detachment faulting mantle serpentinization and serpentinite mud volcanism beneath the porcupine basin southwest of ireland the porcupine basin southwest of ireland provides an opportunity to study the symmetry of rifting at stretching factors approaching continental breakup profiles across the basin image a bright reflection that appears to represent a detachment fault and may in part be a decollement at the top of partially serpentinized mantle although overall the basin appears symmetric the consistent westward structural dip of the detachment implies that at high stretching factors extension was asymmetric farther south the porcupine median high appears in cross section to be a triangular construction overlying tilted fault blocks and onlapped by postrift sediment despite no evidence for synrift magmatism this high has previously been interpreted as a basaltic structure however it may represent a serpentinite mud volcano or diapir we suggest that such structures produce the serpentinite breccias found within the rifted continent ocean transition of nonvolcanic margins

end permian catastrophe by a bolide impact evidence of a gigantic release of sulfur from the mantle our studies in southern china have revealed a remarkable sulfur and strontium isotope excursion at the end of the permian along with a coincident concentration of impact metamorphosed grains and kaolinite and a significant decrease in manganese phosphorous calcium and microfossils foraminifera these data suggest that an asteroid or a comet hit the ocean at the end of permian time and caused a rapid and massive release of sulfur from the mantle to the ocean atmosphere system leading to significant oxygen consumption acid rain and the most severe biotic crisis in the history of life on earth

evidence for abrupt latest permian mass extinction of foraminifera results of tests for the signor lipps effect we used published biostratigraphic data on ranges of fusulinids and other foraminifera from permian triassic boundary sections in the southern alps italy to test the effects of sampling and species abundance on the record of the timing of the latest permian extinction the number of last occurrences of taxa reaches a maximum close to the local base of the tesero horizon of the werfen formation taxa that have 15 stratigraphic abundance percent of sample intervals in which a taxon occurs show last occurrences well before that level whereas taxa with more complete records tend to disappear at or close to that level these results are in agreement with simulations for abrupt extinctions as opposed to gradual or steplike extinction scenarios and support predictions of the signor lipps effect that errors in the end points of biostratigraphic ranges can produce range truncations and apparent gradual decline preceding a sudden extinction boundary on the basis of estimated sedimentation rates for the italian sections the end permian extinctions could have been very sudden 30 k y and the disappearance of most latest permian foraminifers was most likely coincident with a worldwide ecological stress event identified by a global negative 13 c anomaly that occurs in italy near the base or within the time transgressive tesero horizon

subsurface profiling along banni plains and bounding faults kachchh western india using microtremors method the present article is a maiden attempt to map shallow subsurface rheological interfaces laterally across the banni plains and to decode geometry of the antecedent faults associated with the kachchh mainland fault using the microtremor method we conducted microtremor data acquisition for thirty one sites along n s transect from loriya in mainland kachchh to bhirandiara towards patcham island results from h v spectral ratio technique show presence of two distinct rheological interfaces characterised by the resonant frequency f r ranges 0 23 0 27 hz and 0 8252 1 5931 hz respectively the above frequency ranges are correlated with the depths of the mesozoic basement m b interface and the quaternary tertiary q t interface using either the velocity vs of seismic waves at the m b and q t interfaces calculated as 1830 m s and 411 m s respectively or the standard non linear regression relationship derived for the banni plains h 110 18f r 1 97 we estimate the depth range for m b interface to be 1442 1965 m and for q t interface to be 44 160 in the subsurface profile across the banni plains educe cluster of four faults that develop an array of imbricate faults at the forefront of the kachchh mainland fault within the banni footwall syncline the geometry of the faults suggests a positive flower structure indicating step overs and strain restraining bends displaying push ups resulting from localized shortening between converging bends of kachchh mainland fault and the south wagad fault the banni footwall syncline preserves evidence of two episodes of deformations the initial deformation event led to subsidence within the kachchh mainland fault zone bringing mesozoic sequence juxtaposed to the basement rocks whereas the later event is dominated by an uplift developing a positive flower structure in the kachchh mainland fault zone finally the present study provides a mechanism to investigate faults and fault geometries correlating surface structural grains with subsurface structures

basement configuration of on land kutch basin from seismic refraction studies and modeling of first arrival travel time skips abstract the kutch basin is one of the three narmada cambay and kutch major marginal rift basins that are close to each other in mid western part of the indian subcontinent the seismic refraction and wide angle reflection data were acquired and a first order velocity structure of the kutch sedimentary basin along jakhau mandvi mandvi mundra mundra adesar and hamirpur halvad profiles is derived the travel time skip phenomenon has been noticed in the travel time plots and record sections indicating presence of low velocity sediments derived two dimensional velocity depth models revealed a mesozoic sedimentary sequence sandwiched between trap and limestone layers in some of the profiles two thick low velocity layers that corresponds early to late mesozoic era have been identified these are dipping towards mandvi along jakhau mandvi profile the early mesozoic layer that is thinning towards southeast is completely missing in mandvi mundra profile it is also noticed that the early mesozoic bhuj formation exists in the northern parts of the mundra adesar and hamirpur halvad profiles where it directly overlies the granitic basement the derived velocity depth model suggests that the basement is about 3 km deep near jakhau and reaches a depth of about 6 km near mandvi the layered structure may correspond to the tertiary trap late mesozoic sediments and mesozoic limestone the velocity depth model obtained in kutch is very similar to earlier derived model for jamnagar and dwarka sub basins of northwestern saurashtra peninsula suggesting probable continuity linkage between southern on land kutch and across the gulf of kutch to saurashtra peninunsula we also conclude that the evolution of kutch basin as a peri cratonic rift basin is essentially controlled by the four f1 f4 faults inferred from obvious abrupt changes in layer thickness velocity along the seismic refraction profiles

onset of biotic and environmental recovery from the end permian mass extinction within 1 2 million years a case study of the lower triassic of the meishan section south china abstract paleontological sedimentary and geochemical data obtained from the lower triassic strata of the meishan section south china suggest that onset of biotic recovery coincided with amelioration of paleoceanographic conditions and an increase in ocean productivity the griesbachian meishanorhynchia association from meishan indicates biotic recovery between the recovery stages 1 and 2 both the initial biotic recovery and palaeoceanic environmental amelioration occurred within 1 2 myr after the end permian mass extinction in the late griesbachian

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

fluid generation and pathways beneath an active compressional orogen the new zealand southern alps inferred from magnetotelluric data 1 forty one wideband magnetotelluric mt soundings were collected in a 150 km long transect across the southern alps of the central south island of new zealand an active compressional orogen decomposed mt impedance tensors vertical magnetic field relations and reconnaissance soundings at two locations off line imply an approximately two dimensional geometry here with average regional geoelectric strike of n40 e similar to surface geologic trends two independent two dimensional inversion algorithms were applied to the mt data and both imply a concave upward u shaped middle to lower crustal conductive zone beneath the west central portion of the island the average conductivity of this zone in the strike direction appears to be much higher than that required across strike and may represent anisotropy or along strike conductive strands narrower than the transverse magnetic cross strike mode mt data can resolve the deep crustal conductor under the southern alps is interpreted to represent mainly a volume of fluids arising from prograde metamorphism within a thickening crust fluid interconnection and electrical conduction are promoted by shear deformation the conductor rises northwestward toward the trace of the alpine fault but attains a near vertical configuration at a depth of 10 km and reaches close to the surface 5 10 km inland of the fault trace itself the transition to vertical orientation at this depth is interpreted to occur as fluids ascend across the brittle ductile transition in uplifting schist and approach the surface through induced hydrofractures the high grade schist becomes resistive after depletion of fluids and continues to extrude toward the alpine fault shallow extensions of the deep high conductivity are coincident with modern hydrothermal veining and gold mineralization interpreted to be of deep crustal provenance to the southeast high conductivity also reaches the surface coincident with a major back thrust fault zone of the doubly vergent southern alps orogen which also exhibits evidence for expulsion of high temperature fluids the higher conductivity inferred along strike possible anisotropy could reflect more efficient fluid interconnection in this higher strain direction as well as possible contributions by sheared fluid deposited graphite conductivity of the uppermost mantle of the south island is low consistent with advection of cold mantle lithosphere into the underlying asthenosphere as suggested by p wave delay studies

magnetotelluric evidence for thick skinned tectonics in central taiwan taiwan is the type example of an arc continent collision numerous tectonic models have been proposed for this orogen and include both thin skinned and thick skinned lithospheric deformation these models predict very different structures at middle and lower crustal depths but insuffi cient geophysical data exist to unequivocally distinguish between them long period magnetotelluric mt data were collected in central taiwan in 2006 2007 to constrain the crustal resistivity structure a two dimensional inversion of these mt data revealed a prominent electrical conductor that extends across the decollement predicted by the thin skinned model this feature is interpreted to be due to 1 2 saline fl uids and is inconsistent with the thin skinned model in contrast the thick skinned model predicts this feature since fl uids are generated in the crustal root through metamorphism quantitative correlation of the resistivity and seismic velocity models supports small volume high salinity fl uids in a thickened crust as the cause of this conductor

environmental instability prior to end permian mass extinction reflected in biotic and facies changes on shallow carbonate platforms of the nanpanjiang basin south china abstract shallow carbonate platforms exhibit major changes in faunal composition and facies types during the latest permian and earliest triassic although the microbialites that developed following the latest permian mass extinction lpme have attracted wide attention temporal variations in shallow platform facies and faunas prior to the lpme have been less thoroughly studied here we analyze diversity patterns and variation in skeletal composition in three upper permian sections from isolated carbonate platforms of the nanpanjiang basin in addition to the well known transition from fossil rich upper permian limestones to fossil poor permian triassic boundary ptb microbialites these sections exhibit several distinct changes that predate the lpme first foram faunas show a shift from non fusulinid dominated to fusulinid dominated communities in the

