early jurassic late pliensbachian co2 concentrations based on stomatal analysis of fossil conifer leaves from eastern australia the stomatal index a measure of stomatal density of an extinct australian early jurassic araucariacean conifer species allocladus helgei jansson is used to reconstruct the atmospheric carbon dioxide concentration pco 2 in the early jurassic the fossil leaves are preserved in a single bed palynologically dated to late pliensbachian similar to 185 183 mya atmospheric pco 2 is estimated from the ratios between the stomatal index of a helgei and the stomatal indices of three modern analogs nearest living equivalent plants co2 concentration in the range of similar to 750 975 ppm was calibrated from the fossil material with a best estimated mean of similar to 900 ppm the new average pco 2 determined for the late pliensbachian is thus similar to although similar to 10 lower than previously inferred minimum concentrations of similar to 1000 based on data from the northern hemisphere but may help constrain pco 2 during this period our results are the first pco 2 estimates produced using jurassic leaves from the southern hemisphere and show that i paleo atmospheric pco 2 estimates are consistent at a global scale though more investigations of southern hemisphere material are required and ii the stomatal proxy method can now be used without the context of relative change in pco 2 when applying the correct methodology c 2014 the authors published by elsevier b v on behalf of international association for gondwana research less

terrestrial and marine extinction at the triassic jurassic boundary synchronized with major carbon cycle perturbation a link to initiation of massive volcanism mass extinction at the triassic jurassic tr j boundary occurred about the same time 200 ma as one of the largest volcanic eruptive events known that which characterized the central atlantic magmatic province organic carbon isotope data from the uk and greenland demonstrate that changes in flora and fauna from terrestrial and marine environments occurred synchronously with a light carbon isotope excursion and that this happened earlier than the tr j boundary marked by ammonites in the uk the results also point toward synchronicity between extinctions and eruption of the first central atlantic magmatic province lavas suggesting a causal link between loss of taxa and the very earliest eruptive phases the initial isotopic excursion potentially provides a widely correlatable marker for the base of the jurassic a temporary return to heavier values followed but relatively light carbon dominated the shallow oceanic and atmospheric reservoirs for at least 600 k y

hydrocarbon potential and depositional environment of the lower cretaceous black mudstones and shales in the coastal guangdong province china abstract the mesozoic especially the cretaceous sequences in the northern south china sea scs are important potential targets of oil and gas exploration however they are currently poorly understood we use organic petrology and geochemistry to evaluate the hydrocarbon potential and study depositional environment of the cretaceous black mudstones and shales from the dayawan section in the guangdong province china these mudstones and shales yield total organic carbon toc contents of 0 63 2 76 and most samples meet the requirement for higher toc source rocks organic matters in the mudstones and shales were sourced mainly from higher plants as well as subordinate benthic macroalgae organic petrology and geochemical data suggested that the organic matters were dominated by type iii and minor type ii and generally have low thermal maturity thus we evaluated the black mudstones and shales have a potential for hydrocarbon generation especially gas prone pr ph trace elements and mixture source of organic matter suggested that these black mudstones and shales formed in a coastal lacustrine environment characterized by weakly oxidizing weakly reducing conditions and low salinity a marine transgression developing in the middle part of the section was recognized generally the northern scs which exhibits the more marine influence likely contains source rocks with higher toc contents and better organic matter types the cretaceous source rocks with higher liquid hydrocarbon generation potential may occur locally in the pearl river mouth basin

integrated geostructural seismic and infrared thermography surveys for the study of an unstable rock slope in the peloritani chain ne sicily abstract this paper presents a multidisciplinary study about the instability of a rock slope on peloritani chain northeastern sicily several rockfalls affected the studied slope in the last decades also causing the disruption of the main road connecting the shore villages to the city of messina the complex geology and tectonics are the main causes of the poor mechanical properties of the rocks exacerbated by high fracturing and weathering geostructural surveys allowed identifying the main discontinuity sets most of which matches with the regional fault systems kinematic and stability analyses were carried out to define the main failure typologies and to realize two models describing the past rockfalls as well as possible future events for the deep investigation of the slope horizontal borehole drilling and seismic active prospecting were performed so to estimate the thickness of the rock with poor mechanical properties the contours of the most unstable areas along the slope have been better outlined through infrared thermography images giving information about the thermal radiance behavior of the rock constituting the surface slope the integrated approach of different methodologies besides defining the instability features of the study area demonstrates the reliability of such techniques particularly in a geologically complex region where rockfalls represent one of the main causes of landslide fatalities

