alkylbiphenyls in ancient sediments and petroleums abstract c 1 and c 2 alkylbiphenyls have been analysed in crude oils and sediment extracts by capillary gas chromatography after preliminary isolation procedures involving tlc and hplc the abundance of 2 methylbiphenyl relative to 3 methylbiphenyl has been measured in samples from two sedimentary sequences 2 methylbiphenyl decreases in relative abundance with increasing thermal maturity of the sediments in both sedimentary sequences these isomeric methylbiphenyls are potentially useful as thermal maturity indicators for crude oils

the paleogeography of paleozoic and mesozoic storm depositional systems a reply we welcome discussion of our paper on the paleogeography of storm systems but can demonstrate that the major points raised in duke s discussion were considered and discussed already in our original text let s take his points in turn 1 alternative mechanisms for formation of hummocky stratification duke objects to some of the alternative modes of origin which we suggested as possibilities only one of these dealt with stratification within dome dunes readers familiar with mckee s 1979 p 98 102 his figs 57 and 58 work should not experience any difficulty observing similarities between bedding in the upper part of dome dunes and hummocky stratification we did not state that the large angle stratification at the core of the dome dune was hummocky stratification and duke s remarks

the distribution and origin of dimethyldibenzothiophenes in sediment extracts from the liaohe basin east china abstract the distributions of dimethyldibenzothiophenes dmdbts the relationship between dmdbts and dimethylbiphenyls dmbps and the applications of dmdbts as maturity indicators in source rocks have been investigated in a set of 21 lacustrine shales from the eocene shahejie formation well sg1 in the western depression liaohe basin china all source rock samples are characterized by total organic carbon contents of 1 37 3 27 and type ii with minor type iii kerogen they were deposited in suboxic and brackish lacustrine environments and have maturities ranging from immature to mid mature the 3 3 dmbp isomer can potentially react to yield 4 6 dmdbt 2 6 dmdbt and 2 8 dmdbt by incorporating sulfur into biphenyl which may be supported by a strong positive correlation between the absolute concentration changes of 3 3 dmbp and those of 4 6 dmdbt 2 6 dmdbt plus 2 8 dmdbt the relative abundance of dmdbt isomers may be explained by the sulfur radical mechanism and are also controlled by steric hindrance and thermodynamic stability the 4 6 1 4 1 6 dmdbt ratio shows no regular trend with increasing maturity at the low stage and it should be used with caution as a maturity indicator for immature sediments however within the oil generation window the relative concentration of 4 6 dmdbt progressively increases with increasing maturity which can be explained by its higher thermodynamic stability relative to the 1 4 dmdbt isomer the 4 6 1 4 1 6 dmdbt ratio exhibits a linear increase with increasing thermal maturity of the sediments thus this ratio can be applied as an effective maturity indicator for source rocks within oil generation window

the mid cretaceous earth paleogeography ocean circulation and temperature atmospheric circulation a reconstruction of the global paleogeography of the mid cretaceous 100 m y ago including adjustment of continental outlines to account for microplate movements cmstal shortening and accretion in mid cretaceous and later orogenic regions is described and a map presented on the modified continents coastlines and significant mountain ranges are added this paleogeography is used as a framework for a reconstruction of ocean surface circulation and temperature distribution then the main features of the atmospheric circulation are deduced using the paleogeography and ocean temperatures as boundary conditions relative to the present these features are a much weaker westerly wind belt and greater seasonality of wind patterns leading to more extreme surface climates over the continents slightly equatorward positions of the subtropical anticyclones and monsoonal regimes over the continental margins bordering tethys and the central atlantic a comparison of the results with climatic evidence from t

vegetation east of the rocky mountains 18 000 years ago abstract the various lobes and segments of the southern periphery of the laurentide ice sheet reached their maximum extension at different times between 21 000 and 14 000 yr ago but the climap date of 18 000 yr ago is taken as a reference level to review the distribution of major vegetational formations in central and eastern united states tundra was apparently confined to a narrow belt peripheral to the ice margin only in the minnesota area and from northern pennsylvania to new england with extensions down the crest of the appalachian highlands at least as far as maryland some areas south of the great lakes may later have been marked by treeless vegetation briefly as the ice retreated the boreal forest to the south in the central united states was dominated by spruce the jack pine that had prevailed during previous times was apparently eliminated by the time the ice reached its maximum in the appalachian highlands and the atlantic coastal plain however jack pine occurred along with spruce which decreased in importance southward the southern limit of the boreal forest in the southeast was perhaps somewhere in southern georgia and alabama oak and other temperate deciduous trees were minor components of the boreal coniferous forests especially in the southern appalacchians but there is no evidence yet in the southeastern states for a relic mixed mesophytic forest 18 000 yr ago similar to the rich modern deciduous forests of the region except possibly in the lower mississippi valley the climate in much of the southeast was apparently dry as well as cool at that time in florida oak pine scrub and prairie like openings prevailed and all but the deepest lakes dried up

shallow water and sub storm base deposition of lewis shale in cretaceous western interior seaway south central wyoming shallow and deep water below storm base clastics of the lewis shale were deposited in south central wyoming during a part of the late cretaceous maestrichtian core log and outcrop data indicate that the lewis shale consists of a thin transgressive marine shale overlain by a thicker coarser progradational interval the initial transgression of the lewis sea occurred during the maestrichtian baculites eliasi range and the maximum westward and northward extent of submergence was in areas of the rock springs and wind river uplifts the sea in which the lewis shale was deposited opened eastward into the north american western interior seaway shale in the lowermost lewis is black carbonaceous bioturbated and commonly contains shell debris and was deposited in hallow water the central basin floor changed from shallow to sub storm wave and sub storm current depths seemingly in response to eustatic sea level rise and coeval tectonic subsidence deepening of the basin began at the time of dominance of baculites eliasi to b grandis maestrichtian sandstone and shale of the upper lewis shale are mostly related to distributary systems that entered the basin first from the northeast during b grandis to b clinolobatus range and later possibly from the south during b clinolobatus southwest progradation from a northeastern delta suggests significant uplift in the wind river upthrust area concurrent with lewis sedimentation many hydrocarbon producing sandstones in the lewis shale are thickly bedded and massive and some show fluid escape structures thin sandstones are typically characterized by grading bouma sequences and sole markings turbidity currents are believed to be responsible for deposition of all these sandstones unburrowed shale and shale containing burrows made by a restricted infauna are interbedded with reservoir sandstones at wamsutter field the shale is interpreted to indicate anaerobic to dysaerobic conditions and water depths of 500 650 ft 150 200 m or more

the influence of changing orbital parameters and surface boundary conditions on climate simulations for the past 18 000 years abstract general circulation model experiments at 3000 year intervals for the past 18 000 years were made to estimate the magnitude timing and pattern of the climatic response to prescribed changes of orbital parameters date of perihelion axial tilt eccentricity and glacial age lower boundary conditions ice sheets land albedo sea ice and sea surface temperature the experiments used the community climate model ccm of the national center for atmospheric research ncar the response of monsoon circulations and tropical precipitation to the orbitally produced solar radiation changes was much larger than the response to changes of glacial age boundary conditions the continental interior of eurasia was 2 4 k warmer in summer and summer monsoon precipitation of north africa south asia was increased by 10 20 between 12 000 and 6000 yr bp before present when perihelion occurred during northern summer rather than in winter as now and the earth s axial tilt was larger than now southern hemisphe

stratal architecture and platform evolution of an early frasnian syn tectonic carbonate platform canning basin australia facies architecture and platform evolution of an early frasnian reef complex in the northern canning basin of north western australia were strongly controlled by syn depositional faulting during a phase of basin extension the margin attached hull platform developed on a fault block of precambrian basement with accommodation largely generated by movement along the mount elma fault zone recognition of major subaerial exposure and flooding surfaces in the hull platform from outcrop and drillcore has enabled comparison of facies associations within a temporal framework and led to identification of three stages of platform evolution stage 1 records initial ramp development on the hangingwall dip slope with predominantly deep subtidal conditions that prevented any cyclic facies arrangements this stage is characterised by basal siliciclastic deposits and a major deepening upward facies pattern that is capped by a sequence boundary towards the footwall north west and a major flooding surface towards the hangingwall stage 2 reflects the bulk of platform aggradation significant platform growth towards the hangingwall and the development of reef margins and cyclic facies arrangements thickening of this stage towards the hangingwall indicates that accommodation was generated by rotation of the fault block and overlying platform stage 3 records a major flooding and backstep of the platform margin the hull platform illustrates important elements of margin attached carbonate platforms in a half graben setting including i prominent but limited coarse siliciclastic input that does not have a major detrimental effect on carbonate production near the rift margin in arid to semi arid settings ii wedge shaped accommodation created by syn depositional rotation of fault blocks and tilting of the hangingwall dip slope resulting in shallow water facies and subaerial exposure up dip of the rotational axis and deeper water facies down dip and iii evolution of a ramp to rimmed shelf coincident with a sequence boundary flooding surface that is accelerated by tilting of the hangingwall dip slope during fault block rotation

paleoenvironmental and archaeological investigations at qinghai lake western china geomorphic and chronometric evidence of lake level history abstract qinghai lake located on the northeastern qinghai tibet plateau qing zang gaoyuan is china s largest extant closed basin lake its position relative to major asian climate systems makes it sensitive to global climate change the lake has been the subject of numerous paleoenvironmental investigations including dating of shoreline features around the lake basin here we report new age estimates of shoreline features geomorphic exposures and archaeological sites that contribute to the development of a lake level history for qinghai lake and a landscape model of the qinghai lake basin lake highstands above 3230 m 36 m above the modern lake level appear to date to late mis 5 70 110 ka the lake has had much more modest highstands since then no evidence of mis 3 lake stands higher than modern were found and early holocene highstands are no more than 12 m above modern if the age of highstands greater than 3230 m is confirmed through future work then the qinghai lake basin hydrologic balance prior to 70 ka was dramatically different than after that time including during the holocene a simple hydrologic balance model provides insights into the combination of precipitation evaporation and runoff generation needed to sustain the lake at 3260 m the highest shoreline observed a range of factors may explain the difference primarily the relative strength of the east asian monsoon the basin was apparently subject to extensive alluviation during mis 3 interrupted by widespread erosion and development of cryogenic features before and during the last glacial maximum lgm loess that presently drapes much of the lower basin landscape began to be deposited after the lgm 16 18 ka the landscape model outlined here has implications for archaeological visibility of early human occupation of the qinghai tibet plateau

