shallow borehole tilt a reprise we describe results from nearly a decade of tilt measurements produced by two arrays of shallow borehole tiltmeters one in a semiarid environment at pinon flat observatory pfo california depth of burial 4 5 m and the other in a maritime arctic environment at adak alaska depth of burial 2 m although renovation and reinstallation of the instruments at the two sites reduced thermal noise it did not change the secular records significantly this implies that the large tilts observed reflect instability of the ground rather than the sensor so that deeper installations should give better results the pfo data show large rainfall related tilts caused by near surface weathering and also periodic temperature related tilts from several thermoelastic effects the adak data are dominated by tilts from the annual temperature cycle though by a smaller amount than at pfo but at other frequencies they show essentially the same power levels as at pfo both data sets confirm earlier results that burial at such shallow depths even in apparently stable material is inadequate for the measurement of tectonic tilts

an outline of the plate tectonics of china china is principally a part of the eurasian plate but the margins of the indian and philippine sea plates are involved in the himalayas and in the coastal range of taiwan respectively within the eurasian plate the cathaysian paleoplate is separated from the angaraian paleoplate by the junggar hegen suture which contains paleozoic ophiolites and rare blueschists the three microplates of the cathaysian paleoplate consist of precambrian cratons and or phanerozoic accretionary fold belts these coalesced precambrian cratons record at least six stages of intense orogeny before cratonization the paleozoic to cenozoic accretionary fold belts of china can be correlated with similar events now found in west pacific andean and atlantic type active continental margins ophiolites occupying many of these tectonic zones provide evidence for the age and igneous history of oceanic crust formed during the paleozoic to cenozoic the presence of blueschist in some of these chinese sutures reveals evidence of large scale subduction and tectonic exhumation during consolidation of the eurasian plate cenozoic collision of the eurasian and indian plates produced deformation and uplift of the himalayas strongly influencing the tectonics of western china in contrast mesozoic tertiary evolution of eastern china is typical basin range geology similar to that of the western united states which included development of deep sedimentary basins along with calc alkaline plutonic and volcanic activity associated with crustal thinning and high heat flow the complicated tectonic evolution of china is greatly illuminated by the presence of ophiolites and blueschists in proterozoic to tertiary convergent boundaries these petrotectonic assemblages provide evidence of an extremely mobile history of plate movement in china

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

active faulting and paleoseismology along the bree fault lower rhine graben belgium paleoseismic analysis of the 10 km long bree fault scarp in the lower rhine graben yields numerous lines of evidence of earthquake activity in the holocene and late pleistocene this active normal fault a part of the feldbiss fault system dips 70 ne and is expressed at the surface by a prominent nw se trending 7 to 20 m high scarp formed since the deposition of the maas river main terrace 700 kyr b p trenches and geophysical prospecting show that the fault which is known to have 100 m of vertical offset since the late pliocene breaks late pleistocene and holocene deposits ground penetrating radar seismic refraction and electric tomography suggest that at shallow depth the amount of displacement is larger than the youngest vertical offset visible in the trenches and corresponds to cumulative fault displacements the analysis of 36 leveling profiles across the scarp indicates that its height can be classified into three groups likely corresponding to different events a morphologic dating gives approximate ages of 2 1 5 kyr b p 14 5 kyr b p and 41 6 kyr b p for the past three surface faulting earthquakes analysis of faulted stratigraphy and earthquake induced deformation structures exposed in trenches suggests the occurrence of three large earthquakes during the past 45 l03 years and yields 0 07 mm yr of relative vertical deformation rate the most recent seismic event occurred between a d 610 and 890 the first identification of an active fault with surface ruptures in the lower rhine graben area emphasizes that large earthquake sources exist within intraplate europe and that at least some of these events are preserved in the geologic record

long term tilt and acceleration data from the logatchev hydrothermal vent field mid atlantic ridge measured by the bremen ocean bottom tiltmeter 1 long term seafloor deformations in the logatchev hydrothermal vent field lhf at the mid atlantic ridge are largely unexplored and unknown even though the lhf has been the focus of international research for many years as seafloor tilt and vertical acceleration provide key information about seafloor deformations the bremen ocean bottom tiltmeter obt was deployed in may 2005 at position 14 45 11 7 n 44 58 47 0 w 3035 m water depth in the lhf the obt recorded 384 days and was recovered in january 2007 strong tilt steps and strong gradual tilt changes over less than a minute to days in the range of some 10 mrad and aligned mostly with the topography possibly indicate nearby mass movements like avalanches of bulk material due to local uplift or subsidence or may show tectonic activity a vertically aligned high resolution microelectromechanical systems mems accelerometer of type servo k beam in the sensor package seems to be helpful to distinguish between tilt signals caused by a true rotation and fake tilt related to a transient translational motion of the obt in a horizontal direction hodographs show elliptic motion patterns with about 1 mrad total tilt amplitude and distinct orientations of tilt toward hydrothermal vents it is up to speculation whether the latter signals are related to hydrothermal fluid circulation the amplitude spectra of these tilt signals and acceleration show discrete lines mostly between 0 1 and 50 mhz the spectra show the periodic character of those signals and also proof that tides or bottom currents which are known to show lower signal frequencies or tremor which generally has higher frequencies are most likely not the reason compared with studies onshore and offshore the lhf is most likely an area of strong and highly variable seafloor deformations

cenozoic tectonics in the urumgi korla region of the chinese tien shan cenozoic deformation within the tien shan of central asia has accommodated part of the post collisional indentation of the indian plate into asia within the urumgi korla region of the chinese tien shan this occurred dominantly on thrusts with secondary strike slip faulting the gross pattern of deformation is of moderate to steeply dipping thrusts that have overthrust foreland basins to the north and south of the range the junggar and tarim basins respectively smaller foreland basins lie within the margins of the range itself turfan chai wo pu korla and qumishi basins these lie in the footwalls of local thrust systems both the turfan and the korla basins contain major thrusts within them they are complex foreland basins deformation has progressively affected regions further into the interior of the junggar basin and propagated into the interiors of the intermontane basins no unidirectional deformation front has passed across the tien shan in the neogene and quaternary an oligocene unconformity may indicate the time of the onset of the cenozoic deformation but most of the cenozoic molasse has been deposited after the palaeogene the rate of deposition in basins next to the uplifted ranges has increased since the onset of deformation there has been at least about 80 km of cenozoic shortening across this part of the tien shan cenozoic shortening is greater in sections of the range further west these are nearer to the northern margin of the indian indenter cenozoic compression has reactivated structures created by the two late palaeozoic collisions that created the ancestral tien shan these palaeozoic structures have exerted a strong control over the style and location of the cenozoic deformation

