tricyclic terpane maturity parameters response to heating by an igneous intrusion the effects of thermal maturation upon the abundance and composition of the tricyclic terpanes have been investigated within a single sedimentary horizon within the dun caan shale member isle of skye scotland intruded by a 0 9 m thick tertiary dolerite dyke heating by the igneous body caused the concentrations of all 13 h 14 h and 13 h 14 h tricyclic terpanes to increase towards or within the effective oil window recording generation from abundant non hydrocarbon precursors such as kerogen and asphaltene bound components progressive changes in tricyclic terpane composition accompany these concentration changes an increase in the c23 maturity parameter towards the dyke resulted from the relatively greater rate of generation of the isomer combined with the earlier decline in concentration by degradation or isomerisation of the component the tricyclics tricyclics hopanes parameter shows a dramatic increase within the latter part of the oil window due to the greater relative thermal stability of the tricyclic terpanes the quantitative data demonstrate the importance of the processes of generation from non hydrocarbon fractions of the sedimentary organic matter and thermal degradation in the operation of tricyclic terpane maturity parameters

upper oligocene lacustrine source rocks and petroleum systems of the northern qaidam basin northwest china our organic geochemical study of oils from the northern qaidam basin defines a family of genetically related oils that contain biomarkers indicative of source rocks deposited in tertiary hypersaline anoxic lacustrine settings although cenozoic outcrop samples from northern qaidam are too organic lean to be of source quality dark laminated upper oligocene mudstones containing gypsum crystals and pyrite from the shi 28 well yield total organic carbon toc and rock eval data indicative of fair to good source rocks organic matter is derived from algae and bacteria and there apparently was little contribution from terrestrial material biomarker data provide a good correlation between the produced oils and the upper oligocene shi 28 core samples hydrocarbons derived from these source rocks are contained in upper oligocene miocene and pliocene reservoirs although eight of the oil samples are from the northwest corner of the basin one sample in this genetic family of hypersaline oils comes from northeast qaidam an area previously believed to only produce oils derived from jurassic freshwater lacustrine source rocks this sample thus indicates the presence of an unidentified and undocumented source rock in the northeast part of the basin hypersaline oils and the associated source rocks have low biomarker maturity parameters thermal modeling indicates that hydrocarbon generation probably occurred in northwestern qaidam within the last 3 million years

distribution and isomerization of c31 c35 homohopanes and c29 steranes in oligocene saline lacustrine sediments from qaidam basin northwest china abstract the 22s 22s 22r ratios for c 31 c 35 homohopanes and the 20s 20s 20r ratio for c 29 steranes were measured by gas chromatography mass spectrometry gc ms on six oligocene saline lacustrine rock samples from a borehole located in the western qaidam basin northwest china these ratios vary significantly and irregularly with burial depth from 2831 m to 3054 m around the threshold of the oil generation window in addition 22s 22s 22r ratios also vary substantially among different homologs within the same sample generally decreasing from c 31 to c 35 homohopanes the distribution patterns of homohopanes for the six samples are unusual such as c 31 32 c 33 c 34 35 or c 31 c 32 c 33 34 35 or c 31 32 c 33 34 35 all of these observations can be mainly ascribed to the release of bound hopanes and steranes from kerogen and other macromolecules the 22s 22s 22r ratios of c 31 c 32 and c 33 homohopanes decreased while that of c 34 homohopanes increased for two samples yhs1 and yhs6 after pyrolysis at low temperatures 180 270 c a major reversal of 20s 20s 20r ratio for c 29 steranes was observed at 240 c for sample yhs1 but at 270 c for sample yhs6 the distributions of homohopanes for these two samples after pyrolysis changed from their original patterns toward the normal pattern c 31 c 32 c 33 c 34 c 35 these results reflect the influences of thermal degradation and direct isomerization of the free biomarkers and the release of bound biomarkers from kerogen and other macromolecules during pyrolysis

pyrolysis of kerogens in the absence and presence of montmorillonite i the generation degradation and isomerization of steranes and triterpanes at 200 and 300 c abstract the sterane and triterpane biomarker distribution obtained from extracted bitumens and kerogen pb pyrolysate bitumens of immature cretaceous black shale cbs and rocky mountain coal rmc at 200 and 300 c in the presence and absence of montmorillonite reveal that the generation release of biomarkers was more significant than isomerization at 200 c pyrolysis whereas isomerization and degradation were most important at 300 c pyrolysis montmorillonite has a pronounced catalytic effect on these reactions i e generation isomerization and degradation the ratios of c29 20 s s r steranes and c31 and c32 s s r hopanes display reversals with heating time at 200 c pyrolysis irrespective of the presence or absence of montmorillonite whereas they increased uniformly with thermal stress at 300 c pyrolysis the extent of isomerization occurring at chiral centers in ring systems and in acyclic systems are different it has been confirmed that the isomerization at the c22 and c20 position of the extended hopanes and the steranes respectively are slower than those of the hopanes and the steranes in the 300 c pyrolysis the c27 steranes increased relative to c29 steranes with heating time in the pyrolysate of the rocky mountain coal kerogen this phenomenon is more significant in the presence of montmorillonite the increase may indicate either the formation of secondary c27 steranes or the early loss of c29 steranes relative to c27 steranes in a sedimentary basin isomerization probably occurs in the bitumen and kerogen at different rates these data show that maturation indices may be reversed with depth by using the examples of 20 s s r and 22 s s r where the rate of generation of the compounds from kerogen is faster than the rate of isomerization reactions occurring in the bitumen with time and temperature

