global ice sheet system interlocked by sea level abstract denton and hughes 1983 quaternary research 20 125 144 postulated that sea level linked a global ice sheet system with both terrestrial and grounded marine components during late quaternary ice ages summer temperature changes near northern hemisphere melting margins initiated sea level fluctuations that controlled marine components in both polar hemispheres it was further proposed that variations of this ice sheet system amplified and transmitted milankovitch summer half year insolation changes between 45 and 75 n into global climatic changes new tests of this hypothesis implicate sea level as a major control of the areal extent of grounded portions of the antarctic ice sheet thus fitting the concept of a globally interlocked ice sheet system but recent atmospheric modeling results manabe and broccoli 1985 journal of geophysical research 90 2167 2190 suggest that factors other than areal changes of the grounded antarctic ice sheet strongly influenced southern hemisphere climate and terminated the last ice age simultaneously in both polar hemispheres atmospheric carbon dioxide linked to high latitude oceans is the most likely candidate shackleton and pisias 1985 atmospheric carbon dioxide orbital forcing and climate in the carbon cycle and atmospheric co2 natural variations archean to present e t sundquest and w s broecker eds pp 303 318 geophysical monograph 32 american geophysical union washington d c but another potential influence was high frequency climatic oscillations 2500 yr it is postulated that variations in atmospheric carbon dioxide acted through an antarctic ice shelf linked to the grounded ice sheet to produce and terminate southern hemisphere ice age climate it is further postulated that milankovitch summer insolation combined with a warm high frequency oscillation caused marked recession of northern hemisphere ice sheet melting margins and the north atlantic polar front about 14 000 14c yr b p this permitted renewed formation of north atlantic deep water which could well have controlled atmospheric carbon dioxide w s broecker d m peteet and d rind 1985 nature london 315 21 26 combined melting and consequent sea level rise from the three warming factors initiated irreversible collapse of the interlocked global ice sheet system which was at its largest but most vulnerable configuration

effects of silt content and void ratio on the saturated hydraulic conductivity and compressibility of sand silt mixtures the hydraulic conductivity the coefficient of consolidation and the coefficient of volume compressibility play major roles on the pore pressure generation during undrained and partially drained loading of granular soils with fines this paper aims to determine how much these soil parameters are affected by the percentage of fines and void ratio of the soil the results of a large number of flexible wall permeameter tests performed on 60 specimens of two poorly graded sands with 0 5 10 15 20 and 25 nonplastic silt are presented and discussed hydraulic conductivity measurements were done at effective confining stresses of 50 300 kpa the evaluation of the data shows that the hydraulic conductivity and the coefficient of consolidation of sands with 25 silt content are approximately two orders of magnitude smaller than those of clean sands the coefficient of volume compressibility of the sand silt mixtures is affected in a lesser degree by void ratio silt content and confining stress the influence of the degree of saturation on the laboratory measured k values is also discussed

effects of nonplastic fines on static liquefaction of sands des essais triaxiaux en compression non draines ont ete effectues sur des echantillons reconstitues de sable du nevada et d ottawa avec variation systematique de la teneur en fines particules inferieures a 0 074 mm afin d evaluer l effet de la fraction fine sur le potentiel de liquefaction statique lors d un chargement monotonique les fines etaient non plastiques les resultats indiquent clairement que la presence de fines peut augmenter considerablement le potentiel de liquefaction statique des quatre sables propres etudies lorsqu on utilise la technique du montage a sec avec un entonnoir les fines semblent creer dans le sol une structure particulaire tres compressible ce qui accroit ainsi le potentiel de liquefaction alors meme que la densite augmente accroitre la teneur en fines d un sable propre peut aboutir a l augmentation du potentiel de liquefaction jusqu a un seuil maximum pour lequel les fines dominent le comportement non draine du sol a ce point la le potentiel de liquefaction tend a devenir constant vis a vis de l indice de densite on a trouve que la liquefaction statique complete pouvait intervenir a un indice de densite superieur a 60 pour des teneurs en fines elevees

geochronological evidence supporting antarctic deglaciation three million years ago the response of the antarctic ice sheets to increased global temperatures is an important unresolved issue in the assessment of future climate change in particular considerable controversy exists as to whether the east antarctic ice sheet suffered extensive deglaciation during the mid pliocene epoch 3 myr ago when temperatures were only slightly warmer than today although the ice sheet is widely assumed to have existed in something like its present form for the past 14 myr ref 1 marine diatoms eroded from the antarctic interior have been found in glacial till deposits high in the transantarctic mountains2 3 and have been bio stratigraphically dated at 3 myr before present this age has been disputed4 because it implies marine deposition in the antarctic interior and hence substantial deglaciation at a time when other evidence has been marshalled for the persistence of cold polar conditions4 here we report k ar and 40ar 39 ar ages for a volcanic ash bed in diatom bearing glaciomarine strata cored in ferrar fiord east antarctica by the ciros 2 drill hole5 which confirm the age of the diatoms at 3 myr and hence also confirm the mid pliocene deglaciation

closure to liquefaction susceptibility criteria for silts and clays by ross w boulanger and i m idriss the authors study provides valuable insight into the stress strain behavior of fine grained soils silts and clays under monotonic and cyclic undrained loading the distinct behavioral features of sands versus clays under the aforementioned types of loading are first identified with regard to the shape of the hysteresis loops the value of excess pore water pressure ratio and the magnitude of developed strains then a classification of fine grained soils into two classes of materials is proposed namely sand like materials that are susceptible to liquefaction in the classical meaning of the term and clay like materials that are susceptible to cyclic softening in addition the authors emphasize the critical importance of using the appropriate procedure for evaluating the cyclic strength for each class of material following the establishment of the above framework the authors review a database of test results compiled from the literature and found that the plasticity index pi of fines is the single most important parameter for distinguishing between the two types of behavior they propose the use of a limit value of pi 7 as follows 1 for pi 7 the material is susceptible to liquefaction i e exhibits sand like behavior and its liquefaction resistance should be evaluated using the available procedures for sands 2 for pi 7 the soil behaves as a clay like material and its behavior should be analyzed using the procedures available for evaluating the cyclic strength of cohesive soils a transition zone of plasticity index from 3 to 8 is proposed by the authors who also suggest discontinuing the use of the chinese criteria of liquefaction susceptibility finally the authors discuss the applicability of the liquefaction criterion proposed in the paper to soils containing less than 50 fines coarse grained materials they argue that as long as the amount of fines is greater than a threshold value fcthr which is the limit above which the fine grains constitute the loading carrying matrix of soil their criterion could be extended to fines content fc 50 the discussers have recently presented results of cyclic triaxial tests on saturated mixtures of sand with different amounts of nonplastic silt xenaki and athanasopoulos 2003 the tests were conducted to investigate the effect of fines content on the liquefaction resistance of sand silt mixtures in view of the authors study and other recently published data the discussers would like to present some related data not included in their previous publication and compare them to the findings reported in the paper

active pressure on gravity walls supporting purely frictional soils the active earth pressure used in the design of gravity walls is calculated based on the internal friction angle of the retained soil or backfill however the friction angle of a soil changes during the deformation process for drained loading the mobilized friction angle varies between the peak and critical state friction angles depending on the level of shear strain in the retained soil consequently there is not a single value of friction angle for the retained soil mass and the active earth pressure coefficient changes as the wall moves away from the backfill and plastic shear strains in the backfill increase in this paper the finite element method is used to study the evolution of the active earth pressure behind a gravity retaining wall as well as the shear patterns developing in the backfill and foundation soil the analyses relied on use of a two surface plasticity constitutive model for sands which is based on critical state soil mechanics

comparison of the paleoclimatic significance of higher land plant biomarker concentrations and pollen data a case study of lake sediments from the holsteinian interglacial abstract a sediment core from the dethlingen paleolake holsteinian interglacial northern germany was subjected to integrated organic geochemical and palynological paleobotanical analyses in order to reconstruct past environmental conditions the fractionated lipid extracts were investigated using gas chromatography mass spectrometry gc ms and gc combustion isotopic ratio ms ring a aromatized pentacyclic triterpenoids most likely glutinane derivatives were the only higher plant derived pentacyclic triterpenoids found the saturated ring a degraded triterpenoid des a lupane was the most abundant aliphatic hydrocarbon throughout the core based on published pollen data which imply the strong presence of betula and alnus around the paleolake the des a lupane would be expected to originate mainly from lupane type precursors synthesized by betulaceae the carbon isotopic composition of des a lupane varied from 28 2 to 30 6 and no significant trend or isotopic shift was observed however the discrepancy between the variation in pollen data and biomarker concentration i e quasi absence of diterpenoids in the core argues for a scenario in which the two proxies represent different components of the vegetation in the catchment area of the paleolake

