palaeo moisture evolution in monsoonal central asia during the last 50 000 years abstract the late quaternary climate history of monsoonal central asia was inferred from 75 palaeoclimatic records which provide information about moisture conditions in the last 50 ka or part of this period wet conditions occurred during middle and late marine isotope stage 3 while the last glacial maximum lgm was characterized by dry climate conditions in the region a stepwise climate amelioration is suggested by the climate records following the lgm several climate signals of this period which were reported from high latitude ice core records are preserved in archives from monsoonal central asia as well during the early holocene high effective moisture was inferred from most records from the area dominated by the indian monsoon e g the tibetan plateau suggesting that holocene optimal climate conditions occurred there during this period in contrast areas which are dominated by the south east asian monsoon se monsoon and the westerlies in north western and north central china mongolia do not uniformly show an early holocene climate optimum for this area optimal conditions prevailed during the mid holocene these apparent contradictions can possibly be explained by the regional uplift and descent of air masses in the holocene during the early holocene strengthened insolation possibly caused an enhanced low level convergence over the tibetan plateau which led to the intensification of the summer monsoon the strong air uplift caused intensified precipitation and air divergence in the upper troposphere over the tibetan plateau the areas adjacent to the north therefore experienced an intensified descent of air masses and consequently increased aridity the majority of the palaeoclimatic records suggest reduced effective moisture since the late holocene in the region

facies mosaics across the persian gulf and around antigua stochastic and deterministic products of shallow water sediment accumulation abstract among broadly different types of sedimentary successions those that accumulate in nearshore settings are perhaps unique in that a very wide range of rock types recurs with high frequency over relatively short stratigraphic intervals this vertical lithofacies heterogeneity suggests that deposition of any sedimentary unit at any site was short lived that many different sediment types existed within a complex mosaic over the depositional surface and that this facies montage repeatedly moved across surfaces of accumulation in response to eustatic sedimentologic and or tectonic forcing data on numbers and thicknesses of lithofacies units from several dozen such sequences define the size frequency distribution expected if horizons of lithologic change occur randomly within sedimentary successions walther s law suggests that the amount of vertical lithologic heterogeneity manifest in a sedimentary sequence should reflect the degree of lateral heterogeneity in sediment composition that existed across depositional surfaces if so this repetition should also be manifest in sizes and areal distributions of sediment patches constituting the depositional mosaic in order to examine size frequency relations of sediment bodies across surfaces of sediment accumulation we tabulated numbers and areal extents of lithotopes across two rather dissimilar settings across the persian gulf and around the caribbean island of antigua although compositions and lateral extents of different sediment types exhibit broad lateral variation across interior to margin transects in either area lithotope abundances and areal extents define frequency distributions that are in excellent agreement with those anticipated for a facies mosaic of elements whose mean linear widths constitute an exponential frequency distribution these are the size frequency distributions one would expect if mosaic element boundaries occur randomly across regions of sediment accumulation and suggest that distributions of lithotope areas from holocene surfaces are directly analogous to lithofacies thickness frequencies from ancient successions in addition to the fact that both of the size frequency distributions attest to the importance of stochastic processes during sediment deposition they also afford numerical descriptors of abundances and areal extents of holocene lithosomes that can then be used as controlling parameters in computational models of sediment accumulation importantly results derived from such simulations are based not on inference of water depth varying in response to change in subsidence sea level and rate of sediment accumulation but on statistical attributes intrinsic to modern and ancient marginal marine successions

the spatial distribution of precipitation and topography in the qilian shan mountains northeastern tibetan plateau abstract the mutual interrelation of orographic precipitation pattern and topography is key to understanding the competing role of tectonics and climate in landscape evolution however the relationship between precipitation and topography across arid to semiarid orogens has received little attention because of limited data availability as a global successor to tropical rainfall measuring mission trmm the global precipitation measurement gpm extends precipitation measurements to mid and high latitudes since 2014 in this study we process one year of gpm precipitation with a spatial resolution of 0 1 0 1 across the arid to semiarid qilian shan mountains to examine the spatial correlation between topography and precipitation though short this data set provides reasonable precipitation when compared with other weather station relevant estimates we then use nine orogen perpendicular swath profiles to examine the influence of topography on precipitation distribution through the range the results show that precipitation variation displays a significant elevation control with precipitation peaks in the high elevation mountain interior we further compare the gpm precipitation with elevation and local relief within each swath extent the results show that precipitation uniformly increases with increasing elevation for nine swaths which is consistent with the elevation controlled precipitation pattern we find precipitation and local relief are positively correlated for five swaths but not for the remaining four swaths based on published data for uplift and erosion we suggest that the presence or absence of such a correlation indicates whether mountains are in topographic steady state or in a transient state of relief production

plate tectonic history basin development and petroleum source rock deposition onshore china abstract china comprises a mosaic of distinct continental fragments separated by fold belts these fold belts are suture zones resulting from the accretion of various fragments formerly separated by intervening areas of oceanic crust the major sedimentary basins onshore china can be classified into four groups those in western china are flexural developing as a result of north south compression in contrast those in the east are extensional and related to development of the pacific oceanic margin in central china basins have a more problematic origin those of north central china ordos sichuan are flexural basins controlled by eastward directed thrusting along their western margin in contrast basins further south chuxiong shiwandashan are predominantly extensional and related to major strike slip movements by synthesizing basin stratigraphies across china in tectonostratigraphic terms and in particular comparing the nature and timing of unconformities it is possible to formulate a coherent model for the palaeoreconstruction of china we identify five major tectonostratigraphic breaks which equate with the collision of the following continental fragments tarim north china carboniferous permian south china block permian triassic qiantang late triassic early jurassic lhasa block late jurassic early cretaceous and india early tertiary prior to permian times the southern margin of eurasia ran approximately along the northern border of modern china the late carboniferous collision of tarim north china with eurasia resulted in the development of a flexural basin junggar and deposition of non marine clastics to the south of the suture shallow marine deposition continued in the late permian early triassic the progressive collision from east to west of the south china block with the north china block resulted in a change to fluvial lacutrine sedimentation across the entire north china tarim block open marine carbonate deposition in the north of the south china block passed southward into a deeper marine clastic sequence deposited in a backarc basin further south a subduction zone existed along the southeastern margin of the south china block in western china northward subduction throughout the triassic resulted in the development of the songban ganzi accretionary prism with retroarc thrusting resulting in flexure and the first development of the tarim basin oblique collision of the qiantang block in the late triassic along the east of the south china block resulted in east west directed thrusting which initiated the suchuan and ordos basins continued strike slip deformation along the south western margin of the south china block resulted in the development of basins with a significant extensional component such as chuxiong the collision of the qiantang block with the southern edge of the tarim basin early jurassic resulted in a renewed clastic influx in both the tarim and junggar basins along the eastern pacific margin a compressional arc and retroarc basin in the south passed northwards into an extensional arc system subduction rollback of the extensional arc initiated rifting in the late jurassic in the eren and songliao basins the late jurassic early cretaceous collision of the lhasa block in the west rejuvenated the thrust systems bordering the western basin and resulted in a renewed clastic influx in the southeast the compressional arc phase culminated in widespread thrusting and folding of early cretaceous age in the northeast extension continued with the progressive migration of the rift system southward with time the arrival of the indian block in the early tertiary rejuvenated the bounding thrust belts of all the western basins in the east the change in convergence of the pacific plate to a more westerly direction is marked by extension and widespread rifting along the entire length of eastern china throughout most of china mesozoic and cenozoic deposition occurred in predominantly non marine environments source rocks in such settings comprise principally mudstones deposited in lakes organic rich mudstones these can accumulate in both deep and shallow lakes in order to accumulate substantial volumes the lake must be significant in space and time in china lacustrine orms occur in both rift and flexural basins lacustrine orms deposited under humid climatic conditions are restricted to the period of maximum tectonic subsidence in the flexural basins of western china source rock deposition follows basin initiation by 20 30 ma in the extensional basins of eastern china source rock deposition takes place 5 15 ma after basin initiation by contrast semi arid and arid climate lacustrine orms whilst being best developed during the period of maximum tectonic subsidence occur at all stages in the basin history

modeling carbonate sequence development without relative sea level oscillations standard conceptual models propose that stratal patterns in carbonate depositional sequences are controlled predominantly by relative sea level oscillations even during greenhouse periods when amplitudes of relative sea level oscillations were small however numerical experiments with a two dimensional forward model of carbonate systems suggest that variations in sediment transport rate and carbonate productivity are capable of producing similar parasequence stacking patterns without relative sea level oscillations this result suggests two alternative end member models one driven by relative sea level change the other driven by changes in transport rate and productivity controlled ultimately by climatic factors many carbonate systems may represent some combination of these end member possibilities

on the use of cycle thickness diagrams as records of long term sealevel change during accumulation of carbonate sequences analysis of variation in changing rates of accommodation space creation as represented by stratigraphic thickness has become an integral part of ongoing investigations into the origin of ancient meter scale upward shoaling cyclic marine carbonates groupings of thicker than average and thinner than average cycles within long stratigraphic sections have been thought to represent the influence of long term eustatic sealevel variation on rates of accommodation space creation under conditions of constant basin subsidence statistical analysis demonstrates that a large percentage of early paleozoic cyclic carbonate sequences contain thickness distributions indistinguishable from those anticipated for random associations of cycles and that only a few have characteristics commensurate with long term changes in rate of accommodation space creation moreover in those cases where some extraneous control is suggested computational considerations readily demonstrate that change in subsidence rate and or diffe

simulation and characterization of pathway heterogeneity of secondary hydrocarbon migration carriers are important links between sources and traps for hydrocarbon migration and accumulation in a petroleum system oil and gas commonly migrate along narrow and irregular pathways in porous media even in macroscopically homogeneous media a migration simulator based on the invasion percolation theory which couples the buoyancy of a hydrocarbon column as the driving force with capillary pressure as the resisting force satisfactorily explains migration processes in heterogeneous media in macroscopically homogeneous carriers migration pathways are generally perpendicular to equipotential lines but locally the pathways can be irregular because of the influence of microscopic heterogeneity the degree of irregularity of these pathways depends on the difference between competing driving and resisting forces when numerous pathways form in a migration accumulation system the flux of migrating hydrocarbons may vary among these pathways in macroscopically heterogeneous carriers the irregularity of migration pathways is exacerbated when the driving force is relatively weak hydrocarbons tend to migrate in carriers where the hydraulic conductivity is relatively large these pathways differ from those predicted only on the basis of flow potential simulation of the migration process in the middle jurassic carrier beds of the paris basin demonstrates the characteristics of the migration simulator in the analysis of migration pathway heterogeneity results are comparable to or superior to those achieved with previous simulation approaches

holocene climate changes over the desert loess transition of north central china a 2 m trench section at the desert loess transition of north central china was analyzed at 2 cm intervals for grain size distribution md m and total organic carbon toc ams 14c time series of the md and toc records provides direct information on variations of the east asian monsoon climate during the last 10 000 yr md is considered to represent the wind strength and high md reflects strong winter monsoon winds toc denotes the degree of vegetation cover a function of the intensity of summer monsoon circulations from ca 10 000 to 7000 cal yr bp the climate was dominated by a strong winter monsoon and a very weak summer monsoon as indicated by high md and low toc values subsequently climatic conditions became warmer gradually from ca 7000 to 5500 cal yr bp the period between ca 5500 and 2700 cal yr bp displayed the highest toc and lowest md values over the last 10 000 yr marking a stable state of a warm humid climate i e the holocene climatic optimum of china during the interval of ca 2700 1500 cal yr bp the expansion and intensification of agrarian activities could have led to desertification and acceleration of deposition of coarse grained particles resulting in a decreased organic carbon accumulation rate however the toc during this interval still has values as high as during the episode of ca 7000 5500 cal yr bp reflecting a relatively stronger summer monsoon circulation since ca 1500 cal yr ago high amplitude fluctuations of toc that fluctuate in phase with the clay size fraction imply that the climate experienced three major oscillations with a prominent peak of enhanced summer monsoon circulation at ca 1300 cal yr ago and with two intervals of increased winter monsoon strength occurring around ca 1000 and 300 cal yr ago the md and toc records over the past 5000 yr demonstrate a good correlation with the archaeological phenological and historical records of china climate changes in the east asian monsoon region were not only related to the changing seasonality of solar insolation resulting from progressive changes in the earth s orbital parameters but were also controlled by the pattern and intensity of the atmospheric circulation

