thermal structure and seismicity of subducting lithosphere it has recently been suggested that the mechanical behaviour of the oceanic and continental uppermost mantle depends on temperature alone and that there is no strong evidence for compositional effects it seems in the majority of cases that if uppermost mantle temperatures exceed 600 c any deformation that occurs does so in the absence of significant seismicity this observation apparently applies irrespective of whether that mantle material underlies an ocean or a continent this paper investigates whether the same behaviour exists for earthquakes occurring in descending lithospheric slabs namely whether there is some limiting temperature above which deformation occurs without significant seismicity and whether that limiting temperature is consistent with the behaviour seen in the uppermost mantle beneath oceans and continents by re examining the thermal structure in subducting slabs accounting for the temperature dependence of the relevant physical parameters teleseismically recorded seismicity is shown to be limited to material having potential temperatures less than not vert similar570 600 c or homologous temperatures less than not vert similar0 42 the exceptions to this pattern occur in the subhorizontally subducting regions of the nazca plate in which temperatures are probably affected by the relatively cold overriding plate

cyclostratigraphic and δ13c record of the lower cretaceous adriatic platform croatia assessment of milankovitch forcing abstract the 700 m thick hauterivian to albian section from the interior of the large adriatic platform is exposed on mljet and korcula islands croatia the cyclic platform consists of meter scale parasequences bundled into parasequence sets superbundles and then into breccia bounded depositional sequences spectral analysis of time series cycle number vs cycle thickness shows peaks in the short term eccentricity 95 to 130 kyr bands and 160 to 200 kyr bands isotope samples from micrite matrix of mudstone and wackestone have 13c values generally from 1 5 to 2 vpdb and 18o from 1 to 3 5 vpdb adriatic platform 13c values are shifted 2 vpdb more negative than marine pelagic values a 13c and 18o meteoric signal is limited to just beneath sequence boundaries suggesting that the isotopic shift is due mainly to marine phreatic and synorogenic burial diagenesis major excursions on the 5 point smoothed 13c profile of the adriatic platform tied biostratigraphically to 13c curves from pelagic sections include the oceanic anoxic events oae1a 1b and 1c time series constructed from 13c values unsmoothed data vs stratigraphic position show peaks in the milankovitch band especially short term eccentricity most positive peaks are near parasequence set boundaries 50 to 60 and regressive parts of parasequences 20 although diagenetically shifted the 13c record retains a highly clipped memory of astronomically driven global 13c fluctuations albeit modified by platform water restriction during cyclic deposition

palaeoclimate aptian mystery solved the volcanic eruption that created the ontong java plateau released large quantities of carbon dioxide a reconstruction of co2 concentrations suggests that the eruption promoted climate change and the expansion of ocean anoxia

eccentricity paced monsoon like system along the northwestern tethyan margin during the valanginian early cretaceous new insights from detrital and nutrient fluxes into the vocontian basin se france high resolution changes in terrigenous and nutrient fluxes into the vocontian basin northwestern tethyan margin were investigated for the late berriasian late valanginian time interval in order to assess the precipitation patterns in the source areas and to evaluate the effect of orbital forcing on the strength of the hydrological cycle in this study new high resolution mineralogical bulk rock and clay fraction and geochemical phosphorus and oxygen isotope data are used from the astronomically calibrated orpierre section for the first time kaolinite detrital and phosphorus accumulation rates kar dar and par are calculated and compared to a set of 547 geochemical and 260 mineralogical published data from other vocontian sections it appears that three regional increases in the kar document three successive humid episodes during the valanginian this is confirmed by contemporaneous increases in dar and partly also in par which highlight higher terrigenous and nutrient fluxes to the vocontian basin during these episodes concomitant decreases in the 18owhole rock signals may reflect higher sea surface temperatures during the early valanginian and the early late valanginian transition the occurrence of the three humid episodes is interpreted to relate to an orbital paced monsoonal circulation pattern through seasonally reversing movements of air mass heat and precipitation over the northwestern tethyan margin in particular based on the correlation between the 405 kyr eccentricity cycles and the kar signal obtained at orpierre an eccentricity influenced monsoonal circulation is proposed as the possible forcing factor behind these climatic patterns the average duration between the climaxes of the three regional wetter episodes is approximately 2 43 myr the wetter and likely also warmer episode at the early late valanginian transition is in step with the onset of the weissert episode in this regard the intensification of monsoonal driven precipitations appears as a possible external forcing factor leading or at least accelerating the important perturbation in the global carbon cycle associated with the weissert episode

cyclostratigraphy and orbital tuning of the terrestrial upper santonian lower danian in songliao basin northeastern china abstract the songke 1 north sk 1n borehole recovered a continuous 1541 66 m late santonian early danian terrestrial succession in songliao basin sb northeastern china it provides a unique record for improving our understanding of continental paleoclimate and ecological system in cretaceous greenhouse world here we use thorium th logging data as a paleoenvironmental and paleoclimatic proxy to conduct a detailed cyclostratigraphic study on the sk 1n core power spectra evolutionary fast fourier transformation and wavelet analysis all reveal significant decameter to meter scale sedimentary cycles in the nenjiang k 2 n sifangtai k 2 s and mingshui k 2 m formations the ratios of cycle wavelengths in these stratigraphic units are 20 5 2 1 and are interpreted as milankovitch cycles of 405 kyr and 100 kyr eccentricity 38 4 kyr obliquity and 20 kyr precession cycles respectively an astronomical time scale ats is established by tuning filtered 405 kyr eccentricity cycles to a target curve of the astronomical solution la2010d based on the magnetostratigraphic time framework of the sk 1n borehole this ats provides precise numerical ages for stratigraphic boundaries biozones geological and geophysical events and serves as a basis for correlation of strata and events between marine and terrestrial systems the cretaceous paleogene k pg campanian maastrichtian santonian campanian boundaries are estimated at core depths of 318 m 752 8 m and 1751 1 m respectively a 3 8 myr long hiatus between the nenjiang k 2 n and sifangtai k 2 s formations occurs from 76 1 to 79 9 million years ago the ages and durations of magnetochrons c33r to c30n are precisely estimated and provide new constraints on the late cretaceous geomagnetic polarity time scale gpts and south atlantic sea floor spreading rates

relations among subduction parameters clues to the dynamics of the subduction process are found in the many measurable parameters of modern subduction zones based on a critical appraisal of the geophysical and geological literature 26 parameters are estimated for each of 39 modern subduction zones to isolate causal relationships among these parameters multivariate analysis is applied to this data set this analysis yields empirical quantitative relations that predict strain regime and strike slip faulting in the overriding plate maximum earthquake magnitude benioff zone length slab dip arc trench gap and maximum trench depth excellent correlation is found between length of the benioff zone and the product of convergence rate and age of the downgoing slab this relationship is consistent with the conductive heating model of molnar et al 1979 if the model is modified in one respect the rate of heating of the slab is not constant it is substantially slower during passage of the slab beneath the accretionary prism and overriding plate the structural style in the overriding plate is determined by its stress state though the stress state of overriding plates cannot be quantified one can classify each individual subduction zone into one of seven semiquantitative strain classes that form a continuum from strongly extensional class 1 back arc spreading to strongly compressional class 7 active folding and thrusting this analysis indicates that strain class is probably determined by a linear combination of convergence rate slab age and shallow slab dip interplate coupling controlled by convergence rate and slab age is an important control on strain regime and the primary control on earthquake magnitude arc parallel strike slip faulting is a common feature of convergent margins forming a forearc sliver between the strike slip fault and trench optimum conditions for the development of forearc slivers are oblique convergence a compressional environment and a continental overriding plate the primary factor controlling presence of strike slip faulting is coupling strongly oblique convergence is not required the rate of strike slip faulting is affected by both convergence obliquity and convergence rate maximum trench depth is a response to flexure of the underthrusting plate the amount of flexural deflection at the trench depends on the vertical component of slab pull force which is very sensitive to slab age and shallow slab dip shallow slab dip conforms to the cross sectional shape of the overriding plate which is controlled by width of the accretionary prism and duration of subduction deep slab dip is affected by the mantle trajectory established at shallow depth but may be modified by mantle flow much of the structural complexity of convergent margins is probably attributable to terrane juxtaposition associated with temporal changes in both forearc strike slip faulting and strain regime empirical equations relating subduction parameters can provide both a focus for future theoretical studies and a conceptual and kinematic link between plate tectonics and the geology of subduction zones

conjunctive use of spectral gamma ray logs and clay mineralogy in defining late jurassic early cretaceous palaeoclimate change dorset u k abstract detrital clay mineralogy is controlled by weathered source rock climate transport and deposition that in turn influence the spectral gamma ray sgr response of resultant sediments whilst a palaeoclimate signal in clay mineralogy has been established in some ancient successions the sgr response remains contentious largely because the data sets have yet to be collected at the same or appropriate vertical scales to allow comparison in addition the influence of organic matter on sgr is not always considered here we present clay mineralogical total organic carbon toc and sgr analyses from the late jurassic and early cretaceous of the wessex basin a period of previously documented palaeoclimate change the aim of this paper is to estimate the sensitivity of sgr as palaeoclimatic tool sgr and clay mineral data having been collected at the same sample points making this one of the most rigorous comparison of clay mineral and sgr to date overall the correlation between high thorium potassium or thorium uranium and kaolinite associated with a well established palaeoclimate change shows that elevated thorium may be used as a proxy for humid palaeoweathering as suggested by few previous studies

astronomical tuning of the aptian stage from italian reference sections a high resolution grayscale series of the pelagic fucoid marls piobbico core central italy shows strong pervasive lithological rhythms throughout the aptian interval a hierarchy of centimeter to meter scale cycles characterizes the rhythms when calibrating 1 m cycles to earth s 405 k y orbital eccentricity cycle these rhythms correspond to the periods of the eccentricity obliquity and precession index tuning to orbital eccentricity cycles provides a high resolution time scale for the aptian correlation to the cismon core northern italy extends the tuning to the aptian barremian boundary the tuning indicates a minimum duration of 13 42 m y for the aptian stage where previous estimates range from 6 4 to 13 8 m y the combined aptian albian astronomical tuning of the entire 77 m long piobbico core and part of the cismon core provides a 25 85 m y long astronomically calibrated time scale for earth history

intraplate seismicity and stresses in young oceanic lithosphere we have conducted a systematic study of oceanic intraplate seismicity in the period 1964 1983 occurring in lithosphere younger than 35 million years focal mechanisms determined for 26 events using first motions p wave modeling and surface wave amplitude radiation patterns along with 13 previously determined mechanisms indicate a diversity of faulting styles and stress orientations in young oceanic lithosphere there is no evidence for a worldwide transition from extension to compression at a specific lithospheric age tensional axes of normal faulting events are oriented oblique to the spreading direction and do not show extension in the spreading direction congressional axes of thrust events show a weak preferred orientation in the spreading direction presumably due to ridge push stresses however stress axes of thrust events in very young lithosphere age 9 ma do not show a correlation with the spreading direction suggesting that the ridge push force is small near the ridge these observations indicate that tensional stress in the spreading direction is concentrated in a very narrow zone at the ridge axis in agreement with models which assume that the axial region has very little tensile strength normal faulting events occur at greater depths and temperatures than thrust events possibly because rocks under tensional stress have strength maxima at higher temperatures alternatively the depths of the normal faulting events may be a result of the higher thermal gradients at depth in young lithosphere if thermoelastic stresses are important in generating this seismicity differential thermal contraction along fracture zones does not seem to be a significant source of near ridge intraplate seismicity high seismicity rates in young lithosphere noted previously on a global scale seem characteristic of all three major ocean basins additionally most of the total oceanic intraplate moment release takes place in young lithosphere however most of the events and more than 96 of the total moment release of the near ridge intraplate seismicity are contained in five areas two zones in the indian ocean one near chagos bank and the other in the amsterdam st paul region indicate tension parallel to the trend of the plate boundary a region of high seismicity near the east pacific rise between 3 and 7 n shows both normal and thrust faulting while another region on the cocos plate west of the panama fracture zone is characterized by strike slip faulting thrust strike slip and normal faulting events are found in a small seismically active zone of the south central pacific the extremely uneven distribution of seismicity if not a result of the relatively short time period studied 20 years indicates local perturbations strongly affect near ridge seismicity

