holocene climatic changes and vegetation development in the kuril islands abstract the response of kuril island vegetation to climatic changes during the holocene is reconstructed from data obtained from key sections that included various depositional environments these climatic fluctuations were not as marked in the kuril archipelago as they were in nearby continental margins and large islands during the early holocene dwarf stone pine coniferous and birch forest prevailed in the south kurils and tundra landscapes in the north kurils the greatest northward movement of kuril vegetation zones occurred during the holocene optimum 6600 5000 14c bp mean annual temperatures in the kuril islands were 2 3 c higher than modern shifts in the location of warm and cold marine currents which strengthened or dampened insolation driven climatic changes played an important role in vegetation development cool temperate broadleaf forests and mixed coniferous broadleaf forests were widespread on south kurils rising holocene sea levels flooded land bridge connections to hokkaido island and the mainland resulting in the formation of several small islands in the south kurils meadows and boggy landscapes prevailed this flooding had a great effect on repopulation of island biota as did the deep straits that separate southern islands from the central and north kurils all paleovegetation associations can be found on the current landscape although their geographic distribution has changed during the holocene no introduction of plants from adjacent land occurred in the holocene forb and graminoid meadows characterized the middle holocene vegetation of central kurils on north kurils forb meadows were widespread tundra area decreased climatic changes did not occur synchronously throughout the kurils at times not even on the closest islands local volcanism played a special role in kuril vegetation history the considerable microclimatic variability within the islands also has been important in determining the development and preservation of vegetation communities and their reaction to more regional climatic changes

petrologic and stable isotope constraints on the source and evolution of skarn forming fluids at pine creek california a detailed geochemical analysis of the well exposed multistage pine creek california tungsten deposit has constrained the roles of magmatic metamorphic and meteoric fluids in the development of the zoned scheelite ore and calc silicate skarn metamorphic conditions of p 2 kb t 600 degrees c and x sub co 2 0 25 are recorded in the metasedimentary rocks of the septum metamorphism yielded calcite diopside graphite and calcite dolomite periclase brucite forsterite assemblages in the variably dolomitic siliceous carbonate rocks of the pine creek septurn following intrusion of the morgan creek quartz monzonite metasomatism developed the zoned endoskarn exoskarn at the contact the massive garnet andradite sub 20 50 pyroxene hedenbergite sub 20 80 or quartz skarn assemblage carries most of the scheelite calculated t x sub co 2 equilibria corrected for solid solution effects restrict skarn formation to x sub co 2 0 2 at t 500 degrees or 50 degrees c calculated f sub o 2 f sub f 2 f sub s 2 diagrams indicate f sub o 2 values near quartz fayalite magnetite and f sub s 2 values well below pyrrhotite pyrite during skarn formation slightly falling temperatures were accompanied by increased f sub s 2 and hydration of the skarn assemblages stable isotope data for calcites show a mixing trend from unaltered marble delta 18 o 24ppm delta 13 c 3 5 degrees to values in equilibrium with magmatic fluids delta 18 o 8ppm delta 13 c 6ppm biotite quartz thermometry for the quartz monzonite yields temperatures of 410 degrees to 460 degrees c well below the solidus and suggesting later reequilibration pyroxene quartz analyses suggest that these minerals equilibrated at temperatures of 460 degrees to 560 degrees c the delta 18 o values measured for garnets suggest disequilibrium for the garnet quartz and garnet pyroxene pairs d h results for epidote and biotite suggest that meteoric water influx became more important with time sulfur isotope data are consistent with a reduced magmatic source

upb geochronology of layered mafic intrusions in the eastern baltic shield implications for the timing and duration of paleoproterozoic continental rifting abstract paleoproterozoic layered mafic ultramafic intrusions are widespread in the eastern baltic fennoscandian shield and mark the initial stages of continental rifting and outpouring of voluminous flood basalts u pb zircon baddeleyite ages have been determined for seven layered mafic intrusions and a subvolcanic felsic unit associated with two paleoproterozoic volcanic sedimentary belts the pechenga imandra varzuga belt in the kola peninsula and the sumi sariola belt in karelia the layered intrusions in the sumi sariola belt show an age progression from 2449 0 1 1 ma for the burakovka complex located at the southeastern edge of the belt to 2442 1 1 4 ma and 2441 3 1 2 ma for the lukkulaisvaara and tsipringa intrusions of the olanga complex in northern karelia northeastern part of the belt these age results indicate a total duration of mafic magmatism along the ca 800 km belt in karelia to be less than 10 m y the pechenga imandra varzuga belt kola peninsula contains two distinct age groups of layered mafic intrusions and related rocks the younger of these overlaps with the ages obtained for the olanga intrusions and includes the 2441 0 1 6 ma imandra lopolith and a spatially associated felsic subvolcanic unit dated at 2442 2 1 7 ma the older group of mafic layered intrusions in the kola peninsula includes the 2501 5 1 7 ma pana tundra intrusion the 2504 4 1 5 ma monche pluton and the 2505 1 1 6 ma general skaya mountain intrusion the temporal and spatial distribution of the 2 50 2 44 ga rift related igneous activity in the baltic shield is consistent both with the model of starting mantle plume and with the model of passive rifting controlled by pre existing lithospheric weaknesses

extreme 13ccarb enrichment in ca 2 0 ga magnesite stromatolite dolomite red beds association in a global context a case for the world wide signal enhanced by a local environment abstract the palaeoproterozoic positive excursion of 13 c carb is now considered as three positive shifts of 13 c carb separated by returns to 0 which all occurred between 2 40 and 2 06 ma this isotopic event is unique in terms of both duration 300 ma and 13 c enrichment up to 18 the mechanism responsible for one of the most significant carbon isotopic shifts in earth history remains highly debatable to date 13 c of 10 to 15 cannot be balanced by organic carbon burial forg as there is no geological evidence for an enhanced corg accumulation prior to or synchronous with the excursion instead termination of these excursions is followed by formation of a vast reservoir of 13 c depleted organic material 45 at shunga and by one of the earliest known oil generation episodes at 2 0 ga none of the three positive excursions of 13 c carb is followed by a negative isotopic shift significantly below 0 as has always been observed in younger isotopic events reflecting an overturn of a major marine carbon reservoirs this may indicate that forg was constant implying that the mechanism involved in the production of corg was different onset of intensive methane cycling resulting in c change is another possibility the majority of sampled 13 c carb rich localities represents shallow water stromatolitic dolostones red beds and evaporites formed in restricted intracratonic basins and may not reflect global 13 c carb values closely spaced drill core samples n 73 of stromatolitic dolostones from the 1980 27 ma tulomozerskaya formation in the onega palaeobasin russian karelia have been analysed for 13 c carb and 18 o carb in order to demonstrate that different processes were involved in the formation of 13 c carb rich carbonates the 800 m thick magnesite stromatolite dolomite red beds succession formed in a complex combination of environments on the karelian craton peritidal shallow marine low energy protected bights barred basins evaporative ephemeral ponds coastal sabkhas and playa lakes the carbonate rocks exhibit extreme 13 c enrichment with 13 c values ranging from 5 7 to 17 2 vs v pdb mean 9 9 2 3 and 18 o from 18 6 to 26 0 vs v smow mean 22 0 1 6 the tulomozerskaya isotopic excursion is characteristic of the global 2 4 2 06 ga positive shifts of carbonate 13 c 12 c although it reveals the greatest enrichment in 13 c known from this interval an external basin s is considered to have provided an enhanced corg burial and global seawater enrichment in 13 c the global background value for the isotopic shift at tulomozero time ca 2 0 ga is roughly estimated at around 5 an explosion of stromatolite forming microbial communities in shallow water basins evaporative and partly restricted environments high bioproductivity enhanced uptake of 12 c and pene contemporaneous recycling of organic material in cyanobacterial mats with the production and consequent loss of co2 and ch4 are believed to be additional local factors which may have enhanced 13 c from 5 up to 17 such factors should be taken into account when interpreting carbon isotopic data and attempting to discriminate between the local enrichment in 13 c and globally enhanced 13 c values we propose that many previously reported 13 c values from other localities where environmental interpretations are not available or have not been taken into account may not represent the global 13 c values