post seismic relaxation following the 2009 april 6 l aquila italy earthquake revealed by the mass position of a broad band seismometer summary post seismic relaxation is known to occur after large or moderate earthquakes on time scales ranging from days to years or even decades in general long term deformation following seismic events has been detected by means of standard geodetic measurements although seismic instruments are only used to estimate short timescale transient processes albeit inertial seismic sensors are also sensitive to rotation around their sensitive axes the recording of very slow inclination of the ground surface at their standard output channels is practically impossible because of their design characteristics however modern force balance broad band seismometers provide the possibility to detect and measure slow surface inclination through the analysis of the mass position signal this output channel represents the integral of the broad band velocity and is generally considered only for state of health diagnostics in fact the analysis of mass position data recorded at the time of the 2009 april 6 l aquila mw 6 3 earthquake by a closely located sts 2 seismometer evidenced the occurrence of a very low frequency signal starting right at the time of the seismic event this waveform is only visible on the horizontal components and is not related to the usual drift coupled with the temperature changes this analysis suggests that the observed signal is to be ascribed to slowly developing ground inclination at the station site caused by post seismic relaxation following the main shock the observed tilt reached 1 7 10 5 rad in about 2 months this estimate is in very good agreement with the geodetic observations giving comparable tilt magnitude and direction at the same site this study represents the first seismic analysis ever for the mass position signal suggesting useful applications for usually neglected data

geology and geochemistry of bitumen vein deposits at ghost city junggar basin northwest china veins of solid bitumen occur in cretaceous sandstones at the northwest margin of the junggar basin china the bitumen has a low aromaticity and a composition comparable to gilsonite the bitumen contains abundant steranes and terpanes and s carotane although most n and i alkanes have been removed which is characteristic of the local crude oil the sterane and triterpane maturity parameters show that the bitumen local crude oil and source rocks are all mature bitumen wallrock relationships suggest that the host sandstone was not completely consolidated at the time of emplacement of the bitumen veins although bitumen emplacement was a relatively late diagenetic event the burial history for the northwest junggar basin shows that hydrocarbon generation from the assumed upper permian source rocks commenced in late triassic early jurassic times and suggests that rapid hydrocarbon generation may have resulted in overpressure contributing to the bitumen emplacement

displacement of surface monuments vertical motion several measurements of vertical ground motion at pinon flat observatory california indicate the overall weakness and instability of the earth s weathered surface with respect to the underlying rock cumulative long period motions of order 0 5 mm per year dominate these records though smaller elastic deformations caused by precipitation loading atmospheric loading and tidal strains are evident at higher frequencies all of these help to characterize the near surface material the long period records suggest that near surface weathering is the dominant influence on monument motion at least at this site on crystalline rock in a semi arid environment rainfall loading gives an average vertical modulus of 2 6 gpa for the material in the uppermost 26 m of the ground compared with 88 gpa for granite under moderate confining stress atmospheric loading gives similar results but indicates the ground is permeable to airflow at periods longer than a few hours earth tide records show poisson s ratio to be 0 09 in contrast to the normative range of 0 2 0 25 establishing that horizontal strains couple only weakly into vertical ones so that vertical strains near the surface are a poor measure of areal strain the form of the ground surface displacement power spectrum indicates that analyses of geodetic surveys would be improved with the inclusion of a monument positioning error budget that increases with time because of ground instability and the generally small rate of crustal tectonic motions deeply emplaced monuments will be needed for observational programs designed to detect short term changes in crustal deformation over baselengths of order 10 km and less

evidence of sea level rise at the early ostionan coralie site gt 3 c ad 700 grand turk turks and caicos islands abstract soil and sediment analyses were conducted on samples from the early ostionan coralie site c ad 705 60 on grand turk turks and caicos islands the earliest dated settlement site in the bahama islands the focus of these analyses was a sand layer mantling archaeological features discovered on a buried land surface the tapering wedge shaped configuration of the sand body prompted the hypothesis that it was deposited by water either a storm surge or a more gradual rise in sea level this hypothesis was tested using soil morphological descriptions particle size distribution analysis and grain characteristics contents of organic carbon and total phosphorus and identification of invertebrate organisms found in the soil samples a fining upward trend in particle size round and rolled grain shapes and a rich shallow water micro invertebrate infauna indicated a gradual marine transgression over the site as opposed to either a catastrophic storm event or aeolian deposition these results explain the incremental inland shift of settlement activity over time at coralie

point stability at shallow depths experience from tilt measurements in the lower rhine embayment germany and implications for high resolution gps and gravity recordings summary from 1996 to 1999 we have studied ground tilts at depths of between 2 m and 5 m at three sites in the lower rhine embayment lre western germany the lre is a tectonically active extensional sedimentary basin roughly 50 kmr100 km the purpose of the tilt measurements was a to provide insight into the magnitude nature and variability of background tilts and b to assess possible limitations of high resolution gps campaigns and microgravity surveys due to natural ground deformation the tilt readings sensed by biaxial borehole tiltmeters of baselength 0 85 m cover a frequency range from 10 x8 hz to 10 x2 hz periods from minutes to years assuming that the tilt signals represent ground displacements on a scale typically not larger than several times the tiltmeters baselength and that tilt signals at shallow depth could in a simple geometric way be related to changes in surface elevation and gravity we try to estimate the magnitude level of point movements and corresponding bouguer gravity effects that is generally not surpassed the largest tilt signals observed were some t50 mrad yr x1 i f they were observable over a ground section of extension e g 10 m the converted rates may correspond to about t0 5 mm per 10 m yr x1 in vertical ground displacement and t0 1 mgal yr x1 in bouguer gravity effect respectively large signals are mostly related to seasonal effects probably linked to thermomechanical strain other causes of ground deformation identified include seepage effects after rainfalls order of t10 mrad and diurnal strains due to thermal heating and or fluctuations in the water consumption of nearby trees order of t1 mrad episodic step like tilt anomalies with amplitudes up to 22 mrad at one of the observation sites might reflect creep events associated to a nearby active fault except for short term ground deformation caused by the passage of seismic waves from distant earthquakes amplitudes of non identified tilt signals in the studied frequency range seem not to exceed t2 mrad as the larger tilt signals are close to the precision achieved with modern gps systems and superconducting gravimeters when converted into height and gravity changes further enhancement in resolution of these techniques may require simultaneous recording of local ground deformation at the observation sites

