glacier subsurface heat flux characterizations for energy balance modelling in the donjek range southwest yukon canada we apply a point scale energy balance model to a small polythermal glacier in the st elias mountains of canada in order to investigate the applicability and limitations of different treatments of the glacier surface temperature and subsurface heat flux these treatments range in complexity from a multilayer subsurface model that simulates snowpack evolution to the assumption of a constant glacier surface temperature equal to 0 c the most sophisticated model includes dry densification of the snowpack penetration of shortwave radiation into the subsurface internal melting refreezing of percolating meltwater and generation of slush layers measurements of subsurface temperature and surface lowering are used for model validation and highlight the importance of including subsurface penetration of shortwave radiation in the model using an iterative scheme to solve for the subsurface heat flux as the residual of the energy balance equation results in an overestimation of total ablation by 18 while the multilayer subsurface model underestimates ablation by 6 by comparison the 0 c surface assumption leads to an overestimation of ablation of 29 in this study where the mean annual air temperature is about 8 c

compositional variation and palaeoenvironment of the volcanolithic fort cooper coal measures bowen basin australia abstract an integrated analysis of megascopic lithotype microscopic maceral and mineral composition stable carbon isotope and interburden sedimentology from a single well was used to interpret the response of the late permian fort cooper coal measures fccm to regional and global environmental influences the fccm are differentiated from underlying relatively high vitrinite moranbah coal measures and overlying higher inertinite rangal coal measures in the bowen basin by their intercalation with abundant tuff and siliciclastic partings and interbeds besides this there is little described about the variation in the organic composition of the fccm and its causes the fccm can be subdivided into a lower aggradational fair hill formation transgressed by the shallow marine derived black alley shale that interfinger with is overlain by the progradational middle main seams and burngrove formation coal measures the coals are dominantly dull with minor bright bands that are more abundant in the burngrove formation representing a change in plant composition the maceral analysis shows that the coals in the fair hill formation and middle main seams are vitrinite rich 80 90 mmf albeit with high mineral matter suggesting the formation of precursory peat under rising water levels and with high sediment tuff influx and preservation the coals in the burngrove formation have an increased inertinite content 30 mmf but are also high in mineral matter suggesting a shift to increased decomposition arising from a fluctuating water table possibly increased aridity and or microbial activity tuffs occur throughout and although their frequency is higher in the lower fair hill formation the preservation of thicker tuffs in the upper burngrove formation indicates increased intensity of volcanism that could have modified the environment variation in carbon isotope compositions show a parabolic trend from around 24 1 in the fair hill formation to more variable values in the middle main seams with an overall 13 c enrichment upwards in the burngrove formation prior to the 13 c values becoming negative depleted between 1 to 4 from the average 24 1 in the top seams and into the overlying rangal coal measures the 13 c depletion trend in the upper part of the section is unexpected in view of corresponding increase in inertinite content of the coals indicating that the 13 c values plant composition and inertinite content are decoupled unless the inertinite origin is from intense microbial decay similar stable carbon isotope depletion trends have been observed elsewhere in an equivalent stratigraphic interval of the bowen basin suggesting that the carbon isotope values are responding to global conditions that cause negative excursions in carbon isotopes before the p t boundary overall the basin was continuously subsiding and peats accumulated with constant interruptions from excessive sedimentation and volcanic eruptions the low proportion of visible thick bright bands coupled with high telovitrinite mmf content suggests a marsh to fen environment with an open canopy and ponding able to preserve volcanic ash falls

carbon isotope stratigraphy across the permian triassic boundary a review abstract the palaeozoic mesozoic transition is marked by distinct perturbations in the global carbon cycle resulting in a prominent negative carbon isotope excursion at the permian triassic p t boundary well known from a plethora of marine and continental sediments potential causes for this negative 13 c trend and their links to the latest permian mass extinction have been intensively debated in the literature in order to draw conclusions regarding causation a general 13 c curve was defined after consideration of all available datasets and with due reference to the biostratigraphic background the most important features of the p t carbon isotope trend are the following the 4 7 13 c decline lasting 500 000 years is gradual and began in the changhsingian at the stratigraphic level of the c bachmanni zone the decreasing trend is interrupted by a short term positive event that starts at about the latest permian low latitude marine main extinction event horizon eh indicating that the extinction itself cannot have caused the negative carbon isotope excursion after this short term positive excursion the 13 c decline continues to a first minimum at about the p t boundary a subsequent slight increase is followed by a second occasionally two peaked minimum in the lower and middle i isarcica zone the negative carbon isotope excursion was most likely a consequence of a combination of different causes that may include 1 direct and indirect effects of the siberian trap and contemporaneous volcanism and 2 anoxic deep waters occasionally reaching very shallow sea levels a sudden release of isotopically light methane from oceanic sediment piles or permafrost soils as a source for the negative carbon isotope trend is questionable at least for the time span a little below the eh and somewhat above the p t boundary

u pb zircon geochronology and tempo of the end permian mass extinction the mass extinction at the end of the permian was the most profound in the history of life fundamental to understanding its cause is determining the tempo and duration of the extinction uranium lead zircon data from late permian and early triassic rocks from south china place the permian triassic boundary at 251 4 0 3 million years ago biostratigraphic controls from strata intercalated with ash beds below the boundary indicate that the changhsingian pulse of the end permian extinction corresponding to the disappearance of about 85 percent of marine species lasted less than 1 million years at meishan a negative excursion in 13 c at the boundary had a duration of 165 000 years or less suggesting a catastrophic addition of light carbon

the permian kungurian cisuralian palaeoenvironment and palaeoclimate of the tregiovo basin italy palaeobotanical palynological and geochemical investigations abstract a transition from widespread humid to more drought tolerant floras characterized tropical terrestrial ecosystems during the permian cisuralian tregiovo southern alps n italy is one of the very few well dated kungurian late cisuralian plant localities in euramerica it was located in eastern palaeoequatorial pangea two units bearing fossil plant assemblages occur in finely laminated sediments deposited in a playa lake environment in this paper the sedimentology of the tregiovo basin is reviewed and new palaeobotanical palynological and stable isotopic data are presented in order to reconstruct the palaeoclimatic and palaeoenvironmental conditions of the kungurian in the southern alps both fossil plant assemblages are dominated by conifers hermitia feysia quadrocladus dolomitia together with sphenophytes annularia ginkgophytes sphenobaiera pteridosperms peltaspermum taeniopterids and sphenopterids these taxa which occur with different abundances in the two plant assemblages both indicate semi arid conditions associated palynoflora dominated by bisaccate pollen and extremely rare spore occurrences is consistent with the xerophytic character of the macroflora and suggests that the fossil plant record was not affected by collection or preservation bias stable isotopic analyses of two stratigraphic sections reveal an upward trend of increasingly negative 13corg vpdb which may correlate with roughly coeval records from marine and continental successions such as in north china and south africa this isotopic shift may be attributed to a global perturbation of atmospheric 13c although the influence of local environmental factors cannot be excluded

carbon isotope compositions of the late permian carbonate rocks in southern china their variations between the wujiaping and changxing formations abstract the carbon isotope compositions of the upper permian marine carbonate rocks in southern and eastern guizhou and central guangxi of southern china have been investigated the results reveal a 13c anomaly at the boundary between the wujiaping and changxing formations of the upper permian the 13c values in limestones of the wujiaping formation are mostly within the range of 3 5 and 5 0 whereas the 13c values in limestones of the changxing formation are mostly less than 3 0 ranging from 0 2 to 3 1 the carbon isotope negative excursion at the boundary between these two formations is helpful to differentiate the two stages wuchiapian and changxingian of the late permian in southern china if substantiated by sufficient fossil materials this also means that the 13c values of the carbonates were decreasing throughout the late permian and this change was accompanied by some rapid falls such as those in the permian triassic boundary and possibly in the wujiapingian and changxingian boundary during the late permian the consumption of organic carbon by the oxidation of the previously formed coals as a result of dry climates and tectonic uplifting must have exceeded the burial of organic carbon as in coal in addition lack of coal deposits during the late tatarian on the gondwana fragments suggests a global reduced coal accumulation consequently more 12c rich co2 was released into the atmosphere which might contribute to the 13c depletion seen in upper permian marine carbonates