oxygen isotope calibration of the onset of ice rafting and history of glaciation in the north atlantic region we report here that dsdp site 552a cored with the hydraulic piston corer on the west flank of rockall bank recovered an undisturbed sequence of alternating white deep sea carbonate oozes and dark coloured layers that are rich in glacial debris oxygen isotope analysis of the sequence together with detailed nannofossil and palaeomagnetic stratigraphy shows that the first major horizon of ice rafting occurred at about 2 4 myr and was preceded by a minor pulse of ice rafting at about 2 5 myr the carbon isotope record shows that the site has been bathed by a water mass of similar characteristics to present day north atlantic deep water at least since 3 5 myr

paleogeographic and paleoclimatic significance of diatoms from middle pleistocene marine and glaciomarine deposits on baldwin peninsula northwestern alaska abstract a newly revised diatom biostratigraphic scheme for the north pacific ocean based on studies of the diatom flora of the cape blossom and hotham inlet formations of baldwin peninsula northwestern alaska provides new information on the paleoceanography of kotzebue sound alaska during middle pleistocene time sediments exposed along coastal bluffs of baldwin peninsula contain subarctic north pacific zonal index species including extinct proboscia barboi pr curvirostris actinocyclus ochotensis var fossilis thalassiosira nidulus var nidulus th jouseae th gravida var fossilis and stephanopyxis dimorpha which are correlated with the middle part of the proboscia barboi zone 0 43 0 36 ma based on the distribution of the zonal diatom species and on changes in the paleoecological structure of the diatom assemblages e g warm vs cold water assemblages we conclude that the marine deposits of the cape blossom formation and lower baldwin silt member of the hotham inlet formation formed under relatively warm high sea level conditions associated with the marine oxygen isotope stage ois 11 transgression glaciomarine sedimentation middle and upper baldwin silt and selawik gravel members of the hotham inlet formation initiated during relatively warm conditions at the end of the stage 11 transgression and continued into stage 10 high latitude glacier growth during a global interglacial period was likely facilitated by warm surface waters on flooded continental shelves and limited regional sea ice cover the biostratigraphic record at baldwin peninsula provides further evidence that high latitude ice growth is favored by increased moisture supply during warm climatic intervals and inhibited by arid conditions during full glacial intervals

geochemistry of precambrian carbonates 3 shelf seas and non marine environments of the archean a comprehensive whole rock study of mineralogical chemical and isotopic attributes of archean carbonates suggests that their lithologies and facies have been controlled by tectonic setting in the first two papers of this series we have shown that the dominant lithology of sedimentary carbonates in greenstone belt settings is limestone fe rich dolostone of ankeritic composition in older examples in this paper we suggest that the archean shelf sequences are mostly dolostone and the contemporaneous lacustrine playa lakes are characterized by limestone facies the present study is of the shelf environments of the archean represented by the pongola supergroup of south africa and the hamersley group wittenoom and carawine dolomite of australia the lacustrine playa examples have been sampled from the ventersdorp supergroup of south africa and the fortescue group of australia geological trace element and oxygen isotope considerations of the shelf carbonates suggest that their original mineralogy may have been aragonite and that the pongola dolostones probably represent a direct dolomitization product of this precursor in contrast the stabilization of the hamersley carbonates may have involved an additional step of transformation of a metastable precursor into limestone prior to dolomitization subsequently both sequences but the pongola supergroup much more so were subjected to pervasive thermal events which overprinted their chemical and isotopic signatures consideration of the best preserved samples yields 0 9 2 1 and 6 l pdb for the 13c and 18o respectively for the initial archean signature if compared to phanerozoic carbonates the archean 13c values are comparable but the oxygen isotope measurements again support the primary nature of 18o depletion in ancient marine sediments regardless of its ultimate cause the 87sr86sr of 2 5 ga old sea water was not more than 0 7033 if this value reflects the contemporaneous sea water it would indicate the commencement of a significant 87sr input from the growing and aging continents it is however entirely possible that the slight enrichment in radiogenic 87sr relative to the contemporaneous mantle represents only an unresolved artefact of post depositional alteration if so the 87sr86sr of the 2 5 ga old sea water may still have been within a mantle range the lacustrine limestones retain a strong facies control in their trace element attributes they are also 4 depleted in 13c compared to marine carbonates and strongly depleted in 18o 19 l pdb these light 18o values are somewhat enigmatic unless the lakes were of the high altitude latitude variety the 87sr86sr of 0 711 for the ventersdorp lakes suggests that their drainage basin incorporated not only volcanic rocks but also aged continental crust archean carbonates of all lithologies and facies are enriched in mn and fe compared to their phanerozoic counterparts

carbon and oxygen isotope systematics of a paleoproterozoic cap carbonate sequence from the sausar group central india abstract well preserved sedimentological features of the paleoproterozoic age sausar group of central india indicate glaciogenic origin for the diamictite in the lower part of the unit deglaciation was responsible for a marine transgression and the deposition of proximal glaciomarine facies and a cap carbonate followed by fine clastics with manganese ore analyses of 13 c and 18 o contents in the carbonate unit overlying the diamictite together with sr and ba contents and ree data indicate the preservation of primary geochemical signatures the average 13 c carb content ranges between 3 1 and 0 1 v pdb having peak negative 13 c excursions of up to 7 4 v pdb similar to paleoproterozoic and neoproterozoic cap carbonates elsewhere high sr and ba contents indicate the presence of aragonite and barite precursors similar to well studied neoproterozoic cap carbonates a single continuous carbonate unit shows 13 c excursions from 4 4 to 2 6 v pdb the lithological association and chemostratigraphy are comparable with the carbonate tillite association of the huronian supergroup of canada the snowy pass supergroup of the usa the transvaal supergroup of south africa and the turee creek group of australia

the early proterozoic pechenga varzuga belt a case of precambrian back arc spreading abstract the pechenga varzuga belt pvb in the kola peninsula russia comprises the western pechenga and the eastern imandra varzuga portions these are two major asymmetric synform structures infilled with proterozoic volcanogenic and sedimentary rocks dated between 2 45 and 1 9 ga two main stages of tectonic magmatic activity took place 1 a 2 45 2 3 ga basal siliceous high mg volcanic series typical for the sumian sariolian episodes and 2 the jutuli ludia and kalevian episodes which began 2 2 ga ago the lower level of the second sequence is made up of subaerial alkali basalts the upper 2 1 1 95 ga old portions of the sequence consist of tholeiitic pillow lavas hyaloclastites and ferropicrite basalt flows associated with deep water sediments such as phyllites silicites and turbidites the tholeiites exhibit ree distribution patterns similar to those of morb while the ferropicrite basalts resemble intraplate olivine basalts of continental and oceanic environments calc alkaline subaerial volcanism took place along the south western flank of the pechenga zone a final igneous stage is characterized by the emplacement of potassium granitic intrusions the main lapland thrust mlt occurs along the southern border of the paleoproterozoic lapland umba granulite belt and is a narrow zone of compression thrusting and folding accompanied by high pressure granulite metamorphism it is approximately coeval with the upper part of the pechenga varzuga belt and is interpreted as representing a complementary structure i e the zone of subduction of the karelian belomorian craton beneath the kola block thus the upper part of the pechenga varzuga belt is considered to have originated as a back arc basin in the rear of a zone of north directed subduction and continent collision it was eventually closed with the appearance of igneous suites typical of such events the pechenga varzuga belt main lapland thrust system thus provides an instance of an ancient 2 0 1 9 ga ago collision of lithospheric plates accompanied by back arc spreading and then closure of the back arc basin the geodynamic development is similar that which occurred more recently within the alpine himalayan belt

strontium and carbon isotope geochemistry applied to dating of carbonate sedimentation an example from high grade rocks of the norwegian caledonides isotope stratigraphy has been applied to an undated high grade carbonate sequence from the norwegian caledonides in order to constrain the depositional age sokumfjell group marbles of the beiarn nappe complex in the uppermost allochthon of the nordland caledonides were subjected to several phases of deformation culminating in amphibolite facies metamorphism the ca 1000 m thick marble sequence studied is composed of five different lithofacies lithofacies 1 4 are calcite marbles and lithofacies 5 is dolomite marble all the calcite marble lithofacies exhibit throughout rhythmic bedding and textural grading on different scales suggesting that carbonate material was deposited in a pelagic turbidite system 123 samples were analysed for major and trace elements and acid soluble mg and ca of which 42 samples of calcite marbles and four samples of dolomite marbles were selected for 13 c 18 oa nd 87 sr 86 sr analyses all selected calcite marbles have high sr contents averaging 2000 ppm they are characterised by 87 sr 86 sr ratios ranging between 0 70642 and 0 70999 and 13 c values ranging between 1 3 and 8 4 v pdb 18 o values are highly variable 14 1 24 8 v smow the best preserved samples selected on the basis of mn sr and rb concentration and mn sr and mg ca ratios yield average 87 sr 86 sr values of 0 70669 0 70697 0 70727 0 70749 and 0 70737 for lithofacies 1 2 3 4 and 5 respectively post sedimentary alterations including amphibolite facies metamorphism resulted in only a slight increase of 87 sr 86 sr values in the marbles studied apparently due to aragonite precursor high sr concentration and a very early and fast diagenetic alteration caused by fluids isotopically comparable with that of seawater projection of these values along with 13 c measurements onto 87 sr 86 sr and 13 c calibration curves for the secular variations of seawater suggests that the lithofacies studied were apparently deposited between 635 and 600 ma 2001 elsevier science b v all rights reserved