calving processes and the dynamics of calving glaciers abstract calving of icebergs is an important component of mass loss from the polar ice sheets and glaciers in many parts of the world calving rates can increase dramatically in response to increases in velocity and or retreat of the glacier margin with important implications for sea level change despite their importance calving and related dynamic processes are poorly represented in the current generation of ice sheet models this is largely because understanding the calving problem involves several other long standing problems in glaciology combined with the difficulties and dangers of field data collection in this paper we systematically review different aspects of the calving problem and outline a new framework for representing calving processes in ice sheet models we define a hierarchy of calving processes to distinguish those that exert a fundamental control on the position of the ice margin from more localised processes responsible for individual calving events the first order control on calving is the strain rate arising from spatial variations in velocity particularly sliding speed which determines the location and depth of surface crevasses superimposed on this first order process are second order processes that can further erode the ice margin these include fracture propagation in response to local stress imbalances in the immediate vicinity of the glacier front undercutting of the glacier terminus by melting at or below the waterline and bending at the junction between grounded and buoyant parts of an ice tongue calving of projecting submerged ice feet can be regarded as a third order process because it is paced by first or second order calving above the waterline first order calving can be represented in glacier models using a calving criterion based on crevasse depth which is a function of longitudinal strain rate modelling changes in terminus position and calving rates thus reduces to the problem of determining the ice geometry and velocity distribution realistic solutions to the problem of modelling ice flow therefore depend critically on an appropriate choice of sliding law models that assume that basal velocities are controlled by basal drag can replicate much of the observed behaviour of calving glaciers with grounded termini but an important limitation is that they cannot be used to model floating glacier termini or ice shelves alternative sliding laws that parameterise drag from the glacier margins provide more flexible and robust ways of representing calving in ice sheet models such models can explain a remarkable range of observed phenomena within a simple unifying framework including downglacier increases in velocity and strain rates where basal and or lateral drag diminishes flow acceleration in response to thinning through time the tendency for glaciers to stabilise at pinning points in relatively shallow water or fjord narrowings the constraints on ice shelf stability and the contrasts in calving rates between tidewater and freshwater calving glaciers many unresolved issues remain however including the role played by the removal of backstress in the acceleration of retreating calving glaciers and the controls on melting at and below the waterline

viscous and viscoelastic stress states at the calving front of antarctic ice shelves calving mechanisms are still poorly understood and stress states in the vicinity of ice shelf fronts are insufficiently known for the development of physically motivated calving laws that match observations a calving model requires the knowledge of maximum tensile stresses these stresses depend on different simulation approaches and material models therefore this study compares results of a two dimensional 2 d continuum approach using finite elements with results of a one dimensional 1 d beam model elaborated in reeh 1968 a purely viscous model as well as a viscoelas tic maxwell model is applied for the 2 d case the maximum tensile stress usually appears at the top surface of an ice shelf its location and magnitude are predominantly influenced by the thickness of the ice shelf and the height of the freeboard the traction free part at the ice front more precisely doub ling the thickness leads to twice the stress maximum while doubling the freeboard based on changes of the ice density results in an increase of the stress maximum by 61 poisson s ratio controls the evolu tion of the maximum stress with time the viscosity and young s modulus define the characteristic time of the maxwell model and thus the time to reach the maximum principal stress

crevasse propagation on brittle ice application to cycloids on europa existing lineaments on the surface of the jovian moon europa are thought to be the result of ongoing brittle crack formation in the elastic regime arcuate features are called cycloids and can be modeled using linear elastic fracture mechanics here we build on existing terrestrial models of rift propagation and extend them to cycloids on the moon we propose that these cracks tend to grow as a series of nearly instantaneous events spaced by periods of inactivity the behavior is similar to what is observed on antarctic ice shelves where rifts can remain dormant for years we argue that dormant periods between growth events could explain the presence of cycloids on europa even without invoking secular motion of the crust furthermore being able to model propagation events and their timing should help future missions exploring the moon

short term biomarker variability in the monterey formation santa maria basin abstract forty eight samples of a 370 ft miocene monterey formation core from the union leroy 51 18 well santa maria basin california are examined for source rock potential and molecular distributions total organic carbon content rock eval pyrolytic yield vitrinite reflectance and distribution of regular steranes tricyclic and pentacyclic terpanes and aromatic steroids are measured the present day temperature range through the sampled interval is estimated to be less than 5 c maturity differences among samples are negligible source rock potential and molecular distribution differences are considered to arise entirely from the effects of source input diagenesis including lithologic effects and migration the sampled section is comprised of siliceous and phosphatic carbonate lithofacies and covariances between geochemical parameters source potential and biomarker distribution and lithofacies are recognized several molecular parameters change systematically with depth lithology including ethylcholestane ratios and c 20 and c 22 sterane and hopane epimer ratios the siliceous lithofacies possesses higher moretane hopane tricyclic pentacyclic terpane and sterane terpane ratios and lower mono mono tri aromatic steroid ratios bisnorhopane hopane ratios are up to 40 times higher in the phosphatic carbonate lithofacies than in the siliceous lithofacies increased relative concentrations of aromatic steroids are attributed to sulfur sterol reactions during very early diagenesis whereas increased relative bisnorhopane amounts are considered to result from massive input of specific anaerobic biota although kerogen elemental ratios change abruptly at the lithofacies boundary molecular distributions within the extractable organic matter change gradually beginning about 30 ft 9m above this interface this gradual change is tentatively attributed to upward migration of hydrocarbons originating in the phosphatic carbonate lithofacies probably through fractures within the lower part of the siliceous lithofacies interval