palaeoseismic investigations along the kachchh mainland fault a comprehensive review and new insights of the past earthquakes in the kachchh basin western india abstract the intraplate kachchh rift basin has been hit by several devastating earthquakes in the historic past including the 1819 allah bund earthquake and the 2001 bhuj earthquake the source region of these earthquakes within the basin have been studied by several workers in the last two decades to understand their potential for earthquake recurrence however very little information is available on the palaeoseismic and geomorphic characterization of kachchh mainland fault kmf therefore in the present study six trenches were excavated across the kmf between lakhpat and nirona to understand ground deformation pattern and timing of the historic earthquakes based on geomorphic and palaeoseismic investigations five palaeoearthquakes of early to late holocene have been identified between 10 000 890 yrs apart from the holocene an earthquake of late quaternary period was also identified which possibly occurred around 19 800 yrs bp fault related parameters were analyzed to understand the geometry of the active fault scarp along kmf the results of the analyzed fault geometric parameters show that the vertical displacement along the kmf is higher than the horizontal displacement the slip rate of the kmf from the western portion to the middle portion decreases from 0 08 to 0 04 mm yr and increases towards east from 0 22 mm yr to 0 36 mm yr as the kachchh district of the gujarat state is rapidly developing in terms of infrastructural development the outcome of this research might provide significant inputs for micro zonation studies and also in the evaluation of the seismic hazard in the kachchh region

a sulfur isotope event at the end of the permian abstract a hypothesis of light sulfur injection to the ocean atmosphere system at the end of the permian was presented by kaiho et al kaiho k kajiwara y nakano t miura y kawahata h tazaki k ueshima m chen z q shi g r 2001 end permian catastrophe by a bolide impact evidence of a gigantic release of sulfur from the mantle geology 29 815 818 based on a negative shift of 34 s 32 s ratio of carbonate associated sulfate in south china this hypothesis was discussed in some papers with additional data in other areas however the cause and distribution of the negative shift has not been clarified here we show that a significant decrease in the 34 s 32 s ratio of carbonate associated sulfate occurred simultaneously in south china and hungary at the end of the permian coincident with the end permian mass extinction the cause of the abrupt negative shift of 34 s 32 s in these two distant sites is the injection of light sulfur to the surface ocean from the deep ocean rich in h 2 s or deposits rich in sulfide or the mantle this sulfur isotope event was likely caused by either an abrupt warming a bolide impact to the ocean mantle plume induced volcanism or a harmonizing of these possible direct causes are 1 massive release of h 2 s gas from the euxinic surface and intermediate waters due to abrupt warming by volcanic co 2 or impact shock wave in the ocean 2 a huge volcanism penetrated sediments or ore rich in sulfide 3 an extraterrestrial impact to sulfide rich sediments or ore deposit and 4 release of mantle origin sulfur by an impact of 70 km asteroid to the ocean these are four possible causes for a mass extinction there is also a possibility of a local oceanic event only in the tethys

seismic imaging of the 2001 bhuj mw7 7 earthquake source zone b value fractal dimension and seismic velocity tomography studies abstract we use precisely located aftershocks of the 2001 mw7 7 bhuj earthquake 2001 2009 to explore the structure of the kachchh seismic zone by mapping the 3 d distributions of b value fractal dimension d and seismic velocities from frequency magnitude analysis we find that the catalog is complete above mw 3 0 thus we analyze 2159 aftershocks with mw 3 0 to estimate the 3 d distribution of b value and fractal dimensions using maximum likelihood and spatial correlation dimension approaches respectively our results show an area of high b d and vp vs ratio values at 15 35 km depth in the main rupture zone mrz while relatively low b and d values characterize the surrounding rigid regions and gedi fault gf zone we propose that higher material heterogeneities in the vicinity of the mrz and or circulation of deep aqueous fluid volatile co2 is the main cause of the increased b d and vp vs ratio values at 15 35 km depth seismic velocity images also show some low velocity zones continuing in to the deep lower crust supporting the existence of circulation of deep aqueous fluid volatile co2 in the region probably released from the eclogitasation of olivine rich lower crustal rocks the presence of number of high and low velocity patches further reveals the heterogeneous and fractured nature of the mrz interestingly we observe that aki 1981 s relation d 2b is not valid for the spatial b d correlation of the events in the gf d2 1 2b zone however the events in the mrz d2 1 7b show a fair agreement with the d 2b relationship while the earthquakes associated with the remaining parts of the aftershock zone d2 1 95b show a strong correlation with the aki 1981 s relationship thus we infer that the remaining parts of the aftershock zone are probably behaving like locked un ruptured zones where larger stresses accumulate we also propose that deep fluid involvement may play a key role in generating seismic activity in the mrz therefore a similar episode of deep fluid inflow could play a crucial role in causing the next strong earthquakes in the surrounding blocks of nwf

timing of the permian triassic biotic crisis implications from new zircon u pb age data and their limitations abstract the most profound biotic crisis in the earth s history causing the near extinction of both terrestrial and marine life occurred at the end of the permian period about 253 myr ago and marks the paleozoic mesozoic era boundary the cause of this event is still a matter of vigorous debate with both brief and catastrophic as well as gradual mechanisms having been proposed similar to a recent landmark study this study uses the u pb method on zircons from the uppermost permian lowermost triassic ash fall deposits at meishan zhejiang province se china in order to examine time and rate constraints for these events the results of both this study and previous work show that for these ash layers the effects of pb loss are combined with varying amounts and sources of inheritance resulting in an age scatter which prohibits the extraction of a statistically robust age in many cases though the effects of pb loss on the zircons analyzed in this study were reduced by leaching the grains in hydrofluoric acid as opposed to commonly applied air abrasion prior to analysis the presence within a single ash layer of multiple generations of older xenocrysts in many cases only slightly older than the depositional age has made quantitative interpretation even more difficult when these combined phenomena bias individual zircon ages by less than a percent they are extremely difficult to deconvolute and if multi grain analyses are used can become impossible to recognize because of the resulting age averaging monte carlo simulations using actual measurements of individual zircon crystals show that age excursions due to pb loss and xenocrystic contamination for the meishan bentonites are easily homogenized to the point of undetectability when replicate analyses of multi grain zircon samples are compared thus this study uses only high precision analyses of single crystals whether from our work or that of previous studies three main conclusions have emerged first our data require a significant increase in the age of the permian triassic boundary by more than 2 myr compared to the previous study which shifts the age to a value older than 253 ma second neither our data nor those from previous work can confirm or negate the possibility of a very abrupt biotic crisis third even large suites of very high quality single zircon u pb analyses for these tuffs cannot in most cases yield objective reliable and robust dates with accuracies at the sub myr level though the temptation to perform arbitrary selection of subsets of the analyses for that purpose is almost irresistible the last conclusion is not an indictment of zircon u pb dating in general other rocks and other zircon populations can and do behave very differently and further technical advances will likely improve our ability to prepare grains or sub grains of adequately enhanced quality for analysis consequently the results of the present study strongly suggest that for problems requiring time scale accuracy inferences from zircon u pb dating must be based on sufficiently large suites of single crystal or crystal domain high precision analyses

magnetotelluric studies in the epicenter zone of 2001 bhuj earthquake abstract some earthquakes to mw5 level are occurring along two faults viz kachchh mainland fault and south wagad fault near the epicenter of mw7 7 bhuj earthquake of 2001 these faults are not the causative fault of the 2001 earthquake and suspect for future large earthquake in absence of detail geophysical surveys the sub surface orientation of these faults was not known and mt profiles have proved useful in delineating the subsurface trends two mt profiles having lengths of 24 km and 15 km with an inter station spacing of 1 3 km are taken about 10 km east and west of the epicenter of mw7 7 2001 bhuj earthquake respectively the profiles are in nearly n s direction to detect the faults which trend e w in the area from 2 d inversion of mt data of 23 stations it is found that there are two distinctive conductive features matching with the south wagad fault and kachchh mainland fault south of it both being about 10 km apart the south wagad fault is seen extending to banni low lying area 30 km west of the present trace

the permo triassic extinction the end permian mass extinction brought the palaeozoic great experiment in marine life to a close during an interval of intense climatic tectonic and geochemical change improved knowledge of latest permian faunas coupled with recent advances in isotopic studies and biostratigraphy have greatly enhanced our understanding of the events of 250 million years ago and have begun to provide answers to many questions about the causes of extinction

magnetic fabric variations along the fault related anticlines of eastern kachchh western india abstract an investigation of the anisotropy of magnetic susceptibility ams along the kachchh mainland fault kmf and south wagad fault swf in the eastern kachchh has been carried out to determine the variation of magnetic fabric in different anticlines 105 cores drilled from 35 jurassic sandstone samples collected from both forelimbs and backlimbs of the anticlines are analyzed the various types of fabrics from the three sites indicate essentially three stages of generation of magnetic fabric the sedimentary fabric type i is affected a initially by layer parallel shortening resulting in the development of type iii fabric with oblique to parallel bedding and magnetic foliation b later by bedding parallel shear associated with the rotation of limbs resulting in the tectonic fabric type iv and c finally by bedding parallel thrusting dominantly in the backlimbs resulting in the imprint of higher tectonic fabric type v vi about 14 of the sampled sites belong to the sedimentary type i fabric 54 to the type iii and 32 show tectonic fabric type iv and v vi the different stages of fabric evolution are not accompanied by linear increase in the degree of anisotropy but show construction and destruction of magnetic fabric during the layer parallel shortening to late stage bedding parallel thrusting the tectonic magnetic lineation orientations are mostly not consistent with the bedding strikes or fold axes the intermediate fabric lineation direction of nne ssw is superimposed by later tectonic lineation with varying orientations of nw se in the western end to nne ssw to nnw sse along the eastern end of kmf we attribute the variations in shortening direction essentially to the transpressional deformation of the basin in general and individual anticlines in particular the variation in slip propagation ratio along individual segmented faults has resulted in the rotation of fold limbs