a review on the provenance discrimination of sediments in the yellow sea the yellow sea has been extensively studied for the understanding of dispersal patterns and limits of sediments from neighboring countries including china and korea although sedimentological mineralogical and geochemical approaches have been tried to solve the problems especially including the identification of sediment sources in and around the yellow sea the published results are not enough for understanding them suggestions on sediment origins budgets sediment accumulation rates mineralogical and geochemical compositions are not coincident to each other and sometimes even controversial for example conflicts on the distribution patterns of smectite and calcium carbonate the provenance of the southeastern yellow sea mud and sedimentation rates in there the ratios of v al and mn al in korea and china river sediments the origin of ba and pb in sandy sediments of the northeastern yellow sea and so on various geochemical indicators from the literature for the provenance discrimination in the yellow sea are reviewed here in depth and corresponding discussions are described separately research topics for the future study also are suggested for the proper access to the understanding of the origin and dispersal patterns of the yellow sea sediments especially focusing on the geochemical approaches d 2003 elsevier science b v all rights reserved

changes in temperature and water depth of a small mountain lake during the past 3000 years in central kamchatka reflected by a chironomid record abstract we investigated chironomid assemblages of a well dated sediment core from a small seepage lake situated at the eastern slope of the central kamchatka mountain chain far east russia the chironomid fauna of the investigated sigrid lake is dominated by littoral taxa that are sensitive to fluctuations of the water level two groups of taxa interchangeably dominate the record responding to the changes in the lake environment during the past 2800 years the first group of littoral phytophilic taxa includes psectrocladius sordidellus type corynoneura arctica type and dicrotendipes nervosus type the abundances of the taxa from this group have the strongest influence on the variations of pca 1 and these taxa mostly correspond to low water levels moderate temperatures and slightly acidified conditions the second group of taxa includes microtendipes pedellus type tanytarsus lugens type and tanytarsus pallidicornis type the variations in the abundances of these taxa and especially of m pedellus type are in accordance with pca 2 and correspond to the higher water level in the lake more oligotrophic and neutral ph conditions water depths wd were reconstructed using a modern chironomid based temperature and water depth calibration data set training set and inference model from east siberia nazarova et al 2011 mean july air temperatures t july were inferred using a chironomid based temperature inference model based on a modern calibration data set for the far east nazarova et al 2015 the application of transfer functions resulted in reconstructed t july fluctuations of approximately 3 c over the last 2800 years low temperatures 11 0 12 0 c were reconstructed for the periods between ca 1700 and 1500 cal yr bp corresponding to the kofun cold stage and between ca 1200 and 150 cal yr bp partly corresponding to the little ice age lia warm periods modern t july or higher were reconstructed for the periods between ca 2700 and 1800 cal yr bp 1500 and 1300 cal yr bp and after 150 cal yr bp wd reconstruction revealed that the lake level was lower than its present level at the beginning of the record between ca 2600 and 2300 cal yr bp and ca 550 cal yr bp between ca 2300 and 700 cal yr bp as well as between 450 and 150 cal yr bp the lake level was higher than it is today most probably reflecting more humid conditions

spectral analysis of the diatom paleotemperature records at dsdp sites 579 and 580 near the subarctic front in the western north pacific abstract maximum entropy spectral analyses and a fitting test to find the best suitable curve for the modified time series based on the non linear least squares method for td diatom temperature values were performed for the quaternary portion of the dsdp sites 579 and 580 in the western north pacific the sampling interval averages 13 7 kyr in the brunhes chron 0 780 ka and 16 5 kyr in the later portion of the matuyama chron 780 1800 ka at site 580 but increases to 17 3 kyr and 23 2 kyr respectively at site 579 among dominant cycles during the brunhes chron there are 411 5 kyr and 126 0 kyr at site 579 and 467 0 kyr and 136 7 kyr at site 580 correspond to 413 kyr and 95 to 124 kyr of the orbital eccentricity minor cycles of 41 2 kyr at site 579 and 41 7 kyr at site 580 are near to 41 kyr of the obliquity tilt during the matuyama chron at site 580 cycles of 49 7 kyr and 43 6 kyr are dominant the surface water temperature estimated from diatoms at the western north pacific dsdp sites 579 and 580 shows correlation with the fundamental earth s orbital parameters during quaternary time

δ13c and δ18o variations in primary and secondary carbonate phases several contrasting examples from palaeoproterozoic 13c rich metamorphosed dolostones abstract the palaeoproterozoic kuetsjarvi sedimentary formation from the pechenga greenstone belt nw russia has been studied with the purpose of determining 13ccarb and 18ocarb values in various carbonate phases from genetically different 13c rich dolostones sampled by micro coring techniques samples were collected from quarries and drillholes this avoids the influence of recent weathering on isotopic composition and allows rocks from different metamorphic facies intersected by deep drillholes to be sampled in the low grade greenschist facies conditions distinct textural components from the same parental impure dolostones have yielded 13c values ranging within 1 and showing no statistical differences between early dolomicrite and late void and fenestra filling dolospar no significant differences have been observed between analyses of the whole rock and microcored samples genetically different dolomites however retain their primary isotopic peculiarities and show 13c differences exceeding 30 no external isotopically light carbon has been introduced during diagenesis and therefore there is no evidence of soil derived co2 which commonly shifts 13c to more negative values 18o values show 2 6 fluctuations in distinct textural components from the same parental dolostones which were caused by syn depositional early diagenetic processes genetically different dolomites largely retain their syn depositional early diagenetic 18o values ranging from 9 mantle influenced to 30 evaporation induced the high grade greenschist facies metamorphism marked by the reaction dolomite quartz h2o tremolite calcite2 co2 significantly reset 13c by 3 in the metamorphic calcite2 and 18o by 6 in all carbonate components in such cases the best proxy for depositional 13c values of impure dolostones can only be provided by microcored samples of the dolomite phase

a widespread positive 13ccarbanomaly at around 2 33 2 06 ga on the fennoscandian shield a paradox carbon isotope measurements carried out on 201 carbonate samples from the early proterozoic of the kola peninsula n karelia and norway yield 13c pdb spanning 20 5 to 11 a general 13c secular trend shows that prior to 2 33 ga values are typically normal marine averaging around 3 0 between 2 33 and 2 06 ga in jatulian time there follows a rapid excursion to positive 13c of around 6 post jatulian time is characterized by 13c of sedimentary carbonates fluctuating between 5 and 3 also it is remarkable for the first pronounced development of diagenetic carbonates which have 13c between 14 and 6 the c 6 positive 13c shift with a duration of about 270 myr coincides with a maximum in the diversity and abundance of stromatolites and with widespread development of red beds but does not coincide with the maximum of buried corg mass the fennoscandian shield represents the largest isotoically anomalous carbonate province yet reported and the positive 13c excursion together with a series of major global palaeoenviromental changes seems to be more intense than the precambrian cambrian transition events however it is still not clear what kind of mechanism this phenomenon could be attributed to an increase of the ronov ratio and or broecker ratio and other possible models are discussed as the target for future investigations

