements are interpreted to be of biogenic origin having precipitated somehow in association with microorganisms fibrous precipitates are interpreted to be largely abiotic since stromatolitic and encrusting precipitates are petrographicaily similar they probably share similar origins there is little evidence of sediment trapping and binding as a mechanism for stromatolite formation the abundance of synsedimentary precipitates varies with platform geometry subtidal ramps subtidal rimmed shelves subtidal open shelves peritidal rimmed shelves while the basic building blocks of the pethei platform synsedimentary precipitates carbonate grains and detrital micrite are the same as those in phanerozoic platforms their distribution and relative proportions are different these differences reflect a proterozoic carbonate factory which extended across the entire platform and which produced carbonate largely by in situ precipitation

deposition and deformation of late archaean sediments and preservation of microfossils in the harris greenstone domain gawler craton south australia abstract late archaean sediments felsic mafic and ultramafic volcanics in the harris greenstone domain central gawler craton south australia are interpreted to have been deposited at 2520 ma in back arc settings and were metamorphosed at 2440 ma sedimentary evidence suggests that the metasediments in the domain might have been deposited in fluvial estuarine to deltaic shelf environments and deformed by intermediate amphibolite facies metamorphism accompanying the sleafordian orogeny at 2440 ma microfossils are preserved in metachert layers that had been boudinaged into lenses these microfossils including spinose acritarchs are organic walled as evidenced by laser raman microscopy fossil bearing off cuts were then treated by hf and similar microfossils degraded organic matter and acid resistant minerals such as zircon were exposed in situ on the etched surface their morphologically complex forms and detailed wall structures suggest that these microfossils are of primary biological origin the microfossils in foliated metachert lenses either from original deposition or from post depositional quartz veins are older than the 2440 ma age of the sleafordian orogeny which provides a minimum age for the host rocks in either case these spinose acritarchs are the oldest protists known to date

textural transition in an aragonite travertine formed under various flow conditions at pancuran pitu central java indonesia abstract a large travertine mound at pancuran pitu central java indonesia displays various types of lamination reflecting different hydrological conditions to understand the geomicrobiological processes of the laminated travertines we investigated the mound s hydrology water chemistry texture microbial composition and volume percentage of carbonate mineral vpc we identified four types of travertines dense travertine 80 vpc flow rate 200 cm s lithified microbial travertine 60 vpc flow rate 70 cm s fragile microbial travertine 30 vpc flow rate 10 cm s and poorly lithified microbial mat

proterozoic ministromatolites with radial fibrous fabric small digitate stromatolites with diameters in the range of 0 2 20 mm ministromatolites are common in early and middle proterozoic carbonate sequences and extend stratigraphically from the archaean to the holocene an occurrence of columnar and stratiform types exhibiting a primary or early diagenetic radial fibrous fabric and microscopically crinkled microcrenate lamination is described from the 1 9 gyr old belcher supergroup mcleary formation in southeastern hudson bay canada the structures which can be considered to be a variety of tufa are unusually well preserved because of early diagenetic silicification columnar types are referable to pseudogymnosolen asperia and are morphologically similar to other occurrences of these taxa in coeval dolostones in northwestern and eastern canada where the fabric is normally preserved by a secondary mosaic of dolomite the textural evidence of angulate cross sections and rectilinear divergent patterns indicates that the radial fibrous fabric represents primary or very early diagenetic precipitation and that pseudogymnosolenids with mosaic dolomite originally also had radial fibrous structure the precipitation may have been within or on microbial mats

