patterns of imbricate thrusting through the use of seismic reflection profiles satellite images and balanced kinematic models we describe patterns that help to identify imbricate structures and define the sequence of thrusting in fold and thrust belts measures of folding shear strains are employed to define break forward systems in which younger deeper faults refold overlying thrust sheets in contrast break backward sequences form a wide range of viable geometries that are not expected to conserve these folding strains thus measures of folding shear strains provide a means to define thrusting sequence we also explore map view patterns of imbricate thrusting by using three dimensional models and stereoscopic satellite images we present an example from the peruvian andes in which these map patterns are combined with seismic reflection profiles to define a complex imbricate system with components of both break forward and break backward thrusting these integrated methods provide new tools for understanding the deformational histories of fold and thrust belts including the definition of complex structural closures with opportunities for hydrocarbon reservoir duplication

exxon global cycle chart an event for every occasion the basic premise of the recent exxon cycle chart that there exists a globally correlatable suite of third order eustatic cycles remains unproven many of the tests of this premise are based on circular reasoning the implied precision of the exxon global cycle chart is not supportable because it is greater than that of the best available chronostratigraphic techniques such as those used to construct the global standard time scale correlations of new stratigraphic sections with the exxon chart will almost always succeed because there are so many exxon sequence boundary events from which to choose this is demonstrated by the use of four synthetic sections constructed from tables of random numbers a minimum of 77 successful correlations of random events with the exxon chart was achieved the existing cycle chart represents an amalgam of regional and local tectonic events and probably also includes unrecognized miscorrelations it is of questionable value as an independent standard of geologic time

a physical explanation of the relation between flank uplifts and the breakup unconformity at rifted continental margins rift flank uplifts and the breakup or postrift unconformity are characteristic features of many rifted passive or atlantic type continental margins but are not predicted as primary features of simple lithospheric stretching models the explanations that have been proposed for their origin remain controversial either because they call upon special circumstances or because they are difficult to test plane strain finite element models are used in this paper to explore the dynamics of lithospheric necking during rifting and rupture the results agree with the conceptual interpretation that uplift of the rift boundaries to form flank mountains and uplift of the basin responsible for the breakup unconformity are related consequences of regional isostatic compensation of mass that is redistributed during the necking and rupture phases although the amplitudes of these uplifts depend on the model parameter values the relations between and relative signs of these two effects appear to be fundamental the explanation we propose may have been missed in recent studies because there has been a tendency to concentrate on kinematic stretching models which assume local isostatic equilibrium through out the rifting process such an approach is predicated on the assumption that the lithosphere has an insignificant strength or flexural rigidity during extension which is not true if our explanation is correct

luminescence chronology of the loess palaeosol sequence toshan northern iran a highly resolved climate archive for the last glacial interglacial cycle loess palaeosol sequences are highly resolved archives for palaeoenvironmental reconstruction and build an important link to correlate european and central asian loess sequences for the loess palaeosol sequence at toshan northern iran a luminescence based chronological framework was established the timing of dust accumulation and soil formation was investigated and thereby information on changes in palaeoenvironmental conditions in the region obtained for luminescence dating the 4e11 mm grain size fraction was used and the pirir290 approach was applied to polyminerals tests concerning bleachability dose recovery and anomalous fading were conducted the results show that residual doses have only minor influence on the determination of the equivalent dose the eemian mis 5e soil seems to be preserved but a chronological classification based on luminescence ages for this soil remains difficult the pirir290 age estimates from the lower part of the profile range from 104 9t o 127 8 ka lumi nescence ages from the central profile part point to an increase in dust accumulation starting around the mis 4 mis 3 transition furthermore a chronological framework for interstadial soils was developed indicating e g soil formation at around 40 ka during mis 3 and 26 ka during mis 2 the top part of the profile was dated to about 22 ka the age estimates show that the toshan loess profile is a highly resolved loess record providing a valuable climate archive for the last glacialeinterglacial cycle reflecting several climatic shifts represented by dust accumulation or enhanced degrees of soil formation stadials and interstadials

review of recent developments in mineral magnetism of the chinese loess mineral magnetism of the chinese loess has been investigated for more than 20 years although there is a consensus that the neoformation of fine grained maghemite particles in the superparamagnetic sp and single domain sd grain size regions accounts for the magnetic enhancement in the chinese paleosols quantitative retrieval of paleoclimatic signals in terms of rock magnetic proxies is still a subject of debate the ambiguities arise from the inherent complexities of magnetic proxies as well as the multiple factors that control the pedogenic processes therefore a better description of the magnetic assemblage including its mineralogy grain size distribution and stoichiometry of two distinct origins pedogenic and eolian can help us better understand mechanisms behind variations in magnetic proxies at different timescales in order to link them to the paleoclimatic processes this review focuses on recent developments in loess magnetism and carefully evaluates merits and limitations of rock magnetic proxies furthermore several currently unsolved problems are addressed

current stress state and principal stress rotations in the vicinity of the chelungpu fault induced by the 1999 chi chi taiwan earthquake 1 we carried out various stress measurements in boreholes penetrating the northern segment of the chelungpu fault drilled about 5 years after the 1999 chi chi taiwan earthquake in the possible depth range of the chelungpu fault three major fault zones were encountered clearly recognizable principal stress rotations in the vicinity of the shallowest major fault zone at 1133 m depth in hole b suggest that this fault zone ruptured during the 1999 earthquake moreover the fault s rupturing altered the stress state in the area surrounding this fault zone in this paper we constrain the possible magnitudes of the current principal horizontal stresses around the fault zone and show that the current stress state belongs to a normal or strike slip fault regime therefore the stress state was changed from that of a reverse fault regime by the rupturing

an evaluation of geochemical weathering indices in loess paleosol studies abstract applying geochemical proxies as measure for the weathering intensity of paleosols and sediments such as loess the quaternary scientist is confronted with various element ratios that have been proposed in literature this paper gives an overview on the principle of geochemical weathering indices different types of indices are evaluated with respect to the suitability for loess paleosol sequences regarding the special characteristics of this type of sediments and paleosols case examples in this study are key sections in southeastern and eastern europe the loess paleosol sequences batajnica stari slankamen serbia mircea voda romania and stary kaydaky ukraine which represent archives of the late and mid pleistocene climate change of the region considering element behavior during weathering or diagenesis the chemical proxy of alteration cpa i e the molar ratio al2o3 al2o3 na2o 100 is proposed as the most appropriate index for silicate weathering the cpa was evaluated against commonly used weathering indices including the chemical index of alteration cia the chemical index of weathering ciw the plagioclase index of alteration pia the index b of kronberg and nesbitt and the ba sr and rb sr ratio depth profiles of sr type indices e g ba sr rb sr are likely to be influenced by the dynamics of secondary carbonate on the other hand common na type indices e g cia pia ciw may suffer from uncertainties in separating carbonate ca from silicate ca or from biases due to k fixation illitization the cpa is insensitive against such effects additionally using the cpa as with other na type indices provides the possibility to evaluate the homogeneity of the parent material regarding the relevant host minerals via the a cn k diagram

understanding tectonic stress in the oil patch the world stress map project knowledge of the present day tectonic stress is essential for numerous applications in petroleum exploration and production and in civil and mining engineering such as improving the stability of boreholes and tunnels and enhancing petroleum production through natural or induced fractures the world stress map wsm project is a collaborative project between academia industry and government that is building a comprehensive global database of present day stress information to better understand the state and sources of contemporary tectonic stress in the lithosphere figure 1

intraplate stresses and dynamical aspects of rifted basins abstract intraplate stresses play a important role during the syn and post rift evolution of sedimentary basins deviations from long term thermal patterns of post rift subsidence as well as the development of unconformities within rifted basins reflect to a large extent the temporal fluctuations of the regional stress fields in the lithosphere it appears that incorporation of intraplate stresses in dynamical models for basin development together with a quantification of the role of petrological changes in the crust lithosphere system can explain some of the observed shortcomings of thermal models of post rift basin subsidence late neogene accelerations in tectonic subsidence in the deeper parts of rifted basins in the northern atlantic and mediterranean regions could reflect a change in the level of intraplate stress over large areas of the globe non thermal contributions to the subsidence record affect estimates of crustal extension and consequently influence the depth at which hydrocarbon source rocks enter the maturity window stress induced changes in basement topography have also important consequences for the budget of fluid flow in the deeper parts of the sediment fill of the rifted basins as well as on the dynamics of diapirism

