the abundance and distribution of diamondoids in biodegraded oils from the san joaquin valley implications for biodegradation of diamondoids in petroleum reservoirs abstract the biodegradability of diamondoids was investigated using a collection of crude oil samples from the san joaquin valley california that had been biodegraded to varying extent in the reservoir our results show that diamondoids are subjected to biodegradation which is selective as well as stepwise adamantanes are generally more susceptible to biodegradation than other diamondoids such as diamantanes and triamantanes we report a possible pathway for the microbial degradation of adamantane this cage hydrocarbon possibly breaks down to a metabolic intermediate through the action of microbes at higher levels of biodegradation in petroleum reservoirs microbial alteration has only a minor effect on diamondoid abundance in oil at low levels of biodegradation our results suggest that most diamondoids with the exception of adamantane are resistant to biodegradation like the polycyclic terpanes e g c19 c24 tricyclic terpanes hopanes gammacerane oleananes ts tm c29 ts steranes and diasteranes microbial alteration of diamondoids has a negligible impact on the quantification of oil cracking achieved using the diamondoid biomarker method

methyl diamantane index mdi as a maturity parameter for lower palaeozoic carbonate rocks at high maturity and overmaturity diamantanes were identified in extracts from the lower ordovician majiagou formations o1m5 of the central gas field shanganning basin china at 3100 3800 m corresponding to ro 1 9 3 9 the mdi methyl diamantane index 4 md 1 md 3 md 4 md ranges from 40 to 65 for the source rock extracts changes in the mdi index in the very mature sections ro 2 0 are relatively small and no linear correlation between mdi and ro o r mdi and depth is noted as previously reported suggesting the possibility that the mdi may have limited applicability in maturity determinations 2000 elsevier science ltd all rights reserved

geochemistry of palaeozoic marine petroleum from the tarim basin nw china part 2 maturity assessment abstract the thermal maturity of forty three crude oil samples collected from the cratonic portion of the tarim basin nw china has been assessed using a variety of parameters while compound ratios of diamondoids alkylated naphthalenes methyl phenanthrenes and methyl dibenzothiophenes showed consistent trends with increasing maturity a large discrepancy was observed for the maturity levels of the oils determined from these parameters equivalent vitrinite reflectance values calculated from methylphenanthrene index 1 mpi1 methyldibenzothiophene ratio mdr and methyldiamontane index mdi were in the range of 0 66 0 97 1 11 1 64 and 0 89 1 74 ro respectively while we caution that some of the discrepancy may be related to calibration problems the difference observed from different compound classes could be real reflecting the multiple charge to petroleum accumulations as the diamondoid hydrocarbons were possibly generated at later maturation stages than most aromatic hydrocarbons as diamondoids with methyl substitution on the bridgehead positions are more stable than those with substitution on other positions several compound ratios based on ethyl admantanes dimethyl admantanes trimethyl admantanes and dimethyl diamantanes also correlated with the established maturity indicators such as mdr and mdi while condensates with high maturity levels represent the late charge hydrocarbons some of them with relatively low maturity levels may be affected by evaporative fractionation processes the normal gravity oils cover a wide maturity range consistent with multiple charges and in reservoir mixing while the waxy oils with high apparent maturity levels may be the products of wax precipitation due to a later gas injection into an oil column heavy oils with low apparent maturity levels could be the residue of oil that has lost its light end

the fate of diamondoids in coals and sedimentary rocks diamondoids were detected in the extracts of a series of coals and rocks varying in maturity lithology source input and depositional environment at the same maturity level diamondoids are generally about a magnitude more abundant in source rocks than in coals the concentrations of diamondoids are maturity dependent however while diamondoids become more abundant with the increasing thermal maturity a diminution in diamondoid concentrations is observed at the maturity value of about r sub o 4 0 in both coals and rocks the occurrence of diamantane destruction at 550 sup o c during pyrolysis suggests that diamondoids may be eventually destroyed at high temperatures in the earth here we propose three main phases of diamondoid life in nature diamondoid generation phase i r sub o 4 0