petrographical and organic geochemical study of the kovin lignite deposit serbia abstract the origin of the organic matter om and the characteristics of the depositional environment of lignites from the upper miocene kovin deposit hosting three coal seams of serbia were evaluated based on petrographic data bulk organic geochemical parameters biomarker analysis and stable isotope geochemistry 13c of individual biomarkers samples were collected from four boreholes gd 601 and gd 603 the a field and kb 79 and kb 91 the b field representing different parts of coal seams i ii and iii investigated lignites are typical humic coals the om of lignites is derived from woody vegetation and herbaceous peat forming plants with prevalence of the former in most samples peat forming vegetation is characterized by abundant decay resistant gymnosperm coniferous plants followed by a low amount of angiosperms lignite forming plants mostly belonged to the gymnosperm families cupressaceae taxodiaceae phyllocladaceae and pinaceae slight input of ferns fungi and aquatic macrophyta to lignite om is also evident distributions of hopanoids and isotopic compositions of these biomarkers reflect the activity of various microbial populations represented by methanotrophic chemoautotrophic and heterotrophic bacteria during diagenesis prominent c28 28 30 bisnorneohop 13 18 ene was observed for the first time in the lignite extracts according to the 13c value it was probably derived from chemoautotrophic bacteria c28 28 30 bisnorneohop 13 18 ene could be one of the possible precursors of a series of orphan aromatic hopanoids bearing an ethyl group at c 21 via progressive aromatization peatification proceeded in a fresh water environment under variable redox conditions from anoxic to slightly oxic all three coal seams are heterogeneous the lower parts of the coal seams represent a topogenous fresh water peat mire with open water areas which was subjected to inundations the upper parts of coal seams represent a wet forest swamp with relatively stable conditions despite the observed variations in all three coal seams the mean values of petrographic and organic geochemical parameters suggest general increasing of wetness and establishment of more stable conditions from seam iii to seam i maceral and biomarker data indicate that rapid flooding of the bogs stopped peat growth in all three coal seams relatively frequent variations in all three coal seams followed by repetition of lignite characteristics depict well the pronounced seasonality e g short term cycles of the climate during late miocene in investigated area

preservation of miocene glacier ice in east antarctica antarctic climate during the pliocene has been the subject of considerable debate one view holds that during part of the pliocene east antarctica was largely free of glacier ice and that vegetation survived on the coastal mountains1a 4 an alternative viewpoint argues for the development of a stable polar ice sheet by the middle miocene which has persisted since then5a 10 here we report the discovery of buried glacier ice in beacon valley east antarctica which appears to have survived for at least 8 1 million years we have dated the ice by 40ar 39ar analysis of volcanic ash in the thin overlying glacial till which we argue has undergone little if any reworking isotope and crystal fabric analyses of the ice show that it was derived from an ice sheet we suggest that stable polar conditions must have persisted in this region for at least 8 1 million years for this ice to have avoided sublimation

index properties based criteria for liquefaction susceptibility of clayey soils a critical assessment the cooper marl in charleston s c a deep layer of clayey soils approximately 5 21 m below the ground surface is generally recognized as nonliquefiable material data from field cone penetration tests and laboratory tests of samples taken from the cooper marl are used to investigate the adequacy of index properties based criteria for assessing liquefaction susceptibility of clayey soils in particular the criterion based on soil behavior type index ic and that based on atterberg limits are examined the results show that the atterberg limits based criterion adequately reflected the characteristics of the marl whereas the ic based criterion erroneously identified the marl as being liquefiable a possible reason for the deficiency of ic and a modification to overcome this deficiency are presented

molecular stable carbon isotope compositions of alkylphenanthrenes in coals and marine shales related to source and maturity abstract phenanthrene phe and methylphenanthrenes mps extracted from coaly shale and coal samples containing terrestrial organic matter are compared with the same compounds from marine shales in terms of yields and 13 c values at marginally to fully mature stages of thermal evolution the shales derived from four boreholes in the hils half graben area northwestern germany were shown to be representative of a greater number of samples from the same sites the 13 c values of extractable phe and mps are less negative in the terrestrial 24 3 to 26 0 than in the marine 28 8 to 30 5 samples since these values are unrelated to mean vitrinite reflectance r r values in the range of 0 5 0 9 it appears that the stable carbon isotope composition of phe and mps is controlled by organic matter type rather than maturity

holocene glacier fluctuations in south america and antarctica abstract glacial geologic evidence indicates that glaciers throughout the andes and antarctica fluctuated during the holocene radiocarbon dating and other age determinations suggest that glaciers readvanced significantly only during the last 5 ka reaching positions from several 100 m to a few kilometres beyond their present limits in south america tenuous evidence from radiocarbon dates with dendrochronological data and environmental interpretations from pollen analyses indicate four main periods of neoglacial advance culminating 5000 4000 bp 3000 2000 bp 1300 1000 bp and 15th late 19th centuries smaller advances may have occurred at ca 8400 bp ca 7500 bp and ca 6300 bp the meagre data are consistent in indicating broad synchrony throughout the andes during the last 5 ka suggesting response to global climatic changes anomalies exist in patagonia where some tide water glaciers reached their maximal holocene limits recently this century the broad spectrum of differing antarctic environments produces interesting contrasts some local glaciers in the mcmurdo sound area of the east artarctic continent are more extensive now than during the global glacial maximum ca 18 ka bp when they were starved of precipitation consistent agreement among 14 radiocarbon dates from the south shetland islands indicates two main holocene glacier advances the most extensive 2 3 km peaking in the 12th century the other culminating in the 18th 19th century glaciers in south georgia reached their most advanced holocene limits before 2200 bp moraine fjord glacier which culminated as a 6 km advance between 1460 1700 radiocarbon bp may have lagged 400 650 years behind the climatic forcing because it could only advance in its deep water fjord by building a moraine bank smaller advances in south georgia culminated in the 17th 19th centuries and during the 1920s 30s there is no firm evidence of glacier advances before 3 ka bp in the southern ocean sub antarctic domain but broad synchrony in glacier advances during the last ca 3000 years appears to have occurred throughout the andes antarctic transect caution is required in the interpretation and correlation of moraines associated with calving glaciers and of those with poorly constrained dating

satellite radar interferometry for monitoring ice sheet motion application to an antarctic ice stream satellite radar interferometry sri provides a sensitive means of monitoring the flow velocities and grounding line positions of ice streams which are indicators of response of the ice sheets to climatic change or internal instability the detection limit is about 1 5 millimeters for vertical motions and about 4 millimeters for horizontal motions in the radar beam direction the grounding line detected by tidal motions where the ice goes afloat can be mapped at a resolution of 0 5 kilometer the sri velocities and grounding line of the rutford ice stream antarctica agree fairly well with earlier ground based data the combined use of sri and other satellite methods is expected to provide data that will enhance the understanding of ice stream mechanics and help make possible the prediction of ice sheet behavior

liquefaction testing of stratified silty sands the cyclic behavior of stratified silty sandy soils is at present poorly understood yet these materials are commonly found in alluvial deposits and hydraulic fill which have a history of liquefaction during earthquakes the main objective of this research project was to compare the behavior of stratified and homogeneous silty sands during seismic liquefaction conditions for various silt contents and confining pressures a comprehensive experimental program was undertaken in which a total of 150 stress controlled undrained cyclic triaxial tests were performed two methods of sample preparation were used for each soil type these methods included moist tamping representing uniform soil conditions and sedimentation representing layered soil conditions the silt contents ranged from 10 to 50 and confining pressures in the range of 50 to 250 kpa were considered the results indicated that the liquefaction resistances of layered and uniform soils are not significantly different despite the fact that th

cenozoic marine sedimentation and ice volume variation on the east antarctic craton recycled cretaceous and cenozoic marine microfossils have been recovered from samples of the pliocene sinus formation samples were collected from outcrops in the reedy beardmore and ferrar glacier areas of the transantarctic mountains between lat 77 and 86 s the glaciogene sediments contained diatoms foraminifera calcareous nannoplankton silicoflagellates radiolarians sponge spicules palynomorphs and ostracodes of late cretaceous paleocene eocene late oligocene late miocene and pliocene age this suggests the presence of open marine basins on the east antarctic craton during late mesozoic and cenozoic time the apparent absence of early oligocene and early through middle and earliest late miocene assemblages suggests either that marine regression exposed the basin floors or that ice filled the basins during these times the high elevation setting of sirius formation outcrops suggests one of two hypotheses for their origin 1 they are in situ pliocene glaciomarine deposits that were uplifted 1 750 2 500 m with the transantarctic mountains to their present elevation 2 the sirius formation deposits are a mixture of derived sediments stripped from sub ice intracratonic basins and subsequently redeposited by ice flowing up the inland slope of the transantarctic mountains we favor the second hypothesis with transport to sites sometime within the past 3 m y