geostatistical estimations of bathymetric lidar errors on rivers the geometry of river channels is a key descriptive element for hydromorphology hydraulics and hydroecology gravel bed rivers usually have a mean water depth of 0 5 m for such shallow waters the accuracy of bathymetric lidar data has to be precisely assessed alongside this accuracy investigation methodological questions arise how to assess the data quality of elevation lidar when comparing reference topographic points on river beds to laser beam footprints of several square metres at different locations what are the consequences of uncertainties and scaling in accuracy estimations in this study we designed a methodology to assess the quality of lidar topographical data within rivers using a specific geostatistical method that conducts upscaling as well as interpolation of reference data that takes into account uncertainties this method uses an anisotropic block kriging from dgps points on lidar footprint areas within a channel fitted coordinate system this assessment focused on a 1 5 km long reach of the gardon gravel bed river in the south of france dgps points pseudo regularly located along the river were acquired at the same time as the lidar survey with the hawkeyeii system lidar accuracy results for river bottom elevation show a negative bias for high depth added to that bias a random error with 0 32 m standard deviation was found by considering upscaling and uncertainties in reference data and a 0 20 m standard deviation was found if they were not considered consequently if lidar bias can be corrected measuring a water depth less than 32 cm i e for 28 of the river area is unrealistic however this experiment shows that lidar provides an accurate representation of the riverbed forms it also provided a useful continuous topographic surface from the underwater river bed up to riparian areas copyright 2010 john wiley and sons ltd

representation of sharp rifts and faults mechanics in modeling ice shelf flow dynamics application to brunt stancomb wills ice shelf antarctica ice shelves play a major role in buttressing ice sheet flow into the ocean hence the importance of accurate numerical modeling of their stress regime commonly used ice flow models assume a continuous medium and are therefore complicated by the presence of rupture features crevasses rifts and faults that significantly affect the overall flow patterns here we apply contact mechanics and penalty methods to develop a new ice shelf flow model that captures the impact of rifts and faults on the rheology and stress distribution of ice shelves the model achieves a best fit solution to satellite observations of ice shelf velocities to infer the following 1 a spatial distribution of contact and friction points along detected faults and rifts 2 a more realistic spatial pattern of ice shelf rheology and 3 a better representation of the stress balance in the immediate vicinity of faults and rifts thus applying the model to the brunt stancomb wills ice shelf antarctica we quantify the state of friction inside faults and the opening rates of rifts and obtain an ice shelf rheology that remains relatively constant everywhere else on the ice shelf we further demonstrate that better stress representation has widespread application in examining aspects affecting ice shelf structure and dynamics including the extent of ice melange in rifts and the change in fracture configurations all are major applications for better insight into the important question of ice shelf stability

melting of ice shelves and the mass balance of antarctica we calculate the present ice budget for antarctica from measurements of accumulation minus iceberg calving run off and in situ melting beneath the floating ice shelves the resulting negative mass balance of 469 gt year 1 differs substantially from other recent estimates but some components are subject to high temporal variability and budget uncertainties of 20 50 annual accumulation from an earlier review is adjusted to include the antarctic peninsula for a total of 2144 gt year 1 an iceberg production rate of 2016 gt year 1 is obtained from the volume of large icebergs calculated from satellite images since 1978 and from the results of an international iceberg census project ice shelf melting of 544 gt year 1 is derived from physical and geochemical observations of meltwater outflow glaciological field studies and modeling of the sub ice ocean circulation the highest melt rates occur near ice fronts and deep within sub ice cavities run off from the ice sheet surface and from beneath the grounded ice is taken to be 53 gt year 1 less than half of the negative mass balance need come from the grounded ice to account for the unattributed 0 45 mm year 1 in the ipcc best estimate of the recent global sea level rise

guidelines for evaluating petroleum source rock using programmed pyrolysis rock eval pyrolysis is used to rapidly evaluate the petroleum generative potential and thermal maturity of rocks accurate conclusions require programs every 30 60 ft 9 18 m understanding of interpretive pitfalls and supporting data such as visual kerogen vitrinite reflectance and elemental analyses the generative potential of coals is commonly overestimated by pyrolysis and is best determined by elemental analysis and organic petrography most coals show high s2 s3 5 and low hi values 300 mg hc g toc migrated oil and mud additives which alter rock eval data can sometimes be removed by special processing for immature rocks bimodal s2 peaks and pi values over 0 2 indicate contamination pyrolysis downgrades organic poor clay rich rocks which show lower hi and higher tmax values than isolated kerogen because of adsorption of pyrolyzate on the clays tmax values for small s2 peaks 0 2 mg hc g toc are unreliable tmax is affected by maturation organic matter type contamination and the mineral matrix s3 is sensitive to inorganic and adsorbed carbon dioxide and to instrumentation problems acidification of carbonate rich samples and proper maintenance improves s3 measurement constant sample weights 100 mg are recommended below a threshold weight tmax increases by up to 10 c and other parameters decrease organic rich samples which overload the detector can be diluted with carbonate detector linearity is determined by pyrolyzing various weights of an organic rich rock