an experimental study of secondary oil migration experiments using long glass columns packed with glass beads or sand have been done to investigate secondary oil migration under hydrostatic conditions different combinations of bead sizes oil densities oil water interfacial tensions and column orientations have been tested in some experiments the oil was replaced by air the observations included the oil migration pathway the minimum oil column height needed for migration and the rate of advance of the migration front migration was found to take place along restricted pathways and an imbibition front often formed at the bottom of the oil zone the minimum oil zone height needed for migration can be predicted accurately if the values of the drainage and imbibition capillary pressures are known for the saturations at which the oil just becomes disconnected in most experiments the migration front advanced at a constant rate which depended on the fluid properties bead size initial oil height and pore structure migration rate is dependent on buoyant and capillary forces but the dependence on capillary forces becomes weaker as the oil length increases column orientation also has been found to affect migration efficiency

mid holocene east asian summer climate as simulated by the pmip2 models abstract in the present study datasets derived from twelve coupled ocean atmosphere general circulation models oagcms in the paleoclimate modelling intercomparison project phase two were used to analyze the east asian summer climate during the mid holocene about 6000 calendar years ago on the whole the oagcms reproduced warmer and wetter summer climate conditions in east asia during the mid holocene the multi model ensemble showed that in east asia the regionally averaged summer surface air temperature sat increased by 0 89 c summer precipitation was 5 8 higher and an obviously strengthened southerly wind corresponded to a strong summer monsoon in the mid holocene when compared to preindustrial levels the data model comparison in china reveals a good agreement between the oagcms results and the reconstructed changes in the summer sat in east china during the mid holocene in north china the simulated sat anomalies are 0 5 c lower overall than reconstruction in contrast the oagcms fail to capture the strongest warming in the southern qinghai tibetan plateau on the other hand the simulated precipitation agrees well with proxy data except for in the central parts of china where the simulated summer precipitation disagrees in sign with reconstruction in addition there is a large spread among the simulations particularly over and around the qinghai tibetan plateau and inter model discrepancies are larger for precipitation than for sat as a whole

tracking millennial scale climate change by analysis of the modern summer precipitation in the marginal regions of the asian monsoon abstract the asian summer monsoon and the westerly winds interact in the mid latitude regions of east asia so that climate change there is influenced by the combined effect of the two climate systems the holocene millennial scale asian summer monsoon change shows the out of phase relationship with the moisture evolution in arid central asia although much research has been devoted to the long term climate change little work has been done on the mechanism summer precipitation in the marginal regions of the asian monsoon is strongly affected by the monsoon and the westerly winds the purpose of this paper is to examine the mechanism of the millennial scale out of phase relationship by modern summer precipitation analysis in the northwest margin of the asian monsoon 95 110 e 35 45 n first the method of empirical orthogonal function eof analysis was carried out to the 1960 2008 summer rainfall data from 64 stations in that region then the water vapor transportation and geopotential height field data were studied in order to explain and understand the factors that influence the summer precipitation lastly the east asian summer monsoon index easmi south asian summer monsoon index sasmi summer westerly winds index swi were compared with the eof time series the results indicate the complicated interannual scale interaction between the asian summer monsoon and the westerly winds which can result in the modern out of phase relationship in the study area this study demonstrates that the interaction between the two climate systems can be considered as a factor for the millennial scale out of phase relationship

patterns of stratigraphic cyclicity abstract all stratigraphic cyclicity results from cyclic sedimentation therefore patterns of stratigraphic cyclicity can be interpreted correctly only once cyclic sedimentation has been properly understood cyclic sedimentation occurs at any site at which there is cyclic variation in either or both of the two proximate controls on sedimentation these are sediment budget here defined as a generalization of sediment supply and sedimentation capacity here defined as a generalization of accommodation different patterns of cyclic variation in these controls produce different types of sedimentation cycle which result in different patterns of stratigraphic cyclicity a quantitative model for cyclic sedimentation suggests that the possible types of sedimentation cycle fall naturally into four families of these families the most difficult to use for reconstructing sedimentation conditions is the sawtooth family sawtooth cyclicity occurs when changing sedimentation conditions prevent stability from ever being reached the model shows that sequence boundaries in cyclic successions need not be closely tied to inflection points in baselevel curves sequences can start at any time from shortly after the baselevel null point on a cycle s falling baselevel limb to shortly before the baselevel high point on a cycle s rising baselevel limb i e a time range of almost three quarters of a cycle the model also suggests that cyclic successions may intrinsically be more complete than noncyclic ones

mesozoic cenozoic tectonic evolution and dynamics of the songliao basin ne asia implications for the closure of the paleo asian ocean and mongol okhotsk ocean and subduction of the paleo pacific ocean abstract the songliao basin in northeast china in the eastern part of the central asia orogenic belt is the largest accretionary orogen belt in the world however to date previous studies have not extensively examined the dynamic mechanism of its formation and evolution especially the pre cretaceous in this study the mesozoic cenozoic tectonic style stratigraphic records sedimentary time magmatic activity and tectonic evolution in the songliao basin were systematically analysed and summarised we propose that songliao basin experienced multi stage basin superposition processes the foreland compression stage syn rift and post rift stage and structural inversion stage after palaeozoic deposition the basin experienced a strong orogeny with the formation of the triassic middle jurassic foreland basin during the syn rift period three tectonic movements occurred at the end of the shahezi formation late valangnian 135 ma the end of first member of the yingcheng formation late hauterivian 129 ma and the end of the yingcheng formation late barrenian 125 ma in the songliao basin which ended the evolutional history of the rift in the post rift period three tectonic events occurred at the end of the nenjiang formation middle campanian 79 ma the mingshui formation late maastrichtian 66 ma and the yi an formation late chattian 23 ma which determined the deformation characteristics of the middle and shallow strata of the basin such as folding and reverse faults the rudimentary shape formed at the end of the nenjiang formation was finalised at the end of the mingshui formation and formed at the end of the yi an formation the largest depth and width influence of the two events was at the end of the mingshui and yi an formations which played a decisive role in the generation migration and accumulation of oil and gas in the middle and shallow strata of songliao basin after a series of asthenospheric mantle upwelling crustal uplift and extension and volcanic activity songliao basin was eventually formed the formation and structural evolution of the songliao basin were mainly influenced by the paleo asian ocean the mongol okhotsk ocean and the pacific ocean the closure of the paleo asian ocean in the late permian early triassic was influenced by the siberian plate which began to contact and collide with the xingan mongolian block from west to east causing the mongol okhotsk ocean to close in a scissor like structure from west to east in the early middle jurassic the subduction and movement of pacific rim tectonic systems such as the farallon izanagi pacific and philippine plates led to the formation of songliao basin which has experienced a foreland period via compressive pressure since the triassic syn rift period and post rift period via extensional stress and then a structural inversion period

the origin of high frequency platform carbonate cycles and third order sequences lower ordovician el paso gp west texas constraints from outcrop data and stratigraphic modeling abstract the passive margin succession of the diablo platform lower ordovician west texas is represented by the second order sauk c supersequence set consisting of a basal transgressive clastic unit the bliss sandstone above the breakup unconformity marking the second order basal lowstand transgressive phase overlain by 750 m of drift related shallow marine platform carbonates the el paso group recording the second order highstand due to late paleozoic structuring of the gondwanan passive margin present exposures in texas are in an updip shelf position and lack internal stratal geometries across depositional strike so sequences and systems tracts are identified solely by the vertical stacking patterns of depositional subfacies and higher frequency fifth order cycles accommodation plots fischer plots of high frequency cycles gauge systematic shifts in third order accommodation of two complete third order sequences each about 2 m y long and 60 140 m thick within the el paso group this is expressed in the vertical succession of cycle types systematic changes in cycle thickness and variations in subfacies as revealed by histograms of subfacies types tied to fischer plots a complete el paso shelf sequence contains a thin lowstand systems tract of quartz arenite a thick transgressive systems tract dominated by upward thickening thrombolitic subtidal cycles and a highstand systems tract marked by dolomitic thinning upward peritidal cycles containing quartz sand the el paso third order depositional sequences have been correlated by biostrat graphy and cycle stacking pattern from the franklin mountains southeast to the diablo arch northeast into the ardmore basin and thence to the appalachian basin hence the third order sequences appear to be eustatic based on biostratigraphic correlation of accommodation plots around the periphery of gondwana time series analyses suggest that a strict allocyclic milankovitch driven glacio eustatic mechanism alone is insufficient to account for the higher frequency fifth order and lower frequency third order accommodation cycles we used a two dimensional forward computer simulation to compare allocyclic and autocyclic models for high frequency cycles the allocyclic simulation superimposes a deterministic milankovitch glacio eustatic driver on a lower frequency third order accommodation cycle and generates a two dimensional synthetic cross section composed of high frequency peritidal and subtidal cycles stacked into third order sequences the autocyclic simulation is generated by a ginsburg autocyclic mechanism for high frequency cyclicity triggered by third order accommodation changes the autocyclic simulation quantitatively replicates an autocyclic mechanism for fifth order cycle development linked to onshore sediment transport and seaward progradation of tidal flats the two dimensional internal facies architecture of a third order sequence and the high frequency cycle stacking patterns are simulated in both scenarios important differences in patterns of cycles and subfacies stacking in the simulations shed light on the interpretation of the diablo platform cycles and sequences as an alternative or a supplement to autocyclicity or milankovitch forced glacio eustasy we have studied stochastic models for driving high frequency changes in relative sea level these intriguing results maintain essentially all the features observed in the rock record our smoothed sto hastic simulations suggest that the cycle problem is much more complex than presently realized

paleosols capping regressive carbonate cycles in the pennsylvanian black prince limestone arizona abstract the lower pennsylvanian morrowan to early derryan black prince limestone exposed in southeastern arizona consists of shallowing upward regressive carbonate cycles that accumulated on a shallow shelf platform a typical complete cycle from the base upward consists of the following fades mixed skeletal mudstones to grainstones subtidal shelf open circulation mixed skeletal to nonskeletal packstones and grainstones restricted shelf lagoon nonskeletal fenestral mudstones to grainstones intertidal nonskeletal cryptalgally laminated brecciated mudstones to wackestones supratidal and paleosol horizons terrestrial two paleosol types occur calcrete and terra rossa calcrete occurs as thin 5 10 cm profiles consisting of laminar micrite coated grains aggregate grains and vadose diagenetic features terra rossa paleosols consist of subspherical nodules derived from pedogenic alteration of parent limestones separated by a reddish insoluble accumulation ofclays iron oxides calcite skeletal debris and quartz silt the terra rossa paleosols occur as in situ preserved c horizons and as reworked soil residuum the first occurrence is marked by parent limestone in completely brecciated into nodules whereas reworked paleosols consist of nodules enveloped in red matrix both calcrete and terra rossa paleosols record subaerial exposure although the terra rossa paleosols suggest that signi icant amounts of limestone were removed during pedogenesis the terra rossa paleosols also favor an extrinsic versus anintrinsic mechanism for the origin of the cycles

petroleum migration pathways and charge concentration a three dimensional model petroleum migration pathways through a basin are determined by the three dimensional distribution of discontinuous sealing surfaces which are usually parallel to bedding the petroleum migrates below the sealing surface taking the structurally most advantageous route the three dimensional distribution of migration pathways within the petroleum system can be modeled on a personal computer using a program based on the parameters discussed in this paper application of the model to the paris and williston basins demonstrates that a good correlation between predicted pathways and discovered accumulations can be made using simple models pathways form a dense network overlying generating areas in the central parts of basins toward the basin margins these routes commonly become increasingly focused into discrete pathways by the sealing surface morphologies eventually these pathways may reach the surface as seepages it is important to integrate surface outcrops of migration routes surface seepages into migration modeling deflection of the pathways from the structurally most advantageous route below the sealing surface may be caused by lateral sealing barriers due to facies variation in the carrier rock below the seal fault juxtaposition or cross formational seals such as salt intrusions deflection of pathways also occurs where there are hydrodynamic conditions in response to topography driven groundwater flow zones of vertical migration are associated with facies changes along the horizon of the sealing surface into a nonsealing facies or juxtaposition to nonsealing strata by faults vertical migration from either normally or abnormally pressured strata is most likely to occur into normally or lesser pressured strata at intrabasinal highs where hydrocarbons can be stored and transferred at times of temporary seal rupture reverse modeling of individual pathways from fields and seepages to potential sources is a powerful exploration tool it assists in predicting the boundaries of the leaking accumulations or areas of petroleum expulsion