a comparison of gcm simulated cretaceous greenhouse and icehouse climates implications for the sedimentary record abstract two general circulation model simulations of mid cretaceous climate are presented one representing a greenhouse and the other representing an icehouse world through a comparison of greenhouse and icehouse palaeoclimates differences in processes which are intrinsically linked with climate such as continental weathering and snow and ice accumulation may be observed a number of conspicuous and discrete climatic differences can be seen between the two simulations which may be translated into a number of identifiable signatures in the sedimentary record the climate at mid high latitudes in the icehouse simulation was more arid than the greenhouse simulation and could result in deposition of smectite dominated clay suites in contrast the climate of low latitudes of the icehouse simulation resulted in a moister climate than the greenhouse simulation which could affect the weathering regimes and result in deposition of kaolin dominated clay suites thus cool climate episodes do not necessarily result in a global increase in aridity the icehouse simulation predicts a small permanent icecap at high latitudes which could account for the origin of dropstones in marine sediments furthermore a sea level fall as a consequence of an accumulation of ice at high latitudes may also increase continentality and surface albedo which may also contribute to the causes of the drier climate at high latitudes hurricanes are likely to be more frequent in greenhouse than icehouse climates mid latitude depressions also important for generating storms are likely to be both intense and frequent during icehouse and greenhouse periods of the middle cretaceous

early to mid holocene lake high stand sediments at lake donggi cona northeastern tibetan plateau china lake high stand sediments are found in three onshore terraces at lake donggi cona northeastern tibetan plateau and reveal characteristics of hydrological changes on lake shorelines triggered by climate change geomorphological processes and neo tectonic movements the terraces consist of fluvial alluvial to littoral lacustrine facies end member modeling of grain size distributions allowed quantification of sediment transport processes and relative lake levels during times of deposition radiocarbon dating revealed higher than modern lake levels during the early and mid holocene lake levels follow the trend of asian monsoon dynamics and are modified by local non climatic drivers site specific impacts explain fluctuations during the initial lake level rise 11 cal ka bp maximum lake extension reached 9 2 cal ka bp at 16 5 m above present lake level a p l l littoral and lacustrine sediment deposition paused during a phase of fluvial activity and post depositional cryoturbations at 8 5 cal ka bp when the lake level fell to 8 m a p l l after a second maximum at 7 5 cal ka bp lake level declined slightly at 6 8 cal ka bp probably due to a non climatic pulse that caused lake opening the level remained high until a transition towards drier conditions 4 7 cal ka bp though discontinuous high stand sediments provide a unique high resolution archive

variability of southwest indian summer monsoon precipitation during the bolling allerod we have generated a high resolution 20 yr 2 3 0 th dated stalagmite oxygen isotope record from timta cave in the western himalaya in india that documents southwest indian summer monsoon ism precipitation variations during the bolling allerod interstadial from 15 2 to 11 7 ka compared with the glacial and younger dryas ism precipitation was enhanced during the bolling allerod ism precipitation was apparently coupled to variations in the east asian monsoon and north atlantic climate on millennial and multicentennial time scales during the deglaciation analyses of a high growth rate interval 2 5 yr resolution encompassing the late bolling early alterod suggest that multidecadal monsoon variability was an important aspect of ism behavior at that time the frequency spectrum of ism precipitation during this time interval is similar to that of the 1 4 c record and other ism precipitation records during the latest holocene this raises the hypothesis that multidecadal climate dynamics during the late boiling early allerod may have been similar to those that operated during the last several millennia even though the boundary conditions of these two time intervals were very different

biomarker signatures of upper cretaceous latrobe group hydrocarbon source rocks gippsland basin australia distribution and palaeoenvironment significance of aliphatic hydrocarbons abstract upper cretaceous maastrichtian and campanian hydrocarbon source rocks from the latrobe group gippsland basin australia have been analysed using gas chromatography mass spectrometry gc ms in order to understand their geochemical characteristics and to reconstruct palaeovegetation and palaeoclimate changes n alkanes ranging from c10 to c37 dominate the aliphatic hydrocarbons in the rock extracts both the carbon preference index and the odd to even predominance values of n alkanes are higher than 1 0 suggesting an input from terrigenous higher plants low wax indices mostly 3 0 a low gammacerane index

spatial and temporal variability of coastal storms in the north atlantic basin over the past three to four decades there has been a growing awareness of the important controls exerted by large scale meteorological events on coastal systems for example definitive links are being established between short term timescales of 5 10 years beach dynamics and storm frequency this paper assesses temporal variability of coastal storms both tropical and extratropical and the wave climatology in the north atlantic basin nab including the gulf of mexico with both storm types the empirical record shows decadal scale variability but neither demonstrates highly significant trends that can be linked conclusively to natural or anthropogenic factors tropical storm frequencies have declined over the past two or three decades which is perhaps related to recent intense and prolonged el ninos some forecasts predict higher frequencies of tropical storms like that experienced from the 1920s to the 1960s to occur in coming decades results from general circulation models gcms suggest that overall frequencies of tropical storms could decrease slightly but that there is potential for the generation of more intense hurricanes these data have important implications for the short term evolution of coastal systems there is strong suggestion that extratropical systems have declined overall over the past 50 100 years but that there is an increase in frequency of very powerful storms especially at higher latitudes both enso and the north atlantic oscillation nao are shown to have associations with frequencies and tracking of these systems these empirical results are in general agreement with gcm forecasts under global warming scenarios analyses of wave climatology in the nab show that the last two to three decades have been rougher at high latitudes than several decades prior but this more recent sea state is similar to conditions from about 100 years ago the recent roughness at sea seems to be related to high nao index values which are also expected to increase with global warming thus when coupled to an anticipated continued rise in global sea level this trend will likely result in increasing loss of sediment from the beach nearshore system resulting in widespread coastal erosion

general circulation gcm modelling of palaeoclimates a critique the best method so far devised for testing the ability of a general circulation model gcm to simulate climates very different from today is to conduct snapshot experiments for specific times in the past at which the climatic forcing can be prescribed in detail this paper focuses on the period from the last glacial maximum through the holocene during this interval changes in atmospheric circulation were driven primarily by variations in the seasonality of insolation and secondarily by variations in surface boundary conditions accompanying deglaciation changes in atmospheric transparency are usually neglected apart from lower co2 at 18 ka bp palaeoclimatic simulations have yielded important insights into the dynamics of glacial interglacial climate change the results have been tested in three main ways 1 qualitative comparison of the spatial patterns of climate anomalies 2 comparison of the simulated climate at individual grid points or groups of grid points with quantitative estimates derived

hummocky cross stratification tropical hurricanes and intense winter storms most previous workers have inferred a storm origin for hummocky cross stratification which typically occurs in shallow marine deposits on the modern earth the only storms capable of profoundly affecting shallow marine depositional environments are severe tropical cyclones hurricanes and mid latitude winter wave cyclones intense winter storms this paper examines the palaeogeographic distribution including palaeolatitude and palaeogeographic setting of 107 occurrences of hummocky cross stratification ranging in age from the proterozoic to recent in each of these stratigraphic units both palaeolatitude and palaeogeography are consistent with a direct storm influence associated with the passage of hurricanes or winter storms directly over the site of deposition this palaeogeographic evidence lends support to the inferred storm origin for hummocky cross stratification further the distribution of the structure suggests that most occurrences 73 were generated by tropical hurricanes the remaining 27 being generated by intense mid latitude winter storms the preferential generation of hummocky cross stratification by hurricanes is consistent with 1 the known differences in the nature of the bottom flows generated by the two major storm types and 2 the inferred nature of the flows which form hummocky cross stratification hurricanes couple less effectively with the water column than do intense winter storms due to this ineffective coupling hurricane generated bottom flows tend to be oscillatory or multidirectional dominant with only minor unidirectional components of motion in contrast intense winter storms generally do couple effectively with the water column generating bottom flows which possess a dominant or significant unidirectional component most previous workers have suggested that hummocky cross stratification forms under oscillatory or multidirectional dominant flow thus it is conceptually reasonable that the vast majority of ancient occurrences of hummocky cross stratification were probably hurricane generated as suggested by the aforementioned palaeogeographic distribution the proterozoic palaeozoic neogene and quaternary were times when global climate was similar to that of today the distribution of hummocky cross stratification deposited during these times suggests that both hurricanes and intense winter storms occupied latitudinal belts during these times which were essentially identical to those occupied by their modern counterparts the mesozoic and palaeogene were non glacial times when global climate was much warmer than that of today the distribution of hummocky cross stratification deposited during this interval suggests that hurricanes occurred more frequently at higher latitudes during non glacial times than they do at present the possibility of a broadened hurricane belt during the mesozoic and palaeogene is consistent with climatic considerations a limited number of mesozoic and palaeogene rock units containing hummocky cross stratification were deposited in palaeogeographic settings that preclude a direct hurricane influence these examples were deposited in the middle latitudes suggesting that intense winter storms continued to form hummocky cross stratification in the middle latitudes during these much warmer times some previous workers have suggested that tsunamis may be capable of generating hummocky cross stratification the palaeogeographic distribution of the structure does not support an origin due to tsunamis lacustrine examples of hummocky cross stratification reported herein are the first known non marine occurrences they suggest that storm effects strongly influence the sedimentary record of some lakes

geological record of meltwater events at qinghai lake china from the past 40 ka abstract we report here on a previously unpublished sediment core from qinghai lake china that preserves a continuous record of sedimentation for the past 40 ka a striking feature of the record is a set of distinct meltwater events recorded at 35 19 and 14 ka respectively these events are manifest as distinct pulses of relatively old organic radiocarbon in the sediments we interpret these as a signal of glacial melting in the qinghai lake watershed the meltwater signals are closely correlated to temperature and precipitation records associated with deglaciation the events at 19 ka and 14 ka correspond to well established high latitude melt water pulse mwp events during marine isotope stage mis 2 and the 35 ka event corresponds to a period of pervasive high lake levels in western china during late mis 3 we interpret these anomalous dates as the result of relatively old carbon that was destabilized by the glaciers and released into the lake as the glaciers melted the data indicate that this process takes thousands of years we expect that the approach employed here to identify these events is generally applicable to any lake system with a significant glacial meltwater component

geosynthesis of dibenzothiophene and alkyl dibenzothiophenes in crude oils and sediments by carbon catalysis sediment extracts and crude oils have been shown to contain methyl substituted biphenyls and dibenzothiophenes with isomer distributions suggesting a geochemical relationship between the two compound classes laboratory simulation experiments have shown that carbon catalyses the reaction between surface adsorbed sulfur and biphenyl to form dibenzothiophene similarly the methyl substituted biphenyls reacted to yield corresponding methyl dibenzothiophenes we suggest that the widespread distribution of dibenzothiophene and alkylated dibenzothiophenes in sediments and crude oils is the result of a catalytic reaction of biphenyl ring systems and surface adsorbed sulfur on the surface of carbonaceous material

oligocene storm induced lacustrine deposits in the yaxi area of the jiuxi basin northeastern margin of the tibetan plateau abstract storm induced deposits in the sedimentary record can now be easily identified on account of a better understanding of processes of unidirectional and oscillatory flow thin bedded sandstone siltstone and interlayered mudstone deposits of the oligocene jianquanzi member in the yaxi area of the jiuxi basin along the northeastern margin of the tibetan plateau were formed by shallow lacustrine storm generated flows petrologic analysis reveals that the sandstones exhibit moderate to high compositional maturity but are texturally sub mature to immature based on investigation of drill cores six storm deposit lithofacies are identified including massive or graded sandstone parallel and trough cross bedded sandstones hummocky cross stratified sandstone wave rippled sandstone and siltstone massive or horizontal bedded mudstone and structurally deformed sandstone and mudstone in a vertical succession these lithofacies occur as three fining upward lithofacies associations each of which represents different architectural elements and depositional processes of proximal to distal storm deposits the relatively coarse proximal architectural element is formed by strong density flows and unidirectional dominated combined flows the transitional architectural element is dominated by unidirectional and oscillatory dominated combined flows to pure oscillatory flows resembling tb e divisions of the classic bouma sequence the relatively fine distal architectural element is dominated by unidirectional dominated combined flows with a very weak oscillatory flow component the origin of storms responsible for these deposits is attributed to asian winter monsoons associated with the paleoclimatic and paleogeographic setting