biogeochemistry and paleoclimate variability during the holocene a record from mansar lake lesser himalaya investigation of biogeochemistry and amino acids on a 30 m long core from mansar lake has thrown light on palaeoclimate variability during the holocene period the c n ratio between 6 and 10 with some deviations and 13c mostly between 20 and 22 in the shallow core as well as a c n ratio greater than 13 reaching from 19 to 20 and correspondingly lower 13c of 28 in the deeper core suggest an aquatic source of carbon in the former and a cellulose rich land plant source in the latter this is supported by the abrupt increase in organic carbon content in the deeper core compared to the shallow core which indicates a hot and wet climatic regime during the early holocene and dry and cold during the late holocene period the amino acid data aa c c and aa n n are higher in shallow sediments compared to deeper sediments indicating an aquatic plant source in the shallow core and greater supply of land plant sources in the deeper core the lower percentage of the non protein amino acids alanine ala and amino butyric acid in the shallow core compared to the deeper core indicates different sources of organic matter in the lake basin the higher amino acid ratio asp ala 16 99 av and glu aba 18 18 av in the shallow core and lower ratios 10 32 and 12 41 av in the deeper core and asp glu 1 52 av and ala aba 1 61 av ratios in the former which are potential indicators of the nature of the organic matter are higher in the shallow core relative to the deeper core 1 33 and 1 23 av indicating relative biodegradation of organic matter in deeper sediments it has been observed that the organic matter associated with the dry season is relatively less biodegraded as evidenced from their higher ratios and is more biodegraded in the wet season as their ratios are lower in the river sediments in the absence of a bacterial contribution of organic matter from the soil source in this lake since mansar lake is a non drainage type it is envisaged that the climatic variation may be responsible for biodegradation in the deeper core sediments therefore the c n ratio and 13c values supported by amino acid data the latter being significant in revealing primary productivity and a terrestrial source of organic matter suggest a hot and wet climatic regime during the early holocene ca 7580 bp and a dry and cold in the late holocene period ca 4050 bp

stromatolite assemblages of the late precambrian in china abstract the late precambrian as used in this paper is represented by the sections in the jixian chihsien and yangtze gorges these rocks correspond to the middle late proterozoic of some authors and range in age from c 1900 to 600 ma the succession can be subdivided into four systems the changcheng jixian qingbaikou and sinian systems all of which yield abundant stromatolites based on the latest studies we suggest a new sixfold classification scheme supertype type subtype family genus and species and refer the stromatolites to 13 families and 50 genera including some material published already in china the stromatolites of the late precambrian of china may be represented by elements from yanshan southern liaodong peninsula and kaiyang of guizhou etc they are subdivided into eight stromatolite assemblages and correlated throughout most of china

stable isotopic compositions of carbonates from the mesoproterozoic bangemall group northwestern australia marine carbonate rocks from the mesoproterozoic bangemall group of northwestern australia show little deviation 1 3 in whole rock delta 13c carb values about a mean of 0 5 this narrow range persists despite close sampling every 10 20 m through long sections up to 2500 m that are geographically widespread up to 250 km apart over many depositional environments supralittoral to outer shelf sediment sources stromatolitic bioherms to detrital calcilutites and rock types pure limestones to dolomitic shales the only major excursions from the norm seem related to unusual environmental or post depositional processes as they are correlated with large enrichments to 3 or depletions to 16 in 18o relatively heavy delta 13c values up to 2 5 occur in a single bed of brecciated ferruginous dolostone at a single locality these abnormal values may result from local evaporitic conditions limey and shaley nodular dolostones have delta 13c values as low as 4 3 probably caused by remineralization of organic matter during late and patchy dolomitization most notably sharp negative excursions in delta 13c up to 8 4 occur in bleached kerogen free rocks with mineral assemblages of dolomite quartz calcite tremolite talc reflecting isotopic re equilibration in thick metamorphic aureoles around dolerite intrusions general environmental variations are minor with delta 13c values of peritidal facies tending to be slightly positive whereas those of subtidal facies are slightly negative there are no strong secular trends but subtle fluctuations within the range 2 to l can be correlated along the northwestern margin of the basin this resembles the pattern seen in other mesoproterozoic successions but is markedly unlike the heavy background 5 and extreme variations up to l0 in delta 13c evident in neoproterozoic successions of similar thickness and environmental setting hence in contrast to the neoproterozoic the global rate of organic carbon burial was probably fairly constant during deposition of the bangemall group and perhaps generally during the mesoproterozoic as was the redox state of the atmosphere and hydrosphere