undrained monotonic response of clean and silty sands a series of undrained monotonic triaxial compression tests were performed on ottawa sand containing 0 5 10 and 15 of non plastic silt the paper focuses on distinctive states of the monotonic undrained response of sands namely the critical state the phase transformation state the quasi steady state and the state of undrained instability onset of flow liquefaction specimens were prepared using slurry deposition and moist tamping to investigate the effect of the initial sand fabric on these states it was observed that an increase in the non plastic fines content leads to a downward shift of the critical state line in the void ratio mean effective stress space and to an increase of the critical state friction angle the present data suggest that the initial fabric of the sand appears to have a significant effect on the undrained behaviour in the early stages of shearing with its influence vanishing at large strains moist tamped specimens demonstrate considerably larger undrained instability s

paleoenvironmental reconstruction of the coal and oil shale bearing interval in the lower cretaceous muling formation laoheishan basin northeast china abstract the laoheishan basin in northeast china has been filled with lower cretaceous coal and oil shale bearing sediments the basin fill includes from base to top alluvial conglomerate lower member of muling formation fan delta sediments interbedded with coal and oil prone mudstone denominated as oil shale layers in the upper member of muling formation and volcaniclastic rocks dongshan formation in the present study the maturity of organic matter oil shale quality and paleoenvironment of the coal and oil shale accumulation are investigated based on macro and micropetrographic data proximate and ultimate analyses bulk geochemical parameters biomarkers analysis and stable isotope geochemistry in the laoheishan basin both coal and oil shale layers are derived from land plant organic matter this contrast the oil shale of this basin from oil shale coal intercalations in fault related basins in which oil shale has been found to be of algal origin the coal is sub bituminous in rank hydrogen rich and oil prone the oil shale is of low medium grade and the relatively low oil yield may relate to the abundant resinite and sporinite because of their lower generation potential compared with alginite accumulation of the high ash coal commenced in low lying mire drowned during frequent floodings subsequently high ash low sulfur coal was deposited in a stable low lying mire under oxic conditions and limited bacterial activity afterwards the mire was drowned and formed a freshwater dysoxic to oxic shallow lake in which oil shale layers accumulated finally the depositional environment returned to low lying mire but probably with a brackish influence as indicated by elevated sulfur contents in the uppermost samples petrography and biomarker based proxies indicate that gymnosperms dominated the paleovegetation of the mire accompanied by variable amounts of herbaceous plants such as ferns

ice distal upper miocene marine strata from inland antarctica abstract glacimarine strata of the battye glacier formation 130 m thick pagodroma group exposed in the amery oasis of east antarctica provide a record of late miocene palaeoenvironmental conditions in an ice distal setting the formation overlies the amery erosion surface 300 m to 270 m above sea level that formed during an advance of the lambert glacier into prydz bay odp site 739 at least 750 km further north than today two lithological members a grey and muddier lower member and a brown sand rich upper member reflect variation in proximity to the terminus of the lambert glacier ice distal glacimarine diatom bearing mud up to 12 biogenic silica and in situ articulated molluscs occur in the lower member the battye glacier formation is significant because of its inland location which indicates that ice distal marine conditions existed 250 km inland from the current amery ice shelf edge similar neogene strata are known on land only from the pliocene sorsdal formation in the vestfold hills near the antarctic coast three stratigraphic intervals of diatom bearing mud are recognized from glacially reworked clasts and from in situ strata informally referred to as the mcleod beds and bed a the diatom bearing mud also contains sponge spicules and minor silicoflagellates and ebridians marine diatom biostratigraphy constrains the age of the beds to between 10 7 and 9 0 ma late miocene abundant benthic diatoms suggest deposition within shallow euphotic waters the high abundance of intercalary valves of eucampia antarctica from an interval of the mcleod beds suggests that there was less winter sea ice than in prydz bay today it is unlikely that sea ice was perennial because the presence of thalassionema spp and stellarima stellaris roper hasle et sims suggests that summer sea surface temperatures were too warm 0 c and 3 c respectively the palaeoclimate at the time of deposition appears to have been analogous to that in modern fjords of east greenland e g kangerdlugssuaq fjord which is consistent with the depositional model proposed previously for the pagodroma group the three diatom bearing mud intervals were deposited in the amery oasis 250 km inland of the current amery ice shelf edge when the east antarctic ice sheet was reduced in size relative to today

aliphatic and diterpenoid hydrocarbons and their individual carbon isotope compositions in coals from the liaohe basin china abundant tricyclic diterpanes i e pimarane dehydroabietane and simonellite and tetracyclic diterpanes e g phyllocladane were detected in coal samples from the third member of the shahejie formation lower eogene liaohe basin china gas chromatography isotope ratio mass spectrometry gc irms analyses show that the carbon isotopic composition of terrigenous tricyclic and tetracyclic diterpenoid hydrocarbons are about 4 6 enriched in 13c compared to n alkanes in the same samples in addition the pimaranes and phyllocladane have comparatively narrow stable carbon isotopic compositions among the different samples with a slightly wider range in 13c compositions for the abietanes i e abietane dehydroabietane and simonellite the n alkanes and triterpenoids reflect the 13c compositions of higher plant wax

paleoenvironment of the eocene coal seam in the fushun basin ne china implications from petrography and organic geochemistry abstract the fushun basin in northeast china is a strike slip basin filled with coal bearing eocene sediments the basin fill includes from base to top volcaniclastic rocks a 20 to 145 m thick coal seam lower eocene guchengzi formation and lacustrine oil shale up to 300 m thick jijuntun formation the sub bituminous coal of the guchengzi formation famous for the amber inclusions is exploited in the largest opencast coal and oil shale mine in asia in the present contribution the depositional environment and the thermal history of the guchengzi formation are investigated based on macro and micropetrographic data bulk geochemical parameters biomarker analysis stable isotope geochemistry and vitrinite reflectance measurements according to our interpretation accumulation of the low sulfur coal commenced in a low lying mire near a shallow lake subsequently low ash coal was deposited either in a low lying mire protected from clastic influx or in a raised mire finally high subsidence rates typical for strike slip basins caused the flooding of the mire and terminated peat accumulation pristane phytane ratios suggest a gradual change from oxic to less oxic conditions during the drowning phase of the seam organic rich shales accumulated in the newly formed freshwater lake and resulted in the deposition of the overlying oil shale bearing jijuntun formation the coal is rich in liptinite macerals especially sporinite gymnosperms dominated the paleovegetation of the mire something that is also reflected by the frequent occurrence of resinite and amber and their biomarker composition the coal reached the sub bituminous or even the high volatile bituminous stage despite the limited burial depth simple 1d models suggest that this is a result of high heat flow rather than of deep burial and erosion the hydrogen rich coal is oil prone

effect of penetration rate on cone penetration resistance in saturated clayey soils in this paper the effects of penetration rate on cone resistance in saturated clayey soils are investigated shear strength rate effects in clayey soils are related to two physical processes the increase of shear strength with increasing rate of loading and the increase of shear strength as the process transitions from undrained to drained special focus is placed on this second effect cone penetration tests were performed at various penetration rates both in the field and in a calibration chamber and the resulting data were analyzed the field cone penetration tests were performed at two test sites with fairly homogeneous clayey silt and silty clay layers located below the groundwater table additionally tests with both cone and flat tip penetrometers in sand clay mixtures were performed in a calibration chamber to investigate the change in drainage conditions from undrained to partially drained and from partially drained to fully drained a series of flexible wall permeameter tests were conducted in the laboratory for various clayey sand mixtures prepared at various mixing ratios in order to obtain values of the coefficient of consolidation which is required to estimate the penetration rates below which penetration is drained and above which penetration is undrained a correlation between cone resistance and drainage conditions was established based on the results of the calibration chamber and field penetration tests