stratal thickness frequencies and the prevalence of orderedness in stratigraphic sequences assuming the existence of discernable hierarchies in the thickness and or temporal recurrence of stratal units within sedimentary sequences has become an increasingly important axiom of sequence and cyclostratigraphic studies and multiple orders of stratigraphic cyclicity are now commonly associated with inferred durations and magnitudes of rhythmic variation in global sea level beyond the desire to establish an informal nomenclature relating stratigraphic thickness to periodicity of eustatic change an assumption of stratigraphic orderedness also supports the inference that groups of sedimentary units with distinct modal dimensions in fact do occur with some generally distinct frequency in stratigraphic sequences in contrast to such perceived patterns of stratigraphic order many groupings of sedimentary units exhibit lognormal frequency distributions wherein most of the population has an exponentially increasing frequency of occurrence with linearly decreasing class size such thickness distributions

oxygen isotopes in lacustrine carbonates of west china revisited implications for post glacial changes in summer monsoon circulation five lakes in the qinghai tibet plateau and north xinjiang have provided oxygen isotope records covering the past 17 11 cal kyr bp the modern lakes are first presented within the major atmospheric circulation and climate patterns of china with the climate related isotope composition of input water equations used to extract hydrological and climatic information from 18o in carbonates are then given after a discussion on potential causes for 18o changes each of the five isotope profiles is interpreted in the light of its specific environmental data the most significant event observed in all records occurred at 12 11 cal kyr bp an abrupt intensification of summer rainfall associated with an extremely rapid 1000 1500 km westward migration of the monsoon fronts the monsoon regime weakened in stages after 8 7 cal kyr bp holocene maximal aridity is recorded at all sites between about 4 5 and 3 5 cal kyr bp long term changes in monsoon strength as inferred from our isotopic interpretation are in good agreement with climate model reconstructions in the tibet qinghai plateau while observed hydrological changes in north xinjiang are not simulated by the models also the non linearity of the holocene monsoon variations cannot be accounted for by orbital forcing

minimum saturations and buoyancy in secondary migration percolation theory it is often argued requires a minimum nonwetting phase saturation of approximately 15 for hydrocarbon migration but field measurements usually fail to find residual oil on the pathway taken during hydrocarbon migration from a source to a reservoir we use numerical simulations and experiments to show that percolation theory when applied to the process of oil invading a pore space leads to the conclusion that field scale saturations in secondary migration can be on the order of 1 or less our capillary invasion experiments on berea sandstone and numerical simulations of fluid invasion on networks show that the minimum saturation for flow of the nonwetting phase decreases as the reciprocal square root of the linear size this result applies to cyli drical samples that have height equal to diameter our numerical simulations include the effects of sample aspect ratio buoyancy and pore size distribution all the numerical results reduce to a single relation between threshold saturations and sample size normalized by a function of the pore size distribution we find that a pore size distribution that has many more small pores than large pores as is typical in rocks and soils substantially reduces the influence of buoyancy on threshold saturations the common practice of using uniform flat pore size distributions to simulate rocks overestimates the effects of buoyancy experiments show that for larger samples the permeability at threshold for flow is higher than conventionally expected in a typical geological situation this h gh permeability is large enough to carry oil to a reservoir over geologic time at saturations of less than 1 of the pore volume our laboratory permeability and saturation experiments confirm the expectations of percolation theory including the fractal dimension of the first invasion path size dependent saturation is the prediction of invasion percolation theory the percolation model is applicable to the secondary migration problem as well as to migration of gas in reservoirs migration of gas or fluids from radioactive waste repositories and migration of nonaqueous phase liquid pollutants in groundwater

poisson processes of carbonate accumulation on paleozoic and holocene platforms abstract cambro ordovician carbonate lithofacies units in the elbrook and conococheague formations exposed at wytheville virginia as well as those in many other phanerozoic peritidal sequences exhibit exponential thickness frequency distributions that is occurrence frequency decreases exponentially with linear increase in unit thickness such distributions are characteristic of waiting times between independent poisson events this relative frequency of spaces of different size between horizons of lithologic change is what one would expect if the horizons were distributed randomly throughout carbonate successions abundances of different lithologies both as net stratigraphic thickness and as number of occurrences also decreases exponentially among successively rare sediment types with each lithology being about 60 as plentiful as the next more abundant rock type relations between net thickness and number of occurrences for each facies define a linear trend coincident with a mean thickness for all wytheville units of 0 48 m a relation indicating that thickness distribution is independent of facies type similar relations are apparent for the horizontal extent of carbonate sediment bodies from the holocene florida bahama platform areal extents of individual facies units lithotopes are described by a frequency distribution in agreement with that anticipated for a population of equidimensional facies elements whose diameter distribution follows an exponential frequency distribution although regional gradients in sediment texture and composition are also apparent along most transects from platform margin to interior such frequency distributions indicate that lateral extents of individual sediment reflect a largely stochastic distribution of facies boundaries across this holocene surface lithotope abundances also yield trends of exponentially decreasing dominance among successively subordinate facies with each being about 70 as extensive the next more abundant sediment type relations between areas and abundances for all lithotopes define a covariant trend corresponding to a mean area of 2 2 103 km2 for all florida bahamas lithotopes we consider several numerical models of stochastic carbonate accumulation although not demonstrably unique scenarios incorporating the sequential superposition of randomly placed coniform lithotopes result in thickness and area frequency distributions that are the same as those observed in ancient and modern platform deposits such simulations of poisson processes of sediment accumulation are in general agreement with stochastic models of lithologic heterogeneity that have been more widely applied to petroleum reservoirs and groundwater aquifers to the as yet unknown degree that peritidal lithofacies area and thickness are correlated data from paleozoic and holocene platforms suggest that carbonate units should exhibit length height ratios of approximately 105 given the decimeter scale over which facies are designated in most paleozoic peritidal successions these relations predict mean lateral extents on the order of several tens of kilometers a value in general agreement with the few data that exist on spatial continuities of peritidal lithotopes in paleozoic carbonate sequences

spatial patterns of sediment accumulation on a holocene carbonate tidal flat northwest andros island bahamas abstract to characterize spatial patterns of sedimentation and analyze the morphology of part of the modern tidal flats of northwest andros island in the bahamas this study integrated remote sensing geographic information systems gis and carbonate sedimentology the fundamental data are a landsat tm image that has been classified to create a thematic map of eight subfacies interpreted to represent a distinct tidal flat subenvironment such as adjacent marine exposed levee beach ridge pond and algal marsh spatial statistics of the thematic map characterize the patterns of sediment accumulation quantitative analysis highlights several interesting results concerning subfacies character and distribution 1 of the eight mapped subfacies low algal marsh is most widespread representing 27 5 of the total area whereas exposed levee beach ridge is the least widespread accounting for 10 of the area 2 the patches of different subfacies have different shape complexities with low algal marsh high algal marsh and mangrove ponds being the least complex and exposed levee beach ridge being the most complex 3 markov chain analysis suggests that lateral transitions between different subfacies are highly ordered and 4 frequency distribution of subfacies patch area and lacunarity gap size distribution data exhibit power law relationships over several orders of magnitude consistent with fractal characteristics the fractal nature of patch size and gaps between facies illustrate that on this tidal flat neither the size nor the spatial distribution of subfacies has a characteristic scale this statistical behavior is consistent with the presence of self organization or emergence of pattern in the absence of a template or external forcing the statistical self organization on the tidal flat is the cumulative expression of local processes but it becomes apparent only through analysis of the whole system these results are inconsistent with models suggesting that tidal flats include a migrating complex of randomly distributed randomly sized subenvironments ancient successions that include random patterns may reflect the more pronounced influence of forces external to the sedimentary system instead of an absence of those forces

remote sensing of geomorphology and facies patterns on a modern carbonate ramp arabian gulf dubai u a e abstract the occurrence of power law relationships in the spatial distribution of sedimentary lithotopes has been identified in both modern and ancient carbonate depositional bodies in this study facies patterns and their spatial relationships are investigated quantitatively in an arabian gulf shallow subtidal carbonate ramp setting using a synergy of ikonos satellite imagery and vessel based acoustic bathymetry survey three dimensional reconstruction of the facies distribution on the seabed enabled quantification of relationships between eight dominant facies classes and the association of particular lithotopes to water depth fractal behavior was investigated using a combination of boundary and patch based metrics and the spatial distribution of early diagenetically cemented hardgrounds and unconsolidated carbonate sand were shown to display strong fractal properties in contrast we show that landscape scale processes can be treated as essentially deterministic and facies neighborhood patterns are strongly probabilistic identifying that the heterogeneity of shallow subtidal carbonate facies scales with a power law within certain thresholds has the potential to serve as a tool in environmental reconstruction in the ancient where information on the lateral persistence of facies units is difficult to obtain the findings are relevant to the interpretation of stratigraphic sequences and paleo depth analysis

stratal order in peritidal carbonate sequences abstract speculation on the depositional origins and geological significance of meter scale cycles in peritidal carbonates is becoming an increasingly prominent facet of sequence stratigraphic theory the understanding of which bears directly on their appropriateness as chronostratigraphic entities as well as their usefulness as records of periodic extrabasinal forcing during sediment accumulation in spite of the generally wide acceptance of the stratigraphic importance and interpretational significance of meter scale parasequences little has been done to quantitatively document the stratigraphic nature of regularly recurring lithologic associations or to verify the predominance of such cyclicity in shallow water limestone dolostone sequences in order to determine the statistical extents and stratigraphic scales of stratal order in such sequences we have examined several long sections of peritidal carbonate both with respect to the presence or absence of markovian lithologic transitions and with respect to the upward shallowing character of lithofacies associations in contrast to common wisdom these measures of stratal order suggest that lithologic manifestation of meter scale cyclicity is relatively uncommon all of the several sequences deemed cyclic via qualitative inspection in fact contain relatively few intervals of demonstrable lithologic order and even fewer exhibit any tendency for contained units to shallow upsection in reality most parts of most shallow water carbonate sequences exhibit little more str tal order than would be apparent in random sequences of peritidal lithologies on the basis of these considerations we suggest that discrimination of meter scale cyclicity in epicratonic carbonates is perhaps more perceptional artifact than stratigraphic reality imminent and future efforts intended to fruitfully evaluate the importance of intrabasinal versus extrabasinal processes of sedimentation in shallow low latitude settings should perhaps eschew more generic perceptions of periodic paleoclimatic forcing in favor of a less regimented view toward the importance of stochastic processes of carbonate accumulation

a holocene east asian winter monsoon record at the southern edge of the gobi desert and its comparison with a transient simulation the east asian winter monsoon eawm exhibits significant variability on intraseasonal interannual and interdecadal time scales and the variability can be extended to holocene centennial and millennial scales previous holocene eawm proxy data records which were mostly located in central eastern and southern china did not show a consistent holocene eawm history therefore it is difficult to provide insights into mechanisms of the long term winter monsoon variability on the basis of the records eolian sediments at the southern edge of the gobi desert western china are sensitive to the eawm changes and less affected by the east asian summer monsoon due to an obstruction of the qinghai tibet plateau this paper presents a comparison between a well dated holocene eawm record and coupled climate model simulations so as to explore physical processes and influencing factors of the holocene eawm sediment samples from two holocene eolian sedimentary sections huangyanghe a and huangyanghe b were acquired at the southern edge of the gobi desert chronologies were established based on twenty bulk organic matter ams 14c ages and five pollen concentrates ams 14c ages proxy data including grain size total organic carbon magnetic susceptibility and carbonate content were obtained from the two eolian sections the grain size standard deviation model was applied to determine components sensitive to variability of the holocene eawm after a comparison of environmentally sensitive grain size components and proxy data the 20 200 m component at the huangyanghe a and the 20 159 m component at the huangyanghe b section were selected as indicators of the holocene eawm which show a strong early holocene winter monsoon and a decline of the winter monsoon since the mid holocene we also present equilibrium and transient simulations of the climate evolution for the holocene using a state of art coupled climate model the community climate system model version 3 ccsm3 indices for the holocene eawm were calculated and are consistent with the reconstructed holocene eawm intensity the simulations indicate that orbital forcing effects on the land sea temperature and sea level pressure contrast can account for the observed eawm trends other forcings that were present in the early holocene including the remnant laurentide ice sheet and meltwater forcing in the north atlantic were not responsible for the holocene trends

determining the spatial and temporal patterns of climate changes in china s western interior during the last 15 ka from lacustrine oxygen isotope records china s western interior is a climatologically complex region where climatic conditions are primarily controlled by the westerly jet stream and the asian monsoon system observations reveal that the 18o signatures of these atmospheric elements as expressed in their meteoric waters are different and these differences are reflected in the lacustrine systems that are ultimately fed by the meteoric waters empirical orthogonal function eof decomposition of 17 lacustrine 18o records from this area clearly reveals the spatial and temporal structures of climate changes during the last 15 ka the first eof mode dominated by sites in the nw sector captures the temperature effect on the variability of the 18o dataset we interpret the variations through time in the amplitude of this mode to be indicative of changes in summer air temperature the second eof mode heavily weighted by sites in the se sector reveals the amount effect on 18o and thus its amplitude time series indicates changes in the intensity of the asian summer monsoon our eof based reconstructions of regional climate are generally consistent with the 18o records of ice cores cave speleothems and marine carbonates copyright 2008 john wiley sons ltd