carbon isotope chemostratigraphy of the middle riphean type section avzyan formation southern urals russia signal recovery in a fold and thrust belt abstract the avzyan formation of the southern ural mountains russia forms part of the middle riphean 1300 1000 ma type section its age is constrained to be younger than 1348 ma and older than 1080 ma and thus may preserve all or part of the mid mesoproterozoic isotopic shift this shift represents a significant reorganization of the carbon cycle and separates pre 1300 ma carbonates with 13c near 0 from post 1200 ma mesoproterozoic successions having average 13c values greater than 3 5 because the avzyan formation is a significant reference section for the mesoproterozoic and because it has the potential to record this mid mesoproterozoic shift a chemostratigraphic profile was constructed for this strongly folded and thrust faulted succession best preserved 13c values from carbonates of the avzyan formation lie mainly between 0 and 2 but the unit contains a single excursion represented by several data points to values greater than 4 the chemostratigraphy of the avzyan formation does not provide a definitive match to a better dated succession however the character of the carbon isotopic curve is most similar to that of the dismal lakes group arctic canada suggesting that the avzyan formation was deposited during the mid mesoproterozoic isotopic shift and may have an age near 1270 ma best preserved sr isotopic values of 0 70587 are also consistent with a later mesoproterozoic age

the carbon isotopic composition of proterozoic carbonates riphean successions from northwestern siberia anabar massif turukhansk uplift thick carbonate dominated successions in northwestern siberia document secular variations in the c isotopic composition of seawater through mesoproterozoic and early neoproterozoic early to early late riphean time mesoproterozoic dolomites of the billyakh group anabar massif have delta 13c values that fall between 0 and 1 9 permil versus pdb with values in the upper part of the succession yusmastakh formation consistently higher than those of the lower ust il ya and kotuikan formations consistent with available biostratigraphic and radiometric data delta 13c values for billyakh carbonates compare closely with those characterizing early mesoproterozoic carbonates about 1600 1200 ma worldwide in contrast late mesoproterozoic to early neoproterozoic limestones and dolomites in the turukhansk uplift exhibit moderate levels of secular variation only the lowermost carbonates in the turukhansk succession linok formation have delta 13c values that approximate billyakh values higher in the turukhansk succession delta 13c values vary from 2 7 to 4 6 permil with outliers as low as 5 0 permil interpreted as diagentically altered again consistent with paleontological and radiometric data these values compare well with isotopic values from 1200 to 850 ma successions elsewhere five sections measured in different parts of the turukhansk basin show nearly identical patterns of variation confirming that carbonate delta 13c correlates primarily with time and not facies the siberian sections illustrate the potential of integrated biostratigraphic and chemostratigraphic data in the intra and interbasinal correlation of mesoproterozoic and early neoproterozoic rocks

highly 13c enriched carbonate and organic matter in the neoproterozoic sediments of the bambuigroup brazil abstract paleontological and radiometric dating methods rb sr k ar and pb pb suggest neoproterozoic ages for sedimentary carbonate rocks of the bambuigroup in the southern part of the sa o francisco basin of central brazil the 13c values for carbonates fall within two ranges 2 to 2 and 10 to 16 for both groups coexisting organic carbon is depleted in 13c by 28 2 relative to the carbonates similar to numerous neoproterozoic examples worldwide secular variations in 13c in the bambuigroup show a significant positive excursion beginning with values near 0 in carbonates immediately above a diamictite and rising to values as high as 16 upsection the sr isotope data for carbonates from the bambuigroup agree with the age inferred from the secular variation in oceanic 13c values the striking feature in this study is that both the carbonate and total organic carbon are considerably more enriched in 13c than previously reported for neoproterozoic carbonates elsewhere it is not clear if these unusual 13c values are caused by primary or secondary processes