structural geometry microstructural and strain analyses of l tectonites from paleoproterozoic orthogneiss insights into local transport parallel constrictional strain in the sikkim himalayan fold thrust belt paleoproterozoic lingtse orthogneiss shows three dominant structural associations in the sikkim himalayan fold thrust belt ftb a these rocks locally define the pelling thrust pt zone that lies in the footwall of the main central thrust mct b they occur as linear almost n s trending imbricates within the pt sheet and c they form a n s trending 13 5 km long 2 km wide discontinuous linear mylonitic klippen within the daling formation of the lower lesser himalayan sequence lhs that lie east of the n s trending teesta valley the klippe records n s trending strong l tectonites that are spatially associated with ls and sl tectonites the stretching lineations are oriented along the transport direction these rocks are exposed along three mylonite zones from north to south these are the phodong mylonite zone the tumin eingee mylonite zone and the rumtek mylonite zone all the three mylonite zones are overall folded along gently plunging transport parallel n s trending synform with the strongest l fabric developed along the hinge zone and its dominance decreases progressively toward the eastern and western structural contacts of the klippen the highest constrictional strain is recorded in phodong and tumin eingee mylonite zones and decreases south toward rumtek mylonite zone the long axes x of the quartz strain ellipsoids show n s trend and gentle plunge that agrees with the stretching lineations observed in the field additionally the xy plane of the generated ellipsoids overall agree with the observed variation of the mylonitic foliation planes in the field from all the three locations microstructural analysis from the mylonite klippe suggests that quartz and feldspar have undergone 35 and 76 grain size reduction with respect to the protolith dislocation creep and microfracturing are the dominant deformation mechanisms in quartz and feldspar respectively the grain size reduction is more prominent near the eastern and the western boundaries as they mark structural contacts between the l tectonites and the daling phyllites strain is partitioned between quartz and feldspar in the mylonite zones with quartz recording constrictional strain while feldspar records flattening strain we explain this variation due to their different deformation mechanisms shear sense analysis of feldspar porphyroclasts suggest dominantly transport parallel flow along with a component of transport perpendicular flow in the mylonite zones existing models on mechanism of l tectonite formation and transport parallel folds do not completely explain our observations we propose the possible existence of a lateral ramp beneath the pt sheet to explain the generation of l tectonites and transport parallel fold in the study area

response of carbon isotopic compositions of early middle permian coals in north china to palaeo climate change abstract to investigate the magnitude to which the carbon isotopic ratio 13c varies in coals in response to their contemporary terrestrial environment the early middle permian huainan coals including coals from the shanxi formation lower shihezi formation and upper shihezi formation in north china were systematically sampled a 2 5 variation range of 13c values 25 15 to 22 65 was observed in huainan coals with an average value of 24 06 as coal diagenesis exerts little influence on carbon isotope fractionation 13c values in coals were mainly imparted by those of coal forming flora assemblages which were linked to the contemporary climate the 13c values in coals from the shanxi and lower shihezi formations are variable reflecting unstable climatic oscillations heavy carbon isotope is enriched in coals of the capitanian upper shihezi formation implying a shift to high positive 13c values of coeval atmospheric co2 notably our study provides evidence of the kamura event in the terrestrial environment for the first time

initial assessment of the carbon emission rate and climatic consequences during the end permian mass extinction numerous lines of geochemical and stable isotopic evidence indicate that the end permian mass extinction was accompanied by abrupt climate change induced by co2 addition catastrophic end permian siberian volcanism may have released a large amount of co2 into the atmosphere and pushed the earth s system beyond a critical threshold causing the mass extinction however the injection rate total amount and source of co2 are largely unknown we conducted a suite of simulations using the recently published carbon isotope records and u pb ages from meishan section in zhejiang province china an earth system model of intermediate complexity cgenie http www genie ac uk was used to extract the pattern of co2 release needed to replicate the observed carbon isotope excursion across the permian triassic boundary this analysis leads us to suggest that the source of co2 must have been significantly heavier than typical biogenic or thermogenic methane to explain the significant warming that occurred during and after the extinction event nevertheless as with the paleocene eocene thermal maximum end permian rates of co2 addition were likely small compared with modern fossil fuel burning but considerably more protracted such that the likely total co2 emitted significantly exceeded the modern fossil fuel reserves peak emission rates corresponded to the onset of the maximum extinction interval consistent with carbon cycle disruption including volcanogenic co2 induced warming and perhaps ocean acidification as a trigger for the end permian mass extinction

reconstruction of atmospheric co2 concentration during the late changhsingian based on fossil conifers from the dalong formation in south china abstract a single species of fossil conifer with well preserved cuticles from multiple layers of the dalong formation in two sections in duanshan town guizhou province southwest china has been used to reconstruct palaeo atmospheric pco2 the age of these layers can be dated back to the late changhsingian latest permian corresponding to the clarkina changxingensis and clarkina yini conodont zones two calibration approaches were employed in this study using the stomatal ratio method the pco2 curves of the two sections showed matching trends with levels decreasing in the middle of the profiles and similar ranges at ca 340 510 ppm and ca 300 440 ppm similar values ca 360 520 ppm yet with wider error ranges were obtained when the mechanistic model proposed by franks et al in 2014 was applied to one of the sections our values are lower than the mean pco2 values from coeval palaeosols but partly overlap with them when error ranges are taken into consideration thus more independent studies are needed to evaluate the discrepancies between the two proxy methods the low atmospheric co2 concentrations in this study suggest a cool climate rather than extensive glaciation for the brief period of late changhsingian which is supported by the oxygen isotope record of conodont apatite and a major restructuring of late permian flora and fauna

physical experiments of transpressional folding abstract in order to understand the process of folding in obliquely convergent settings we formed folds within a shear box capable of creating homogeneous transpressional deformations folds were created in a single layer of stiff mixed plasticine and silicone that overlay a newtonian silicone for a variety of plate convergence angles as small amplitude folds became visible they were parallel to the long axis of the horizontal finite strain ellipse with increasing deformation the fold hinges rotated parallel with the long axis of the horizontal finite strain ellipse for all angles of convergence this parallelism indicates that fold hinges once formed rotate with the horizontal strain ellipse rather than as material lines the experiments highlight several interesting effects of transpression dynamics the fold hinges initiate parallel to either 1 or 2 and are parallel to either s 1 or s 2 with increasing deformation neither infinitesimal strain stress nor finite strain is resolvable solely from fold geometry further the net amount of contraction determined by folding across the zone was overestimated in all cases except pure contraction this effect is obvious for the case of wrenching where folding implies that the zone contracts if elongation parallel to the fold hinge is not considered therefore attempts to balance cross sections in transpressional zones will tend to overestimate contraction unless the wrench component of deformation is addressed this result is validated by applying the modeling results in folding in central california adjacent to the san andreas fault where cross section balancing indicates higher amounts of contraction than predicted by plate motion

vorticity determination distribution partitioning and the heterogeneity and non steadiness of natural deformations abstract an investigation on vorticity in general heterogeneous and non steady flows is presented the bulk vorticity of a flow is solely determined by the imposed boundary conditions and it exerts no constraints on local flow the distribution of bulk vorticity in different rheological domains and the partitioning of the distributed vorticity into shear induced vorticity and spin are both time dependent this indicates that heterogeneous flows are inevitably non steady in a quantitative example it is demonstrated that even though the imposed boundary movement is a constant simple shear local flow can be non steady spinning and non coaxial super simple shear flow with internal kinematic vorticity number greater than i occurs but the finite strain does not necessarily pulsate the geological implications of this investigation are discussed the significance of heterogeneity and non steadiness in natural deformations are emphasized it is concluded that vorticity distribution and partitioning is the link between different scale structures the internal kinematic vorticity number is not a criterion of finite strain oscillation

permian triassic boundary ptb in the lower yangtze region southeastern china a new discovery of deep water archive based on organic carbon isotopic and u pb geochronological studies abstract the lower yangtze region of southeastern china is an important area for the study of permian triassic boundary ptb in this region many well known ptb sections e g meishan have been investigated widely and extensively however these sections are dominantly in shallow water settings and data from deep water areas are lacking to fill the gap we conducted a field survey recently and found a deep water ptb section with relatively continuous deposition using integrated organic carbon isotopic and u pb geochronological studies this well exposed and fresh section is located at niushan xuancheng city anhui province 90 km west of the well known meishan section which is the ptb global boundary stratotype section and point the organic carbon isotope curve of the section contains three positive excursions pcies and two negative excursions ncies which can be well correlated with other ptb sections as well as with wuchiapingian changhsingian boundary wcb sections worldwide they archive the original ptb and wcb signatures further u pb dating of magmatic zircons in volcanic ashes validates this new finding i e the ptb interval between 252 49 0 76 ma and 251 74 0 77 ma carbon isotopes of ptb sections in south china reflect the regional paleogeography the two ncies ncie 2 and ncie 3 across the ptb transition are most likely caused by widespread large scale volcanic activity in contrast the ncie 1 near the wcb is possibly related to an increase in the productivity of organic matter as a result of transgression and a change in the organic matter type from terrigenous to marine