sinking mafic body in a reactivated lower crust a mechanism for stress concentration at the new madrid seismic zone we propose a geodynamic model for stress concentration in the new madrid seismic zone nmsz the model postulates that a high density mafic body situated in the deep crust directly beneath the most seismically active part of the nmsz began sinking several thousands of years ago when the lower crust was suddenly weakened based on the fact that deformation rates in the nmsz have accelerated over the past 9 k y we envision the source of this perturbation to be related to the last north american deglaciation excess mass of the mafic body exerts a downward pull on the elastic upper crust leading to a cycle of primary thrust faulting with secondary strike slip faulting after which continued sinking of the mafic body reloads the upper crust and renews the process this model is consistent with the youth of activity the generation of a sequence of earthquakes and the velocity evolution during interseismic periods which depend upon the density contrast of the mafic body with respect to the surrounding crust its volume and the viscosity of the lower crust

middle phanerozoic mass extinctions and a tribute to the work of professor tony hallam tony hallam s contributions to mass extinction studies span more than 50 years and this thematic issue provides an opportunity to pay tribute to the many pioneering contributions he has made to this field early work 1961 on the jurassic in europe revealed a link during the toarcian stage between extinction and the spread of anoxic waters during transgression the first time such a common leitmotif had been identified he also identified substantial sea level changes during other mass extinction intervals with either regression end triassic or early transgression end permian coinciding with the extinction phases hallam s 1981 study on bivalves was also the first to elevate the status of the end triassic crisis and place it amongst true mass extinctions changing previous perceptions that it was a part of a protracted period of turnover although debates on the duration of this crisis continue hallam 2002 conflicting views on the nature of recovery from mass extinctions have also developed especially for the aftermath of the end permian mass extinction these discussions can be traced to hallam s seminal 1991 paper that noted the considerable delay in benthic recovery during early triassic time and attributed it to the persistence of the harmful high stress conditions responsible for the extinction itself this idea now forms the cornerstone of one of the more favoured explanations for this ultra low diversity interval

transient electromagnetic investigations in a tectonic domain of the kachchh intraplate region western india a morphotectonic study of the kachchh mainland fault

an integrated biomarker isotopic and palaeoenvironmental study through the late permian event at lusitaniadalen spitsbergen abstract the largest extinction of the phanerozoic occurred near the permian triassic p tr boundary some 252 ma ago several scenarios and drivers have been proposed for this event here we report for the first time an integrated study comprising sedimentological data biomarker distributions abundances and selected stable carbon and hydrogen isotopes along with bulk isotopes 34spyrite 13ccarb 13corg for a late permian section from lusitaniadalen spitsbergen norway sedimentological and geochemical data support a marine transgression and collapse of the marine ecosystem in the late permian strong evidence for waxing and waning of photic zone euxinia throughout the late permian is provided by chlorobiaceae derived biomarkers including 13c data and 34spyrite implying multiple phases of h2s outgassing and potentially several pulses of extinction a rapid decrease in abundance of various land plant biomarkers prior to the marine collapse event indicates a dramatic decline of land plants during the late permian and or increasing distance from palaeoshoreline as a consequence of sea level rise changes in d of selected biomarkers also suggest a change in source of organic matter om or sea level rise we also found biomarker and isotopic evidence for a phytoplanktonic bloom triggered by eutrophication as a consequence of the marine collapse compound specific isotope analyses csia of algal and land plant derived biomarkers as well as 13c of carbonate and bulk om provide strong evidence for synchronous changes in 13c of marine and atmospheric co2 attributed to a 13c depleted source the source could be associated with isotopically depleted methane released from the melting of gas clathrates and or from respired om due to collapse of the marine ecosystem

the age of the permian triassic boundary abstract the 5 cm boundary clay bed in the chinese stratotype section through the permian triassic boundary has been recognised as a bentonite shrimp ion microprobe dating of zircons in the bentonite indicates a magmatic age of 251 2 3 4 ma 2 this is the first direct constraint on the numerical age of the permian triassic boundary future refinements of ages at this important but poorly constrained level of the phanerozoic timescale may depend on re analysis of this uniquely placed volcanic horizon and other bentonites in the fossiliferous chinese upper permian and lower triassic the utility of defining the permian triassic boundary in the chinese stratotype section in the vicinity of known dateable horizons should be considered

close up of the end permian mass extinction horizon recorded in the meishan section south china sedimentary elemental and biotic characterization and a negative shift of sulfate sulfur isotope ratio abstract the permian triassic p tr boundary beds of the meishan section south china have been re studied in detail based on complete samples across the p tr transition under the microscope the end permian mass extinction horizon is calibrated to a 12 mm stratal interval the top being 19 mm below the top of bed 24e of the changhsing formation this abrupt disappearance of skeletal fragments of major benthos characterizes the end permian extinction event suggesting a catastrophic event an abrupt decrease in the 34s 32s ratios of seawater sulfate is confirmed to coincide with the end permian event horizon the sulfur isotope event is thought to have been caused by an overturn of a stratified ocean dominated by h2s implying coincidence of the oceanic mixing and the mass extinction coincident siberian flood volcanism may have triggered a long term 103 years cooling leading an ocean mixing a presumed comet impact to the ocean could have directly caused ocean mixing and the mass extinction

platinum element group variations at the permo triassic boundary in kashmir and british columbia and their significance abstract the end permian marks the greatest extinction in the geological record but there is no consensus on whether it was caused by terrestrial or extraterrestrial factors platinum group elements pge can readily separate extraterrestrial from terrestrial sources and the few studies so far from china and europe indicate terrestrial sources for the pge we report here detailed pge analyses of two expanded sections from the late permian northern and southern hemispheres that allow separate events to be distinguished and confirm a terrestrial source for the pge these sources are either contemporaneous seawater or older basaltic volcanics associated with the sections and the pge were precipitated by a possible combination of development of anoxia in the oceans and post depositional redistribution the pge content in sections at the permo triassic boundary is the result of geochemical and lithological control on metal precipitation that is found in many other black shales throughout geological time

crustal and lithospheric thinning beneath the seismogenic kachchh rift zone gujarat india its implications toward the generation of the 2001 bhuj earthquake sequence a high resolution passive seismic experiment in the kachchh rift zone of the western india has produced an excellent dataset of several thousands teleseismic events from this network 500 good teleseismic events recorded at 14 mobile broadband sites are used to estimate receiver functions for the 30 310 back azimuth ranges which show a positive phase at 4 5 6 1 s delay time and a strong negative phase at 8 0 11 0 s these phases have been modeled by a velocity increase at moho i e 34 43 km and a velocity decrease at 62 92 km depth the estimation of crustal and lithospheric thicknesses using the inversion of stacked radial receiver functions led to the delineation of a marked thinning of 3 7 km in crustal thickness and 6 14 km in lithospheric thickness beneath the central rift zone relative to the surrounding un rifted parts of the kachchh rift zone on an average the kachchh region is characterized by a thin lithosphere of 75 9 5 9 km the marked velocity decrease associated with the lithosphere asthenoshere boundary lab observed over an area of 120 km 80 km and the isotropic study of xenoliths from kachchh provides evidence for local asthenospheric updoming with pockets of partial melts of co2 rich lherzolite beneath the kachchh seismic zone that might have caused by rifting episode at 88 ma and the associated deccan thermal plume interaction at 65 ma episodes thus the coincidence of the area of the major aftershock activity and the moho as well as asthenospheric upwarping beneath the central kachchh rift zone suggests that these pockets of co2 rich lherzolite partial melts could perhaps provide a high input of volatiles containing co2 into the lower crust which might contribute significantly in the seismo genesis of continued aftershock activity in the region it is also inferred that large stresses in the denser and stronger lower crust at 14 34 km depths induced by ongoing banni upliftment crustal intrusive marked lateral variation in crustal thickness and related sub crustal thermal anomaly play a key role in nucleating the lower crustal earthquakes beneath the kachchh seismic zone

association of 34s depleted pyrite layers with negative carbonate δ13c excursions at the permian triassic boundary evidence for upwelling of sulfidic deep ocean water masses 1 a marine permian triassic boundary ptb section at nhi tao vietnam contains a series of at least 9 pyritic horizons characterized by concurrent decreases in pyrite s 34spy and carbonate c isotopic compositions 13ccarb the first and largest of the events that precipitated these pyritic horizons was coincident with the late permian mass extinction while subsequent events were generally smaller and occurred at quasiperiodic intervals of 20 to 30 ka a near complete lack of organic carbon to drive bacterial sulfate reduction in sediment pore waters among other considerations argues against a diagenetic control for these relationships rather the covariant patterns documented herein are most easily explained as the product of recurrent upwelling of anoxic deep ocean waters containing 34s depleted hydrogen sulfide and 13c depleted dissolved inorganic carbon the sulfide 34s record of the study section represents a mixture of a small amount of isotopically heavy authigenic pyrite formed via in situ bacterial sulfate reduction with a generally larger quantity of isotopically light syngenetic pyrite precipitated within the water column during upwelling episodes although upwelling of toxic deepwaters has been invoked in earlier studies as a mechanism for the late permian marine mass extinction this is the first study to 1 document patterns of pyrite 13ccarb covariation that strongly support upwelling as a major process at the ptb and 2 provide evidence of multiple quasiperiodic upwelling events that may reflect reinvigoration of global ocean overturn following a prolonged interval of late permian deep ocean stagnation