studies on the early cretaceous longzhaogou and jixi groups of eastern heilongjiang northeast china and their bearing on the age of supposedly jurassic strata in eastern asia abstract the coal bearing longzhaogou and jixi groups in eastern heilongjiang northeast china consist of alternating marine and non marine deposits containing abundant marine animal and plant fossils the jixi group also yields members of the johel fauna that is widely distributed in northern and eastern china the two groups have been considered as jurassic or mainly jurassic in age for a long time however recent studies documented that the ammonites bivalves dinoflagellates angiosperms and sporopollens are all of early cretaceous rather than jurassic age it has been demonstrated that 1 the longzhaogou and jixi groups and their equivalents the johel group of china and the transbaikalian group of russia are of early cretaceous age 2 the barremian albian was also a very important period of coal accumulation in northeastern china and perhaps in all of eastern asia 3 there existed a large shallow embayment connecting with the palaeo pacific in eastern heilongjiang and it was the climate of the embayment that controlled the origin and development of the animal and plant communities of northeastern china during the early cretaceous correlation between formations in the jixi and longzhaogou groups has also been revised in this paper

a back analysis method using an intelligent multi objective optimization for predicting slope deformation induced by excavation abstract a multi objective inverse analysis method for slope excavation was proposed in which orthogonal design numerical simulation back propagation neural network bpnn and elitist non dominated sorting genetic algorithm nsga ii were integrated the multi objective model is constructed by minimizing a set of multi objective error functions between the time series of observations and corresponding calculated values compared with the back analysis methods that uses traditional algorithms the proposed method is validated by a numerical example to be more effective for multi objective optimization the methodology is also applied to the excavation of a right bank slope at the dagangshan hydropower station located in the sichuan province china the obtained inversion parameters are used in forward analysis to predict displacements in this case application three types of field observations are used simultaneously in the back analysis which include displacements in the dadu river water flow y direction transverse x direction and vertical z direction compared with the field displacement data the trend of the predicted displacements agrees well with the measurements the results indicate that the proposed method can more precisely and reliably predict the slope deformation induced by excavation

three dimensional stability evaluation of a preexisting landslide with multiple sliding directions by the strength reduction technique landslide 1 is located on the right bank of the downstream side of the dam for hongjiadu hydropower station in guizhou province china in view of its close proximity to important workings the stability of the slide is of great concern ground investigation showed that the slide is potentially unstable and has two sliding directions reinforcement mainly by piles was proposed as the stabilization measure but two key questions were raised during the design of the piles 1 how could the stability of the slope be evaluated as there are two major sliding directions 2 how could the shear strength parameters of the slip band be determined as it contains a significant proportion of coarse particles in this paper we demonstrate how these issues can be addressed by the strength reduction technique first the strength parameters of the slip band are back analyzed by assuming a factor of safety of unity second the major sliding directions are determined by carrying out finite difference analyses third

fusulinid bearing oolites from the tengchong block in western yunnan sw china early permian warming signal in the eastern peri gondwana abstract discovery of fusulinid bearing oolites from the tengchong block in western yunnan china provides new insights into permian paleoclimatic history of the eastern peri gondwana in the northern tengchong block new carbonate samples from the lower part of the dadongchang formation yield a monotonous fusulinid assemblage comprising eoparafusulina tschernyschewi tschernyschewi e tschernyschewi oblonga e tibetica e aff tschernyschewi tschernyschewi and e aff laudoni this assemblage correlates well to late sakmarian artinskian fusulinids widespread among the cimmerian blocks in peri gondwana which were characterized by low diversity and dominance of cosmopolitan taxa such fusulinids have been interpreted to indicate temperate water environment in the aftermath of late paleozoic glaciation moreover the eastern cimmerian region has been suggested by both paleontological and sedimentological data to be even cooler than the western region especially during the early permian however the fusulinids of this study unexpectedly occur within oolites as ooids diagnostic for warm water settings have never been recorded from early permian strata of any eastern cimmerian block this new finding in the northern tengchong block indicate that the shallow marine there was warm enough to accommodate not only poorly diversified fusulinids but also oolites even immediately posterior to the late paleozoic glaciation the appearance of these oolites is more likely ascribed to a warming pulse of sea surface temperature in the context of post glacial climatic amelioration than to the northward drift of the tengchong block