pangea extravagant sedimentary resource formation during supercontinent configuration an overview abstract the pangea supercontinent stage the interval from the late carboniferous to earliest jurassic is known for its rich and diverse economic resources from sedimentary systems their uniqueness is not the abundance but the resource association on a global scale and even more the time space distributions the evolution of the supercontinent configuration in context of icehouse to coldhouse stages generated maximum coal evaporite and phosphate deposition furthermore important hydrocarbon uranium and sedimentary metal deposits sedimentary fe and al deposits are very rare also typical is the absence of resources from organic deposition during the early triassic the extravagant spatial distribution of these resource systems but also the timing of their occurrences is linked to the tectonic evolution of pangea during accretion zenith amalgamation and breakup as well as to the resulting paleogeographic climatic oceanographic and ecological reorganization of the biosphere the published data on pangean resources are reviewed and reveal a conspicuous pangean pattern these time space relationships are explained in the context of paleotectonic and ecological changes during the supercontinent stage

constraining assembly time of some blocks on eastern margin of pangea using permo triassic non marine tetrapod records abstract the supercontinent pangea was mainly formed during the permian but when it reached maximum land is unsure because the configuration of the east asian blocks during the permo triassic is still highly debated fossil tetrapods provide one of the best calibrations to the time of connection between continents but the data of permo triassic tetrapods have rarely been applied in the previous reconstructions here we review the oldest records of non marine tetrapods on the east asia blocks and use them to discuss the timing of connection between continents during the permian and triassic the distribution of seymouriamorpha shows the kazakhstanian was connected to the baltica by land from the cisuralian the diverse dashankou fauna indicates that the alxa block amalgamated to pangea at least in the guadalupian older than 266 ma the questionable footprints and late permian dicynodont assemblage from the north china show the north china craton may have been connected to the main part of pangea from the guadalupian and became part of pangea at least by 256 ma the late permian laotian tetrapods support the hypothesis that the south china block already collided with the north china and the indochina blocks by the end of the permian and there was a land route for the migration of non marine tetrapods

cretaceous terrestrial paleoenvironments of northeastern asia suggested from carbon isotope stratigraphy increased atmospheric pco2 induced climate abstract terrestrial organic carbon from cenomanian turonian sequences in hokkaido island japan has retained an isotopic record of the response of terrestrial higher plants to the paleoenvironment superimposed on a carbon isotope ratio fluctuation of atmospheric co 2 the stratigraphic record of organic carbon isotopic compositions from the hokkaido sections has been correlated to the carbonate carbon isotope record from europe and north america however considerable discrepancy in the long term time stratigraphic pattern of these isotope ratio curves exists through the middle upper cenomanian and lower turonian contrary to the marine carbonate profiles from europe and north america which show consistent positive migration through the upper cenomanian terrestrial organic carbon isotope values display a negative shift through the upper cenomanian followed by a positive recovery in the lower turonian environmental pressures that only affected carbon isotope values of terrestrial organic carbon but not those of carbonate carbon are causal factors for this discrepancy variations in atmospheric temperature and humidity and related conditions of carbon cycling in forests may have acted as factors to shift isotope values of terrestrial organic carbon negatively this causal relationship between climate and carbon isotope ratio fractionation is best explained when an increasing atmospheric p co 2 as suggested from a decoupling between isotope ratio curves of marine organic carbon and carbonate is understood as a driving force for a climatic optimum during the middle cenomanian through early turonian

geochemical evidence for lacustrine microbial blooms in the vast permian main karoo parana falkland islands and huab basins of southwestern gondwana early permian black pyritic shale units i e the whitehill irati and huab formations and black rock member in southwestern gondwana basins have elevated 13c values of total organic carbon up to 17 pdb hydrogen indices between 300 and 1000 mg co2 g c and oxygen indices 30 mg co2 g c these data suggest a manifestation of a microbial bloom event values for 13c between 26 and 22 pdb hydrogen 100 mg co2 g c and oxygen indices of total organic carbon above and below these rock units are typical for palaeozoic terrestrial type iii organic matter carbon 13 isotope stratigraphy concur with palaeontological evidence that these formations are stratigraphical equivalents and therefore that the microbial blooms covered a vast area 5 million km2 possibly earth s most expansive microbial bloom the palaeoenvironment of the rock units preceding and including the black shales was most likely lacustrine with fresh to brackish water as shown by stable isotope c o and s evidence from organic matter carbonates and pyrite the implication is that a broad tectonic belt which formed as a result of compressional tectonics during the late carboniferous to early permian from the palaeo west must have been sufficiently well developed to cut off any contact with seawater earlier than predicted late permian from previous stratigraphic and sedimentological studies stable isotope data supported by mineralogical evidence indicate that conditions particularly in the upper portions of the lacustrine oil shales were brackish and locally may have been evaporitic we envisage that the microbial blooms possibly botryococcus peaked in the upper half of the black shale units conditions rapidly became unfavourable for microbial blooms across the entire basin in the overlying formations manifested by a change from oil shales type i organic matter to organic poor type iii shales this may possibly have been a consequence of tectonic activity and interrelated causes stable isotope data of carbonates in the overlying sediments indicate that in the palaeo north the basin became evaporitic drying up and in the palaeo southern part of the basin high latitude altitude water flooded the basin and so brought to a close the microbial blooms

using along strike variation in strain and kinematics to define the movement direction of curved transpressional shear zones an example from northwestern superior province manitoba a review of current understanding of structures in shear zones reveals that correlating the orientation of stretching lineations with movement direction once a common practice based on the simple shear model is not generally applicable to transpressional zones it is difficult to determine the movement direction of a transpressional zone based on internal structures we show that the movement direction can be better defined by considering the variation in strain geometry and kinematics of differently oriented and kinematically related shear zones or different segments of a curved shear zone application of this method to a shear zone in the northwestern superior province of manitoba shows that the movement direction there is approximately north south in contrast to a commonly held view for similarly oriented shear zones in the superior province that the movement direction is approximately east west

low 18o terranes tracking mesozoic polar climates in the south pacific abstract substantially negative 18 o values of altered rocks are an unfailing guide to 18 o depleted meteoric water of low mean annual temperature and therefore of cold climates at times of hydrothermal alteration however because water rock interaction is often incomplete even where it has occurred the lack of depleted values is poor evidence for lack of cold climate a now established average surface rock composition of 6 6 c 18 o with a lower limit of 16 for an igneous and metamorphic terrane of some 6 000 km 2 in west antarctica indicates cretaceous meteoric water of less or much less than 20 c this new anomaly and similar anomalies in new zealand date from before rifting along the antarctic pacific rise and are tracking terranes originating from the mesozoic south polar archipelago in this area subaerial or subglacial hydrothermal isotope exchange has been particularly effective and or meteoric waters were isotopically unusually depleted the discovery mapping and dating of further isotopically depleted zones in the geologic record will improve constraints for paleozoic and mesozoic greenhouse climates

the motion of deformable ellipsoids in power law viscous materials formulation and numerical implementation of a micromechanical approach applicable to flow partitioning and heterogeneous deformation in earth s lithosphere abstract earth s lithosphere is heterogeneous in rheology on a wide range of observation scales when subjected to a tectonic deformation the incurred flow field can vary significantly from one rheologically distinct element to another and the flow field in an individual element is generally different from the bulk averaged flow field kinematic and mechanical models for high strain zones provide the relations between prescribed tectonic boundary conditions and the resulting bulk flow field they do not determine how structures and fabrics observed on local and small scales form to bridge the scale gap between the bulk flow field and minor structures eshelby s formalism extended for general power law viscous materials is shown to be a powerful means this paper first gives a complete presentation of eshelby s formalism from the classic elastic inclusion problem to newtonian viscous materials and to the most general case of a power law viscous inhomogeneity embedded in a general power law viscous medium the formulation is then implemented numerically the implications and potential applications of the approach are discussed it is concluded that the general eshelby formalism together with the self consistent method is a powerful and physically sound means to tackle large plastic deformation of earth s lithosphere