stable isotopic evidence for climate and basin evolution of the late cretaceous songliao basin china abstract because of the need to understand the links and feedbacks of the carbon cycle during times of global greenhouse conditions numerous studies have focused on the cretaceous climate much of what we know about this warm period in earth s history comes from the study of ocean sediments recovered from both ocean drill cores and marine sediments exposed at the earth s surface in contrast there are few studies of cretaceous terrestrial sediments the songliao basin located in northeast china offers a unique opportunity to understand cretaceous paleoclimate of terrestrial settings because it contains a nearly complete record of lacustrine sediments deposited throughout the cretaceous and there is an active drilling program to recover core from this paleolake we present carbon oxygen and strontium isotopic data from ostracods collected from two drill cores sk 1 n and sk 1 s that cover a time interval that extends from the turonian through the maastrichtian these data record robust isotopic trends with numerous carbon and oxygen isotope shifts that are both rapid and long term we tentatively interpret this record to reflect changes in both global climate and regional basin evolution in the turonian and coniacian qingshankou formation we observe several carbon isotope shifts that appear to be correlative to marine isotopic records based upon timing and magnitude of the isotopic changes we suggest that the carbon isotope record in the songliao basin reflect the decrease in carbon isotope ratios following the strong positive excursion at the cenomanian turonian boundary a positive isotope excursion in the late turonian and the negative isotope shift that occurs at the turonian coniacian boundary upward in the section however the marine and songliao isotopic records diverge as sediment sources shift from the southwest east and north to more northerly strontium isotopes record the change in source region as they increase markedly between the coniacian santonian yaojia and santonian campanian nenjiang formations as this is the first isotopic record of the songliao basin we are cautious about many of our interpretations of these isotopic data yet it is clear that with tighter age constraints and focused sampling centered on many of the isotope excursions presented here will allow for a deeper understanding of the terrestrial response to changing climate and the hydrologic response to basin evolution

axial obliquity control on the greenhouse carbon budget through middle to high latitude reservoirs carbon sources and sinks are key components of the climate feedback system yet their response to external forcing remains poorly constrained particularly for past greenhouse climates carbon isotope data indicate systematic million year scale transfers of carbon between surface reservoirs during and immediately after the late cretaceous thermal maximum peaking in the cenomanian turonian circa 97 91 million years myr ago here we calibrate albian to campanian 108 72 myr ago high resolution carbon isotope records with a refined chronology and demonstrate how net transfers between reservoirs are plausibly controlled by 1 myr changes in the amplitude of axial obliquity the amplitude modulating terms are absent from the frequency domain representation of insolation series and require a nonlinear cumulative mechanism to become expressed in power spectra of isotope time series mass balance modeling suggests that the residence time of carbon in the ocean atmosphere system is by itself insufficient to explain the myr scale variability it is proposed that the astronomical control was imparted by a transient storage of organic matter or methane in quasi stable reservoirs wetlands soils marginal zones of marine euxinic strata and potentially permafrost that responded nonlinearly to obliquity driven changes in high latitude insolation and or meridional insolation gradients while these reservoirs are probably underrepresented in the geological record due to their quasi stable character they might have provided an important control on the dynamics and stability of the greenhouse climate

determinations of focal depths of earthquakes associated with the bending of oceanic plates at trenches abstract the earthquakes examined in this paper are all within the oceanic lithosphere and are associated with the bending of plates before subduction accurate determinations of the depth of these earthquakes are needed to study the stress pattern within a bending plate routinely determined depths of shallow sub oceanic earthquakes published in bulletins are unreliable the depths can be accurately determined to within a few kilometers if the original seismograms from these events are studied in some cases the reflected phases pp and pwp can be clearly identified there exists the possibility that the wave reflected at the water air interface pwp may be misidentified as pp leading to erroneous estimates of depth additional methods of analysis such as surface wave radiation patterns or the apparent frequency dependence of reflection at the crust water interface can remove this possible source of confusion one of the most powerful techniques for depth analysis is the modelling of long period waveforms the pattern of stresses within the bending oceanic lithosphere revealed by the depths and focal mechanisms of these intraplate earthquakes is one of horizontal deviatoric tension down to a depth of about 25 km with horizontal compression at greater depths

the depths of the deepest deep earthquakes the maximum depth of seismic activity is a fundamental observation providing a constraint on models of mantle dynamics although most recent investigations of mantle seismicity and dynamics state that seismicity extends to about 700 km focal depths of 720 km have been reported for large earthquakes as well as depths greater than 800 km for small events we have examined focal depths of events in several catalogs and conclude that 1 the deepest reliable focal depths are at about 670 680 km and events with focal depths beneath 600 km occur in several widely separated geographic regions 2 observations supporting focal depths exceeding 680 km are usually few poor or inconsistent 3 the reduction of seismic activity beneath about 650 km is quite abrupt however we cannot determine whether activity stops completely at 670 680 km or the maximum size of events decreases gradually beneath 650 km with magnitudes of 6 5 7 0 occasionally occurring at 650 km magnitudes of 5 5 6 0 at 680 km 4 0 4 5 at 695 km etc several models can explain the absence of seismic activity in the lower mantle two models are consistent with the abrupt termination of activity at about 650 680 km in widely separated areas a barrier which resists penetration by the subducting lithosphere or a phase transition which modifies the properties of the subducted material as it goes into the lower mantle

whole mantle convection and the thermal evolution of the earth abstract three recent results in the fields of geophysics and geochemistry have combined to rejuvenate the study of the earth s thermal history the first and perhaps most important of these is the new understanding of the planetary accretion process which has been realized as a consequence of work by v s safronov and others this work shows that the terrestrial planets accrete on a time scale of 10 8 y by the accumulation of planetesimal sized objects and that they probably form sufficiently hot to induce immediate differentiation of iron from silicates the second important recent contribution has been from geochemistry and concerns the net complement of radioactivity of the earth as a whole although the net complement of radioactive elements has usually been inferred on the basis of the assumption of equilibrium with the surface heat flow a priori analysis based upon elemental condensation temperatures in the primitive solar nebula yields a model in which the net radioactivity is at least a factor of two less than would be required to explain the mean surface heat flow there are good reasons to believe that this model is valid for the earth the third result has been the successful development of a technique for incorporating the influence of convective heat transfer in a thermal evolution model which does not require explicit solution of the dynamical equations this paper begins with an analysis of the mantle convective circulation which is required to understand plate tectonics and continental drift an analysis which presents the arguments for and against the crucial notion that the main circulation has a depth scale equal to the mantle thickness using the idea of parameterized convection the radial heat transfer by the mantle convective circulation is included in a thermal history model of the earth this model turns out to contain within it an interesting explanation of the fact that no crustal rocks with ages in excess of 3 8 ga have ever been found an observation that has heretofore proven enigmatic

astronomically forced variations in multiresolution resistivity logs of lower upper cretaceous cenomanian coniacian terrestrial formations from the songliao basin northeastern china abstract continuous and high resolution well logs from the sk 2 east sk 2e borehole in the songliao basin provide an opportunity to understand the relationship between astronomically forced climate and electrical responses in terrestrial cretaceous strata here we present well logs mud logs and core measurement data of lacustrine deposits in the upper cretaceous qingshankou fm and of fluvial deltaic deposits in the quantou fm the multiresolution resistivity logs used for the cyclostratigraphic analysis include deep laterolog resistivity logs resistivity image logs and array induction logs the results show that the resistivity of strata in quantou fm mainly reflects changes in clay content and that resistivity logs can be used as paleoenvironmental and paleoclimate proxies in cyclostratigraphic studies of the quantou fm for the qingshankou fm formation resistivity is mainly affected by clay minerals which contribute to the overall electrical conductivity as well as nonconductive organic carbon increasing clay and organic carbon contents usually correspond to wetter and warmer climatic conditions the phase relationship between resistivity logs and astronomical cyclicity depends on factors that control resistivity spectral analyses of lithological changes and resistivity logs indicate the presence of eccentricity obliquity and precession cycles throughout the quantou fm this provides strong evidence that climate was the dominant control on cyclic sedimentation in the quantou fm the floating astronomical timescale which was established by calibrating extracted 405 kyr cycles from resistivity logs reveals that the duration of quantou fm was approximately 5 5 myr comparative analysis of power spectra reveals that the sensitivity of resistivity logs with specific resolutions to milankovitch cycles with different frequencies is variable comprehensive analysis of multiresolution resistivity logs is a new method in cyclostratigraphy analysis that has the potential to be effective in detecting signals of milankovitch cycles in terrestrial deposits

slab pull and the seismotectonics of subducting lithosphere this synthesis links many seismic and tectonic processes at subduction zones including great subduction earthquakes to the sinking of subducted plate earthquake data and tectonic modeling for subduction zones indicate that the slab pull force is much larger than the ridge push force interactions between the forces that drive and resist plate motions cause spatially and temporally localized stresses that lead to characteristic earthquake activity providing details on how subduction occurs compression is localized across a locked interface thrust zone because both the ridge push and the slab pull forces are resisted there the slab pull force increases with increasing plate age thus because the slab pull force tends to bend subducted plate downward and decrease the force acting normal to the interface thrust zone the characteristic maximum earthquake at a given interface thrust zone is inversely related to the age of the subducted plate the 1960 chile earthquake mw 9 5 the largest earthquake to occur in historic times began its rupture at an interface bounding oceanic plate 30 m y old however this rupture initiation was associated with the locally oldest subducting lithosphere weakest coupling the rupture propagated southward along an interface bounding progressively younger oceanic lithosphere terminating near the subducting chile rise prior to a great subduction earthquake the sinking subducted slab will cause increased tension at depths of 50 200 km with greatest tension near the shallow zone resisting plate subduction plate sinking not only leads to compressional stresses at a locked interface thrust zone but may load compressional stresses at plate depths of 260 350 km provided that the shallow sinking occurs faster than the relaxation time of the deeper mantle this explains k mogi s observations of m 7 thrust earthquakes at depths of 260 350 km immediately downdip and within 3 years prior to five great shallow earthquakes of northern japan the slab pull model explains the lower layer of double seismic zones as due to tension from the deeper sinking plate and the upper layer as due to localized in plate compression as plate motion is resisted by the bounding mantle just downdip of the interface thrust zone there occurs an aseismic 20 50 dip increase of subducted plate this slab bend reflects the summed slab pull force of deeper plate and probably is at the crustal basalt to eclogite phase change resistance to subduction provided by a continually developing slab bend may be an important factor in the size of slab pull force delivered to an interface thrust zone

astrochronology of the valanginian stage from reference sections vocontian basin france and palaeoenvironmental implications for the weissert event abstract high resolution gamma ray measurements performed on five biostratigraphically well dated reference sections from the vocontian basin south eastern france are used to develop a new astrochronology of the valanginian stage and its subdivisions i e ammonite and calcareous nannofossil zones and subzones spectral analyses show a pervasive dominance of 405 kyr eccentricity cycles with the expression of 100 kyr eccentricity obliquity and precession previous rough estimates of valanginian stage duration ranged from 3 9 to 6 5 myr but were generally based on less reliable or indirect methods this study provides a precise duration of 5 08 myr tuning the series to the 405 kyr eccentricity cycle thus further enhancing the accuracy of the geologic time scale new durations of magnetochrons are proposed based on intercalibration between ammonite and calcareous nannofossil biozones cyclostratigraphy and carbon isotope stratigraphy after integrating orbitally calibrated durations and available radio isotopic ages for the berriasian hauterivian interval a link between the weissert event and the emplacement of the parana etendeka traps now appears unlikely strontium carbon and oxygen isotope stratigraphy sedimentological and palaeontological features clay mineralogy and the orbital record during the upper valanginian all suggest that a transient cool arid climate occurred after the carbon isotope event possibly associated with limited polar ice