borehole tilt measurements aperiodic crustal tilt in an aseismic area abstract nine months of tilt measurements at tidal sensitivity with an askania tiltmeter at a depth of 12m show aperiodic tilts with time scales of two days and upwards statistically significant correlations are found with meteorological variables and in particular with variations in the local groundwater table typically a variation in the tilt of 1 microradian is associated with a variation in the groundwater table of about 1 m the seasonal variation over the last two years in groundwater has a range of 3 m about a mean level approximately 2 5 m below the ground surface these variations have been continuously measured by a neyrpic tide gauge in a 50 m uncased borehole in addition to this seasonal variation are episodic events some in excess of 1m associated with heavy rainfall 2 3 cm these events have a rapid onset lasting 1 day followed by a decay lasting 10 days or more tilt events associated with similar groundwater variation could in a seismic region be easily mistaken for precursory tilt and this work emphasises the necessity of taking a complete account of meteorology in seismic zones where strain and tilt measurements are in progress further work is in progress with the askania tiltmeter which is now installed in an adjacent borehole at a depth of 30 m and a hughes tm 3 bubble tiltmeter installed at 12m with the aim of investigating mechanisms by which meteorology including groundwater level affects tilt most similar measurements of tilt e g in north america new zealand and germany using various techniques at different depths in different geological conditions indicate meteorological perturbations of the tilt signal and it is suggested that continuous monitoring of water table level will enable these perturbations to be better understood

water table effects on the measurement of earth strain abstract forced changes in the water head within a granite penetrating borehole were found to induce anomalously large free surface strains and tilts in the vicinity of the hole this deformation is shown to be due to fluid pressure induced changes in the aperture of a compliant hydraulically conductive fracture at a depth of 100 m and a quantitative analysis of the deformation data is performed to recover fracture characteristics the importance of the effect for secular earth strain measurements is discussed in the light of the ubiquitous nature of both water table fluctuations and fractures in the shallow crust

a mid cretaceous change from fast to slow exhumation of the western chinese altai mountains a climate driven exhumation signal abstract the chinese altai mountains in western china are bound by cenozoic transpressional strike slip faults many of which show quaternary activity to better understand how mesozoic cenozoic deformation has affected the history of exhumation and uplift of the chinese altai mountains we collected paleozoic granitoid samples for apatite fission track and apatite u th sm he thermochronology central apatite fission track ages for n 6 samples range from 68 to 104 ma whereas apatite u th sm he ages range from 56 to 272 ma for n 23 samples n 80 individual analyses across four transects in the western chinese altai our results indicate fast cooling during the late early cretaceous followed by slow cooling since thermal modeling results suggests

displacement of surface monuments horizontal motion measurements of tectonic deformation depend on both accurate instrumentation and adequate coupling of the apparatus to the earth s crust existing techniques capable of resolving the signals of interest strain rates of 10 n yr are mainly observatory based the limitation in the baselength of these instruments 1 km results in a requirement that the reference monuments be exceptionally stable 10 tzm yr however records from pition flat observatory california show that the actual horizontal displacements for massive near surface monuments eraplaced in competent weathered granite are of the order of 50 tzm yr the low noise level of the strain measurements at this site indicates that this magnitude of monument displacement is abnormally small until high accuracy geodetic techniques are developed sophisticated monuments or monument monitoring devices will be necessary to record faithfully continuous crustal deformation

origin and accumulation mechanisms of petroleum in the carboniferous volcanic rocks of the kebai fault zone western junggar basin china abstract the kebai fault zone of the west junggar basin in northwestern china is a unique region to gain insights on the formation of large scale petroleum reservoirs in volcanic rocks of the western central asian orogenic belt carboniferous volcanic rocks are widespread in the kebai fault zone and consist of basalt basaltic andesite andesite tuff volcanic breccia sandy conglomerate and metamorphic rocks the volcanic oil reservoirs are characterized by multiple sources and multi stage charge and filling history characteristic of a complex petroleum system geochemical analysis of the reservoir oil hydrocarbon inclusions and source rocks associated with these volcanic rocks was conducted to better constrain the oil source the petroleum filling history and the dominant mechanisms controlling the petroleum accumulation reservoir oil geochemistry indicates that the oil contained in the carboniferous volcanic rocks of the kebai fault zone is a mixture the oil is primarily derived from the source rock of the permian fengcheng formation p 1 f and secondarily from the permian lower wuerhe formation p 2 w compared with the p 2 w source rock p 1 f exhibits lower values of c 19 tt c 23 tt c 19 20 tt tt ts ts tm and 20r sterane c 27 c 28 ratios but higher values of tt c 23 c 21 hhi gammacerane c 30 hopane hopane 20s c 34 c 33 c 29 and c 29 20s 20s 20r ratios three major stages of oil charge occurred in the carboniferous in the middle triassic late triassic to early jurassic and in the middle jurassic to late jurassic periods respectively most of the oil charged during the first stage was lost while moderately and highly mature oils were generated and accumulated during the second and third stages oil migration and accumulation in the large scale stratigraphic reservoir was primarily controlled by the top carboniferous unconformity with better porosity and high oil enrichment developed near the unconformity secondary dissolution pores and fractures are the two major reservoir storage space types in the reservoirs structural highs and reservoirs near the unconformity are two favorable oil accumulation places the recognition of the large scale carboniferous volcanic reservoirs in the kebai fault zone and understanding of the associated petroleum accumulation mechanisms provide new insights for exploring various types of volcanic reservoir plays in old volcanic provinces and will undoubtedly encourage future oil and gas exploration of deeper strata in the region and basins elsewhere with similar settings