archean granite greenstone tectonics at kolar south india interplay of diapirism and bulk inhomogeneous contraction during juvenile magmatic accretion 1 the structural study of the kolar greenstone belt and surrounding granite gneiss terrains combined with u pb dating reveals that the middle and lower crustal tectonoplutonic pattern of the eastern dharwar craton developed during a major magmatic accretion event between 2550 and 2530 ma the granite greenstone pattern resulted from the interference of gravity driven sagging of the greenstones i e diapirism e w bulk inhomogeneous shortening combined with horizontal n s stretching and syntectonic juvenile pluton emplacement bulk inhomogeneous contraction is accommodated by the synchronous development of a pervasive n s trending vertical foliation shallow stretching lineation and conjugate strike slip shear zone pattern within and outside the greenstone belt resulting in regional horizontal pure shear deformation the plutons around the greenstone belt record regional contraction by developing one set of strike slip c s fabrics of the shear zone pattern the development of the granite greenstone pattern was coeval and compatible with deformation during juvenile magmatic accretion melting and granulite metamorphism in the lower crust the kolar example points to a specific crustal rheology that allowed sagduction of the greenstones and regional distributed bulk inhomogeneous strain due to mechanical homogeneity and low viscosity provided by large scale melting during the accretion event this example further suggests specific boundary conditions to the craton that allowed e w inhomogeneous shortening to be accommodated by n s stretching and spreading of the crust without significant tectonic thickening such tectonoplutonic pattern is specific to the archean and may develop as a consequence of mantle plume activity in intracontinental settings

fine scale partitioning of contemporary strain in the southern walker lane implications for accommodating divergent strike slip motion treating the crust as a micropolar continuum and inverse modeling a high quality catalog of earthquake focal mechanisms reveals that km scale heterogeneous strain is partitioned at km scales into pairs of plane strains with sub perpendicular principal axes these earthquakes occurred in a shallow crustal volume centered on the western indian wells valley of eastern california the site of divergent right lateral strike slip motion along the boundary between the sierran microplate and the southern basin and range province the seismic events defining the plane strains occur in a diffuse seismic source zone and cannot be additionally subdivided on the basis of the type of strain they accommodate the results indicate that seismic moment release for background earthquakes is partitioned into events associated with either fault zone perpendicular extension by normal faults or horizontal shearing by conjugate strike slip faults the spatial scales over which this partitioning occurs suggest that outcrop scale brittle faults may in some cases record nearly perpendicular plane strains related to a single continuous deformation

late permian global coal hiatus linked to 13c depleted co2 flux into the atmosphere during the final consolidation of pangea at a time when all continents were finally arrayed in their pangea supercontinental configuration 250 50 ma earth9s stratigraphy records a global and very abrupt coal discontinuity from the tartarian stage of the late permian to the middle triassic reduced coal productivity and or preservation overlaps with a period of anomalous oceanic and atmospheric decrease in 13 c as recorded in marine carbonates and organic matter and terrestrial plant and animal fossils from the northern and southern hemispheres during the same short period the peripheral margin of the entire supercontinent pangea except for the southern shores of tethys was effectively under compressive stress this unique tectonic state caused deformation and uplift of coal bearing foreland basins and oxidation of pangea9s vast peat deposits the latter resulted in a rapid massive 13 c depleted co 2 flux into the atmosphere which in turn may have forced global warming

kinematics of rock flow and the interpretation of geological structures with particular reference to shear zones abstract current interpretations of structures are generally based on homogeneous and steady deformation models despite the fact that both the heterogeneity of rocks materially rheologically and geometrically and the time dependence of imposed geological conditions give rise to significant heterogeneous and non steady flow in concert with field observations we emphasize that the expectation of heterogeneity and non steadiness is the key to understanding natural deformation and that in order to carry out successful structural analysis and tectonic interpretation it is necessary to recognize the first order distinction between imposed boundary conditions typically used to define the tectonic regime e g transcurrent transpression and the response recorded by rocks within the zone structures and fabrics using s c fabric as an example it is demonstrated how flow with a non zero spinning component resulting from the rheological contrasts and or geologically realistic time dependent boundary displacement can drastically change the ideal geometric and kinematic relations between the fabric and the host zone in agreement with both theoretical analysis and field observation it is shown that natural flow regimes range from pure shear to pure rotation including super simple shear in consideration of the heterogeneity and non steadiness of natural deformation kinematic analysis is justifiable only within a homogeneous domain and steady period flow kinematics and mechanisms are interrelated in that firstly mechanisms provide internal constraints on kinematics ensuring that only certain flows are possible and secondly flow kinematics will favour development of certain mechanisms

isotopic reconstruction of past continental environments abstract vertebrate fossils and continental sediments provide a rich record of variations in the isotopic composition of surface environments to interpret these records a greater understanding of isotopic sources as well as fractionations associated with animal physiology soil geochemistry and diagenesis has been essential tooth enamel and fish otoliths yield subannual records of surface environments whereas soil minerals may integrate signals over many thousands of years carbon isotope variations in fossil vertebrates and soils record changes in the structure of vegetation and the isotope composition and concentration of atmospheric co2 oxygen isotope variations may be indirectly related to climate through reconstruction of the oxygen isotope composition of meteoric water or directly related to temperature through application of oxygen isotope paleothermometry to soil minerals or otoliths in africa nitrogen isotope variations show promise as a proxy for rainfall abundance though the gen

a microbialite carbonate crust at the permian triassic boundary in south china and its palaeoenvironmental significance a 1 m thick carbonate crust layered and commonly domal caps crinoidal limestones on reef complexes of the top permian changxing formation in the huaying mountains eastern sichuan china the crust s stratigraphic level lies at a sharp change in facies and is overlain by poorly fossiliferous laminated micrites and shales of the lower triassic feixianguan formation the crust therefore appears to coincide with the end permian extinction event although the dating of the strata is currently imprecise the crust is composed mostly of digitate carbonate locally thrombolitic with remnant lobate fabric and resembles microbialites but is mostly recrystallised and a microbial origin is unconfirmed it is enclosed in micrite with pyrite crystals ostracode and other shell debris the crust is absent from interreef areas previous interpretations of karstification and calcrete formation are not upheld and the facies were deposited under water overlying sediments are low energy with abundant ferroan calcite and pyrite reflecting anoxia associated with rising sea level various interpretations of the crust are possible 1 it was organic and microbia grew preferentially on topographic highs of reef tops 2 microbia were a disaster biota in the absence of grazers 3 microbia took advantage of favourable conditions for calcification associated with a rapidly rising environmental co2 content during the late permian 4 the crust was an inorganic precipitate associated with co2 rich water microbial crusts are rare after the cambrian but whether this crust is organic or not its presence in these strata reinforces the view that oceanic atmospheric conditions in the permian triassic boundary interval were unusual

emplacement kinematics of a granite diapir the chindamora batholith zimbabwe the geometric features of a large 50 40 km granitic batholith and its surrounding greenstone belt envelope are described the batholith is made up of several intrusive components and an intrusion sequence based on contact relations and xenoliths has been established the igneous rocks show a local foliation s fabric and preferred orientation of minerals the intensity of this fabric accords with the finite strain determined from xenolith shape analysis when the strain variations are analysed in detail it appears that the batholith was built up by a succession of magmatic pulses each of which led to a stretching of the previously consolidated igneous material so called balloon tectonics evidence is presented that xenolith deformation commences only when the surrounding igneous material has crystallized and a method is suggested whereby the position of the surface separating crystal supported phase plastic behaviour from melt supported phase liquid behaviour at different stages in the plutonic history can be determined ductile shear zones are present and their geometry accords well with the shape changes necessary to allow the outer parts of the pluton to stretch

sustainable transpression an examination of strain and kinematics in deforming zones with migrating boundaries most orogenic belts owe their development to oblique convergence and commonly have many orogen parallel transpressional high strain zones to constrain the tectonic history of orogenic belts by structural and fabric analysis of rocks it is desirable to understand quantitatively the relationship between the boundary conditions and the resulting strain distribution and kinematics in these zones most current models for transpression assume homogeneous deformation confined by boundaries that are fixed to material planes this creates a strain compatibility problem at the margins of the active deforming zone and also requires that the strain rate normal to the zone boundaries increase to implausibly high values soon after the onset of oblique convergence transpressional motion the latter contradicts with the observation that transpressional motion can be sustained throughout an orogeny the assumption that zone boundaries are fixed to material planes is unrealistic the outstanding problems of current transpressional models are resolved in this paper by allowing the zone boundaries to migrate through the rock material the consequence of zone boundary migration for the strain field and kinematics within a transpressional high strain zone is investigated mathematically the implications of the modeling for fabric interpretation are discussed the modeling makes general predictions consistent with observed planar and linear fabric patterns in natural transpressional high strain zones it predicts that foliations in transpressional high strain zones are subparallel to the zone boundaries regardless of variation in the imposed boundary conditions lineations cluster along the great circle girdle subparallel to the average foliation the spread of the lineations may vary from point maxima to complete girdles