investigation of land ice ocean interaction with a fully coupled ice ocean model 1 model description and behavior 1 antarctic ice shelves interact closely with the ocean cavities beneath them with ice shelf geometry influencing ocean cavity circulation and heat from the ocean driving changes in the ice shelves as well as the grounded ice streams that feed them we present a new coupled model of an ice stream ice shelf ocean system that is used to study this interaction the model is capable of representing a moving grounding line and dynamically responding ocean circulation within the ice shelf cavity idealized experiments designed to investigate the response of the coupled system to instantaneous increases in ocean temperature show ice ocean system responses on multiple timescales melt rates and ice shelf basal slopes near the grounding line adjust in 1 2 years and downstream advection of the resulting ice shelf thinning takes place on decadal timescales retreat of the grounding line and adjustment of grounded ice takes place on a much longer timescale and the system takes several centuries to reach a new steady state during this slow retreat and in the absence of either an upward or downward sloping bed or long term trends in ocean heat content the ice shelf and melt rates maintain a characteristic pattern relative to the grounding line

tidal motion ice velocity and melt rate of petermann gletscher greenland measured from radar interferometry over a floating glacier ice tongue or an ice shelf the glacier motion measured by a single repeat pass radar interferogram is difficult to analyze because the long term steady motion of the ice is intermixed with its cyclic downward motion induced by tidal forcing multiple interferograms and a quadruple difference technique are necessary to separate the tidal signal from the long term steady motion of the ice an example of application of this technique is given here using ers 1 radar images of petermann gletscher a major outlet glacier of northern greenland tidal displacements are measured with 5 mm statistical noise the long term ice velocity is measured with a precision of 1 m a 1 the inferred tidal displacements agree well with model predictions from a fixed elastic beam with an elastic damping factor of 0 47 0 01 km 1 the hinge line is mapped with a precision of 20 80 m combining the interferometric ice velocities with ice thickness data the glacier ice discharge is calculated at and below the hinge line at the hinge line the ice flux is 12 1 1 km3 a 1 at the ice front calf ice production is only 0 59 km3 a 1 meaning that 95 of the ice that crosses the grounding line melts before it reaches the calving front assuming steady state conditions the melt rate of the glacier tongue averages 12 1 m a 1 with peak values exceeding 20 m a 1 near the hinge line this high melt rate cannot be accommodated by surface ablation alone only about 2 3 m a 1 and is attributed to pronounced basal melting of the ice tongue basal melting often assumed to be negligible in greenland is the dominant process of mass release from the floating section of petermann gletscher

the origin of 4 methyl steranes and pregnanes from tertiary strata in the qaidam basin china abstract a geochemical study of oils and source rocks in tertiary saline lake facies from the qaidam basin of china demonstrates that pregnanes are mainly derived from the thermal degradation of organic matter in source rocks synchronous with hydrocarbon genesis whereas 4 methyl steranes may principally be a product of microbial activity during diagenesis

calving of large tabular icebergs from ice shelf rift systems 1 we used interferometric synthetic aperture radar to study the detachment process that allowed two large icebergs to calve from the ross ice shelf antarctica time series of rift geometries indicate that rift widths increased steadily whereas rift lengths increased episodically through several discrete rift tip propagation events we also conducted modeling experiments constrained by the observed rift geometry both the observations and model suggest that rift opening and thus tabular iceberg calving are largely driven by glaciological stresses stress introduced by the effect of gravity on the ice shelf rather than by stress introduced by the ocean and atmosphere e g tides and storms this style of rift propagation is expected to determine the steady background calving rate of ice shelves and thus differs significantly from styles that led to the recent disintegration of ice shelves in response to climate warming e g the larsen b ice shelf on the antarctic peninsula

release of kerogen bound hopanoids by hydropyrolysis hydropyrolysis was used to determine the concentrations of kerogen bound hopanoid hydro carbons the samples characterized were a recent sediment priest pot english lake district and three source rock kerogens green river shale draupne shale and jet rock shale the hydropyroly zate of a hopanoid producing bacterium methylobacterium organophilum showed that this procedure does not overly obscure the original isomer compositions of the samples characterized although signifi cant side chain cleavage does occur which is inevitable with any pyrolysis method notable diaerences are observed between the composition of pyrolyzates and bitumen extracts for each of the source rock kerogens the overall level of hopane isomerization within the pyrolyzate is significantly lower than in the corresponding extracts this is particularly the case for the draupne sample the pyrolyzate of which contains 17b 21b hopanes though these are absent in the bitumen diaerences in isomeric com position of the pyrolyzates are in line with the isomer contents of the bitumen extracts the abundance of kerogen derived hopanes is highly variable both in terms of absolute concentration and also relative to the concentration of hopanes in the bitumen this is in part due to maturity diaerences but deposi tional environment and diagenetic conditions may also exert a control on kerogen bound hopane con centration these results show that hydropyrolysis provides valuable data on the concentration of kerogen bound hopanes whilst largely preserving their original isomeric composition 1998 elsevier science ltd all rights reserved

a structural glaciological analysis of the 2002 larsen b ice shelf collapse this study provides a detailed structural glaciological analysis of changes in surface structures on the larsen b ice shelf on the antarctic peninsula prior to its collapse in february march 2002 mapped features include the ice shelf front rifts crevasses longitudinal linear surface structures and meltwater features we define domains on the ice shelf related to glacier source areas and demonstrate that prior to collapse the central larsen b ice shelf consisted of four sutured flow units fed by crane jorum punchbowl and hektoria green evans glaciers between these flow units were suture zones of thinner ice where the feeder glaciers merged prior to collapse large open rift systems were present offshore of foyn point and cape disappointment these rifts became more pronounced in the years preceding break up and ice blocks in the rifts rotated because of the strong lateral shear in this zone velocity mapping of the suture zones indicates that the major rifts were not present more than about 20 years ago we suggest that the ice shelf was preconditioned to collapse by partial rupturing of the sutures between flow units this we believe was the result of ice shelf front retreat during 1998 2000 reducing the lateral resistive stress on the upstream parts of the shelf and glacier flow units ice shelf thinning and pre shelf break up glacier acceleration