landslide monitoring with high resolution tilt measurements at the dollendorfer hardt landslide germany abstract to continuously monitor ground movement at the dollendorfer hardt landslide in konigswinter bonn germany a borehole and a platform tiltmeter both with a resolution of 0 1 rad were installed the station is complemented with two pressure transducers to control pore pressure and four thermistors installed at different depths precipitation data is from frankenforst manor about 2 km away the data shows clear correlation between tilt pressure and precipitation as well as daily temperature induced tilt oscillations to decompose the tilt signal we first differentiated the series three times with respect to time to separate the trend we then expanded the remaining signal into a fourier series that was truncated to cutoff signal corresponding to shorter periods than 10 days this way we separate the seasonal variation from the shorter period residual component the trend is predominantly linear amounting to a 1000 rad down slope tilt per year the residual is characterized by rainfall events we attempt to describe the tilt response to rain by a linear system with precipitation data as input and tilt signal as output the analysis shows that this model qualitatively explains several features of the tilt signal but there is also a dependence of the tilt signal on pore pressure and temperature the study shows that a continuous high resolution monitoring of slope deformation allows decomposition into different processes and is thus a reasonable basis to verify theoretical models

borehole tilt measurements from charlevoix quebec an array of three borehole tiltmeters near quebec city in eastern canada is designed to study the tidal and secular response of the crust in the charlevoix seismic zone the objectives of this study of the first year of data from two boreholes of the array are to investigate the spatial coherency of the tidal observations and determine whether there are time variations in the tidal amplitudes and phases and to describe the main features of the secular tilt signal the tidal analysis was done using a modified version of the hycon harmonic analysis program with which the time varying tidal amplitudes and phases were determined by the sequential analysis of overlapping 2 monthly subsets of the data the admittance observed for the major semidiurnal m2 and diurnal o1 constituents varies by up to 10 and 30 respectively and is strongly correlated between boreholes comparison with admittance variations determined from two nearby tide gauges indicates a strong correlation in the amplitude fluctuations pointing to a predominantly marine loading source for the time varying tilt admittance differences of up to 20 in amplitude and 5 in phase were found between the mean m2 results determined from boreholes 1 and 2 located only 80 m apart indicating small scale distortion of the local tilt field by lateral inhomogeneities the secular tilt from both boreholes correlates strongly with transient and seasonal water table fluctuations suggesting the dominant influence of pore pressure effects on the nontidal tilt a preliminary estimate of the detectability of long term regional trends in tilt is 0 4 rad yr

an investigation into shallow borehole tiltmeters shallow borehole tiltmeters are frequently used for ground deformation monitoring in volcanic areas where they are usually installed within a few meters of the surface a major problem concerns the noise affecting the installation at shallow depth where large tilt and strain are caused by temperature effects the long term stability of these instruments and the best shallow depth of installation in terms of best cost benefit are the crucial points we conducted an experiment in order to compare the signals of three shallow borehole electronic tiltmeters installed in the same place at different depths we verified the signal reliability in revealing the long term slow deformation and looked into the reduction of the temperature effects with depth we present three years of data and discuss the limits and the advantages of the different installation depths

implications of palaeozoic ophiolites from western junggar nw china for the tectonics of central asia western junggar nw china contains fragments of several palaeozoic island arcs accretionary prisms and ophiolites which were accreted to each other and possibly to the southern margin of eurasia by the end of the palaeozoic the ophiolites of western junggar are important in reconstructions of these events four ophiolite belts are recognized from south to north these are tangbale mayila dalabute and barleik honggulueleng hebukesair they record the production and destruction of oceanic tracts in this region from the cambrian to the carboniferous the following characteristics are representative of them all 1 the ophiolitic successions are strongly deformed 2 sheeted dyke swarms are not preserved 3 basic igneous rocks show a range of chemical characteristics from depleted island arc tholeiite to ocean island basalt altered n type mid ocean basalts may be represented 4 large scale thrusts typically directed towards the southeast lie at the base of many individual ophiolitic bodies 5 the ophiolites rarely mark the position of possible sutures between arcs they are normally highly deformed and imbricated with other lithologies accretion of palaeozoic arcs and obduction of ophiolites was complete by the end of the carboniferous but the timing and sequence of events remain obscure no continental collisions occurred during this period of assembly crustal growth occurred by the amalgamation of non continental blocks

a simple pendulum borehole tiltmeter based on a triaxial optical fibre displacement sensor sensitive instruments like strainmeters and tiltmeters are necessary for measuring slowly varying low amplitude earth deformations nonetheless laser and fibre interferometers are particularly suitable for interrogating such instruments due to their extreme precision and accuracy in this paper a practical design of a simple pendulum borehole tiltmeter based on laser fibre interferometric displacement sensors is presented a prototype instrument has been constructed using welded borosilicate with a pendulum length of 0 85 m resulting in a main resonance frequency of 0 6 hz by implementing three coplanar extrinsic fibre fabry perot in terferometric probes and appropriate signal filtering our instrument provides tilt measurements that are insensitive to parasitic deformations caused by temperature and pressure variations this prototype has been installed in an underground facility rustrel france where results show accurate measurements of earth strains derived from earth and ocean tides local hydro logic effects as well as local and remote earthquakes the large dynamic range and the high sensitivity of this tiltmeter render it an invaluable tool for numerous geophysical applications such as transient fault motion volcanic strain and reservoir monitoring