estimating pore fluid pressure stress coupling abstract fracture pressure fp prediction is a vital component in well planning for safe drilling in high pressure areas in the estimation of seal capacity and seal breach risk analysis for fluid injection and in fracture stimulation for oil gas recovery from tight reservoirs and mature source rocks coupling of pore fluid pressure pp and fp at basin scale has been recognised for several decades with coupling ratio values mostly between 0 46 and 0 87 i e for every 10 mpa of pp increase at constant depth fp increases by 4 6 8 7 mpa these values are similar to estimates for reduction of fp with reservoir depletion of an oil gas field during production poroelasticity has been suggested as the principal reason for coupling most previous coupling values were generated by examination of pressure gradients a new method to estimate pore fluid pressure stress coupling is proposed which plots the measured value of fp from a leak off test lot minus the expected fp value on the trend for normal pressures termed the fracture pressure residual fpr against overpressure op which is the magnitude of pp above normal at the same depth the coupling value is now the slope of fpr against op fpr op coupling values from 11 global basin datasets range from 0 24 to 0 43 approximately half the previous quoted basin scale coupling values a pressure depth model for rapid deposition on a continental margin with op exclusively generated by disequilibrium compaction and no change in effective stress in the overpressured section represents a base case for compaction op without poroelasticity this model helps to reveal 1 that coupling values vary with the ratio of fp to lithostatic pressure sv 2 since the 11 case study coupling values exceed the base case one or more other minor coupling mechanisms are involved potentially including poroelasticity 3 values may be independent of tectonic environment 4 one case study involving carbonate chalk is within the same range as those from siliciclastic sediments and 5 the high coupling pore pressure stress coupling values in the literature result from using fluid and fracture gradients including the shallow data where pp is normal which distort the analysis

grain size of loess palaeosol and red clay deposits on the chinese loess plateau significance for understanding pedogenic alteration and palaeomonsoon evolution abstract to assess pedogenic modification to grain size distributions of loess palaeosol and red clay deposits on the chinese loess plateau and to understand long term evolution of the east asian palaeomonsoon since the late miocene we investigate a continuous loess palaeosol red clay sequence at lingtai south chinese loess plateau and another parallel red clay sequence at zhaojiachuan central chinese loess plateau by analyzing the grain size distributions of bulk samples and chemically isolated quartz samples the relative intensity of pedogenic alteration of the loess palaeosol and red clay deposits can be quantified comparisons of the grain size distributions and contents of different grain size fractions between the bulk and the quartz samples suggest that pedogenic alteration is apparently stronger in the red clay sequence than in the overlying loess palaeosol deposits furthermore grain size parameters derived from the bulk and the quartz samples such as mean grain size coarse fraction content and u ratio exhibit similar variations in the loess palaeosol sequence quaternary 0 2 6 ma whereas these grain size parameters of quartz samples show different variability from those of bulk samples in the red clay sequence late miocene to pliocene 2 6 7 ma grain size of quartz from the loess palaeosol and red clay deposits exhibits distinct and persistent oscillations from the late miocene to the pleistocene implying that significant fluctuations of the palaeomonsoon climate in east asia might have occurred at least since late miocene time

variation of rb sr ratios in the loess paleosol sequences of central china during the last 130 000 years and their implications for monsoon paleoclimatology abstract rb sr and magnetic susceptibility have been measured in the last interglacial glacial loess profiles at luochuan and huanxian central china a high degree of similarity between the parameters in both profiles suggests that variations of rb sr ratios in the sequence can be regarded as an indicator of east asian summer monsoon strength matching the rb sr record with the specmap 18o curve suggests that the rb sr ratio responds sensitively to changes of the east asian monsoon induced by global ice volume variation

moisture variations in arid central asia and its out of phase relationship with the asian monsoon during mis 5 evidence from loess records an out of phase relationship between moisture variations in arid central asia aca and monsoon asia is revealed in various holocene sedimentary records to determine whether this relationship also occurred during previous warm intervals we reconstructed the history of moisture variations during marine isotope stage 5 mis 5 recorded in a loess profile from the yili valley in the tienshan mountains in aca and compared it with the record from the chinese loess plateau clp three humid episodes in the yili valley are recorded at 72 79 5 93 5 101 and 113 5 125 5 ka in addition intervals of fine grain size indicating a low incidence of dust storms and thus low ice volume in the northern hemisphere occurred during 76 83 5 97 106 and 117 5 130 ka our findings indicate that during mis 5 variations in humidity in aca lagged by similar to 3 5 ka variations in the asian monsoon recorded by magnetic and grain size proxies from the clp furthermore we propose that precipitation variations in aca were negatively correlated with the intensity of the asian monsoon because of corresponding movements in pressure and rain belts and were positively correlated with sea surface temperature variations in the north atlantic copyright c 2018 john wiley sons ltd

source regions and formation of the loess sediments on the high mountain regions of northwestern china loess on the high mountains of northwestern china is largely controlled by the topographic features distributed mainly on the northern slopes of the tianshan and kunlun mountains as well as in the ili valley between the northern and central tianshan ranges loess distributed in different regions has different ages with the oldest early pleistocene loess occurring in the ili valley geochemical mineralogical and granulometric analyses demonstrate that the loess in the three different regions has different provenance the loess on the northern tianshan and kunlun mountains is mainly derived from the junggar and taklimakan deserts respectively whereas the loess in the ili valley is derived mainly from the sary ishikotrau desert located in the republic of kazakhstan however these deserts serve mostly as holding areas for the silts rather than original source regions the production of the silt sized particles is mainly associated with glacial abrasion and tectonic induced rock denudation thus the loess in the studied regions can be described as mountainous loess rather than simply glacial loess or desert loess it is unlikely that the mechanisms of loess formation are the same in different regions given their dependence on specific geomorphological conditions and associated processes

continental lithosphere folding in central asia part i constraints from geological observations abstract geological observations support the occurrence of long wavelength surface undulations in central asia which can be treated in terms of folding of the whole lithospheric plate the characteristic wavelength of the whole lithosphere folding is 360 km in the western part of the gobi sub plate superimposed on the long wavelength deformation two shorter wavelength scales of spatially periodical deformation are also observed an intermediate wavelength of 30 50 km of the intraplate deformation reflects the response of the mechanically strong upper crustal part of the central asian lithosphere small wavelength 4 9 km deformation corresponds to faulting in the uppermost crustal layer and folding and faulting in the sedimentary cover folding of the lithosphere controls the location and geometry of compressional basin formation in the western part of the gobi sub plate a number of folding and faulting characteristics of continental intraplate deformation in central asia presented in this study are strikingly similar to observed styles of intraplate deformation in oceanic lithosphere in the northeastern indian ocean

bimodal grain size distribution of chinese loess and its palaeoclimatic implications grain size analysis indicates that chinese loess generally shows a bimodal distribution with a coarse and a fine component the coarse component comprising the main part of the loess has pronounced kurtosis and is well sorted which is interpreted to be the product of dust storms generated by low altitude northwesterly winds its grain size reflects the strength of the low altitude circulation in the dust seasons of the year and its percentage provides an indicator of the source area aridity and the frequency of dust storms conversely the fine component has a wide grain size range and is poorly sorted sedimentary illustrations based on the grain size distribution characteristics of bulk samples and of detrital quartz suggest that the fine component probably represents the background dust load of the atmosphere and is mainly transported by high altitude westerly airstreams its grain size provides an estimate of the westerly air stream intensity the coarse and fine components of a loess sample can be mathematically separated by fitting a designated mathematical distribution function to the measured grain size data and this procedure constitutes an approach for reconstructing the palaeowind system of northern china c 2003 elsevier b v all rights reserved

