shelf to basin temperate skeletal carbonate sediments three kings plateau new zealand abstract three kings plateau is 10 000 km2 in area less than 500 m deep and includes the mainland shelf and submarine ridges and banks centered on three kings islands 34 s off northernmost new zealand the plateau receives little input of terrigenous sediment and lies in a zone of active nutrient upwelling and vigorous wind wave and tidal current activity as a consequence surficial sediments on and about the margins of the plateau are dominantly pure skeletal carbonate sands and gravels which lack mud to depths of 1500 to 3000 m plateau top sediments include a bryozoan calcareous red algal barnacle lithofacies on coarse and rocky substrates and a bivalve bryozoan lithofacies associated with particulate bottoms plateau edge sediments include a bryozoan ahermatypic co al serpulid lithofacies in areas of rugged topography and a bivalve gastropod lithofacies on sandy substrates both grading down slope into a planktic foraminiferal lithofacies by 1500 to 3000 m depth depending on locality the carbonates are dominated by a high mg calcite and or low mg calcite mineralogy with only subordinate aragonite active skeletal production is presently restricted to only about 10 percent of the plateau area principally in regions of rough sea floor topography on submarine cliff faces on bank tops and in in shore portions of the mainland shelf about these areas modern carbonates occur down to depths of 50 to 200 m below which the sediments are mainly relict and include rare glauconite redeposition of plateau derived skeletal carbonates into surrounding basins was especially active during the last glacial low sea level s it is inferred that this is the ultimate fate of the bulk of the shallow marine sediment and that the plateau top itself preserves only a thin laterally discontinuous mixed age and highly condensed sequence of quaternary temperate skeletal carbonates

stable isotope geochemistry and phase equilibria of coesite bearing whiteschists dora maira massif western alps peak metamorphic temperatures for the coesite pyrope bearing whiteschists from the dora maira massif western alps were determined with oxygen isotope thermometry the 18o smow values of the quartz after coesite 18o 8 1 to 8 6 n 6 phengite 6 2 to 6 4 n 3 kyanite 6 1 n 2 garnet 5 5 to 5 8 n 9 ellenbergerite 6 3 n 1 and rutile 3 3 to 3 6 n 3 reflect isotopic equilibrium temperature estimates based on quartz garnet rutile fractionation are 700 750 c minimum pressures are 31 32 kb based on the pressure sensitive reaction pyrope coesite kyanite enstatite in order to stabilize pyrope and coesite by the temperature sensitive dehydration reaction talc kyanite pyrope coesite h2o the a h2o must be reduced to 0 4 0 75 at 700 750 c the reduced a h2o cannot be due to dilution by co2 as pyrope is not stable at x co2 0 02 t 750 c p 30 kb in the absence of a more exotic fluid diluent e g ch4 or n2 a melt phase is required granite solidus temperatures are 680 c 30 kb at a h2o 1 0 and are calculated to be 70 c higher at a h2o 0 7 consistent with this hypothesis kyanite jadeite quartz bands may represent a relict melt phase peak p t f h2o estimates for the whiteschist are 34 2 kb 700 750 c and 0 4 0 75 the oxygen isotope fractionation between quartz 18o 11 6 and garnet 18o 8 7 in the surrounding orthognesiss is identical to that in the coesitebearing unit suggesting that the two units shared a common final metamorphic history hydrogen isotope measurements were made on primary talc and phengite d smow 27 to 32 on secondary talc and chlorite rite after pyrope d 39 to 44 and on the surrounding biotite d 64 and phengite d 44 gneiss all phases appear to be in nearequilibrium the very high d values for the primary hydrous phases is consistent with an initial oceanicderived connate fluid source the fluid source for the retrograde talc chlorite after pyrope may be fluids evolved locally during retrograde melt crystallization the similar d but dissimilar 18o values of the coesite bearing whiteschists and hosting orthogneiss suggest that the two were in hydrogen isotope equilibrium but not oxygen isotope equilibrium the unusual hydrogen and oxygen isotope compositions of the coesite bearing unit can be explained as the result of metasomatism from slab derived fluids at depth

evaluating zr rb ratio from xrf scanning as an indicator of grain size variations of glaciomarine sediments in the southern ocean the ln zr rb count ratio derived from x ray fluorescence xrf core scanning holds potential as a high resolution tracer for grain size variations of glaciomarine sediments to evaluate this appro

r selected benthic foraminifera with associated bacterial colonies in upper pleistocene sediments of the ross sea antarctica implications for calcium carbonate preservation investigations on foraminifera from upper pleistocene holocene sediments cored in the continental slope of the western ross sea 2383 m water depth revealed that the record of calcareous assemblages was restricted to a limited time interval approximately 6 kyr and characterized by a dominance of phytodetritus exploiting taxa such as alabaminella weddellensis and epistominella exigua rod shaped calcified fossil bacteria infest the partially dissolved calcareous foraminiferal surfaces either as clusters or as isolated cells suggesting that significant changes from underto oversaturated conditions with respect to calcium carbonate in the chemistry of the seawater developed before the final burial of the foraminiferal tests we postulate that bacterial activity on a microenvironmental scale interface and pore water in the sea floor could influence pore water conditions in such a way as to preserve carbonate in deep marine regions where environmental conditions usually prevent the establishment of carbonate secreting communities 1999 elsevier science b v all rights reserved

source rock heterogeneity and migrated hydrocarbons in the triassic shublik formation and their implication for unconventional resource evaluation in arctic alaska abstract this organic geochemical study of the triassic shublik formation aims to investigate source rock heterogeneity facies variation and source and maturity of migrated hydrocarbons in the tenneco phoenix 1 well ocs y 0338 drilled in offshore arctic alaska in 1986 recovered continuous core is nearly 90 m thick continuous section throughout the entire shublik formation guided by previously published analyses of the phoenix 1 core by robison et al 1996 this study provides the most detailed core based analysis of the shublik formation to date analysis of biomarkers and diamondoids combined with rock eval pyrolysis results indicates evidence of mature migrated hydrocarbons that may have affected previous interpretations of organic matter type and maturity of this core despite the variable lithology four identified source rock intervals contain oil prone type i kerogens with maturity ranging from immature to marginally mature biomarker analysis indicates the presence of two organic facies deposited under anoxic clay poor and suboxic clay rich environments that likely generated genetically distinct oils

fluids in granulite facies metamorphism a comparative oxygen isotope study on the south india and adirondack high grade terrains oxygen isotope compositions have been determined for samples from the south india archean to pro terozoic and northwest adirondack late proterozoic high grade terrains delta 18 o values of charnockites and related orthogneiss protolith from the prograde amphibolite facies to granulite facies transition zone in south india range from 5 9 to 8 4 charnockites khondalites sillimanite gneisses and retrogressed gneisses from the interior of the granulite facies terrain average 2 higher than orthogneisses of the transition zone individual minerals in incipient charnockitic net veins as at kabbaldurga karnataka and ponmudi kerala have delta 18 o identical to minerals of their non charnockitic host rocks quartz delta 18 o values of the northwestern adirondack granites and gneisses average 3 4 higher than those from the indian rocks the two terrains are thus isotopically distinct which may reflect differences in premetamorphic history or different degrees of communication with external

a geochemical reconstruction of oil generation in the barrow sub basin of western australia abstract a suite of crude oils and petroleum source rock extracts from the barrow sub basin of western australia have been analysed for biological marker compounds by capillary gc ms and for volatile hydrocarbons by whole oil capillary gc these analyses were used to calculate values for twenty three biomarker parameters in order to assess aspects of source type maturity migration and biodegradation of the hydrocarbons the crude oils had a source in the upper jurassic dingo claystone formation these hydrocarbons accumulated in the reservoir sands and in some cases were biodegraded several accumulation and biodegradation episodes have been recognised while the basin continued to subside which resulted in a suite of oils showing marked differences in composition

palynological evidence for the latest oligocene early miocene paleoelevation estimate in the lunpola basin central tibet uplift of the tibetan plateau is ultimately driven by the cenozoic collision between the indian and eurasian plates and their continued convergence one approach for studying the tibetan plateau uplift is to verify the paleoelevation changes from collision to present day this is important for understanding both the tectonics and the climatic effects the new high resolution palynological record of the uppermost oligocene to the lowest miocene strata from the lunpola basin indicates that the vegetation types during the latest oligocene earliest miocene were dominated by mixed coniferous broadleaved forests being different from the modern steppe vegetation by using the coexistence approach to the fossil pollen records after calibration the effects of temperature difference and the lapse rate a maximum paleoelevation of 3190 100 m asl was estimated in the lunpola basin in the latest oligocene earliest miocene being 1500 to 2000 m lower compared with the previous oxygen isotope paleoelevation in the same region

carbonates within a pleistocene glaciomarine succession yakataga formation middleton island alaska uplifted during the 1964 alaskan earthquake extensive intertidal flats around middleton island expose 1300 m of late cenozoic early pleistocene yakataga formation glaciomarine sediments these outcrops provide a unique window intooutershelfandupperslopestratathatareotherwiseburiedwithinthesoutheast alaska continental shelf prism the rocks consist of five principal facies in descending order of thickness i extensive pebbly mudstone diamictite containing sparse marine fossils ii proglacial submarine channel conglomerates iii burrowedmudstoneswithdiscretedropstonelayers iv boulderpavements whose upper surfaces are truncated faceted and striated by ice and v carbonates rich in molluscs bryozoans and brachiopods the carbonates are decimetre scale in thickness typically channellized conglomeratic event beds interpreted as resedimented deposits on the palaeoshelf edge and upper slope biogenic components originated in a moderately shallow ca 80 m relatively sediment free mesotrophic sub photicsetting thesecomponentsareamixture of parautochthonous large pectenids or smaller brachiopods with locally important serpulid worm tubes and robust gastropods augmented by sand size bryozoan and echinoderm fragments ice rafted debris is present throughout these cold water carbonates that are thought to have formed during glacial periods of lowered sea level that allowed coastal ice margins to advance near to the shelf edge such carbonates were then stranded during subsequent sea level rise productivity was enabled by attenuation of terrigenous mud deposition during these cold periods via reduced sedimentation together with active wave and tidal current winnowing near the ice front redeposition was the result of intense storms and possibly tsunamis these sub arctic mixed siliciclasticcarbonate sediments are an end member of the phanerozoic global carbonate depositional realm whose skeletal attributes first appeared during late palaeozoic southern hemisphere deglaciation