first triassic palaeomagnetic constraints from junggar nw china and their implications for the mesozoic tectonics in central asia northwestern china belts result from the palaeozoic collage of central asia and the subsequent reactivations due to far field effects of the mesozoic tibetan and the cenozoic himalayan collisions triassic is a crucial period to understand and decipher the tectonics related to these two episodes about 250 oriented palaeomagnetic cores from 43 sites were collected from six sections of upper permian to late triassic sandstone in south and west junggar northwestern china thermomagnetic irm and hysteresis measurements reveal magnetite as the main carrier of the magnetic remanence with minor hematite and maghemite stepwise thermal demagnetisation has generally isolated two components the low temperature component up to 300 350 c displays a direction consistent with the present day geomagnetic field the locality mean directions related to the high temperature component above 350 c were also calculated two out of six sections display intense viscous magnetisation and the occurrence of maghemite reveals a possible cenozoic chemical remagnetisation for these two localities for the other four localities we assume that the magnetisation is primary because 1 ams measurements reveal a primary fabric 2 there are local occurrences of antipodal polarities and 3 palaeolatitudes of tilt corrected poles are compatible with previous studies the consistency between the early triassic poles of west and south junggar indicates that junggar evolved as a rigid block only since early mesozoic the comparison of the late palaeozoic and the early mesozoic poles of junggar and those of siberia and tarim shows major rotations between the late permian and the late jurassic early cretaceous these periods of discrete rotations are characterized by strike slip faulting in tianshan and altai and they may correlate with the major episodes of coarse grained detrital sedimentation and uplift of the range especially the counter clockwise rotations of junggar relative to tarim and siberia which occurred between the early and the late triassic and between the late triassic and the late jurassic are accommodated by transpressive tectonics in the tianshan and the altai belts this reactivation is a far field effect of tibetan blocks diachronous collisions therefore these first triassic palaeomagnetic results from junggar infer that post carboniferous rotations were due to the combined effect of the post orogenic transcurrent movement and the mesozoic oblique reactivation

gravity changes and natural gas extraction in groningen gravity observations made over the groningen gasfield from 1978 onwards are available the existing gravity data were reanalysed and a new survey was carried out the observed gravity changes obtained during four surveys spanning an 18 year period were compared with the gravity effect due to natural gas extraction computed from the reservoir model and the production data the random error in the gravity values is small enough to detect the effect of gas extraction after a few years up to 2 gal year the trends obtained from observed and calculated gravity changes agree well within their expected error margins after statistical data snooping due to the inadequate measurement set up of the previous surveys systematic errors present in the gravity data hampered the use of this data for refinement of the reservoir and the production models however with improved gravity monitoring in particular a very systematic network set up and well calibrated instruments this should now be feasible by using the network analysis from the 1996 measurements for the planning of a network in space and time most of the current problems can be avoided

upper permian lacustrine organic facies evolution southern junggar basin nw china abstract the jingjingzigou lucaogou and hongyanchi formations of the southern junggar basin together comprise over 1000 m of organic rich lacustrine facies they record an overall evolution from relatively shallow evaporative lakes to freshwater lakes associated with fluvial systems the jingjingzigou formation is characterized by low toc and hi and biomarker features such as abundant carotane consistent with a specialized saline or hypersaline biota biomarker distributions in jingjingzigou formation extracts most closely resemble oils from the giant karamay oilfield the lucaogou formation represents one of the richest and thickest lacustrine source rock intervals in the world yet it contradicts conventional lacustrine source rock models in at least two important aspects first deposition occurred at middle paleolatitudes 39 43 n rather than in the tropics second limited nutrient supply in a drainage basin dominated by intermediate volcanic rocks appears to have caused low to moderate primary productivities stable salinity stratification and low inorganic sedimentation rates in a deep lake nonetheless resulted in deposits with up to 20 toc and hi near 800 the overlying hongyanchi formation has 1 5 toc but low hi and was deposited in freshwater oxic to sub oxic lakes

intact microbial fossils in the permian lucaogou formation oil shale junggar basin nw china abstract the permian lucaogou formation was deposited in a deep stratified lake with good preservation of the organic matter in the sediments likely due to anoxic bottom waters the lucaogou formation oil shale contains excellent source rocks with high toc contents 12 4 32 9 wt and high hi values 547 869 mg hc g toc the maceral compositions of the oil shales are dominated by lamalginite with some higher plant debris spherical structures about 75 150 m in diameter having yellow fluorescence were observed in the shale edx sem showed that these contained c o p and ca two kinds of well preserved microbial fossils with different morphology were found in these spherical structures using a confocal laser scanning microscope and sem ellipsoidal cells 1 1 5 m long and 0 5 1 m wide occurred inside the spherical structure whereas microspherical cells occur within the outer layers through excluding modern contaminants and endolithic microbes we propose that these microbial fossils are indigenous and syngenetic with oil shale deposition their close physical association in the sediments suggests a symbiotic relationship hydrocarbon extracts of these oil shales have relatively depleted carbon isotopic signatures which is suggestive of methane oxidation this was confirmed by analysis of abundant c 29 and c 30 17 21 h hopanes which show distinctly negative 13 c values typical of those found in methanotrophs several possibilities are presented for the identity of these microorganisms but it is not yet possible to state unequivocally that they are related to methane production and consumption

exploring deformation scenarios in timanfaya volcanic area lanzarote canary islands from gnss and ground based geodetic observations abstract we report on a detailed geodetic continuous monitoring in timanfaya volcanic area tva where the most intense geothermal anomalies of lanzarote island are located we analyze about three years of gnss data collected on a small network of five permanent stations one of which at tva deployed on the island and nearly 20 years of tiltmeter and strainmeter records acquired at los camelleros site settled in the facilities of the geodynamics laboratory of lanzarote within tva this study is intended to contribute to understanding the active tectonics on lanzarote island and its origin mainly in tva after characterizing and filtering out the seasonal periodicities related to non tectonic sources from the geodetic records a tentative ground deformation field is reconstructed through the analysis of both tilt strain records and the time evolution of the baselines ranging the gnss stations the joint interpretation of the collected geodetic data show that the area of the strongest geothermal anomaly in tva is currently undergoing a se trending relative displacement at a rate of about 3 mm year this area even experiences a significant subsidence with a maximum rate of about 6 mm year moreover we examine the possible relation between the observed deformations and atmospheric effects by modelling the response functions of temperature and rain recorded in the laboratory finally from the retrieval of the deformation patterns and the joint analysis of geodetic and environmental observations we propose a qualitative model of the interplaying role between the hydrological systems and the geothermal anomalies namely we explain the detected time correlation between rainfall and ground deformation because of the enhancement of the thermal transfer from the underground heat source driven by the infiltration of meteoric water