permian paleoclimate data from fluid inclusions in halite abstract this study has yielded surface water paleotemperatures from primary fluid inclusions in mid permian nippewalla group halite from western kansas a cooling nucleation method is used to generate vapor bubbles in originally all liquid primary inclusions then surface water paleotemperatures are obtained by measuring temperatures of homogenization to liquid homogenization temperatures ranged from 21 c to 50 c and are consistent along individual fluid inclusion assemblages indicating that the fluid inclusions have not been altered by thermal reequilibration homogenization temperatures show a range of up to 26 c from base to top of individual cloudy chevron growth bands petrographic and fluid inclusion evidence indicate that no significant pressure correction is needed for the homogenization temperature data we interpret these homogenization temperatures to represent shallow surface water paleotemperatures the range in temperatures from base to top of single chevron bands may reflect daily temperatures variations these permian surface water temperatures fall within the same range as some modern evaporative surface waters suggesting that this permian environment may have been relatively similar to its modern counterparts shallow surface water temperatures in evaporative settings correspond closely to local air temperatures therefore the permian surface water temperatures determined in this study may be considered proxies for local permian air temperatures

palaeosol stratigraphy across the permian triassic boundary bogda mountains nw china implications for palaeoenvironmental transition through earth s largest mass extinction abstract upper permian and lower triassic palaeosols from northeastern tethyan localities exposed within the bogda mountains nw china provide a wealth of information regarding long term palaeoclimatic and palaeoenvironmental variations wuchiapingian palaeosols are characterized by intense redoximorphy accumulation of vascular plant matter accumulation of clay minerals and fe oxides slickensides and clastic dikes suggesting a soil moisture regime that ranged from perennially wet to distinctly seasonal in soil moisture budget changsinghian to early induan palaeosols include subsurface accumulations of clay and carbonate as well as surficial accumulations of organic matter indicative of sub humid to sub arid soil moisture and variable soil moisture regimes induan to olenekian palaeosols contain pedogenic caco 3 accumulations and gypsum pseudomorphs indicating a drier environment characterized by net soil moisture deficiency elemental composition of palaeosol matrix was used to estimate palaeoprecipitation through the chemical index of alteration minus potassium cia k proxy estimates from various wuchiapingian strata indicate relatively stable palaeoprecipitation during the late changsinghian and early induan palaeoprecipitation appears to have decreased from 1100 to 230 180 mm year over less than 100 m of vertical stratigraphic section in the induan and olenekian palaeoprecipitation appears much less stable than in wuchiapingian with values vacillating from 290 to 1014 mm year the transition to a relatively unstable precipitation state coincides generally with the permian triassic boundary and may reflect climatic disturbances associated with the end permian extinction event in addition to altered atmospheric circulation patterns resulting from regional tectonics moisture availability and expansion of the subtropical high pressure belt

contributions of soot to 13c of organic matter in cretaceous lacustrine deposits gyeongsang basin korea implication for paleoenvironmental reconstructions abstract this study reports that soot carbon sc derived from biomass burning is an important constituent of total organic carbon toc 30 90 in two cretaceous lacustrine deposits middle albian jinju formation and early cenomanian banyaweol formation of the gyeongsang basin korea and that sc contributed significantly to the carbon isotope composition 13 c of the toc 13 c of the toc and 13 c of the sc corrected non sc organic matter range from 24 7 to 21 9 and 25 1 to 20 7 in the jinju formation and 24 7 to 23 0 and from 26 4 to 21 7 in the banyaweol formation respectively based on the 13 c values of coeval charcoal the calculated 13 c of the original plant material in the surrounding watershed of the paleo jinju lake ranged from 21 8 to 17 8 av 19 3 these values are considerably different from 13 c of vegetation av 24 3 estimated from sc the estimated 13 c values of non sc organic carbon are different from those of the toc by up to 3 5 either an enrichment or depletion across this value this discrepancy indicates that the presence of sc in sedimentary organic carbon affected carbon isotope composition of toc in the studied lacustrine deposits and led to increase uncertainty of interpretation of paleoenvironment of the watershed for improving the paleoenvironmental reconstructions by utilizing the 13 c values of toc in ancient lacustrine sediments a correction for the contribution of sc to toc needs to be considered

structural evolution of the whipple and south mountains shear zones southwestern united states the whipple and south mountains of the southwestern united states have undergone a strikingly similar sequence of deformations in both ranges gently dipping mylonitic fabrics have been overprinted by successively more brittle structures associated with a low angle detachment fault kinematic indicators reveal that the mylonitic rocks brittle structures and detachment faults are kinematically coordinated and were all formed by top to the northeast shear the structural evolution of both areas can be explained in terms of major shallow dipping shear zones that accommodated tertiary crustal extension we suggest that detachment faults and associated zones of brecciation cataclasis and seismic slip were originally continuous downdip along the low angle shear zones into mylonitic gneisses formed below or near the ductile brittle transition as the mylonites were drawn out from beneath the brittlely extending upper plate they were progressively uplifted above the ductile brittle transition and were overprinted by successively more brittle structures

the relationship between strain rates crustal thickening palaeomagnetism finite strain and fault movements within a deforming zone the deformation of continental lithosphere generally does not occur on a single fault but is distributed over a zone up to a few hundred kilometers wide if the deformation rate is constant throughout the zone and if the velocity is continuous everywhere and does not change with time the deformation gradient tensor can be obtained analytically this tensor directly determines the amount of crustal thickening and is related in a complicated manner to the finite strain tensor the declination of remnant magnetization measured within the zone can also be rotated by the deformation because palaeomagnetic measurements are generally made on rigid blocks which have not been deformed there is no simple relationship between such rotations and the finite strain expressions for all these quantities are obtained in terms of the velocity gradients which are taken to be constant the history of western north america is used to illustrate the relationship between the present deformation by strike slip and thrust motions the rotations of the remnant magnetization vectors and the shape of accreted terranes at the surface distributed deformation is taken up by motion on faults which separate the zone into blocks the displacement rate on the faults their strike and the finite rotations of the blocks are all controlled by the velocity gradients analytic expressions relating these quantities are obtained a deforming zone containing normal faults which crosses central greece takes up both strike slip and extension and illustrates the relationship between the structures within and the motion across the zone a similar but more complicated zone in northeastern iran involves both strike slip and shortening

mechanisms for the formation of domal and basinal detachment faults a three dimensional analysis detachment faults i e regional low angle normal faults in metamorphic core complexes of the north american cordillera commonly exhibit doubly plunging antiformal domal and synformal basinal geometries these geometries have been previously attributed to the superposition of two processes 1 the antiforms and synforms with axes parallel to the extension direction originated as primary fault undulations or corrugations developed coevally with fault slip and 2 the antiforms and synforms with axes perpendicular to the extension direction were produced by isostatic uplift due to tectonic denudation however the coaxial relationship between undulations of detachment faults and the sedimentary beds and metamorphic foliations in both the upper and lower plates of some detachment fault systems in the u s cordillera suggests that the synforms and antiforms with axes parallel to the extension direction may have formed as folds and that the domal and basinal geometry of detachment faults may have formed synchronously by a single process a three dimensional elastic thin plate model is developed to investigate possible mechanisms for the formation of domal and basinal detachment faults this model explores the interactions among the vertical horizontal and basal shearing forces during the formation of warped detachment faults the model considers the role of compression perpendicular to the extension direction and stress reduction parallel to the extension direction the results of the model suggest that the stress reduction itself in the extension direction is insufficient to cause buckling of a thin elastic crust two mechanisms are most likely to explain the formation of domal and basinal geometries of detachment faults 1 an upward pushing by undulatory crustal roots or buoyant synextensional plutons beneath the extensional belt and 2 buckling caused by a compression perpendicular to the extension direction both mechanisms are consistent with the geologic constraints during the development of cordilleran core complexes in addition to isostatic uplift due to tectonic denudation upward warping of detachment faults can also be caused by buckling basal shearing and buoyant forces

secular episodic changes in stable carbon isotope composition of crude oils abstract stable carbon isotopic compositions of c15 saturate and aromatic hydrocarbon fractions from 514 crude oils from known source rocks were examined for secular episodic variations the oils have been correlated by means of biomarker analyses and or geological inferences to their respective source rocks and were further categorized into seven source rock types based on geochemical and petrologic indicators of depositional environments thus these oil samples represent a wide range of source paleoenvironments from thirteen age divisions riphean to neogene the stable carbon isotopic compositions of both fractions become enriched in 13 c with decreasing geologic age three major abrupt shifts toward 13 c enrichment occurred at the precambrian cambrian ordovician triassic jurassic and paleogene neogene boundaries analysis of smaller scale isotopic shifts reveals four distinct groups of oils generally independent of organic facies and secondary alteration processes comparison of evolutionary changes in the biosphere to episodic changes in stable carbon isotopic compositions throughout the phanerozoic indicates that isotopic shifts of crude oils may generally be related to the diversity of preserved phytoplankton