shore platform downwearing in eastern canada a 9 14 year micro erosion meter record abstract downwearing rates erosion in the vertical plane were measured with a micro erosion meter mem in eastern canada on an argillacious sub horizontal shore platform at mont louis in eastern quebec and on two sloping basaltic and sandstone platforms at respectively scots bay and burntcoat head in the bay of fundy nova scotia the original data covered a period from 2002 to 2009 this dataset was extended by measurements repeated at surviving mem stations in 2017 producing records ranging over 9 14 years depending on when each station was installed because of rapid surface downwearing many of the original mem stations were inoperable in 2017 especially at burntcoat head nevertheless data were obtained from 19 stations at burntcoat 35 of the 2009 original 25 at mont louis 83 of the original and 38 at scots bay 75 of the original for the stations at mont louis and scots bay that were still functioning in 2017 there were no significant differences in rates of downwearing over the shorter from station installation up to 2009 and extended periods from installation to 2017 mean rates of downwearing calculated from all the stations in each area declined through time however due to the loss of the more rapidly eroding stations a simple procedure which was proposed to compensate for this decrease produced mean downwearing rates that were broadly similar to those reported over the original measurement period there were significant relationships between downwearing rates and elevation r2 0 32 and downwearing rates and rock hardness r2 0 41 in the extended record at scots bay and a small but significant relationship between downwearing rates and rock hardness at mont louis r2 0 17 differences in downwearing rates across the platforms suggest that salt weathering and wetting and drying are dominant weathering mechanisms at scots bay and mont louis chemical weathering of the sandstone cementing agent and the premature removal of weathered grains by wave generated bottom currents may however be more important at burntcoat head

numerical dating of a late quaternary spit shoreline complex at the northern end of silver lake playa mojave desert california a comparison of the applicability of radiocarbon luminescence terrestrial cosmogenic nuclide electron spin resonance u series and amino acid racemization methods a late quaternary spit shoreline complex on the northern shore of pleistocene lake mojave of southeastern california usa was studied with the goal of comparing accelerator mass spectrometry ams radiocarbon luminescence electron spin resonance esr terrestrial cosmogenic radionuclide tcn surface exposure amino acid racemization aar and u series dating methods the pattern of ages obtained by the different methods illustrates the complexity of processes acting in the lakeshore environment and highlights the utility of a multi method approach tcn surface exposure ages mostly 20 30 ka record the initial erosion of shoreline benches whereas radiocarbon ages on shells determined in this and previous studies within the spit supported by aar data record its construction at fluctuating lake levels from 16 to 10 ka luminescence ages on spit sediment 6 7 ka and esr ages on spit shells 4 ka are anomalously young relative to radiocarbon ages of shells within the same deposits the significance of the surprisingly young luminescence ages is not clear the younger esr ages could be a consequence of post mortem enrichment of u in the shells high concentrations of detrital thorium in tufa coating spit gravels inhibited the use of single sample u series dating detailed comparisons such as this provide one of the few means of assessing the accuracy of quaternary dating techniques more such comparisons are needed

evaluating the size and extent of paleolakes in central tibet during the late pleistocene subhorizontal lake shorelines allow a geodynamic test of the size and extent of a hypothesized paleo lake in central tibet the east qiangtang lake eql during the last interglacial period marine isotope stage mis 5e reconstructions based on relict lake deposits suggest that the eql would have been 400 m deep and over 66 000 km2 models of flexural rebound driven by lake recession predict that shorelines near the eql center at the present day location of siling co would have rebounded 60 90 m above their initial elevation new 36cl chronology of the highest relict shorelines around siling co indicates that they reflect lake levels between 110 190 ka these shorelines however are presently 300 m below their predicted elevations implying a substantially smaller water load our results reveal that the expansion of tibetan lakes during mis 5e was relatively limited instead individual lakes were supplied by river networks much as they are today

the occurrence and distribution of phenylnaphthalenes terphenyls and quaterphenyls in selected lacustrine shales and related oils in china abstract phenylnaphthalenes phns terphenyls trps quaterphenyls qtps and triphenylbenzenes were identified by the use of authentic standards in gc ms analysis phenyl derivatives of fused ring polycyclic aromatic hydrocarbons phpahs and polyphenyls pphs were observed in selected lacustrine shales and related oils from the tarim liaohe and bebuwan basins in china all isomers of phenylnaphthalene and terphenyl were observed in these oils the more stable 2 phn and m trp p trp isomers are predominant among phenylnaphthalenes and terphenyls respectively the effect of maturity on the distribution patterns of phenylnaphthalenes and terphenyls in a set of lacustrine shales from the liaohe basin east china was investigated the depth trends of three currently used maturity indicators were investigated analysis was based on the relative abundance of phenylnaphthalene and terphenyl isomers namely phnr 2 phn 1 phn trp1 p trp o trp and trp2 m trp p trp o trp in lacustrine shales from well s202 in the liaohe basin east china the indicators increase slightly with relatively great deviations within low to intermediate maturation stages and then increase abruptly in high maturity stages therefore they are not suitable maturity indicators for lacustrine source rocks in this study an alternative thermal maturity indicator defined as p trp m trp was proposed it exhibits a uniform increase with increasing maturity and is probably a more suitable indicator for use in maturity assessment in lacustrine source rocks and related oils this study broadens the current understanding of the occurrence and distribution of phpahs and pphs in sedimentary organic matter of various origins

holocene lake level history of the tangra yumco lake system southern central tibetan plateau massive carbonate banks representing ancient lacustrine deposits are exposed in the catchment of the lake tangra yumco southern central tibetan plateau and nearby lake xuru co nine sediment samples were taken below and above these lacustrine deposits to determine periods of changing lake level using optically stimulated luminescence osl applying a multiple aliquot regeneration mar protocol according to facies and stratigraphy samples below the carbonate banks indicate a rising and samples from above a falling lake level the results indicate that the rising lake level of tangra yumco passed the sampling location at 10 5 and 2 1 ka while a falling lake level passed the sampling location at 0 9 ka the rising lake level of xuru co passed the sampling location at 7 9 and 1 7 ka and a falling lake level at 0 5 ka showing a similar trend as at tangra yumco combining these results with recalculated cosmogenic nuclide ages and previously published feldspar luminescence data allows the establishment of

storm deposits and storm generated coarse carbonate breccias on a pelagic outer shelf south east basin france uppermost jurassic limestones of the south east basin france are organized into four facies associations that were deposited in four distinct zones 1 peritidal lagoonal limestones 2 bioclastic and reefal limestones 3 pelagic lime mudstones 4 lime mudstones calcarenites coarse breccias calcarenite deposits of zone 4 exhibit sedimentary structures that are diagnostic of deposition under wave induced combined flow in subzone 4a both vertical and lateral transitions from lime mudstone calcarenite to breccia indicate in situ brecciation under wave cyclic loading breccias were produced by heterogeneous liquefaction of material previously deposited on the sea floor deposits in subzone 4a record relatively long periods 400 kyr of sedimentation below wave base alternating with periods of deposition under wave induced currents and periods of in situ deformation in this zone storm waves were attenuated by wave sediment interaction and wave energy was absorbed by the deformation of soft sediment with reference to present day wave attenuation water depths in this zone ranged between 50 and 80 m landwards of the attenuation zone in zone 3 storm waves were reduced to fair weather wave heights storm wave base was not horizontal and became shallower landwards as a consequence water depth and wave energy were not linearly related on a small area of the seaward edge of subzone 4a cobbles were removed by traction currents and redeposited in subzone 4b there they formed a 100 m thick wedge which prograded over 3 km and was built up by the stacking of 5 to 20 m thick cross stratified sets of coarse breccia this wedge records the transport and redeposition of cobbles by a high velocity unidirectional component of a combined flow the increase in flow velocity in a restricted area is proposed to result from flow concentration in a channel like structure of the downwelling in the gulf formed by the basin in more distal subzone 4c the hydrodynamic effect of wave induced currents was quasi permanent and brecciation by wave sediment interaction occurred only episodically this indicates that seawards of the attenuation zone hydrodynamic storm wave base was deeper than mechanical storm wave base uppermost jurassic carbonates were deposited and soft sediment deformed on a hurricane dominated ramp of very gentle slope and characterized by a zone of storm wave degeneration located seawards of a zone of sedimentation below wave base

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

cosmogenic 10be and 26al dating of paleolake shorelines in tibet abstract we have used in situ produced cosmogenic nuclides 10be and 26al to date lacustrine shorelines around eight lakes in tibet two lakes located south of the yarlung tsangpo river discharged at high lake levels one of them drolung co co is a local term meaning lake became closed its water level fell below its outlet channel at 3 8 ka and lowered over 120 m vertically since then this implies a significant change in intensity of precipitation driven by the indian monsoon over southern tibet in the middle late holocene nam co and dajia co located to the north of the yarlung tsangpo river also drained at high lake levels and became closed 53 36 ka and 48 ka respectively of four other lakes developed closely in the qiangtang basin north of the yarlung tsangpo river tangra yum co and siling co located at 31 32 n show exposure ages for high lake shorelines of over 220 ka the oldest lake shorelines reported for tibet while towards the north and west the high lake of zhari nam co appeared after the last glacial maximum lgm the different pattern of lake development to the north of yarlung tsangpo river may reflect regional climate effects

age constraints on the late quaternary evolution of qinghai lake tibetan plateau dating and geomorphology of shoreline features in the qinghai lake basin of northwestern china suggest that contrary to previous interpretations the lake likely did not reach levels 66 140 m above modern within the past 90 000 yr maximum highstands of 20 66 m above modern probably date to marine isotope stage mis 5 mis 3 highstands are undated and uncertain but may have been at or below post glacial highs the lake probably reached 3202 3206 m 8 12 m during the early holocene but stayed below 3202 m after 8 4 ka this shoreline history implies significantly different hydrologic balances in the qinghai lake basin before 90 ka and after 45 ka possibly the result of a more expansive asian monsoon in mis 5