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

an experimental study of secondary oil migration in a three dimensional tilted porous medium a three dimensional physical experiment was conducted to study secondary oil migration under an impermeable inclined cap light colored oil was released continuously at a slow rate of about 0 1 ml min from a point at the base of an initially water saturated porous model with buoyancy as a primary driving force a vertical cylindrical shape of an oil migration pathway was observed first and then a layer shaped lateral migration pathway was observed beneath the top inclined sealing plate once the oil cluster had reached the top cap magnetic resonance imaging was used to observe the migration processesmdashfor example morphology of the migration pathway intermittency of oil bubbles and variation of oil saturation within the migration paths results show that the snap off phenomenon related to fast local imbibition processes occurred more commonly during vertical migration than it did during lateral migration the lateral migration pathway that parallels to the top inclined cap has a typical vertical thickness of 2 to 4 cm 0 8ndash1 6 in i e roughly 40ndash80 pores this thickness is consistent with the prediction derived from scaling laws related to pore size and bond number along the lateral migration direction the sectional area and the horizontal width of the migration pathway fluctuate significantly although the average oil saturation along the pathway remains almost the same after stopping the initial oil injection the sectional area of the migration pathway shrinks significantly therefore we believe that this significant shrinking of the migration pathway is the main reason why only a relatively small volume of oil and gas has been lost during secondary migration

the cyclic hierarchy of the purbeckian sierra del pozo section lower cretaceous berriasian southern spain the lowermost cretaceous berriasian sierra del pozo formation is divisible into metre scale cycles that are bundled in a four tiered hierarchy of cycles and cyclic sequences at the smallest scale sixth order cycles thought to be the product of precessionally forced sea level fluctuations c 20 ka average less than a metre in thickness shallow upward and are bounded by surfaces where deeper facies abruptly overlie shallower facies bundles of sixth order cycles called fifth order sequences are recognized by two types of asymmetric patterns in facies distribution first more pronounced facies changes occur at sixth order cycle boundaries lower in a sequence whereas smaller facies changes occur at cycle boundaries higher in a sequence secondly subtidal marine limestones i e biomicrites and biosparites are the dominant facies lower in a cyclic sequence whereas more restricted or shallower water facies i e mud cracked microbial laminites dolomites shale and clay are more predominant higher in a cyclic sequence the bundling of sixth order cycles is explained as a product of periodic change 100 ka in the eccentricity of the earth s orbit the degree of orbital eccentricity modulates the magnitude of precessional sea level fluctuations which in turn determine the relative facies contrasts at sixth order cycle boundaries larger scale fourth and third order sequences are defined by similar patterns in facies contrast at successive sequence boundaries and by a change in predominant facies type from bottom to top these patterns are explained as the product of 400 ka and 2 ma periodic variations in the eccentricity of the earth s orbit in summary the strength of the precessional signal varies in consort with periodic changes in orbital eccentricity at three time scales producing a stacked hierarchy of cycles and sequences of cycles change in obliquity of the earth s axis may modulate the effects of the precessional signal and thereby modify patterns of preserved cyclic structure this interpretation of cyclicity in the sierra del pozo section is markedly different from that of

the global monsoon as seen through the divergent atmospheric circulation a comprehensive description is given of the global monsoon as seen through the large scale overturning in the atmosphere that changes with the seasons and it provides a basis for delimiting the monsoon regions of the world the analysis focuses on the mean annual cycle of the divergent winds and associated vertical motions as given by the monthly mean fields for 1979 93 reanalyses from the national centers for environmental prediction national center for atmospheric research ncep ncar and european centre for medium range weather forecasts ecmwf which are able to reproduce the dominant modes a complex empirical orthogonal function analysis of the divergent circulation brings out two dominant modes with essentially the same vertical structures in all months of the year the first mode which depicts the global monsoon has a simple vertical structure with a maximum in vertical motion at about 400 mb divergence in the upper troposphere that is strongest at 150 mb and decays to zero amplitude above 70 mb and convergence in the lower troposphere with a maximum at 925 mb ecmwf or 850 mb ncep however this mode has a rich three dimensional spatial structure that evolves with the seasons it accounts for 60 of the annual cycle variance of the divergent mass circulation and dominates the hadley circulation as well as three overturning transverse cells these include the pacific walker circulation an americas atlantic walker circulation both of which comprise rising motion in the west and sinking in the east and a transverse cell over asia the middle east north africa and the indian ocean that has rising motion in the east and sinking toward the west these exist year round but migrate and evolve considerably with the seasons and have about a third to half of the mass flux of the peak hadley cell the annual cycle of the two hadley cells reveals peak strength in early february and early august in both reanalyses a second monsoon mode which accounts for 20 of the variance features relatively shallow but vigorous overturning with the maximum vertical velocities near 800 mb outflow from 750 to 350 mb and inflow peaking at 925 mb it is especially strong over africa where the shallow mostly meridional overturning migrates back and forth across the equator with the seasons it influences the middle east has a signature over australia and is also an important component of the overturning in the tropical eastern pacific and atlantic and thus of the convergence zones in these regions the relationship of the global monsoon to the regional monsoons is described over six zonal sectors africa australia asia north america south america and the pacific and atlantic oceans only the two ocean areas do not undergo a seasonal reversal required for monsoons although they have direct overturning cells and they nevertheless participate in the global monsoon through the changes in large scale overturning the regional meridional cross sections highlight the importance of the shallow overturning cell in lower troposphere monsoon activity the steadiness of the overturning circulation is determined by comparing the signal of the seasonal mean vertical motions at 500 mb with the standard deviation of the transient daily variations locations where this signal exceeds 60 of the daily noise correspond closely with the regional centers of the monsoon

ice age terminations 230th dated oxygen isotope records of stalagmites from sanbao cave china characterize asian monsoon am precipitation through the ends of the third and fourthmost recent ice ages as a result am records for the past four glacial terminations can now be precisely correlated with those from ice cores and marine sediments establishing the timing and sequence of major events in all four cases observations are consistent with a classic northern hemisphere summer insolation intensity trigger for an initial retreat of northern ice sheets meltwater and icebergs entering the north atlantic alter oceanic and atmospheric circulation and associated fluxes of heat and carbon causing increases in atmospheric co2 and antarctic temperatures that drive the termination in the southern hemisphere increasing co2 and summer insolation drive recession of northern ice sheets with probable positive feedbacks between sea level and co2

carbonate cycle stacking patterns and hierarchies of orbitally forced eustatic sealevel change ordered stacking of meter scale upward shallowing cycles manifested as repeated thickness hierarchies within cratonic carbonate sequences has been considered primary evidence for causal relations between orbitally forced climate change and eustatic sealevel variation explicit in this argument is the assumption that each individual cycle represents a single sealevel rise sensitivity testing of one dimensional forward models incorporating a depth threshold of carbonate accumulation indicates that multiple upward shallowing cycles may originate during any single rise in sealevel variation in resultant cycle stacking pattern is sensitive to changes in sealevel amplitude sedimentation rate and subsidence rate with highest stacking ratios ratio of number of cyclic units to number of eustatic periods produced by low sealevel amplitudes and high sedimentation and subsidence rates these relations indicate that direct correlation between multiple frequency eustatic sealevel variations and meter scale cycle stacking hierarchies is unwarranted thus prevalent interpretations regarding the stacking record of orbital forcing in ancient carbonate rock sequences should be reevaluated

buoyancy and interfacial force effects on two phase displacement patterns an experimental study modeling secondary migration of oil currently is difficult because the physics governing the movement is complex and information on heterogeneity of carrier beds is always incomplete to better understand the basic physical process of secondary migration we discuss displacement patterns based on relative magnitudes among buoyancy interfacial and viscous forces using the results of one dimensional vertical oil water displacement experiments oil was injected at a constant rate from the lower inlet of a glass tube packed with sorted glass beads the injection pressure and oil outflow rate were measured while we observed the displacement pattern runs were done using different grain sizes and injection rates two displacement patterns were recognized during the experiments type a consisted of stable piston like displacement and type b consisted of capillary fingering the difference coincided with the relative magnitudes of the driving forces which can be characterized by the dimensionless modified bond bo and capillary ca numbers type a pattern was produced for high ca bo ratios and type b pattern for low ca bo ratios a flow regime diagram showing the regions of the two displacement patterns was constructed in ca bo space including the effects of gravity our results also showed that excess pressure for the nonwetting phase fluid to intrude into a porous medium was rate dependent

lagged response of summer precipitation to insolation forcing on the northeastern tibetan plateau during the holocene the precipitation changes on the northeastern tibetan plateau during the holocene remain unclear due to discrepancies among different proxy records we compared proxy records with the results from a transient simulation performed using the kiel climate model forced by orbital variations to analyse summer precipitation changes in this area during the holocene 9 5 0 ka bp the model results suggested increasing amounts of summer precipitation from 9 5 to 6 2 ka bp and a persistent decline thereafter which matched well with pollen records but was inconsistent with ostracod 18o records the holocene climatic optimum lagged the northern hemisphere summer insolation maximum by 3 5 ka caused by the interplay between the east asian summer monsoon easm circulation and the mid latitude westerlies the ostracod 18o values reflected the strength of the easm circulation a strong easm circulation increased the transport of water vapour towards the northeastern tibetan plateau from the northwestern pacific weakened mid latitude westerlies increased the incursion of cold air masses into the northeastern tibetan plateau during the early holocene relatively strong mid latitude westerlies resulting from an enhanced arctic oscillation reduced summer precipitation on the northeastern tibetan plateau in spite of a strong insolation driven easm circulation the weakening easm circulation and the strengthening westerlies together induced the decreasing trend of summer precipitation from the middle to late holocene in addition summer precipitation variations were further modulated by sea surface temperatures in the northwestern pacific through weakening the strength of the easm