detachment faulting and the evolution of passive continental margins major detachment faults play a key role in the lithospheric extension process in the basin and range province and may also be important in other continental extension terranes such detachment faulting leads to an inherent asymmetry of extensional structure and of uplift subsidence patterns detachment models developed for the formation of metamorphic core complexes can also be applied to the formation of passive continental margins we therefore suggest the existence of upper plate and lower plate passive margins these give rise to a complementary asymmetry of opposing margins after continental breakup transfer faults offset marginal features and allow margins to switch from upper plate to lower plate characteristics along strike

basaltic volcanism and mass extinction at the permo triassic boundary environmental impact and modeling of the global carbon cycle the siberian traps represent one of the most voluminous continental flood basalt provinces on earth the mass extinction at the end of the permian was the most severe in the history of life in the present paper these two major concurrent events that occurred are analysed and a geochemical model coupled with an energy balance model is used to calculate their environmental impact on atmospheric co2 oceanic 13c and marine anoxia the latitudinal temperature gradient is reduced relative to today resulting in warmer temperatures at high latitudes the warmer climate and the presence of fresh basaltic provinces increase the weatherability of the continental surfaces resulting in an enhanced consumption of atmospheric co2 through weathering first the eruption of the siberian traps is accompanied by a massive volume of 13c depleted co2 degassed from the mantle and added to the ocean through silicate weathering thus lowering marine 13c second the rapid collapse in productivity induces a strong decrease in the global organic carbon burial this too tends to increase the proportion of light carbon in the ocean these two effects can explain the low 13c values across the pt boundary and methane release need not be invoked to explain the 13c fluctuations it is proposed that the phosphorus cycle which drives primary production in the model plays an important role on the recovery of productivity and the 13c variations

structural geology meets micromechanics a self consistent model for the multiscale deformation and fabric development in earth s ductile lithosphere abstract earth s lithosphere is made of rheologically heterogeneous elements of a wide range of characteristic lengths a micromechanics based self consistent multiorder power law approach is presented to account for lithospheric deformations and the accompanying multiscale fabric development the approach is principally based on the extended eshelby theory for the motion of a power law viscous ellipsoid in a power law viscous matrix and the idea of embedding inhomogeneities within inhomogeneities the extended theory provides a general means for investigating deformation partitioning in heterogeneous rocks the inhomogeneities within inhomogeneities method allows multi hierarchical levels of flow field partitioning and hence multiscale deformations to be investigated partitioned flow fields are used to investigate fabric development being based fully on micromechanics the approach generates model predictions of both kinematic quantities strain strain rates and vorticity and stress histories the former can be directly compared with field and laboratory structural observations while the latter can help to understand the physics of natural deformations the self consistent and multiscale approach is applied to a natural example of the cascade lake shear zone in the east sierra nevada of california the modeling shows that the fabrics are most consistent with a steeply dipping transpression zone with a convergence angle of 20 and a strike slip displacement about 26 km further the strength evolution of the model zone confirms that a transpression zone is a weakening system with respect to the simple shearing component and a hardening one for the pure shearing component this is consistent with slip partitioning in obliquely convergent plate boundaries boundary normal convergence tends to spread over a broad area whereas boundary parallel shear tends to localize in major strike slip zones

lower triassic δ13c isotope curve from shallow marine carbonates in japan panthalassa realm confirmation of the tethys δ13c curve abstract 13 c data from tethyan sections provide evidence of profound changes in the carbon cycle during the lower triassic sections from the panthalassa realm were investigated to establish whether these variations are also present there in the jurassic accretionary wedges in japan exotic blocks having a panthalassan affinity have been incorporated the majority of the blocks are pelagic cherts but rare shallow water carbonates are also present we present a 13 c study on the lower triassic of a shallow water carbonate succession deposited on a mid oceanic seamount and accreted to the chichibu belt japan two sections have been measured at kamura central kyushu island the carbon isotope curve shows depleted values across the permian triassic boundary ptb subsequently followed by an increase to heavier values into the dienerian culminating in a maximum of almost 4 v pdb before a steep drop at a stratigraphic gap low values are recorded in the smithian but rise to enriched 13 c values 3 5 near the smithian spathian boundary the observed trend of the stable carbon isotope curve from japanese sediments mirrors the curves derived from sections in the tethys e g italy iran turkey oman and the south china nanpanjing basin our results support the interpretation of this curve as representing a global trend across the ptb and in the lower triassic although some distinct features are absent around the dienerian smithian boundary profound variations of the carbon isotope curve in the lower triassic are presented for the first time from a marine section outside of the tethys they indicate severe global changes in the lower triassic carbon cycle and the causative processes must have significantly contributed to the delayed biotic recovery after the ptb large amounts of carbon were shifted between carbon reservoirs most probably between shallow and deep ocean waters and or ocean and sediment anoxia followed by overturn of the ocean water masses may have been the mechanism which quickly altered ecological conditions in the ocean leading to variable availability of nutrients and oxygen and changes in isotope composition of the available carbon in the surface waters that was incorporated in the precipitated carbonate

dynamic palaeogeographic reconstructions of the wuchiapingian stage lopingian late permian for the south china block abstract as an important tool in natural resource exploration palaeogeography provides a portrayal of deep time earth the south china block located in the eastern palaeotethys includes multiple natural resources e g coal shale gas bauxite etc in the permian which are well known for their important economic significance in this paper data gathered from literature amount to 431 stratigraphic sections of wuchiapingian age from south china these data were quantitatively analyzed and dynamically reconstructed in the global context under the revised plate motion model by gplates software for the first time a schematic 3 d model was constructed based on the high resolution reconstructions in this paper showing two relatively large highlands developed in the south china block during the wuchiapingian including the kangdian highland in the west and the cathaysia highland in the east and a small yunkai highland in the south a broad platform dominated depositional system with small uplifts and depressions was developed between these two highlands these reconstructions show great potential to explore enriched coal seams and shale gas in the peripheral areas of the two ancient highlands in the west and east of the south china block based on the dynamic evolution of this depositional system south china experienced an overall sea level rise with frequent secondary transgressions and regressions during the wuchiapingian this is in contrast to the widespread continental and evaporite deposits on much of pangea and its surrounding margins after the end guadalupian global regression compilation of conodont biostratigraphic data suggest that the temporal and spatial constraints on the unconformity across the guadalupian lopingian boundary glb resulted from dongwu uplift movement the regression began during the jinogondolella shannoni zone and ended in the clarkina leveni zone but the response time varies in different localities of south china these results provide detailed information about sea level eustacy tectonic uplift sedimentary hiatus resource accumulation and palaeoclimate change from the south china block during the wuchiapingian

strain distribution in a fold in the west norwegian caledonides abstract strain has been measured from clasts within a deformed conglomerate layer at 17 localities around an asymmetric fold in the rundemanen formation in the bergen arc system west norwegian caledonides strain is very high and a marked gradient in strain ellipsoid shape exists to either side of the fold strain within the conglomerate bed is of the extreme flattening type in the fold especially on the lower fold closure the strain is constrictional mathematical models of perturbations of flow in glacial ice have produced folds of the same geometry as this fold with a strikingly similar pattern of finite strain the fold geometry and strain pattern as well as other field observations suggest that the fold developed passively as the result of a perturbation of flow in a shear zone where the strain was accommodated by simple shear accompanied by extension along y

interpreting environmental and biological signals from the stable carbon isotope composition of fossilized organic and inorganic carbon stable carbon isotope studies on marine and terrestrial organic and inorganic carbon provide a means for detecting global climate change and for reconstructing past concentrations of atmospheric co 2 comparison between the co 2 estimates reconstructed from carbon isotope studies for the past 150ma show good agreement with the predictions of a long term carbon cycle model based on mass balance studies further the co 2 estimates from these sources over the entire phanerozoic show agreement with the fossil record of leaf stomatal density change a feature inversely related to the concentration of atmospheric co 2 isotopic studies on temporal sequences of fossilized terrestrial organic matter have contributed to palaeoecological studies on shifts in the dominance of plants with the c 4 photosynthetic pathway in ecosystems and historical changes in the metabolic processes of leaves of individual species the long term perspective offered by these studies provides critical information for assessing the responses of biological systems to future global environmental change