a new semi deterministic block theory method with digital photogrammetry for stability analysis of a high rock slope in china abstract this study proposed a new semi deterministic block theory nsdbt method in which the sizes and spatial positions of discontinuities along with their orientations were incorporated hence the locations volumes and sliding forces of key rock blocks could be obtained which could directly provide quantitative reference for support design the nsdbt method was applied to analyze the stability of a high rock slope of changhe dam located in sichuan province southwest china required geological data for the analyses was obtained from field and laboratory investigations the mechanical parameters of discontinuities were obtained by laboratory direct shear tests and geometric characteristics of discontinuities were obtained by digital photogrammetry a total of 3540 discontinuities were identified the analysis results showed that a 57 7 key blocks were excluded owing to taking the formation probability of key blocks into consideration b comparing the results of the calculation and field investigation it was found that the calculated locations of dangerous discontinuities were in good agreement with the failed blocks investigated in the field note the failed blocks include blocks that have developed into real rockfalls and dangerous blocks identified by a field survey c on the studied slope 355 key blocks were searched of which 175 123 and 57 were tetrahedral pentahedral and hexahedral blocks respectively d the volumes of key blocks ranged from 0 01 to 22 83 m 3 and most of them were smaller than 4 m 3 e the sliding forces of key blocks were range from 0 01 to 390 98 kn and most of them were smaller than 50 kn and f water had a great impact on the stability of the slope especially for sampling window 3 in summary the studied slope was stable on the whole but there existed some local small key blocks

microseismic monitoring and stability analysis of the left bank slope in jinping first stage hydropower station in southwestern china risks associated with the left bank slope of jinping first hydropower station in southwestern china are growing as a result of excavation of the dam foundation ditch and various tunnels as well as grouting to soft strata to improve our understanding of the slope instability and resolve the complex subsurface conditions of the highly fractured rock mass a microseismic monitoring system was installed in june 2009 which is the first time such a technique has been introduced into stability analysis of a high steep rock slope in china the microseismic monitoring system consists of a data acquisition unit a data processing unit and a three dimensional array of uniaxial accelerometers in order to analyze the correlation between seismicity and potential slip surface of the slope a numerical model was implemented to analyze the failure processes and stability of the slope the monitoring results illustrate that microseismic events mainly occur as a strip along the spandrel groove of the dam which coincides with the potential slip surface obtained from numerical analysis especially at the bottom of the slope therefore the comprehensive method incorporating microseismic monitoring and numerical analysis has been proven to be very promising in instability prediction of rock slope subject to identification and delineation of potential slip surface and failure regions

the nonmarine triassic jurassic boundary in the newark supergroup of eastern north america abstract for the last three decades the position of the triassic jurassic boundary tjb in nonmarine strata has largely been based on its palynostratigraphic placement just below the oldest basalts of the central atlantic magmatic province camp in the newark supergroup of eastern north america this boundary however is demonstrably older than the tjb as it is defined in marine strata thus the palynostratigraphic change used to place this tjb in the newark most resembles a late norian change in the european section and does not correspond to any palynological event at the marine defined tjb conchostracan biostratigraphy suggests that the tjb is in the newark extrusive zone above the oldest camp basalt and vertebrate biostratigraphy is consistent with this placement of the tjb radioisotopic ages indicate that the tjb defined in marine strata is no older than 200 ma but the oldest camp basalts of the newark supergroup consistently yield ages averaging about 201 ma magnetostratigraphic correlation of the newark section to the tjb section at st audrie s bay in england also indicates that the onset of camp volcanism in the newark supergroup is older than the marine tjb correlations based on carbon and osmium isotopes are also consistent with this correlation thus all data indicate that the tjb in the newark supergroup is above the lowest camp basalt in the newark extrusive zone correct placement of the tjb in the newark supergroup allows key nonmarine and marine events to be sequenced across the tjb indicating the following succession of events crurotarsan thecodont extinction the palynofloral turnover in the newark the first camp eruptions the extinctions of rhaetian ammonites and conodonts and the first appearance of jurassic psiloceratid ammonites