the variation of summer monsoon precipitation in central china since the last deglaciation abstract two stalagmites c996 1 and c996 2 collected from the jiuxian cave in the shaanxi province in central china have been studied with u series dating and stable isotope analysis thirty eight 230 th dating results showed that the stalagmite c996 1 was continuously deposited through the last 8 5 ka bp thousand years before present present 1950 ad and c996 2 was deposited through the last 19 ka bp excluding two growth hiatuses between 8 3 and 5 7 ka bp and 15 4 and 11 9 ka bp with a relatively stable boundary condition we interpret the 18 o of speleothem calcite as most indicative of the amount of summer monsoon precipitation although temperature and other factors might have some minor impact the 18 o records show notable changes within the last glacial maximum lgm resembling other east asian monsoon records such as those from the hulu and sanbao caves suggesting that significant monsoonal climate changes occurred in eastern asia as far north as the qinling mountains during the lgm interval a comparison of our records to precisely dated contemporaneous speleothem records from other caves shows that the increasing trend of 18 o during the holocene commenced as early as 7 5 ka bp in the low latitude monsoonal area i e the hoti cave while at higher latitudes this shift occurred later such as 7 0 ka bp in the dongge cave 5 3 ka bp in the heshang cave 4 7 ka bp in the sanbao cave and 4 5 ka bp in the jiuxian cave these results imply an asynchronous change of the summer monsoon precipitation occurred in east asia during the holocene the asynchrony may be related to the responses of a coupled tropical and subtropical monsoon system to changes of the insolation and the differences in thermal forcing which result from the complex geographical configuration the variation of sea surface temperature sst in the western tropical pacific may also have important impacts on the summer monsoon precipitation changes in central and northern china because it affects the northwestern pacific subtropical high a monsoon front regulator more robust tests are needed to confirm this phenomenon and to evaluate the contribution of different factors in detail

the signal and the noise forward modeling of allocyclic and autocyclic processes influencing peritidal carbonate stacking patterns recent carbonate sequence stratigraphic models suggest that the degree of order present in successions of carbonate parasequences is determined by temporal variations in eustatic amplitude and by varying levels of autocyclicity ordered parasequence stacking is suggested to occur during greenhouse periods dominated by low amplitude eustatic oscillations conversely disordered vertical successions are said to occur when amplitudes of eustatic oscillations are high or when autocyclic processes dominate and thus drown the periodic external signal these assertions of causal mechanism are tested here by application of a three dimensional stratigraphic forward model the three dimensional model generates parasequences via a ginsburg type mechanism of sediment transport and shoreline progradation parasequence stacking is controlled by a superimposed longer term eustatic oscillation and parasequences generated are analyzed using runs analysis and durbin watson autocorrelation results from the modeling suggest that autocyclic parasequences generated by shoreline progradation form ordered vertical successions when accommodation changes driven by a low amplitude relative sea level oscillation suggesting that partly autocyclic strata may not be inherently any less ordered than entirely allocyclic strata addition of stochastic processes such as mosaic carbonate production and fluctuations in regional sediment transport direction tend to decrease the level of measurable order present in the autocyclic strata increasing the frequency and amplitude of relative sea level oscillations also tends to decrease the measurable order in stacked autocyclic peritidal parasequence thicknesses these results suggest that controls on parasequence stacking patterns are likely to be more complex and varied than suggested by recent sequence stratigraphic models more outcrop and modeling investigation is required with appropriately circumspect interpretations applied

thermal structure and water ice heat transfer in a shallow ice covered thermokarst lake in central qinghai tibet plateau abstract a large number of lakes and ponds are unevenly distributed over the qinghai tibet plateau qtp little is known about their ice processes and thermal regimes seasonal ice mass balance thermal regime and stratification of under ice water were investigated in a shallow thermokarst lake in central qtp using in situ observations and global reanalysis data congelation ice grew to 60 70 cm depth while continuous surface sublimation caused a total ice loss of over 30 cm the bulk lake temperature below ice remained above 3 0 c through the ice freezing period and rose gradually up to 7 9 c during the melting period the vertical thermal structure of under ice water consisted of a stable strongly stratified interfacial layer il and an underlying convective layer reaching the lake bottom a warm layer existed just beneath the il since the middle equilibrium period and increased in thickness and temperature there was seasonal variation of il depth and temperature gradient in response to the ice thermodynamics and atmospheric conditions the calculated daily water ice heat flux fw was of 10 w m 2 magnitude seasonal variation of fw manifested both diffusive and convective heat transport to the ice water interface this study suggests that strong penetration of solar radiative flux is the dominant contributor to high fw which results in a relatively thin ice compared with other equivalent high latitude climate

transient simulation of last deglaciation with a new mechanism for bolling allerod warming we conducted the first synchronously coupled atmosphere ocean general circulation model simulation from the last glacial maximum to the bolling allerod ba warming our model reproduces several major features of the deglacial climate evolution suggesting a good agreement in climate sensitivity between the model and observations in particular our model simulates the abrupt ba warming as a transient response of the atlantic meridional overturning circulation amoc to a sudden termination of freshwater discharge to the north atlantic before the ba in contrast to previous mechanisms that invoke amoc multiple equilibrium and southern hemisphere climate forcing we propose that the ba transition is caused by the superposition of climatic responses to the transient co 2 forcing the amoc recovery from heinrich event 1 and an amoc overshoot

petrofacies prediction and 3 d geological model in tight gas sandstone reservoirs by integration of well logs and geostatistical modeling abstract these effective reservoir rocks that can have sufficient porosity and permeability and hydrocarbon accumulations determine economic reserves and high yield of tight oil and gas understanding the origin and distribution of these effective reservoir rocks is important for sorting out sweet spots in tight reservoirs multiple scale analyses from the microscopic via drill core to single wellbore have been conducted to examine reservoir heterogeneity of the upper paleozoic shanxi formation in the southeastern ordos basin five sandstone petrofacies have been defined in terms of texture and framework composition detrital matrix diagenesis and pore types quartz arenite tuffaceous quartz arenite ductile lithic lean sub litharenite ductile lithic rich sandstone and tightly carbonate cemented sandstone the various petrofacies show fundamentally different pathways of diagenetic and reservoir quality evolutions due to the complexity of texture and detrital composition in the shanxi formation directly related to the provenance and depositional environment quartz arenites and ductile grain lean sub litharenites both form effective reservoir rocks by translating petrofacies to well log signatures corrected from petrographic and core analysis data a model based on factor analysis has been built to predict petrofacies at the well scale for investigating the distribution of each petrofacies at the field scale sequential indicator simulation method has been used to construct a 3 d petrofacies model with facies conditioning the isopach maps of quartz arenites and ductile lithic lean sub litharenites have been made from the 3 d petrofacies model to quantify their areal distributions and to define the sweet spots by combining isopach maps of these effective reservoir rocks and gas production data from well tests the concept of reservoir petrofacies is an important tool for the characterization of tight sandstone reservoirs

computer simulation of reef growth light is one of the major controls on reef growth and carbonate production the growth of present reef builders depends largely upon the amount of light available for photosynthesis as light decreases with water depth so does reef growth the computer model presented extends this principle by combining two functions one for photosynthesis and the other for the extinction of light in water the model is used to simulate the growth of alacran reef mexico two reefs of the great barrier reef and the reefs of the windward platform of st croix us virgin islands the model also gives an accurate simulation of the growth of fore reef walls in belize in agreement with the accretion hypothesis developed for this feature

the spatial temporal patterns of asian summer monsoon precipitation in response to holocene insolation change a model data synthesis highlights slice and transient simulations of holocene climate change were performed spatial temporal patterns of holocene asian summer precipitation are investigated a tripole pattern of summer precipitation can be seen over monsoonal asia insolation change is a key factor for holocene asian summer monsoon change internal feedbacks are important to holocene asian summer precipitation changes abstract paleoclimate proxy records of precipitation effective moisture show spatial temporal inhomogeneous over asian monsoon and monsoon marginal regions during the holocene to investigate the spatial differences and diverging temporal evolution over monsoonal asia and monsoon marginal regions we conduct a series of numerical experiments with an atmosphere ocean sea ice coupled climate model the kiel climate model kcm for the period of holocene from 9 5 ka bp to present 0 ka bp the simulations include two time slice equilibrium experiments for early holocene 9 5 ka bp and present day 0 ka bp respectively and one transient simulation ht using a scheme for model acceleration regarding to the earth s orbitally driven insolation forcing for the whole period of holocene from 9 5 to 0 ka bp the simulated summer precipitation in the equilibrium experiments shows a tripole pattern over monsoonal asia as depicted by the first modes of empirical orthogonal function eof1 of h0k and h9k the transient simulation ht exhibits a wave train pattern in the summer precipitation across the asian monsoon region associated with a gradually decreased trend in the strength of asian summer monsoon as a result of the response of asian summer monsoon system to the holocene orbitally forced insolation change both the synthesis of multi proxy records and model experiments confirm the regional dissimilarity of the holocene optimum precipitation effective moisture over the east asian summer monsoon region monsoon marginal region and the westerly dominated areas suggesting the complex response of the regional climate systems to holocene insolation change in association with the internal feedbacks within climate system such as the air sea interactions associated with the el nino southern oscillation enso and shift of the intertropical convergence zone itcz in the evolution of asian summer monsoon during the holocene

field and modelling studies of cambrian carbonate cycles virginia appalachians reply abstract field studies coupled with computer modelling of carbonate cycles in the elbrook conococheague formations middle to upper cambrian in the appalachians have helped define the mechanisms of formation the sequence is up to 1 6 km thick and composed of cyclic peritidal carbonates these formed on an aggraded rimmed shelf on a mature passive continental margin the cycles 1 7 m thick have lower parts of subtidal intertidal carbonate and caps of dolomitic laminite containing minor quartz arenite shale and breccia sedimentation rates for these peritidal carbonate environments exceeded long term subsidence of the platform 0 01 to 0 1 m 1 000 yr thus the shelf stayed near to sea level i e was aggraded milankovitch 20 000 to 100 000 yr low amplitude sea level fluctuations few meters superimposed on 3rd order sea level fluctuation of 1 to 3 m y duration and less than 20 m amplitude caused periodic submergence of the gently sloping platform less than 0 02 m km slopes resulting in deposition of over 400 peritidal cycles in about 26 m y cycles that formed during 3rd order sea level rise are thick and limestone rich whereas those formed during 3rd order fall are thin quartzose and highly dolomitized the modelling suggests that fewer and thinner cycles formed during the long term falls compared to the rises reflecting decreased accommodation cycle frequency decreases into areas of lower subsidence rate open marine cycles typical of the outer shelf and cycles formed during 3rd order sea level rise contain digitate bioherms grainstone and ribbon carbonates in lower parts they reflect high subsidence rate and an open marine setting inner shelf cycles and cycles that formed during 3rd order sea level fall commonly are thrombolitic or have thin subtidal parts grainstone conglomerate or stromatolite and reflec the low subsidence rates interior areas of quaternary carbonate shelves are characterized by incipiently drowned facies and pinnacle reefs and are punctuated by soil caliche horizons and karst surface that reflect 100 m glacio eustatic sea level fluctuations in contrast many ancient shelves like the cambro ordovician shelf of the appalachians were flat topped and dominated by cyclic peritidal sequences lacking evidence of high amplitude sea level fluctuations such aggraded shelves may represent the typical state of mature carbonate shelves that formed in response to low amplitude milankovitch sea level fluctuations as opposed to the large scale fluctuations that typified the quaternary

palaeoclimatic changes in the qinghai lake area during the last 18 000 years abstract multi proxy analysis of a sediment core from qinghai lake including pollen carbonate toc tn and 13 c of organic matter was used to document regional climatic changes during the last 18 000 years climate was very cold and dry before 16 9 cal kyr bp the warm and wet period which began at about 14 1 cal kyr bp culminated at 6 5 cal kyr bp and came to its end at about 4 5 cal kyr bp after that the climate gradually became colder and drier during the transitional period from the late glacial to the holocene the climate fluctuated frequently the short term climatic oscillations including the bolling allerod younger dryas and the cooling event at ca 8 2 cal kyr bp appear to be recorded in the qinghai lake sedimentary record the climatic evolution in the qinghai lake area during the past 18 000 years indicates that solar insolation changes on the ten thousand year scale are the likely driving force of the east asia monsoon