the rupture process and asperity distribution of three great earthquakes from long period diffracted p waves moment tensor source mechanisms for the largest twenty nine shallow earthquakes from 1981 m s 6 5 have been determined using long period rayleigh wave spectra and p wave first motions recorded by the international deployment of accelerograms ida global digital seismic network gdsn and world wide standardised seismic network wwssn these are compared with the centroid moment tensor mechanisms presented by dziewonski and woodhouse which were obtained in a contrasting manner in most cases the source is well represented by a single double couple mechanisms with good agreement of scalar moment and orientation between the two studies apparent mismatches for other cases may be interpreted in terms of source complexity we emphasise the objectivity of comparing moment tensor elements apparent discrepancies in the moment and orientation of double couple fault plane solutions are usually due to differences in the mxz and myz moment tensor elements which are poorly constrained by long period data

timing of the north south china collision from new middle to late mesozoic paleomagnetic data from the north china block we collected paleomagnetic samples from 43 sites of middle and upper jurassic and cretaceous rocks along a 250 km wide east west trending belt located north of the suture between the north and south china blocks in each case laboratory treatment isolates dual polarity antipodal magnetizations that are demonstrably pre folding the paleomagnetic poles show very good coherence with coeval poles from other localities from the north china block ncb suggesting the apparent polar wander path apwp from the ncb is not distorted by post middle jurassic local vertical axis block rotations a comparison of the ncb apwp with that from the south china block suggests that collision continued after the early jurassic and ended no later than the late jurassic a cusp in the ncb apwp coincides with a marked angular unconformity that separates middle jurassic from upper jurassic and younger sediments together these observations indicate that the scissor like collision and associated deformation ceased at the middle to late jurassic boundary 159 ma the time of rapid 1 ma relative angular velocity between the two plates 225 to 190 ma coincides with a peak in u pb and ar ar dates obtained from metamorphic rocks in the suture the combined late jurassic and cretaceous paleomagnetic data from both blocks suggest that the united china plate traveled 2000 km north relative to eurasia during the late jurassic before docking in the cretaceous this younger collision event is also marked by a cusp on the cretaceous part of the eurasian apwp

influence of palaeoclimate and hydrothermal activity on organic matter accumulation in lacustrine black shales from the lower cretaceous bayingebi formation of the yin e basin china abstract the lacustrine black shales of the lower cretaceous bayingebi formation are an important hydrocarbon source rock in the yin e basin it is important to understand the mechanism of organic matter accumulation in these shales to reconstruct the palaeoenvironment and palaeoclimate in the early cretaceous in northwestern china and search for potential oil and gas resources based on petrological elemental geochemical and organic geochemistry analyses of typical field profile samples the influence of palaeoclimate and hydrothermal activity on organic matter accumulation in different sedimentary units unit i ii and iii is revealed unit ii has the highest total organic matter abundance tocavg 5 95 mainly type i kerogen lamalginite which is in the immature to low mature stage organic carbon isotope data 13corg element ratios sr cu and c value and weathering indexes including cia ciw and pia together revealed that the region experienced a semihumid to semiarid palaeoclimate in the middle of the early cretaceous the increase in rainfall in unit ii enhanced the abundance of lake algae and surrounding terrestrial vascular vegetation and elevated the lake level which contributed to adequate sources and favourable preservation conditions for organic matter accumulation several lines of evidence including high sulfur contents the combination of vein pyrite and micritic dolomite positive eu anomalies and element geochemical correlations confirm the existence of intermittent low temperature white smoker type hydrothermal activity the decrease of oxygen content in lake bottom water may be related to the input of hydrothermal fluid which provided necessary nutrient elements for biological productivity according to palaeontological and radioisotope dating data it can be inferred that the black shales of the bayingebi formation are the product of the combined effect of global palaeotemperature rise in the early aptian stage of the early cretaceous and intermittent low temperature hydrothermal activity

from tectonic reconstruction to upper mantle model an application to the alpine mediterranean region abstract de jonge m r wortel m j r and spakman w 1993 from tectonic reconstruction to upper mantle model an application to the alpine mediterranean region in m j r wortel u hansen and r sabadini editors relationships between mantle processes and geological processes at or near the earth s surface tectonophysics 223 53 65 the seismic velocity structure of the upper mantle and lithosphere in the mediterranean region is very complex many areas with anomalous p wave velocities can be recognized by means of seismic tomography in view of the complicated tectonic evolution of the peri mediterranean orogens and basins this is not surprising in this study we will show results of a modelling approach we have recently developed to predict this structure in this approach we make a quantitative connection between the tectonic evolution on one hand and the present seismic velocity structure on the other our model predicts the evolution of temperature distributions in the lower lithosphere and upper mantle by simulating the flow of material inferred from a kinematic description of lithosphere scale processes from the modelled present thermal state the endpoint of an evolution we calculate expected seismic velocity anomalies that can be compared with results obtained by seismic tomography thus the method enables us to compare the implications of geological reconstructions describing the past tectonic processes with seismological results for the present structure the predicted mantle models show a good correlation with the tomographic results obtained for the mantle this means we can verify many features present in the tectonic scenarios with the seismologically determined deep structure

dynamic models of subduction geophysical and geological evidence in the tyrrhenian sea summary predictions based on a 2 d finite element model for subduction underneath the calabrian arc in southern italy are compared with a variety of geophysical and geological data such as the present day stress pattern within the slab uplift from the elevation of marine terraces in calabria and subsidence in the tyrrhenian marsili basin from odp leg 107 we model the behaviour of the slab driven by slab pull in agreement with the present tectonic style in this part of the mediterranean as suggested by several investigators the model accounts for the crustal lithospheric and mantle structures in a vertical cross section perpendicular to the calabrian subduction zone the shape of the slab is constrained on the basis of new tomographic images in the southern tyrrhenian sea which were obtained from the regional seismic stations of the istituto nazionale di geofisica while the rheological properties of the mantle are taken from global dynamic models density contrasts between the subducted slab and the surrounding mantle based on petrological models drive the flow in our viscoelastic model stress values displacements and vertical velocities at the surface are sampled at different times after loading until dynamic equilibrium is reached our estimates are appropriate for a time window of 100 kyr the validity of our comparison with the geological record is based on the assumption that the tectonic configuration in the past was not substantially different from that of the present day two families of models with unlocked and locked subduction faults are considered the unlocked models allow for roll back of the trench of about 20 mm yr in agreement with some geological estimates the same family of models predicts uplift of the calabrian arc of about 1 mm yr l and subsidence in the marsili basin of 1 2 mm yr in agreement with geological surveys the deviatoric stress obtained from the unlocked model is consistent with the continuous distribution of deep seismicity in the southern tyrrhenian sea with minor concentration within the lithospheric wedge locked models fail to reproduce these geophysical and geological observations predictions derived from a detached slab model are not consistent with the continuous hypocentral distribution of deep seismicity in the southern tyrrhenian sea deformation at the surface and the stress patterns at depth for a detached slab differ substantially from those of a continuous plate dynamic topography and horizontal motions are reduced when compared with the continuous plate with deviatoric stresses concentrated within the relict slab our results indicate that subduction is a major tectonic process in the southern tyrrhenian sea

chronology of the terrestrial upper cretaceous in the songliao basin northeast asia the cretaceous was a period of great environmental biological and geodynamical change but a paucity of an accurate time frame for continental strata has prevented our understanding of the terrestrial processes and the integration of marine and terrestrial records here we present an integrated chronology for the terrestrial upper cretaceous in east asia based on new high resolution magnetostratigraphic results and previously published sims u pb zircon analyses of the cretaceous continental scientific drilling borehole sequence from the songliao basin in northeast china hereafter termed ccsd sk i which consists of a sedimentary sequence from the upper quantou formation k2q to the mingshui formation k2m correlation to the geomagnetic polarity timescale was achieved by combining magnetostratigraphic and sims u pb zircon geochronologic data and lithostratigraphy our correlation suggests that the ccsd sk i sedimentary sequence spans from the upper chron c34n to chron c29r the age of the sedimentary sequence from the upper quantou formation k2q to the mingshui formation k2m in the songliao basin can thus be constrained to an interval from the turonian to the maastrichtian ages in addition our correlation puts the cretaceous paleogene boundary in the upper part of member 2 of the mingshui formation k2m2 the constructed comprehensive chronology allows the precise correlation of the terrestrial upper cretaceous of the songliao basin to marine strata as well as other continental sequences

subduction zone seismicity and the thermo mechanical evolution of downgoing lithosphere in this paper we discuss characteristic features of subduction zone seismicity at depths between about 100 km and 700 km with emphasis on the role of temperature and rheology in controlling the deformation of and the seismic energy release in downgoing lithosphere this is done in two steps after a brief review of earlier developments we first show that the depth distribution of hypocentres at depths between 100 km and 700 km in subducted lithosphere can be explained by a model in which seismic activity is confined to those parts of the slab which have temperatures below a depth dependent critical valuetcr

deep seismicity and modes of deformation in tonga subduction zone the geometry of deep 400 km earthquakes in the subducting western edge of the pacific plate when related to the local distribution of seismic activity reveals a complex pattern of planes of shear failure enabling the modes of deformation by which the descending plate shortens and thickens to be identified the deepest part of the slab is displaced laterally suggesting that it fails to penetrate the discontinuity at 670 km

rupture history of the great bolivian earthquake slab interaction with the 660 km discontinuity teleseismic body waves of the great bolivian earthquake of june 9 1994 are analyzed to determine the focal parameters and rupture history broadband seismograms reveal a complex rupture process a small initial event mw 7 2 was followed about 10 s later by a large moment release pulse of about 40 s duration focal mechanisms determined for the mainshock indicate normal faulting with one very shallow ne dipping plane azimuthal variation in body wave displacement pulse widths suggest northward rupture from master event and body wave inversion the main moment release is located 25 50 km ne of the initiation point at about 650 km depth with only small depth variations between the initial and main event this suggests that rupture was n directed on the near horizontal plane because the slab along other parts of the andean arc at about 600 km depth dips steeply a sub horizontal plane may imply shearing perpendicular to slab dip downdip compression on a sub horizontal plane would then imply that the slab does not penetrate the 660 km seismic discontinuity but rather is being sheared out to the ne this interpretation is not unique as other scenarios are also possible such an event immediately above the 660 km discontinuity suggests massive deformation above the discontinuity with no smooth slab penetration into the lower mantle

stratigraphy correlation depositional environments and cyclicity of the early cretaceous yixian and jurassic cretaceous tuchengzi formations in the sihetun area ne china based on three continuous cores abstract three continuous cores acquired in the sihetun area of liaoning province famous for feathered non avian dinosaurs of the jehol biota reveal the stratigraphic and facies relationships of the divisions of the early cretaceous yixian and underlying jurassic early cretaceous tuchengzi formations based on these cores we propose a modified lithostratigraphic nomenclature in the sihetun sub basin in which the yixian formation is divided into three members the lujiatun member a fluvial and alluvial volcaniclastic sandstone and conglomerate unconformably overlying the tuchengzi formation with articulated tetrapods plausibly preserved in burrows the xiatulaigou member an extrusive basaltic flow and breccia comprising the only true lavas in the area and the jianshangou member a cyclical lacustrine mudstone containing a taphocoenosis of articulated compression fossils with soft tissue preservation including non avian dinosaurs birds pterosaurs mammals fish crustaceans insects mollusks and plants the latter is divided into 4 units the basal dajianshanzi bed a shallow water lacustrine unit with abundant mollusks and rooted zones the anjiagou bed the main tetrapod bearing unit consisting of microlaminated dark gray mudstones with many interbedded airfall ashes deposited in a meromictic lake the hengdaozi bed comprised of thin and rhythmically to medium bedded light gray to tan mudstones and sandstones with few discrete ashes famous for its diverse insects and plants including early angiosperms deposited in alternating dysoxic and oxygenated bottom water and the huangbanjigou bed the most obviously cyclical of the units with dark gray microlaminated intervals with articulated vertebrates alternating with more massive lighter colored mudstones and volcaniclastic sandstones deposited in lakes that oscillated in depth cyclicity in the jianshangou member is dominated by meter scale cycles that may be paced by orbital variations unambiguous relatively rapid lateral facies changes within the yixian formation are suggestive of local relief not the bottom of a giant flat bottomed basin