luminescence chronometry and geomorphic evidence of active fold growth along the kachchh mainland fault kmf kachchh india seismotectonic implications abstract the kachchh region of western india is a pericratonic basin experiencing periodic high magnitude earthquakes events in 2001 a catastrophic seismic event occurred at bhuj measuring mw 7 7 the epicenters of both the 1956 and 2001 earthquakes were along the kachchh mainland fault kmf proximal to the eastern end of the northern hill range nhr the latter is a topographic expression of an active fault related fold on the hanging wall and is controlled by a south dipping blind thrust the present study deals with the eastern sector of nhr and uses optical dating to reconstruct the chronology of tectonically caused incisions along the backlimb of the nhr incision ages on channel fills and valley fill terraces progressively decrease from 12 ka to 4 3 ka this age progression along with geomorphic evidences decrease in topographic relief drainage capture and drainage migration across the fold nose suggests an active vertical and lateral fold growth along the kmf optical ages suggest that during the late holocene the average uplift rate along the eastern nhr was 10 1 mm a recent gps based estimates on crustal shortening are 12 mm a the kmf and the south wagad fault swf represent the bounding faults of a transtensional basin that formed during the initial rifting this basin is termed as the samakhiali basin the compressive stresses on account of structural inversion from normal to reverse phase resulted in lobate shaped anticlines along kmf and swf zone these anticlines subsequently coalesced and formed linked and overlap segments the present study suggests that eastward lateral deformation across the eastern portion of kmf has continued and has now resulted in its interaction with a left step over transfer fault called the south wagad master fault swmf this implies an increasing transpersional deformation of the samakhiali basin we therefore suggest that the eastward nhr ridge propagation along kmf resulted in the thrust faulting on the south dipping swmf resulting in the bhuj 2001 event the increasing strain on this basin may cause enhanced seismicity in the future along the eastern kmf and wagad region

magnetotelluric evidence on the southward extension of the eastern ghats mobile belt from ongole india abstract there has been a longstanding and scientifically contentious issue concerning whether or not the eastern ghats mobile belt egmb extends southward beyond ongole in the state of andhra pradesh in south india various geological and geophysical investigations carried out in different campaigns could not conclusively address this important issue some argued that the egmb that originates near mahanadi in the northeast of india and extends along the eastern continental boundary is abruptly cut near ongole in the south swerves eastward towards the bay of bengal and joins the erstwhile east antarctica boundary others opined differently and debated about its southward extension beyond ongole in the present study we provide a conclusive evidence for the first time on this perplexing issue by determining the deep earth electrical resistivity structure of the egmb region through broad band magnetotelluric mt investigations carried out along two different profiles laid out one near the ongole region profile aa of 35 km length and the other near the nellore region profile bb of 52 km length the latter is located at a distance of about 125 km south of the former the lengths of both these profiles are sufficiently far from the influences of the electrical nature of the subsurface of the adjoining geological terrains namely the east dharwar craton the cuddappah basin and the southern granulite terrain this enables to determine the electrical nature of the egmb alone and examine whether or not it extends south of ongole two dimensional inversion of mt data of both the profiles revealed a very thin top conductive layer of about 1 10 m with an average thickness of about 500 m representing the alluvium this layer is underlain by very high resistive subsurface with resistivity of about 107 m extending up to about 30 km and probably further beyond not shown in the present study since the major rock types in the study area namely khondalites calc granulites charnockites and granitic gneisses of archaean age have large overlapping resistivities mt data could not explicitly discern the nature of the multilayered crust beneath the egmb as a result the subsurface beneath both the regions shows up as a very thick single layer of very high resistivity the high grade rocks of the ongole domain and supracrustals of nellore schist belt nsb which lies south of ongole domain have undergone synchronous tectonic activity at ca 1 6 by this is evident by the kanigiri and kandra ophiolites within nsb that signify the proterozoic subduction of the egmb this geological evidence together with the similar nature of the high electrical resistivity of the subsurface observed at ongole and nellore regions confirm the southward extension of the egmb beyond ongole

age and timing of the permian mass extinctions u pb dating of closed system zircons the age and timing of the permian triassic mass extinction have been difficult to determine because zircon populations from the type sections are typically affected by pervasive lead loss and contamination by indistinguishable older xenocrysts zircons from nine ash beds within the shangsi and meishan sections china pretreated by annealing followed by partial attack with hydrofluoric acid result in suites of consistent and concordant uranium lead u pb ages eliminating the effects of lead loss the u pb age of the main pulse of the extinction is 252 6 0 2 million years synchronous with the siberian flood volcanism and it occurred within the quoted uncertainty

electrical structures of the source area of the 1999 chi chi taiwan earthquake spatial correlation between crustal conductors and aftershocks abstract wide band magnetotelluric mt data were collected on an east west profile approximately perpendicular to the local strike of the chelungpu thrust through the hypocentral area of the chi chi earthquake for imaging the seismogenic structure mt data were then inverted for two dimensional resistivity models plus best fitting static shift parameters using a nonlinear conjugate gradient algorithm that minimizes the sum of the normalized data misfits and the smoothness of the model as shown in the inverted 2d resistivity models presented in this paper an electrical conductor beside the hypocenter of the chi chi earthquake indicates that deep crustal fluids may participate in the rupture process of the chi chi earthquake a striking spatial correlation between the crustal conductor and occurrence of aftershocks beneath the chelungpu fault suggests a postseismic pore pressure adjustment ongoing after the mainshock additionally the hypocenter exhibits an electrical resistive zone consistent very well with a predicted compact zone from a crustal deformation and transient fluid flow modeling

an evaporite based high resolution sulfur isotope record of late permian and triassic seawater sulfate abstract variations in the sulfur isotope composition of dissolved marine sulfate through time reflect changes in the global sulfur cycle and are intimately related to changes in the carbon and oxygen cycles a large shift in the sulfur isotope composition of sulfate at the permian triassic boundary has been recognized for long time and a number of studies were carried out to understand the causes and significance of this shift however data for the middle and late triassic are very sparse and the stratigraphic evolution of the sulfur isotope composition of seawater is poorly constrained due to the small number of samples analyzed and or due to the limited stratigraphic intervals studied moreover in the last few years the triassic timescale has significantly changed due to a wealth of new radiometric and stratigraphic data in this study we show that for the late permian and the triassic it is possible to obtain a precise reconstruction of the evolution of the sulfur cycle for parts of it at sub million year resolution by analyzing exclusively gypsum and anhydrite deposits we base our reconstruction on new data from the middle and late triassic evaporites of northern switzerland and literature data from evaporites from germany austria italy and the middle east we propose a revised correlation between the well dated marine tethyan sections in northern italy and the evaporites from northern switzerland and from the germanic basin calibrated to the newest radiometric absolute age scale this new correlation allows for a precise dating of the evaporites and constructing a composite sulfur isotope evolution of seawater sulfate from the latest permian lopingian epoch to the norian we show that a rapid positive shift of approximately 24 at the permian triassic boundary can be used to constrain seawater sulfate concentrations in the range of 2 6 mm thus higher than previous estimates but with less rapid changes finally we discuss two possible evolution scenarios for the middle triassic negative shift to values of 15 that subsequently remain constant during the late triassic

an experimental investigation of the mechanical behavior and microstructural features of a volcanic soil isparta turkey and stability of cut slopes in this soil abstract volcanic soils are widely distributed group of soils which cover significant parts of the world s surface and include areas occupied by urban settlements structures and infrastructures and may create geo engineering problems these soils exhibit a distinctive behaviour that is a consequence of their formation history mineralogy and structure some part of the subsoil of a large area surrounding the city of isparta western turkey mainly consists of volcaniclastic deposits this paper presents the results of the part of a research programme aiming at geotechnically characterizing the uppermost layer of this volcaniclastic sequence particularly focusing on its collapse potential shear behaviour and the influence of microstructure on these behaviours in addition its main futures were compared with those of some similar volcanic soils at different parts of the world and the stability of sub vertical cuts in this soil was also assessed the experimental investigation mainly consisted of index and classification tests double oedometer and direct shear box tests to assess the collapse potential and shear behaviour of the soil respectively matric suction of the samples was also determined for preliminary evaluation of the influence of suction on collapse and shear behaviours of the soil in addition thin section studies and x ray diffraction xrd and scanning electron microscopy sem analyses were also conducted to determine mineralogical and microstructural features and to evaluate their influences on the mechanical behaviour of the volcanic soil the deposit is composed of weakly bonded firm silty sand with an open structure low unit weight and high porosity generally unsaturated in situ the results of the double oedometer tests suggest that the volcanic soil generally falls in the category of slight collapse potential at normal stresses ranging between 5 and 100 kpa while at normal stresses greater than 100 kpa its collapse potential increases and ranges between moderate and moderately severe collapse potential classes at normal stresses lower than 100 kpa matric suction may have an effect on collapse behaviour the direct shear box test results indicated that the volcanic soil has two different types of shear strength behaviour represented by bi linear failure envelopes in other words the shear strength parameters of the volcanic soil within a low normal stress range generally between about 6 and 200 kpa exceed those of determined at higher normal stresses since no matric suction was measured during the direct shear box tests it could not be possible to evaluate the effect of suction on the bi linear failure envelopes however some differences between the suction and degree of bonding of the samples taken from different locations might probably have been contributed to the separation of the bi linear behaviour at different normal stress levels the destruction of the bonding cementation between the particles is probably more responsible from the bi linear form of the failure envelope comparisons between the sem micrographs taken from natural and tested specimens revealed that the mechanical behaviour of the volcanic soil is strongly influenced by the bonding material the results of the stability analyses showed a good agreement with the current situation of the cut slopes observed in the study site and suggested that vertical cut slopes with a height of 14 15 m will maintain their stability based on a reasonable factor of safety such as 1 5

carbon sulfur oxygen and strontium isotope records organic geochemistry and biostratigraphy across the permian triassic boundary in abadeh iran pelagic deposits at abadeh represent a complete biostratigraphic record across the permian triassic boundary ptb the presumed water depth during deposition of these sediments was between 60 and 90 m similar to other permian triassic boundary sections the succession at abadeh is characterised by a negative carbon isotope shift of approximately 4 the values start to decrease in the lower c changxingensis c deflecta s l zone reach 0 12 v pdb in the uppermost permian just below the ptb remain low to the early i isarcica zone 0 32 and increase subsequently in the upper i isarcica zone for the time interval of the ptb negative carbon isotope excursion between the c iranica and the i isarcica zones no correlation exists between the 13ccarb and the 18ocarb the above observations argue against the conclusion of heydari et al 2001 that the carbon isotope event at the p t transition is an alteration artefact and not a global signal the decrease in 13ccarb is accompanied by a 5 and potentially up to 10 increase in 34ssss together these features are thought to reflect a complex global event notably the development of widespread anoxic oceans with anoxic bottom layers rising onto the shelves for the carbon isotope drop other factors such as the collapse of ocean primary productivity may also have played a role the 87sr 86sr ratios of dzhulfian seawater show only a minor increase from 0 70705 to 0 70710 reaching 0 70720 in the dorashamian the increase becomes steeper in the early triassic reaching 0 70754 in the n dieneri zone the rise of the strontium isotope values is thought to be related to enhanced continental weathering under humid climatic conditions in the uppermost permian c meishanensis h praeparvus zone and the lack of a dense land vegetation in the early triassic prior to the spathian upper olenekian