chemical and carbon isotopic fractionations of gaseous hydrocarbons during abiogenic oxidation abstract the variations of chemical and carbon isotopic compositions in gaseous hydrocarbons upon abiogenic oxidation by sulfates hematite and both in laboratory studies were clearly demonstrated through a unique two step experimental approach in the first step a large number of small gold capsules containing gaseous hydrocarbons were prepared by kerogen pyrolysis experiments which were conducted under the same condition 450 c and 50 mpa for 72 h using the same kerogen the analytical results demonstrated that the chemical and carbon isotopic compositions of gases were almost identical among the capsules in the second step each of these gaseous hydrocarbon bearing capsules along with mineral oxidant hematite or magnesium sulfate heptahydrate or both and deionized water 15 of the amount of the oxidant was placed into a large gold capsule after welding sealing the small gaseous hydrocarbon bearing capsule was forced to leak while the large capsule remained undamaged by compressing the large capsule from the outside at the position where this small capsule was located then these large capsules containing gas and mineral reactants were heated isothermally at 350 c and 50 mpa for 72 144 216 and 288 h respectively the results of the oxidation experiments with increasing heating time can be outlined as follows 1 the amount of methane remained almost unchanged in the experiments using hematite and the mixed oxidants hematite mgso4 while it increased substantially in the experiment using mgso4 after 72 h indicating methane was one of the final products of c2 oxidation 2 the amounts of c2 c5 hydrocarbons decreased consistently and more rapidly in the experiment using mgso4 than that using hematite and the mixed oxidants 3 the oxidation rates of gas hydrocarbons increased with increasing carbon number of hydrocarbons 4 the oxidation rates of i butane and i pentane were substantially higher than those of the corresponding n butane and n pentane 5 the amount of h2s increased substantially in the experiment using mgso4 whereas it was below the detection level in the experiments using hematite and the mixed oxidants 6 the 13c values of c1 c5 hydrocarbons became less negative and the isotopic fractionation extent increased with increasing carbon number of hydrocarbons and oxidation extent 7 carbon isotopic fractionation factor k12 k13 decreased with increasing oxidation rate of gas hydrocarbons and 8 the rate of thermochemical sulfate reduction tsr was strongly dependent upon the presence and concentrations of h2s

surface structure and stability of the larsen c ice shelf antarctic peninsula a structural glaciological description and analysis of surface morphological features of the larsen c ice shelf antarctic peninsula is derived from satellite images spanning the period 1963 2007 the data are evaluated in two time ranges a comparison of a 1963 satellite image photomosaic with a modern digital mosaic compiled using 2003 04 austral summer data and an image series since 2003 showing recent evolution of the shelf we map the ice shelf edge rift swarms crevasses and crevasse traces and linear longitudinal structures called flow stripes or streak lines the latter are observed to be continuous over distances of up to 200 km from the grounding line to the ice shelf edge with little evidence of changes in pattern over that distance integrated velocity measurements along a flowline indicate that the shelf has been stable for 560 years in the mid shelf area linear longitudinal features may be grouped into 12 units each related to one or a small group of outlet feeder glaciers to the shelf we observe that the boundaries between these flow units often mark rift terminations the boundary zones originate upstream at capes islands or other suture areas between outlet glaciers in agreement with previous work our findings imply that rift terminations within such suture zones indicate that they contain anomalously soft ice we thus suggest that suture zones within the larsen c ice shelf and perhaps within ice shelves more generally may act to stabilize them by reducing regional stress intensities and thus rates of rift lengthening

simple kinetic models of petroleum formation part i oil and gas generation from kerogen modern basin analysis uses kinetic models to predict the extent of petroleum generation within potential source rocks the global kinetic model presented here assigns kinetic parameters based on gross depositional environment and stratigraphic age this is useful in areas of low geochemical knowledge including exploration frontiers five kerogen kinetic organofacies each characterized by a specific organic matter input and early diagenetic overprint can broadly be related to sedimentary facies age associations even using seismic sequence stratigraphy alone a aquatic marine siliceous or carbonate evaporite any age b aquatic marine siliciclastic any age c aquatic non marine lacustrine phanerozoic d e terrigenous non marine ever wet coastal mesozoic and younger and f terrigenous non marine coastal late palaeozoic and younger routine pyrolysis data allow partitioning of organic carbon in the immature source rock into four initial components oil oil generative gas generative and inert separate kinetic parameters for the oil and gas generative fractions allow computation of the evolving concentration and composition of the products it was assumed that the activation energy distributions for each fraction were normally distributed non linear regression of large combined laboratory and field data sets varying by up to 12 orders of magnitude in heating rate established optimum values for the required ten 5 2 kinetic parameter sets a emean e differences in kinetic parameters can be reconciled with known chemical properties although our knowledge base is still inadequate to construct kinetic models from first principles mean activation energies governing oil generation increase systematically in the order a f causing a corresponding increase in generation temperature at a reference heating rate 2 c ma 1 the oil generation window 10 90 oil generative kerogen degraded increases from ca 95 135 c to 145 175 c organofacies c has the tightest energy distribution and narrowest oil generation window the gas generation window ranges from ca 105 155 c to 175 220 c thermal stress results from a combination of temperature and time an order of magnitude increase decrease in heating rate elevates depresses reaction temperatures by ca 15 c heating rates in subsiding sedimentary basins can vary by two orders of magnitude dramatic differences in generation temperature can result if the heating rate and organofacies effects compound thus global oil and gas generation temperature thresholds constitute blunt instruments with which to screen the petroleum potential of sedimentary basins because unexpelled oil provides a potential feedstock for oil to gas cracking in the source rock quantitative models of petroleum generation become really useful only when coupled with models of oil gas cracking and expulsion for example the frequently observed association between gas provinces and coals cannot be explained solely by their generation behaviour