persistent positive north atlantic oscillation mode dominated the medieval climate anomaly the medieval climate anomaly mca was the most recent pre industrial era warm interval of european climate yet its driving mechanisms remain uncertain we present here a 947 year long multidecadal north atlantic oscillation nao reconstruction and find a persistent positive nao during the mca supplementary reconstructions based on climate model results and proxy data indicate a clear shift to weaker nao conditions into the little ice age lia globally distributed proxy data suggest that this nao shift is one aspect of a global mca lia climate transition that probably was coupled to prevailing la nina like conditions amplified by an intensified atlantic meridional overturning circulation during the mca

changing color of chinese loess geochemical constraint and paleoclimatic significance abstract two loess paleosol sequences on the central chinese loess plateau were investigated to understand spatial and temporal variations in the soil color e g lightness and redness and factors that control those variations color difference between the original samples and pretreated samples suggests that loess lightness is influenced by the pedogenic matter e g iron oxides organic matter and calcium carbonate to varying degrees depending on the concentrations iron oxides and organic matter darken the loess lightness whereas carbonate lightens the loess lightness by contrast the redness is dominantly controlled by the types and concentrations of iron oxides variations in magnetic susceptibility and redness are associated with different magnetic minerals that formed mainly during post depositional processes and therefore both proxies can be employed to reconstruct the history and variability of the east asian summer monsoon since the sensitivity of these two proxies to the summer monsoon variation is different we generate a stacked summer monsoon index by combining these two records and interpret the stacked index as most indicative of precipitation variability the fidelity of this new index is supported by an independent ratio estimated from the first derivative values of the color reflectance spectra our loess based proxies provide a new understanding of the east asian summer monsoon variability as a two phase strengthening of summer monsoon intensity during the penultimate deglaciation

origin of loess deposits in the north tian shan piedmont central asia abstract loess deposits are widely distributed along the mountain piedmonts of central asia the transport processes and origins of central asian loess sediments remain poorly understood here we investigate the origin and formation of loess along the northern piedmont of the tian shan based on trace element including rare earth element ratios and multidimensional scaling analysis our results indicate that the loess has undergone weak chemical weathering using a selection of geochemical fingerprinting techniques based on pearson correlation and kruskal wallis h tests we establish a genetic link between alluvial proluvial fans plains deserts and loess along the tian shan piedmont in northern kyrgyzstan and southern kazakhstan the unsorted sediments on the piedmont slopes and alluvial proluvial plains are common sources for both deserts and loess to the north of the tian shan dune sediments are not the main source of the fine grained loess origin and formation of central asian loess is strongly dependent on local topographic context and wind dynamics only once loess provenance and formation has been understood across both space and time can reliable interpretations of palaeoclimatic proxies in these deposits be made

on crustal seismicity of the amazonian foothill of the central peruvian andes a microearthquake survey of crustal seismicity conducted in 1985 on the eastern cordillera and the amazonian foothills in central peru gives a description of the present tectonic activity related to the uplift of the andes hypocenters on the huaytapallana fault are shallower than 10 km and their focal mechanism is in agreement with the fault trace corresponding to the earthquakes of 1969 and suggests a reverse strike slip movement on a plane striking n130 an active tectonic zone is evidenced along a nw se direction passing through the amauta subandean region the vertical distribution of hypocenters and the comparison of shallow and deep focal mechanisms suggest a reverse fault dipping to the west depths vary between 0 and 20 km and never exceed 32 km the huaytapallana cordillera is uplifted by thrust faults on both sides

detection of overpressure zones and a statistical model for pore pressure estimation from well logs in the krishna godavari basin india abnormally high pressures measured by repeat formation tester rft and detected by well log data from 10 wells in the krishna godavari k g basin occur in the vadaparru shale of miocene and raghavapuram shale of early cretaceous age overpressures generated by disequilibrium compaction and pore pressures have been estimated using the conventional eaton sonic equation with an exponent of 3 0 the observed abnormal pore pressure gradient ranges from 11 85 to 13 10 mpa km whereas fracture pressure gradient varies from 17 40 to 19 78 mpa km the magnitude of vertical stress sv has a gradient from 21 00 to 23 10 mpa km the minimum horizontal principal stress sh magnitude is found to vary from 64 to 77 of the sv in normally pressured to overpressured sediments a multiple linear regression model with a squared multiple correlation coefficient r2 of 0 94 is proposed for pore pressure prediction from gamma ray density and sonic logs to focus on efficient drilling operations and to prevent borehole instability the statistical model has been calibrated with the rft data from five wells covering about 3400 sq km area of the onshore k g basin the model predicted pore pressure values are in close agreement with the actual rft data for another four wells including a well in the offshore k g basin hence the proposed regression model may be useful for predicting pore pressure from other well logs in the k g basin

the investigation of magnetic susceptibility variation mechanism of tien mountains modern loess pedogenic or wind intensity model it had been widely accepted that in situ pedogenic enhancement of fine grained ferromagnetic content provides the well established patterns of magnetic susceptibility variation within mid latitude loess deposition such as those of chinese loess plateau and central europe an entirely different phenomenon is present in higher latitude loess deposition of alaska and siberia with high magnetic susceptibility in loess and low in soil this inverse relationship has suggested that magnetite grain size is related to wind velocity the tien mountains are located at the transition zone between the chinese loess plateau and siberia and have extensive loess deposits previous investigations have displayed a more complex correlation between pedogenesis and magnetic susceptibility with positive and negative relationships coexisting further research has indicated that a reducing environment must be an important influence in decreasing magnetic susceptibility of basal soil units in this area tien mountains loess has similar magnetic mineralogy to chinese loess plateau loess and pedogenic magnetite effectively influences magnetic properties however magnetic susceptibility does not perfectly correspond to weathering intensity change the result of high concentration and unstable primary magnetite among loess samples pedogenic magnetic material controls magnetic susceptibility variation gradually as pedogenic intensity increases magnetic susceptibility is not a great proxy of loessic soil unit pedogenic intensity in this region especially for weakly pedogenic soil units

a persistent holocene wetting trend in arid central asia with wettest conditions in the late holocene revealed by multi proxy analyses of loess paleosol sequences in xinjiang china abstract there are significant differences in the interpretation of the moisture precipitation history of arid central asia aca during the holocene as inferred on one hand from speleothem oxygen isotope records and on the other from lake sediments here we present the results of measurements of climatically sensitive magnetic properties and soil color from four well dated loess paleosol sequences from the northern slopes of the tienshan mountains and the yili river valley xinjiang china in the core area of aca our results demonstrate that the characteristic holocene paleosol indicating relatively moist conditions generally formed after 6 ka 1 ka 1000 cal yr bp in the study region and that the accumulation of unweathered loess prevailed during the early holocene indicating a dry climate at that time the magnetic proxies further reveal a trend of generally increasing moisture since the last glacial maximum with the wettest climate occurring during the late holocene this trend of increasing moisture during the holocene is representative of the xinjiang region and possibly of the whole of the core area of aca and is in marked contrast both to the mid holocene moisture maximum observed in the east asian summer monsoon region and to the general decrease in the strength of the indian summer monsoon since the early holocene our findings are supported by the results of a climate simulation which indicate a trend of increasing summer and winter precipitation during the holocene in the core area of aca caused mainly by an increase in the strength of the westerlies effected by an increasing latitudinal insolation gradient and by a negative trend of the arctic oscillation ao or north atlantic oscillation nao