bioclastic carbonate sediments on the southwestern svalbard shelf the poleward continuation of one of the largest known arctic carbonate factories the western spitsbergenbank of the barents sea has been surveyed along the narrow sw svalbard shelf on this shelf formation of cold water carbonate sediments occurs under glaciomarine environmental conditions mya truncata and hiatella arctica colonized a soft glacio marine diamicton 3000 6000 years after the final retreat of the icedome from the sw svalbard shelf since 2600 yr b p an increase of along shelf bottom currents washed out the fine terrigenous deposits leaving behind a shelly lag deposit and winnowed boulders on a morainic shelf topography the most favourable depth interval promoting the establishment of an amalgamated bioclastic blanket is located in 50 80 m water depth in this interval strong bottom currents prevent sedimentation thus facilitating colonisation of filter feeding benthic communities dominated by balanus balanus and chlamys islandica additional skeletal components are supplied by echinoderms bryozoans serpulids brachiopods and gastropods in shallower water depths carbonate production is hampered by intense iceberg scouring and release of ice rafted debris from the still glaciated hinterland of svalbard in deeper water 80 m olive grey muds with dispersed pebbles rich in benthic foraminiferans clinocardium ciliatum and taxodont bivalves are present on all surveyed shelf banks the deepest unit is a blue mud in water depths 120 m with benthic foraminiferans taxodont bivalves and sipunculids compared to spitsbergenbank carbonate production is much more restricted and impoverished on the sw svalbard shelf but is still an instructive modern example for the formation of skeletal carbonates resting on tillites in the geological record

sedimentology and organic properties of lower tertiary lacustrine source rocks lunpola basin central tibetan plateau implications for hydrocarbon potential abstract the tertiary lacustrine niubao formation is well exposed in the middle western part of the lunpola basin central tibetan plateau where crude oil was once discovered during drilling campaigns sedimentological organic petrographic and geochemical work was performed on the upper and middle members of this formation in order to investigate its hydrocarbon source rock potential sedimentological analyses indicate that both members were deposited in relatively deep lake conditions away from the influence of big stream system with the upper niubao formation unf having higher sand content the two members contain abundant high quality type i kerogen derived mainly from plankton algae and bacteria compared with samples of the middle niubao formation mnf unf samples also contain more type ii and type iii kerogens of terrestrial origin biomarkers of source rock extracts suggest that a long standing anoxic stratified and saline ancient lake occupid the basin during deposition of the two members which was conducive to the preservation of organic matter however higher gammacerane content and the presence of carotane in mnf samples imply a more saline lake condition rock eval t max and biomarker parameters reveal marginal maturity and immaturity for samples from mnf and unf respectively therefore mnf has better source rocks of higher maturity might be the main hydrocarbon generating member of the basin similar diagnostic biomarkers and biomarker parameters reported in the crude oil also imply its affiliation with the source rocks of mnf

timing and pathways of east antarctic ice sheet retreat abstract a lack of reliable chronology often leaves antarctic ice sheet reconstructions incomplete despite being the most heavily investigated region of the antarctic continental shelf the post last glacial maximum lgm record of marine based ice sheet dynamics in the ross sea has remained largely elusive and at odds with fringing terrestrial records of ice sheet decay issues with radiocarbon dating stem primarily from poorly preserved carbonate contamination by glacially recycled carbon and insufficient consideration for glacial geomorphic context and sedimentary facies we assess nearly 70 newly acquired and more than 200 published radiocarbon ages in the context of a consistent sedimentary facies and geomorphic framework to interpret the timing of the local glacial maximum and subsequent retreat of the east antarctic ice sheet eais in the ross sea and potential causes of retreat compound specific radiocarbon ages help to provide good constraints on open marine onset and we demonstrate that with proper corrections and considerations acid insoluble organic aio radiocarbon ages can be reliable in open marine sediments and carbonate ages can be reliable in grounding zone proximal sediments we find that the ice flowing through pennell and joides troughs remained at maximum extent for approximately 10 000 years before retreating at 15 1 and 13 cal ka bp respectively an ice shelf covered the outer continental shelf until 9 5 cal ka bp after which it collapsed in joides trough creating deep iceberg furrows retreat through pennell trough was more episodic marked by grounding zone wedges that backstep upstream and onto lateral banks creating deglacial emergent ice rises as ice retreated from 9 to 4 cal ka bp there was considerable reorganization of drainage and at least one episode of readvance through southern joides trough that began drawdown of terrestrial ice near ross island at 7 8 cal ka bp the ice shelf appears to have retreated to a near present configuration by 2 cal ka bp however due to inconsistencies in calendar ages grounding line position must be inferred from relative chronology based on glacial landforms which suggests grounded ice retreated nearly to drygalski ice tongue and lingered atop crary bank where it was maintained by ice from david glacier our reconstruction further suggests that the eais in the western ross sea was not a discernible contributor to meltwater pulse 1a but likely contributed to eustatic sea level rise well through the middle perhaps even late holocene

ross sea paleo ice sheet drainage and deglacial history during and since the lgm onshore and offshore studies show that an expanded grounded ice sheet occupied the ross sea embayment during the last glacial maximum lgm results from studies of till provenance and the orienta

geochemical and mineralogical variations as indicators of provenance changes in late quaternary deposits of se po plain combined geochemical and mineralogical characterisation of mudstone prone successions can provide suitable indicators of sediment provenance a case study from the late quaternary depositional sequence of southeastern po plain shows that major changes in geochemical and mineralogical composition can be ascribed to changes in sediment dispersal patterns occurring during the last 30 ka in response to fluctuating sea level the po river with a mixed contribution from the alpine and apenninic chains and its southern tributaries flowing from the apennines acted as the major feeders for the study area during the late quaternary chromium and nickel among trace elements and serpentine and dolomite among minerals appear as the major provenance indicators for the study succession allowing distinction of an apenninic chromium and serpentine poor province from a mixed alpine apenninic po related chromium and serpentine rich province the relatively low cr al2o3 and serpentine silicate ratios recorded in sediments of late pleistocene age 30 ka bp which accumulated at the last glacial maximum suggest that during lowstand times and early stages of transgression the southeastern po plain was beyond the po river influence being fed uniquely by rivers of apenninic provenance increasing cr al2o3 and serpentine silicate ratios recorded within back barrier transgressive deposits 8 10 ka bp in the comacchio and ravenna sectors reflect a major change in sediment supply taking place during the holocene when partially barred environments largely connected with the open sea became established in the study area and po derived detritus was delivered to estuaries and lagoons by littoral drift maximum chromium and serpentine values are recorded at peak transgression and during the following sea level highstand 6 ka bp present when sediment supply exceeded the rate at which new accommodation space was created leading to extensive po delta progradation the drop in cr al2o3 and serpentine silicate ratios recorded in some cores at top of the holocene succession reflects the local reestablishment behind the prograding po delta complexes of an alluvial plain drained by rivers of apenninic provenance as a result of distributary channel switching and delta lobe abandonment geochemical and mineralogical analyses show negligible compositional variations between pleistocene and holocene deposits landward of the line of maximum marine incursion especially close to the basin margin in these instances sample composition throughout the entire stratigraphic succession clearly suggests an ongoing supply from the adjacent apenninic chain comparison with sand compositional analyses from major sand bodies of the same stratigraphic succession highlights the complementary but fundamental role of geochemical and mineralogical characterisation of clays for provenance research

petroleum systems in the jiangling dangyang area jianghan basin china source related geochemical data define at least four petroleum systems in the jiangling dangyang area of the jianghan basin eocene paleocene anoxic evaporitic lacustrine source rocks generated most of the crude oils in the area eocene qianjiang rock from the sha 13 well 1322 m contains fast reacting sulfur rich type is organic matter and its extract is most similar to the sha 13 oil sand bitumen qianjiang reservoir lower eocene paleocene xingouzhui rocks from the xin 73 well 842 and 862 m contain slow reacting low sulfur type i organic matter and their extracts are most similar to the sha 26 oil sand bitumen eocene jinsha reservoir and the ling 2 sha 24 and tuo 3 oils xingouzhui reservoirs two unidentified middle triassic or older marine carbonate evaporite source rocks or different facies of the same source rock generated the daxiakou oil triassic jialingjiang formation outcrop xingshan county and the moderately biodegraded tianwan seep oil permian changxing outcrop chengxi county respectively one or more unidentified marine source rocks which could include the lower permian qixia or the upper sinian doushantuo formations generated the miaoshi and yanmenkuo seep oils permian qixia outcrops the jingshan seep oil ordovician baota outcrop probably is related to these oils but could represent another petroleum system different kinetics for hydrocarbon generation among eocene qianjiang and lower eocene paleocene xingouzhui formation source rocks and chemical differences among the related oils are caused by organic facies variations high salinity and low eh enhanced the preservation of oil prone organic matter in these lacustrine settings and facilitated incorporation of sulfur into the organic matter anoxia and the unusual presence of abundant sulfate as gypsum resulted in the microbial reduction of sulfate to sulfide and incorporation of this sulfur into the kerogen for example biomarkers show that source rock in the sha 13 well 1322 m was deposited under more saline lower eh conditions than that in the ling 80 well 1808 m although both are from the qianjiang formation the sha 13 rock sample is more organic rich 6 62 vs 1 27 wt toc and has a higher hydrogen index 794 vs 501 mg hc g toc and faster reaction kinetics than the ling 80 sample kerogen from the sha 13 sample is type is because it has a high hydrogen index and an atomic s c ratio 0 074 in the range of sulfur rich fast reacting kerogens of the monterey formation s c 0 040 organic rich lower jurassic coaly rocks from outcrops at daxiakou contain immature to mature gas prone organic matter that is not related to any oils in the study several organic rich upper sinian to permian samples could have been source rocks in the past but are now highly mature based on high tmax 464 540 c and estimated vitrinite reflectance ro values mass balance calculations were used to estimate the original toc toc c in these samples prior to maturation these samples could not be correlated with the oils using biomarkers because of high maturities and low extract yields however stable carbon isotope type curves suggest that the miaoshi yanmenkuo permian qixia formation and the jingshan ordovician baota formation seep oils originated from source rocks in the lower permian qixia 3 00 wt toc or upper sinian doushantuo formations 5 96 wt toc lack of triaromatic dinosteroids in the miaoshi and yanmenkuo seep oils supports but does not prove a permian source rock very negative stable carbon isotope ratios for kerogens from the lower cambrian shuijintuo formation 33 5 to 33 6 8 85 16 64 wt toc show that they are not related to any of the analyzed oils