interferometric estimation of three dimensional ice flow using ascending and descending passes satellite radar interferometry sri provides an important new tool for determining ice flow velocity interferometric measurements made from a single track direction are sensitive only to a single component of the three component velocity vector observations from along three different track directions would allow the full velocity vector to be determined a north south looking synthetic aperture radar sar could provide these observations over large portions of the globe but not over large areas of the polar ice sheets the authors develop and demonstrate a technique that allows the three component velocity vector to be estimated from data acquired along two track directions ascending and descending under a surface parallel flow assumption this technique requires that there are accurate estimates of the surface slope which are also determined interferometrically to demonstrate the technique the authors estimate the three component velocity field for the ryder glacier greenland their results are promising although they do not have yet ground truth data with which to determine the accuracy of their estimates

ice shelf dynamics near the front of the filchner ronne ice shelf antarctica revealed by sar interferometry fifteen synthetic aperture radar sar images of the ronne ice shelf also referred to as the filchner ronne ice shelf antarctica obtained by the european remote sensing satellites ers 1 and 2 are used to study ice shelf dynamics near two ends of the iceberg calving front interferograms constructed from these sar images are used to resolve the ice shelf displacement along several directions in response to both ocean tide and long term creep flow tidal motion is separated from creep flow using differential interferometry i e two or more interferograms in which fringe patterns common to all are predominantly associated with creep flow creep flow velocities thus determined compare well with prior ice shelf velocity surveys using these data we studied the influence of large scale rifts ice rises and coastal separation on the ice shelf flow many of the large rifts that appear to form the boundaries where tabular icebergs may eventually detach from the ice shelf are filled with a melange of sea ice ice shelf debris and wind blown snow the interferograms show that this melange tends to deform coherently in response to the ice shelf flow and has sufficient strength to trap large tabular ice shelf fragments for several decades before the fragments eventually become icebergs in many instances the motion of the tabular fragments is a rigid body rotation about a vertical axis that is driven by velocity shear within the melange the mechanical role of the rift filling melange may be to bind tabular ice shelf fragments to the main ice shelf before they calve this suggests two possible mechanisms by which climate could influence tabular iceberg calving first spatial gradients in oceanic and atmospheric temperature may determine where the melange melts and thus the location of the iceberg calving margin second melting or weakening of ice melange as a consequence of climate change could trigger a sudden or widespread release of tabular icebergs and lead to rapid ice shelf disintegration

the influence of pressure on petroleum generation and maturation as suggested by aqueous pyrolysis because fluid pressures are transient in sedimentary basins over geologic time the effect of increasing fluid pressure on organic matter metamorphism is difficult to determine and conflicting opinions exist concerning its influence properly performed aqueous pyrolysis experiments can closely simulate hydrocarbon generation and maturation in nature and thus offer an excellent way to study the influence of pressure such experiments carried out on the retort phosphatic shale member of the lower permian phosphoria formation type ii s organic matter at different constant temperatures demonstrated that increasing pressure significantly retards all aspects of organic matter metamorphism including hydrocarbon generation maturation and thermal destruction this conclusion results from detailed quantitative and qualitative analyses of all products from hydrocarbon generation from the c1 to c4 hydrocarbon gases to the asphaltenes and also from analyses of the reacted rocks we have documented that our aqueous pyrolysis experiments closely simulated natural hydrocarbon generation and maturation thus the data taken as a function of pressure have relevance to the influence of normal and abnormal fluid pressures as related to 1 depths and temperatures of mainstage hydrocarbon generation 2 the thermal destruction of deposits of gas or light oil or their preservation to unexpectedly high maturation ranks and 3 the persistence of measurable to moderate concentrations of c15 hydrocarbons in fine grained rocks even to ultra high maturation ranks

processes involved in the propagation of rifts near hemmen ice rise ronne ice shelf antarctica interferometric radar images collected by ers 1 ers 2 and radarsat 1 are used to observe the rupture tip of rifts that propagate along hemmen ice rise on the ronne ice shelf antarctica interferograms generated in 1992 and 1997 allow for the observation of ice deformation accumulated over 9 and 24 days respectively these interferograms are combined in order to separate the continuous process of creep deformation from the more cyclic motion caused by variations in ocean tide an examination of local gradients in creep deformation reveals the pattern of ice deformation around and near the rupture tips and rifts with great precision up to 10 cm a 1 we compare the observations with a deformation model for ice and obtain the following results 1 the tidal oscillation of the ronne ice shelf only yields small deformations along the rifts and near the rupture tips 2 along the ice front the rifts and at the rupture tips vertical bending is observed which is well explained by a model of viscous deformation of ice furthermore the model indicates that the deformation pattern observed at the rupture tips is a sensitive indicator of the propagation state of the rifts i e active vs inactive 3 the viscous adjustment of ice is the dominant mode of deformation masking the deformation pattern predicted by linear elastic fracture mechanics lefm 4 yet at a spatial scale equivalent to the length of a rift the propagation rate is well predicted by lefm