impact of climate and humans on the range dynamics of the woolly mammoth mammuthus primigenius in europe during mis 2 the woolly mammoth mammuthus primigenius was widespread in almost all of europe during the late pleistocene however its distribution changed because of population fluctuations and range expansions and reductions during marine oxygen isotope stage 2 mis 2 these processes were highly dynamic our analyses of 318 radiocarbon dates from 162 localities obtained directly from mammoth material confirmed important changes in mammoth range between 28 6 and 14 1 ka the greenland stadial 3 interval 27 5 23 3 ka was the time of maximum expansion of the mammoth in europe during mis 2 the continuous range was soon fragmented and reduced resulting in the disappearance of mammuthus during the last glacial maximum from 21 4 to 19 2 ka in all parts of the north european plain it is not clear whether mammoths survived in the east european plain the mammoth returned to europe soon after 19 0 ka and for the next 3 4 millennia played an important role in the lifeways of epigravettian societies in eastern europe mammoths became extinct in most of europe by 14 0 ka except for core areas such as the far northeast of europe where they survived until the beginning of the holocene no significant correlation was found between the distribution of the mammoth in europe and human activity

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

the permeability of a melting snow cover data from snow lysimeters in california and vermont are used to find the saturated permeability of a melting snow cover in the range of 10 40 10 10 m2 depending on snow density the unsaturated permeability increases as about the third power of liquid saturation the gravity flow theory is shown to be an accurate representation of meltwater drainage from snow covers in two diverse areas even though the snow covers are treated as homogeneous units the variation of saturated permeability with snow density occurs about as predicted by shimizu s formula for dry snow although ice layers decrease the permeability somewhat

lava and ice interaction at stratovolcanoes use of characteristic features to determine past glacial extents and future volcanic hazards structures resulting from lava and ice interaction are common at glaciated stratovolcanoes during summit eruptions at stratovolcanoes meltwater is produced and travels freely down steep slopes and thin permeable valley glaciers eroding the ice and enlarging preexisting glacial drainages as a result eruptions in this environment have produced few catastrophic floods lava flowing into the open channels and voids in the glaciers becomes confined and grows thicker filling the available space and producing steep sided bodies with smooth bulbous contact surfaces quenching of lava against ice or by water forms small scale features such as tensional fractures and glass as the amount of meltwater in contact with the lava increases the type and abundance of smaller scale features become similar to those produced during subglacial eruptions into meltwater lakes identification of large and small scale lava ice contact features in the field can be used to reconstruct paleoglacial extent and combined with geochronology of lavas to determine past paleoclimate an understanding of lava ice interaction allows us to better assess the hazards posed by future eruptions at glaciated volcanoes

the relative importance of supraglacial versus subglacial meltwater escape in basaltic subglacial tuya eruptions an important unresolved conundrum the hydraulic behaviour of meltwater during subglacial basaltic eruptions in temperate ice is of paramount importance in understanding the eruptive processes lithofacies and architecture of the edifices formed hydraulics also determines the timing location and volume of meltwater discharge which may be sudden and catastrophic and via subglacial and or supraglacial routes increasing our knowledge of meltwater hydraulics is therefore important for understanding predicting and mitigating the impact of meltwater release on vulnerable human communities new observations about eruption related meltwater hydraulics are presented for well exposed glaciovolcanic lava fed deltas on james ross island antarctica and accounts of historical eruptions are also re examined to identify the major meltwater discharge routes the study provides the first conceptual model for how meltwater escapes supraglacially in the absence of a crevassed layer which will dominate any meltwater flow overflowing may be initiated by enhanced rates of seepage despite the intrinsically low hydraulic conductivities of snow and firn once overflowing is established the rate of spillway incision is a likely overriding control on the evolution of the system and whether the discharge is unstable fast or stable slower the james ross island sequences demonstrate that meltwater discharge is highly dynamic and may have involved both subglacial and supraglacial escape subglacial discharge probably occurs throughout basaltic tuya eruptions but some periods may be dominated by concurrent overflowing it is still unclear if overflowing systems are sufficiently stable to enable the growth of laterally extensive glaciovolcanic lava fed deltas

cretaceous tertiary high latitude palaeoenvironments james ross basin antarctica high latitude settings are sensitive to climatically driven palaeoenvironmental change and the resultant biotic response climate change through the peak interval of cretaceous warmth late cretaceous cooling onset and expansion of the antarctic ice sheet and subsequently the variability of neogene glaciation are all recorded within the sedimentary and volcanic successions exposed within the james ross basin antarctica this site provides the longest onshore record of cretaceous tertiary sedimentary and volcanic rocks in antarctica and is a key reference section for cretaceous tertiary global change the sedimentary succession is richly fossiliferous yielding diverse invertebrate vertebrate and plant fossil assemblages allowing the reconstruction of both terrestrial and marine systems the papers within this volume provide an overview of recent advances in the understanding of palaeoenvironmental change spanning the mid cretaceous to the neogene of the james ross basin and related biotic change and will be of interest to many working on cretaceous and tertiary palaeoenvironmental change