diagenetic and detrital origin of moretane anomalies through the permian triassic boundary abstract many biogeochemical anomalies coincide with the late permian extinction lpe 252 28 ma several mechanisms have been proposed to explain the moretane hopane anomaly that has been identified in samples from meishan gssp section in southeastern china here we report homohopane 2 and 3 methylhomohopane and lithological data for a drill core from the meishan section in southeastern china three intervals of elevated c 30 moretane hopane ratios are recorded in the lungtan yinkeng and helongshan formations moretane hopane ratios of c 31 34 homohopanes and the 2 and 3 methylhomohopanes display the same stratigraphic patterns as the c 30 moretane hopane record in light of the multiple and parallel moretane anomalies for the homohopane and 2 and 3 methylhomohopane series enhanced input from higher plant organic matter such as coal and peat does not adequately explain the observed isomer patterns correlation of high moretane hopane ratios with low c 35 homohopane index hhi and high hopane sterane values suggest increased input of hopanoids from oxic soils additionally moretane hopane ratios show excellent correlations with total clay percentages and specific clay types particularly chlorite illite and mixed layer illite smectite we conclude that a combination of episodic hopanoid input from soil bacteria and diagenetic effects related to redox and detrital clays generated the unique moretane hopane patterns at meishan similar relationships of ts ts tm with redox source indicators and lithology indicate that ts ts tm is affected by the same factors controlling the moretane hopane ratios berthierine a clay that requires reducing conditions for formation was detected in samples from the lungtan formation we are unable to determine from our results whether the berthierine is authigenic or detrital but future determination of the origin of berthierine at meishan may offer additional environmental insight no link between diasteranes and lithology was observed in this study suggesting that diasteranes are relatively unaffected by the detrital clay component of the meishan sediments in total the results point toward the complex role of source input lithology and depositional redox conditions in the transformation of organic matter during maturation future work is required to elucidate the lithological effects on diagenetic processes including biomarker genesis isomerization and thermal degradation

massive volcanism at the permian triassic boundary and its impact on the isotopic composition of the ocean and atmosphere abstract bulk carbonate and conodonts from three permian triassic p t boundary sections at guryul ravine kashmir abadeh central iran and pufels bula bulla italy were investigated for 13 c and 18 o carbon isotope data highlight environmental changes across the p t boundary and show the following features 1 a gradual decrease of 4 to more than 7 starting in the late permian changhsingian c bachmanni zone with two superimposed transient positive excursions in the c meishanensis h praeparvus and the m ultima s mostleri zones 2 two 13 c minima the first at the p t boundary and a higher occasionally double minimum in the lower i isarcica zone it is unlikely that the short lived phenomena such as a breakdown in biological productivity due to catastrophic mass extinction a sudden release of oceanic methane hydrates or meteorite impact s could have been the main control on the latest permian carbon isotope curve because of its prolonged 0 5 ma duration gradual decrease and the existence of a 1 positive shift at the main extinction horizon the p t boundary 13 c trend matches in time and magnitude the eruption of the siberian traps and other contemporaneous volcanism suggesting that volcanogenic effects such as outgassed co 2 from volcanism and even more thermal metamorphism of organic rich sediments as the likely cause of the negative trend

isotopic evidence for an anomalously low oceanic sulfate concentration following end permian mass extinction abstract the cataclysmic end permian mass extinction was immediately followed by a global expansion of microbial ecosystems as demonstrated by widespread microbialite sequences disaster facies in shallow water settings here we present high resolution carbonate carbon 13 c carb and carbonate associated sulfate sulfur isotope 34 s cas records from the microbialite in the cili permian triassic p tr section in south china a stepwise decline in 13 c carb begins in the underlying skeletal limestone predating the main oceanic mass extinction and the first appearance of microbialite and reaches its nadir in the upper part of the microbialite layer the corresponding 34 s cas in the range of 17 4 to 27 4 is relatively stable in the underlying skeletal limestone and increases gradually from 2 m below the microbialite rising to a peak at the base of the microbialite two episodes of positive and negative shifts occurred within the microbialite layer and exhibit a remarkable co variance of sulfur and carbon isotope composition the large amplitude of the variation in 34 s cas as high as 7 per 100 kiloyears suggests a small oceanic sulfate reservoir size at this time furthermore the 13 c carb and 34 s cas records co vary without phase lag throughout the microbialite interval implying a marine driven c cycle in an anoxic ocean with anomalously low oceanic sulfate concentrations on the basis of a non steady state box model we argue that the oceanic sulfate concentration may have fallen to less than 15 perhaps as low as 3 of that in the modern oceans low oceanic sulfate concentration likely was the consequence of evaporite deposition and widespread anoxic sulfidic conditions prior to the main mass extinction by promoting methanogenesis and a build up of atmospheric ch 4 and co 2 low oceanic sulfate may have intensified global warming exacerbating the inimical environmental conditions of the latest permian

electrical conductance map for the kachchh rift basin constraint on tectonic evolution and seismotectonic implications geomagnetic field variations recorded by an array of magnetometers spread across the kachchh rift basin are reduced to a set of induction arrows as a diagnostic of lateral electrical conductivity variations a non uniform thin sheet electrical conductance model is developed to account for the salient induction patterns it indicates that the imaged conductivity anomalies can be related to the sediment filled structural lows in between the fault bounded uplifts it is suggested that sagging structural lows preserved the marine sediments deposited during the mesozoic sea transgression and later developed into first order embayment basins for the deposition of sediments in association with late eocene transgression depth integrated electrical conductance helped in mapping two depo centres along the ene wsw trending banni half graben bounded by the kachchh main fault on the south and second along the vinjan depression formed in response to the subsidence between the vigodi fault and westward extension of the katrol hill fault together with the westward bending of the median high presence of metamorphosed graphite schist clasts in shale dominated mesozoic sequence and or thin films of carbon resulting from the thermal influence of deccan activity on carbonate rich formations can account for the high electrical conductivity anomalies seen in the depo centres of thick mesozoic and tertiary sediments additionally two high conductivity zones are imaged encompassing a block defined by the 2001 bhuj earthquake and its aftershocks in agreement with gravity magnetic and seismic velocity signatures aqueous fluids released by recrystallizing magmatic bodies intruded in association with deccan trap activity account for mapped high conductivity zones high fluid pressure in such a fractured domain surrounding the intruded magmatic plugs perturb the regional stress concentrations to produce frequent and low magnitude aftershocks in the shallow section of the epicentral track of the 2001 bhuj earthquake

catastrophic environmental transition at the permian triassic neo tethyan margin of gondwanaland geochemical isotopic and sedimentological evidence in the spiti valley india abstract interpreting global consequences of the permian triassic p tr extinction requires examination across paleogeographic realms of pangaea the spiti valley in india remnant of the peri gondwanan shelf preserved trails of this environmental catastrophe in the neo tethys ocean we document new sedimentological observations and high resolution trace element concentrations and carbon oxygen lead isotope data across the p tr boundary in spiti framboidal pyrites fossils and laminated lithology of the late permian shales indicate deeper anoxic depositional environment while 13 c org excursions of 2 4 and 3 1 in atargu and guling outcrops respectively identify the p tr transition across a clayey partly gypsiferous ferruginous layer sedimentological similarities of this layer to other neo tethyan sections from transcaucasia and iran indicate subaqueous oxidation of shallow marine sediments on a regional scale light rare earth element enriched late permian shales with conspicuous ce eu anomalies reflect their source from the adjacent panjal trap basalts ca 289 ma of kashmir continental crustal nb ta and zr hf anomalies appear at the p tr boundary sediments and prevail through the overlying early triassic carbonates original pb isotope ratios along with an increasing pb abundance closer to the p tr boundary distinguish the volcanic source of the late permian shales from the continental crustal siliciclastic signature of the early triassic carbonates our 13 c org trace element and pb isotope record from spiti indicate catastrophic changes in sediment sources and facies with effects on carbon cycle and are consistent with an abrupt episode of marine regression and erosional forcing also observed elsewhere along northern gondwanaland simultaneous eruption of siberian volcanics and bolide impacts in parana basin of brazil and elsewhere implicating impact triggered volcanism left catastrophic regional global imprints on sea level climate marine anoxia and tectonic stability that connected the p tr crisis across terrestrial and marine realms worlwide

sulfur geochemistry across a terrestrial permian triassic boundary section in the karoo basin south africa concentrations of sulfur and carbon and isotopic compositions of sulfur were determined in sedimentary rocks from a section across the terrestrial permian triassic p tr boundary in the northern karoo basin south africa high concentrations of sulfide produced by sulfate reducing bacteria were found in the sedimentary rocks at and just below the perceived p tr boundary the ratios of organic carbon to sulfide of the sedimentary rocks with high concentrations of sulfide are relatively constant and similar to those of marine environments this means that the enhanced accumulation of sulfide is a result of the enrichment of sulfate in the water as the sulfide concentrations do not correlate with concentrations of any major elements indicative of weathering intensity the supply of sulfate was independent of environmental factors such as temperature and co2 concentrations in the atmosphere which control weathering intensity therefore it is reasonable to consider that the sulfate might have been supplied to the freshwater directly as acid rain by an event such as a bolide impact or a volcanic eruption the absence of evidence for an impact event in the geological record though favors volcanic input as the cause of the acid rain