a joined rock magnetic and colorimetric perspective on the late pleistocene climate of orlovat loess site northern serbia abstract this study represents the first detailed joined colorimetric and rock magnetic investigation on a loess paleosol sequence in the vojvodina region northern serbia the aim of this paper is to derive new information on the late pleistocene paleoenvironment from a high resolution multi proxy assessment of the iron mineralogical composition at the orlovat loess paleosol sequence the orlovat section is the first site from the banat loess region analyzed for quaternary paleoclimate information and accordingly it is the easternmost loess section in the serbian loess region studied in contrast to other serbian sites the orlovat site is not located in a plateau rock magnetic analysis and the luminescence dating based chronology revealed active slope processes at this site during the late pleistocene this is the most strikingly evidenced by the absence of a middle wurmian mis 3 interstadial pedocomplex present as marker horizon in the serbian plateau loess sites nevertheless important stratigraphic units and distinct pattern of the proxy records can be correlated to other key sites of the vojvodina loess region hence this section provides an opportunity to reconstruct local as well as regional environmental and climatic conditions during the late pleistocene the applied multiproxy approach especially allowed valuable insight in the environmental conditions that prevailed during formation of the last interglacial pedocomplex accordingly in the eemian pronounced summer dryness prevailed during the formation of the eemian soil the dry period was warmer and lasted longer or was characterized by less precipitation as during formation of the modern soil although the soil moisture deficit in the eemian summers was most likely higher the rainfall was more pronounced in the period of from spring to early summer and or autumn as during the holocene these findings support previous observations from the batajnica site a key site of the vojvodina loess region and highlight the eemian as potential past analogue to future climate warming in serbia this study points out the potential of a joined colorimetric or spectrometric analyses and rock magnetic analyses in paleoenvironmental investigations on loess paleosol sequences

lithology dependent minimum horizontal stress and in situ stress estimate abstract based on the generalized hooke s law with coupling stresses and pore pressure the minimum horizontal stress is solved with assumption that the vertical minimum and maximum horizontal stresses are in equilibrium in the subsurface formations from this derivation we find that the uniaxial strain method is the minimum value or lower bound of the minimum stress using anderson s faulting theory and this lower bound of the minimum horizontal stress the coefficient of friction of the fault is derived it shows that the coefficient of friction may have a much smaller value than what it is commonly assumed e g f 0 6 0 7 for in situ stress estimate using the derived coefficient of friction an improved stress polygon is drawn which can reduce the uncertainty of in situ stress calculation by narrowing the area of the conventional stress polygon it also shows that the coefficient of friction of the fault is dependent on lithology for example if the formation in the fault is composed of weak shales then the coefficient of friction of the fault may be small as low as f 0 2 this implies that this fault is weaker and more likely to have shear failures than the fault composed of sandstones to avoid the weak fault from shear sliding it needs to have a higher minimum stress and a lower shear stress that is the critically stressed weak fault maintains a higher minimum stress which explains why a low shear stress appears in the frictionally weak fault

westerlies asia and monsoonal asia spatiotemporal differences in climate change and possible mechanisms on decadal to sub orbital timescales abstract the westerlies dominated climatic regime wdcr in the present interglacial period was proposed because precipitation moisture variations between arid central asia and mid latitude monsoonal asia are out of phase or anti phased on different timescales during the holocene in this study we first review the development of the theoretical framework of the wdcr and then outline the boundary of its core area from the caspian sea in the west to the western hexi corridor in the east with the northern and southern limits coinciding with the domain of arid central asia next we present a synthesis of multiple lines of evidence for the occurrence of the wdcr on multi millennial sub orbital herein to decadal timescales during the holocene finally we examine the possible physical mechanisms responsible for the wdcr we find that external factors insolation changes induced by orbital factors generated the wdcr on a sub orbital timescale whereas a circum global teleconnection silk road pattern was the most significant factor responsible for the wdcr on centennial and decadal timescales the study provides a comprehensive summary of the development of our knowledge of the wdcr over the past several decades together with a tentative theoretical framework for understanding climatic and environmental changes within its region of influence in addition it forms a scientific basis for environmental management and ecological restoration in this arid region in the context of global warming

the niger delta basin fracture pressure prediction accurate knowledge of formation fracture pressure is essential to optimize well design at all stages of the field development however erroneous prediction of formation fracture pressure can lead to process safety incidents such as surface and underground blowouts while fracture pressure prediction models have been developed for some sedimentary basins it is difficult to transfer these models to areas beyond the regions of study in the niger delta basin few fracture pressure prediction models have been developed however these models were developed primarily from leak off test data acquired from the normally pressured intervals basically the existing niger delta fracture pressure prediction models lack the leak off test measurements in the overpressure intervals because such data are not available in this paper a new fracture pressure prediction model that can be applied to normally pressured intervals and overpressure zones is being proposed model development is based on establishing a relationship between fracture pressure true vertical depth and magnitude of overpressure using several leak off test data acquired from over 100 wells in various fields scattered across the basin unlike the previous models the newly developed model incorporates leak off test measurements from the overpressure intervals in the basin in general the newly proposed model can be used with a high degree of confidence to predict the fracture pressure required for safe and economic well planning across the entire basin

the loess sequence from remisowka northern boundary of the tien shan mountains kazakhstan part i luminescence dating abstract similar to the chinese loess the loess deposits surrounding the high mountain regions of central asia play an important role in understanding the climate and environmental change during the pleistocene in eurasia despite their thickness and widespread distribution the loess deposits in southeast kazakhstan have so far not been investigated in detail the remisowka loess palaeosol sequence is located in the vicinity of the north tien shan mountains at an altitude of 1070 m above sea level in the profile under study nine loess layers were distinguished intercalated by eight pedocomplexes and so indicating a similar cyclicity like the loess palaeosol sequences in central asia and china at the remisowka section 12 loess samples were taken to set up a more reliable chronological model for the section using a luminescence dating approach polymineral fine grains were investigated by infrared optically stimulated luminescence applying the multiple aliquot additive dose protocol preliminary fading experiments were carried out for one sample taken from the uppermost loess layer while the results of the uppermost layer are in agreement with geological age estimates and indicate a correlation to the late glacial age underestimation is very likely for the samples below the first weak palaeosol no significant age increase with depth was recognised the reason for this age underestimation is not yet fully understood but could be related to anomalous fading further methodological approaches are necessary as well as a combination of different chronometric techniques for improvement of the results

circumglobal teleconnection in the northern hemisphere summer analysis of the 56 yr ncep ncar reanalysis data reveals a recurrent circumglobal teleconnection cgt pattern in the summertime midlatitude circulation of the northern hemisphere this pattern represents the second leading empirical orthogonal function of interannual variability of the uppertropospheric circulation the cgt having a zonal wavenumber 5 structure is primarily positioned within a waveguide that is associated with the westerly jet stream the spatial phases of cgt tend to lock to preferred longitudes the geographically phase locked patterns bear close similarity during june august and september but the pattern in july shows shorter wavelengths in the north pacific north america sector the cgt is accompanied by significant rainfall and surface air temperature anomalies in the continental regions of western europe european russia india east asia and north america this implies that the cgt may be a source of climate variability and predictability in the above mentioned midlatitude regions the cgt has significant correlations with the indian summer monsoon ism and el nino southern oscillation enso however in normal ism years the cgt enso correlation disappears on the other hand in the absence of el nino or la nina the cgt ism correlation remains significant it is suggested that the ism acts as a conductor connecting the cgt and enso when the interaction between the ism and enso is active enso may influence northern china via the ism and the cgt additionally the variability of the cgt has no significant association with the arctic oscillation and the variability of the western north pacific summer monsoon the circulation of the wave train shows a barotropic structure everywhere except the cell located to the northwest of india where a baroclinic circulation structure dominates two possible scenarios are proposed the abnormal ism may excite an anomalous west central asian high and downstream rossby wave train extending to the north pacific and north america on the other hand a wave train that is excited in the jet exit region of the north atlantic may affect the westcentral asian high and thus the intensity of the ism it is hypothesized that the interaction between the global wave train and the ism heat source may be instrumental in maintaining the boreal summer cgt

the loess record in southern tajikistan and correlation with chinese loess in the present study the chashmanigar loess soil sequence in southern tajikistan is studied this loess section has a paleomagnetic basal age of about 1 77 myr magnetic susceptibility color reflectance and grain size were systematically measured for closely spaced samples from the section paleosols consistently have a finer grain size distribution higher magnetic susceptibility redder color reflectance and lower dust sedimentation rate than loess horizons suggesting a colder drier and dustier environment during glacial periods than in interglacial periods the grain size record was tuned to variations in obliquity and precession of the earth s orbit the resulting magnetic susceptibility grain size and color reflectance time series all show well expressed astronomical periodicities during the pleistocene the mid pleistocene climate transition characterized by a shift of dominant climatic periods from 41 kyr to 100 kyr at about 1 0 0 8 myr is clearly documented in these proxy records comparison of the chashmanigar loess record with the lingtai loess section in china and the odp site 677 n 18 o record shows that during the entire pleistocene the climate cycles recorded by the central asian loess can be well correlated to the chinese loess and deep sea oxygen isotope records it is suggested that alternations of loess and soil horizons both in central asia and china could be basically forced by global ice volume variations although different wind systems have controlled the pleistocene loess transport and sedimentation in the two areas 2002 elsevier science b v all rights reserved