diamondoid hydrocarbon ratios novel maturity indices for highly mature crude oils abstract diamondoid hydrocarbons have been identified in oil and source rock samples from the tarim yinggehai qiongdongnan and other chinese basins two diamondoid hydrocarbon ratios have been used as novel high maturity indices to evaluate the maturation and evolution of crude oils and condensates in these chinese basins the two ratios 1 ma 1 ma 2 ma mai methyl adamantane index and 4 md 1 md 3 md 4 md mdi methyl diamantane index were found to increase with increasing vitrinite reflectance the initial values for the ratios are ca 50 and 30 respectively diamondoid hydrocarbons are products of rearrangement of polycyclic hydrocarbons and their ratios are found to be affected by organic input to a minor extent based on this study crude oils from the tarim basin are generally believed to be very mature ro 1 1 the cambrian ordovician source beds are the major source rocks of crude oils and natural gases in this basin condensates from the tarim yinggehai and qiongdongnan basins have higher maturities equivalent to ro values of 1 6 2 0 gases and condensates from the yinggehai and qiongdongnan basins are generated mainly from tertiary source rocks below 4000 5000 m

source and thermal maturity of crude oils in the junggar basin in northwest china determined from the concentration and distribution of diamondoids abstract here we discuss three types of diamondoid parameters for oils from the junggar basin these are absolute concentrations concentration ratios and isomerization ratios according to the absolute diamondoid concentrations the oils collected from different areas of the basin were broadly divided into three maturity stages 1 low mature 1000 ppm adamantanes 50 ppm diamantanes the oils in the northwestern region of the junggar basin are in the low mature to mature stages based on a combination of diamondoid concentration ratios and biomarker indices these oils can be divided into three groups i e group i oils in the wuxia zone derived from the lower permian fengcheng formation p1f group ii oils in the kebai zone sourced from middle permian lower wuerhe formation p2w and group iii oils in the mahu depression generated from more mature source rocks of jiamuhe formation p1j or the p1f diamondoid concentrations and isomerization ratios were used to precisely evaluate the thermal maturity of mature oils and highly mature condensates respectively our results indicate that the oils in the central part of the basin have decreasing thermal maturity from south to north whereas the oils in the kelameili area display increasing thermal maturity from east to west in this study we found that different diamondoid indices are useful only in certain thermal maturity ranges therefore at least for the junggar basin it is crucial to know which thermal region one is in before using diamondoid ratios for maturity assessment

generation and evolution of diamondoids in source rock abstract thermal maturation related variations in the abundance and distribution of diamondoids in source rocks were investigated by thermal simulation experiments on extracts and kerogen obtained from a same marine shale and by quantitative analysis of diamondoids within pyrolysates using highly sensitive and selective gas chromatography triple quadrupole mass spectrometry gc ms ms the results indicate that diamondoids within the marine shale are generated mainly during 0 8 1 7 easyro generally deriving from extractable organic matter within source rocks and are destroyed after 1 7 easyro to be entirely removed by ca 3 0 easyro ternary plots of the relative distribution of diamondoids and bivariate diagrams for diamondoid parameters e g dma md vs dmai 1 and dma md vs tmai 1 show systematic changes in diamondoids with increasing thermal maturity expressed as easyro

effects of the november 13 1985 eruption on the snow pack and ice cap of nevado del ruiz volcano colombia abstract about twenty five to thirty percent of the ice on the ice cap of nevado del ruiz was fractured and destabilized by earthquakes and explosive activity on november 13 1985 comparison of aerial and ground photographs taken before and after the eruption allows calculation of the volume of snow and ice removed from each glacial basin during the eruption about 16 4 2 km 2 of the surface area of the ice and snow was lost the corresponding volume is estimated to be close to 0 06 km 3 or 9 of the total volume of ice and snow at least four distinct processes including explosions ice avalanches surficial erosion of snow and slush avalanches were responsible for transporting snow firn and ice downslope heat from pyroclastic flows and surges and their deposits was responsible for melting snow and ice both at the surface of the ice cap in situ and during its downslope transport voluminous lahars were triggered in 3 of the 4 main drainages on the volcano by the approximately 43 million m 3 of liquid water about 62 million m 3 of snow firn and ice produced by these combined processes thermal and mechanical effects of the pyroclastic flows and surges included scouring direct melting and entraining snow firn and ice which left several erosional features on the ice cap and deposits both on the ice and on the edges of the ice cap subsurface and englacial drainage of water through crevasses was deduced from depositional and morphological features at the ice margins some meltwater might have been trapped in reservoirs but some water was also released shortly after the eruption the estimated volume of released meltwater is about 43 million m 3 i e 2 4 times more than the approximate 11 12 million m 3 of water incorporated into the lahars thus roughly 21 million m 3 of water were released but did not contribute to lahar generation this non contributing water was 1 included in snow avalanches and sediment laden slush avalanches outside the lahars channels or bound up in the wet pyroclastic surge deposits 2 incorporated in the phreatic explosive products or saturated firn by meltwater which issued from the thermal effect of the tephra fall 3 sublimated into steam during the passage of the pyroclastic flows or 4 stored within the ice meltwater may still be be trapped within the ice cap and may be a potential source of water for future lahars