a permian triassic boundary microbialite deposit from the eastern yangtze platform jiangxi province south china geobiologic features ecosystem composition and redox conditions abstract a permian triassic p tr boundary microbialite ptb microbialite deposit occurs near xiushui on the southern margin of the eastern yangtze platform south china this 2 m thick microbialite overlies uppermost permian bioclastic limestone with a 5 cm thick oolite like grainstone layer at the contact this ptb microbialite consists of lower thrombolite 1 5 m thick and an upper dendrolite 0 5 m thick the thrombolite interval is characterized by a clotted texture of reddish sparitic patches embedded in a gray micritic matrix whereas the dendrolite texture consists of brownish sparitic patches embedded within a yellow micritic matrix abundant calcified microbes occur in both the thrombolite and the dendrolite including 1 columnar and clustered fabrics which are especially rich in the thrombolite assigned as products of gakhumella or related microorganisms and 2 microspheroids 40 60 m in diameter with different interior structures these calcimicrobes are considered to have played an important role in constructing the xiushui ptb microbialite the demise of the microbialite was likely due to a sea level fall during the early griesbachian lowermost triassic which resulted in a lowering of the wave base thereby destroying the microbialite frameworks and facilitating the deposition of winnowed skeletal grainstone metazoan community structures within the microbialite changed sharply across the end permian extinction horizon which is placed at a sharp negative shift in 13 c carb quantitative analyses show that the xiushui microbialite community is similar to that of chongyang and cili microbialites this is probably because all of these microbialites grew along the margins of the lower yangtze region during the p tr transition however unlike other ptb microbialites the xiushui ecosystem contains fairly abundant metazoans which are dominated by ostracods with minor occurrences of foraminifers microgastropods and microconchids both the ostracod assemblage and the pyrite framboid analyses indicate an upper dysoxic zone to a well oxygenated condition for the xiushui microbialite this implies that some ptb microbialite ecosystems developed in conditions that were not always harsh instead some were hospitable for some metazoans to survive immediately after the end permian crisis considering that the redox conditions indicated by ptb microbialites are quite variable we infer that oxygen levels probably were not the crucial factor affecting the growth of the ptb microbialites

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

electrical imaging of deep crustal features of kutch india summary a regional magnetotelluric mt study was carried out with 55 mt soundings distributed along five traverses across the kutch mainland unit kmu on the west coast of india a region characterized by a series of successive uplifts and intervening depressions in the form of half graben bounded by master faults we obtain the deeper electrical structure of the crust beneath kutch from 2 d modelling of mt data along the 5 traverses in order to evaluate the geo electrical signatures if any of the known primary tectonic structures in this region the results show that the deeper electrical structure in the kutch region presents a mosaic of high resistive crustal blocks separated by deep rooted conductive features two such crustal conductive features spatially correlate with the known tectonic features viz the kutch mainland fault kmf and the katrol hill fault khf an impressive feature of the geo electrical sections is an additional well defined conductive feature running between jakhau and mundra located at the southern end of each of the five mt traverses and interpreted to be the electrical signature of yet another hidden fault at the southern margin of the kmu this new feature is named as jakhau mundra fault jmf it is inferred that the presence of jmf together with the kathiawar fault nkf further south located at the northern boundary of the saurashtra horst would enhance the possibility of occurrence of a thick sedimentary column in the gulf of kutch the region between the newly delineated fault jmf and the kathiawar fault nkf could thus be significant for hydrocarbon exploration

significance of δdkerogen δ13ckerogen and δ34spyrite from several permian triassic p tr sections for the first time we report d of kerogen dkerogen for three permian triassic p tr sequences hovea 3 perth basin western australia jameson land east greenland and lusitaniadalen spitsbergen we have compared dkerogen with 13c of kerogen 13ckerogen and 34s of total reduced inorganic sulfur tris essentially pyrite 34spyrite of all the sections and for one sample set with 13c of carbonate 13ccarbonate to establish i similarities between the sections and ii evaluate whether these signals are local and or global stable isotope shifts occur for all three sample sets either at the p tr transition western australia or coinciding with the marine ecosystem collapse spitsbergen and east greenland dkerogen reflects organic matter om kerogen type and is not sensitive to the low level of thermal maturation reliable palaeoenvironmental information in terms of the use of d can therefore only be obtained for the p tr transition from hydrogen compound specific isotope analyses csia of biomarkers nabbefeld et al 2010b the negative shifts in 13ccarbonate primary and 13ckerogen are attributed to the release of 13c depleted carbon into the atmosphere whereas the isotopic excursions in 34spyrite relate to palaeoredox changes however the global coincidence in timing of the shifts in dkerogen 34spyrite and 13ckerogen suggests a relation between the sulfur carbon and hydrogen cycles the negative shifts in 13ccarbonate primary are in general attributed to the release of 13c depleted source of carbon into the oceans and atmosphere whereas 13ckerogen can reflect the latter in certain cases but can also be superimposed by varying sources of om kerogen type isotopic excursions in 34spyrite relate to global changes in the palaeoredox conditions that affect sulfur cycling in the ancient seas

latest permian to early triassic basin to shelf anoxia in the sverdrup basin arctic canada a combined sequence stratigraphic and geochemical study of the latest permian extinction event in nw pangea provides new insight into the onset and extension of basin anoxia onto the adjacent shallow shelf the latest permian transgression in the sverdrup basin of arctic canada initiated prior to onset of deep water anoxia and continued past the latest permian extinction event deep water anoxia initiated after the shelf was flooded in mid to late changhsingian time requiring a much more rapid and much greater vertical rise in the chemocline than that associated with relative sea level supporting the chemocline upward excursion model our work also extends evidence of global euxinc conditions to nw pangea euxinic conditions developed just prior to the main extinction event and we suggest that this was associated with a significant pyrite rain out event which stripped bio essential nutrients from anoxic seawater prior to the main disruption of the global carbon cycle as recorded by shifts in the carbon isotope record

two episodes of environmental change at the permian triassic boundary of the gssp section meishan abstract high resolution stratigraphic records through the permian triassic boundary ptb interval of the global stratotype section and point gssp at meishan zhejiang province china reveal that the ptb crisis was not a single abrupt catastrophe a bed by bed analysis of environmental and biotic changes makes clear that the crisis can be resolved into two discrete episodes each consisting of three stages a unstably oscillating conditions b peak crisis conditions and c ameliorating conditions the first crisis episode commenced in bed 23 peaked in beds 24e 26 and ameliorated in beds 27 and 28 while the second crisis episode commenced in bed 29 peaked in beds 34 38 and ameliorated in beds 39 and higher the macroscopic mass extinctions happened not at the beginning nor the end of each cycle but at times when the crisis or perturbation of environments began these extinction events do not show detectable feedbacks to concurrent environmental changes in each episode cyanobacteria proliferation postdated the macroscopic extinction while proliferation of green sulfur bacteria predated the environmental crisis causational analysis between environmental and microbial changes show that geomicrobial functional groups exercised pronounced effects on the marine c n s cycles and ocean redox conditions during the ptb crisis it is possible thus that the microbial crises played an important role in strengthening or evening triggering the environmental crisis

pattern of marine mass extinction near the permian triassic boundary in south china the meishan section across the permian triassic boundary in south china is the most thoroughly investigated in the world a statistical analysis of the occurrences of 162 genera and 333 species confirms a sudden extinction event at 251 4 million years ago coincident with a dramatic depletion of 13ccarbonate and an increase in microspherules

conodont survival and low iridium abundances across the permian triassic boundary in south china the permian triassic sedimentary sequence of china includes one of the most complete and fossiliferous paleozoic mesozoic boundaries known closely spaced sampling across the boundary which is an important extinction event for most organisms has produced good conodont faunas that show little diversity change a drop in conodont abundance is the only apparent response to the extinction event a low concentration of iridium in the boundary clay 0 002 part per billion 20 percent as well as in samples immediately below and above that range from 0 004 to 0 034 part per billion do not support the proposal of an extraterrestrial impact event at this boundary in china

weak mantle in nw india probed by geodetic measurements following the 2001 bhuj earthquake abstract far reaching transient surface deformation following the 2001 mw 7 6 bhuj intraplate earthquake in nw india reveals visco elastic flow in the mantle with only modest contributions from crustal relaxation processes the relatively rapid decay of gps measured deformation rates indicates increasing effective viscosities of the mantle from 3 1018 pa s in the first 6 months to 2 1019 pa s during the 6 year observation period consistent with a time and stress dependent rheology such as power law flow by dislocation creep the observed data do not require relaxation of the lower crust over these time scales and indicate a lower bound of 1020 pa s on its effective viscosity the unusually low viscous strength of the mantle below the earthquake epicentral region may be the long lasting result of thermal weakening by the late cretaceous deccan plume and may be responsible for the unusually active intraplate seismicity in the region

a unique geochemical record at the permian triassic boundary a 330 metre core drilled through the marine permian triassic boundary in the carnic alps of austria allows closely correlated studies of geochemistry petrography and palaeontology across the boundary the isotope shifts and metal concentrations are extended multiple and complex and do not resemble those seen at the cretaceous tertiary boundary both the carbon isotope shifts and the chemical events including an indium anomaly may have causes related to a major regression of the sea

evolutionary dynamics of the permian triassic foraminifer size evidence for lilliput effect in the end permian mass extinction and its aftermath abstract there is growing evidence of the lilliput effect in the end permian mass extinction and its aftermath however very little has been published on assessing the lilliput effect on protozoans in the early triassic based on quantitative analysis of a great quantity of samples from outcrop sections this study investigates foraminiferal test size variations through the changhsingian to the olenekian based on fossil records from three outcrop sections in south china the sharp reduction in foraminifer sizes coincides with the first or main episode of the end permian mass extinction foraminifers remained small in sizes in the early induan their body sizes increased slowly in the late induan to olenekian but never recovered to the pre extinction test size levels the lilliput effect on foraminifera in the aftermath of the end permian crisis is indicated by the extinction of large taxa decrease in size for surviving taxa and rise of small sized new forms physiological reactions of various foraminifer groups reveal that several defaunation events such as anoxia ocean acidification and global warming that prevailed through the permian triassic interval may be responsible for both the end permian crisis and the lilliput effect