holocene monsoon climate documented by oxygen and carbon isotopes from lake sediments and peat bogs in china a review and synthesis there has been much recent debate about holocene climate variation in the monsoon region of china especially the temporal pattern of variations in precipitation the time transgressive nature of the holocene precipitation maximum and the extent to which variations in regions influenced by the indian summer monsoon ism and the east asian summer monsoon easm have been synchronous we summarize and compare carbonate oxygen isotope records delta o 18 carb from ten lakes within the present day ism region we discuss their paleoclimate significance considering the present day moisture source isotopic composition of precipitation and the hydrological setting the delta o 18 carb records are controlled mainly by the isotopic composition of lake water which in turn is a function of regional precipitation evaporation p e balance and the proportion of precipitation that is monsoon derived we normalized the delta o 18 carb data and used these records to generate an integrated moisture index this index along with oxygen isotope records from speleothems and carbon isotope records delta c 13 org from peats within the monsoon region suggests that holocene climate was broadly synchronous across the monsoon region and within the limits of accuracy of the existing age models provides no strong evidence for previously proposed anti phasing of the ism and the easm stable isotope records from lake sediments and peat bogs have excellent potential for providing high quality paleoclimate data for monsoon asia and complement high resolution speleothem sequences which are only found in certain localities c 2011 elsevier ltd all rights reserved

asynchronous holocene optimum of the east asian monsoon abstract the spatial and temporal distribution of summer monsoon precipitation or effective moisture during the holocene has been reconstructed on the basis of geological data including lake levels pollen profiles and loess paleosol records in addition the summer july precipitation increment effective precipitation and monsoon strength index have been obtained from numerical modeling experiments both geological data and numerical modeling indicate that the holocene optimum as defined by peak east asian summer monsoon precipitation was asynchronous in central and eastern china reaching a maximum at different times in different regions e g ca 10 000 8000 yr ago in northeastern china 10 000 7000 yr ago in north central and northern east central china ca 7000 5000 yr ago in the middle and lower reaches of the yangtze river and ca 3000 yr ago in southern china in southwestern china the maximum appeared ca 11 000 yr ago but probably was related to the maximum landward extension of the indian summer monsoon the regional shift in the maximum precipitation belt from northwest to southeast over the past 10 000 yr is interpreted as a response to changing seasonality related to orbital forcing of the climate the southeastward shift of the east asian summer monsoon maximum is consistent with the progressive weakening of the summer monsoon as the summer solar radiation anomaly decreased progressively through the holocene and the east asian monsoon index declined while the early maximum in southwestern china matches the maximum of the indian monsoon index

quantitative assessment of petroleum loss during secondary migration in the yaojia formation ne songliao basin ne china abstract in the nw songliao basin ne china petroleum is produced from fluvio deltaic sandstones in the upper cretaceous yaojia formation source rocks are dark colored lacustrine shales of the qinshankou formation in this paper two models were developed to characterize the petroleum migration pathways in the lower member member 1 of the yaojia formation in the first model which applies to the northern region of the study area petroleum migrates only in the lowermost carrier bed in member 1 immediately above the area of the source kitchen and later in multiple carrier beds outside this area in the second model which represents migration patterns in the central and southern regions of the study area petroleum migrates in multiple carrier beds both within and outside the area of the source kitchen pressures in the yaojia formation were inferred to be hydrostatic while petroleum expulsion and migration took place therefore seven migration accumulation i e local palaeo drainage systems were defined according to the fluid potential gradients migration loss was found to vary markedly between migration accumulation systems in the study area and was controlled by factors including the shape width and area of the effective source rocks the thickness and distribution of carrier beds inside the source area the migration distance outside the source area and the number of carrier beds involved in petroleum migration using these two models petroleum loss during secondary migration was estimated the loss during secondary migration was approximately 5 21 billion bbl of petroleum which is approximately 6 of the petroleum expelled into the first member of the yaojia formation nearly 80 of the total migration loss occurred in all the carrier beds above the source area

effects of temperature and humidity upon the transport of sedimentary particles by wind aeolian transport of sedimentary particles is a well recognized phenomenon in cold regions but the effect of low temperature t and specific humidity q upon particle entrainment has not previously been investigated this study reports on wind tunnel experiments 12 c t 32 c and 1 g kg 1 q 10 g kg 1 that suggest the aerodynamic drag required to entrain sand sized particles can be 30 lower in cold or high latitude settings as compared to hot deserts for any given regional wind velocity this effect will increase the wind strength index and thereby the proportion of time a surface is active at low temperature

the verification of millennial scale monsoon water vapor transport channel in northwest china summary long term changes of the asian summer monsoon water vapor transport play a pivotal role in the variability of monsoon precipitation paleo climate simulations have shown that there is an important monsoon vapor transport channel in western china previous studies mostly focused on the correlation between monsoon precipitation and intensity little research has been done on the verification of the water vapor channel compared with speleothem and lacustrine systems the hydrological cycle of land surface sediments is more directly related to the monsoon water vapor in this study we used carbonate 18 o and organic matter 13 c of the surface eolian sediments from the piedmont of the northern qilian mountains to verify the monsoon water vapor on the holocene millennial scale two surface sedimentary sections were selected to study paleo monsoon water vapor transport proxy data including carbonate 18 o and organic matter 13 c of surface eolian sediments as well as total organic matter and carbonate content were obtained from the two eolian sections we also synthesized transient simulations of the ccsm3 and the kiel climate models the pmip 3 0 project and trace isotopic simulations were also compared with the reconstructed monsoon water vapor transport our findings indicate that the strength of the holocene asian summer monsoon is consistent with the water vapor transport in western china that has significant impacts to long term monsoon precipitation in northern china this study verifies a significant millennial scale correlation between the monsoon strength and monsoon water vapor transport intensity along the eastern qinghai tibet plateau

response of the african monsoon to orbital forcing and ocean feedbacks in the middle holocene simulations with a climate model that asynchronously couples the atmosphere and the ocean showed that the increased amplitude of the seasonal cycle of insolation in the northern hemisphere 6000 years ago could have increased tropical atlantic sea surface temperatures in late summer the simulated increase in sea surface temperature and associated changes in atmospheric circulation enhanced the summer monsoon precipitation of northern africa by more than 25 percent compared with the middle holocene simulation with prescribed modern sea surface temperatures and provided better agreement with paleorecords of enhanced monsoons

petroleum migration faults and overpressure part ii case history the haltenbanken petroleum province offshore norway abstract petroleum inclusion and geochemical data from core extracts were applied to deduce a model for oil migration overpressure development and palaeo leakage of oil from currently dry structures in the haltenbanken vest area the existence of fluorescent oil type inclusions in quartz in the smorbukk asgard 2 field suggest that oil migrated into this structure 70 50 million years before present ma bp this is also the case for the dry structures 6506 12 4 6506 11 3 and 6506 11 1 west of the main smorbukk fault zone black oil inclusions with medium gas oil ratio gor occur in these fields together with condensate type petroleum inclusions this suggests that the dry structures transformed from containing oil to condensate before leakage petroleum extracted from inclusions in these structures and in nearby fields have identical marine type ii kerogen signatures source rocks at the spekk formation level in the current drainage area of smorbukk and these dry structures were immature 70 50 ma bp and the smorbukk sor asgard 3 field did not fill at this early time thus oil must initially have entered into smorbukk from areas to the w sw through the currently pressure sealing smorbukk fault zone which today marks the westward limit of the smorbukk field diagenesis in this fault zone caused the much later overpressure development and petroleum was lost from the 6506 12 4 6506 11 3 and 6506 11 1 structures as overpressure built up regionally petroleum loss from these structures with their often thick seals must have occurred via self propagating open fracture induced mechanisms lack of petroleum in the cretaceous strata above these structures suggests that leakage occurred to even shallower strata this could imply that the cretaceous strata in halten vest were overpressured at the time of leakage in contrast the oil in the cretaceous lysing and lange formation above the jurassic reservoirs in smorbukk and smorbukk sor most likely originated based on geochemistry and gors from the jurassic reservoirs below and not from cretaceous strata this migration event would have been facilitated if it occurred before these sands became overpressured as they are today modelling suggests that the spekk formation became mature in the smorbukk sor region

scaled physical model of secondary oil migration a scaled physical model was constructed to simulate gravity and capillary controlled flow of oil into a water saturated sand during secondary hydrocarbon migration the model provided both visualization of the flow patterns and estimates of hydrocarbon transport rates and efficiencies the dimensions and physical properties of the model were designed so the balance of gravity capillary and viscous forces was the same in the model as in the geologic system the physical model was a sand pack between glass plates the pack was 52 cm high 100 cm long 2 5 cm thick and inclined at a 5 dip its porosity was 42 and its permeability was 7 0 10 10 m2 710 d it modeled a geologic carrier bed 27 m thick with 20 porosity and 9 9 10 14 m2 100 md permeability overlying a source rock a dyed oil was injected into the lowest corner at a rate of 1 cm3 day and it exited the highest corner at atmospheric pressure oil movement was followed both visually and by ultrasonic velocity measurements the behavior of fluids in the model led us to the following conclusions for oil transport through water wet homogeneous carrier beds the rate limiting step in charging a trap is not secondary migration but rather the rate of oil release from the source rock high hydrocarbon loss may occur during vertical migration when the carrier bed lies above the source because of extensive dispersion losses during lateral migration are probably minimal because flow is concentrated below the top seal

chinese stalagmite δ 18 o controlled by changes in the indian monsoon during a simulated heinrich event carbonate cave deposits in india and china are assumed to record the intensity of monsoon precipitation because the 18 o of the carbonate tracks the isotopic signature of precipitation these records show spatially coherent variability throughout the last ice age and suggest that monsoon strength was altered during the millennial scale climate variations known as dansgaard oeschger events and during the heinrich cooling events here we use a numerical climate model with an embedded oxygen isotope model to assess what caused the shifts in the oxygen isotope signature of precipitation during a climate perturbation designed to mimic a heinrich event our simulations show that a sudden increase in north atlantic sea ice extent during the last glacial period leads to cooling in the northern hemisphere reduced precipitation over the indian basin and weakening of the indian monsoon the precipitation is isotopically heavier over india and the water vapour exported to china is isotopically enriched our model broadly reproduces the enrichment of 18 o over northern india and east asia evident in speleothem records during heinrich events we therefore conclude that changes in the 18 o of cave carbonates associated with heinrich events reflect changes in the intensity of indian rather than east asian monsoon precipitation

westerly jet stream controlled climate change mode since the last glacial maximum in the northern qinghai tibet plateau abstract climate change from the northern qinghai tibet plateau qtp is affected by the combined effects of the asian summer monsoon and the westerlies however changes in monsoon vapor transport and the westerly jet stream as well as their effect to climate change mode there are not clear at different time scales here we present composite research using paleoclimate reconstructions and ensemble simulations since the last glacial maximum lgm on the basis of an eolian sedimentary sequence in the northern qtp results from 317 surface sediment samples show that pedogenic carbonate 18 o is affected both by precipitation and temperature and organic carbon isotope 13 corg reflects the vegetation growth status in areas where precipitation is greater than 290 mm proxies from the sedimentary sequence and the paleoclimate modeling intercomparison project 3 pmip3 simulations show a close relationship between climate change mode in the northern qtp and the westerly jet stream whose movement is triggered by warm or cold conditions in the high latitude regions that is when the climate is in cold glacial period the westerly jet stream strengthens and moves southward and the mountains become wetter this climate change mode can be validated by records from mountains of north america and africa according to the cmip5 simulations the westerly jet stream will strengthen in the future and climate in the northern qtp and the high altitude region of the mid latitudes will become wetter with global warming

periodicity of mesoscale phanerozoic sedimentary cycles and the role of milankovitch orbital modulation data on more than 200 mesoscale sedimentary cycles indicate that phanerozoic cycle periods are randomly distributed with respect to the four major milankovitch orbital parameters except late mississippian through late pennsylvanian cycles which show positive clustering about the 413 000 yr eccentricity period cycle periods calculated from average thicknesses and accumulation rates are strongly dependent on the former correlation coefficient 0 802 but relatively independent of the latter correlation coefficient 0 360 hence calculated period is largely a function of average cycle thickness and milankovitch range periods will be preferentially calculated for cycles with average thicknesses between 1 m and 20 m regardless of actual causes of cyclicity for individual cyclic sequences arguments for milankovitch control based solely on average period are unfounded comparison of short term holocene sedimentation rates and long term phanerozoic accumulation rates for cyclic peritidal and delta