geochemical and organic carbon isotope studies across the continental permo triassic boundary of raniganj basin eastern india abstract organic carbon isotope and geochemical changes across a continental interior permo triassic boundary section from the raniganj basin india indicate a 9 drop in organic carbon 13c in the early triassic and synchroneity of this event throughout the pangea the study demands a common causative mechanism for the perturbation of the global carbon reservoir and not a combination of multiple causes a global sea level fall and oxidation of marine gas hydrates possibly increased the 12co2 input in the ocean atmosphere system which caused a climatic shift from humid to warm semi arid type and consequent extinction of land plants simultaneous increase in erosion from near barren lands change in the erosional base level and provenance deposited the boundary sandstone with positive europium anomaly and debris flow type matrix rich conglomerate no extraterrestrial source therefore is needed to explain this eu anomaly the response of the terrestrial plant community to this perturbation of the carbon reservoir was however sluggish and the 13c drop took place slowly being maximal in the early triassic only

effects of chemical preparation protocols on δ13c values of plant fossil samples abstract for over a half century studies of the stable carbon isotope compositions of plant fossils have provided noteworthy conclusions about the evolution of earth climate however different preparation protocols were used prior to carbon isotope analysis of plant fossils and the accuracy of measured 13c 12c ratios may strongly depend on them we have applied the most frequently used chemical preparation protocols to frenelopsis leaves from four cretaceous localities of western europe our results indicate that procedures to extract plant fossils from sediments are not adequate to retrieve the original plant 13c values the use of schulze s reagent to bleach cuticles in paleobotany allows misleading 13c values of specimens from a same locality with positive shifts of up to 13 6 and increases intra specimen and inter specimen variances sample treatment involving hcl or hcl hf gives consistent 13c mean values for a same leaf and for leaves from a same sedimentary bed however although hf does not provide any advantage in removing potential contamination sources it alters plant fossil tissues slightly increasing the intra and inter leaf variances of 13c values our results indicate that processing plant fossils with hcl only is the most accurate and conservative way to retrieve original 13c values

the land plant δ13c record and plant evolution in the late palaeozoic abstract based on the evaluation of 1323 carbon isotope values for silurian to permian terrestrial organic carbon measured on plant fossils cuticules humic coals and bulk terrestrial organic matter tom we conclude that the temporal trend in 13ctom records variations in the global carbon cycle notably an increase in the fractional burial of light terrestrial organic matter in late palaeozoic sediments 13ctom values suggest that the late palaeozoic po2 peak could have been restricted to a time frame of 40 ma carbon isotope data from four taxonomic groups reveal small differences that could be a consequence of habitat conditions no significant differences in organic carbon isotopic composition in relation to variable climatic conditions are discernible the carbon isotopic composition solely reflects c3 plant metabolism

the permian triassic boundary at nhi tao vietnam evidence for recurrent influx of sulfidic watermasses to a shallow marine carbonate platform the permian triassic boundary at nhi tao cao bang province vietnam was sampled in a 7 5 m thick outcrop section at high resolution 5 cm intervals for chemostratigraphic and magnetic susceptibility analysis the section consists entirely of slightly argillaceous limestone representing shallow marine facies of the jinxi platform one of several large carbonate platforms within the nanpanjiang basin located on the southern margin of the south china craton upper permian strata beds 1 7 are mainly dark gray cherty fossiliferous wackestones and packstones containing a diverse open marine fauna whereas uppermost permian and lower triassic strata beds 9 and higher are medium gray calcimicrobial framestones containing rare macrofossils these facies are separated by a 12 cm thick oolitic pisolitic grainstone bed 8 that coincides with the disappearance of most late permian faunal elements as well as with the first appearance of various geochemical anomalies that continue into the lower triassic part of the section this late permian event horizon is characterized by 1 an abrupt decline in total organic carbon to near zero values 2 the onset of a sustained decline in carbonate 13c and 3 the first of eight concentration peaks in pyrite sulfur significantly each sulfide peak is associated with lower pyrite 34s values as well as with the onset of a negative carbonate 13c excursion or the acceleration of an excursion already in progress these chemostratigraphic relationships are consistent with multiple episodes of upwelling of sulfidic 34s and 13c depleted deep ocean waters onto the jinxi platform the first upwelling event was the most intense and caused a drastic reduction in primary productivity and the demise of the late permian fauna subsequent episodes were less intense but may have contributed to a delay in recovery of early triassic marine ecosystems a ten fold increase in magnetic susceptibility in bed 9 may record the influx of fine detrital particles following destruction of terrestrial ecosystems and massive soil erosion the terrestrial signal of the end permian catastrophe thus follows the marine signal with a 12 cm lag which may reflect the time of transit of soil derived particles across the nanpanjiang basin suggesting that the marine and terrestrial crises in the nhi tao region occurred more or less synchronously these observations suggest a model in which renewal of global ocean overturn followed a prolonged interval of deep ocean stagnation during the late permian with upwelling intensity modulated by short term 20 kyr climate cyclicity

strain and kinematic analysis in general shear zones we present a unifying theory for the development and distribution of strain markers and kinematic indicators in zones of general shear and thus provide a framework in which data previously considered contradictory may be understood rigid and deformable porphyroclast systems including and complex grains are potential indicators of both strain and flow the shapes and distribution of such porphyroclast systems may be used to distinguish among different tectonic regimes general shear is divided into two fields sub simple shear in which the rotational component of the strain is less than that for simple shear and super simple shear in which the rotational component is greater than for simple shear sub simple shear may involve narrowing or broadening of shear zones super simple shear regimes are possible in local regions such as the vicinities of deformable porphyroclasts but must be enclosed by regimes of sub simple shear the polar mohr constructions for finite deformation and flow are useful to analyze general shear in theory the hyperbolic net is employed for practical plotting of real data and derivation of the kinematic vorticity number wn this number represents the relative contributions of pure and simple shear in steady flow in nature deformation is thought to build up and decay by processes that may invalidate the assumption of constant flow regime we therefore introduce the concept of accelerating deformation and analyze the implications of non steady flow for the shearing histories of deformed objects

the partitioning of deformation in flowing rock masses abstract most geological structures owe their development to heterogeneous and or non steady flow flow partitioning refers to the division of the instantaneous velocity field into components related to translation strain and rotation flow partitioning during the development of a geological structure usually changes with time and different histories of flow are involved at different points in the developing structure heterogeneity leads to the development of flow domains with different characteristics notably the degree of non coaxiality of deformation and different partitionings of the rotational component of flow into shear induced vorticity and spin during non steady flow there is often continual repartitioning of vorticity between the spin and shear induced components spin is an important aspect of flow leading to the development of structure this paper discusses the partitioning of deformation in a flowing rock mass coaxial flow tends to occur in isotropic materials in regions near weakly constrained boundaries non coaxial flow is favoured by suitably oriented material anisotropy and or the presence of well defined boundary constraints involving parallel relative displacements a developing anisotropy e g a crystallographic fabric in a shear zone can induce a change from coaxial to non coaxial flow other effects are related to the scale of approximation for example bulk shear induced vorticity can be locally converted to spin flow in the crust and mantle of the earth produces geological structures on all scales and involves many different types of rheological response the factors that affect flow partitioning e g spin versus non coaxial deformation are therefore of interest

stepwise and large magnitude negative shift in δ13ccarb preceded the main marine mass extinction of the permian triassic crisis interval abstract large perturbations to the global carbon cycle occurred during the permian triassic boundary mass extinction the largest extinction event of the phanerozoic eon 542 ma to present controversy concerning the pattern and mechanism of variations in the marine carbonate carbon isotope record of the permian triassic crisis interval ptci and their relationship to the marine mass extinction has not been resolved to date herein high resolution carbonate carbon isotope profiles 13ccarb accompanied by lithofacies were generated for four sections with microbialite taiping zuodeng cili and chongyang in south china to better constrain patterns and controls on 13ccarb variation in the ptci and to test hypotheses about the temporal relationship between perturbations to the global carbon cycle and the marine mass extinction event all four study sections exhibit a stepwise negative shift in 13ccarb during the late permian early triassic with the shift preceding the end permian crisis being larger 3 than that following it 1 2 the pre crisis shifts in 13ccarb are widely correlatable and hence represent perturbations to the global carbon cycle the comparatively smaller shifts following the crisis demonstrate that the marine mass extinction event itself had at most limited influence on the global carbon cycle and that both late permian 13ccarb shifts and the mass extinction must be attributed to some other cause their origin cannot be uniquely determined from c isotopic data alone but appears to be most compatible with a mechanism based on episodic volcanism in combination with collapse of terrestrial ecosystems and soil erosion