long term shore platform surface lowering rates revisiting gill and lang after 32 years abstract in 1978 e d gill and j g lang installed 53 micro erosion meter mem sites on shore platforms along the otway coast in south eastern australia surface lowering rates were originally determined from 2 yr of measurements 1979 and 1980 and showed that the mean annual rate of lowering from all sites was 0 37 mm yr 1 we re measured these mem sites 32 yr after the first set of readings were taken in february 1979 we relocated 49 of the original 53 bolt sites and were able to measure 45 of them from the sites we measured the mean annual rate of shore platform lowering was 0 31 mm yr 1 rates of surface lowering on shore platforms are commonly reported from studies of only two or three years and only one other record exceeds 30 yr kaikoura peninsula nz 1 09 mm yr 1 in that case fewer than half of the original bolt sites were functioning because erosion had removed bolts along the otway coast rates of erosion are much slower hence the greater number of still readable sites after 32 yr compared to other micro erosion meter studies the rates reported here are at the lower end of the range of values from around the world but nevertheless consistent with rates from the otway coast and others in similar lithology we found no statistical difference between erosion rates calculated over 2 yr 1979 to 1980 and 32 1979 to 2011 years supporting the view that shore platform lowering rates measured over 2 yr are representative of decadal scales

lake level reconstruction for 12 8 2 3 ka of the ngangla ring tso closed basin lake system southwest tibetan plateau article i nfo we present a shoreline based millennial scale record of lake level changes spanning 12 8 2 3 ka for a large closed basin lake system on the southwestern tibetan plateau fifty three radiocarbon and eight u th series ages of tufa and beach cement provide age control on paleoshorelines ringing the basin supplemented by nineteen ages from shell and aquatic plant material from natural exposures generally recording lake regressions our results show that paleo ngangla ring tso exceeded modern lake level 4727 m asl continuously between 12 8 and 2 3 ka the lake was at its highstand 135 m 4862 m asl above the modern lake from 10 3 ka to 8 6 ka this is similar to other closed basin lakes in western tibet and coincides with peak northern hemisphere summer insolation and peak indian summer monsoon intensity the lake experienced a series of millennial scale oscillations centered on 11 5 10 8 8 3 5 9 and 3 6 ka consistent with weak monsoon events in proxy records of the indian summer mon soon it is unclear whether these events were forced by north atlantic or indian ocean conditions but based on the abrupt lake level regressions recorded for ngangla ring tso they resulted in significant periodic reductions in rainfall over the western tibetan plateau throughout the holocene

late quaternary palaeolake levels in tengger desert nw china comprehensive field investigations and laboratory analyses show that palaeolakes including the megalake tengger and other semi connected and isolated water bodies during late pleistocene covered an area of more than 20 000 km 2 this is an area more than half the size of the tengger desert in nw china stratigraphic correlations and chronological evidence indicate that the palaeolakes started to develop around 42 000 14 c year bp uncalibrated all throughout the paper but their extent was limited until 37 000 14 c year bp based on the chronology of representative lacustrine deposits it can be deduced that the megalake tengger was established around 35 000 14 c year bp and maintained until 22 000 14 c year bp leading to the formation of the baijian hu terraces which are regarded as firm evidence of the existence of palaeolakes the formation mechanism is unclear and the climate situation at the time is still an open question the holocene palaeolakes started to develop around 12 000 14 c year bp the baijian hu terraces indicate that the high water levels in the area occurred around 8500 5400 5100 3500 and 1860 1370 14 c year bp the extent of the holocene palaeolakes primarily migratory lakes was smaller than that of the late pleistocene palaeolakes d 2004 elsevier b v all rights reserved

variations in titan s dune orientations as a result of orbital forcing abstract wind blown dunes are a record of the climatic history in titan s equatorial region through modeling of the climatic conditions associated with titan s historical orbital configurations arising from apsidal precessions of saturn s orbit we present evidence that the orientations of the dunes are influenced by orbital forcing analysis of 3 titan general circulation models gcms in conjunction with a sediment transport model provides the first direct intercomparison of results from different titan gcms we report variability in the dune orientations predicted for different orbital epochs of up to 70 although the response of the gcms to orbital forcing varies the orbital influence on the dune orientations is found to be significant across all models furthermore there is near agreement among the two models run with surface topography with 3 out of the 5 dune fields matching observation for the most recent orbital cycle through comparison with observations by cassini we find situations in which the observed dune orientations are in best agreement with those modeled for previous orbital configurations or combinations thereof representing a larger portion of the cycle we conclude that orbital forcing could be an important factor in governing the present day dune orientations observed on titan and should be considered when modeling dune evolution

erosion history of the tibetan plateau since the last interglacial constraints from the first studies of cosmogenic 10be from tibetan bedrock abstract the cosmogenic 10be exposure histories of in situ bedrock surfaces from the tibetan plateau indicate low erosion rates of

hazard from himalayan glacier lake outburst floods sustained glacier melt in the himalayas has gradually spawned more than 5 000 glacier lakes that are dammed by potentially unstable moraines when such dams break glacier lake outburst floods glofs can cause catastrophic societal and geomorphic impacts we present a robust probabilistic estimate of average glofs return periods in the himalayan region drawing on 5 4 billion simulations we find that the 100 y outburst flood has an average volume of 33 5 3 7 3 7 106 m3 posterior mean and 95 highest density interval hdi with a peak discharge of 15 600 2 000 1 800 m3 s 1 our estimated glof hazard is tied to the rate of historic lake outbursts and the number of present lakes which both are highest in the eastern himalayas there the estimated 100 y glof discharge 14 500 m3 s 1 is more than 3 times that of the adjacent nyainqentanglha mountains and at least an order of magnitude higher than in the hindu kush karakoram and western himalayas the glof hazard may increase in these regions that currently have large glaciers but few lakes if future projected ice loss generates more unstable moraine dammed lakes than we recognize today flood peaks from glofs mostly attenuate within himalayan headwaters but can rival monsoon fed discharges in major rivers hundreds to thousands of kilometers downstream projections of future hazard from meteorological floods need to account for the extreme runoffs during lake outbursts given the increasing trends in population infrastructure and hydropower projects in himalayan headwaters

alkylbiphenyls and alkyldiphenylmethanes as indicators of petroleum biodegradation abstract gas chromatographic mass spectrometric analyses of alkylbiphenyls and alkyldiphenylmethanes have been performed on a series of crude oils reservoired in the gippsland basin australia as well as in some marine coastal sediments contaminated with a condensate changes in the isomeric distribution of the alkylbiphenyls and alkyldiphenylmethanes with increasing biodegradation were investigated the relative abundance and distributions of the isomers were found to change significantly with increasing biodegradation isomers with the 4 substituent s generally increase in abundance relative to isomers that lack this feature thus alkylbiphenyl and alkyldiphenylmethane isomeric distributions are useful indicators of the extent of petroleum biodegradation in reservoirs and surface sediments it is suggested that geosynthetic processes and or relative susceptibilities of certain isomers to microbial attack can account for changes in the isomeric distribution of these components with increasing biodegradation significant differences in the relative abundances of the methylbiphenyls are apparent and are probably due to variations in the conditions that the petroleum had been subjected to in the two contrasting environments

quaternary ecological responses and impacts of the indian ocean summer monsoon at nam co southern tibetan plateau the transition from the last glacial to the current interglacial the holocene represents an important period with climatic and environmental changes impacting ecosystems in this study we examined the interplay between the indian ocean summer monsoon iosm and the westerlies at lake nam co southern tibet to understand the climatic effects on the ecosystem different organic geochemical proxies n alkanes glycerol dialkyl glycerol tetraethers d 13corg 15n are applied to reconstruct the environmental and hydrological changes on one of the longest available paleorecords at the tibetan plateau based on our paleohydrological d proxies the aquatic signal lags the terrestrial one due to specific ecological thresholds which in addition to climatic changes can influence aquatic organisms the aquatic organisms response strongly depends on temperature and associated lake size as well as ph and nutrient availability because the terrestrial vegetation reacts faster and more sensitively to changes in the monsoonal and climatic system the d of n c29 and the reconstructed inflow water signal represent an appropriate iosm proxy in general the interplay of the different air masses seems to be primarily controlled by solar insolation in the holocene the high insolation generates a large land ocean pressure gradient associated with strong monsoonal winds and the strongest iosm in the last glacial period however the weak insolation promoted the westerlies thereby increasing their influence at the tibetan plateau our results help to elucidate the variable iosm and they illustrate a remarkable shift in the lake system regarding ph 13corg and 15n from the last glacial to the holocene interglacial period

late pleistocene lake and glaciation evolution on the northeastern qinghai tibetan plateau a review late pleistocene paleoclimatic history on northeastern qinghai tibetan plateau qtp has been reconstructed mainly from lake sediments however data regarding dry wet climate changes reported in this region are still not clear and controversial based on shoreline features and highstand lacustrine sediments around lakes on the qtp high lake level histories in this paper were summarized and compared with paleoclimatic records from lake sediments ice core and glaciation evolution surrounding mountains on the ne qtp during late pleistocene the results indicate that periods of high lake level occurred at mis 5 mis 3 and early middle holocene and most likely corresponding to warm and wet climate periods while periods of low lake level existed in intervening intervals corresponding to cold and dry climate periods which most likely coincide with glacial advances surrounding high mountains with an exception no wide glacial advance in study area was found during mis 3 possibly suggesting that effective moisture is lower than that in the other region of ne qtp in this period

the paleogeography of paleozoic and mesozoic storm depositional systems present day hurricane belts are confined to 5 45 latitude along the western edges of oceans whereas winter storms occur ubiquitously above 25 latitude both hurricanes and winter storms occur between 25 and 45 latitude in some areas storm zones can be identified on global paleogeographic maps with the assumption that this latitudinal zonation of storm systems existed in the geological past evaluation of 69 previously recognized paleozoic and mesozoic storm depositional systems on such maps showed that only 70 of them occur in ancient hurricane mixed hurricane and winter storm and winter storm belts the remainder occur on the western sides of continents and or at low paleolatitudes and therefore well may be of different origin mesozoic storm depositional systems containing hummocky stratification tend to occur in counterpart paleo winter storm belts whereas hummocky stratification in suggested paleozoic examples occur in both winter storm and hurricane belts and in paleolatitudes where we in

cosmogenic 10be surface exposure dating and glacier reconstruction for the last glacial maximum in the quemuqu valley western nyainqentanglha mountains south tibet the nature and timing of glaciations enable inferences to be made about glacial climates however the paucity of reliable glacial chronologies impedes a full understanding of the last glacial maximum lgm climate in the western nyainqentanglha mountains south tibet in this study we investigated the lgm glacial history in the quemuqu valley western nyainqentanglha using 10be surface exposure dating we used a physically based glacier model to reconstruct the lgm glacial surfaces and estimated the lgm equilibrium line altitude ela using integrated methods combined with previously published 10be exposure ages from the western nyainqentanglha ten 10be exposure ages imply a relatively restricted glacial extent in the lgm but extensive growth in the early last glacial the modeled lgm glaciers had ice areas of 36 3 km2 3 21 km3 in volume and 89 m m in average thickness in the quemuqu valley the reconstructed lgm elas have values of 5463 5583 m asl with a depression of 244 364 m by combining the reconstructed elas with an equation deduced from glacier mass balance we concluded that the temperature dropped by 2 6 4 6 c in the lgm relative to the present with 30 70 lower precipitation than the present global cooling induced the lgm glacial advance in the western nyainqentanglha despite decreased precipitation