influence of bottom water anoxia on nitrogen isotopic ratios and amino acid contributions of recent sediments from small eutrophic lonar lake central india lonar lake is a eutrophic saline soda lake with permanently anoxic deep water the high ph and deoxygenation result in very elevated d15n of suspended particulate matter spm and sediments due to denitrification and ph related loss of gaseous ammonium spm and sinking particles are predominantly aquatic in origin whereas surface sediments are of mixed terrestrial plant and planktonic source an indicator of degradation intensity was derived from a principal component analysis of the spectral distribution of amino acids and named lonar degradation index li a ratio of individual amino acids ox anox ratio was additionally used to determine the relative degree of aerobic vs anaerobic degradation these two biogeochemical indicators can be used to detect changes in degradation intensity and redox conditions in the geological history and thus the paleoclimatic interpretation of lonar sediments surface sediments can be divided into three zones 1 a nearshore oxic zone of predominantly aquatic organic matter in which oxidation leads to a strong diagenetic increase of d15n 2 an alluvial zone with a predominance of isotopically depleted land plant and soil organic

problems in applying preservation facies and sequence models to sinian neoproterozoic glacial sequences in australia and asia abstract the sinian 800 530 ma is an extraordinary period of earth history characterized by the transition from simple to complex multicellular organisms and by extreme variations in climate eustasy and possibly tectonics understanding sinian stratigraphy may help interpret the co evolution of life and environment during the period though sinian successions are poorly dated and difficult to correlate preservation facies and sequence models based on mesozoic recent successions may be used to interpret them preservation models based on basin subsidence permit estimates of how thick and complete successions can be in different tectonic settings and how long it took for them to be deposited facies models for rift craton shelf slope and basin environments help in identification of these different tectonic settings sequence models facilitate interpretation of the interplay of tectonic subsidence eustasy rates of sedimentation and climate such models applied to the sinian successions of australia and asia indicate the following great shallowing upwards megacycles occur in sinian successions and each ends with regional glaciations deep rift basins formed around 850 800 ma preserve the oldest megacycles but these basins soon were filled with rapidly deposited glaciogenic sediments relatively complete sequences are found only in deep basins subject to repeated rifting cratons and shallow shelves preserve only the youngest megacycles older deposits have been removed by younger glacial advances deep shelves and slopes preserve one to three megacycles depending on the timing of the start of passive margin subsidence megasequences can be correlated based on limited radiometric dating and inferred regional distribution of unique rock types but these sequences are not developed to the same extent in all blocks problems in correlating the four great megacycles recognized elsewhere with those of asia will persist until the requisite facies analysis and u pb dating of interbedded volcanics are done

environmental evolution and hydrodynamic process of dongping lake in shandong province china over the past 150 years sporopollen when recorded in the sedimentary record is a characterization factor of vegetation over geological time of an area the grain size characteristics are direct reflection of the hydrodynamic conditions based on analyses of high time resolution sporopollen and grain size of a 55 cm long sediment core of dongping lake it is shown that the sedimentary environment and hydrodynamic processes of dongping lake have seen significant changes over the past 150 years from 1855 to 1865 the lake is in a hydrostatic depositional environment where submerged plants were in great abundance emergent and floating leaved aquatic plants were comparatively fewer and reworked sporopollen fossils were not observed these indicate a weak and stable hydrodynamic condition during this stage however fluctuation of mz amounts of clay and silt were present which may be due to high volumes of sediments around dongping lake basin transported into dongping lake via the yellow river during the early lake forming stages from 1865 to 1922 the lake is in a backswamp depositional environment where aquatic plants are nearly nonexistent appearing occasionally in some layers with relatively low abundance fern spores show a twofold increase in occurrence and reworked sporopollen fossils are frequently identified all of these indicate a strong hydrodynamic condition and frequent environmental change grain size characteristics also support this interpretation from 1922 to 1961 aquatic plants appeared at the upper layers of this zone at relatively low amounts and reworked sporopollen fossils were frequently identified grain size characteristics show an obvious change in grain size distribution indicating a strong hydrodynamic condition and unstable depositional environment these relationships were attributed to a backswamp depositional environment from 1961 to 2007 dongping lake is in a hydrostatic depositional environment where the hydrodynamic condition is weak and stable evidence for this is shown by a remarkable increase in submerged plants a rapid decrease in fern spores and occasional appearances of reworked sporopollen fossils in the lower part of the zone however grain size characteristics reveal that fluctuation of mz amounts of clay silt and sand are noticeable and frequent which may be mainly related to impacts of ever enhancing human activities in recent years