double seismic zones and stresses of intermediate depth earthquakes data from japanese local seismograph networks suggest that the stresses in double seismic zones are in plate compression for the upper zone and in plate tension for the lower zone the stresses do not necessarily appear to be down dip it may therefore be possible to identify other double seismic zones on the basis of data which indicate that events with differing orientations of in plate stresses occur in a given segment of slab a global survey of published focal mechanisms for intermediate depth earthquakes suggests that the stress in the slab is controlled at least in part by the age of the slab and the rate of convergence old and slow slabs are under in plate tensile stresses and the amount of in plate compression in the slab increases with increasing convergence rate or decreasing slab age young and fast slabs are an exception to this trend all such slabs are down dip tensile since these slabs all subduct under continents they may be bent by continental loading double seismic zones are not a feature common to all subduction zones and are only observed in slabs which are not dominated by tensile or compressive stresses unbending of the lithosphere and upper mantle phase changes are unlikely to be the causes of the major features of double zones although they may contribute to producing some of their characteristics sagging or thermal effects possibly aided by asthenospheric relative motion may produce the local deviatoric stresses that cause double zones

foraminiferal response to seasonality modulated by orbital cycles in the cretaceous mid latitudes the albian record from the lower saxony basin abstract the mid cretaceous serves as an excellent laboratory for testing the dynamics of the climate under greenhouse state of the earth this study is focused on the cyclicity record of foraminiferal assemblages in the lower saxony basin during the middle albian the short eccentricity obliquity and precession cycles are consistently recorded in absolute and relative abundance of most opportunistic benthic and planktic foraminifers the question is why foraminifers reacted to orbital cycles and what they actually record in the equable global climate it is suggested that seasonality changes modulated by orbital cycles are responsible for the milankovitch cyclicity records it is well known that the axial obliquity directly influences seasonal contrasts in mid and high latitudes the precession modulated by the eccentricity of the earth orbit further affects the contrast of seasons therefore seasonal dynamics of precipitation runoff and storm tracks patterns and to a lesser extent temperature contrasts are most likely factors controlling milankovitch scale cyclic fluctuations of foraminiferal assemblages and other proxies sensitive to productivity changes it can be deduced that periods of the highest seasonal contrasts were dominated by opportunistic abundant taxa such as benthic valvulineria gyroidinoides group and planktic hedbergellids which record the strongest obliquity signals the lower saxony and adjacent boreal basins were possibly controlled by humid climate with relatively dry summers and wet winter seasons this study confronted with the presented conceptual model and former climate models supports the conclusion that the temperate zone surrounding tethys was sensitive to seasonal changes modulated by orbital cyclicity the mid latitudinal climate of the greenhouse earth seems to be more dynamic and more seasonal than expected

resolution experiments for nw pacific subduction zone tomography we investigate the resolving power of isc neic p travel time data in tomographic inversions for the geometry of the subduction zones in the nw pacific from thermal models for the kurile japan izu bonin mariana and ryukyu slabs we generate three dimensional synthetic velocity anomalies for subducting slabs which are then projected onto a cell model for the uppermost 1400 km of the mantle using these synthetic models we compute synthetic delay times for ray paths corresponding to the source and receiver locations used for the actual data add gaussian noise invert the synthetic data and compare the resulting velocity structure to the initial synthetic models this comparison is illustrated for sections through the kuriles and the mariana arcs a variety of resolution artifacts are observed which in many cases resemble features visible in the tomographic results obtained from inverting the actual isc neic data

cretaceous paleogeography and paleoclimate and the setting of ski borehole sites in songliao basin northeast china article i nfo as a paradigm of greenhouse climate in earth s history the cretaceous provides significant rock records of global climate changes under conditions of greenhouse climate the songliao basin among the longest dura tion 85 90 m y of continental sedimentary basins provides an excellent opportunity to recover a nearly complete cretaceous terrestrial sedimentary record extensive lake deposits ten kilometers deep and cover ing an area of 260 000 km 2 of the songliao basin provide unique detailed records that can be tied to the glob al stratigraphic time scale thereby improving our understanding of the continental paleoclimate and ecological system the two coreholes at skis and skin sites were drilled into this basin and completed with a total length of 2485 89 m of recovered core that spanned the complete middle to upper cretaceous strata in the basin the unique geological setting of long term continuous subsidence within the largest cretaceous landmass in the world makes the cretaceous songliao basin of northeastern china an ideal place to study cretaceous climate change on the continent this paper reviews the literature on the paleogeography and paleoclimate of the northern east asia and the songliao basin during the cretaceous based on the climatolog ically sensitive deposits oxygen isotope studies and paleontology the climate during the cretaceous in the songliao basin was temperate and humid with relatively abundant rainfall during the period significant changes four cooling three warming and three semiarid events are generally consistent with the oxygen isotope data from east asia and the four cooling events in berriasian valanginian aptian albian early santonian and campanian maastrichtian may be related to potential glaciations in cretaceous

cyclostratigraphy and astrochronology case studies from china abstract a high precision geologic time scale is the essential key for understanding the earth s evolutionary history and geologic processes astronomical tuning of orbitally forced stratigraphic records to construct high resolution astronomical time scales ats has led to a progressive refinement of the geologic time scale over the past two decades in turn these studies provide new insights regarding the durations and rates of major earth events evolutionary processes and climate changes all of which provide a scientific basis for contextualizing and predicting future global change trends south china hosts some of the best exposed and well dated neoproterozoic through mesozoic stratigraphic sections in the world many of which are suitable for cyclostratigraphy and calibrating the geologic time scale in north china several cenozoic oil bearing basins have deep boreholes with continuous sampling and or well logging that enable derivation of astronomically tuned time scales for an improved understanding of basin evolution and hydrocarbon generation this special issue focuses on case studies of astrochronology and applied cyclostratigraphy research using reference sections within china in this introductory overview we 1 summarize all existing astrochronology studies of the neoproterozoic through cenozoic sections within china that have been used to enhance the international geologic time scale 2 examine briefly the astronomically forced paleoclimate information recorded in various depositional systems and the modern techniques employed to analyze the periodicity of these signals encoded within the sedimentary record and 3 summarize the 20 contributions to this special issue of palaeogeography palaeoclimatology palaeoecology on cyclostratigraphy and astrochronology case studies from china

asperities barriers characteristic earthquakes and strong motion prediction recent results from paleoseismology suggest that earthquakes recurrent on a given fault may often have the same characteristic length and amount of slip stable asperities and barriers which survive many earthquakes can explain these results the activity of volcano usu japan since 1977 which produced a dacite dome with a total upheaval of 180 m offered a great opportunity to study the recurrence behavior of a fault seismologists at hokkaido university revealed a family of repeated earthquakes with nearly the same amount of slip generated from the same fault plane on the crater wall along which the dome moved upward this family can be explained by the existence of a stable asperity on the crater wall and is called the asperity type family they found however another type of family of earthquakes which share the same fault plane but show a great range of variation in the amount of slip the behavior of the latter family can be explained by the presence of weak barriers over a fault plane defined by strong stable barriers and this family is referred to as the barrier type family this type of earthquake model has been used successfully in the interpretation of observed strong motion acceleration spectra from california and the results reveal the stability of local stress drop among different earthquakes the agreement found between local stress drops estimated from strong motion data and those inferred from geological observation supports the possibility for predicting earthquake strong motion directly from geological observation of the causative fault

seismological constraints on the mechanism of deep earthquakes temperature dependence of deep earthquake source properties abstract seismological observations are of vital importance for understanding the mechanism of deep earthquakes most of the seismological observables for earthquakes deeper than 300 km are similar to shallow earthquakes deep earthquakes clearly represent shear failure on a planar surface as shown by their double couple mechanisms deep earthquake aftershock sequences show temporal decay rates and magnitude frequency relations b values that are similar to shallow earthquakes with the aftershocks occurring preferentially along the mainshock fault planes in addition deep earthquake rupture velocities are similar to those of shallow earthquakes however there are also some observations that are clearly distinctive relative to shallow earthquakes stress drops of deep earthquakes show a large variation but are larger on average than shallow earthquakes different deep seismic zones show very different b values in contrast to shallow earthquakes which show similar b values worldwide in addition deep earthquakes show fewer aftershocks than shallow earthquakes a variety of observations suggest that deep earthquakes are highly sensitive to the temperature of the slab both deep earthquake b values and the rate of deep earthquake aftershock occurrence are inversely correlated with the temperature of the deep slabs suggesting that these factors are temperature controlled to an extent much greater than with shallow earthquakes large deep earthquakes in warm slabs show slower rupture velocities larger stress drops and lower seismic efficiencies than similar earthquakes in cold slabs the width of deep seismic zones is also probably temperature controlled but deep earthquake rupture can propagate outside the normal limits of benioff zone seismicity simple thermal models for the tonga slab near the 1994 deep earthquake suggest that the temperature at the rupture termination point was at least 200 c warmer than the temperature that limits smaller earthquakes in the slab these observations can be used to evaluate physical models for deep earthquakes including brittle slip along fluid weakened faults transformational faulting and thermal and perhaps melt lubricated shear instabilities it is difficult to explain the large fault widths of some deep earthquakes using a fluid weakening model since hydrated materials are expected in only a narrow depth zone at the top of the slab and the fault planes do not have the expected orientations for reactivated faults the lateral extent of the largest deep earthquakes cast doubt on the transformational faulting model in which events should be confined within a narrow metastable wedge seismological studies have also failed to find evidence for the existence of metastable olivine in slabs the temperature dependence of deep earthquakes argues in favor of a temperature activated phenomenon such as thermal shear instabilities and perhaps fault zone melting

melting of forsterite mg2sio4 up to 15 gpa the melting curve of forsterite has been studied by static experiment up to a pressure of 15 gpa forsterite melts congruently at least up to 12 7 gpa the congruent melting temperature is expressed by the kraut kennedy equation in the following form tm k 2163 1 3 0 v0 v v0 where the volume change with pressure was calculated by the birch managhan equation of state with the isothermal bulk modulus k0 125 4 gpa and its pressure derivative k 5 33 the triple point of forsterite mg2sio4 liquid will be located at about 2600 c and 20 gpa assuming that congruent melting persists up to the limit of the stability field of forsterite the extrapolation of the previous melting data on enstatite and periclase indicates that the eutectic composition of the forsterite enstatite system should shift toward the forsterite component with increasing pressure and there is a possibility of incongruent melting of forsterite into periclase and liquid at higher pressure although no evidence on incongruent melting has been obtained in the present experiment