confined pyrolysis of tertiary lacustrine source rocks in the western qaidam basin northwest china implications for generative potential and oil maturity evaluation abstract the parameter s 1 s 2 genetic potential of rock eval analysis is widely used as an evaluation of the genetic potential for the source rocks oligocene miocene saline lacustrine source rocks in the western qaidam basin have low total organic c contents toc most around 0 5 with a few exceptions 1 0 mineral matrix effects are substantial for source rocks with low toc resulting in relatively low s 1 and s 2 peaks based on the results of confined pyrolyses sealed au capsules on 6 oligocene miocene source rocks from the western qaidam basin with toc ranging between 0 48 and 2 22 the relationship between the s 1 s 2 parameter and the maximum amount of extracted bitumen or saturated and aromatic hydrocarbons sa after the confined pyrolysis has been established as follows bitumen mg g rock 1 4924 s 1 s 2 0 3201 r 0 987 or sa saturates aromatics mg g rock 0 7083 s 1 s 2 0 4045 r 0 992 based on these formulas the amounts of hydrocarbons generated from source rocks can be reasonably estimated the typical crude oils with low biomarker maturities in this region appear substantially different to the pyrolysates of these six rocks at 180 300 c but comparable to the pyrolysates at 320 c and higher temperatures based on molecular parameters this result in combination with the physical and gross compositions of the crude oils suggests that the majority of these crude oils were generated from the source rocks during the main oil generative stage possibly at a maturity higher than r o 0 74

modelling of rift propagation on ronne ice shelf antarctica and sensitivity to climate change 1 the calving of icebergs from large antarctic ice shelves is controlled mainly by the formation and propagation of rifts originating from the side margins of the ice shelf and local areas of grounding using insar we observe the evolution of rifts along hemmen ice rise on ronne ice shelf antarctica prior to the large calving event of october 1998 we couple these observations with a computer model combining the viscous flow of an ice shelf with a linear elastic fracture mechanics description of the propagation of rifts the model reveals that the ice melange trapped in between the rifts exerts a major control on the propagation of rifts and in turn on ice shelf stability melting of the ice melange from oceanic or atmospheric warming would significantly increase the propagation rate of rifts and threaten the ice shelf stability

fracture field for large scale ice dynamics recent observations and modeling studies emphasize the crucial role of fracture mechanics for the stability of ice shelves and thereby the evolution of ice sheets here we introduce a macroscopic fracture density field into a prognostic continuum ice flow model and compute its evolution incorporating the initiation and growth of fractures as well as their advection with two dimensional ice flow to a first approximation fracture growth is assumed to depend on the spreading rate only while fracture initiation is defined in terms of principal stresses the inferred fracture density fields compare well with observed elongate surface structures since crevasses and other deep reaching fracture structures have been shown to influence the overall ice shelf dynamics we propose the fracture density field introduced here be used as a measure for ice softening and decoupling of the ice flow in fracture weakened zones this may yield more accurate and realistic velocity patterns in prognostic simulations additionally the memory of past fracture events links the calving front to the upstream dynamics thus the fracture density field proposed here may be employed in fracture based calving parameterizations the aim of this study is to introduce the field and investigate which of the observed surface structures can be reproduced by the simplest physically motivated fracture source terms

geochemical characteristics of tertiary saline lacustrine oils in the western qaidam basin northwest china abstract based on the systematic analyses of light hydrocarbon saturate aromatic fractions and c isotopes of over 40 oil samples along with related tertiary source rocks collected from the western qaidam basin the geochemical characteristics of the tertiary saline lacustrine oils in this region was investigated the oils are characterized by bimodal n alkane distributions with odd to even c11 c17 and even to odd c18 c28 predominance low pr ph mostly lower than 0 6 high concentration of gammacerane c35 hopane and methylated mttcs reflecting the high salinity and anoxic setting typical of a saline lacustrine depositional environment mango s k1 values in the saline oils are highly variable 0 99 1 63 and could be associated with the facies dependent parameters such as pr ph and gammacerane indexes compared with other tertiary oils the studied tertiary saline oils are marked by enhanced c28 sterane abundance 30 or more of c27 c29 homologues possibly derived from halophilic algae it is noted that the geochemical parameters of the oils in various oilfields exhibit regular spatial changes which are consistent with the depositional phase variations of the source rocks the oils have uncommon heavy c isotopic ratios 24 to 26 and a flat shape of the individual n alkane isotope profile and show isotopic characteristics similar to marine organic matter the appearance of oleanane and high 24 24 27 norcholestane ratios 0 57 0 87 in the saline oils and source rocks confirm a tertiary organic source

observation of ocean tides below the filchner and ronne ice shelves antarctica using synthetic aperture radar interferometry comparison with tide model predictions tides near and under floating glacial ice such as ice shelves and glacier termini in fjords can influence heat transport into the subice cavity mixing of the under ice water column and the calving and subsequent drift of icebergs free surface displacement patterns associated with ocean variability below glacial ice can be observed by differencing two synthetic aperture radar sar interferograms each of which represents the combination of the displacement patterns associated with the time varying vertical motion and the time independent lateral ice flow we present the pattern of net free surface displacement for the iceberg calving regions of the ronne and filchner ice shelves in the southern weddell sea by comparing sar based displacement fields with ocean tidal models the free surface displacement variability for these regions is found to be dominated by ocean tides the inverse barometer effect i e the ocean s isostatic response to changing atmospheric pressure also contributes to the observed vertical displacement the principal value of using sar interferometry in this manner lies in the very high lateral resolution tens of meters obtained over the large region covered by each sar image small features that are not well resolved by the typical grid spacing of ocean tidal models may contribute to such processes as iceberg calving and cross frontal ventilation of the ocean cavity under the ice shelf