stable carbon isotope stratigraphy across the permian triassic boundary in shallow marine carbonate platforms nanpanjiang basin south china a distinct negative 13c excursion is documented in two permian triassic sections heping and taiping in shallow marine carbonate platform deposits in the nanpanjiang basin south china these sections span from the changhsingian to the dienerian and are characterized by a distinct marine boundary facies change from massive skeletal lime packstone in the changhsingian to distinctive calcimicrobial framestone in the griesbachian hindeodus parvus zone the 13corg and 13ccarb excursions occur directly after the onset of the calcimicrobial framestone herein termed the permian triassic boundary event and before the first occurrence of h parvus the isotope shifts are associated with a sharp drop in species abundance and diversity and coincide with a decrease in total organic carbon toc content the shift towards depleted values in 13corg and 13ccarb at the permian triassic boundary event together with low toc contents persists throughout the griesbachian h parvus zone these data document a corresponding negative shift of 13corg and 13ccarb values and low toc contents with the onset of growth of calcified microbial framestones a postextinction disaster facies immediately below the base of the griesbachian h parvus zone based on paleontological evidence the first occurrence of the disaster facies follows the extinction event which implies that the 13c depleted values above this facies postdate the event this suggests that two separate events had to account for the initiation of the extinction and the 13c excursion however the consequences that led to the negative isotopic shift might be linked to the intriguing recovery lag of early triassic ecosystems based on data from ptb sections worldwide of a greater 13c offset in high compared with low latitudes we propose that methane eruptions from thermal destabilization of high latitude clathrate deposits may have led to the negative 13c shift and may have caused long term adverse ecological conditions

the grootegeluk formation in the waterberg coalfield south africa facies palaeoenvironment and thermal history evidence from organic and clastic matter the grootegeluk formation of the waterberg coalfield is about 70 m thick and consists of relatively thin coal beds interbedded with numerous mudstone and carbonaceous mudstone layers maceral analyses of the coal seams and the interbedded carbonaceous mudstones show that vitrinite is the dominant maceral up to 90 vol whereas inertinite liptinite and reactive semifusinite generally occur in minor proportions the vitrinite content increases upward in the formation with a concomitant decrease in inertinite including reactive semifusinite from around 60 inertinite at the base of the formation the upward increase in the vitrinite concentration is associated with an increase in the energy of the depositional environment which is also considered to have been instrumental in the enhanced preservation of the vitrinite the repetitive nature of the coal mudstone succession the lateral persistence of cycles and the maceral and ash proportions indicate that the formation may have resulted from a combination of allogenic controls tectonism and climate and authigenic controls environments of deposition the vitrinite reflectance rmax of the grootegeluk formation mean 0 72 and palynological evidence indicate that the grootegeluk formation was subjected to maximum post depositional temperatures of about 100 c the lower portion of the grootegeluk formation is dominated by kaolinite quartz and minor amounts of apatite and the upper parts by quartz kaolinite and minor amounts of montmorillonite illite and microcline the base of the grootegeluk formation is considered to have been relatively more distal and the upper portions more proximal to the source of the sediments at the base of the grootegeluk formation a 2 m thick tonstein zone occurs which is dominated by well crystallised kaolinite organic matter 40 wt siderite calcite and minor proportions of apatite the tonstein zone has mineralogical maceral and chemical characteristics distinctive from the other mudstones calcite lenses which occur predominantly in the upper half of the grootegeluk formation are interpreted as syndepositional early diagenetic globular pyrite and spherulitic siderite occur in the coals and organic rich mudstones of the grootegeluk formation fine grained granular siderite is present predominantly in the organic poor mudstones of the grootegeluk formation and the overlying beaufort group systematic changes in the mineralogy and major element chemistry make major element whole rock chemistry an ideal stratigraphic indicator tool for the grootegeluk formation the tonstein has anomalously high concentrations of the trace elements sc v cr mn ni cu ge se br rb sr y zr nb mo ba la ce nd pb th and u and low concentrations of s co as and zn which in addition to its mineralogical character and correlation throughout the basin make the tonstein an important chronostratigraphic marker for local and intrabasinal correlation the overlying beaufort group mudstones contain no organic matter however interpretation of the mineralogical and chemical data indicates that they were deposited with organic matter which was later degraded the mineralogy of the mudstones and the concentration of trace elements suggest that the sediments were deposited in fresh rather than in marine waters

high strain zones a unified model abstract where a shear zone is bounded by undeformed wall rocks and there is no volume change the deformation path within the zone on the bulk scale approximates a simple shear where the zone boundaries are stretched and the shear direction between the two boundaries is parallel to one of the principal stretching directions of the boundaries the deformation path within the zone is not a simple shear but still has monoclinic symmetry both simple shear and general monoclinic deformation paths should be regarded as special cases in nature because generally not only are the zone boundaries stretched but also the shear is oblique to the principal stretching directions of the boundaries in this general case the deformation path is triclinic we establish a model which includes this general case also taking into consideration volume change five independent parameters are required to characterize the rate of deformation of the flow four are sufficient to characterize the flow kinematics the model is generally triclinic and orthorhombic and monoclinic deformations are subgroups by varying the values of the characterizing parameters the various types of high strain zones can be represented the kinematics of flow within such zones and the accumulated finite deformation geometry are investigated many field observations such as for example lineations in transcurrent shear zones that vary between vertical and horizontal cleavage transected folds and the absence of sheath folds in some shear zones where folds have been significantly rotated can sometimes be better interpreted in the context of our general model

biogeochemical evidence for euxinic oceans and ecological disturbance presaging the end permian mass extinction event article i nfo the permian triassic boundary event at 252 2 ma marks the largest extinction of marine fauna in the phanerozoic and there is a wide consensus that the extinction coincided with an intense oceanic anoxic event thestratotypeofthechanghsingianstage preciselyconstrainedbytheptbglobalstratotypesectionandpoint gssp and the gssp for the wuchiapingian changhsingian boundary both at meishan in southern china is well documented in respect to geochronology and the pattern of extinction here we report secular trends in bulk isotopic parameters and lipid biomarkers in a core spanning 214 m of stratigraphic section across the ptb and through the entire changhsingian interval our analysis of these data viewed in the context of relative sea level change and strontium isotopes reveals distinct shifts in paleoenvironmental conditions and profound changes in plankton ecology well before and following the biological extinction event specifically patterns of steroids and triterpenoids indicate a marine plankton community that was heavily dominated by bacteria during the late wuchiapingian middle changhsingian and early griesbachian stages secular trends in aromatic hydrocarbons diagnostic for anoxygenic green sulphur bacteria chlorobiaceae identify periods when euxinic conditions extended into the photic zone during the entire changhsingian stage here also the 15

the permian triassic boundary in western slovenia idrijca valley section magnetostratigraphy stable isotopes and elemental variations stable isotope analyses of carbonate 13ccarb and total organic carbon toc 13corg together with geochemical analyses of 54 major minor and trace elements and magnetic susceptibility measurements were carried out on whole rock samples of the undisturbed permian triassic p tr limestone boundary sequence in the idrijca valley w slovenia at the p tr boundary there is a 0 8 cm thick clayey marl layer ptb showing a characteristic magnetic susceptibility pulse and considerable enrichment in most major minor and trace elements the p tr transition is characterized by 1 an abrupt decrease in sedimentation rate from 32 to 5 cm 100 ka 2 a well known prominent negative excursion of 13ccarb and 13corg reflecting global perturbations in the carbon cycle and 3 the drastic disappearance of typically upper permian marine fauna although the shape of the 13ccarb curve indicates gradual long term change across the p tr boundary the sharp negative 13corg anomaly within an interval from 30 cm below to 6 cm above the boundary suggests an interruption of those gradual processes our observations for selected redox sensitive elements mo u v and zn abundances for organic carbon and sulphur and the rare earth elements ree distribution in the boundary sequence as well as the shape of the ce ce curve suggest that oceanic anoxia was typical of the upper permian and that the transition to oxygenated conditions occurred at the p tr boundary oxygenation at the p tr transition is coincidental with the terminal phase of the upper permian marine regression the shape of the ce ce curve indicates that the redox environmental conditions changed again in the earliest triassic resulting once more in oxygen deficient conditions

a fundamental problem with the kinematic interpretation of geological structures abstract non steady flows are ubiquitous in nature not only do imposed boundary conditions vary with time and rock rheology change during the course of deformation but also deformation is generally heterogeneous and all of these conditions lead to non steady flow histories in modern kinematic analysis flow apophyses the instantaneous stretching axes and the vorticity vector collectively referred to as the eigen directions of deformation are used in place of bruno sander s kinematic axes for deformation with a steady flow history this practice is well justified and has led to great advances in structural geology but for non steady flow histories the geometrical relationships among eigen directions flow pattern vary with time this makes it inappropriate to correlate an association of structures and fabrics with certain time invariant flow patterns and hence raises the question how should we interpret geological structures and fabrics kinematically without the assumption of homogeneous and steady deformation we suggest that the answer lies primarily in forward modeling of deformation based on a knowledge of rock properties