stress in the indo australian plate cloetingh s and wortel r 1986 stress in the ind austr ian plate in b johnson and a w bally editors intraplate deformation characteristics processes and causes tectonophysics 132 49 67 we modelled the state of stress in the indo australian plate in order to investigate quantitatively variations observed in tectonic style the numerical procedure incorporates the dependence of slab pull and ridge push on the age of the oceanic lithosphere estimates are presented for the average net resistive forces at the himalayan collision zone the suction force acting on the overriding indo australian plate segment at the tonga kermadec trench and the drag at the base of the lithosphere our modelhng shows a concen ation of compressive stresses of the order of 3 5 lcbar in the ninetyeast ridge area the effects of the compressive resistance associated with himalayan collision and subduction of young lithosphere off the northern part of the sunda arc are focused in this region the stress field as calculated gives a consistent explanation for the observed concentration of seismic activity stein and okal 1978 and significant deformation in the oceanic crust weissel et al 1980 mcadoo and sandwell 1985 in the area the calculated stress field in the area adjacent to the southeast and central india ridges is characterized by tension parallel to the spreading axis this explains the concentration of near ridge normal faulting seismicity with t axes subparaile1 to the spreading ridge in the indian ocean as recently observed by bergman et al 1984 and wiens and stein 1984 the regional stress field along the strike of the sunda arc varies from compression seaward of and parallel to the sumatra trench segment to tension perpendicular to the java flores segment this explains the selective occurrence of well developed grabens seaward off the java flores segment of the trench observed by hilde 1983 our modelling shows that the observed rotation of the stress field denham et al 1979 in the australian continent is mainly the consequence of its geographic position relative to the surrounding trench segments and the variations of the forces acting on the down going slab in each of these the state of compression in west and central australia is induced by the action of resistive forces at the himalayan and banda arc collision zones the joint occurrence of high levels of compression in the plate s interior and normal faulting seismicity in the near ridge areas is a transient feature unique to the present dynamic situation of the indo australian plate

water and geodynamics hydrogen is the most abundant element fig 1 in the galaxy and our solar system lodders 2003 therefore it is not astonishing that hydrogen is a key player in the geodynamic evolution of planets its fate in the early earth after condensation of the solar nebula the accretion of our planet and hydrogen reprocessing through early asteroidal and cometary bombardment dauphas et al 2000 and segregation of a proto earth into iron core and silicate mantle is described elsewhere in this volume marty and yokochi 2006 figure 1 abundance of elements in the solar system in numbers of atoms per 106 atoms of silicon lodders 2003 this chapter concerns itself with the geodynamics of the modern earth where nowadays hydrogen occupies only a very small mass fraction less than 0 1 wt although its abundance is thus drastically diminished it is still believed to have a profound influence on the geodynamics of the present planet the reason why hydrogen can have a profound influence on geodynamics even when it is diluted to ppm levels relies on its fundamental influence on both rock mechanics kohlstedt 2006 and the melting relationships kohn 2006 however both the micromechanical mechanism and the large scale implications are not yet fully understood in this review geodynamic processes which may be triggered by a rock mechanical hydrogen threshold value are reviewed in addition to resulting styles of planetary convection controlled by melt and rock mechanics this review will conclude with a more speculative discussion of the possible implications for planetary evolution from an early earth to the present day and highlight areas of future work following current practice in the literature the term water will be used interchangeably for hydrogen recent breakthroughs in computational geodynamics are throwing a new light on the possible evolution of planetary tectonics simulations

the floating astronomical time scale for the terrestrial late cretaceous qingshankou formation from the songliao basin of northeast china and its stratigraphic and paleoclimate implications abstract the upper cretaceous qingshankou formation k 2 qn in the songliao basin slb of northeast china consists of up to 550 m thick lacustrine mudstone and shale that constitute one of the most important source rocks of the daqing oil field a high resolution cyclostratigraphic analysis of the natural gamma ray logging from 10 wells of the qingshankou formation k 2 qn reveals orbital cycles of precession 20 ka obliquity 40 ka and eccentricity 100 ka and 405 ka providing strong evidence for astronomically driven climate changes in the late cretaceous terrestrial environments floating astronomical time scales ats are established for all sections which demonstrate variable durations of k 2 qn across the basin 1 09 ma 5 20 ma and strong diachroneity of the lacustrine strata four periods of high depositional rates can be identified in the central parts of the basin possibly recording deposition during times of sustained wet climate and high chemical weathering an ats established from well m206 in the central depression zone of the basin where the most complete and stable milankovitch cycles are present suggests that the maximum duration of the k 2 qn is 5 20 ma from 94 27 ma to 89 07 ma late cenomanian to early coniacian the lacustrine anoxic event 1 lae1 at the cenomanian turonian boundary lasted 210 310 ka during which the most prolific petroleum source rocks in slb were deposited the onset 94 21 94 18 ma and duration 210 310 ka of lae1 in slb are comparable to those of the oceanic anoxic event 2 oae2 onset at 94 21 ma and duration of 320 900 ka suggesting that the same trigger mechanism such as increased atmospheric co 2 from large scale igneous activity may have initiated high primary productivity and organic carbon burial in both marine and terrestrial systems

subduction zone stresses constraints from mechanics and from topographic and geoid anomalies abstract there are in principle direct relations between several important phenomena associated with subduction zones the depth of oceanic trenches the magnitude of the net force from trenches acting on subducting plates the distribution and fault plane orientations of earthquakes the magnitude of stresses on subduction faults the bathymetry of back arc regions and the magnitudes of gravity and geoid anomalies these phenomena are related through the stresses transmitted through surface and subducted lithosphere and are associated with the mass anomaly of the subducted lithosphere quantitative estimates suggest that observed trench depths imply a trench pull force on subducting plates which is comparable to the ridge push force but much less than the excess weight of the subducted lithospheric slab it is further suggested that either the mass anomaly of subducted lithosphere is much less than would be expected on the basis of conventional thermal and compositional models or that a a large resistance acts on the upper part of slabs due to high stress corner flow and b the mass anomaly of the slab is 70 90 compensated either by a broad 1 km deep back arc depression or a low density mantle wedge above the slab or both

early eocene carbon isotope excursions and landscape destabilization at eccentricity minima green river formation of wyoming repeated global reorganizations of carbon cycling and biotic oceanic and terrestrial processes occurred during the early eocene and appear to have been paced by cyclic variations in the eccentricity of the earth s orbit the phase relationship s between insolation variation terrestrial paleoclimate and atmospheric pco2 during these events remains enigmatic however due to their poorly constrained timing relative to specific orbital configurations here we use tiered interpolation between radioisotopic ages and paleomagnetic polarity chrons to compare high resolution 13c and lithofacies records from the wilkins peak member of the green river formation of western north america to a fe intensity xrf record from the western atlantic ocean and to numerical solutions for earth s orbital configuration wilkins peak member lithofacies stacking patterns record cyclic geomorphic responses to insolation and climate fluctuations spanning an interval of 1 8 ma previous macrostratigraphic analyses using 40ar 39ar and u pb ash bed ages indicate that these cycles reflect long and short eccentricity modulation of precession hydrologic variance appears to have occurred inversely with intervals of maximum sediment advection with carbonate and evaporite dominated lacustrine modes during eccentricity maxima and siliciclastic dominated alluvial modes during eccentricity minima stable carbon isotope analyses of 126 meters of wilkins peak member strata reveal a regular 5 per mil oscillation between high 13c lacustrine modes and low 13c alluvial modes tiered interpolation between paleomagnetically characterized terrestrial ash beds facilitates the integration of 11 radioisotopic ages with the geomagnetic polarity timescale resulting in significant expansion of chron c23 and shortening of chron c22 relative to timescales based on seafloor magnetic anomaly profiles the new proposed timescale permits direct comparison of terrestrial and marine climate proxy records from the early eocene climatic optimum at ca 250 kyr 250 kyr resolution and reveals prominent 100 kyr and 405 kyr scale oscillations within both records wilkins peak member 13c minima which occurred during low eccentricity alluvial modes likely coincided with global 13c minima scenario 1 but may alternatively reflect productivity driven local effects within lake gosiute scenario 2 if scenario 1 proves accurate early eocene negative 13c hyperthermal excursions occurred during eccentricity minima rather than maxima as formerly believed

high precision u pb geochronologic constraints on the late cretaceous terrestrial cyclostratigraphy and geomagnetic polarity from the songliao basin northeast china abstract the cretaceous continental sedimentary records are essential to our understanding of how the terrestrial geologic and ecologic systems responded to past climate fluctuations under greenhouse conditions and our ability to forecast climate change in the future the songliao basin of northeast china preserves a near complete predominantly lacustrine cretaceous succession with sedimentary cyclicity that has been tied to milankocitch forcing of the climate over 900 meters of drill core recovered from the upper cretaceous turonian to campanian of the songliao basin has provided a unique opportunity for detailed analyses of its depositional and paleoenvironmental records through integrated and high resolution cyclostratigraphic magnetostratigraphic and geochronologic investigations here we report high precision u pb zircon dates ca id tims method from four interbedded bentonites from the drill core that offer substantial improvements in accuracy and a ten fold enhancement in precision compared to the previous u pb sims geochronology and allow a critical evaluation of the songliao astrochronological time scale the results indicate appreciable deviations of the astrochronologic model from the absolute radioisotope geochronology which more likely reflect cyclostratigraphic tuning inaccuracies and omitted cycles due to depositional hiatuses rather than suspected limitations of astronomical models applied to distant geologic time age interpolation based on our new high resolution geochronologic framework and the calibrated cyclostratigraphy places the end of the cretaceous normal superchon c34n c33r chron boundary in the songliao basin at 83 07 0 15 ma this date also serves as a new and improved estimate for the global santonian campanian stage boundary

cyclostratigraphy and its revolutionizing applications in the earth and planetary sciences over the past 25 yr the science of stratigraphy has evolved to include time correlative data from vastly disparate components of the earth system not least of these is the global signal afforded by cyclostratigraphy which has recorded the evolution of earth s astronomical milankovitch forcing of insolation and the paleoclimate system fossil astronomical signals are collected from cyclic sedimentary sequences by detailed sampling and study of facies geochemistry mineralogy rock magnetism color etc in step with the documentation of astronomically forced paleoclimate from ever older older geologic times innovations in computational science have provided ever longer high accuracy astronomical model targets that can be used for time scale calibration the earth s orbit is affected by motions of other planets notably the orbital perihelia of venus and jupiter which impose a dominant 405 k y eccentricity cycle on earth s orbital evolution the large mass of jupiter stabilizes this cycle over hundreds of millions of years the cyclostratigraphic record of 405 k y cycles is therefore often used to correct chronologies affected by variable sedimentation earth s shape and rotation rate are influenced by tidal dissipation and climate friction these effects affect earth s precession rate through time thus a record of earth moon evolution is also embedded in cyclostratigraphy the geochronologic value of cyclostratigraphy has been affirmed through intercalibration with high precision radioisotope dating which today has the potential to define the ages of stratigraphic horizons with 2 uncertainties at the scale of a precession cycle precession index phasing relative to that of the obliquity elucidates the seasonal nature of astronomical forcing of the paleoclimate system cyclostratigraphy contributes to our knowledge of planetary dynamics for times prior to the current ca 50 ma limit of accurate astronomical solutions and it will guide our future understanding of solar system evolution and the evidence for chaotic diffusion astronomical modeling is undergoing its own revolution with development of new numerical integrators to extend accuracy further back in time finally space exploration has revealed prominent sedimentary bedding and ice stratigraphy on the surface of mars with patterns suggestive of astronomical forcing analogous to earth

regional scale tectonic evolution and the seismic velocity structure of the lithosphere and upper mantle the mediterranean region we present a numerical modeling approach designed for the verification of tectonic reconstructions and for a quantitative analysis of the seismic velocity structure of the lower lithosphere and upper mantle in this forward modeling procedure we use published reconstructions of the tectonic evolution of a region to predict the thermal structure from which we calculate physical quantities like p wave velocity basin subsidence and basement heat flow we show an application of this approach to two reconstructions of the late mesozoic and cenozoic evolution of the mediterranean region the resulting synthetic velocity models are tested against seismological models of the mantle structure obtained independently by delay time tomography subsidence and heat flow predictions are compared with actual observations to further constrain the geological assumptions underlying the forward models the mantle models predicted from reconstructions of the evolution of the mediterranean region correlate with major features in the tomographic images from our model results we conclude that the present distribution of seismic velocities in the mediterranean region is largely determined by the tectonic evolution during at least the last 40 m y this means we can verify processes represented in different tectonic scenarios with the seismologically determined velocity structure seen from a different perspective the model results contribute to understanding the causes of the velocity structure imaged by delay time tomography by showing how the tectonic evolution results in this structure