holocene variations in the asian monsoon inferred from the geochemistry of lake sediments in central tibet we present a record of monsoon variations for the early and middle holocene that is inferred from the geochemistry of sediment cores from ahung co a lake in central tibet the resolution of this record is better than 50 yr and the age model is derived from radiocarbon ages of terrestrial charcoal which eliminates errors associated with the lake hard water effect we made down core geochemical measurements of carbonate organic carbon c n and 13c of bulk organic matter 13c and 18o of carbonate and dolomite proxy calibration and modern water balance reconstruction show that these are proxies for lake depth and the amount of monsoon precipitation we find that lake level and monsoon precipitation have been decreasing at ahung co since the early holocene 7500 cal yr b p superimposed on this trend are rapid declines in monsoon rainfall at 7000 7500 and 4700 cal yr b p and seven century scale wet dry oscillations the cores do not contain sediment from the last 4000 yr surface sediments from the lake accumulated during the 20th century however from this we argue that lake levels have risen again recently following a late holocene dry period

holocene moisture evolution in arid central asia and its out of phase relationship with asian monsoon history we synthesize palaeoclimate records from the mid latitude arid asian region dominated today by the westerlies arid central asia aca to evaluate spatial and temporal patterns of moisture changes during the holocene sediment records from i i takes with reliable chronologies and robust proxies were selected to reconstruct moisture histories based on a five class ordinal wetness index with assigned scores from the driest to wettest periods at individual sites for 200 year time slices the proxies used in these records include pollen and diatom assemblages sediment lithology lake levels and geochemistry mainly isotope data the results of our synthesis show that aca as a whole experienced synchronous and coherent moisture changes during the holocene namely a dry early holocene a wetter less dry early to mid holocene and a moderately wet late holocene during the early holocene most of the lakes experienced very low water levels and even dried out before ca 8 ka 1 ka 1000cal a bp hence the effective moisture history in aca is out of phase with that in monsoonal asia as documented by numerous palaeoclimate records in monsoonal asia a strong summer monsoon and humid climate characterized the early holocene and a weakened summer monsoon and drier climate prevailed during the late holocene which were mainly controlled by changes in low latitude summer insolation in contrast we propose that the pattern of holocene effective moisture evolution in the westerly dominated aca was mainly determined by north atlantic sea surface temperatures ssts and high latitude air temperatures that affect the availability amount and transport of water vapor also topography of the tibetan plateau and adjacent asian highlands could have contributed to the intensification of dry climate in aca during the early holocene as a result of strengthening the subsidence of dry air masses associated with stronger uplift motion on the plateau by intense heating under a stronger summer insolation summer insolation might have played a key role in directly controlling moisture conditions in aca but only after the northern hemisphere ice sheets had disappeared in the mid and late holocene c 2007 elsevier ltd all rights reserved

on the interpretation of shallow shelf carbonate facies and habitats how much does water depth matter abstract many stratigraphic studies of ancient shallow water carbonate platforms focus interpretation on the primacy of changes in accommodation inferred by assuming a direct and deterministic link between depositional facies and water depth the purpose of this study is to test this assumption explicitly and quantitatively by exploring relations between substrate type classified on the basis of both habitats and facies and the water depth at which they occur on a modern well studied shallow rimmed shelf margin gis analysis of digital benthic habitat and bathymetry maps of the shallow 8 m south florida shelf illustrate that most substrate types occur across a range of water depths similarly at greater water depths habitats and facies are more constrained more dominance of one class more deterministic with generally decreasing dominance more diversity at shallower water depths at a scale of shelf to basin transects facies and habitats clearly are related to water depth yet on this narrower 10 km shallow shelf margin at the scale of this study water depth and habitats and facies are not uniquely related or linked this general lack of correspondence between bottom type and water depth may be a manifestation of landscape disequilibrium a state in which habitats and facies do not fully reflect ambient environmental conditions perhaps recording the influence of rapid change in sea level alternatively it may reflect the impact of variables other than water depth although more general consequences of these results for other depositional settings remains to be evaluated they do emphasize the fact that variables other than bathymetry may significantly influence the ecological and sedimentologic attributes of depositional surfaces they do allow for the quantification of some of the potential uncertainties inherent in the interpretation of analogous ancient platforms and can serve to focus future observations on the causes and consequences of vertical and lateral heterogeneity in ancient stratigraphic sequences

palaeoclimatic changes deduced from 13c 12c and c n ratios of karewa lake sediments india most long palaeoclimatic records based on isotope studies have come from deep sea cores however in order to obtain information on regional climatic variations it is essential to study continental deposits the chief limitation has been the lack of well preserved datable geological records with the exception of cave formations we report here values for the stable carbon isotope ratio 13c 12c and the elemental carbon to nitrogen c n ratio of the organic fraction of the palaeomagnetically and radiometrically dated pleistocene karewa lake sediments from kashmir india together the two ratios which are anticorrelated provide an excellent marker of the source of organic matter in the lake the karewa sediments indicate at least three major episodes of shallower than normal levels these episodes of shallow lake levels and hence a cold dry climatic regime are broadly correctable with deep sea records

principles of geochemical prospect appraisal our current understanding of the geochemical processes responsible for the creation of commercial accumulations of oil and gas can be reduced to simple rules and equations to allow the petroleum geologist to use geochemistry to estimate before drilling the likely volumes and compositions of oil and gas delivered to the trap in most sedimentary basins oil is expelled from source rocks between 120 and 150 c whereas most gas and gas condensate are released between 150 and 230 c when the initial potential of source rocks exceeds 10kg mt oil expulsion efficiencies are between 60 and 90 expelled oil and gas migrate as petroleum rich phases driven by fluid potential gradients most flow is laterally updip in beds with effective horizontal permeabilities greater than 1 md in lower permeability rocks the petroleum fluids move vertically up or down along the path of least resistance i e the most permeable or thinnest beds separating them from a high permeability lateral carrier bed the residual saturations of petroleum left behind along the migration pathway are of the order of a few percent of the porosity geochemical analysis of source rocks helps determine the yields and compositions of petroleum fluids expelled in the catchment area of a prospect these fluid masses are converted to volumes from knowledge of the phase relations and densities of petroleum fluids evaluation of the total volume of rock through which the petroleum potentially can migrate and the mean porosity of the rocks that constitute the migration pathway allow migration losses to be assessed these losses constrain both the range of migration of petroleum fluids away from the mature source rock and the volumes of petroleum remaining for entrapment in the prospect

on the labeling length and objective basis of fischer plots abstract fischer plots of the accumulation of shallow marine carbonate cycles track the cumulative departure from mean cycle thickness through a vertical sequence of contiguous upward shallowing units this is a simple objective treatment of residuals in a time series and is applicable to other stratigraphic phenomena to reflect the noninterpretive construction of fischer plots the vertical axis should be labeled cumulative departure from mean cycle thickness and the horizontal axis cycle number the typical fischer plot is an erratic bridge that begins and ends at the same elevation but has the form of an irregular train of asymmetric waves which rise steeply and fall gradually the asymmetry of the individual waves arises because thinner than average cycles typically outnumber thick r cycles two to one the overall form of the wave train is sensitive to mean cycle thickness but can guide correlation and may have considerable interpretive potential provided that enough cycles are included to ensure a robust estimate of mean thickness runs tests demonstrate that fischer bridges for peritidal carbonates are unlikely to be the result of random stacking processes since this anticipated result does not emerge unequivocally for fischer plots of less than 50 cycles however we recommend against plotting such short sections

a high resolution absolute dated holocene and deglacial asian monsoon record from dongge cave china abstract we present a continuous record of the asian monsoon over the last 16 ka from 18o measurements of stalagmite calcite over 900 oxygen isotopic measurements providing information on shifts in monsoon precipitation are combined with a chronology from 45 precise 230th dates 18o and therefore asian monsoon intensity generally follows changes in insolation although changes in 18o are generally accommodated in abrupt shifts in contrast to smoothly varying insolation indicating that threshold effects may be important 18o decreased dramatically 3 at the start of the holocene 11 5 ka and remained low for 6 ka four positive 18o events centered at 11225 97 yr bp 1 05 10880 117 yr bp 1 15 9165 75 yr bp 1 4 and a double event centered at 8260 64 yr bp 1 1 and 8080 74 yr bp 1 0 punctuated this period of high monsoon intensity all four events correlate within error with climate changes in greenland ice cores thus the relationship between the asian monsoon and the north atlantic observed during the glacial period appears to continue into the early holocene in addition three of the four events correlate within error with outburst events from lake agassiz the decline of monsoon intensity in the mid late holocene is characterized by an abrupt positive shift in 18o which occurs at 3550 59 yr bp 1 1 in 100 yr in addition the holocene is punctuated by numerous centennial and multi decadal scale events amplitudes 0 5 to 1 up to half the amplitude of the glacial interstadial events seen in the last glacial period thus holocene centennial and multi decadal scale monsoon variability is significant although not as large as glacial millennial scale variability the monsoon shows a strong connection with northern south american hydrological changes related by changes in itcz position spectral analysis of the 18o record shows significant peaks at solar periodicities of 208 yr and 86 yr suggesting variation is influenced by solar forcing however there are numerous other significant peaks including peaks at el nino frequencies observed for high resolution portions of the record between 8110 and 8250 yr which suggest that changes in oceanic and atmospheric circulation patterns in addition to those forced by solar changes are important in controlling holocene monsoon climate in addition for this high resolution portion we observe a distinctive biennial oscillation of the asian monsoon which has been associated with the tropospheric biennial oscillation tbo

material balance assessment of the new albany chesterian petroleum system of the illinois basin the new albany chesterian petroleum system of the illinois basin is a well constrained system from which petroleum charges and losses were quantified through a material balance assessment this petroleum system has nearly 90 000 wells penetrating the chesterian section a single new albany shale source rock accounting for more than 99 of the produced oil well established stratigraphic and structural frameworks and accessible source rock samples at various maturity levels a hydrogen index hi map based on rock eval analyses of source rock samples of new albany shale defines the pod of active source rock and extent of oil generation based on a buoyancy drive model the system was divided into seven secondary migration catchments each catchment contains a part of the active pod of source rock from which it derives a petroleum charge and this charge is confined to carrier beds and reservoirs within these catchments as accountable petroleum petroleum losses or undiscovered petroleum a well constrained catchment with no apparent erosional or leakage losses is used to determine an actual petroleum charge from accountable petroleum and residual migration losses this actual petroleum charge is used to calibrate the other catchments in which erosional petroleum losses have occurred petroleum charges determined by laboratory pyrolysis are exaggerated relative to the actual petroleum charge rock eval charges are exaggerated by a factor of 4 14 and hydrous pyrolysis charges are exaggerated by a factor of 1 7 the actual petroleum charge provides a more meaningful material balance and more realistic estimates of petroleum losses and remaining undiscovered petroleum the total petroleum charge determined for the new albany chesterian system is 78 billion bbl of which 11 4 billion bbl occur as accountable in place petroleum 9 billion bbl occur as residual migration losses and 57 6 billion bbl occur as erosional losses of the erosional losses 40 billion bbl were lost from two catchments that have highly faulted and extensively eroded sections anomalies in the relationship between erosional losses and degree of erosion suggest there is potential for undiscovered petroleum in one of the catchments these results demonstrate that a material balance assessment of migration catchments provides a useful means to evaluate and rank areas within a petroleum system the article provides methodologies for obtaining more realistic petroleum charges and losses that can be applied to less data rich petroleum systems

millennial scale erosion rates in three inland drainage basins and their controlling factors since the last deglaciation arid china abstract in the regions surrounding the qinghai tibet plateau changes in erosion rates have been linked to the tectonics climate and topography over different time scales to understand the mechanisms governing the changes of erosion rates it is important to study erosion rates by different methods and for different time scales in inland drainage basins deposition rates of terminal lake sediments can indicate basin wide erosion rates at the millennial scale this paper presents three lake records of the last deglaciation and holocene huahai lake zhuye lake and yanchi lake from the hexi corridor north of the qilian mountains in arid china organic matter terrestrial pollen concentrates seeds grasses and plant debris are used for conventional and ams 14 c dating on the basis of 66 radiocarbon dates lithology and grain size we infer relatively high basin wide erosion rates during the last deglaciation and early holocene in the three drainage basins when the three lake sediments were seriously affected by reworking the deposition rates were an order of magnitude or greater in these lakes during the last deglaciation and early holocene than during the mid to late holocene during the transition period of the last glacial interglacial cycle significant climatic changes occurred in east and central asia corresponding to the strengthening of the asian summer monsoon and to increasing effective moisture in arid central asia which can have strong impacts on basin wide erosion rates north of the qinghai tibet plateau moreover melting glaciers in the qilian mountains probably also contributed to the high basin wide erosion rates at the same time tectonic activity was not recognizable in the study area during that period in the arid and semiarid regions surrounding the qinghai tibet plateau dramatic changes in erosion rates appear during the transition periods of the glacial interglacial cycles which illustrate the climatic controls on erosion rates at this time scale