a comparison of tiltmeters at tidal frequencies different techniques for measuring crustal deformation are now being tested at pinon flat geophysical observatory in southern california as a part of this comparison we have analyzed five months of data from four different tiltmeters three borehole instruments two 4 5 m and one 26 m deep and a long base 535 m instrument at the surface for periods from 1 hour to 10 days the signals from the deep borehole and long base instruments show comparable noise levels the shallow instruments are much noisier tidal analyses give results for the different sensors which agree to within the errors which are several percent

the role of recent tectonics and hydrological processes in the evolution of recurring landslides on the danube s high bank in dunafoldvar hungary abstract there are high loess banks prone to landslide along the river danube in hungary one of these is the high loess bank in dunafoldvar where several landslides occurred in the last decades quantitative relationships between the movements of the high loess bank and the variation of the water level of the river danube the ground water table precipitation and temperature are investigated by two borehole tiltmeters and a vertical borehole extensometer the twelve year long observation from 2002 to 2014 made it possible to distinguish between the high bank movements due to slow recent tectonic and geomorphologic processes and the short period from hours to months movements caused by hydrometeorological effects the results revealed that besides geomorphologic processes recent tectonics can play an important role in the recurrence of landslides in the area in the investigated period the total tilt of the high bank was 162 rad in the sse direction according to the geomorphologic and recent tectonic processes in the surroundings of dunafoldvar investigations of the relationships between the high bank movements and the water level of the river danube ground water table changes and the precipitation revealed that the tilt magnitudes caused by the ground water table variations are two orders of magnitude greater than the tilts caused by the water level regime of the river and the direct effect of the precipitation on the high bank tilts can be disregarded

tilt observations from shallow and deep borehole arrays measurements of the earth tide using tilt and strainmeter data can be used to infer crustal structure however in almost all measurements of crustal motion using shallow tiltmeters and strainmeters reference is made to the degradation of the data implied to be caused by influence of meteorological parameters on near surface layers for example studies by wood and king and goulty et al indicated that a substantial portion of measured crustal motion by shallow tilt and strain data may be attributed to the weather these studies were limited to data outside the tidal band however it is important to determine the effects of weather on these data within the tidal band if shallow tiltmeters are to be used to determine crustal structure collocated deep and shallow borehole tiltmeter arrays were operated by the air force geophysics laboratory in eastern massachusetts and provided an opportunity to investigate weather effects on shallow tilt the tiltmeters installed in deep boreholes 100 m yielded internally consistent m2 amplitudes 2 and phases 3 cabaniss and mcconnell but the collocated shallow 4 m borehole tilt array did not produce the same results least squares analyses of the shallow tilt data revealed variations of 20 for m2 tidal amplitude compared to the deep data a multichannel wiener filter technique was used to investigate the hypothesis that this discrepancy was due to meteorological influence results indicated that approximately one half of the anomalous m2 power was correlated with air and borehole temperatures it is suggested that the remaining anomalous power may be due to ground deformation caused by the action of groundwater if this is true shallow tiltmeters might not be measuring the same deformation as the deep instruments and therefore not capable of measuring the earth tide with the accuracy required to determine crustal structure

dynamics of fault creep observations along the surface traces of active faults in california and elsewhere indicate that tectonic displacement can occur as seismic slip or as aseismic fault creep fault creep occurs as secular displacement and as displacement episodes called creep events which last a few hours to days and include from a millimeter or less to a few tens of millimeters of displacement instrumental measurements of displacement versus time during creep events show that many events have a characteristic simple form including a steep beginning followed by a gradual decay in the rate of displacement some creep events display small amounts of precursory slip and many seem to be composed of several discrete simple events propagation of creep events along the san andreas calaveras and imperial faults in california has been inferred from the nearly simultaneous observation of creep events at nearby creepmeters and from kinematic modeling of continuous measurements of strain during creep events fault creep can be viewed as arising from the interplay of three factors stress applied to the fault from external sources stress caused by the geometry and distribution of displacement on the fault arising from the elastic response of the surrounding medium to the displacements within the anelastic fault zone itself and the constitutive relations characterizing the resistance to slip on the fault analytic solutions are presented for a simple rectangular dislocation quasi static model of nonpropagating fault creep assuming viscous and quasi plastic power law creep fault zone rheology and for a multi element composed of several rectangular or striplike dislocation surfaces quasi static model assuming a viscous rheology viscous rheology implies solutions composed of exponentials that decay with time the simple one element quasi plastic model is in agreement with the form of creep events observed at melendy ranch california a matrix formulation is presented to calculate dislocation stresses on a fault zone in a half space or plate the formulation involves the division of the dislocation surface into strips or rectangles and the use of published solutions to calculate the stress resulting from displacement on each individual element results from the matrix method agree with analytic results for equilibrium displacements on stress free cracks the matrix formulation is then used as the basis for a numerical method to simulate one and two dimensional propagating creep assuming a quasi plastic rheology on the fault zone results from this method agree reasonably well with observations of afterslip from the 1966 parkfield 1975 oroville and 1979 imperial valley california earthquakes and of a propagating creep event observed along the southern calaveras fault central california during july 1977 this method of analysis and the assumption that creep at each point on the fault zone follows a power law rheology after the applied stress reaches a spatially varying yield stress can explain the secular and episodic nature of fault creep afterslip the simple shape of some individual events and the multiple composite shape of others and the propagation of creep events on the southern calaveras fault observations of propagating creep indicate a yield stress near zero at the surface and throughout much of the fault zone however they also indicate the presence of a zone at a depth of about 0 5 km and about 5 km long with a yield stress of about 15 bars 1 5 mpa the methods of solution presented here should be applicable to many problems in the dynamics of faulting