cosmogenic 10be inferred lake level changes in sumxi co basin western tibet abstract most tibetan lakes are surrounded by conspicuous regressive shorelines attesting to high water levels in the past concentrations of the in situ produced cosmogenic radionuclide 10 be in bedrock from the three highest terraces surrounding sumxi co situated in western kunlun indicate that the highest lake level appeared before 10 000 11 500 yr and most likely between 11 000 and 12 800 yr younger ages for the two lower terraces imply regression of sumxi co during the early mid holocene the concurrency of the highest lake level with orbitally induced maximum northern hemisphere summer insolation suggests that the increase in water supply to sumxi co was most likely associated with increased recharge from melting glaciers we conclude that the enhanced indian monsoon during the early holocene did not penetrate the tibetan plateau and affect the northwestern part of tibet significantly

shrinking lakes in tibet linked to the weakening asian monsoon in the past 8 2 ka expansion or shrinkage of closed lakes is a natural response to fluctuations in precipitation and evaporation linked closely to changes in strength or position of atmospheric circulation in tibet there are many such lakes with paleo shorelines that can be used for reconstructions of climate history despite the fact that many paleo shorelines are well preserved in tibet dating them has been seriously hindered by various difficulties here we present the first optical dating chronology for a series of paleo shorelines in zhari namco the third largest inland lake in central tibet our results indicate that the lake level has dropped 128m over the past 8 2ka younger shorelines are found at lower altitudes indicating that the shorelines follow a geomorphic chronological order and a broadly continuous trend of stepwise shrinkage the surface area of zhari namco has shrunk in size from 4605km2 at 8 2ka ago to 996km2 at present 300km3 of water has been lost from this lake such a loss in water implies a significant reduction in precipitation over the past 8 2ka a likely result of a weakening asian monsoon following the decreasing precipitation since the early holocene this area has become increasingly arid

summer temperature fluctuations in southwestern china during the end of the lgm and the last deglaciation abstract we present a sub centennial resolution summer temperature record from the se tibetan plateau tiancai lake sw china 3900 m a s l derived from a chironomid stratigraphy covering the last c 19 5 ka the record highlights the interaction between tropical and high latitude climate forcing through the changes in atmospheric circulation during the last deglaciation the scale of the last glacial maximum lgm cooling is consistent with other tropical mountain regions at c 5 c and a rapid recovery of temperatures at 19 0 ka is related to changes in adiabatic lapse rates at the end of the glaciation the overall pattern of change shows that north atlantic deglaciation climate events the heinrich 1 and younger dryas cooling events and the bolling allerod warm period are all recorded but the influence of the events decline as the deglaciation progresses we relate these patterns to north atlantic deep water ventilating the southern ocean and to the consequent movements of the intertropical convergence zone itcz in the indian ocean basin as transmitted through changes in the southern mid latitude circulation

climatic and topographic controls on the style and timing of late quaternary glaciation throughout tibet and the himalaya defined by 10be cosmogenic radionuclide surface exposure dating abstract temporal and spatial changes in glacier cover throughout the late quaternary in tibet and the bordering mountains are poorly defined because of the inaccessibility and vastness of the region and the lack of numerical dating to help reconstruct the timing and extent of glaciation throughout tibet and the bordering mountains we use geomorphic mapping and 10 be cosmogenic radionuclide crn surface dating in study areas in southeastern gonga shan southern karola pass and central western nyainqentanggulha shan and tanggula shan tibet and we compare these with recently determined numerical chronologies in other parts of the plateau and its borderlands each of the study regions receives its precipitation mainly during the south asian summer monsoon when it falls as snow at high altitudes gonga shan receives the most precipitation 2000 mm a 1 while near the margins of monsoon influence the karola pass receives moderate amounts of precipitation 500 600 mm a 1 and in the interior of the plateau little precipitation falls on the western nyainqentanggulha shan 300 mm a 1 and the tanggula shan 400 700 mm a 1 the higher precipitation values for the tanggula shan are due to strong orographic effects in each region at least three sets of moraines and associated landforms are preserved providing evidence for multiple glaciations the 10 be crn surface exposure dating shows that the formation of moraines in gonga shan occurred during the early mid holocene neoglacial and little ice age on the karola pass during the lateglacial early holocene and neoglacial in the nyainqentanggulha shan date during the early part of the last glacial cycle global last glacial maximum and lateglacial and on the tanggula shan during the penultimate glacial cycle and the early part of the last glacial cycle the oldest moraine succession in each of these regions varies from the early holocene gonga shan lateglacial karola pass early last glacial western nyainqentanggulha shan and penultimate glacial cycle tanggula shan we believe that the regional patterns and timing of glaciation reflect temporal and spatial variability in the south asian monsoon and in particular in regional precipitation gradients in zones of greater aridity the extent of glaciation has become increasingly restricted throughout the late quaternary leading to the preservation of old 100 ka glacial landforms in contrast in regions that are very strongly influenced by the monsoon 1600 mm a 1 the preservation potential of pre lateglacial moraine successions is generally extremely poor this is possibly because lateglacial and holocene glacial advances may have been more extensive than early glaciations and hence may have destroyed any landform or sedimentary evidence of earlier glaciations furthermore the intense denudation mainly by fluvial and mass movement processes which characterize these wetter environments results in rapid erosion and re sedimentation of glacial and associated landforms which also contributes to their poor preservation potential

cyclic deposits and hummocky cross stratification of probable storm origin in upper cretaceous rocks of the cape sebastian area southwestern oregon abstract cyclic deposits containing hummocky cross stratification occur in the upper part of the cape sebastian sandstone of bourgeois 1980 a shallow marine transgressive sandstone of late cetaceous age on the southern oregon coast the cycles average 1 6 m in thickness and consist where complete of a lower hummocky cross stratified sandstone a middle planar and ripple bedded sandstone with a shale bed in its middle part and an upper bioturbated sandstone noteworthy features of the hummocky cross stratification include the presence of depositional domes in addition to scoured depressions the absence of significant bedform migration and the presence of a small proportion of dip angles greater than the angle of repose 34 in addition to the large proportion of low 15 deg dip angles the lower stratified fining upward part of the cycle up to the top of the shale bed is interpreted as having accumulated under conditions of initially great but gradually decreasing current velocity and deposition rate the currents probably had a strong oscillatory component and the depositional event is inferred to have been a storm the part of the planar and ripple bedded sandstone above the shale bed was probably deposited during relatively fair weather after the storm but before re establishment of a normal benthic fauna the bioturbated sandstone is interpreted to have been deposited during fair weather or during minor storms separated by long intervals of fair weather

shore platform abrasion in a para periglacial environment galicia northwestern spain abstract the schmidt rock test hammer was used to study the effect of abrasion on shore platforms in galicia northwestern spain on platforms where tidally induced weathering salt wetting and drying etc is dominant rock strength is significantly lower than in areas where abrasion is or has been active in the recent past this suggests that abrasion removes weathered surface material exposing the stronger less weathered rock below abrasion downwearing measured with a transverse micro erosion meter ranged between 0 13 and 1 8 mm yr 1 over the last year most active abrasion occurs in the upper part of the intertidal zone but weathering is slowly destroying formerly abraded surfaces at lower elevations these abandoned surfaces were abraded by materials supplied by erosion of fluvio nival and periglacial slope deposits that covered or partially covered parts of the galician coast during the middle and late weichselian during the holocene rising sea level and erosion of the slope deposits caused the abrasion zone to gradually migrate up to its present position near the high tidal level the spatial and temporal role of abrasion on this coast is therefore closely associated with the exhumation and inheritance of ancient platform surfaces from beneath weichselian deposits

the impact of severe biodegradation on the molecular and stable c h n s isotopic compositions of oils in the alberta basin canada abstract although the effects of biodegradation on the composition and physical properties of crude oil have been well studied effects of in reservoir petroleum biodegradation on molecular and isotopic compositions of crude oils are not yet clearly understood the alberta basin in western canada is one of the world s largest petroleum accumulations and constitutes an ideal example of a natural suite of sequentially biodegraded oils the basin hosts moderately to severely biodegraded petroleum regionally distributed and in single more or less continuous oil columns in this study a series of oil samples from the alberta heavy oil and oil sands provinces with varying degrees of biodegradation were analyzed to assess the impact of progressive biodegradation on the molecular and c h n and s isotopic compositions of oils the results of the molecular characterization of the hydrocarbon fraction of the studied oils show that the oils have suffered biodegradation levels from 2 to 10 toward the alberta saskatchewan border on the peters and moldowan scale of biodegradation abbreviated pm 2 to pm 10 and from tens to hundreds on the manco scale within single reservoirs increasing biodegradation was observed from top to bottom of the oil columns at all sites studied the whole oil stable isotopic compositions of the samples varied in the ranges 13 c 31 2 to 29 0 2 h 147 to 133 15 n 0 3 4 7 and 34 s 0 4 6 4 the maximum differences between values of samples within single oil columns were 13 c 1 4 2 h 7 15 n 1 7 and 34 s 1 0 regional variations in the isotopic compositions of oil samples from different wells averaged values from top to bottom were 1 2 for 13 c 12 for 2 h 4 1 for 15 n and 5 5 for 34 s and hence generally significantly larger variations were seen than variations observed within single oil columns especially for n and s it appears that even severe levels of biodegradation do not cause observable systematic variations in carbon nitrogen or sulfur isotope composition of whole oils this indicates that sulfur and nitrogen isotopic compositions may be used in very degraded oils as indicators for oil charge from different source rock facies

storm and tide dominated shorelines in cretaceous moosebar lower gates interval outcrop equivalents of deep basin gas trap in western canada the moosebar and gates formations crop out in the deformed foothills belt south of fort st john british columbia they permit examination of the depositional environments of sandstones and conglomerates that are gas bearing in the equivalent wilrich falher interval of the deep basin of alberta and british columbia the moosebar gates interval consists of several upward coarsening and marine to nonmarine sequences moosebar bioturbated shales pass upward into turbidites and offshore storm deposits flow directions indicate a north dipping paleoslope a second coarsening upward sequence at the top of the moosebar and base of the gates terminates in a lenticular fluvial conglomerate up to 30 m thick which is overlain by coals carbonaceous mudstones and sandstones above the carbonaceous zone a major lateral facies change is observed fluvial conglomerates in the south grade into beach conglomerates northward the upper part of the beach conglomerate consists of exposed three dimensional storm berms at least 500 m long up to 1 5 m high with wavelengths of 12 to 24 m the berms trend east west seaward of the conglomerate beach are herringbone cross bedded tidal sandstones with a marine trace fauna graded sharp based conglomerates also are present probably washed out to sea by storms farther north at the same stratigraphic level is a series of partly overlapping conglomerate bars up to 5 m thick and 40 to 50 m across the tops of these bars are covered with storm formed symmetric conglomeratic dunes details of the orientation and geometry of these conglomerate bodies along with their internal structure and pebble fabrics suggest that four major environments fluvial beach offshore conglomerate bars and offshore graded storm conglomerates should be identifiable and predictable in the subsurface