jurassic paleogeography of the tian shan an evolution driven by far field tectonics and climate abstract the strongly intracontinental tian shan region in central asia represents a key area to understand the long term evolution of continents in general and asia in particular if its paleozoic and cenozoic geodynamics are well understood its mesozoic evolution remains poorly constrained in order to decipher the paleogeographic and large scale tectonic evolution of the tian shan area during the jurassic we compiled detailed field analyses of sedimentary rocks acquired within and around the chinese tian shan region together with previously published data we present three paleogeographical maps corresponding to the late early early middle jurassic late middle early late jurassic and late jurassic early cretaceous transition periods we provide a large scale picture of the jurassic paleogeographic and climatic evolution of the tian shan region and discuss the geological evolution of the range together with the possible driving mechanisms during the early to early middle jurassic the topographic evolution of the tian shan range was dominated by progressive planation of late paleozoic to early mesozoic relief locally interrupted by short lived tectonic uplift throughout the region contemporaneous sedimentation was characterized by alluvial to lacustrine strata deposited under humid conditions during this period recurrent limited deformation events associated with strike slip and compressive tectonics occurred that cannot be explained by far field effect of the qiangtang collision but could instead be associated to the coeval subduction related extension affecting the caspian turan domains during the late middle to early late jurassic the planation of the paleozoic early mesozoic tian shan range then continued a shift to more semi arid conditions during the late jurassic is also recorded in the sedimentary series all over the region at that time few evidences of deformation exists in the tian shan or within the caspian turan domains we propose that the late middle early late jurassic corresponded to a period of relative tectonic quiescence in the area finally the late jurassic early cretaceous transition was marked by a tectonic reactivation leading to the inversion of the yarkand fergana basin and to localized relief building in the tian shan this renewed transpressive deformation phase could be mainly related to the coeval accretion of the helmand block to the south west and possibly to the onset of the accretion of the lhasa block along the southwestern margin of eurasia finally this period was also characterized by the climax of aridification which played a major role on the emplacement of extensive alluvial fan systems in the basins surrounding the range

mesozoic ecosystems climate and biotas this issue of palaeogeography palaeoclimatology palaeoecology is devoted to papers on mesozoic ecosystems and is an outcome of the international geoscience program igcp 632 igcp is a joint opera

synchrony between early jurassic extinction oceanic anoxic event and the karoo ferrar flood basalt volcanism a well known second order mass extinction took place during the pliensbachian and toarcian stages of the early jurassic first recognized as a minor pliensbachian peak in the global extinction rate it has alternatively been interpreted as a regional response to the early toarcian oceanic anoxic event detailed studies established it as a global long term event spanning five successive ammonoid zones here we present a revised time scale based on highprecision u pb ages resolved to the zone level which suggests that elevated extinction rates were sustained for about 4 m y and peak extinction occurred at 183 ma recent isotopic dating of flood basalts from the southern gondwanan karoo and ferrar provinces documents a culmination in volcanic activity ca 183 ma the onset of volcanism is recorded as an inflection and start of a rapid rise of the seawater 87 sr 86 sr curve the synchrony of voluminous flood basalt eruptions and biotic crises as already noted for three of the major mass extinctions permits a causal relationship which in this case may be mediated by widespread oceanic anoxia

mechanism of deep cracks in the left bank slope of jinping first stage hydropower station abstract the proposed jinping first stage hydropower station is located on the middle reach of the yalongjiang river sichuan province pr china it consists of a double curvature arch dam with a maximum height of 305 m which will be the highest in the world cracks are well developed in the left bank slope of the pusiluogou the dam site of jinping first stage hydropower station some cracks are even developed at the horizontal distance into rock face in this paper the term horizontal depth was used to describe the horizontal distance into face of the slope beyond 200 m and these cracks are here referred to as deep cracks the distribution of these deep cracks is far beyond people s experiences in common unloading zones so the mechanism of the deep cracks is put forward as a new subject since these cracks are significant for the stability of the slope their mechanism becomes one of the key engineering geology problems a comprehensive study is made in this paper on the distribution characteristics of the cracks as well as their deformation features the factors that influence their distribution and deformation feature are also analyzed by means of geology mechanics and numerical simulation an important conclusion is consequently reached that deep cracks occurred as a result of release of high ground stress including gravitational stress and tectonic stress the formation of the deep cracks in the slope is a result of unloading process under favorable geology conditions fast crust uplift and quick river cutting and high tectonic stress are indispensable regional geological condition steep and high geometry condition provides favorable geometry condition hard at the lower part and soft at the upper part of the slope offers suitable rock combination condition and back facing bending planes and consequent discontinuities supply suitable structure of the slope

reinforcement effects and safety monitoring index for high steep slopes a case study in china abstract high and steep slopes which have developed fractures and intercalations are a great threat to the operation of dams and reservoirs in this work the geological conditions and potential modes of failure of the slope found in the right bank of suofengying hydropower station are investigated for the slope stability and the results are presented in order to strengthen the slope an innovative stabilization scheme is employed the stabilization techniques include development of anti shear tunnels anti slide piles anchor cables concrete support structure etc further the slope stability and reinforcement effects using various stabilization techniques are studied by using finite element strength reduction method moreover in situ monitoring is carried out and the data obtained is analyzed from the results it is observed that the deformations that are detected using multipoint extensometers have decreased after the installation of remedial reinforcements from the analysis of remedial reinforcement methods it is found that the most critical reinforcement is the development of anti shear tunnels in order to monitor the stresses in stirrups and the propagation of cracks in the anti shear tunnels three levels of safety monitoring index are proposed the safety monitoring index is developed based on the results obtained by the simulation of the process of failure of the reinforced slope the developed safety monitoring index is further applied to the suofengying project in order to evaluate the overall stability of the slope the results obtained by monitoring indicate that the performance of the reinforcement structures is satisfactory and the slope has better stability the methodology proposed in this work shall be useful for similar projects to obtain stability of slopes