magnetic investigation of late quaternary loess deposition ili area china abstract a late quaternary loess section in ili river valley xinjiang northwest china has been studied magnetically samples from two sections exhibit variations in magnetic susceptibility which displays a positive relationship with pedogenesis intensity in s 0 and negative in s 1 and l 1 the detailed magnetic properties investigation reveals that concentration of initial magnetite and maghemite fm varies and may be dominated by wind intensity and source mineralogy furthermore this is the most important magnetic component influencing magnetic properties of loess paleosol sequences and controls magnetic properties of loess deposition in contrast concentration of pedogenic fm is low and has little influence on magnetic properties of loess however it is an ideal magnetic parameter to assess paleoclimate the magnetic minerals in s 1 soil units might be linked to reducing environments reflected by the enhancement of the coercive force of remanence

geochemical characterization of the luochuan loess paleosol sequence china and paleoclimatic implications abstract chemical major and trace element and isotopic sr nd analyses of the luochuan loess paleosol sequence in china were performed in order to examine the following problems 1 potential source heterogeneity 2 element behavior during pedogenesis 3 paleoclimatic implications and 4 the use of loess data to determine the average composition of the upper continental crust new results clearly indicate that rb sr u and ce abundances are severely depleted in paleosols relative to their parental loess the behavior of these elements is strongly controlled by the breakdown of primary minerals such as carbonate sr or by alteration processes in highly oxidizing environments ce and u the pattern of element variations through the upper section of the luochuan sequence mimics the magnetic susceptibility signal both in position and in intensity thus reinforcing the pedogenesic origin of the enhanced magnetic susceptibility in paleosols all loess samples display highly uniform ree patterns except for ce characterized by the upper continental crust ucc ratios la yb n 10 and eu eu 0 66 the paleosol ree patterns are similar to those of the loess with the same lree hree fractionation but they also show distinct and variable negative ce anomalies nd and sr isotopic compositions are rather uniform in both loess and paleosols and do not vary with stratigraphic position nd 10 5 to 9 2 87 sr 86 sr 0 715 to 0 719 the isotopic homogeneity in the luochuan sequence strongly suggests a uniform source region during the entire period of deposition since 800 ka ago to the present several conclusions may be drawn from the present study 1 1 no geochemical distinction can be made between loess layers l1 to l7 the sources and the dust storm trajectories must have been essendally the same for the last 800 ka 2 2 some elements e g ca rb sr u ce are strongly fractionated by pedogenesis between loess and paleosols ce mobility in soils is clearly demonstrated but the process responsible for this leaching is still poorly understood 3 3 systematic variations of element abundances and ratios between loess and paleosols can be used as chemical indicators for pedogenesic intensity and so for paleoclimatic change these chemical indicators serve a function similar to that of oxygen isotopes in deep sea sediments pelagic foraminifera or that of magnetic susceptibility in loess sequences they are different recorders of paleoclimatic change 4 4 the striking uniformity of ree patterns and la th ratios in the luochuan loess and paleosols as well as in loess worldwide is an excellent starting point for estimating the average composition of the upper continental crust

integrated wellbore quality and risk assessment study guides successful drilling in amazon jungle significant lost circulation and wellbore instability problems in the form of bit balling stuck pipe and adverse mud shale interactions have been experienced in wells drilled prior to the study at three prospects in the amazon jungle an integrated borehole stability and risk assessment study has been carried out to enable successful drilling by optimizing borehole fluid pressures and predicting safe openhole times in various troublesome zones the guidelines for hole cleaning parameters and well trajectory optimization have been obtained using improved fracture gradient and horizontal stress anisotropy proprietary models based on special drill cuttings data monopole and dipole sonic and imaging logs along with drilling data from the prospect wellshave been used to determine in situ stresses rock properties andformation strength these parameters have been utilized in borehole stability hole cleaning and open hole time analyses for a comprehensive risk assessment and for selection of the optimum we

in situ stress variations associated with regional changes in tectonic setting northeastern brooks range and eastern north slope of alaska abstract the northeastern brooks range of northern alaska is an active north directed fold and thrust belt that is advancing on the barrow arch and the north facing passive margin of the arctic basin density logs leak off tests and mud weight profiles from 57 wells from the northeastern north slope were used to determine the magnitude of the present day in situ stresses and document significant regional lateral and vertical variations in relative stress magnitude preliminary analysis of the in situ stress magnitudes indicates two distinct stress regimes across this region of alaska areas adjacent to the eastern barrow arch exhibit both strike slip and normal stress regimes this in situ stress regime is consistent with fault patterns in the subsurface and with north south extension along the barrow arch and the northern alaska margin to the south in and near the northeastern brooks range thrust front in situ stress magnitudes indicate that an active thrust fault regime is present at depths up to 6000 ft 1829 m this is consistent with the fold and thrust structures in surface exposures and in the subsurface however at depths greater than 6000 ft 1829 m the relative in situ stress magnitudes indicate a change to a strike slip regime this observation is consistent with the few earthquake focal mechanisms in the area and suggests deep north northeast oriented strike slip faults may underlie the western margin of the northeastern brooks range

subsidence analysis and tectonic evolution of the external carpathian moesian platform region during neogene times abstract the miocene pliocene subsidence of the tectonic platforms in the romanian carpathians foreland is analysed using standard 1d backstripping techniques for individual wells combined in two regional sections and six contour maps the subsidence patterns were integrated together with previous paleostress and kinematic studies in order to derive the tertiary kinematics of the buried faults in the carpathians lower plate the study revealed accelerated subsidence during the early miocene in the western part of the moesian platform getic depression in direct relationship with the opening of a wsw ene trending extensional basin the largest subsidence recorded in the front of the carpathians took place during the late miocene due to final e ward emplacement of the thrust sheets the late miocene subsidence showed anomalous high values between the intramoesian and trotus faults as a result of the orogenic collision with the east european platform northward and acceleration of the subduction process in the se carpathians corner further pliocene subsidence continued only in the latter region the depocenter being shifted southward near the junction with the south carpathians foreland

east asian monsoon evolution during the eemian as recorded in the western chinese loess plateau abstract we present a high resolution environmental magnetic record of the east asian summer monsoon spanning paleosol s1 corresponding to marine oxygen isotope mis 5 from the jiuzhoutai jzt loess section in lanzhou on the northwestern edge of the chinese loess plateau we use a chronology based on a sediment grain size age model frequently used for chinese loess the eemian is dated to 127 37 121 31 ka bp and can be divided into three sub stages based on variations in summer monsoon intensity early eemian 127 37 125 67 ka bp with an intermediate summer monsoon intensity mid eemian 125 67 124 24 ka bp with weakest summer monsoon intensity and late eemian 124 24 121 31 ka bp with the strongest summer monsoon intensity contrasting the winter monsoon weakened at the beginning of mis5e reached its weakest intensity during the late eemian 121 ka bp and then commenced an irreversible strengthening trend furthermore the eemian exhibits a similar climatic trend to the holocene optimum since both are divided into two parts by an intervening arid interval and the most humid period occurs in the secondary pedogenic stage therefore we suggest that the climate evolution during eemian and later may provide useful information about climate forecast in the future