the evolution of pleistocene climate a time series approach abstract in the later part of the pleistocene variations in global ice volume have been dominated by an approximate 100 000 year cycle analysis of 2 myr long oxygen isotope record from an equatorial pacific core indicates that this is true only for the last 900 000 years prior to this time the amplitude of the 100 000 year cycle is much reduced as is the variance of all oscillations with periods greater than 60 000 years based on results of time series analysis of this 2 myr long record the pleistocene glacial cycles can be divided into three sections 1 the late pleistocene 0 900 kyr b p where the variations in the isotope record are dominated by the 100 000 year cycle 2 the middle pleistocene 900 1450 kyr b p in which low frequency components are not as important as in the later period of the pleistocene and 3 the early pleistocene late pliocene 1450 2000 kyr b p where general reductions of importance at all frequencies is seen as compared to the later intervals recent modeling efforts which describe variations in global ice volume show that the dominant low frequency component observed in the late pleistocene can result from different time constants for the rate of glacial growth and decay in response to variations in the earth s orbital parameters it is hypothesized that during the early pleistocene the rate of growth and decay of glaciers were more similar and that continental erosion by successive glacial advances lowered the land surface in areas of ice cap formation to below sea level when the ice caps became marine based more rapid decay of the ice became possible

late pliocene onset of glaciation ice rafting and diatom stratigraphy of north pacific dsdp cores abstract the revised diatom biostratigraphy for the north pacific allows the timing of ice rafting as recorded in deep sea drilling project cores to be determined significant ice rafting began at the time of the matuyama gauss reversal boundary about 2 48 ma other bio and lithostratigraphic data from the pacific atlantic and arctic oceans and the black sea all indicate that northern hemispherical cooling and the accumulation of continental ice began at 2 4 2 5 ma we interpret all these data to indicate northern hemisphere ice cap formation at that time if so the closing of the isthmus of panama approximately 3 2 m y ago was not the immediate cause of the plio pleistocene glaciations

evolving pliocene pleistocene climate a north pacific perspective abstract siliceous microfauna in sediments from north pacific deep sea drilling project sites record the response of the regional surface and near surface waters to global climate change over the past 3 0 ma during the late pliocene 2 7 3 0 ma the northern subtropical and subpolar pacific experienced warmer climate conditions than those of today the first predominant polar assemblage maximum occurs in the north pacific at 2 45 ma signifying this region s response to the initiation of significant northern hemisphere glaciation north pacific faunal data show that late pliocene 1 8 2 5 ma glacial maxima were only about half to two thirds as severe as those which occurred during the late pleistocene low faunal assemblage variability during a 200 ka interval in the latest pliocene 1 6 1 82 ma in the north pacific indicates minimal variations in the surface water properties and climate conditions most like those which existed just prior to 2 5 ma a distinct change in faunal assemblage registered in sediments from site 580 between 1 2 and 1 2 ma marks the first cooling in the north pacific comparable in intensity to those of the late pleistocene since 1 26 ma high amplitude high frequency variations in the north pacific polar assemblage have continued to occur providing further evidence that the interglacial glacial extremes that characterize the late pleistocene have persisted since this time the frequency distribution of north pacific winter sea surface temperature time series for the late pliocene and early pleistocene includes major concentrations of variance power centered at a frequency corresponding to a 41 ka period with variance dominance of the temperature time series for the last 800 ka shifting to lower frequencies 110 ka period

sedimentology of a subtidal tide dominated sand body in the yellow sea southwest korea abstract odanam satoe a subtidal tide dominated sand body in the yellow sea korea is linear in plan and asymmetrical in cross section it consists of fine to medium grained well sorted subangular sand bedforms consist of high amplitude 1 2 m sandwaves on the lower flanks of the gentler sloping bar surface and medium amplitude 0 5 1 m sandwaves on the sand body trough adjoining the steeper face the bar crest and shallower parts of the gently sloping bar surface bedforms are absent on the relatively steeper bar surface which is characterized by 2 slopes bedform orientation on the gentler slope is oblique by 30 to the bar crest parallel to the sand body crest on the crest itself and opposite to the steeper sand body face in the trough below the steeper slope of the bar bottom current velocity data show that tidal currents are semi rotary with a flood time velocity asymmetry over the gentler slope and ebb time velocity asymmetry over the steeper slope during most of the tidal cycle tidal current flow parallels bar elongation over the steeper slope whereas over the gentler slope tidal current flow is directed at 30 to the bar crest and changes to normal to the crest one hour prior to low tide bedform orientation mapped with side scan sonar shows agreement with these flow directions sand dispersal around the sand body is controlled by time velocity asymmetry and partial rotary flow directions of tidal currents this circulation causes not only a trapezoidal mode of grain dispersal but also westerly migration of the sand body documented from comparative bathymetric surveys in 1964 and 1980

trace element and stable c o and radiogenic sr isotope geochemistry of stromatolitic carbonate rocks of the mesoarchaean pongola supergroup implications for seawater composition abstract the mesoarchaean pongola supergroup hosts one of the oldest well preserved stromatolitic carbonate successions major and trace element geochemistry along with c o and sr isotopic analyses of three stratigraphic sections of stromatolitic carbonate rocks were undertaken in order to infer the depositional environment and to unravel the chemical characteristics of contemporaneous seawater the carbonate rocks consist mainly of dolomite and to a lesser extent ankerite their variable sr concentrations of 95 to 450 mg kg are interpreted as resulting from early to late dolomitization of metastable carbonates aragonite and or high mg calcite facies control and calcitization during meteoric diagenesis 18o values range from 19 6 to 12 0 vpdb and reflect recrystallization of carbonates caused by high water rock interactions during diagenesis and metamorphism a 13c value of 2 5 vpdb was measured in carbonate samples least affected by alteration and we suggest that it approximates the composition of dissolved inorganic carbon in coeval seawater the samples display variable 87sr 86sr isotopic ratios from as low as 0 708 to 0 777 these ratios are considerably higher than those expected in archaean open ocean water masses buffered by hydrothermal interaction with the mantle we interpret the highly radiogenic sr isotopic ratios in some carbonate samples to reflect isotopic exchange with radiogenic sr from siliciclastic volcaniclastic components in the samples and fluids from clay rich layers intercalated with the carbonates the least radiogenic sr isotopic ratio may approximate the mixed isotopic composition of seawater in the epicontinental basin and of riverine freshwater draining the kaapvaal craton the dolomitic carbonate samples show shale normalized rare earth element and yttrium distribution patterns that resemble those of modern ocean water with positive lasn gdsn and ysn anomalies superchondritic y ho ratios a small negative cesn anomaly and depleted light rare earth elements relative to the heavy rare earth elements these anomalies are not as pronounced as expected for an open marine setting which together with the sr isotopic results support a more restricted setting with riverine input and fluctuations in marine ingressions a convex upward shale normalized rare earth element and yttrium pattern is probably a result of several factors including organic matter complexation and element fractionation during estuarine mixing the small negative cesn anomaly may suggest small amounts of free oxygen in shallow waters due to local oxygenic microbial activity

pore fluid evolution distribution and water rock interactions of carbonate cements in red bed sandstone reservoirs in the dongying depression china the compositions distribution and its interaction with rocks of the evolving pore fluids controls the distribution of carbonate cements and reservoir storage spaces the reservoir quality of the red bed sandstone reservoirs in the dongying depression was investigated by an integrated and systematic analysis including carbonate cement petrology mineralogy carbon and oxygen isotope ratios and fluid inclusions the investigation was also facilitated by probing the mineral origins precipitation mechanisms pore fluid evolution and distribution and water rock interaction of carbonate cements and their influences on reservoir quality diagenetic evolving fluids in the interbedded mudstones are the main source for the precipitation of calcite cements that completely fill the intergranular volume cfiv calcite with heavier oxygen and carbon isotopes the ferro carbonate cements in the reservoir sandstone are enriched in lighter carbon and oxygen isotopes in addition to the cations released by the conversion of clay minerals in reservoirs products of organic acid decarboxylation and the associated feldspar dissolution process provide important sources for such carbonate cementation the carbon isotopes of co2 and the oxygen isotopic composition of fluids equilibrated with the cfiv calcite ferro calcite dolomite and ankerite cements indicate that the pore in the red bed reservoirs experienced high salinity fluids which evolved from the early formed interbedded mudstones through organic acid input and to organic acid decarboxylation pore fluids from nearby mudstones migrated from the edge to the centre of sandbodies causing strong calcite cementation along the sandbody boundaries and forming tight cementation zones pore fluids associated with organic co2 and acids and organic acid decarboxylation are mainly distributed in the internal portion of sandbodies causing feldspar dissolution and precipitation of ferro carbonate cements the distribution of pore fluids caused the zonal distribution of carbonate cements in sandbodies during different periods this may be advantageous to preserve the porosity of reservoirs as exemplified by the distribution of high quality reservoirs in the red bed sandbodies