late quaternary glacial history of george vi sound area west antarctica during the last glacial maximum in west antarctica separate ice caps developed on alexander island and on palmer land became confluent in george vi sound and discharged northward from latitude 72 s radiocarbon 32 000 yr and amino acid approximately 120 000 yr age determinations on shell fragments hiatella solida found in basal till suggest a wisconsin age for the glaciation that incorporated them the pattern of ice flow differed from that deduced for this area in the climap reconstruction following the maximum stage there was a stadial event when outlet valley glaciers flowed from smaller ice caps into george vi sound more widespread recession permitted the george vi ice shelf to deposit palmer land erratics on eastern alexander island before isostatic recovery raised them to final elevations of about 82 m the ice shelf may have been absent at about 6500 yr b p when large barnacles bathylasma corolliforme were living in the sound small glaciers readvanced to form at least two terminal moraines before the ice shelf re formed and incorporated the barnacle shells into its moraine on alexander island the shells gave a 14c age corrected for antarctic conditions of about 6500 yr b p and an amino acid ratio consistent with a holocene age valley glaciers readvanced over the ice shelf moraine before oscillations of both valley glaciers and the ice shelf led to the formation of the present sequence of contiguous ice cored moraines probably during the little ice age such oscillations may represent a climatic control not yet observed in the dry valleys of victoria land the only other part of antarctica studied in detail for glacier fluctuations

laboratory investigation on assessing liquefaction resistance of sandy soils by shear wave velocity shear wave velocity vs offers engineers a promising alternative tool to evaluate liquefaction resistance of sandy soils and the lack of sufficient in situ databases makes controlled laboratory study very important in this study semitheoretical considerations were first given based on review of previous liquefaction studies which predicted a possible relationship between laboratory cyclic resistance ratio crrtx and vs normalized with respect to the minimum void ratio confining stress and exponent n of hardin equation undrained cyclic triaxial tests were then performed on three reconstituted sands with vs measured by bender elements which verified this soil type dependent relationship further investigation on similar laboratory studies resulted in a database of 291 sets of data from 34 types of sandy soils based on which the correlation between liquefaction resistance and vs was established statistically and further converted to equivalent field conditions with well defined parameters reve

carbon isotopic composition of individual biomarkers in gilsonites utah abstract carbon isotopic compositions of saturated hydrocarbon aromatic hydrocarbon nso resin and asphaltene fractions of vein forming gilsonites cowboy bonanza independence wagonhound and harrison veins in the ne uinta basin utah are all similar and isotopically resemble mahogany zone shale extracts of the green river formation 13 c 29 to 31 individual molecular fossils in the gilsonites show a wider variability in compositions indicative of their paleoecological origins within the eocene uinta greater green river paleolake system carbon isotopic compositions of c28 and c29 steranes 13 c 25 to 32 pristance and phytane 33 to 34 and perhydro carotene carotane 13 c 33 2 suggest that organisms producing these compounds grew near the lake surface the c33 carotenoid lexane is isotopically identical to the c40 carotenoid carotane supporting a common c40 carotenoid precursor two groups of hopanes can be differentiated in the gilsonites based on carbon isotopic compositions c29 c31 and c32 hopanes and moretanes 40 9 to 44 3 consistent with a source from midwater bacteria and c30 hopanes and moretanes 51 0 and 60 5 for which the strong 13c depletion suggests at least partial derivation from methylotrophs the isotopic signatures of these molecular fossils suggest the source beds of the gilsonites were deposited in a stratified paleolake system with a depositional environment similar to that which formed the mahogany zone shales of the piceance creek basin algal biomarkers in the gilsonites are isotopically uniform throughout the area of the gilsonite vein occurrence 1500 km3 and resemble those in the mahogany zone shale in the piceance creek basin over 50 km to the east this remarkable lateral uniformity suggests that very similar photic zone water conditions existed across the entire uinta piceance creek paleolake system at the time of deposition of the gilsonite source bed mahogany zone shale sterane isotopic compositions are effective for the genetic correlation of the solid bitumens immature oils in contrast the carbon isotopic compositions of the bacterial biomarkers in the gilsonites vary significantly suggesting that conditions in deeper waters of the paleolake system were more variable carbon isotopic signatures of individual hopane biomarkers in the green river formation appear to be valuable for identifying different source facies characteristics within the same paleolake depositional system

the middle miocene climatic transition east antarctic ice sheet development deep ocean circulation and global carbon cycling abstract the middle miocene represents a major change in state in cenozoic climatic evolution following the climax of neogene warmth in the late early miocene at 16 ma the early stage of this climatic transition from 16 to 14 8 ma was marked by major short term variations in global climates east antarctic ice sheet eais volume sea level and deep ocean circulation in the later stage from 14 8 to 12 9 ma climatic developments included major growth of the eais and associated antarctic cooling a distinct increase in the meridional temperature gradient large fluctuations in sea level followed by a global sea level fall and important changes in deep water circulation including increased production of southern component water east antarctic ice sheet growth and polar cooling also had large effects on global carbon cycling and on the terrestrial biosphere including aridification of mid latitude continental regions increased stability of the eais after 14 8 ma represents a crucial step in the establishment of late neogene global climate systems what controlled these changes in polar climates and the east antarctic ice sheet deep ocean circulation changes probably played a major role in the evolution and variation in polar climates as they have throughout the cenozoic oxygen and carbon isotopic evidence for warm saline deep water production in the eastern tethyan northern indian ocean indicates that meridional heat transport to the antarctic inhibited cenozoic polar cooling and eais growth during the early middle miocene from 16 to 14 8 ma inferred competition between warm low latitude sources derived from the eastern tethyan northern indian ocean and a cold high latitude source southern component water from 16 to 14 8 ma may have been associated with instability in the antarctic climate and cryosphere reduction of warm saline deep water flow to the southern ocean at 14 8 ma may have decreased meridional heat transport to the antarctic cooling the region and leading to increased production of southern component water these middle miocene climatic and cryospheric changes in the antarctic had profound effects on marine and terrestrial climates as the meridional surface temperature gradient increased boundaries between climatic zones strengthened leading to increased aridification of mid latitude continental regions in australia africa and north and south america enhancing the development of grasslands and stimulating the evolution of grazing mammals

strength and dilatancy of silty sand abstractfines content can have a great influence on the mechanical behavior of sand the effect of fines content has not been taken into account in most of the strength dilatancy relationships for sand an attempt was made in this paper to account for the influence of fines content on the strength dilatancy relationship of silty sands the test data on ottawa sands with nonplastic fines were reanalyzed to examine the strength and dilatancy relationship for silty sand with different fines contents the ratio of excess angle which is the difference between the peak friction angle and the critical state friction angle to the relative dilatancy index was found to be a function of fines content furthermore a strength dilatancy relationship was also modified to account for the influence of confining pressure on the strength dilatancy relationship of silt sands

is there evidence for a substantial contribution of prokaryotic biomass to organic carbon in phanerozoic carbonaceous sediments the role of prokaryotes bacteria and archaea in producing biomass and reworking settling and buried organic matter is of paramount importance since it exerts a major impact on the composition of sedimentary organic matter and ultimately petroleum this key role of prokaryotes in combination with a biomarker fingerprint often dominated by prokaryotic molecular fossils e g hopanoids has led to the assumption that prokaryotic biomass is a substantial source for organic carbon in carbonaceous sediments however biosynthesising and reworking organic matter does not necessarily imply sourcing organic matter by the prokaryotes and the abundance of biomarkers does not always reflect relative contributions to sedimentary organic matter in this paper the existing evidence for a substantial prokaryotic biomass contribution to sedimentary organic carbon oc is critically evaluated this shows that despite the often prominent presence of prokaryotic biomarkers in sediments evidence for a substantial prokaryotic contribution to sedimentary oc is generally lacking this is demonstrated by i the application of the carbon isotopic mass balance principle in various sedimentary settings ii an alternative explanation for the proposed dominant role of heterotrophic reworking in the oxford clay iii a summary of the effects of bacterial oxidation in organic matter rich turbidites and iv recent data showing that the evidence for recalcitrant carbon in prokaryotes is scant although these observations do not rule out substantial contributions of prokaryotic carbon to oc in phanerozoic carbonaceous sediments this remains to be demonstrated and the final answer awaits the development of new technologies to full characterise sedimentary oc

monotonic and cyclic liquefaction of very loose sands with high silt content the results from an experimental study on sands with high nonplastic silt content are presented drained and undrained triaxial compression tests undrained cyclic triaxial tests and drained undrained instability tests were performed on specimens of loose nevada sand with 40 silt content the behavior was observed to be somewhat different from previously published tests with sands at lower silt content the greater silt content appears to provide a more volumetrically contractive response throughout the entire stress strain curve however some aspects of the response were similar to sands with lower silt content monotonic undrained tests indicated reverse behavior i e static liquefaction occurred at low confining pressures and increasing dilatant volume change tendency was observed with increasing confining pressure analyzing the results using the concepts of steady state resulted in a unique steady state line only when undrained tests were sheared from the same isotropic compression line when