double seismic zones kinematics the kinematics of a double seismic zone of subducting lithosphere at an intermediate depth is studied a simple geometrical argument shows that the strain rate due to unbending of subducting lithosphere can be as large as 10 15 s 1 and large enough to account for the seismic strain rate in this depth range the geometrical unbending of subducting lithosphere in the mantle and the presence of a double seismic zone there can be therefore considered essentially equivalent phenomenon we model a double seismic zone required from this unbending in order to investigate what constraint the presence of a double seismic zone can place on the properties of the descending lithosphere the thickness of a double seismic zone is controlled by the thermal structure and the rheological properties of the subducting slab a preliminary result for the double seismic zone beneath tohoku japan indicates a possibility that the currently available flow law of dry olivine does not properly describe the double seismic zone or at least presents some inconsistency in our knowledge of the mechanical properties e g thermal structure rheology of oceanic lithospheres

orogens and slabs vs their direction of subduction abstract subduction zones appear primarily controlled by the polarity of their direction i e w directed or e to nne directed probably due to the westward drift of the lithosphere relative to the asthenosphere the decollement planes behave differently in the two end members in the w directed subduction zone the decollement of the plate to the east is warped and subducted whereas in the e to nne directed it is ramping upward at the surface there are w directed subduction zones that work also in absence of active convergence like the carpathians or the apennines w directed subduction zones have shorter life 30 40 ma than e or ne directed subduction zones even longer than 100 ma the different decollements in the two end members of subduction should control different ptt paths and therefore generate variable metamorphic assemblages in the associated accretionary wedges and orogens these asymmetries also determine different topographic and structural evolutions that are marked by low topography and a fast eastward migrating structural wave along w directed subduction zones whereas the topography and the structure are rapidly growing upward and expanding laterally along the opposite subduction zones the magmatic pair calc alkaline and alkaline tholeiitic volcanic products of the island arc and the back arc basin characterise the w directed subduction zones magmatic rocks associated with e or ne directed subduction zones have higher abundances of incompatible elements and mainly consist of calc alkaline shoshonitic suites with large volumes of batholithic intrusions and porphyry copper ore deposits the subduction zones surrounding the adriatic plate in the central mediterranean confirm the differences among subduction zones as primarily controlled by the geographic polarity of the main direction of the slab the western margin of the adriatic plate contemporaneously overridden and underthrust europe toward the west to generate respectively the alps and the apennines while the eastern margin subducted under the dinarides hellenides these belts confirm the characters of the end members of subduction zones as a function of their geographic polarity similarly to the pacific subduction zones

shallow methane hydrate system controls ongoing downslope sediment transport in a low velocity active submarine landslide complex hikurangi margin new zealand morphological and seismic data from a submarine landslide complex east of new zealand indicate flow like deformation within gas hydrate bearing sediment this creeping deformation occurs immediately downslope of where the base of gas hydrate stability reaches the seafloor suggesting involvement of gas hydrates we present evidence that contrary to conventional views gas hydrates can directly destabilize the seafloor three mechanisms could explain how the shallow gas hydrate system could control these landslides 1 gas hydrate dissociation could result in excess pore pressure within the upper reaches of the landslide 2 overpressure below low permeability gas hydrate bearing sediments could cause hydrofracturing in the gas hydrate zone valving excess pore pressure into the landslide body 3 gas hydrate bearing sediment could exhibit time dependent plastic deformation enabling glacial style deformation we favor the final hypothesis that the landslides are actually creeping seafloor glaciers the viability of rheologically controlled deformation of a hydrate sediment mix is supported by recent laboratory observations of time dependent deformation behavior of gas hydrate bearing sands the controlling hydrate is likely to be strongly dependent on formation controls and intersediment hydrate morphology our results constitute a paradigm shift for evaluating the effect of gas hydrates on seafloor strength which given the widespread occurrence of gas hydrates in the submarine environment may require a reevaluation of slope stability following future climate forced variation in bottom water temperature

thermal stresses in subducting lithosphere can explain double seismic zones the discovery of double planed zones of intermediate depth seismicity associated with subducting oceanic lithosphere refs 1 7 and l s h and k h j in preparation has generated much interest in the origin and distribution of stresses in descending plates several mechanisms have been proposed to explain why double zones occur8 here we investigate the role of thermal stresses for the state of stress in a descending plate and test whether they can account for the observed characteristics of double seismic zones by modelling the descending slab as a thin elastic plate and using the temperatures in the slab estimated by toksoz et al 9 we find that the polarities of thermally generated stresses agree with those obtained from the focal mechanisms of earthquakes in the two zones thermal stresses also can explain the separation between the two zones of seismicity at shallow depths and their gradual merging at greater depth

astrochronology of the late turonian implications for the behavior of the carbon cycle at the demise of peak greenhouse abstract a series of prominent carbon cycle perturbations indicated by carbon isotope excursions of up to 2 marked climatic and oceanographic changes that followed the peak mid cretaceous greenhouse the nature and forcing mechanisms of these changes remain poorly understood partly due to the lack of a detailed temporal control in this interval here we present an orbitally calibrated time scale which is based on hemipelagic rhythmites in the bohemian cretaceous basin and which can be linked to the established chronostratigraphic framework using inoceramid biostratigraphy and carbon isotope signature in the new age model the late turonian defined by the first occurrence of i perplexus below and the first occurrence of c deformis erectus above spans 1 56 0 07 myr when anchored to the newly refined age of the turonian coniacian boundary sageman et al in press the onset of the late turonian is 91 31 0 45 ma inoceramid zones i perplexus and m scupini span 0 76 0 05 myr and 0 80 0 05 myr respectively a time domain record of carbon isotope variations was obtained by pinning published 13ccarb data to the orbital time scale using 9 biostratigraphic and carbon isotope markers the timing of major carbon isotope excursions suggests a link to 405 kyr eccentricity changes and in the early late turonian to 100 kyr eccentricity variations however over 80 of the variance in the late turonian 13 c occurs at longer million year scales the key features of the 13ccarb signature including the amplified long term variance can be reproduced with simple models of orbitally driven isotopic mass balance at a constant carbon isotope fractionation the best fit to the 13ccarb signature is obtained with enhanced organic burial at high eccentricity in accordance with monsoonal forcing of organic accumulation in the low latitude atlantic and or buildup of low latitude terrestrial carbon reservoirs alternative solutions should consider changing carbon isotope fractionation due to pco2 and or nutrient flux changes

the interaction of a subducting lithospheric slab with a chemical or phase boundary we have used a finite element model of time dependent convection to determine the conditions for penetration of the subducted plate into the lower mantle a temperature dependent and non newtonian rheology is applied to achieve platelike behavior of the upper and sinking thermal boundary layer of convection the 650 km discontinuity is taken as either a chemical or phase boundary or as a combination of both it is represented by a marker chain which effects additional buoyancy when distorted out of its equilibrium position when the compositional density contrast is greater than about 5 the descending slab is deflected sidewards at the boundary and two layer convection prevails a resulting depression of the boundary in the range of 50 200 km should be detectable with seismic methods below 5 density difference the slab plunges several hundred kilometers into the lower mantle and below 2 it will probably not stop before reaching the core mantle boundary and extensive mixing would be expected with a pure phase change a negative clapeyron slope of about 6 mpa k 60 bar k is required to establish a type of leaky double layer convection a more moderate slope can aid a small compositional density difference to prevent slab penetration into the lower mantle with the present uncertainties about the physical nature of the 650 km discontinuity a variety of convective styles appears possible on dynamical grounds

astrochronology for the early cretaceous jehol biota in northeastern china article i nfo the early cretaceous jehol biota in northeastern china provides an evolutionary window for feathered dinosaurs primitive birds insects and early flowering plants it also provides critical information for the bio diversity changes of the early cretaceous terrestrial ecosystem here we report a time series analysis for the 11 2 m thick fossil bearing lacustrine deposits at the sihetun section in western liaoning northeastern china on the basis of high resolution magnetic susceptibility ms and anhysteretic remanent magnetization arm measurements a hierarchy of sedimentary cycle bands of 120 260 cm 50 67 cm and 18 42 cm was recorded in the ms and arm series with available radioisotope age constraints from the same section sedimentary cycles of 120 260 cm 50 67 cm and 18 42 cm were interpreted as milankovitch cycles of short eccentricity 130 and 95 kyr obliquity 36 6 and 46 kyr and precession 22 1 20 9 and 18 kyr respectively the 100 kyr tuned floating astronomical time scale indicates that the duration of the 11 2 m thick section is 0 67 myr and the average depositional rate is 1 70 cm kyr the duration of the 1 8 m thick main fossil bearing interval that contains 8 beds of feathered dinosaur primitive bird fossils can be estimated as short as 150 kyr the results suggest that climate fluctuations manifested in paleobotanical sedimentological and geo chemical records of the yixian formation may have been controlled by orbital forcing during early cretaceous 2013 elsevier b v all rights reserved

deccan volcanism caused coupled pco2 and terrestrial temperature rises and pre impact extinctions in northern china evaluating the terrestrial climate record provides a critical test of the roles of chicxulub impact and deccan traps volcanism during the cretaceous paleogene k pg mass extinction most evidence came from marine records but our new clumped isotopes data from paleosol carbonates in the songliao basin provide a terrestrial climate history from northern china this reveals there was a pre impact warming caused by the onset of deccan traps volcanism whereas the following short term cooling then another warming episode were likely caused by chicxulub impact and post boundary volcanism our study suggests that the pco levels were probably the main control on the latest cretaceous cooling and the climatic fluctuations across the k pg boundary interval in northern china in the songliao basin the pre impact deccan traps volcanism links to losses of half of the lacustrine algae species charophytes and almost all of the lacustrine ostracodes this suggests that the deccan traps volcanism had already destabilized the ecosystem and caused extinctions prior to the chicxulub impact

life of an oceanic plate cooling time and assimilation time an oceanic plate undergoes two different thermal stages in its life from its creation at the spreading center to its assimilation under the subduction zone first the cooling stage and secondly the heating stage introducing the terms cooling time and assimilation time as measures of intervals of the former and latter stages we discussed the quantitative correlation between the two the cooling time ac is defined as the time required for the oceanic plate to move from a spreading center to a trench and is equivalent to the age of the oceanic plate when it just reached the trench the assimilation time tm is defined as the time required for the subducting plate to lose the ability to generate earthquakes since it began to subduct we estimated the values tm and ac at 50 sites in major subduction zones of the world the result indicates a positive linear relation between ac and tm simply expressed by tm ac9 2 ma while mckenzie s subduction model and the thickening plate model theoretically expect the relationship to be expressed as tm ac the discrepancy between our result and the theoretical model suggests the delay of effective heating of the subducting plate under the subduction zone and or the rapid increase of the plate thickness around the spreading center