controls on reservoir heterogeneity of tight sand oil reservoirs in upper triassic yanchang formation in longdong area southwest ordos basin china implications for reservoir quality prediction and oil accumulation abstract compared to conventional reservoirs pore structure and diagenetic alterations of unconventional tight sand oil reservoirs are highly heterogeneous the upper triassic yanchang formation is a major tight oil bearing formation in the ordos basin providing an opportunity to study the factors that control reservoir heterogeneity and the heterogeneity of oil accumulation in tight oil sandstones the chang 8 tight oil sandstone in the study area is comprised of fine to medium grained moderately to well sorted lithic arkose and feldspathic litharenite the reservoir quality is extremely heterogeneous due to large heterogeneities in the depositional facies pore structures and diagenetic alterations small throat size is believed to be responsible for the ultra low permeability in tight oil reservoirs most reservoirs with good reservoir quality larger pore throat size lower pore throat radius ratio and well pore connectivity were deposited in high energy environments such as distributary channels and mouth bars for a given depositional facies reservoir quality varies with the bedding structures massive or parallel bedded sandstones are more favorable for the development of porosity and permeability sweet zones for oil charging and accumulation than cross bedded sandstones authigenic chlorite rim cementation and dissolution of unstable detrital grains are two major diagenetic processes that preserve porosity and permeability sweet zones in oil bearing intervals nevertheless chlorite rims cannot effectively preserve porosity permeability when the chlorite content is greater than a threshold value of 7 and compaction played a minor role in porosity destruction in the situation intensive cementation of pore lining chlorites significantly reduces reservoir permeability by obstructing the pore throats and reducing their connectivity stratigraphically sandstones within 1 m from adjacent sandstone mudstone contacts are usually tightly cemented carbonate cement 10 with low porosity and permeability lower than 10 and 0 1 md respectively the carbonate cement most likely originates from external sources probably derived from the surrounding mudstone most late carbonate cements filled the previously dissolved intra feldspar pores and the residual intergranular pores and finally formed the tight reservoirs the petrophysical properties significantly control the fluid flow capability and the oil charging accumulation capability of the chang 8 tight sandstones oil layers usually have oil saturation greater than 40 a pore throat radius of less than 0 4 m is not effective for producible oil to flow and the cut off of porosity and permeability for the net pay are 7 and 0 1 md respectively

subaerial exposure surfaces in a palaeoproterozoic 13c rich dolostone sequence from the pechenga greenstone belt palaeoenvironmental and isotopic implications for the 2330 2060 ma global isotope excursion of 13c 12c abstract this article reports the discovery of numerous subaerial exposure surfaces which occur in the ca 2200 ma kuetsjarvi sedimentary formation ksf from the pechenga greenstone belt ne fennoscandian shield russia the formation was accumulated within an intraplate rift and is composed of fluviatile deltaic siliciclastic deposits and lacustrine dolostones the dolostones are enriched in 13 c 13 c 6 6 to 7 6 v pdb 18 o 16 7 to 21 5 v smow which is in general assigned to a global perturbation of the carbon cycle the lacustrine dolostone unit contains desiccated and in situ brecciated carbonate beds subaerial erosion and dissolution surfaces epikarst surficial silicification silcretes and hot water spring travertines the dissolution surfaces marked by formation of a few centimetre thick vuggy non laminated dolomicrite capped by silicified nodular zone resemble modern calcretes which formed by capillary rise of surface waters per ascensum calcrete following saturation of the regolith zone under arid or semi arid conditions abundant red iron stained superficial dolocrete implies the existence of an o 2 rich atmosphere rezolith black pebbles alveolar septal structures microcodium and other fabrics associated with plant roots and input of terrestrial organic matter which are typical for post cretaceous pedogenic calcretes have not been identified alfa fabrics can be applied to describe dolocretes though rhombic calcite crystals are lacking neither 13 c depletion nor 13 c enrichment has been documented in the dolocrete which suggests no contribution of co 2 derived from soil or from any other c org rich sources enriched in 12 c and apparent lack of biological uptake of 12 c during formation of the dolocrete both petrographic and carbon isotope data do not support earlier assertions that palaeoproterozoic subaerial surface was colonised by microbial mats a few samples have high 18 o values up to 30 despite diagenetic and metamorphic resetting of the oxygen isotope system suggesting evaporation during formation of the superficial dolocrete such documented episodes of subaerial exposure formation of hot water travertines superficial dolocrete and silcrete suggest that there must have been frequent decoupling between the kuetsjarvi depositional system and the bordering sea this imposes an additional restriction on the use of the isotopic composition of the ksf dolostones for reconstruction of the 13 c carb global secular curve

sedimentological and geochemical basin analysis of the paleoproterozoic penrhyn and piling groups of arctic canada abstract paleoproterozoic metasedimentary successions on the western churchill province record a history of regional tectonic events spanning the breakup and amalgamation of supercontinents metasedimentary successions in the northeastern part of the trans hudson orogeny including the penrhyn and piling groups of melville peninsula and baffin island respectively have been understudied with respect to their basin evolution records we present new sedimentological geochemical and geochronological data for the penrhyn and piling groups that record deposition on the rae craton new detrital zircon u pb age data indicate that deposition of the penrhyn group started after 1897 ma and post dates deposition of most of the piling group the new maximum age constraints and stratigraphy of the penrhyn group do not support previous lithostratigraphic correlation with the piling group deposition of the lower piling group likely occurred in an epicontinental basin setting the occurrence of detritus from the meta incognita microcontinent in the upper piling group bravo lake and longstaff bluff formations is interpreted to signal the onset of foreland basin deposition the details of sedimentation in the piling foreland basin provide an additional constraint to discerning the polarity of subduction between the rae craton and meta incognita microcontinent that closed the piling basin we conclude that the piling foreland system shows characteristics of a pro foreland basin implying that the rae craton was the lower plate in the collision with the meta incognita microcontinent finally with new stratigraphic and detrital zircon geochronological data for the penrhyn and piling groups we provide a comparison with other sedimentary successions on the rae craton whose histories were influenced by similar regional tectonic events

late precambrian marbles of unusual carbon isotope composition southeastern british columbia carbon and oxygen isotope analyses were made of both carbonates and graphites from several precambrian metamorphic samples from british columbia the carbon isotope data are unusual in that the 13c values of many marbles are very high up to 9 9 and the most positive values occur in the sillimanite zone rocks the 13c values of graphite are also relatively high and the 13c fractionations between calcite and graphite suggest that 1 the rocks attained and retained carbon isotope equilibrium during metamorphism and 2 the temperature of graphite equilibration in marbles from the sillimanite zone is 650 690 c in agreement with temperatures estimated from mineralogical phase equilibria possible precursor carbonates for the 13c rich marbles in british columbia include 1 precambrian carbonate secreting organisms such as algae that participate in reactions with large kinetic isotope effects 2 carbonates that exchanged carbon isotopes with a large reservoir of organic material prior to metamorphism

is the lomagundi event present on the rae craton a case study from the murmac bay group shortly after the initial rise of atmospheric oxygen in the paleoproterozoic era a major perturbation occurred in the global carbon cycle which is manifested as a long lived positive carbon isotope excursion recorded in 2 22 2 06 ga carbonate rocks known as the lomagundi event beyond its significance for evolving seawater composition this geochemical event can be used as an indirect age marker in paleoproterozoic sedimentary successions documenting further occurrences of this event in other paleoproterozoic carbonate rocks confirms that the event was global and reflects ambient seawater composition this event however has only been documented in two successions in canada despite the ubiquity of paleoproterozoic aged rocks on the canadian shield our study focuses on metacarbonate rocks from the paleoproterozoic aged murmac bay group on the southwestern margin of the rae craton in northern saskatchewan measured 13c values up to 7 8 fall within the range of the lomagundi event but most value

on the lomagundi jatuli carbon isotopic event the evidence from the kalix greenstone belt sweden we report a significant new database on the carbon and oxygen isotopic analyses 233 whole rock and 43 microcored samples obtained from sedimentary dolostones in the kalix greenstone belt from the fennoscandian shield of sweden this characterises the second half of the prominent palaeoproterozoic lomagundi jatuli positive carbon isotope excursion within a 600 m thick succession of alternating volcanic volcaniclastic siliciclastic and dolomitic rocks from greenschist epidote amphibolite metamorphic facies the least altered dolostone samples show a gentle oscillation between 2 and 4 throughout stratigraphy with a second order positive excursion from 4 through 8 and gradually back again to 4 in the c 150 m thick unit in the middle and upper parts of the succession this second order excursion is superimposed on the general relatively rapid 13c decline at the second half of the lomagundi jatuli isotopic event and coincides with the transition from a marine influenced rift to a passive margin setting if the excursion is global it would reveal internal fine structure of the lomagundi jatuli isotopic excursion if not basinal local factors are the main players lithostratigraphic and c isotope correlation between kalix and neighbouring perapohja schist belt successions 40 km apart suggest an incomplete geological record in both successions despite the absence of obvious non depositional unconformities