applications of petroleum geochemistry to exploration and reservoir management abstract petroleum geochemistry improves exploration efficiency by accounting for many of the variables that control the volumes of crude oil and natural gas available for entrapment including source rock distribution richness and quality thermal maturity and the timing of generation migration accumulation relative to trap formation it is most powerful when used with other disciplines such as seismic sequence stratigraphy and reservoir characterization four key technology milestones form the basis for most modern applications of geochemistry to exploration these are the concepts and applications of 1 petroleum systems and exploration risk 2 biomarkers stable isotopes and multivariate statistics for genetic oil oil and oil source rock correlation 3 calibrated three dimensional thermal and fluid flow modeling and 4 controls on petroleum composition by secondary processes petroleum geochemistry offers rapid low cost evaluation tools to aid in understanding development and production problems some technology milestones in reservoir geochemistry include 1 assessment of vertical and lateral fluid continuity 2 determination of proportions of commingled production from multiple zones and leaky casing 3 prediction of oil quality in reservoir zones and 4 prediction of gas oil and oil water contact locations as described in the conclusions future research will continue a trend toward predictive geochemistry examples of predictive tools that draw major research support include piston core surveys to assess deepwater petroleum systems prior to drilling and three dimensional basin modeling to predict the regional timing of generation migration and accumulation of petroleum among other research objectives models are needed to better predict the distribution and quality of petroleum in reservoirs

swell dominated carbonates on a mississippian ramp in the canadian rocky mountain front ranges abstract the livingstone formation and the middle opal member of the mount head formation of western canada are mississippian carbonate deposits tens to hundreds of meters thick that are interpreted to have accumulated in a mid ramp wave dominated sub thermocline environment at water depths up to 100 m or more the rocks are predominantly pelmatozoan grainstones and packstones that contain abundant physical sedimentary structures the most common sedimentary structures are planar lamination swaly and hummocky cross stratification and normally graded event beds that are interpreted as having been formed by oscillatory wave currents or oscillatory dominated combined flows the abundant oscillatory currents are interpreted to have been generated by swell waves and to a lesser extent by local storms high angle planar tabular cross bedding is also present in rare discrete beds produced by unidirectional offshore directed currents the unidirectional currents that produced the dunes are interpreted to have been generated by coastal set up that produced downwelling storm currents during the rare storms that occurred along the mississippian coastline it is hypothesized that local storms were not common due to the west coast location and the tropical latitude of the study area instead it is postulated that swell waves approaching from the broad panthalassa ocean to the west were responsible for most sediment remobilization and deposition across the mid and outer ramp swell waves are believed to have resuspended sediment to greater depths than short period less organized storm waves these mississippian deposits suggest that in situ grain production on the ramp without need for the offshore transport of sediment from the shoreface resulted in two major differences from siliciclastic wave dominated settings 1 swaly cross stratification was not restricted to environments shallower than hummocky cross stratification on the upper shoreface because sand size sediment was generated across a large portion of the ramp and 2 aggradation by means other than sediment supply from shallower water caused preservation of deep water swell dominated deposits

storm generated sedimentary structures in subtidal marine facies with examples from the middle and upper ordovician of southwestern virginia abstract the role of storms is of major importance in forming stratification in open shelf facies though storm processes on modern shelves are not fully understood enough is known to see how sediments are influenced storms transport sand away from coastal areas and suspend and transport sand and mud on the open shelf when wave base is lowered storms generate winnowed lag deposits of shells or gravel but coarser sediment and shells of megafauna are little transported except in very near shore environments the martinsburg formation middle and upper ordovician of southwestern virginia was deposited on a storm influenced open marine platform in contrast to the classic turbidite flysch basin of the martinsburg in the great valley of virginia to the northeast deposition of most martinsburg sediments was due to storms sediments deposited during single storm events occur in characteristic fining upward sequences 1 to 80 cm thick in both carbonate and terrigenous clastic dominated areas of the platform individual storm deposits consist of a sharp erosional base overlain by a couplet of whole fossil packstone and laminated calcarenite siltite or quartzose siltstone to very fine sandstone which is gradational to shale packstones are typically intraclastic have shells aligned parallel o bedding and convex up often with adhering or contained mud and have abundant infiltration textures such as cement filled shelter voids packstones grade abruptly to a laminated bed with horizontal plane lamination large and small scale in phase undulatory lamination and wave ripple cross lamination commonly occurring in ordered vertical sequences laminated beds contain escape burrows are weekly graded and have irregularly mounded upper bed surfaces laminated beds grade upward to shale containing horizontal branching burrows and marine fossils the faunal content of the fining upward sequences matches that of the interbedded shale storm generated beds vary greatly in thickness laterally and frequently pinch out completely fining upward sequences formed by scouring winnowing and suspension of the sand and mud during the height of the storm to form the erosional base and autochthonous lag of whole fossils storms preferentially preserve whole fossils rather than fragmenting them infiltration of finer sediment into the lag deposit and deposition of the laminated bed occurred as the storm waned laminated beds are molded into a distinctive suite of sedimentary structures by wave generated currents the shale represents deposition of finest storm suspended material and continued hemipelagic sedimentation similar sequences are widely distributed in the geologic record variability of storm generated sequences can be related to changing water depth thus storm deposits may be useful in basin analysis to estimate relative water depths and trace transgressive and regressive events

tropical climate instability the last glacial cycle from a qinghai tibetan ice core an ice core record from the guliya ice cap on the qinghai tibetan plateau provides evidence of regional climatic conditions over the last glacial cycle 36 cl data suggest that the deepest 20 meters of the core may be more than 500 000 years old the 18 o change across termination i is 5 4 per mil similar to that in the huascaran peru and polar ice cores three guliya interstadials stages 3 5a and 5c are marked by increases in 18 o values similar to that of the holocene and eemian 124 000 years ago the similarity of this pattern to that of ch 4 records from polar ice cores indicates that global ch 4 levels and the tropical hydrological cycle are linked the late glacial stage record contains numerous 200 year oscillations in 18 o values and in dust nh 4 and no 3 levels

bakken madison petroleum systems in the canadian williston basin part 4 diphenylmethanes and benzylcyclohexanes as indicators for oils derived from the madison petroleum system alkyl derivatives of diphenylmethane and benzylcyclohexane were identified as significant components of the family c oils and related mississippian source rocks in the canadian williston basin the co occurrence of these two structurally related compound classes in this specific source rock interval and their relatively low abundance in other petroleum systems indicates the great utility of these aromatic hydrocarbons as effective molecular markers for oil oil and oil source correlation particularly for highly mature light oils

constraining holocene lake level highstands on the tibetan plateau by 10be exposure dating a case study at tangra yumco southern tibet abstract many lakes on the tibetan plateau are surrounded by palaeo shorelines that document former lake level highstands and hence past changes in climate establishing accurate chronologies for these shorelines is crucial to correlate lake level fluctuations with palaeo environmental histories that are commonly inferred from lake sedimentary records here we apply surface exposure dating to constrain the age of two lake level highstands at one of the largest tibetan lakes tangra yumco which has well developed palaeo shorelines located up to 185 m above the current lake for sampling we focussed on wave cut bedrock terraces that vary considerably in width because they were carved into rocks of different erodibility samples from the highest strath terrace 180 185 m above the lake at three different sites yield tightly clustered 10 be ages between 7 39 0 19 ka and 7 87 0 27 ka internal errors which constrain the end of an early holocene lake level highstand at 7 6 0 6 ka external error the consistency of the 10 be ages indicates that bedrock erosion by wave attack reduced the inherited 10 be component to negligible amounts because otherwise samples would show considerable age scatter two bedrock samples from a lower terrace 140 145 m above the lake and one amalgamated clast sample from a beach ridge on the same terrace yield 10 be ages between 4 04 0 14 ka and 4 50 0 15 ka these ages document that the lake level dropped by 40 m between 7 6 ka and 4 3 ka granite boulders from the two investigated terraces yield apparent 10 be ages that are 6 ka and 27 ka older than the ages of the respective terraces indicating that this sample type is not reliable in this setting overall our results demonstrate that exposure dating of bedrock terraces provides a valuable tool to reconstruct lake level histories on the tibetan plateau

the influence of palaeotopography on facies architecture and pyroclastic flow processes of a lithic rich ignimbrite in a high gradient setting the abrigo ignimbrite tenerife canary islands abstract the late pleistocene 188 19 ka abrigo ignimbrite represents the last major explosive caldera forming eruption on tenerife it consists almost entirely of a moderate volume 1 8 km 3 light grey phonolitic lithic rich ignimbrite deposit although a possible abrigo member thin fall deposit is locally preserved beneath the ignimbrite suggesting an initial short lived stable plinian eruption column the ignimbrite deposit is dispersed radially around the lower flanks of the las canadas edifice and correlates to a clast supported lithic breccia on the eastern and northern caldera wall much of the ignimbrite was probably deposited offshore or within the caldera now buried by more recent lavas two major depositional units separated by a co ignimbrite ash cloud deposit and which display dramatic variations in thickness pyroclastic flows were channelised along and deposited within the same valleys that exist today and were commonly continuous and sheet like across the interfluves the basal zones of pyroclastic flows are envisaged as a bed load of coarse lithic lapilli and blocks transported under their own momentum and with the support of the surrounding fine ash gas granular flow

long term east west asymmetry in monsoon rainfall on the tibetan plateau variations in the strength and duration of the asian monsoon affect more than half the population of the planet and there is intense interest in where and how much rainfall amounts will change regionally in response to warmer climate conditions the modern monsoon region is divided into distinct subsystems so the response may be regionally heterogeneous northern hemisphere monsoon systems intensified during the early to mid holocene increasing summer rainfall and creating wetter conditions across much of eastern asia in this study we use the area encompassed by high shorelines of early holocene paleolakes in tibet to reconstruct paleorainfall and hence paleomonsoon patterns during this very wet period we found that the early holocene relative paleolake expansions of 130 closed basin lake systems in the central tibetan plateau display a strong east west gradient paleolake areas expanded by approximately fourfold in the western plateau compared to approximately twofold expansion in the eastern region this early holocene pattern mirrors the modern west east climate division on the plateau rainfall in the west is closely tied to the indian summer monsoon ism subsystem and in the east is closely tied to a probable mix of ism and east asian summer monsoon easm subsystems our results suggest that these modern climate divisions are an enduring feature of the plateau and that ism rainfall increased much more than easm rainfall in response to the same insolation forcing

cosmogenic 10be and 26al exposure dating of nam co lake terraces since mis 5 southern tibetan plateau abstract lake paleo shorelines can be used to reconstruct lake level fluctuations which serve as sensitive indicators of climate change the tibetan plateau tp contains the highest areal proportion of lakes in china and dramatic past lake level changes have led to the formation of numerous relict shorelines here we present 24 10be and 26al exposure ages for five of seven lake terraces situated north of nam co on the southern tp the ages of four high stands marked by terraces t7 t6 t5 and t4 are 81 5 9 0 ka 33 6 1 9 ka 19 9 1 9 ka and 15 2 0 4 ka the topographically highest terrace t7 correlates with periods of enhanced indian summer monsoon ism and supports an mis 5 maximum lake expansion on the tp as opposed to mis 3 ages of two lower terraces t5 and t4 possibly correspond to melt water pulse mwp events we also evaluate different possible sources of uncertainty from geologic processes on 10be exposure ages of lake terraces subaerial erosion following terrace exposure has the most significant influence on 10be exposure ages on ancient high terraces for example 80 ka while inherited 10be from prior exposure and partial shielding by shallow water beach or talus are the most important geological source error of 10be exposure ages for relatively low and young terraces for example