changes in the trophic state of lake erie discordance between molecular δ13c and bulk δ13c sedimentary records abstract prior to 1980 anthropogenic phosporus p loadings resulted in increased algal productivity and the deterioration of water quality within lake erie we measured c and n elemental compositions geolipid concentrations and 13 c values for bulk organic material and individual alkanes in samples taken from a 40 cm sediment core from the eastern basin of lake erie to infer recent trends in primary productivity and diagenesis the predominance of autochthonous algal derived c throughout the core is evidenced by low c n values 9 10 and the persistent abundance of n c 15 to n c 17 alkanes throughout the core the 13 c values of bulk organic c from lake erie vary between 25 9 and 24 9 with a maximum corresponding to the period of elevated historical p loading within lake erie 13 c values of short chained algal derived alkanes n c 18 are lower approximately 1 0 than their terrestrial derived homologs n c 25 down core variations in the 13 c composition of algal derived short chained alkanes do not exhibit the same trend as that observed for bulk organic c down core variation in 13 c values of individual alkanes likely reflect multiple diagenetic effects including kinetic fractionation effects variations in the relative contributions of isotopically unique n alkanes to the sediments and or temporal changes in 13 c enrichments of n alkanes associated with a single source high sedimentation rates characteristic of this core emphasize temporal variations in molecular 13 c values that might not otherwise be observed whereas 13 c data for bulk sedimentary organic c appear to reflect variation in trophic state the isotopic record for algal derived n alkanes e g n c 17 and pristane from lake erie must be considered from the perspective of molecular transformations

aliphatic and aromatic hydrocarbons in candiota coal samples novel series of bicyclic compounds abstract aliphatic and aromatic fractions obtained from nine samples taken from two different seams of five boreholes in the candiota coalfield lower permian were analysed by gas chromatography mass spectrometry the occurrence of the tetracyclic diterpenoids 16 h phyllocladane and ent 16 h kaurane among the aliphatic hydrocarbons and the tricyclic diterpenoids simonellite and retene in the aromatic hydrocarbon concentrates suggest an important input from conifers to the sedimentary biomass this may explain the origin of a novel series of saturated and aromatic bicyclic compounds detected in the extracts which may be structurally related to the same precursor possibly a conifer resin derived tricyclic diterpenoid

evidence of rapid cenozoic uplift of the shoulder escarpment of the cenozoic west antarctic rift system and a speculation on possible climate forcing the cenzoic west antarctic rift system characterized by cenozoic bimodal alkalic volcanic rocks extends over a largely ice covered area from the ross sea nearly to the bellingshausen sea it is bounded on one side by a spectacular 4 to 5 km high rift shoulder scarp maximum bedrock relief 5 to 7 km from northern victoria land queen maud mountains to the ellsworth whitmore horlick mountains jurassic tholeiites crop out with the late cenozoic volcanic rocks along the section of the transantarctic mountains from northern victoria land to the horlick mountains the cenozoic rift shoulder diverges here from the jurassic tholeiite trend and the tholeiites are exposed discontinuously along the lower elevation 1 2 km section of the transantarctic mountains to the weddell sea various lines of evidence no one of which is independently conclusive lead the authors as others have also suggested to interpret the following the transantarctic mountains part of the rift shoulder and probably the entire shoulder has been rising since about 60 ma at episodic rates of approximately 1 km m y most recently since mid pliocene time rather than continuously at the mean rate of 100m m y uplift rates vary along the scarp which is cut by transverse faults the authors speculate that this uplift may have climatically forcedmore the advance of the antarctic ice sheet since the most recent warm period they suggest a possible synergistic relation between episodic tectonism mountain uplift and volcanism in the cenozoic west antarctic rift system and waxing and waning of the antarctic ice sheet beginning about earliest oligocene time less

late cenozoic glacial history of the ross embayment antarctica abstract the ross ice drainage system comprises about 25 per cent of the surface area of the antarctic ice sheet its fluctuations during the late quaternary have been determined in two ways from analyses of three deep ice cores extracted at byrd west antarctica and at vostok and dome circe east antarctica and from the distribution stratigraphy and chronology of glacial drifts in the transantarctic mountains the ice core studies give time series records for the last 160 ka that correspond well with the marine isotope record and clearly show glacial interglacial stadial and interstadial intervals they also suggest that during glaciation maxima the polar plateau was characterised by an accumulation rate 50 per cent lower and temperature 7 9 c lower than present values glacial geological studies reveal a hiatus in the drift record between older miocene early pleistocene glacial sediments and drifts of the last two glaciations isotope stages 6 and 2 there are two leading but contradictory interpretations of the older drift sirius formation one is based primarily on biological data and favours partial deglaciation of antarctica in the pliocene early pleistocene followed by regrowth of the east antarctic ice sheet to dimensions larger than now and then substantial uplift of the transantarctic mountains the other is founded on glacial geological observations and implies a larger than present ice sheet over antarctica during the miocene and only 200 m of uplift subsequently for the late quaternary reconstructed ice surface profiles based on detailed mapping and dating of drift sheets show that large outlet glaciers from the east antarctic polar plateau became about 1000 m thicker during glaciation maxima while the plateau ice barely thickened at all this is attributed to extensive northward migration of the ice grounding line in the ross embayment as global sea level fell dates obtained from the drift sheets confirm that glaciers in the ross embayment area reached maximal limits at 190 160 ka bp and at 23 14 ka bp recession from the last glaciation maximum was underway by 13 ka bp and was complete by ca 6 ka bp alpine glaciers terminating in dry valleys fluctuate asynchronously with the ross embayment glaciers they retreat during glacial maxima when they become starved of accumulation and readvance during warmer intervals because of their dependence on grounding line position glacier fluctuations in much of antarctica are primarily led by sea level changes controlled by ice sheets in the northern hemisphere

carbon isotope variability of triassic amber as compared with wood and leaves southern alps italy abstract the carbon isotope signatures of carnian late triassic amber drops from rifugio dibona southern alps italy were studied and compared with that of other middle early late triassic fossil plant remains namely wood and leaves amber wood and leaf carbon isotope data are highly variable within the same beds 13camber values vary by up to 5 4 and are enriched by 2 5 with respect to associated wood 13cwood and 13cleaf ranges are narrower than that of amber 2 3 and the isotopic offset within each bed is similar over time the high triassic amber carbon isotope variability is similar to that of recent resin despite the high variability 13cwood and 13cleaf illustrate a middle early late triassic secular positive trend that is similar to that of marine 13cinorg data and must record the carbon isotope evolution of the ocean atmosphere system

liquefaction at moss landing during loma prieta earthquake a study of liquefaction at five sites in the moss landing area during the 1989 loma prieta earthquake is presented results of this case history study include 1 a large set of cone penetration test cpt data for sites where evidence of liquefaction was and was not observed 2 information regarding the influence of thin soil strata on overall site behavior 3 inclinometer data on deformations at depth due to lateral spreading of a shoreline 4 a description of the apparent liquefaction of a marshland clayey silt deposit 5 seismic shear wave velocity data at sites where evidence of liquefaction was and was not observed and 6 an evaluation of how interpretation methods affect the development and use of cpt based liquefaction correlations

carbon isotopic compositions of 28 30 bisnorhopanes and other biological markers in a monterey crude oil abstract an immature tar like oil api 3 13 c 23 6 vs pdb from the miocene monterey formation offshore california was selected for a study of carbon isotopic signatures of individual biomarkers the three principal stereoisomers of 28 30 bisnorhopane c 28 have within analytical precision identical carbon isotopic compositions average 13 c 32 3 0 4 and are considerably depleted in 13 c compared to the whole oil these 28 30 bisnorhopanes bnh differ isotopically from c 29 and c 30 17 h hopanes 25 8 and 26 1 and c 31 c 35 extended hopanes 13 c 27 7 and suggest different precursors for the c 28 hopanes than for c 29 c 35 hopanes the relative depletion of bnh of almost 9 compared to the isotopic composition of the whole oil suggests that these hopanes derive from chemoautotrophic bacteria possibly not yet identified h 2 s oxidizers which utilize 13 c depleted substrates the c 29 and c 30 hopanes are within analytical precision isotopically identical 26 and similar to algal derived compounds e g c 27 steranes 25 9 which is consistent with a cyanobacterial source for these hopanes an archaebacterial biomarker 1 1 biphytane 13 c 25 5 likely derived from methanogens is also isotopically similar to c 27 sterane norpristane pristane and phytane liberated by desulfurization of the aromatic and polar maltene fractions show isotopic compositions similar to the same isoprenoids in the free lipids of the bitumen total range from 24 5 to 27 5 this isotopic similarity supports a common origin for the free and sulfur bound forms of these isoprenoids this origin could be algal and or archaebacterial lipids which both show isotopic compositions within the range of the c 18 c 20 isoprenoids like other marine derived organic matter this monterey oil does not show the strong 13 c depletion typical for methylotroph derived compounds characteristically found in organic matter of lacustrine origin this may indicate fundamental differences of methane recycling processes in marine sulfate dominated as compared to lacustrine environments