late holocene climate and environmental changes in kamchatka inferred from the subfossil chironomid record this study presents a reconstruction of the late holocene climate in kamchatka based on chironomid remains from a 332 cm long composite sediment core recovered from dvuyurtochnoe lake two yurts lake tyl in central kamchatka the oldest recovered sediments date to about 4500 cal years bp chironomid head capsules from tyl reflect a rich and diverse fauna an unknown morphotype of tanytarsini tanytarsus type klein was found in the lake sediments our analysis reveals four chironomid assemblage zones reflecting four different climatic periods in the late holocene between 4500 and 4000 cal years bp the chironomid composition indicates a high lake level well oxygenated lake water conditions and close to modern temperatures w13 c from 4000 to 1000 cal years bp two consecutive warm intervals were recorded with the highest reconstructed temperature reaching 16 8 c between 3700 and 2800 cal years bp cooling trend started around 1100 cal years bp led to low temperatures during the last stage of the holocene comparison with other regional studies has shown that termination of cooling at the beginning of late holocene is relatively synchronous in central kamchatka south kurile bering and japanese islands and take place around 3700 cal years bp from ca 3700 cal years bp to the last millennium a newly strengthened climate continentality accompanied by general warming trend with minor cool excursions led to apparent spatial heterogeneity of climatic patterns in the region some timing differences in climatic changes reconstructed from chironomid record of tyl sediments and late holocene events reconstructed from other sites and other proxies might be linked to differences in local forcing mechanisms or caused by the different degree of dating precision the different temporal resolution and the different sensitive responses of climate proxies to the climate variations further high resolution stratigraphic studies in this region are needed to understand the spatially complex pattern of climate change in holocene in kamchatka and the surrounding region

kolosjoki sedimentary formation a record in the aftermath of the paleoproterozoic global positive δ13c excursion in sedimentary carbonates abstract the kolosjoki sedimentary formation of the pechenga greenstone belt north eastern fennoscandia records the aftermath of the paleoproterozoic global positive 13 c excursion in sedimentary carbonates the lomagundi jatuli isotope excursion the goals of this research were to provide detailed new data on the 13 c trend in the kolosjoki sedimentary formation and generate a secular 13 c curve for the time period immediately succeeding the lomagundi jatuli isotope excursion for these purposes sedimentary carbonate samples from two new drillcores representing the kolosjoki sedimentary formation were collected in total 88 whole rock samples and 67 micro drilled subsamples ca 1 3 mg were analyzed for the isotope composition of c and o the whole rock elemental abundances and for the composition of the acid soluble fraction the kolosjoki carbonate rocks are dolostone or calcitic dolostone mg ca 0 50 0 67 with minor limestone mg ca 0 04 0 06 only weak correlation was observed between the mn sr ratios and the 13 c and 18 o values and the carbonate samples have likely retained their near primary 13 c values the sedimentary carbonate rocks show first low 13 c values at 2 to 1 and then a subtle upward increasing 13 c trend from ca 1 to 3 the increasing 13 c trend is interpreted to record a recovery from a 13 c minimum following the lomagundi jatuli isotope excursion

petrography and geochemistry of carbonate rocks of the paleoproterozoic zaonega formation russia documentation of 13c depleted non primary calcite the norwegian research council grant 191530 v30 to v a melezhik fully funded the work of aec vam and al atb was supported by nerc grant ne g00398x 1 to aef and arp we are grateful for sample preparation and analyses to all the personnel at ngu lab we appreciate the work on carbon and oxygen isotope analyses by julie dougans and chris taylor bojan otonicar organized and helped with the cl work at the karst research institute at postojna arrangement of toc ic and tc analyses at university of munster is acknowledged to harald strauss

geochemistry of precambrian carbonates iv early paleoproterozoic 2 25 0 25 ga seawater in an effort to narrow down the first and second order variations in isotopic composition of the early paleoproterozoic 2 25 0 25 ga seawater we report a comprehensive study of mineralogy chemistry and isotopic composition of the malmani dolomite transvaal supergroup south africa duck creek dolomite wyloo group australia and bruce limestone member of the espanola formation huronian supergroup canada based on trace element data their diagenetic rank increases in the order duck creek bruce malmani the interpolation of alteration trends to best values yields an estimate of 0 70550 for 87sr86sr comparable to our previously published value of 0 70496 for 13c the measured range of 0 1 5 pdb is similar to that observed for phanerozoic marine carbonates in contrast the best 18o value for dolostones is 5 pdb depleted in 18o relative to phanerozoic counterparts but comparable to the estimates obtained by similar approach for archean facies the isotope geochemistry and mineralogy of bruce limestone member is consistent with the proposition that the sequence may have been deposited in a lacustrine environment possibly related to the recession of the brace glaciers if such interpretation proves unacceptable from a sedimentological standpoint the origin of the unusual isotopic signatures must be sought despite the above trace element interpretation in as yet unspecified post depositional alteration phenomena in contrast to phanerozoic carbonates the early paleoproterozoic as well as the previously described archean counterparts are enriched in mn and fe

depositional patterns of sand ridges in tide dominated shallow water environments yellow sea coast and south sea of korea abstract the continental shelf of the yellow sea and the korean south sea is a tide dominated shelf a number of sand ridges occur in this area which form bathymetric highs surveyed were one large sand ridge jangan satoe along the western yellow sea coast and a group of mid shelf sand ridges in the south sea to delineate their depositional pattern and probable origin in tide dominated shallow water environments analyses of sediment samples side scan sonographs and seismic profiles reveal that these ridges show regionally different characteristics in morphology bedforms and sediment the sand ridge in the yellow sea shows a composite form of various bedforms including sand waves and megaripples this ridge is interpreted to be in an accretional active stage maintained by strong tidal currents in contrast the sand ridges on the mid shelf of the south sea show rounded single forms without bedforms on them they are interpreted to represent moribund type sand ridges in the shelf environment which were formed near the shoreline during the holocene sea level transgression these ridges developed off the paleo seomjin river during a period of a stillstand or slow sea level rise approximately between 10 000 and 7000 yrs b p

large 18o and 13c depletions in greenschist facies carbonate rocks western arizona strongly deformed greenschist facies carbonate rocks in western arizona exhibit large 18 o and 13 c depletions relative to unmetamorphosed correlative rocks in northeastern arizona unmetamorphosed permian kaibab formation carbonates on the colorado plateau yield 13 c values of 1 to 5 and 18 o values of 28 to 37 in contrast greenschist facies kaibab formation in the little harquahala and granite wash mountains yields 13 c values of 6 to 4 and 18 o values of 9 to 24 the magnitude of the observed 13 c and 18 o depletions cannot be explained by decarbonation reactions and requires extensive exchange with low 13 c and 18 o fluids the 13 c depletions may reflect isotopic exchange with lower 13 c carbonate in the underlying paleozoic section and exchange with co 2 derived from oxidation of methane via reaction with hematite or sulfate in interbedded rocks these data demonstrate that large 13 c and 18 o depletions can occur in strongly deformed terranes during very low grade metamorphism depletions in 13 c and 18 o observed in some high grade metamorphic terranes may be inherited from much lower metamorphic grades

isotopic paleoceanography of the caribbean and east pacific role of panama uplift in late neogene time comparisons of carbon isotopic data on benthic foraminifera from deep sea drilling project sites 502 western caribbean and 503 eastern pacific indicate that the difference between the atlantic and the pacific in the per mil enrichment in carbon 13 of total dissolved carbon dioxide increased about 6 million years ago and again 3 million years ago when the difference reached the modern level 1 per mil comparisons of planktonic foraminiferal oxygen isotopic data for the caribbean and the pacific suggest that the salinity of caribbean surface waters began increasing 4 million years ago possibly in response to shoaling of the panama isthmus these results suggest that modern circulation patterns in the caribbean and eastern pacific developed by 3 million years ago in concert with changing tectonic climatic and biogeographic patterns