effects of biodegradation on australian permian coals abstract permian coals from blackwater poitrel and moura bowen basin queensland have been extracted and characterised by detailed organic geochemical techniques a variety of source related aliphatic and aromatic biomarker parameters indicate that these coals from three different locations are similar in terms of organic matter type and palaeoenvironment of deposition the hydrocarbons extracted from these coals appear to have been generated from predominantly plant derived organic matter deposited in a fluvio deltaic environment moderately high pr ph ratios the high proportion of c 29 steranes and very low sterane to hopane ratios are indicative of their largely terrestrial source molecular maturity parameters derived from aliphatic and aromatic biomarkers corroborate a measured maturity of 1 0 1 1 r o for these medium volatile bituminous coals the aliphatic and aromatic hydrocarbon distributions in these coals also allow their differentiation into two groups biodegraded moura coals and non degraded blackwater and poitrel coals comparison of various compound ratios from the degraded and non degraded coals indicate the dependence of susceptibility to biodegradation on precise molecular structures major aromatic compound classes in coals generally regarded as being more resistant may be microbially altered before branched cyclic alkanes are affected and even before the n alkanes are completely removed as reported in crude oils susceptibility to biodegradation of aromatic hydrocarbons decreases with increasing number of aromatic rings and with increasing number of alkyl substituents furthermore alkylnaphthalenes with 1 6 dimethyl substitution patterns are more susceptible to degradation than other alkylnaphthalene isomers this study reveals that biodegradation may alter the hydrocarbon composition of coals in a similar way to that observed in crude oils or oil spills except that aromatic hydrocarbons are altered relatively earlier than aliphatic hydrocarbons in coals compared to oils

involvement of fluids in the metamorphic processes within different zones of the southern marginal zone of the limpopo complex south africa an oxygen isotope perspective abstract we present oxygen isotope data obtained by laser fluorination for three outcrops from the south marginal zone smz of the limpopo granulite complex south africa these outcrops are located within the granulite zone bandelierkop quarry on the retrograde anthophyllite in isograd manamead locality and within the zone of rehydrated granulite south of the retrograde isograd klipbank locality studied samples also include felsic granitoid rocks that occur as intrusive bodies veins and veinlets in the host tonalite gneisses or the metapelite the tonalite gneiss tg and the k feldspar rich segregations kfs g at klipbank have marginally different 18 whole rock wr values 7 9 and 7 3 correspondingly the kfs g may have formed by partial melting of the tg in the presence of external saline h 2 o co 2 fluid metapelites at manamead locality have 18 o values 9 5 10 3 lower than those at bandelierkop quarry 10 0 11 4 the two mineral oxygen isotope temperature estimates for metapelite minerals from manamead cluster around two values 620 30 and 730 40 c oxygen isotope temperature estimates for the metapelites from bandelierkop quarry define a narrow temperature range of 700 740 the oxygen isotope temperatures are in reasonable agreement with the results of classical geothermobarometry the 18 values of the whole rocks and individual constituent minerals of metapelites strongly negatively correlate with the rocks volatile content loi values this suggests that a fluid phase was involved in the hydration of metapelites in the vicinity of the regional anthophylite in isograd of the southern marginal zone the fluid may have been released during crystallization of leucogranite melt oxygen isotope and geochemical features of the leucogranite indicate genetic relation to the tonalitic baviaanskloof gneisses but do not support the formation of leucogranite via in situ partial melting of metapelites

geochemistry and isotope sr nd o study of al mg granulites from the in ouzzal archaean block hoggar algeria the in ouzzal al mg granulites are found within sedimentary units deposited after 2 7 ga the whole association being metamorphosed under extreme temperature conditions c 1000 c at 2 ga the al mg granulites are interlayered with other metasediments including metapelites quartzites and magnetite bearing quartzites forsterite spinel marbles and a few meta igneous rocks mainly pyroxenites they do not occur at a specific position in the sedimentary suite and they do not reflect any particular structural control the major and trace element compositions of al mg granulites especially the high cr ni co contents show that their peculiar refractory chemistry is more compatible with premetamorphic sedimentary characteristics rather than with metasomatic metamorphic or partial melting processes sedimentary admixtures of a common mature detrital component coming from the weathering of the local acidic igneous crustal protoliths normal pelitic component with an extremely immature component derived from reworking of basic ultrabasic lithologies al mg cr co ni rich chloritic component is consistent with the geochemistry of such rocks as in other instances the quartz garnet oxygen isotopic thermometer here records an apparent temperature close to the peak metamorphism c 1000 c although the persistence of pre existing 18o variations on a small scale during the metamorphism does not support a major pervasive fluid flow during metamorphism it does not rule out the presence of syn to post metamorphic co2 the low 18o c 5 to 6 of the most typical al mg granulites indicate that the chloritic component in these rocks was derived from hydrothermally altered mafic ultramafic protoliths rather than dominantly from palaeosols it is suggested that the presence of such al mg cr co ni rich sediments is indirect evidence for the presence of greenstone belts in the local crust of the in ouzzal at 2 6 2 7 ga

biomarker signatures of the ediacaran early cambrian origin petroleum from the central sichuan basin south china implications for source rock characteristics abstract hydrocarbons with an ediacaran early cambrian origin from the central sichuan basin south china were investigated for biomarker compositions they were obtained by solvent extraction from the upper ediacaran reservoir core samples which contain abundant solid bitumen the solid bitumen is widely believed to be formed by thermal cracking of early charged oils in the reservoirs which have presumed source rocks of an ediacaran early cambrian age thermal maturity parameters based on phenanthrenes and aromatic steroids suggest a very high thermal maturity for the extracted hydrocarbons which is consistent with the severe maturation undergone by their host reservoirs age diagnostic biomarkers including c30 24 isopropylcholestanes and mid chain monomethyl alkanes support source rocks of an ediacaran early cambrian age the extracted hydrocarbons have very similar biomarker signatures which include high relative abundance of acyclic isoprenoids and pristane phytane 1 and the presence of c26 norcholestanes methyl and ethylsteranes the presence of hopanoids including extended series and methylhopanes indicates contributions from prokaryotic bacteria while the presence of various steroids including regular steranes and methylsteranes indicates contributions from the eukaryotic algae parameters based on tricyclic terpane and hopane dibenzothiophene phenanthrene ratios and c27 diasteranes diasteranes regular steranes ratios suggest a major shale source but a mixed shale carbonate source cannot be completely excluded presence of c30 demethylsteranes low pristane phytane ratios high gammacerane index and presence of 28 30 dinorhopane and 2 methyhopanes indicate that the source rocks were deposited in a stratified anoxic marine depositional environment with enhanced salinity conditions

skeletal and isotopic composition and paleoclimatic significance of late pleistocene carbonates ross sea antarctica abstract carbonates cover an extensive area of the northwestern ross sea continental shelf radiocarbon dates yield late pleistocene stage 3 ages for these deposits hence the carbonates appear to be correlative with widespread tills and glacial marine deposits in the region four carbonate facies are recognized on the basis of skeletal composition a barnacle foraminifer facies a muddy bryozoan facies a bryozoan barnacle pelecypod foraminifer facies and a planktonic foraminiferal facies these deposits occur on the shelf and upper slope while carbonate turbidites derived from them occur on the adjacent continental slope and rise compositional analyses of ross sea carbonates lend support to previously recognized criteria for identifying cold water carbonates these include 1 the presence of an associated ice rafted component including dropstones 2 a dominance of calcite relative to other carbonate minerals the remaining fraction consists solely of aragonite 3 allochems that are entirely skeletal and 4 heavy oxygen isotopic compositions in the range of 3 0 to 5 1 pdb

late cretaceous to middle tertiary basin evolution in the central tibetan plateau changing environments in response to tectonic partitioning aridification and regional elevation gain located in the bangong suture zone between the lhasa and qiangtang terranes of central tibet the nima basin records cretaceous late miocene sediment accumulation during a period of drastically changing paleogeography and paleoelevation the bangong suture zone originally formed during late jurassic early cretaceous time as the lhasa terrane collided with the qiang tang terrane during early to middle cretaceous time the region lay at northern near equatorial paleolatitudes near sea level by aptian time the nima basin was above sea level and was strongly influenced by nearby volcanic activity and crustal shortening in the reactivated bangong suture zone in the southern nima basin an 50 m y late cretaceous eocene depositional hiatus correlates with major crustal shortening and ensuing voluminous ignimbrite eruptions in the lhasa terrane in the northern nima basin deposition continued during latest cretaceous time recording arid paleoclimate in evaporitic lacustrine and eolian dunefield deposits by oligocene time the nima basin comprised two independent depocenters that accumulated coarse grained alluvial fluvial lacustrine evaporitic and fan delta deposits in close association with reactivated thrusts in the bangong suture zone carbon and oxygen isotope data from oligocene paleosol carbonate reported elsewhere indicate that regional paleoelevation during the late oligocene was 4 6 km as it is today overall the depositional record of the nima basin combined with ongoing structural and geochronologic studies demonstrates that the bangong suture zone was reactivated during middle cretaceous and middle tertiary time that the intervening 50 m y interval was a time of regional upper crustal shortening in the lhasa terrane followed by regional ignimbrite eruptions and that arid paleoclimate and high paleoelevation were established by the late cretaceous and late oligocene respectively within the context of other data sets from the lhasa terrane the record of deposition in the nima basin is consistent with low angle subduction of neotethyan oceanic lithosphere and reactivation of the bangong suture zone during the early cretaceous followed by shortening within the gangdese retroarc and northern lhasa terrane thrust belts during the late cretaceous lithospheric delamination dripping and regional magmatic flare up during latest cretaceous through early tertiary time and underthrusting of indian lower crust and lithosphere as far north as the bangong suture zone during late oligocene time

glacial retreat patterns and processes determined from integrated sedimentology and geomorphology records abstract although hundreds of cores have been collected on the antarctic continental shelf over the past five decades definitive interpretations of depositional environments associated with marine based ice advance and retreat are hindered by similarities in sediment facies and a lack of geomorphic context the recent use of an advanced multibeam bathymetry system allows for more detailed ice sheet reconstructions from glacial landforms that were previously not resolved with older generation systems here we present results from a recent cruise to the ross sea antarctica that focuses on integrating sediment facies analyses into a geomorphic framework to confidently determine depositional environments and sedimentological processes since the last glacial maximum grain size analysis geotechnical properties and micropaleontology from targeted sediment cores are used to develop improved criteria for making the distinction between subglacial diamictons and ice proximal diamictons which can be applied to geomorphically blind sediment cores our consideration of geomorphic context while interpreting sediment facies has also allowed us to determine that most debris melted out of the base of paleo ice shelves in the ross sea only 1 2 km seaward of the grounded ice margin additionally we find that agglutinated foraminifera specimens are characteristic of sluggish marine currents and a resulting accumulation of siliceous detritus rich in organic matter however calcareous specimens dominate in higher energy current settings and in ice proximal environments with lesser amounts of siliceous detritus and associated organic material overall sedimentary successions record contrasting behaviors of the west antarctic and east antarctic ice sheets that extended onto the continental shelf during the last glacial maximum not only is this coupled geomorphic and sedimentologic approach useful for understanding glacimarine processes and ice sheet retreat patterns but it is essential for selecting appropriate facies transitions for chronological constraints of past ice sheet behavior