the relationship between wadati benioff zone geometry and p t and b axes of intermediate and deep focus earthquakes for 865 earthquakes with focal depths exceeding 90 km this paper presents a concise global summary of the distributions of p t and b axes of their focal mechanisms with respect to the downdip along strike and normal axes of wadati benioff zones the focal mechanisms are best double couple solutions for the centroid moment tensors reported by the harvard group with the p t and b axes corresponding to the principal axes of the individual moment tensors we find as did previous investigators that events below 300 km have predominantly downdip p axes with 50 of all p axes of deep focus events lying within 28 of downdip for events between 90 and 300 km depth there are regional differences but most regions possess events with nearly downdip p axes or events with nearly downdip t axes in almost all regions having downdip p or t axes bingham statistics show that the greatest concentration of p or t axes lies somewhat below the plane of the wadati benioff zone for events of all focal depths in nearly all regions b axes cluster along the strike direction with 50 occurring within 38 of the strike from these regional results we define a typical focal mechanism as one having the b axis within 30 of the along strike and having either the t or p axis within 30 of the downdip such a focal mechanism might occur in response to a stress tensor having its greatest or least principal stresses channeled approximately along the downdip direction of the subducting slab with the intermediate principal stress lying horizontally within the slab controlled possibly by slab bending however by this criterion only 29 of the focal mechanisms for deep and intermediate events are typical thus the majority of the individual events cannot be explained simply as occurring in response to a downdip and slab normal greatest and least principal stress system with a horizontal along strike intermediate principal stress a few regions such as java and the marianas are clearly anomalous in that they possess significantly fewer typical focal mechanisms than do most other regions

paleoclimate proxies for cyclostratigraphy comparative analysis using a lower triassic marine section in south china abstract multiple proxies for paleoclimatic and paleoenvironmental change within sedimentary sequences have been developed but understanding their relationships and their relative strengths or weaknesses are required to access a wealth of untapped paleoclimate information we propose two main criteria for multiple proxy datasets to estimate their individual signal to noise levels and to decipher the relationship between multiple proxies first for proxies affected by similar processes then their time dependent changes should be similar second a paleoclimate proxy that is more sensitive to an external forcing such as astronomical forcing is more useful than those that do not have such a response we introduce two methods to evaluate these criteria 1 hierarchical cluster analysis hca probes the relationships among multiple proxies based on similarities of their oscillation patterns and 2 power decomposition analysis pda tests proxy sensitivity to external climate forcing we evaluate 16 high resolution paleoclimate proxies in detail for their applications in paleoclimatology from the marine lower triassic daye formation at the daxiakou section in the three gorges region of south china which has carbonate claystone cycles deposited on an outer ramp the proxies are spectral gamma ray gamma ray intensity potassium uranium thorium thorium uranium and thorium potassium rock color lightness l redness a and yellowness b magnetic susceptibility measured in both laboratory and outcrop anhysteretic remanent magnetization arm lithologic rank simplified lithologic rank and non carbonate fraction carbonate thickness and couplet thickness hierarchical cluster analysis hca gathers these proxies into groups likely affected by the same process the arm and thorium uranium proxies seem to reflect the hinterland weathering process during the early triassic gamma ray potassium uranium thorium magnetic susceptibility and non carbonate fraction proxies refer to terrestrial input the l a and lithologic rank proxies indicate the productivity the redox state and the relative sea level respectively at this section this case study contributes to the understanding of the sensitivity of these types of proxies within marine strata for deep time paleoclimate and astronomical tuned time scales

phase transition buoyancy contributions to stresses in subducting lithosphere the sequence of phase transitions undergone by minerals with increasing depth in earth s mantle is perturbed within subducting lithospheric slabs by their thermal structure such perturbation of equilibrium phase relations gives rise to relative buoyancy contrasts between slab and mantle that contribute to the state of stress within the slab while other factors contribute to overall slab stresses thermal and phase transition effects largely control the structure of the stress field within the slab the resulting maximum in down dip compressive stress within the slab corresponds to the observed peak in depth distribution of deep seismicity furthermore metastable persistence of lower pressure phases within the cold slab should give rise to localized shear stresses whose distribution corresponds to observed features of subduction zone seismicity these observations are independent of the variety of failure mechanisms proposed for deep seismogenesis

age dependence of oceanic intraplate seismicity and implications for lithospheric evolution we have determined depths for 16 oceanic intraplate earthquakes using body wave modeling a data set composed of these and 11 other well constrained depths shows that the maximum depth of seismicity deepens with increasing lithospheric age and appears to be bounded by a 700 800 c isotherm the maximum depth to which intraplate earthquakes occur is approximately equal to the flexural elastic thickness but much less than the seismic thickness from surface wave dispersion the maximum faulting depth is consistent with the predictions of rapid weakening at high temperatures for dry olivine rheologies determined by experimental rock mechanics oceanic intraplate earthquakes can occur at greater depths and temperatures than has previously been reported for continental crustal events presumably because oceanic lithosphere is stronger at high temperatures both the number of earthquakes and the cumulative seismic moment decrease with lithospheric age the cause of this trend is unclear possibilities include nonrandom location of preexisting weak zones with respect to the age provinces fault strengthening with age or a decrease in the stress level a decrease in intraplate stress with age is opposite that expected from ridge push stresses which increase with age but may result either from thermoelastic stresses which are greatest in young lithosphere or near ridge stress concentrations due to local heterogeneities in the spreading process

mid latitude terrestrial climate of east asia linked to global climate in the late cretaceous reply the late cretaceous late campanian to maastrichtian was characterized by a variable greenhouse climate with evidence for cooling and or glaciation and warming events most of these climatic signals are derived from marine records and knowledge of the terrestrial climate especially in the mid latitudes is limited due to fragmentary geological records on continents here we report mid latitude terrestrial stable oxygen and carbon isotope data from pedogenic carbonates in the nearly continuous late cretaceous age sk 1 core drilled in the songliao basin northeastern china our data indicate a punctuated mid latitude terrestrial climate in the late cretaceous we interpret the negative excursion of pedogenic carbonate 18o in the early maastrichtian to be the result of decreasing temperature and or strengthened westerlies during global cooling and possible glaciation providing valuable mid latitude terrestrial evidence for this event the negative 13c isotopic excursion ca 66 ma is modeled as higher primary productivity caused by increasing temperature and precipitation in response to a warming climate in the latest cretaceous our continuous stable isotopic records in the songliao basin are in accordance with previously published global late cretaceous records of climate variability from marine and terrestrial regions and demonstrate the sensitivity of mid latitude terrestrial climate in a greenhouse world

continental scientific drilling project of cretaceous songliao basin scientific objectives and drilling technology abstract the continental scientific drilling project at the cretaceous age songliao basin is a drilling initiative under the framework of the international continental scientific drilling program to recover a nearly complete cretaceous terrestrial sedimentary record in the songliao basin northeastern china the recovered cores will provide unique opportunities for the geosciences community to advance the understanding of climate change in the cretaceous greenhouse world and provide a documentation of geological events relevant to the carbon cycle during this time period this drilling project will address significant geological questions such as the identification of important stratigraphic boundaries and the marine terrestrial correlations of stratigraphy the reasons for the biotic response to the terrestrial environmental changes the terrestrial response to the cretaceous oceanic anoxic events the formation of terrestrial petroleum source rocks and the mechanisms for the cretaceous magnetic normal superchron cns in the first stage of this drilling project the ski drilling rock cores of 2485 89 m in total length were recovered and the recovery ratio reached 96 46 a series of drilling and coring technologies including regular confined directional and sealed coring were utilized to ensure a higher recovery ratio for the core and will be described at the end of this paper well loggings were conducted right after coring core handling and storage were arranged in such a way that the scientific research was conducted on half of each core whereas the other half of each core was preserved for long term storage the upcoming second stage the skii drilling will combine with data from the existing ski to provide complete high resolution climate records of the terrestrial environment for the whole cretaceous time period

seismicity and rheology of subducted slabs since the incorporation of the inclined zones of intermediate and deep seismic activity into the theory of plate tectonics1 2 it has been generally accepted that earthquakes with focal depths 100 km occur in subducted slabs of predominantly oceanic lithosphere yet our understanding of the processes which generate intermediate and in particular deep earthquakes is still incomplete this is largely due to our limited knowledge of the rheological behaviour of subducted oceanic lithosphere at depths between 100 and 700 km however recently considerable insight has been gained into the rheology of oceanic lithosphere in near surface conditions and i investigate here whether the seismic activity at depths 100 km can be understood on the basis of this information i first present results of temperature calculations performed for all subduction zones for which adequate data on seismicity relative plate motion and age of the descending oceanic lithosphere exist sub sequently i adapt the temperature conditions governing the rheology near the surface by including depth dependence this leads to a depth dependent critical temperature tcr z above which the subducted lithosphere cannot sustain the stresses necessary to generate seismic events seismicity data and calculated temperature versus depth relationships are in good agreement with the rheological model predictions this implies that the absence of seismic activity at depths 700 km should not be interpreted as direct evidence for the hypothesis that the 650 km discontinuity in the mantle acts as a barrier to vertical motion of subducted slabs

astrochronology of the early turonian early campanian terrestrial succession in the songliao basin northeastern china and its implication for long period behavior of the solar system abstract the first complete early turonian early campanian lacustrine succession has been recovered from the sk i south sk is borehole in the songliao basin slb northeastern china we conducted a detailed cyclostratigraphic study of natural gamma ray gr log thorium th log and magnetic susceptibility ms data from this core spectral analysis of the upper quantou formation k 2 q 3 4 qingshankou formation k 2 qn yaojia formation k 2 y and lower nenjiang formation k 2 n 1 2 reveals a hierarchy of meter to decameter scale cycling in the data the wavelength ratios of the cycles in these stratigraphic units are 20 5 2 1 corresponding with those of milankovitch cycle periods of 405 kyr long eccentricity 100 kyr short eccentricity 37 kyr obliquity 20 kyr precession indicating astronomical control on sedimentation an astronomical time scale ats was established by tuning interpreted 405 kyr cycles to a 405 kyr orbital eccentricity target curve and to four sims u pb zircon radioisotope ages this absolute ats provides precise numerical ages for stratigraphic boundaries biozones geological and geophysical events and serves as a basis for correlation of strata and events between marine and terrestrial systems the ages of the c33r c34n geomagnetic polarity boundary in k 2 n 2 and three short reversal events in k 2 y are estimated as 83 633 ma 84 819 84 862 ma 84 982 85 092 ma and 85 240 85 629 ma respectively long period amplitude modulations in the obliquity and eccentricity bands of the 405 kyr tuned gr th series provide strong evidence that long period orbital forcing influenced climate change and depositional processes in the slb the extracted amplitude modulations provide evidence that the orbits of earth and mars were not in secular resonance and were undergoing chaotic interactions during this time although the modulations do not match those of recent astronomical models

40ar 39ar and k ar dating on the volcanic rocks in the songliao basin ne china constraints on stratigraphy and basin dynamics precise 40ar 39ar and k ar ages were determined on sanidine and whole rock separates of volcanic rocks in the songliao basin sb the volcanism is characterized by a series of continual and episodic eruptions in the late jurassic 147 157 ma and early cretaceous 113 136 ma a fairly accurate chronostratigraphic column was first established based on those data the volcanic activities happened synchronously with closure of the mongolia okhotsk ocean north to the sb structures of the volcanogenic successions are s dipping or se dipping fault blocks coupled with n dipping or nw dipping major detachment systems distribution of the volcanics revealed by high resolution seismic reflections is neither restricted within nor in agreement with the framework of the overlying sedimentary sequence striking nne this new evidence fits the overlap model proposed in the present paper that formation of the volcanic successions in the sb is related to the subduction of the mongolia okhotsk plate under the mongolia north china block during the jurassic and early cretaceous whereas the overlying sedimentary sequence unconformably on the volcanics is tectonically controlled by the oblique subduction of the pacific plate under the eurasian plate since late aptian in addition the coal bearing epiclastic sediments intercalating the volcanics were deposited at the subduction quiescence episodes when extensional collapse occurred