abrupt changes in indian summer monsoon strength during 33 800 to 5500 years b p speleothem proxy records from northeastern ne india reflect seasonal changes in indian summer monsoon strength as well as moisture source and transport paths we have analyzed a new speleothem record from mawmluh cave meghalaya india in order to better understand these processes the data show a strong wet phase 33 500 32 500 years b p followed by a weak dry phase from 26 000 to 23 500 years b p and a very weak phase from 17 000 to 15 000 years b p the record suggests abrupt increase in strength during the bolling allerod and early holocene periods and pronounced weakening during the heinrich and younger dryas cold events we infer that these changes in monsoon strength are driven by changes in temperature gradients which drive changes in winds and moisture transport into northeast india

microbial degradation of aromatic components of crude oils a comparison of laboratory and field observations abstract small aliquots of crude oil brent north sea were incubated aerobically for periods of up to 14 days with an inoculum of recent sediment the saturated and aromatic hydrocarbon components were then isolated and the latter were compared by capillary gas chromatography with similar fractions isolated from four oils from the barrow sub basin of western australia which had experienced different degrees of biodegradation biodegradation of the aromatic hydrocarbons of brent oil produced a series of altered oils whose compositions were comparable to those of the naturally reservoir degraded oils compounds such as naphthalene phenanthrene and alkylated homologues of these hydrocarbons were oxidised but individual isomers were oxidised to different extents

ice age hurricanes and tropical storms we compare pleistocene tropical cyclones with present day storms in this study through the use of a three dimensional numerical model simulating hurricane development and processes1 the characteristics of atlantic ice age tropical storms are derived from reconstructions of the 18 000 bp climate the last glacial maximum or lgm and the giss goddard institute of space studies general circulation model s lgm simulation2 3 the simulation results indicate that although the structure of the ice age atmosphere was colder and more stable it had the potential to support development of tropical cyclones such storms however would be substantially weaker than contemporary storms this investigation demonstrates the value of integrating numerical models of varying spatial scales in climatic research

potential forcing mechanisms of holocene lake level changes at nam co tibetan plateau inferred from the stable isotopic composition of shells of the gastropod radix the timing of lake level fluctuations on the tibetan plateau and their relationship with climatic changes is still under debate and the main reason for this is the lack of suitable archives for reconstructing the paleohydrology and paleoclimatology of the lakes here we present the results of analyses of the shell geochemistry of radix sp from an exposed terrace of nam co lake on the south central tibetan plateau optically stimulated luminescence osl dating reveals that deep water lacustrine sediments formed between ca 4 4 and 2 2 ka suggesting a high and stable lake level significantly above the present the results of sr ca 13c and 18o analyses of the fossil shells of radix sp indicate that during the mid to late holocene lake level variations in nam co were mainly controlled by variations in the indian summer monsoon a trend of decreasing evaporation also played an important role comparison with other results suggests a consistent pattern of mid to late holocene lake level changes acro

reconstruction of the 30 40 ka bp enhanced indian monsoon climate based on geological records from the tibetan plateau abstract multi proxy records from ice caps lakes and pollen records from the tibetan plateau are used to reconstruct the palaeoclimate during the period 30 40 ka bp lake geomorphological and lacustrine sedimentological studies show that numerous high lake level stands and or freshwater lakes occurred in large areas of western china at this time including over the tibetan plateau where the area contains mostly shallow water and saline hypersaline water lakes under extremely dry conditions of today pollen based reconstruction of tibetan vegetation shows systematic differences from the present alpine steppe forests were shifted ca 400 km further north and the alpine conifer forest extended ca 400 800 km beyond their present western limits variations in 18 o curves from ice cores from the plateau suggest that the temperature was 2 4 c higher and precipitation was 40 to over 100 higher than today all of the evidence consistently suggests the existence of an exceedingly strong summer monsoon climate over the plateau the vigorous evaporation of the tropical ocean surface would also play an important role in promoting the penetration of moisture rich southwest monsoon over the tibetan plateau these climate patterns with strong summer monsoon circulation during the period 30 40 ka bp reflect the 20 ka earth orbital precessional cycle when the tibetan plateau region received greater solar radiation which thus enlarged the thermodynamical contrast between the plateau and the mid south portion of the indian ocean

organic geochemistry of venezuelan extra heavy crude oils 2 molecular assessment of biodegradation abstract the extent of biodegradation of extra heavy crude oils from the eastern venezuelan basin orinoco tar belt has been assessed using biological marker compounds which include steranes triterpanes aromatic steroids and phenanthrenes analyzed by gc ms and petroporphrins analyzed by hplc the analyses indicate that biodegradation takes place in two regions namely surface or close to surface and subsurface with a different pattern of biodegradation taking place at each type of location some oils show patterns of biomarkers which may be the combined result of degradation at both main sites of biodegradation however two empirical biodegradation parameters are proposed to achieve this classification the classification of crude oils in terms of degree of biodegradation is further complicated by the identification of mixed crudes

large variations of oxygen isotopes in precipitation over south central tibet during marine isotope stage 5 oxygen isotope 18 o records of two stalagmites from tianmen cave on the south central tibetan plateau grew during much of marine isotope stage 5 the tianmen record the fi rst cave record from the tibetan plateau characterizes a precipitation 18 o history larger in amplitude but similar in structure to asian monsoon records from the adjacent regions providing essential evidence that the asian monsoon system including the east asian and indian monsoon subsystems responds largely to changes in northern hemisphere summer insolation extremely low 18 o values during marine isotope stages 5a 5c and 5e suggest that precipitation rather than temperature was a major factor controlling 18 o in precipitation on orbital time scales in the south central tibetan plateau the tianmen record may help in the interpretation of regional ice core 18 o records the large range of orbital scale shifts in meteoric 18 o 9 raises important considerations related to reconstructing the uplift history of the plateau

landscape evolution of a bedrock peneplain on the southern tibetan plateau revealed by in situ produced cosmogenic 10 be and 21 ne article i nfo 10 be cosmogenic 21 ne low relief bedrock surfaces that occur at high altitude are a common feature of cenozoic mountain belts and have often been used to infer a significant amount of rock uplift after their generation at low elevation the timescale over which such surfaces can be preserved at high elevation and the rate at which they are modi fied by weathering and erosion are poorly known here we use cosmogenic 10 be and 21 ne to quantify the landscape evolution of a bedrock peneplain in southern tibet that occurs at an altitude of 5300 m the pe neplain is developed in cretaceous granitoids and jurassic metasediments of the northern lhasa block 90 e 31 n and originally had a minimum extent of 150 km east west and 75 km north south it has been dissected by small rivers that generated a few hundred meters of relief and formed additional bedrock sur faces of limited extent at lower elevation local denudation rates for the peneplain and the lower bedrock surfaces based on 10 be concentrations in grus samples and amalgamated quartz clasts cluster between

carbonate ramp to deeper shale shelf transitions of an upper cambrian intrashelf basin nolichucky formation southwest virginia appalachians the nolichucky formation 0 300 m thick formed on the cambrian pericratonic shelf in a shallow intrashelf basin bordered along strike and toward the regional shelf edge by shallow water carbonates and by nearshore clastics toward the craton lateral facies changes from shallow basinal rocks to peritidal carbonates suggest that the intrashelf basin was bordered by a gently sloping carbonate ramp peritidal facies of the regional shelf are cyclic upward shallowing stromatolitic carbonates these grade toward the intrashelf basin into shallow ramp cross bedded ooid and oncolitic intraclast grain stones that pass downslope into deeper ramp subwave base ribbon carbonates and thin limestone conglomerate ribbon limestones are layers and lenses of trilobite packstone parallel and wave ripple laminated quartzose calcisiltite and lime mudstone arranged in storm generated fining upward sequences 1 5 cm thick that may be burrowed shallow basin facies are storm generated upward coarsening and upward fining sequences of green calcareous shale with open marine biota parallel to hummocky laminated calcareous siltstone and intraformational flat pebble conglomerate there are also rare debris flow paraconglomerate 10 60 cm thick and shaly packstone wackestone with trace fossils glauconite horizons and erosional surfaces hardgrounds a 15 m thick tongue of cyclic carbonates within the shale package contains subtidal digitate algal bioherms which developed during a period of shoaling in the basin understanding the nolichucky facies within a ramp to intrashelf basin model provides a framework for understanding similar facies which are widely distributed in the lower palaeozoic elsewhere the study demonstrates the widespread effects of storm processes on pericratonic shelf sedimentation finally recognition of shallow basins located on pericratonic shelves is important because such basins influence the distribution of facies and reservoir rocks whose trends may be unrelated to regional shelf edge trends

rapid and punctuated late holocene recession of siling co central tibet this work was supported by a national science foundation grant from the tectonics program ear 0911587 to e k and k p f additional support to e w was provided by grants from the chinese academy of sciences xdb03010500 x s also thanks the support from the earth observatory of singapore nanyang technological university through its funding from the national research foundation singapore and the singapore ministry of education under the research centers of excellence initiative

hydrological variations on the central tibetan plateau since the last glacial maximum and their teleconnection to inter regional and hemispheric climate variations decadal to sub decadal variability of inflow evaporation and biological productivity derived from lake nam co was used to reconstruct hydrological changes for the past ca 24 k cal a bp the timing of these variations corresponds to known climatic shifts on the northern hemisphere after a dry and cold last glacial maximum the lake level of nam co initially rose at ca 20 k cal a bp moist but further cold conditions between ca 16 2 and 14 k cal a bp correspond to heinrich event 1 a warm and moist phase between ca 14 and 13 k cal a bp is expressed as a massive enhancement in inflow and biological productivity and might be associated with a first intensification of the indian ocean summer monsoon coinciding with the bolling allerod complex a two step decrease in inflow and a contemporaneous decline in biological productivity until ca 11 8 k cal a bp points to cool and dry conditions during the younger dryas lake levels peak at ca 9 4 k cal a bp although hydrological conditions remain relatively stable during the holocene with only low amplitude variations observed

an unusual muddy epeiric carbonate reservoir the lower muschelkalk middle triassic of the netherlands the mud dominated lower muschelkalk carbonates middle triassic are a unique reservoir currently producing gas in the dutch de wijk field numerous gas shows scattered over the netherlands onshore and offshore suggest further currently unrecognized potential this study complements an extensive subsurface data set with selected outcrop information to localize missed opportunities and evaluates the factors controlling the development of this unusual reservoir type the muddy carbonates are deposits of a storm dominated epeiric carbonate ramp with negligible depositional gradient different marlstone dolomudstone and lime mudstone facies types reflect the low energy coastal plain to inner ramp and higher energy midramp to proximal outer ramp depositional environments the best reservoir facies is recognized in distal inner ramp algal dolomudstones porosity up to 24 and permeability up to 32 md because of the variable intensity of early facies related diagenesis the reservoir quality of dolomudstones decreases markedly in landward and seaward direction from the distal inner ramp the stacking of decimeter to meter thick reservoirs is reflected by a fourfold hierarchy of depositional cycles that can largely be recognized with conventional wire line logs high resolution outcrop and subsurface correlations reveal that stacks of thin bedded reservoir units most probably pinch out within a few kilometers and that their lateral continuity should not be overestimated despite the epeiric layer cake setting local reservoir occurrences are commonly situated above paleohighs of tectonic or halokinetic origin not only the reduced thickness of the lower muschelkalk above these paleohighs but also the presence and lateral extent of local reservoirs might be detected with seismic data the general facies and reservoir patterns exemplified by the lower muschelkalk may also be of use for reservoir prediction in similar epeiric settings elsewhere for instance in the middle east