late pleistocene paleoceanographic changes in the ross sea glacial interglacial variations in paleoproductivity nutrient utilization and deep water formation abstract the outer ross sea continental shelf has experienced large variations in ice sheet extent over the pleistocene that are theorized to be largely driven by changes in the westward flowing antarctic slope current asc at the continental shelf break this current regulates southward incursions of warm modified circumpolar water and it is thought to have triggered past marine ice sheet retreat additionally expansions of grounded ice sheets on the continental shelf have fundamentally altered the ross sea water mass formation processes influencing surface water salinity sea ice cover nutrient utilization deep water ventilation and primary productivity here we report the geochemical physical properties grain size bulk 15n and diatom records during the late pleistocene from two sediment cores from the iselin bank on the outermost continental shelf in the ross sea these core sites were not overridden by grounded ice sheets during the late pleistocene glacial interglacial cycles allowing for a continuous archive of glacimarine environments that were influenced by the asc interglacial periods are typically characterized by high surface water productivity and nutrient utilization with chaetoceros resting spores indicating nutrient limitation under open ocean conditions and glacial periods are typically characterized by low surface water productivity and nutrient utilization with sea ice diatoms and planktonic foraminifers indicating light limitation under extensive sea ice ice margin proximal conditions a grain size analysis indicates coarse skewed distributions and winnowing in the iselin bank region during cold periods the winnowing may be related to enhanced asc flow instead of density driven shelf water outflow

sedimentary and organic geochemical investigation of tertiary lacustrine oil shale in the central tibetan plateau palaeolimnological and palaeoclimatic significances article i nfo the zhuonai lake and lunpori oil shale located in the central tibetan plateau were deposited in a tertiary lacustrine environment in the hoh xil and lunpola basins respectively a combined investigation of sedimentary organic geochemistry and organic carbon isotope was performed to define source rock potential the palaeoenvironment and source of the organic matter three types of facies sequences are developed in the zhuonai lake section and oil shale mainly occurs in the oil shale marl sequence the oil shale silty claystone and oil shale marl facies sequences are developed in the lunpori section both oil shales are finely stratified especially for the lunpori oil shale with thickness of the laminae about 10 m which contains abundant pyrite crystals and fossilized fish bones both the zhuonai lake and lunpori oil shale contain high values of total organic matter toc s2 and hydrogen index hi indicating the oil shales have good oil source rock potential tmax values show an immature stage of organic matter for the zhuonai lake oil shale and thermally marginally mature for the lunpori oil shale because of difference in their burial history lunpori oil shale shows the characteristics of amorphous organic matter aom dominance odd over even predominance maximum n alkanes peak at nc25 or nc23 higher proportion of c29 sterane light 13 corg values 30 0 to 27 4 high concentrations of phytane pr ph ratio ranging from 0 02 to 0 18 high values of gammacerane index up to 25 26 and presence of carotane which are consistent with a reducing stratified and hypersaline palaeo lake with main contribution of algae and bacteria to the organic matter om oil shale samples from the lower and upper part of the zhuonai lake section are characterized by low h c ratios and high o c ratios amorphous humic om and vitrinite dominance odd over even predominance with long chain n alkanes dominance heavy organic carbon isotope and c29nc27 sterane distribution in agreement with a main contribution of land plant the heavy organic carbon isotope suggests the expanding of c4 land plant during the early miocene while the most samples show characteristics of aom dominance maximum peak at nc29 or nc31 and high c27 sterane concentration consistent with a main contribution from algae to the om the pr ph ratio cannot be applied as a measure for redox conditions in the section because of maturity effects biomarker analysis indicates that the salinity during the deposition of the zhuonai lake oil shale was not enhanced the oligocene lunpori oil shale and the early miocene zhuonai lake oil shale recorded the variation of palaeolimnological water chemistry the development history of the palaeo lakes from the oligocene saline to the early miocene fresh water reflects the variation of palaeoclimate from dry to humid in the central tibetan plateau

organic matter accumulation in the oil shale and coal bearing huadian basin eocene ne china abstract the huadian basin located in northeastern china is a fault controlled basin filled by eocene non marine sediments assigned to the huadian formation the formation is subdivided from bottom to top into three members pyrite member oil shale member and carbonaceous shale member using bulk geochemical data from borehole hd3 and core descriptions from a high number of wells the factors controlling organic matter accumulation have been evaluated the organic matter content of the pyrite member is relatively low average toc 0 9 wt mudstones deposited in shallow lacustrine environments contain between 1 and 2 wt toc max 6 wt and a kerogen type ii hi 400 600 mg hc g toc an arid climate prevented the accumulation of thick coal the overlying oil shale member contains 13 oil shale layers which are mined underground the oil shale member has been interpreted as a 3rd order sequence significant differences exist between oil shales deposited in different systems tracts 2 m thick coaly oil shale of low quality oil yield 3 5 wt developed in the lowstand systems tract oil shale up to 7 m thick of moderate quality oil yield 4 1 8 0 wt was deposited during the transgressive systems tract tst thinner the carbonaceous shale member representing the balanced fill to overfilled stage of basin evolution hosts economic coal seams which are occasionally accompanied by shallow lacustrine shales with abundant hydrogen rich organic matter otherwise non coal layers are typically low in organic matter average toc 0 9 wt in contrast to the huadian basin a very thick coal seam overlain by a single oil shale layer more than 100 m thick developed in the eocene fushun basin this indicates major differences in the evolution of basins with similar tectonic setting and age

the oxygen isotopic composition of granulites and retrogressed granulites from the limpopo belt as a monitor of fluid rock interaction abstract from the southern marginal zone of the limpopo belt three rock systems cordierite bearing metapelites mafic rocks and ultramafic rocks are studied by whole rock oxygen isotope analysis in order to decide wether the observed variation in the o isotopic composition of the metapelites is due to granulite facies fluid rock interactions or due to earlier processes a discrimination index pelite index pi is proposed in combination with the whole rock oxygen isotopic composition this index enables one to put some constraints on the origin of the precursor rocks in the case of the limpopo metapelites it is concluded that the cordierite anthophyllite bearing metapelites are only in part true metasediments a metasomatic alteration of mafic precursors in an ocean crust environment could be responsible for both low pi indices and high with respect to unaltered mantle material 18 o values fluid rock interactions in this environment are also thought to be responsible for the observed chemical and o isotopic variation of mafic and ultramafic rocks the data do not support significant large scale co 2 infiltration during granulite facies metamorphism the retrograde regionally extended anthophyllite formation in the southern marginal zone of the limpopo belt is certainly triggered by some fluid infiltration model calculations show that the amount of fluids necessary for this readjustment is too small to have an imprint on the whole rock oxygen isotope composition

geochemistry of pelitic and psammopelitic precambrian metasediments from southwestern sri lanka implications for two contrasting source terrains and tectonic settings most of the pelitic and psammopelitic metasediments of southwestern sri lanka are compositionally transitional between shales and greywackes and are of two isotopically distinct types metasediments of the northern part have nd model ages of 1 5 ga and belong to the relatively younger nd model age province of wanni complex wc model ages of two southerly located samples are 2 8 ga being compatible with those of the highland complex hc in accordance with mostly mesoproterozoic to late archaean crustal residence ages cr ni la th and ree data also suggest that the sources of these metasediments are plagioclase fractionated post archaean upper crustal material crustal differentiation of source terrains corresponding to the hc and the wc probably occurred at distinctly different time intervals significant differences exist between the major and trace element chemistry of the metapelites from the wc north and the hc south suggesting derivation from two different source terrains metasediments of the south are slightlymmore siliceous low in sc and v and highly enriched in lree 220 ppm their sources have been chemically evolved felsic igneous rocks and or recycled sediments relatively high v sc feo mgo tio2 and slightly low sio2 in the rocks of the wc indicate contribution of more basic sources cia chemical index of alteration estimates and comparative alkali alkaline earth element patterns suggest relatively fresh source material the o isotope data indicate that the pre metamorphic isotope signatures are preserved and the clay component of the original sediments mainly consisted of illite typifying continental weathering conditions sediments of the south hc were probably deposited in a passive continental margin continental rift environment while those of the northern part wc were probably formed at an andean type active continental margin the two units were tectonically juxtaposed prior to pan african granulite metamorphism

biological markers in lacustrine chinese oil shales s u m m a r y a major objective in molecular organic geochemistry is the assessment and characterization of sedimentary depositional environments from the occurrence of specific biological marker compounds related to particular source organisms the aliphatic hydrocarbon distributions of petroleums and or sediments from chinese freshwater and hypersaline lacustrine environments are described and contrasted in the search for diagnostic features among their biological marker distributions the eocene maoming oil shale which crops out in guangdong province shows major differences in hydrocarbon composition through its stratigraphic succession these variations reflect changes in lithology and in the origins of the sedimentary organic matter as seen from petrographic examination the lower lignite and vitrinite layers contain significant contributions of biological markers from bacterial sources plus components derived from terrigenous higher plants such as c29 steroids in contrast the overlying shales show a dominance of dinoflagellate derived 4methylsteroids and culminate in an horizon with botryococcane homologues as their dominant alkanes thus the geochemical profile suggests that a swampy environment in which peats accumulated deepened to support populations of dinoflagellate and finally blooms of botryococcus green algae the aliphatic hydrocarbons of a series of sediments and petroleums from the eocene hypersaline sequence of the jianghan basin in southern hubei province shows various features that may be typical of such facies these include a dominance of even numbered n alkanes high amounts of phytane and gammacerane and an abundance of c35 hopanes similar characteristics are observed in shales from the eocene green river formation and in rozel point crude oil a petroleum thought to originate from sediments deposited under hypersaline conditions the same features also appear in a lower tertiary evaporitic mudstone from south of the renqui oil field in hebei province together with 4 methylsteranes fl carotane and 18c h oleanane a marker for terrigenous higher plants these data illustrate the potential of biological markers in the differentiation of different lacustrine environments and suggest that such characteristics may provide signatures for environmentally similar but geographically distant deposits