characterization of the causative fault system for the 2001 bhuj earthquake of mw 7 7 abstract precise hypocenters erh m w 2 0 5 3 delineate a east west trending blind thrust dipping 45 towards south named as north wagad fault nwf about 25 km north of kachchh main land fault kmf as the causative fault for the 2001 bhuj earthquake of m w 7 7 the aftershock zone involves a crustal volume of 60 40 35 km 3 lying between kmf and nwf the waveform inversion of 45 aftershocks of m 3 0 5 3 suggest that the e w trending south dipping reverse faulting mainly characterizes the aftershock zone however some reverse faulting along nw se as well as ne sw planes and some strike slip faulting along nw se trending vertical plane are also noticed the estimated p axes point on an average towards n s while t axes orient in e w agreeing well with the prevailing regional plate tectonic stress directions the estimated velocity model from one dimensional inversion of 8000 p and 5000 s travel times from 600 aftershocks deciphers a detailed crustal structure of the region upper 0 6 km on an average suggests a low velocity zone characterizing the jurassic and younger sediments the depth range 6 42 km is characterized on an average by larger values of v p 6 31 to 6 98 km s with an average of 6 71 km s v s 3 64 to 4 05 km s with an average of 3 85 km s and v p v s 1 69 to 1 81 with an average of 1 75 the high crustal velocities can be attributed to the existence of a high velocity mafic intrusive rift pillow structure beneath the region probably emplaced during the rifting time this brittle competent high velocity zone beneath the epicentral area in response to the compression due to the northward movement of the indian plate could induce sufficient local stress perturbation for generating large intraplate earthquakes of m w 7 5 in the lower crust further within the overall higher velocity depth range a layer characterized by large values of v p 6 98 km s v s 3 854 km s and v p v s 1 81 is found in the depth range of 20 5 30 km which is inferred to be fractured and saturated high crack density and probably fluid filled presence of numerous fractures in this layer is confirmed by a high b value 0 75 1 1 in this layer this layer might have facilitated the nucleation process of the 2001 bhuj earthquake the major rupture and 47 of the aftershocks have occurred within this layer

3d crustal resistivity structure beneath the wagad aftershock zone of the 2001 bhuj earthquake kutch india heterogeneous resistivity structure controlled by widespread fluid infiltration and clues to aftershocks pattern abstract the epicentral region of the 26 january 2001 bhuj earthquake 7 7 m w in the kutch region of india has been experiencing a vigorous and unique intraplate aftershock activity which shows a v shaped pattern and n ne migration along the western margin of the wagad uplift located to the northeast of the mainshock this study presents 3d resistivity structure of the wagad aftershock zone imaged using magnetotelluric mt data to understand the crustal geoelectric structure and subsurface geometry of faults lineaments which could provide critical inputs to evaluate and strengthen the earthquake generation mechanism and aftershocks pattern the obtained 3d conductivity structure showed a thick 3 km and homogeneous conductive 1 30 m layer of tertiary mesozoic sedimentary cover in the area a highly heterogeneous upper and middle crust characterized by a mix of conductive 300 m structures is imaged below the sedimentary cover enhanced conductivity zones showed spatial correlation with the surface trace of various faults lineaments and are interpreted as fluid enriched zones in the crust which play a critical role in earthquake triggering significantly higher fluid enrichment noticed in the crust below two minor faults khadir transverse fault ktf and manfara fault mf which are hitherto considered to have an insignificant role in the seismogenesis of the area the aftershock events seem to occur mostly on the resistive parts of the crust and its pattern shows good alignment with the anomalous conductive zones associated to the above two faults the results provide a strong clue to infer that the ktf and mf have a vital role in the observed aftershock activity and control the v shaped aftershocks pattern

impacts do not initiate volcanic eruptions eruptions close to the crater many papers on meteorite impact suggest that large impacts can induce volcanic eruptions through decompression melting of the underlying rocks we perform numerical simulations of the impact of an asteroid with a diameter of 20 km striking at 15 km s 1 into a target with a near surface temperature gradient of 13 k km 1 cold case or 30 k km 1 hot case the impact creates a 250 300 km diameter crater with 10 000 km3 of impact melt however the crater collapses almost flat and the pressure field returns almost to the initial lithostat even an impact this large cannot raise mantle material above the peridotite solidus by decompression statistical considerations also suggest that impacts cannot be the common initiator of large igneous provinces any time in post heavy bombardment earth history

a new hypothesis for the deep subsurface structures near the bhuj 2001 earthquake mw 7 6 hypocentre zone and its tectonic implications summary we provide a new hypothesis for the deep subsurface structures near the bhuj 2001 earthquake region based on magnetotelluric mt investigations carried out close to the epicentre zone 2 d inversion of broad band mt data of two profiles of lengths 32 km aa and 52 km bb revealed a thick 3 km highly conductive 1 4 m surface layer of fluvio marine mesozoic cenozoic sediments the models delineate the hypocentre zone located at 20 25 km depth that manifests the high resistivity conductivity transition zone the accumulation of compressive stresses post rifting along this weak zone has resulted in the reverse slip of bhuj 2001 earthquake the reverse fault f1 associated with the earthquake is believed to be an ancient normal fault formed during the rifting phase contrary to earlier suggested theories we suggest that f1 got initiated along the high resistivity conductivity transition zone causing the bhuj 2001 event the geoelectric models revealed a laterally extending partially resistive zone at 20 30 km depth range showing a tendency to extend further deep model calculations using synthetic data also support this observation therefore we hypothesize the presence of a basal detachment marking the transition zone between the continental crust and the lithospheric upper mantle at 40 km depth intersected by the f1 the geoelectric models suggest that the crustal thinning caused the asthenospheric upwelling and or serpentinization leading to the ascent of volatiles and melts the subsurface geometry in kachchh basin suggests the thick skinned deformation

end permian catastrophe by bolide impact evidence of a gigantic release of sulfur from the mantle comment and reply kaiho et al report sulfur isotope and chemical data for samples from the meishan china permo triassic p tr boundary section they interpret the s isotope data as well as the occurrence of fe and ni rich particles as evidence for a large scale impact event that penetrated the earth s mantle and formed a crater 1000 km in diameter we disagree with their interpretation in all major points

synchrony and causal relations between permian triassic boundary crises and siberian flood volcanism the permian triassic boundary records the most severe mass extinctions in earth9s history siberian flood volcanism the most profuse known such subaerial event produced 2 million to 3 million cubic kilometers of volcanic ejecta in approximately 1 million years or less analysis of 40 ar 39 ar data from two tuffs in southern china yielded a date of 250 0 0 2 million years ago for the permian triassic boundary which is comparable to the inception of main stage siberian flood volcanism at 250 0 0 3 million years ago volcanogenic sulfate aerosols and the dynamic effects of the siberian plume likely contributed to environmental extrema that led to the mass extinctions

magnetotelluric study to characterize kachchh mainland fault kmf and katrol hill fault khf in the western part of kachchh region of gujarat india abstract the kachchh mainland fault kmf is a major e w trending fault in the kachchh region of gujarat extending 150 km from lakhpat village in the west to the bhachau town in the east the katrol hill fault khf is an e w trending intrabasinal fault located in the central region of kachchh basin and the south of kmf the western parts of both of the faults are characterized and the sediment thickness has been estimated in the region using a magnetotelluric mt survey at 17 sites along a 55 km long north south profile with a site spacing of 2 3 km the analysis reveals that the maximum sediment thickness is 2 3 km quaternary tertiary and mesozoic in the region out of which the mesozoic sediments feature a maximum thickness of 2 km the estimated sediment thickness is found consistent with the thickness suggested by a deep borehole depth approx 2 5 km drilled by oil and natural gas corporation ongc at nirona northern part of the study area from 2 d inversion of the mt data three conductive zones are identified from north to south the first conductive zone is dipping nearly vertical down to 7 8 km depth it becomes north dipping below 8 km depth and is inferred as kmf the second conductive zone is found steeply dipping into the southern limbs near manjal village 28 km south of nirona which is inferred as the khf a vertical dipping down to 20 km depth conductive zone has also been observed near ulat village located 16 km north of manjal village and 12 km south of nirona village this conductive zone becomes listric north dipping beyond 20 km depth it is reported first time by a geophysical survey in the region

causes and consequences of extreme permo triassic warming to globally equable climate and relation to the permo triassic extinction and recovery permian waning of the low latitude alleghenian variscan hercynian orogenesis led to a long collisional orogeny gap that cut down the availability of chemically weatherable fresh silicate rock resulting in a high co2 atmosphere and global warming the correspondingly reduced delivery of nutrients to the biosphere caused further increases in co2 and warming melting of polar ice curtailed sinking of o2 and nutrient rich cold brines while pole to equator thermal gradients weakened wind shear and associated wind driven upwelling lessened further diminishing productivity and carbon burial as the earth warmed dry climates expanded to mid latitudes causing latitudinal expansion of the ferrel circulation cell at the expense of the polar cell increased coastal evaporation generated o2 and nutrient deficient warm saline bottom water wsbw and delivered it to a weakly circulating deep ocean warm deep currents delivered ever more heat to high latitudes until polar sinking of cold water was replaced by upwelling wsbw with the loss of polar sinking the ocean was rapidly filled with wsbw that became increasingly anoxic and finally euxinic by the end of the permian rapid incursion of wsbw could have produced 20 m of thermal expansion of the oceans generating the well documented marine transgression that flooded embayments in dry hot pangaean mid latitudes the flooding further increased wsbw production and anoxia and brought that anoxic water onto the shelves release of co2 from the siberian traps and methane from clathrates below the warming ocean bottom sharply enhanced the already strong greenhouse increasingly frequent and powerful cyclonic storms mined upwelling high latitude heat and released it to the atmosphere that heat trapped by overlying clouds of its own making suggests complete breakdown of the dry polar cell resulting rapid and intense polar warming caused or contributed to extinction of the remaining latest permian coal forests that could not migrate any farther poleward because of light limitations loss of water stored by the forests led to aquifer drainage adding another 5 m to the transgression non peat forming vegetation survived at the newly moist poles climate feedback from the coal forest extinction further intensified warmth contributing to delayed biotic recovery that generally did not begin until mid triassic but appears to have resumed first at high latitudes late in the early triassic current quantitative models fail to generate high latitude warmth and so do not produce the chain of events we outline in this paper future quantitative modeling addressing factors such as polar cloudiness increased poleward heat transport by deep water and its upwelling by cyclonic storms and sustainable mid latitude sinking of warm brines to promote anoxia warming and thermal expansion of deep water may more closely simulate conditions indicated by geological and paleontological data