physical mechanisms of summer precipitation variations in the tarim basin in northwestern china abstractthe tarim basin tb in northwestern china is one of the most arid regions in the middle latitudes where water is scarce year round this study investigates the variations of summer precipitation in the tb and their association with water vapor fluxes and atmospheric circulation the results suggest that the variations of summer precipitation in the tb are dominated by the water vapor fluxes from the south and east although the long term mean water vapor mostly comes from the west the anomalous water vapor fluxes are closely associated with the meridional teleconnection pattern around 50 80 e and the zonal teleconnection pattern along the asian westerly jet in summer the meridional teleconnection connects central asia and the tropical indian ocean the zonal teleconnection resembles the silk road pattern the two teleconnections lead to negative height anomalies in central asia and positive height anomalies in the arabian sea and india and in northern central china the anomalous pressure g

a review of deformation pattern templates in foreland basin systems and fold and thrust belts implications for the state of stress in the frontal regions of thrust wedges aesthetically appealing thrust systems and related large scale anticlines in both active and fossil foreland fold and thrust belts and the economic potential associated with the m have captured the interest of structural geologists for many decades as a consequence a large amount of data on sub seismic deformation patterns from thrust related an ticlines is available in the literature we provide a review of deformation pattern templates from fi eld data in foreland fold and thrust belts and show that the most frequent tre nds of sub seismic syn orogenic deformation structures hosted in km scale thrust related folds frequently and pa radoxically indicate a syn th rusting strike slip stress fi eld con fi guration with a near vertical 2 and a sub horizontal 3 rather than a contractional one where the latter is expected to be the vertical principal axis of the stress ellipsoid this a pparent inconsistency between sub seismic syn orogenic deformation structures and stress fi eld orientation is here named the 2 paradox field data support a possible expla nation of the paradox provided by the major role played by i nherited early orogenic extensional deformation struc tures on thrust fault nucleation nucleation of major thru sts and their propagation is facilitated and driven by the positive inversion and linkage of the early orogenic sub s eismic extensional inheritance developed in the foreland basin this process eventually leads to the development of l argereversefaultzonesandcanoccurbothincontractional and strike slip stress fi eld con fi gurations

a radiometric calibration of the specmap timescale the astronomical theory of climate change asserts that earth s climate is affected by changes in its orbit which vary the seasonal and latitudinal distribution of solar radiation this theory is the basis of the orbitally tuned specmap timescale a key constraint for this important chronology was the mid point of the penultimate deglaciation initially dated to 127 000 years ago recent work suggests this event may be considerably older casting doubt on the astronomical theory the specmap timescale and the accuracy of orbitally tuned chronologies difficulties with u th coral dating of sea level events have impeded progress on this problem because most corals are not closed systems here we use a new approach to u th dating that corrects for open system behavior and produces a sea level curve of sufficient resolution to confidently correlate with specmap over the last 240 000 years permitting a reassessment of both this critical chronology and a central tenet of climate change theory high precision ages for 24 oxygen isotope events provide a 240 000 year chronology for marine 18o records that is independent of orbital tuning assumptions although there appear to be significant differences between the radiometric and orbitally tuned timescales near the lastglacial maximum and at the marine isotope stage 7 6 boundary a comparison of radiometric and specmap ages for identical isotope events suggest that the specmap timescale is quite accurate and that its errors were in general overestimated despite suborbital complexity orbital cyclicity is clearly evident in our record high amplitude sea level oscillations at periods greater than 20 000 years are very close in phase to summer insolation in the northern hemisphere although sea level changes cannot be uniquely tied to a specific season or latitude of insolation forcing the simplest explanation is that long period high amplitude sea level change is linked to northern hemisphere insolation forcing these results validate the principles of orbital tuning and suggest such timescales are generally robust

mechanics of triangle zones and passive roof duplexes implications of finite element models abstract finite element models of passive roof duplexes simulate the evolution and distribution of fault slip and deformation as functions of boundary conditions friction on the roof fault cover strength and amount of overburden a foreland buttress is essential for backthrust displacement in the models this foreland buttress is analogous to a pin line between the cover and footwall forelandward of the triangle zone in a balanced cross section and could be caused by a stratigraphic pinchout of the upper detachment or a strong cover in the foreland with boundary conditions that prevent the cover from slipping toward the hinterland relative to the wedge incipient forethrust and backthrust ramps zones of high equivalent plastic strain cut through the cover in the models there is more backthrust displacement with a lower friction coefficient on the upper detachment and with a stronger cover because of pressure dependence both fault strength and material strength increase with increasing overburden therefore the effect of overburden on backthrust displacement is determined by the nature of the pressure dependencies for fault friction and material strength in models with multiple imbricate faults the distribution of equivalent plastic strain adjacent to each fault is similar to that in single fault models with differences resulting from bending strains in the wedge and cover the strain distribution in the cover of the models is similar to that above natural passive roof duplexes characterized by layer parallel shortening above the tip of each horse in the duplex

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

zr rb ratio in the chinese loess sequences and its implication for changes in the east asian winter monsoon strength abstract the long term dust accumulation sequences on the chinese loess plateau clp provide a valuable opportunity to study the evolution of east asian winter monsoon strength grain size of bulk samples of loess deposits though widely used is a modified measure of the strength of winter monsoon wind due to modification by post depositional weathering and pedogenesis this study proposes a new and reliable geochemical climate proxy that records the variability of the east asian winter monsoon on the clp six loess paleosol sections on the plateau were selected for measuring concentrations of the trace elements zr and rb as well as grain size variations of the zr rb ratio in all the sections encompassing the last 130 ka display a generally similar pattern to that of mean grain size of bulk samples mgsb though a positive correlation exists between the zr rb ratio and mgsb the correlation coefficient decreases in southern and eastern sections where intense pedogenesis occurred in the relatively warm and humid climates long term zr rb variation in the lingtai section exhibits amplitudes and frequencies similar to those in mgsb and the mean grain size of quartz particles mgsq accepted as a more reliable proxy than mgsb in the upper loess paleosol sequence over the past 2 6 ma however for the underlying red clay formation in the interval from about 7 2 6 ma b p the mgsb record is relatively stable whereas both the zr rb ratio and mgsq show distinct variability and display amplitudes similar to those observed in the overlying loess paleosol sequence these results demonstrate that the zr rb ratio reflects original eolian grain size and may serve as a reliable index of the strength of east asian winter monsoon winds

geochemical discrimination of clastic sedimentary rock sources abstract factors controlling the geochemistry of a clastic sedimentary rock can include 1 composition of source terrain 2 chemical weathering 3 hydraulic sorting 4 diagenesis 5 metamorphism and 6 hydrothermal alteration a linear solution inferring source terrain composition from geochemistry of the sediment is impossible in this multivariate system as several unknowns will commonly be present the use of graphical analysis of element pairs circumvents the problem chemically immobile elements will maintain invariant ratios during rock mass change caused by either addition or depletion of mobile elements this results in chemically immobile element scattergrams exhibiting linear trends along radians extending from the origin if the major mineral phases of the immobile elements have behaved in a hydrodynamically similar manner as chemically mobile element plots will produce a scatter of points this relationship can be used to test chemical immobility and similarity in hydrodynamic sorting history the constraint on analysis is that the source area must be compositionally uniform or the sediment well mixed prior to delivery to the basin a second technique using sio2 plots has also been developed to investigate element mobility and hydrodynamic behaviour of the mineral phases containing the elements sio2 immobile element plots result in a linear arrangement of points extending towards either 0 or 100 sio2 the 0 intercept position occurs for elements with major mineral phases concentrated in sand the 100 intercept for those concentrated in clays plotting chemically mobile elements produces different patterns and this can be used to gain information on alteration and sorting history elemental ratios for chemically immobile elements with similar hydrodynamic behaviour will be the same as those for the weighted average composition of the source material this provides a powerful tool for deducing source terrain from sediment geochemistry techniques outlined above were tested on archaean metasandstones from superior province canada immobile element ratio diagrams for nb al ti and zr al ti indicate that a calc alkaline extrusive intrusive suite lying to the north of the study area was the source and not five other volcanic suites in the region this conclusion agrees with previous clast lithology studies and accentuates the applicability of the geochemical techniques