recent crustal movements of tectonic or human originborehole tilt measurements aperiodic crustal tilt in an aseismic area nine months of tilt measurements at tidal sensitivity with an askania tiltmeter at a depth of 12m show aperiodic tilts with time scales of two days and upwards statistically significant correlations are found with meteorological variables and in particular with variations in the local groundwater table typically a variation in the tilt of 1 microradian is associated with a variation in the groundwater table of about 1 m the seasonal variation over the last two years in groundwater has a range of 3 m about a mean level approximately 2 5 m below the ground surface these variations have been continuously measured by a neyrpic tide gauge in a 50 m uncased borehole in addition to this seasonal variation are episodic events some in excess of 1m associated with heavy rainfall 2 3 cm these events have a rapid onset lasting 1 day followed by a decay lasting 10 days or more tilt events associated with similar groundwater variation could in a seismic region be easily mistaken for precursory tilt and this work emphasises the necessity of taking a complete account of meteorology in seismic zones where strain and tilt measurements are in progress further work is in progress with the askania tiltmeter which is now installed in an adjacent borehole at a depth of 30 m and a hughes tm 3 bubble tiltmeter installed at 12m with the aim of investigating mechanisms by which meteorology including groundwater level affects tilt most similar measurements of tilt e g in north america new zealand and germany using various techniques at different depths in different geological conditions indicate meteorological perturbations of the tilt signal and it is suggested that continuous monitoring of water table level will enable these perturbations to be better understood

late paleozoic paleogeographic reconstruction of western central asia based upon paleomagnetic data and its geodynamic implications abstract carboniferous to permian volcanoclastic rocks have been collected from south junggar and west junggar primary magnetizations have been observed from the characteristic components of 10 sites of early permian p1 and late permian p2 red beds of south junggar area the 14 early carboniferous sites from west junggar mountains expose post folding secondary magnetizations and according to their spatial distribution 9 remagnetized sites are related to late carboniferous early permian granite emplacement whereas 5 sites are located at the vicinity of late permian mafic dykes two new paleomagnetic poles have been consequently calculated for the periods of p1 at 79 5 n 36 6 e and of p2 at 60 4 n 4 7 e with a95 of 6 8 and 5 4 respectively they yield two paleomagnetic poles at 65 3 n 329 7 e with a95 of 6 3 and 64 8 n 179 5 e with a95 of 6 9 respectively compilation of available data shows stationary and consistent poles for south junggar area during the carboniferous and permian whereas nw junggar underwent a significant anticlockwise rotation between the late carboniferous early permian and the late permian indicating that junggar was not a rigid block up to the end of the paleozoic west junggar and south junggar may have experienced contrasting tectonic evolutions comparisons of late paleozoic poles of central asia blocks show 1 counterclockwise rotation of west junggar with respect to siberia contrasting with the clockwise rotation of north kazakhstan with respect to siberia 2 no significant movements between west junggar north kazakhstan and siberia since late permian indicating that they were rigidly welded since that time and 3 anticlockwise rotations of tarim yili and south junggar with respect to the welded siberia kazakhstan west junggar block such rotations may have been accommodated by late permian to early triassic strike slip faults with an estimation of the displacements of 1570 280 km along the irtysh gornotsaev shear zone 410 380 km along the nikolaiev nalati tectonic line and 490 250 km along the chingiz alakol north tian shan fault since late permian time

strainmeters and tiltmeters despite steady effort over the last century continuously recording tiltmeters and strainmeters have not yet been successful except for earth tide measurements this article reviews the techniques and instrument designs that have been developed in this field the continuous measurement of true tectonic motions which have rates of 10 14 s 1 requires extremely high instrument stability but more rapid motions tides and seismic waves apart are even smaller and not much more easily detectable much past effort has been spent improving the transducers used in these instruments which usually measure small displacements the commonest choices are optical the most accurate capacitive the most sensitive and inductive the most rugged nowadays building a transducer is the easiest part a much harder task equally important to a good design is attaching the instrument to the ground so that it can detect the signal wanted this part of the design includes choosing a location a large underground opening is thermally stable but distorting a surface installation is easy to build but noisy because of soil weathering and a borehole is inaccessible to weather but also to the operator all such installations and indeed the whole field of strain and tilt measurement of course rely on the assumption that the deformations of interest can be measured over baselengths of a few hundred meters or less this is true for tides and seismic waves but unproven for tectonic motions appropriate attachment techniques differ for each location and many mundane details such as cementing techniques for borehole instruments remain to be worked out the goal of measuring tectonic and tidal tilt has created many tiltmeter designs most are relatively small instruments that use some form of pendulum or bubble level a few use a liquid surface to measure tilts over a long baseline repeated experience has shown the latter type when well built to be superior to the former proving end monument motions to be a dominant source of noise the same appears to hold true for strainmeters the best results coming from long base laser instruments though strainmeters using rigid or flexible material length standards are useful for special purposes and borehole instruments show promise because achieving a good design has been so difficult it is important to select the goals an instrument must meet and be prepared to compromise on others the difficulty of validating results from this type of instrument makes comparison tests essential such tests as have been made so far show that good results cannot be gotten at low cost or without careful attention to details

poroelasticity observations of anomalous near surface tilt induced by ground water pumping abstract ground tilt signals observed at three different test sites in germany confirm earlier observations of surface deformation occurences caused by the withdrawal of ground water from nearby wells the strength of the signals presented here ranges from a few rad to 230 rad whereby ground tilt was measured in shallow boreholes at depths between 2 and 4 m analysis of the tilt signals suggests that local inhomogeneities in the subsoil can have significant impact on several signal parameters namely its maximum amplitude its variation in time and its strike with respect to the direction of the productive well the observed data emphasize the likelihood of various causes for deviations from the normal tilt response that holds for an isotropic poroelastic half space in particular at one site a reverse well level change also known as noordbergum effect in hydrogeology is seen together with a respective response in the tilt signal the study concludes that near surface deformation in the vicinity of pumped wells bears a wealth of information that may be useful to constrain the conditions of fluid flow at depth and that there is a need for model calculations to fully understand the involved phenomena