influence of bitumen 2 on rock eval pyrolysis abstract extractable organic matter bitumen 2 remaining in previously extracted whole rocks or in kerogen concentrates that have not been thoroughly extracted after rock demineralization can severely affect rock eval data for kerogens appearing in the s2 rather than the s1 peak the bitumen 2 acts to increase s2 yield we illustrate the results from the analyses of a mature source rock from offshore norway

biomarker maturity parameters the role of generation and thermal degradation abstract the effects of burial maturation upon seven molecular maturity parameters and the concentrations of individual biomarkers employed in these parameters have been studied in a well in the barents sea the depth interval between 1400 and 3000 m comprises homogenous eocene claystones with effectively uniform organic carbon content 0 4 0 6 and kerogen type hi of 100 200 mg hc g toc the quantitative biomarker data thus contain minimal interference from organic facies hydrocarbon expulsion effects and the presence of migrated hydrocarbons bulk geochemical data define the hydrocarbon generation threshold or oil window at around 2300 m molecular maturity parameters proceed to equilibrium and in some cases demonstrate inversion at high maturity these molecular changes are associated with major changes in biomarker concentrations the hopane 22 s c 31 hopane and 20 s c 29 sterane parameters proceed as a result of the balance between the relative rates of generation and thermal degradation of the different isomers increased concentrations of the individual isomers are interpreted to be the result of biomarker generation from the kerogen mainly and other macromolecular polar fractions the c 29 sterane parameter and the three parameters involving rearranged hopanes ts 29ts and diahopane operate at higher maturity levels and proceed as a result of the relative rates of thermal degradation of the compound pairs isomerisation in the bitumen may also influence the operation of the parameters involving stereoisomers but must be a relatively minor contribution

crack propagation and fracture resistance in saline ice crack propa gation in saline ice a model sea ice is investigated in this study in an atte mpt to under stand the processes of crack growth at one loading rate and two temperatu res as has been previou sly observed in cold sea ice and warm or cold fresh water ice crack growth occurs in initiat ion arrest incr ement s the energetic stabil ity cri teria of crack growth are exa mined in saline ice and growth is charact erized in terms of the fractu re resistance param eter kr this paper offers the development of a new fractu re geom etry capable of sustained stable crack growth and the prese ntation of fractu re resis tance curves for saline ice at 25 and 15 c the important findi ngs of this paper are that i in warm sal ine ice ext ensive local crack tip dama ge is acco mpanied by a limited amount of slow stable crack extension ii fracture in cold saline ice is characte rized by locally negative kr behavior and iii fracture in cold or warm saline ice is cha racterized by glob ally posit ive kr curve behavior

constraints upon the use of 24 ethylcholestane diastereomer ratios as indicators of the maturity of petroleum abstract we have measured the ratio 20 s 20 s 20 r the relative abundances of the 24 ethylcholestane diastereomers in nine pairs of closely adjacent samples of coals and shales which represent a range of geological ages and different sedimentary basins within some sample pairs the values were similar in others they were very different the differences between the values for coal and shale members of pairs are attributed to effects of sediment matrix type upon the processes which cause the changes in the ratio the kinetic parameters e and s for the changes in the 20 s 20 s 20 r ratio have been estimated using previously published measurements for the hod 1 well shale and jupiter 1 well coal and these values were found to be very different the process in the coal sequence has a much lower activation energy and is therefore less responsive to differences in heating rate regimes than is the case for the shale sequence values of the 20 s 20 s 20 r ratio in two other sequences are shown to be consistent with this explanation and the implications of these observations for the practice of using sterane isomer ratios for assessment of maturity of sediments and crude oils are discussed

glaciological advances made with interferometric synthetic aperture radar spaceborne interferometric synthetic aperture radar insar techniques for measuring ice flow velocity and topography have developed rapidly over the last decade and a half revolutionizing the study of ice dynamics spaceborne interferometry has contributed to major progress in many areas of glaciological study by providing the first comprehensive measurements of ice stream flow velocity over the major outlets of greenland and antarctica revealing that ice stream and outlet glacier flow can change rapidly months to years improving understanding of several ice sheet and ice shelf processes providing velocity for flux gate based mass balance assessment mapping flow of mountain glaciers and capturing the geomorphic traces of past ice flow we review the basic technique development the measurement characteristics and the extensive set of results yielded by these measurements

hopanoid hydrocarbon maturation by an igneous intrusion abstract the thermal effects of an igneous intrusion 0 9 m thick dyke upon the abundance and composition of hopanes and hopenes are reported for a suite of samples within a single sedimentary horizon a carbonate concretion 1 6 m in diameter from the jurassic dun caan shale member bearreraig bay isle of skye scotland the conventional hopane maturity parameters show normal trends towards the dyke and through the oil window approximately 22 45 cm from the dyke i e 25 50 dyke thickness with the exception of the ts ts tm parameter which shows a progressive fall with increasing maturity until the middle of the oil window when it increases markedly molecular abundances demonstrate that the observed changes in the hopane maturity parameters result from the combined effects of generation presumed to be from kerogen and degradation of individual compounds with isomerization in the free phase being minimal or unimportant the unexpected behaviour of ts ts tm results from the minimal generation of ts compared with tm our data indicate that the ts skeleton is not present in the kerogen and at least under the elevated heating associated with an igneous intrusion may be derived from 18 h 22 29 30 trisnorneohop 13 18 ene in the bitumen thermally induced modifications to hopane carbon number distributions are also reported and show that oil source rock correlations between samples of different maturity must consider the effects of generation degradation of kerogen bound hopanes