asynchronous holocene climate optimum across mid latitude asia abstract the holocene climate optimum hco was an important interval in the development of human civilization and has been the focus of many paleoclimatic studies however there are significant regional differences in the timing of the hco due to the complex response of regional climates to insolation changes associated with internal feedbacks within the climate system here we present the results of a study of magnetic and geochemical properties of loess paleosol sequences from across mid latitude asia with the aim of assessing differences in the timing of the hco the hco generally occurred after 5 ka in tajikistan and xinjiang during 5 2 5 ka in the western chinese loess plateau clp and during 8 2 5 ka in the central clp this asynchroneity reflects differences in the response of regional climates to global climate change specifically the difference in timing between the central and western clp may have been related to shifts in the position of the east asian summer monsoon rain belt due to the changing longitudinal position of the western pacific subtropical high together with changes in the east west thermal gradient in the equatorial pacific i e shifts between la nina and el nino conditions

in situ stress pore pressure and stress dependent permeability in the southern qinshui basin this study focuses on the in situ stress pore pressure and permeability in the southern qinshui basin one of largest coalbed methane basins in china well tests show that permeability in this basin is higher than other coalbed methane reservoirs this is because it is located in an extensional basin where the normal faulting stress regime is dominated this in situ stress regime is advantageous to keep coal cleats open hydraulic fracturing tests indicate that the fracture gradient or minimum horizontal stress is much lower than the shales in the gulf of mexico and other oil basins the minimum horizontal stress model is proposed with consideration of the stress coefficient based on the uniaxial strain method this model provides a fairly good prediction on the minimum stress permeability data show that the effective stress dependent permeability is pronounced in the coalbed methane reservoir this is significant for the dual porosity and dual permeability coal reservoirs which consist of coal porous matrices and cleats the reason is that a rapid increase in effective stress can induce the closure of cleats which may cause a permanent loss of permeability in the cleats this reduces the connectivity between the cleats and coal matrices hence the coal matrices cannot deliver gas pressure to the cleats for supporting the cleat space therefore slowing down the effective stress change during production e g slowing reservoir drawdown can decelerate the permeability reduction this is particularly important for the reservoir in which the pore pressure is not significantly overpressured such that in the southern qinshui basin

late pliocene quaternary tectonics in the frontal part of the se carpathians insights from tectonic geomorphology abstract the romanian east carpathians display large scale heterogeneities along the mountain belt unusual foredeep geometries significant post collisional and neotectonic activity and major variations in topography mostly developed in the aftermath of late miocene sarmatian 11 ma subduction underthrusting and continental collision between the east european scythian moesian foreland and the inner carpathians tisza dacia unit in particular the se corner of the arcuate orogenic belt represents the place of still active large scale differential vertical movements between the uplifting mountain chain and the subsiding focsani foredeep basin in this key area we have analysed the configuration of the present day landforms and the drainage patterns in order to quantify the amplitude timing and kinematics of these post collisional late pliocene quaternary vertical movements a river network is incising in the upstream a high topography consisting of the external carpathians nappes and the pliocene lower pleistocene sediments of the foreland further eastwards in the downstream this network is cross cutting a low topography consisting of the middle pleistocene holocene sediments of the foreland geological observations and well preserved geomorphic features demonstrate a complex succession of geological structures the late pliocene holocene tectonic evolution is generally characterised by coeval uplift in the mountain chain and subsidence in the foreland at a more detailed scale these vertical movements took place in pulses of accelerated motion with laterally variable amplitude both in space and in time after a first late pliocene uplifting period subsidence took place during the earliest pleistocene resulting in a basal quaternary unconformity this was followed by two quantifiable periods of increased uplift which affected the studied area at the transition between the carpathians orogen and the focsani foreland basin in the late early pleistocene and the late middle to late pleistocene both large scale deformation events affected the western focsani basin flank tilting the entire structure with 9 during the late early pleistocene and uplifted it as a block during the early late pleistocene the late early pleistocene tilting resulted in 750 m uplift near the frontal monocline and by extrapolation in a presumed 3000 m uplift near the central parts of the carpathians the late middle to late pleistocene cumulative uplift reaches 250 m and correlates with a contemporaneous progradation of the uplifted areas towards the focsani basin the uplifting events are separated by a second quaternary unconformity on the whole the late pliocene quaternary evolution of the carpathians orogen focsani basin structure indicate large scale differential uplift during the latest stages of a continuous post collisional orogenic evolution

predicting pore pressure in active fold thrust systems an empirical model for the deepwater sabah foldbelt abstract measurements related to mudrock shale and siltstone porosity such as acoustic velocity density or electrical resistivity have traditionally been used to predict pore pressures in extensional stress settings the underlying assumption is that burial and vertical effective stress ves which is the overburden minus the pore pressure controls the compaction of these rocks through porosity loss the dataset presented here compares ves and acoustic velocity of similar composition mudrocks in both an extensional and a compressional stress setting in the extensional stress environment the mudrocks follow a typical compaction trend with a porosity loss and increase in acoustic velocity that can be related to ves in an active fold thrust belt the compressive stresses further reduce the porosity and increase the acoustic velocity of the mudrocks first a layer parallel shortening compacts sediments beyond what is observed for the ves this additional compaction is further enhanced near thrust faults and in anticlinal forelimbs presumably due to additional shear stress in these areas the mudrocks located in folds that are buried by additional sedimentation do not compact again until the tectonic compaction is overridden by enough new burial after that the mudrocks follow the observed extensional setting compaction trend in the fold thrust belt the observed reduction in porosity by stresses other than burial leads to an under prediction of pore pressure using traditional methods to account for this we present a correction that can be applied to the acoustic velocity or porosity using two parameters a proximity to thrust faults and anticlinal forelimbs and b the amount of burial after fold formation with these corrections the extensional velocity ves compaction trend can be used to accurately predict pore pressure within the active fold thrust belt the correction is calibrated with well data and is empirical none the less it is a first step toward understanding the magnitudes of the compressive lateral stresses involved in generating the observed porosity loss within the fold thrust belt

stress determination in active thrust belts an alternative leak off pressure interpretation abstract in thrust belts fluid flow through critically stressed fractures will occur at pressures less than the overburden stress which is the minimum stress we propose that low leak off pressures obtained in active thrust belts may result from this mechanism leading workers to infer that apparent minimum stresses are 30 60 less than the overburden stress in some compressional settings traditionally leak off pressure data have been used to constrain the magnitude of minimum stress assuming that the rock is dilating against the minimum stress during a leak off test in our new interpretation we constrain the stress state by assuming that the leak off test causes shear failure along pre existing weaknesses rather than tensile opening while this mechanism has been discussed in a small number of borehole stability and hydraulic fracture papers it has not been directly applied to leak off tests we considered this interpretation because we observed that some leak off tests imply an apparent contradiction between the stress states from the standard interpretation of leak off tests versus the stress state inferred from geologic and geophysical evidence in tectonically active thrust belts we present two examples with one in an onshore fold thrust belt and one in a deepwater fold thrust belt our new interpretation of stresses based on shear failure resolves the contradiction and also provides a constraint on the maximum horizontal stress in the fold thrust belts