holocene forcing of the indian monsoon recorded in a stalagmite from southern oman a high resolution oxygen isotope record from a thorium uranium dated stalagmite from southern oman reflects variations in the amount of monsoon precipitation for the periods from 10 3 to 2 7 and 1 4 to 0 4 thousand years before the present ky b p between 10 3 and 8 ky b p decadal to centennial variations in monsoon precipitation are in phase with temperature fluctuations recorded in greenland ice cores indicating that early holocene monsoon intensity is largely controlled by glacial boundary conditions after approximately 8 ky b p monsoon precipitation decreases gradually in response to changing northern hemisphere summer solar insolation with decadal to multidecadal variations in monsoon precipitation being linked to solar activity

asian summer monsoon instability during the past 60 000 years magnetic susceptibility and pedogenic evidence from the western chinese loess plateau abstract the 28 m high resolution shajinping loess section in lanzhou on the western chinese loess plateau records a 60 ka millennial summer monsoon variation the record shows that asian summer monsoons have rapid episodic pulse enhancements spanning only ca 1 2 ka in high frequency domain and having sub milankovitch cycles of progressive weakening in low frequency domain in the last glaciation soil formation seems to occur with a surprisingly fast response to these summer monsoon enhancements resulting in weakly or moderately developed paleosol sequences both the pattern and timing of the summer monsoon enhancements show that they can be correlated to most major warm dansgaard oeschger episodes and long term cooling bond cycles of the north atlantic climatic records indicating a possible teleconnection between tropic oceanic air masses and the north atlantic climatic system but differences exist for the transition of mis 2 3 and the holocene where extraordinarily heavy dust input events and fairly variable climatic fluctuations occur for the former and latter respectively a westerlies swing model is proposed to interpret this link

how to measure the strength of the east asian summer monsoon defining the intensity of the east asian summer monsoon easm has been extremely controversial this paper elaborates on the meanings of 25 existing easm indices in terms of two observed major modes of interannual variation in the precipitation and circulation anomalies for the 1979 2006 period the existing indices can be classified into five categories the east west thermal contrast north south thermal contrast shear vorticity of zonal winds southwesterly monsoon and south china sea monsoon the last four types of indices reflect various aspects of the leading mode of interannual variability of the easm rainfall and circulations which correspond to the decaying el nino while the first category reflects the second mode that corresponds to the developing el nino the authors recommend that the easm strength can be represented by the principal component of the leading mode of the interannual variability which provides a unified index for the majority of the existing indices this new index is extremely robust captures a large portion 50 of the total variance of the precipitation and three dimensional circulation and has unique advantages over all the existing indices the authors also recommend a simple index the reversed wang and fan index which is nearly identical to the leading principal component of the easm and greatly facilitates real time monitoring the proposed index highlights the significance of the mei yu baiu changma rainfall in gauging the strength of the easm the mei yu which is produced in the primary rain bearing system the east asian ea subtropical front better represents the variability of the easm circulation system this new index reverses the traditional chinese meaning of a strong easm which corresponds to a deficient mei yu that is associated with an abnormal northward extension of southerly over northern china the new definition is consistent with the meaning used in other monsoon regions worldwide where abundant rainfall within the major local rain bearing monsoon system is considered to be a strong monsoon

mid holocene moisture maximum revealed by ph changes derived from branched tetraethers in loess deposits of the northeastern tibetan plateau abstract the patterns of holocene moisture variability inferred from different proxies remain controversial in the northeastern tibetan plateau netp which impedes our understanding of the behavior and dynamics of the east asian summer monsoon easm here we present two ph records spanning the last 12 kyr from well dated loess paleosol sections ywy14 and shd09 from the netp based on the modified cyclization ratio index cbt of the branched glycerol dialkyl glycerol tetraethers brgdgts and regional cbt ph empirical relationship the reconstructed ph values from topmost samples are consistent with the instrumental ph values of the surrounding surface soil our results illustrate generally similar ph trends from two loess sections characterized by alkaline conditions from 12 0 to 8 5 cal kyr bp neutral or acidic during the mid holocene and alkaline conditions again during the late holocene the intervals of lowest cbt derived ph values during the mid holocene in our records correlate with those of highest tree pollen percentage from adjacent lake sediments and the regionally weakest aeolian activity from records of paleosol development synthesized from the chinese loess plateau clp in northern china suggesting a moisture maximum during that period taken together we conclude that cbt derived ph variability can be potentially used as an indicator of easm evolution and the wettest climate occurred during the mid holocene in the netp the changes in summer precipitation during the holocene on the netp can be attributed to the interaction between the mid latitude westerlies and the easm circulation

orbital scale timing and mechanisms driving late pleistocene indo asian summer monsoons reinterpreting cave speleothem δ18o 1 southeast china cave 18o often interpreted as a pure east asian summer monsoon proxy lags maximum northern hemisphere summer insolation by 2 9 0 3 kyrs at the precession cycle the arabian sea summer monsoon stack lags by 8 1 kyr consistent with 13 other indian and east asian summer monsoon proxies from marine lake and terrestrial archives this 5 kyr phase difference cannot be attributed to age control inadequacies in the marine chronology it requires reconciliation in the context of proxy interpretation both of these lags are incompatible with a direct response to northern hemisphere summer insolation implicating additional forcing mechanisms analysis of heterodynes in the cave 18o spectrum demonstrates that variance contained in the arabian sea summer monsoon proxies also resides in the cave 18o record this variance is subtracted from the cave 18o record yielding a residual that is highly coherent and in phase with precession minima reflecting the impact of winter temperature change on cave 18o meteorological precipitation under cold conditions thus we argue that the timing of light cave 18o peaks cannot be interpreted as reflecting the timing of strong summer monsoons alone the 2 9 kyr precession band phase lag of cave 18o reflects the combined influence of summer monsoon forcing with a phase lag of 8 kyrs relative to precession minima and winter temperature forcing that is in phase with precession minima this interpretation is consistent with modern seasonality in the amount and isotopic composition of rainfall in southeast china

global glacial isostasy and the surface of the ice age earth the ice 5g vm2 model and grace abstract the 100 kyr quasiperiodic variation of continental ice cover which has been a persistent feature of climate system evolution throughout the most recent 900 kyr of earth history has occurred as a consequence of changes in the seasonal insolation regime forced by the influence of gravitational n body effects in the solar system on the geometry of earth s orbit around the sun the impacts of the changing surface ice load upon both earth s shape and gravitational field as well as upon sea level history have come to be measurable using a variety of geological and geophysical techniques these observations are invertible to obtain useful information on both the internal viscoelastic structure of the solid earth and on the detailed spatiotemporal characteristics of glaciation history this review focuses upon the most recent advances that have been achieved in each of these areas advances that have proven to be central to the construction of the refined model of the global process of glacial isos

carbonate leaching processes in the red clay formation chinese loess plateau fingerprinting east asian summer monsoon variability during the late miocene and pliocene 1 high resolution variations in carbonate minerals from the jiaxian red clay section located at the northern limit of the present east asian summer monsoon easm on chinese loess plateau were quantified using fourier transform infrared spectroscopy we analyzed a large quantity of sediments dated from the late miocene to pliocene 8 2 2 6 ma the carbonates in this interval show high frequency variations alternating between leached and calcareous horizons the low carbonate contents and high values of magnetic susceptibility and high rb sr ratios were found in the leached zones a pattern that is consistent with that observed in the overlying quaternary loess paleosol sequences this pattern suggests that east asian monsoon eam rainwater enhanced leaching and accumulation processes of carbonate minerals in the red clay formation in a way similar to the loess paleosol sequence seven alternating leached and calcareous zones are identified suggesting oscillations of the easm and east asian winter monsoon intervals the calcareous zones were also found to have high zr rb ratio these indications of shifts from a strong easm to east asian winter monsoon dominance correlate well with the cooling transition indicated by deep sea 18o isotopes this evidence suggests that the eam was active during the late miocene and pliocene and was similar to the quaternary monsoon the presence of a strong eam during the pliocene warm period also raises questions about the hypothesis that past and future warm climate conditions could produce a permanent el nino like state

timing duration and transitions of the last interglacial asian monsoon thorium 230 ages and oxygen isotope ratios of stalagmites from dongge cave china characterize the asian monsoon and low latitude precipitation over the past 160 000 years numerous abrupt changes in 18o 16o values result from changes in tropical and subtropical precipitation driven by insolation and millennial scale circulation shifts the last interglacial monsoon lasted 9 7 1 1 thousand years beginning with an abrupt less than 200 years drop in 18o 16o values 129 3 0 9 thousand years ago and ending with an abrupt less than 300 years rise in 18o 16o values 119 6 0 6 thousand years ago the start coincides with insolation rise and measures of full interglacial conditions indicating that insolation triggered the final rise to full interglacial conditions

oxygen 18 and carbon 13 records for the last 14 000 years from lacustrine carbonates of siling co lake in the qinghai tibetan plateau to understand paleoenvironmental changes for the central qinghai tibetan plateau we analyzed stable isotopes of oxygen and carbon from calcium carbonates in a bottom sediment core collected from siling co lake five conventional and two tams 14c dates indicate that the core recovered sediments of the last 14 000 years calcium carbonates in the sediments seem to be primary carbonates precipitated chemically in the lake and not clastic particles from limestones distributed around the lake because of large variation of isotopic ratios isotopic covariance since 6 000 yr bp and similarity between dates from total calcium carbonates and organic carbon their isotopic composition therefore reflects that of the lake water we present the following paleoenvironmental history over the last 14 000 years in the central part of the plateau from secular variations of 18o 13c and caco3 content throughout the core 1 desiccation was dominant during the latter part of the last glacial stage 14 000 to 11 000 yr bp 2 the last glacial stage abruptly terminated at 11 000 yr bp 3 a temperate and stable climate was dominant from 11 000 to 5 000 yr bp 4 climatic conditions fluctuated from 5 000 to the present including two strong desiccation periods 5 000 to 4 000 yr bp and 3 000 to 2 000 yr bp and an intermediate period of heavy rainfall 4 000 to 3 000 yr bp this period is also characterized by a covariant o and c isotopic trend

petroleum migration and accumulation modeling and applications subsurface hydrocarbon observations at any scale serve as critical clues to understand and reconstruct migration pathways and charge histories through geological time to assess the risk of petroleum exploration targets hydrocarbon migration commonly occurred millions of years ago and the pathways can rarely be observed in wells or in outcrops therefore hydrocarbon migration modeling tools are important to test and quantify the processes and elements which impact hydrocarbon migration this paper presents a new method of analyzing migration in superimposed basins which have experienced multiple stages of basin subsidence and inversion during which multiple episodes of hydrocarbon generation migration and accumulation occurred the new modeling method first identifies the character of the migration and accumulation units by synthesizing geological factors such as heterogeneity of carrier beds and reservoirs second hydrocarbon migration is analyzed as a geologic process for which the invasion percolation ip migration method seems to be most suitable the ip migration method demonstrates a good relationship between migration driving and resisting forces along pathways and thus can be used to reasonably model hydrocarbon migration processes at any scale of units in a basin the new migration method provides insights into quantitative methods that can be applied to petroleum system analysis the new method has been applied to several chinese basins and has proven to be useful for defining exploration targets and resource assessments in mature frontier and especially tectonically complex basins a case study of the upper triassic chang 7 and chang 8 units in the southern ordos basin central china is presented to demonstrate a multistage hydrocarbon accumulation unit modeling results show that the same pairs of reservoir seal sets contained different accumulation units in the geological past with different styles of hydrocarbon migration and different accumulation patterns it can be concluded that the style and character of early hydrocarbon migration have significantly affected the more recent hydrocarbon migration and the present day distribution of hydrocarbons