shear strength and stiffness of silty sand the properties of clean sands pertaining to shear strength and stiffness have been studied extensively however natural sands generally contain significant amounts of silt and or clay the mechanical response of such soils is different from that of clean sands this paper addresses the effects of nonplastic fines on the small strain stiffness and shear strength of sands a series of laboratory tests was performed on samples of ottawa sand with fines content in the range of 5 20 by weight the samples were prepared at different relative densities and were subjected to various levels of mean effective consolidation stress most of the triaxial tests were conducted to axial strains in excess of 30 the stress strain responses were recorded and the shear strength and dilatancy parameters were obtained for each fines percentage bender element tests performed in triaxial test samples allowed assessment of the effect of fines content on small strain mechanical stiffness

experimental study of cone penetration in silica sand using digital image correlation the problem of cone penetration particularly deep penetration remains one of the most challenging in geotechnical engineering it involves large displacements rotations and deformation of soil elements in the path of the cone as well as complex response of the soil including crushing and the development of large mean stresses to the displacements imposed by the penetration process as a result rigorous theoretical solutions are not available for this problem and experimental simulations of penetration provide insights that would not otherwise be available this paper presents the results of a series of cone penetration tests performed in a half circular chamber in sand samples prepared with three silica sands with different crushability cone resistance was measured and digital images of the cone penetrating into the sand samples were acquired simultaneously during the entire penetration process the digital image correlation dic technique was then used to process these images to obtain the soil

influence of nonplastic fines on shear wave velocity based assessment of liquefaction many false positives no liquefaction detected when the normalized shear wave velocity cyclic stress ratio vs1 csr combination indicated that it should have been are observed in the database used in the simplified liquefaction assessment procedure based on shear wave velocity two possible reasons for false positives are the presence of a thick surface layer of nonliquefiable soil and the effects of fines on cyclic shear resistance crr and vs1 about 67 of the false positives that could not have been caused by an overlying thick surface layer are associated with silty sands with less than 35 fines the effects of fines on the liquefaction resistance of silty sands and on the shear wave velocity are analyzed theoretical crrfield versus vs1 curves for silty sands containing 0 to 15 nonplastic fines are established they show that the theoretical crr vs1 correlations for silty sands with 5 to 15 nonplastic fines are all located to the far left of the semi empirical curves that separate liquefac

influence of non low plastic fines on cone penetration and liquefaction resistance abstract uncertainties prevail at the current liquefaction screening method based on the cone penetration test cpt as to whether the existence of fines increases liquefaction resistance or decrease cone penetration resistance in this study field based data are used to evaluate the effects of non low plastic fines on liquefaction resistance at the current cpt based liquefaction assessment method the first part of this paper examines the effects of the coefficient of consolidation or drainage characteristics of soils containing fines on cone penetration resistance the coefficient of consolidation is influenced by the fines content and the relative density of the soil the second part of this paper investigates the contribution of fines content less than 30 by weight on the liquefaction resistance of soils at different relative densities fines content over 30 by weight and or high plasticity of fines can cause additional complications therefore it needs different valuation methods which is beyond the scope of this paper the liquefaction resistance of sands and silty sands is reinterpreted from the current cpt based liquefaction assessment method the trend which presents the change of liquefaction resistance with fines content at the same relative density is compared with the available laboratory based data in the literature the results show that the interpreted trend is not consistent with the laboratory based correlations obtained by several previous researchers therefore there will be probably some inaccuracies in estimation of liquefaction potential of silty sand using the current cpt based liquefaction assessment method

the neogene east antarctic ice sheet a dynamic or stable feature abstract this paper is a review of the history and behaviour of the east antarctic ice sheet during the late neogene and is a response to the publication of sugden et al 1993a the case for a stable east antarctic ice sheet in geografiska annaler 75a 4 the antarctic ice sheet is a critical factor in the global climate and oceanographic system knowledge of its historical development is critical to understanding global palaeoceanographic and palaeoclimatic systems and their development the webb harwood hypothesis proposes that the ice sheet while being present in antarctica for more than 40 ma was until recently ca 2 5 ma a dynamic feature waxing and waning under a more temperate climatic and glaciologic regime the stabilistic hypothesis proposes that the current ice sheet has existed in its present cold and polar form for at least the last 14 ma the case for a stable east antarctic ice sheet is the clearest statement of the stabilistic argument to date the authors find support for their viewpoint by presenting evidence from several geologic data bases that does not support their own null meltdown hypothesisr which they deem to be equivalent to the webb harwood hypothesis thereby they conclude supporting the stabilistic hypothesis however their conclusions are weakened by failure to reject their null hypothesis conflict between the meltdown and webb harwood hypotheses infraction of geological laws and poor application of stratigraphic principles several issues are highlighted here as important for direction of future research and discussion concerning late cenozoic antarctic glacio climatic history

a comparison of deep antarctic ice cores and their implications for climate between 65 000 and 15 000 years ago abstract three ice cores drilled in the central part of the antarctic continent extend back to the last glacial period one from west antarctica byrd and two from east antarctica vostok and dome c this period is also partly covered by a few cores from the coastal areas in these cores climatic information is mostly derived from the isotopic profiles d or 18 o from which surface temperature and more indirectly precipitation rate can be estimated the main objective has been to compare thoroughly the three deep ice cores for the main part of the last glacial period from ca 65 000 15 000 yr b p the time scales have been examined in detail and a new 40 000 yr chronology for the dome c core adopted special emphasis is placed on the link between the concentration of 10 be and past accumulation changes and on the use of peaks in the concentration of this cosmogenic isotope as stratigraphic markers elevation changes of the ice sheet derived from gas content and isotopic data bear directly on interpretations of past temperature and precipitation rate changes

unusual carbon isotope compositions of biomarker hydrocarbons in a permian tasmanite abstract the permian oil shale sample of this study is from a deposit in tasmania in which the only recognizable structures are large thick walled unicellular specimens of the green alga tasmanites the fossils are so densely packed that this shale is termed tasmanite the carbon isotopic composition of bulk kerogen carbon c 13 c org 16 6 vs pdb is unusually enriched in 13 c compared to marine permian organic carbon 25 to 30 this 13 c enrichment suggests specific environmental conditions co 2 draw down and or physiological specialties cell size and growth rate of tasmanites which in modern environments are known to cause 13 c enrichment in marine phytoplankton isotope signatures of extractable organic species unlike in normal immature oil shales are considerably enriched in 13 c compared to the kerogen the bitumen 10 9 is composed predominantly of extended saturated c 18 c 25 tricyclic terpane hydrocarbons 9 9 to 12 2 total range with an average of 10 8 these tricyclics are not only found as free lipids in the extract but also in pyrolysates with similar isotopic signatures and are therefore likely biosynthesis products of tasmanites the monoaromatic and diaromatic tricyclic terpane hydrocarbons c 17 c 19 have similar isotopic signatures 9 3 to 12 8 total range with an average of 10 6 two monoaromatic tetracyclic hydrocarbons c 23 and c 24 a quantitatively minor but biogenetically interesting group average at 10 2 in contrast pristane and phytane as well as n alkanes 18 to 22 are depleted in 13 c compared to kerogen carbon the isotopic similarity of all the cyclic terpanes in this sample together with their occurrence in the free lipids and kerogen suggests that they have a common origin and are biosynthesis products of the marine unicellular green algae tasmanites the tetracyclic terpanes therefore are not des a oleananes derived from land plants but are possibly monoaromatic des a gammaceranes or other des a triterpenoids derived from marine sources the unusual enrichment in 13 c in the cyclic hydrocarbons is hypothesized to result from the special growth conditions of the algae isoprenoids and n alkanes are also likely biosynthesis products of tasmanites possibly during the spore formation stage when physiological and environmental conditions were different than during planktonic biosynthesis