geochemistry of terrestrial oil shale from the lunpola area northern tibet china abstract the lunpola oil shale is the largest oil shale resource in tibet twenty four samples of oil shale mudstone and dolomite were collected from the lunpola oil shale for mineralogical and trace element analyses the vertical distribution and mode of occurrence of trace elements in this terrestrial oil shale were also discussed oil shale samples from the lunpola area have high toc contents 5 1 10 6 high ash yields 74 8 84 7 low total sulfur contents 0 19 1 03 and high shale oil contents 5 0 10 3 the major minerals in the oil shale samples are clays quartz calcite and dolomite with minor quantities of feldspar siderite hematite magnesite and pyrite other minerals such as halite zeolite barite anhydrite and mirabilite were detected in some oil shale samples the contents of as ba be bi cd ce cs hg la li mo nd pb pr rb se sm th u w and zr are enriched from 1 30 to 125 times as compared to their average crust abundance clarke values whereas the other elements are slightly higher or lower than their respective clarke values compared to common australian oil shale the lunpola oil shales contain higher as ba be ce co cs ga gd hf nb nd pb pr rb sc sm sn th and zr but lower cd cu lu mo ni se sr u v and zn elements associated with organic matter and or fe sulfides are highly enriched in all oil shale deposits suggesting that their speciation in oil shale is governed by general processes e g high organic matter content and anoxic environment whereas elements associated with clay minerals exhibit various enrichments indicating that their speciation in oil shale is governed by individual geochemical mechanisms e g source rocks the elements in the lunpola oil shale may be classified into three groups of associations according to their modes of occurrence group a elements tio 2 sc hf zr be li w v zn sio 2 al 2 o 3 rb ga sn cr ta cs k 2 o th na 2 o rees and ash yield have high positive correlations with ash yield and a mainly inorganic affinity group b elements as toc mno ni fe 2 o 3 cd co cu mo se mgo bi pb and hg show a negative correlation with ash yield and most elements possibly have a likely organic affinity and or fe sulfide affinity group c elements sr cao u and p 2 o 5 show a weak or negligible correlation with ash yield with the exception of cao elements of environmental concern as bi hg mo pb se and u are present in high contents and are clustered in the second association i e they are hosted mainly in fe sulfides and or organic matter

petroleum source rock evaluation of the sebahat and ganduman formations dent peninsula eastern sabah malaysia the sebahat middle miocene to early pliocene and ganduman early pliocene to late pliocene formations comprise part of the dent group the onshore sebahat and ganduman formations form part of the sedimentary sequence within the sandakan sub basin which continues offshore in the southern portion of the sulu sea off eastern sabah the ganduman formation lies conformably on the sebahat formation the shaly sebahat formation represents a distal holomarine facies while the sandy ganduman formation represents the proximal unit of a fluvial deltaic system based on organic geochemical and petrological analyses both formations posses very variable toc content in the range of 0 7 48 wt for sebahat formation and 1 57 wt for ganduman formation both formations are dominated by type iii kerogen and are thus considered to be gas prone based on hi vs tmax plots although the hi tmax diagram indicates a type iii kerogen petrographic observations indicate a significant amount of oil prone liptinite macerals petrographically it was observed that significant amounts 1 17 by volume of liptinite macerals are present in the ganduman formation with lesser amounts in the sebahat formation both formations are thermally immature with vitrinite reflectance values in the range of 0 20 0 35 ro for ganduman formation and 0 25 0 44 ro for sebahat formation although these onshore sediments are thermally immature for petroleum generation the stratigraphic equivalent of these sediments offshore are known to have been buried to deeper depth and could therefore act as potential source rocks for gas with minor amounts of oil

the antarctic ice sheet during the last glacial maximum and its subsequent retreat history a review abstract an emerging body of evidence from studies of the last glacial interglacial cycle suggests that the east and west antarctic ice sheets have not advanced and retreated in concert the west antarctic ice sheet advanced to the outer shelf in most regions during the last glacial maximum lgm the retreat from the shelf commenced shortly after the lgm and continued into the late holocene the west antarctic ice sheet in ross and amundsen seas slid across a deforming bed at least during the final phases of extended glaciation this implies that at this time the ice sheet had a low profile differences in the number and locations of grounding zone wedges and smaller grounding zone features from trough to trough imply that individual west antarctic ice sheet ice streams retreated episodically details concerning the expansion retreat and behavior of the east antarctic ice sheet eais are more sparse the picture emerging is that the eais did not expand to the continental shelf edge during the lgm rather it achieved a maximum extent of a mid shelf position in some locations while in other areas the ice terminus was situated near its present location the timing of retreat along sectors within the eais appears diachronous and in places occurred prior to the lgm the antarctic peninsula shelf contained considerably more ice during the lgm than previously proposed the results presented in this paper support more recent published ice sheet models that call for greater contributions of melting ice from west antarctica including the antarctic peninsula to the post glacial rise in sea level

glacigenic and associated marine sediments in the weddell sea fjords of spitsbergen and the barents sea a review abstract studies of glacigenic and associated marine sediments in the weddell sea fjords of spitsbergen and barents sea show that during periods of limited glacial coverage interstadials large amounts of material may be brought into the sea mainly by meltwater the major load is deposited relatively close to the icefront 1 at times of maximum glacial extent grounded ice extends onto the shelf with the shelf edge as the outer limit and land and inner shelf areas are eroded main glacial depositional sites are then the outer shelf and shelf edge the sedimentary environment outside an ice shelf is characterized by low clastic supply mainly deposited from icebergs due to low turbidity and a supply of nutrient rich water biogenic matter accumulates leading to a glaciomarine sequence rich in bioclastics sea level lowering results in grounding and seaward expansion of the ice shelf subsequent eustatic rise causes the grounded ice to float deglaciation and sea level rise reduces clastic input to the shelves glacial sediments are reworked and carbonates may accumulate forming tillite carbonate sequence e g late precambrian break up of marine ice sheets such as the barents sea ice sheet seems to have taken place stepwise in response to eustatic rise and climatic changes

deposition of polar carbonates during interglacial highstands on an early permian shelf tasmania abstract the early permian lower parmeener supergroup contains two bioclastic limestones that accumulated during the period of prolonged deglaciation of southern gondwana as the region moved equatorward from 80 s to 70 s the darlington and berriedale limestones formed in neritic environments in areas where abundant ice rafted debris testifies to numerous icebergs and glendonites indicating near freezing seawater these limestones consist of argillaceous and clean bioclastic floatstone rudstone and grainstone that contain a high abundance low diversity heterozoan assemblage of calcareous invertebrates the components are dominated by large robust brachiopods bryozoans and eurydesma bivalves sponge spicules and crinoids are also common whereas coralline algae and conodonts are conspicuously absent carbonates were deposited on the middle shelf during sea level highstands below the iceberg grounding line where the faunal communities remained undisturbed in this setting the organisms were outboard of significant terrigenous sediment influx and brackish water which were trapped on the inner shelf by bathymetry and icebergs strong bottom currents also prevented the deposition of fine grained siliciclastics by continuous winnowing of the pure limestone facies upwelling of nutrient rich water inferred from the distribution of phosphate promoted high primary productivity which fueled this carbonate factory and inhibited dissolution of the biogenic carbonate

late quaternary carbonate deposition at the bottom of the world abstract carbonate sediments on polar shelves hold great potential for improving understanding of climate and oceanography in regions of the globe that are particularly sensitive to global change such deposits have however not received much attention from sedimentologists and thus remain poorly understood this study investigates the distribution composition diagenesis and stratigraphic context of late quaternary calcareous sediments recovered in 15 piston cores from the ross sea shelf antarctica results are used to develop a depositional model for carbonate deposition on glaciated polar shelves the utility of the deposits as analogs for the ancient record is explored in the ross sea carbonate rich lithofacies consisting of poorly sorted skeletal sand and gravel are concentrated in the west and along the outer reaches of the continental shelf and upper slope analysis of fossil assemblages shows that deposits were produced by numerous low diversity benthic communities dominated locally by stylasterine hydrocorals barnacles or bryozoans radiocarbon dating indicates that carbonate sedimentation was episodic corresponding to times of reduced siliciclastic deposition most accumulation occurred during a time of glacial expansion in the lead up to the last glacial maximum a more recent interval of carbonate accumulation postdates the early holocene sea level rise and the establishment of the modern grounding line for the ross ice shelf when carbonate factories were inactive fossil debris was subjected to infestation by bioeroders dissolution fragmentation and physical reworking this study reveals the episodic nature of carbonate deposition in polar settings and a reciprocal relationship with processes that deliver and redistribute siliciclastic debris carbonate production is most active during colder periods of the glacial interglacial cycle a potential new sedimentological paradigm for polar carbonate systems low accumulation rates and long residence times on the seafloor leave sediments vulnerable to significant post depositional modification processes that profoundly affect the appearance of deposits as they enter the rock record comparison with other examples of polar carbonates highlights the utility of these late quaternary deposits as a well constrained analog that can aid in the recognition and interpretation of similar deposits from the ancient record

biogenic facies in the antarctic glacimarine environment basis for a polar glacimarine summary abstract the association of glacial deposits diamicts or tillites with biogenic and or chemically derived sedimentary rocks in the ancient record is one which continues to challenge interpretation an analogous association can be found on portions of the east antarctic continental shelf where relict glacial and glacimarine diamictons are overlain by a varied and complex suite of modern biogenic deposits carbonate bioclastic material can be found in two distinct zones and its deposition may have been contemporaneous with partial glacial expansion onto the shelf a nearshore carbonate facies consists of in situ and partially reworked barnacles bryozoans ostracods pelycepods gastropods planktonic and benthonic foraminifera a siliceous biogenic component is intermixed within the shallow water 500 m siliceous facies of pelagic hemipelagic and sediment gravity flow origin is found within inner shelf depressions and consists predominantly of diatom frustules and radiolaria these accumulations of siliceous ooze and mud clearly post date glacial recession from the shelf and contain laminated cross laminated and massive interbeds which are accumulating at rates of 0 3 cm yr the extreme polar climate inhibits meltwater production and terrigenous influx into marine basins this allows for the accumulation of biogenic rich material which is also favored by the high seasonal productivity inherent in the south polar oceans ancient analogs to these modern deposits exist and their association with glacimarine strata could be used to infer polar climatic settings and glacial retreat that is related to eustatic sea level rather than regional warming

novel cyclised and aromatised diagenetic products of β carotene in the green river shale abstract a suite of novel diagenetic products of carotene has been identified in an extract of a sample from the green river shale identification is mainly based on comparison of mass spectra with those of diagenetic products of another carotenoid isorenieratene these compounds were formed by i cyclisation and aromatisation of the polyene isoprenoid chain ii explusion of toluene and m xylene from the polyene isoprenoid chain and iii aromatisation of the 1 1 5 trimethylcyclohex 5 enyl moieties resulting in 1 2 dimethylbenzene end groups reduction of the double bonds of carotene is the most important diagenetic process however as judged from the high relative amount of carotane 63 of quantified diagenetic products of carotene these results indicate that the fossilisation potential of carotenoids is greater than previously thought