a review of the broad pattern of jurassic sea level changes and their possible causes in the light of current knowledge abstract an assessment is made of the current state of research into jurassic sea level changes based on new insights into depositional patterns in relation to these changes and new stratigraphic information from several widely separated regions across the world the bearing of this information on alternative models respectively involving sea level rise interrupted by stillstands or falls is then evaluated the gross pattern appears to be one of more or less gradual rise of sea level through the period interrupted by episodes of comparative stillstand rather than eustatic fall and several episodes of significant regression are shown to be the result of regional tectonics major episodes of eustatic rise took place in the early hettangian early sinemurian early pliensbachian early toarcian early and late bajocian middle callovian and late oxfordian to kimmeridgian a significant episode of rapid and very extensive regression possibly global took place at the end of the triassic but other regressive episodes in the late aalenian bathonian late oxfordian kimmeridgian and tithonian are clearly only regional in extent there is no evidence for glacioeustasy and most if not all of the regional or global changes recognised can readily be related to plate tectonics the events at the triassic jurassic boundary seem to be the result of mantle plume activity centred on the central atlantic region

temporal and spatial distribution patterns of the marine brackish water bivalve waagenoperna in china and its implications for climate and palaeogeography through the triassic jurassic transition abstract waagenoperna was a genus of epi byssate marine to brackish water littoral bivalves it used to be regarded as late permian late triassic in age however a review of the genus reveals that it did not occur until the late triassic and in the early jurassic some species of waagenoperna i e w lilingensis w mytiloides and w cf lilingensis had a wide distribution in the areas southwest of the shanghai altay mountain range including parts of southern china the sediments hosting these bivalves are intercalated with non marine strata including coal the geographic and stratigraphic distribution patterns of waagenoperna can not only aid in the correlation of the non marine coal bearing strata spanning the triassic jurassic transition and constrain their age but also particularly demonstrate a history of transgressions flooding the areas southwest of shanghai altay during the sinemurian these extensive transgressions influenced the climate and changed the palaeo topography of southwestern shanghai altay they ensured a humid climate and resulted in the formation of marsh and even paralic swamp environments these environments allowed the flora and fauna to thrive and led to the accumulation of large quantities of organic matter that eventually formed coal and probably oil as well

stability investigation and stabilization of a heavily fractured and loosened rock slope during construction of a strategic hydropower station in china abstract this paper presents a case history of the 205 m high intake slope at the huangjinping hjp hydropower station on the dadu river deformation and cracks developed on the cut slope during excavation and the deformation extended onto the natural slope above the cut giving rise to serious safety concerns research was conducted to study the engineering geological conditions and the deformation characteristics of the slope during excavation in situ monitoring data and possible causes of cracking were analyzed the results show that the zone of loosened rock mass extended much deeper into the rock mass than it did at other sites in the region because of the tectonic history of the site and cutting the empirically designed cable anchors with lengths of 40 m or 45 m were insufficient to stabilize the slope while the remedial cable anchors as long as 100 m successfully stabilized the slope the analytic method and procedure used in this paper could be useful to similar projects

influence of a fault system on rock mass response to shaft excavation in soft sedimentary rock horonobe area northern japan abstract this paper focuses on the stress field that produced a fault system in the horonobe area of japan and considers the relationship between the fault system and the rock mass response to shaft excavation in soft sedimentary rocks in this area hydraulic fracturing investigations in boreholes and tectonic plate movements indicate that the major horizontal principal stress is oriented e w however during shaft excavation the greatest convergence in the shaft was oriented nne ssw therefore it is necessary to understand the influence of the fault system on the rock mass response to shaft excavation we performed a fault slip analysis of faults in the shaft wall and reconstructed the paleostress field that produced the fault system the maximum horizontal principal stress was oriented mainly nne ssw and the minimum horizontal principal stress was oriented mainly wnw ese these directions are similar to the directions of maximum and minimum convergence in the shaft respectively the results show that a fault system can affect the rock mass response to shaft excavation in soft rock and it is considered that the rock mass deformation is controlled by the fault system in addition it may be possible to assess and predict the rock mass behavior by focusing on paleostress field that produced the fault system