application of diamondoids to distinguish source rock facies abstract diamondoid distributions in solvent extracts from marine siliciclastic shales marine carbonates and coals of a wide variety of maturities were determined by gc msd for this sample set published diamondoid maturity parameters did not change systematically throughout the oil window it was found that several novel diamondoid ratios were indicative of source it was possible to distinguish between terrigenous marine carbonate and marine siliciclastic facies the proposed dimethyl diamantane facies ratios are virtually unaffected by maturity while the ethyl adamantane ratio appears to be affected by maturity in the late gas window range

the effect of organic matter type on formation and evolution of diamondoids abstract a series of anhydrous pyrolysis experiments using sealed gold tubes were performed on three types of kerogen to investigate the effect organic matter type has on the generation and evolution of thermogenic diamondoids based on the compositional variation of pyrolysis products the cracking of kerogens can be divided into three stages oil generation 0 6 1 5 easyro wet gas generation 1 5 2 1 easyro and dry gas generation 2 1 easyro the experimental results indicate that diamondoids were mainly generated in the oil and wet gas generation stages and decomposed in the dry gas generation stage in addition to thermal maturity the formation of diamondoids is also influenced by the type of organic matter type i and iia kerogens produced more diamondoids than type iii kerogen and diamondoids generated from type iii kerogen were dominantly adamantanes therefore the concentration and concentration ratios of diamondoids can be used to assess the maturity of source rocks 1 0 1 5 easyro and determine the type of organic matter 1 0 2 0 easyro isomerization ratios of diamondoids depend mainly on thermal maturity and the type of organic matter has little effect the use of isomerization ratios to determine thermal maturity is best for source rocks at higher maturity levels 1 5 3 0 easyro therefore bivariate diagrams of concentration versus isomerization indices of diamondoids e g dmas mds vs dmai 1 and dmas mds vs tmai 1 can be used to evaluate the source rock maturity over a wider easyro range 1 0 3 0 easyro than single diamondoid parameters as there are differences in the concentration and distribution of diamondoids in the extracts of three source rocks the possibility exists to use diamondoid indices of immature rocks to determine the type of source rock

diamondoid hydrocarbon ratios as indicators of biodegradation in australian crude oils the effect of biodegradation on diamondoid distributions in petroleum has been investigated on a series of crude oils reservoired in two australian sedimentary basins the gippsland basin and the carnarvon basin the ratio of methyladamantanes to adamantane rises with increasing biodegradation significant changes in the ratio occur at extreme levels indicating that diamondoids can be indicators of petroleum biodegradation especially when most other hydrocarbons have been removed the methyladamantane adamantane ratio can also be used to assess the composition of crude oils that are comprised of a mixture of severely biodegraded and non biodegraded oil

theoretical analysis of snow dam decay snow dams have been observed in many stream channels in the arctic and the sub arctic but there is no theoretical analysis of their decay processes these processes include snowmelt seepage erosion down cutting snow slope failure and flotation of the snow dam snowmelt can be determined by the energy balance seepage of water will cause serious erosion at the point where the stream or pond level in front of the dam intersects the dam face erosion by water overflowing the dam is due to down cutting under cutting and thermal erosion down cutting increases with discharge but decreases with the shear strength of the snow where a hydraulic jump occurs downstream of the dam under cutting can accelerate dam decay thermal erosion depending mainly on water temperature may be less significant than the previous two processes slope failure occurs when the driving forces exceed the resisting forces and these are affected by snow property and snow load when the stream or pond level downstream of the dam rises rapidly the dam is prone to float as peak flow often occurs during the break up period results of the theoretical study of the mechanisms of snow dam decay will improve flood forecasting for arctic streams