a 5000 yr record of climate change in varved sediments from the oxygen minimum zone off pakistan northeastern arabian sea the upper holocene marine section from a kasten core taken from the oxygen minimum zone off karachi pakistan at water depth 700 m contains continuously laminated sediments with a sedimentation rate of 1 2 mm yr and a unique record of monsoonal climatic variability covering the past 5000 years our chronostratigraphy is based on varve counts verified by conventional and ams 14 c dating individual hemipelagic varve couplets are about 0 8 1 5 mm thick with light colored terrigenous laminae a deposited mainly during the winter monsoon alternating with dark colored laminae b rich in marine organic matter coccoliths and fish debris that reflect deposition during the high productivity season of the late summer monsoon august october precipitation and river runoff appear to control varve thickness and turbidite frequency we infer that precipitation decreased in the river watershed indicated by thinning varves after 3500 4000 yr b p this is about the time of increasing aridification in the near east and middle east as documented by decreasing nile river runoff data and lake level lowstands between turkey and northwestern india this precipitation pattern continued until today with precipitation minima about 2200 1900 yr b p 1000 yr b p and in the late middle ages 700 400 yr b p and precipitation maxima in the intervening periods as documented by spectral analysis the thickness of varve couplets responds to the average length of a 250 yr cycle a 125 yr cycle the gleissberg cycle of solar activity 95 yr and a 56 yr cycle of unknown origin higher frequency cycles are also present at 45 39 29 31 and 14 yr the sedimentary gray value also shows strong variability in the 55 yr band plus a 31 yr cycle because high frequency cyclicity in the enso band ca 3 5 and 5 yr is only weakly expressed our data do not support a straightforward interaction of the pacific enso with the monsoon driven climate system of the arabian sea

a high resolution palaeoclimatic record for the last 27 500 years in tropical west africa from the carbon and nitrogen isotopic composition of lacustrine organic matter variations in the carbon and nitrogen isotopic composition of bulk organic matter in the sediments of lake bosumtwi ghana reflect climatically induced changes to the lake and the catchment flora cores spanning the last 27 5 kyr of sedimentation in the lake show large oscillations in 13corg pdb and 15norg air the late pleistocene record is particularly detailed showing changes of ca 20 in carbon and ca 10 in nitrogen isotopic compositions these variations are of complex origin although different in magnitude major isotopic excursions in the two records are generally in phase and reveal the occurrence of two major dry intervals at and immediately following the last glacial maximum the allerod younger dryas period also seems to have been marked by generally dry conditions in this part of tropical west africa nitrogen isotopic evidence suggests that during the period 9 2 3 2 kyr the lake had an extremely stable water column probably due to the absence of a windy or cool dry season or both regular circulation of the water column recommenced during the late holocene and has persisted until the present day

diagenetic changes of lignin compounds in a more than 0 6 million year old lacustrine sediment lake biwa japan a vertical profile of lignin in the upper 700 m layer of a 1400 m sediment core of lake biwa an oligotrophic freshwater lake in japan was determined using a cuo oxidative degradation method the results indicated that lignin is found throughout the core demonstrating lignin to be very stable for over 0 6 million years moreover the upper 250 m approximately 0 6 million years old segment of the sediment core was investigated to determine the apparent long term degradation rate of lignin a downward lignin concentration decrease is observed over the upper 250 m of the core which corresponds to a calculated half life of at least approximately 40 104 years assuming that lignin decrease is due to its in situ degradation diagenesis