late oligocene early miocene evolution of the lunpola basin central tibetan plateau evidences from successive lacustrine records abstract widespread cenozoic sediments in and around the tibetan plateau tp are thought to have played an important role in explaining the process of the india asia collision as well as its interactions with global and regional paleoclimate however high resolution temporal frameworks of sedimentary sequences and controls on geological and climatic events are still absent to study the abovementioned issues we investigate the oligocene miocene lacustrine sequences the dingqinghu formation of the lunpola basin central tp in this work cyclostratigraphic analyses are conducted with gamma ray log and pollen data to establish a high resolution temporal framework ranging from ca 25 4 to 18 0 ma for the sections along these sections sediment accumulation rates are calculated with orbital signals to monitor clastic input of the lake basin elemental palynological and isotopic data are summarized to depict the paleoclimate and paleoelevation evolution of this drainage system integrating all these clues together we sort out a chronological list of events including lake basin tectonics and paleoclimate regional uplift took place at 23 7 ma simultaneously a distinct lake basin transition characterized by accelerated sediment accumulation rate is recognized about 0 2 ma later at 23 5 ma catchment scale drought occurred and maintained to the end of the sections our results demonstrate that paleoclimate did not impose decisive influence on the late oligocene early miocene evolution of the lake basin instead regional uplift and its associated accelerated exhumation of the source area resulted in the lake basin transition and paleoclimatic drought after reviewing the oligocene miocene sedimentary records distributed in and around the tp we argue that the 23 7 ma geological event of the lunpola basin is probably not a single case but a regional effect of a dramatic tectonic transition of the plateau

sedimentology of shell rich deposits coquinas in the glaciomarine upper cenozoic yakataga formation middleton island alaska the yakataga formation in southern alaska contains the longest and most accessible record of late cenozoic glaciation in the world glacially influenced marine sedimentation began in the late miocene 6 ma and continues in the area to the present day upper yakataga formation sediments 1 25 km thick are exposed on middleton island gulf of alaska facies are dominated by massive glaciomarine diamicts that record deposition in an outer shelf setting of terrigenous mud and ice rafted debris released from expanded temperate glaciers around the gulf margin diamicts contain intraformational coquina beds as much as 1 m thick composed of cemented bioclastic debris and ice rafted boulders that can be traced several kilometers along strike analysis of foraminifera contained within diamicts and coquinas suggests that coquinas record intervals of relative sea level change bottom winnowing and nondeposition of mud allowing molluscan communities to develop coquinas show graded beds produced by storms and wave rippled commonly armored upper surfaces composed of densely packed chlamys valves these bioclastic deposits are of considerable significance with regard to the origin of mixed glacial and carbonate successions in the rock record analogous depositional settings can be identified from the permian of australia

oxygen isotope thermometry based on a refined increment method and its application to granulite grade rocks from sri lanka abstract in this paper we first present a revision of the increment method a semi empirical technique which allows the calculation of o isotope fractionation factors between all silicates provided their structure and chemical composition is known for the temperature dependency the experimentally calibrated high pressure mineral calcite fractionation factors of chiba et al 1989 are taken as a basis then this method is applied to granulite facies parageneses from sri lanka including quartz k feldspar sillimanite garnet pyroxenes amphiboles cordierite magnetite and ilmenite it can be shown that o isotope equilibration occurred at granulite facies conditions at about 830 c due to static recrystallization locally retrograde re equilibration occurred also at much lower temperatures due to late d4 in most cases however o isotope disequilibria resulted from retrograde oxygen intracrystalline diffusion it can be proved by model calculations that the o diffusion data for water saturated systems reported in the literature are too high by two orders of magnitude to explain the measured isotopic compositions the fractionation patterns allow the discrimination between open and closed system behaviour the regional distribution of open and closed system patterns corresponds to the frequency of occurrence of late stage migmatization western part and to differences in amount and composition of fluid inclusions

feast to famine sediment supply control on laramide basin fill erosion of laramide style uplifts in the western united states exerted an important first order influence on paleogene sedimentation by controlling sediment supply rates to adjacent closed basins during the latest cretaceous through paleocene these uplifts exposed thick intervals of mud rich upper cretaceous foreland basin fill which was quickly eroded and redeposited cretaceous sedimentary lithologies dominate paleocene conglomerate clast compositions and the volume of eroded foreland basin strata is approximately twice the volume of preserved paleocene basin fill as a result of this sediment oversupply clastic alluvial and paludal facies dominate paleocene strata and are associated with relatively shallow and ephemeral freshwater lake facies in contrast large long lived carbonate producing lakes occupied several of the basins during the eocene basement derived clasts granite quartzite and other metamorphic rocks simultaneously became abundant in lower eocene conglomerate we propose that eocene lakes developed primarily due to exposure of erosion resistant lithologies within cores of laramide uplifts the resultant decrease in erosion rate starved adjacent basins of sediment allowing the widespread and prolonged deposition of organic rich lacustrine mudstone these observations suggest that geomorphic evolution of the surrounding landscape should be considered as a potentially important influence on sedimentation in many other interior basins in addition to more conventionally interpreted tectonic and climatic controls

controls on deposition of aquatic and terrestrial organic matter in the lacustrine namling oiyug basin oligocene miocene southern tibet abstract the namling oiyug basin is the only cenozoic lake basin that has hydrocarbon potential in southern tibet china coal was once exploited in the basin from the early miocene mangxiang formation which also hosts oil prone source rock layers herein a combined investigation of sedimentological features and organic geochemistry is performed on a measured outcrop section of the mangxiang formation to study the lake basin types as well as the depositional history of aquatic and terrestrial organic matter om there are two periods in the lake basin evolution history the balanced fill and overfilled stages in the balanced fill basin stage oil prone laminated shale was deposited in a relatively deep lake environment with total organic carbon toc contents around 5 wt and hi values up to 316 mg hc g toc indicating hydrogen poor type ii kerogen with transition to type iii kerogen comparison between maceral composition and geochemical properties suggests that the relative low hi values are results of thermal maturity the high value of the gammacerane index indicates water stratification of the lake in this stage water and sediment input approximately equaled potential accommodation the lake was relatively stable and hosted large amounts of lacustrine algae and accumulated om with low terrestrial input in an anoxic environment after the onset of the thrusting the potential accommodation was decreased large volumes of clastic sediments also drained into the lake from the surrounding area resulting in an overfilled lake basin during this stage peat was deposited in freshwater environment with 30 wt toc low hi and type iii om the high pr ph 3 implies oxic conditions

the palaeoclimatic significance of cenozoic marine macrofossil assemblages from cape roberts project drillholes mcmurdo sound victoria land basin east antarctica abstract the cape roberts project crp drilled three sedimentary cores at 77 00 s and 163 7 e about 12 14 km east of cape roberts mcmurdo sound in the ross sea east antarctica the total crp recovery consists of about 1500 m of cenozoic strata and 100 m of paleozoic age beacon supergroup rocks as many as 594 horizons produced macrofossils that prove to be significant to understand past ross sea depositional environments and contribute new information about antarctic climate in particular the cape roberts project opened important windows on the paleoclimatic history of east antarctica during the early pleistocene early miocene and oligocene the early pleistocene carbonate unit in crp 1 holds a truly polar macrofauna but also documents a peculiar interglacial climatic event with strongly reduced seasonal sea ice formation in the ross sea the early miocene crp 1 and crp 2 2a and late oligocene macrofossil assemblages crp 2 2a and crp 3 are consistent with cold water environments and may be interpreted to indicate sub polar conditions the early oligocene assemblages contain modiolid mussels that are definitely not truly polar and suggest significantly warmer than present seawater conditions although definitely colder than during the middle upper eocene known in james ross basin and mcmurdo erratics finally the suggestion that crp reached upper eocene strata is considered possible on the base of an undescribed modiolid mussel found at the bottom of pre beacon sediments in the crp 3 drill core

early stall of west antarctic ice sheet advance on the eastern ross sea middle shelf followed by retreat at 27 50014cyrbp abstract marine geological and geophysical data suggest that the west antarctic ice sheet wais deposited three thick seismically resolvable units in the eastern ross sea since the last glacial maximum lgm but the chronology of these grounding events is debated existing ice retreat chronologies for the eastern ross sea are considered suspect because nearly all have been developed using radiocarbon dating of acid insoluble organics aio from bulk sediment we used a new strategy to isolate in situ forams from diamict sediment deposited at the middle shelf grounding zone wedge gzw a subaqueous ice marginal landform previously interpreted to represent deposition during the third grounding event since the lgm advance to the shelf edge here we present a synthesis of our new radiocarbon dates of foram tests and aio with previously published radiocarbon dates we propose that the wais s lgm advance in the eastern ross sea sector reached the middle shelf circa 27 500 14c yr bp and that open marine sedimentation began shortly thereafter there is as of yet no clear explanation for why wais retreat in this sector of antarctica apparently began prior to the peak of the last glacial cold period a precipitation deficit localized warm water intrusion an ice dynamic response in the absence of climate forcing or another as of yet unknown forcing mechanism could be responsible

quaternary calcareous nannofossils from periantarctic basins paleoecological and paleoclimatic implications abstract currently coccolithophores have a widespread oceanic distribution and are reported from most latitudes but not those higher than 65 s fifteen piston cores were sampled with the aim of investigating the distribution and abundance variation of quaternary calcareous nannofossils of the antarctic region south of the antarctic divergence 65 s particularly from maud rise bausan bank and from weddell ross and bellingshausen seas a calcareous nannofossil cold taxa association is present in most of the cores examined and their discontinuous occurrence is thought to indicate key environmental relationships the presence of calcareous nannofossils is correlated with interglacial intervals with warmer ssts and may indicate high productivity and an open ocean environment our results confirm that during short periods of the late quaternary coccolithophorids occurred at southern high latitudes in the western antarctic basins while in the eastern antarctic basins they are nearly absent suggesting more variable ssts near west antarctic ice sheet

petroleum potential of oligocene lacustrine mudstones and coals at dong ho vietnam an outcrop analogue to terrestrial source rocks in the greater song hong basin the outcrop of oligocene age at dong ho northern vietnam may constitute an immature analogue to offshore terrestrial source rocks in the greater song hong basin the outcrop includes an interval with two source rocks 1 highly oil prone carbonaceous mudstones containing kerogen types iia and iia i and with toc contents from 6 48 to 16 89 wt and hi values from 472 to 690 and 2 oilprone humic coals kerogen type iii with hi values from 200 to 242 the mudstones were deposited in oxygen deficient lakes which on occasion were subject to marine influence and the coals accumulated in freshwater peat forming mires the coals have broad activation energy ea distributions while the mudstones have ea distributions characterised by a pronounced principal ea during artificial maturation about 16 17 of the organic carbon in the coals and 45 50 of the organic carbon in the mudstones participated in petroleum formation the two source rocks primary generate oil and secondary generate gas however the mudstones realised the majority of their potential over a more narrow temperature range than the coals the excellent generative potential of the terrestrial source rocks at dong ho is encouraging for offshore exploration for reservoirs charged by cenozoic rift lake successions q 2001 elsevier science ltd all rights reserved