using surface deformation to image reservoir dynamics the inversion of surface deformation data such as tilt displacement or strain provides a noninvasive method for monitoring subsurface volume change reservoir volume change is related directly to processes such as pressure variations induced by injection and withdrawal the inversion procedure is illustrated by an application to tiltmeter data from the hijiori test site in japan an inversion of surface tilt data allows us to image flow processes in a fractured granodiorite approximately 650 barrels of water injected 2 km below the surface produces a peak surface tilt of the order of 0 8 microradians we find that the pattern of volume change in the granodiorite is very asymmetrical elongated in a north northwesterly direction and the maximum volume change is offset by more than 0 7 km to the east of the pumping well the inversion of a suite of leveling data from the wilmington oil field in long beach california images large scale reservoir volume changes in 12 one to two year increments from 1

reconciling geodetic and geological rates of vertical crustal motion in intraplate regions abstract tectonic motion rates of individual faults and regional deformation in an intraplate setting are estimated based on the analysis of ten yearly surveys of a regional levelling network in ne ardenne w europe owing to the frequency and number of measurement epochs much greater than in classical comparisons of general surveys the tectonic and near surface components of ground motion are clearly separated the marked temporal variability in ground motion strongly depends on the amount of precipitation fallen during the six months preceding each survey and the subsequent drying off of the subsoil at the time of the surveys moreover the ground response to this influence varies from place to place leading to high differential movements at the local scale taking into account the percentage of surveyed faults which moved tectonically during the time of the study i calculate fault motion rates of 0 06 0 09 mm yr similar to geological rates moreover the data indicate that one way for intraplate normal faults to accommodate tectonic strain aseismically is intermittent fault creep with short episodes of a few mm displacement separated by many year long time intervals of fault quiescence a flexural deformation shows the superposition of a tilt event on a trend corresponding to a tilt rate of 0 16 rad yr for a 2 8 km long segment

diagenesis and reservoir potential of permian triassic fluvial lacustrine sandstones in the southern junggar basin northwestern china the junggar basin is one of the largest oil producing areas in china and contains upper permian lacustrine oil shales with some of the greatest hydrocarbon potental in the world in this study we present the diagenetic characteristics of permian triassic sandstones from the southern junggar basin and evaluate their reservoir potential the uppermost permian and lower triassic cangfanggou group in the southern junggar basin is characterized by alternating fluvial and lacustrine deposits whereas the middle upper triassic xiaoquangou group was deposited predominantly in a lacustrine environment fluvial and deltaic sedimentation was subordinate the sandstones of the cangfanggou and xiaoquangou groups are volcanic litharenites their detrital modes and textures of volcanic fragments suggest a primarily andesitic basaltic volcanic arc provenance early diagenesis of the sandstones is characterized by nonferroan calcite cementation grain coating pore lining clay minerals and the initial dissolution of detrital grains authigenic quartz pore filling phyllosilicates pore filling grain replacive zeolites albitized detrital plagioclase authigenic k feldspar copyright 1997 the american association of petroleum geologists all rights reserved 1manuscript received april 15 1996 revised manuscript received november 4 1996 final acceptance may 2 1997 2department of earth sciences university of western ontario london ontario n6a 5b7 canada 3school of geosciences queen s university of belfast belfast bt7 1nn united kingdom this work was done at the queen s university of belfast with funding from exxon bhp mobil and itotal which we gratefully acknowledge the karamay institute of petroleum exploration and development generously provided borehole samples geng ansong at the institute of geochemistry guangzhou academia sinica and zhou yisheng at the xinjiang institute of petroleum are thanked for assistance with field work and for valuable discussions special thanks go to the staff of the electron microscopy unit at the queen s university of belfast we also thank a h ruffell and s r lawrence for their constructive comments on an earlier version of the manuscript stable isotope analysis and ongoing research concerning the junggar basin at the university of western ontario have been supported by the natural science and engineering research council of canada the manuscript benefited substantially from critical commentary by kevin t biddle suzanne kairo w r kaiser and an anonymous reviewer

upper permian junggar and upper triassic ordos lacustrine source rocks in northwest and central china organic geochemistry petroleum potential and predicted organofacies abstract two sets of lacustrine source rocks in the junggar basin and ordos basin have been analysed by organic geochemical approach and organic petrographic technique one of these source rocks the junggar shales lucaogou formation and hongyanchi formation was deposited in a hydrologically closed brackish lake under a sub humid climate in higher latitude 39 43 n and consisted of organic rich profundal lake shales lucaogou formation and lean fluvial lacustrine lake margin mudstones the other one the chang 7 shale was deposited in a hydrologically open freshwater lake under a humid climate in a 31 n palaeolatitude and was characterized by high concentration of alginite rich organic matter the profundal lucaogou shale and chang 7 3 shale possess abundant total organic carbon high generative potential s2 and high hydrogen indices which rank as the best prolific source rocks in both basins followed by chang 7 1 shale hongyanchi formation and chang 7 2 are much leaner than their counterparts and contain relatively small portion of alginite but more terrigenous macerals this nature of organic matter makes them less prolific and becoming gas prone potential these differences in petroleum potential mirror depositional environment changes in source rocks formation potential source rocks in both basins have the potential for generating high wax oil but the brackish system clearly contains more pna oil the kerogen structures revealed by pyrolysis gas chromatography allowexplaining this trend the lucaogou chang 7 3 and chang 7 1 shales enriching in long and moderate alkyl chains share a nature of high wax oil generation trend in contrast the hongyanchi and chang 7 2 shales appears to be dominated by short to moderated chain length distribution and higher overall aromaticity to generate more pna oil even gas and condensate thermal liability was shown to be linked to kerogen structure in particular the presence of alicyclic and oxygen containing moieties and these in turn are correlate with total organic carbon content