sulfur and carbon isotope records from 1700 to 800 ma carbonates of the jixian section northern china implications for secular isotope variations in proterozoic seawater and relationships to global supercontinental events abstract this study is a comprehensive stable isotope survey of the marine carbonate dominated upper paleo to lower neoproterozoic stratigraphy of jixian county china carbonate associated sulfate cas was extracted and measured for 34 s cas using the same samples analyzed for 13 c carbonate this integrated proxy approach is a step towards a more comprehensive picture of secular variation in the composition of proterozoic seawater we specifically sampled marine carbonate intervals from the lower section of the chuanlinggou formation changcheng group ca 1700 ma to the top of the jingeryu formation qingbaikou group ca 800 ma 13 c carbonate values are mostly negative in the upper paleoproterozoic changcheng group with an ascending trend from 3 to 0 we observed variation of approximately 0 1 in the mesoproterozoic jixian group and positive values of 2 2 characterize the lower neoproterozoic qingbaikou group stratigraphic variations in 34 s cas are more remarkable in their ranges and magnitudes including conspicuously high values exceeding 30 in the three intervals at ca 1700 ma 1300 1100 ma and 1000 900 ma in the changcheng group 34 s cas values are typically higher than 25 with only a few values of less than 15 in contrast most of the data spanning from the mesoproterozoic tieling formation of the jixian group to the lower neoproterozoic jingeryu formation of the qingbaikou group are highly variable between 10 and 25 with some values exceeding 25 in the late paleoproterozoic 1700 1600 ma a 10 decrease in 34 s cas and 3 increase in 13 c carbonate are coincident with and likely related to the breakup of columbia a supercontinent that predated rodinia carbon and sulfur isotope data from the mesoproterozoic when global tectonic activity was comparatively weaker fall mostly in the ranges of 15 10 and 0 1 respectively but fluctuations of 20 for 34 s cas and 3 for the 13 c carbonate at ca 1450 1400 ma may reflect subduction and large scale magmatic activity in island arcs marking the end of columbia breakup from the late mesoproterozoic ca 1300 1100 ma to the early neoproterozoic ca 800 ma the 13 c and 34 s of seawater increased gradually with increasing variability most impressive are 34 s cas values that exceed 30 in two intervals at ca 1300 1100 ma and ca 1000 900 ma which may reflect the assembly and early breakup of rodinia although gaps in the record remain and studies of even higher resolution are warranted our results suggest that changes in paleoceanographic conditions linked to global tectonics strongly influenced the biogeochemical cycles of c and s furthermore periods of the proterozoic previously noted for their isotopic invariability show clear isotopic expressions of this tectonic activity

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

sharp decrease in summer monsoon strength 4000 3500 cal yr b p in the central higher himalaya of india based on pollen evidence from alpine peat age constrained pollen data and magnetic susceptibility of an alpine peat profile from the garhwal higher himalaya display a continuous record of climate and monsoon trends for the past 7800 yr about 7800 cal yr b p dominance of evergreen oak quercus semecarpifolia alder alnus and grasses in the pollen record reflect a cold wet climate with moderate monsoon precipitation from 7800 to 5000 cal yr b p vegetation was progressively dominated by conifers indicating ameliorated climate with a stronger monsoon a warm humid climate with highest monsoon intensity from 6000 4500 cal yr b p represents the mid holocene climatic optimum between 4000 and 3500 cal yr b p the abundance of conifers sharply decreased with the greatest increase in evergreen oak this trend suggests progressive cooling with a decrease in the monsoon to its minimum about 3500 cal yr b p two relatively minor cold dry events at ca 3000 and 2000 cal yr b p marked step wise strengthening of the monsoon until ca 1000 cal yr b p after a cold dry episode that culminated ca 800 cal yr b p the monsoon again strengthened and continued until today a sharp decrease in temperature and rainfall at 4000 3500 cal yr b p represents the weakest monsoon event of the holocene record this cold dry event correlates with proxy data from other localities of the indian subcontinent arabian sea and western tibet

vegetation climate and sea level in the past 55 000 years hanjiang delta southeastern china abstract pollen in quaternary deposits from the subtropical hanjiang delta records three major phases in the local vegetation and climate history during the last 55 000 yr 1 a prevalent cool to temperate and humid climate at ca 24 000 14c yr b p is indicated by abundant pollen of temperate trees including conifers 2 between 20 000 and 15 000 14c yr b p a cold dry environment was associated with low sea level during the last glaciation leading to subaerial exposure weathering and interruption of sedimentation as well as departure from the region of dacrydium and sonneratia 3 a short term expansion of grassland at ca 10 300 14c yr b p reduced the predominant lauraceae fagaceae evergreen forest possibly corresponding to the younger dryas cooling the combined data indicate a maximum sea level rise in the mid holocene 7500 4000 14c yr b p and a marine influence in the late pleistocene at 45 000 20 000 14c yr b p the holocene warming however did not bring back moisture sensitive taxa indicating high seasonal aridity probably caused by renewed monsoon conditions