glacial geology and cosmogenic nuclide exposure ages from the tucker glacier whitehall glacier confluence northern victoria land antarctica we describe glacial geological observations and cosmogenic nuclide exposure ages from the vicinity of the present grounding line of tucker glacier a large alpine glacier flowing from the mountains of northern victoria land east antarctica into the outer ross sea these data are relevant for constraining the extent of ice sheet expansion and retreat in the ross sea and associated eustatic sea level impact between the last glacial maximum lgm and the present in addition a terrestrial geological record of ice thickness change from this region could provide evidence for or against the hypothesis that rapid eustatic sea level rise during meltwater pulse 1a mwp 1a at 14 6 ka was in part the result of rapid large scale thinning or breakup of a marine based portion of the lgm ice sheet in the outer ross sea glacial geological observations exposure ages on glacial deposits and a novel application of in situ produced cosmogenic 14c in quartz bearing bedrock to identify the limits of lgm ice cover in the absence of direct geomorphic evidence show that tucker glacier near its present grounding line was 300 to 350 m thicker than present during the lgm and thinned steadily between 17 to 5 ka the largest possible rapid thickness change in the time period 14 to 15 ka that could be accommodated by the exposure age data is 50 m which is a small fraction of that predicted for the western ross sea by model simulations of the antarctic contribution to mwp 1a there do exist possible scenarios in which hypothesized marine ice sheet collapse in the outer ross sea during mwp 1a might not be recorded by ice thickness changes at tucker glacier however our record of ice thickness changes spanning this time period is the closest such record to the outer ross sea that is likely to exist and it agrees with all exposure age deglaciation chronologies from other regions of the ross embayment in providing no evidence for such an event

pressure temperature time paths and a tectonic model for the evolution of granulites petrologic studies and application of well calibrated mineralogic thermometers and barometers reveal several important features common to many granulite terrains 1 peak metamorphic pressure and temperature conditions cluster around values of 7 5 pm 1 kbar and 800 pm 50 c implying average geothermal gradients of 30 35 c km 2 in comparison with upper amphibolite facies rocks especially in paired amphibolite granulite terrains it is evident that granulites are distinguished from amphibolites by the former s higher metamorphic temperatures but not higher pressure 3 initial cooling of granulite terrains from peak conditions is nearly isobaric for garnet closure temperatures of 600 pm 50 c the dp dt retrograde paths inferred from compositionally zoned garnet rims are 2 8 b c in most granulites 4 primary coarse sillimanite is found in most granulites and retrograde kyanite is known in a few these data suggest that granulites form as a result of anomalous thermal gradients

organic matter accumulation of the lacustrine lunpola oil shale central tibetan plateau controlled by the paleoclimate provenance and drainage system abstract the cenozoic lacustrine lunpola oil shale located in the central tibetan plateau has received little research interest in its depositional history although it is estimated to be a huge resource reserve this study investigates the palaeoclimate provenance and regional drainage system of the ancient lakes using a combined analysis of element geochemistry and stratigraphy to elucidate the depositional history of the lunpola oil shale most of the samples in the lower part of the section have chemical index of alteration cia values between 65 and 75 reflecting a moderate weathered source while samples in the upper part the section have cia values between 60 and 65 which indicate relatively weak chemical weathering in the source area this stratigraphic grouping suggests a paleoclimate transition from a relatively warm or humid period to a cold or dry period the zr sc and th sc ratios of the samples reveal that sorting and recycling were minor during deposition of the oil shale the geochemical results al2o3 cao na2o k2o a cn k diagrams high contents of th plots of co th la sc and cr th sc th demonstrate that the sedimentary sources were felsic rocks plots of la th sc th sc zr 10 th co zr 10 and ti zr versus la sc illustrate that the source rocks were from continental arc and active continental margin the baingoin batholiths to the south of the lunpola basin consisting mainly of cretaceous granodiorite and adamellite are likely responsible for supplying materials to the lunpola oil shale similar special ree patterns further suggest the affiliation of the oil shale with the batholiths provenance analyses indicate a main river from the south moreover stratigraphic study confirms an upstream ancient baingoin lake between the source area and the ancient lunpola lake in this drainage system paleoclimate clearly restricted the development of rivers around the lakes although terrestrial organic matter higher plants dominated the drainage area the main river originating from the south could only bring a certain amount of them to the lakes moreover considering the filtration of the upstream ancient baingoin lake minor terrestrial organic matter could be carried and deposited in the ancient lunpola lake therefore lacustrine algae could proliferate as the main organic source and preserve in the stratified hypersaline lake to form the largest oil shale resource in tibet

the organic geochemistry of the eocene oligocene black shales from the lunpola basin central tibet abstract this paper reports on the depositional paleoenvironment and the potential hydrocarbons of the eocene oligocene black shales from the dingqinghu and niubao formations in the lunpola basin central tibet nineteen samples from two outcrop profiles were analysed the contents of the total organic carbon toc and sulphur were measured other analyses included rock eval pyrolysis solvent extraction and gas chromatography mass spectrometer gc ms the results indicated that the shales from the dingqinghu and niubao formations are thermally immature the pyrolysis data show that the shales contain type i organic matter and that lacustrine algal are the main organic matter sources the low pristane to phytane ratios and the high gammacerane indices indicate that the shales were deposited in a reducing stratified and hypersaline palaeo lake which is consistent with the climate information provided by the development history of palaeo lakes from the eocene to the oligocene epochs

lake type controls on petroleum source rock potential in nonmarine basins based on numerous empirical observations of lacustrine basin strata we propose a three fold classification of lacustrine facies associations that accounts for the most important features of lacustrine petroleum source rocks and provides a predictive framework for exploration in nonmarine basins where lacustrine facies are incompletely delineated 1 the fluvial lacustrine facies association is characterized by freshwater lacustrine mudstones interbedded with fluvial deltaic deposits commonly including coal shoreline progradation dominates basin fill resulting in the stacking of indistinctly expressed cycles up to 10 m thick in map view the deposits may be regionally widespread but laterally discontinuous and contain strong facies contrasts transported terrestrial organic matter contributes to mixed type i iii kerogens that generate waxy oil type i kerogen is hydrogen rich and oil prone type iii kerogen is hydrogen poor and mainly gas prone the luman tongue of the green river formation wyoming and the honyanchi formation junggar basin china provide examples of this facies association which is also present in the songliao basin of northeastern china the central sumatra basin and the cretaceous doba doseo basins in west central africa 2 the fluctuating profundal facies association represents a combination of progradational and aggradational basin fill and includes some of the world s richest source rocks deposits are regionally extensive in map view having relatively homogenous source facies containing oil prone type i kerogen examples include the laney member of the green river formation wyoming the lucaogou formation junggar basin china the bucomazi formation offshore west africa and the lagoa feia formation campos basin brazil 3 the evaporative facies association represents dominantly aggradational fill related to desiccation cycles in saline to hypersaline lakes and may include evaporite and eolianite deposits sublittoral organic rich mudstone facies are relatively thin but may be begin page 1034 quite rich and widespread the highest organic enrichment coincides with the deepest lake stages low input of land plant organic matter results in minimal lateral contrasts in organic content in some cases a distinctive type i s sulfur rich kerogen may generate oil at thermal maturities as low as 0 45 vitrinite reflectance equivalent examples include the wilkins peak member of the green river formation wyoming the jingjingzigou formation junggar basin china the jianghan and qaidam basins china and the blanca lila formation argentina

diagenesis of early permian high latitude limestones lower parmeener supergroup tasmania the darlington sakmarian and berriedale artinskian limestones are neritic deposits that accumulated in high latitude environments along the south eastern margin of pangea in what is now tasmania these rocks underwent a series of diagenetic processes that began in the marine palaeoenvironment continued during rapid burial and were profoundly modified by alteration associated with the intrusion of mesozoic igneous rocks marine diagenesis was important but contradictory although dissolution took place there was also coeval precipitation of fibrous calcite cement phosphate and glauconite as well as calcitization of aragonite shells these processes are interpreted as having been promoted by mixing of shelf and upwelling deep ocean waters and enabled by microbial degradation of organic matter in contrast to warm water carbonates where meteoric diagenesis is important the darlington and berriedale limestones were largely unaffected by meteoric diagenesis only minor dissolution and local cementation took place in this diagenetic environment although mechanical compaction was ubiquitous correlation with burial history curves indicates that chemical compaction became important as burial depths exceeded 150 m promoting precipitation of extensive ferroan calcite this effect resulted from burial by rapidly deposited overlying thick late permian and triassic terrestrial sediments this diagenetic pathway was however complicated by the subsequent intrusion of massive mesozoic diabases and associated silicifying diagenetic fluids finally fractures most probably connected with cretaceous uplift were filled with late stage non ferroan calcite cement this study suggests that both carbonate dissolution and precipitation occur in high latitude marine palaeoenvironments and therefore the cold water diagenetic realm is not always destructive in terms of diagenesis furthermore it appears that for the early permian of southern pangea at least there was no real difference in the diagenetic pathways taken by cool water and cold water carbonates

phase equilibria and oxygen isotopes in the evolution of metapelitic migmatites a case study from the pre alpine basement of northern switzerland metapelites that have undergone variable degrees of migmatization were encountered in two deep boreholes in northern switzerland microtextures and calculated phase diagrams yield three successive stages of metamorphism consistent with one p t loop 1 amphibolite grade metamorphism biotite sillimanite garnetoligoclase quartz ilmenite p t conditions are estimated at 4 5 6 5 kbars 550 650 c 2 anatectic migmatization melting reactions leucosomes do not represent pure crystallized melt but rather a mixture of melt cordierite and k feldspar grown at the expense of biotite and sillimanite 3 retrograde hydration recorded by the growth of large amounts of muscovite at the expense of cordierite and k feldspar p t conditions are estimated at 2 5 kbars 600 c oxygen isotope measurements were obtained for whole rocks and eight mineral species isotopic equilibrium among three or even four minerals grown during stage 1 can be demonstrated calculated isotopic temperatures are consistent with phase petrology migmatization did not re equilibrate the isotopic composition of the pre existing quartz grown in stage 1 even over distances as little as 10 cm high 18o in migmatitic quartz is best explained by disequilibrium melting in coexistence with an infiltrating isotopically heavy fluid lack of equilibration of oxygen isotopes between different quartz generations suggests that mineralogical and geochemical changes were rapid relative to diffusion rates a meteoric hydrothermal alteration at 300 400 c probably genetically linked to the intrusion of variscan granites strongly affected the rocks quartz did not exchange isotopes with hydrothermal fluids except in segregations where it is recrystallized the 18o values of micas feldspars and cordierite are often very low and fractionations with quartz very large which reflects significant hydrothermal effects that were previously detected in the black forest by other workers