diagenetic constraints on the heterogeneity of tight sandstone reservoirs a case study on the upper triassic xujiahe formation in the sichuan basin southwest china abstract heterogeneity is an essential feature of tight sandstones because it is directly related to reservoir quality the upper triassic xujiahe formation in the sichuan basin was used as a case study to analyse the diagenetic constraints on the heterogeneity of tight sandstone reservoirs the three main diagenetic processes of interest are mechanical compaction cementation and dissolution a dissolution facies quartz cement facies and carbonate cement facies present sequentially from the centre to the margin of sand bodies abundant feldspars and rock fragments were dissolved to form secondary porosity or filled by carbonate cement authigenic chlorite coatings generated from eogenesis to the deep burial stage are thickest in high porosity samples the 13 c of carbonate cement ranges from 10 56 to 1 15 pdb suggesting multiple sources of carbon including carbonate fragments early inorganic carbonate cement and organically derived co 2 based on 18 o carbonate cementation occurred from 33 c to 110 c microthermometric data of aqueous inclusions indicate that quartz cement precipitated at a temperature range of 120 c 140 c a summary model of the diagenetic constraints on the heterogeneity of sandstones was constructed the spatial distribution of digenetic facies is controlled by differences in fluid flow velocity and ph fluids especially hydrocarbons migrated preferentially within the centre of sand bodies and caused dissolution dissolution generated secondary porosity and provided materials for authigenic mineral precipitation carbonate fragments were better preserved and superimposed with later carbonate cement along the sandstone mudstone boundary quartz overgrowths formed after carbonate cementation and developed in the transition zone between the intervals of carbonate cementation and dissolution consequently the reservoir quality of the xujiahe sandstones decreases gradually moving from the centre to the margin of the sand bodies

documenting basin scale geometry and provenance through detrital geochemical data lessons from the neoproterozoic to ordovician lesser greater and tethyan himalayan strata of bhutan abstract detrital zircon dz ages augmented with end 0 and 13 c isotopic values from 18 new and 22 published samples collected from lesser himalayan lh greater himalayan gh and tethyan himalayan th rocks in bhutan support deposition of 7 km of sedimentary rock in late cambrian ordovician time and provide a stratigraphic framework for the pre collisional indian margin youngest gh dz grains become younger upsection from 900 ma to 477 ma youngest dz grains in th samples are 490 460 ma both the lh jaishidanda formation fm and the lh baxa group overlie paleoproterozoic lh rocks the jaishidanda fm exhibits distinct populations of youngest dz peaks 475 550 ma and 800 1000 ma the baxa group manas pangsari and phuntsholing formations contains youngest dz peaks at both 500 525 ma and 0 9 1 0 ga however most samples from the baxa group in western bhutan contain no grains younger than 1 8 ga samples from the lh paro fm which sits directly under the mct in western bhutan have youngest dz peaks at 0 5 0 8 1 0 1 7 1 8 ga end values generally match dz spectra with samples that contain old youngest grain populations corresponding to more negative end signatures the paro fm is an exception where end 0 values from quartzite samples are quite negative 19 to 24 whereas the end 0 values from interbedded schist contain younger detritus 12 to 17 13 c values from the jaishidanda paro and manas formations have 13 c values 1 8 to 6 suggestive of deposition over late neoproterozoic to ordovician time 13 c values from the pangsari fm vary from 2 8 to 1 8 compatible with deposition in the early to middle neoproterozoic the young latest cambrian ordovician grains preserved in th gh and lh rocks suggest that the late cambrian ordovician orogeny documented in gh rocks throughout the orogen served as a significant sediment source in bhutan

high δ13c neoproterozoic carbonate rocks in western north america 13 c rich marbles from the neoproterozoic mccoy creek group having 13 c values up to 12 have been discovered at three separate localities in eastern nevada and western utah detailed isotopic profiles measured across individual amphibolite facies metre thick marble layers have extremely uniform 13 c 12 c ratios which probably represent depositional values because individual carbonate horizons have distinctly different but abnormally high values of 13 c the discovery permits the use of 13 c 12 c ratios for stratigraphic correlation within the generally nonfossiliferous neoproterozoic sedimentary sequences of western north america even where these rocks have been strongly metamorphosed the anomalous values add to a growing array of data from western north america and elsewhere delineating a large and geographically widespread neoproterozoic carbon isotope anomaly

general geology and evolutionary history of the early proterozoic polmak pasvik pechenga imandra varzuga ust ponoy greenstone belt in the northeastern baltic shield abstract the early proterozoic polmak pasvik pechenga imandra varzuga ust ponoy greenstone belt is situated in the northeastern part of the baltic shield and is discontinuously developed over a length of ca 1000 km it comprises five main zones which are separated by longitudinal and a number of transverse syndepositional faults each zone contains a number of lithostratigraphic units at the rank of groups that are subdivided into several sedimentary and volcanic formations with a total thickness over 16 000 m the sequence comprises a series of sedimentary volcanic rhythms usually separated by stratigraphic breaks marked by palaeo weathering the groups are separated by major disconformities which may mark record rift inversion or orogenic episodes at least seven distinctive lithostratigraphic markers occur in the belt including two komatiitic volcanic series separated by immature conglomerates two red coloured proto evaporitic formations separated by the alkaline volcanics and two different black shale formations perhaps the main characteristic of the belt is the apparently long history of sedimentary volcanic development at the same site spanning a time period of 2500 to 1800 ma a three stage rift development model is considered 1 an intracontinental rift stage 2500 2100 ma separated by the major inversion 2400 2330 ma and comparable with present day afar triangle and east african rifts 2 a transitional from intracontinental to to intercontinental rift stage 2100 1970 ma with possible short lived spreading about 1990 1970 ma 3 a collision related intercontinental rift stage 1970 1800 ma followed by the svecofenian orogeny 1800 1700 ma the observed distribution of platinum group elements pge mineralization is related to layered gabbro norite complexes fedorova and panskie tundry gora general skaya intrusions dated at 2470 ma which are apparently co magmatic and coeval with the first komatiitic volcanic series seidorechka formation found in the eastern part of the belt only the major chromite occurences are connected with a layered gabbro norite intrusion imandra lopoloth which is co magmatic and coeval between 2440 2330 ma with the second komatiitic volcanic series rusinga polisarka akhmalahti and malbekk formations the ni cu deposits of the belt are connected with a differentiated gabbro werhlite complex which is co magmatic and coeval ca 1970 ma with the specific fe and ti rich ferropicrites with komatiitic affinities

carbonate deposition in the palaeoproterozoic onega basin from fennoscandia a spotlight on the transition from the lomagundi jatuli to shunga events abstract several deep drillholes were made in the onega palaeobasin by the fennoscandian arctic russia drilling early earth project far deep of the international continental scientific drilling program icdp these provided fresh core material documenting the lomagundi jatuli isotopic event ljie its termination and the start of the shunga event she of an enhanced accumulation of organic matter the cored section represents the most complete known record of the end of the ljie the late phase of the ljie recorded in far deep core 11a is represented by the upper part of the tulomozero formation tf a 300 m thick unit composed of variegated dolostones siltstones and shales accumulated under oxic conditions on a shallow water carbonate platform the tf hosts the earliest known thick formations of halite and massive anhydrite low temperature greenschist facies metamorphism caused partial recrystallisation of the rocks however a primary carbonate phase the dolomite exhibits a negligible degree of post depositional alteration of the carbon isotope system the dataset of 46 bulk carbonate analyses of carbon and oxygen isotopes yielded 13 c carb ranging between 6 8 and 11 8 and revealed a positive excursion from 8 to 11 8 followed by a decline to 8 towards the top of the 300 m thick succession the cored part of the overlying zaonega formation zf recovered in holes 12ab and 13a is an 800 m thick unit composed of mixed siliciclastic carbonate facies with numerous mafic lava flows and tuff beds intruded by gabbro sills the formation represents an unprecedented episode of enhanced accumulation of organic rich rocks and preserves the earliest known supergiant petrified oilfield all typifying the she the sedimentological petrographic geochemical and c and o isotopic study of over 800 m of core throughout the zf suggests that the initial carbonate deposition occurred in a lacustrine environment then rapidly proceeding through a lagoonal setting to a rifted deepwater shelf and finally to a carbonate platform both the deepwater shelf and the platformal settings are marked by organic rich environments the primary dolomite was potentially exposed to syn and post depositional hydrothermal metasomatic alterations organic matter diagenesis metamorphic mineral reactions co 2 degassing and finally a low temperature post metamorphic calcitisation resulting in overall large fluctuations of 13 c carb between 22 and 8 the dataset of over 413 bulk carbonate analyses of carbon and oxygen isotopes screened petrographically and geochemically against post depositional alteration revealed 28 least altered samples within three stratigraphic intervals suggesting multiple positive and negative 13 c carb excursions throughout over 1000 m of stratigraphy a shift from 5 to 9 followed by a drop to near zero values marks the lower part of the zf a 13 c carb decline from 8 to below zero in the middle and upper part of the zf defines the end of the ljie a subsequent prominent negative excursion down to 6 does not show convincing isotopic evidence for influence of methanogenesis and hence appears to be of primary depositional origin an erratic positive excursion in the uppermost part of the drilled section indicates return of 13 c carb to a near normal marine value