abundant tetracyclic terpenoids in a middle devonian foliated cuticular liptobiolite coal from northwestern china cuticular liptobiolite coal defined by its dominant cutinite is rare and only known in a few regions of the world an occurrence of this type of coal found in the devonian of the hefeng basin xinjiang northwestern china is described for the first time by organic petrography and biomarker analysis the cuticular liptobiolite has distinct sheet like layers and thus splits easily into leafy laminae which are segregated during weathering forming a so called paper coal it is comprised dominantly of cutinites 75 vol on a mineral free basis with minor vitrinites 20 lycopsids are suggested to be the dominant coal forming plants the aliphatic fractions of these samples contain only small amounts of n alkanes and common biomarkers such as steranes and hopanes tetracyclic diterpanes cnh2n 6 with mainly beyerane and atisane skeletons are the dominant constituents the abundant tetracyclic diterpanes present in this and other devonian cuticle rich coals indicate that their parent natural product precursors occurred abundantly in the early vascular land plants of the devonian i e lycopsid and psilopsid species it seems that these early land plants secreted massive amounts of resins from their vascular tissues coating their cuticle surfaces to protect against water evaporation massive cuticle accumulation in the middle devonian likely resulted from a simple assemblage of unique early land plants

late tertiary history of the antarctic ice sheet evidence from the dry valleys data from the dry valleys antarctica suggest that outlet glaciers of a local ice cap carved primary valley systems on both flanks of the transantarctic mountains while coeval alpine glaciers eroded exposed intervalley mountain ranges subsequently a thick ice sheet overrode the transantarctic mountains at least twice flowing northeastward across major pre existing valleys the youngest overriding episode postdated and the older episode antedated middle to early late miocene time we think that an extensive ice sheet covered east and west antarctica during overriding episodes

formation and disintegration of the antarctic ice sheet a model of the antarctic ice sheet has been used to simulate the ice sheet in warmer climates in order to investigate what kind of ice sheet geometries one canreasonably expect under what kind of climatic conditions and to find out which physical mechanisms may be involved to explain them the results of theseexperiments reveal the large stability of in particular the east antarctic ice sheet it would require a temperature rise of between 17 and 20k above presentlevels to remove this ice sheet from the subglacial basins in the interior of the continent and of 25k to melt the antarctic ice sheet completely down for atemperature rise below 5k the model actually predicts a larger antarctic ice sheet than today as a result of increased snowfall whereas the west antarctic icesheet was found not to survive temperatures more than 8 10k above present values furthermore basal temperature conditions in these experiments point tothe problems involved to raise the base to the pressure melting point over the large areas necessary to consider the possibility of sliding instability theseresults bear on a lively debate regarding the late cenozoic glacial history of antarctica in particular based on these findings it appears difficult to reconcile ahighly variable east antarctic ice sheet up to the pliocene with the modest warmings recorded in for instance the deep sea records for the late neogene

insights into the origin of perylene from isotopic analyses of sediments from saanich inlet british columbia perylene is an abundant and common polycyclic aromatic hydrocarbon in sedimentary settings yet its origin remains puzzling we have investigated the relation of perylene to the amount and type of organic matter in the sediments of saanich inlet a coastal marine anoxic basin organic matter is predominantly marine in origin but the proportions of marine and land derived components have varied perylene concentrations generally increase with sediment depth relative to toc which indicates continued formation of this compound by microbially mediated diagenesis perylene 13c values range between 27 7 and 23 6 whereas toc 13c values vary narrowly from 21 7 to 21 2 over the same sediment depth interval the variation in isotopic difference suggests that perylene originates from more than one precursor material both aquatic and continental organic matter different microbial processes or some combination of these possibilities

sea level change a philosophical approach the present cenozoic era is an lsquoicehousersquo episode characterized by a low sea level since the beginning of the industrial revolution the human race has been emitting greenhouse gases increasing the global atmospheric temperature and causing a rise in sea level if emissions continue to increase at the present rate average global temperatures may rise by 1 5 c by the year 2050 accompanied by a rise of about 30 cm in sea level however the prediction of future climatic conditions and sea level is hampered by the difficulty in modelling the interactions between the lithosphere kryosphere biosphere and atmosphere in addition the buffering capacity of our planet is still poorly understood as scientists cannot offer unambiguous answers to simple questions sorcerer s apprentices fill in the gaps presenting plans to save planet without inconveniencing us the geological record can help us to learn about the regulation mechanisms of our planet many of which are connected with or expressed as sea level changes global changes in sea level are either tectono eustatic or glacioeustatic plate tectonic processes strongly control sea levels and climate in the long term there is a strong feed back mechanism between sea level and climate both can influence and determine each other although high sea levels are a powerful climatic buffer falling sea levels accelerate climatic accentuation the growth of the polar ice caps and will hence amplify the drop in sea level important sources of fossil greenhouse gases are botanic co2 production co2 released by volcanic activity and water vapour the latter is particularly important when the surface area of the sea increases during a rise in sea level lsquomaritime greenhouse effectrsquo a lsquovolcanogenic greenhouse effectrsquo release of volcanogenic co2 is possibly not equally important as intense volcanic activity may take place both during icehouse episodes as well as during greenhouse episodes the hydrosphere land vegetation and carbonate platforms are major co2 buffers which may both take up and release co2 co2 can be released from the ocean due to changes in the pco2 caused by growth of coral reefs and by uptake of co2 rich freshwater from karst provinces efficient sinks of co2 are the weathering products of silicate rocks long term sinks are organic deposits caused by regional anoxic events which preferrably develop during sea level rises and highstands and coal bearing strata deposition of limestone also removes co2 from the atmospheric hydrospheric cycle at a long term biotic crises are often related to either sea level lows or sea level highs long term sea level lows characteristic of glacial periods indicate cooling as major cause of extinction during verly long lasting greenhouse episodes the sea level is very high climate and circulation systems are stable and biotic crises often develop as a consequence of oxygen depletion on land niche splitting complex food web structures and general overspecialization of biota will occur whether the crisis is caused by a single anoxic event e g in the late devonian or a disturbance by an asteroid impact e g the cretaceous tertiary boundary it will only trigger total collapse of an ecosystem if a large part of it was already in decline the regulatory mechanisms and buffers are thermodynamically extremely efficient if they are given sufficient time in which to deploy their power however after major catastrophes the re establishment of successful ecosystems will take millions of years the present rate of sea level and associated temperature rise is much too fast to be compensated and buffered by the network of natural controls it is likely that the transitional time towards a new steady state will be an extremely variable and chaotic episode of unpredictable duration

vostok ice core a continuous isotope temperature record over the last climatic cycle 160 000 years a continuous deuterium profile along the 160 000 year vostok ice core antarctica is interpreted in terms of atmospheric temperature changes this climatic record is the awaited terrestrial complement of the deep sea records supporting the existence of a relation between the pleistocene climate and orbital forcing

liquefaction resistance of sands containing plastic fines with different plasticity abstractsoils in the field or at reclaimed sites commonly contain some amount of silt or clay rather than clean sand only the effect of a low fraction of plastic fines within sand matrix on liquefaction resistance is not clearly understood in this study clean sand was mixed with 10 plastic fines having different plasticity indexes pis and the effect on liquefaction resistance was evaluated in terms of cyclic stress ratio a series of undrained cyclic triaxial tests were carried out on loose medium and dense specimens that were reconstituted in the laboratory by the undercompaction method the results showed that liquefaction resistance tended to decrease as the pi of 10 fines in the specimens increased liquefaction resistance of loose specimens was marginally influenced by the plasticity of fines however in the case of dense specimens liquefaction resistance decreased up to 40 as the pi of 10 fines increased it was shown that even though a low fraction of plastic fines was included within

liquefaction mitigation using bentonite suspensions abstractottawa sand specimens premixed with 0 3 and 5 bentonite by dry mass of sand were tested under undrained static and cyclic loading to investigate the effects of bentonite on the static and cyclic shear strength of the sand the results show that allowing the bentonite to hydrate within the sand pore space increases the cyclic resistance of the sand for the same skeleton relative density and cyclic stress ratio cyclic tests on specimens with sufficient hydration times showed a significant increase in the number of cycles required for liquefaction compared with clean sand when the specimens were allowed an extended postconsolidation aging period the cyclic resistance increased further resonant column and cyclic triaxial tests showed that this is a result of the delay in the generation of excess pore pressure in the presence of the bentonite suspension in the pore space the improvement in cyclic behavior does not occur at the expense of the static resistance of the soil under working loads be