evaluation of sedimentary features and biomarkers in the paleogene niubao formation in the lunpola basin tibetan plateau implications for the oil source rocks and exploration the paleogene niubao formation is mainly exposed in the central part of the lunpola basin in the hinterland of the tibetan plateau and has high potential for oil and gas exploration and development the biomarkers of source rocks are systematically studied by selecting representative samples the middle and upper niubao formation contain rhythmically inter bedded mudstone and sandstone that show periodic variations characteristic of the lake water environment additionally the large volumes of muddy dolomite in the upper niubao formation unf are associated with high salinity in the lake environment under a hot and arid climate the organic geochemical analysis shows that the middle niubao formation mnf and unf have high organic abundance total organic carbon toc contents of 1 48 8 96 in the mnf and 1 52 12 83 in the unf and type i ii kerogen the analysis shows that the unf was deposited in a persistent anoxic stratified and highly saline paleo lake environment which was beneficial to the preservation of organic matter the high phytoalkane and paraffin contents in the unf indicate a strongly reducing and highly saline lacustrine depositional environment the high pregnane contents and ascending sterane in the source rocks in the mnf indicate high maturity and the distribution of n alkanes and regular sterane indicates the input of some terrestrial organic matter the high maturity indicates that the source rock in the mnf may represent the main hydrocarbon generating layer in the basin

biological marker compounds as indicators of the depositions history of the maoming oil shale abstract the eocene maoming oil shale from guangdong province occurs as a laterally uniform stratigraphic section typically 20 25 m thick from which the aliphatic hydrocarbon constituents of six representative samples were investigated using gc and c gc ms the sediments evaluated included the basal lignite a vitrinite lens from the overlying claystone and four intervals from the massive oil shale bed as expected the lignite and vitrinite differ markedly from the oil shales the lignite is dominated by bacterial hopanoids and components of higher plant origin including c 29 steroids and triterpenoids such as oleanenes visually the oil shale samples show corroded and degraded phytoclasts spores wispy particles of fluorescent organic material attributable to dinoflagellates and especially in the uppermost sample colonial algal bodies the distributions of biological markers in the oil shales show many features in common notably a dominance of dinoflagellate derived 4 methylsteroids and a significant proportion of higher plant derived n alkanes with marked odd over even carbon number predominance overall they exhibit several features that resemble characteristics of the messel shale the hydrocarbons of the lowest shale horizon suggest that there may have been a gradual transition between deposition of the original peat and the subsequent oil shales the aliphatic hydrocarbons of the uppermost shale are dominated by a number of c 31 and c 33 botryococcane homologues and other unusual branched alkanes possibly derived from green algae all of the samples are immature overall molecular and microscopic examination of the stratigraphic succession of the maoming oil shale suggests a shallow lacustrine environment within which peats were deposited this lake subsequently deepened to support abundant algal populations especially dinoflagellates culminating in a dominance of botryococcoid algae

when was the limpopo orogeny abstract the term limpopo orogeny refers to the common high grade metamorphic and tectonic event that affected the archaean rocks of the central and southern marginal zones of the limpopo belt and its influence on the adjacent portions of the kaapvaal craton available geochronological data from muscovite kyanite prograde metamorphic assemblages zircon in igneous charnoenderbite and enderbite muscovite in syntectonic pegmatite bodies formed in shear zones partial melts and syn and post tectonic plutons of granodiorite and granite indicate that this orogeny occurred during the time interval from 2700 ma ago to 2650 ma ago the retrograde phase of this orogeny from the onset of the response phase m 2 until the rocks were subjected to rehydration m 3 was very rapid probably lasting 7 ma from 2671 ma to 2664 ma ago similar but limited data from the northern marginal zone and adjacent portions of the zimbabwe craton suggest that rocks there were subjected to a more recent interval of high grade metamorphism and tectonism extending from 2600 ma until 2550 ma

petroleum source rock evaluation of upper eocene kopili shale bengal basin bangladesh abstract the upper eocene kopili shale occurs throughout the bengal basin including in the northwestern indian platform and deeper basin areas e g sylhet trough of bangladesh mudrocks presumed to be equivalent to the kopili shale in india are known hydrocarbon source rocks however the source rock potential of the kopili shale in bangladesh is not well established thus prompting the current study of abundance character and maturity of organic matter in kopili shale samples from the bengal basin organic petrologic observations and rock eval pyrolysis data indicate that organic matter in the kopili shale is largely terrigenous including an admixture of type i ii liptodetrinite cutinite bituminite type iii vitrodetrinite and type iv inertodetrinite macerals mean vitrinite reflectance values ro 0 86 1 32 and a single reliable tmax value 433 c indicate that organic matter from all sampled sections is thermally mature total organic carbon toc contents of samples from core and outcrop are generally low an understanding of differences in kopili source rock potential between india and parts of the bengal basin will require more comprehensive comparative facies analyses

effects of source thermal maturity and biodegradation on the distribution and isomerization of homohopanes in petroleum abstract the distributions of c31 c35 17 21 h homohopanes in marine petroleums can be used to describe redox conditions in the source rock depositional environment for example high c35 homohopane indices c35 c31 c35 are typical of petroleums generated from source rocks deposited under anoxic marine conditions where the c35 backbone of the precursor bacteriohopanetetrol is preferentially preserved homohopane distributions have been used to distinguish petroleums from different organic facies of the same source rock homohopane distributions are altered by secondary processes for example the c35 homohopane index decreases with increasing api gravity and thermal maturity of related oils from the monterey formation offshore california similar decreases in the homohopane index are observed for expelled oils from monterey source rock during hydrous pyrolysis biodegradation can result in selective loss of high or low molecular weight homologs apparently depending on the bacterial population in the reservoir bacterial demethylation of homohopanes appears necessary to explain 25 norhopanes in at least one biodegraded oil hydrous pyrolysis studies of the phosphatic and siliceous members in the monterey formation show that identical heating conditions result in different homohopane c 22 epimer ratios furthermore a reversal in the trend of the epimer ratio at high experimental temperatures is observed for the phosphatic but not for the siliceous lithology this could be caused by the combined effects of isomerization and differential thermal destruction of epimers at high temperatures possibly mediated by rock mineralogy

oxygen isotope perspective on crustal evolution on early earth a record of precambrian shales with emphasis on paleoproterozoic glaciations and great oxygenation event abstract we present stable isotope and chemical data for 206 precambrian bulk shale and tillite samples that were collected mostly from drillholes on all continents and span the age range from 0 5 to 3 5 ga with a dense coverage for 2 5 2 2 ga time interval when earth experienced four snowball earth glaciations and the irreversible rise in atmospheric o2 we observe significant downward shift of several and a smaller range of 18 o values 7 to 9 in shales that are associated with the paleoproterozoic and potentially neoproterozoic glaciations the paleoproterozoic samples consist of more than 50 mica minerals and have equal or higher chemical index of alteration than overlying and underlying formations and thus underwent equal or greater degrees of chemical weathering their pervasively low 18 o and d down to 85 values provide strong evidence of alteration and diagenesis in contact with ultra low 18 o glacial meltwaters in lacustrine deltaic or periglacial lake sikussak type environments associated with the paleoproterozoic glaciations the d silicate values for the rest of precambrian shales range from 75 to 50 and are comparable to those for phanerozoic and archean shales likewise these samples have similar ranges in 13 c org values 23 to 33 pdb and corg content 0 0 to 10 wt to phanerozoic shales precambrian shales have a large range of 18 o values comparable to that of the phanerozoic shales in each age group and formation suggesting similar variability in the provenance and intensity of chemical weathering except for the earliest 3 3 3 5 ga archean shales which have consistently lower 18 o values moreover paleoproterozoic shales that bracket in age the great oxidation event goe overlap in 18 o values absence of a step wise increase in 18 o and d values suggests that despite the first order change in the composition of the atmosphere weathering cycle was not dramatically affected by the goe at 2 4 2 3 ga shales do not show comparable 18 o rise in the early phanerozoic as is observed in the coeval 18 o trends for cherts and carbonates there is however a sharp increase in the average 18 o value from the early archean to the late archean followed by a progressively decelerating increase into the phanerozoic this decelerating increase with time likely reflects declining contribution of mantle extracted normal 18 o crust and lends support to crustal maturation and increasing 18o sequestration into the crust and recycling of high 18 o and 87sr 86sr sedimentary rocks this secular increase in the 18 o composition of the continental crust could have also had a mild effect on seawater 18 o composition

microfossil and stable isotope evidence for changes in late holocene palaeoproductivity and palaeoceanographic conditions in the prydz bay region of antarctica microfaunal and microfloral data from two gravity cores and stable isotope results from one of these cores taken on fram bank near prydz bay antarctica indicate changes in sea ice patterns and oceanographic conditions which may have been linked to regional and global climate changes that occurred over the past 8000 yr modern diatom assemblages indicative of ice free conditions 1 2 months of the year and dominated by nitzschia species became prevalent some time around 2000 2700 yr b p the occurrence of chaetoceros spp diatom spore dominated assemblages and increased abundances of benthic and planktonic foraminifera ostracods and diatoms coupled with carbon and oxygen isotope changes around 2700 3400 yr b p strongly suggests that this area of the shelf experienced conditions conducive to increased productivity during this time period based on diatom assemblage associations recognized in modern environments the upper water column of fram bank shelf waters was probably stratified during that time due to the presence of low salinity melt water and a very shallow mixed layer protected from storms with sea ice cover for less than 10 months per year the close correspondence of 13c and 18o values from n pachyderma r2 0 74 throughout one core suggests that whatever oceanographic conditions influenced 18o also influenced 13c changes in prydz bay microfossil abundances and isotopes may result from alterations in circulation patterns upwelling conditions or sea ice patterns which significantly affected benthic and planktonic productivity in the area the environmental conditions indicated by older sediments in the cores are less clear but an ice tongue may have been in place 3200 3800 yr b p and minor fluctuations in productivity are indicated around 6000 and 7000 7500 yr b p the lower 100 cm of both cores may not represent in situ deposition but if the corrected ams dates reflect the actual age of the sediments analyzed microfossil and isotope data indicate that productivity and oceanographic conditions were very variable around 8500 8600 yr b p the chronology adopted herein must be regarded as tentative until further study of the area has been undertaken