photic zone euxinia during the permian triassic superanoxic event carbon and sulfur isotopic data together with biomarker and iron speciation analyses of the hovea 3 core that was drilled in the perth basin western australia indicate that euxinic conditions prevailed in the paleowater column during the permian triassic superanoxic event biomarkers diagnostic for anoxygenic photosynthesis by chlorobiaceae are particularly abundant at the boundary and into the early triassic similar conditions prevailed in the contemporaneous seas off south china our evidence for widespread photiczone euxinic conditions suggests that sulfide toxicity was a driver of the extinction and a factor in the protracted recovery

paleoredox biotic and sulfur isotopic changes associated with the end permian mass extinction in the western tethys abstract detailed cm scale s toc total organic carbon 34ssulfide and pyrite morphological analysis of the permian triassic boundary beds at the bulla section northern italy suggests that marine waters at this site saw the influx of two dysoxic euxinic intervals that mark the end permian extinction event this suggests reduced oxygen conditions and the presence of h2s is the cause of the end permian extinction the bulla section also shows three troughs in 34ssulfate of which the latter two coincide with the dysoxic euxinic intervals this suggests that the latter two 34ssulfate troughs are the result of h2s oxidation in surface waters but the first trough is the result of a different mechanism we propose that h2s was oxidized in another region either to low 34ssulfate water or elemental s which then moved to the bulla area at the balvany section hungary there are two 34ssulfate troughs near the extinction and no evidence of euxinia a similar mechanism to the first bulla 34ssulfate trough is proposed with the suggestion that these waters were also depleted in oxygen in order to effect the extinction at balvany

high frequency fluctuations in redox conditions during the latest permian mass extinction abstract new high resolution geochemical and sedimentological data from fiskegrav east greenland reveal fluctuations in marine redox conditions associated with the final disappearance of bioturbating organisms during the latest permian mass extinction lpme sedimentological observations imply a transgressive episode and associated geochemical evidence for decreasing oxygen availability and the establishment of persistently ferruginous fe 2 rich conditions implies the shoreward migration of oxygen deficient waters the long term decline in dissolved oxygen do availability could have been exacerbated by increasing water temperatures reducing the solubility of oxygen and promoting thermal stratification mixing of the water column could have been further inhibited by freshwater influxes that could have generated salinity contrasts that reinforced thermal stratification enhanced runoff could also have increased the delivery of nutrients to the marine shelf stimulating biological oxygen demand bod during the transition to persistently ferruginous conditions we identify intervals of intermittent benthic meiofaunal recolonization events that we attribute to small transient increases in do availability the mechanism controlling these fluctuations remains speculative but given the possible centennial to millennial scale frequency of these changes we hypothesise that the mid latitude setting of fiskegrav during the late permian was sensitive to changes in atmospheric circulation patterns which may have influenced local precipitation and intermittently modulated some of the processes promoting anoxia

magnetotelluric imaging of the fault rupture area of the 1999 izmit turkey earthquake abstract wide band 320 0 001 hz and long period 0 01 0 0001 hz magnetotelluric mt data were acquired along two profiles crossing the western part of the north anatolian fault zone nafz turkey which consists of two main fault branches the first profile izmit profile crosses the epicentral area of the 17 august 1999 izmit earthquake in fact the mt measurements along this profile started just a few weeks before the occurrence of the mainshock and four instruments happened to be in operation in the vicinity of the fault when the earthquake took place the second profile adapazari profile is located about 30 km east of the first profile two dimensional modeling shows the following results first the hypocenters of mainshock and aftershocks are located on the highly resistive side near the edge of a conductive zone second the long period mt data show a low resistivity zone extending down to 50 km between the two fault branches such a deep conductive zone is interpreted as representing partial melting resulted from the past complex tectonics in this region and it is related to the non seismic after slip in the layer below the seismogenic zone characterized by the highly resistive layer

fungal event and palynological record of ecological crisis and recovery across the permian triassic boundary the end of the permian period was marked by the most severe mass extinction in the geologic record detailed quantitative study of pollen and spores from shallow marine deposits spanning the permian triassic p tr boundary in israel reveals a sequence of palynological ecological stages reflecting a major crisis among land plants the disappearance of the gymnosperm dominated palynoflora of the late permian lueckisporites virkkiae zone is recorded at a claystone horizon containing almost exclusively abundant fungal remains and carbonized terrestrial plant debris this fungal spike is followed by a zone dominated by marine acritarchs and a succession showing ecological recovery with abundantlycopodsporesandeventualreappearanceofbisaccategymnospermpolleninthe earlytriassic thelatestpermianproliferationoffungiisrecognizableworldwideandcan be correlated with other paleontological and geochemical markers of a global ecological disaster

complete biotic and sedimentary records of the permian triassic transition from meishan section south china ecologically assessing mass extinction and its aftermath abstract the meishan section south china is the global stratotype section and point gssp for the permian triassic boundary ptb and is also well known for the best record demonstrating the permian triassic mass extinction ptme all over the world this section has also been studied using multidisciplinary approaches to reveal the possible causes for the greatest phanerozoic biocrisis of life on earth many important scenarios interpreting the great dying have been proposed on the basis of data from meishan nevertheless debates on biotic extinction patterns and possible killers still continue this paper reviews all fossil and sedimentary records from the permo triassic p tr transition based on previously published data and our newly obtained data from meishan and assesses ecologically the ptme and its aftermath to determine the biotic response to climatic and environmental extremes associated with the biocrisis eight updated conodont zones clarkina yini clarkina meishanensis hindeodus changxingensis clarkina taylorae hindeodus parvus isarcicella staeschei isarcicella isarcica and clarkina planata zones are proposed for the ptb beds at meishan major turnover in fossil fragment contents and ichnodiversity occurs across the boundary between bed 24e 5 and bed 24e 6 suggesting an extinction horizon in a thin stratigraphic interval the irregular surface in the middle of bed 27 is re interpreted as a firmground of glossifungites ichnofacies rather than the previously proposed submarine dissolution surface or hardground surface both fossil fragment contents and ichnodiversity underwent dramatic declines in beds 25 26a coinciding with metazoan mass extinction fossil fragment content ichnodiversity and all ichnofabric proxies including burrow size tiering level bioturbation level indicate that the p tr ecologic crisis comprises two discrete stages coinciding with the first and second phases of the ptme in meishan ecologic crisis lagged behind biodiversity decline during the ptme pyrite framboid size variations suggest that depositional redox condition was anoxic to euxinic in the latest changhsingian became euxinic in beds 25 26a turned dysoxic in bed 27 then varied from euxinic to anoxic through most of the griesbachian the 9 c increase in seawater surface temperature from bed 24e to bed 27 at meishan seems to result in dramatic declines in biodiversity and fossil fragment contents in beds 25 26a but had little effect on all ecologic proxies both metazoans and infauna seem not to have been affected by the pre extinction anoxic euxinic condition the anoxic event associated with the ptme may have occurred in a much shorter period than previously thought and is only recorded in beds 25 26a at meishan fossil fragment contents ichnofaunas ichnofabrics and pyrite framboid size all show that no signs of oceanic acidification and anoxia existed in bed 27 the early griesbachian anoxia may have resulted in rarity of ichnofauna and metazoans in the lower yinkeng formation in which the ichnofauna is characterized by small simple horizontal burrows of planolites and metazoan faunas are characterized by low diversity high abundance opportunist dominated communities the rapid increase of 9 c in sea surface temperature and a short anoxia or acidification coincided with the first pulse biocrisis while a prolonged and widespread anoxia probably due to a long period of high seawater temperate condition may be crucial in mortality of most organisms in the second pulse ptme marine ecosystems started to recover coupled with environmental amelioration in the late griesbachian

geochemistry of the end permian extinction event in austria and italy no evidence for an extraterrestrial component the end permian mass extinction 251 ma was the largest in earth s history and the great extent of biospheric perturbation is recorded as dramatic shifts in carbon isotope ratios of sedimentary materials both terrestrial and extraterrestrial events are commonly invoked as causative mechanisms for the crisis and the primary reason for the event remains the subject of controversy geochemical indicators sensitive to the influence of extraterrestrial material involve platinum group elements and osmium and helium isotope ratios analyses of extinction levels in two sections from austria and italy reveal no evidence of an extraterrestrial impact the end permian crisis it appears was a homegrown catastrophe

search for evidence of impact at the permian triassic boundary in antarctica and australia life on earth was almost destroyed some 250 m y ago in the most profound of all known mass extinction events we investigated the possible role of impact by an extraterrestrial bolide through chemical and mineralogical characterization of boundary breccias search for shocked quartz and analysis for iridium in permian triassic boundary sections at graphite peak and mount crean antarctica and wybung head australia thin claystone breccias at the isotopically and paleobotanically defined boundary at all three locations are interpreted as redeposited soil rather than impact ejecta the breccias at all three locations also yielded shocked quartz but it is an order of magnitude less abundant 0 2 vol and smaller only as much as 176 micrometers m diameter than shocked quartz at some cretaceous tertiary boundary sites faint iridium anomalies were detected up to 134 pg g 1 these values are an order of magnitude less than iridium anomalies at some cretaceous tertiary boundary sites furthermore peak iridium values are as much as 1 m below the isotopically and paleobotanically defined boundary the idea that impact caused the extinctions thus remains to be demonstrated convincingly