magnetic properties of modern soils and quaternary loessic paleosols paleoclimatic implications the magnetic properties of paleosols developed in quaternary sequences of loess have been used for stratigraphic definition correlation with other terrestrial and deep sea sequences and paleoclimatic paleorainfall reconstruction in some loess paleosol sequences including those of the chinese loess plateau tajikistan and the czech republic maxima in magnetic susceptibility values correspond with the paleosol horizons and minima with the least weathered loess layers in other loess soil sequences including those of siberia alaska and argentina the relationship is completely opposite with susceptibility minima associated with the most developed paleosols to account for these opposite relationships the respective roles of 1 magnetic enhancement and 2 magnetic depletion and or dilution in determining soil magnetic properties are investigated for a range of modern soil types most magnetic enhancement is seen in the upper horizons of well drained cambisols absence or loss of magnetic iron oxides is apparent in acid podsol profiles and waterlogged soils for the cambisol profiles significant correlation is found between susceptibility and organic carbon cation exchange capacity and clay content the mineralogy morphology and grain size of soil magnetic carriers extracted from three modern enhanced soils and a paleosol from the chinese loess plateau are also identified by independent petrographic means microscopy and x ray diffraction of magnetic extracts magnetite and maghemite of ultrafine grain size from 0 4 to 0 001 i m are the major contributors to the magnetically enhanced soils weathering can concentrate detrital magnetic grains especially in the fine silt size fractions of soils the magnetic data from the modern soils indicate that interpretation of paleosol magnetic properties must be done on a site specific basis taking into account the possibilities of pedogenic enhancement pedogenic dilution or depletion and allochthonous inputs of magnetic minerals excessively arid wet or acid soils are unable to form significant amounts of pedogenic ferrimagnets well drained intermittently wet dry soils with reasonable buffering capacity and a substrate source of fe show most magnetic enhancement for those soils which favour magnetic enhancement processes correlation has been found between the maximum value of the pedogenic susceptibility and the annual rainfall the almost unique pedogenic system in the chinese loess plateau where variation in soil forming factors other than climate is reduced to a global minimum allows use of the paleo susceptibility values as proxy paleorainfall values to identify the mechanism of any link between magnetic properties for example susceptibility and climate change the mineralogy and grain size of soil magnetic carriers requires detailed investigation given the prospect of 1 quantitative paleorainfall records from continental loess records 2 predictions of present and future climate change and 3 the value of paleoclimate data for testing of numerical climate models such magnetic investigations can contribute significantly to our understanding of past and future environmental change

incompatible stress regimes from geological and geomechanical datasets can they be reconciled an example from the carnarvon basin western australia abstract knowledge of the in situ stress field is essential in petroleum basins as it exerts a prime control over seal integrity fracture stimulation wellbore stability and fluid flow previous geomechanical analysis of australia s carnarvon basin the continent s premier hydrocarbon region highlights a normal to strike slip fault stress regime however neotectonic evidence and contemporary seismicity suggest the possibility of a strike slip to reverse fault stress regime we attempt to reconcile these conflicting datasets through new analysis of the in situ stresses principal stress magnitudes and orientations were defined with data from 76 previously unanalysed petroleum wells wellbore image logs yield a maximum horizontal stress orientation of 113 n consistent with modelling of the stress field throughout the indo australian plate vertical stress magnitudes are estimated to range from 20 mpa km 1 to 22 4 mpa km 1 leak off tests lot from 42 wells are analysed using two methodologies one assuming tensile failure as traditionally accepted the other assuming shear failure as outlined by couzens schultz and chan 2010 and result in two different sets of horizontal stress magnitude estimates traditional interpretation of lots results in a minimum horizontal stress gradient of 16 8 mpa km 1 and a maximum horizontal stress gradient of 21 8 mpa km 1 the new method for lot interpretation results in a minimum horizontal stress gradient of 18 1 mpa km 1 and a maximum horizontal stress gradient of 25 4 mpa km 1 inclined natural fractures observed at lot depths supports application of the new method of lot interpretation traditional interpretation of stress magnitudes implies a normal to strike slip fault stress regime while the new method implies a strike slip fault stress regime this latter interpretation is favoured by the authors as it allows for a reconciliation of the geological and geomechanical datasets the assessment undertaken herein allows for reinterpretation of stress magnitudes in seismically active basins hosting differing geomechanical and neotectonic regimes potentially altering existing understanding of seal integrity fracture stimulation wellbore stability and fluid flow

delayed build up of arctic ice sheets during 400 000 year minima in insolation variability an east asian winter monsoon proxy record using grain size variations in chinese loess over the past 900 000 years shows that for up to 20 000 years after the interglacials at 400 000 year intervals the weak monsoon winds maintain a mild non glacial climate at high northern latitudes qingzhen hao and colleagues present a record of grain size variations in the chinese loess plateau a proxy of variations in the strength of the east asian winter monsoon and show that relatively high insolation at 400 000 year intervals held off the inception of the subsequent ice age for about 20 000 years relative to other glacial inceptions mechanistically the extension of warm conditions was probably linked to a weak siberian high pressure system associated with a delayed build up of northern ice and snow the authors speculate that these observations imply that arctic climate may remain in non glacial mode for more than 40 000 years even in the absence of anthropogenic greenhouse gases knowledge of the past variability of climate at high northern latitudes during astronomical analogues of the present interglacial1 may help to inform our understanding of future climate change unfortunately long term continuous records of ice sheet variability in the northern hemisphere only are scarce because records of benthic 18o content represent an integrated signal of changes in ice volume in both polar regions2 however variations in northern hemisphere ice sheets influence the siberian high3 an atmospheric pressure system so variations in the east asian winter monsoon eawm as recorded in the aeolian dust deposits on the chinese loess plateau can serve as a useful proxy of arctic climate variability before the ice core record begins here we present an eawm proxy record using grain size variations in two parallel loess sections representative of sequences across the whole of the chinese loess plateau over the past 900 000 years the results show that during periods of low eccentricity and precessional variability at approximately 400 000 year intervals the grain size inferred intensity of the eawm remains weak for up to 20 000 years after the end of the interglacial episode of high summer monsoon activity and strong pedogenesis in contrast there is a rapid increase in the eawm after the end of most other interglacials we conclude that for both the 400 000 year interglacials the weak eawm winds maintain a mild non glacial climate at high northern latitudes for much longer than expected from the conventional loess and marine oxygen isotope records during these times the less severe summer insolation minima at 65 n ref 4 would have suppressed ice and snow accumulation leading to a weak siberian high and consequently weak eawm winds

the interdisciplinary use of overpressure abstract overpressure is a polysemic word that has a variety of meanings within and across different disciplines this is likely to be a particular problem in analysis of geothermal resources where reservoir engineers volcanologists and structural geologists may each confidently use overpressure but mean different things we suggest that to avoid confusion the term should be carefully and accurately defined whenever used and ideally only used to mean fluid pressure in excess of hydrostatic pressure

geomechanical modeling using finite element method for prediction of in situ stress in krishna godavari basin india abstract this study provides quantitative rock mechanical properties and analyses of in situ stress and pore pressure in several oil gas fields of east and west godavari sub basins high pore pressure gradients varying from 11 85 to 12 80 mpa km exist within these oil gas fields vertical stress sv gradients in the range 21 00 to 22 85 mpa km are seen to exist minimum horizontal principal stress sh magnitude is found to vary from 64 to 76 of sv while maximum horizontal principal stress sh magnitude is observed to vary from 90 to 92 of sv within normally pressured to over pressured sediments the breakout derived sh orientation from two well varies from n14 e to n22 5 e in the krishna godavari basin rock mechanical properties such as young s modulus poisson s ratio and unconfined compressive strength have been estimated from logs of compressional and shear wave travel time two dimensional 2d stress modeling using finite element analysis has been carried out for some important oil gas fields situated within east and west godavari sub basins as a part of the current study regional sh orientation has been used for application of stress at the model boundary discontinuities in the stress pattern which can be associated with interfaces between weak and competent layers have been commonly observed and especially where silici clastic and volcanic inter bedded sequences are encountered the model predicted stress orientations are verified with the formation micro imager fmi log data of wells at the above mentioned sub basins

correlation between climate events in the north atlantic and china during the last glaciation episodes of massive iceberg release heinrich events 1 3 into the north atlantic ocean during the last glaciation were associated with recurring episodes of unusually cold north atlantic surface water bond cycles 4 and cold air temperatures over greenland dansgaard oeschger events 5 6 four of the youngest of these cold events have also been reported in climate records from sites outside the north atlantic region7 but until now the entire suite has been identified only in north atlantic marine sediments greenland ice core records and tentatively in french lake sediments8 here we examine grain size data from chinese loess and intercalated accretionary palaeosols of last glacial age for evidence of similar climate signals remote from the north atlantic region we see grain size maxima with ages that match those of the last six heinrich events which we interpret as an indication of the changing strength of the east asian winter monsoon which largely controls the transport and deposition of central asian aeolian dust thus it seems that these heinrich events have left their signature in the chinese loess record this is consistent with simulations of the glacial climate9 which imply that the climates of the north atlantic and china were linked by the effect of westerly winds