an 11 million year long record of astronomically forced fluvial alluvial deposition and paleoclimate change in the early cretaceous songliao synrift basin china abstract in the cretaceous songliao basin northeastern china boreholes have recovered detailed geologic data from sub basins that developed during the early rifting of the basin among these the lower cretaceous shahezi formation k1s in the songshen 4 ss4 well is represented by an 836 m thick succession of fluvial alluvial deposits with coals distributed throughout the upper part of the formation gamma ray gr logging data are quantitatively related to grain size defined litho facies that recur throughout the succession with high gr values in mudstones and low gr values in sandstones cyclostratigraphic analysis of the gr log reveals depositional cycling at frequencies that are consistent with those of the earth s astronomical parameters the results also indicate that occurrence of coal beds occur every 100 kyr when development of vegetation at the depositional site was promoted by humid climate we propose a model of astronomically forced hydroclimate change to explain the cycling of depositional environments between fluvial and alluvial conditions the model describes a principally fluvial environment that episodically experienced at one extreme advancing alluvial conditions involving a drop in base level lake recession and increased aridity conglomerates and coarse sands and at the other extreme an advancing lakeshore with a rise in base level and increased humidity fine sands silts muds and coal a floating astronomical time scale was established by calibrating long orbital eccentricity 405 kyr cycles interpreted along the gr series the results indicate that the duration of the k1s is 11 14 myr 27 5405 kyr long orbital eccentricity cycles corresponding to an average sedimentation rate of 6 55 cm kyr the recognition of astronomical forcing in this early cretaceous fluvial alluvial dominated depositional setting offers a new framework for interpreting the sedimentary cyclicity and dynamics of early rift basins and for developing time scales

late cretaceous stratigraphy songliao basin ne china sk1 cores abstract the songliao basin is the largest cretaceous oil and gas producing lacustrine basin in china with its greatest aerial extent in the middle cretaceous a coring program sk1 has to date yielded 2485 89 m of continuous core 96 46 recovery and provides significant material for cretaceous research the sequence of the core consists mainly of lacustrine sandstone dark grey mudstone shale and oil shale the upper cretaceous stratigraphic section has been subdivided into the quantou qingshankou yaojia nenjiang sifangtai and mingshui formations in ascending order late cretaceous microfossils are diverse and abundant a detailed biostratigraphic study has subdivided the sequence into high precision biozones 21 ostracode assemblages 10 phytoplankton assemblages 7 palynological zones and 4 charophyta assemblages respectively in addition marine foraminifera were first discovered from the basin three 206pb 238u ages and one 40ar 39ar age were analysed ten local magnetozones have been recognised in the sk1 north and two magnetozones have been indicated in the sk1 south based on biostratigraphy high resolution magnetostratigraphy and sims u pb zircon analyses the sk1 stratigraphy is correlated with upper cretaceous stages in the international geologic time scale the upper part of the quantou formation is the lower turonian the qingshankou formation is the upper turonian lower coniacian the yaojia formation is from the upper coniacian to middle santonian the nenjiang formation is the upper santonian to middle campanian the sifangtai formation is limited to the upper campanian and the mingshui formation is the uppermost campanian to maastrichtian it is likely that the upper part of the mingshui formation belongs to the paleocene and the k pg boundary is within the member 2 of the mingshui formation around the depth of 328 m by new micropalaeontologic and magnetostratigraphic data

tempo of the end permian event high resolution cyclostratigraphy at the permian triassic boundary the permian triassic p t boundary is marked by the most severe mass extinction in the geologic record high resolution cyclostratigraphy on a 10 4 yr scale across the p t boundary in a core from the carnic alps austria revealed significant cycles in the ratio 40 10 4 7 2 3 m identified with milankovitch cycles of 412 100 40 20 k y eccentricity 1 and 2 obliquity and precession wavelet analysis indicates continuity of deposition across the boundary with an average accumulation rate of 10 cm k y the dramatic faunal changes at the p t boundary can be constrained within an interval of 60 k y possibly 8 k y with the accompanying sharp negative global carbonisotope shift within 30 k y suggesting a catastrophic cause

stress magnitude estimates from earthquakes in oceanic plate interiors we propose a method to estimate stress magnitudes in oceanic plate interiors from focal depths and focal mechanisms using a depth dependent rheology we show it is possible to estimate the differential stress 1 3 averaged over some reference lithospheric thickness the resolving power of the method is investigated by evaluating the effect of uncertainties in parameters that are involved in the analysis we apply the method to the central indian ocean where intraplate seismicity is high from well studied earthquakes we estimate differential stresses of the order of hundreds of rnegapascals this result is consistent with the high level of stress that was found from numerical model calculations by cloetingh and wortel 1985 1986 from the few intraplate events in the pacific plate we also estimate differential stresses in this area

deep earthquakes and the thermal assimilation of subducting lithosphere two problematic aspects of deep seismic zones are investigated the maximum depth about 700 km of seismic activity and the relative maximum in seismic energy release in the 500 700 km depth range it is shown that both features can be accounted for by a model based on thermal assimilation this implies that no barrier is required at a depth of 650 700 km to explain the observations

quantifying k u and th contents of marine sediments using shipboard natural gamma radiation spectra measured on dv joides resolution during international ocean discovery program iodp expeditions shipboard generated data provide the first insights into the cored sequences the natural gamma radiation ngr of the recovered material for example is routinely measured on the ocean drilling research vessel dv joides resolution at present only total ngr counts are readily available as shipboard data although full ngr spectra counts as a function of gamma ray energy level are produced and archived these spectra contain unexploited information as one can estimate the sedimentary contents of potassium k thorium th and uranium u from the characteristic gamma ray energies of isotopes in the 40 k 232 th and 238 u radioactive decay series dunlea et al 2013 quantified k th and u contents in sediment from the south pacific gyre by integrating counts over specific energy levels of the ngr spectrum however the algorithm used in their study is unavailable to the wider scientific community due to commercial proprietary reasons here we present a new matlab algorithm for the quantification of ngr spectra that is transparent and accessible to future ngr users we demonstrate the algorithm s performance by comparing its results to shore based inductively coupled plasma mass spectrometry icp ms inductively coupled plasma emission spectrometry icp es and quantitative wavelength dispersive x ray fluorescence xrf analyses samples for these comparisons come from eleven sites u1341 u1343 u1366 u1369 u1414 u1428 u1430 u1463 cored in two oceans during five expeditions in short our algorithm rapidly produces detailed high quality information on sediment properties during iodp expeditions at no extra cost

shear instability in a viscoelastic material as the cause of deep focus earthquakes the mechanism of deep focus earthquakes has been examined by numerical and linear analysis of shear instability in subducting slabs we assume subducting slabs deform such that the spatially averaged strain rate becomes time independent furthermore we assume that rheology depends on temperature in the manner of an activation process using this model we investigate quantitatively the conditions under which shear instability takes place i e the deformation in the material concentrates in a thin layer whose temperature increases explosively until melting occurs first we study instability in a material whose rheological properties are spatially homogeneous shear instability takes place in a homogeneous material when exceeds a certain critical level e c which depends strongly on the stress in the slabs but does not depend on the detail of the creep law the value of the activation energy next we study instability in a material that contains shear zones similar to those often observed by field geologists i e a thin layer made of material with lower vicosity than the surrounding region we find that shear zones trigger shear instability even for the case of provided that g the ratio of characteristic time of thermal diffusion to that of shear heating in shear zones exceeds 1 and that f the ratio of stiffness of elastic deformation in the surrounding region to that of ductile deformation in shear zones becomes lower than 1 applying this condition to subducting slabs with shear zones we find that shear zones trigger shear instability even when the average strain rate is lower than by an order of magnitude from these results and from an estimate of in subducting slabs we conclude that shear instability is a mechanism likely to induce deep focus earthquakes

metastable mantle phase transformations and deep earthquakes in subducting oceanic lithosphere earth s deepest earthquakes occur as a population in subducting or previously subducted lithosphere at depths ranging from about 325 to 690 km this depth interval closely brackets the mantle transition zone characterized by rapid seismic velocity increases resulting from the transformation of upper mantle minerals to higher pressure phases deep earthquakes thus provide the primary direct evidence for subduction of the lithosphere to these depths and allow us to investigate the deep thermal thermodynamic and mechanical ferment inside slabs numerical simulations of reaction rates show that the olivine spinel transformation should be kinetically hindered in old cold slabs descending into the transition zone thus wedge shaped zones of metastable peridotite probably persist to depths of more than 600 km laboratory deformation experiments on some metastable minerals display a shear instability called transformational faulting this instability involves sudden failure by localized superplasticity in thin shear zones where the metastable host mineral transforms to a denser finer grained phase hence in cold slabs such faulting is expected for the polymorphic reactions in which olivine transforms to the spinel structure and clinoenstatite transforms to ilmenite it is thus natural to hypothesize that deep earthquakes result from transformational faulting in metastable peridotite wedges within cold slabs this consideration of the mineralogical states of slabs augments the traditional largely thermal view of slab processes and explains some previously enigmatic slab features it explains why deep seismicity occurs only in the approximate depth range of the mantle transition zone where minerals in downgoing slabs should transform to spinel and ilmenite structures the onset of deep shocks at about 325 km is consistent with the onset of metastability near the equilibrium phase boundary in the slab even if a slab penetrates into the lower mantle earthquakes should cease at depths near 700 km because the seismogenic phase transformations in the slab are completed or can no longer occur substantial metastability is expected only in old cold slabs consistent with the observed restriction of deep earthquakes to those settings earthquakes should be restricted to the cold cores of slabs as in any model in which the seismicity is temperature controlled via the distribution of metastability however the geometries of recent large deep earthquakes pose a challenge for any such models transformational faulting may give insight into why deep shocks lack appreciable aftershocks and why their source characteristics including focal mechanisms indicating localized shear failure rather than implosive deformation are so similar to those of shallow earthquakes finally metastable phase changes in slabs would produce an internal source of stress in addition to those due to the weight of the sinking slab such internal stresses may explain the occurrence of earthquakes in portions of lithosphere which have foundered to the bottom of the transition zone and or are detached from subducting slabs metastability in downgoing slabs could have considerable geodynamic significance metastable wedges would reduce the negative buoyancy of slabs decrease the driving force for subduction and influence the state of stress in slabs heat released by metastable phase changes would raise temperatures within slabs and facilitate the transformation of spinel to the lower mantle mineral assemblage causing slabs to equilibrate more rapidly with the ambient mantle and thus contribute to the cessation of deep seismicity because wedge formation should occur only for fast subducting slabs it may act as a parachute and contribute to regulating plate speeds wedge formation would also have consequences for mantle evolution because the density of a slab stagnated near the bottom of the transition zone would increase as it heats up and the wedge transforms to denser spinel favoring the subsequent sinking of the slab into the lower mantle

cyclostratigraphic analysis of magnetic records for orbital chronology of the lower cretaceous xiagou formation in linze northwestern china abstract in this study we report a tuned astronomical time scale for a sedimentary formation in early cretaceous the lower linze section located in the zhangye basin of the central hexi corridor northwestern china based on detailed field investigations we identified this sediment as the xiagou formation which is widely distributed in the region a thick prominent limestone layer crops out in the middle portion of the linze section and can be correlated to a similar limestone layer in the liupanshan group which has been dated via high resolution magnetostratigraphy this correlation places an age constraint of around 114 ma for the top of the underlying strata a total of 1245 samples were collected from the 474 m thick lower linze section for magnetic susceptibility measurements and cyclostratigraphic analysis spectral and continuous wavelet analyses were applied to the low frequency magnetic susceptibility series and the percentage frequency dependent magnetic susceptibility series as well as to specific subsections exhibiting visible rhythmic bedding a hierarchy of sedimentary cycles was identified with wavelengths of 21 5 37 0 m 7 5 9 5 m 2 1 4 4 m and 1 4 1 7 m the ratios between these lengths correspond well to the ratios between the durations of earth s orbital long eccentricity short eccentricity obliquity and precession cycles we interpret these sedimentary cycles to reflect the effects of orbital forcing on sedimentary processes using band pass filtering to specifically extract eccentricity cycles we established a tuned astronomical time scale for the xiagou formation in the lower linze section with a total duration of about 6 1 myr 114 1 ma to 120 2 ma based on this timescale the sedimentation rate of the xiagou formation is estimated to be in the range of 62 105 m myr with most intervals yielding rates in the 70 80 m myr range