tracking lateral δ13ccarb variation in the paleoproterozoic pechenga greenstone belt the north eastern fennoscandian shield abstract the kuetsjarvi sedimentary formation ksf records the global paleoproterozoic ca 2200 2100 ma positive 13 c excursion of sedimentary carbonates this event is here called as the lomagundi jatuli isotopic excursion in this study lateral 13 c carb variation in the ksf and local basinal factors amplifying global 13 c carb value were investigated and a secular 13 c curve for the ksf was constructed sedimentary carbonate samples from a new drillcore drillcore 5a from the ksf were analysed for 13 c 18 o and selected major and trace elements the 13 c values of the samples vary from 5 to 8 vpdb and the 18 o values from 18 to 10 vpdb most of the samples have retained their primary c isotopic composition as they do not show correlation between the mn sr ratios and the 13 c and 18 o values the new results were compared to those previously obtained from another drillcore drillcore x from the ksf ca 25 km along strike from drillcore 5a both cores show a similar kind of generally upward decreasing trend in 13 c excluding some negative and positive spikes in drillcore x and samples close to a contact with a fe picrite dyke in drillcore 5a a secular 13 c curve of the ksf was constructed based on the least altered 13 c data from the cores 5a and x the secular 13 c curve of the ksf may represent the latest part of the lomagundi jatuli isotopic excursion

fractionation of carbon and oxygen isotopes in 13c rich palaeoproterozoic dolostones in the transition from medium grade to high grade greenschist facies a case study from the kola superdeep drillhole samples from the kola superdeep drillhole 12 262 m a deep drillhole 1060 m and from the surface seaprated by only around 10 km provided a unique opportunity for direct tracing of 13 c and 18 o changes through a low to high grade greenschist facies transition within impure 13 c rich palaeoproterozoic dolostones the least altered dolostones have 13 c of 9 and 18 o of 22 the metamorphic transition is expressed by dolomite calcite 1 quartz k feldspar tremolite calcite 2 dolomite calcite 1 and defined by 13 c depletion of calcite 2 c 3 0 calcite 1 1 0 2 0 and dolomite 18 o shows a considerable resetting in all carbonate components by around 6 caused by a rayleigh distillation process coupled with isotopic exchange between the carbonates and fluids with an external source of oxygen the retrograde alteration is expressed by the formation of quartz chlorite veinlets within tectonically bound zones of brecciated and sheared dolostones the maximum 18 o depletion in dolomite 9 and calcite 1 c 4 were probably controlled by infiltration into permeable zones of external fluids associated with retrograde alteration 13 c remains largely unaffected

fluid rock interaction and its effects on the upper triassic tight sandstones in the sichuan basin china insights from petrographic and geochemical study of carbonate cements abstract tight sandstone gas is an important unconventional hydrocarbon resource but its exploration is made difficult by the compactness and heterogeneity of the sandstone fluid rock interaction and subsequent cementation play key roles in developing this heterogeneity we conducted a petrographic trace element and isotopic study of the upper triassic xujiahe sandstones from the sichuan basin to investigate fluid rock interactions and associated diagenetic effects carbonate fragments and cements are widespread in these sandstones and are the primary control on the nature of the xujiahe sandstone reservoirs the carbonate cements primarily comprise of calcite and are typically distributed around the margins of sandstone bodies and along fine grained beds carbonate minerals in the centre or at the margin of sandstone units have heavy 13ccarb values of ca 0 whereas 13ccarb is markedly depleted in the transition zone with values as low as 10 reflecting a contribution from organic carbon manganese strontium and barium generally become enriched in the carbonate cements with diagenesis and their concentrations correlate with porosity and 13ccarb redox sensitive mn and fluid mobile sr and ba were analysed to reveal the diagenetic processes and environment of carbonate precipitation we propose that fluids flowed preferentially along the central parts of sandstone units associated with mineral dissolution whereas cementations took place near the margins of the units fluid rock interaction especially that involving late hydrocarbon related fluids greatly enhances the heterogeneity of sandstones and can potentially create high quality reservoirs in the central parts of tight sandstone units

fluid heterogeneity during granulite facies metamorphism in the adirondacks stable isotope evidence the preservation of premetamorphic whole rock oxygen isotope ratios in adirondack metasediments shows that neither these rocks nor adjacent anorthosites and gneisses have been penetrated by large amounts of externally derived hot co2 h2o fluids during granulite facies metamorphism this conclusion is supported by calculations of the effect of fluid volatilization and exchange and is also independently supported by petrologic and phase equilibria considerations the data suggest that these rocks were not an open system during metamorphism that fluid rock ratios were in many instances between 0 0 and 0 1 that externally derived fluids as well as fluids derived by metamorphic volatilization rose along localized channels and were not pervasive and thus that no single generalization can be applied to metamorphic fluid conditions in the adirondacks

geochemistry of precambrian carbonates v late paleoproterozoic seawater in an effort to obtain better constrained data for the first and second order variations in the isotopic composition of late paleoproterozoic 1 8 0 2 ga seawater we report a study of mineralogy chemistry and isotopic composition of the coronation supergroup 1 9 ga nwt canada and the mcarthur group 1 65 ga nt australia petrologically both carbonate sequences are mostly dolostones the mcarthur population however contains more abundant textural features that attest to the former presence of sulfates and halite and the facies investigated herein probably represent ancient equivalents of modern evaporitic sabkhas and lacustrine playa lakes this is reflected in 18 o enrichment up to 2 9 pdb and high mn fe and sr concentrations nonetheless the available 18 o data indicate that the best estimate for the archean to late paleoproterozoic limestones is about 7 pdb with dolostones some 3 2 heavier the observed 18 o doiomitc calcite is thus within the range of the proposed fractionation factor for a cogenetic mineral pair this together with the consistency of isotopic patterns for sedimentological facies over almost 2 billion years from the late paleoproterozoic to the present suggest that dolomitization was an early diagenetic event and that the 18 o depletion of the archean to late paleoproterozoic carbonates is not an artefact ofpost depositional alteration the 13 c although within the range of other precambrian and phanerozoic carbonates indicates a possible secular evolution from 0 2 pdb at 1 9 ga ago to 1 1 5 at 1 65 ga ago the secular evolution for reflects the 87 sr increase from 0 7031 0 0008 at 3 5 0 1 ga ago through 0 7025 0 0015 at 2 8 0 2 ga 0 7033 at 2 5 ga 0 7050 at 2 25 0 25 ga 0 7047 at 1 91 to 0 706 at 1 65 ga ago

sand waves and sediment transport around the end of a tidal sand bank two detailed surveys have been made of the north western end of the haisborough sand off the norfolk coast using echosounder 3 5 khz reflection profiler and side scan sonar asymmetrical sand waves indicate north westerly sand movement on the southern side and south easterly sand movement on the steeper northern side of the bank secondary superimposed megaripples which are probably better indicators of sediment movement give evidence of a cross bank component between the north westerly and south easterly facing sand waves on the tip of the bank there is a zone of symmetrical sand waves these are usually taken to indicate zero net transport but in this case the oblique orientation of megaripples in their troughs indicates transport parallel to the sand wave crests this suggests the route by which sand travels around the end of the bank to form a roughly closed circulation sediment textural parameters support the notion that sand is winnowed from the foot of the bank on both sides and is transported to the middle with an overall net transport from the south to the north analysis of charts dating back to 1886 shows that the bank is stable within the error limits of position fixing though that could allow more than 0 25 km shift to the north east in 100 years to pass undetected a box model is drawn up for the estimated sediment fluxes around the end of the bank and implications for residence times and circulation rates are drawn from it