internal wave deposits in jurassic kermanshah pelagic carbonates and radiolarites kermanshah area west iran abstract we report eventites generated by turbulence events triggered by breaking internal waves in jurassic pelagic muds deposited in a graben area located between the arabian and bisotoun carbonate platforms at the kermanshah basin west iran the 43 m thick studied pliensbachian aalenian succession at kermanshah includes sponge spicule radiolarian limestones and cherts with cm to dm thick intercalations of pyroclastic beds and coarse grained deposits formed by neritic derived grains and reworked pelagic material breaking of internal waves in localized areas reworked the available sediment on sea floor including the erosion of cohesive pelagic muds and the resuspension of neritic derived grains which were resedimented from the bisotoun platform most probably by storms or turbidity currents the generated internal wave deposits include flat and round pebble limestone conglomerates formed by deposition of pelagic clasts and neritic derived grains near the breaker zone laminated packstone grainstones deposited by high energy upslope swash and downslope backswash flows cm thick packstone grainstones with asymmetrical starved ripples and hummocy crossstratification generated downdip by waning of backwash flows and internal wave oscillatory flows these internal wave deposits predominate in the pliensbachian early toarcian and were related to internal waves developed along a thermocline linked to climate warming and excited by submarine volcanic eruptions storms or tectonic shaking

a dynamic biodegradation model suggested by petroleum compositional gradients within reservoir columns from the liaohe basin ne china abstract a suite of petroleum reservoir extracts from the liaohe basin ne china was analyzed to investigate the effects and controls of biodegradation on petroleum composition systematic changes seen as marked gradients in petroleum bulk composition component concentrations and molecular indicators have been observed in two biodegraded oil columns in the es3 column 1700 1850 m biodegradation has removed substantial amounts of normal and isoprenoid alkanes more severe biodegradation occurs in the shallower es1 column 1500 1650 m with both steranes and hopanes being partially removed temperature has an overall control on biodegradation in the two columns a lower reservoir temperature leading to a higher degree of biodegradation however observed variation in the degree of biodegradation in the es3 column at different sites is controlled by water leg size with a higher level of degradation being associated with a thicker water leg the supply of nutrients from the water leg is thought to have a significant impact upon the degree of biodegradation in addition to water leg size nutrient supply the compositional gradients also are controlled by the relative rate of mixing of fresh oil charge gradients can only be conserved in biodegraded petroleum columns if the rate of diffusive mixing is similar to or lower than the rate at which the hydrocarbons are removed a biodegradation model is proposed that couples geochemical and geological factors to provide a coherent approach for assessing the impact of degradation on petroleum our geochemical study indicates that biodegradation occurs mainly within a narrow region at or near the base of the oil column the stable compositional gradients are produced after an initial induction period involving diffusive transport of alkanes to the oil water contact owc and diffusion of biodegradation products such as 25 norhopanes and other metabolites away from the reaction site the mixing of continuously charged oil with residential biodegraded oil by diffusion may be considered as one of the most important factors controlling the biodegradation process the conceptual model illustrates all of these processes and opens the possibility of model driven prediction of oil properties and sweetspot location in reservoirs

constraints on the late quaternary glaciations in tibet from cosmogenic exposure ages of moraine surfaces abstract this contribution provides new constraints on the timing of tibetan glacial recessions recorded by the abandonment of moraines we present cosmogenic radionuclide 10 be inventories at 17 sites in southern and western tibet 32 crests 249 samples and infer the range of permissible emplacement ages based on these analyses individual large embedded rock and boulder samples were collected from the crests of moraine surfaces and analyzed for 10 be abundance we consider two scenarios to interpret the age of glacial recession leading to the moraine surface formation from these sample exposure ages 1 erosion of the moraine surface is insignificant and so the emplacement age of the moraines is reflected by the mean sample age and 2 erosion progressively exposes large boulders with little prior exposure and so the oldest sample age records the minimum moraine emplacement age we found that depending on the scenario chosen the moraine emplacement age can vary by 50 for 100 ka old samples we consider two scaling models for estimating the production rates of 10 be in tibet which has an important although lesser effect on inferred moraine ages while the data presented herein effectively increase the database of sample exposure ages from tibet by 20 we find that uncertainties related to the interpretation of the 10 be abundance within individual samples in terms of moraine emplacement ages are sufficient to accommodate either a view in which glacial advances are associated with temperature minima or precipitation maxima that are recorded by independent paleoclimate proxies a reanalysis of published data from moraines throughout tibet shows that the variation we observe is not unique to our dataset but rather is a robust feature of the tibetan moraine age database thus when viewed in a similar way with other samples collected from this area uncertainties within moraine exposure ages obscure attribution of tibetan glacial advances to temperature minima or precipitation maxima our work suggests that more reliable chronologies of tibetan glaciations will come from improvements in production rate models for this portion of the world as well as a better understanding of the processes that form and modify these geomorphic surfaces

variations in water level and glacier mass balance in nam co lake nyainqentanglha range tibetan plateau based on icesat data for 2003 09 water level fluctuations of inland lakes are related to regional scale climate changes and reflect variations in evaporation precipitation and glacier meltwater flowing into the lake area in its catchment in this paper ice cloud and land elevation satellite icesat altimeter data and landsat imagery 2002 09 are used to estimate nam co lake nyainqentanglha range tibetan plateau water elevation changes during 2002 09 in 2003 nam co lake covered an area of 1998 8 4 2 km 2 and was situated at 4723 m a s l over such inland water bodies icesat altimeter data offer both wide coverage and spatial and temporal accuracy we combine remote sensing and gis technology to map and reconstruct lake area and increased volume changes during a 7 year time series nam co lake water level increased by 2 4 0 12 m 0 33 m a 1 between 23 february 2003 and 1 october 2009 and lake volume increased by 4 9 0 5 km 3 in the past 7 years nam co lake area has increased from 1998 78 5 4 to 2023 8 3 4 km 2 the glacier covered area has decreased from 832 34 to 821 0 km 2 and the drainage basin area has decreased from 201 1 4 2 to 196 1 2 3 km 2 however the most spectacular feature is the continual water level rise from 2003 to 2009 without an obvious associated increase in precipitation based on digital elevation models dems from shuttle radar topography mission srtm dem data and corrected icesat elevation data significant changes to glacier mass balance in the western nyainqentanglha mountains are indicated nyainqentanglha mountain glacier surface elevations decreased by 8 39 0 45 m during 2003 09 over the same period at least 1 01 km 3 of glacial meltwater flowed into nam co lake assuming a glacial runoff coefficient of 0 6 the mean glacier mass balance value is 490 mm w e over the corresponding period indicating that glacier meltwater in the catchment contributes to lake level rise the contribution rate of glacial meltwater to lake water volume rise is 20 75 the temporal lake level fluctuation correlates with temperature variations over the same time span

the timing and cause of glacial activity during the last glacial in central tibet based on 10be surface exposure dating east of mount jaggang the xainza range abstract mountain glaciers are sensitive to climate change and can provide valuable information for inferring former climates on the tibetan plateau tp the increasing glacial chronologies indicate that the timing of the local last glacial maximum lgm recorded across the tp is asynchronous implying different local influences of the mid latitude westerlies and asian summer monsoon in triggering glacier advances however the well dated sites are still too few especially in the transition zone between regions controlled by the two climate systems here we present detailed last glacial chronologies for the mount jaggang area in the xainza range central tibet with forty three apparent 10be exposure ages ranging from 12 4 0 8 ka to 61 9 3 8 ka these exposure ages indicate that at least seven glacial episodes occurred during the last glacial cycle east of mount jaggang these include a local lgm that occurred at 61 9 3 8 ka possibly corresponding to marine isotope stage 4 mis 4 subsequent glacial advances at 43 2 2 6 ka and 35 1 2 1 ka during mis 3 one glacial re advance standstill at mis3 2 transition 29 8 1 8 ka and three glacial re advances standstills that occurred following mis 3 at 27 9 1 7 ka 21 8 1 3 ka and 15 1 0 9 ka the timing of these glacial activities is roughly in agreement with north atlantic millennial scale climate oscillations heinrich events suggesting the potential correlations between these abrupt climate changes and glacial fluctuations in the mount jaggang area the successively reduced glacial extent might have resulted from an overall decrease in asian summer monsoon intensity over this timeframe

orbital signals in the diurnal cycle of radiation time of day plays a critical role in determining the dominance of the earth s orbital parameters involving eccentricity precession and obliquity extension of orbital radiation data to the diurnal cycle permits the recognition of well defined temporally separate signals corresponding to all three major orbital parameters and to combinations of these parameters past research involving computed radiation changes at the daily and seasonal scales has not shown significant eccentricity cycles results of this study show 1 at the solstices a marked change in dominance from precession for the solar elevation classes associated with early morning late afternoon to obliquity for the elevation class containing solar noon occurs in solar radiation 2 at the equinoxes cycles corresponding to those associated with eccentricity are evident in the radiation data at all individual time intervals of the day past studies have shown that the daily radiative total reflects only the influence of precession a third set of cycles at the equinoxes centered near 11 kyr corresponds to a combination of orbital signals these results imply that paleoclimatic proxy data displaying strong spectral peaks corresponding to eccentricity 100 kyr and obliquity 41 kyr such as records of global ice volume may be related to radiation changes occurring in the solar elevation class containing solar noon while paleoclimatic proxy data displaying strong spectral peaks corresponding to precession for example sea surface temperatures appear to be showing the dominance of precession on the daily total radiation

is holocene storm generated stratification in florida bay a reflection of solar storm cycles a descriptive analysis of surficial sediments of crane key florida bay showed that the sediments consist of storm layers winter storm and hurricane deposits and algal laminated sediments storm layers are riddled with the following types of cavities gas escape vugs dissolution vugs burrows rootholes and cryptalgal vugs structures and sediment types are arranged into a 15 cm thick thickening upward storm generated sequence which formed in approximately 100 yr under a deepening trend periodograms of sea level variations match the frequency distribution of strong intensity storms which occurred in south florida since the beginning of this century the calculated recurrence time of strong storms 10 3 yr and the time interval of formation of the sequence 100 25 yr are probably a response of climatic parameters to short period 11 yr and longer period 90 110 yr cycles of solar activity comparison with the ancient record shows analogous dm thick storm generated sequences probably linked to solar cycles and 102 yr sea level rises

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