organic geochemistry and coal petrology of tertiary brown coal in the zhoujing mine baise basin south china 4 biomarker sources inferred from stable carbon isotope compositions of individual compounds abstract carbon isotopic compositions of extractable compounds derived from higher land plants are within 2 0 00 of the bulk coal 13 c 27 0 0 00 from baise basin this data suggests that either similar species contributed these compounds or that the plants from which this coal was formed imposed similar biosynthetic fractionations the terpenoid hydrocarbons form two isotopically distinct groups the diterpenoids 13 c 25 0 1 4 0 00 and the sesquiterpenoids 13 c 25 9 1 5 0 00 are on 1 2 0 00 enriched in 13c compared to the bulk coal whereas the oleanane ursane lupane derivatives 13 c 29 0 0 8 0 00 are on average 1 2 0 00 depleted in 13c compared to the bulk coal the n alkanes ranging from c15 to c35 have a mean 13c value of 32 4 0 6 0 00 whereby averages for the c17 c22 and c23 c33n alkanes do not significantly differ from the overall average hopane derivatives in this coal extract are depleted in 13c compared to the bulk coal by 8 34 0 00 suggesting that bacterial cycling of methane played a role during formation of this coal

late wisconsin and early holocene glacial history inner ross embayment antarctica abstract lateral drift sheets of outlet glaciers that pass through the transantarctic mountains constrain past changes of the huge ross ice drainage system of the antarctic ice sheet drift stratigraphy suggests correlation of reedy iii reedy glacier beardmore beardmore glacier britannia hatherton darwin glaciers ross sea mcmurdo sound and younger terra nova bay drifts radiocarbon dates place the outer limits of ross sea drift in late wisconsin time at 24 000 13 000 yr b p outlet glacier profiles from these drifts constrain late wisconsin ice sheet surface elevations within these constraints we give two extreme late wisconsin reconstructions of the ross ice drainage system both show little elevation change of the polar plateau coincident with extensive ice shelf grounding along the inner ross embayment however in the central ross embayment one reconstruction shows floating shelf ice whereas the other shows a grounded ice sheet massive late wisconsin holocene recession of grounded ice from the western ross embayment which was underway at 13 040 yr b p and completed by 6600 6020 yr b p was accompanied by little change in plateau ice levels inland of the transantarctic mountains sea level and basal melting probably controlled the extent of grounded ice in the ross embayment the interplay between the precipitation low late wisconsin and high holocene values and the influence of grounding on outlet glaciers late wisconsin thickening and late wisconsin holocene thinning with effects dying out inland probably controlled minor elevation changes of the polar plateau

shear strength and stiffness of sands containing plastic or nonplastic fines this paper presents the results of a systematic laboratory investigation on the static behavior of silica sand containing various amounts of either plastic or nonplastic fines specimens were reconstituted using a new technique suitable for element testing of homogeneous specimens of sands containing fines deposited in water e g alluvial deposits hydraulic fills tailings dams and offshore deposits the fabric of sands containing fines was examined using the environmental scanning electron microscope esem static monotonic isotropically consolidated drained triaxial compression tests were performed to evaluate the stress strain volumetric response of these soils piezoceramic bender element instrumentation was developed and integrated into a conventional triaxial apparatus shear wave velocity measurements were made to evaluate the small strain stiffness of the sands tested at various states the intrinsic parameters that characterize critical state dilatancy and small strain stiffness of clean silty and clayey sands were determined all aspects of the mechanical behavior investigated in this study e g stress strain volumetric response shear strength and small strain stiffness are affected by both the amount and plasticity of the fines present in the sand microstructural evaluation using the esem highlighted the importance of soil fabric on the overall soil response

a chronology of pliocene sea level fluctuations the u s middle atlantic coastal plain record abstract the sequence of marine and marginal marine silts and sands of the u s middle atlantic coastal plain preserves a relatively complete record of pliocene sea level highstands a general chronology for the deposition of these units has been developed previously from studies of the microfossil biostratigraphy complemented by a limited number of paleomagnetic and radiometric dates within this broad temporal framework it is currently difficult to assign ages to individual transgressive events with a resolution much better than 0 5 ma the age model proposed here attempts to refine the depositional history of the atlantic coastal plain by correlation with the more continuous deep ocean record the model assigns probable ages to the pliocene transgressions onto the atlantic coastal plain based on evidence for sea level highstands inferred from high resolution deep ocean 18 o records at least five major transgressive regressive events can be correlated with presumed eustatic fluctuations the temporal resolution for the timing of the transgressive events is greatly improved over that of the biostratigraphy alone many aspects of the proposed chronology require verification by more detailed field study but it is offered as a testable working hypothesis

liquefaction resistance of clean and nonplastic silty sands based on cone penetration resistance liquefaction of granular soil deposits is one of the major causes of loss resulting from earthquakes the accuracy in the assessment of the likelihood of liquefaction at a site affects the safety and economy of the design in this paper curves of cyclic resistance ratio crr versus cone penetration test cpt stress normalized cone resistance qc1 are developed from a combination of analysis and laboratory testing the approach consists of two steps 1 determination of the crr as a function of relative density from cyclic triaxial tests performed on samples isotropically consolidated to 100 kpa and 2 estimation of the stress normalized cone resistance qc1 for the relative densities at which the soil liquefaction tests were performed a well tested penetration resistance analysis based on cavity expansion analysis was used to calculate qc1 for the various soil densities a set of 64 cyclic triaxial tests were performed on specimens of ottawa sand with nonplastic silt content in the range of 0 15 by

pore pressure generation in sand with bentonite from small strains to liquefaction the paper examines the effect of small percentages of bentonite on pore pressure generation in loose sands from small strains all the way to liquefaction it relies on resonant column static tria

des a lupane in an east african lake sedimentary record as a new proxy for the stable carbon isotopic composition of c3 plants we studied the high resolution and well dated 25 000 year sedimentary record of lake challa a deep tropical crater lake in equatorial east africa to explore new proxies for paleoenvironmental and paleohydrological change sedimentary biomarker analysis revealed the presence of des a triterpenoids with oleanane ursane and lupane carbon skeletons microbial degradation products of angiosperm plant triterpenoids their increased influx from 16 000 years ago corresponds with previously documented changes in the terrestrial vegetation of the lake challa basin during postglacial warming in particular the relative increase in c3 c4 plant ratio inferred from the stable carbon isotopic signature 13c of sedimentary n alkanes derived from plant leaf waxes in contrast to this n alkane 13c signature the 13c of des a lupane maintains a constant value of 27 4 1 1 across the glacial interglacial transition since des a lupane is derived from c3 plants its 13c signature is here proposed to represent a novel and independent proxy for the time variable carbon isotopic composition of local terrestrial c3 plants which can improve estimates of the c3 c4 plant ratio based on two end member mixing models of n alkane 13c values

liquefaction and flow failure during earthquakes two aspects of seismically induced liquefaction are discussed which are of vital engineering significance the triggering condition and the consequences of liquefaction the triggering condition is examined with respect to liquefaction analysis note being taken of the onset condition which is governed by cyclic strength consequences of liquefaction are discussed with respect to post seismic stability analysis in which the residual strength plays a major role procedures used for liquefaction analysis based on the results of in situ sounding tests are introduced and the applicability of this method for estimating associated ground settlements is discussed the evaluation of residual strength requires a better understanding of undrained sand behaviour results of extensive laboratory rests on japanese standard sand are examined and new index parameters are proposed to quantify undrained sand behaviour better the results of laboratory tests on silty sands are examined in the same way ah the results are

reaction of the accumulation zone portions of glaciers to climatic change the response of the accumulation regions of glaciers to changes in accumulation rate and in surface temperature is calculated by considering perturbations to the ice flow the analysis is limited to glaciers in which flow is dominated by internal shear and not by bottom sliding and for which flowlines are geographically parallel in general glaciers begin to alter thickness immediately after a change in accumulation rate but the effect of a change in surface temperature is delayed by the time for this temperature change to penetrate to depth in the glacier a warming leads to glacial thinning the amount and timing of the response is very different for different glaciers characteristic times are on the order of tens of years for mountain glaciers and tens of thousands of years for the east antarctic ice sheet as an example the theory is applied to the ice sheet near byrd station antarctica for hypothetical changes in surface accumulation rate and temperature rates and amounts of thickness change are calculated and it is found that the measured thinning is probably too fast to have been caused by climatic variation alone the effects of hypothetical climatic variations on the depth age and depth temperature relationships through the ice sheet are also calculated it is hoped that the theory will prove valuable in the interpretation of future drill hole results