evidence for primary aragonite precipitation lower proterozoic 1 9 ga rocknest dolomite wopmay orogen northwest canada abundant precipitation of aragonite is suggested by well preserved fabrics in dolostones of the lower proterozoic 1 9 ga rocknest formation fabrics include dolomite and silica after botryoidal aragonite in tepee structures and seafloor cement fans and cement crusts in cryptalgal tufas aragonite was common on the 1 9 ga rocknest shelf as it is on modern tropical shelves a search for similar marine cement fabrics in other precambrian carbonates should help resolve whether aragonite was an important precipitate from precambrian tropical seas implying an ocean carbonate chemistry similar to today or if aragonite precipitation was restricted to rare times in the past calcite and even dolomite being the main carbonates precipitated as recently suggested by some authors

neoproterozoic fossils in mesoproterozoic rocks chemostratigraphic resolution of a biostratigraphic conundrum from the north china platform abstract siliciclastic rocks of the ruyang group southern shanxi and the broadly equivalent gaoshanhe group shaanxi contain exceptionally well preserved large o 150 m acanthomorphic acritarchs recently interpreted as late neoproterozoic sinian c 800 544 ma in age this biostratigraphic interpretation is based on the presence of large acanthomorphs in sinian successions of south china and elsewhere and the perceived absence of comparable forms in older rocks it casts doubt on the long accepted interpretation of ruyang and correlative rocks as mesoproterozoic in age 1600 1000 ma in contrast thick marine dolomites in overlying units contain abundant radial fibrous fabrics and a narrow range of 13c values c 0 1 vs pdb features which characterize unambiguously mesoproterozoic carbonates elsewhere on the north china platform and on other continents age estimates based on petrofabrics and chemostratigraphy are corroborated by a u pb zircon age of 999 ma no recorded error for granites which intrude overlying carbonates thus in combination the available data constrain the ruyang siliciclastics and overlying carbonates to be older than about one billion years making shuiyousphaeridium yan and other large process bearing acritarchs from these units among the oldest known distinctly ornamented eukaryotic microfossils

a new paleoproterozoic tectonic history of the eastern capricorn orogen western australia revealed by u pb zircon dating of micro tuffs abstract the earaheedy basin is one of several paleoproterozoic siliciclastic basins in the eastern part of the capricorn orogen in western australia in the absence of an adequate chronostratigraphic framework multiple conflicting models have been proposed for the tectonic history of the basin we present in situ shrimp u pb zircon dates of 1971 11 ma 1954 5 ma and 1949 10 ma from three thin tuff horizons micro tuffs in the yelma formation at the base of the basin succession these micro tuffs are only slightly younger than the 1990 6 ma imbin porphyry which has been interpreted as a basement inlier our new dates combined with field mapping suggest that the imbin porphyry is a volcanic subvolcanic complex within the basin micro tuffs in the yelma formation are more than 50 m y older than c 1890 ma micro tuffs within the overlying frere formation deposition of the yelma formation was coeval with continent continent collision farther west in the orogen marked by the 2005 1950 ma glenburgh orogeny and the formation is possibly correlative with peripheral foreland deposits of the padbury group the frere formation was deposited in shallow marine conditions within an intracratonic basin about 60 m y after the glenburgh orogeny the frere formation is unconformably or disconformably overlain by the miningarra group the youngest unit of which is the mulgarra sandstone this sandstone was deposited after c 1865 ma and derived either from exposed frere formation or from a now buried source within the capricorn orogen that was uplifted by inception of the 1820 1770 ma capricorn orogeny therefore the earaheedy basin comprises at least three distinct unconformity bound successions deposited in contrasting tectonic settings